| 1. |
- Ara, Kazi Zubaida Gulshan, et al.
(författare)
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Engineering CGTase to improve synthesis of alkyl glycosides
- 2021
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Ingår i: Glycobiology. - : Oxford University Press (OUP). - 1460-2423. ; 31:5, s. 603-612
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Tidskriftsartikel (refereegranskat)abstract
- Alkyl glycoside surfactants with elongated carbohydrate chains are useful in different applications due to their improved biocompatibility. Cyclodextrin glucanotransferases can catalyse the elongation process through the coupling reaction. However, due to the presence of a hydrophobic tail, the interaction between an alkyl glycoside acceptor and the active site residues is weaker than the interaction with maltooligosaccharides at the corresponding site. Here we report the mutations of F197, G263 and E266 near the acceptor subsites in the CGTase CspCGT13 from Carboxydocella sp. The results showed that substitutions of both F197 and G263 were important for the binding of acceptor substrate dodecyl maltoside during coupling reaction. The double mutant F197Y/G263A showed enhanced coupling activity and displayed a 2-fold increase of the primary coupling product using γ-cyclodextrin as donor when compared to wildtype CspCGT13. Disproportionation activity was also reduced, which was also the case for another double mutant (F197Y/E266A) that however not showed the corresponding increase in coupling. A triple mutant F197Y/G263A/E266A maintained the increase in primary coupling product (1.8-fold increase) using dodecyl maltoside as acceptor, but disproportionation was approximately at the same level as in the double mutants. In addition, hydrolysis of starch was slightly increased by the F197Y and G263A substitutions, indicating that interactions at both positions influenced the selectivity between glycosyl and alkyl moieties.
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| 2. |
- Bramer, Tobias, 1974-
(författare)
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Prolonged Drug Release from Gels, using Catanionic Mixtures
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of catanionic drug-surfactant mixtures was proven to be an efficient novel method of obtaining prolonged drug release from gels. It was shown that various commonly used drug compounds are able to form catanionic mixtures together with oppositely charged surfactants. These mixtures exhibited interesting phase behaviour, where, among other structures, vesicles and large worm-like or branched micelles were found. The size of these aggregates makes them a potential means of prolonging the drug release from gels, as only monomer drugs in equilibrium with larger aggregates were readily able to diffuse through the gel. When the diffusion coefficient for drug release from the formulation based upon a catanionic mixture was compared to that obtained for the drug substance and gel alone, the coefficient was some 10 to 100 times smaller.The effects of changes in the pH and ionic strength on the catanionic aggregates was also investigated, and this method of prolonging the release was found to be quite resilient to variations in both. Although the phase behaviour was somewhat affected, large micelles and vesicles were still readily found. The drug release was significantly prolonged even under physiological conditions, that is, at a pH of 7.4 and an osmolality corresponding to 0.9% NaCl.Surfactants of low irritancy, capric and lauric acid, may successfully be used instead of the more traditional surfactants, such as sodium lauryl sulfate (SDS), and prolonged release can still be obtained with ease.Some attempts to deduce the release mechanism from the proposed systems have also been made using transient current measurements, dielectric spectroscopy, and modelling of the release using the regular solution theory. In these studies, the previous assumptions made concerning the mechanism responsible for the release were confirmed to a large extent. Only small amounts of the drug existed in monomer form, and most seemed to form large catanionic aggregates with the oppositely charged surfactant.
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| 3. |
- Dew, Noel, 1980-
(författare)
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Catanionic Aggregates in Gels : Prolonged Drug Release and Potential Implications for Topical Use
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gels are popular dosage forms. This topical dosage form may be advantageous compared to oral or parenteral dosage forms. Favorable rheological or bioadhesive properties of gels might provide extended contact times at the site of administration compared to aqueous solutions. However, due to the high water content of gels, these are usually quickly emptied of the drug substance. One way of prolonging the drug release from gels is to contain the drug substance in catanionic aggregates in the gel. These aggregates are formed in solutions of oppositely charged surfactants and a drug can be used instead of one of the surfactants. In this thesis catanionic aggregates composed of drug substances and oppositely charged surfactants were studied and the possibility to use these aggregates for the purpose of prolonged drug release was investigated. The formation of catanionic aggregates when using drugs was found to be a common occurrence in addition to which, the oppositely charged surfactant can be varied and surfactants of natural origin with a low toxicity were used. Most combinations tested rendered either vesicles or elongated micelles. When the catanionic aggregates were contained in gels the drug release was substantially prolonged. The apparent diffusion coefficients were lowered 10-100 times compared to the reference gels. When gels with catanionic vesicles with substantial prolonged drug release were applied to skin the penetration rate was lowered extensively. No morphological differences were observed between skin samples that had been exposed to formulations containing catanionic aggregates and skin samples exposed to saline solution, air or formulations containing only the drug. Both conventional, covalently linked pre-formed gels and physical gels, where the catanionic vesicles form the cross-links upon interaction with the polymer, can be used for these purposes. When the effect of drug release on aggregate structure was studied, it was shown that vesicles are present in both conventional and physical gels throughout the drug release process. This thesis shows that catanionic aggregates contained in gels can present an advantageous formulation strategy to prolong the drug release, thereby improving the efficiency of gel formulations.
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| 4. |
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| 5. |
- 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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| 6. |
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| 7. |
- 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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| 8. |
- Ericsson, Caroline, et al.
(författare)
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Solid-state phase behaviour of dodecylglycosides
- 2005
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Ingår i: Carbohydrate Research. - : Elsevier BV. - 1873-426X .- 0008-6215. ; 340:8, s. 1529-1537
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Tidskriftsartikel (refereegranskat)abstract
- The solid-state phase behaviour of lyophilised n-dodecyl-beta-D-glucoside (beta-C(12)G(1)), n-dodecyl-beta-D-maltoside (beta-C(12)G(2)) and n-dodecyl-beta-D-maltotrioside (beta-C(12)G(3)) has been investigated by differential scanning calorimetry (DSC) and X-ray techniques. For beta-C(12)G(1), lyophilisation results in a formation of a crystalline anhydrate. The lamellar spacing (37 angstrom) is consistent with an alkyl chain packing in which the chains are not interdigitated. At 80 degrees C, the material melts into a lamellar liquid crystal with a lamellar spacing of 32 angstrom, which suggests that the non-interdigitated chain packing of the crystalline state is retained in the liquid crystal. In contrast, lyophilisation of beta-C(12)G(2) and beta-C(12)G(3) results in the formation of a glassy state, best described as a frozen version of the lamellar liquid crystal. For beta-C(12)G(2), the lamellar spacing in the glass and liquid crystal suggests interdigitation of the alkyl chains. The glass transition temperature was found to be 65 degrees C for beta-C(12)G(3), and 100 degrees C for K12G3, which compares favourably with the glass transition of the parent carbohydrates. A second crystalline modification of beta-C(12)G(1) was prepared by precipitation from an aqueous solution at temperatures below the Krafft point (38 degrees C). For this modification, the lamellar distance (24 angstrom) is consistent with interdigitated alkyl chains. At 50 degrees C, the crystalline material melts into a liquid crystalline phase. The material also readily loses water and rapidly re-crystallises to the anhydrate. The amount of water lost upon drying is consistent with the idea that the material is a monohydrate of beta-C(12)G(1). The drying and re-crystallisation processes give rise to 'pre-transitions' in the DSC thermograms and illustrate the importance of careful control of water in any analysis of the phase behaviour of alkylglycosides. (c) 2005 Elsevier Ltd. All rights reserved.
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| 9. |
- 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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| 10. |
- Gillgren, H., et al.
(författare)
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Morphology and Molecular Conformation in Thin Films of Poly-gamma-methyl-L-glutamate at the Air-Water Interface
- 2002
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 18:2, s. 462-469
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of poly-gamma-methyl-L-glutamate (pMeE) at the air-water interface has been studied with the surface film balance technique. In addition, Langmuir-Blodgett (LB) films of pMeE deposited on mica and quartz have been studied by atomic force microscopy (AFM) and circular and linear dichroism (CD and LD) spectroscopy. Depending on the spreading solvent, pMeE displays strikingly different compression isotherms. When spread from chloroform or trifluoroacetic acid (TFA) the surface pressure isotherms are consistent with that of a peptide in a-helix conformation. However, the latter solvent gives rise to isotherms with a considerably smaller apparent mean molecular area, A(0). When spread from pyridine, on the other hand, pMeE yields an isotherm that is expanded and inconsistent with the presence of a monolayer consisting entirely of a-helical peptides. Isotherms and AFM images strongly suggest that peptide aggregation and solvent retention are the main factors behind the isotherm differences. When the water-soluble spreading solvent TFA is used, pMeE forms discrete wormlike aggregates embedded in a monolayer matrix. In the pyridine case, aggregation in the spreading solvent and retention of pyridine in the film result in a rough aggregate network coexisting with discrete aggregates. No aggregation takes place when chloroform is used as spreading solvent. CD and LD spectra of the LB films reveal a pronounced lateral orientation of the alpha-helices in films spread from chloroform and TFA, while spectra of films spread from pyridine are consistent with unordered peptide strands in beta-sheet conformation. In conclusion, the results show that if water-soluble and/or low-volatile solvents are used as spreading media, hydrophobic peptides cannot, a priori, be assumed to form proper monolayers.
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| 11. |
- Heidarian Höckerfelt, Mina, 1969-
(författare)
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On the chemical and processing stability of pharmaceutical solids : Solid form dependent water presenting capacity and process induced solid form transformation
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is a need for improving our knowledge and understanding about formation mechanisms and nature of amorphous state in order to prevent the unintended presence of disorder in solid pharmaceutical products and reduce the related stability issues. The suggested theory that water binding capacity of amorphous cellulose affects the chemical stability of hydrolysis sensitive drugs in formulations with cellulose based excipients needs a clarification and water-cellulose interaction profiles need to be examined. This thesis has addressed these questions.Chemical, mechanical and thermal methods have been used to create partially or predominantly amorphous solids. Mechanisms and the pathways for transformation to amorphous phase and the characteristic qualities of this phase is studied in order to give some tools to predict, to control or prevent the creation of disorder in a crystalline structure. The water interaction with amorphous pharmaceutical materials has been studied to improve stability of hydrolysis sensitive drugs. The transition to amorphous state during handling of pharmaceutical material, referred to as mechanical activation in processes like blending, mixing and compression is substantially a consequence of vitrification. The process is described as creation of hot spots where friction caused by particle sliding raise the temperature above the melting point of the material. The fast cooling process promotes creation of a local disordered molecular arrangement. It is possible to decrease the degree of amorphisation and undesired stability problems by reducing the friction and inhibit the creation of crystal defects during processing. The glass-forming propensity is an inherent material characteristic related to molecular size and structure and is not process dependent. Molecules with a couple of aromatic rings are often poor glass-formers. Less symmetrical, branched molecular structures with presence of electronegative atoms are more readily transformed to and exist in amorphous state when handled and stored at temperatures below their glass transition temperature. The interaction profile of cellulose with water is strongly dependent on solid state structure of cellulose. Crystallinity is the key parameter in water presenting capacity of cellulose. Amorphous regions have a capacity to bind the water and decrease water mobility and in that way reduce cellulose water presenting capacity despite higher moisture content in partially amorphous cellulose compared to crystalline cellulose. The fact that higher amorphous content decreases cellulose water presenting capacity is a promising lead to improve stability of hydrolysis sensitive drugs in compositions with cellulose. This knowledge could be applicable to other pharmaceutical materials as the differences between crystalline and amorphous states of material are generally the same for different kind of materials.
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| 12. |
- Knöös, Patrik, et al.
(författare)
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Effects of Added Surfactant on Swelling and Molecular Transport in Drug-Loaded Tablets Based on Hydrophobically Modified Poly(acrylic acid)
- 2014
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:32, s. 9757-9767
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Tidskriftsartikel (refereegranskat)abstract
- A combination of NMR chemical shift imaging and self-diffusion experiments is shown to give a detailed molecular picture of the events that occur when tablets of hydrophobically modified poly(acrylic acid) loaded with a drug (griseofulvin) swell in water in the presence or absence of surfactant (sodium octylbenzenesulfonate). The hydrophobic substituents on the polymer bind and trap the surfactant molecules in mixed micelles, leading to a slow effective surfactant transport that occurs via a small fraction of individually dissolved surfactant molecules in the water domain. Because of the efficient binding of surfactant, the penetrating water is found to diffuse past the penetrating surfactant into the polymer matrix, pushing the surfactant front outward as the matrix swells. The added surfactant has little effect on the transport of drug because both undissolved solid drug and surfactant-solubilized drug function as reservoirs that essentially follow the polymer as it swells. However, the added surfactant nevertheless has a strong indirect effect on the release of griseofulvin, through the effect of the surfactant on the solubility and erosion of the polymer matrix. The surfactant effectively solubilizes the hydrophobically modified polymer, making it fully miscible with water, leading to a more pronounced swelling and a slower erosion of the polymer matrix.
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| 13. |
- Knöös, Patrik, et al.
(författare)
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Release of a Poorly Soluble Drug from Hydrophobically Modified Poly (Acrylic Acid) in Simulated Intestinal Fluids.
- 2015
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:10
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Tidskriftsartikel (refereegranskat)abstract
- A large part of new pharmaceutical substances are characterized by a poor solubility and high hydrophobicity, which might lead to a difference in drug adsorption between fasted and fed patients. We have previously evaluated the release of hydrophobic drugs from tablets based on Pemulen TR2 and showed that the release can be manipulated by adding surfactants. Here we further evaluate the possibility to use Pemulen TR2 in controlled release tablet formulations containing a poorly soluble substance, griseofulvin. The release is evaluated in simulated intestinal media that model the fasted state (FaSSIF medium) or fed state (FeSSIF). The rheology of polymer gels is studied in separate experiments, in order to gain more information on possible interactions. The release of griseofulvin in tablets without surfactant varied greatly and the slowest release were observed in FeSSIF. Addition of SDS to the tablets eliminated the differences and all tablets showed a slow linear release, which is of obvious relevance for robust drug delivery. Comparing the data from the release studies and the rheology experiment showed that the effects on the release from the different media could to a large extent be rationalised as a consequence of the interactions between the polymer and the surfactants in the media. The study shows that Pemulen TR2 is a candidate for controlled release formulations in which addition of surfactant provides a way to eliminate food effects on the release profile. However, the formulation used needs to be designed to give a faster release rate than the tablets currently investigated.
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| 14. |
- Knöös, Patrik, et al.
(författare)
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Surfactants modify the release from tablets made of hydrophobically modified poly (acrylic acid)
- 2013
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Ingår i: Results in Pharma Sciences. - : Elsevier BV. - 2211-2863. ; 3, s. 7-14
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Tidskriftsartikel (refereegranskat)abstract
- Many novel pharmaceutically active substances are characterized by a high hydrophobicity and a low water solubility, which present challenges for their delivery as drugs. Tablets made from cross-linked hydrophobically modified poly (acrylic acid) (CLHMPAA), commercially available as Pemulen™, have previously shown promising abilities to control the release of hydrophobic model substances. This study further investigates the possibility to use CLHMPAA in tablet formulations using ibuprofen as a model substance. Furthermore, surfactants were added to the dissolution medium in order to simulate the presence of bile salts in the intestine. The release of ibuprofen is strongly affected by the presence of surfactant and/or buffer in the dissolution medium, which affect both the behaviour of CLHMPAA and the swelling of the gel layer that surrounds the disintegrating tablets. Two mechanisms of tablet disintegration were observed under shear, namely conventional dissolution of a soluble tablet matrix and erosion of swollen insoluble gel particles from the tablet. The effects of surfactant in the surrounding medium can be circumvented by addition of surfactant to the tablet. With added surfactant, tablets that may be insusceptible to the differences in bile salt level between fasted or fed states have been produced, thus addressing a central problem in controlled delivery of hydrophobic drugs. In other words CLHMPAA is a potential candidate to be used in tablet formulations for controlled release with poorly soluble drugs.
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| 15. |
- Knöös, Patrik, et al.
(författare)
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Using NMR Chemical Shift Imaging To Monitor Swelling and Molecular Transport in Drug-Loaded Tablets of Hydrophobically Modified Poly(acrylic acid): Methodology and Effects of Polymer (In)solubility
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:45, s. 13898-13908
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Tidskriftsartikel (refereegranskat)abstract
- A new technique has been developed using NMR chemical shift imaging (CSI) to monitor water penetration and molecular transport in initially dry polymer tablets that also contain small low-molecular weight compounds to be released from the tablets. Concentration profiles of components contained in the swelling tablets could be extracted via the intensities and chemical shift changes of peaks corresponding to protons of the components. The studied tablets contained hydrophobically modified poly(acrylic acid) (HMPAA) as the polymer component and griseofulvin and ethanol as hydrophobic and hydrophilic, respectively, low-molecular weight model compounds. The water solubility of HMPAA could be altered by titration with NaOH. In the pure acid form, HMPAA tablets only underwent a finite swelling until the maximum water content of the polymer-rich phase, as confirmed by independent phase studies, had been reached. By contrast, after partial neutralization with NaOH, the polyacid became fully miscible with water. The solubility of the polymer affected the water penetration, the polymer release, and the releases of both ethanol and griseofulvin. The detailed NMR CSI concentration profiles obtained highlighted the clear differences in the disintegration/dissolution/release behavior for the two types of tablet and provided insights into their molecular origin. The study illustrates the potential of the NMR CSI technique to give information of importance for the development of pharmaceutical tablets and, more broadly, for the general understanding of any operation that involves the immersion and ultimate disintegration of a dry polymer matrix in a solvent.
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| 16. |
- Kocherbitov, Vitaly, et al.
(författare)
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Hydration of a natural polyelectrolyte xanthan gum : Comparison with non-ionic carbohydrates
- 2010
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Ingår i: Carbohydrate Polymers. - : Elsevier. - 0144-8617 .- 1879-1344. ; 82:2, s. 284-290
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Tidskriftsartikel (refereegranskat)abstract
- In dilute solutions, polyelectrolytes exhibit more hydrophilic properties than non-charged polymers do. However, extension of this statement on almost dry systems is questionable. In this study we present sorption calorimetric data on hydration of a natural carbohydrate polyelectrolyte xanthan gum and make comparison with analogous data of three types of cellulose which is a non-charged carbohydrate polymer. An analysis of the sorption isotherm shows that at given relative humidities xanthan gum absorbs greater amount of water than non-charged cellulose does. Nonetheless, the enthalpies of hydration of xanthan gum and of all three considered types of cellulose at zero water content are equal to −18 kJ/mol. Thus, entropy of hydration plays an important role in water sorption behaviour of xanthan gum. The apparent absence of an ion effect on polymer–water interactions can be explained by solvation of ions by OH-groups of the dry xanthan gum. Ab initio calculations presented here show that solvation of an ionic group of xanthan gum by a carbohydrate hydroxyl is as strong as hydration of the same group by water. The exothermic heat effect of hydration arises from the loss of the mobility of water on the rigid glassy environment of the polymer. For the first time, the glass transition temperature of dry xanthan gum is reported to be 60 °C.
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| 17. |
- Kocherbitov, Vitaly, et al.
(författare)
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Hydration of microcrystalline cellulose and milled cellulose studied by sorption calorimetry.
- 2008
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Ingår i: Phys. Chem. B.. - : American Chemical Society (ACS). ; 112:12, s. 3728-3734
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Tidskriftsartikel (refereegranskat)abstract
- The hydration of two different polymorphs of microcrystalline cellulose (cellulose I and II), as well as the hydration of amorphous cellulose was studied using water sorption calorimetry, gravimetric water vapor sorption, nitrogen sorption, and X-ray powder diffraction. Amorphous cellulose was prepared by means of ball-milling of microcrystalline cellulose (MCC). Whereas X-ray data showed the untreated MCC to consist of cellulose I, the amorphous cellulose was found to recrystallize into cellulose II after contact with water or water vapor at relative humidities (RHs) above 90%. Sorption isotherms show an increase of water sorption in the sequence cellulose I < cellulose II < amorphous cellulose. The enthalpy of water sorption becomes more exothermic in the same sequence. The specific area of cellulose is dramatically higher when calculated from the water adsorption than when calculated from nitrogen adsorption. A proposed mechanism of water sorption by MCC implies the adsorption of water molecules at solid-solid interfaces, i.e., between neighboring microfibrils, which explains the observed difference between water and nitrogen. The Brunauer-Emmett- Teller (BET) model is therefore not appropriate for the description of the hydration of cellulose. Rather, the Langmuir model represents a more accurate description of water sorption by MCC at low RH. At higher RH, the water adsorption competes with capillary condensation. The thickness of microfibrils, as calculated using the fitting of the sorption isotherm of MCC with the Langmuir equation, is about 4 nm. This value compares favorably with literature data.
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| 18. |
- Larsson, Johan, et al.
(författare)
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Molecular structure of maltoside surfactants controls micelle formation and rheological behavior
- 2021
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 581, s. 895-904
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Tidskriftsartikel (refereegranskat)abstract
- Hypothesis: The anomeric configuration (α or β) of n-hexadecyl-D-maltopyranoside (C16G2) has been shown to affect the morphology of the micelle, from elongated for α-C16G2 to worm-like micelles for β-C16G2. The entanglement of worm-like micelles often leads to strong modifications of the rheological behavior of the system and, as such, the anomeric configuration of C16G2 could also provide the possibility of controlling this. Furthermore, mixing these surfactants are hypothesized to result in mixed micelles allowing to finely tune the rheology of a system containing these sustainable surfactants. Experiments: The rheology of α- and β-C16G2, and mixtures of those, was determined by rotational and oscillatory rheology at different temperatures and surfactant concentrations. Micelle structure and composition for these systems were characterized using contrast variation small-angle neutron scattering and small-angle X-ray scattering. The results from these were connected in order to elaborate a molecular understanding of the rheological response of the system. Findings: The self-assembly of these surfactants have been found to result in different rheological properties. β-C16G2 show a high viscosity with a non-Newtonian viscoelastic behavior, which was linked to the formation of worm-like micelles. In contrast, α-C16G2 self-assembled into short cylindrical micelles, resulting in a Newtonian fluid with low viscosity. Furthermore, mixtures of these two surfactants lead to systems with intermediate rheological properties as a result of the formation of micelles with intermediate morphology to those of the pure anomers. These results also show that the rheological properties of the system can be tuned to change the micelle morphology, which in turn depends on the anomeric configuration of the surfactant. Also, surfactant concentration, temperature of the system, and micelle composition for surfactant mixtures provide control over the rheological properties of the system in a wide temperature range. Therefore, these results open new possibilities in the development of sustainable excipients for formulation technology, where the characteristics of the system can be easily tailored through geometric variations in the monomer structure whilst maintaining the chemical composition of the system.
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| 19. |
- Larsson, Johan, et al.
(författare)
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Shear-induced nanostructural changes in micelles formed by sugar-based surfactants with varied anomeric configuration
- 2022
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 606, s. 328-336
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Tidskriftsartikel (refereegranskat)abstract
- Hypothesis: The self-assembly of long tail sugar-based surfactants into worm-like micelles has recently been demonstrated, and the rheological properties of such systems have been shown to be tuneable through subtle modifications of the molecular characteristics of the surfactant monomer. In particular, the anomeric configuration of the hexadecylmaltoside headgroup was shown to induce profound changes in the nanostructure and rheology of the system. The origin of such changes is hypothesised to arise from differences in the structure and relaxation of the micellar networks in the semi-dilute regime. Experiments: Here we explore the molecular background to the flow properties of the two anomers of hexadecylmaltoside (alpha- and beta-C(16)G(2)) by directly connecting their rheological behaviour to the micelle morphology. For this purpose, 1-3 plane rheo-small-angle neutron scattering measurements, using a Couette cell geometry, probed the structural changes in the micellar phase under shear. The effect of surfactant anomeric configuration, surfactant concentration, temperature and mixing ratio of the two anomers were investigated. The static micelle structure in the semi-dilute regime was determined using the polymer reference interaction site model. Findings: The segmental alignment of the micellar phase was studied under several flow conditions, showing that the shear-thinning behaviour relates to the re-arrangement of beta-C(16)G(2) worm-like micelles, whilst shorter alpha-C(16)G(2) micelles are considerably less affected by the flow. The results are rationalised in terms of micelle alignment and disruption of the entangled network, providing a detailed mechanism by which sugar-based surfactants control the rheology of the fluid. To further enable future studies, we provide the complete code for modelling micelle structure in the semi-dilute regime using the polymer reference interaction site model. (C) 2021 The Authors. Published by Elsevier Inc.
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| 20. |
- Larsson, Johan, et al.
(författare)
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Tail unsaturation tailors the thermodynamics and rheology of a self-assembled sugar-based surfactant
- 2021
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 585, s. 178-183
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Tidskriftsartikel (refereegranskat)abstract
- Hypothesis: The self-assembly of long-tail surfactants results in the formation of nanoscale structures, e.g. worm-like micelles, with the ability to modify the rheology of the system. However, micelle formation, and thus the alteration of the rheology, is subject to the high Krafft temperature of saturated long-tail surfactants. Hexadecylmaltosides are sustainable surfactants that, in solution, form tailorable viscoelastic fluids. The preparation of monounsaturated sugar-based surfactants is hypothesised to reduce the Krafft point compared to the saturated analogues, therefore increasing the temperature range where the surfactant remains in the micellar form.Experiments: Here we report the synthesis and characterisation of a novel sugar-based surfactant with an unsaturated C16-tail, namely palmitoleyl-β-D-maltoside (β-C16-1G2). Differential scanning calorimetry was used to probe the temperature stability of the system. The rheology of β-C16-1G2 solutions was investigated by means of rotational and oscillatory rheology, and these results were connected to the mesoscopic structure of the system as shown by small-angle neutron and X-ray scattering, and dynamic light scattering. Findings: The presence of a double bond on the alkyl chain moiety leads to a depression in the Krafft point, allowing the surfactant to form a thermodynamically stable micellar solution over a wide range of temperatures, i.e. 5–95 °C. The surfactant self-assembles into worm-like micelles which, upon entanglement in the semi-dilute regime, result in the formation of a non-Newtonian, viscoelastic fluid. These observations have important implications in the development of new sustainable formulated products, enabling the preparation of surfactant phases with remarkable thermal resilience.
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| 21. |
- Larsson, Johan, et al.
(författare)
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The effect of the anomeric configuration on the micellization of hexadecylmaltoside surfactants
- 2019
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 35:43, s. 13904-13914
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Tidskriftsartikel (refereegranskat)abstract
- The self-assembly of the two anomeric forms of n-hexadecyl-D-maltopyranoside (denoted α-C16G2 and β-C16G2) has been studied in dilute aqueous solution by means of surface tension measurements, scattering methods (dynamic light scattering, static light scattering, and small-angle X-ray and neutron scattering) and cryo-transmission electron microscopy at different surfactant concentrations and temperatures. Surface tension measurements demonstrate differences in the surfactant adsorption at the air-water interface, where α-C16G2 shows a lower CMC than β-C16G2. Similarly, micelle morphology was found to profoundly depend on anomerism. β-C16G2 preferentially forms very elongated micelles with large persistence lengths, whereas α-C16G2 assembles into smaller micelles for which the structure varies with concentration and temperature. The differences between the two surfactant anomers in terms of self-assembly can be attributed to the interaction between neighboring headgroups. Specifically, β-C16G2 allows for a closer packing in the palisade layer, hence reducing the micelle curvature and promoting the formation of more elongated micelles. Strong intermolecular headgroup interactions may also account for the observed rigidity of the micelles.
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| 22. |
- Sanchez-Fernandez, Adrian, et al.
(författare)
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An integrative toolbox to unlock the structure and dynamics of protein-surfactant complexes
- 2020
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Ingår i: Nanoscale Advances. - : Royal Society of Chemistry (RSC). - 2516-0230. ; 2:9, s. 4011-4023
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between protein and surfactants play an important role in the stability and performance of formulated products. Due to the high complexity of such interactions, multi-technique approaches are required to study these systems. Here, an integrative approach is used to investigate the various interactions in a model system composed of human growth hormone and sodium dodecyl sulfate. Contrast variation small-angle neutron scattering was used to obtain information on the structure of the protein, surfactant aggregates and surfactant-protein complexes. 1H and 1H-13C HSQC nuclear magnetic resonance spectroscopy was employed to probe the local structure and dynamics of specific amino acids upon surfactant addition. Through the combination of these advanced methods with fluorescence spectroscopy, circular dichroism and isothermal titration calorimetry, it was possible to identify the interaction mechanisms between the surfactant and the protein in the pre- and post-micellar regimes, and interconnect the results from different techniques. As such, the protein was revealed to evolve from a partially unfolded conformation at low SDS concentration to a molten globule at intermediate concentrations, where the protein conformation and local dynamics of hydrophobic amino acids are partially affected compared to the native state. At higher surfactant concentrations the local structure of the protein appears disrupted, and a decorated micelle structure is observed, where the protein is wrapped around a surfactant assembly. Importantly, this integrative approach allows for the identification of the characteristic fingerprints of complex transitions as seen by each technique, and establishes a methodology for an in-detail study of surfactant-protein systems. This journal is
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| 23. |
- Sanchez-Fernandez, Adrian, et al.
(författare)
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Topological Dynamics of Micelles Formed by Geometrically Varied Surfactants.
- 2022
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 38:33, s. 10075-10080
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Tidskriftsartikel (refereegranskat)abstract
- The molecular architecture of sugar-based surfactants strongly affects their self-assembled structure, i.e., the type of micelles they form, which in turn controls both the dynamics and rheological properties of the system. Here, we report the segmental and mesoscopic structure and dynamics of a series of C16 maltosides with differences in the anomeric configuration and degree of tail unsaturation. Neutron spin-echo measurements showed that the segmental dynamics can be modeled as a one-dimensional array of segments where the dynamics increase with inefficient monomer packing. The network dynamics as characterized by dynamic light scattering show different relaxation modes that can be associated with the micelle structure. Hindered dynamics are observed for arrested networks of worm-like micelles, connected to their shear-thinning rheology, while nonentangled diffusing rods relate to Newtonian rheological behavior. While the design of novel surfactants with controlled properties poses a challenge for synthetic chemistry, we demonstrate how simple variations in the monomer structure can significantly influence the behavior of surfactants.
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| 24. |
- Sjögren, Helen, et al.
(författare)
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Comparison of the helix-coil transition of a titrating polypeptide in aqueous solutions and at the air-water interface
- 2005
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Ingår i: Biophysical Chemistry. - : Elsevier BV. - 1873-4200 .- 0301-4622. ; 116:1, s. 11-21
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Tidskriftsartikel (refereegranskat)abstract
- The transition from a-helix to random coil of the titrating polyamino acid Co-poly-L-(lysine, phenylalanine), (p-(Lys,Phe)), has been investigated as a function of pH and ionic strength in aqueous solution and at the air water interface by means of circular dichroism (CD) spectroscopy and the Langmuir surface film balance technique. The results strongly suggest that the helix-coil transition for peptides at the air-water interface can be determined by using the two-dimensional Flory exponent, v, to express the pH dependent peptide surface conformation. The helix-coil titration curve of p-(Lys,Phe) shifts approximately 2.5 pH units towards lower pH at the air-water interface, as compared with the bulk solution. This finding is of relevance for the understanding of conformation and conformational changes of membrane-tran sporting and membrane penetrating peptides as well as for the use of peptides in molecular devices. (c) 2005 Elsevier B.V All rights reserved.
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| 25. |
- Sjögren, Helen, et al.
(författare)
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Effects of pH, ionic strength, calcium, and molecular mass on the arrangement of hydrophobic peptide helices at the air-water interface
- 2004
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 108:52, s. 20219-20227
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Tidskriftsartikel (refereegranskat)abstract
- The influence of subphase characteristics (ionic strength, pH, and the presence of bridging cations) on the conformation and lateral orientation of the hydrophobic polypeptide poly-(L)-leucine (p-leu) has been investigated at the air-water interface with the surface film balance technique as well as with Brewster angle microscopy (BAM). In addition, Langmuir-Blodgett films of p-leu deposited on quartz and mica from different subphases have been studied by circular dichroism (CD) spectroscopy and atomic force microscopy (AFM). P-leu forms alpha-helices at the interface regardless of subphase characteristics. Long-range lateral orientation of the alpha-helical strands in the p-leu monolayer was obtained under conditions where attractive interpeptide end-group interactions prevail. These interactions were obtained under conditions where (1) end-group charges lend a zwitterionic character to the peptide, thus enabling strong electrostatic attraction between adjacent strands, (2) there is a possibility for formation of carboxylic acid dimers, or (3) calcium bridges form between carboxylate end groups. These three cases correspond to an increase of the effective molecular mass of the peptide. It was concluded that such an increase, and thereby an increased long-range lateral orientation, can be obtained by enabling peptide end group attraction, but not by screening peptide end group repulsion. Kinetic studies of monolayer relaxation strongly suggest that the end-group effects influence the thermodynamic, as well as the kinetic, properties of peptide monolayers.
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| 26. |
- Sjögren, Helen, et al.
(författare)
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Interactions between charged polypeptides and nonionic surfactants
- 2005
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Ingår i: Biophysical Journal. - : Elsevier BV. - 1542-0086 .- 0006-3495. ; 89:6, s. 4219-4233
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Tidskriftsartikel (refereegranskat)abstract
- The influence of molecular characteristics on the mutual interaction between peptides and nonionic surfactants has been investigated by studying the effects of surfactants on amphiphilic, random copolymers of alpha-L-amino acids containing lysine residues as the hydrophilic parts. The hydrophobic residues were either phenylalanine or tyrosine. The peptide-surfactant interactions were studied by means of circular dichroism spectroscopy and binding isotherms, as well as by 1D and 2D NMR. The binding of surfactant to the peptides was found to be a cooperative process, appearing at surfactant concentrations just below the critical micellar concentration. However, a certain degree of peptide hydrophobicity is necessary to obtain an interaction with nonionic surfactant. When this prerequisite is fulfilled, the peptide mainly interacts with self-assembled, micelle-like surfactant aggregates formed onto the peptide chain. Therefore, the peptide-surfactant complex is best described in terms of a necklace model, with the peptide interacting primarily with the palisade region of the micelles via its hydrophobic side chains. The interaction yields an increased amount of alpha-helix conformation in the peptide. Surfactants that combine small headgroups with a propensity to form small, nearly spherical micelles were shown to give the largest increase in alpha-helix content.
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| 27. |
- Svensson, David, et al.
(författare)
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Efficient synthesis of a long carbohydrate chain alkyl glycoside catalysed by cyclodextrin glycosyltransferase (CGTase).
- 2009
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 1097-0290 .- 0006-3592. ; 104:5, s. 854-861
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Tidskriftsartikel (refereegranskat)abstract
- Alkyl glycosides with long carbohydrate groups are surfactants with attractive properties but they are very difficult to synthesize. Here, a method for extension of the carbohydrate group of commercially available dodecyl-beta-D-maltoside (DDM) is presented. (DDM) was converted to dodecyl-beta-D-maltooctaoside (DDMO) in a single step by using a CGTase as catalyst and alpha-cyclodextrin (alpha-CD) as glycosyl donor. The coupling reaction is under kinetic control and the maximum yield depends on the selectivity of the enzyme. The B. macerans CGTase favoured the coupling reaction while the Thermoanaerobacter enzyme also catalysed disproportionation reactions leading to a broader product range. A high ratio alpha-CD/DDM favoured a high yield of DDMO and yields up to 80 % were obtained using the B. macerans enzyme as catalyst. (c) 2009 Wiley Periodicals, Inc.
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| 28. |
- Svensson, David, et al.
(författare)
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Enzymatic route to alkyl glycosides having oligomeric head groups
- 2009
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Ingår i: Green Chemistry. - : Royal Society of Chemistry (RSC). - 1463-9270 .- 1463-9262. ; 11:8, s. 1222-1226
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Tidskriftsartikel (refereegranskat)abstract
- Cyclodextrin glycosyl transferase (CGTase) from Bacillus macerans was used to catalyse the coupling of alpha-cyclodextrin to alkyl beta-glycosides. The acceptor substrate dodecyl beta-maltoside was thus converted to dodecyl beta-D-maltooctaoside. Further coupling steps and disproportionation reactions occurred, but by optimisation of the reaction time, a yield of 50% of the primary coupling product was obtained. The method worked well for a range of acceptors with different length of the carbohydrate part (1-3 glucose residues) and the hydrocarbon chain (10-14 carbon atoms). With respect to the principles of green chemistry, the method is superior to previously used methods involving protection/deprotection reactions.
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| 29. |
- Ulvenlund, Stefan, et al.
(författare)
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Hard Acid and Soft Base Stabilisation of Di- and Trimercury Cations in Benzene Solution - A Spectroscopic, X-ray Scattering, and Quantum Chemical Study
- 1999
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Ingår i: European Journal of Inorganic Chemistry. - 1434-1948 .- 1099-1948. ; :4, s. 633-642
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Tidskriftsartikel (refereegranskat)abstract
- Hg2Cl2 dissolves in GaCl3/benzene solution to yield Hg-2(2+) and chlorogallate(III) ions, GanCl3n+1-. In such solutions, Hg-2(2+) can be reduced to Hg-3(2+) by metallic mercury. Solubility measurements show that one mol of Hg is oxidised per mol of Hg-2(2+). The Hg-3(2+) ion gives a strong band at 110 cm(-1) in the Raman spectrum and Hg-Hg correlations at about 2.60 and 5.15 Angstrom in the radial distribution function obtained by Liquid X-ray scattering. - Hg-3(2+) can also be synthesised in high yield by direct oxidation of metallic mercury by Ga-III in GaCl3/benzene solution. In contrast, mercury is insoluble in neat Liquid GaCl3 and only sparingly soluble in GaCl3/KCl melts. It therefore seems likely that the thermodynamic stabilisation of subvalent mercury species in benzene solution not only relies on the traditional acid stabilisation provided by the hard Lewis acid GaCl3, but also on a "soft-base stabilisation" provided by interactions between the aromatic molecules and the cations. Evidence for such specific interactions between Hg-m(2+) cations and C6H6 are observed in the Raman spectra: The totally symmetric C6H6 band at 991 cm(-1) is found to split in the presence of Hg-m(2+) ions and to give new peaks at 978 (m = 2) and 982 (m = 3) cm(-1). - In order to further elucidate the cluster-arene interactions, ab initio and density functional calculations were performed for the model compounds Hg-m(C6H6)(2)(2+) and HgmCl2(C6H6)(2), m = 2 and 3. The calculations show that both models represent coordinations modes which are feasible for Hg-m(2+) ions. However, the calculated vibrational frequencies for the Hg-m(C6H6)(2)(2+) models with eta(1)/quasi-eta(3) coordination of the benzene molecules along the Hg-Hg vector are most consistent with the body of experimental and literature data. The counterions are thus suggested to occupy secondary coordination sites.
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| 30. |
- Ulvenlund, Stefan, et al.
(författare)
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Hydrophobic homopolymers of native α-L-amino acids at the air-water interface : A study by circular dichroism spectroscopy, atomic force microscopy, and surface balance experiments
- 2001
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797. ; 242:2, s. 346-353
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Tidskriftsartikel (refereegranskat)abstract
- Films of poly-L-leucine, poly-L-valine, and poly-L-isoleucine have been studied at the air-water interface by surface balance experiments. In addition, Langmuir-Blodgett (LB) films of these polypeptides deposited onto quartz and mica have been studied by circular dichroism (CD) spectroscopy and atomic force microscopy (AFM) to elucidate the effects of polypeptide conformation and spreading agent (chloroform and trifluoroacetic acid, TFA) on film morphology and phase behavior. Monolayers of poly-L-leucine contain α-helical polypeptide strands. When spread from chloroform, the compression isotherm displays a collapse plateau and a limiting molecular area (A0) of 19 Å2 per amino acid residue. The corresponding LB films are flat and featureless. When a water-soluble solvent (TFA) is used as a spreading agent, the AFM results reveal an extensive formation of polypeptide aggregates. The aggregation is accompanied by a substantial decrease in A0 but has little effect on polypeptide conformation, film compressibility, and phase behavior. According to CD spectroscopy, films of poly-L-valine and poly-L-isoleucine contain polypeptide strands in β-sheet conformation. The corresponding isotherms are steep and lack a collapse plateau. When TFA is used as a spreading agent, the limiting area decreases, but AFM data do not give direct evidence for any aggregation.
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