The aim of the work was to study the peculiarities of interaction of the surface of bacterial lectin of Bacillus subtilis IMB B-7724 inthe native state and under different model conditions with water molecules by 1 H NMR; to create a composite system based on the studied lectin, in which the protein molecule is minimally affected by the surface of the carrier, because protein molecules are capable to bind a significant amount of water localized in the spaces between the polymer chains. A method of “dry” immobilization of bacterial lectin on the surface of hydrophobic silica has been developed. Hydration of native lectin and lectin fixed on the surface of hydrophobic silica AM-1-175 was studied by low-temperature 1 H NMR spectroscopy. It has been shown that the immobilization of lectin on the surface of AM1 is accompanied by an increase in the interfacial energy gS from 4.1 to 5.2 J/g. This is due to an increase in the concentration of strongly bound water. Analysis of changes in the distributions of radii R of clusters of adsorbed water allows us to state that in water adsorbed by native lectin, there are two main maxima at R = 1 and 3 nm. In the immobilized state, the maximum at R = 1 nm is present in both types of water (of different order), but the second maximum is observed only for more ordered associates. Chloroform medium slightly reduces the binding energy of water to native lectin molecules (from 4.3 to 4.1 J/g), but in the case of immobilized lectin in CDCl3 medium, the value of ΣgS increases from 5.2 to 7.4 J/g. That is, the weakly polar medium promotes to increase in the interaction of water with interfaces, which is manifested in a relative increase in the number of water clusters of smaller size (Fig. 4). It should be noted that weakly associated forms of water (signal 3) are also represented by several types of clusters that have a radius in the range R = 1–10 nm, and their size distribution changes significantly during immobilization of lectin on the surface of AM1. Probably, weakly associated types of water are formed both in cavities, between polymer chains of protein molecules, and on the surface of AM1, free of protein.
Heterogeneous composite systems created on the basis of nanosized methylsilica AM1-200 and microcrystalline cellulose were investigated using the method of low-temperature 1H NMR spectroscopy. Thermodynamic parameters of bound water in hydrated microcrystalline cellulose (MSC) powders and AM1/MSC composites at different ratios of hydrophobic and hydrophilic components were measured. It was established that the hydrophobic component is able to stabilize the aqueous system in the MSS/AM1 composite powders even when the amount of water is twice the amount of the solid phase. From the distributions of the radii of adsorbed water clusters, it follows that in highly hydrated composites, a significant part of the water is in the form of nanodroplets with a radius of several tens of nm
Low-temperature 1H NMR spectroscopy and DSC methods were used to study the hydration process of Lactobacillus, the influence of a weakly polar organic environment on it, and the encapsulation of cells with silica and the possibility of penetration of such an active substance as trifluoroacetic acid (TFAA) into them. It is shown that the spectral parameters of water in concentrated cell suspensions of Lactobacillus significantly depend on the concentration of the suspensions, which is probably related to the possibility of forming a stable cell gel, which can be encapsulated by silica particles both in the air environment and in the environment without its destruction chloroform with the addition of trifluoroacetic acid. There are two maxima corresponding to R = 2 and 20-100 nm on the distribution curves of the radii of clusters of unfreezing water. The contribution to the distribution of the second maximum increases with increasing water concentration. On the DSC-thermograms of lactobacilli, the value of the thermal effect related to the amount of bound water is much smaller than the thermal effect of ice melting, which is due to the presence of a significant amount of non-freezing water.
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