Cyclization of N-alkyldithiocarbamates in alkaline media,a counter example of well-known chemistry – an experimental and theoretical study

In strong alkaline media, the reaction of 2-(tert-butylamino)ethanol (3: R?=?Bu^t) with CS₂ at 0°C produced a cyclic dithiocarbamate, 3-tert-butylthiazolidine-2-thione (1: R?=?Bu^t), rather than alkaline metal or ammonium salts of [S₂CN(Bu^t)CH₂CH₂OH]^?. This is in contrast to isolation of stable alkaline metal or ammonium salts of [S₂CN(R)CH₂CH₂OH]^? (R?=?Me, Et, Pr, or CH₂CH₂OH) obtained in analogous reactions. The use of Ni(OAc)₂, both as a source of Ni(II) and a weaker base, in a one-pot reaction with (3: R?=?Bu^t) and CS₂, successfully gave the first reported metal complex of [S₂CN(Bu^t)CH₂CH₂OH]^?, namely [Ni{S₂CN(Bu^t)CH₂CH₂OH}₂] (2: R?=?Bu^t). Compounds 1 and 2 have been fully characterized by infrared and NMR spectroscopies, and by X-ray crystallography. DFT calculations on the cyclization and stabilities of [S₂CN(R)CH₂CH₂OH]^? (R?=?Pr and Bu^t) have been carried out.     

Corrosion inhibition of zinc in aqueous acidic media using a novel synthesized Schiff base – an experimental and theoretical study

Abstract

The kinetics of H₂ production during Zn corrosion in 0.5?M HCl without and with various additives of N,N'-bis-(1-hydroxyphenylimine)-2,5-thiophenedicarboxaldehyde (HPTD) was studied using gasometry and electrochemical techniques. The surface of the corroded Zn samples was investigated using SEM and Optical Profilometry. The rate of H₂ production (RHP) increased with the immersion time and temperature. Presence of HPTD mitigated RHP due to an adsorption process. The electrochemical impedance spectroscopy showed that HPTD had a good inhibitive effect. Polarization data proved that HPTD acted as a surface-active mixed-type inhibitor. Some thermodynamic parameters were deduced and discussed. Theoretical calculations were also conducted to corroborate the capability of HPTD to protect Zn surface from corrosion process.     

Chemical composition and antioxidant activities of the essential oil of Hypericum gaitii Haines – an endemic species of Eastern India

The present study reports the chemical composition and antioxidant activities of the essential oil extracted from the leaves and tender branches of Hypericum gaitii Haines (Hypericaceae) – an endemic plant of Eastern India. On hydrodistillation, the fresh leaves and tender parts of H. gaitii yielded 0.43% (v/w) of pale yellowish essential oil. Gas chromatography mass spectrometry analysis revealed the presence of 40 compounds, which represent 96.9% of the total oil. Monoterpene hydrocarbons (79.3%) predominated followed by sesquiterpene hydrocarbons (12.6%). Of these, α-pinene (69.5%), β-caryophyllene (10.5%), sabinene (5.6%), myrcene (3.0%) and geranyl acetate (2.0%) were the main constituents. Antioxidant activities of oil were evaluated by three different systems namely 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) and reducing power assay. Essential oil exhibited moderate antioxidant activities compared to butylated hydroxytoluene (BHT) and ascorbic acid.     

The Diels–Alder reactions of para-benzoquinone nitrogen-derivatives: an experimental and theoretical study

An experimental and theoretical study of the comparative reactivity and selectivity of the Diels–Alder reactions of para-benzoquinones and three nitrogen derivatives have been performed. The mono-oximes derivatives do not react under the tested reaction conditions, whereas the tosylated mono-oximes react slowly. However, the mono N-tosyl imines show excellent reactivity, and superior to the parent para-benzoquinones. DFT calculations support these experimental results.     

Experimental study on combustion characteristics of diesel–hydrogen dual-fuel engine

As a clean and sustainable energy source, hydrogen is widely considered as an engine fuel by top researchers. In view of the fact that the uneven fuel mixture of diesel fuel deteriorated the combustion and emissions process, it is expected to adopt diesel and hydrogen dual-fuel combustion technology to optimize combustion and heat release of diesel engine. In this study, experiments are carried out on a diesel engine and the combustion characteristics of the engine with different hydrogen ratios (RH) are compared. It has been found that hydrogen addition is conducive to accelerate the heat release rate and improve the thermal efficiency. Specifically, compared with pure diesel conditions, the peak pressure increased by 7.7% and the cumulative heat release rate increased by 3.7% under the condition of RH of 20%. Moreover, although the effect on the ignition delay period is not clear, the higher RH brings about earlier heat release center and more cumulative heat release while enhancing the heat release of premixed combustion reducing the diffusion combustion and post-combustion.

     

Antioxidant activity of clove oil – A powerful antioxidant source

The number of methods to measure the antioxidants in botanicals, foods, nutraceuticals and other dietary supplements has increased considerably in the last decade. Clove oil is obtained by distillation of the flowers, stems and leaves of the clove tree. In the present paper, clove oil was evaluated by employing various in vitro antioxidant assay such as α,α-diphenyl-β-picryl-hydrazyl free radical (DPPH) scavenging, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, total antioxidant activity determination by ferric thiocyanate, total reducing ability determination by Fe³⁺–Fe²⁺ transformation method, superoxide anion radical scavenging by riboflavin/methionine/illuminate system, hydrogen peroxide scavenging and ferrous ions (Fe²⁺) chelating activities. Clove oil inhibited 97.3% lipid peroxidation of linoleic acid emulsion at 15 μg/mL concentration. However, under the same conditions, the standard antioxidant compounds such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), α-tocopherol and trolox demonstrated inhibition of 95.4, 99.7, 84.6 and 95.6% on peroxidation of linoleic acid emulsion at 45 μg/mL concentration, respectively. In addition, clove oil had an effective DPPH scavenging, ABTS⁺ scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, ferric ions (Fe³⁺) reducing power and ferrous ions (Fe²⁺) chelating activities. Also, these various antioxidant activities were compared to BHA, BHT, α-tocopherol and trolox as reference antioxidant compounds.     

Production of α-amylase with Aspergillus oryzae on spent brewing grain by solid substrate fermentation

Ten Aspergillus oryzae strains were screened in solid substrate fermentation for α-amylase production on spent brewing grain (SBG) and on corn fiber. SBG proved to be a better substrate for enzyme production than corn fiber. A Plackett-Burman experimental design was used to optimize the medium composition for the best strain. Solid substrate fermentation on optimized medium with A. oryzae NRRL 1808 (=ATCC 12892) strain in stationary 500-mL Erlenmeyer flask culture yielded 4519 U of α-amylase/g of dry matter substrate in 3 d. The whole solid substrate fermentation material (crude enzyme, in situ enzyme) may be considered a cheap biocatalytic material for animal feed rations and for bioalcohol production from starchy materials.     

Enantioselective conjugate addition of nitro compounds to α,β-unsaturated ketones: an experimental and computational study

A series of chiral thioureas derived from easily available diamines, prepared from α-amino acids, have been tested as catalysts in the enantioselective Michael additions of nitroalkanes to α,β-unsaturated ketones. The best results are obtained with the bifunctional catalyst prepared from L-valine. This thiourea promotes the reaction with high enantioselectivities and chemical yields for aryl/vinyl ketones, but the enantiomeric ratio for alkyl/vinyl derivatives is very modest. The addition of substituted nitromethanes led to the corresponding adducts with excellent enantioselectivity but very poor diastereoselectivity. Evidence for the isomerization of the addition products has been obtained from the reaction of chalcone with [D(3)]nitromethane, which shows that the final addition products epimerize under the reaction conditions. The epimerization explains the low diastereoselectivity observed in the formation of adducts with two adjacent tertiary stereocenters. Density functional studies of the transition structures corresponding to two alternative activation modes of the nitroalkanes and α,β-unsaturated ketones by the bifunctional organocatalyst have been carried out at the B3LYP/3-21G* level. The computations are consistent with a reaction model involving the Michael addition of the thiourea-activated nitronate to the ketone activated by the protonated amine of the organocatalyst. The enantioselectivities predicted by the computations are consistent with the experimental values obtained for aryl- and alkyl-substituted α,β-unsaturated ketones.     

Hydride generation – in-atomizer collection of Pb in a quartz trap-and-atomizer device for atomic absorption spectrometry – an interference study

Interferences of selected hydride forming elements (As, Sb, Bi, Se and Sn) on lead determination by hydride generation atomic absorption spectrometry were extensively studied in both on-line atomization and preconcentration (collection) modes. The commonly used on-line atomization mode was found free of significant interferences, whereas strong interference from Bi was observed when employing the preconcentration mode with plumbane collection in a quartz trap-and-atomizer device. Interference of Bi seems to take place in the preconcentration step. Interference of Bi in the collection mode cannot be reduced by increased hydrogen radical amount in the trap and/or the atomizer.     

Dye J-aggregate—semiconductor nanocrystal hybrid nanostructures in reverse micelles: an experimental study

Reverse micelle solutions can be used for the assembly of hybrid nanostructures of the composition dye monomer—Ag₂S nanocrystal, dye J-aggregate—CuI nanocrystal, and dye J-aggregate—PbI₂ nanocrystal. The assembly is effected by means of adsorption of the dye (3,3′-di-(γ-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine pyridinium salt) onto the nanocrystal surface. Factors responsible for the dye adsorption onto semiconductor nanocrystals in reverse micelle solutions are analyzed. It is suggested that adsorption can be the outcome of forces induced by both van der Waals and chemical interactions. The surfactants used for stabilization of reverse micelle solutions also influence the assembly of the hybrid nanostructures.     

Intramolecular homolytic substitution of seleninates – a computational study

Ab initio and density functional theory (DFT) calculations predict that intramolecular homolytic substitution by alkyl radicals at the selenium atom in seleninates proceeds through smooth transition states in which the attacking and leaving radicals adopt a near collinear arrangement. When forming a five-membered ring and the leaving radical is methyl, G3(MP2)-RAD calculations predict that this reaction proceeds with an activation energy (ΔE₁³) of 30.4 kJ mol^?1. ROBHandHLYP/6-311++G(d,p) calculations suggest that the formation of five-membered rings through similar intramolecular homolytic substitution by aryl radicals, with expulsion of phenyl radicals, proceeds with the involvement of a hypervalent intermediate. This intermediate further dissociates to the observed products, with overall energy barriers of about 40 kJ mol^?1. Homolytic addition to the phenyl group was found not to be competitive with substitution, with a calculated barrier of 57.6 kJ mol^?1. This computational study provides insight into homolytic substitution chemistry involving seleninates.     

Molecular interpretation of the main relaxations found ID dielectric spectra of cellulose – experimental arguments

ID dielectric spectra of cellulose two relaxation processes dominate ID the low temperature range (–120 °C–0 °C). For application of the dielectric method as a diagnostic tool, these relaxations must be assigned to molecular motions of the polymeric system. This paper summarizes and discusses all experimental facts found by dielectric spectroscopy, which can help to solve this interpretation problem. ID ID necessary to include two other relaxation processes ID this discussion: the _wet- relaxation found ID all wet materials and the -relaxation evidently found ID all derivatives. The main result of our investigations ID that the dominant process ID the dielectric spectra at low temperatures (called -relaxation) ID the segmental motion of the chain and not methylol side-group reorientation. Additionally, for the first time, the dielectric spectra of Valonia (and also of bacterial cellulose) clearly indicate that the methylol side-group relaxation ID represented ID the dielectric spectra of pure polysaccharides. This -process ID only masked by the -process for the most pure celluloses. For low molecular weight saccharides and derivatives of cellulose both processes are simultaneously found ID the dielectric spectra. For the first time a correlation ID presented between the intensity of the local motion mode (-relaxation) and the degree of crystallinity for various cellulosic materials.     

Enantioselective synthesis of β-pyrazole-substituted alcohols through an asymmetric ring-opening reaction of meso-epoxides

An efficient and practical synthesis of optically pure β-pyrazole-substituted alcohols was achieved by an asymmetric ring-opening reaction of meso-epoxides with pyrazole derivatives as the nucleophile. In the presence of 1?mol?% of an N,N'-dioxide-Sc(OTf)(3) complex, excellent enantioselectivity and yields were obtained from meso-epoxides. The process could also be used for a mixture of cis- and trans-stilbene oxides. A proposed transition-state model is provided.     

An experimental study of the stability of TiO2 particles in organic–water mixtures

The stability of TiO₂ (Anatase) particles in various organic-water mixtures is examined experimentally. The results obtained reveal that the addition of AlCl₃ to a methanol–water dispersion leads to charge reversal on particle surface. If the concentration of methanol is high, CaCl₂ also leads to charge reversal, but NaCl does not have this effect. This implies that if the concentration of methanol is low, the coagulation between TiO₂ particles is due to double-layer compression for Na⁺ and Ca²⁺, and due to charge adsorption and neutralization for Al³⁺. A methanol dispersion is unstable without the addition of electrolyte, and the addition of both CaCl₂ and AlCl₃ has the effect of stabilizing the dispersion; the addition of NaCl does not have this effect. The qualitative behaviors of an acetone–water dispersion are similar to those of a methanol–water dispersion. It is interesting to observe, however, that the absolute mobility of a pure acetone dispersion has a maximum as the concentrations of both CaCl₂ and AlCl₃ vary, but charge reversal does not occur. Among the dispersions without the addition of electrolyte, a 50% organic–water mixture is most stable. Also, a methanol–water dispersion is more stable than an acetone–water dispersion, which can be explained based on the degree of dissociation of an electrolyte.     

Production of chiral matrices with hybrid silver–thiocholesterol nanosystems and study of their properties

A new type of chiral matrix based on silver–thiocholesterol hybrid nanosystems adsorbed on silica gel has been proposed. The molar ratio of stabilized thiocholesterol (L) ligand and silver (Ag) was found to have little effect on the size of the resulting silver nanoparticles (SNPs). The average diameter of SNPs was 2.7 ± 0.4, 2.2 ± 0.4, and 2.1 ± 0.6 nm upon the ratios Ag: L = 1: 5, Ag: L = 1: 2, and Ag: L = 1: 0.5, respectively. The resulting chiral matrices possess enantioselectivity relative to the 1,1’-binaphthyl-2,2’-diamine (BNDA) and trifluoroanthranyl ethanol (TFAE) optical isomers. The TFAE optical isomers were successfully separated using thin layer chromatography (α = 1.56).     

Structural properties of montmorillonite intercalated with tetraalkylammonium cations—Computational and experimental study

Several tetraalkylammonium (TAA) cations intercalated in layered clay mineral montmorillonite were studied by a combination of theoretical approach based on density functional theory (DFT) and infrared spectroscopy. DFT calculations revealed positions of TAA cations in the interlayer space and a dependence of d₀₀₁ parameter on the cation size. A finite difference method and molecular dynamic simulations were used to analyze and interpret vibrational modes observed in the experimental spectra with a specific focus on the CH₃ and CH₂ stretching modes. MD simulations on the tetraethylammonium-montmorillonite (TEA-M) model showed a high sensitivity of the position of the stretching vibrations of the CH₃ and CH₂ groups on the d₀₀₁ value. MD calculations also helped to distinguish vibrations of the parallel and perpendicular CH₃ groups of the tetramethylammonium-montmorillonite (TMA-M) which was not possible from the experimental infrared spectra because of many overlapping broad bands.