RESUMO
The crystallization of liquid crystal (LC) trimer-nanoparticle blends resulted in the formation of striped patterns in the crystals. The stripes were initially blurry but became sharper in the nematic LCs formed with heating. When the striped patterns began to collapse, many micron-scale colloidal particles were found out. Both the colloidal particles and stripes disappeared after an increase of 1.0-1.5 °C beyond the temperature at which the colloidal particles appeared. These results suggested that the stripes consisted of the colloidal particles. The distance between stripes depended on the shapes and sizes of the colloidal particles and the cooling rate during the crystallization. There were two melting peaks on the DSC chart of the LC trimer-nanoparticle blends. The two peaks corresponded to the melting of the LC trimers and the disappearance of the colloidal particles, respectively. On the basis of these data, we think that the colloidal particles are composed of hybrid structures in which LC trimers enclose the nanoparticles. The relationship between the striped patterns and the colloidal particles is discussed.
RESUMO
Aromatic stacking of 9,9'-(alpha,omega-alkanediyl)bis[adenine] (1), 1,1'-(alpha,omega-alkanediyl)bis[benzimidazole] (2), and 9-[omega-(benzimidazol-1-yl)alkyl]adenine (3) were studied at low concentrations of these compounds by means of UV and NMR spectroscopies. The UV hypochromic effect at T degrees C was determined as the ratio of the integration strength B at T degrees C (T = 27, 40, and 50) to that at 60 degrees C. The UV hypochromic effects of 1 and 3 were remarkable in water, suggesting a formation of intramolecular aromatic stacking, while the UV data of 2 did not present unambiguous evidence supporting aromatic stacking. A difference of chemical shift of each aromatic ring proton between 27 and 80 degrees C, that is Deltadelta = delta(80 degrees C) - delta(27 degrees C), was given as an indication of the aromatic stacking in the NMR study. On the basis the data of Deltadelta, 1 and 3 were stabilized by a stacking interaction in the buffer solution at pD 7.0 but not in the organic solvents. On the other hand, the NMR data did not indicate the formation of aromatic stacking of 2 either in the organic solvents or in the aqueous solution. The thermodynamic parameters of the intramolecular aromatic stacking of 3 were determined by means of NMR spectroscopy.
RESUMO
An intramolecular stacking between adenine and thymine rings of 9-[omega-(thymin-1-yl)alkyl]adenine was investigated by means of NMR and UV spectroscopy. The stacking conformation was presumed on the basis of the temperature dependence on the chemical shifts of the adenine and thymine ring protons in the buffer solution at pD 7.0.
