Laser Desorption Mass Spectrometry of Some Organic Acids

Abstract

Positive and negative ion laser desorption (LD) mass spectra of organic acids are characterized by the emission of the quasimolecular ions (M+H)⁺ and (M-H)^?. Generation of (M+H)⁺ ions is interpreted as evidence for the occurence of high pressure proton transfer reactions in LD. Fragment ions can be rationalized by loss of stable neutral molecules from quasimolecular ions although decomposition may also be occuring prior to ionization. Features unique to LD, including the detection of pyrolysis products along with ions characteristic of the sample, are discussed in terms of the internal energy distribution in the irradiated microvolume. Negative ion mass spectra of acids are dominated by (M-H)^?, while positive ion spectra contain abundant fragment ions, underlining the utility of detecting negative ions for acidic compounds.     

HEAT AND MASS TRANSFER AND WALL SHEAR STRESS IN VERTICAL GAS-LIQUID FLOW

Results of an experimental investigation of heat and mass transfer and wall shear stress at gas-liquid flow in a vertical tube are presented. Local wall shear stress and mass transfer coefficients were measured by an electrochemical method. Experiments were performed in the range of Reynolds number variation with respect to liquid Rc_i, = 8.5 × 10³-5.4 × 10⁴, gas Re_g = 3 × 10³-1.4 × 10⁵, pressure 0.1-1 MPa. The relationship between heat and mass transfer and wall shear at gas-liquid flows is shown to exist. The results of measuring heat and mass transfer coefficients are generalized by formulas applied to calculate heat and mass transfer in single-phase turbulent flow.     

Highly sensitive and selective fluorescent “turn-on” probe for determination of aluminum ion in aqueous solution

ABSTRACT

A novel fluorescent sensor, 1-((2-hydroxynaphthalen-1-yl)methylene) semicarbazide, was synthesized and characterized by infrared spectra, elemental analysis, electrospray ionization mass spectra. The fluorescent sensing behaviors of the sensor toward different metals ions, anions, and amino acids were determined by UV–vis and fluorescence spectroscopy. The fluorescent sensor exhibited obvious changes in its electronic and fluorescent spectral behavior in the visible region of the spectrum in the presence of aluminum ion with the lower detection limit was 8.9 × 10^?9 M.     

The partial 1H NMR spectra of Al–OH and molecular H2O in hydrous aluminosilicate glasses: Component-Resolved analysis of 27Al–1H cross polarization and 1H spin-echo MAS NMR spectra

The Component-Resolved methodology was applied to ¹H spin-echo and ²⁷Al–¹H cross polarization (CP) MAS NMR data of aluminosilicate glasses. The method was able to resolve two components with different T2 relaxation rates, hydroxyl groups (OH) and molecular water (H₂O_mol), from the spin-echo data and to determine partial spectra and the relative abundances of OH and H₂O_mol. The algorithm resolved two to three components with different ²⁷Al–¹H CP dynamics from the ²⁷Al–¹H cross polarization data; the obtained partial NMR spectra for Al–OH are in excellent agreement with those obtained previously from the difference spectra between spectra with various contact times and confirm previous quantitative results and models for the Al–OH, Si–OH and H₂O_mol speciation (Malfait and Xue, 2010).     

Formation of positive and negative ions of thymine molecules under the action of slow electrons

The formation of positive and negative molecules of thymine—a base of nucleic acids—under the action of slow electrons is investigated by the method of crossed electron and molecular beams. The method developed makes it possible to measure the molecular beam intensity and determine the energy dependences and absolute values of total cross sections for the formation of positive and negative ions of thymine molecules. It is found that the maximal cross section for the formation of positive ions is reached at an energy of 95 eV and its absolute value is, accordingly, 1.4 × 10^?15 cm². The total cross section for the formation of negative ions is 8.2 × 10^–18 cm² at an energy of 1.1 eV. The mass spectra of thymine molecules are measured and the cross sections of dissociative ionization are determined.     

Heavy Quark Potential and Quarkonium Spectrum in Nonperturbative pNRQCD

The charmonium and bottomonium mass spectra are investigated systematically in potential nonrelativistic QCD with the heavy quark potential computed by lattice QCD simulations nonperturbatively. The potential consists of a static potential and relativistic corrections classified in powers of the inverse of heavy quark mass m, and the effects of the O(1/m) correction, the O(1/m ²) spin–orbit and spin–tensor corrections on the mass spectra are examined systematically. The pattern of the mass spectra is found to be in fairly good agreement with the experimental data, in which the O(1/m) correction gives an important contribution.     

Isotope effects in Raman spectra of crystalline sulfur α-S8

The Raman spectra of ³²S, ³³S, and ³⁴S powders, as well as ^naturS powder with the natural isotopic composition, have been measured in the temperature range of 5–300 K. The isotope mass dependences of the vibrational frequencies have been obtained. It has been shown that such a dependence in the region of mixed translational-librational modes differs from the dependences known for monatomic inorganic crystals. The role of zero-point vibrations for low- and high-frequency modes has been revealed throughout the entire temperature range.     

Compound nucleus contribution and even-odd effect for (3He,p) reactions in the Ni region

The compound nucleus contributions to the proton spectra from 8 MeV and 10 MeV ³He induced (³He, p) reactions on even-A Ni isotopes were obtained. The relative cross sections for ⁵⁸Ni/⁶⁰Ni/⁶²Ni in the high excitation region are in fair agreement with predictions of statistical theory, but the absolute cross sections in the same region are smaller than the prediction by a factor of 3 to 8, and the shapes of the measured spectra for heavier isotopes do not agree with the prediction. These discrepancies between experiment and theory are in sharp contrast to the situation in (p, p′), (p, α), (α, p) and (α, α′), where good agreement was found.The proton spectra from (³He, p) reactions on nuclei in the A = 54–68 mass range have a systematic difference in slope between even-A targets and odd-A targets; it is similar to the systematic difference found previously in (p, p′) and (α, p) reactions, but none of these is readily explainable by theory.     

Measurement of δ13C values of soil amino acids by GC–C–IRMS using trimethylsilylation: a critical assessment

In this study, we evaluated trimethylsilyl (TMS) derivatives as derivatization reagents for the compound-specific stable carbon isotope analysis of soil amino acids by gas chromatography–combustion–isotope ratio mass spectrometry (GC–C–IRMS). We used non-proteinogenic amino acids to show that the extraction–derivatization–analysis procedure provides a reliable method to measure δ¹³C values of amino acids extracted from soil. However, we found a number of drawbacks that significantly increase the final total uncertainty. These include the following:

• production of multiple peaks for each amino acid, identified as di-, tri- and tetra-TMS derivatives;

• a number of TMS-carbon (TMS-C) atoms added lower than the stoichiometric one, possibly due to incomplete combustion;

• different TMS-C δ¹³C for di-, tri- and tetra-TMS derivatives.

For soil samples, only four amino acids (leucine, valine, threonine and serine) provide reliable δ¹³C values with a total average uncertainty of 1.3?‰. We conclude that trimethylsilyl derivatives are only suitable for determining the ¹³C incorporation in amino acids within experiments using ¹³C-labelled tracers but cannot be applied for amino acids with natural carbon isotope abundance until the drawbacks described here are overcome and the measured total uncertainty significantly decreased.     

Microwave spectra and centrifugal distortion constants of formic acid containing 13C and 18O: Refinement of the harmonic force field and the molecular structure

Pure rotational spectra of H¹³COOH, HC¹⁸OOH, and HCO¹⁸OH have been measured in the frequency region 8–185 GHz. Analysis of the spectra has given improved rotational constants and quartic and sextic centrifugal distortion constants. The quartic distortion constants have been combined with previously published distortion constants of four other isotopic species, and with the vibrational wavenumbers of seven isotopic species, to produce a refined harmonic force field. An improved substitution structure and the ground state average structure have been obtained. Some unmeasured transition frequencies which may be of importance in radioastronomy are also presented.     

Experimental results on π−p interactions in the cm energy range 1.50–1.74 GeV

Channel cross sections, elastic differential cross sections and single pion production mass spectra and angular distributions are presented for π^?p interactions, based on 139 000 events observed at six energies in the center of mass region 1.50–1.74 GeV.     

Comparison of unfolding approaches for monoenergetic and continuous fast-neutron energy spectra

Proton-recoil detectors offer the possibility to unfold fast-neutron energy spectra of various sources. However, quantifying the confidence of the unfolding methodology is a complex task. In this paper, we present a comparative analysis of the maximum-likelihood, expectation-maximization (MLEM) method and one-step-late (OSL) method for neutron energy spectra unfolding. The analysis is performed on Monte Carlo simulated data for several monoenergetic neutron sources and continuous-in-energy ²⁵²Cf, ²⁴¹Am–Be and ²⁴¹Am–Li neutron sources. The results obtained for the monoenergetic neutron spectra show that both unfolding methods provide results that are in good agreement with the reference data. Very good agreement between the unfolded and the reference data is achieved for ²⁵²Cf, ²⁴¹Am–Be, and ²⁴¹Am–Li neutron spectra by using the OSL method. In the paper it is demonstrated that the MLEM and OSL methods can be applied to accurately unfold the simulated pulse-height distributions for organic liquid scintillation detectors. Comparative analysis between the two unfolding methods has shown that the OSL method has superior unfolding performance than the MLEM method.     

FT‐IR and FT‐Raman investigations of the chemosensing material para‐hexafluoroisopropanol aniline

As an important chemosensing material involving hexafluoroisopropanol (HFIP) for detecting nerve agents, para‐HFIP aniline (p‐HFIPA) has been firstly synthesized through a new reaction approach and then characterized by nuclear magnetic resonance and mass spectrometry experiments. Fourier transform infrared absorption spectroscopy (FT‐IR) and FT‐Raman spectra of p‐HFIPA have been obtained in the regions of 4000–500 and 4000–200 cm⁻¹, respectively. Detailed identifications of its fundamental vibrational bands have been given for the first time. Moreover, p‐HFIPA has been optimized and vibrational wavenumber analysis can be subsequently performed via density functional theory (DFT) approach in order to assist these identifications in the experimental FT‐IR and FT‐Raman spectra. The present experimental FT‐IR and FT‐Raman spectra of p‐HFIPA are in good agreement with theoretical FT‐IR and FT‐Raman spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Spectral Investigation of Phosphorus Compounds in Spinacia Oleracea Using Fourier Transform Infrared Method

The study uses the Fourier transform infrared spectroscopy method to evaluate the influence of phosphogypsum from the soil on the growth and accumulation of nutrients in Spinacia oleracea. Attenuated total reflectance spectra of Spinacia oleracea roots and stems originated from plants cultivated on 28% to 52% phosphogypsum enriched soil have been studied in the 4000–600 cm^?1 area. The structure of the infrared absorption bands for spinach roots and stems and for the soil where plants were grown was analyzed. Thus, it was observed that phosphorus–oxygen bonds contribution can be identified both in roots and stems absorption spectra. The significance of the research is the possibility to use the infrared investigation as rapid technique, particularly useful for agriculture, to study the extraction and assimilation process of the compounds containing phosphorus and nitrogen from the soil in which the spinach seedlings grew. In the case of this study, it was observed that the absorption of phosphorus in the spinach roots and stems has not the same effect. The analysis of obtained data indicated that the assimilation of phosphorus from phosphogypsum enriched soil induces changes in spinach roots structure that are most likely due to an increase synthesis of proteins, rather than to a decrease in carbohydrates quantity.     

Fluid synthesis and structure of a new polymorphic modification of boron nitride

A new previously unknown phase of boron nitride with a hardness of 0.41–0.63 GPa has been pre-pared by the supercritical fluid synthesis. The presence of a new phase is confirmed by the X-ray spectra and IR absorption spectra, where new reflections and bands are distinguished. The fundamental reflection of the X-ray diffraction pattern is d = 0.286–0.291 nm, and the characteristic band in the infrared absorption spectrum is observed at 704 cm^?1. The X-ray diffraction pattern and the experimental and theoretical infrared absorption spectra show that a new synthesized boron nitride phase can be a cluster crystal (space group 211) with a simple cubic lattice. Cage clusters of a fullerene-like morphology B₂₄N₂₄ with point symmetry O are arranged in lattice sites.     

Dithiane Based Boronic Acid as a Carbohydrate Sensor in an Aqueous Solution at pH 7.5: Theoretical and Experimental Approach

Carbohydrate sensing in an aqueous solution remains a very challenging area of interest. Using the idea of covalent reversible interaction between boronic acids and the diol groups in carbohydrates enable us to design a carbohydrate sensor 1-thianthrenylboronic acid (1T), which has high selectivity towards fructose. To elucidate the sensing and binding properties of 1T with sugars, we have incorporated theoretical (DFT and TD-DFT) and spectroscopic techniques. For an optimized geometry, the complete vibrational assignments were done with FT-IR and FT-Raman spectra. Physiochemical parameters were obtained by implementing frontier molecular orbital (FMO) analysis. Further, excited state properties were determined by performing TD-DFT calculations in solvent and these properties were in good agreement with the experiment. The steady state fluorescence measurements with varying concentration of sugars, revealed that the fluorescence intensity of boronic acid is enhanced by studied sugars due to the structural modification. We also noticed remarkable changes in fluorescence lifetimes and quantum yield after adding sugars. The article also reports influence of pH on boronic acid’s fluorescence intensity with and without sugars. The fluorescence of boronic acid increases with the increase in pH. These changes are due to acid–base equilibrium of boronic acid and led us to estimate the pKa value of 7.6. All the theoretical and experimental evidences suggested that 1T can be used as a possible fluorescent sensor for fructose. In addition, 1T showed very good affinity for Cu²⁺ ion with K_a?=?150?×?10² M^?1, which suggests that 1T can also be used as a chemosensor for Cu²⁺ ions.

     

Assignments of Carbon-Sulphur Vibrations by Selenation: An FT-IR and FT-Raman Study on 1, 3, 5-Trithiacyclohexane

Abstract

The IR and Raman spectra of 1, 3, 5-trithiacyclohexane (1) and 1, 3, 5-triselenocyclohexane (2) have been recorded with FT-instrumentation within 3500–100 cm^?l, and the C-S vibrations of 1 have been reviewed by comparing its spectra with those of 2. The IR and Raman spectra slightly differ from those previously reported and some vibrations, previously assigned to C-H modes in 1on the basis of NCT calculations, are reassigned to C-S modes on the basis of the selenation effect. “Selenation” has proved to be a very simple and effective tool in recognizing carbon-sulfur vibrations both in IR and Raman. The Raman peaks due to carbon-chalcogen vibrations are less intense in 1 than in 2, according to the higher polarizability of the selenium atom.     

Study of Ξ− and Ω− production from K−n and K−p interactions at 4.93 GeV/c

Cross sections, mass spectra, angular distributions and several other features of Ξ^? and Ω^? production from photons and neutrons in K^?d interactions at 4.93 GeV/c are presented. A five standard deviation peak is observed in ΞKπ mass spectra near 2.6 GeV/c². A sharp rise in the Ξ^? three- and four-body cross sections from K^?n interactions suggests direct-channel Σ¹ (3.0–3.5) formation.     

Raman spectroscopy of the OH group vibrations in structural complexes of liquid water

A number of spectral features in the structure of the OH band of water located at ～3450 cm^?1 are registered in a series of 34 Raman spectra. Each spectrum of the series is excited by a pair of successive secondharmonic pulses of a moderate intensity (15–20 MW/cm²) from a Nd:YAG laser operating at a pulse repetition frequency of 1 Hz. The pairs of pulses in the series follow at an interval of 15–20 s. It is found that, in ten measurements of the first series, there occur three successively reproduced spectra with an anomalously narrow band (down to 260 cm^?1) and spectra with a local minimum in the range of 3400 cm^?1. The occurrence of the latter spectra was predicted previously as a manifestation of the occurrence of structural fragments of water. In the range 3690–3700 cm^?1, a narrow peak of free OH vibrations is observed, whose intensity decreases in subsequent series. Some Raman spectra are similar to the spectra of the OH vibrations of water clusters in molecular beams and surface layers. These data make it possible to assume that structural complexes exist in the volume of water irradiated by the laser beam, with the lifetime of some of them being no shorter than 40 s.     

Inelastic electron tunneling spectroscopy of carboxylic acids on alumina at low coverage

The difficulties in assigning certain modes of carboxylic acids adsorbed on alumina are discussed. The study of the spectra of marked acetic acid CH₃C¹⁸O¹⁸OH adsorbed on alumina has allowed us to clarify the assignments of the acetate ion formed. Then an examination of the spectra at very low coverages has enabled us to propose a model for the adsorption, which occurs on (at least) two different sites.