Growth, structural, optical, thermal and mechanical properties of ammonium pentaborate single crystal

Nonlinear optical single crystals of ammonium pentaborate (APB) were grown by the slow cooling method from aqueous solution. Grown crystal was characterized by powder X-ray diffraction (PXRD) and FT-IR spectral analysis. Perfection of the grown crystal was evaluated by high-resolution X-ray diffractometry (HRXRD). The effect of nylon threading on the perfection of the grown bigger crystal was also studied by HRXRD. The range and percentage of optical transmission was ascertained by recording UV-vis-NIR spectrum. Thermal properties were investigated by TG-DTA and DSC analyses. Its mechanical hardness was estimated by Vickers microhardness tester.     

Oxidative DNA damage following photoexcitation of daunomycin: Direct role of oxygen

The chemistry of the photoactivation of daunomycin–DNA complexes is reported and the mechanism is elucidated. We quantitatively assessed the type of DNA damage, such as strand breaks, oxidized bases, and abasic sites, that arise using a plasmid relaxation assay coupled with DNA repair endonucleases. Photoexcitation of daunomycin leads to oxidative DNA damage in a dose- and irradiation time-dependent manner and guanine-specific oxidized purines are substantially produced under these conditions. Oxidative DNA base damage was also inhibited by argon degassing, indicating that guanine-specific damage arises from an oxygen-dependent mechanism. In addition, photoexcitation of daunomycin–DNA complexes leads to superoxide anion radical formation. From these studies of the actual product formed, we conclude that a charge transfer is a main driving force of the mechanism.     

Density functional approach to thermodynamics of self-assembly

A local density functional approximation for predicting the surface crystallization of a thermodynamically small system under gravity is described and tested. Using the model of the classical soft-sphere fluid, the state parameters for such systems are identified. A generalized phase diagram based upon the scaling variables is obtained; systems with the same reduced-state parameters exhibit identical profiles of thermodynamic properties such as density, pressure, and intrinsic chemical potential, measured in the direction of the applied field. The point-thermodynamic approximation of Rowlinson and the local density approximation of the density functional formalism are found to be remarkably accurate. A configurational temperature is defined and shown to agree with the corresponding kinetic temperature for inhomogeneous systems at equilibrium. The structural profiles at the crystal-fluid interface are indicative of a mesolayer of lower density crystal, not seen in the field-free isobaric crystal-liquid interface.     

A novel catalyst-free mechanochemical protocol for the synthesis of 2,3-dihydro-1H-perimidines

A rapid, efficient, and green grinding assisted method for the synthesis of 2,3-dihydro-1H-perimidines has been developed. 1,8-Diaminonaphthalene and aldehydes were ground using mortar and pestle for 5 minutes affording the product in moderate to excellent yields. The methodology minimises the use of conventional workup and column chromatographic techniques.     

Growth and characterization of glycine lithium sulphate single crystal

Single crystal of glycine lithium sulphate, a nonlinear optical material, was grown from aqua solution by temperature reduction method. The solubility and metastable zonewidth of glycine lithium sulphate were estimated using aqueous solution. The cell parameters of the grown crystal were estimated by single crystal X‐ ray diffraction analysis. The presence of functional groups was identified from FTIR spectrum. Thermal analysis was performed to study the thermal stability of the grown crystal. The transmission and absorption spectra of this crystal show that the lower cut off wavelength lies at 330 nm. Powder Second Harmonic Generation efficiency of the grown crystal measured by Kurtz technique is 0.75 times that of potassium dihydrogen orthophosphate. Vickers microhardness study was carried out on the well developed (011) face of the grown crystal. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of 2,6‐dibenzylidenecyclohexanone single crystal

Following the temperature reduction method, growth of single crystals of organic 2,6‐dibenzylidenecyclohexanone (DBCH) material from ethanol solution is reported in the present work. Solubility and metastable zone width measurements were carried out under stirring and nonstirring conditions of solution. Cell dimensions were obtained from single crystal X‐ray diffraction study. From FT‐IR spectral analysis, various functional groups of this crystal were identified. UV‐Visible spectral analysis was made. Mechanical strength of the grown crystal was estimated on the prominent (110) face using a Vickers microhardness tester. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mass Spectrometric Analysis of Cyclotides from Clitoria ternatea: Xxx-Pro Bond Fragmentation as Convenient Diagnostic of Pro Residue Positioning

Cyclotides, a class of macrocyclic plant peptides, characterized by a cyclic backbone and three inter-locking disulfide bonds, may be divided into two major structural subfamilies, Möbius and Bracelet, based on the presence or absence of a specific proline residue. The present study describes the suite of cyclotides obtained from Clitoria ternatea, characterized by LC−MS and MS/MS techniques. Notable variations in product ion distributions were observed in cyclotides belonging to different structural subfamilies based on the number and positions of proline residues. For instance, Cter M which is an abundant Möbius cyclotide in this plant containing three proline residues, displayed distinct b- and y- ion characteristics in the MS/MS spectra compared to Cliotide T1, another commonly identified cyclotide but belonging to the Bracelet subfamily having two proline residues. The distinct fragmentation pattern of prototypical cyclotides of each structural subfamily, determined by Xxx-Pro bond fragmentation, was used to rapidly identify and sequence a novel cyclotide ctr pep 30 from this plant.