Abstract:We synthesized nine quaternary ammonium compounds (QUATs) starting from phenylalanine, N-alkyl-N,N-dimethyl-(1-hydroxy-3-phenylpropyl)-2-ammonium bromides, which were prepared as optically pure substances. Five compounds were prepared as S-enantiomers and four compounds as R-enantiomers. These compounds were evaluated by their activities against bacteria and fungi. Three microbial strains were used in the study: the gram-negative bacteria Escherichia coli, the gram-positive bacteria Staphylococcus aureus and the fungi Candida albicans. The activities were expressed as minimum bactericidal or fungicidal concentrations (MBC). The most active compounds were (2S)-N-tetradecyl-N,N-dimethyl-(1-hydroxy-3-phenylpropyl)-2-ammonium bromide and (2R)-N-tetradecyl-N,N-dimethyl-(1-hydroxy-3-phenylpropyl)-2-ammonium bromide, with MBC values exceeding those of commercial benzalkoniumbromide (BAB) used as standard. The relationships between structure and biological activity of the tested QUATs were quantified by the bilinear model (QSAR) and are discussed.

The present study is focused on the synthesis and investigation of the physicochemical and biological properties of silver nanoparticles stabilized with a series of cationic gemini surfactants having a polymethylene spacer of variable length. UV-VIS spectroscopy, dynamic light scattering, scanning electron microscopy and zeta potential measurements were applied to provide physicochemical characterization of the silver nanoparticles. The mean size values of the nanoparticles were found to be in the 50 to 115 nm range. From the nanoparticle size distributions and scanning electron microscopy images it results that a population of small nanoparticles with the size of several nanometers was confirmed if the nanoparticles were stabilized with gemini molecules with either a short methylene spacer (two or four −CH2− groups) or a long spacer (12 −CH2− groups). The average zeta potential value for silver nanoparticles stabilized with gemini molecules is roughly independent of gemini surfactant spacer length and is approx. +58 mV. An interaction model between silver nanoparticles and gemini molecules which reflects the gained experimental data, is suggested. Microbicidal activity determinations revealed that the silver nanoparticles stabilized with gemini surfactants are more efficient against Gram-negative bacteria and yeasts, which has a direct relation to the interaction mechanism of nanoparticles with the bacterial cell membrane and its structural composition.

ABSTRACT:The antimicrobial properties of three potential probiotic strains of lactobacilli isolated from a lamb (Lactobacillus murinus C, Lactobacillus mucosae D and Lactobacillus reuteri E) were studied using the streak line method and the agar well diffusion assay. The probiotic lactobacilli strains Lactobacillus rhamnosus ATCC 53103, Lactobacillus reuteri ATCC 55730, Lactobacillus reuteri ATCC 55845 and Lactobacillus plantarum DSM 9843 were used for comparison. Using the streak line method the inhibitory activity of lactobacilli products towards ten Gram-positive and Gram-negative potential pathogenic bacteria under different cultivation conditions (anaeorobic or microaerobic preincubation of lactobacilli for 24 h or 48 h) was tested. The strongest inhibitory activity was demonstrated by the Lactobacillus reuteri E strain. The most sensitive strains to the antimicrobial activity of lactobacilli were Yersinia enterocolitica clinical isolate (19.9 ± 6.8 mm) and Listeria monocytogenes ATCC 51774 (17.7 ± 6.0 mm) after microaerobic and anaerobic preincubation, respectively. Generally, microaerobic conditions and longer preincubation of lactobacilli resulted in stronger inhibition of target bacteria. The inhibitory activity of lactobacilli towards selected lactobacilli strains was also tested. Only low inhibition of growth was observed. In the agar well diffusion assay the inhibitory effect of natural and modified lactobacilli culture cell-free supernatants, obtained from MRS broth cultures, on Staphylococcus aureus ATCC 6538 growth was determined. Supernatants were modified by heat (10 min/60 °C; 60 min/100 °C) and protease treatment and neutralization of pH. Neutralization elicited the most significant impact on the activity of supernatants and resulted in total loss of activity. After all other modifications supernatants retained some residual activity. The highest inhibitory activity was observed for the cell-free supernatant produced by Lactobacillus mucosae D.

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A series of novel phospholium amphiphilic compounds with straight alkyl chains with different numbers of carbon atoms (12,14,15,16,17,18) were synthesized. The quaternary phosphorus, phosphonium cation, is incorporated into a five-membered heterocyclic ring. Their physicochemical properties were investigated by measurements of surface tension, conductivity and dynamic light scattering. The critical micelle concentration (c M ), the surface tension value at the c M (c cmc ), the surface area at the surface saturation per head group (A cmc ), the ionization degree of micelle (a), the free energy of micellization (DG°m ic ), and hydrodynamic diameter (d h ) were determined. Antimicrobial activity was tested against bacteria and yeast. The structure-activity relationship was determined. 3 J CP = 17.3 Hz, = C-CH 3 ) 22.5 (d, 1 J CP = 46.2 Hz, a CH 2 of alkyl chain), 22.6 (d, 2 J CP = 4.1 Hz, b CH 2 of alkyl chain), 22.7 (x CH 2 of alkyl chain), 29.1, 29.3, 29.4, 29.5, 29.6(0), 29.6(4), 29.7 (d-x-2 CH 2 of alkyl chain), 30.5 (d, 3 J CP = 15.6 Hz, c CH 2 of alkyl chain), 31.9 (x-1 CH 2 of alkyl chain), 113.6 (d, 1 J CP = 80.0 Hz, = CHP), 115.9 (d, 1 J CP = 83.9 Hz, Ph C 1 ), 130.0 (d, 3 J CP = 12.9 Hz, Ph C meta ), 133.6 (d, 2 J CP = 10.7 Hz, Ph C ortho ), 134.6 (d, 4 J CP = 3.0 Hz, Ph C para ), 163.2 (d, 2 J CP = 16.4 Hz, = C-CH 3 ); 31 P NMR (CDCl 3 , H 3 PO 4 ) d: 38.5; IR t max /cm -H NMR (CDCl 3 , TMS) d: 0.88 (t, 3 J H,H = 6.7 Hz, 3H, CH 3 of alkyl chain), 1.13-1.38 (m, 22H, 11 9 CH 2 of alkyl chain), 1.38-1.62 (m, 4H, b, c CH 2 of alkyl chain) 2.29 (s, 6H, 2 9 = C-CH 3 ), 3.08-3.22 (m, 2H, a CH 2 of alkyl chain), 7.08 (d, 2 J HP = 30.9 Hz, 2H, = CHP), 7.54-7.61 (m, 2H, Ph H meta ), 7.61-7.75 (m, 1H, Ph H para ), 8.15-8.23 (m, 2H, Ph H ortho ); 13 C NMR (CDCl 3 , TMS) d: 14.1 (CH 3 of alkyl chain), 18.5 (d, 3 J CP = 17.3 Hz, = C-CH 3 ) 22.5 (d, 1 J CP = 46.1 Hz, a CH 2 of alkyl chain), 22.6 (d, 2 J CP = 4.1 Hz, b CH 2 of alkyl chain), 22.7 (x CH 2 of alkyl chain), 29.1, 29.3, 29.4, 29.5, 29.6, 29.7 (d-x-2 CH 2 of alkyl chain), 30.5 (d, 3 J CP = 15.4 Hz, c CH 2 of alkyl chain), 31.9 (x-1 CH 2 of alkyl chain), 113.6 (d, 1 J CP = 80.0 Hz, = CHP), 115.8 (d, 1 J CP = 83.8 Hz, Ph C 1 ), 130.0 (d, 3 J CP = 12.9 Hz, Ph C meta ), 133.5 (d, 2 J CP = 10.4 Hz, Ph C ortho ), 134.7 (d, 4 J CP = 3.0 Hz, Ph C para ), 163.2 (d, 2 J CP = 16.5 Hz, = C-CH 3 ); 31 P NMR (CDCl 3 , H 3 PO 4 ) d: 38.5; IR t max /cm -

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with the maximum antimicrobial activity found at the spacer length of 6 CH2 groups for bacteria and 8 CH2 groups for fungi. This is related to a different composition of cell membrane of the used microorganisms.

In the present investigation, the basic esters of meta-alkoxyphenylcarbamic acid bearing variously substituted N-phenylpiperazine fragment were screened for their in vitro antimicrobial activity against Staphylococcus aureus, Escherichia coli and Candida albicans, respectively. The most effective againstEscherichia coli was found the compound 6d (MIC=195,3 μg/mL) bearing simultaneously para-fluoro substituent at the 4-phenylpiperazin-1-yl core and meta-methoxy side chain in the lipophilic part of the molecule. From whole analyzed set of the molecules the substance 8e with propoxy side chain forming meta-alkoxyphenylcarbamoyl fragment and lipophilic, sterically bulky meta-trifluoromethyl group attached at N-phenylpiperazine moiety was evaluated as the most active against Candida albicans (MIC=97,7 μg/mL). On the contrary, all investigated structures were practically inactive against Staphylococcus aureus (MIC>1000 μg/mL)