Adsorption of Chiral [5]-Aza[5]helicenes on DNA Can Modify Its Hydrophilicity and Affect Its Chiral Architecture: A Molecular Dynamics Study

Helicenes are interesting chiral molecules without asymmetric carbon atoms but with intrinsic chirality. Functionalized 5-Aza[5]helicenes can form non-covalent complexes with anticancer drugs and therefore be potential carriers. The paper highlights the different structural selectivity for DNA binding for two enantiopure compounds and the influence of concentration on their adsorption and self-aggregation process. In this theoretical study based on atomistic molecular dynamics simulations the interaction between (M)- and (P)-5-Aza[5]helicenes with double helix B-DNA is investigated. At first the interaction of single pure enantiomer with DNA is studied, in order to find the preferred site of interaction at the major or minor groove. Afterwards, the interaction of the enantiomers at different concentrations was investigated considering both competitive adsorption on DNA and possible helicenes self-aggregation. Therefore, racemic mixtures were studied. The helicenes studied are able to bind DNA modulating or locally modifying its hydrophilic surface into hydrophobic after adsorption of the first helicene layer partially covering the negative charge of DNA at high concentration. The (P)-enantiomer shows a preferential binding affinity of DNA helical structure even during competitive adsorption in the racemic mixtures. These DNA/helicenes non-covalent complexes exhibit a more hydrophobic exposed surface and after self-aggregation a partially hidden DNA chiral architecture to the biological environment

Sintesi e proprietà di aza-[5]-eliceni.

Sono stati sintetizzati e caratterizzati alcuni nuovi mono- e diaza-[5]-eliceni, ne sono state studiate la struttura cristallina e le proprietà di fotoluminescenza, sono stati separati e studiati gli enantiomer

Sintesi e caratterizzazione spettroscopica di alcuni aza-[5]-eliceni

Sono state sintetizzate nove molecole della classe degli azaeliceni, delle quali sono state studiate le proprietà ottiche, spettroscopiche e cristallografiche

Nucleophilic character of acyl radicals. Absolute rate constant for the acylation of protonated benzothiazole by pivaloyl radical

The absolute rate constant for the addition of pivaloyl radical to protonated benzothiazole is determined by evaluating the ratio of decarbonylation and aromatic attack. The high rate constant (7.1 × 105 l mol–1 s–1 at 5 °C) is discussed in terms of polar effects and a divergence from the classical reactivity: selectivity relationship is suggested

Nucleophilic character of alkyl radicals-XIII. Absolute rate constants for the addition of alkyl radicals to acrylonitrile and methyl acrylate

The absolute rate constants for the addition of alkyl radicals to acrylonitrile and methyl acrylate are determined by evaluating the ratio of ligand-transfer oxidation and addition to the double bond. Secondary alkyl radi c combining short stroke overlayals appear to be more reactive than primary alkyl radicals, despite the less favourable energetics. The classical selectivity : reactivity relationship is reversed owing to the nucleophilic character of the alkyl radicals. © 1977