Control of plasmon resonance of gold nanoparticles via excimer laser irradiation

A significant shift of the surface plasmon resonance absorption spectrum of gold nanoparticles was obtained by the oxidation of the nanoparticle surface via pulsed excimer laser irradiation. The high UV-light absorption of gold nanoparticles chemically produced by citrate reduction led to the important surface oxidation up to 26%. As a result of laser irradiation, the gold/gold oxide core-shell nanoparticles with little variation of the nanoparticle size were produced. After only 5 min of laser irradiation, a 12-nm blue shift in surface plasmon resonance was obtained. The possible mechanisms governing the modification in surface plasmon resonance by laser irradiation of gold nanoparticles were discussed.     

HEMATOPORPHYRIN DERIVATIVE-INDUCED PHOTODYNAMIC INHIBITION OF Na+/K+-ATPase IN L929 FIBROBLASTS, CHINESE HAMSTER OVARY CELLS AND T24 HUMAN BLADDER TRANSITIONAL CARCINOMA CELLS

The photodynamically induced inhibition of Na⁺/K⁺-ATPase with hematoporphyrin derivative as photosensitizer was studied in murine L929 fibroblasts, Chinese hamster ovary (CHO) cells and T24 human bladder transitional carcinoma cells. In T24 cells the inhibition of the enzyme activity appeared to be caused by ATP depletion rather than by direct damage from the enzyme itself. In L929 and CHO cells, on the other hand, the inhibition was caused by photodynamic damage from the enzyme molecule. For all three cell lines it was shown that a causal relationship between photodynamically induced reduction in Na⁺/K⁺-ATPase activity and the loss of clonogenicity is highly unlikely.     

PHOTODYNAMIC GENERATION OF HYDROXYL RADICALS BY HEMATOPORPHYRIN DERIVATIVE AND LIGHT

In a reaction mixture containing hematoporphyrin derivative, deoxyribose, Fe³⁺-EDTA and either methionine or tryptophan, hydroxyl radicals were formed during illumination with visible light. When either hematoporphyrin derivative, Fe³⁺-EDTA or the amino acid was omitted from the reaction mixture, the generation of hydroxyl radicals ceased. These observations suggest an iron-catalyzed Haber-Weiss reaction, involving superoxide and hydrogen peroxide in the generation of hydroxyl radicals. It could be shown that with methionine H₂O₂ was indeed an essential intermediate in the reaction sequence. With tryptophan, however, H₂O₂, was not generated. Apparently a photooxidation product of tryptophan could replace H₂O₂ in the OH-generating reaction with Fe²⁺-EDTA. Although superoxide was generated in the reaction mixture, it was not an indispensable intermediate. Apparently a porphyrin radical, formed via photoexcitation of hematoporphyrin derivative, could replace superoxide in the Haber-Weiss reaction.     

Axial dispersion and flow phenomena in helically coiled tubular reactors for flow analysis and chromatography

Open tubular reactors for flow analysis and post-column reactors for chromatography are commonly designed as rather tightly coiled helices. It is shown experimentally that the dynamics of flow and axial dispersion in such coiled tubes can differ substantially from behaviour in straight tubes. The differences are almost quantitatively accounted for by the existence of secondary flow phenomena in coiled tubes. On the basis of these coiling effects, practical parameters such as sampling rate, reagent consumption, tube dimensions, pressure drop, etc. are estimated, optimized and compared with those in other systems (segmented-flow and packed-bed reactors).     

Improving the power to detect differentially expressed genes in comparative microarray experiments by including information from self-self hybridizations

Our ability to detect differentially expressed genes in a microarray experiment can be hampered when the number of biological samples of interest is limited. In this situation, we propose the use of information from self-self hybridizations to acuminate our inference of differential expression. A unified modelling strategy is developed to allow better estimation of the error variance. This principle is similar to the use of a pooled variance estimate in the two-sample t-test. The results from real dataset examples suggest that we can detect more genes that are differentially expressed in the combined models. Our simulation study provides evidence that this method increases sensitivity compared to using the information from comparative hybridizations alone, given the same control for false discovery rate. The largest increase in sensitivity occurs when the amount of information in the comparative hybridization is limited.     

Rapid detection of compositional drift of polydisperse copolymers using thermal field-flow fractionation and multi-angle light scattering

Summary The use of thermal field-flow fractionation (ThFFF) with multi-angle light scattering (MALS) for the rapid detection of compositional heterogeneity in random copolymers is demonstrated. Soret coefficients were directly calculated from the ThFFF retention times while the MALS detector provided the polymer's radius of gyration (R _g) distribution. FromR _g, the diffusion coefficient (D) could be calculated and this allowed, in combination with the Soret coefficient, the calculation of the thermal diffusion coefficient (D _T). It was shown that theD _T distribution can serve as a measure for the chemical composition distribution of random styrene acrylonitrile copolymers. Comparison of ThFFF-MALS results with literature data from ThFFF-hydrodynamic chromatography (HDC) cross-fractionation experiments showed a fair agreement.     

Quantitative Aspects of Comprehensive Two-Dimensional Gas Chromatography (GC×GC)

A software program was developed to enable the quantification of the complex 3D-data sets as produced by GC×GC. Using this software, it was demonstrated that the detectability limit of GC×GC in our study is 18 times better than that of ‘normal’ capillary gas chromatography (CGC). This enhancement is due to the signal increase produced by the thermal modulation effect. The relative standard deviation of 0.9% as measured on a test mixture was excellent. Furthermore, a comparison was made for the group-type separation of heavy gas oils between the hyphenation of LC and GC (LC-GC) and GC×GC. Although these separations are different in nature, the agreement of the results of both methods was very good. The results of GC×GC may even be more accurate, since, different from CGC, even in the most complex chromatograms the baseline in the second dimension chromatograms is always present.