Search

The conformational behaviour of poly( l -tyrosine) has been studied in dimethylsulphoxide/water and dimethylsulphoxide/trimethylphosphate solvent systems. The evidence provided by nuclear magnetic resonance and infrared spectroscopy shows that the conformation of the polymer in dimethylsulphoxide is most probably the random coil. Addition of 20% D 2 O or 50% trimethylphosphate to the dimethylsulphoxide/poly( l -tyrosine) solution results in a conformational transition of the polymer which can be followed by both infra-red and nuclear magnetic resonance spectroscopy and changes in optical rotation. The evidence supports the conclusion that this transition is to a largely, though not fully, right-handed α-helical conformation.

A study has been made of the reversible solid state transitions in a series of eleven zinc(II) di-n-alkylphosphinate polymers, [Zn(R2PO2)2]n, with R from C4 to C18, by means of differential scanning calorimetry and x-ray analysis. Wide line n.m.r. measurements have been also made for some compounds. The existence of two crystal forms, denoted α and β, has been established for the compounds examined. The results indicate that the α→β polymorphic transition is associated with disordering of the hydrocatbon side chains.

The results of an investigation on the interaction of proflavine and of ethidium bromide with DNA (calf thymus) in dilute aqueous solution are reported. The binding of the two dyes by DNA has been studied by means of microcalorimetric and of equilibrium dialysis measurements. Data on the thermodynamics of dimerization of both proflavine and ethidium bromide in aqueous solution obtained on the basis of spectroscopic and/or calorimetric experiments are also reported. The enthalpy data show that dye-dimerization and dye "strong" interaction with DNA are energetically favourable and quite similar while only in the latter case the phenomenon is also entropy driven. This is taken as further evidence in support of the concept that "strong" interaction-of both proflavine and ethidium bromide with DNA means dye molecules intercalation into the native, double helical structure of the biopolymer.

Résumé. — Dans cet article nous avons essayé de présenter les éléments essentiels de la culture de Cris de Roumanie, qui constitue le Néolithique le plus ancien du Bas-Danube. Les thèses principales soutenues dans l'article sont au nombre de quatre. 1) Le synchronisme de Starcevo (en Yougoslavie), Koros (en Hongrie) de la Céramique Linéaire (en Tchécoslovaquie), ainsi que de Karanovo I et Kremicovci en Bulgarie avec Cris. 2) Le refus d'une division des cultures de Starcevo et de Cris en quatre phases. 3) Le développement indépendant de toutes les cultures du Néolithique ancien de Roumanie, sans relations notables avec le Proche-Orient et la Méditerranée Occidentale. 4) Le postulat d'une continuité Cris-Vinca-Turdas et Petresti., Giancotti-Tassone Vicente. Observations sur quelques aspects de la culture de Cris du Néolithique ancien de la Roumanie. In: Bulletin de la Société préhistorique française. Études et travaux, tome 67, n°1, 1970. pp. 323-334.

The mixed-ligand species Zn[(R12PO2)2 – 2x(R22PO2)2x](R1= Bun; R2= n-C6H13 or n-C10H21) are linear coordination copolymers with a random distribution of two different bridging phosphinate groups along the molecular chains. Single crystals of the copolymer {Zn[Bun2PO2(n-C6H13)2PO2]}n are disordered. A three-dimensional X-ray analysis has been attempted. The crystals contain chains characterised by a backbone structure with alternate single and triple bridging phosphinate groups between tetrahedral metal atoms. The structural features common to those of the β-form of zinc(II) di-n-butylphosphinate polymer are discussed.

The characterisation of beryllium phosphinates of stoicheiometry Be(Bun2PO2)2, Be(Ph2PO2)2, and of some mixed-ligand species Be[(Bun2PO2)2 – 2x(Ph2PO2)2x] is reported. The compounds richer in alkyl groups give stable solutions in hydrocarbon and halogenated solvents. Solution properties indicate that these compounds are linear polymers which undergo a reversible degradation influenced by the nature of the solvent, concentration, and temperature. The mixed-ligand species can be crystallised and are formulated as random copolymers. Isomorphous replacement of the two kinds of phosphinate groups within the crystal lattice of the related homopolymers is observed. The X-ray diffraction fibre photographs indicate that the homopolymer [Be(Bun2PO2)2]n and the copolymers {Be[(Ben2PO2)2 – 2x(Ph2PO2)2x]}n(x= 0·20 or 0·33) have a backbone structure with alternate single and triple bridging phosphinate groups between tetrahedral metal atoms. The same chain-type structure is proposed for the homopolymer [Be(Ph2PO2)2]n and the copolymers richer in diphenylphosphinate groups.

A study has been made of the iso- and poly-morphism phenomena in a series of mixed-ligand species, {M[(Bun2PO2)2 – 2x(Ph2PO2)2x]}n(M = ZnII or CoII), by means of differential scanning calorimetry and X-ray analysis. These compounds are linear copolymers and the di-n-butylphosphinate and diphenylphosphinate groups are randomly distributed along the molecular chains. The homopolymer, [Zn(BunPhPO2)2]n, has been studied as a model system with a disordered positioning of the n-butylphenylphosphinate groups along the molecular chains. This compound exhibits polymorphism and its γ-form is isomorphous with that of [Zn(Ph2PO2)2]n.The zinc(II) mixed-ligand species are crystalline and isomorphous with the blue cobalt(II) compounds. Their solubility in non-co-ordinating solvents decreases with increasing the content of Ph2PO2– groups. Isomorphous substitution of some Ph2PO2– groups with Bun2PO2– groups in the crystal lattice of the [Zn(Ph2PO2)2]n homopolymer or of some Bun2PO2– groups with Ph2PO2– groups in the crystal lattice of the [Zn(Bun2PO2)2]n homopolymer takes place. On the basis of the structures of the crystalline form of [Zn(Bun2PO2)2]n, stable at room temperature, and of the γ-form of [Zn(BunPhPO2)2]n, the solid-state transitions and the isomorphism and polymorphism phenomena of the various co-ordination polymers are discussed.