Mass spectrometry structural studies

Wang Y., Gross M.L. Application of hydrogen exchange and electrospray ionization mass spectrometry in studies of protein structure and dynamics, in Applied Electrospray Mass Spectrometry (Practical Spectroscopy), ed. Pramanik BN, Ganguly AK, Gross ML 2002, pp 389-410. 

Schulten (110, 111) has used laser-assisted field desorption mass spectrometry to study some inorganic and organometallic systems. This method is intermediate between LAMMA and simple FD. Metal cations predominate from inorganic salts. The technique also showed clusters of the type reported from both FAB and SIMS studies. By carefully controlling the laser, a chlorophyll molecular ion could be obtained as well as fragments relating to its structure. 

Konermann, L., Pan, J.X., Liu, Y.H. (2011) Hydrogen exchange mass spectrometry for studying protein structure and dynamics. Chemical Society Reviews, 40 (3), 1224-1234. 

Mass spectrometry is a convenient method for identifying structures of compounds, either in their pure form or in mixtures. It should be noted that in mass spectrometry structure refers to atom and group connectivity, rather than to bond distances and bond angles. Also, the elucidation of structures of ions is performed by inducing their chemical transformations and detecting the reaction products. In other words, a mass spectrometer should be considered as a mini-chemical laboratory, in which ions can be produced and their structure and reactivity can be studied. 

Mass spectrometry (MS) studies have played a key role in the study of metathesis reactions, particularly in the hands of Chen and coworkers, who have identified intermediates in the catalytic cycle,and probed the energetics of their reactions, using electrospray MS techniques. Species such as 14e ruthenium carbene complexes can be detected by MS in the presence of different alkene substrates, the different carbene products (from CM or ROMP, for example) can be detected. Further, the fragments into which any proposed species can be broken by successively higher lens potentials can be used to check the species structure. In successive and more advanced studies, interpretation of data from the energy-resolved, coUision-induced dissociation cross-section measurements allowed the construction of potential energy surfaces for some steps of the metathesis reaction.Metathesis precatalysts were typically custom-made species, modified with ionic tags, to facilitate detection by MS. 

Buko, A. M., L. R. Phillips, and B. A. Fraser Peptide Studies Using a Fast Atom Bombardment High Field Mass Spectrometer and Data System 1-Sample Introduction, Data Acquisition and Mass Calibration. Biomed. Mass Spectrom. 10, 324 (1983). McLafferty, F. W., ed. Tandem Mass Spectrometry. New York Wiley. 1983. Cheng, M. T, M. P. Barbalas, R. F. Pegues, and F. W. McLafferty Tandem Mass Spectrometry Structural and Stereochemical Information from Steroids. J. Amer. Chem. Soc. 105, 1510 (1983). 

Knyazkov, D. Shmakov, A. Korobeinichev, O. (2007). Application of molecular beam mass spectrometry in studying the structure of a diffusive counterflow flame of CH4/N2 and O2/N2 doped with trimethylphosphate. Combustion and Flame, Vol. 151, No.1-2 pp. 37-45, ISSN 0010-2180... 

See also Ion Energetics in Mass Spectrometry Ion Imaging Using Mass Spectrometry Ion Structures in Mass Spectrometry Isotopic Labelling in Mass Spectrometry Metastable Ions Photoionization and Photodissociation Methods in Mass Spectrometry Stereochemistry Studied Using Mass Spectrometry. 

One has seen that the number of individual components in a hydrocarbon cut increases rapidly with its boiling point. It is thereby out of the question to resolve such a cut to its individual components instead of the analysis by family given by mass spectrometry, one may prefer a distribution by type of carbon. This can be done by infrared absorption spectrometry which also has other applications in the petroleum industry. Another distribution is possible which describes a cut in tei ns of a set of structural patterns using nuclear magnetic resonance of hydrogen (or carbon) this can thus describe the average molecule in the fraction under study. 

The chemical structure of 8 was also confirmed by mass spectrometry studies (98MI89). 

This tool has been of great value in the elucidation of the structures of some important biologically-derived amino (14) and deoxy (13) sugars in the form of their dialkyl dithioacetals. Tedious degradation reactions which would require both time and valuable material could be avoided in many cases by resorting to mass spectrometry. The antibiotic sugars (22) paramose (1), mycinose (2) and chalcose (3) were, for example, studied by mass spectrometry (13, 14). 

The present work involves the study of methyl glycosides and O-isopropylidene ketals of various isomeric deoxy sugars by mass spectrometry. Several of the compounds selected for the present study have free hydroxyl groups, and interpretation of their mass spectra shows the scope of the study of these and related deoxy sugar derivatives by mass spectrometry without prior substitution of all hydroxyl groups. Some of the candidates (compounds 4, 7, 8 and 10) are structurally related to biologically-derived deoxy sugars. 

A comparison of the electron impact (El) and chemical ionization (Cl-methane) mass spectra of 1//-azepine-1-carboxylates and l-(arylsulfonyl)-l//-azepines reveals that in the El spectra at low temperature the azepines retain their 8 -electron ring structure prior to fragmentation, whereas the Cl spectra are complicated by high temperature thermal decompositions.90 It has been concluded that Cl mass spectrometry is not an efficient technique for studying azepines, and that there is no apparent correlation between the thermal and photo-induced rearrangements of 1//-azepines and their mass spectral behavior. 

Properties of luciferin precursors. About one dozen of the luciferin precursors of M. citricolor isolated by HPLC had a strong tendency of isomerization, as mentioned above. Their molecular weights could not be established by mass spectrometry, which is probably due to isomerization, although they appear to be in a range of 300-600. The precursors showed an absorption peak at about 369 nm in methanol and aqueous acetonitrile (Fig. 9.13). According to an NMR study, all precursors probably contain the following common partial structure (personal communication from Dr. H. Nakamura, 1998). 

Structure determination of luciferin. Once a luciferin is obtained in a sufficient purity, the determination of luciferin structure should be attempted most of the important properties of luciferin are usually already obtained during the course of purification as a necessity. The structural study is considerably more straightforward than the extraction and purification, due to the availability of advanced methods, such as high-resolution mass spectrometry and various NMR techniques. If help or collaboration is needed in structure determination, the attractiveness of a luciferin will make it easy to find a good collaborator. However, the purified luciferin is usually an extremely precious material considering the effort spent in preparing it. To avoid accidental loss of the purified material, the chosen collaborator must have solid knowledge and experience in structure determination a criterion to be considered is that the person has successfully done the structure determination of at least one new natural product. 

Electrospray is an unusual mass spectrometry technique in that it allows the study of the three-dimensional structure of compounds, particularly proteins, in solution as it is believed that this is relatively unchanged when ions are transferred to the vapour phase. This type of application will be discussed in more detail in Chapter 5 but attention is drawn at this point to the previous comments regarding the effect that the HPLC conditions, such as pH, may have on the appearance of an electrospray spectrum and the conformational deductions that may be made from them. 

MS-MS is a term that covers a number of techniques in which two stages of mass spectrometry are used to investigate the relationship between ions found in a mass spectrum. In particular, the product-ion scan is used to derive structural information from a molecular ion generated by a soft ionization technique such as electrospray and, as such, is an alternative to CVF. The advantage of the product-ion scan over CVF is that it allows a specific ion to be selected and its fragmentation to be studied in isolation, while CVF bring about the fragmentation of all species in the ion source and this may hinder interpretation of the data obtained. 

Method development is important. LC-MS performance, probably more than any other technique involving organic mass spectrometry, is dependent upon a range of experimental parameters, the relationship between which is often complex. While it is possible (but not always so) that conditions may be chosen fairly readily to allow the analysis of simple mixtures to be carried out successfully, the widely variable ionization efficiency of compounds with differing structures often makes obtaining optimum performance for the study of all components of a complex mixture difficult. In such cases, the use of experimental design should be seriously considered. 

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