Abstract
This study hypothesized that long carbon chain cationic arginine (Arg) esters can be considered as toxicologically harmless preservatives. Arg-esters with C18 and C24 carbon chains, namely, arginine-oleate (Arg-OL) and arginine-decyltetradecanoate (Arg-DT), were synthesized. Structures were confirmed by FT-IR, 1H NMR, and mass spectroscopy. Both Arg-esters were tested regarding hydrophobicity in terms of log Poctanol/water, critical micelle concentration (CMC), biodegradability, cytotoxicity, hemolysis, and antimicrobial activity against Escherichiacoli (E. coli), Staphylococcusaureus (S. aureus), Bacillussubtilis (B. subtilis), and Enterococcusfaecalis (E. faecalis). Log Poctanol/water of arginine was raised from −1.9 to 0.3 and 0.6 due to the attachment of C18 and C24 carbon chains, respectively. The critical micelle concentration of Arg-OL and Arg-DT was 0.52 and 0.013 mM, respectively. Both Arg-esters were biodegradable by porcine pancreatic lipase. In comparison to the well-established antimicrobials, benzalkonium chloride (BAC) and cetrimide, Arg-esters showed significantly less cytotoxic and hemolytic activity. Both esters exhibited pronounced antimicrobial properties against Gram-positive and Gram-negative bacteria comparable to that of BAC and cetrimide. The minimum inhibitory concentration (MIC) of Arg-esters was <50 μg mL–1 against all tested microbes. Overall, results showed a high potential of Arg-esters with long carbon chains as toxicologically harmless novel preservatives.
Highlights
Many cationic lipophilic compounds such as benzalkonium chloride (BAC), cetrimide, and chlorhexidine are used as antiseptics and preservatives because of their excellent antimicrobial properties.[1−3] They are frequently used as preservatives in topical formulations for dermal, intraoral, ocular, or nasal applications
Arg-OL and Arg-DT esters were synthesized by esterification of Bocarginine with long carbon chain alcohols, followed by Boc deprotection
For over half a century, cationic lipophilic compounds derived from quaternary ammonium compounds are being used as antimicrobials.[3]
Summary
Many cationic lipophilic compounds such as benzalkonium chloride (BAC), cetrimide, and chlorhexidine are used as antiseptics and preservatives because of their excellent antimicrobial properties.[1−3] They are frequently used as preservatives in topical formulations for dermal, intraoral, ocular, or nasal applications. They show antimicrobial action against a broad range of microbes including Grampositive and Gram-negative bacteria, viruses, and yeast, their usefulness remains questionable because of safety concerns.[4] There are numerous studies reporting about the adverse effects of BAC, cetrimide, and chlorhexidine.[5−10]. Stinchcomb et al observed complete hydrolysis of lipophilic alkyl esters of naltrexone by esterases on passing through the human skin.[12]
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