Experimental and computational investigation of thiolate alkylation in Ni(II) and Zn(II) complexes: role of the metal on the sulfur nucleophilicity.

The biologically relevant S-alkylation reactions of thiolate ligands bound to a transition metal ion were investigated with particular attention paid to the role of the metal identity: Zn(II) versus Ni(II). The reactivity of two mononuclear diamine dithiolate Zn and Ni complexes with CH(3)I was studied. With the [ZnL] complex (1) (LH(2) = 2,2'-(2,2'-bipyridine-6,6'-diyl)bis(1,1-diphenylethanethiolate)), a double S-methylation occurs leading to [ZnL(Me2)I(2)] (1(Me2)), while with [NiL] (2), only the mono-S-methylated product [NiL(Me)]I (2(Me)) is formed.

Sensitive determination of glyoxal, methylglyoxal and hydroxyacetaldehyde in environmental water samples by using dansylacetamidooxyamine derivatization and liquid chromatography/fluorescence.

In this study we improved the dansylacetamidooxyamine (DNSAOA)-LC-fluorescence method for the determination of aqueous-phase glyoxal (GL), methylglyoxal (MG) and hydroxyacetaldehyde (HA). As derivatization of dicarbonyls can potentially lead to complex mixtures, a thorough study of the reaction patterns of GL and MG with DNSAOA was carried out. Derivatization of GL and MG was shown to follow the kinetics of successive reactions, yielding predominantly doubly derivatized compounds.

Thermal and mechanical denaturation properties of a DNA model with three sites per nucleotide.

In this paper, we show that the coarse grain model for DNA, which has been proposed recently by Knotts et al. [J. Chem.

Photochromic and redox properties of bisterpyridine ruthenium complexes based on dimethyldihydropyrene units as bridging ligands.

We report herein the synthesis and characterization of four new bisterpyridine dinuclear ruthenium complexes containing the dimethyldihydropyrene (DHP) photochrome as bridging ligand. A synthetic strategy has been developed based on a Suzuki coupling reaction to synthesize these novel terpyridine-DHPs. The reactivity of these different ligands and dinuclear ruthenium complexes with light was examined by (1)H NMR and monitoring the changes in their absorption spectra upon irradiation at controlled wavelengths.

Apicomplexan parasites and subversion of the host cell microRNA pathway.

RNA silencing plays a major role in innate antiviral and antibacterial defenses in plants, insects, and animals through the action of microRNAs (miRNAs). miRNAs can act in favor of the microorganism, either when it is pathogen-encoded or when the microorganism subverts host miRNAs to its benefit. Recent data point to the possibility that apicomplexan parasites have developed tactics to interfere with host miRNA populations in a parasite-specific manner, thereby identifying the RNA-silencing pathway as a new means to reshape their cellular environment.

Effects of age, gender and time on receptor expression and anti-Aspergillus functions of human phagocytes.

Phagocytes play a central role in immune defense. Their dysfunction predisposes to infections. This study determined the expression level of nine receptors involved in Aspergillus immune response as well as the values of phagocytosis and production of radical oxygen species after Aspergillus stimulation, in a healthy adult population.

Role of putative second transmembrane region of Nox2 protein in the structural stability and electron transfer of the phagocytic NADPH oxidase.

Flavocytochrome b(558) (cytb) of phagocytes is a heterodimeric integral membrane protein composed of two subunits, p22(phox) and gp91(phox). The latter subunit, also known as Nox2, has a cytosolic C-terminal "dehydrogenase domain" containing FAD/NADPH-binding sites. The N-terminal half of Nox2 contains six predicted transmembrane α-helices coordinating two hemes.

Role of phosphatidic acid in plant galactolipid synthesis.

Phosphatidic acid (PA) is a precursor metabolite for phosphoglycerolipids and also for galactoglycerolipids, which are essential lipids for formation of plant membranes. PA has in addition a main regulatory role in a number of developmental processes notably in the response of the plant to environmental stresses. We review here the different pools of PA dispatched at different locations in the plant cell and how these pools are modified in different growth conditions, particularly during plastid membrane biogenesis and when the plant is exposed to phosphate deprivation.

Influence of mixed thiolate/thioether versus dithiolate coordination on the accessibility of the uncommon +I and +III oxidation states for the nickel ion: an experimental and computational study.

Sulfur-rich nickel metalloenzymes are capable of stabilizing Ni(I) and Ni(III) oxidation states in catalytically relevant species. In an effort to better understand the structural and electronic features that allow the stabilization of such species, we have investigated the electrochemical properties of two mononuclear N(2)S(2) Ni(II) complexes that differ in their sulfur environment. Complex 1 features aliphatic dithiolate coordination ([NiL], 1), and complex 2I is characterized by mixed thiolate/thioether coordination ([NiL(Me)]I, 2I).

Mechanical model of the ultrafast underwater trap of Utricularia.

The underwater traps of the carnivorous plants of the Utricularia species catch their prey through the repetition of an "active slow deflation followed by passive fast suction" sequence. In this paper, we propose a mechanical model that describes both phases and strongly supports the hypothesis that the trap door acts as a flexible valve that buckles under the combined effects of pressure forces and the mechanical stimulation of trigger hairs, and not as a panel articulated on hinges. This model combines two different approaches, namely (i) the description of thin membranes as triangle meshes with strain and curvature energy, and (ii) the molecular dynamics approach, which consists of computing the time evolution of the position of each vertex of the mesh according to Langevin equations.

Entanglement and chaos in the kicked top.

The standard kicked top involves a periodically kicked angular momentum. By considering this angular momentum as a collection of entangled spins, we compute the bipartite entanglement dynamics as a function of the dynamics of the classical counterpart. Our numerical results indicate that the entanglement of the quantum top depends on the specific details of the dynamics of the classical top rather than depending universally on the global properties of the classical regime.

An expeditious access to 5-pyrimidinol derivatives from cyclic methylglyoxal diadducts, formation of argpyrimidines under physiological conditions and discovery of new CFTR inhibitors.

In the study of previously reported modulators of CFTR chloride channels that are cyclic methylglyoxal (MG) diadducts (CMGD) to aromatic α-aminoazaheterocycles, we optimized a new expeditious one pot route for preparing in water novel aromatic polycyclic azaheterocycles and described 5-pyrimidinols antioxidants through the formation of 2-oxoaldehyde diadducts to aromatic α-aminoazaheterocycles, amidines, guanidines and thiourea. In regard to the importance as biomarkers of diabetic complications of the 5-pyrimidinols "argpyrimidines" formed in proteins from MG and arginine residues, we demonstrated that argpyrimidines are slowly formed under physiological conditions from CMGD to arginine derivatives according to the synthesis route described. Among the 5-pyrimidinol derivatives prepared, two polycyclic derivatives appeared to inhibit strongly the activity of CFTR channels in wt-CHO cells.

Efficient solvent boundary potential for hybrid potential simulations.

A common challenge in computational biophysics is to obtain statistical properties similar to those of an infinite bulk system from simulations of a system of finite size. In this work we describe a computationally efficient algorithm for performing hybrid quantum chemical/molecular mechanical (QC/MM) calculations with a solvent boundary potential. The system is partitioned into a QC region within which catalytic reactions occur, a spherical region with explicit solvent that envelops the quantum region and is treated with a MM model, and the surrounding bulk solvent that is treated implicitly by the boundary potential.

Towards new molecular photocatalysts for CO2 reduction: photo-induced electron transfer versus CO dissociation within [Os(NN)(CO)2Cl2] Complexes.

Optical excitation in the visible region of trans-(Cl)-[Os(bpy)(CO)(2)Cl(2)] (bpy=2,2'-bipyridine; C1) and trans-(Cl)-[Os(dmbpy)(CO)(2)Cl(2)] (dmbpy=4,4'-dimethyl 2,2'-bipyridine; C2) is known to induce the common CO dissociation reaction. However, the quantum yield of the reactions is less than 0.15, although C1 and C2 display pronounced photoluminescence in the visible region at room temperature with a lifetime of few tens of nanoseconds.

Histidine 416 of the periplasmic binding protein NikA is essential for nickel uptake in Escherichia coli.

Escherichia coli require nickel for the synthesis of [NiFe] hydrogenases under anaerobic growth conditions. Nickel import depends on the specific ABC-transporter NikABCDE encoded by the nik operon, which deletion causes the complete abolition of hydrogenase activity. We have previously postulated that the periplasmic binding protein NikA binds a natural metallophore containing three carboxylate functions that coordinate a Ni(II) ion, the fourth ligand being His416, the only direct metal-protein contact, completing a square-planar coordination for the metal.

Highly sensitive routine method for urinary 3-hydroxybenzo[a]pyrene quantitation using liquid chromatography-fluorescence detection and automated off-line solid phase extraction.

Many workers and also the general population are exposed to polycyclic aromatic hydrocarbons (PAHs), and benzo[a]pyrene (BaP) was recently classified as carcinogenic for humans (group 1) by the International Agency for Research on Cancer. Biomonitoring of PAHs exposure is usually performed by urinary 1-hydroxypyrene (1-OHP) analysis. 1-OHP is a metabolite of pyrene, a non-carcinogenic PAH.

Forming spirocyclohexadienone-oxocarbenium cation species in the biomimetic synthesis of amomols.

The oxidation of appropriate 2-(4-hydroxyphenyl)ethyl ketones gives direct access to amomols by means of the formation of a transient spirocyclohexadienone-oxocarbenium ion that is intermolecularly intercepted by an alcohol. Furthermore, homochiral amomols and other new analogues were synthesized for the first time and were biologically evaluated on Plasmodium falciparum.

Solution X-ray scattering study of a full-length class A penicillin-binding protein.

Penicillin binding proteins (PBPs) catalyze essential steps in the biosynthesis of peptidoglycan, the main component of the bacterial cell wall. PBPs can harbor two catalytic domains, namely the glycosyltransferase (GT) and transpeptidase (TP) activities, the latter being the target for β-lactam antibiotics. Despite the availability of structural information regarding bi-functional PBPs, little is known regarding the interaction and flexibility between the TP and GT domains.

“Deterministic” quantum plasmonics.

We demonstrate “deterministic” launching of propagative quantum surface-plasmon polaritons at freely chosen positions on gold plasmonic receptacles. This is achieved by using as a plasmon launcher a near-field scanning optical source made of a diamond nanocrystal with two nitrogen-vacancy color-center occupancy. Our demonstration relies on leakage-radiation microscopy of a thin homogeneous gold film and on near-field optical microscopy of a nanostructured thick gold film.

Analytical progress in the theory of vesicles under linear flow.

Vesicles are becoming a quite popular model for the study of red blood cells. This is a free boundary problem which is rather difficult to handle theoretically. Quantitative computational approaches constitute also a challenge.

The synthesis of pABA: Coupling between the glutamine amidotransferase and aminodeoxychorismate synthase domains of the bifunctional aminodeoxychorismate synthase from Arabidopsis thaliana.

Aminodeoxychorismate (ADC) synthase in plants is a bifunctional enzyme containing glutamine amidotransferase (GAT) and ADC synthase (ADCS) domains. The GAT domain releases NH(3) from glutamine and the ADCS domain uses NH(3) to aminate chorismate. This enzyme is involved in folate (vitamin B9) biosynthesis.

Phenotypic and genetic characterization of macrolide resistance in Francisella tularensis subsp. holarctica biovar I.

Objectives: Francisella tularensis subsp. holarctica strains are classified as biovars I and II, which are susceptible and naturally resistant to the macrolide erythromycin, respectively. The present study was aimed at both selecting biovar I strains with increased levels of erythromycin resistance and characterizing the underlying genetic mechanisms.

Systematic theoretical study of the zero-field splitting in coordination complexes of Mn(III). Density functional theory versus multireference wave function approaches.

This paper presents a detailed evaluation of the performance of density functional theory (DFT) as well as complete active space self-consistent field (CASSCF)-based methods (CASSCF and second-order N-electron valence state perturbation theory, NEVPT2) to predict the zero-field splitting (zfs) parameters for a series of coordination complexes containing the Mn(III) ion. The physical origin of the experimentally determined zfs's was investigated by studying the different contributions to these parameters. To this end, a series of mononuclear Mn(III) complexes was chosen for which the structures have been resolved by X-ray diffraction and the zfs parameters have been accurately determined by high-field EPR spectroscopy.