Chemical binding

About: Chemical binding is a research topic. Over the lifetime, 1822 publications have been published within this topic receiving 52516 citations.

The concept of pressure in density functional theory

Abstract: Using density functional theory, a prescription is given for determining the internal scalar pressure at a point within an atom or molecule. From this expression for the pressure, a thermodynamic expression for the energy is obtained in terms of the chemical potential of the reference system, forces acting on the system, the internal pressure and an additional component X[ρ]; namely, Here μ0 is the chemical potential in the absence of fields, v is the potential due to nuclei, φ is the potential due to electrons, P is the scalar pressure, and X[ρ] is defined by the formula where T[ρ] and K[ρ] are the exact kinetic energy and exchange–correlation functionals. The functional X[ρ] vanishes as N approaches infinity, or in Thomas–Fermi or Thomas–Fermi–Dirac approximation, yet it is necessary to account for chemical binding.

Sulfur-35 labeled acetazolamide in cat brain.

Abstract: Combined radioassay and autoradiographic techniques have shown that acetazolamide enters selected areas of the brain in significant quantities. The drug occurs in brain, cerebrospinal fluid and plasma as unchanged acetazolamide. Two portals of entry of acetazolamide into the brain are utilized. The early pattern is one of diffusion from the cerebrospinal fluid with those tissues having easy access to the cerebrospinal fluid showing the highest drug content. This early diffusional pattern from the cerebrospinal fluid becomes less distinct in time. The second route of entry is blood-to-brain transport. The distribution of acetazolamide is not well correlated with the known pattern of vascularity in the brain. It is suggested that the early acetazoamide picture may represent in part a distribution in the interstitial fluid compartment. To this end experiments using the sulfate-S35 ion have been designed to measure the extracellular space. Hippocampus, hypothalamus and caudate nucleus are areas of high acetazolamide uptake and show a discrete retention over contiguous areas. Whether or not this retention is a function of local chemical binding of the drug is a matter of speculation.

Molecular SCF calculations for the ground state of some three-membered ring molecules: Cis and trans diaziridine, oxaziridine and the corresponding imminium ions

Abstract: LCAO SCF MO calculations with minimal basis sets of Slater-type orbitals are performed for some three-membered heterocycles. A reinterpretation of the resulting wavefunctions in terms of localized (exclusive) orbitals is employed to show the bending of the ring bonds and to measure the degree of transferability of some groups among chemically different yet related molecules. The electrostatic potentials produced in the neighbouring space by the nuclear and electronic charge distributions are evaluated and employed to indicate the molecular sites most likely subject to electrophilic attack. Some features of the electrostatic potential may be easily related to the entities employed in the usual intuitive description of chemical binding (lone pairs, etc.).

Low-temperature thermochromism marks a change in coordination for the metal ion in manganese superoxide dismutase.

Abstract: We have observed thermochromism (temperature-dependent absorption) for anion complexes of manganese superoxide dismutase indicating a change in coordination number for the metal complex at low temperatures. The ligand field spectra for the Mn(III) ion, characteristic of five-coordination for the azide complex at 295 K, cleanly convert to spectra reflecting six-coordination at low temperature, with a midpoint for the transition near 200 K. The active site structure is temperature-dependent, a relatively rigid, distorted octahedral low-temperature Mn complex melting with dehydration (or displacement of one of the protein ligands) to form a five-coordinated complex under physiological conditions. Thermodynamic parameters for the transition estimated from van't Hoff analysis (ΔHvH = 5 kcal/mol; ΔSvH = 22 cal/mol K) are consistent with reduced chemical binding and increased fluxionality at room temperature. This thermochromism of MnSD demonstrates the existence of distinct isomeric forms of the active site met...