H2-release from alcohols,diols, and compounds with amino functionality promoted by titanium(II) sandwich complex, [Cp2Ti]: a theoretical approach

Structural Chemistry - The role of Ti(II) sandwich complex, [Cp2Ti], generated by the combination of [Cp2TiCl2] and two equivalents of nBuLi, in situ, in toluene has been investigated theoretically...     

Peak effect at microwave frequencies in swift heavy ion irradiated YBa2Cu3O7-δ thin films

The vortex dynamics at microwave frequencies in YBa₂Cu₃O_7-δ (YBCO) films have been studied. We observe a peak in the microwave (4.88 and 9.55 GHz) surface resistance in some films in magnetic fields up to 0.8 T. This is associated with the ‘peak-effect’ phenomenon and reflects the order-disorder transformation of the flux line lattice near the transition temperature. Introduction of artificial pinning centers like columnar defects created as a result of irradiation with 200 MeV Ag ion (at a fluence of 4×10¹⁰ ions/cm²) leads to the suppression of the peak in films previously exhibiting ‘peak effect’.     

Fuzzy measures for color image retrieval

In this paper we present a scheme for fuzzy similarity based strategy to retrieve an image from a library of color images. Color features are among the most important features used in image database retrieval. Due to its compact representation and low complexity, direct histogram comparison is the most commonly used technique in measuring color similarity of images. A gamma membership function, derived from the Gamma distribution, has been proposed to find the membership values of the gray levels of the histogram. We present here an image retrieval scheme with some popular vector fuzzy distance measures using a gamma membership function for finding the membership values of the gray levels and evaluate the matching function to select the appropriate retrieval mechanism.     

Interaction of moderately reactive molecules with organic superhalogens: a theoretical perspective

The interaction of four moderately reactive molecules (MRMs), benzene (BZ), water, ammonia and silicon dioxide, with three aromatic organic superhalogens (OSHs) has been investigated at the density functional theory (DFT) level. The strength of the interaction is analysed from the distortions in the structures of both the MRMs and OSHs after complexation and the calculated binding energy (BE) values between the two interacting moieties. The interaction becomes stronger as we move from BZ to H₂O to NH₃ and strongest for SiO₂ molecule. Contributions from different terms in total interaction energy have been examined by energy decomposition analysis (EDA). The charge flow values between MRMs and OSHs, and Mulliken spin density localised on the moderately reactive molecules have been evaluated to ensure whether the interaction is ionic or not. Atoms in Molecules (AIM) analysis has been performed to characterise the bonds formed between the two. Overall, our study gives a comprehensive account of the interaction between the moderately reactive molecules and three theoretically designed aromatic organic superhalogens, which will further motivate researchers in the field of superhalogen chemistry.     

Effect of swift heavy ion irradiation on surface resistance of DyBa2Cu3O7-δ thin films at microwave frequencies

We report the observation of a propounced peak in surface resistance at microwave frequencies of 4.88 GHz and 9.55 GHz and its disappearance after irradiation with swift ions in laser ablated DyBa₂Cu₃O_7-δ (DBCO) thin films. The measurements were carried out in zero field as well as in the presence of magnetic fields (up to 0.8 T). The films were irradiated using 90 MeV oxygen ions at Nuclear Science Centre, New Delhi at a fluence of 3×10¹³ ions/cm². Introduction of point defects and extended defects after irradiation suppresses the peak at 9.55 GHz whereas no suppression is observed at 4.88 GHz. These results and the vortex dynamics in the films at microwave frequencies before and after irradiation are discussed.     

Formation of stable ionized complexes between coinage metal containing superhalogens and moderately reactive molecules: a DFT approach

Structural Chemistry - The possibility of ionization of six moderately reactive molecules (Y), namely silicon dioxide (SiO2), ammonia (NH3), water (H2O), carbon dioxide (CO2), chloroform (CHCl3)...     

Theoretical analysis of tautomerization of succinimide and analogous compounds: insights from DFT approach

Tautomerizations of biologically and medicinally important heterocyclic compound, 2,5-pyrrolidinedione, commonly known as succinimide and two of its analogous compounds, 2,4-pyrrolidinedione and 3,4-pyrrolidinedione have been investigated at the density functional theory (DFT)/M06-2X level in aqueous medium, implementing polarizable continuum model (PCM). We have extended our investigation of tautomerism to the sulfur analogues of the aforementioned compounds also, i.e., 2,5-pyrrolidinedithione, 2,4-pyrrolidinedithione, and 3,4-pyrrolidinedithione. Tautomerism observed in these compounds are mainly keto-enol, thio-thiol and amine-imine, but we have detected two new kind of tautomerization shown by some of the abovementioned compounds, named as keto-epoxy (for the oxygen analogue) and thio-thioepoxy (for the sulfur analogue) which have not yet been reported in the literature. Relative energies (E_r) and activation energies (E_a) have been calculated for all the tautomers and tautomerization processes. The potential energy surfaces (PESs) have been constructed using the M06-2X energy values. It has been observed that the energy difference found in the tautomers of sulfur analogues is relatively lower than that of the corresponding oxygen analogues, so does the activation energy barrier. As one-electron redox properties play an important role in biological systems, we have also explored the effect of conformational changes on the overall redox properties of the said compounds by calculating the adiabatic and vertical ionization potentials (AIPs and VIPs, respectively) and adiabatic electron affinities (AEAs).