Triplet annihlation in pyrene-d10 doped fluorene

Triplet exciton concentration inferred from delayed fluorescence measurements of pyrene-d₁₀ doped fluorene crystals has been examined as a function of temperature in order to study the correlation between exciton density and electronic triplet spin lattice relaxation (T_ie). The results have indicated a poor correlation between the delayed fluorescence intensity and the electronic relaxation rate although a qualitative correlation exists between the growth of trap phosphorescence and relaxation rate.     

Optically modified mass spectrum of n-pentane

A technique using simultaneous photon and electron bombardment in the ionization chamber of a mass spectrometer has allowed us to gain information concerning the excited ionic states responsible for fragmentation in n-pentane. Correlations of the photon energies that produce an optically modified mass spectrum are made with the known ionic states and the observed fragment production.     

Label Free Fluorometric Characterization of DNA Interaction with Cholate Capped Gold Nanoparticles Using Ethidium Bromide as a Fluorescent Probe

We demonstrated label free ethidium bromide assisted characterization of DNA interaction with cholate capped AuNPs. Interactions between ss/ds DNA and AuNPs with two different lengths (0.5 and 0.85 kb) were analyzed through fluorescence spectrophotometer and agrose gel electrophoresis analysis. Further results were confirmed by UV–globally visible spectrophotometer, DLS and TEM. As 0.5 and 0.85 kb of ssDNA effectively interacted with AuNPs through the van der Waals interaction which consequently led to the prevention of salt induced aggregation, EtBr intercalations as well as fluorescence shift with less binding constant 0.098 and 0.108 μM, respectively. On the contrary, the same length of dsDNA (0.5 and 0.85 kb) not interacted with AuNPs which led to the NPs aggregation, EtBr intercalation as well as fluorescence shift with increased binding constant 0.166 and 0.599 μM, respectively. This approach helped to understand the mode of interactions of DNA with cholate capped AuNPs without any modifications in a simple method and the results could be readout through the naked eye under the UV transilluminator. Figure

Fluorometric characterization of interaction of different lengths of ss/dsDNA with cholate capped AuNPs using EtBr as fluorescence probe     

A new high precision measurement of the muonium hyperfine structure interval Δv1

At LAMPF we have observed muonium resonance curves in low pressure argon and krypton at very weak magnetic field using two line narrowing techniques, and have obtained Δv = 4 463 302.2 (1.4) kHz (0.3 ppm). This is the most precise value of Δν yet quoted, and from it we obtain improved values for the muon magnetic moment and mass: $\text{μ}{}_{\mathrm{\mu }}{}_{\mathrm{<mtext>p</mtext>}}\text{= 3.183 329 9 (25) (0.8}\text{ppm}\text{);}\text{m}{}_{\mathrm{\mu }}\text{m}{}_{\mathrm{<mtext>e</mtext>}}\text{= 206.769 27 (17) (0.8}\text{ppm}\text{)}$.     

Optically modified mass spectra of CO2

The optically modified mass spectra of CO₂ has been studied with respect to various experimental parameters. The proposed mechanism of ionization is photoionization from electron impact excited states of the neutral CO₂. An estimate for the cross section is 1.5 × 10^?16 cm².     

Scope, limitations and mechanistic aspects of the photo-induced cross-linking of proteins by water-soluble metal complexes

BACKGROUND: Chemical cross-linking is a valuable tool with which to study protein-protein interactions. Recently, a new kind of cross-linking reaction was developed in which the photolysis of associated proteins with visible light in the presence of ammonium persulfate and tris(2,2'-bipyridyl)ruthenium(II) dication or palladium(II) porphyrins results in rapid and efficient covalent coupling (Fancy, D.A. & Kodadek, T. (1999). Proc. Natl. Acad. Sci. USA 96, 6020-6024 and Kim, K., Fancy, D.A. & Kodadek, T. (1999). J. Am. Chem. Soc. 121, 11896-11897). Here, mechanistic and practical aspects of the reaction of importance for its application to biochemical problems are examined. RESULTS: It is shown that the photo-initiated cross-linking chemistry can be optimized for the analysis of protein-protein interactions in crude cell extracts. A number of commonly used epitope or affinity tags survive the reaction in functional form, allowing the simple visualization of the cross-linked products, or their isolation. It is shown that very little light-independent oxidation of protein residues occurs and that significant perturbation of complexes of interest prior to the brief photolysis period does not occur. Finally, evidence is presented that is consistent with a mechanistic model in which ammonium persulfate functions simply as an electron acceptor, facilitating the generation of the key high valent metal complex from the photoexcited species by electron transfer. In the absence of an electron acceptor, a much lower efficiency reaction is observed that appears to involve products resulting from reaction of the excited state metal complex with molecular oxygen. CONCLUSIONS: These results provide useful practical information for chemists and biochemists who may wish to employ this new cross-linking chemistry for the analysis of protein complexes. They also shed new light on the mechanism of this interesting reaction.     

Data-directed scan sequence for the general assignment of C-glycosylflavone O-glycosides in plant extracts by liquid chromatography-ion trap mass spectrometry

An ion trap LC-MS/MS method is described for the analysis of C-glycosylflavone O-glycosides in crude methanolic extracts of plants. The method employs survey scans with and without the application of up-front collision induced dissociation (CID) to generate diagnostic ions for data-directed MS/MS. The spectra acquired allow assignment of the C-linked sugar to either the C-6 or C-8 position of the aglycone and provide data on the molecular mass of the compound, the number and type of O-linked sugars and the molecular mass of the flavone aglycone. These data for the majority of C-glycosylflavone O-glycosides in an extract are obtained automatically in one LC-MS/MS analysis without manual pre-programming. Key to the assignment of the C-6 or C-8 site of C-glycosylation is the generation, by up-front CID, of the (0,1)X+ product ion formed by internal cleavage of the C-linked sugar. MS/MS of this ion is found to have diagnostic value in addition to the (0,2)X+ product ion described by other authors. Ion trap MS/MS spectra of [M+H]+ of the 6,8-di-C-glycosylflavones schaftoside and isoschaftoside show an additional and previously unreported diagnostic product ion that is useful in determining the type of sugar at the C-6 position. The product ion spectra of protonated kaempferol 3-O-glucosylrhamnosides show similarities to the spectra of C-glycosylflavone O-glycosides; this is a potential source of confusion if the analysis of such glycosides is limited solely to MS/MS of [M+H]+.