Essen, Universiẗat, Diss., 2005--Duisburg.

This thesis focuses on solution antimicrobial effectiveness for copolyoxetanes with quaternary ammonium and PEG-like side chains. Ring opening copolymerization of 3-((4-bromobutoxy)methyl)-3-methyloxetane (BBOx) and 3-((2-(2-methoxyethoxy) ethoxy) methyl)-3-methyloxetane (ME2Ox) yielded random copolymers with 14-100 (m) mole% BBOx designated P[(BBOx-m)(ME2Ox)]. Reaction of P[(BBOx-m)(ME2Ox)] with dodecyl dimethylamine gave the corresponding quaternary P[(C12-m)(ME2Ox)] polycation salts, designated C12-m. Mole ratios and molecular weights were obtained from 1H-NMR and end group analysis. Differential scanning calorimetry (DSC) studies showed Tg’s between 69 and -34 °C. Minimum inhibitory concentrations (MIC) against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa showed MIC decreasing with increasing C12 mole% reaching a minimum between C12-43 and C12-60. C12-43 had the lowest MIC for all strains. At 5× MIC (challenge:108 cfu/ml), C12 43 kills ≥ 99% of the tested strains within 1 hr. C12-m copolyoxetane cytotoxicity toward human red blood cells, HFF (Human Foreskin Fibroblast) and HDF (Human Dermal Fibroblast) was low, indicating good prospects for biocompatibility. Cx-m copolyoxetane antimicrobial efficacy, hemolytic activity and cytotoxicity were further explored by changing quaternary alkyl chain length. Copolyoxetanes are represented as Cx-50, where 50 is the mole percent quaternary repeat units and ‘x’ is quaternary alkyl chain length (2 to 16 carbons). Reaction of P[(BBOx-m)(ME2Ox)] with a series of tertiary amines yielded the desired quaternary ammonium segment. DSC studies showed Tg’s between -40 °C and -60 °C and melting endotherms for C14-50 and C16-50. A systematic dependence of alkyl chain length on MIC was found with C8-50 being the most effective antimicrobial. Kill kinetics for C8-50 (5× MIC, challenge: 108 cfu/ml) effected >99% kill in 1 hour for S. aureus (7 log reduction). C8-50 efficacy on biomass and cell viability of P. aeruginosa biofilms was investigated. Crystal violet (CV) staining assays demonstrate that C8-50 had no effect on adhesion of already established P. aeruginosa biofilms, but reduced biofilm formation by killing cells prior to attachment. For anti-adhesion assays, noticeable reduction in biofilm mass occurred at concentrations greater than 2× MIC. Viability studies show a substantial log reduction of 2.1 at MIC. The low cytotoxicity of Cx-m copolyoxetanes coupled with low MICs and favorable biofilm results indicate good prospects for therapeutic applications.

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