Two-photon excitation of rhenium metal-ligand complexes

We describe the emission spectral properties of two rhenium metal-ligand complexes with one and two-photon excitation, Re(bpy)2(CO)3Cl and [Re(bpy)(CO)3CH3CN]+, where bpy is 2,2’-bipyridyl and CH3CN is acetonitrile. Similar emission spectra and intensity decay times characteristic of the metal-to-ligand charge transfer state were observed for one- and two-photon excitation. The lifetime and quantum yield of the acetonitrile complex are approximately 14-fold higher than that of the chloride complex. Both complexes display high anisotropies near 0.33 in frozen solution with one-photon excitation. Two-photon excitation results in anisotropies about 40% larger, consistent with the increased photoselection expected for two-photon absorption. These complexes display single rotational correlation times in glycerol, but the correlation time of the charged acetonitrile complex is 3 to 4-fold larger. These results show that rhenium complexes can be used as hydrodynamic probes with one- or two-photon excitation

Observation of erythrocyte dynamics in the retinal capillaries and choriocapillaris using ICG-loaded erythrocyte ghost cells.

Purpose To find evidence of retinal vasomotion and to examine the relationship between erythrocyte dynamics and previously observed high-frequency pulsatile blood flow through the choriocapillaris. Methods An osmotic shock technique was used to encapsulate indocyanine green (ICG) dye in erythrocyte ghost cells at a concentration that produced maximum cell fluorescence. By obviating the plasma staining that results from aqueous ICG's high affinity for plasma proteins, high contrast was maintained between reinjected ICG-loaded erythrocytes and their plasma background. High-speed, high-magnification ICG angiograms showing individual cell movement were recorded from the intact eyes of four monkeys and three rabbits for periods up to 30 seconds. Results In monkey retinal perifoveal capillaries, numerous erythrocytes were seen to pause for as long as 20 seconds and then resume transit. Similar pausing behavior was observed in the subfoveal choriocapillaris. Individual erythrocytes also were seen to pause in the rabbits' choriocapillaries below the medullary rays, where visualization of the cells was uninhibited by overlying retinal vasculature or dense pigment. Conclusions Reinjected ICG-loaded erythrocytes permit routine visualization of retinal capillary and choriocapillaris hemodynamics of the intact eye. It is speculated that erythrocyte-pausing in both microcirculations facilitates metabolic exchange across capillary walls. In retinal capillaries, pausing is presumed to result from vasomotion-which has been postulated as necessary for the inhibition of retinal edema-and in choriocapillaries, to result from the shifting distributions of local perfusion pressures within the network of capillary vessel segments that comprise each lobular area of the choriocapillaris vascular plexus

Time-resolved and Temperature-dependent Broadband Emission of Plasmon-coupled Quantum Dots

The broadband photoluminescence (PL) emissions from CdSe QDs and plasmon-coupled QDs were characterized with time-resolved and temperature-dependent spectroscopy for the application of solid-state white light. The origin of broad spectral emission includes the transitions from bandedge and surface-trapped states. The emission intensity enhancement of plasmon-coupled QDs with respect to that of bare QDs is attributable to the reduction of nonradiative decay and the local field enhancement with plasmon-exciton coupling through the Coulomb interaction. The temperature-dependent and time-resolved PL spectroscopy revealed the existence of selective contribution strength of both the local field enhancement and the reduction of nonradiative decay with plasmon-exciton coupling at different spectral regions

A triazine-based BODIPY trimer as a molecular viscometer

Photophysical behaviour of a novel trimeric BODIPY rotor with a high extinction coefficient is reported. Steady state and time resolved fluorescence measurements established that the trimer could be used as a viscometer for molecular solvents, membrane-like environments and several cancer cell lines

Extraction of Stevioside from Stevia Rebaudiana Leaves Using Cellulase

Stevioside is a diterpene glycoside present in Stevia Rebaudiana leaves that has the ability to sweeten at rated between 70 to 350 times than sucrose (0.4% w/v). It has no calorific value. Unlike many low calorie sweeteners, stevioside is stable at high temperature. The objective of this research is to extract stevioside from stevia rebaudiana leaves by using cellulase from Aspergillus Niger. Acetate buffer and ethanol were used as a medium for enzyme and as a solvent, respectively. In this present study, the enzymatic extraction of stevioside from stevia rebaudiana leaves was carried out using cellulase with various parameters that affect the production of stevioside such as concentration of enzyme, incubation time and temperature. Cellulase was observed to give the highest stevioside yield (16230 ± 0.3 μg/ml) at 40oC. This indicated that the maximum temperature for cellulase activity was 40oC. The results signify that the enzymatic extraction method is an alternative to solvent based stevioside extraction, based on its higher efficiency. Thus, it can be concluded that the extraction of stevioside from Stevia rebaudiana leaves using cellulase can be maximized under the maximum conditions for the cellulase activity where the used of solvent can be minimized in degrading the cell wall Together with the maximum heat and correct combination of the solvent used, a new and efficient way of extracting high yield of stevioside can be obtained