E. A. Komarova

Sterically hindered phenol–dextran conjugates: synthesis and radical scavenging activity

A new synthesis of the covalently bound conjugates of dextran and a sterically hindered phenol has been described. Some features of the synthetic procedure have been discussed. The conjugates were investigated as polymeric forms of antioxidants and their radical scavenging activity was studied in the reaction with diphenylpicrylhydrazyl. It was found that the radical scavenging activity of the conjugates was about three times higher in comparison with that of the mixture of a sterically hindered phenol and dextran.

Sterically hindered phenol–dextran conjugates: radical scavenging activity in water and water–organic media

The radical scavenging activity investigation of sterically hindered phenols–dextran conjugates was carried out in water and water–dioxane mixtures with use of sodium salt of 2,2-diphenyl-1-picryl-hydrazyl sulfonic acid (DPPH-SO3Na). The suggestion was made that the reaction mechanism includes the one-electron transition stage. It was found that the reaction rate constants of DPPH-SO3Na with the conjugates are higher than the ones with low-molecular weight model. One of possible reasons for obtained data could be the fact that dextran hydration shell stabilizes the cation-radical intermediate in case of conjugates better than bulk water.

Structural factors responsible for the activity of macromolecular phenolic antioxidants

Hybrid macromolecular antioxidants based on hydrophilic polymers with chemically grafted sterically hindered phenol fragments in aqueous solution exhibited considerably higher antiradical activity than that typical of compositions consisting of a polymer and low-molecular phenol analogs. The activity of the examined antioxidants is determined mainly by formation of supramolecular structures in solution, as well as by the position of the phenolic fragment inside or outside hydrate shell. An important structural factor is the size of the spacer connecting the redox-active phenol ring with the polymer.

Aggregation of dextran hydrophobically modified by sterically hindered phenols

The process of aggregation of conjugates of dextran hydrophobically modified by sterically hindered phenols in an aqueous medium was studied by dynamic light scattering, transmission electron microscopy, atomic force microscopy, and fluorescent spectroscopy. It was found that, in solutions of dextran and related conjugates, individual molecules and their aggregates are present. The concentration, size, and shape of aggregates, as well as aggregation number, are determined by the degree of substitution of glycoside groups of dextran. It was shown that the critical concentration of conjugate aggregation decreases as the degree of substitution of dextran molecules increases.

Molecular properties of hybrid macromolecular antioxidants: Dextran hydrophobically modified by sterically hindered phenols

The conformation properties of clinically relevant hybrid macromolecular antioxidants (dextran hydrophobically modified by sterically hindered phenols) in aqueous solution were characterized by a combination of dynamic light scattering (DLS), size exclusion chromatography (SEC), and small-angle neutron scattering (SANS). We were able to split and analyze separately two different types of polydispersity —polydispersity over molecular weights and the one over substitution degree. The properties of the hybrid macromolecules are determined by the number of hydrophobic antioxidants in a single molecule. An insertion of hydrophobic groups into a hydrophilic chain changes the conformation of a single conjugate macromolecule. We have established that with the increasing of a number of hydrophobic antioxidant groups, a conformational transition occurs where a single conjugate undergoes a transition from a Gaussian coil conformation to a more compact structure.

Indicator properties of oligoethylene glycol hybrids with sterically hindered phenols

Aqueous solutions of hybrid compounds (conjugates) formed by polyethylene glycols modified at the terminal hydroxy groups with sterically hindered phenol lose their phase stability at a certain temperature which depends on the molecular weight of polyethylene glycol, structure of sterically hindered phenol, conjugate concentration, and composition of the medium. This property may be used to estimate the effect of structural factors on the hydrophobic-hydrophilic balance in the conjugate-water system.