Ultrashort Hδ+ ··· Hδ- intermolecular distance in a supramolecular system in the solid state

Herein we report experimental evidences for the shortest intermolecular distance reported for two electronically-different hydrogen atoms in the solid state. The Hδ+ ··· Hδ- non-covalent interaction was studied by theoretical...

Effect of Salts and Organic Osmolytes is Due to Conservative Forces

Background: The impression given in the literature was that the net interaction potential energy, V is the difference between columbic-columbic and total weaker interaction energies. It is proposed however, that in aqueous solution all particles with full formal charges and partial charge (dipoles) contribute to the total interaction as applicable to conservative field but not to the exclusion of hydrophobic interaction if applicable. Objectives: The objectives are 1) To theoretically elucidate the basis of the intermolecular interaction, 2) To show that effectiveness of an osmolyte which may include inorganic ion to force macromolecular, (un)folding, the m-value, is a function of the implicit mobility (or translational velocity) of the cosolute, 3) To link the m-value to conservative forces (or potential energies, V) and 4) Quantitate the values of V. Methods: A major theoretical investigation and experimentation using Bernfeld method. Results and Discussion: There were higher velocities of amylolysis with salt than without it in the presence of ethanol. The magnitude of the calculated V and energy equivalent of the entropic term were higher with higher concentration of ethanol unlike was the case with graphically determined values which were generally higher in magnitude than calculated values. The values of the calculated V and intermolecular distance were respectively higher in magnitude and longer with higher concentration of the salt. Conclusion: The attractive interaction between a macromolecule and a cationic counter ion is due to long ranged ion-ion interaction which ultimately enhances the effect of short ranged interaction. Higher salt concentration promotes long ranged interaction. The translational velocity of the solvent and cosolute has a role in the quantification of intermolecular distance. A mathematical relationship exists between m-value and - V (or 2 K.E.). The values of V can be calculated based on the derived equations.

Variational Forward-Backward Charge Transfer Analysis Based on Absolutely Localized Molecular Orbitals: Energetics and Molecular Properties

<div> <div> <div> <p>To facilitate the understanding of charge transfer (CT) effects in dative complexes, we propose a variational forward-backward (VFB) approach to decompose the overall CT stabilization energy into contributions from forward and backward donation in the framework of energy decomposition analysis based on absolutely localized molecular orbitals (ALMO-EDA). Such a decomposition is achieved by introducing two additional constrained intermediate states in which only one direction of CT is permitted. These two “one-way” CT states are variationally relaxed such that the associated nuclear forces can be readily obtained. This allows for a facile integration into the previously developed adiabatic EDA scheme so that the molecular property changes arising from forward and back donation can be separately assigned. Using ALMO-EDA augmented by this VFB model, we investigate the energetic, geometric, and vibrational features of complexes composed of CO and main group Lewis acids (BH3, BeO/BeCO3), and complexes of the N2, CO, and BF isoelectronic series with [Ru(II)(NH3)5]2+. We identify that the shift in the stretching frequency of a diatomic π-acidic ligand (XY), such as CO, results from a superposition of the shifts induced by permanent electrostatics and backward CT: permanent electrostatics can cause an either red or blue shift depend- ing on the alignment of the XY dipole in the dative complex, and this effect becomes more pronounced with a more polar XY ligand; the back-donation to the antibonding π orbital of XY always lowers the X−Y bond order and thus red-shifts its stretching frequency, and the strength of this interaction decays rapidly with the intermolecular distance. We also reveal that while σ forward donation contributes significantly to energetic stabilization, it affects the vibrational feature of XY mainly by shortening the intermolecular distance, which enhances both the electrostatic interaction and back- ward CT but in different rates. The synergistic effect of the forward and backward donations appears to be more significant in the transition metal complexes, where the forward CT plays an essential role in overcoming the strong Pauli repulsion. These findings highlight that the shift in the XY stretching frequency is not a reliable metric for the strength of π back-donation. Overall, the VFB-augmented EDA scheme that we propose and apply in this work provides a useful tool to characterize the role played by each physical component that all together lead to the frequency shift observed. </p> </div> </div> </div>

Variational Forward-Backward Charge Transfer Analysis Based on Absolutely Localized Molecular Orbitals: Energetics and Molecular Properties

<div> <div> <div> <p>To facilitate the understanding of charge transfer (CT) effects in dative complexes, we propose a variational forward-backward (VFB) approach to decompose the overall CT stabilization energy into contributions from forward and backward donation in the framework of energy decomposition analysis based on absolutely localized molecular orbitals (ALMO-EDA). Such a decomposition is achieved by introducing two additional constrained intermediate states in which only one direction of CT is permitted. These two “one-way” CT states are variationally relaxed such that the associated nuclear forces can be readily obtained. This allows for a facile integration into the previously developed adiabatic EDA scheme so that the molecular property changes arising from forward and back donation can be separately assigned. Using ALMO-EDA augmented by this VFB model, we investigate the energetic, geometric, and vibrational features of complexes composed of CO and main group Lewis acids (BH3, BeO/BeCO3), and complexes of the N2, CO, and BF isoelectronic series with [Ru(II)(NH3)5]2+. We identify that the shift in the stretching frequency of a diatomic π-acidic ligand (XY), such as CO, results from a superposition of the shifts induced by permanent electrostatics and backward CT: permanent electrostatics can cause an either red or blue shift depend- ing on the alignment of the XY dipole in the dative complex, and this effect becomes more pronounced with a more polar XY ligand; the back-donation to the antibonding π orbital of XY always lowers the X−Y bond order and thus red-shifts its stretching frequency, and the strength of this interaction decays rapidly with the intermolecular distance. We also reveal that while σ forward donation contributes significantly to energetic stabilization, it affects the vibrational feature of XY mainly by shortening the intermolecular distance, which enhances both the electrostatic interaction and back- ward CT but in different rates. The synergistic effect of the forward and backward donations appears to be more significant in the transition metal complexes, where the forward CT plays an essential role in overcoming the strong Pauli repulsion. These findings highlight that the shift in the XY stretching frequency is not a reliable metric for the strength of π back-donation. Overall, the VFB-augmented EDA scheme that we propose and apply in this work provides a useful tool to characterize the role played by each physical component that all together lead to the frequency shift observed. </p> </div> </div> </div>

Synthesis and Spectroscopic Determination of the Coordination Differences of Cadmium and Zinc Complexes of Dehydroacetic Acid with Pyridine and g-Picoline

Various complexes of DHA with transition-metal cations are known for their antifungal properties. Here, four novel Zn and Cd complexes were prepared via the substitution of water by pyridine andg-picoline using Zn(DHA)2(H2O)2 (2) and Cd(DHA)2(H2O)2 (3) as starting materials. The products were characterized by IR, UV, elemental analysis, TGA and NMR techniques, including correlation times and intermolecular distance measurements using the NULL pulse sequence. The experimental data were compared to the molecular modeling results using DFT and the semiempirical method PM3, confirming that the pentacoordinated Zn complexes have bipyramidal geometry while the Cd complexes have the expected octahedral geometry. These results show that substitution of Zn by Cd leads to an important modification of the coordination structure, especially when strong ligands are involved.