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The dipole moment (μ), linear polarizability (α), and first hyperpolarizability (β(tot)) of the asymmetric unit of L-arginine phosphate (LAP) monohydrate crystal are investigated using the supermolecule approach in combination with an iterative electrostatic polarization scheme. Environment polarization effects are attained by assuring the convergence of the dipole moment of LAP embedded in the polarization field of the surrounding molecules whose atomic sites are treated as point charges. The results obtained show that in the presence of the embedding charges, the value of μ is increased by 9% but the static values of α and β(tot) are decreased, respectively, by 3% and 13%, as compared with the isolated situation. The MP2/6-311+G(d) model predicts for the in-crystal dipole moment the converged value of 33 D, in good concordance with the available experimental result of 32 D. Our estimates for the converged results of α and β(tot) are, respectively, 22.51×10(-24) and 5.01×10(-30)?esu. Dispersion effects are found to have a small impact on the nonlinear optical responses of LAP in the visible region. In addition, MP2/6-311G results obtained for β(tot) by using isolated and embedded LAP dimers show that crystal packing effects have a significant contribution of the electrostatic interactions. Our results suggest that the role of the crystal environment is to minimize the effects of the intermolecular interactions in the electric properties. That is, μ and β(tot) gain a more additive character in the presence of the field of the embedding charges. This is specially marked for β(tot). 相似文献
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The influence of the relevant reaction conditions on the molecular weight and polydispersity during the cationic ring-opening polymerization of epichlorohydrin has been studied using an experimental design. The polymerization was conducted in the presence of an alcohol (diol and triol), a Lewis acid at two temperatures (5 °C and 25 °C), and with two monomer addition rates. FT-IR spectra were used for the chemical characterization of the polymer, and MALDI-TOF mass spectrometry was used to determine the oligomeric composition and the masses of the initiator or transfer agent. The FT-IR showed the characteristic peaks of polyepichlorohydrin, and the mass spectra indicate that the alcohol was incorporated in the polymer structure. The MW and polydispersity were determined using gel permeation chromatography. We observed that the two most significant parameters that affected MW were the monomer addition rate and the reaction temperature, whereas polydispersity was most strongly affected by the monomer addition rate. 相似文献
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Luis?Alberto?B.?Moraes Ad?o?A.?Sabino Eduardo?C.?Meurer Marcos?N.?EberlinEmail author 《Journal of the American Society for Mass Spectrometry》2005,16(4):431-436
A general method based solely on mass spectrometric techniques for the absolute configuration assignment of ortho, meta, or para isomers of acyl nitrobenzenes and derivatives is described. Instead of comparing the mass spectra of the three intact molecules
of each positional isomer and investigating each one of the many sets of positional isomers, the method generalizes the effort
by performing structural analysis on configurationally diagnostic fragment ions that are common for a given class of compounds.
These ions must therefore retain the positional information of the parent molecules and be unequivocally distinguished. Nitrobenzoyl
cations are common and stable fragment ions of most acyl nitrobenzenes and derivatives retaining the respective ortho, meta, or para configuration of the precursor molecules. The different NO2 and CO+ ring alignments profoundly influence their collision-induced dissociation and bimolecular reactivity, and the isomeric 2-,
3-, and 4-nitrobenzoyl cations are found to be unequivocally distinguished using both approaches. Absolute ortho, meta, or para positional assignment by tandem MS of every isomeric molecule of the acyl nitrobenzene class and derivatives forming detectable
amounts of any of those diagnostic nitrobenzoyl cations is, therefore, possible. The ability to perform absolute (non-comparative)
configuration assignment using such diagnostic ions is exemplified for a single test molecule of (2R)-(−)-2-methylglycidyl
4-nitrobenzoate. The general application of this absolute MS-only method for other classes of positional isomers is discussed. 相似文献
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It is shown that three-dimensional nonparaxial beams are described by the oblate spheroidal exact solutions of the Helmholtz equation. For what is believed to be the first time, their beam behavior is investigated and their corresponding parameters are defined. Using the fact that the beam width of the family of paraxial Gaussian beams is described by a hyperbola, we formally establish the connection between the physical parameters of nonparaxial spheroidal beam solutions and those of paraxial beams. These results are also helpful for investigating exact vector nonparaxial beams. 相似文献
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Triantafyllos A. Albanis Dominga Bochicchio Sabino A. Bufo Isabella Cospito Maurizio D'Auria Marilena Lekka 《International journal of environmental analytical chemistry》2013,93(8-9):561-569
Photodegradation of two sulfonylurea herbicides, triasulfuron and thifensulfuron-methyl adsorbed on Preveza or Nea Malgara soils (Greece) was studied in outdoor and laboratory experiments. Herbicides on adsorbed phase and kept in the dark were characterised by a high reactivity, giving depletion curves that can be all described by a first order equation. In the irradiation experiments the kinetic behaviour of photodegradation was complex and characterised by a double step photoreaction. After a first period varying from 8 to 24 h the rate of reaction was reduced to 7-31% of the initial rate. The kinetic constant related to the degradation of triasulfuron practically showed the same values of those obtained for thifensulfuron-methyl. The half-lives obtained on Nea Malgara soil were generally higher than those obtained using Preveza soil. The observed behaviour is explained considering the photochemical properties of the herbicides, and the organic matter content of the soils. 相似文献
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Manuel Sergi Sabino Napoletano Camilla Montesano Roberto Iofrida Roberta Curini Dario Compagnone 《Analytical and bioanalytical chemistry》2013,405(2-3):725-735
An LC–MS–MS-based procedure for determination in hair of 14 different drugs of abuse belonging to the classes cocaine, amphetamine-like compounds, opiates, and hallucinogens has been developed. A pressurized-liquid extraction procedure was used and proved useful for quantitative recovery of all the analytes tested. This procedure, in conjunction with a simple decontamination step, performed to avoid false-positive samples, enabled the detection of all the analytes with LOQ ranging from 1.8 to 16 pg mg?1 and accuracy varying from 85 to 111 %. The procedure was validated in accordance with the SOFT/AAFS guidelines and seems to be suitable for routine determination of the drugs tested in hair. 相似文献
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Harald Brzezinka Sabino Goenechea und Michael Langer 《Fresenius' Journal of Analytical Chemistry》1986,323(3):220-224
Zusammenfassung Für die Trennung von Glucuroniden wurde die Hochdruckflüssigkeits-Chromatograpie mit einer RP-18 Säule und einem phosphatgepuffertem Laufmittel mit wechselnden Anteilen an Acetonitril eingesetzt. Massenspektrometrisch (chemische Ionisation mit NH3 als Reaktandgas unter Bedingungen der Direkteinführung) zeigten die Glucuronide ein unterschiedliches Verhalten. Bei einigen erhielt man Informationen über den Aglykonanteil, den Glucuronsäureanteil und über das Molekülion. Glucuronide mit einem heterocyclischen Ring (Stickstoff) ergaben dagegen als intensivstes Ion das (Aglykon + H)+ -Ion; die Ionen für (M + NH4)+ fehlten vollständig bei Morphin-3- und Pentazocin-Glucuronid. Bei Codein-Glucuronid war das (M + NH4-H2O)+-Ion als intensives Ion vorhanden. Über pos/neg- Ionen-FAB konnte das Molekülion oder Ionen von Matrix- bzw. Alkaliionenanlagerungen an das Molekülion bestimmt werden.
Auszugsweise vorgetragen bei der 65. Tagung der Deutschen Gesellschaft für Rechtsmedizin in Gießen. 12.–15. September 1984 相似文献
High-pressure liquid chromatographic separation of glucuronides and their mass-spectrometric identification
Summary For the separation of glucuronides high-pressure liquid chromatography with a RP-18 column and a phosphate buffered liquid phase with different amounts of acetonitrile was used. The mass spectra (chemical ionization with ammonia as reactant gas and direct evaporation) of glucuronides were different. Some gave information about the aglycone part, the glucuronic acid part and the molecular ion. Glucuronides with a heterocyclic ring (nitrogen) showed the intensive ion (aglycone + H)+ and no ions belonging to the (M + NH4)+ -ion were found with morphine-3-glucuronide and pentazocine-glucuronide. With codeineglucuronide the ion (M + NH4–H2O)+ was of high intensity. With positive and negative FAB mass spectrometry the molecular ion or ions of matrix- or alkali-ion-attachement to the molecular ion were obtained.
Auszugsweise vorgetragen bei der 65. Tagung der Deutschen Gesellschaft für Rechtsmedizin in Gießen. 12.–15. September 1984 相似文献
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We show that propagation of optical beams in periodic lattices induces power oscillations between the Fourier spectrum peaks, with the indices related by the Bragg resonance condition. In the spatial coordinates, this is reflected in the beam position oscillations. A simple resonant theory explains the phenomenon. The effect can be used for controlled generation of the Floquet-Bloch modes in photonic lattices. 相似文献