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•Rheological properties of mixed gels are determined by mass ratio of components, Z.•κ-Carrageenan admixture induces formation of additional gelatin triple helixes.•Increase in the ...gelatin helix units leads to increase in the strength of mixed gel.•Electrostatic interactions determine the mutual orientation of biopolymer chains.•Model of complex junction zones is proposed.
Rheological studies, FTIR spectroscopy and a molecular docking approach were used to explore the structural basis of the peculiar physicochemical properties of gelatin gels modified with a κ-carrageenan admixture. Mixed gel properties are affected by the polysaccharide-to-gelatin ratio, Z, and can be divided into two categories. At low ratios, the strength of mixed gels varies insignificantly compared to gelatin due to the similar structures of the gels. Above the threshold content of κ-carrageenan (Z > 0.1), the storage modulus and yield stress of mixed gels are significantly enhanced. The nonadditivity and threshold character of the rheological properties could be the result of conformational ordering of both gelatin and κ-carrageenan, leading to the formation of additional junction zones in the gel network. According to molecular docking studies, the junctions could be formed as a result of complementary interactions between the gelatin triple helix and the κ-carrageenan double helix. The stack formation increases the interaction energy, which explains the strengthening of the gel network.
Diffusive behavior of human serum albumin (HSA) in the presence of Mg
2+
and Cu
2+
ions was studied by pulsed field gradient nuclear magnetic resonance (PFG NMR) and dynamic light scattering (DLS). ...According to NMR data yielding measurements of HSA self-diffusion coefficient, a weighted average of the protein monomers and oligomers diffusion mobility in the presence of metal ions was observed. While the short-time collective diffusion measured by DLS showed one type of diffusing species in ion-free HSA solution and two molecular forms of HSA in the presence of metal ions. The light intensity correlation function analysis showed that HSA oligomers have a limited lifetime (lower limit is about 0.4 ms) intermediate between characteristic time scales of PFG NMR and DLS experiments. For a theoretical description of concentration dependence of HSA self- and collective diffusion coefficients, the phenomenological approach based on the frictional formalism of non-equilibrium thermodynamics was used (Vink theory), allowing analysis of the solvent–solute and solute–solute interactions in protein solutions. In the presence of metal ions, a significant increase of HSA protein–protein friction coefficient was shown. Based on theoretical analysis of collective diffusion data, the positive values of second virial coefficients
A
2
for HSA monomers were obtained. The
A
2
values were found to be higher for the HSA with metal ions compared with the ion-free HSA solution. This is due to the more pronounced contribution of repulsion in protein–protein interactions of HSA monomers in the presence of Mg
2+
and Cu
2+
ions.
Achieving efficient localization of white light at the nanoscale is a major challenge due to the diffraction limit, and nanoscale emitters generating light with a broadband spectrum require ...complicated engineering. Here we suggest a simple, yet highly efficient, nanoscale white-light source based on a hybrid Si/Au nanoparticle with ultrabroadband (1.3–3.4 eV) spectral characteristics. We incorporate this novel source into a scanning-probe microscope and observe broadband spectrum of photoluminescence that allows fast mapping of local optical response of advanced nanophotonic structures with submicron resolution, thus realizing ultrabroadband near-field nanospectroscopy.
The structural state of ionic surfactant sodium dodecyl sulfate (SDS) on passing through the Krafft point (classical characteristic parameter determining the relationship between surfactant ...solubility and micelle formation) was studied by two independent physical methods, NMR and dielectric spectroscopies. It was established that the micellar structure of concentrated SDS solution is preserved on cooling down to 10 °C, which is much lower than the reported Krafft point of SDS lying near 18 °C.
•k-Carrageenan retains its overall secondary structure upon complexation with lysozyme.•Unordered k-carrageenan perturbs lysozyme loops and stabilizes β-structure.•Helical k-carrageenan does not ...remarkably affect lysozyme structure.
The interactions between κ-carrageenan and hen egg-white lysozyme have been studied. In dilute solutions, the insoluble complexes with constant κ-carrageenan/lysozyme ratio of 0.3, or 12 disaccharide units per mole of protein are formed. FTIR-spectroscopy revealed that κ-carrageenan retains its unordered conformation and induces the rise of β-structure in lysozyme. In the complexes formed in concentrated mixtures, κ-carrageenan adopts helical conformation and lysozyme retains its native-like structure. These complexes contain 21 disaccharide units per mole of protein. Molecular modeling showed that flexible coil and rigid double helix of κ-carrageenan have different binding patterns to lysozyme surface. The latter has a strong preference to positively charged spots in lysozyme α-domain while the former also interacts to protein β-domain and stabilizes short-living β-structures. The obtained results confirm the preference of unordered κ-carrageenan to β-structure rich protein regions, which can be further used in the development of carrageenan-based protection of amyloid-like aggregation of proteins.
An enzymatic microreactor was designed on the basis of sodium alginate hydrogel containing a lipolytic enzyme (
Candida rugosa
lipase) in the polymer matrix pores. The functional properties of lipase ...were characterized in polysaccharide hydrogel of different concentrations. The polysaccharide hydrogel matrix was shown to act as a microreactor, where the enzyme retains activity during numerous catalytic cycles and allows designing long-acting drug systems of enzymatic nature.
The effect of carbon nanotubes (CNTs) on the morphology and properties of alginate hydrogel was studied. The addition of CNTs leads to a change in the structural characteristics of the hydrogel, ...which is expressed in a decrease in the pore size and gaining a more uniformity by the internal structure. To study the encapsulating properties of the designed compositions, a set of dyes was used that are traditionally applied for testing the drug release rate. It was found that the CNTs do not affect the efficiency of inclusion and the release rate of the anionic and neutral dyes. The change in the kinetics of cationic dye release is caused by the reinforcing effect of the CNTs on the alginate hydrogel and a change in its morphological characteristics.
The structures of a protein-polysaccharide composite hydrogel and its modifications prepared using carbon nanotubes (CNTs) were studied by small-angle X-ray scattering and scanning electron ...microscopy. A correlation between the morphology and physicochemical properties of the hydrogels is demonstrated taking the specific electrical conductivity of the hydrogels as an example. It is shown that the specific electrical conductivity is unambiguously related to the structure of the systems studied,
viz.
, the higher the density of cross-links between biopolymer chains the lower the conductivity, and
vice versa.
It is found that the addition of CNTs to K-carrageenan—gelatin composite hydrogels can lead to either increase or decrease in their electrical conductivity.
Association of sodium dodecyl sulfate (SDS) ionic surfactant in concentration range of 1–100 mmol L
−1
in binary water—ethanol media with alcohol volume concentrations of 0–92.3 vol.% was studied by ...conductometry and nuclear magnetic resonance spectrometry. The dynamic properties of surfactant solutions including self-diffusion processes and diffusive transfer of charges in SDS solutions under alteration of solvent micro-heterogeneous structure were studied. The transformation of structure and size of SDS associates upon change of ethanol content in the solution was discussed. The correlation between SDS association processes and changes in micro-heterogeneous structure of binary solvent was analyzed.
-
The chitosan derivatives (carboxymethylchitosan and
N
-(2-hydroxy)propyl-3-trimethylammoniumchitosan) with molecular weight of 200, 350, and 600 kDa were synthesized. The ficin complexes with ...chitosan and the aforementioned derivatives were prepared. IR spectra of chitosan, carboxymethylchitosan,
N
‑(2-hydroxy)propyl-3-trimethylammoniumchitosan, and their complexes with ficin were recorded. An analysis of these spectra confirmed a formation of the conjugates between the macromolecules of polysaccharides and ficin. The optimum ratio of the protein content (0.7 mg/g of the carrier) and the special activity (1590 units/mg of the protein) was found after a formation of the ficin complex with
N
-(2-hydroxy)propyl-3-trimethylammoniumchitosan with a molecular weight of 350 kDa. The efficacy of the formation of the complex of ficin (according to the special catalytic activity) with
N
-(2-hydroxy)propyl-3-trimethylammoniumchitosan (350 kDa) was higher than that for chitosan (350 kDa) and carboxymethylchitosan (350 kDa) by 2.4 and 9.8 times, respectively. Types of interactions, energy of the first binding, amino acid composition of the ficin surfaces which contacted with the carriers during the complex formation were studied by the method for a molecular docking. The bonds and interactions with chitosan and its derivatives were found to be formed, in particular, with a participation of the amino acid residues that were placed near the ficin active site (Cys25 and His162). This fact explained a change in the proteolytic activity of the prepared complexes. The complexes of ficin with
N
-(2-hydroxy)propyl-3-trimethylammoniumchitosan were soluble in a wide pH range of the medium and could be more promising (than the ficin–chitosan complexes) for a design of medicines and biocatalysts for the food, brewing, and tanning industry.
