Correlation studies on dielectric and thermodynamic parameters in the binary mixtures of N-methyl aniline and alcohols

The dielectric and thermodynamic studies on polar binary mixtures of N- methyl aniline with alcohols — propan-1-ol and propan-2-ol have been carried out, at different temperatures and mole fractions. LF impedance analyzer, Microwave bench and Abbe’s refractometer are used respectively in radio, microwave (X-Band) and high frequency regions to determine the dielectric data. The experimental data is used to correlate the dielectric and thermodynamic parameters — static permittivity, high frequency permittivity, Kirkwood effective correlation factor, corrective Kirkwood correlation factor, excess permittivity, excess Helmholtz free energy, dipole moment, excessive dipole moment, relaxation time, excess inverse relaxation time and the excess thermodynamic parameters. These parameters are used to interpret the molecular interactions between the molecular species of the liquid mixtures.     

Liquid crystal films on curved surfaces: An entropic sampling study

The confining effect of a spherical substrate inducing anchoring (normal to the surface) on rod-like liquid crystal molecules contained in a thin film spread over it has been investigated with regard to possible changes in the nature of the isotropic-to-nematic phase transition as the sample is cooled. The focus of these Monte Carlo simulations is to study the competing effects of the homeotropic anchoring due to the surface inducing orientational ordering in the radial direction and the inherent uniaxial order promoted by the intermolecular interactions. By adopting an entropic sampling procedure, we could investigate this transition with a high temperature precision, and we studied the effect of the surface anchoring strength on the phase diagram for a specifically chosen geometry. We find that there is a threshold anchoring strength of the surface below which uniaxial nematic phase results, and above which the isotropic fluid cools to a radially ordered nematic phase, besides of course expected changes in the phase transition temperature with the anchoring strength. In the vicinity of the threshold anchoring strength we observe a bistable region between these two structures, clearly brought out by the characteristics of the corresponding microstates constituting the entropic ensemble.     

Sequence, structure, and active site analyses of p38 MAP kinase: exploiting DFG-out conformation as a strategy to design new type II leads

A new knowledge, structure, and sequence based strategy involving the effective exploitation of the DFG-out conformation is delineated. A comprehensive analysis of the structure, sequence, cocrystals, and active sites of p38 MAP kinase crystal structures present in Protein Data Bank (PDB) and the FDA approved MAP kinase drugs has been done, and the information is used for the design of type II leads. The 98 crystal structures, 138 cocrystals, and 31 FDA drugs comprise of 7 different sequences of 2 organisms viz., Homo sapiens and Mus musculus differing in sequence length, constituting both homo- and heterochains. Multiple sequence alignment with ClustalW showed >95% sequence similarity with highly conserved domains and a high propensity for mutations in the activation loop. The bound ligands were extracted, and their interactions with DFG in and out conformations were studied. These cocrystals and FDA drugs were fragmented on the basis of their binding interactions and their affinity to ATP and allosteric sites. The fragment library thus generated contains 106 fragments with overlapping drug fragments. A blue print constituting three main parts viz., head (ATP region), linker (DFG region), and tail (allosteric region) has thus been formulated and used to design 64 type II p38 MAP kinase inhibitors. The above strategy has been employed to design potent type II p38 MAP kinase inhibitors, which are shown to be very promising.     

Image analysis method to study electro-optic parameters of nematogens

This paper demonstrated the image analysis technique for the investigation of electro-optic behaviour of homogeneously aligned nematic liquid crystals p-n alkyl benzoic acids (nBA) where n = 5 and 6 under the application of direct current (DC) electric field. Textures of the liquid crystals in the mesophase region of particular temperature were recorded in three monochromatic image planes at the wavelengths of 635 (red), 530 (green) and 475 nm (blue) as a function of applied DC voltage. Electro-optic properties such as transmittance, birefringence, phase retardation and contrast ratio were measured by analysing the optical intensities of the recorded textures using MATLAB software. The changes in the textural features and formation of new textures as a function of voltage provided information for better understanding of the electro-optic characteristics of liquid crystals. Results of this study were compared with the data of the other standard techniques: laser source (633 nm) experiment and United Detector Technology (UDT) sensor of model UV- 35P silicon photo diode which uses white light as source and filters the wavelengths using three colour filters of wavelengths 635, 530 and 475nm.     

Conformational studies of intermolecular hydorgen bonding through induced crystal G phase in nBA:7HB

This paper exploits the physical investigation on liquid crystal complexes obtained by self-organisation of p-n-alkyl benzoic acid (nBA) mesogens with non-mesogenic materials heptyl p-hydroxy benzoate (7HB). Intermolecular interactions of the molecules result the hydrogen bond between the proton donor (COOH) of nBA and proton acceptor (OH) of 7HB. The formation of hydrogen bond is attributed to the quenching of the nematic phase and inducement of crystal G phase in liquid crystal complex. A comparative study of phase abundance is presented with respect to the pure nBAs and other hydrogen bonded liquid crystal complexes of nBAs. Thermal and phase behaviour of the complexes are determined by polarising optical microscope (POM), differential scanning calorimetry (DSC) and image moments approach. Intermolecular interactions which result the hydrogen bond in complexes are investigated using Fourier transform infrared (FTIR) spectroscopy. Molecular structure of the liquid crystal complexes in the solid phase was elucidated using powder X-ray diffraction and proton nuclear magnetic resonance (¹HNMR).     

Competition between folding and aggregation in a model for protein solutions

We study the thermodynamic and kinetic consequences of the competition between single-protein folding and protein-protein aggregation using a phenomenological model, in which the proteins can be in the unfolded (U), misfolded (M) or folded (F) states. The phase diagram shows the coexistence between a phase with aggregates of misfolded proteins and a phase of isolated proteins (U or F) in solution. The spinodal at low protein concentrations shows non-monotonic behavior with temperature, with implications for the stability of solutions of folded proteins at low temperatures. We follow the dynamics upon “quenching” from the U-phase (cooling) or the F-phase (heating) to the metastable or unstable part of the phase diagram that results in aggregation. We describe how interesting consequences to the distribution of aggregate size, and growth kinetics arise from the competition between folding and aggregation.     

Binding propensity and selectivity of cationic,anionic, and neutral guests with model hydrophobic hosts: A first principles study

Computations play a critical role in deciphering the nature of host–guest interactions both at qualitative and quantitative levels. Reliable quantum chemical computations were employed to assess the nature, binding strength, and selectivity of ionic, and neutral guests with benzenoid hosts. Optimized complex structures reveal that alkali and ammonium ions are found to be in the hydrophobic cavity, while halide ions are outside, while both complexes elicit substantial binding energy. The origin of the selectivity of host toward the guest has been traced to the interaction and deformation energies, and the nature of associated interactions is quantified using energy decomposition and the Quantum Theory of Atoms in Molecules analyses. While the larger hosts lead to loosely bound complexes, as assessed by the longer intermolecular distances, the binding strengths are proportional to the size of the host systems. The binding of cationic complexes is electrostatic or polarization driven while exchange term dominates the anionic complexes. In contrast, dispersion contribution is a key in neutral complexes and plays a pivotal role in stabilizing the polyatomic complexes.     

Study of Electrical Conduction Behaviour of the System Sr1-xLaxSn1-xCoyO3 (x = y ⩽ 0.5; x ⩽ 0.5, y = 0.00; x = 0.00; y ⩽ 0.05)

Single phase solid solution forms in the Sr_1-xLaSn_1-xCo_yO₃ (x = y) system for x⩽0.05 in the samples prepared by solid state ceramic method. A few compositions were prepared in the Sr_1-3x/2La_xSnO₃ and SrSn_1-yyCo_yO_3-y/2 to understand the role of La³⁺ and Co³⁺ in the electrical conduction behaviour of the system. Resistivity increases with incorppration of La³⁺ ions and decreases with doping of Co³⁺ ions. These results have been explained in terms of the defect structures of these materials.     

Spectroscopic and Transport Properties of (NH4)2CuCl4 · 2 H2O Single Crystal

Electron paramagnetic resonance (EPR), Optical absorption and Transport properties of (NH₄)₂CuCl₄ 2 H₂O single crystals have been studied. An anisotropic g tensor was observed with gl = 2.241 and g∥ = 2.081 by EPR method. The spin orbit coupling constant is found to be 540 cm⁻¹. The optical absorption in UV region are characterized by charge transfer band, in the visible and near infrared region at 13,333, 4,480, 4,336, and 3,998 cm⁻¹ attributed to the transitions between the (d-d) stark energy levels of the copper (II) ion in an extended octahedral crystal field. Dc electrical conductivity measurements with temperature reveal an anisotropic characteristic of a two-dimensional layered structure, and exhibits two first order structural phase transitions at about 383 K and 413 K. These transitions are attributed to loss of the two water inolecules of hydration and free rotation of NH⁺₄ ion from a state of torsional oscillation.