Spectroscopic MS

Spectroscopic (MS, NMR, IR) studies of quinoxalines were conducted . The structure and vibrational spectra of 2,3-bis(2-pyridyl)quinoxaline (bpq) and 2(A -methylpyridyl)-3-pyridylquinoxaline (meppq) useful for building blocks for dendrimers were measured by crystal X-ray diffraction and IR spectral experiments, respectively <2002JMT(589/90)301>. Those results were compared with ones calculated from the ab initio Hartee-Fock and the hybrid density functional methods. 

This chapter summarizes results obtained during the past 5 years, on the design, preparation and study of titanium and vanadium compounds as candidate precursors to TiC, TiN, VC, and VN. The study of the precursor molecules was conducted through several steps. After their synthesis, thermoanalytical studies (TG-DTA), coupled to simultaneous mass spectroscopic (MS) analysis of the decomposition gases, were carried out to determine their suitability as precursors. CVD experiments were then conducted and were followed by characterization of the deposits by scanning electron microscopy (SEM) energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron microprobe analysis with wavelength dispersion spectroscopy (EPMA-WDS). 

GC combined with mass spectroscopic (MS) detection provides very accurate identification and quantification of FFAs. Pinho et al. (2003) monitored changes in the FFA content during the ripening of ewe cheese. Sampling was done by headspace solid-phase microextraction (SPME). An excellent correlation was observed between the initial concentration of the sample and the amount absorbed on the SPME fiber. SPME sampling was done at 65 °C with a fiber coated with 85-p.m polyacrylate film. After equilibration at 65 °C for 40 min, the fiber was exposed to the sample headspace for 20 min and inserted into the GC port. Despite its accuracy, the GC-MS method is not widely used, presumably because of its cost and complexity. 

Traditional methods to map posttranslational modification sites, like those of phosphorylation, have been anchored by protein digest and mass spectroscopic (MS) approaches (for a review on the classic evaluation and for MS analyses of O-glycans, see Reference (56)). Unfortunately, like many posttranslational modifications, O-GlcNAcylation occurs routinely on a protein population with substoichiometric frequency, which results in a very small detectable population of a O-GlcNAc-modified product. Also, much like O-phosphate additions, the protein-O-GlcNAc bond is labile and is detached by collision-induced dissociation (CID) during MS analysis. Often, the bond is lost before it can be detected on the peptides analyzed (57, 58). Phosphate modifications, however, can overcome this limitation by emiching the peptide mixtures... 

A new alkaloid phamine (430), which is a phenanthridone alkaloid belonging to the narciclasine group, has been isolated from the bulbs of Hippeastrum equestre along with known Amarylldaceae alkaloids (47). Its structure was determined by spectroscopic (MS, UV, H and NMR) analyses. Also, phamine indicated interesting antimitotic activity. The alkaloids isolated since 1987 are shown in Fig. 25. 

For a better understanding of many successful applications of the rare earth-alkali metal containing LnM3tris (binaphthoxide) complexes (LnMB, Ln=rare earth, M=alkali metal) to catalytic asymmetric synthesis, intense investigations also focused on the determination of the structure. It has been shown that these complexes, which can be readily prepared from the corresponding rare earth trichlorides and/or rare earth isopropoxides [5],possess a structure as presented in Fig. 2. This structure was supported by various NMR spectroscopic, MS spectrometric, X-ray crystallographic and other analytic investigations of a variety of LnMB complexes. 

The new tetrodotoxin derivative fractions were collected and lyophilized three times by adding water to eliminate ammonium acetate completely. The combined fractions were then rechromatographed on the same column using 0.1 V acetic acid as eluent. After passing through small Chelex 100 and Bio-Gel P-2 columns (0.5 x 1.5 cm, elution with 0.1 N acetic acid), the new compound was obtained in spectroscopically (MS and NMR) pure state. (Yield 1.2 mg.)... 

Usually, sample analysis combines the use of different analytical techniques, such as spectroscopic (MS (mass spectrometry), NMR (nuclear magnetic resonance), IR (infra-red), FL, among others), electrochemical (voltammetry, conduc-timetry), separation (CE [capillary electrophoresis], GC [gas chromatography], LC [liquid chromatography]), or hyphenated techniques. All of them have been applied, to a greater or lesser extent, for food analysis [88]. As can be seen in Table 8.1, the... 

F Frappier, M Jouany, A Marquet, A Olesker, JC Tabet. On the mechanism of the conversion of dethiobiotin to biotin in E. coli. Studies with deuterated precursors using tandem mass spectroscopic (MS-MS) techniques. J Org Chem 47 2257-2261, 1982. 

Specinfo, from Chemical Concepts, is a factual database information system for spectroscopic data with more than 660000 digital spectra of 150000 associated structures [24], The database covers nuclear magnetic resonance spectra ( H-, C-, N-, O-, F-, P-NMR), infrared spectra (IR), and mass spectra (MS). In addition, experimental conditions (instrument, solvent, temperature), coupling constants, relaxation time, and bibliographic data are included. The data is cross-linked to CAS Registry, Beilstein, and NUMERIGUIDE. 

Modem analytical techniques have been developed for complete characteri2ation and evaluation of a wide variety of sulfonic acids and sulfonates. The analytical methods for free sulfonic acids and sulfonate salts have been compiled (28). Titration is the most straightforward method of evaluating sulfonic acids produced on either a laboratory or an iadustrial scale (29,30). Spectroscopic methods for sulfonic acid analysis iaclude ultraviolet spectroscopy, iafrared spectroscopy, and and nmr spectroscopy (31). Chromatographic separation techniques, such as gc and gc/ms, are not used for free... 

Other spectroscopic methods such as infrared (ir), and nuclear magnetic resonance (nmr), circular dichroism (cd), and mass spectrometry (ms) are invaluable tools for identification and stmcture elucidation. Nmr spectroscopy allows for geometric assignment of the carbon—carbon double bonds, as well as relative stereochemistry of ring substituents. These spectroscopic methods coupled with traditional chemical derivatization techniques provide the framework by which new carotenoids are identified and characterized (16,17). 

The physical data index summarizes the quantitative data given for specific compounds in the text, tables and figures in Volumes 1-7. It does not give any actual data but includes references both to the appropriate text page and to the original literature. The structural and spectroscopic methods covered include UV, IR, Raman, microwave, MS, PES, NMR, ORD, CD, X-ray, neutron and electron diffraction, together with such quantities as dipole moment, pX a, rate constant and activation energy, and equilibrium constant. 

Sample concentration, and hence enrichment, is certainly a key issue in this area of analysis, since complementary information obtained from NMR or IR spectroscopic detection is often desirable in conjunction with mass spectrometry. Detection methods such as these have far higher concentration thresholds than MS and obtaining adequate quantities of material for detection becomes a significant challenge. 

Figure 5.22 HC traces obtained from LC-MS analyses of trypsin digests of (a) CMY-2 /3-lactamase, and (b) tazobactam/CMY-2 /S-lactamase. Reprinted from Biochim. Biophys. Acta, 1547, Bonomo, R. A., Liu, 1., Chen, Y., Ng, L., Hujer, A. M. and Anderson, V. E., Inactivation of CMY-2 /S-lactamase by tazobactam initial mass spectroscopic characterization , 196-205, Copyright (2001), with permission from Elsevier Science.

Spectroscopic techniques as 13C-NMR [28], ESR [29], pyrolysis-GC/MS, and pyrolysis-Fourier transform infrared (FTIR) [30], x-ray diffraction [31], and SEM [32] techniques are also used to study mbber oxidation. 

Other spectroscopic properties such as nuclear magnetic resonance (NMR), mass spectrometry (MS), infra-red (IR), and circular dichroism (CD) spectra of chlorophyll compounds and derivatives have been valuable tools for structural elucidation. - ... 

The use of mass spectroscopic analyses for characterization of anthocyanins has increased dramatically over the past decade. Most reports cite the use of HPLC coupled to MS detectors or isolating individual pigments prior to the mass spectroscopic analysis. - - " ... 

Ito, S., Toitani, N., Pan, L., Tamai, N. and Miyasaka, H. (2007) Fluorescence correlation spectroscopic study on water-soluble cadmium telluride nanocrystals fast blinking dynamics in the ps-ms region. J. Phys. Condens. Matter, 19, 486208. 

Sets of spectroscopic data (IR, MS, NMR, UV-Vis) or other data are often subjected to one of the multivariate methods discussed in this book. One of the issues in this type of calculations is the reduction of the number variables by selecting a set of variables to be included in the data analysis. The opinion is gaining support that a selection of variables prior to the data analysis improves the results. For instance, variables which are little or not correlated to the property to be modeled are disregarded. Another approach is to compress all variables in a few features, e.g. by a principal components analysis (see Section 31.1). This is called... 

In reality, the queue size n and waiting time (w) do not behave as a zero-infinity step function at p = 1. Also at lower utilization factors (p < 1) queues are formed. This queuing is caused by the fact that when analysis times and arrival times are distributed around a mean value, incidently a new sample may arrive before the previous analysis is finished. Moreover, the queue length behaves as a time series which fluctuates about a mean value with a certain standard deviation. For instance, the average lengths of the queues formed in a particular laboratory for spectroscopic analysis by IR, H NMR, MS and C NMR are respectively 12, 39, 14 and 17 samples and the sample queues are Gaussian distributed (see Fig. 42.3). This is caused by the fluctuations in both the arrivals of the samples and the analysis times. 

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