Chimie

We measured C02, CO, CH4, H2, and NO2 in air masses polluted by savanna fires over C6te d'Ivoire, western Africa. Elevated concentrations of these trace gases were found in fire plumes and aIso in extensive haze layers. Trace gas mixing ratios ranged as high as 605 ppmv for CO2, 14.8 ppmv for CO, 2.7 ppmv for CH4, 4.2 ppmv for H2, and 25 ppbv for NO2. We compare our emission ratios to those obtained in previous field and laboratory studies. The emission ratios, expressed as an average and as a range or as an average only, were: dCO/dCO2 5.3 x 10-2 (3-18 x 10-2); dCH4/dCO 5.3 x 10-2; dH2/dCO 2.4 x 10-I and dNO2/dCO2 1.8 x 10-4 (1.5-2.2 x 10-4). The values found match those found during similar measurements, though our results point to rather vigorous burning in the savanna of western Africa.

The Environmental Effects Assessment Panel Report for 2006 205 REVIEWERS OF THE 2006 UNEP EFFECTS ASSESSMENT PANEL Professor Ayite-Lo Nohende Ajavon Atmospheric Chemistry Laboratory FDS/Université de Lome BP 1515 Lome TOGO Phone:+ 228-225 5094 Fax:+ 228-221 8595 Mobile+ 228-904-1593/944 9444 Home+ 228-226-9170 noajavon@ tg. refer. org Dr. Pedro J. Aphalo Department of Biological and Environmental Sciences Plant Biology/Plant Ecology PO Box 65 00014 University of Helsinki Finland pedro. aphalo@ ...

A multiscale simulation of a complex between the lac repressor protein (LacI) and a 107-bp-long DNA segment is reported. The complex between the repressor and two operator DNA segments is described by all-atom molecular dynamics; the size of the simulated system comprises either 226,000 or 314,000 atoms. The DNA loop connecting the operators is modeled as a continuous elastic ribbon, described mathematically by the nonlinear Kirchhoff differential equations with boundary conditions obtained from the coordinates of the terminal base pairs of each operator. The forces stemming from the looped DNA are included in the molecular dynamics simulations; the loop structure and the forces are continuously recomputed because the protein motions during the simulations shift the operators and the presumed termini of the loop. The simulations reveal the structural dynamics of the LacI-DNA complex in unprecedented detail. The multiple domains of LacI exhibit remarkable structural stability during the simulation, moving much like rigid bodies. LacI is shown to absorb the strain from the looped DNA mainly through its mobile DNA-binding head groups. Even with large fluctuating forces applied, the head groups tilt strongly and keep their grip on the operator DNA, while the remainder of the protein retains its V-shaped structure. A simulated opening of the cleft of LacI by 500-pN forces revealed the interactions responsible for locking LacI in the V-conformation.

The bandgap and band bowing parameter of semiconductor alloys are calculated with a fast and realistic approach. The method is a dielectric scaling approximation that is based on a scissor approximation. It adds an energy shift to the bandgap provided by the local density approximation (LDA) of the density functional theory (DFT). The energy shift consists of a material-independent constant weighted by the inverse of the high-frequency dielectric constant. The salient feature of the approach is the fast calculation of the dielectric constant of alloys via the Green function (GF) of the TB-LMTO (tight-binding linear muffin-tin orbitals) in the atomic sphere approximation (ASA). When it is applied to highly mismatched semiconductor alloys (HMAs) like Zn Te x Se 1−x , this method provides a band bowing parameter that is different from the band bowing parameter calculated with the LDA due to the bowing exhibited also by the high-frequency dielectric constant.

The existence of a broad, mid-infrared absorption ranging from 1000 to 3000 cm -1 is usually interpreted as a signature for the existence of protonated water networks. Herein, we use cryogenic mixtures of water and hydrogen fluoride (HF) and show experimental and computational evidence that similarly wide absorptions can be generated by a broad distribution of proton-shared and ion pair complexes. In the present case, we demonstrate that the broadening is mainly inhomogeneous, reflecting the fact that the topology of the first solvation shell determines the local degree of ionization and the shared-proton asymmetric stretching frequency within H 2O · HF complexes. The extreme sensitivity of the proton transfer potential energy hypersurface to local hydrogen bonding topologies modulates its vibrational frequency from 2800 down to ∼1300 cm -1 , the latter value being characteristic of solvation geometries that yield similar condensed-phase proton affinities for H 2O and fluoride. By linking the local degree of ionization to the solvation pattern, we are able to propose a mechanism of ionization for HF in aqueous solutions and to explain some of their unusual properties at large concentrations. However, an important conclusion of broad scientific interest is our prediction that spectral signatures that are normally attributed to protonated water networks could also reveal the presence of strong hydrogen bonds between un-ionized acids and water molecules, with important consequences to spectroscopic investigations of biologically relevant proton channels and pumps.

The methodology of ab initio molecular dynamics, wherein finite-temperature dynamical trajectories are generated by using forces computed "on the fly" from electronic structure calculations, has had a profound influence in modern theoretical research. Ab initio molecular dynamics allows chemical processes in condensed phases to be studied in an accurate and unbiased manner, leading to new paradigms in the elucidation of microscopic mechanisms, rationalization of experimental data, and testable predictions of new phenomena. The purpose of this work is to give a brief introduction to the technique and to review several important recent developments in the field. Several illustrative examples showing the power of the technique have been chosen. Perspectives on future directions in the field also will be given.

Dipole polarizabilities of individual ions and molecules are computed from first principles in three condensed-phase systems: pure water, pure hydrofluoric acid, and an equimolar mixture of water and hydrofluoric acid in which HF is mostly ionized. We find that the polarizability of fluorine and oxygen centers varies linearly with the value of the bond order, which measures the local degree

Introduction and Aims: Interstitial fibroblasts are the principal effector cells of organ fibrosis. Transforming growth factor (TGF)-β-activated myofibroblasts express α-smooth muscle actin (α-SMA), secrete connective tissue growth factor (CTGF) that functions as a downstream mediator of TGF-β action on fibroblastic cell types, and are important in the synthesis of collagen I. The aim of this study was to investigate the effect of PBI-4050, a first-in-class anti-fibrotic compound, on CTGF, α-SMA and collagen I expression in TGF-β1-stimulated human fibroblasts (normal human dermal fibroblasts (NHDF)). Methods: The effect of PBI-4050 on the mRNA expression of fibrotic markers was analyzed by qPCR in TGF-β1-stimulated NHDF and in kidney from models of ESRD (5/6-nephrectomized rats) and AKI (doxorubicin-induced nephrotoxicity in mice). Results: Activation of NHDF fibroblasts by TGF-β1 resulted in a strong increase in mRNA expression of CTGF (30 times), α-SMA (10 times) and collagen I (2.5 times). PBI-4050 significantly reduced TGF-β1-induced overexpression of CTGF (78%), α-SMA (85%) and collagen I (21%) mRNA in NHDF to the control level (untreated/no TGF-β stimulation). This is also translated at the protein level, as TGF-β1-induced CTGF production is also significantly inhibited by PBI-4050 in NHDF. Furthermore, in non-stimulated NHDF, PBI-4050 reduced basal CTGF (60%), α-SMA (40%) and collagen I (25%) mRNA expression. These results correlate with in vivo inhibition of CTGF, α-SMA and collagen I mRNA expression observed in different models of kidney fibrosis. In 5/6-nephrectomized rats (CKD/ESRD model), oral administration of PBI-4050 (200 mg/kg) significantly decreased the mRNA overexpression of CTGF (50%), α-SMA (30%) and collagen I (50%) in the remnant kidney. In doxorubicin-induced nephrotoxicity (AKI model), oral administration of PBI-4050 (100 mg/kg) significantly decreased the overexpression of CTGF, α-SMA and collagen I mRNA expression close to the control level (no doxorubicin). Conclusions: These results indicate a direct effect of PBI-4050 on fibroblasts as observed by an inhibition of CTGF, α-SMA and collagen I mRNA expression, and this is translated by a reduction of fibrosis in the kidney.