| 1. |
- Cabaleiro-Lago, Celia, et al.
(författare)
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Self-diffusion NMR studies of the host-guest interaction between beta-cyclodextrin and alkyltrimethylammonium bromide surfactants
- 2005
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Ingår i: Langmuir. - Lund Univ, Ctr Chem & Engn, SE-22100 Lund, Sweden. : AMER CHEMICAL SOC. - 0743-7463 .- 1520-5827. ; 21:25, s. 11637-11644
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion measurements by nuclear magnetic resonance (NMR) spectroscopy were used to investigate the host-guest association between beta-cyclodextrin (CD) and alkyltrimethylammonium bromide surfactants with different chain lengths, ranging from 6 up to 16 carbons. The scope and limitations of the method in the study of formation of inclusion complexes are discussed. The influences of the presence of CD in the micellization process have been studied, and the apparent critical micellar concentration and the self-diffusion coefficients of the species present in the systems have been calculated. The stoichiometries of the different complexes have been determined. Evidence for the formation of a 2:1 complex in the case Of C(16)TAB has been found.
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| 2. |
- Nilsson, Markus, et al.
(författare)
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Interactions between gemini surfactants, 12-s-12, and beta-cyclodextrin as investigated by NMR diffusometry and electric conductometry
- 2006
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Ingår i: Langmuir. - Lund Univ, Ctr Chem & Chem Engn, SE-22100 Lund, Sweden. Univ Coimbra, Dept Chem, P-3004535 Coimbra, Portugal. : AMER CHEMICAL SOC. - 0743-7463 .- 1520-5827. ; 22:21, s. 8663-8669
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between beta-cyclodextrin (CD) and gemini surfactant of the type alkyl-alpha,omega-bis(dodecyldimethyl-ammonium bromide) with different spacer lengths of 2, 8, and 10 carbons has been investigated by means of electric conductivity (EC) and proton self-diffusion NMR at 298 K. The formation of a 2: 1 (CD: gemini) complex in a two-step mechanism is observed with the first association constant (K-11) higher than the second one (K-21), but both relatively small in comparison with single C-12-tailed surfactant. The value of the association constants increased with spacer length both for the first and second associated CD, which indicates that the available space on the gemini molecule is important. The magnitudes of the association constant both for the first and second complexation are discussed. The first association constant is small ( when compared with the homologous single-chain surfactant) due to hydrophobic interaction between the hydrocarbon tails within the gemini molecule, while the second association constant shows no cooperativity and its magnitude is discussed in terms of steric constrains.
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| 3. |
- Algotsson, Jenny, et al.
(författare)
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Electrostatic interactions are important for the distribution of Gd(DTPA)(2-) in articular cartilage.
- 2015
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 76:2, s. 500-509
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Tidskriftsartikel (refereegranskat)abstract
- The delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) method can be used to assess the content of glycosaminoglycan in cartilage. In in vitro and model studies, the content of glycosaminoglycan is often expressed in terms of a fixed charge density (FCD). Values of the fixed charge density obtained using the dGEMRIC method differs from values obtained using other methods. The purpose of this work was to further clarify the origin of this discrepancy.
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| 4. |
- Algotsson, Jenny, et al.
(författare)
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Intermolecular interactions play a role in the distribution and transport of charged contrast agents in a cartilage model
- 2019
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 14:10
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Tidskriftsartikel (refereegranskat)abstract
- The transport and distribution of charged molecules in polyelectrolyte solutions are of both fundamental and practical importance. A practical example, which is the specific subject addressed in the present paper, is the transport and distribution of charged species into cartilage. The charged species could be a contrast agent or a drug molecule involved in diagnosis or treatment of the widespread degenerative disease osteoarthritis, which leads to degradation of articular cartilage. Associated scientific issues include the rate of transport and the equilibrium concentrations of the charged species in the cartilage and the synovial fluid. To address these questions, we present results from magnetic resonance micro-imaging experiments on a model system of articular cartilage. The experiments yield temporally and spatially resolved data on the transport of a negatively charged contrast agent (charge = -2), used in medical examinations of cartilage, into a polyelectrolyte solution, which is designed to capture the electrostatic interactions in cartilage. Also presented is a theoretical analysis of the transport where the relevant differential equations are solved using finite element techniques as well as treated with approximate analytical expressions. In the analysis, non-ideal effects are included in the treatment of the mobile species in the system. This is made possible by using results from previous Monte Carlo simulations. The results demonstrate the importance of taking non-idealities into account when data from measurements of transport of charged solutes in a system with fixed charges from biological polyelectrolytes are analyzed.
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| 5. |
- Aslund, Ingrid, et al.
(författare)
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Diffusion NMR for determining the homogeneous length-scale in lamellar phases.
- 2008
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Ingår i: Journal of Physical Chemistry B. - : The American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 112:10, s. 2782-2794
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Tidskriftsartikel (refereegranskat)abstract
- The size of the anisotropic domains in a lyotropic liquid crystal is estimated using a new protocol for diffusion NMR. Echo attenuation decays are recorded for different durations of the displacement-encoding gradient pulses, while keeping the effective diffusion time and the range of the wave vectors constant. Deviations between the sets of data appear if there are non-Gaussian diffusion processes occurring on the time-scale defined by the gradient pulse duration and the length-scale defined by the wave vector. The homogeneous length-scale is defined as the minimum length-scale for which the diffusion appears to be Gaussian. Simulations are performed to show that spatial variation of the director orientation in an otherwise homogeneous system is sufficient to induce non-Gaussian diffusion. The method is demonstrated by numerical solutions of the Bloch-Torrey equation and experiments on a range of lamellar liquid crystals with different domain sizes.
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| 6. |
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| 7. |
- Brito, Rodrigo O., et al.
(författare)
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Self-assembly in a catanionic mixture with an aminoacid-derived surfactant: From mixed micelles to spontaneous vesicles
- 2006
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 110:37, s. 18158-18165
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Tidskriftsartikel (refereegranskat)abstract
- The aqueous self-assembly of a novel lysine-derived surfactant with a gemini-like architecture, designated here as 12-Lys-12, has been experimentally investigated for the amphiphile alone in water and in a mixture with dodecyltrimethylammonium bromide (DTAB). The neat surfactant forms interesting micrometer-sized rigid tubules in the dilute region, resulting in very viscous solutions. For the catanionic mixture with DTAB, various single and multiphase regions were identified (up to a total surfactant concentration of 1.5 wt %) by means of combined polarizing light microscopy, cryo-TEM, and NMR. In the DTAB-rich side, for a mixing molar ratio in the range 2 < DTAB/12-Lys-12 < 4, a region of stable, unilamellar vesicles can be found. Furthermore, it was found that upon addition of 12-Lys-12 to pure DTAB solutions, the mixed micelles grow and beyond a given mixing ratio, vesicles assemble and coexist with small micelles. The transition is not continuous, since there is a narrow mixing range where phase separation occurs. Self-diffusion measurements and cryo-TEM imaging show that the average vesicle radius is on the order of 30-40 nm.
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| 8. |
- Cabaleiro-Lago, Celia, et al.
(författare)
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NMR diffusometry and conductometry study of the host-guest association between beta-cyclodextrin and dodecane 1,12-bis(trimethylammonium bromide)
- 2006
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 300:2, s. 782-787
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Tidskriftsartikel (refereegranskat)abstract
- Surfactants form association complexes with cyclodextrins. In the present investigation we have used NMR-diffusometry and electrical conductivity to follow the interactions which take place between ss-cyclodextrm and a bolaform surfactant: dodecane 1, 1 2-bis(trimethylammonium bromide). Both H-1 NMR self-diffusion and conductometry data indicate the formation of a 1: 1 inclusion complex. Assuming this stoichiometry, it was possible to calculate the association constant; from the analysis of the self-diffusion coefficients of free ss-cyclodextrin and the bolaform surfactant an association constant K = 3 x 10(3) Mb(-1) was obtained while the analysis of conductivity data gave a comparable value of K = 2.5 x 10(3) M-1. (c) 2006 Elsevier Inc. All rights reserved.
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| 9. |
- Cabaleiro-Lago, Celia, et al.
(författare)
-
Self-diffusion NMR studies of the host-guest interaction between beta-cyclodextrin and alkyltrimethylammonium bromide surfactants
- 2005
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:25, s. 11637-11644
-
Tidskriftsartikel (refereegranskat)abstract
- Diffusion measurements by nuclear magnetic resonance (NMR) spectroscopy were used to investigate the host-guest association between beta-cyclodextrin (CD) and alkyltrimethylammonium bromide surfactants with different chain lengths, ranging from 6 up to 16 carbons. The scope and limitations of the method in the study of formation of inclusion complexes are discussed. The influences of the presence of CD in the micellization process have been studied, and the apparent critical micellar concentration and the self-diffusion coefficients of the species present in the systems have been calculated. The stoichiometries of the different complexes have been determined. Evidence for the formation of a 2:1 complex in the case Of C(16)TAB has been found.
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| 10. |
- Carvalho, R. A., et al.
(författare)
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The effect of the head-group spacer length of 12-s-12 gemini surfactants in the host-guest association with beta-cyclodextrin
- 2011
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 354:2, s. 725-732
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Tidskriftsartikel (refereegranskat)abstract
- NMR spectroscopy has been used to study and characterize the interactions in solution between beta-CD and alkyl-alpha,omega-bis(dodecyldimethyl ammonium bromide) gemini surfactants with the following head-group spacer lengths: 2, 4, 6, 8, and 10. The application of the method of continuous variation gives as a result that 1:1 and 2:1 (beta-cyclodextrin-gemini) complexes are formed; the association stoichiometry is dependent on the spacer chain length, varying from 1.5 (for s = 2) to 1.8 (for s = 10). Assuming a two-step mechanism, the binding constants have been computed. In general, the overall binding constant slightly increases with an increase of the number of methylene groups in the spacer. The H-1 NMR spectra of the N-(CH3)(2) groups in beta-cyclodextrin/gemini mixed solutions are split into two peaks for 12-10-12, suggesting that the gemini spacer can thread the beta-cyclodextrin so that the latter is positioned between the gemini head-groups. Inspection of the ROESY spectra allowed the establishment of several spatial proximities between the protons from the beta-CD and the gemini and for a spacer length of 10, the data indeed indicate that complexes are formed with the CD molecule positioned between the two charged head groups with the spacer passing through the CD molecule. (C) 2010 Elsevier Inc. All rights reserved.
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| 11. |
- Colsenet, Roxane, et al.
(författare)
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Diffusion of polyethyleneglycols in casein solutions and gels as studied by pulsed field gradient NMR
- 2005
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Ingår i: Magnetic Resonance Imaging. - : Elsevier BV. - 1873-5894 .- 0730-725X. ; 23:2, s. 347-348
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Tidskriftsartikel (refereegranskat)abstract
- Molecular transport characterized by diffusion coefficients is a key feature of food processes and especially in dairy processes. Caseins represent 80% of the protein content in milk and are directly involved in the formation of dairy gels. Consequently, providing a quantitative description of the solute diffusion in casein gels should contribute significantly to rationalization of the dairy processes. The objectives of this study were to study the self-diffusion coefficient of molecular probes [polyethyleneglycol (PEGs)] in casein solutions and gels, in particular with regard to the effects of the probe molecular size and casein concentration. We have shown that the PEG diffusion was an efficient tool to reveal the structural information relative to the gel matrix structure. (c) 2005 Elsevier Inc. All rights reserved.
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| 12. |
- Colsenet, Roxane, et al.
(författare)
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Effect of casein concentration in suspensions and gels on poly(ethylene glycol)s NMR self-diffusion measurements
- 2005
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:22, s. 9171-9179
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Tidskriftsartikel (refereegranskat)abstract
- PFG-NMR spectroscopy was used to study the diffusion of molecular probes (poly(ethylene glycol)s) in casein suspensions and gels in terms of the effects of probe molecular size (molecular mass between 1080 and 634 000 g/mol), casein concentrations (from 3.24 to 16.22 g/100 g), and effects of rennet coagulation. A strong dependency of diffusion on probe size was observed, both in casein suspensions and in gels: as the PEG size increased, the diffusion was reduced. This effect was more pronounced for higher casein concentrations. Changes in casein structure after addition of rennet increased the diffusion coefficient for 82 250 and 634 000 g/mol PEG. The PEG self-diffusion coefficients in casein gels were compared to the casein gel structures characterized by scanning electron microscopy. Assuming high internal micelle porosity, a diffusion model with two diffusion pathways, one outside and one inside the micelles, was used to explain the PEG diffusion in casein solutions and gels. The results were discussed in the context of variations in casein micelle voluminosity after renneting.
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| 13. |
- Colsenet, Roxane, et al.
(författare)
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Effects of ionic strength and denaturation time on polyethyleneglycol self-diffusion in whey protein solutions and gels visualized by nuclear magnetic resonance
- 2006
-
Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 54:14, s. 5105-5112
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Tidskriftsartikel (refereegranskat)abstract
- Pulsed field gradient NMR spectroscopy was used to determine the poly(ethylene glycol) (PEG) self-diffusion coefficient (D-PEG) as a function of NaCl concentration (C-NaCl) and denaturation time (t(D)) in whey protein solutions and gels. D-PEG in the gel decreased with increasing C-NaCl concentrations and increased with increasing t(D); the increase ceased for all PEGs when the gel was fixed. This increase was more pronounced for the 82250 g/mol PEG than the 1080 g/mol PEG. Moreover, the diffusion coefficient of nonaggregated whey protein was measured and an increase for longer t(D) was also observed. Scanning electron microscopy images and H-1 spectra demonstrated that D-PEG were related to the structure changes and to the percentage of beta-lactoglobulin denaturation.
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| 14. |
- Colsenet, Roxane, et al.
(författare)
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Pulsed field gradient NMR study of poly(ethylene glycol) diffusion in whey protein solutions and gels
- 2006
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 39:3, s. 1053-1059
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Tidskriftsartikel (refereegranskat)abstract
- PEG self-diffusion coefficients of poly(ethylene glycol)s (PEGs) (1080, 8500, and 82 250 g/mol) were measured by PFG-NMR spectroscopy in whey protein solutions and gels in relation to whey protein concentration effects (from 6.49 to 40.45 g/100 g) and whey protein heat denaturation effects (30 min at 70 degrees C). A strong dependency of diffusion on probe size was observed in both whey protein solutions and gels: as PEG size increased, diffusion was reduced. This effect was more pronounced for higher protein concentrations. Changes in whey structure after thermal aggregation increased the diffusion coefficient for all PEGs, particularly for the 8500 g/mol PEG. The PEG self-diffusion coefficients in whey protein gels were compared to the gel structures characterized by scanning electron microscopy. The results are discussed in relation to a reptation model and compared to PEG diffusion in casein micelle suspensions and gels.
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| 15. |
- da Silva, Fernando L B, et al.
(författare)
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Titration of fatty acids solubilized in catonic, nonionic and anionic micelles: Theory and experiment.
- 2002
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 106:13, s. 3515-3522
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Tidskriftsartikel (refereegranskat)abstract
- The titration properties of a fatty acid solubilized in different types of micelles, cationic, anionic and nonionic, have been investigated experimentally and theoretically. The solution containing micelles, counterions, and added salt was treated as a dielectric continuum in the Monte Carlo simulations. The dielectric permittivity of the interior of the micelle can have a profound effect on the calculated pK shifts depending on how the dielectric discontinuity is chosen in the model. The simulated results are compared to data from Poisson-Boltzmann calculations and from experiments. The experimentally observed apparent pKa value changes from 7.6 to 4.9 when solubilizing lauric acid in anionic (SDS) and cationic (DoTAC) micelles, respectively. For the nonionic micelle it is found to be approximately 6.6. A significant ion specificity in the pKa value is observed for the DoTAC and DoTAB systems and surprisingly enough both systems show an upward pK shift.
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| 16. |
- Ericsson, Caroline, et al.
(författare)
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Aggregate morphology and flow behaviour of micellar alkylglycoside solutions
- 2005
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Ingår i: Colloid and Polymer Science. - : Springer Science and Business Media LLC. - 0303-402X. ; 283:12, s. 1313-1320
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Tidskriftsartikel (refereegranskat)abstract
- Solutions of n-nonyl-beta-D-glucoside (C(9)G(1)), n-decyl-beta-D-glucoside (C(10)G(1)), n-dodecyl-beta-D-maltoside (C(12)G(2)) n-tetradecyl-beta-D-maltoside (C(14)G(2)) and C(9)G(1)/C(10)G(1) mixtures have been characterised by capillary viscometry and rheology in H2O and D2O, in order to map the influence of surfactant characteristics on micellisation over a wide concentration range. For the maltosides, the micellar solutions are shear thinning with a zero-shear viscosity that scales with concentration according to a power law with an exponent of about 5.8. In contrast, solutions of the glucosides C(9)G(1), C(10)G(1) and their mixtures show Newtonian flow behaviour and a much lower scaling exponent (< 2.4). In C(9)G(1)/C(10)G(1) mixtures, the scaling exponent decreases monotonously with increasing C(10)G(1) content. The flow behaviour correlates with the packing requirements of the various surfactants, and are compatible with the idea that the maltosides form worm-like micelles, whereas the glucosides form branched, interconnected micelles (C(9)G(1)) and space-filling micellar networks (C(10)G(1)).
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| 17. |
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| 18. |
- Ericsson, Caroline, et al.
(författare)
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Effects of temperature, salt, and deuterium oxide on the self-aggregation of alkylglycosides in dilute solution. 2. n-Tetradecyl-beta-D-maltoside
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:4, s. 1507-1515
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Tidskriftsartikel (refereegranskat)abstract
- The effects of salt, temperature, and deuterium oxide on the self-aggregation of n-tetradecyl-beta-D-maltoside (C(14)G(2)) in dilute solution have been investigated by static light scattering, dynamic light scattering (DLS), small-angle neutron scattering (SANS), tensiometry, and capillary viscometry. SANS data show that the micelles can be described as relatively flexible polymer-like micelles with an elliptical cross section, at least at temperatures between 35 and 50 degreesC. The micelles grow in one dimension with increasing temperature and concentration. DLS and viscometry data suggest that the micelle size reaches a maximum at 60-70 degreesC. Comparison of DLS data in D2O and H2O shows that the micelles are larger in the former case. The effect of salt on the micelle size was found to follow the Hofmeister series. Thus, at constant salt concentration, the micelle size decreases according to the sequence SO42- > Cl (-)> NO3 > I- > SCN-, where I- and SCN- act as salting-in anions. From tensiometric data, it can be concluded that the temperature effects on micelle morphology do not correlate directly with those on unimer solubility. Rather, the temperature effect on the hydrocarbon chain conformation seems to be decisive for the micelle morphology. At constant temperature, on the other hand, the effect of salt and deuterium isotope is attributable to changes in effective headgroup area, including intermolecular interactions and water of hydration.
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| 19. |
- Ericsson, Caroline, et al.
(författare)
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Thermotropic phase behaviour of long-chain alkylmaltosides
- 2005
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 7:15, s. 2970-2977
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Tidskriftsartikel (refereegranskat)abstract
- The thermotropic phase behaviour and phase structure of crystalline and non-crystalline n-tetradecyl-beta-D-maltoside (C(14)G(2)) and n-hexadecyl-beta-D-maltoside (C(16)G(2)) have been investigated by means of differential scanning calorimetry and X-ray techniques. Upon lyophilisation, both compounds form a solid, lamellar phase comprising disordered head groups and hexagonally packed alkyl chains that are suggested to be tilted and interdigitated. This ordered lamellar phase melts into a metastable lamellar liquid crystal, which re-crystallises to a high-temperature crystalline polymorph comprising interdigitated, non-tilted alkyl chains. Remarkably, the high-temperature polymorph of C(14)G(2) has the same melting point as that of C(16)G(2), namely 105 degrees C for both surfactants. A low-temperature polymorph of anhydrous C(14)G(2) crystallises from water at room temperature, whereas the hemihydrate of C(14)G(2) crystallises at 6 degrees C from water, or from chloroform containing trace water. X-ray data suggest both these crystalline modifications to comprise interdigitated and tilted alkyl chains.
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| 20. |
- Eriksson, Stefanie, et al.
(författare)
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NMR quantification of diffusional exchange in cell suspensions with relaxation rate differences between intra and extracellular compartments
- 2017
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- Water transport across cell membranes can be measured non-invasively with diffusion NMR. We present a method to quantify the intracellular lifetime of water in cell suspensions with short transverse relaxation times, T2, and also circumvent the confounding effect of different T2 values in the intra- and extracellular compartments. Filter exchange spectroscopy (FEXSY) is specifically sensitive to exchange between compartments with different apparent diffusivities. Our investigation shows that FEXSY could yield significantly biased results if differences in T2 are not accounted for. To mitigate this problem, we propose combining FEXSY with diffusion-relaxation correlation experiment, which can quantify differences in T2 values in compartments with different diffusivities. Our analysis uses a joint constrained fitting of the two datasets and considers the effects of diffusion, relaxation and exchange in both experiments. The method is demonstrated on yeast cells with and without human aquaporins.
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| 21. |
- Ferreira, Guilherme A., et al.
(författare)
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Molecular assembly in block copolymer-surfactant nanoparticle dispersions : Information on molecular exchange and apparent solubility from high-resolution and pfg nmr
- 2021
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 13:19
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Tidskriftsartikel (refereegranskat)abstract
- Internally structured block copolymer-surfactant particles are formed when the complex salts of ionic-neutral block copolymers neutralized by surfactant counterions are dispersed in aqueous media. Here, we report the1H NMR signal intensities and self-diffusion coefficients (D, from pulsed field gradient nuclear magnetic resonance, PFG NMR) of trimethyl alkylammonium surfac-tant ions and the poly(acrylamide)-block-poly(acrylate) (PAAm-b-PA) polyions forming such parti-cles. The results reveal the presence of an “NMR-invisible” (slowly exchanging) fraction of aggre-gated surfactant ions in the particle core and an “NMR-visible” fraction consisting of surface sur-factant ions in rapid exchange with the surfactant ions dissociated into the aqueous domain. They also confirm that the neutral PAAm blocks are exposed to water at the particle surface, while the PA blocks are buried in the particle core. The self-diffusion of the polyions closely agree with the self-diffusion of a hydrophobic probe molecule solubilized in the particles, showing that essentially all copolymer chains are incorporated in the aggregates. Through centrifugation, we prepared mac-roscopically phase-separated systems with a phase concentrated in particles separated from a clear dilute phase. D values for the surfactant and block copolymer indicated that the dilute phase con-tained small aggregates (ca. 5 nm) of surfactant ions and a few anionic-neutral block copolymer chains. Regardless of the overall concentration of the sample, the fraction of block copolymer found in the dilute phase was nearly constant. This indicates that the dilute fraction represented a tail of small particles created by the dispersion process rather than a true thermodynamic solubility of the complex salts.
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| 22. |
- Gavelin, Patrik, et al.
(författare)
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Amphiphilic polymer gel electrolytes. 4. Ion transport and dynamics as studied by multinuclear pulsed field gradient spin-echo NMR
- 2002
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:13, s. 5097-5104
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Tidskriftsartikel (refereegranskat)abstract
- The transport dynamics in gel electrolytes based on amphiphilic polymers was found to be faster than in gel electrolytes based on corresponding nonamphiphilic polymers. The amphiphilic polymer studied was a polymethacrylate grafted with fluorocarbon and (EO)(9) side chains, and the nonamphiphilic one was a polymethacrylate carrying only (EO)(9) side chains. Self-diffusion coefficients of gel electrolytes based on the two polymers with different contents of 1 M lithium bis(trifluoromethylsulfonyl) imide (LiTFSI) salt in gamma-butyrolactone were determined by H-1, F-19, and Li-7 pulsed field gradient spin-echo NMR spectroscopy. The polymer self-diffusion coefficients showed that the amphiphilic polymer molecules diffused faster than the nonamphiphilic ones and seemed more intramolecularly aggregated than intermolecularly. At electrolyte contents above 43 wt %, the ion conductivity of the amphiphilic polymer gel electrolytes was higher than for the corresponding gel based on the nonamphiphilic polymer under identical conditions, as measured by impedance spectroscopy. Moreover, the lithium ion diffusion coefficient in the amphiphilic gel electrolytes was found to be significantly higher than that for corresponding gels based on the nonamphiphilic polymer, The higher ethylene oxide content of the nonamphiphilic polymer decreased the mobility of the lithium ions due to cooperative coordination of lithium ions by ether oxygens in comparison with gamma-BL. The TFSI anion diffusion was however approximately the same in the two gel systems. Consequently, the apparent lithium transference number (taudivided by) of the amphiphilic gels was higher by almost a factor of 3 as compared to that of the gels based on the nonamphiphilic polymer. A splitting of the TFSI signal in the F-19 NMR spectra suggested that the TFSI anions in the amphiphilic polymer gels were partly present in a solvent-rich environment and partly associated with the aggregates formed by the fluorinated side chains. This kind of splitting was not observed in the spectra of the gels based on the nonamphiphilic polymer. The association of TFSI anions to the aggregated fluorinated side chains may thus also play a role in increasing the value of taudivided by for the amphiphilic polymer gels.
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| 23. |
- Greene, George W., et al.
(författare)
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Anisotropic dynamic changes in the pore network structure, fluid diffusion and fluid flow in articular cartilage under compression
- 2010
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Ingår i: Biomaterials. - : Elsevier BV. - 1878-5905 .- 0142-9612. ; 31:12, s. 3117-3128
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Tidskriftsartikel (refereegranskat)abstract
- A compression cell designed to fit inside an NMR spectrometer was used to investigate the in situ mechanical strain response, structural changes to the internal pore structure, and the diffusion and flow of interstitial water in full-thickness cartilage samples as it was deforming dynamically under a constant compressive load (pressure). We distinguish between the hydrostatic pressure acting on the interstitial fluid and the pore pressure acting on the cartilage fibril network. Our results show that properties related to the pore matrix microstructure such as diffusion and hydraulic conductivity are strongly influenced by the hydrostatic pressure in the interstitial fluid of the dynamically deforming cartilage which differ significantly from the properties measured under static i.e. equilibrium loading conditions (when the hydrostatic pressure has relaxed back to zero). The magnitude of the hydrostatic fluid pressure also appears to affect the way cartilage's pore matrix changes during deformation with implications for the diffusion and flow-driven fluid transport through the deforming pore matrix. We also show strong evidence for a highly anisotropic pore structure and deformational dynamics that allows cartilage to deform without significantly altering the axial porosity of the matrix even at very large strains. The insensitivity of the axial porosity to compressive strain may be playing a critical function in directing the flow of pressurized interstitial fluid in the compressed cartilage to the surface, to support the load, and provide a protective interfacial fluid film that 'weeps' out from the deforming tissue and thereby enhances the (elasto)hydrodynamic efficacy of sliding joints. Our results appear to show a close synergy between the structure of cartilage and both the hydrodynamic and boundary lubrication mechanisms. (C) 2010 Elsevier Ltd. All rights reserved.
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| 24. |
- Greene, George W., et al.
(författare)
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Changes in pore morphology and fluid transport in compressed articular cartilage and the implications for joint lubrication
- 2008
-
Ingår i: Biomaterials. - : Elsevier BV. - 1878-5905 .- 0142-9612. ; 29:33, s. 4455-4462
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Tidskriftsartikel (refereegranskat)abstract
- Cartilage sections were cut from the middle zone of pig knee articular cartilage and attached to substrates in two different kinds of newly designed 'pressure cells', one for fluorescence the other for NMR measurements, The fluorescence cell was filled with buffer solution containing fluorescently marked 70 kDa dextran which was allowed to diffuse into the cartilage pores. A second glass surface was then pressed down onto the thin cartilage sample under different loads (pressures), and the resulting compression (strain) and change in pore volume were measured as a function of time, simultaneously with measurements of the lateral diffusion and flow pattern of the dextran molecules using Fluorescence Recovery After Photobleaching (FRAP). Complementary experiments were made on the normal diffusion coefficients of pure electrolyte solutions (no dextran) in thicker cartilage sections with pulse-gradient NMR using a new pressure cell suitable for such measurements. Taken together our results show that the highly anisotropic structure of cartilage has a strong effect on the way fluid diffuses laterally and normally at different stages of compression. Our results also show how geometric constraints on a cartilage network and trapped high MW polymer such as HA during normal compressions are likely to affect both the normal and the lateral mobilities of polyelectrolytes and water. (C) 2008 Elsevier Ltd. All rights reserved.
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| 25. |
- Greene, George W., et al.
(författare)
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Hyaluronic acid-collagen network interactions during the dynamic compression and recovery of cartilage
- 2012
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 8:38, s. 9906-9914
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Tidskriftsartikel (refereegranskat)abstract
- A compression cell designed to fit inside an NMR spectrometer was used to investigate (i) the in situ dynamic strain response and structural changes of the internal pore network, and (ii) the diffusion and flow of interstitial water, in full thickness cartilage samples as they were mechanically deformed under a constant compressive load (pressure) and then allowed to recover (swell again) when the load was removed. Selective enzymatic digestion of the collagen fibril network and the glycopolysaccharide hyaluronic acid (HA) was performed to mimic some of the structural and compositional changes associated with osteoarthritis. Digestion of collagen gave rise to mechanical 'dynamic softening' and-perhaps more importantly-nearly complete loss in the ability to recover through swelling, both effects due to the disruption of the hierarchical structure and fibril interconnectivity in the collagen network which adversely affects its ability to deform reversibly and to properly regulate the pressurization and resulting rate and direction of interstitial fluid flow. In contrast, digestion of HA inside the collagen pore network caused the cartilage to 'dynamically stiffen' which is attributed to the decrease in the osmotic (entropic) pressure of the digested HA molecules confined in the cartilage pores that causes the network to contract and thereby become less permeable to flow. These digestion-induced changes in cartilage's properties reveal a complex relationship between the molecular weight and concentration of the HA in the interstitial fluid, and the structure and properties of the collagen fibril pore network, and provide new insights into how changes in either could influence the onset and progression of osteoarthritis.
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| 26. |
- Hagslätt, H, et al.
(författare)
-
Predictions of pulsed field gradient NMR echo-decays for molecules diffusing in various restrictive geometries. Simulations of diffusion propagators based on a finite element method
- 2003
-
Ingår i: Journal of Magnetic Resonance. - 1096-0856. ; 161:2, s. 138-147
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Tidskriftsartikel (refereegranskat)abstract
- Pulsed field gradient NMR diffusometry is a promising tool for investigating structures of porous material through determinations of dynamic displacements of molecules in porous systems. A problem with this approach is the lack of closed analytical expressions for echo-decays in anything but idealized pore geometries. We present here an approach based on calculating the appropriate diffusion propagator by means of finite element calculations. The suggested method is quite general, and can be applied to arbitrary porous systems. The protocol for the calculations is outlined and we show results from some different cases: diffusion in confined geometries and in systems that are spatially inhomogeneous with respect to concentration.
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| 27. |
- Jansson, Jörgen, et al.
(författare)
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Small-angle X-ray scattering, light scattering, and NMR study of PEO-PPO-PEO triblock copolymer/cationic surfactant complexes in aqueous solution
- 2005
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 109:15, s. 7073-7083
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Tidskriftsartikel (refereegranskat)abstract
- The formation of triblock copolymer/surfactant complexes upon mixing a nonionic Pluronic polymer (PEO-PPO-PEO) with a cationic surfactant, hexadecyltrimethylammonium chloride (CTAC), has been studied in dilute aqueous solutions using small-angle X-ray scattering, static and dynamic light scattering, and self-diffusion NMR. The studied copolymer (denoted P123, EO20PO68EO20) forms micelles with a radius of 10 nm and a molecular weight of 7.5 x 101, composed of a hydrophobic PPC-rich core of radius 4 nm and a water swollen PEO corona. The P123/CTAC system has been investigated between 1 and 5 wt % P123 and with varying surfactant concentration up to approximately 170 mM CTAC (or a molar ratio n(CTAC)/n(P123) 19.3). When CTAC is mixed with micellar P123 solutions, two different types of complexes are observed at various CTAC concentrations. At low molar ratios (>= 0.5) a '' P123 micelle-CTAC '' complex is obtained as the CTAC monomers associate noncooperatively with the P123 micelle, forming a spherical complex. Here, an increased interaction between the complexes with increasing CTAC concentration is observed. The interaction has been investigated by determining the structure factor obtained by using the generalized indirect Fourier transformation (GIFT) method. The interaction between the P123 micelle-CTAC complexes was modeled using the Percus-Yevick closure. For the low molar ratios a small decrease in the apparent molecular weight of the complex was obtained, whereas the major effect was the increase in electrostatic repulsion between the complexes. Between molar ratios 1.9 and 9 two coexisting complexes were found, one P123 micelle-CTAC complex and one '' CTAC-P123 '' complex. The latter one consists of one or a few P123 unimers and a few CTAC monomers. As the CTAC concentration increases above a molar ratio of 9, the P123 micelles are broken up and only the CTAC-P123 complex that is slightly smaller than a CTAC micelle exists. The interaction between the P123/CTAC complexes was modeled with the hypernetted-chain closure using a Yukawa type potential in the GIFT analysis, due to the stronger electrostatic repulsion.
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| 28. |
- Kanai, Noriko, et al.
(författare)
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Self-diffusion coefficients of heavy water in low n-alkanes
- 2023
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Ingår i: Journal of Molecular Liquids. - 0167-7322. ; 388
-
Tidskriftsartikel (refereegranskat)abstract
- The self-diffusion coefficients of D2O (i.e., heavy water or 2H2O) in eight n-alkanes at 298 K were investigated using 2H NMR diffusometry. D tended to decrease in the n-alkanes with increasing carbon number and be inversely proportional to the n-alkane viscosity to a fractional power. The hydrodynamic radius of D2O in the n-alkanes, calculated from Stokes-Einstein-Sutherland equation with stick boundary conditions, decreased with increasing n-alkane size and was smaller in the n-alkanes than in the bulk phase due to the absence of hydrogen bonds. This study provides fundamental data on the diffusion properties of water molecules dissolved in n-alkanes with applications to, for instance, molecular dynamics simulations or interpretation of Ostwald ripening.
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| 29. |
- Karlson, L, et al.
(författare)
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Complex formed in the system hydrophobically modified polyethylene glycol/methylated alpha-cyclodextrin/water. An NMR diffusometry study
- 2003
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 228:1-3, s. 171-179
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Tidskriftsartikel (refereegranskat)abstract
- In aqueous solutions hydrophobically modified polyethylene glycol (HM-PEG) forms a transient polymer network held together by intermolecular hydrophobic associations. In the present investigation we have used NMR-diffusometry to study how the addition of methylated alpha-cyclodextrin (M-alpha-CD) influences the polymer network. The addit on of M-alpha-CD resulted in an increased mean self-diffusion of HM-PEG, DHM-PEG, which is referred to a degradation of the polymer network when hydrophobic associations are disrupted due to complex formation between the hydrophobic groups of HM-PEG and M-alpha-CD. Addition of small amounts of M-alpha-CD results in a dramatic increase in DHM-PEG. Upon further addition of M-a-CD the increase in DHM-PEG is less dramatic and at excess M-alpha-CD, DHM-PEG levels off and equals the mean self-diffusion coefficient for unmodified PEG with the same molecular weight. The suggested interpretation is that the addition of the first molecules of M-alpha-CD mainly reduces the probability for hydrophobic associations inter-connecting different clusters of polymer micelles whereas at higher M-alpha-CD concentrations a disengagement of the individual clusters into separate HM-PEG molecules becomes important. (C) 2003 Elsevier B.V. All rights reserved.
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| 30. |
- Karlsson, L, et al.
(författare)
-
Compaction of DNA by gemini surfactants: Effects of surfactant architecture
- 2002
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 252:2, s. 290-296
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between bacteriophage T4 DNA and cationic gemini surfactants was studied by the use of fluorescence microscopy. Upon addition of surfactant, DNA undergoes a transition from random coil to globule, with an intermediate coexistence region. The state behavior of a DNA-gemini surfactant system was found to depend on spacer length, valency, head group size, and tail length. A series of alkanediyl-alpha,omega-bis-(dimethylalkylammonium bromide) surfactants with fixed tail length and variable spacer length s showed a minimum of compaction efficiency at s = 6 due to the competition between entropy loss and enthalpy gain. This occurs at roughly the same spacer length at which the critical micellization concentration shows a maximal value (at s = 5). In comparison with a single-tailed divalent surfactant (12-3-1) it was shown that the two-tailed equivalent (12-3-12) was more efficient in compacting DNA. A series of gemini surfactants based on cationic peptides with a alpha,omega-diamino alkyl spacer showed similar behavior upon changing the spacer length. Additionally, two surfactants based on diastereomers of tartaric acid with hexadecanoic acid tails and alpha,omega-diaminopropanyl and spermidine head groups, respectively, showed effects of head group size that depended strongly on entropy effects. The dependence on valency of the head group is found to be similar to what is known for mono- and multivalent ions, the latter being more efficient per unit of charge. (C) 2002 Elsevier Science (USA).
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| 31. |
- Kirby, A J, et al.
(författare)
-
Gemini surfactants: New synthetic vectors for gene transfection
- 2003
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Ingår i: Angewandte Chemie International Edition in English. - : Wiley. - 0570-0833 .- 1433-7851 .- 1521-3773. ; 42:13, s. 1448-1457
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Forskningsöversikt (refereegranskat)abstract
- The superior surfactant properties of cationic gemini surfactants are applied to the complex problem of introducing genes into cells. Of almost 250 new compounds tested, of some 20 different structural types, a majority showed very good transfection activity in vitro. The surfactant is shown to bind and compact DNA efficiently, and structural studies and calculations provide a working picture of the lipoplex formed. The lipoplex can penetrate the outer membranes of many cell types, to appear in the cytoplasm encapsulated within endosomes. Escape from the endosome - a key step for transfection - may be controlled by changes in the aggregation behavior of the lipoplex as the pH falls. The evidence suggests that DNA may be released from the lipoplex before entry into the nucleus, where the new gene can be expressed with high efficiency.
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| 32. |
- Kocherbitov, Vitaly, et al.
(författare)
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Effect of Oligomerization of Counterions on Water Activity in Aqueous Cationic Surfactant Systems
- 2016
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 120:28, s. 6961-6968
-
Tidskriftsartikel (refereegranskat)abstract
- A sorption calorimetry study of cationic cetyltrimethyl ammonium surfactants with four different counterions was performed. The counterions were acetate, succinate, citrate, and butyl tetracarboxylate with formal charges ranging from 1 to 4, respectively. The counterions with 2–4 charges can be considered as oligomers. In all the cases, hydration experiments started with dry solid phases that upon water uptake went through solid-state phase transitions and hexagonal to micellar cubic phase transitions. It was found that in liquid-crystalline phases the activity of water increased with the degree of oligomerization or, equivalently, the formal charge of the counterions. The results are discussed in terms of the forces acting between the colloidal aggregates. It is argued that under the conditions investigated, the so-called strong-coupling theory can be used to describe the electrostatic forces between the charged colloidal objects. Therefore, we suggest that the observed dependence of water activity on the degree of polymerization is due to the entropy of mixing of the counterions in the water volume, which we describe using Flory–Huggins theory.
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| 33. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Glassy crystalline state and water sorption of alkyl maltosides
- 2004
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:8, s. 3056-3061
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Tidskriftsartikel (refereegranskat)abstract
- A differential scanning calorimetric and sorption calorimetric study of two alkyl maltosides, C(8)G(2) and C(10)G(2), was performed. In the dry state, C(8)G(2) and C(10)G(2) do not form solid crystals but undergo a glass transition upon temperature change. The glass is partly ordered and has the same lamellar structure as the liquid crystals formed by the two maltosides. To reflect the presence of the glass transition and the structure, the terms "glassy crystals" and "glassy liquid crystals" can be used. A mechanism of the relaxation of the glassy crystals based on the results of small-angle X-ray scattering experiments is proposed. Experiments on water sorption showed that the glassy crystals turn into lyotropic liquid crystals upon sorption of water at constant temperature. This isothermal glass transition can be characterized by water content and change of partial molar enthalpy of mixing of water. A method to calculate the phase diagram liquid crystals-glassy liquid crystals is proposed.
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| 34. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Hydration of dimethyldodecylamine-N-oxide: Enthalpy and entropy driven processes
- 2006
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 110, s. 13649-13655
-
Tidskriftsartikel (refereegranskat)abstract
- Dimethyldodecylamine-N-oxide (DDAO) has only one polar atom that is able to interact with water. Still, this surfactant shows very hydrophilic properties: in mixtures with water, it forms normal liquid crystalline phases and micelles. Moreover, there is data in the literature indicating that the hydration of this surfactant is driven by enthalpy while other studies show that hydration of surfactants and lipids typically is driven by entropy. Sorption calorimetry allows resolving enthalpic and entropic contributions to the free energy of hydration at constant temperature and thus directly determines the driving forces of hydration. The results of the present sorption calorimetric study show that the hydration of liquid crystalline phases of DDAO is driven by entropy, except for the hydration of the liquid crystalline lamellar phase which is co-driven by enthalpy. The exothermic heat effect of the hydration of the lamellar phase arises from formation of strong hydrogen bonds between DDAO and water. Another issue is the driving forces of the phase transitions caused by the hydration. The sorption calorimetric results show that the transitions from the lamellar to cubic and from the cubic to the hexagonal phase are driven by enthalpy. Transitions from solid phases to the liquid crystalline lamellar phase are entropically driven, while the formation of the monohydrate from the dry surfactant is driven by enthalpy. The driving forces of the transition from the hexagonal phase to the isotropic solution are close to zero. These sorption calorimetric results are in good agreement with the analysis of the binary phase diagram based on the van der Waals differential equation. The phase diagram of the DDAO-water system determined using DSC and sorption calorimetry is presented.
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| 35. |
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| 36. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Hydration of trimethylamine-N-oxide and of dimethyldodecylamine-N-oxide: An ab initio study
- 2007
-
Ingår i: Journal of molecular structure. Theochem. - : Elsevier BV. - 0166-1280. ; 808:1-3, s. 111-118
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory (B3LYP) calculations of the hydration of trimethylamine-N-oxide (TMAO) and a surfactant dimethyldodecylamine-N-oxide (DDAO) are reported. Hydrogen-bonded complexes of DDAO with up to three water molecules and of TMAO with up to five water molecules are studied. Interactions of both TMAO and DDAO with water give rise to the binding energies that are much higher than that in the water dimer. A significant charge transfer from amine oxide to water is observed. Energies of water-water interactions increase in the presence of amine oxides. The hydration number of TMAO in the hydrogen bonded complexes is shown to be three. The energies of amine oxide-water interactions in the hydrogen bonded complexes have been analyzed using differential energetic parameters analogous to the parameters measured in calorimetric experiments.
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| 37. |
- Kocherbitov, V, et al.
(författare)
-
Lysozyme-Water Interactions Studied by Sorption Calorimetry
- 2004
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:49, s. 19036-19042
-
Tidskriftsartikel (refereegranskat)abstract
- Hydration of hen egg white lysozyme was studied by using the method of sorption calorimetry at 25, 40, and 50 °C. Desorption calorimetric measurements were performed at 25 and 40 °C. The activity of water and partial molar enthalpy of mixing of water were determined as functions of water content. Hydration of lysozyme occurs in four steps: slow penetration of water into the protein−protein interface; gradual glass transition, which occurs in every protein molecule independently of other molecules; further water uptake with disaggregation of protein aggregates and formation of a monolayer of water; and accumulation of free water. The amount of bound water found in desorption experiments is 420 water molecules per lysozyme molecule. Two hysteresis loops were found in the sorption isotherm of lysozyme. The small loop is caused by the slow penetration of water molecules into the protein−protein interface at very low water contents, while the large loop is due to the slow kinetics of aggregation of protein molecules upon desorption. The phase diagram of the lysozyme−water system is presented.
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| 38. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Lysozyme-water interactions studied by sorption calorimetry
- 2004
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:49, s. 19036-19042
-
Tidskriftsartikel (refereegranskat)abstract
- Hydration of hen egg white lysozyme was studied by using the method of sorption calorimetry at 25, 40, and 50degreesC. Desorption calorimetric measurements were performed at 25 and 40degreesC. The activity of water and partial molar enthalpy of mixing of water were determined as functions of water content. Hydration of lysozyme occurs in four steps: slow penetration of water into the protein-protein interface; gradual glass transition, which occurs in every protein molecule independently of other molecules; further water uptake with disaggregation of protein aggregates and formation of a monolayer of water; and accumulation of free water. The amount of bound water found in desorption experiments is 420 water molecules per lysozyme molecule. Two hysteresis loops were found in the sorption isotherm of lysozyme. The small loop is caused by the slow penetration of water molecules into the protein-protein interface at very low water contents, while the large loop is due to the slow kinetics of aggregation of protein molecules upon desorption. The phase diagram of the lysozyme-water system is presented.
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| 39. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Phase diagram and physicochemical properties of the n-octyl alpha-D-glucoside/water system
- 2003
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084. ; 5:23, s. 5262-5270
-
Tidskriftsartikel (refereegranskat)abstract
- Four experimental methods were used to study the phase diagram, as well as the thermodynamic and structural properties of the binary system n-octyl alpha-D-glucoside water in the temperature range 25-130degreesC. Sorption calorimetry allows one to determine the activity of water and enthalpy of mixing as functions of water content at constant temperature, while DSC scans temperature at constant composition and provides information on enthalpies of phase transitions. Therefore, the combination of the two calorimetric methods is a powerful too] to study composition-temperature phase diagrams. While calorimetry can be used to determine boundaries of the phases, NMR and SAXS methods are used to study their structures. A detailed phase diagram of the system is presented. A liquid crystalline cubic phase previously not reported in the system was found. The hydration in the system is endothermic, excluding the exothermic formation of hydrates. Using the sorption calorimetric method the lengths of the very short tie lines between the isotropic micellar and liquid crystalline phases were determined. Van der Waals's differential equation was used to calculate the slopes of t e phase boundaries. The parameters of the lamellar, cubic and hexagonal liquid crystalline phases were determined by means of SAXS. It was found that the area per surfactant headgroup in the liquid crystalline phases varied with composition.
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| 40. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Phase diagram and physiochemical properties of the n-octyl a D-glucoside/water system
- 2003
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 5:23, s. 5262-5270
-
Tidskriftsartikel (refereegranskat)abstract
- Four experimental methods were used to study the phase diagram, as well as the thermodynamic and structural properties of the binary system n-octyl -D-glucoside/water in the temperature range 25-130°C. Sorption calorimetry allows one to determine the activity of water and enthalpy of mixing as functions of water content at constant temperature, while DSC scans temperature at constant composition and provides information on enthalpies of phase transitions. Therefore, the combination of the two calorimetric methods is a powerful tool to study composition-temperature phase diagrams. While calorimetry can be used to determine boundaries of the phases, NMR and SAXS methods are used to study their structures. A detailed phase diagram of the system is presented. A liquid crystalline cubic phase previously not reported in the system was found. The hydration in the system is endothermic, excluding the exothermic formation of hydrates. Using the sorption calorimetric method the lengths of the very short tie lines between the isotropic micellar and liquid crystalline phases were determined. Van der Waalss differential equation was used to calculate the slopes of the phase boundaries. The parameters of the lamellar, cubic and hexagonal liquid crystalline phases were determined by means of SAXS. It was found that the area per surfactant headgroup in the liquid crystalline phases varied with composition.
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| 41. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Phase diagram and thermodynamics of the n-octyl beta-D-glucoside/water system
- 2002
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 106:11, s. 2910-2917
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we describe the application of a sorption calorimeter to study the binary system n-octyl beta-D-glucoside/water at 25, 40, and 60 degreesC. At 25 degreesC we also carried out experiments with heavy water which showed similar results to those with normal water. The method used allows one to simultaneously obtain information about the activity of water and the enthalpy of mixing in binary systems. The obtained results show that the hydration in the system is endothermic and hence driven by entropy. We have also specified the concentration ranges and thermodynamic properties of the different phases in the system. The first step of isothermal hydration in the system when the lamellar phase is formed involves high endothermic effect and is similar to the transition observed during the heating of the pure surfactant. Forces between the layers of the lamellar phase in the next step of hydration have also been studied at three temperatures. Using the calorimetric method, we have detertrimed concentration ranges of the narrow two-phase regions of the transitions from lamellar to cubic and isotropic phases. We have used van der Waals differential equation to calculate temperature-composition slopes of the phase boundaries using the isothermal properties of the system.
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| 42. |
- Lafitte, Géraldine, et al.
(författare)
-
Diffusion of nutrients molecules and model drug carriers through mucin layer investigated by magnetic resonance imaging with chemical shift resolution
- 2007
-
Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549. ; 96:2, s. 258-263
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic resonance imaging (MRI) with chemical shift resolution is a recent extension of MRI and it provides information about species resolved molecular transport on the macroscopic scale in complex systems. In this contribution, we show that by using this novel method, one can predict the behavior of drug and food molecules when they are in contact with the mucosal layer in the gastrointestinal tract. For the first time, the transport properties of a mixture of nutrients (i.e., a solution of ethanol and glucose) and of a model drug carrier (i.e., an equimolar solution of cationic and nonionic surfactants) through a mucin gel have been investigated. This study shows that transport properties of the diffusing molecules through a mucin gel are dependent on their size and physicochemical properties. In addition, we show that mucin gel acts as an efficient selective barrier. It favors the disintegration of mixed micelles of nonionic and cationic surfactants by stopping the diffusion of cationic surfactants with slightly affecting the diffusion of the nonionic surfactants. (c) 2006 Wiley-Liss, Inc.
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| 43. |
- Lafitte, Géraldine, et al.
(författare)
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Mixtures of mucin and oppositely charged surfactant aggregates with varying charge density. Phase behavior, association, and dynamics
- 2005
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:16, s. 7097-7104
-
Tidskriftsartikel (refereegranskat)abstract
- The nonionic surfactant Tween80 is a commonly used excipient in drug formulations containing an active substance with low aqueous solubility. Model drug vehicles with varying charge density were obtained by mixing Tween80 (PS-80) with the cationic surfactant Tetradecyltrimethylammonium chloride (TTAC), thus forming mixed micelles. The micelles were mixed with the negatively charged polyelectrolyte mucin, which is a component in the protective mucus layer covering epithelial cell linings. Depending on the composition of the mixture, complex-formation could be followed by precipitation. Using X-ray diffraction, it was found that the precipitate contained a lamellar phase with properties sensitive to the proportion of PS-80. Higher amounts of PS-80 were found to oppose phase separation. Further analysis in the one-phase region, or alternatively of the supernatant of two-phase samples, by H-1 NMR, HPLC, and diffusion measurements with PGSE-NMR led to the conclusions that at low proportion of PS-80 aggregates composed of mixed (PS-80 and TTAC) micelles and mucin were formed, whereas increased concentrations of PS-80 favored the dissolution of the precipitate and limited the interactions between mixed micelles and the polymer.
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| 44. |
- Lafitte, Géraldine, et al.
(författare)
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PFG-NMR diffusometry: A tool for investigating the structure and dynamics of noncommercial purified pig gastric mucin in a wide range of concentrations
- 2007
-
Ingår i: Biopolymers. - : Wiley. - 0006-3525 .- 1097-0282. ; 86:2, s. 165-175
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, Pulsed Field Gradient-Nuclear Magnetic Resonance, a powerful noninvasive tool for studying the dynamics and structure of complex-gels, has been used to measure diffusion of probe molecules in aqueous solutions/gels of noncommercial purified pig gastric mucin (PGM), in a concentration range up to 5 wt%. Complementary data were obtained from rheology measurements. The combination of techniques revealed a strong pH dependency of the structure of the PGM samples while changes in concentration, ionic strength, and temperature appeared to induce less pronounced alterations. Viscosity was found to vary in a nonmonotonous way with pH, with the more viscous solutions found at intermediate pH. We propose that this finding is due to a reduced charge density at lower pH, which is expected to continuously increase the relative importance of hydrophobic associations. The results suggest a loose network of expanded fully charged PGM molecules woth considerable mobility at neutral pH (pH 7.4). At intermediate pH (pH 4), a three-dimensional expanded network is favored. At pH 1, the charge density is low and microphase seperation occurs since hydrophobic associations prevail. This leads to the formation of clusters concentrated in PGM molecules seperated by regions depleted in PGM. The results obtained increase our knowledge about the gastric mucosal layer, which in vivo contains mucin in the same concentration range as that of the samples investigated here. (c) 2007 Wiley Periodicals, Inc.
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| 45. |
- Lasic, Samo, et al.
(författare)
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Investigations of vesicle gels by pulsed and modulated gradient NMR diffusion techniques
- 2011
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 7:8, s. 3947-3955
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Tidskriftsartikel (refereegranskat)abstract
- Vesicle gels are surfactant systems that form stiff gels with rather low amounts of surfactant. So far their structures have mostly been investigated using scattering techniques, which are generally appropriate for the study of structures on the nm-length-scale. Here we examine these gels using two complementary diffusion NMR techniques, which are both sensitive to structures on the mu m-scale. The presented results imply structural features on the mm-scale, indicating a more complex structure than just that of densely packed small vesicles, as previously found for these systems. It is demonstrated that a combination of the diffusion NMR methods, described here, can provide useful insights, when morphological features extend over a wide range of length scales.
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| 46. |
- Malmborg, Carin, et al.
(författare)
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Diffusion in an inhomogeneous system: NMR studies of diffusion in highly concentrated emulsions
- 2003
-
Ingår i: Journal of Colloid and Interface Science. - 1095-7103. ; 263:1, s. 270-276
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Tidskriftsartikel (refereegranskat)abstract
- In this study the self-diffusion of different species in highly concentrated water-in-oil emulsions was investigated by means of the NMR diffusometry approach. The emulsions contained 96% aqueous solutions of salt or other additives; hept ne was used as the oil phase. The surfactants, used to stabilize the emulsion, were soybean phosphatidylcholine and C12EO4. The water drops were about 1.5 mum in diameter according to diffusion measurements performed on water. Diffusion of tetramethyl ammonium ions and glucose between the emulsion droplets was found to be negligible on the relevant time-scale (<1 s). On the contrary, acetic acid/acetate ions diffused between the droplets and had exchange times which were a function of pH. (C) 2003 Elsevier Science (USA). All rights reserved.
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| 47. |
- Malmborg, Carin, et al.
(författare)
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Mapping the intracellular fraction of water by varying the gradient pulse length in q-space diffusion MRI
- 2006
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Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1096-0856 .- 1090-7807. ; 180:2, s. 280-285
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Tidskriftsartikel (refereegranskat)abstract
- Finite gradient pulse lengths are traditionally considered a nuisance in q-space diffusion NMR and MRI, since the simple Fourier relation between the acquired signal and the displacement probability is invalidated. Increasing the value of the pulse length leads to an apparently smaller value of the estimated compartment size. We propose that q-space data at different gradient pulse lengths, but with the same effective diffusion time, can be used to identify and quantify components with free or restricted diffusion from multi-exponential echo decay curves obtained on cellular systems. The method is demonstrated with experiments on excised human brain white matter and a series of model systems with well-defined free, restricted, and combined free and restricted diffusion behavior. Time-resolved diffusion MRI experiments are used to map the spatial distribution of the intracellular fraction in a yeast cell suspension during sedimentation, and observe the disappearance of this fraction after a heat treatment. (c) 2006 Elsevier Inc. All rights reserved.
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| 48. |
- Malmborg, Carin, et al.
(författare)
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NMR diffusometry and the short gradient pulse limit approximation
- 2004
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Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1096-0856 .- 1090-7807. ; 169:1, s. 85-91
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Tidskriftsartikel (refereegranskat)abstract
- In NMR diffusometry, one often uses the short gradient pulse (SGP) limit approximation in the interpretation of data from systems with restricted diffusion. The SGP limit approximation means that the gradient pulse length, delta, is so short that the spins do not diffuse during the pulse duration, but this condition is rarely met. If the length scale of the pores corresponds to the molecular mean square displacement during the gradient pulse, the measured echo intensities become a function of the gradient pulse length. Here, we have studied highly concentrated emulsions to show how the length of the gradient pulse influences NMR diffusion experiments. We have focused on molecules confined to one pore and molecules that can migrate through the porous system. For the former the echo decays give smaller pores than the actual case and for the latter we show large changes in echo decay depending on the gradient pulse length, everything else being equal. (C) 2004 Elsevier Inc. All rights reserved.
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| 49. |
- Mariette, F, et al.
(författare)
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H-1 NMR diffusometry study of water in casein dispersions and gels
- 2002
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 50:15, s. 4295-4302
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Tidskriftsartikel (refereegranskat)abstract
- The self-diffusion coefficients of water in casein solutions and gels were measured using a pulsed-gradient spin-echo nuclear magnetic resonance technique (PGSE NMR). The dependence of the self-diffusion coefficient of water on the concentration and structure-of casein is reported. The results were analyzed using a cell model. It was found that the water self-diffusion coefficient is insensitive to the structure of the casein in solution or in a gelled state. The influence of casein concentration on the water self-diffusion coefficient could be explained by obstruction from the casein molecule. Assuming a simple model with two water regions, each characterized by a specific water concentration and value of the water diffusion coefficient, the water mobility reduction induced by the casein can be rationalized.
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| 50. |
- Marques, Eduardo, et al.
(författare)
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Spontaneous Vesicle Formation in Catanionic Mixtures of Amino Acid-Based Surfactants: Chain Length Symmetry Effects.
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:19, s. 11009-11017
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Tidskriftsartikel (refereegranskat)abstract
- The use of amino acids for the synthesis of novel surfactants with vesicle-forming properties potentially enhances the biocompatibility levels needed for a viable alternative to conventional lipid vesicles. In this work, the formation and characterization of catanionic vesicles by newly synthesized lysine- and serine-derived surfactants have been investigated by means of phase behavior mapping and PFG-NMR diffusometry and cryo-TEM methods. The lysine-derived surfactants are double-chained anionic molecules bearing a pseudogemini configuration, whereas the serine-derived amphiphile is cationic and single-chained. Vesicles form in the cationic-rich side for narrow mixing ratios of the two amphiphiles. Two pairs of systems were studied: one symmetric with equal chain lengths, 2C 12/C 12, and the other highly asymmetric with 2C 8/C 16 chains, where the serine-based surfactant has the longest chain. Different mechanisms of the vesicle-to-micelle transition were found, depending on symmetry: the 2C 12/C 12 system entails limited micellar growth and intermediate phase separation, whereas the 2C 8/C 16 system shows a continuous transition involving large wormlike micelles. The results are interpreted on the basis of currently available models for the micelle-vesicle transitions and the stabilization of catanionic vesicles (energy of curvature vs mixing entropy).
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