Structure dissociating

P. Politzer, P. Lane, M. E. Grice, M. C. Concha, P. C. Redfem, Comparative Computational Analysis of Some Nitramine and Difluoramine Structures, Dissociation Energies and Heats of Formation, J. Mole. Struct. (Theory), 338 (1995) 249-256. 

In conclusion, it is worthwhile mentioning that a number of common Pis without an aromatic carbonyl group in their structure dissociate via an excited singlet state and demonstrate not an E/A but an A/E (absorptive/emissive) CIDEP pattern. An A/E CIDEP pattern was observed under photolysis of AIBN and of HABI dimers (see Fig. 12.6). 

Palladium(O) compounds have a configuration and unlike most transition metals this oxidation state is dominated by phosphine complexes rather than carbonyls. In fact binary carbonyl complexes with palladium are unstable at room temperature. The highest coordination number known for Pd is four and [PdLj complexes adopt a square planar structure. Dissociation of ligands from [PdLJ occurs readily to generate the 16- and 14-electron species [PdLs] and [Pdl ] these are trigonal planar and linear respectively. Another notable feature of Pd° is that facile oxidation to cr Pd occurs. 

Positive modulation (protection) by substrate has been explained in terms of the stiffness of the enzyme structure that it promotes (Villaume et al. 1990). Negative modulation (destabilization) has also been reported for substrate (Illanes et al. 1998a) and other catalytic modulators (Alvaro et al. 1991). This behavior can be explained in terms of the promotion of quaternary structure dissociation (Misset 1993) and alteration of the oxidation stage in the active site of the enzyme (Bourdillon et al. 1985). 

Von Zelewsky and co-workers have produced silver hexanuclear circular helicates with high enantiomeric purity by incorporating chiral pinene moieties on the bis-bipyridine ligands. Matsumoto and co-workers have reported pH-dependent Cu circular helicate formation. The cyclic hexameric structure dissociates to monomeric units when the imidazole nitrogen is protonated. 

Associations of two or more protein molecules lead to the so-called quaternary structures. At infinite dilution and with suitable solvents, quaternary structures dissociate into subunits. The thermodynamic stability of quaternary structures is often so high that no noticeable dissociation... 

In the case of dense and regular crystalline lattice, the isotope transfer implies the exchange between neighboring oxygen atoms included into the crystalline lattice. In the defect-rich structure, dissociatively adsorbed oxygen can diffuse easily into the bulk via the defects and domain boundaries. The rate of oxygen diffusion is thus determined by the length and surface of boundaries and by the concentration of defects. 

Timofeeva, V.G. and Kozlov, P.V., Effect of the depth of supramolecular structure dissociating on vitrification temperatures of some cellulose ethers. In Cellulose and its Derivatives, Moscow AN SSSR Publ, 1963, pp. 167-173 (in Russian). 

What, then, is the biochemical reason for the inactivation of the CBP complex and the structural dissociation of the polypeptides The 24-CBP appears to remain in infected cells, able to recognize and bind to mRNA cap groups, but no detailed structural analyses of the protein from either uninfected or infected cells have been performed (see above). The 50,000-dalton subunit represents only a subset of the cell s eIF-4A population, and may contain a covalent modification, as evidenced by a small difference in tryptic peptide maps between the polypeptide isolated from the CBP complex and the majority of eIF-4A isolated independently (Fdery et al., 1983). Thus, although total cellular eIF-4A has been reported to be both structurally (Duncan et al., 1983) and functionally (Etchison et al., submitted) identical in poliovirus-infected HeLa cells compared with uninfected cells, the possibility still remains that virus infection affects the subset of elF-4A in the CBP complex. 

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