Molecular Recognition of Nucleic Acid Bases in Water by Hydrogen Bonding of Poly(vinyldiaminotriazine)

Poly(2-vinyl-4,6-diamino-1,3,5-triazine) efficiently binds nucleic acid bases and nucleosides in water by using complementary hydrogen bonding. The binding activity decreases in the order: U, T > A C, G. The corresponding monomer shows virtually no activity, indicating a predominant role of polymer effect for the molecular recognition in water.     

Towards advanced circuit board materials: adhesion of copper foil to ultra‐high molecular weight polyethylene composite

Polyethylene based composites are attractive materials for advanced circuit board applications because of their unique combination of properties: low dielectric constant and loss factor, light weight, high flexural modulus and low thermal expansion coefficient controlled in all spatial directions. This investigation describes a process to consolidate chopped fibers of ultra‐high molecular weight polyethylene concurrently with its bonding to a copper foil. Bonding is affected by a thin sheet of low‐density polyethylene, incorporating a crosslinking agent with a concentration gradient across the sheets thickness. In this single step process, the composite material is formed and bonded to the metal foil, achieving good adhesion without the use of extraneous glue. Copyright © 2002 John Wiley & Sons, Ltd.     

The crystal and molecular structures of 1,1′-divinyl-2,2′-biimidazolyl

The crystal and molecular structures of 1,1-divinyl-2,2-biimidazolyl (L) were determined by x-ray crystallographic analysis. It was established that the molecule of L has crystallographic symmetry 2 and a cisoid conformation with an angle of rotation of 128° between the imidazole rings. The length of the C²-C² bond is increased to 1.485(11) Å compared with the length of the analogous bond in unsubstituted 2,2-biimidazolyl (1.423 Å). Localization of the N=C multiple bond is observed [1.297(9) Å]. The other N-C bonds of the ring are almost equalized (1.374 Å) and are close to the standard values for bonds of the C _sp ²-N type in imidazoles. The angle between the plane of the heterocycle and the plane passing through the atoms of the vinyl group amounts to 7°.N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 117907 Moscow. Irkutsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 664033 Irkutsk. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1376–1380, June, 1992.     

Moment characterization of localized orbitals

The parallel between orbital first and second electric moments and statistical first and second central moments is noted. Three measures of orbital spatial distribution in terms of their moments are proposed, and applied to the LMO's in a series of ten-electron hydrides. Consistent differences between bond and lone pair distributions are found. Using the statistical interpretation, for each LMO an effective solid angle around the central atom is postulated.     

Cavitands bearing four fluorophores

The synthesis of novel cavitands containing four fluorophores [tert-butoxycarbonyl protected 2,2′-bis(furyl)benzidine (t-BOC FurylBz) or 5,5′-bis(4-aminophenyl)-2,2′-bifuryl (t-BOC PFDA)] and ionophoric functional groups on the upper rim is reported. The cavitands bearing the four fluorophores emit blue light photoluminescence. In particular, the cavitand containing PFDA moieties exhibits a high photoluminescence quantum yield.     

Molecular structure of potassium [N,N′-bis(salicylideneamino)nitroguanidonate-N,N′,-O,O′]nickel(ii), the product of condensation of (salicylideneamino)nitroguanidine with salicylaldehyde on a Ni2+ ion template

The crystal structure of the product of the condensation of (salicylideneamino)nitroguanidine with salicylaldehyde on a Ni²⁺ ion template, K[Ni(C₁₅H₁₀N₅O₄)] · DMF, has been studied. It was established that a planar Ni complex, consisting of isolated [NiL]^– anions and solvated [K⁺ · DMF] cations, is formed. The negative charge of the anion is localized mainly on the O atoms of the nitro group. The nitroguanidine fragment of the ligand occurs in the tautomeric form, which was not reported previously.Deceased in 1995Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2273–2277, September, 1996.     

Solvent effect on pyridine derivatives. Molecular iodine donor-acceptor equilibria. The isoquinoline-I2-organic solvent system and the 2,4-lutidine-I2-organic solvent system

The absorption spectra of isoquinoline-iodine or 2,4-lutidine-iodine solutions in organic solventsn-hexane,n-heptane, cyclohexane, carbon tetrachloride, benzene, toluene, chlorobenzene, ando-dichlorobenzene have been measured and interpreted in terms of the D+I₂=DI₂ equilibrium, where D is isoquinoline or 2,4-lutidine. Values ofK (288–320°K), ΔH^o, and ΔS^o for the reaction were calculated. A correlation between theK values and the solubility parameter of the solvent (Buchowski's relation) has been found.     

Symmetry or asymmetry in cheletropic additions forming cyclopropanes

Cheletropic additions forming cyclopropane rings were studied theoretically. Ten addition paths were traced by means of density-functional-theory calculations. Two 1,4-dienes, 1,4-pentadiene, and tricyclo[5.3.1.0^4,9]undeca-2,5-diene were adopted as substrates. CO, SO₂, C₂H₅PCl₂, CCl₂ and SiCl₂ were employed as cheletropic reagents (Xs). An orbital correlation diagram of the Woodward–Hoffmann (W–H) rule and frontier molecular orbital (FMO) interactions between them were investigated in detail. The FMO interactions, HOMO (1,4-diene)lumo (X) and homo (X)LUMO (diene), work reasonably for the progress of the reactions. Those cause the formation of two C–X bonds and a cyclopropane ring, and alternation of double bonds to single bonds. All the additions are concerted. The easiness of the ring formation depends upon the energy gap between HOMO and lumo and that between homo and LUMO, and the spatial directions of HOMO and LUMO extensions. Symmetry conservation of the W–H rule does not hold necessarily for those addition paths. The symmetry-breaking was discussed in terms of FMO interactions.Acknowledgement This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, Japan and by Nishida Memorial Foundation for Fundamental Chemical Research.     

The effect of the counterion composition on the chain restriction in the cationic polymerization of isobutylene

The effects of the nature of halogens in the initiatingtert-butyl halide-aluminum-containing Lewis acid system on the number average molecular weightM _n and the structure of end groups of polyisobutylene macromolecules obtained in the cationic polymerization of isobutylene in hexane at -78 °C were studied. An increase inM _n is observed in the transition from chlorine to bromine and iodine, accompanied by a decrease in the fraction of end C=C groups and an increase in the relative content of C-Hal groups (Hal = Cl, Br, and I). When atoms of different halogens are present in the counterion, more bulky atoms preferentially participate in the formation of the end groups. The results are interpreted within the framework of the principle of hard and soft acids and bases.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1184–1187, May, 1996.     

MENTHOR,a database system for the storage and retrieval of three-dimensional molecular structures and associated data searchable by substructural,biologic, physical,or geometric properties

Summary MENTHOR is a database system for the storage and retrieval of three-dimensional coordinate and charge information on molecules as well as of traditional biological and physical properties. Our molecular graphics system retrieves from MENTHOR structural information in individual molecules and receptor map/macromolecular binding site hypotheses. Substructural searches of MENTHOR are used to find starting coordinates for molecular modeling and traditional database searches of MENTHOR identify compounds for which modeling is needed. It also forms the data to be searched with ALLADDIN, our substructure/geometric search program. MENTHOR expedites molecular modeling by organizing previous work and facilitating transmission of information between individuals. Examples from modeling of D-2 receptor agonists are shown.