Insights into the Halogen Oxidative Addition Reaction to Dinuclear Gold(I) Di(NHC) Complexes

Gold(I) dicarbene complexes [Au₂(MeIm‐Y‐ImMe)₂](PF₆)₂ (Y=CH₂ ( 1 ), (CH₂)₂ ( 2 ), (CH₂)₄ ( 4 ), MeIm=1‐methylimidazol‐2‐ylidene) react with iodine to give the mixed‐valence complex [Au(MeIm‐CH₂‐ImMe)₂AuI₂](PF₆)₂ ( 1 a^I ) and the gold(III) complexes [Au₂I₄(MeIm‐Y‐ImMe)₂](PF₆)₂ ( 2 c^I and 4 c^I ). Reaction of complexes 1 and 2 with an excess of ICl allows the isolation of the tetrachloro gold(III) complexes [Au₂Cl₄(MeIm‐CH₂‐ImMe)₂](PF₆)₂ ( 1 c^Cl ) and [Au₂Cl₄(MeIm‐(CH₂)₂‐ImMe)₂](Cl)₂ ( 2 c^Cl‐Cl ) (as main product); remarkably in the case of complex 2 , the X‐ray molecular structure of the crystals also shows the presence of I‐Au‐Cl mixed‐sphere coordination. The same type of coordination has been observed in the main product of the reaction of complexes 3 or 4 with ICl. The study of the reactivity towards the oxidative addition of halogens to a large series of dinuclear bis(dicarbene) gold(I) complexes has been extended and reviewed. The complexes react with Cl₂, Br₂ and I₂ to give the successive formation of the mixed‐valence gold(I)/gold(III) n a^X and gold(III) n c^X (excluding compound 1 c^I ) complexes. However, complex 3 affords with Cl₂ and Br₂ the gold(II) complex 3 b^X [Au₂X₂(MeIm‐(CH₂)₃‐ImMe)₂](PF₆)₂ (X=Cl, Br), which is the predominant species over compound 3 c^X even in the presence of free halogen. The observed different relative stabilities of the oxidised complexes of compounds 1 and 3 have also been confirmed by DFT calculations.     

The Role of Aqueous Aerosols in the “Glyoxylate Scenario”: An Experimental Approach

The origin of life is one of the fundamental questions in science. Eschenmoser proposed the “glyoxylate scenario”, in which plausible abiotic synthesis pathways were suggested to be compatible with the constraints of prebiotic chemistry. In this proposal, the stem compound is HCN. In this work, we explore the “glyoxylate scenario” through several syntheses of HCN polymers, paying particular attention to the role of the aqueous aerosols, together with statistical methods, as a step to elucidate the synthetic problem of the origin of life. The soluble and insoluble HCN polymers synthetized were analyzed by GC‐MS. We identified, for the first time, glyoxylic acid in these polymers, together with some constituents of the reductive tricarboxylic acid cycle, amino acids and several N‐heterocycles. The findings presented herein, as the first global approach to the “glyoxylate scenario”, give full effect to this hypothesis and prove that aqueous aerosols could play an important role in this plausible scene of the origin of life.     

A throughput method using the quick easy cheap effective rugged safe method for the quantification of ibuprofen and its main metabolites in soils

Quick, easy, cheap, effective, rugged, and safe extraction is a modern sample preparation method that involves a number of steps with a low susceptibility to error. The efficiency of a laboratory can be improved not only through labor reduction and consumable savings but also through the use of high‐throughput methods and the reduction of wastes. In commercially available kits, different salts and buffers are mixed in anhydrous packages. The composition of these kits are optimized and fixed for particular applications by the suppliers. In this work three model compounds (ibuprofen and two of its main metabolites: hydroxyibuprofen and carboxyibuprofen) were chosen and the amount of each salt (magnesium sulfate, sodium chloride, sodium citrate, and disodium citrate sesquihydrate) in the quick, easy, cheap, effective, rugged, and safe content was optimized for three different soil samples (soils A, B, and C) with different organic carbon contents, using a 2⁴ factorial design. The optimized extraction procedure was applied to 12 soil samples; ranging from river sediments to agricultural soils. Based on the analysis 100 samples, a price reduction of 5.1‐ (soil B), 5.7‐ (Soil C), and 6.1‐fold (soil A) was achieved without compromising the performance of the method when compared to commercial kits.     

A path following method for box-constrained multiobjective optimization with applications to goal programming problems

We propose a path following method to find the Pareto optimal solutions of a box-constrained multiobjective optimization problem. Under the assumption that the objective functions are Lipschitz continuously differentiable we prove some necessary conditions for Pareto optimal points and we give a necessary condition for the existence of a feasible point that minimizes all given objective functions at once. We develop a method that looks for the Pareto optimal points as limit points of the trajectories solutions of suitable initial value problems for a system of ordinary differential equations. These trajectories belong to the feasible region and their computation is well suited for a parallel implementation. Moreover the method does not use any scalarization of the multiobjective optimization problem and does not require any ordering information for the components of the vector objective function. We show a numerical experience on some test problems and we apply the method to solve a goal programming problem.     

Molecular dynamics simulation of Matrix Metalloproteinase 2: fluctuations and time evolution of recognition pockets

We report a molecular dynamics simulation study of a zinc-protease--gelatinase A or MMP2--which is a major target for drug design, being involved in tumor metastasis and other degenerative diseases. Two structures have been employed as starting conditions, one based on the crystal of multi-domain proMMP2, the other consisting of the catalytic domain only. The overall fold of the two models is maintained over the 1260 ps trajectory, enabling us to analyze correlations of fluctuations among domains, and to observe the presence of correlations within the catalytic domain in the multi-domain enzyme only, hence due to the presence of hemopexin and fibronectin domains. In the multi-domain protein, two cavities are conserved over the trajectory, one of them pointing to a key region, a crevice surrounding the catalytic zinc. The other one is localized across the three domains of the MMP2 metalloproteinase. These areas are partially covered by the propeptide in the crystal structure of proMMP2. We propose a model of MMP2-collagen interaction that involves both identified cavities and takes into account the inter/intra domain cross-correlations.     

A two-channel molecular dosimeter for the optical detection of copper(II)

A cyclam-like macrocycle with an integrated push-pull chromophore selectively detects Cu2+ inclusion through both orange-to-yellow colour change and quenching of the green fluorescence.     

Synthesis of conjugated 2,7-bis(trimethylsilylethynyl)-(phenylethynyl)nfluoren-9-one and 9-(p-methoxyphenyl)-9-methyl derivatives: optical properties

2,7-Substituted 9-fluorenones and 9,9-disubstituted fluorene have been synthesized and their fluorescence properties analyzed. The synthesis of conjugated 2,7-bis(trimethylsilylethynyl)-(phenylethynyl)_nfluoren-9-one (or the 9-(p-methoxyphenyl)-9-methyl) structures was carried out by the heterocoupling reaction between the 2,7-di(halo)fluoren-9-one (or 2,7-dibromo-9-(p-methoxyphenyl)-9-methylfluorene) and p-trimethylsilylethynyl(phenylethynyl)_n (n=1,2), catalyzed by the dichloro bis(triphenylphosphine)palladium and cuprous iodide system, in a divergent synthesis.The π-extended conjugated compounds exhibit fluorescence radiation emission (blue light-emitting), with important quantum yield for the 9-(p-methoxyphenyl)-9-methyl-2,7-bis(trimethylsilylethynyl)-(phenylethynyl)_nfluorenes which increases with the conjugation.     

Preparation of a new C18 stationary phase containing embedded urea groups for use in high-performance liquid chromatography

A new C18 urea stationary phase was prepared by a single-step modification process through the reaction of ProntoSil spherical silica (3 microm, Bischoff) with the trifunctional alkoxysilane (CH3CH2O)3-Si-(CH2)3-NH-C(O)-NH-(CH2)17-CH3, prepared in our laboratory. The phase was characterized by elemental analysis and solid-state 29Si and 13C nuclear mangnetic resonance spectrometry. Chromatographic evaluations of the new phase in 150 x 3.9 mm HPLC columns involving the separation of different test mixtures, indicate good performance for both polar and basic mixtures and also show promising results for further applications.     

Brønsted acidity of ceric ammonium nitrate in anhydrous DMF. The role of salt and solvent in sucrose cleavage

The generation of an unexpected Brønsted acidity in anhydrous DMF at 50 °C was evidenced by NMR measurements during the investigation on the course of sucrose cleavage by ceric ammonium nitrate (CAN). The formation of a nitrooxy derivative of DMF by reaction with CAN is responsible for this acidity. The reactivity of CAN at 50 °C with several solvents was evaluated by voltammetric and potentiometric measurements. The possible release of protons from these reactions, particularly when aqueous solvent mixtures are used, should always be taken into account in the mechanistic interpretation of CAN synthetic applications.