Reactive diffusion in the Ti–Si system and the significance of the parabolic growth constant

Solid diffusion couple experiments are conducted to analyse the growth mechanism of the phases and the diffusion mechanism of the components in the Ti–Si system. The calculation of the parabolic growth constants and the integrated diffusion coefficients substantiates that the analysis is intrinsically prone to erroneous conclusions if it is based on just the parabolic growth constants determined for a multiphase interdiffusion zone. The location of the marker plane is detected based on the uniform grain morphology in the TiSi₂ phase, which indicates that this phase grows mainly because of Si diffusion. The growth mechanism of the phases and morphological evolution in the interdiffusion zone are explained with the help of imaginary diffusion couples. The activation enthalpies for the integrated diffusion coefficient of TiSi₂ and the Si tracer diffusion are calculated as 190 ± 9 and 197 ± 8?kJ/mol, respectively. The crystal structure, details on the nearest neighbours of the components, and their relative mobilities indicate that the vacancies are mainly present on the Si sublattice.     

Study of Interfacial Charge Transfer from an Electron Rich Organic Molecule to CdTe Quantum Dot by using Stern-Volmer and Stochastic Kinetic Models

Photoinduced electron transfer (PET) from N-methylaniline (NMA) to a photoexcited CdTe quantum dot (QD*) is studied in toluene. The PET mechanism at low to moderate quencher (NMA) concentrations (<0.08 M) remains mostly collisional with some contributions from QD-NMA complex formation. However, at high quencher concentrations (>0.10 M), QDs form larger numbers of static complexes with NMA molecules leading to a steep positive deviation in the steady-state Stern–Volmer curves. An isothermal titration calorimetry (ITC) study confirms the formation of QD-NMA complexes (K∼150 M⁻¹) at high quencher concentrations. Fitting our experimental data using a stochastic kinetic model indicates that the number of NMA molecules attached per QD at highest NMA concentration (∼0.16 M) used in this study decreases from ∼0.76 to ∼0.47 with reducing the QD size from ∼5.2 nm to ∼3.2 nm. However, the PET rate increases with decreasing QD size, which is commensurate with the observation that the chemical driving force (ΔG) increases with decreasing the QD particle size. We have analyzed the PET kinetics mainly by using Stern-Volmer fittings. However, in some cases Tachiya's stochastic kinetic model is used for stoichiometric analysis, which seems to be useful only at high quencher concentrations. The measured PET rate coefficients in all the cases are found to be at least an order of magnitude lower when compared to the diffusion-controlled rate of the reaction medium.     

Palladium‐Catalyzed Annulation of Diarylamines with Olefins through C?H Activation: Direct Access to N‐Arylindoles

A palladium‐catalyzed dehydrogenative coupling between diarylamines and olefins has been discovered for the synthesis of substituted indoles. This intermolecular annulation approach incorporates readily available olefins for the first time and obviates the need of any additional directing group. An ortho palladation, olefin coordination, and β‐migratory insertion sequence has been proposed for the generation of olefinated intermediate, which is found to produce the expected indole moiety.     

Catalytic Microcapsules Assembled from Enzyme–Nanoparticle Conjugates at Oil–Water Interfaces

Involuntary association : Anionic β‐galactosidase enzymes associate with positively charged Au nanoparticles to produce reduced‐charge conjugates, which assemble at oil–water interfaces to result in stable microcapsules (see picture). The microcapsules were formed quickly and showed high enzymatic activity, which makes them promising materials for biotechnology applications.

     

Reactions of Cp2MCl2 (M=Ti or Zr) with imine-oxime ligands. Formation of metallacycles

The reactions of bis(cyclopentadienyl)titanium(IV)/zirconium(IV) dichloride with a series of imine-oxime ligands (LH2), derived by condensing benzil-alpha-monoxime and 2-phenylenediamine, 4-phenylenediamine, 4-methyl-2-phenylenediamine, 2,6-diamino-pyridine, have been studied in anhydrous tetrahydrofuran in the presence of base and metallocycles of the [Cp2M(L)] (M=Ti or Zr) type have been isolated. Tentative structures have been proposed for the products based on elemental analysis, electrical conductance and spectral (electronic, IR and (1)H-NMR) data. Proton NMR spectra indicate that on the NMR time scale there is rapid rotation of the cyclopentadienyl ring around the metal-ring axis at 25 degrees C. Studies were conducted to assess the growth inhibiting potential of the complexes synthesized and the ligands against various bacterial strains.     

The Raychaudhuri equations: A brief review

We present a brief review on the Raychaudhuri equations. Beginning with a summary of the essential features of the original article by Raychaudhuri and subsequent work of numerous authors, we move on to a discussion of the equations in the context of alternate non-Riemannian spacetimes as well as other theories of gravity, with a special mention on the equations in spacetimes with torsion (Einstein-Cartan-Sciama-Kibble theory). Finally, we give an overview of some recent applications of these equations in general relativity, quantum field theory, string theory and the theory of relativisitic membranes. We conclude with a summary and provide our own perspectives on directions of future research.      

Synthesis,physico-chemical and biological studies on oxovanadium(IV) derivatives of mercaptotriazoles

Summary Complexes of 3-methyl- or 3-ethyl-4-amino-5-thiolato-1,2,4-triazole (LH) and its Schiff base derivatives with oxovanadium(IV), of the types [VOL₂(H₂O)], [VOL₂-(H₂O)] and [VOL(H₂O)₂] (where LH = Schiff bases derived from condensation of LH with benzaldehyde, 2-chlorobenzaldehyde, 4-methoxybenzaldehyde or acetophenone; LH₂ = Schiff bases derived from condensation of LH with salicylaldehyde or o-hydroxyacetophenone) have been prepared and characterized by elemental analyses, electrical conductance, magnetic moments and spectral data. The thermal behaviour of selected complexes was investigated by t.g., d.t.g. and d.s.c. techniques. The antifungal and antiviral activities of the Schiff bases and their corresponding complexes were also investigated.Author to whom all correspondence should be directed.