RESUMO
The NaCaGaSi2O7:Ce3+ãNaCaGaSi2O7:Tb3+ and NaCaGaSi2O7:Ce3+/Tb3+ phosphors were synthesized under a weak reducing atmosphere by the traditional high temperature solid state reaction method. The synthesized phosphors were characterized by X-ray diffraction (XRD), fluorescent decay times, photoluminescence (PL) emission and excitation spectra including temperature-dependent PL properties. The effects of Ce3+ singly doped and Ce3+/Tb3+ co-doped concentrations on the structure, luminescence properties and energy transfer of NaCaGaSi2O7 phosphors were studied in detail. The results indicated that the energy transfers between Ce3+ and Tb3+ in the host occurred mainly via a dipole-dipole mechanism, and the critical distances of the ion pairs (Rc) were calculated by the quenching concentration method and spectral overlap method. The Ce3+ emission intensity and decay lifetimes decrease with the raise of Tb3+ concentration in NaCaGaSi2O7:Ce3+/Tb3+ samples. The above results indicate that NaCaGaSi2O7:Ce3+/Tb3+ can be a candidate as a host material for solid-state lighting and display fields.
RESUMO
Extracellular adenosine triphosphate (ATP) functions as a signaling molecule in many cell regulation processes. The traditional firefly luciferase assays measure the ATP release as a signal increase with time using a luminometer. Recently, advanced cell imaging techniques using charge-coupled device (CCD) cameras have enabled two-dimensional (2D) high-resolution detection providing both spatial and temporal information. Real-time imaging of ATP release from astrocyte cells has been reported. However, the observed chemiluminescence propagation wave reflects both ATP release and diffusion in the extracellular bulk solution. The dynamic ATP efflux at the cell surface could not be accurately measured. Hence, we constructed biotinylated fused firefly luciferase proteins, immobilized the proteins on 1 microm beads, and attached the beads to the cell surface to detect ATP release from mechanically stimulated astrocyte cells. This novel detection method enables us to monitor the actual ATP concentration at the surface of single live cells. The localized ATP release was found to be prominent but lasted only <20 s, which is very different from the results obtained by free firefly luciferase detection.
Assuntos
Trifosfato de Adenosina/análise , Astrócitos/metabolismo , Vaga-Lumes/química , Proteínas de Insetos/química , Luciferases de Vaga-Lume/química , Medições Luminescentes/métodos , Microesferas , Trifosfato de Adenosina/metabolismo , Animais , Astrócitos/química , Biotinilação , Carcinoma Hepatocelular/metabolismo , Permeabilidade da Membrana Celular , Escherichia coli/genética , Proteínas Imobilizadas/química , Proteínas Imobilizadas/genética , Proteínas Imobilizadas/isolamento & purificação , Proteínas de Insetos/genética , Proteínas de Insetos/isolamento & purificação , Fígado/citologia , Neoplasias Hepáticas/metabolismo , Luciferases de Vaga-Lume/genética , Luciferases de Vaga-Lume/isolamento & purificação , Pressão Osmótica , RatosRESUMO
In order to gain an insight into the mechanism of membrane insertion of the pore-forming protein colicin E(1) and the structure of its membrane-bound form, circular dichroism, fluorescence spectroscopy experiments were carried out. The results revealed the law of conformational changes by lipid membrane induction of the colicin E(1) molecule, and suggest that the lipid membranes with negative charges have a strong inducing action on colicin E(1) molecules. With the induction of membrane, the colicin E(1) molecules in different conformational states can all be recovered to the conformation of membrane insertion in native state. The induction intensity of different kinds of lipids on colicin E(1) was in the following order: DMPG>DMPE>DMPC. The binding of colicin E(1) with lipid vesicles was tight and the membrane-bound proteins were resistant to denaturation.
