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

Time resolved infrared laser photochemistry and spectroscopy: the methyl fluoride sensitized decomposition of tetramethyl-1,2-dioxetane. An example of infrared laser induced electronic excitation

Despite its great industrial importance, many aspects of free radical polymerization (FRP)1 remain poorly understood. One of the few methods that can directly probe propagating radicals, i.e., living chains which are at the heart of FRP, is electron paramagnetic resonance (EPR), a very sensitive and nondestructive technique that provides information on the local structure and dynamics and the number density of the propagating radical centers.2,3 Unfortunately, in many cases the concentration of the FRP living chains is too low during the early stages (low conversions) to allow for good EPR signals. This results in poorly resolved, noisy spectra that are prone to misinterpretations. A second problem is the measurement of many different living chain lengths simultaneously, leading to speculations that are difficult to test.4 The field would be significantly advanced if one could obtain spectra unambiguously corresponding to a single living chain length. In this article we demonstrate how the time-resolved EPR (TR-EPR) technique5-7 can be used to overcome these problems. Using TR-EPR in well characterized systems, we have studied the FRP of methyl methacrylate (MMA) and its analogues and obtained well-resolved, intense spectra of monodisperse living chains. To the best of our knowledge there has been only one other study where TREPR was applied to study FRP.8 The work reported here is also one of the few systematic exploitations of the transfer of “spin polarization” via chemical reactions8-11 and the application of TR-EPR in polymer research in general.8,10,12 In conventional EPR, time scales for data acquisition are slow (typically seconds to minutes) compared to the time to add a monomer to a living chain, 1/(kp [M]) (typically milliseconds13). This usually limits conventional EPR measurements to steady state FRPs, where inevitably a broad distribution of living chain lengths exists. Nevertheless there has been some clever efforts to measure conventional EPR of single length living chains. Fischer and Giacometti14 obtained well-resolved spectra of 1-mer living chains of methacrylic acid by creating a stationary concentration of these in the EPR cavity using a flow system. More recently, Matsumoto and Giese15 succeeded in measuring 1-, 2-, and 3-mer living chains of MMA and related monomers, by reduction of the corresponding bromide precursors in an inert solvent. In contrast, TR-EPR probes submicrosecond processes, much faster than 1/(kp[M]); thus, taking a “snapshot” of living chains is possible by this method. These chains are created by very fast addition of a primary radical (created by a short laser pulse) to monomer. This first addition step is complete within 100-300 ns. Subsequent addition rates are much slower (on the order of 1 ms) due to the lower reactivity of living chains. Our TR-EPR observation times (typically 1-2 μs following the laser pulse) fall in a range well after the creation of living chains, yet well before these can react further: only a single living chain length is monitored. To study spectra of living chains as a function of their degree of polymerization, N, one can use photoinitiators which give primary radicals attached to progressively longer polymeric chains. Here we report results for the shortest living chains, N ) 1, created using small molecule photoinitiators. Now, the matrix (consisting of monomer and pre-dissolved polymer) remains fixed during the TR-EPR observation times, allowing one to study the effect of polymer concentration on the spectra. This is not easy to do in conventional EPR in the early stages of FRP where one often needs to accumulate a large number of acquisitions to improve signals. During these times conversion (roughly equal to polymer volume fraction accumulated in the matrix) may change considerably. The conventional EPR spectra of poly(methyl methacrylate) (PMMA) radicals in both glassy and nonglassy matrices have generated considerable controversy since the first observations in the 1950s3 of a 9-line spectrum with an unusual intensity distribution. Studying oligomeric living chains of methacrylic acid Fischer16 observed 16 lines in nine main groups, and interpreted these in terms of nonequivalent â-protons of the CH2 group due to hindered rotation. More recently, Shen et al.17 and Zhu et al.18 observed a “13-line” EPR spectrum at low conversions (j20%) in the bulk FRP of MMA, which gradually turned into a “9-line” spectrum that persisted as the mixture became glassy. Zhu et al.18 suggested that the 9-line signal is due to living chains “trapped” in microscopic glassy domains. Finally, Gilbert and co-workers4 argued, based on computer simulations, that the 13-line signal must be due to oligomeric radicals (N j 5), which must have been abundant in the experiments of Shen et al.17 and Zhu et al.18 where unusually high rates of initiation were used. Resolving these various interpretations based on conventional EPR alone has clearly proven to be very difficult. The EPR signal intensity is proportional to the difference in the populations of the energy levels involved in the observed transitions.2,3 This difference is typically very small in conventional EPR where spin systems are in thermal equilibrium (EZeeman , kT at room temperature). However, just after their creation, free radicals may be in a far-from-equilibrium spin state (i.e. in a “spin polarized” state) where the difference in energy level populations is far greater than that in thermal equilibrium. Hence one may observe greatly enhanced signal intensities by monitoring EPR transitions before the spin system relaxes to equilibrium, typically within microseconds. That is the essence of * To whom correspondence should be addressed at the Department of Chemistry. 7992 Macromolecules 1998, 31, 7992-7995

Time-Resolved EPR: A Novel Method For Studying Living Chains

Chemiluminescent techniques have been employed to investigate electronic energy transfer from ketone donors (ace- tone, acetophenone) to acceptors (e.g., 9,lO-diphenylanthracene and biphenyl) in films of polystyrene and polymethyl methac- rylate at 50 "C. Tetramethyl-l,2-dioxetane and 3,4-diphenyl-3,4-dimethyldioxetane were used to generate excited (singlet and triplet) acetone and (triplet) acetophenone, respectively. Analysis of quenching data in terms of the Perrin, Forster, or Dexter models all yielded critical transfer radii, R,, in the range of 23-29 8, for singlet-singlet and for triplet-singlet energy transfer. For triplet-triplet energy transfer, the values of R, were in the range of 11-17 8, with the exception of the acetone triplet to 1,4-dibromonaphthalene transfer in polystyrene, for which R, = 21 8,. Evidence is presented which supports the postulate that triplet energy migration among the pendant phenyl groups on the polystyrene backbone may cause unexpectedly large R, values for triplet-triplet energy transfer.

http://turroserver.chem.columbia.edu/pdf_db/publications_151_200/192.pdf

Electronic excitation transfer in polymers. 3. Singlet-singlet, triplet-singlet, and triplet-triplet energy transfers. Evidence for triplet migration among pendant phenyl groups of polystyrene

Chemically induced dynamic nuclear polarization from the selective recombination of radical pairs in micelles

Amphiphilic polymers can be used as tools to manipulate the behavior of reverse microemulsions. EPR spectroscopy employing the spin probe 5-doxyl stearic acid was used to study the adsorption of a comb type polymer (polymaleic anhydride octyl vinyl ether) and a diblock polymer (polybutadiene–ethylene oxide) onto reverse microemulsion droplets formed from Aerosol-OT/heptane/water. The findings indicate that the comb type polymer was adsorbed by the reverse microemulsion drops at low polymer concentrations causing a structural change of the micelle.

Nicholas J. Turro

Papers

Time resolved infrared laser photochemistry and spectroscopy: the methyl fluoride sensitized decomposition of tetramethyl-1,2-dioxetane. An example of infrared laser induced electronic excitation

Time-Resolved EPR: A Novel Method For Studying Living Chains

Electronic excitation transfer in polymers. 3. Singlet-singlet, triplet-singlet, and triplet-triplet energy transfers. Evidence for triplet migration among pendant phenyl groups of polystyrene

Chemically induced dynamic nuclear polarization from the selective recombination of radical pairs in micelles

Investigation of the mobility of amphiphilic polymer--AOT reverse microemulsion systems using electron spin resonance.