Bimetallic neutral palladium (II) bis(dithiolene) complex: Unusual synthesis,structural and theoretical study

The unusual synthesis of the dimeric dithiolene complex [(PPh₃)Pd(ethylene-1,2-dithiolate)]₂ (1), containing the simplest dithiolene ligand, has been achieved through the reaction between tetrathiafulvalene (TTF) and Pd(PPh₃)₄. The complex shows a folded structure in the solid state, according to single crystal X-ray analysis performed on crystals grown from two different system solvents and conditions, with a central [Pd₂S₂] ring folded about the S···S hinge by 67.9°. The optimized geometry at the DFT level is in excellent agreement with the experimental structure. Moreover, TD-DFT calculations allowed the assignment of the low energy band arising at 576 nm to the HOMO→LUMO transition, between frontier orbitals having mixed metal and dithiolene character.     

Mutagenicity of flavonoids assayed by bacterial reverse mutation (Ames) test

The mutagenicity of ten flavonoids was assayed by the Ames test, in Salmonella typhimurium strains TA98, TA100 and TA102, with the aim of establishing hydroxylation pattern-mutagenicity relationship profiles. The compounds assessed were: quercetin, kaempferol, luteolin, fisetin, chrysin, galangin, flavone, 3-hydroxyflavone, 5-hydroxyflavone and 7-hydroxyflavone. In the Ames assay, quercetin acted directly and its mutagenicity increased with metabolic activation. In the presence of S9 mix, kaempferol and galangin were mutagenic in the TA98 strain and kaempferol showed signs of mutagenicity in the other strains. The absence of hydroxyl groups, as in flavone, only signs of mutagenicity were shown in strain TA102, after metabolization and, among monohydroxylated flavones (3-hydroxyflavone, 5-hydroxyflavone and 7-hydroxyflavone), the presence of hydroxyl groups only resulted in minor changes. Luteolin and fisetin also showed signs of mutagenicity in strain TA102. Finally, chrysin, which has only two hydroxy groups, at the 5-OH and 7-OH positions, also did not induce mutagenic activity in any of the bacterial strains used, under either activation condition. All the flavonoids were tested at concentrations varying from 2.6 to 30.7 nmol/plate for galangin and 12.1 to 225.0 nmol/plate for other flavonoids. In light of the above, it is necessary to clarify the conditions and the mechanisms that mediate the biological effects of flavonoids before treating them as therapeutical agents, since some compounds can be biotransformed into more genotoxic products; as is the case for galangin, kaempferol and quercetin.     

Design, synthesis, evaluation, and structure of vitamin D analogues with furan side chains

Based on the crystal structures of human vitamin D receptor (hVDR) bound to 1α,25-dihydroxy-vitamin D(3) (1,25 D) and superagonist ligands, we previously designed new superagonist ligands with a tetrahydrofuran ring at the side chain that optimize the aliphatic side-chain conformation through an entropy benefit. Following a similar strategy, four novel vitamin D analogues with aromatic furan side chains (3a, 3b, 4a, 4b) have now been developed. The triene system has been constructed by an efficient stereoselective intramolecular cyclization of an enol triflate (A-ring precursor) followed by a Suzuki-Miyaura coupling of the resulting intermediate with an alkenyl boronic ester (CD-side chain, upper fragment). The furan side chains have been constructed by gold chemistry. These analogues exhibit significant pro-differentiation effects and transactivation potency. The crystal structure of 3a in a complex with the ligand-binding domain of hVDR revealed that the side-chain furanic ring adopts two conformations.     

The role of nuclear chemistry and radiochemistry in nanosafety studies

ABSTRACT

Nowadays there is an increasing demand of engineering nanoparticles – ENPs – thanking the excellent characteristics and properties of the products in which nanoparticles (NPs) are used. On the other hand, many are the unresolved questions about their potential adverse health and environmental impacts arising from exposure to these innovative materials. The growing utilisation of ENPs in consumer and industrial products have led to a potential increase of human exposure, thus raising concerns of many scientists and governments regarding health risks to workers and the public. Research on the impact of ENPs is strongly hampered by a lack of reliable tools to detect, visualise, and quantitatively trace particles movement and transfer in complex environmental and biological systems. The research tries to give some answers in this field using many different analytical techniques. In this paper, the types of information that can be obtained using nuclear techniques will be presented, with some examples of applications related to studies with metallic NPs.     

NP-completeness results for edge modification problems

The aim of edge modification problems is to change the edge set of a given graph as little as possible in order to satisfy a certain property. Edge modification problems in graphs have a lot of applications in different areas, and many polynomial-time algorithms and NP-completeness proofs for this kind of problems are known. In this work we prove new NP-completeness results for these problems in some graph classes, such as interval, circular-arc, permutation, circle, bridged, weakly chordal and clique-Helly graphs.     

Response of a designed metalloprotein to changes in metal ion coordination, exogenous ligands, and active site volume determined by X-ray crystallography

The de novo protein DF1 is a minimal model for diiron and dimanganese metalloproteins, such as soluble methane monooxygenase. DF1 is a homodimeric four-helix bundle whose dinuclear center is formed by two bridging Glu side chains, two chelating Glu side chains, and two monodentate His ligands. Here, we report the di-Mn(II) and di-Co(II) derivatives of variants of this protein. Together with previously solved structures, 23 crystallographically independent four-helix bundle structures of DF1 variants have been determined, which differ in the bound metal ions and size of the active site cavity. For the di-Mn(II) derivatives, as the size of the cavity increases, the number and polarity of exogenous ligands increases. This collection of structures was analyzed to determine the relationship between protein conformation and the geometry of the active site. The primary mode of backbone movement involves a coordinated tilting and sliding of the first helix in the helix-loop-helix motif. Sliding depends on crystal-packing forces, the steric bulk of a critical residue that determines the dimensions of the active site access cavity, and the intermetal distance. Additionally, a torsional motion of the bridging carboxylates modulates the intermetal distance. This analysis provides a critical evaluation of how conformation, flexibility, and active site accessibility affect the geometry and ligand-binding properties of a metal center. The geometric parameters defining the DF structures were compared to natural diiron proteins; DF proteins have a restricted active site cavity, which may have implications for substrate recognition and chemical stability.     

Health benefits of pistachios consumption

The health benefits of nuts, mainly in relation to the improvement of dysmetabolic conditions such as obesity, type 2 diabetes mellitus and the related cardiovascular diseases, have been widely demonstrated. Compared to other nuts, pistachios have a lower fat and caloric content, and contain the highest levels of unsaturated fatty acids, potassium, γ-tocopherol, phytosterols and xanthophyll carotenoids, all substances that are well known for their antioxidant and anti-inflammatory actions. This variety of nutrients contributes to the growing body of evidence that the consumption of pistachios improves health, leading to a greater potential of healthy antioxidant and anti-inflammatory activity, glycemic control, and endothelial function. The present review examines the nutrients and phytochemicals present in pistachios as well as the potential health benefits of including pistachios in a diet.