Complexes of tetra-and hexa-coordinated germanium Adr Cat 2 Ge (1, Adr Cat = adrenaline catecholate), Ald Cat 2 Ge (2, Ald Cat = 4-formylcatecholate), Ald Cat 3 Ge(Et 3 NH) 2 (3) were synthesized by the reaction of germanium dioxide with adrenaline and 3,4-dihydroxybenzaldehyde in aqueous solution. The structures of the complexes were confirmed by 1 H and 13 C NMR and IR spectroscopy, HRMS, and elemental analysis. Cyclic voltammetry in phosphate buffer solutions (pH = 6.86) has shown the oxidation potentials E p of these complexes to be shifted by ca. 330-360 mV to more positive potentials compared to the parent aromatic diols, which means that their electron-releasing properties were diminished by about 7.6-8.3 kcal mol -1 . A study of the kinetics of the reaction of these complexes with 2,2diphenyl-1-picrylhydrazyl (DPPH) free radical in the presence of [a] N.

New antioxidants are commonly evaluated via two main approaches, i.e., the ability to donate an electron and the ability to intercept free radicals. We compared these approaches by evaluating the properties of 11 compounds containing both antioxidant moieties (mono- and polyphenols) and auxiliary pharmacophores (pyrrolidone and caprolactam). Several common antioxidants, such as butylated hydroxytoluene (BHT), 2,3,5-trimethylphenol (TMP), quercetin, and dihydroquercetin, were added for comparison. The antioxidant properties of these compounds were determined by their rates of reaction with 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and their oxidation potentials from cyclic voltammetry. Although these methods test different chemical properties, their results correlate reasonably well. However, several exceptions exist where the two methods give opposite predictions! One of them is the different behavior of mono- and polyphenols: polyphenols can react with DPPH more than an order of magnitude faster than monophenols of a similar oxidation potential. The second exception stems from the size of a “bystander” lactam ring at the benzylic position. Although the phenols with a seven-membered lactam ring are harder to oxidize, the sterically nonhindered compounds react with DPPH about 2× faster than the analogous five-membered lactams. The limitations of computational methods, especially those based on a single parameter, are also evaluated and discussed.

Using cyclic voltammetry, UV and 1H NMR spectroscopy, we have investigated the effect of 2‐carboxyethylgermanium (Ge‐132), the most common germanium‐containing dietary supplement, on the antioxidant activity of adrenaline in aqueous solutions. The complex formed by adrenaline and Ge‐132 is oxidizable at 400 mV more positive potentials compared to non‐coordinated adrenaline which corresponds to its 9 kcal/mol more difficult oxidation. An equilibrium constant of the complex formation was estimated (1300 m–1). It was shown that at the concentrations <10–3 m the complex Ge‐132‐adrenaline is mostly dissociated to the initial compounds, and the influence of Ge‐132 on the antioxidant properties of adrenaline becomes significant only when the former is in excess. Considering that such concentrations are typical for physiological conditions, this fact can be significant in identifying the mechanism of the biological action of Ge‐132 and its interference with the biological catechols.