A study of the 1s core region of atomic magnesium by X-ray photoelectron spectroscopy

The 1s core region of atomic magnesium has been measured by X-ray photoelectron spectroscopy using AlKα (1486.6 eV) radiation in order to determine the energy and intensity of the main satellite corresponding to 3_s → 4_s excitation accompanying core ionization. It was found to lie at 11.56 eV higher bonding energy than the main 1s?1 peak, with a relative intensity of 17%. The accent ab initio Cl calculation of Kosugi and Kuroda gives a separation which is in good agreement with experiment but somewhat overestimates the relative intensity.     

反转区电子转移速率的理论研究

利用级联方程方法研究了反转区的电子转移速率与电子态耦合常数以及溶剂弛豫时间的关系.结果表随着电子态间耦合强度的增加,反应速率先增加然后减小,而随着溶剂弛豫时间的减小反应速率增加.我们将这些结果与近似理论费米黄金规则、Landau-Zener公式进行了比较,由于费米金规则基于一阶微扰论,所以只适用于耦合常数较小的情况.而Landau-Zener公式假设电子在跃迁区域弹道运动,在电子态耦合大的情况下也存在问题.     

Theoretical-experimental study of formic acid photofragmentation in the valence region

Photoionization and photofragmentation studies of formic acid (HCOOH) are performed for the valence shell electron ionization process. The total and partial ion yield of gaseous HCOOH were collected as a function of photon energy in the ultraviolet region, between 11.12 and 19.57 eV. Measurements of the total and partial ion yield of gaseous formic acid molecule are performed with a time-of-flight mass spectrometer at the Synchrotron Light Brazilian Laboratory. Density functional theory and time dependent density functional theory are employed to calculate the ground and excited electronic state energies of neutral and ionic formic acid as well as their fragments and normal vibration modes. The ionization potential energies, the stability of electronic excited states of HCOOH(+), and the energies of opening fragmentation channels are estimated from theoretical-experimental analysis. Additionally, the main formic acid photofragmentation pathways by exposition of photons within that energy range are determined experimentally. These produced ions primarily have the following mass/charge ratios: 46 (HCOOH(+)), 45 (COOH(+)), 29 (HCO(+)), and 18 (H(2)O(+)).     

A study of the structure of water in electrolyte solutions by differential infrared absorption spectroscopy in the overtone region

Theoretical and Experimental Chemistry -     

A study of the Raman spectra of alkanes in the Fermi-resonance region

The experimental and theoretically predicted Raman spectra for the first few alkanes in the homologous series: methane, ethane, propane and butane are presented for the region 2700–3100 cm⁻¹. The structure of the spectra is rather complex. Analysis of the results obtained shows that Fermi resonance occurs between the CH stretching vibrations in the 3000 cm⁻¹ region and the 2ν overtones of deformation vibrations in the low frequency (1450–1500 cm⁻¹) region.     

Mass spectrometric study of peptides secreted by the skin glands of the brown frog Rana arvalis from the Moscow region

A high‐performance liquid chromatography nano‐electrospray ionization Fourier transform mass spectrometry (HPLC/nanoESI‐FTMS) approach involving recording of collision‐activated dissociation (CAD) and electron‐capture dissociation (ECD) spectra of an intact sample and two its modifications after performic oxidation and reduction followed by carboxamidomethylation helps to establish peptide profiles in the crude secretion of frog species at mid‐throughput level, including de novo sequencing. The proposed derivatization procedures allow increasing of the general sequence coverage in the backbone, providing complementary information and, what is more important, reveal the amino acid sequence in the cystine ring (‘rana box’). Thus purely mass spectrometric efficient sequencing becomes possible for longer than usual proteolytic peptides. Seventeen peptides belonging to four known families were identified in the secretion of the European brown frog Rana arvalis inhabiting the Moscow region in Russia. Ranatuerins, considered previously a unique feature of the North American species, as well as a new melittin‐related peptide, are worth special mention. The developed approach was previously successfully used for the identification of peptides in the skin secretion of the Caucasian green frog Rana ridibunda. Copyright © 2009 John Wiley & Sons, Ltd.     

Infrared study of substrate effects in the surface region of polyethylene

The surface of thin polyethylene films (ca. 1 mil) nucleated on high- and low-energy surfaces was studied. It was found that the degree of crystallinity in the surface region, as determined by transmission and reflection infrared spectroscopy, was dependent on the nature of the substrate. Relatively small and randomly oriented spherulites were observed in the surface region of thin polyethylene films nucleated on gold, a high-energy surface. The surface region of a thin polythylene film nucleated on polytetrafluoroethylene, a low-energy substrate, was observed to have considerably fewer spherulites, but much larger in size, with orientation restricted, in general, to the plane of the film. The relative intensity of the 720 cm^?1 to the 730 cm^?1 band in the reflectance spectra (ATR) indicates that the surface region of a polyethylene film nucleated on a high surface energy substrate is more crystalline than the surface region of a film nucleated on a low surface energy substrate.     

Low-frequency dielectric study of the pretransition region in DPL-water model membrane

A low-frequency dielectric investigation of the pretransition region in dipalmitoylphosphatidylcholine (DPL)-water bilayers is reported. Results show a marked increase of the permittivity in the pretransition region. A possible interpretation in terms of capillary waves is suggested.     

Ab initio study on the electronic structures of styrene in the Franck-Condon region

The electronic structures of styrene in the Franck‐Condon region have been theoretically examined by means of ab initio complete active space self‐consistent field (CASSCF) and the second order multireference Møller‐Plesset calculations. The optimized structure of styrene in S₀ is planar but the torsional motion of the phenyl group is very floppy. The S₁ state is assigned to the local π–π* excitation within the benzene ring. On the other hand, S₂, above S₁ by 0.561 eV, is assigned to a state that resembles the so‐called V‐state of ethylene. The transition intensity of S₀–S₁ is weak, while that of S₀–S₂ is strong. This is in good agreement with the experimental absorption spectrum where the S₀–S₁ and S₀–S₂ transitions are in the energy range of 290–220 nm. The optimized geometry of S₁, characterized by an enlarged benzene ring and its vibrational analyses, further justifies the assignment of the S₁ state. © 2002 Wiley Periodicals, Inc. J Comput Chem 9: 928–937, 2002     

灌注色谱法的发展和应用

介绍了灌注色谱法的发展、应用及其相关技术,并对灌注色谱法的特征、理论和应用作了评述。     

A Mass-spectrometric study of propionaldehyde oxidation in the negative temperature coefficient region

The oxidation of propionaldehyde has been investigated in a 1-L Pyrex reactor at total pressures of 50–120 torr and temperatures 553–713 K. Detection of reactants and products was principally by molecular beam mass spectrometry, although certain species could only be measured by gas-chromatographic analysis. At 553 K the yield of water was ～83% of the propionaldehyde consumed, leading to the conclusion that OH is the principal chain carrier near the beginning of the negative temperature coefficient region. Many oxygenated organics (CH₂O, CH₃CHO, C₂H₅OH, C₂H₅O₂H, CH₃O₂H) and C₂H₄ are formed during the oxidation process. These oxidation products are consistent with the important role of O₂ addition to C₂H₅ radicals at 553 K followed by subsequent reactions of the C₂H₅O₂ radical. As the temperature is increased, the product concentrations smoothly change to a much simpler distribution in which C₂H₄, H₂O₂, and CO are the dominant products.     

A dielectric study of the glass transition region in segmented polyether-urethane copolymers

Ten polyether-urethane thermoplastic elastomers of varying chemical structure have been characterized by dielectric spectroscopy and scanning calorimetry. In the temperature range corresponding to the glass-rubber transition of the predominantly polyether phase, modification of the primary dielectric transition and the occurrence of a second transition at somewhat higher temperature have been observed. Through comparison with calorimetric data, these events have been related to supercooling of crystallizable polyether segments. Supercooling suppresses dielectric loss processes in some regimes and enhances losses in others. By systematic variation of chemical structure these phenomena have been classified.     

Two-dimensional near-infrared correlation spectroscopy study the methanol in acidic pH region

The effect of pH on the structure of methanol was investigated by FT-NIR (Fourier transform near-infrared) spectroscopy and generalized two-dimensional (2D) correlation spectroscopy. pH perturbed 2D correlation spectra are calculated for the spectra in the 5,500-4,000, 7,500-5,500 cm(-1) regions at different pH values. We observed that the stretching of CH(3) was shifted because of the direct interaction of the CH(3) group of methanol with the OH group of water, the change of free OH is more sensitive to pH than the cyclic dimmer and CH.O.     

Audio to microwave frequency dielectric study of the pretransition region in DPL-water systems

Abstract

The phospholipid–water mixtures are used as model systems to investigate the structure and function of biological membranes. The dielectric behaviour of DPPC–water and DPPE–water systems was explored at audio (≥ 2kHz) and microwave (10 GHz) frequencies versus temperature. Particular care was devoted to the pretransition below the main gel-liquid-crystalline phase transition. A possible interpretation of the pretransition mechanism is given in terms of capillary waves.     

Light scattering by cubic particles in the Rayleigh-Gans region

Summary The light scattered by cubic particles in theRayleigh-Gans domain is considered and an expression is derived for the particle scattering factor of a dispersion of randomly oriented cubes. Numerical results are presented for the dissymmetry as a function of the side length of the cube and the wavelength of the incident radiation. The total scattering cross section is also considered.

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Zusammenfassung Das von kubischen Teilchen imRayleigh-Gans-Bereich gestreute Licht wird untersucht und ein Ausdruck für den Teilchen-Streufaktor einer statistisch orientierten Verteilung von Würfeln abgeleitet. Die numerischen Ergebnisse für die Dissymmetrie sind dargestellt als Funktion der ScitenlÄnge des Würfels und der WellenlÄnge der einfallenden Strahlung. Der totale Streuquerschnitt wird ebenfalls angegeben.

     

Contribution of uniformly 13C-enriched sterigmatocystin to the study of its pulmonary metabolism

Mycotoxins are secondary metabolites of filamentous fungi which can cause a wide range of systemic effects. Human health effects of inhaled mycotoxins remain poorly documented, despite the large amounts present, associated with air-borne particles. Among these mycotoxins, sterigmatocystin is one of the most prevalent. Because its chemical structure is close to that of the aflatoxins, we studied its metabolism and its cellular consequences when in contact with the airway epithelium, using the mass spectral signature from the 10% (13)C uniformly enriched sterigmatocystin. The metabolism was studied in vitro, using recombinant cytochrome P450s enzymes, and in porcine tracheal epithelial cell (PTEC) primary cultures at an air-liquid interface. The metabolites were analyzed by high-performance liquid chromatography coupled with tandem mass spectrometry detection. Expressed enzymes and PTECs were exposed to uniformly (13)C-enriched sterigmatocystin to confirm the relationship between sterigmatocystin and its metabolites because this isotopic cluster shape is conserved for all metabolites and their product ions. Incubation of sterigmatocystin with recombinant cytochrome P450 1A1 led to the formation of three metabolites identified as monohydroxysterigmatocystin, dihydroxysterigmatocystin and one glutathione adduct, the latter after the formation of a transient intermediate. In the PTEC cultures, sterigmatocystin metabolism resulted in a glucuro-conjugate. Two other products were detected, a sulfo-conjugate and a glucuro-conjugate of hydroxysterigmatocystin upon cytochrome P450 1A1 induction. This is the first study to report sterigmatocystin metabolism in airway epithelium, and it suggests that, contrary to the aflatoxins, sterigmatocystin is mainly detoxified into its conjugates and is unable to produce significant amounts of reactive metabolites in respiratory cells, at least in pigs.     

Molecular-dynamics study of anomalous volumetric behavior of water-benzene mixtures in the vicinity of the critical region

Molecular-dynamics simulations of water-benzene mixtures at 573 K and pressures in the 85-140 bars range have been performed to examine local structure and dynamics of the mixtures, which exhibit anomalously large volume expansion on mixing as recently found by in situ near-infrared measurements. Fractional charges for a simple-point-charge-type potential of water were adjusted so as to reproduce liquid densities and the gas-to-liquid transition pressure of neat water at 573 K. A Lennard-Jones-type potential for benzene was used and the Lorentz-Berthelot combination rule was applied to the water-benzene interaction. Simulations with a N-P-T ensemble of 800-molecule system have been performed and the results reproduce well the anomalous volumetric behavior of the mixtures with the mole fraction of benzene in the 0.3-0.8 range. Pair distribution functions, coordination numbers, and self-diffusion coefficients for the mixtures are calculated, and it is suggested that the local structure around water molecules undergoes drastic change by dissolution of benzene in the vicinity of the critical region, but that around benzene molecules seems to be understood as that of ordinary liquid mixtures.     

Two-dimensional near-IR correlationspectroscopy study the interaction of protein and famotidine in acidic pH region

The changing of protein in secondary structure and the binding between protein and famotidine in acid aqueous solutions were studied by Fourier-transform near-infrared spectrospy combined two-dimensional correlation analysis, pH-perturbed 2-D correlation spectra are calculated for the spectra in the 4850-4200, 7500-5350 and 6000-5000cm(-1) regions at different pH values. We observed that there is a binding between atom S of sulfanilamide radical and -COOH of protein in 5742cm(-1) and we also can explore the change of protein in the secondary structure simultaneously.