Samplers for VOCs in air based on cyclodextrin-silica hybrid microporous solid phases

Samplers for VOCs in air based on cyclodextrin-silica hybrid microporous solid phases are proposed. The solid phase preparation is very easy and inexpensive. Proposed samplers compared with other solid phases present the advantages of a wider range of operative conditions for VOCs desorption. Samplers are tested based on results for the determination of benzene, toluene, ethylbenzene and o-xylene, m-xylene and p-xylene (BTEX) in air. Operational parameters are optimized and quantitative recovery is obtained using a solid phase from 2-hydroxypropyl-β-cyclodextrin and acetonitrile as the extraction solvent. The recoveries obtained are 89 ± 4%, 90 ± 6%, 91 ± 2%, 87.0 ± 0.9%, 88 ± 4%, and 88 ± 4% for benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene, respectively. Moreover results indicate a good reproducibility with a coefficient of variation below 6% and no significant difference between the reproducibility intra-synthesis and inter-synthesis. The proposed procedure has been applied to the determination of BTEX in several contaminated air samples and compared with results provided by a reference method.     

In vitro fungicidal photodynamic effect of hypericin on Candida species

Hypericin is a natural photosensitizer considered for the new generation of photodynamic therapy (PDT) drugs. The aim of this study was to evaluate the in vitro fungicidal effect of hypericin PDT on various Candida spp., assessing its photocytotoxicity to keratinocytes (HaCaT) and dermal fibroblasts (hNDF) to determine possible side effects. A 3 log fungicidal effect was observed at 0.5 McFarland for two Candida albicans strains, Candida parapsilosis and Candida krusei with hypericin concentrations of 0.625, 1.25, 2.5 and 40 μm, respectively, at a fluence of 18 J cm(-2) (LED lamp emitting at 602 ± 10 nm). To obtain a 6 log reduction, significantly higher hypericin concentrations and light doses were needed (C. albicans 5 μM, C. parapsilosis 320 μM and C. krusei 320 μM; light dose 37 J cm(-2)). Keratinocytes and fibroblasts can be preserved by keeping the hypericin concentration below 1 μm and the light dose below 37 J cm(-2). C. albicans appears to be suitable for treatment with hypericin PDT without significant damage to cutaneous cells.     

A theoretical analysis of rate constants and kinetic isotope effects corresponding to different reactant valleys in lactate dehydrogenase

In some enzymatic systems large conformational changes are coupled to the chemical step, in such a way that dispersion of rate constants can be observed in single-molecule experiments, each corresponding to the reaction from a different reactant valley. Under this perspective here we present a computational study of pyruvate to lactate transformation catalyzed by lactate dehydrogenase. The reaction consists of a hydride transfer and a proton transfer that seem to take place concertedly. The degree of asynchronicity and the energy barrier depend on the particular starting reactant valley. In order to estimate rate constants we used a free energy perturbation technique adapted to follow the intrinsic reaction coordinate for several possible reaction paths. Tunneling effects are also obtained with a slightly modified version of the ensemble-averaged variational transition state theory with multidimensional tunneling contributions. According to our results the closure of the active site by means of a flexible loop can lead to the formation of different reactant complexes displaying different features in the disposition of some key residues (such as Arg109), interactions with the substrate and number of water molecules in the active site. The chemical step of the reaction takes place with a different reaction rate from each of these complexes. Finally, primary kinetic isotope effects for replacement of the transferring hydrogen of the cofactor with a deuteride are in good agreement with experimental observations, thus validating our methodology.     

Optimisation of focused ultrasound extraction (FUSE) and microwave-assisted extraction (MAE) of hydrocarbons in geological chert samples

The analysis of hydrocarbons in chert rocks provides a worthwhile source of information regarding the geochemical features of a depositional setting. Since the typical analytical procedure requires long Soxhlet extractions and the use of large quantities of sample (30-50 g), in this work we have optimised the focused ultrasound extraction (FUSE) and the microwave-assisted extraction (MAE) to make available a less severe procedure. In both cases a full experimental design including solvent mixture composition (Dichloromethane/Hexane/Acetone) and process variables (sonication time and cycles, and extraction temperature and time) by means of D-optimal designs. In the extracted fractions hydrocarbons (C₁₆-C₄₀) were analysed by gas-chromatography-mass spectrometry. In the case of FUSE the process variables were the most sensitive variables and the optimum conditions were defined at 60:40 DCM/Hex mixture and a sonication time of 30 min and 9 cycles. In the case of MAE all the variables shown a significant effect on the extraction yield and the most adequate conditions (60:30:10 DCM/Hex/Ace mixture and an irradiation time of 15 min at 110 °C) were established from the analysis of the response surface. Both methods were systematically applied with different chert samples collected in Cucho (Trebiño County, Burgos, Spain) and we were able to assure quantitative extractions (>85%) in the first extraction. Additionally, from the distribution patterns of n-alkanes obtained in the different chert samples (nodular chert, laminar chert and massive-brechoid chert) collected in Cucho, we were able to distinguish different origins and diagenetic history.     

Novel Amperometric Sensor Based on Rigid Near‐Percolation Composite

A novel amperometric sensor based on a rigid graphite‐epoxy composite of which composition is near to the percolation is reported. The electrochemical response of the novel transducer material was evaluated in terms of reproducibility of the fabrication process and reproducibility and repeatability of the analytical signal. The signal to noise ratio was improved. atomic force microscopy (AFM) technique was used to obtain qualitatively information. Amperometric detection of chlorine in water was carried on at a set potential of ?250 mV vs. Ag/AgCl. The developed flow injection analysis (FIA) system responded linearly to chlorine concentration between 0.15 mg L^?1 and 4 mg L^?1with a sensitivity of ?0.20 μA L mg^?1. The proposed system was applied to real samples from swimming‐pool water. No significant difference was observed regarding the standard method.     

Benchmark calculations on models of the phosphoryl transfer reaction catalyzed by protein kinase A

Protein phosphorylation has been proved to be of great importance in many stages of cell life. In the last few years, its reaction mechanism has been extensively studied. In this work we present the analysis of the performances of several computational methods with different computational costs (from multilevel to semiempirical) to point out the best method to be used at each level in the study of phosphoryl transfer. Finally, we center on the semiempirical methods, and mainly on the AM1/d Hamiltonian with different sets of parameters, which will permit hybrid quantum mechanics/molecular mechanics (QM/MM) free energy calculations on big models at an acceptable computational cost. We have used quite a large set of molecules and model reactions to test the computational methods, reproducing all the chemical steps involved in the mainly accepted reaction pathways for the protein phosphorylation. In the end, we also present the results for an enlarged model, cut out from an entire biological model: we compare the 2-D PES at the B3LYP and AM1/d levels with the purpose of obtaining a correction for the semiempirical method. The AM1/d-PhoT semiempirical parameterization corrected using single-point energy calculations at the B3LYP/MG3S level seems to be suitable to carry out reliable QM/MM calculations of the complete biological system.     

Peroxygenase-Catalysed Selective Oxidation of Silanes to Silanols

A peroxygenase-catalysed hydroxylation of organosilanes is reported. The recombinant peroxygenase from Agrocybe aegerita (AaeUPO) enabled efficient conversion of a broad range of silane starting materials in attractive productivities (up to 300 mM h⁻¹), catalyst performance (up to 84 s⁻¹ and more than 120 000 catalytic turnovers). Molecular modelling of the enzyme-substrate interaction puts a basis for the mechanistic understanding of AaeUPO selectivity.