Charge distribution, metals

Agonists - The existence of two receptor populations for histamine raises the interesting question of whether the chemical mechanism of histamine interaction differs between the two receptor types. Some indications of the chemical properties which may differentiate receptor action come from studies of histamine chemistry and from structure-activity considerations of congeners. Histamine in aqueous solution is a mixture of equilibrating species, viz. ionic forms, tautomers and conformers nmr studies confirm earlier pK work indicating a N -H N -H (structures 1 and 2) tautomer ratio of approximately 4 1 for histamine monocation, and a comparable ratio for histamine base. The latter result contrasts with crystal structure data and molecular orbital predictions, and may indicate an influence of solvent on tautomer stability. Recent studies of properties pertinent to consideration of ligand-receptor interactions are conformation (MO calculations and infra-red comparison of solid state and chloroform solutions of histamine base ), electronic charge distribution, metal complexation, and phospholipid inter-... 

X-ray diffraction and the charge distribution in transition metal complexes. P. Coppens, Coord. Chem. Rev., 1985, 65, 285 (56). 

Oxidation state is a frequently used (and indeed misused) concept which apportions charges and electrons within complex molecules and ions. We stress that oxidation state is a formal concept, rather than an accurate statement of the charge distributions within compounds. The oxidation state of a metal is defined as the formal charge which would be placed upon that metal in a purely ionic description. For example, the metals in the gas phase ions Mn + and Cu are assigned oxidation states of +3 and +1 respectively. These are usually denoted by placing the formal oxidation state in Roman numerals in parentheses after the element name the ions Mn- " and Cu+ are examples of manganese(iii) and copper(i). 

Bergmann D, Hinze J (1987) Electronegativity and Charge Distribution. 66 145-190 Berners-Price SJ, Sadler PJ (1988) Phosphines and Metal Phosphine Complexes Relationship of Chemistry to Anticancer and Other Biological Activity. 70 27-102 Bertini I, see Banci L (1990) 72 113-136... 

Diffusion is not straightforward inside the resin phase, and this is due to the restrictive influences of the polymer network and because of the charge distribution connected with the fixed ions of the functional groups. The resin phase is consequently related to a porous solid. The effectual diffusivities of metal ions in the resin phase may differ but are largely less than those in the aqueous phase external to the resin phase. If Fick s law is applied to diffusion in a resin bead of radius, r, it may be represented as... 

Vigalok, A. Rybtchinski, B. Shimon, L. J. W. Ben-David, Y. Milstein, D. Metal-stabilized methylene arenium and c-arenium compounds synthesis, structure, reactivity, charge distribution, and interconversion. Organometallies 1999, 18, 895-905. 

Charge. The small amount of charge distribution data for carbyne complexes (based on Mulliken population analyses) indicates that the metal-carbon bond is generally polarized Ms+—C5- and that the carbyne carbon is always more negative than adjacent carbonyl carbons (28,30). These conclusions are directly analogous to those derived for carbene complexes. 

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