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

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Large polycyclic aromatic hydrocarbon (PAH) molecules carry the infrared (IR) emission features that dominate the spectra of most galactic and extragalactic sources. This review surveys the observed mid-IR characteristics of these emission features and summarizes laboratory and theoretical studies of the spectral characteristics of PAHs and the derived intrinsic properties of emitting interstellar PAHs. Dedicated experimental studies have provided critical input for detailed astronomical models that probe the origin and evolution of interstellar PAHs and their role in the universe. The physics and chemistry of PAHs are discussed, emphasizing the contribution of these species to the photoelectric heating and the ionization balance of the interstellar gas and to the formation of small hydrocarbon radicals and carbon chains. Together, these studies demonstrate that PAHs are abundant, ubiquitous, and a dominant force in the interstellar medium of galaxies.

Interstellar Polycyclic Aromatic Hydrocarbon Molecules

IR spectroscopy is an excellent method for biological analyses. It enables the nonperturbative, label-free extraction of biochemical information and images toward diagnosis and the assessment of cell functionality. Although not strictly microscopy in the conventional sense, it allows the construction of images of tissue or cell architecture by the passing of spectral data through a variety of computational algorithms. Because such images are constructed from fingerprint spectra, the notion is that they can be an objective reflection of the underlying health status of the analyzed sample. One of the major difficulties in the field has been determining a consensus on spectral pre-processing and data analysis. This manuscript brings together as coauthors some of the leaders in this field to allow the standardization of methods and procedures for adapting a multistage approach to a methodology that can be applied to a variety of cell biological questions or used within a clinical setting for disease screening or diagnosis. We describe a protocol for collecting IR spectra and images from biological samples (e.g., fixed cytology and tissue sections, live cells or biofluids) that assesses the instrumental options available, appropriate sample preparation, different sampling modes as well as important advances in spectral data acquisition. After acquisition, data processing consists of a sequence of steps including quality control, spectral pre-processing, feature extraction and classification of the supervised or unsupervised type. A typical experiment can be completed and analyzed within hours. Example results are presented on the use of IR spectra combined with multivariate data processing.

/pdf/using-fourier-transform-ir-spectroscopy-to-analyze-u6jjupfc5y.pdf

Using Fourier transform IR spectroscopy to analyze biological materials

The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.

/pdf/optical-gas-sensing-a-review-4uaf589xiq.pdf

Optical gas sensing: a review

Gas-phase infrared multiple photon dissociation spectroscopy of mass-selected molecular ions

A new method for identifying and characterizing cluster ion isomers is presented Results indicate that most carbon clusters have more than one stable form, with 29≤n≤45 indicating three or four different structures Fullerenes first appear at C+30 and begin to dominate above C+45 From small to large the isomeric progression is from linear to rings to fullerenes

Structures of carbon cluster ions from 3 to 60 atoms: Linears to rings to fullerenes

THE discovery1–6 of the spherical carbon cage compound buck-minsterfullerene (C60) and the recent development of methods to produce it in bulk7 have led to an explosion in research in the physical and chemical properties of this unique species8,9. Nevertheless, the question of the formation mechanism of C60 (or of the other fullerenes) is still far from settled. We have shown elsewhere that carbon clusters in the gas phase develop from linear chains to planar ring systems to fullerenes as their size increases. One can easily envisage the transformation from chains to rings, but how the three-dimensional near-spherical fullerenes evolve from large planar rings is not obvious. Here we show that 'heating' these large ring systems above their 'melting' point leads to 100% fullerene formation accompanied by the evaporation of a small carbon fragment (C1 or C3 for odd systems and C2 for even systems). We propose a mechanism, based on these data, for efficient C60 production in carbon arcs.

Experimental evidence for the formation of fullerenes by collisional heating of carbon rings in the gas phase

Conformational data for macromolecules in the gas phase have been obtained by the coupling of a matrix-assisted laser desorption ion source to an ion chromatograph. A series of polyethylene glycol (PEG) polymers "cationized" (converted to a cation) by sodium ions (Na+PEG9 to Na+PEG19) and a protonated neurotransmitter protein, bradykinin, were studied. Mobilities of Na+PEG9 to Na+PEG19 are reported. Detailed modeling of Na+PEG9 with molecular mechanics methods indicates that the lowest energy structure has the Na+ ion "solvated" by the polymer chain with seven oxygen atoms as nearest neighbors. The agreement between the model and experiment is within 1 percent for Na+PEG9, Na+PEG13, and Na+PEG17, giving strong support to both the method and the deduced structures. Similar agreement was obtained in initial studies that modeled experimental data for arginine-protonated bradykinin.

https://science.sciencemag.org/content/sci/267/5203/1483.full.pdf

Gert von Helden

Papers

Gas-phase infrared multiple photon dissociation spectroscopy of mass-selected molecular ions

Structures of carbon cluster ions from 3 to 60 atoms: Linears to rings to fullerenes

Experimental evidence for the formation of fullerenes by collisional heating of carbon rings in the gas phase

Conformation of macromolecules in the gas phase: use of matrix-assisted laser desorption methods in ion chromatography.

Effect of the long-range potential on ion mobility measurements