Solvent polarity effects on thermochemical and NMR parameters of spilanthol pharmacological agent: an experimental and DFT investigation

Structural Chemistry - Through experimental and appropriate quantum chemical approaches, we perform a systematic investigation of the solvent effects on thermochemical and nuclear magnetic...     

The Solute Polarization and Structural Effects on the Nonlinear Optical Response of Based Chromone Molecules

The solute polarization due to solvent is a an electrostatic quantum effect that impacts diverse molecular properties, including the nonlinear optical response of a material. An iterative procedure that allows updating the solute charge distribution in the presence of the solvent is combined with a sequential Monte Carlo/Quantum Mechanics methodology and Density Functional Theory methods to evaluate the nonlinear optical (NLO) response using the hyper Rayleigh scattering (HRS) of a series of chromones recently identified in Chamaecrista diphylla, an herbaceous plant abundant throughout the Americas and used in folk medicine. From this study, it is determined that from gas to solvent environment, the systems acquire low refractive index (n) and an improvement of the first hyperpolarizability (β_HRS), signaling potential NLO uses. It is shown that the octupolar contributions (β^J=3) superate the dipolar ones (β^J=1) and dominate the second-order optical response in both gas and liquid phases, which indicate nontrivial optical materials. Moreover, the solvent environment and structural changes in the periphery can tune significantly the dipolar/octupolar balance, showing a key to control the decoupling between these contributions.     

Interfacial polarisation effect on the interlayer couplings in Co/Rh sandwiches

The structural, magnetic and transport properties of Co/Rh sandwiches grown by ultra high vacuum evaporation and sputtering have been studied. High-energy electron diffraction observations during the growth reveal that both Co and Rh layers have been stabilised in the (111) fcc structure for the evaporated sandwiches. X-ray measurements performed on sputtered samples show a predominant fcc polycrystalline structure of the stacks with a preferential (111) texture. Magnetisation and magnetoresistance measurements show a very strong antiferromagnetic exchange coupling for thin Rh layers, reaching for 4.8? Rh, the strongest ever observed in exchange coupled systems. This value is in good agreement with the value of obtained by ab initio calculations for Co/Rh (hcp) superlattices. This is explained by the magnetic nature of the Co/Rh interfaces. Indeed, the variation of the measured saturation magnetisation as a function of the Co layer thickness shows no evidence of Co moment reduction for the Co atoms located at the interfaces, even for the very thin layers. The value of the preserved magnetic moments of the cobalt atoms at the interfaces is confirmed by ab initio calculations for Co/Rh superlattices taking the intermixing into account. Received: 18 February 1998 / Received in final form: 30 April 1998 / Accepted: 29 May 1998