Molecular Serum Albumin Unmask Nanobio Properties of Molecular Graphenes in Shungite Carbon Nanoparticles.

Serum albumin is a popular macromolecule for studying the effect of proteins on the colloidal stability of nanoparticle (NP) dispersions, as well as the protein-nanoparticle interaction and protein corona formation. In this work, we analyze the specific conformation-dependent phase, redox, and fatty acid delivery properties of bovine albumin in the presence of shungite carbon (ShC) molecular graphenes stabilized in aqueous dispersions in the form of NPs in order to reveal the features of NP bioactivity. The formation of NP complexes with proteins (protein corona around NP) affects the transport properties of albumin for the delivery of fatty acids. Being acceptors of electrons and ligands, ShC NPs are capable of exhibiting both their own biological activity and significantly affecting conformational and phase transformations in protein systems.

Fatty acid transfer between serum albumins and shungite carbon nanoparticles and its effect on protein aggregation and association.

The bioactivity of the natural ultrafine carbon form shungite nanocarbon (ShC) is of particular interest both for biomedical applications of such nanomaterials and their negative impact on the aquatic environmental. Here we studied the interaction of serum albumin (SA) with ShC nanoparticles in aqueous dispersion with respect to its structural-dynamic, thermodynamic, and hydrodynamic effects. Electron spin resonance (EPR) with a 5-DOXYL-stearic acid spin probe (5DSA) demonstrates that ShC can affect fatty acid (FA) binding by SA, protein conformation in the stearic FA spin probe binding region, and protein aggregation due to the partial transfer of FA to the ShC nanoparticles. The ratio of SA fractions changes in the presence of ShC in favor of the fraction that is less saturated with FA as shown by differential scanning calorimetry (DSC). The stability of interaction with ShC is significantly higher for aggregates of SA molecules that carry physiological amounts of FA, compared to aggregates of the FA-free protein, as studied by dynamic light scattering (DLS) analysis. Generally, the mixed dispersion of SA and ShC nanoparticles is more homogeneous than the SA solution alone. This is manifested both in the size of the molecular associates and in the microenvironment of the protein-bound FA. The formation of the SA-ShC interface is likely to result in a greater uniformity of the FA binding sites and a decrease in protein fractions and "hot patches" on the protein surface responsible for the supramolecular heterogeneity of the protein in solution.

Thermodynamic study of protein phases formation and clustering in model water-protein-salt solutions.

Thermodynamic analysis of the water-protein-salt system, based on the description of the spinodal curve, has been carried out in various coordinate systems: (water chemical potential, protein concentration m(2)); (protein "solubility" log S, salt concentration m(3)); (effective temperature, critical composition of the system m(2)/m(3)). Such presentations explain the existence of diagrams with normal and retrograde protein solubility as a result of straightforward effect of ions present in solution as well as some features of the widely used phase diagram in coordinates (temperature, protein concentration). Analytic expressions for coefficients K and b of the salting out equation log S=-K.m(3)+b as functions of protein charge and protein adsorbed ions have been obtained and identified with the spinodal characteristic points reflecting quasi-equilibrium between protein-lean phase and dense protein-rich phase. Liquid-liquid, liquid-solid phase transitions, dynamic protein clusters and second virial coefficient that characterize interaction between solution components have been thus interrelated. The results of our thermodynamic analysis have been compared with the data reported for lysozyme .