RESUMO
The absorption spectra of all-trans-beta-carotene in n-hexane and carbon disulfide (CS(2)) solutions are measured under high pressure at ambient temperature. The common redshift and broadening in the spectra are observed. Simulation of the absorption spectra was performed by using the time-domain formula of the stochastic model. The pressure dependence of the 0-0 band wavenumber is in agreement with the Bayliss theory at pressure higher than 0.2 GPa. The deviation of the linearity at lower pressure is ascribed to the reorientation of the solvent molecules. Both the redshift and broadening are stronger in CS(2) than that in n-hexane because of the more sensitive pressure dependence of dispersive interactions in CS(2) solution. The effect of pressure on the transition moment is explained with the aid of a simple model involving the relative dimension, location, and orientation of the solute and solvent molecules. The implication of these results for light-harvesting functions of carotenoids in photosynthesis is also discussed.
Assuntos
Dissulfeto de Carbono/química , Hexanos/química , beta Caroteno/química , Luz , Complexos de Proteínas Captadores de Luz/química , Fotossíntese , Pressão , Soluções/química , Solventes/química , Espectrofotometria Ultravioleta/métodos , Estereoisomerismo , TemperaturaRESUMO
Comparative studies of the properties of murine haemopoietic stem cells from different sources revealed that the peripheral haemopoietic stem cell is relatively weaker than the haemopoietic stem cell from bone marrow in promoting the recovery of hemopoiesis in the irradiated animals. This is due to the heterogenity of stem cell population in which some aged cellsubpopulations are co-existing. The modified potential in proliferation and differentiation of haemopoietic stem cells in the peripheral blood seems to be irreversible under normal physiological conditions. In a preliminary experiment, the use of an anti-thymocyte immunoglobulin to eliminate immunocompetent cells proved effective in reducing the severity and incidence of secondary diseases and in increasing the number of survivors of lethally irradiated semi-isologous mice after transplantation of parental peripheral mononuclear cells.