Synthesis, surface tension properties and antibacterial activities of amphiphilic d -galactopyranose derivatives

Alkyl Xylosides: Physico-Chemical Properties and Influence on Environmental Bacteria Cells

A group of four selected non-ionic surfactants based on carbohydrates, namely octyl d-xyloside (C8X), nonyl d-xyloside (C9X), decyl d-xyloside (C10X) and dodecyl d-xyloside (C12X), have been investigated to accomplish a better understanding of their physico-chemical properties as well as biological activities. The surface-active properties, such as critical micelle concentration (CMC), emulsion and foam stability, the impact of the compounds on cell surface hydrophobicity and cell membrane permeability together with their toxicity on the selected bacterial strains have been determined as well. The studied group of surfactants showed high surface-active properties allowing a decrease in the surface tension to values below 25 mN m-1 for dodecyl d-xyloside at the CMC. The investigated compounds did not have any toxic influence on two Pseudomonas bacterial strains at concentrations below 25 mg L-1. The studied long-chain alkyl xylosides influenced both the cell inner membrane permeability and the cell surface hydrophobicity. Furthermore, the alkyl chain length, as well as the surfactant concentration, had a significant impact on the modifications of the cell surface properties. The tested non-ionic surfactants exhibited strong surface-active properties accompanied by the significant influence on growth and properties of Pseudomonas bacteria cells.

Trimodal Control of Ion-Transport Activity on Cyclo-oligo-(1→6)-β-D-glucosamine-Based Artificial Ion-Transport Systems

Cyclo-oligo-(1→6)-β-D-glucosamines functionalized with hydrophobic tails are reported as a new class of transmembrane ion-transport system. These macrocycles with hydrophilic cavities were introduced as an alternative to cyclodextrins, which are supramolecular systems with hydrophobic cavities. The transport activities of these glycoconjugates were manipulated by altering the oligomericity of the macrocycles, as well as the length and number of attached tails. Hydrophobic tails of 3 different sizes were synthesized and coupled with each glucosamine scaffold through the amide linkage to obtain 18 derivatives. The ion-transport activity increased from di- to tetrameric glucosamine macrocycles, but decreased further when flexible pentameric glucosamine was introduced. The ion-transport activity also increased with increasing length of attached linkers. For a fixed length of linkers, the transport activity decreased when the number of such tails was reduced. All glycoconjugates displayed a uniform anion-selectivity sequence: Cl(-) >Br(-) >I(-) . From theoretical studies, hydrogen bonding between the macrocycle backbone and the anion bridged through water molecules was observed.

FTIR metabolomic fingerprint reveals different modes of action exerted by structural variants of N-alkyltropinium bromide surfactants on Escherichia coli and Listeria innocua cells

Surfactants are extremely important agents to clean and sanitize various environments. Their biocidal activity is a key factor determined by the interactions between amphiphile structure and the target microbial cells. The object of this study was to analyze the interactions between four structural variants of N-alkyltropinium bromide surfactants with the Gram negative Escherichia coli and the Gram positive Listeria innocua bacteria. Microbiological and conductometric methods with a previously described FTIR bioassay were used to assess the metabolomic damage exerted by these compounds. All surfactants tested showed more biocidal activity in L. innocua than in E. coli. N-tetradecyltropinium bromide was the most effective compound against both species, while all the other variants had a reduced efficacy as biocides, mainly against E. coli cells. In general, the most prominent metabolomic response was observed for the constituents of the cell envelope in the fatty acids (W1) and amides (W2) regions and at the wavenumbers referred to peptidoglycan (W2 and W3 regions). This response was particularly strong and negative in L. innocua, when cells were challenged by N-tetradecyltropinium bromide, and by the variant with a smaller head and a 12C tail (N-dodecylquinuclidinium bromide). Tail length was critical for microbial inhibition especially when acting against E. coli, maybe due the complex nature of Gram negative cell envelope. Statistical analysis allowed us to correlate the induced mortality with the metabolomic cell response, highlighting two different modes of action. In general, gaining insights in the interactions between fine structural properties of surfactants and the microbial diversity can allow tailoring these compounds for the various operative conditions.

A novel, rapid and automated conductometric method to evaluate surfactant-cells interactions by means of critical micellar concentration analysis

Conductometry is widely used to determine critical micellar concentration and micellar aggregates surface properties of amphiphiles. Current conductivity experiments of surfactant solutions are typically carried out by manual pipetting, yielding some tens reading points within a couple of hours. In order to study the properties of surfactant-cells interactions, each amphiphile must be tested in different conditions against several types of cells. This calls for complex experimental designs making the application of current methods seriously time consuming, especially because long experiments risk to determine alterations of cells, independently of the surfactant action. In this paper we present a novel, accurate and rapid automated procedure to obtain conductometric curves with several hundreds reading points within tens of minutes. The method was validated with surfactant solutions alone and in combination with Saccharomyces cerevisiae cells. An easy-to use R script, calculates conductometric parameters and their statistical significance with a graphic interface to visualize data and results. The validations showed that indeed the procedure works in the same manner with surfactant alone or in combination with cells, yielding around 1000 reading points within 20 min and with high accuracy, as determined by the regression analysis.