Surface speciation of Eu3+ adsorbed on kaolinite by time-resolved laser fluorescence spectroscopy (TRLFS) and parallel factor analysis (PARAFAC)

Time-resolved laser fluorescence spectroscopy (TRLFS) is an effective speciation technique for fluorescent metal ions and can be further extended by the parallel factor analysis (PARAFAC). The adsorption of Eu(3+) on kaolinite as well as gibbsite as a reference mineral was investigated by TRLFS together with batch adsorption measurements. The PAFAFAC modeling provided the fluorescence spectra, decay lifetimes, and relative intensity profiles of three Eu(3+) surface complexes with kaolinite; an outer-sphere (factor A) complex and two inner-sphere (factors B and C) complexes. Their intensity profiles qualitatively explained the measured adsorption of Eu(3+). Based on the TRLFS results in varied H(2)O/D(2)O media, it was shown that the outer-sphere complex exhibited more rapid fluorescence decay than Eu(3+) aquo ion, because of the energy transfer to the surface. Factor B was an inner-sphere complex, which became dominant at relatively high pH, high salt concentration and low Eu(3+) concentration. Its spectrum and lifetime were similar to those of Eu(3+) adsorbed on gibbsite, suggesting its occurrence on the edge face of the gibbsite layer of kaolinite. From the comparison with the spectra and lifetimes of crystalline or aqueous Eu(OH)(3), factor C was considered as a poly-nuclear surface complex of Eu(3+) formed at relatively high Eu(3+) concentration.     

Uranium(VI) speciation by spectroscopy

The application of UV-Vis and time-resolved laser-induced fluorescence (TRLF) spectroscopies to direct speciation of uranium(VI) in environmental samples offers various prospects that have, however, serious limitations. While UV-Vis spectroscopy is probably not sensitive enough to detect uranium(VI) species in the majority of environmental samples, TRLFS is principially able to speciate uranium(VI) at very low concentration levels in the nanomol range. Speciation by TRLFS can be based on three parameters: excitation spectrum, emission spectrum and lifetime of the fluorescence emission process. Due to quenching effects, the lifetime may not be expected to be as characteristic as, e.g., the emission spectrum. Quenching of U(VI) fluorescence by reaction with organic substances, inorganic ions and formation of carbonate radicals is one important limiting factor in the application of U(VI) fluorescence spectroscopy. Fundamental photophysical criteria are illustrated using UV-Vis and fluorescence spectra of U(VI) hydrolysis and carbonato species as examples.     

Modeling the Electronic Absorption Spectra of the Indocarbocyanine Cy3

Accurate modeling of optical spectra requires careful treatment of the molecular structures and vibronic, environmental, and thermal contributions. The accuracy of the computational methods used to simulate absorption spectra is limited by their ability to account for all the factors that affect the spectral shapes and energetics. The ensemble-based approaches are widely used to model the absorption spectra of molecules in the condensed-phase, and their performance is system dependent. The Franck–Condon approach is suitable for simulating high resolution spectra of rigid systems, and its accuracy is limited mainly by the harmonic approximation. In this work, the absorption spectrum of the widely used cyanine Cy3 is simulated using the ensemble approach via classical and quantum sampling, as well as, the Franck–Condon approach. The factors limiting the ensemble approaches, including the sampling and force field effects, are tested, while the vertical and adiabatic harmonic approximations of the Franck–Condon approach are also systematically examined. Our results show that all the vertical methods, including the ensemble approach, are not suitable to model the absorption spectrum of Cy3, and recommend the adiabatic methods as suitable approaches for the modeling of spectra with strong vibronic contributions. We find that the thermal effects, the low frequency modes, and the simultaneous vibrational excitations have prominent contributions to the Cy3 spectrum. The inclusion of the solvent stabilizes the energetics significantly, while its negligible effect on the spectral shapes aligns well with the experimental observations.     

A new maximum likelihood approach with asymmetric residual distribution for multicomponent mass spectra analysis

This paper proposes a new maximum likelihood approach for the deconvolution of identity and quantity of individual compounds based on the multicomponent mass spectra measured by mass spectrometry (MS). Mixture analysis of multicomponent mass spectra is, typically, based on a linear multicomponent mass spectrum model, where the compounds of the measured spectra to be solved are explicitly stated and assumed to be known. In many cases, however, the measured spectrum may contain unknown compounds that are not explicitly stated in the model and a commonly used least square (LS) solution fails. Moreover, a standard improvement over the LS method in these cases, namely the M-estimation (ME) approach, also suffers from this same problem. Our method overcomes the limitations of the LS and ME methods by modeling the effect of the unknown compound(s) to the residual of the linear model. The experimental results presented show that this new approach can separate more robustly the complex multicomponent mass spectra into their individual constituents compared to the LS and ME methods.     

化学修饰在质谱中的应用 I:长链不饱和脂肪酸的双键定位: 2-烯基取代杂环化合物的质谱

作者提出了一种用"远端基团修饰法"来确定双键位置的新途径.长链不饱和脂肪酸环化为相应的2-烯基杂环化合物后,这些杂环母核的强大的正荷定域作用使产物的质谱的结构专一性大为提高,并能直接提供有关双键位置的信息.本文报道了微量衍生化方法与八类代表性杂环衍生物与四种苯并唑衍生物的质谱比较.     

Kinetic energy release in fragmentation processes following electron emission: a time-dependent approach

A time-dependent approach for the kinetic energy release (KER) spectrum is developed for a fragmentation of a diatomic molecule after an electronic decay process, e.g., Auger process. It allows one to simulate the time-resolved spectra and provides more insight into the molecular dynamics than the time-independent approach. Detailed analysis of the time-resolved emitted electron and KER spectra sheds light on the interrelation between wave packet dynamics and spectra.     

Determination of phosphorus, sulfur and the halogens using high-temperature molecular absorption spectrometry in flames and furnaces—A review

The literature about the investigation of molecular spectra of phosphorus, sulfur and the halogens in flames and furnaces, and the use of these spectra for the determination of these non-metals has been reviewed. Most of the investigations were carried out using conventional atomic absorption spectrometers, and there were in essence two different approaches. In the first one, dual-channel spectrometers with a hydrogen or deuterium lamp were used, applying the two-line method for background correction; in the second one, a line source was used that emitted an atomic line, which overlapped with the molecular spectrum. The first approach had the advantage that any spectral interval could be accessed, but it was susceptible to spectral interference; the second one had the advantage that the conventional background correction systems could be used to minimize spectral interferences, but had the problem that an atomic line had to be found, which was overlapping sufficiently well with the maximum of the molecular absorption spectrum. More recently a variety of molecular absorption spectra were investigated using a low-resolution polychromator with a CCD array detector, but no attempt was made to use this approach for quantitative determination of non-metals. The recent introduction and commercial availability of high-resolution continuum source atomic absorption spectrometers is offering completely new possibilities for molecular absorption spectrometry and its use for the determination of non-metals. The use of a high-intensity continuum source together with a high-resolution spectrometer and a CCD array detector makes possible selecting the optimum wavelength for the determination and to exclude most spectral interferences.     

A theory of elementary photophysical processes with the participation of excess electrons in polar liquids

The main concepts of the new theory of processes with the participation of excess electrons in polar liquids are considered. The theory takes into account that (1) polar liquids are electrostatically inhomogeneous (local potentials on molecules are different) and (2) a molecule can accept an electron for a short time to produce an anion in an unstable state with a certain energy and lifetime. A discrete model of a substance consisting of molecules with constant dipole moments is used. Excess electrons in a liquid are described by energy distribution density, and the behavior of electrons, by quantum mechanics equations. The experimental data on the photoionization of water and aqueous solutions of salts and the low threshold energy of photons (～6.5 eV) at which solvated electrons appear in water are explained. The absorption spectra of water with excess electrons at the first and subsequent time moments after their photogeneration are reproduced theoretically. The dependence of the photoemission of solvated electrons from potassium-ammonia solutions on the energy of photons is interpreted. The continuous spectrum of spontaneous radiation of solvated electrons in liquid ammonia and water is calculated. The optical absorption spectra of solvated electrons in such polar liquids as water and ammonia are reproduced.     

Chemical modification in mass spectrometry. 1.: The double bond location of long-chain fatty acids: The mass spectra of 2-alkenyl substituted heterocycles

A novel approach to double bond location in long-chain olefinic acids has been elaborated by means of “remote functional group modification”. This method consists in converting the carboxylic acid into corresponding 2-alkenyl substituted heterocycle followed by measuring its 70 eV electron-impact mass spectrum. The inherited tendency of random migration of the double bond along the aliphatic chain under electron impact is strongly suppressed by incorporating the terminal carboxyl group into a heterocycle. The derivatives thus prepared show more informative spectra which clearly indicate the site of unsaturation of the parent acids. Submilligram scale derivatization of the olefinic acids, as exemplified by the model compound oleic acid, and a comparison of the spectra of the resulting heterocycles (3—10) as well as benzoxazole derivatives (3a—3d) of selected carboxylic acids is described in the present paper.     

Solid-state fluorescence organic materials as a tool for spectral modification of ZnS-based screen-printed thick layer electroluminescence devices

This work is focused on modification of spectral characteristic of light emitted by alternating current powder-based ZnS electroluminescent device by addition of a color conversion material. A suitable diketopyrrolopyrrole (DPP) derivative with absorption spectrum compatible with emission spectrum of phosphor was found and was added into the printing formulation. Electroluminescent panel was printed by screen printing method and the influence of fluorophore was evaluated from the emission spectra of the electroluminescent device. Color space coordinates of emitted light of pure phosphor and phosphor modified by DPP were plotted into the CIE space for better visualization of the color change. It was found that the presence of fluorophore increased the value of measured quantity—absolute spectral irradiance—more than seven times at 587 nm which corresponds to the maximum of fluorescence emission of DPP. This approach provides useful tool to obtain colors of various wavelengths and therefore various hues without the need to look for new challenging and expensive chemical modifications of the phosphor.     

A comparative study of rotational temperatures using diatomic OH,O2 and N2+ molecular spectra emitted from atmospheric plasmas

From the application point of view, gas temperature is one of the most important parameters for atmospheric plasmas. Based on the fact that the gas temperature is closely related with the rotational temperature of an atmospheric plasma, a spectroscopic method of measuring the rotational temperature is described in this work by analyzing OH, O₂ and N₂⁺ molecular spectra emitted from the atmospheric plasma in ambient air. The OH and N₂⁺ molecular spectra are emitted because of the oxygen, hydrogen and nitrogen atoms existing in the ambient air. The O₂ diatomic molecular spectrum is emitted from the oxygen plasma that is frequently produced for atmospheric plasma applications. In order to utilize a spectrometer with modest spectral resolution, a synthetic diatomic molecular spectrum was compared with the experimentally obtained spectrum. The rotational temperatures determined by the above three different molecular spectra are in good agreement within 2.4% error. In the case of a plasma with low gas temperature, the temperature measured by a thermocouple was compared to verify the accuracy of the spectroscopic method, and the results show excellent agreement. From the study, it was found that an appropriate diatomic molecular species can be chosen to be used as a thermometer depending on experimental circumstances.     

Triplet-triplet optical energy transfer from benzophenone to naphthalene in the vapor phase

In principle the optical energy absorbed by a complex molecule raises that molecule to one of its excited states, and afterwards this excitation energy decays through the different relaxation channels. Initially, electronically excited benzophenone emits photons in the phosphorescence band of benzophenone and these emitted photons, as a stream of particles, are absorbed by the acceptor molecule naphthalene, then excited naphthalene phosphoresces. In this investigation, sensitized phosphorescence decay times in different conditions were measured for benzophenone-naphthalene system in the vapor phase. The ultraviolet-visible spectra of the system in the vapor phase at room temperature conditions were broad and structureless.     

Radiative electronic energy transfer-time studies of naphthalene-biacetyl system by one and two-photon excitation, and optical antenna mechanism

In principle, the optical energy absorbed by a complex molecule raises that molecule to one of its excited states, and afterwards this excitation energy decays through the relaxation channels. Initially, electronically excited naphthalene emits photons and these emitted photons are absorbed by the acceptor molecule biacetyl, then excited biacetyl fluoresces. In this investigation radiative energy transfer-time is measured in cyclohexane by one and two-photon excitations. The UV-vis spectrum of biacetyl vapor at room temperature conditions was broad and structureless.     

An integrated method for spectrum extraction and compound identification from gas chromatography/mass spectrometry data

A method is presented for extracting individual component spectra from gas chromatography/mass spectrometry (GC/MS) data files and then using these spectra to identify target compounds by matching spectra in a reference library. It extends a published “model peak” approach which uses selected ion chromatograms as models for component shape. On the basis of this shape, individual mass spectral peak abundance profiles are extracted to produce a “purified” spectrum. In the present work, ion-counting noise is explicitly treated and a number of characteristic features of GC/MS data are taken into account. This allows spectrum extraction to be reliably performed down to very low signal levels and for overlapping components. A spectrum match factor for compound identification is developed that incorporates a number of new corrections, some of which employ information derived from chromatographic behavior. Test results suggest that the ability of this system to identify compounds is comparable to that of conventional analysis.     

Study of Doppler broadening of gamma-ray spectra in 14-MeV neutron activation analysis

Neutron reactions producing characteristic photons of isotopes are important for nondestructive analysis of materials. Technique to determine the intensity of neutron induced gamma rays by fitting a spectrum with a Gaussian function using detector resolution curves derived from isotopic sources may fail if the peak is Doppler-broadened. This leads to the miscalculation of the area of the peak and, therefore, to misidentification of the material. This work shows that Doppler broadening occurs in the 14-MeV neutron analysis with photons emitted in inelastic scattering reactions on light nuclei with excited states whose lifetimes are much smaller than the time of flight of a recoiling nucleus in the material. It provides groundwork for analysis of gamma ray spectra utilizing detector response functions measured with a 14-MeV neutron source using actual geometry of an active interrogation system.     

Computational study of pulsed neutron induced activation analysis of cargo

Pulsed neutron induced activation analysis is a nondestructive technique to detect threats hidden in bulk objects such as cargo pallets, trucks, etc. Isotopic content of cargo can be measured by counting photons emitted with characteristic energies as a result of neutron induced reactions within cargo’s materials. Neutron and gamma radiation transport in active interrogation system consisting of a 14-MeV neutron source, photon detector, and a cargo truck was analyzed with MCNPX code. Gamma ray signatures of cargo with hidden explosive threat were analyzed during the neutron pulse and between neutron pulses for varying system’s geometry and material composition of cargo.     

Reversible low-light induced photoswitching of crowned spiropyran-DO3A complexed with gadolinium(III) ions

Photoswitchable spiropyran has been conjugated to the crowned ring system DO3A, which improves its solubility in dipolar and polar media and stabilizes the merocyanine isomer. Adding the lanthanide ion gadolinium(III) to the macrocyclic ring system leads to a photoresponsive magnetic resonance imaging contrast agent that displays an increased spin-lattice relaxation time (T?) upon visible light stimulation. In this work, the photoresponse of this photochromic molecule to weak light illumination using blue and green light emitting diodes was investigated, simulating the emission spectra from bioluminescent enzymes. Photon emission rate of the light emitting diodes was changed, from 1.75 × 101? photons·s?1 to 2.37 × 1012 photons·s?1. We observed a consistent visible light-induced isomerization of the merocyanine to the spiropyran form with photon fluxes as low as 2.37 × 1012 photons·s?1 resulting in a relaxivity change of the compound. This demonstrates the potential for use of the described imaging probes in low light level applications such as sensing bioluminescence enzyme activity. The isomerization behavior of gadolinium(III)-ion complexed and non-complexed spiropyran-DO3A was analyzed in water and ethanol solution in response to low light illumination and compared to the emitted photon emission rate from over-expressed Gaussia princeps luciferase.     

中药复杂组效关系的变结构神经网络辨识方法

针对中药复杂组效关系的辨识问题,研究了变结构多层前馈神经网络,推导出一种新型的变结构网络学习算法,成功地应用于中药川芎药效活性预测计算.该方法从一个规模较小的网络出发,当网络无法达到预定的学习精度时,自动增加隐含层神经元个数,并在原有学习结果的基础上确定新的网络参数,自适应地确定前馈神经网络结构,可用于处理复杂化学模式信息.计算机仿真实验结果表明,该方法能有效地确定多层前馈神经网络的最佳结构,提高网络学习效率和函数逼近精度,解决复杂非线性函数映射关系准确建模问题.     

Experimental verification of a radiative model of laser-induced plasma expanding into vacuum

A radiation dynamic model of the postbreakdown stage of laser-induced plasma solves a twofold task: first, the direct problem, it yields an analytical expression for the plasma radiation dynamics under arbitrarily chosen initial conditions allowing the computation of synthetic spectra; second, the inverse problem, it allows finding of the initial conditions by a direct comparison of calculated synthetic spectra with experimentally measured ones. In this work, we carry out experimental verification of the model, thus dealing with the inverse problem. We vary the initial parameters of the model (plasma initial temperature and the initial concentrations of species) until a close fit between the synthetic and the experimental spectrum is obtained. Some of the model inputs (e.g., the initial radius of the plasma) are measured and introduced into the model as fixed constants. Calculations and measurements are performed on a binary SiC system; on a series of multicomponent aluminum samples doped with Si, Mg, Cu, Zn, and Fe; and on pure iron, silicon, and carbon. From two to six elements and up to 500 spectral lines were involved in the calculations. The Monte Carlo optimization (the simulated annealing method) is used for finding initial plasma temperature and number densities. A reasonably good agreement is obtained between the computed and the experimental spectra. This approach can be considered as a valuable step towards the achievement of absolute analysis.     

Theory and application of dissociative electron capture in molecular identification

The coupling of an electron monochromator (EM) to a mass spectrometer (MS) has created a new analytical technique, EM-MS, for the investigation of electrophilic compounds. This method provides a powerful tool for molecular identification of compounds contained in complex matrices, such as environmental samples. In particular, EM-MS has been applied to the detection of nitrated aromatic compounds, many of which are potent mutagens and/or carcinogens and are considered environmental hazards. EM-MS expands the application and selectivity of traditional MS through the inclusion of a new dimension in the space of molecular characteristics-the electron resonance energy spectrum. EM-MS also enhances detection sensitivity as well because the entire electron flux of the proper energy can be delivered into the negative ion resonance that is analytically most useful to solving the problem at hand. However, before this tool can realize its full potential, it will be necessary to create a library of resonance energy scans from standards of the molecules for which EM-MS offers a practical means of detection. Unfortunately, the number of such standards is very large and not all of the compounds are commercially available, making this library difficult to construct. Here, an approach supplementing direct measurement with chemical inference and quantum scattering theory is presented to demonstrate the feasibility of directly calculating resonance energy spectra. This approach makes use of the symmetry of the transition-matrix element of the captured electron to discriminate between the spectra of isomers. As a way of validating this approach, the resonance values for 25 nitrated aromatic compounds were measured along with their relative abundance. Subsequently, the spectra for the isomers of nitrotoluene were shown to be consistent with the symmetry-based model. The initial success of this treatment suggests that it might be possible to predict negative ion resonances and thus create a library of EM-MS standards.