Software algorithm for automatic interpretation of mass spectra of glycerolipids

A new software algorithm for automatic interpretation of mass spectra of glycerolipids has been developed. The algorithm utilizes a user-specified list of parameters needed to process the spectra. The compounds in mass spectra are identified according to range of measured m/z values, after which the spectra are automatically corrected by the content of naturally occurring isotopes and ion intensities of identified compounds by response correction factors. Automatic processing of the spectra was shown to be accurate and reliable by testing with numerous spectra of glycerophospholipids obtained by liquid chromatography/electrospray ionization mass spectrometry and by comparing the results with manual interpretation of the spectra. If quantitative analysis using internal standards is performed, all the identified compounds in the sample are quantified automatically. A dilution factor may be defined for each sample and is applied to correct the alterations in sample concentration during sample preparation. Processing of several replicate spectra simultaneously produces mean results with standard deviations. The software may also be used to subtract the results of two analyses and to calculate the mean result of replicate subtractions. The algorithm was shown to save time and labor in repetitive processing of mass spectra of similar type. It may be applied to processing of spectra obtained by various mass spectrometric methods.     

Sites of protonation in phenothiazines: Methane and ammonia chemical ionization mass spectra

Positive ion methane and ammonia chemical ionization mass spectra for ten phenothiazine derivatives are reported. The fragmentations observed in the chemical ionization mass spectra are rationalized in terms of the location of the added proton. High-resolution measurements are used to confirm empirical formulae of the ions in the mass spectra. Changes in the mass spectra with a change in the chemical ionization reagent gas from methane to ammonia are described. A comparison with positive ion secondary ion mass spectra of the same compounds show that the amount of fragmentation is higher in the secondary ion mass spectra, but the same types of ions are observed in spectra produced by both ionization methods.     

Spectral variations in background light emission of surface-enhanced resonance hyper Raman scattering coupled with plasma resonance of individual silver nanoaggregates

We demonstrate the origin of spectral variations in background light emission of surface enhanced resonance hyper Raman scattering (SERHRS) from single Ag nanoaggregates. Ag nanoaggregate-by-nanoaggregate variations in background light emission spectra are related to plasma (plasmon) resonance spectra. Temporal variations in background light emission spectra with temporal blueshifts in plasma resonance spectra are also observed under continuous laser excitation. Both types of the variations in background light emission are reproduced by multiplying background light emission spectra measured from a Ag microaggregate by Lorentz function spectra derived from plasma resonance spectra. The reproduction reveals that second electromagnetic (EM) enhancement by plasma resonance is the origin of the variations. Additionally, spectral variations in background light emission of SERHRS are similar to that of surface enhanced resonance Raman scattering (SERRS). The similarity indicates that both types of background light emission commonly obtain second EM enhancement from identical plasma resonance.     

简并谱的涨落统计特征分析

通过引入权重的方式,使简并谱的积累函数形式上连续递增,并用带权重的多元线性拟合提取涨落谱,由此建立一套适用于分析简并谱的NNS分布、谱刚度、能谱分维函数等涨落统计特征的方法,并具体分析了H2O、NH3及CH4分子的振动能谱进行涨落统计特征分析:发现它们的规则谱和约化非简并谱的涨落统计特征均已非Poigson化;而且约化非简并谱的非Poisson化程度较规则谱明显,即前者的能级斥力较后者大;此外,随着简并度的增加,H2O、NH3、CH4的涨落统计特征由非Poisson型向近Poisson型过渡.     

Calculation of IR spectra of the elementoorganic dendrimers

Various approximations to the analysis of the dendrimer vibrational spectra are introduced. The merits and demerits of the fragment method, calculation of the first generation and linear chains containing different number of the repeated units are discussed. The experimental spectra of two series of the phosphorus-containing starburst dendrimer generations are interpreted on the basis of the calculation of the frequencies of the normal vibrations and the band intensities in their IR spectra. The analysis of spectra enables one to assign the characteristic bands for the groups in the core, in the repeating unit and the terminal groups of the dendrimers. This assignment is supported by the calculation of the absorption curves with the force constants and electro-optical parameters (EOP). The vibrational spectra of studied starburst dendrimers (SD) (up to 11 generations) are in general identical to begin with four generation. The most marked changes of band position and their intensities are seen in spectra of the first generations, when all fragments of molecule contribute appreciably to the spectral pattern. The comparative study of vibrational spectra of SD and linear polymers reveal their main characteristic features, which are determined by their structural peculiarities.     

Isomer selective infrared spectroscopy of neutral metal clusters

We report experimental infrared spectra of neutral metal clusters in the gas phase. Multiple photon dissociation of the argon complexes of niobium clusters is used to obtain vibrational spectra in the 80-400 cm(-1) region. The observed spectra for Nb(9)Ar(n) (n=1-4) are different for different values of n. This is explained by the presence of two isomers of Nb(9) that have different affinities towards Ar and the isomer specific infrared spectra are obtained. The structures of the isomers are determined by comparing the observed spectra with the outcome of density-functional theory calculations.     

A quantitative measure of the reliability of searches of spectral libraries

A quantitative measure of library search reliability has been developed. Applications of the quantitative reliability metric (QRM) for evaluating the reliability of library searches for unknown target spectra and the use of this measure to detect the failure of a library search caused by noise, contaminant peaks and missing library spectra are discussed. The effects of noise and composite infrared spectra of mixtures on the QRM are examined for test sets of 561 infrared spectra. The QRM is also used to evaluate the performance of a search of an infrared library compressed by eigenvector projection.     

The fast atom bombardment mass spectra of xanthane dyes

The Fast Atom Bombardment mass spectra of a number of xanthane dyes are reported. These dyes are insufficiently volatile to give spectra by conventional electron impact ionization. Fragmentation pathways have been determined by metastable linked scan techniques and accurate masses obtained by peak matching. The xanthane dyes may be readily identified from their FAB spectra by the presence of characteristic ions.     

Excited and ionized states of RuO4 and OsO4 studied by SAC and SAC-CI theories

The excitation and ionization spectra of RuO₄ and OsO₄ are studied theoretically by the symmetry-adapted cluster (SAC ) and SAC-CI theories. This is the attempt to assign whole of the spectra by ab initio calculations including electron correlations. In the ground state, electron correlations work to reduce the polarity of the M–O bond overestimated in the Hartree–Fock calculation. The Os–O bond is stronger than is the Ru–O bond, which is reflected in the differences of the excitation and ionization spectra of RuO₄ and OsO₄. The excitation energies of the experimental spectra are well reproduced by the SAC-CI theory, though the calculated intensities of some peaks are very small in comparison with the experiments. The outer-valence ionization spectra calculated by the SAC-CI theory agree well with the experimental photoelectron spectra. Some shake-up peaks that are accompanied with an electron-transfers from oxygen to metal are also calculated.     

Structure of the naphthalene dimer from rare gas tagging

Excitation spectra of naphthalene dimer-argonn (n = 1-3) clusters are obtained by resonance enhanced multiphoton ionization time-of-flight mass spectroscopy. The spectra are generally independent of the number of attached argon atoms and reveal sharp structures which are fitted by superimposing independent monomer spectra. It is concluded that the rare-gas tagging technique reveals the presence of a T-shaped naphthalene dimer chromophore in the molecular beam.     

An infrared and resonance Raman spectroscopic study of phenylazonaphthol pigments

The IR, resonance Raman (RR) and electronic spectra of two phenylazonaphthol pigments, LRC Scarlet and 4BL Red, have been measured and assignments of the vibrational and electronic spectra were facilitated by ab initio calculation s at the B3-LYP/DZ level. Vibrational spectra indicate that the major species in the solid state are the hydrazo tautomers. Electronic spectra are in accordance with the nature of the electronic transitions predicted by time-dependent B3-LYP/DZ calculations.     

A procedure for analysis of densitometric spectra

Computer-aided quantitative analysis of densitometric spectra is presented. The densitometric spectra are decomposed into component bands using the Powell and Marquardt minimizers. Several different functions for the component bands are utilized. It is shown that the densitometric spectra can be decomposed into component bands with high accuracy only if the proper shapes of the bands are chosen. The method described was used for quantitative analysis of densitometric spectra of DNA cleaved by neocarzinostatin. The procedure is general and can be applied to analyses of autoradiographic films and to direct scans of electrophoretic gels. It is shown that densitometric spectra which show highly overlapped bands are well approximated by asymmetric Cauchy and Gauss functions. Well separated densitometric bands which have substantial asymmetry can be fitted to more sophisticated shapes formed by combinations of symmetric and asymmetric Cauchy and Gauss functions. High accuracy fitting to asymmetric densitometric curves may only be achieved using the cosine function introduced by Mignot and Rondot, J. Appl. Cryst. 1976, 9,460-465.     

系列大环草酰胺配合物的合成与表征——推荐一个综合化学实验

采用加热回流和溶剂热两种方法合成了三种大环草酰胺系列配合物,并对所得配合物进行单晶结构解析。使用元素分析、红外光谱、电子光谱、ESR谱对配合物进行了表征和性质研究。该实验原料简单易得,实验方法简便易行,可操作性强,有利于培养学生的实践能力和创新能力。     

Additivity in the optical kerr effect spectra of binary ionic liquid mixtures: implications for nanostructural organization

Low-frequency spectra of binary room-temperature ionic liquid (RTIL) mixtures of 1-pentyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and 1-pentyl-3-methylimidazolium bromide in the 0-250 cm(-1) region were studied as a function of mole fraction at 295 K. The spectra were obtained by use of optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The spectra of these binary mixtures are well described by the weighted sums of the spectra for the neat RTILs. This surprising result implies that the intermolecular modes giving rise to the spectra of the neat liquids must also produce the spectra of the mixtures. Additivity of the OKE spectra can be explained by a model in which locally ordered domains are assumed to exist in the neat liquid with the structures of these locally ordered domains preserved upon mixing. Recently published molecular dynamics simulations show that RTILs are nanostructurally organized with ionic networks and nonpolar regions. If ionic networks also exist in the mixture, the additivity of the OKE spectra implies that there are "blocks" along the network of the mixture that are ordered in the same way as in the neat liquids. These "block co-networks" would have a nanostructural organization resembling that of a block copolymer.     

Adjustment of numerical models for gamma-ray spectra of samples when subtracting spectra of matrix elements in neutron activation analysis

Approaches to adjustment of numerical models for gamma-ray spectra of matrix elements are considered. These approaches are aimed at (1) the elimination of the substrate effect in the preparation of the initial spectra of individual elements, (2) the energy calibration of spectra, (3) the improvement of agreement between model and actually observed spectra using the comparison test for peak amplitudes of matrix elements, and (4) special processing of the spectra obtained after the subtraction of matrix elements in the test samples. The adjustment allows the contribution of matrix elements to be more precisely subtracted from the spectra of the samples under study. Thus, additional analytical lines are obtained for some elements, and detection limits are lowered for the majority of lines produced by the standard method of spectrum processing. This extends the potential of neutron activation analysis in solving scientific and practical problems.     

芳香杂环聚合物紫外-可见光谱性质的理论研究

在AM₁方法优化构型的基础上,用ZINDO/CI方法计算了系列芳香杂环聚合物的紫外-可见光谱,探索分子结构与其光学性质之间的关系.理论计算结果表明,模型化合物ABPBO,PBO,PBOV和PBODV的紫外-可见光谱最大吸收波长(λ_max)依次增加,且相应吸收强度与分子链共轭长度相关.根据线性递变规律推导的理论λ_max值与其实验值(薄膜干态紫外吸收)符合得较好.由于质子化效应等环境因素,溶液中测量值较理论值和薄膜紫外吸收偏大.     

Detection of gaseous organic compounds by their infra-red emission stimulated by a laser beam

Excitation by a carbon dioxide laser has been used to obtain the infra-red emission spectra of a number of gaseous aliphatic hydrocarbons. The experimental set-up is described and the spectra obtained are correlated with bond vibrations and are shown to be similar to infra-red absorption spectra. The future requirements of this technique are discussed and its analytical possibilities are indicated.     

Cyclic voltammetric studies of certain industrially potential iron chelate catalysts

 For the analysis of infrared spectroscopic bands and complex patterns partial cross correlation functions of a sample spectrum with reference spectra are calculated. The chosen ranges of the spectra are based on empirical knowledge of infrared spectrum structure correlations. The normalised maxima of the partial cross correlation functions are interpreted as fuzzy truth values and are combined by fuzzy logical operators. By application of that procedure larger common substructures will be derived from the reference spectra than by a maximum common substructure search based on the complete spectra. Received: 30 October 1996/Revised: 24 February 1997/Accepted: 26 February 1997     

Fourier transform infrared study of the effects of irradiation on polyethylene

Fourier transform infrared spectra have been obtained for polyethylene irradiated in oxygen and nitrogen atmospheres. The spectra before and after irradiation have been compared by digital subtraction. The difference spectra are indicative of changes caused by irradiation. Crosslinking and chain scission reactions produce the observed changes.