A new procedure for the preparation of biocompatible gold nanoparticles using biofla vonoids: rutin, quercetin, and luteolin as reducing agents and stabilizers was proposed. On varying the bioflavonoid concentration, nanoparticles of different size are formed. By the combined use of spectroscopy and atomic force microscopy, the nanoparticle size was estimat ed (40-50 nm). Uniform and highly dispersed gold nanoparticles were obtained at Au : rutin ratios of 1 : 1, 2 : 1, and 4 : 1 and Au : quercetin ratios of 2 : 1 and 4 : 1. The nanoparticle yield remains almost constant as the Au : rutin ratio varies over a broad range from 1 : 1 to 12 : 1. It was suggested that complete reduction of Au III to Au 0 with a large excess of Au is accompanied by extensive oxidation of bioflavonoid involving an intermediate oxidant formed in the system due to the high oxidative capacity of Au III . For elucidating the catalytic role of bioflavonoids in the formation of gold nanoparticles, quantum chemical modeling of the process was performed.

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The effect of metal ions (iron, nickel, zinc) in concentration range (1÷60)×10−5 M on biological propylene oxidation by bacteria Methylococcus capsulatus (M) was evaluated. The influence of metal varied from activation to inhibition. It was found that at low concentrations (up to (1÷10) ×10−5 M) iron ions stimulate the biological propylene oxidation, while nickel and zinc ions have no that effect. When the metal concentration increases to 60×10−5 M, it leads to inhibition of propylene oxidation by both nickel and zinc ions, but the inhibition by iron was not observed. The minimum inhibitory concentrations for the studied metals were determined.

Protective properties of gold nanoparticles and gold-rutin complexes were studied. Aurophilic bacteria Micrococcus luteus and methanotrophic bacteria Methylococcus capsulatus were studied. Gold-rutin nanoparticles and complexes protect the respiratory activity of the bacteria against toxins. Pretreatment of the cells with gold is more efficient than the treatment after the action of toxin.Increased interest in the use of gold in chemistry, med icine, and biology is observed in the recent time. Special attention is given to gold nanoparticles 1-3 and gold complexes with natural compounds, including flavo noids. 4 This direction is one of the most important in green chemistry. As for the use of gold in medicine and biology, unique medicinal properties of this metal known from the ancient time (chrisotherapy) should be men tioned. Studies on the application of gold preparations for point diagnostics and treatment of such severe diseas es as cancer and tuberculosis are carried out in many la boratories. 5In our opinion, it is also interesting that metalo philic organisms that assimilate gold including it in cell metabolism exist in nature. 6,7 We showed that in the presence of colloidal gold in an incubation medium aurophilic bacteria Micrococcus luteus incorporate the Au atoms into the active site of specific membrane bound NADH oxidase, which was named Au protein. 8 A specific feature of this protein is the presence of flavin and flavonoid cofactors. 9 It is the flavonoid cofactor that chelates gold. As a result, Au protein gains a new function, viz., the ability to oxidize methane and its homologs. 10,11Taking into account the medicinal properties of gold and the ability of aurophilic bacteria to include it in their metabolism, it seemed of interest to study the possi bility of appearance of other new functions in bacte ria cells under the action of gold, in particular, protec tion of biological systems against toxins. Since respira tion is the main process providing vital activity to all living organisms, in the present work we studied the ability of Au-flavonoid nanoparticles and complexes to pro tect cells against poisons and toxins inhibiting respirato ry activity. ExperimentalThe studies were carried out on aurophilic microorganisms Micrococcus luteus and methanotrophs Methylococcus capsulatus. Inhibitors of the respiratory chain, 1 naphthol and 2,2´ bipyridyl, were used as toxins. The respiratory activity was determined by polarography using the Clark electrode. 12 The protein concen tration was determined by the biuret method after the prelimi nary disintegration of cells and spheroplasts on an UZDN 1 sonicator at 22 kHz and 0 °С. The Au protein was isolated from bacteria Micrococcus luteus. 8 The complexes and nanoparticles Au-rutin were prepared according to a method developed earli er. 4,13,14 Colloidal gold prepared by the Zsigmondy method 15 was used as the standard. Absorption spectra were recorded on a Specord M 40 spectrophotometer (Carl Zeiss).The following reagents were used: HAuCl 4 •4 H 2 O, rut...