Molecular scanning

Vohl MC, Lepage P, Gaudet D, Brewer CG, Betard C, Perron P, et al. Molecular scanning of the human PPARa gene. Association of the 1162v mutation with hyperapobetalipoproteinemia. J Lipid Res 2000 41 945-952. 

Boniface, J. J., Reich, Z., Lyons, D. S., and Davis, M. M. (1999). Thermodynamics of T cell receptor binding to peptide-MHC Evidence for a general mechanism of molecular scanning. Proc. Natl. Acad. Sci. USA 96, 11446-11451. 

Yen, C.-J., Beamer, B. A., Negri, C., Silver, K., Brown, K. A., Yarnell, D. P., Burns, D. K., Roth, J., and Shuldiner, A. R. (1997). Molecular Scanning of the Human Peroxisome Proliferator Activated Receptor y Gene in Diabetic Caucasians Identification of a Prol2Ala PPARy2 Missense Mutation. Biochem. Biophys. Res. Commun. 241, 270-274. 

Wang, H., Chu, W.S., Hemphill, C, and Elbein, S.C. 2002. Human resistin gene molecular scanning and evaluation of association with insulin sensitivity and type 2 diabetes in Caucasians. J. Clin. Endocrinol. Metab. 87 2520-2524. 

Taki, T. 2012. An approach to glycobiology from glycolipidomics Ganglioside molecular scanning in the brains of patients with Alzheimer s disease by TLC-blot/ matrix assisted laser desorption/ionization-time of flight MS, Biol Pharm. Bull, 35 1642-1647. 

Valdes-Gonzalez, T., Goto-Inoue, N., Hirano, W., Ishiyama, H., Hayasaka, T., Setou, M. and Taki, T. (2011) New approach for glyco- and Upidomics—molecular scanning of human brain gangliosides by TLC-Blot and MALDI-QIT-TOF MS. J. Neurochem. 116, 678-683. 

The development of scanning probe microscopies and x-ray reflectivity (see Chapter VIII) has allowed molecular-level characterization of the structure of the electrode surface after electrochemical reactions [145]. In particular, the important role of adsorbates in determining the state of an electrode surface is illustrated by scanning tunneling microscopic (STM) images of gold (III) surfaces in the presence and absence of chloride ions [153]. Electrodeposition of one metal on another can also be measured via x-ray diffraction [154]. 

These equations indicate that the energy of the scattered ions is sensitive to the mass of the scattering atom s in the surface. By scanning the energy of the scattered ions, one obtains a kind of mass spectrometric analysis of the surface composition. Figure VIII-12 shows an example of such a spectrum. Neutral, that is, molecular, as well as ion beams may be used, although for the former a velocity selector is now needed to define ,. ... 

We have considered briefly the important macroscopic description of a solid adsorbent, namely, its speciflc surface area, its possible fractal nature, and if porous, its pore size distribution. In addition, it is important to know as much as possible about the microscopic structure of the surface, and contemporary surface spectroscopic and diffraction techniques, discussed in Chapter VIII, provide a good deal of such information (see also Refs. 55 and 56 for short general reviews, and the monograph by Somoijai [57]). Scanning tunneling microscopy (STM) and atomic force microscopy (AFT) are now widely used to obtain the structure of surfaces and of adsorbed layers on a molecular scale (see Chapter VIII, Section XVIII-2B, and Ref. 58). On a less informative and more statistical basis are site energy distributions (Section XVII-14) there is also the somewhat laige-scale type of structure due to surface imperfections and dislocations (Section VII-4D and Fig. XVIII-14). 

Stroscio J A and Eigler D M 1991 Atomic and molecular manipulation with the scanning tunneling microscope Science 254 319... 

Tang S L, McGhie A J and Suna A 1993 Molecular-resolution imaging of insulating macromolecules with the scanning tunnelling microscope via a nontunnelling, electric-field-induced mechanism Phys. Rev. B 47 3850... 

Salmeron M, Liu G-Y and Ogletree D F 1995 Molecular arrangement and mechanical stability of self-assembled monolayers on Au(111) under applied load Force in Scanning Probe Methods ed H-J Guntherodt et al (Amsterdam Kluwer)... 

Vanden Bout D A, Kerimo J, Higgins D A and Barbara P F 1996 Spatially resolved spectral inhomogeneities in small molecular crystals studied by near-field scanning optical microscopy J. Chem. Phys. 100 11 843-9... 

Minimizing Spectral Interferences The most important spectral interference is a continuous source of background emission from the flame or plasma and emission bands from molecular species. This background emission is particularly severe for flames in which the temperature is insufficient to break down refractory compounds, such as oxides and hydroxides. Background corrections for flame emission are made by scanning over the emission line and drawing a baseline (Figure 10.51). Because the temperature of a plasma is... 

The importance of linked scanning of metastable ions or of ions formed by induced decomposition is discussed in this chapter and in Chapter 34. Briefly, linked scanning provides information on which ions give which others in a normal mass spectrum. With this sort of information, it becomes possible to examine a complex mixture of substances without prior separation of its components. It is possible to look highly specifically for trace components in mixtures under circumstances in which other techniques could not succeed. Finally, it is possible to gain information on the molecular structures of unknown compounds, as in peptide and protein sequencing (see Chapter 40). 

Metastable and collisionally induced fragment ions can be detected efficiently by a triple quadrupole instmment. By linking the scanning regions of the first and third quadrupoles, important information about molecular structure is easily obtained. 

The study of metastable ions concerns substances that have been ionized by electrons and have undergone fragmentation. The stable molecular ions that are formed by soft ionization methods (chemical ionization. Cl field ionization, FI) need a boost of extra energy to make them fragment, but in such cases other methods of investigation than linked scanning are generally used. 

In an EW- of a B/E-linked scan using an electric/magnetic-sector instrument, a precursor ion is selected. In this case it is m, which might be a molecular ion but equally could be any fragment ion. All product ions (mj, m3, m4) from decomposition of m, in the first field-free region between the ion source and the ion collector are found, thereby giving connections mpm, m -m3, m -m4. 

In a B /E-linked scan, a product ion (fragment ion) is selected. In this case it is m4, which can be any fragment ion but not a molecular ion (connects with itself). All precursor ions (m, mj, m3), which decompose to give the product ion m4, are found, giving connections m -m4, m2-m4, m3-m4. Any one of the precursor ions could be a molecular ion. 

In a process similar to that described in the previous item, the stored data can be used to identify not just a series of compounds but specific ones. For example, any compound containing a chlorine atom is obvious from its mass spectrum, since natural chlorine occurs as two isotopes, Cl and Cl, in a ratio of. 3 1. Thus its mass spectrum will have two molecular ions separated by two mass units (35 -i- 2 = 37) in an abundance ratio of 3 1. It becomes a trivial exercise for the computer to print out only those scans in which two ions are found separated by two mass units in the abundance ratio of 3 1 (Figure 36.10). This selection of only certain ion masses is called selected ion recording (SIR) or, sometimes, selected ion monitoring (SIM, an unfortunate... 

Linked scanning provides important information about molecular structure and the complexities of mixtures, and it facilitates the detection of trace components of mixtures. 

Triple quadrupole instruments can be used to detect metastable ions or can be used for linked scanning to obtain information about molecular structure. 

Automated linked scanning of metastable ions is valuable for deducing a whole or partial molecular structure of an unknown substance. 

MS", application of successive mass spectrometric measurements n of them), particularly in linked scanning of m/z, which is the ratio of the mass (m) of an ion and the number of charges (z) on it. Older publications used m/e, but as e is the actual charge on an electron and not the number of charges on the ion, the use of m/e was abandoned, m/z. mass-to-charge ratio, a measure of molecular mass PDB. PeeDee Belemnite (a carbon isotope standard see VPDB)... 

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