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

4. Survey of Novel Multiphoton Active Materials 1257 4.1. Multiphoton Absorbing Systems 1257 4.2. Organic Molecules 1257 4.3. Organic Liquids and Liquid Crystals 1259 4.4. Conjugated Polymers 1259 4.4.1. Polydiacetylenes 1261 4.4.2. Polyphenylenevinylenes (PPVs) 1261 4.4.3. Polythiophenes 1263 4.4.4. Other Conjugated Polymers 1265 4.4.5. Dendrimers 1265 4.4.6. Hyperbranched Polymers 1267 4.5. Fullerenes 1267 4.6. Coordination and Organometallic Compounds 1271 4.6.1. Metal Dithiolenes 1271 4.6.2. Pyridine-Based Multidentate Ligands 1272 4.6.3. Other Transition-Metal Complexes 1273 4.6.4. Lanthanide Complexes 1275 4.6.5. Ferrocene Derivatives 1275 4.6.6. Alkynylruthenium Complexes 1279 4.6.7. Platinum Acetylides 1279 4.7. Porphyrins and Metallophophyrins 1279 4.8. Nanoparticles 1281 4.9. Biomolecules and Derivatives 1282 5. Nonlinear Optical Characterizations of Multiphoton Active Materials 1282

Multiphoton Absorbing Materials : Molecular Designs, Characterizations, and Applications

Publisher Summary This chapter describes the coherent population trapping in laser spectroscopy. Coherent population trapping may be also described as the pumping of the atomic system in a particular state, the coherent superposition of the atomic states, which is a nonabsorbing state. The exciting radiation creates an atomic coherence, such that the atom's evolution is prepared exactly out of phase with the incoming radiation and no absorption takes place. The chapter discusses the basic properties of an atomic system prepared with the coherent population-trapping superposition of states and outlines experimental observations concerned with the establishment of coherent trapping in different discrete systems. The chapter also discusses the theoretical and experimental aspects of trapping that involve states of the continuum and reviews the theoretical and experimental features associated with coherent population trapping in laser cooling, adiabatic transfer, lasing without inversion, pulse matching, and photon statistics. The theoretical aspect of coherent population trapping created by spontaneous emission is also discussed in the chapter.

Coherent Population Trapping in Laser Spectroscopy

1. Understanding chemical reactions at the molecular level 2. Molecular collisions 3. Introduction to reactive molecular collisions 4. Scattering as a probe of collision dynamics 5. Introduction to polyatomic dynamics 6. Structural considerations in the calculation of reaction rates 7. Photoselective chemistry: access to the transition state region 8. Chemistry in real time 9. State-changing collisions: molecular energy transfer 10. Stereodynamics 11. Dynamics in the condensed phase 12. Dynamics of gas-surface interactions and reactions.

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Molecular reaction dynamics

The primary adsorption sites for Ar and N2 within metal-organic framework-5, a cubic structure composed of Zn4O(CO2)6 units and phenylene links defining large pores 12 and 15 angstroms in diameter, have been identified by single-crystal x-ray diffraction. Refinement of data collected between 293 and 30 kelvin revealed a total of eight symmetry-independent adsorption sites. Five of these are sites on the zinc oxide unit and the organic link; the remaining three sites form a second layer in the pores. The structural integrity and high symmetry of the framework are retained throughout, with negligible changes resulting from gas adsorption.

https://science.sciencemag.org/content/sci/309/5739/1350.full.pdf

Gas Adsorption Sites in a Large-Pore Metal-Organic Framework

It is now known that tunable dye laser light leads to resonance enhanced photoionization of molecules in a mass spectrometer via multiphoton absorption. In some cases this process also leads to ion fragmentation. Time delayed tandem laser pulses of different wavelengths are employed to study the mechanism of this multiphoton ionization and fragmentation process in benzene. The experimental results strongly indicate that excitation does not proceed up an autoionization ladder of the neutral molecule, rather the multiphoton process is shown to be due to the climbing of two independent ladders, one up to the ionization potential in the neutral molecule, the second in the new species of molecular parent ions produced. Hence multiphoton ionization could also form a new basis of ion spectroscopy.

Visible and UV multiphoton ionization and fragmentation of polyatomic molecules

Multiphoton mass spectrometry of metastables: direct observation of decay in a high-resolution time-of-flight instrument

High resolution laser excitation was combined with the technique of mass‐selected two‐photon ionization via a resonant intermediate state to measure rotationally resolved UV spectra of benzene–Ar van der Waals clusters. When the second laser pulse in the two color experiment is delayed by 7 ns no line broadening due to the second ionizing absorption step is observed. Spectra of three vibronic bands in the S1 ←S0 transition of benzene (h6)–Ar and benzene (d6)–Ar were measured yielding a line spectrum with a linewidth of 130 MHz. Resolution is sufficient to demonstrate that no asymmetry splitting of the rotational lines occurs and the spectrum is to a high precision that of a symmetric rotor. A detailed analysis of the rotational structure yields an accurate set of rotational constants. We find that the Ar is located on the C6 rotational axis. Its distance from the benzene ring plane is 3.582 A in the electronic ground state and decreases by 59±3 mA in the electronically excited state due to the increased polarizability of the benzene molecule after electronic excitation.

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Rotationally resolved ultraviolet spectrum of the benzene–Ar complex by mass‐selected resonance‐enhanced two‐photon ionization

Multi-photon ionization (MPI) with tunable visible/UV laser light is shown to be a sensitive tool for analysis of traces in gas mixtures when combined with a mass spectrometer. Mass spectra of six different organic molecules, obtained with low intensity laser light, are presented and demonstrate the facility of ionization without fragmentation (soft ionization) under proper experimental conditions. Quantitative values for the cross sections for both two photon steps are obtained from the measured intensity dependence and the absolute ion numbers. Such quantitative data help in the evaluation and definition of this new ionization technique in mass spectrometry. Efficiencies of ionization for some molecules are as high as 25% leading to 106 ions in a single pulse from the dye laser (1 kW). Detectability as low as 2 parts in 109 is thus predicted.

Multi-photon ionization in the mass spectrometry of polyatomic molecules: Cross sections

Measuring transient absorptions on the nanosecond time range, we observed the magnetic field ( H = 40 Oe) modulation of the pyrene triplet and pyrene anion concentrations formed through quenching of singlet excited pyrene molecules by N,N -diethylaniline in methanol at room temperature. We interpret this effect as being due to a magnetic field dependent triplet production in the geminate radical ion pair, induced by hyperfine interaction of the unpaired electrons. The discussion is based on a simple model related to the radical pair model in CIDNP theory. Moreover, the sign of the magnetic field modulation of triplets and radical ions allows to infer on the relative probability for the formation of excited and ground state molecules in ion recombination processes.

Hans Jürgen Neusser

Papers

Visible and UV multiphoton ionization and fragmentation of polyatomic molecules

Multiphoton mass spectrometry of metastables: direct observation of decay in a high-resolution time-of-flight instrument

Rotationally resolved ultraviolet spectrum of the benzene–Ar complex by mass‐selected resonance‐enhanced two‐photon ionization

Multi-photon ionization in the mass spectrometry of polyatomic molecules: Cross sections

Magnetic field modulation of geminate recombination of radical ions in a polar solvent