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.

Synthesis and Structural Properties of Aza[n]helicene Platinum Complexes: Control of Cis and Trans Stereochemistry.

The synthesis and structural characterization of azahelicene platinum complexes obtained from cis-PtCl2(NCEt)(PPh3) and from ligands that differ in terms of both the position of the nitrogen atom and the number of fused rings are reported. These square-planar complexes of the general formula PtCl2(nHm)(PPh3) (n = 4, 5; m = 5, 6) display mainly a cis configuration. However, by X-ray crystallographic analysis, we show that for both PtCl2(4H6)(PPh3) and PtCl2(5H6)(PPh3) there is chirality control of the cis/trans stereochemistry.

A Combined Experimental and Theoretical Study on the Stereodynamics of Monoaza[5]helicenes: Solvent-Induced Increase of the Enantiomerization Barrier in 1-Aza-[5]helicene.

Helicenes and heterohelicenes are attractive compounds with great potential in materials sciences to be used in optoelectronics as ligand backbones in enantioselective catalysis and as chiral sensors. The properties of these materials are related to the stereodynamics of these helical chiral compounds. However, little is known about features controlling stereodynamics in helicenes; in particular, for heterohelicenes the position of the heteroatom could be relevant in this respect.

Aza[6]helicene platinum complexes: chirality control of cis-trans isomerism.

It was serendipitously observed that cis-[PtCl2(NCEt)PPh3] reacted differently with either racemic or enantiopure 4-aza[6]helicene, giving respectively cis (racemic) and trans (enantiopure) [Pt(II)Cl2(4-aza[6]helicene)PPh3] complexes. This unexpected reactivity is explained through a dynamic process (crystallization-induced diastereoselective transformation) and enables a new aspect of reactivity in chiral transition-metal complexes to be addressed.

Quantum mechanics calculations, basicity and crystal structure: the route to transition metal complexes of azahelicenes.

Quantum mechanics density functional calculations provided gas-phase electron distributions and proton affinities for several mono- and diaza[5]helicenes; computational results, together with experimental data concerning crystal structures and propensity to methylation of the nitrogen atom(s), provide a basis for designing azahelicene complexes with transition metal ions.

Photophysical properties of N-alkylated azahelicene derivatives as DNA intercalators: counterion effects.

In this work, three compounds having the same organic moiety (N-methyl-5-azahelicenium salts) but different counterions (I-, NO3- and COOCF3-) have been investigated in buffered aqueous solutions and in the presence of DNA to give information on the counterion effects on the binding. In particular, the absorption spectra, fluorescence quantum yields and fluorescence lifetimes in aqueous solution for free organic molecules have been determined by steady-state and time-resolved spectrofluorimetric measurements. The obtained values are compared with those of the chromophores in the presence of increasing concentrations of DNA.

Experimental and calculated vibrational and electronic circular dichroism spectra of 2-Br-hexahelicene.

The vibrational circular dichroism (VCD) and IR absorption spectra of the (-)-enantiomer of 2-Br-hexahelicene have been measured and interpreted by use of density functional theory (DFT) calculations. From time dependent DFT calculations we also interpret the electronic circular dichroism (ECD) spectra of 2-Br-hexahelicene. We compare the calculated IR, VCD and ECD spectra to the corresponding calculated data of hexahelicene and 2-aza-hexahelicene; for the last compound we also recorded the ECD spectra.

Oxidation of aromatic alcohols in irradiated aqueous suspensions of commercial and home-prepared rutile TiO(2): a selectivity study.

The photocatalytic oxidation of benzyl alcohol (BA) and 4-methoxybenzyl alcohol (MBA) has been performed in pure water by using commercial TiO(2) samples (Sigma-Aldrich, Merck, Degussa P25) and rutile TiO(2) prepared from TiCl(4) at low temperature. Particular attention has been devoted to the identification of the produced aromatic compounds along with the formed CO(2). Oxidation products such as the corresponding aromatic aldehyde and acid, as well as mono- and dihydroxylated aldehydes have been detected.

Intersystem crossing processes in nonplanar aromatic heterocyclic molecules.

A comprehensive study of the photophysical properties of a series of monoaza[5]helicenes is presented on the basis of joint optical spectroscopy and quantum chemistry investigations. The molecules have been characterized by absorption and CW/time-resolved luminescence measurements. All quantities related to spin-orbit-coupling processes, such as intersystem crossing rates and radiative phosphorescence lifetimes, were found to depend strongly on the nitrogen position within the carbon backbone.

Study of confined 5-aza[5]helicene in ytterbium(III) bis(2-ethylhexyl) sulfosuccinate reversed micelles.

Some relevant physicochemical properties of 5-aza[5]helicene (H5) in solutions of ytterbium bis(2-ethylhexyl) sulfosuccinate (Yb(DEHSS)3) reversed micelles have been investigated by UV-vis-NIR, photoluminescence, and FT-IR techniques with the aim of emphasizing the role played by specific Yb(III)/H5 interactions and confinement effects as driving forces of its binding to reversed micelles, preferential solubilization site, and local photophysical properties. It has been found that the binding strength of 5-aza[5]helicene to reversed micelles, triggered by steric and orientational constrains as well as the water content, is mainly regulated by its interaction with the Yb(III) counterion. Moreover, when H5 is entrapped in Yb(DEHSS)3 reversed micelles, the combined action of this interaction and of confinement effects leads to marked changes of its photophysical properties with respect to those of H5 molecularly dispersed in apolar medium.

Excited-state properties and emission spectra of nonplanar heterocyclic helicenes.

We discuss the electron-vibration coupling in mono-aza-[5]helicenes on the basis of a Franck-Condon analysis and density functional theory (DFT) calculations of the fluorescence and phosphorescence spectra measured in ethanol. The geometries of the initial states were obtained from time-dependent DFT (S(1)) and unrestricted DFT (T(1)) excited-state optimizations. In general, the position of the nitrogen atom has only a minor impact on the vibronic fine-structure in both absorption and emission.

Influence of the substituent on selective photocatalytic oxidation of aromatic compounds in aqueous TiO2 suspensions.

Experimental results are reported showing that the photocatalytic oxidation of aromatic compounds containing an electron-donor group (EDG) gives rise mainly to ortho- and para-monohydroxy derivatives while in the presence of an electron-withdrawing group (EWG) all the monohydroxy derivatives are obtained.

Halogen bonding and pi...pi stacking control reactivity in the solid state.

The halogen bonding and the pi...