Lanthanide Shift Reagents: Acetylacetone Complex of Yb(III) Ion

It has recently been shown that the 2,2,6,6-tetra-methylheptane-3,5-dione (tmhd) complexes of a number of lanthanide ions possess the useful property of inducing large chemical shifts in the proton NMR spectra of certain compounds containing OH or other nucleophilic groups^1–8. The resulting spectra are frequently more readily assignable and analysable. Although europium and praseodymium appear to be the most suitable ions for such studies, the shifting effect is also observed with other lanthanide ions.^5,6     

Nanosecond laser ablation for pulsed laser deposition of yttria

A thermal model to describe high-power nanosecond pulsed laser ablation of yttria (Y₂O₃) has been developed. This model simulates ablation of material occurring primarily through vaporization and also accounts for attenuation of the incident laser beam in the evolving vapor plume. Theoretical estimates of process features such as time evolution of target temperature distribution, melt depth and ablation rate and their dependence on laser parameters particularly for laser fluences in the range of 6 to 30 J/cm² are investigated. Calculated maximum surface temperatures when compared with the estimated critical temperature for yttria indicate absence of explosive boiling at typical laser fluxes of 10 to 30 J/cm². Material ejection in large fragments associated with explosive boiling of the target needs to be avoided when depositing thin films via the pulsed laser deposition (PLD) technique as it leads to coatings with high residual porosity and poor compaction restricting the protective quality of such corrosion-resistant yttria coatings. Our model calculations facilitate proper selection of laser parameters to be employed for deposition of PLD yttria corrosion-resistive coatings. Such coatings have been found to be highly effective in handling and containment of liquid uranium.     

Computational study of hydrogen-bonded complexes of HOCO with acids: HOCO⋯HCOOH, HOCO⋯H(2)SO(4), and HOCO⋯H(2)CO(3)

Quantum chemistry calculations at the density functional theory (DFT) (B3LYP), MP2, QCISD, QCISD(T), and CCSD(T) levels in conjunction with 6-311++G(2d,2p) and 6-311++G(2df,2p) basis sets have been performed to explore the binding energies of open-shell hydrogen bonded complexes formed between the HOCO radical (both cis-HOCO and trans-HOCO) and trans-HCOOH (formic acid), H(2)SO(4) (sulfuric acid), and cis-cis-H(2)CO(3) (carbonic acid). Calculations at the CCSD(T)∕6-311++G(2df,2p) level predict that these open-shell complexes have relatively large binding energies ranging between 9.4 to 13.5 kcal∕mol and that cis-HOCO (cH) binds more strongly compared to trans-HOCO in these complexes. The zero-point-energy-corrected binding strengths of the cH?Acid complexes are comparable to that of the formic acid homodimer complex (～13-14 kcal∕mol). Infrared fundamental frequencies and intensities of the complexes are computed within the harmonic approximation. Infrared spectroscopy is suggested as a potential useful tool for detection of these HOCO?Acid complexes in the laboratory as well as in various planetary atmospheres since complex formation is found to induce large frequency shifts and intensity enhancement of the H-bonded OH stretching fundamental relative to that of the corresponding parent monomers. Finally, the ability of an acid molecule such as formic acid to catalyze the inter-conversion between the cis- and trans-HOCO isomers in the gas phase is also discussed.     

Single-molecule enzyme kinetics in the presence of inhibitors

Recent studies in single-molecule enzyme kinetics reveal that the turnover statistics of a single enzyme is governed by the waiting time distribution that decays as mono-exponential at low substrate concentration and multi-exponential at high substrate concentration. The multi-exponentiality arises due to protein conformational fluctuations, which act on the time scale longer than or comparable to the catalytic reaction step, thereby inducing temporal fluctuations in the catalytic rate resulting in dynamic disorder. In this work, we study the turnover statistics of a single enzyme in the presence of inhibitors to show that the multi-exponentiality in the waiting time distribution can arise even when protein conformational fluctuations do not influence the catalytic rate. From the Michaelis-Menten mechanism of inhibited enzymes, we derive exact expressions for the waiting time distribution for competitive, uncompetitive, and mixed inhibitions to quantitatively show that the presence of inhibitors can induce dynamic disorder in all three modes of inhibitions resulting in temporal fluctuations in the reaction rate. In the presence of inhibitors, dynamic disorder arises due to transitions between active and inhibited states of enzymes, which occur on time scale longer than or comparable to the catalytic step. In this limit, the randomness parameter (dimensionless variance) is greater than unity indicating the presence of dynamic disorder in all three modes of inhibitions. In the opposite limit, when the time scale of the catalytic step is longer than the time scale of transitions between active and inhibited enzymatic states, the randomness parameter is unity, implying no dynamic disorder in the reaction pathway.     

Photocatalytic performance of combustion synthesized β-Ga2O3 for the degradation of tri-n-butyl phosphate in aqueous solution

Nanostructures of β-Ga₂O₃ were prepared by solution combustion route using urea as the fuel. Transmission electron microscopic measurements and powder X-ray diffraction measurements confirmed the crystalline nature of β-Ga₂O₃ with particle size in the range of 10–15 nm. Surface area measurements indicated that the synthesized semiconductor catalyst had a specific surface area of 30 m²/g. In this work, photocatalytic degradation studies of tri-n-butyl phosphate using nano sized β-Ga₂O₃ is presented. A cylindrical photoreactor was used for the degradation studies and gas chromatographic estimation was adopted to follow the extent of degradation. Complete degradation of tributyl phosphate could be achieved in less than 40 min using 10 mg of photocatalyst and 0.5 mL of H₂O₂ for 1000 mL of 400 ppm TBP. Degradation of TBP was found to follow pseudo first order kinetics and the rate of TBP degradation was found to be superior for β-Ga₂O₃ photocatalyst compared to P-25 TiO₂.     

A New Bifunctional Chitosanase Enzyme from Streptomyces sp. and Its Application in Production of Antioxidant Chitooligosaccharides

Chitosanases produced by microbes and plants are getting attention to explore vastly available marine waste. Chitooligosaccharides and glucosamine can be produced using chitosanase enzyme and have applications in food, pharma and other industries. A potential microbial chitosanase source was found after isolation and screening of chitosan degrading microbes from garden soil. An isolate, designated as C6 produced chitosanase enzyme upon induction by chitosan substrates. Production of 6 U/ml of chitosanase enzyme was achieved from this isolate on chitosan minimal salt broth medium at 32?°C after 3?days of growth. The enzyme was able to hydrolyse both chitosan and cellulosic substrates. Enzymatic production of d-glucosamine and chitooligosaccharides were studied with various chitosan substrates using crude enzyme. The yield of glucosamine was found to be 40% after 2?h of reaction at 40?°C, and chitosan oligomers were produced having two to six polymerizations at 60?°C reaction temperature. The hydrolysates showed 50% antioxidant activity as compared to ascorbic acid.     

Isolation and Characterization of Pseudomonas sp. STM 997 from Soil Sample having Potentiality to Degrade 3,6-Dimethyl-1-keto-1,2,3,4-tetrahydrocarbazole: A Novel Approach

A pure colony of a bacterium from contaminated soil was isolated by exploiting 3,6-dimethyl-1-keto-1,2,3,4?Ctetrahydrocarbazole, a novel carbazole derivative, having indole moiety as well as 3-methyl functionality both in aromatic and hydro-aromatic moiety, as a sole source of carbon and energy. Taxonomical studies, biochemical analysis, and 16S rDNA sequence analysis indicated that the isolated strain has close similarity with Pseudomonas sp. Thin-layer chromatography followed by HPLC and mass spectroscopic study indicates that the isolated Pseudomonas sp. STM 997 degrades 3,6-dimethyl-1-keto-1,2,3,4?Ctetrahydrocarbazole, and this strain may be useful in the bioremediation of environments contaminated by the compounds containing carbazole moiety with methyl substituents at various reactive sites. This study also provides an evidence in favor of the suggested biodegradation of 3-methylcarbazole to carbazole in plants.     

Photoisomerization dynamics of N-1-methyl-2-(tolylazo) imidazole and the effect of complexation with Cu(ii)

Azo-compounds containing an imidazole moiety have the potential to photoregulate biofunctions, such as gene-expression and enzymatic action. Photoinduced isomerization of the azo-backbone is the vital process for such applications, but the photoisomerization dynamics of azo-imidazole compounds has not been well explored. We investigated the photoisomerization dynamics of trans-N-1-methyl-2-(tolylazo) imidazole (trans-MTAI) using femtosecond transient absorption spectroscopy following photoexcitation to the S(2) state. Time evolution of the transient electronic spectra and the global analysis of the temporal profiles reveal a three state relaxation (S(2) → S(1) → S(0)) process in different kinds of solvents. The lifetime of the S(2) state is independent of the viscosity of solvent, whereas that of the S(1) state becomes longer with increasing solvent viscosity. This observation clearly indicates that the large amplitude motion that leads to the trans → cis isomerization occurs only in the S(1) state and relaxation of the S(2) state is not associated with the isomerization process. We have also investigated the excited state dynamics of [Cu(trans-MTAI)(2)]Cl(2) to examine the effect of complexation with the metal ion on the isomerization dynamics of trans-MTAI. It is observed that the photoinduced isomerization of the azo-backbone in trans-MTAI is completely inhibited upon complexation with Cu(ii).     

Synthesis, crystal structure, dielectric and optical properties of a new rare earth double perovskite: Ca2CeNbO6

In order to develope and understand the phenomena involved in producing advanced materials, a rare earth double perovskite oxide calcium cerium niobate, Ca₂CeNbO₆ (CCN) is synthesized for the first time. The x-ray diffraction pattern of CCN at room temperature (300K) shows orthorhombic perovskite structure, with the lattice parameters, a=9.36Å, b=6.61Å and c=5.88Å and α=β=γ= 90°. A scanning electron micrograph shows the formation of grains with average size ∼2μm. Impedance spectroscopy and Fourier transform infrared spectroscopy are applied to investigate the dielectric and optical properties of CCN. The frequency-dependent electrical data are analyzed in the framework of the conductivity and modulus formalisms. The experimental data of real part of dielectric permittivity (ε′) and imaginary part of electric modulus (M″) are fitted with Davidson-Cole equation to explore the idea of dielectric relaxation (conduction) mechanism in CCN. The frequency-dependent conductivity spectra follow a power law. The scaling behaviour of imaginary electric modulus (M″) suggests that the relaxation describes the same mechanism at various temperatures.     

Functional, mesoporous, superparamagnetic colloidal sorbents for efficient removal of toxic metals

γ-Fe(2)O(3) incorporated mesoporous silica particles of 50-100 nm size have been synthesized which are functionalized with chelating agents of metal ions. These particles are water dispersible but aggregate in response to the external magnetic field and have been used for high performance and selective removal of Cd, Pb, Hg and As.