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1.
Chemistry ; 19(22): 7173-80, 2013 May 27.
Artigo em Inglês | MEDLINE | ID: mdl-23576271

RESUMO

The interaction of a series of chiral cationic [4]helicene derivatives, which differ by their substituents, with double-stranded DNA has been investigated by using a combination of spectroscopic techniques, including time-resolved fluorescence, fluorescence anisotropy, and linear dichroism. Addition of DNA to helicene solutions results to a hypochromic shift of the visible absorption bands, an increase of fluorescence quantum yield and lifetime, a slowing down of fluorescence anisotropy decay, and a linear dichroism in flow-oriented DNA, which unambiguously points to the binding of these dyes to DNA. Both helicene monomers and dimeric aggregates, which form at higher concentration, bind to DNA, the former most probably upon intercalation and the latter upon groove binding. The binding constant depends substantially on the dye substituents and is, in all cases, larger with the M than the P enantiomer, by factors ranging from 1.2 to 2.3, depending on the dye.


Assuntos
DNA/química , Corantes Fluorescentes/química , Dicroísmo Circular , Fluorescência , Polarização de Fluorescência , Substâncias Intercalantes/química , Estrutura Molecular , Análise Espectral , Estereoisomerismo
2.
Chirality ; 24(11): 928-35, 2012 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-22566063

RESUMO

1,13-Dimethoxyquinacridinium ions of type 3 are highly configurationally stable [4]helicenes that can be synthesized in racemic form in a single step from tris(2,6-dimethoxyphenyl)methylium ion. Previously, it had been shown that the single enantiomers can be routinely obtained from racemic mixtures through Pummerer fragmentations of diastereomerically pure sulfoxide adducts that release the enantiopure cations after a C-C bond rupture. This resolution protocol is readily performed because of a (normally) large retention difference of the diastereomers over silica gel. Herein, we report that it is not always the case. Introduction of N-methyl side chain(s) at the periphery of the helical quinacridinium cations, which are needed for photophysical and biological studies, has a large negative effect of this separation. Instead of simple, rapid, and multigram separations by flash chromatography, extensive semi-preparative high-performance liquid chromatography sequences are now required.

3.
Dalton Trans ; 41(22): 6777-82, 2012 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-22523756

RESUMO

A new tripodal ligand has been designed by coupling pyridyldicarbonyl binding strands with a triazatriangulenium platform (TATA). The complexation reaction with europium provides a C(3)-symmetrical mononuclear compound that is characterized with NMR, ESMS and qualitatively with single-crystal X-ray crystallography. In addition, photophysical studies of this dual emissive system have been performed, since the combination of the TATA fluorophore with trivalent lanthanides is of potential interest for the further development of imaging applications.


Assuntos
Acridinas/química , Corantes/química , Európio/química , Compostos Heterocíclicos de 4 ou mais Anéis/química , Compostos Organometálicos/química , Cristalografia por Raios X , Medições Luminescentes , Modelos Moleculares , Conformação Molecular , Compostos Organometálicos/síntese química , Espectrofotometria
4.
Photochem Photobiol Sci ; 11(4): 623-31, 2012 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-22246477

RESUMO

The photophysical properties of a series of helicene cations in various solvents have been investigated using stationary and time-resolved spectroscopy. These compounds fluoresce in the near infrared region with a quantum yield ranging between 2 and 20% and a lifetime between 1 and 12 ns, depending of the solvent. No clear solvent dependence could be recognized except for a decrease of fluorescence quantum yield and lifetime with increasing hydrogen-bond donating ability of the solvent. In water, the helicene cations undergo aggregation. This effect manifests itself by the presence of a slow fluorescence decay component, whose amplitude increases with dye concentration, and by a much slower decay of the polarization anisotropy in water compared to an organic solvent of similar viscosity. However, aggregation has essentially no effect on the stationary fluorescence spectrum, whereas relatively small changes can be seen in the absorption spectrum. Analysis of the dependence of aggregation on the dye concentration reveals that the aggregates are mostly dimers and that the aggregation constant is substantially larger for hetero- than homochiral dimers.


Assuntos
Compostos Policíclicos/química , Cátions/química , Ligação de Hidrogênio , Teoria Quântica , Solventes/química , Espectrometria de Fluorescência , Estereoisomerismo
5.
J Org Chem ; 76(8): 2716-22, 2011 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-21417308

RESUMO

Using a two-step reduction/metalation procedure, highly stable chiral carbenium ions are transformed into reactive carbanion intermediates. Interesting polar ketone and thioamide products are the results of this umpolung that occurs with complete retention of configuration of the helical backbone.

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