Rhamnogalacturonans I are complex pectin polysaccharides extremely variable in structure and properties and widely represented in various sources. The complexity and diversity of the structure of ...rhamnogalacturonans I are the reasons for the limited information about the properties and supramolecular organization of these polysaccharides, including the relationship between these parameters and the functions of rhamnogalacturonans I in plant cells. In the present work, on the example of rhamnogalacturonan I from flax gelatinous fibers, the ability of this type of pectic polysaccharides to form at physiological concentrations hydrogels with hyperelastic properties was revealed for the first time. According to IR spectroscopy, water molecules are more tightly retained in the gelling rhamnogalacturonan I from flax fiber cell wall in comparison with the non-gelling rhamnogalacturonan I from primary cell wall of potato. With increase in strength of water binding by rhamnogalacturonan I, there is an increase in elastic modulus and decrease in Poisson’s ratio of gel formed by this polysaccharide. The model of hyperelastic rhamnogalacturonan I capture by laterally interacting cellulose microfibrils, constructed using the finite element method, confirmed the suitability of rhamnogalacturonan I gel with the established properties for the function in the gelatinous cell wall, allowing consideration of this tissue- and stage-specific pectic polysaccharide as an important factor in creation of gelatinous fiber contractility.
The concentration dependences of self-diffusion coefficient for intrinsically disordered milk protein α
S
-casein were studied by pulsed field gradient nuclear magnetic resonance. The experimental ...data were analyzed in a view of phenomenological approach based on the frictional formalism of non-equilibrium thermodynamics by Vink. The results of α
S
-CN hydrodynamic study showed that at low- and high-protein concentrations, α
S
-CN exists in the different structural forms. At low concentrations in the rather broad concentration range, protein remains monomeric but with greater hydrodynamic size than have rigid globular proteins of the equal mass. At high concentrations beyond the definite protein content, α
S
-CN tends to form associates. The application of the Vink’s approach to α
S
-CN testifies that the role of flexible domains in the process of self-diffusion is mainly in increasing the friction of between α
S
-CN molecules due to their inter-entanglement. The latter physically means that when α
S
-CN molecules cling each other by their flexible domains, this phenomenon provides much more efficient friction than their interaction with solvent molecules.
Due to the physical, chemical, biological characteristics and high biocompatibility, the hydrogels based on plant polysaccharides and proteins became a sought-after material in many fields. Such ...hydrogels are the water swelling biopolymer matrices that react reversibly on minor changes in composition and in the external environment. However, the mechanical and electrical properties of "pure" hydrogels inhibit their wide practical application. One of approachs to improve their properties is the usage of carbon nanotubes, which provide good electrical conductivity and can significantly improve the characteristics of materials. The effects of carbon nanotubes on electric conductivity and mechanic properties of hydrogels based on natural biopolymers (gelatin and κ-carrageenan) of different composition were investigated. The electrical conductivity of the gels was studied using InoLab Cond 7310 SET1 conductometer. The rheological properties of hydrogels were investigated by Anton Paar MCR 302 rheometer. Such characteristics as temperature, frequency and amplitude dependencies of the storage modulus and the loss modulus of hydrogels were obtained. It was found that the addition of carbon nanotubes led to the increase in electrical conductivity of hydrogels. The morphology and rheological properties of studied hydrogels alter significantly in the presence of carbon nanotubes. The obtained data indicate the possibility of a purposeful change in electrical and mechanical properties of hydrogels by the addition of carbon nanotubes.
The concentration dependences of self-diffusion coefficient for irregular-shaped fibrinogen, for globular, spheroidal trypsin and α-chymotrypsin were studied by pulsed field gradient nuclear magnetic ...resonance. The experimental data were analyzed in a view of two known theoretical approaches—the hydrodynamic model of rigid spheres by Tokuyama and Oppenheim and the phenomenological approach based on the frictional formalism of non-equilibrium thermodynamics by Vink. The detailed discussion of their merits and drawbacks is presented. Our results testify that the Vink’s approach is quite universal, providing a satisfactory description of experimental data for proteins of complicated structure and different shape while the model of Tokuyama and Oppenheim is applicable only to proteins of more regular shape.
The dispersing action of the surfactant (sodium dodecyl sulfate, SDS) on the carbon nanotubes (CNT) in aqueous medium has been studied. Electron microscopy, molecular docking, NMR and IR ...spectroscopies were applied to determine the physical-chemical properties of CNT dispersions in SDS—water solutions. It was established that micellar adsorption of the surfactant on the surface of carbon material and solubilization of SDS in aqueous medium contribute to improving CNT dispersing in water solutions. It was shown that the non-polar hydrocarbon radicals of a single surfactant molecule form the highest possible number of contacts with the graphene surface. Upon increase of the SDS in solution these radicals form micelles connected with the surface of the nanotubes. At the sufficiently high SDS concentration the nanotube surface becomes covered with an adsorbed layer of surfactant micelles. Water molecules and sodium cations are concentrated in spaces between micelles. The observed pattern of micellar adsorption is somewhat similar to a loose bilayer of surfactant molecules.
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•K+ and Na+ are able to bind specifically to both helix and coil of k-carrageenan.•Two types of binding site are formed upon local rearrangements in neocarrabiose unit.•Cation-bound ...neocarrabiose unit adopts conformation favorable for helix formation.
It is widely accepted that cation binding specifically favors chain ordering and gelling of κ-carrageenan. However, current insights into the exact sequence of binding and conformational rearrangements as well as into the structure of binding sites are controversial. In the present work, the FTIR-spectroscopy combined with the computer modelling has been used to reveal the relation between cation binding and the secondary structure transition upon thermoreversible gelation of the κ-carrageenan. Three states of sulfate groups were defined spectroscopically: one cation-free and two specific cation-bound states. The DFT calculations reveal two energetically inequivalent spatial structures of cation binding unit, formed due to the local conformational adjustment in neocarrabiose moiety. Besides a charge screening effect, the cation-bound conformation of neocarrabiose also favors the helix formation.
We studied the influence of lipid surface composition on the kinetics of fibrin clot formation and its structure. It was shown that lipid surface affects all phases of fibrin polymerization and ...chances clot morphology. The magnitude and character of the effect depend on the charge and phase state of lipids that determine the interaction of fibrinogen with the lipid surface and its conformational changes, which modulated the process of fibrinogen conversion into fibrin and, as a result, the formation and morphology of the fibrin clot.
A novel dicationic surfactant with morpholinium head groups and hexadecyl tails (MP 16-6-16) has been synthesized. The self-assembly properties of the amphiphile have been evaluated and compared with ...their monocationic counterpart (MP-16) and trimethylammonium analogs. The critical micelle concentration of gemini (0.01mM) is lower as compared to MP-16 and slightly lower compared to conventional gemini 16-6-16. It was shown that the micelle surface potential increases and the aggregation number decreases upon the transition from a monocationic to a gemini analog. Morpholinium surfactants demonstrate a much higher solubilizing capacity toward the hydrophobic probe Orange OT as compared to the typical trimethylammonium surfactant. Both morpholinium surfactants form lipoplexes with a DNA decamer, which is strongly supported by the ethidium bromide exclusion assay and charge neutralization data. The high solubilizing and complexing activity and the ability to integrate with a lipid bilayer allow us to recommend morpholinium surfactants as candidates for drug and gene carriers.
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•Self-assembly of mono- and dicationic morpholinium surfactants is quantified.•Aggregation capacity of gemini is ca.100-fold higher than for monomeric one.•Morpholinium surfactants show higher solubilizing capacity compared to CTAB.•Morpholinium amphiphiles can form lipoplex with DNA decamer.•Morpholinium gemini is capable to integrate with lipid bilayer.
This paper presents the data of a graph-theoretic analysis of asymmetric and symmetric inclusion relations on descriptive sets of 22 hormones and 32 enzymes in the structure of hormonal regulation of ...enzyme activity in adipose tissue of rats under stress. The results of the analysis are interpreted in terms of the asymmetry of changes in enzyme activity under the stress-adaptation syndrome and expand the understanding of the system structure of hormonal regulation of metabolism.
