Antibacterial and Fungicidal Activity of Guanidinium Oligomers

Abstract

Guanidinium oligomers are a poorly studied class of organic compounds and attract attention due to their antimicrobial properties. Strengthening the antimicrobial properties and simplifying and reducing the cost of the synthesis of these compounds is promising for obtaining functional guanidine-containing oligomers with alkyl radicals of different lengths in their composition. The aim of this work is to study the bactericidal and fungicidal activities of newly synthesized oligomeric guanidinium bromides with alkyl radicals of various lengths. Methods. The synthesis of tetraalkyl-substituted guanidine-containing oligomers with an aromatic and aliphatic oligoether component was carried out by the reaction of guanidine-containing oligomers with terminal guanidine fragments and alkyl bromides (Alk=-C3H7, -C7H15, -C10H21) at a molar ratio (1:4) of components. Different types of microorganisms (clinical isolates, gram-positive and gramnegative bacteria, microscopic fungi) were used as test cultures to determine the biocidal activity of the obtained compounds. The bacteria were grown on meat-peptone agar for 48 hours, micromycetes – on beer wort agar (6°B) for 14 days. The hydrocarbon-oxidizing bacteria and micromycetes were incubated at a temperature of 28±2°C, and clinical bacterial isolates – at a temperature of 37±2°C. Antimicrobial activity of oligomers was determined by the standard disco-diffusion method, and fungicidal – by the method of wells in agar. Results. Tetraalkyl-substituted guanidinium bromide oligomers with various radicals (-C3H7, -C7H15, -C10H21) were obtained and their bactericidal and fungicidal activity against various groups of microorganisms was shown. It was found that the obtained oligomers at a concentration of 1–3% in aqueous solution inhibited the growth of gram-negative and gram-positive bacteria. Antimicrobial and fungicidal properties depended on the length of the alkyl radical, and as its length increased, the diameter of growth inhibition zones of bacteria and micromycetes were increased. For 3% solutions of tetraalkyl-substituted guanidine oligomer with aromatic oligoepoxide (Alk=-C10H21), the growth inhibition zones of bacteria were 18–21 mm. The bactericidal effect of oligomer based on aromatic oligoepoxide with alkyl radicals Alk=-C7H15, -C10H21 was 20–25% higher than that for variants with aliphatic oligoepoxide. All the tetraalkyl-substituted (Alk=-C7H15, -C10H21) guanidine-containing oligomers at a concentration of 1% solution showed fungicidal activity to almost all micromycetes, the growth inhibition zones for microscopic fungi on the 7th day were 7–20 mm. The largest growth inhibition zones of micromycetes (in the range 15–20 mm) were observed for oligomers with aromatic oligoepoxide and radicals Alk=-C10H21 and -C7H15 and aliphatic oligoepoxide with radical Alk=-C10H21 (in the range 15–20 mm). Conclusions. The length of the alkyl radical and the nature of the oligoether component affected the bactericidal and fungicidal properties of newly synthesized oligomers. With an increase of the length of the alkyl radical of guanidine-containing oligomers, their bactericidal and fungicidal properties increase, tetralkyl-containing oligomers are promising for use as disinfectants for indoor treatment and as additives in polymer compositions to protect them from bio-damage.