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.