Study of the reaction of chalcone analogs of dehydroacetic acid and o-aminothiophenol: synthesis and structure of 1,5-benzothiazepines and 1,4-benzothiazines

Treatment of α,β-unsaturated carbonyl compounds, obtained by the reaction of DHA and aromatic (or heteroaromatic) aldehydes, with o-aminothiophenol results in the formation of 1,5-benzothiazepines and/or 1,4-benzothiazines depending upon the reaction conditions and structure of the aldehydes. The products were characterized by the combined use of multinuclear 1D and 2D NMR and GIAO/DFT calculations of ¹H, ¹³C and ¹⁵N chemical shifts. The tautomerism of these compounds in solution was determined, they have an exocyclic CC double bond.     

Comparison of the catalytic activity of Au3, Au4+, Au5, and Au5- in the gas-phase reaction of H2 and O2 to form hydrogen peroxide: a density functional theory investigation

We report a detailed density functional theory (B3LYP) analysis of the gas-phase H2O2 formation from H2 and O2 on Au3, Au4+, Au5, and Au5-. We find that H2, which interacts only weakly with the Au clusters, is dissociatively added across the Au-O bond, upon interaction with AunO2. One H atom is captured by the adsorbed O2 to form the hydroperoxy intermediate (OOH), while the other H atom is captured by the Au atom. Once formed, the hydroperoxy intermediate acts as a precursor for the closed-loop catalytic cycle. An important common feature of all the pathways is that the rate-determining step of the catalytic cycle is the second H2 addition to form H2O2. The H2O2 desorption is followed by O2 addition to AunH2 to form the hydroperoxy intermediate, thus leading to the closure of the cycle. On the basis of the Gibbs free energy of activation, out of these four clusters, Au4+ is most active for the formation of the H2O2. The 0 K electronic energy of activation and the DeltaGact at the standard conditions are 12.6 and 16.6 kcal/mol respectively. The natural bond orbital charge analysis suggests that the Au clusters remain positively charged (oxidic) in almost all the stages of the cycle. This is interesting in the context of the recent experimental evidence for the activity of cationic Au in CO oxidation and water-gas shift catalysts. We have also found preliminary evidence for a correlation between the activation barrier for the first H2 addition and the O2 binding energy on the Au cluster. It suggests that the minimum activation barrier for the first H2 addition is expected for the Au clusters with 7.0-9.0 kcal/mol O2 binding energy, i.e., in the midrange of the expected interaction energy. This represents a balance between more favorable H2 dissociation when the Aun-O2 interaction is weaker and high O2 coverage when the interaction is stronger. On the basis of this work, we predict that the hydroperoxy intermediate formation can be both thermodynamically and kinetically viable only in a narrow range of the O2 binding energy (10.0-12.0 kcal/mol)-a useful estimate for computationally screening Au-cluster-based catalysts. We also show that a competitive channel for the OOH desorption exists. Thus, in propylene epoxidation both OOH radicals and H2O2 can attack the active Ti in/on the Au/TS-1 and generate the Ti-OOH sites, which can convert propylene to propylene oxide.     

Thermal analysis of polysiloxanes, aromatic polyimide and their blends

Low molecular weight poly(dimethylsiloxane) and poly(methylphenylsiloxane) were synthesized and blended with polyimide (PI) at its precursor poly(amic acid) stage. FTIR analysis has proven the retention of polysiloxanes in polyimide after the ultimate curing of blends. Differential scanning calorimetric analysis was performed on polysiloxanes to elucidate the structures present in polymers while thermogravimetric analysis (TGA) was performed on polysiloxanes, polyimide as well as their blends to evaluate the thermal stability and to analyze the effect of polysiloxane incorporation in blends. Blends have shown synergistic improvement as compared to neat polyimide.     

A simplified assay of furosemide in plasma and urine by high-pressure liquid chromatography.

A simplified high-pressure liquid chromatograhic method for determination of furosemide in plasma and urine has been developed using a fluorometric detector directly coupled to the column effluent. The method includes an ether extraction from acidified biologic samples. The mobile phase used for chromatography on a reversed-phase column (C15 hydrocarbon permanently bonded to silica particles) is sufficiently acidic to induce fluorescence of furosemide. The methylester of furosemide is employed as an internal standard. The sensitivity is 0.1 and 0.25 microgram per ml plasma and urine, respectively. The applicability to pharmacokinetic studies of furosemide is shown.     

Many-body interaction in glycine-(water)3 complex using density functional theory method

Various configurations were investigated to find the most stable structures of glycine-(water)3 complex. Five different optimized conformers of glycine-(water)3 complex are obtained from density functional theory calculations using 6-311++G* basis set. Relaxation energy and many body interaction energies (two, three, and four body) are also calculated for these conformers. Out of the five conformers, the most stable conformer has the BSSE corrected total energy -513.917 967 7 Hartree and binding energy -27.28 Kcal/mol. It has been found that the relaxation energies, two body energies and three body energies have significant contribution to the total binding energy whereas four body energies are very small. The chemical hardness and chemical potential also confirmed the stability of the conformer having lowest total energy.     

Some new organotin(IV), aluminium(III)-μ-oxoisopropoxides and their benzoylacetone derivatives

The first organotin(IV), aluminium(III)-μ-oxoisoprovides of the type [R₃SnOA](OⁱPr)₂] (R = Me or Ph) have been made by heating of trimethyl- or triphenyl-tin acetate with aluminium isopropoxide. The reactions of these μ-oxoisopropoxides with benzoylacetone in 1:1 and 1:2 molar ratios yielded the compounds of the type [R₃SnOAl(OⁱPr)(bzac)] and [R₃SnOAl(bzac)₂] (where R = Me or Ph and BZAC = deprotonated benzoylacetone), respectively.     

Flexible ligand docking without parameter adjustment across four ligand–receptor complexes

Understanding molecular recognition is one of the fundamental problems in molecular biology. Computationally, molecular recognition is formulated as a docking problem. Ideally, a molecular docking algorithm should be computationally efficient, provide reasonably thorough search of conformational space, obtain solutions with reasonable consistency, and not require parameter adjustments. With these goals in mind, we developed DIVALI (Docking wIth eVolutionary AlgorIthms), a program which efficiently and reliably searches for the possible binding modes of a ligand within a fixed receptor. We use an AMBER-type potential function and search for good ligand conformations using a genetic algorithm (GA). We apply our system to study the docking of both rigid and flexible ligands in four different complexes. Our results indicate that it is possible to find diverse binding modes, including structures like the crystal structure, all with comparable potential function values. To achieve this, certain modifications to the standard GA recipe are essential. © 1995 John Wiley & Sons, Inc.     

Microwave assisted synthesis of an unusual dinitro phytochemical

A novel dinitro secondary metabolite, 2-nitro-4-(2^′-nitroethenyl)phenol from a marine source, has been prepared via highly accelerated, microwave assisted, nitration reactions using mild reagents. ipso-Substitution of a carboxy group by a nitro group is discussed.     

Large scale Biginelli reaction via water-based biphasic media: a green chemistry strategy

An important stage in process development is kilo scale preparation of the target compound. For this reason, a procedure involving water-based biphasic reaction media has been developed for conducting some exothermic reactions on a large scale. This protocol is illustrated by the energy-efficient and rapid preparation of dihydropyrimidinones by a solvent-free, green chemistry procedure applied to the Biginelli reaction using p-toluenesulfonic acid as catalyst.