N. S. Domnina

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.

Novel thermosensitive telechelic PEGs with antioxidant activity: synthesis, molecular properties and conformational behaviour

We report on the synthesis and solution properties of novel tailor-made polymer conjugates, which are highly compelling for biomedical applications due to their antioxidant activity and the potential to fine-tune their thermosensitive properties. These conjugates consist of polyethylene glycol (PEG) polymers containing antioxidant moieties, namely 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate or 2-benzamido-3-(3,5-di-tert-butyl-4-hydroxyphenyl)acrylate, as end groups that differ in activity and hydrophobicity. It was shown that all of the synthesized conjugates have low critical solution temperatures (LCSTs) characteristic of type II polymers on a phase diagram. By simply varying the PEG molecular weight, the solution properties, including the LCST value, could be easily tuned across a broad temperature range of 20–90 °C, providing an ideal method for the creation of thermosensitive polymers. It was also established that the LCST value and the polymer conjugate conformation depend on the antioxidant structure. From dynamic light scattering and small-angle X-ray scattering data, we were able to construct a complete sequence diagram of the conformational phase behaviour of the polymers with increasing temperature. It was observed that the conjugate conformation changes are the result of water shifting from a thermodynamically favourable solvent to an unfavourable one. This process then leads to compaction of the conjugate, followed by its aggregation.

Molecular Properties of the Copolymers of N,N-Diallyl-N,N-Dimethylammonium Chloride and Maleic Acid

The hydrodynamic and conformational properties of molecules of poly(N,N-diallyl-N,N-dimethylammonium chloride) and N,N-diallyl-N,N-dimethylammonium chloride-maleic acid copolymers of different compositions in solutions with various ionic-strength and pH values, as well as of the polyelectrolyte complex based on the copolymer with dodecyl sulfate anions in chloroform, are studied. For poly(N,N-diallyl-N,N-dimethylammonium chloride) molecules in a 1 M NaCl solution, the Kuhn segment length and the hydrodynamic diameter of the chain are estimated as A = 3.9 nm and d = 0.48 nm, respectively. In acidic solutions with pH 3.5, the copolymers demonstrate behavior typical for polyelectrolytes. In an alkaline solution with pH 13, when 1 M NaCl is added to the solution of the copolymer containing 29 mol % maleic acid units, there is an antipolyelectrolyte effect that manifests itself as an increase in the intrinsic viscosity of the copolymer and in the hydrodynamic radius of its molecules. It is found that an increase in the fraction of maleic acid units in the copolymer from 12 to 42 mol % brings about a reduction in the equilibrium rigidity of its macromolecules from 4.1 to 2.2 nm. The equilibrium rigidity of polyelectrolyte-complex molecules is higher than that of initial copolymer molecules owing to steric interactions arising between the aliphatic chains of dodecyl sulfate anions. In an electric field, the molecules of the complex are oriented owing to the induced dipole moment resulting from the displacement of dodecyl sulfate anions along the chain contour.

Molecular properties of conjugates formed by synthetic hydrophilic polymers and sterically hindered phenols

Water-soluble conjugates are prepared via the chemical modification of poly(vinyl alcohol) and poly(ethylene glycol) by antioxidants taken from the family of sterically hindered phenols. The effects of the degree of substitution of conjugates on the dimensions of molecules and their aggregates are studied by viscometry and light scattering in dilute solutions. It is shown that an increase in the amount of antioxidant groups incorporated into the poly(vinyl alcohol) chain leads to a decrease in the dimensions of single conjugate molecules owing to attraction of hydrophobic groups. Poly(ethylene glycol) molecules carrying end groups of sterically hindered phenols form micellar aggregates that are absent in the solution of the initial polymer. The mean number of molecules involved in such an aggregate is 83. It is found that the presence of hydrophobic end groups in poly(ethylene glycol) molecules causes a sharp reduction in the lower critical solution temperature of a solution relative to that of the initial polymer.

Synthesis and biological activity of metal chitosan complexes

A series of complexes of chitosans of various molecular weights (3000–150000) with copper, iron(II), and zinc sulfates were examined. Participation of amino groups of the polymer in coordination bonding with the metal was proved by IR spectroscopy. The affinity of chitosan for iron ions was enhanced by introducing phenolic fragments into the polymer.

MACROMOLECULAR ANTIOXIDANTS BASED ON POLYSACCHARIDES AND 2,6-DIISOBORNYL-4-METHYLPHENOL DERIVATIVES

New macromolecular antioxidants that were conjugates of dextran or hydroxyethylated starch with functionalized derivatives synthesized from 2,6-diisobornyl-4-methylphenol were prepared. Their antiradical activity compared with derivatives of 2,6-di-tert-butyl-4-methylphenol was studied in a model reaction with 2,2-diphenyl-1-picrylhydrazyl. The studied conjugates exhibited greater activity than sterically hindered phenols not bonded to a polymer chain. The synthesized isobornyl derivatives were more active than previously studied tert-butyl analogs.

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.

Molecular properties of poly(carboxybetaine) in solutions with different ionic strengths and pH values

Viscometry and dynamic and static light scattering are employed to study the molecular properties of water-soluble poly(carboxybetaine), that is, poly(2-(diallyl(methyl)ammonium) acetate). It is shown that, in solutions with pH 1, the polymer behaves as a polyelectrolyte. In media with pH 6 and 13, an increase in the concentration of sodium chloride increases the intrinsic viscosity of the polymer and the hydrodynamic radius of its macromolecules, thereby indicating the antipolyelectrolyte effect typical of polymer zwitterions. In water and 0.1 M NaOH, the second virial coefficient of the polymer is close to zero, while exponent ν, which relates the sizes of macromolecules to their molecular masses, is 0.5. In 1 M NaCl, the second virial coefficient becomes positive, while exponent increases to 0.58. The Kuhn segment lengths of poly(carboxybetaine) molecules are 6.3 and 6.6 nm in water and 1 M NaCl, respectively. An increase in the hydrodynamic radius of macromolecules with the ionic strength of the solution is due to the shielding of attraction between zwitterions belonging to polybetaine monomer units located far apart along a macromolecular chain.

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.