Linking single-molecule blinking to chromophore structure and redox potentials

Intensity fluctuations between an ON-state and an OFF-state, also called blinking, are common to all luminescent objects when studied at the level of individuals. We studied blinking of three dyes from a homologous series (Cy3, Cy5, Cy7). The underlying radical anion states were induced by removing oxidants (i.e. oxygen) and by adding the reductant ascorbic acid. We find that for different conditions with distinct levels of oxidants in solution the OFF-state lifetime always increases in the order Cy3相似文献   

Ionic Conductivity of the NASICON-Related Thiophosphate Na1+xTi2−xGax(PS4)3

Inspired by the recent interest in fast ionic conducting solids for electrolytes, the ionic conductivity of a novel ionic conductor Na_1+xTi_2−xGa_x(PS₄)₃ has been investigated. Using X-ray diffraction and impedance spectroscopy the sodium ionic conductivity in this compound was demonstrated, in which bond valence sum analysis suggests a tunnel diffusion for Na⁺. Substitution with Ga³⁺ leads to an increasing Na⁺ content, an expansion of the lattice and an increasing conductivity with increasing x in Na_1+xTi_2−xGa_x(PS₄)₃. Given the relation to the NASICON family, upon replacement of the phosphate by a thiophosphate group, a rich structural chemistry can be expected in this class of materials. This work demonstrates the potential for making NaTi₂(PS₄)₃ an ideal system to study structure-property relationships in ionic conductors.     

Investigation of the biotransformation of melarsoprol by electrochemistry coupled to complementary LC/ESI–MS and LC/ICP–MS analysis

Melarsoprol is the only currently available drug for treatment of the late stage of African trypanosomiasis (sleeping sickness). Unfortunately, the arsenic-containing drug causes serious side effects, for which the mechanisms have not been elucidated so far. This investigation describes the study of the melarsoprol biotransformation processes by electrochemical (EC) techniques. Based on EC, potential oxidation reactions of melarsoprol are examined. Moreover, the reactivity of melarsoprol, its metabolite melarsen oxide, and their oxidation products toward the tripeptide glutathione and the proteins hemoglobin and human serum albumin is evaluated. The combination of different analytical techniques allows the identification as well as the quantification of the biotransformation products. The hyphenation of liquid chromatography (LC) and electrospray ionization mass spectrometry (ESI–MS) is applied for identification and structure elucidation, which implies the determination of exact masses and fragmentation patterns. For the selective detection of arsenic containing metabolites, LC coupled to inductively coupled plasma mass spectrometry is utilized. Based on the obtained data, the oxidative biotransformation of melarsoprol can be predicted, revealing novel species which have been suspected, but not been identified up to now. The results of the protein studies prove that melarsen oxide, the active derivative of melarsoprol, strongly binds to human hemoglobin and forms different adducts via the free cysteinyl groups of the hemoglobin α- and β-chain.     

Conformational Analysis,Thermal Rearrangement,and EI‐MS Fragmentation Mechanism of (1(10)E,4E,6S,7R)‐Germacradien‐6‐ol by 13C‐Labeling Experiments

An uncharacterized terpene cyclase from Streptomyces pratensis was identified as (+)‐(1(10)E,4E,6S,7R)‐germacradien‐6‐ol synthase. The enzyme product exists as two interconvertible conformers, resulting in complex NMR spectra. For the complete assignment of NMR data, all fifteen (¹³C₁)FPP isotopomers (FPP=farnesyl diphosphate) and (¹³C₁₅)FPP were synthesized and enzymatically converted. The products were analyzed using various NMR techniques, including ¹³C, ¹³C COSY experiments. The (¹³C)FPP isotopomers were also used to investigate the thermal rearrangement and EI fragmentation of the enzyme product.