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

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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.

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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

Monodisperse and uniform γ-Fe2O3 (maghemite) nanocrystals of variable size were prepared by thermal decomposition of iron pentacarbonyl [Fe(CO)5] in the presence of surfactants, following controlled oxidation with trimethylamine N-oxide as a mild oxidant. The influence of carboxylic acids with variable alkyl carbon chain lengths on the synthesis of γ-Fe2O3 nanocrystals was investigated. The effect of the molar ratios of surfactant to iron precursor was also studied. The nanocrystals were characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD showed the particles were highly crystalline at the nanometer scale. The results showed that the size and shape of the nanocrystal is strongly influenced by the decomposition temperature of iron pentacarbonyl and closely related to the length of carbon chain of the capping groups and the molar ratio of surfactant to iron precursor. Following controlled evaporation from nonpolar solvents, self-assembly into two-dimensional arrays could be observed by TEM. It was also found that the distance between the nanocrystals in self-assembled structures matched the length of the capping molecules very well.

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Influence of Capping Groups on the Synthesis of γ-Fe2O3 Nanocrystals

In this paper some examples of reactions which yield electronically excited products are presented. In particular, the 1 ,2-dioxetanes are discussed. These molecules cleave cleanly into two carbonyl fragments when heated or irradiated. It will be shown that these simple, high energy, four atom arrays can efficiently generate electronically excited carbonyl fragments when they decompose. Surprisingly, tetramethyl1,2-dioxetane (V) yields acetone triplet selectively upon thermolysis or photolysis. A study of the kinetics of thermal decomposition of V as a function of solvent, and the mechanistic implications of these observations will be discussed. Based on summation of available evidence, we propose that the thermolyses of I ,2-dioxetanes require specific vibrational motions which enhance spin—orbit coupling as the molecule fragments, and allow efficient decomposition into triplet states. In the photochemistry of V an exceptional 'anti-Stokes' sensitization is demonstrated, which suggests the possibility of efficient execution of 'blue light' photochemistry with 'red light', and a 'quantum chain' reaction. It is demonstrated that, at 77°K, naphthvalene undergoes efficient photochemical conversion to naphthalene triplets. Finally, the relationship of radiationless electronic relaxation and primary photochemical processes is discussed in the framework of our results. INTRODUCTION In this paper we shall be concerned with organic reactions in solution that generate electronically excited products by either thermal (equation 1) or photochemical (equation 2) activation of reactants. R 4p* (1) R hv .R* p* (2) Such reactions are of potential interest to photochemists, spectroscopists, kineticists and photobiologists for any number of reasons. Photochernists may see in the study of such reactions a unique method of selectively produc-

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Thermal and photochemical generation of electronically excited organic molecules. Tetramethyl-1,2-dioxetane and naphthvalene

Dye-exchanged Y zeolite is shown to be an effective medium to control the stereoselectivity in the photooxygenation of chiral oxazolidinone-functionalized Z/E-1 enecarbamates. An enantioselectivity (ee) as high as 80% was observed in the methyldesoxybenzoin (MDB) product, obtained in the methylene-blue-exchanged NaY zeolite at room temperature. The efficacy of the asymmetric induction in the MDB product depends on the Z/E geometry of the alkene, the Z-isomer being more effective than the corresponding E-isomer. The stereoselectivity is rationalized in terms of conformational effects through cationic interactions between the zeolite and the substrate.

Stereocontrol within confined spaces: enantioselective photooxidation of enecarbamates inside zeolite supercages.

Photochemistry of 1,3-Cyclobutanediones. Decomposition Modes and Chemical Intermediates1

Introduction During the past decade a number of reports have appeared on the subject of “living free radical” polymerizations which are characterized by a critical feature of reversible termination of growing polymer chains that are capable of stepwise chain growth.1 Some of the more successful systems employ a nitroxide-stable, free radical to produce a “pseudo-living” free radical polymerization system and to produce polymers with low polydispersity.2 The reversible nature of the poly(styrene)nitroxide system has been established3 by EPR and exchange4 studies. The usual irreversible termination of two living chains to form a dead polymer is inhibited by the continuous capture of growing chains by nitroxides, which exist in relatively large excess compared to the stationary concentration of growing chains. The concentration of nitroxide is controlled by the reversible equilibrium of the capped living polymer with the growing chain and free nitroxide radical.5 The equilibrium is controlled, in the main, by the strength of the key, weak NO-C(polymer) bond. In the case of poly(styrene)TEMPO (cf. structure 2, Chart 1), the bond strength of the key bond is ca. 130 kJ/mol.6 For other poly(styrene)nitroxide systems, the bond energies are in the range 130-100 kJ/mol. The dissociation of these living polymers shows A factors6 in the range of 1013-14 s-1. We have synthesized a number of nitroxides covalently attached to photochemically and photophysically active groups for investigations of chemically induced dynamic electron polarization.7 It occurred to us that the “living” free radical method allows a convenient method for the preparation of “monodisperse” polymers with a wide variety of end groups by a simple nitroxide exchange under equilibrium conditions. This synthetic strategy, if successful, would offer an alternative to the classical living anionic methods of synthesizing monodisperse end-labeled polymers. The basic strategy of this synthetic method is to first synthesize a monodisperse nitroxide (e.g., T ) TEMPO, 2,2,6,6-tetramethylpiperidine-1-oxyl) capped polymer in the usual way with an appropriate alkoxylamine initiator such as 1 (e.g., eq 1, where P denotes a monodisperse polymer, T represents a Tempo cap, and T′ represents the desired cap to replace T). Previous studies have demonstrated that effective initiators must possess an R-methyl substituent at the benzylic carbon in order to generate monodisperse polymer chains.1,8 An alternative approach to the synthesis of end-labeled monodisperse polymers starts with the end-labeled nitroxide as part of the alkoxyamine initiator. This method has the advantage of not requiring an exchange of the labeled nitroxide but the disadvantage of having to run a series of polymerizations if a family of monodisperse endlabeled polymers is desired. In practice, it is expected that the latter method, in addition to the one reported here will be useful, once the appropriate end-labeled nitroxide is synthesized. The method reported will be particularly useful when the comparison of a family of identical monodisperse polymers with different end groups is desired. Using this synthetic strategy, a single monodisperse polymer, P-T, serves as the precursor for an exchange reaction that will substitute any desired nitroxide (without the structural limitations of the original initiator addend) which is added to the system, in excess, at equilibrium conditions. Since TEMPO nitroxides can be readily prepared with a wide variety of groups in the 4 position (cf. eq 2),7 the overall substitution reaction provides a general strategy for preparing a range of photoactive, monodisperse polymers that take advantage of controlled macromolecular architectures.

Nicholas J. Turro

Papers

Influence of Capping Groups on the Synthesis of γ-Fe2O3 Nanocrystals

Thermal and photochemical generation of electronically excited organic molecules. Tetramethyl-1,2-dioxetane and naphthvalene

Stereocontrol within confined spaces: enantioselective photooxidation of enecarbamates inside zeolite supercages.

Photochemistry of 1,3-Cyclobutanediones. Decomposition Modes and Chemical Intermediates1

A Living Free Radical Exchange Reaction for the Preparation of Photoactive End-Labeled Monodisperse Polymers