Anna Akinshina | University of Salford (original) (raw)
Papers by Anna Akinshina
Physical Chemistry Chemical Physics, 2016
A systematic study of the effect of saturated and unsaturated oil additives on a ceramide bilayer... more A systematic study of the effect of saturated and unsaturated oil additives on a ceramide bilayer (skin lipids) using MD simulations.
BMC Biophysics, 2013
Background: Keratins are important structural proteins found in skin, hair and nails. Keratin Int... more Background: Keratins are important structural proteins found in skin, hair and nails. Keratin Intermediate Filaments are major components of corneocytes, nonviable horny cells of the Stratum Corneum, the outermost layer of skin. It is considered that interactions between unstructured domains of Keratin Intermediate Filaments are the key factor in maintaining the elasticity of the skin. Results: We have developed a model for the interactions between keratin intermediate filaments based on self-consistent field theory. The intermediate filaments are represented by charged surfaces, and the disordered terminal domains of the keratins are represented by charged heteropolymers grafted to these surfaces. We estimate the system is close to a charge compensation point where the heteropolymer grafting density is matched to the surface charge density. Using a protein model with amino acid resolution for the terminal domains, we find that the terminal chains can mediate a weak attraction between the keratin surfaces. The origin of the attraction is a combination of bridging and electrostatics. The attraction disappears when the system moves away from the charge compensation point, or when excess small ions and/or NMF-representing free amino acids are added. Conclusions: These results are in concordance with experimental observations, and support the idea that the interaction between keratin filaments, and ultimately in part the elastic properties of the keratin-containing tissue, is controlled by a combination of the physico-chemical properties of the disordered terminal domains and the composition of the medium in the inter-filament region.
Soft matter, Jan 28, 2015
Atomistic molecular dynamic simulations have been performed for the non-ionic chromonic liquid cr... more Atomistic molecular dynamic simulations have been performed for the non-ionic chromonic liquid crystal 2,3,6,7,10,11-hexa-(1,4,7-trioxa-octyl)-triphenylene (TP6EO2M) in aqueous solution. TP6EO2M molecules consist of a central poly-aromatic core (a triphenylene ring) functionalized by six hydrophilic ethyleneoxy (EO) chains, and have a strong tendency to aggregate face-to-face into stacks even in very dilute solution. We have studied self-assembly of the molecules in the low concentration range corresponding to an isotropic solution of aggregates, using two force fields GAFF and OPLS. Our results reveal that the GAFF force field, even though it was successfully used previously for modelling of ionic chromonics, overestimates the attraction of TP6EO2M molecules in water. This results in an aggregation free energy which is too high, a reduced hydration of EO chains and, therefore, molecular self-assembly into compact disordered clusters instead of stacks. In contrast, use of the OPLS f...
Food Hydrocolloids, 2014
Colloidal interaction potentials induced by the overlap of mixed protein + polysaccharide interfa... more Colloidal interaction potentials induced by the overlap of mixed protein + polysaccharide interfacial layers, formed solely as a result of electrostatic attraction between these two biopolymers, have been calculated using the Self Consistent Field Theory. A significant difference between the nature and magnitude of these interactions, depending on the manner in which the charge is distributed along the length of the polysaccharide molecules, was predicted. For chains with an even distribution of charge, the repulsive interactions are in general weaker than those mediated by pure protein layers. For strongly charged polysaccharide chains, these become even attractive at a certain range of particle-particle separations. In part this is due to bridging by polysaccharides, occurring between opposite layers. However, in systems containing strongly charged polyelectrolyte, it is also the result of what in practice may be interpreted as a coacervate of protein + polysaccharide, with a tendency for aggregation, forming interfacial layers on the surface of the particles. In contrast, when the charge of the polysaccharide chains is unevenly distributed, the induced repulsive forces are much enhanced and become longer ranged compared to those for pure protein layers. Once the layers begin to overlap, the electro-steric interactions produced are found to completely overwhelm any van der Waals attraction, thus dictating the inter-particle interactions. We also present some preliminary calculations investigating the competitive adsorption of different polysaccharides onto the protein layer. The initial results, for polysaccharides of the same size and overall charge, suggest that the heterogeneously charged polyelectrolyte completely dominates the adsorption onto the surface, displacing all uniformly charged chains from the interface.
Faraday Discussions, 2008
Mixed interfacial films of protein and polysaccharide have been investigated using self consisten... more Mixed interfacial films of protein and polysaccharide have been investigated using self consistent field (SCF) calculations. The colloidal interactions mediated by such composite layers between two approaching surfaces have been considered. Two types of systems have been studied: (a) covalently-bonded polysaccharide and protein, and (b) the excess presence of polysaccharide at the interface, occurring through electrostatic interaction with an already existing, oppositely charged, protein layer. Our calculations show that for covalently-bonded complexes, depending on the location of the protein-polysaccharide bond, the attachment of short uncharged chains to the protein can be detrimental to provision of repulsive colloidal forces by such complexes. We have attributed this to an increased tendency of the hybrid polymer to adopt bridging configurations in the gap between two nearby surfaces. For larger grafted chains this bridging effect is eliminated, and the expected enhanced steric stabilization of the protein-polysaccharide conjugate is achieved. For adsorbed films formed through electrostatic interactions between these two biopolymers, stronger repulsive forces between the surfaces are produced, at an intermediate level of charging for the polysaccharides. This has been related to a maximum level of adsorption of polysaccharide, as the number of charged segments of the chain is varied. The peak occurs at higher levels of charging as the salt concentration in the bulk solution is increased. We have also observed the experimentally-reported phenomenon of charge overcompensation, arising from adsorption of the polysaccharide chains onto the primary protein layer. The importance of the non-uniform charge distribution of the polysaccharide molecule, in providing an explanation for this effect, has been demonstrated.
Biomacromolecules, 2008
The effect on the adsorbed layer properties of the modification of R S1-casein by covalent bondin... more The effect on the adsorbed layer properties of the modification of R S1-casein by covalent bonding with an uncharged polysaccharide side chain has been investigated using lattice-based self-consistent field (SCF) theory. Interactions between two hydrophobic planar surfaces coated by a layer of adsorbed modified R S1-casein have been studied as a function of pH and ionic strength. While the interactions of the unmodified R S1-casein layers become attractive at high ionic strength, it has been shown that the presence of polysaccharide attachment to the R S1-casein molecule can confer net repulsive interactions over a wide range of salt concentration. The disordered protein is represented as a linear flexible polyampholyte with a sequence of hydrophobic, polar, and charged units based on the known R S1-casein primary structure. The hydrophilic side chain is attached at various fixed positions along the casein backbone. Different lengths and locations of the attached polysaccharide side chain are examined. Interfacial structures and colloidal stability properties of the system are determined, including the surface-surface interaction potential, the extent of protein bridging, and the distribution of protein segments from the surface under different conditions of pH and ionic strength. It has been found that the covalent bonding of short hydrophilic chains may not only enhance but can also worsen the colloidal stabilizing properties of the modified protein, depending on the position of the attachment.
ACS Symposium Series, 2009
The adsorption of a linear polyelectrolyte onto an existing layer of protein at an interface has ... more The adsorption of a linear polyelectrolyte onto an existing layer of protein at an interface has been investigated. Calculations using a simple model, involving only the short range interactions, show that the polyelectrolyte forms a more extended distinct secondary layer if only ceratin sections of the molecule interact with the protein layer. These results are also confirmed for a more sophisticated model that accounts for the electrostatic interactions between the two biopolymers. It is found that there is a maximum level of adsorption of polyelectrolyte as the number of charged segments of the chains is varied. The peak occurs at higher levels of charging as the background salt concentration is increased. We also consider the effects of pH on the adsorption. The influence of the structure of the mixed layers on colloidal forces, mediated between two surfaces covered by such films, is also discussed.
Physical Chemistry Chemical Physics, 2016
A systematic study of the effect of saturated and unsaturated oil additives on a ceramide bilayer... more A systematic study of the effect of saturated and unsaturated oil additives on a ceramide bilayer (skin lipids) using MD simulations.
BMC Biophysics, 2013
Background: Keratins are important structural proteins found in skin, hair and nails. Keratin Int... more Background: Keratins are important structural proteins found in skin, hair and nails. Keratin Intermediate Filaments are major components of corneocytes, nonviable horny cells of the Stratum Corneum, the outermost layer of skin. It is considered that interactions between unstructured domains of Keratin Intermediate Filaments are the key factor in maintaining the elasticity of the skin. Results: We have developed a model for the interactions between keratin intermediate filaments based on self-consistent field theory. The intermediate filaments are represented by charged surfaces, and the disordered terminal domains of the keratins are represented by charged heteropolymers grafted to these surfaces. We estimate the system is close to a charge compensation point where the heteropolymer grafting density is matched to the surface charge density. Using a protein model with amino acid resolution for the terminal domains, we find that the terminal chains can mediate a weak attraction between the keratin surfaces. The origin of the attraction is a combination of bridging and electrostatics. The attraction disappears when the system moves away from the charge compensation point, or when excess small ions and/or NMF-representing free amino acids are added. Conclusions: These results are in concordance with experimental observations, and support the idea that the interaction between keratin filaments, and ultimately in part the elastic properties of the keratin-containing tissue, is controlled by a combination of the physico-chemical properties of the disordered terminal domains and the composition of the medium in the inter-filament region.
Soft matter, Jan 28, 2015
Atomistic molecular dynamic simulations have been performed for the non-ionic chromonic liquid cr... more Atomistic molecular dynamic simulations have been performed for the non-ionic chromonic liquid crystal 2,3,6,7,10,11-hexa-(1,4,7-trioxa-octyl)-triphenylene (TP6EO2M) in aqueous solution. TP6EO2M molecules consist of a central poly-aromatic core (a triphenylene ring) functionalized by six hydrophilic ethyleneoxy (EO) chains, and have a strong tendency to aggregate face-to-face into stacks even in very dilute solution. We have studied self-assembly of the molecules in the low concentration range corresponding to an isotropic solution of aggregates, using two force fields GAFF and OPLS. Our results reveal that the GAFF force field, even though it was successfully used previously for modelling of ionic chromonics, overestimates the attraction of TP6EO2M molecules in water. This results in an aggregation free energy which is too high, a reduced hydration of EO chains and, therefore, molecular self-assembly into compact disordered clusters instead of stacks. In contrast, use of the OPLS f...
Food Hydrocolloids, 2014
Colloidal interaction potentials induced by the overlap of mixed protein + polysaccharide interfa... more Colloidal interaction potentials induced by the overlap of mixed protein + polysaccharide interfacial layers, formed solely as a result of electrostatic attraction between these two biopolymers, have been calculated using the Self Consistent Field Theory. A significant difference between the nature and magnitude of these interactions, depending on the manner in which the charge is distributed along the length of the polysaccharide molecules, was predicted. For chains with an even distribution of charge, the repulsive interactions are in general weaker than those mediated by pure protein layers. For strongly charged polysaccharide chains, these become even attractive at a certain range of particle-particle separations. In part this is due to bridging by polysaccharides, occurring between opposite layers. However, in systems containing strongly charged polyelectrolyte, it is also the result of what in practice may be interpreted as a coacervate of protein + polysaccharide, with a tendency for aggregation, forming interfacial layers on the surface of the particles. In contrast, when the charge of the polysaccharide chains is unevenly distributed, the induced repulsive forces are much enhanced and become longer ranged compared to those for pure protein layers. Once the layers begin to overlap, the electro-steric interactions produced are found to completely overwhelm any van der Waals attraction, thus dictating the inter-particle interactions. We also present some preliminary calculations investigating the competitive adsorption of different polysaccharides onto the protein layer. The initial results, for polysaccharides of the same size and overall charge, suggest that the heterogeneously charged polyelectrolyte completely dominates the adsorption onto the surface, displacing all uniformly charged chains from the interface.
Faraday Discussions, 2008
Mixed interfacial films of protein and polysaccharide have been investigated using self consisten... more Mixed interfacial films of protein and polysaccharide have been investigated using self consistent field (SCF) calculations. The colloidal interactions mediated by such composite layers between two approaching surfaces have been considered. Two types of systems have been studied: (a) covalently-bonded polysaccharide and protein, and (b) the excess presence of polysaccharide at the interface, occurring through electrostatic interaction with an already existing, oppositely charged, protein layer. Our calculations show that for covalently-bonded complexes, depending on the location of the protein-polysaccharide bond, the attachment of short uncharged chains to the protein can be detrimental to provision of repulsive colloidal forces by such complexes. We have attributed this to an increased tendency of the hybrid polymer to adopt bridging configurations in the gap between two nearby surfaces. For larger grafted chains this bridging effect is eliminated, and the expected enhanced steric stabilization of the protein-polysaccharide conjugate is achieved. For adsorbed films formed through electrostatic interactions between these two biopolymers, stronger repulsive forces between the surfaces are produced, at an intermediate level of charging for the polysaccharides. This has been related to a maximum level of adsorption of polysaccharide, as the number of charged segments of the chain is varied. The peak occurs at higher levels of charging as the salt concentration in the bulk solution is increased. We have also observed the experimentally-reported phenomenon of charge overcompensation, arising from adsorption of the polysaccharide chains onto the primary protein layer. The importance of the non-uniform charge distribution of the polysaccharide molecule, in providing an explanation for this effect, has been demonstrated.
Biomacromolecules, 2008
The effect on the adsorbed layer properties of the modification of R S1-casein by covalent bondin... more The effect on the adsorbed layer properties of the modification of R S1-casein by covalent bonding with an uncharged polysaccharide side chain has been investigated using lattice-based self-consistent field (SCF) theory. Interactions between two hydrophobic planar surfaces coated by a layer of adsorbed modified R S1-casein have been studied as a function of pH and ionic strength. While the interactions of the unmodified R S1-casein layers become attractive at high ionic strength, it has been shown that the presence of polysaccharide attachment to the R S1-casein molecule can confer net repulsive interactions over a wide range of salt concentration. The disordered protein is represented as a linear flexible polyampholyte with a sequence of hydrophobic, polar, and charged units based on the known R S1-casein primary structure. The hydrophilic side chain is attached at various fixed positions along the casein backbone. Different lengths and locations of the attached polysaccharide side chain are examined. Interfacial structures and colloidal stability properties of the system are determined, including the surface-surface interaction potential, the extent of protein bridging, and the distribution of protein segments from the surface under different conditions of pH and ionic strength. It has been found that the covalent bonding of short hydrophilic chains may not only enhance but can also worsen the colloidal stabilizing properties of the modified protein, depending on the position of the attachment.
ACS Symposium Series, 2009
The adsorption of a linear polyelectrolyte onto an existing layer of protein at an interface has ... more The adsorption of a linear polyelectrolyte onto an existing layer of protein at an interface has been investigated. Calculations using a simple model, involving only the short range interactions, show that the polyelectrolyte forms a more extended distinct secondary layer if only ceratin sections of the molecule interact with the protein layer. These results are also confirmed for a more sophisticated model that accounts for the electrostatic interactions between the two biopolymers. It is found that there is a maximum level of adsorption of polyelectrolyte as the number of charged segments of the chains is varied. The peak occurs at higher levels of charging as the background salt concentration is increased. We also consider the effects of pH on the adsorption. The influence of the structure of the mixed layers on colloidal forces, mediated between two surfaces covered by such films, is also discussed.