Thermal,spectral, and thermodynamic studies for evaluation of calf thymus DNA interaction activity of some copper(II) complexes

The square-pyramidal copper(II) complexes with ciprofloxacin in the presence of bipyridine derivatives have been synthesized and characterized using elemental analysis, magnetic moment measurement, thermal analysis (TG), IR, mass and reflectance spectra. The thermal denaturation study has been used for evaluating calf thymus DNA interaction activity. Spectral and hydrodynamic measurements have been used for validating the DNA interaction study. The thermodynamic profile was established for proper understanding of DNA binding Gibbs free energy.     

Spectrophotometric determination of ciprofloxacin by ion pair formation

Various aspects of application of derivative spectrophotometry to chemical analysis and investigations of equilibria and kinetics of reactions are scrutinised. In this work the viability of a spectrophotometric technique for the determination of ciprofloxacin has been deliberated. The method is based on the formation of ion-association complexes of ciprofloxacin with nickel(II) tetra thiocyanate, which are extracted into organic solvent (40% n-butanol in methylene chloride) having absorption maxima at 623 nm. The precision and accuracy of the method was checked by UV reference methods. The validation study indicated the parameters, which are in good agreement with the data obtained from standard methods. The proposed method was fruitfully applied to determine ciprofloxacin in their tablet formulations.     

Electrical resistance measurements under pressure on NbTe2 single crystal

Transition metal dichalcogenides, because of their layered structure, are well suited for extreme pressure lubrication. These materials being semiconducting and of layered structure may undergo structural and electronic transitions under pressure. Here we report the details of the preparation and characterization of single crystals of NbTe₂ and the results of electrical resistance measurements under pressure carried out on it to investigate this possibility. Single crystals were grown by the chemical vapor transport technique, using iodine as a transporting agent. The composition of the grown crystals was confirmed on the basis of Energy Dispersive Analysis by X-ray (EDAX) and remaining structural characterization was also accomplished by X-ray Diffraction (XRD) studies. Electrical resistance was measured employing a Bridgman anvil set up to 10?GPa and diamond anvil cell (DAC) assembly up to 25?GPa. A technique slightly modified from that described in the literature for carrying out electrical resistivity measurements in the diamond anvil cell (DAC) under pressure has been standardized.     

Beyond microscopic reversibility: Are observable non-equilibrium processes precisely reversible?

Although the principle of microscopic reversibility has been studied for many decades, there remain ambiguities in its application to non-equilibrium processes of importance to chemistry, physics and biology. Examples include whether protein unfolding should follow the same pathways and in the same proportions as folding, and whether unbinding should likewise mirror binding. Using continuum-space calculations which extend previous kinetic analyses, we demonstrate formally that the precise symmetry of forward and reverse processes is expected only under certain special conditions. Approximate symmetry will be exhibited under a separate set of conditions. Exact, approximate, and broken symmetry scenarios are verified in several ways: using numerical calculations on toy and molecular systems; using exact calculations on kinetic models of induced fit in protein-ligand binding; and based on reported experimental results. The analysis highlights intrinsic challenges and ambiguities in the design and analysis of both experiments and simulations.     

All-inorganic solid-state electrochromic devices: a review

Electrochromic devices (ECDs) are currently attracting much interest in academic and industry for both research and their commercial applications because of their controllable transmission, absorption, and/or reflectance. This paper reviews the progress that has taken place from 1969 until the year 2015 with regard to all-solid-state inorganic ECD fabrication. The main aim of this review article is to provide an easy entrance to literature of all-inorganic solid-state ECD.     

Rapid ultraperformance liquid chromatography–tandem mass spectrometry method for quantification of oxcarbazepine and its metabolite in human plasma

A rapid and sensitive ultraperformance liquid chromatography tandem mass spectrometry assay was developed for the simultaneous analysis of oxcarbazepine and its main metabolite in human plasma. The assay involves a simple solid‐phase extraction procedure of 0.3 mL of human plasma and analysis was performed on a triple‐quadrupole tandem mass spectrometer in multiple reaction monitoring mode via electrospray ionization. Separation was achieved on an Acquity UPLC™ BEH C₁₈ column (50 × 2.1 mm, i.d., 1.7 µm) with isocratic elution at a flow‐rate of 0.25 mL/min and imipramine was used as the internal standard. The standard calibration curve was linear over the range 9.580–5070.205 ng/mL for oxcarbazepine (OXC) and 19.444–10290.800 ng/mL for 10,11‐dihydro‐10‐hydroxycarbamazepine (MHD), expressed by the linear correlation coefficient r², which was better than 0.995 for OXC and MHD. The intra‐ and inter‐day precision and accuracy of the quality control samples were within 10.0%. The recoveries were 81.0, 89.6 and 66.6% for OXC, MHD and imipramine, respectively. The total run time was 1.5 min only for each sample, which makes it possible to analyze more than 350 samples per day. Copyright © 2010 John Wiley & Sons, Ltd.     

A system mean void fraction model for predicting various transient phenomena associated with two-phase evaporating and condensing flows

The system mean void fraction model's principle virtue is its simplicity. The model converts the two-phase evaporating or condensing flow system into a type of lumped parameter system, generally yielding simple, closed form solutions in terms of the important system parameters. The particular applications of the model which are demonstrated in this paper are for a class of transient flow problems where complete vaporization or condensation takes place, and where the system mean void fraction can be considered to be time-invariant. This assumption uncouples the problem from the transient form of the momentum principle, an analytical simplification of considerable magnitude. The specific transients under consideration are caused by changes in the inlet flowrate. For evaporating flows, these transients are the effective liquid dry-out point, and the outlet flowrate of superheated vapor. For condensing flows, they are the effective point of complete condensation, and the outlet flowrate of subcooled liquid.     

Clouding Behavior and Thermodynamic Study of Nonionic Surfactants in Presence of Additives

The present study investigates the effect of different additives on the cloud point (CP) of nonionic surfactants Triton X-100 (TX-100) and Triton X-114 (TX-114) in aqueous solutions. The thermodynamic parameters of these mixtures were calculated at different additive concentrations. The cloud point of nonionic surfactants TX-100 and TX-114 decreased with the increment of electrolyte concentrations and increased with alcohol concentrations. The standard Gibbs free energy was found to be positive for both the surfactants, whereas the enthalpy and the entropy of the clouding phenomenon were found to be positive with alcohols and negative with electrolytes. The overall clouding process was endothermic for alcohols and exothermic for electrolytes.     

Synthesis and NMR elucidation of novel amino acid cavitand derivatives

The synthesis of seven novel protected amino acid cavitands is reported. All have four pendant n-undecyl chains and ‘headgroups’ connected by a two-carbon spacer at four positions on the aromatic rings. The amino acids employed are glycine, alanine, phenylalanine, leucine, proline, tryptophan, serine, glutamine and lysine. The structures of the compounds were elucidated using one- and two-dimensional NMR techniques, which verified that all tetra-substituted cavitands have symmetrical C_4v conformation. This is the first example of a complete study for amino acid cavitand derivatives.     

Realizing universal edge properties in graphene fractional quantum Hall liquids

Universal chiral Luttinger liquid behavior has been predicted for fractional quantum Hall edge states, but so far has not been observed experimentally in semiconductor-based two-dimensional electron gases. One likely cause of this absence of universality is the generic occurrence of edge reconstruction in such systems, which is the result of a competition between confinement potential and Coulomb repulsion. We show that due to a completely different mechanism of confinement, edge reconstruction can be avoided in graphene, which allows for the observation of the predicted universality.