Asunto(s)

Citoesqueleto/metabolismo , Folículo Piloso/metabolismo , Queratinas Específicas del Pelo/genética , Pueblo Asiatico/genética , Población Negra/genética , Citoesqueleto/genética , Variación Genética , Células HEK293 , Folículo Piloso/citología , Humanos , Queratinas Específicas del Pelo/metabolismo , Mapas de Interacción de Proteínas , Población Blanca/genética

RESUMEN

This communication describes the base- and acid-induced five-state translational isomerization of a [3]rotaxane containing two pairs of N-arylamine and N-alkylamine centers as binding sites for two dibenzo[24]crown-8 components. Gradual molecular shuttling of this [3]rotaxane is achieved in response to both the amount and strength of the added acid or base.

RESUMEN

Formation dynamics of intramolecular excimer in dioxa[3.3](3,6)carbazolophane (CzOCz) was studied by time-resolved spectroscopic methods and computational calculations. In the ground state, the most stable conformer in CzOCz is the anti-conformation where two carbazole rings are in antiparallel alignment. No other isomers were observed even after the solution was heated up to 150 °C, although three characteristic isomers were found by the molecular mechanics calculation: the first is the anti-conformer, the second is the syn-conformer where two carbazole rings are stacked in the same direction, and the third is the int-conformer where two carbazole rings are aligned in an edge-to-face geometry. Because of the anti-conformation, the interchromophoric interaction in CzOCz is negligible in the ground state. Nonetheless, the intramolecular excimer in CzOCz was dynamically formed in an acetonitrile (MeCN) solution, indicating strong interchromophoric interaction and the isomerization from the anti- to syn-conformation in the excited state. The excimer formation in CzOCz is more efficient in polar solvents than in less polar solvents, suggesting the contribution of the charge transfer (CT) state to the excimer formation. The stabilization in the excited state is discussed in terms of molecular orbital interaction between two carbazole rings. The solvent-polarity-induced excimer formation is discussed in terms of the CT character in the int-conformation.

RESUMEN

In this study, we investigated the effect of pressure on the formation and decomplexation of [2]pseudorotaxanes. High pressure accelerated the formation of [2]pseudorotaxanes in an aprotic nonpolar solvent (CDCl(3)/CD(3)CN) via the slipping approach when using two crown ether/secondary ammonium salt systems: dibenzo[24]crown-8/bis(cyclohexylmethyl)ammonium salt (1a/2a) and tetrabenzo[24]crown-8/dibenzylammonium salt (1b/2b). The influence of pressure on the rate constants for the formation of the [2]pseudorotaxanes 3a and 3b revealed activation volumes (DeltaV(double dagger)) of -2.5 and -4.6 cm(3) mol(-1), respectively, at 303 K and zero pressure. We also investigated the effect of pressure on the decomplexation of the [2]pseudorotaxanes 3a and 3b in a polar solvent (DMSO-d(6)/CDCl(3)), obtaining activation volumes of -0.9 and -0.4 cm(3) mol(-1), respectively, at 303 K and zero pressure. Moreover, we calculated the activation parameters for the decomplexation processes on the basis of transition state theory at each pressure.

RESUMEN

We have synthesized two [2]rotaxanes, each possessing a (Z)-alpha-methylstilbene unit as one of its stoppers, in good yield through the photoisomerization of terminal (E)-alpha-methylstilbene units of dialkylammonium salts in the presence of the crown ether dibenzo[24]crown-8 (DB24C8). The synthesis relies on the formation of pseudorotaxane intermediates through hydrogen bond-guided self-assembly and subsequent end-closing photoisomerization. An (E)-alpha-methylstilbene unit is not sufficiently bulky to prevent dissociation of the DB24C8 unit, whereas a (Z)-alpha-methylstilbene unit acts as a true stopper. We also synthesized these [2]rotaxanes from the (Z)-alpha-methylstilbene-terminated axle-like salts though thermodynamic covalent chemistry by taking advantage of the reversibility of the photoisomerization. To dissociate the components of the [2]rotaxanes, we performed the reverse end-opening process under UV irradiation (i.e., Z-to-E isomerization of the alpha-methylstilbene termini) in a polar solvent. These rotaxanes are stable at room temperature, but dissociate slowly to their two components at elevated temperatures.

Asunto(s)

Rotaxanos/síntesis química , Enlace de Hidrógeno , Isomerismo , Fenómenos Químicos Orgánicos , Procesos Fotoquímicos , Rotaxanos/química , Solventes , Estilbenos/química

RESUMEN

A [2]rotaxane, having (Z)-alpha-methylstilbene as a stopper, is (1) synthesized in good yield by using a (E)- to (Z)-stilbene photoisomerization process, and (2) dissociated by reverse photoisomerization from (Z)- to (E)-stilbene.