Mass spectroscopy modifications

Further, using a combination of X-ray crystallography and mass spectroscopy, Knox et al. [73] has firmly established a central role for Ser-130 in the inhibition of SHV-1 /1-lactamase (class A) by tazobactam. Many additional modifications (Table 3) were carried out on tazobactam with the aim of increasing inhibitory activity against AmpC enzymes, but none of these derivatives (e.g., 13c, 13d, and 13e) had any advantage over tazobactam [74— 77]. Renewed interest in the modification at the C-2 position of sulbactam was developed when scientists from Hoffmann-La Roche disclosed a series of 2/J-alkenyl penam sulfones that possess the ability to simultaneously inactivate both class A penicillinase as well as class C cephalosporinase. Compound... 

X-ray diffraction is not the only spectroscopic technique to determine geometries of different modifications. The range of options includes IR and UV studies as well as NMR and mass spectroscopy [34],... 

The resolving power of mass spectroscopy is further exemplified in posttranslational modification studies of acyl carrier protein from Mycobacterium tuberculosis. Researchers were able to determine both the nature of the modification and also the mechanism by which the protein was regulated (Fung et al., 2001, Reference 7). 

Ligands - 2,2 -Ethylidenebis (4,6-di-tert-butylphenyl) fluorophosphite was purchased from Aldrich Chemical Company. The remaining chlorophosphite and fluorophosphite ligands were prepared by literature procedures or by minor modifications of the published procedures (10). All ligands were characterized by H NMR, P NMR and mass spectroscopy. 

Natural sources of Si3N4 are extremely rare and are a mineralogical curiosity that has no significance as a raw material. The mineral Nierite is named after the pioneer of mass spectroscopy, A.O.C. Nier, and is observed as an inclusion in meteorites. It consists chiefly of the a modification which is interspersed with inclusions of /i-Si3N4 whiskers. The ratio of a to /I in the different finds can show considerable variance [1, 2]. 

Labelled A1- and A6-THC were synthesized starting from 3,5-dimethoxybenzoic acid. The content of unlabelled THC in the final product was determined from mass spectroscopy to be 10%. To increase the number of deuterium atoms in the molecule and to obtain a lower content of unlabelled THC we therefore, with some modifications, used the method of Pitt et al, (6). For the synthesis of d3 or dy-labelled THC 5-TT, 5-dimeth-... 

The development by Muller (393) of the field ion microscope gave a considerable thrust to studying surface structures. In a recent modification of this technique, Panitz (394) designed a field desorption spectrometer that promises determination of the crystallographic distribution of species on metal surfaces. Secondary ion mass spectroscopy can also provide some quantitative information of surface species by sputtering atoms with an inert gas ion beam and detecting them by mass spectrometry. Submonolayers of adsorbed gases can be studied by this method (395). 

With large proteins, the determination of the primary sequence and post-translational modifications is most efficiently done after digestion with tiypsin or another protease to generate smaller peptides. In this case, the peptides are first separated by HPLC, most commonly RP-HPLC, and the column eluant is directed into the MS. In this hyphenated method, known as LC-MS or liquid chromatography-tandem mass spectroscopy (LC-MS/MS), the individual peptides are analyzed, allowing the identification of post-translational modification sites. In some cases, there are potentially multiple sites in a single peptide that may be modified. 

Editing can be studied with small quantities of RNA since a RT-PCR step is included to amplify the RNA. However, studying RNA modifications requires direct analysis of the RNA. Different methods, including HPLC, TLC and mass spectroscopy, have been employed to identify and quantify the modifications. A description of these methods is beyond the scope of this book. 

As at the beginning of the fullerene story, the next development needed in met-car chemistry is the characterization of pure products in macroscopic quantities. In fact, macroscopic quantities of Ti8Ci2 and V8C12 have already been obtained by a modification of the common arc discharge used to produce fullerenes. Soots were obtained in which the presence of met-cars and fullerenes was unambiguously characterized by laser desorption time-of-flight mass spectroscopy. The quantity of met-cars present in the soot was estimated to Unfortunately, chemical... 

An article on the mass-spectrometric analysis of g.l.c. effluents has been published, together with reviews on g.l.c. in combination with mass spectroscopy and with infrared spectroscopy. Although combined g.l.c.-m.s. instruments may be purchased, it is often found necessary to adapt existing apparatus. Several papers give details of such modifications for instance, constructional details for a probe to fit the AEI MS-9 have been published, a simple heated inlet system has been described, and molecule separators have been discussed. Methods for interfacing g.l.c. and m.s. instruments have been reviewed by D. I. 

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