Concentration as the switch for chiral recognition in biomembrane models

Chiral recognition was observed in a biomembrane model. Micellar aggregates formed by enantiopure N-alkyl-N,N-dimethyl-N-(1-phenyl)ethylammonium bromide were in fact able to convert the racemic mixture of bilirubin-IXalpha into an enantiomerically enriched mixture. The stereochemical preference and the extent of enantiomeric enrichment depend on the length of the hydrophobic portion of the surfactant and on the concentration conditions, and changes in the stereochemical bias are reversible.     

Composite planar electrode for sensing electrochemical oxygen demand

This work reports on the development of a graphite-polystyrene composite electrode of planar configuration, containing silver(II) oxide and copper(II) oxide catalysts (AgO-CuO), for the measurement of electrochemical oxygen demand (EOD). Optimisation studies of the composite composition as well as conditions for its processing on planar substrates and generation of an appropriate electrochemical active area resulted in the scalable fabrication of robust composite electrodes. These were evaluated with glucose as target analyte. They showed competitive low limits of detection in a linear concentration range from 5 mg L⁻¹ to 1400 mg L⁻¹ of O₂. Besides, they were stable for at least one year. The determination of EOD in wastewater samples coming from production lines of parenteral food and winemaking was successfully carried out.     

Monitoring of malolactic fermentation in wine using an electrochemical bienzymatic biosensor for l-lactate with long term stability

l-lactic acid is monitored during malolactic fermentation process of wine and its evolution is strongly related with the quality of the final product. The analysis of l-lactic acid is carried out off-line in a laboratory. Therefore, there is a clear demand for analytical tools that enabled real-time monitoring of this process in field and biosensors have positioned as a feasible alternative in this regard. The development of an amperometric biosensor for l-lactate determination showing long-term stability is reported in this work. The biosensor architecture includes a thin-film gold electrochemical transducer selectively modified with an enzymatic membrane, based on a three-dimensional matrix of polypyrrole (PPy) entrapping lactate oxidase (LOX) and horseradish peroxidase (HRP) enzymes. The experimental conditions of the biosensor fabrication regarding the pyrrole polymerization and the enzymes entrapment are optimized. The biosensor response to l-lactate is linear in a concentration range of 1 × 10⁻⁶–1 × 10⁻⁴ M, with a detection limit of 5.2 × 10⁻⁷ M and a sensitivity of – (13500 ± 600) μA M⁻¹ cm⁻². The biosensor shows an excellent working stability, retaining more than 90% of its original sensitivity after 40 days. This is the determining factor that allowed for the application of this biosensor to monitor the malolactic fermentation of three red wines, showing a good agreement with the standard colorimetric method.     

Suberythemal Sun Exposures at Swedish Schools Depend on Sky Views of the Outdoor Environments – Possible Implications for Pupils’ Health

More scheduled outdoor stay is increasingly advocated for school children. This study measured 2^nd, 5^th and 8^th graders’ erythemal UV‐exposure in September, March and May at four Swedish schools. We related those exposures, as fractions of total available ambient radiation, to the schools outdoor environments differing in amount of shade, vegetation, and peripheral city‐scape quantified as percentage of free sky view calculated from fish‐eye photographs. Exposures correlated with the sky views (with exceptions in May) and were suberythemal. The exposures were also below the threshold limit of the International Commission on Non‐Ionizing Radiation Protection (ICNIRP) for hazard evaluation of UVR but were potentially enough for adequate vitamin D formation according to a cited model calculation – as illustrated in the results and discussed. The school environments, typical in southern and middle Sweden, offer enough shade to protect children from overexposure during seasons with potentially harmful solar UV radiation. Pupils’ outdoor stay may be extended during September and March. In May extended outdoor stay of the youngest pupils requires a more UVR‐protective environment.     

Binding of antitumor ruthenium complexes to DNA and proteins: a theoretical approach

The thermodynamics of the binding of the antitumor ammine, amine, and immine complexes of ruthenium(II) and ruthenium(III) to DNA and peptides was studied computationally using model molecules. We performed density functional calculations on several monofunctional ruthenium complexes of the formula [Ru(NH3)5B]z+, where B is an adenine, guanine, or cytosine nucleobase or an 4-methylimidazole, a dimethylthioether, or a dimethylphosphate anion and z = 2 and 3. The pentammineruthenium fragment has been intensively studied and also constitutes a good model for a wide class of antitumor ammine, amine, and imine complexes of Ru(II) and Ru(III), while the considered bases/ligands have been chosen as models for the main binding sites of DNA, nucleobases, and phosphate backbone and proteins, histidyl, and sulfur-containing residue such as methionine or cysteine. Bond dissociation enthalpies and free energies have been calculated for all the considered metal binding sites both in the gas phase and in solution and allow building a binding affinity order for the considered nucleic acid or protein binding sites. The binding of guanine to some bifunctional complexes, [Ru(NH3)(4)Cl2], [cis-RuCl(2)(bpy)2], and [cis-RuCl(2)(azpy)2], has also been considered to evaluate the effect of a second labile chloro or aquo ligand and more realistic polypyridyl and arylazopyridine ligands.     

Redox characteristics of a de novo quinone protein

The electrochemistry of 2,6-dimethylbenzoquinone (DMBQ) has been characterized for three different systems: DMBQ freely solvated in aqueous buffer; DMBQ bound to a neutral, blocked cysteine (N-acetyl-L-cysteine methyl ester) and the resulting DMBQ-bCys compound solvated in aqueous buffer; and DMBQ bound to a small model protein denoted alpha(3)C. The goal of this study is to detect and characterize differences in the redox properties of the protein-ligated DMBQ relative to the solvated quinones. The alpha(3)C protein used here is a tryptophan-32 to cysteine-32 variant of the structurally defined alpha(3)W de novo protein (Dai et al. J. Am. Chem. Soc. 2002, 124, 10952-10953). The properties of alpha(3)C were recently described (Hay et al. Biochemistry 2005, 44, 11891-11902). DMBQ was covalently bound to bCys and alpha(3)C through a sulfur substitution reaction with the cysteine thiol. In contrast to the solvated DMBQ and DMBQ-bCys compounds, diffusion controlled electrochemistry of DMBQ-alpha(3)C showed well-behaved and fully reversible n = 2 oxidation/reduction with a peak separation of approximately 30 mV between pH 5 and 9. DMBQ-alpha(3)C could also be immobilized on a gold electrode modified with a self-assembled monolayer of 3-mercaptopropionoic acid, allowing the measurement, by cyclic voltammetry, of an apparent rate of electron transfer of 22 s(-1). The (cysteine) sulfur substitution significantly lowers one of the hydroquinone pKA's from 10.4 in DMBQ to 6.8 in DMBQ-bCys. This pKA is slightly elevated in DMBQ-alpha(3)C to 7.0 and the E1/2 at pH 7.0 is raised by 110 mV from +190 mV in DMBQ-bCys to +297 mV in DMBQ-alpha(3)C.     

Time-resolved resonance Raman investigation of the 2-fluorenylnitrenium ion reactions with C8 guanosine derivatives

A nanosecond time-resolved resonance Raman (ns-TR3) spectroscopic study of the reactions of the 2-fluorenylnitrenium ion with several C8-substituted guanosine derivatives is reported. The TR3 spectra show that the 2-fluorenylnitrenium ion reacts with the C8-substituted guanosine derivatives (C8-methylguanosine and C8-bromoguanosine) to produce C8 intermediates with the methyl and bromine moieties still attached to the intermediate species at the C8 position. The C8-bromoguanosine species was observed to be less reactive toward the 2-fluorenylnitrenium ion compared to the guanosine and C8-methylguanosine species. Comparison of the TR3 spectra to the results obtained from density functional theory calculations was used to characterize the C8 intermediates observed to learn more about their structure and properties. The implications of these results for the chemical reactivity of arylnitrenium ions toward substituted guanosine derivatives are briefly discussed.     

Precision of Raman depolarization and optical attenuation measurements of sound tooth enamel

The demineralization of enamel that is associated with early caries formation affects the optical properties of the enamel. Polarized Raman spectroscopy and optical coherence tomography have been used to detect these changes and potentially offer a means to detect and monitor early caries development. The total optical attenuation coefficient as measured by optical coherence tomography and the polarization anisotropy of the Raman peak arising from the symmetric ν₁ vibration of at approximately 959 cm⁻¹ have been demonstrated as being sensitive markers of early caries. This ex vivo study on extracted human teeth demonstrates that these measurements can be made with reasonable precision with concomitantly good repeatability and reproducibility in sound enamel. Such reliability is crucial for these techniques to have a practical clinical value.     

Interactions between benzyl benzoate and single- and double-chain quaternary ammonium surfactants

Interactions between benzyl benzoate and two different twin-tailed cationic surfactants have been studied. NMR diffusometry measurements have shown that cationic micelles grow in one dimension when benzyl benzoate is added. The location of benzyl benzoate in the micelles was evaluated by NOESY, showing that benzyl benzoate gave cross-peaks both to the hydrophobic groups in the surfactant and to the surfactant head group. Additions of benzyl benzoate to a lamellar phase of double-tailed quaternary surfactants revealed differences in responses. With an increasing concentration of benzyl benzoate, the structure of the dialkyl quat aggregate goes from lamellar to cubic, while the dialkyl ester quat forms a lamellar structure for all benzyl benzoate concentrations.