Reaction of N-acylhomoserine lactones with hydroxyl radicals: rates, products, and effects on signaling activity.

Chemical communication in bacteria, sometimes called quorum sensing, is a fundamental microbial process that is based on the exchange of molecular signals between cells. The signaling molecules involved in this process are thermodynamically unstable in some environments and their degradation affects microbial communication. This work reports the oxidation of a series of substituted N-acylhomoserine lactones (AHLs, a class of quorum sensing signals) by hydroxyl radicals. The corresponding bimolecular rate constants were obtained and correlated positively with the length of the acyl side chain (C, in numbers of carbon atoms) ranging from 2.4 × 10(9) M(-1) s(-1) to 9.4 × 10(9) M(-1) s(-1) (C4- to C10-AHL), 2.4 × 10(8) M(-1) s(-1) for 3-oxo C6-AHL, and 2.94 × 10(9) M(-1) s(-1) for 3-oxo C8-AHL. Liquid chromatography-mass spectrometric techniques were applied to qualify the identity and quantify the yields of the hydroxyl radical oxidation products of C6-AHL (aldo, keto, and hydroxylated C6-analogues identified). The biological activity of C6-AHL and associated products was determined using the Vibrio harveyi bioluminescence bioassay. Oxidation resulted in a net increase in assay response indexed against the starting AHL. This result suggested that the application of HO• based technologies such as advanced oxidation processes for biofilm control may result in unintended quorum sensing responses by microbial communities.

Identification of hydroxyl radical oxidation products of N-hexanoyl-homoserine lactone by reversed-phase high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry.

A reversed-phase high-performance liquid chromatography/electrospray tandem mass spectrometry method was developed for the characterization of hydroxyl radical oxidation products of N-hexanoyl-homoserine lactone (C6-HSL), a member of the N-acylhomoserine lactone (AHL) class of microbial quorum-sensing signaling molecules identified in many Gram-negative strains of bacteria. Six products were identified: four with molecular weight (MW) of 213 and two with MW of 260. The characteristic product ions formed through collision-induced dissociation (CID) provided diagnostic structural information. One of the photolysis products was determined to be N-(3-oxohexanoyl)homoserine lactone (3OC6-HSL), a highly active quorum-sensing signal, by comparison with a reference standard. Three structural isomers with the same mass as 3OC6-HSL were identified as acyl side chain oxidized C6-HSL (keto/enol functionalized) by accurate mass measurement and the structures of these products were proposed from CID spectral interpretation. Two structural isomers formed from concurrent oxidation and nitration of C6-HSL were also observed and their structures were postulated based on CID spectra. In addition to the six hydroxyl radical oxidation products formed from the C6-HSL precursor, five additional compounds generated from combined oxidation and lactonolysis of C6-HSL were identified and structures were postulated.

Gold nanorods as nanoadmicelles: 1-naphthol partitioning into a nanorod-bound surfactant bilayer.

As-prepared gold nanorods, stable in aqueous solution, bear a bilayer of the cationic surfactant cetyltrimethylammonium bromide (CTAB). This bilayer provides a approximately 3 nm thick hydrophobic layer that could be used to sequester hydrophobic organic molecules from aqueous solution. We have investigated the uptake of 1-naphthol as a model hydrophobic compound by CTAB-coated gold nanorods using both ultraviolet-visible spectroscopy and gas chromatography with flame ionization detection. We find the adsorption isotherm of 1-naphthol partitioning into the CTAB bilayer on gold nanorods fits the Langmuir model. The maximum number of bound 1-naphthol molecules is 14.6 +/- 2.2 x 10(3) molecules per gold nanorod, with an equilibrium binding constant of 1.97 +/- 0.79 x 10(4) M(-1) at room temperature.