Fluorescence methods are being used increasingly in biochemical, medical, and chemical research. This is because of the inherent sensitivity of this technique. and the favorable time scale of the phenomenon of fluorescence. 8 Fluorescence emission occurs about 10- sec (10 nsec) after light absorp tion. During this period of time a wide range of molecular processes can occur, and these can effect the spectral characteristics of the fluorescent compound. This combination of sensitivity and a favorable time scale allows fluorescence methods to be generally useful for studies of proteins and membranes and their interactions with other macromolecules. This book describes the fundamental aspects of fluorescence. and the biochemical applications of this methodology. Each chapter starts with the -theoreticalbasis of each phenomenon of fluorescence, followed by examples which illustrate the use of the phenomenon in the study of biochemical problems. The book contains numerous figures. It is felt that such graphical presentations contribute to pleasurable reading and increased understand ing. Separate chapters are devoted to fluorescence polarization, lifetimes, quenching, energy transfer, solvent effects, and excited state reactions. To enhance the usefulness of this work as a textbook, problems are included which illustrate the concepts described in each chapter. Furthermore, a separate chapter is devoted to the instrumentation used in fluorescence spectroscopy. This chapter will be especially valuable for those perform ing or contemplating fluorescence measurements. Such measurements are easily compromised by failure to consider a number of simple principles."

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Principles of fluorescence spectroscopy

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

/pdf/self-assembled-monolayers-of-thiolates-on-metals-as-a-form-1neb0hj3k4.pdf

Self-assembled monolayers of thiolates on metals as a form of nanotechnology.

Demand has never been greater for revolutionary technologies that deliver fast, inexpensive and accurate genome information. This challenge has catalysed the development of next-generation sequencing (NGS) technologies. The inexpensive production of large volumes of sequence data is the primary advantage over conventional methods. Here, I present a technical review of template preparation, sequencing and imaging, genome alignment and assembly approaches, and recent advances in current and near-term commercially available NGS instruments. I also outline the broad range of applications for NGS technologies, in addition to providing guidelines for platform selection to address biological questions of interest.

/pdf/sequencing-technologies-the-next-generation-599pyrfdla.pdf

Sequencing technologies-the next generation

The efficiency of electroluminescent organic light-emitting devices1,2 can be improved by the introduction3 of a fluorescent dye. Energy transfer from the host to the dye occurs via excitons, but only the singlet spin states induce fluorescent emission; these represent a small fraction (about 25%) of the total excited-state population (the remainder are triplet states). Phosphorescent dyes, however, offer a means of achieving improved light-emission efficiencies, as emission may result from both singlet and triplet states. Here we report high-efficiency (≳90%) energy transfer from both singlet and triplet states, in a host material doped with the phosphorescent dye 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II) (PtOEP). Our doped electroluminescent devices generate saturated red emission with peak external and internal quantum efficiencies of 4% and 23%, respectively. The luminescent efficiencies attainable with phosphorescent dyes may lead to new applications for organic materials. Moreover, our work establishes the utility of PtOEP as a probe of triplet behaviour and energy transfer in organic solid-state systems.

Highly efficient phosphorescent emission from organic electroluminescent devices

Cyclopropanones. XVII. Kinetics of the cycloaddition reaction of cyclopropanones with 1,3-dienes

Photochemistry of macrocyclic ketones within zeolites: competition between norrish type I and type II reactivity

Microsomes and reconstituted systems containing cytochrome P450 can oxidize glycerol to formaldehyde in a reaction catalyzed by an oxidant produced from the interaction of nonheme iron with H2O2. To evaluate the mechanism for this oxidation, the generation of glycerol radicals by various systems was compared to rates of formaldehyde production from glycerol. Photolysis of H2O2, oxidation of xanthine by xanthine oxidase in the presence of iron catalysts, or NADPH-dependent microsomal electron transfer in the presence of ferric-EDTA produced hydroxyl radicals. In the presence of glycerol these reaction systems produced DMPO-glycerol radical adducts which were detected by ESR spectroscopy. Despite the production of .OH and glycerol spin-trapped adducts by these reaction systems, very low amounts or nondetectable amounts of formaldehyde were produced from the glycerol. However, significant amounts of formaldehyde were observed when microsomes were incubated in the presence of ferric ammonium sulfate or ferric-ATP, although .OH production was lower with these iron catalysts than with ferric-EDTA. These results fail to support correlation between .OH production and oxidation of glycerol to formaldehyde. Under conditions in which glycerol was oxidized to formaldehyde, no glycerol radical species could be observed with DMPO as the spin-trapping agent. These results suggest the oxidant (not .OH) derived from the interaction of H2O2 with iron apparently cleaves glycerol to formaldehyde without the formation of a radical intermediate. Alternatively, the radical intermediate may be produced at a too low concentration to be detected or the radical intermediate may not be formed as a free species and therefore cannot be spin-trapped.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidation of glycerol to formaldehyde by microsomes: are glycerol radicals produced in the reaction pathway?

Adsorption of polymers onto particles has been a subject of study because of its importance in the behavior of suspensions.1,2 To understand the adsorption/desorption process in detail, studies have been carried out with model systems. Some studies have employed polystyrene (PS) adsorbed onto metals, silica, glass, and mica.3-7 In previous work, we reported on the use of pyrene-labeled PS to study the dynamics of the rearrangement of adsorbed PS after exposing the PS adsorbed on a silica surface to desorption conditions, i.e., after replacing the bulk solution containing unabsorbed PS with pure solvent.8 Pyrene has been used widely in the literature as a probe of structure and dynamics in macromolecular systems.9-11 From the fluorescence emission properties of pyrene labels, such as the I3/I1 ratio, the excimerto-monomer ratio (Ie/Im), and fluorescence polarization value, one obtains information about the conformation, mobility, and dielectric environment of the pyrene probe within the macromolecule being studied. In this note, we report on the photodegradation of the pyrene labels on PS in chloroform (CHCl3) and adsorbed on silica surface contacting with CHCl3 caused by excitation light under conditions typical for photophysical studies of polymers. We feel this effect should be brought to the attention of the community because of the common use of pyrene as a probe.12,13 As published in a previous paper,8 after the adsorption of labeled PS onto a silica surface has proceeded for a predetermined time in dilute PS/CHCl3 solution, replacing the bulk polymer solution with pure solvent CHCl3 causes a progressive relative increase in excimer emission intensity with time, i.e., an increase in Ie/Im ratio over time. In this work, we observe that the increase in Ie/Im ratio was dependent on the total exposure time of the sample to the excitation light in the fluorescence spectrometer. The synthesis and characterization of the pyrenelabeled PS were reported previously.8 The polymer used has a molecular weight of 50K and label density of 15 pyrene labels per chain. Porous silica samples were obtained as gifts from Dupont and had average pore sizes of 57 or 122 A. Solvent CHCl3 was distilled before use. The preparation of adsorbed, pyrene-labeled PS layers on silica was described before.8 The bulk polymer concentration for adsorption was 0.1 g/L in CHCl3. After adsorption for a certain time, the bulk polymer solution was replaced with pure CHCl3 by rinsing the solid and transferring it quickly into a fluorescence cell with a 2 mm path length containing pure CHCl3. The fluorescence emission and excitation spectra were taken on a SPEX Fluorolog 1680 0.22 m double spectrometer with a 450 W xenon lamp using front face excitation. The excitation light beam was directed onto the polymer/silica sediment pack, not the supernatant. First, the effect of the excitation light on the pyrene labels of the polymer adsorbed on a porous silica was investigated. Typical excitation spectra obtained with successive scans are shown in Figure 1. The excitation spectrum monitored at 480 nm (maximum emission wavelength for pyrene excimer) has several broad unexpected bands in the range 350-450 nm when compared to other reports.13 It is well-known that the excitation spectra of the preassociated pyrene molecules have similar vibrational structure as the pyrene monomer excitation spectra but are 1-4 nm red-shifted.13 The observed bands do not correspond to a static excimer of pyrene, which is expected when pyrene molecules are preassociated in the ground state. It was speculated that these bands were caused by other species that emit in the same spectral region as the pyrene excimer. At this point, we decided to investigate whether photodegradation products formed during the spectral collection process while the sample was being irradiated in the sample chamber of the fluorescence spectrometer was the cause of the observation. On the basis of this hypothesis, it was found that the intensity of the excitation spectra of pyrene labels changed dramatically with cumulative exposure to the instrument excitation light under conditions typical for photophysical studies. The typical observation is that intensities in the monomer excitation spectra decrease with the number of scans taken, while that in the excitation spectra monitored at the excimer emission wavelength increase dramatically, especially in the region of 350-450 nm. These changes could be caused by rearrangement of polymer chains on the surface upon exposure to pure solvent, as suggested earlier, or by photodegradation in the instrument as suggested here. To determine which mechanism was operating, an adsorbed layer of labeled PS on silica was prepared at conditions similar to that described in ref 8 and exposed to solvent for 2 days in complete absence of light, and then its fluorescence excitation spectra were acquired. This sample showed changes in its fluorescence excitation spectra similar to those shown Figure 1 which were taken within minutes after sample preparation. Since, after 2 days under desorption conditions, chain rearrangements should have reached an equilibrium, photodegradation of labels is strongly suspected as the cause of spectrum changes rather than conformational changes for which the labels maintain their chemical integrity. Similar spectral and intensity changes were observed for all the silica samples used in ref 8 and for three other pyrene-labeled PS with different molecular weight and different labeling densities.14 For comparison, we tested pyrene-labeled PS in CHCl3 solution under the same conditions in the fluorescence instrument with the results shown in Figure 2. In the fluorescence emission spectra with excitation at 330 nm, multiple scans caused an intensity decrease * To whom correspondence should be addressed. † Department of Chemistry. ‡ Department of Chemical Engineering and Applied Chemistry. 4151 Macromolecules 1999, 32, 4151-4153

Nicholas J. Turro

Papers

Cyclopropanones. XVII. Kinetics of the cycloaddition reaction of cyclopropanones with 1,3-dienes

Photochemistry of macrocyclic ketones within zeolites: competition between norrish type I and type II reactivity

Oxidation of glycerol to formaldehyde by microsomes: are glycerol radicals produced in the reaction pathway?

Photodegradation of pyrene-labeled polystyrene adsorbed on silica surface in chloroform

Influence of binding strength of added electrolytes on the properties of micelles and of micellized radical pairs