| 1. |
- 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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| 2. |
- 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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| 3. |
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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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. - : American Chemical Society (ACS). - 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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| 7. |
- 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
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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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| 8. |
- 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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| 9. |
- 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
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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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| 10. |
- 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
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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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