Biological and Biomedical Aspects of Metal Phenolates

Abstract

The phenol functionality is involved in diverse biological processes and functions, serving as a proton donor and as a metal‐binding ligand. It is commonly found in many biochemicals (such as siderophores and the amino acids tyrosine and tryptophan), pharmaceuticals (including antibiotics, metal‐chelating agents, and diagnostic agents), and natural products (such as polyphenols, flavonoids, and salicylic acid). In association with other functional groups, the phenol moiety forms various types of metal‐binding sites of diverse structures and functions, for example, for iron binding and transport, in enzymes for oxygenation of substrates, and for biotransformation of aromatic compounds. Many environmentally hazardous aromatic compounds such as bisphenol A, PCB, and DDT can be degraded by tyrosinate(phenolate)‐containing metalloenzymes from microorganisms, which provides a clue for bioremediation of these toxic substances. Moreover, the phenol‐containing wet‐adhesive byssal proteins from some clams and mussels has stimulated further development of adhesive materials for medical and other applications; and the study of binding of transferrin with nanoparticles affords better understanding of protein–mineral interfacial interactions. In addition to these naturally occurring metal‐phenolate centers, there are many metal complexes of phenol and derivatives that exhibit various catalytic activities and serve as structural and/or functional model systems for tyrosinate‐containing metalloproteins.

Metal Binding of Flavonoids and Their Distinct Inhibition Mechanisms Toward the Oxidation Activity of Cu2+–β-Amyloid: Not Just Serving as Suicide Antioxidants!

“…Qr has three possible metal-binding sites: β-ketophenolate, α-ketoenolate, and catecholate moieties (Figure ). Many examples are known for metal binding to one or more of these moieties, such as the preferred binding of flaviolin to the active-site metal in cytochrome P450 via the ketophenolate moiety (rather than the ketoenolate moiety) and the spectroscopically characterized metal-binding to the ketophenolate site(s) of the anthracycline anticancer drugs. , Because Qr and Mr are not oxidized by CuAβ, it is possible that the catechol or the polyphenol ring B in these two flavonols does not interact with the metal center. The interactions between Qr and several metal ions were further analyzed to investigate the metal-binding possibilities.…”

Bioactive Phenolate Salts: Thymol Salts

“…In this context, pure phenol metal salts have been reported only for some simple phenols, including phenol and its alkyl derivatives, resorcinol, and some other simple phenols. [34,[42][43][44] Considering the above, the present work demonstrates our initial approach to the conversion of the simple natural bioactive phenolic compound "thymol" into its corresponding metal/ ammonium salts. Various metal (Na, K, Li, Cu, Zn) and ammonium (tetrabutyl ammonium and choline) salts of thymol have been synthesized and characterized using IR, NMR, TGA, CHN and DSC analysis.…”