Antioxidant Activity of Synthetic Polymers of Phenolic Compounds

In recent years, developing potent antioxidants has been a very active area of research. In this context, phenolic compounds have been evaluated for their antioxidant activity. However, the use of phenolic compounds has also been limited by poor antioxidant activity in several in vivo studies. Polymeric phenols have received much attention owing to their potent antioxidant properties and increased stability in aqueous systems. To be truly effective in biological applications, it is important that these polymers be synthesized using benign methods. In this context, enzyme catalyzed synthesis of polymeric phenols has been explored as an environmentally friendly and safer approach. This review summarizes work in enzymatic syntheses of polymers of phenols. Several assays have been developed to determine the antioxidant potency of these polymeric phenols. These assays are discussed in detail along with structure-property relationships. A deeper understanding of factors affecting antioxidant activity would provide an opportunity for the design of versatile, high performing polymers with enhanced antioxidant activity.

Enhancing the therapeutic effects of polyphenols with macromolecules

A review of key macromolecular systems employed to stabilise polyphenols, including direct polymerisation of polyphenol monomers and conjugation with macromolecules.

Artificial Polymeric Flavonoids: Synthesis and Applications

Flavonoids, one of the most numerous and best studied groups of plant polyphenols, are well known to exhibit various biological and pharmacological effects. Functional artificial polymeric flavonoids, flavonoid polymers and amine containing polymer-flavonoid conjugates have been developed. The acid-catalyzed polymerization of catechin and aldehydes proceeds regioselectively to produce catechin-aldehyde polycondensates. Peroxidases and laccases catalyze the oxidative coupling of flavonoids and oxidative conjugation with polyamines. The resulting polymers show much higher antioxidant activities than the flavonoid monomers. In addition, these polymeric flavonoids efficiently inhibit disease related enzymes, such as xanthine oxidase, collagenase, elastase, hyaluronidase and tyrosinase. Based on these results, the molecular design for amplification of the biological and pharmacological properties of flavonoids is proposed.

Multiwavelength Spectrophotometric Determination of Acidity Constants of Morin in Methanol-Water Mixtures

The acid-base properties of morin (2',3,4',5,7-pentahydroxyflavone) in mixtures of methanol- water at 25 °C and an ionic strength of 0.1 M are studied by a multiwavelength spectrophotometric method. To evaluate the pH-absorbance data, a resolution method based on the combination of soft- and hard-modeling is applied. The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data to an established factor analysis model. DATAN program was used for determination of acidity constants. The corresponding pKa values in methanol-water mixtures were determined. There is a linear relationship between acidity constants and the mole fraction of methanol in the solvent mixtures. The effect of solvent properties on acid-base behavior is discussed.

Determination of the overlapping pKa values of resorcinol using UV-visible spectroscopy and DFT methods

In this paper we determine the overlapping pK(a) values of resorcinol in water, applying a UV-Vis spectroscopic method that uses absorbance diagrams. On the other hand, in order to explain the pK(a) values obtained, we also investigate the molecular conformations and solute-solvent interactions of the resorcinate anions, using ab initio and density functional theory methods. Several ionization reactions and equilibria in protic solvents, which possess a high hydrogen-bond-donor capability, are proposed. The mentioned reactions and equilibria constituted the indispensable theoretical basis to calculate the acidity constants of resorcinol. Basis sets at the HF/6-31 + G(d) and B3LYP/6-31 + G(d) levels of theory were used for calculations. Tomasi's method was used to analyze the formation of intermolecular hydrogen bonds between the resorcinate anions and water molecules. In this way, it was determined that in alkaline aqueous solutions the monoanion and dianion of resorcinol are solvated with two and four molecules of water, respectively. The agreement between the experimentally determined pK(a) values and those reported in the literature demonstrates the applicability and accurateness of the spectroscopic method here used. On the other hand, the agreement between the experimental and theoretically calculated pK(a) values provides solid support for the acid-base reactions proposed in this work.

Amplification of Inhibitory Activity of Catechin against Disease-Related Enzymes by Conjugation on Poly(ε-lysine)

A new inhibitor against disease-related enzymes, collagenase, hyaluronidase, and xanthine oxidase, has been developed by the laccase-catalyzed conjugation of catechin on poly(epsilon-lysine). The resulting poly(epsilon-lysine)-catechin conjugate showed greatly improved inhibition effects on activity of these enzymes, whereas the catechin monomer showed very low inhibition activity. The kinetic analysis on the inhibition of collagenase exhibited that the conjugate was a mixed-type inhibitor. The amplified activities might offer high potential as a therapeutic agent for prevention of various enzyme-related diseases.

Enzymatic synthesis of a catechin conjugate of polyhedral oligomeric silsesquioxane and evaluation of its antioxidant activity

The antioxidant activity of catechin was amplified by conjugation with amine-terminated polyhedral oligomeric silsesquioxane (POSS) using horseradish peroxidase as catalyst. Compared to intact catechin, the scavenging activity of the POSS-catechin conjugate against superoxide anion was greatly improved. In addition, the conjugate strongly inhibited xanthine oxidase activity.