Phenazine virulence factor binding to extracellular DNA is important for Pseudomonas aeruginosa biofilm formation

Bacterial resistance to conventional antibiotics necessitates the identification of novel leads for infection control. Interference with extracellular phenomena, such as quorum sensing, extracellular DNA integrity and redox active metabolite release, represents a new frontier to control human pathogens such as Pseudomonas aeruginosa and hence reduce mortality. Here we reveal that the extracellular redox active virulence factor pyocyanin produced by P. aeruginosa binds directly to the deoxyribose-phosphate backbone of DNA and intercalates with DNA nitrogenous base pair regions. Binding results in local perturbations of the DNA double helix structure and enhanced electron transfer along the nucleic acid polymer. Pyocyanin binding to DNA also increases DNA solution viscosity. In contrast, antioxidants interacting with DNA and pyocyanin decrease DNA solution viscosity. Biofilms deficient in pyocyanin production and biofilms lacking extracellular DNA show similar architecture indicating the interaction is important in P. aeruginosa biofilm formation

Size-effects in the chemical modification of carbon black nanoparticles with 4-nitroaniline

The chemical modification of a range of carbon blacks (primary particle diameters ranging from 14 nm to 66 nm) has been investigated and characterised by means of cyclic voltammetry (CV), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and acid-base Boehm titration. An electrochemical probe molecule, 4-nitroaniline, was introduced to the carbon black. Physisorption and intercalation processes were observed and quantified electrochemically. Significantly more 4-nitroaniline per cm2 was present for smaller particles, implying extensive intercalation for particles ca. 14 nm in diameter. The voltammetric reduction of 4-nitroaniline covalently tethered to the carbon black was observed at a potential ca. 0.4 V more negative than the physisorbed and intercalated species, allowing separate quantitative analysis. Nanoscale size effects of carbon black were observed, with an optimum size of 27 nm observed. The electrochemical responses regarding the physisorption process decreased with the increase in surface oxidative pre-treatment time. In contrast, voltammetric signals corresponding to covalently tethered 4-nitroaniline increased with surface oxidation, before decreasing due to over-oxidation of the carbon black. The importance of some oxidation in forming electrochemically stable covalently-tethered groups is noted and discussed. © 2010 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique

Extraction and electrochemical detection of capsaicin and ascorbic acid from fresh chilli using ionic liquids

Ionic liquids can be used as non-volatile, tunable solvents, extractants and electrolytes. This work investigates their ability to extract an organic analyte, capsaicin, from fresh Capsicum annuum Bird's eye chilli peppers (also known as Thai chillies), followed by the electroanalytical quantification of the extracted analyte. Ascorbic acid (vitamin C) was also extracted and quantified. Two ionic liquids were identified to extract capsaicin from fresh chilli more effectively than the conventional ethanol-based process; the inherently basic 1-ethyl-3-methylimidazolium acetate, [Emim][OAc], and the inherently acidic 1-ethyl-3-methylimidazolium hydrogen sulfate, [Emim][HSO4]. The ionic liquid extracts could be electrochemically quantified using a bare glassy carbon electrode either in the pure ionic liquid (one pot extraction and quantification) or after dilution with water/ethanol to assist resolution of the capsaicin (flavour indicator) and ascorbic acid (freshness indicator) features

Irreversible uptake of palladium from aqueous systems using L-cysteine methyl ester physisorbed on carbon black

The uptake of palladium from aqueous systems by l-cysteine methyl ester-modified carbon black (CysOMe-CB) has been investigated. A solution containing 20 ppm PdCl2 could be reduced to below the limit of detection within 15 min by using 2 mg carbon black per mL water. The Pd(ii) was spontaneously reduced to Pd(0) on the carbon black (CB) surface, likely due to the known reducing nature of oxygen-containing carbonaceous materials, although the possible concurrent oxidation of cysteine to cystine is discussed. The presence of Pd(0) was demonstrated by X-ray Photoelectron Spectroscopy (XPS), with ca. 6 sulfur atoms detected for every Pd atom. CysOMe was predominately present on the CB as physisorbed material, and leaching of CysOMe back into solution was determined to be minor (ca. 0.4 mol% per mL water per mg CB over 24 hours). Attempted removal of Pd from the CB surface by extraction with hydrochloric acid or sodium acetate solutions was found to labilise other metal ions already present in the CB subsurface, and accumulate them at the CB surface. © 2011 The Royal Society of Chemistry

Electroanalytical Detection of n-Butylamine at a Nickel/Carbon Nanotube Composite

We report the electroanalytical detection of n-butylamine at a nickel/carbon nanotube (Ni/CNT) composite. Scanning Electron Microscopy (SEM) characterisation of the composite demonstrated that it consisted of bulk nickel particles ca. 2 μm in diameter entangled in CNT bundles. The spontaneous formation of Ni(OH)2 was optimised, and comparison with a 3 mm nickel electrode showed that ca. 4 μg of the Ni/CNT composite cast on a 3 mm GC electrode possessed bulk nickel characteristics while also having higher activity and higher sensitivity towards the electro-chemical detection of n-butylamine. However, the Ni/CNT composite showed no response to ammonia, in contrast to the macro-nickel-electrode.© 2010 Wiley-VCH Verlag GmbHandCo. KGaA, Weinheim

One-step synthesis of fluorescein modified nano-carbon for Pd(II) detection via fluorescence quenching.

Carbon black (CB) nanoparticles modified with fluorescein, a highly fluorescent molecule, were prepared using a facile and efficient methodology. Simply stirring CB in aqueous solution containing fluorescein resulted in the strong physisorption of fluorescein onto the CB surface. The resulting Fluorescein/CB was then characterised by means of X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), fluorescence microscopy and fluorescence spectroscopy. The optimum experimental conditions for fluorescence of Fluorescein/CB viz. fluorescence excitation and emission wavelengths, O(2) removal and the amount of Fluorescein/CB used, were investigated. The Fluorescein/CB was used as a fluorescent probe for the sensitive detection of Pd(II) in water, based on fluorescence quenching. The results demonstrated that the fluorescence intensity of Fluorescein/CB decreased with increasing Pd(II) concentration, and the fluorescence quenching process could be described by the Stern-Volmer equation. The limit of detection (LOD) for the fluorescence quenching of Fluorescein/CB by Pd(II) in aqueous solution was found to be 1.07 μM (based on 3σ). Last, approaches were studied for the removal of Fe(III) which interferes with the fluorescence quenching of Fluorescein/CB. Complexation of Fe(III) with salicylic acid was used to enhance and control the selectivity of Fluorescein/CB sensor towards Pd(II) in the presence of Fe(III)

A green approach to Fenton chemistry: mono-hydroxylation of salicylic acid in aqueous medium by the electrogeneration of Fenton's reagent

First, the electrochemical characteristics of Fenton's reagent (Fe(iii), Fe(ii) and hydrogen peroxide), including its catalytic (EC′) behaviour were investigated. Second, the electrogeneration of hydrogen peroxide by a two-electron reduction of dissolved oxygen was conducted at a carbon electrode in a divided electrolysis cell and the concentration of hydrogen peroxide obtained was determined by the titration. The two approaches were then combined to give a one-pot, relatively green approach to aromatic hydroxylation reactions, with the electro-Fenton method allowing the iron to be used catalytically and the oxygen/water employed as the hydroxylation reagent by the in situ production of hydrogen peroxide. In particular, the preparative-scale hydroxylation of salicylic acid has been studied in an oxygen-saturated 0.1 M Na 2SO 4 pH 3.0 solution containing 5 mM Fe(ii) and 5 mM salicylic acid at the controlled potential of -1.0 V vs. SCE. The study showed that after the attack of the hydroxyl radical produced in situ by the electro-Fenton process on salicylic acid, 2,3- and 2,5-dihydroxybenzoic acids were detected as primary monohydroxylated products with the highest yield of ca. 21.6 ± 2.5%. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012