Rhodium(III) and iridium(III) complexes of thioarylazoimidazoles: Synthesis,structure, spectral characterization,electrochemistry and DFT calculation

[M(SRaaiNR′)Cl₃] (M = Rh(III), Ir(III) and SRaaiNR′ = 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole) complexes are described in this article. The single crystal X-ray structure of one of the complexes, [Rh(SMeaaiNEt)Cl₃] (3b), shows a tridentate chelation of SMeaaiNEt via N(imidazole), N(azo) and S(thioether) donor centres. Spectral characterization has been done by IR, UV–Vis and ¹H NMR data. The electronic structure, redox properties and spectra are well supported by DFT and TDDFT computation on the complexes.     

Alkane bromination revisited: "reproportionation" in gas-phase methane bromination leads to higher selectivity for CH3Br at moderate temperatures

The reaction of methane and bromine is a mildly exothermic and exergonic example of free radical alkane activation. We show here that the reaction of methane and bromine (CH4:Br2 > or = 1) may yield either a kinetically or a thermodynamically determined bromomethane product distribution and proceeds in two main phases between 450 and 550 degrees C under ambient pressure on the laboratory time scale. This is in contrast to the highly exothermic methane fluorination or chlorination reactions, which give kinetic product distributions, and to the endergonic iodination of methane, which yields an equilibrium distribution of iodomethanes. The first phase of reaction between methane and bromine is a relatively rapid consumption of bromine to yield a kinetic methane bromination product distribution characterized by low methane conversion, low methyl bromide selectivity, and higher polybromomethane selectivity. In the second slower phase CHxBr(4-x) reproportionation leads to significantly higher methane conversion and higher methyl bromide selectivity. For methane bromination at 525 degrees C, CH4 conversion and CH3Br selectivity reach 73.5% and 69.5%, respectively, after ample (60 s) time for reproportionation. The high selectivity and simple configuration make this pathway an attractive candidate for scale-up in halogen-mediated methane partial oxidation processes.     

Soft chemical routes to semiconductor nanostructures

Soft chemistry has emerged as an important means of generating nanocrystals, nanowires and other nanostructures of semiconducting materials. We describe the synthesis of CdS and other metal chalcogenide nanocrystals by a solvothermal route. We also describe the synthesis of nanocrystals of AlN, GaN and InN by the reaction of hexamethyldisilazane with the corresponding metal chloride or metal cupferronate under solvothermal conditions. Nanowires of Se and Te have been obtained by a self-seeding solution-based method. A single source precursor based on urea complexes of metal chlorides gives rise to metal nitride nanocrystals, nanowires and nanotubes. The liquidliquid interface provides an excellent medium for preparing single-crystalline films of metal chalcogenides.     

Comparative photophysical behaviour of naphthalene-linked crown ethers and aza crown ethers of varying cavity dimensions

A comparative time-resolved emission studies of several naphtho-crown ethers I–V, where metal ions can be complexed in a predetermined orientation with respect to the naphthalene (Naph) π-plane and naphthalene-linked aza crown ethers (L1 and L2) have been presented. In both the systems, crown ethers and aza crown ethers, naphthalene fluorescence gets quenched. In the systems I to V, the quenching is mainly due to efficient spin-orbit coupling (SOC) leading to greater population of the lowest triplet state of naphthalene. This SOC depends on the orientation of the crown ring with respect to the Naph-π-plane. However, in the systems L1 and L2, the quenching is due to photoinduced electron transfer (PET) from nitrogen lone pair of the aza crown ring to naphthalene moiety and consequent exciplex formation. The results have been interpreted using the time-resolved emission studies of all the compounds in various solvents, their alkali metal ion complexes, and protonated ligands.     

Deciphering the evolution of supramolecular nanofibers in solution and solid-state: a combined microscopic and spectroscopic approach

Supramolecular self-assembly of small organic molecules has emerged as a powerful tool to construct well-defined micro- and nanoarchitecture through fine-tuning a range of intermolecular interactions. The size, shape, and optical properties of these nanostructures largely depend on the specific assembly of the molecular building units, temperature and polarity of the medium, and external stimuli. The engineering of supramolecular self-assembled nanostructures with morphology-dependent tunable emission is in high demand due to the promising scope in nanodevices and molecular machines. However, probing the evolution of molecular aggregates from the solution and directing the self-assembly process in a pre-defined fashion are challenging. In the present study, we have deciphered the sequential evolution of supramolecular nanofibers from solution to spherical and oblong-shaped nanoparticles through the variation of solvent polarity, tuning the hydrophobic–hydrophilic interactions. An intriguing case of molecular self-assembly has been elucidated employing a newly designed π-conjugated thiophene derivative (TPAn) through a combination of steady-state absorption, emission measurements, fluorescence correlation spectroscopy (FCS), and electron microscopy. The FCS analysis and microscopy results revealed that the small-sized nanofibers in the dispersion further agglomerated upon solvent evaporation, resulting in a network of nanofibers. Stimuli-responsive reversible interconversion between a network of nanofibers and spherical nanoaggregates was probed both in dispersion and solvent-evaporated state. The evolution of organic nanofibers and a subtle control over the self-assembly process demonstrated in the current investigation provide a general paradigm to correlate the size, shape, and emission properties of fluorescent molecular aggregates in complex heterogeneous media, including a human cell.

Supramolecular nanofiber evolution in solution and solid-state, including stimuli-responsive reversible interconversion among diverse nanoarchitectures, was probed through a combined spectroscopic and microscopic approach.     

Magnetic, optical and transport properties of GaMnN films

GaMnN films with 1-3% Mn deposited on Si(100) and Al₂O₃(0001) substrates, by the technique of nebulized spray pyrolysis by employing acetylacetonate precursors, have been characterized by X-ray diffraction, photoluminescence spectra and other techniques. The films are ferromagnetic and show magnetic hysteresis. The ferromagnetic T_C increases with the Mn content, with the 3% Mn film showing a T_C of ∼250 K. Anomalous Hall effect is observed below T_C where the films exhibit a small negative magnetoresistance.     

Zinc Oxide Nanoparticles Modulates the Production of β-Glucosidase and Protects its Functional State Under Alcoholic Condition in Saccharomyces cerevisiae

In the present investigation, we have investigated the effect of zinc oxide nanoparticles (ZnONP) on the production of β-glucosidase (BGL) in Saccharomyces cerevisiae under various conditions. ZnONP was synthesized chemically and characterized using various standard techniques. The results revealed that yeast culture administered with 5 mM ZnONP enhanced the intracellular BGL activity up to 28 % compared to control with simultaneous growth of cells. However, at a higher dose of ZnONP (10 and 15 mM), both the activity of the enzyme and yeast growth was dropped. When yeast cells were grown in alcoholic medium (2, 5, and 10 % ethanol), the growth was found inhibited with substantial reduction of intracellular BGL activity. Interestingly, the administration of ZnONP further inhibited the cell growth, however, suppressed the alcoholic effect on enzyme activity. Moreover, under the same condition, ZnONP enhanced the biological activity of the enzyme in cells, indicated a higher yield of BGL production. When the mechanism of ZnONP-mediated cell growth inhibition was investigated, N-acetylcysteine (NAC)-based cell growth study proved that reactive oxygen species (ROS) was not the sole cell death mechanism induced by ZnONP, indicating a second mechanism of cell death. Our findings provide a new insight on the potential application of ZnONP as an external supplement to enhance the active production of BGL like important industrial enzyme in S. cerevisiae in both normal and alcohol stressed condition as well as to produce baker’s yeast in higher amount.     

Separation of Delphinidin-3-O-sambubioside, Cyanidin-3-O-sambubioside and p-Coumaric Acid from Cranberry by CCC Followed by prep-HPLC Using Robotic CCC Solvent System Selection

High-performance counter-current chromatography has been used for the separation of delphinidin-3-O-sambubioside, cyanidin-3-O-sambubioside and p-coumaric acid from crude extract of cranberry. The separation was performed with a two-phase solvent system composed of butanol/0.05% aqueous trifluoroacetic acid/methanol at a volume ratio of 4:5:1. The two-phase solvent system was selected following the determination of partition coefficients (K) in a range of solvent systems using a robotic solvent system selection method. Analytical scale CCC confirmed that this phase system separated the components from a crude cranberry extract (40 mg scale) with acceptable purities. Preparative CCC of 400 mg of crude yielded 4.2 mg of p-coumaric acid at a purity of over 98%, 3.6 mg of delphinidin-3-O-sambubioside at a purity of over 97% and 4.5 mg of cyanidin-3-O-sambubioside at a purity of 73%, which was further purified by preparative high-performance liquid chromatography to yield 3 mg cyanidin-3-O-sambubioside at 95% purity. The identification of delphinidin-3-O-sambubioside, cyanidin-3-O-sambubioside and p-coumaric acid was performed by ESI-MS, 1H-NMR and 13C-NMR spectra.     

Analyses of 4f11 Energy Levels and Transition Intensities Between Stark Levels of Er3+ in Y3Al5O12

ABSTRACT

Absorption and fluorescence spectra obtained at temperatures as low as 4 K were investigated between 200 and 1550 nm on samples containing approximately 1.2 at. wt. % Er in Y₃Al₅O₁₂ (YAG). Within this wavelength range 125 experimental energy (Stark) levels were analyzed, representing data that span 29 ^2S+1 L _J multiplet manifolds of Er³⁺(4f¹¹) in D₂ sites up to an energy of 44,000 cm^?1. Agreement between calculated and observed Stark levels was achieved with an r.m.s. deviation of 11.2 cm^?1. These transitions originate from the ground-state Stark level in the ⁴I_15/2 manifold to J + 1/2 Stark levels associated with each of the 28 excited-state manifolds. A total of 88 ground-state absorption transition line strengths were measured for 19 ^2S+1 L _J multiplet manifolds between 280 and 1550 nm. For line strength measurements, the Er³⁺ ion is assumed to be distributed homogeneously throughout the D₂ cation sites of Y³⁺ in the lattice. The line strengths were analyzed with a weighted (E _i  ? C _i )/E _i , with an r.m.s. error of 0.25. Use of a “vector crystal field” parametrization resolves ambiguities in the transition intensity parameters and allows for the definition of polarization-resolved Judd-Ofelt parameters, which may have wide-ranging applicability for future Judd-Ofelt-type intensity calculations.