Synthesis of new potent “composite” biocides with both N-chloramine and quaternary ammonium moieties and strategies of converting them into selective biocides
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Date
2017
Authors
Ghanbar, Sadegh
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Abstract
Antibiotic resistance is one of many life-threatening problems for humans in the 21st century as mutations in microorganisms become increasingly difficult to treat. Scientists from all over the globe have been trying hard to find a solution for this issue and save people’s lives. This study combines approaches from both organic chemistry and materials science in order to combat these issues. First part of the research includes finding a solution to the quench of active biocides in high protein media (HPM), in which we synthesized “composite” biocides by covalently bonding a long alkyl chain quaternary ammonium salt (QAC) with an amine-based N-chloramine. It was hypothesized that using a secondary amine-based N-chloramine can improve biocides stability in HPM; therefore, 2,2,6,6-tetramethyl-piperidinol was linked to dodecyltrimethylammonium chloride or tetradecyltrimethyl-ammonium chloride via a triazole bridge (5a or 5b). The monofunctional QACs 5a and 5b were then converted to corresponding “composite” biocides 6a and 6b using tertbutyl hypochlorite. The antibacterial challenge was performed against various Gram-negative and Gram-positive bacteria 5a, 5b, 6a, 6b, hydantoin-based composite biocides previously synthesized in our lab [3-(3-chloro-4,4-dimethyl-2,5-dioxo-imidazolidin-1-yl)-propyl]-dimethyl-tetradecyl-ammonium chloride, C18, and its unchlorinated precursor, C17). In this antibacterial assay, the compound with shorter alkyl chain (N-(2-(4-((1-chloro-2,2,6,6-tetramethylpiperidin-4-yloxy)methyl)-1H-1,2,3-triazol-1-yl)ethyl)-N,N-dimethyldodecan-1-ammonium chloride, 6a) showed superior antibacterial activity in both phosphate-buffered saline (PBS) and HPM through higher efficiency in inactivating Methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa (P. aeruginosa), Escherichia coli (E. coli), and wild-type P. aeruginosa (PA01) than the commercially available biocide benzyldimethyltetradecylammonium chloride (BC).
In the second part of this research, we intended to develop a strategy to convert highly potent yet non-selective cytotoxic biocides into selective non-cytotoxic antibacterial agents. We achieved it by encapsulating non-selective biocides in biocompatible solid lipid nanoparticles (SLNs) conjugated with a MRSA-specific antibody (termed as "Ab"). A model biocide (C17) has been utilized for the proof-of-concept study. The C17-loaded Ab-conjugated (C17-SLN-Ab) SLNs demonstrated superior antimicrobial activity over the antibody-free (C17-SLN) and nonspecific antibody conjugated (C17-SLN-IgG) counterparts. To see the effect of the antibody on selective toxicity of SLNs, we developed an assay in which toxicity of SLNs towards fibroblast cells was determined in the presence of MRSA. In this assay, C17-SLN-Ab revealed more selective toxicity towards MRSA than fibroblast cells. C17-SLN-Ab also exhibited double selectivity with higher toxicity to MRSA than P. aeruginosa. The interaction between different SLNs was evaluated using TEM imaging in which SLN-Ab showed more tendency to bind to MRSA than P. aeruginosa. To confirm the versatility of this method, anti E. coli antibody and BC were used, and similar results were achieved.
Overall, we successfully designed a potent biocide with the capacity for use in HPM and PBS, which mitigates the issue of active biocides being quenched in high protein fluids. Also, a nanotechnology method was used to turn potent broad-spectrum non-selective biocides (C17 and BC) into selective ones.
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Keywords
biocide, solid lipid nanoparticle, antibody, selective kill, active targeting, composite biocide, N-chloramine, quaternary ammonium compound