Conformational and configurational dynamics of a highly fluorinated hydrazone

The relative populations of two rotamers in the hydrazone of 2H-perfluoro-2-methyl-3-pentanone can be altered from one extreme to the other by increasing the Lewis basicity of the solvent, and the equilibrium E/Z ratio grows correspondingly. Both trends reflect an increase in the effective size of the amino group as a result of hydrogen bonding. The rate of E/Z interconversion is insensitive to the choice of solvent, consistent with the conclusion that the isomerization occurs via N-inversion and not C=N bond rotation.     

Kinetics of anodic dissolution of Zr in acidic fluoride media

The kinetics of anodic dissolution of Zr in hydrofluoric acid (HF) was investigated using potentiodynamic polarization experiments. At lower potentials, an active region with a rapid increase in current with the potential was observed and at higher potentials, a large passivation current plateau was observed. The current decreased only slightly with potential in the passive region. Scanning electron micrographs confirmed that the passivation is incomplete in the region where current exhibits a plateau and x-ray photoelectron spectroscopic analysis showed that oxides and oxyfluorides are present on the surface. A four-step mechanism with two adsorbed intermediate species was evaluated and the model captures the essential characteristics of the polarization plots. The results suggest that \( {HF}_2^{-} \) species participates in the chemical dissolution step and actual HF participates in the electrochemical dissolution step.     

Fidelity enhancement by logical qubit encoding

We demonstrate coherent control of two logical qubits encoded in a decoherence free subspace (DFS) of four dipolar-coupled protons in an NMR quantum information processor. A pseudopure fiducial state is created in the DFS, and a unitary logical qubit entangling operator evolves the system to a logical Bell state. The four-spin molecule is partially aligned by a liquid crystal solvent, which introduces strong dipolar couplings among the spins. Although the system Hamiltonian is never fully specified, we demonstrate high fidelity control over the logical degrees of freedom. In fact, the DFS encoding leads to higher fidelity control than is available in the full four-spin Hilbert space.     

Anti-leptospiral activities of an endemic plant Glyptopetalum calocarpum (Kurz.) Prain used as a medicinal plant by Nicobarese of Andaman and Nicobar Islands

Leaves of an endemic plant Glyptopetalum calocarpum are used by Nicobarese tribes of Andaman and Nicobar Islands, India, to prepare traditional medicine for treating fever. In the present investigation, pharmacologically active compounds were isolated from this plant and their antimicrobial efficacy was evaluated against the leptospiral strains. The anti-leptospiral activity of six plant-derived compounds was determined by both microdilution and macrodilution methods. Two out of six compounds, namely lupenone and stigmasterol, showed anti-leptospiral activity. The minimum inhibitory concentrations of the two compounds tested against pathogenic leptospiral strains belonging to 10 serovars were in the range of 100–200 μg/mL. The range of minimum bactericidal concentrations was 400–800 μg/mL. Compounds lupenone, stigmasterol, lupeol, β-amyrin and β-amyrin acetate had negligible or no haemolytic activity, exhibiting IC₅₀ values of greater than 5 mg/mL. Further in vivo studies are needed to investigate the pharmacological and toxicological properties of G. calocarpum before it can be considered as a new anti-leptospiral agent.     

Photon irradiation-induced structural and interfacial phenomena in pure and alio-valently doped zirconia thin films

We report on the effect of ultra-violet (UV) irradiation on structural and interfacial phenomena in pure and doped zirconia thin film grown by physical vapour deposition. Interfacial layer formation by substrate oxidation and resultant densification of zirconia layer was found in yttria-doped zirconia (YDZ) films grown on Si, while no change was observed in identical films grown on Ge. A comparison of un-doped zirconia and YDZ films indicates yttria-doping significantly assists structural changes during UV irradiation. Interestingly, the effect of UV photons becomes minimal at ～300°C in films grown on Si, while the effect of UV becomes more pronounced in YDZ films grown on Ge. An interfacial layer was formed between the YDZ and Ge substrate at 300°C in the presence of UV irradiation, in contrast to the sharp interface maintained, even after annealing at 300°C, without UV. The results suggest that photon irradiation may be an elegant approach to tailor structural and interfacial properties at near-atomic length scales.     

��Gold standard�� coupled-cluster study of acetylene pentamers and hexamers via molecular tailoring approach

Due to high scaling order of MP2 and CCSD(T) methods, it is either difficult or at times even impossible to treat even moderately sized molecular systems with elaborate basis sets such as aug-cc-pVXZ (X?=?D, T, Q). In the present work, several structures of acetylene pentamers and hexamers are explored at MP2 and CCSD(T) levels of theory as?prototypical examples of clusters bound by CH···?? interactions. To enable this investigation, fragment-based method Molecular Tailoring Approach (MTA) is employed. It is shown that these acetylene assemblies can be treated with substantial reduction in computational resources and time, yet retaining a sub-millihartree accuracy in the energy. Further, using standard extrapolation methodologies, stabilization energies at the complete basis set limit of the acetylene clusters under consideration are determined at MP2 and CCSD(T) levels of theory. To test out the feasibility of treating a large cluster at MP2 level, a demonstrative calculation on a dodecamer of acetylene is reported.     

Conformations of trimethyl phosphite: a matrix isolation infrared and ab initio study

The conformations of trimethyl phosphite (TMPhite) were studied using matrix isolation infrared spectroscopy. TMPhite was trapped in a nitrogen matrix using an effusive source maintained at two different temperatures (298 and 410 K) and a supersonic jet source. The experimental studies were supported by ab initio computations performed at the B3LYP/6-31++G** level. Computations identified four minima for TMPhite, corresponding to conformers with C(1)(TG(±)G(±)), C(s)(TG(+)G(-)), C(1)(G(±)TT), and C(3)(G(±)G(±)G(±)) structures, given in order of increasing energy. Computations of the transition state structures connecting the C(s)(TG(+)G(-)) and C(1)(G(±)TT) conformers to the global minimum C(1)(TG(±)G(±)) structure were also carried out. The barriers for the interconversion of C(s)(TG(+)G(-)) and C(1)(G(±)TT) to the ground state C(1)(TG(±)G(±)) conformer were 0.2 and 0.6 kcal/mol, respectively. Comparison of conformational preferences of TMPhite with the related carbon compound, trimethoxymethane, and the organic phosphate, trimethyl phosphate, was also made using natural bond orbital analysis.     

Biosynthesis, purification and characterization of silver nanoparticles using Escherichia coli

The application of nanoscale materials and structures, usually ranging from 1 to 100 nanometers (nm), is an emerging area of nanoscience and nanotechnology. Nanomaterials may provide solutions to technological and environmental challenges in the areas of solar energy conversion, catalysis, medicine, and water-treatment. The development of techniques for the controlled synthesis of nanoparticles of well-defined size, shape and composition, to be used in the biomedical field and areas such as optics and electronics, has become a big challenge. Development of reliable and eco-friendly processes for synthesis of metallic nanoparticles is an important step in the field of application of nanotechnology. One of the options to achieve this objective is to use ‘natural factories’ such as biological systems. This study reports the optimal conditions for maximum synthesis of silver nanoparticles (AgNPs) through reduction of Ag⁺ ions by the culture supernatant of Escherichia coli. The synthesized silver nanoparticles were purified by using sucrose density gradient centrifugation. The purified sample was further characterized by UV–vis spectra, fluorescence spectroscopy and TEM. The purified solution yielded the maximum absorbance peak at 420 nm and the TEM characterization showed a uniform distribution of nanoparticles, with an average size of 50 nm. X-ray diffraction (XRD) spectrum of the silver nanoparticles exhibited 2θ values corresponding to the silver nanocrystal. The size-distribution of nanoparticles was determined using a particle-size analyzer and the average particle size was found to be 50 nm. This study also demonstrates that particle size could be controlled by varying the parameters such as temperature, pH and concentration of AgNO₃.