Mass spectrometry, electrospray ionization substrate

Affinity capture-release electrospray ionization mass spectrometry (ACESIMS) is another recently introduced technique for quantification of proteins, and to date has most often been applied to clinical enzymology.60 The product conjugates of the enzymatic reaction between the synthetic substrate and targeted enzyme are captured by immobilized affinity reagents, purified, released into solution, and analyzed by ESI-MS. 

ESI-MS has been used for the quantification of a number of substrates and products of enzymatic reactions [56,57]. Hsieh et al. report the use of ion spray mass spectrometry (a technical variation of electrospray ionization) coupled to HPLC for the kinetic analysis of enzymatic reactions in real time [58]. The hydrolysis of dinucleotides with bovine pancreatic ribonuclease A and the hydrolysis of lactose with 3-galactosidase were monitored and the resulting data were used for the estimation of and v x of these reactions. Another field of application of electrospray mass spectrometry is the screening of combinatorial libraries for potent inhibitors [31,59]. 

Some reviews [5-7] have appeared on NCE-electrospray ionization-mass spectrometry (NCE-ESI-MS) discussing various factors responsible for detection. Recently, Zamfir [8] reviewed sheathless interfacing in NCE-ESI-MS in which the authors discussed several issues related to sheathless interfaces. Feustel et al. [9] attempted to couple mass spectrometry with microfluidic devices in 1994. Other developments in mass spectroscopy have been made by different workers. McGruer and Karger [10] successfully interfaced a microchip with an electrospray mass spectrometer and achieved detection limits lower than 6x 10-8 mole for myoglobin. Ramsey and Ramsey [11] developed electrospray from small channels etched on glass planar substrates and tested its successful application in an ion trap mass spectrometer for tetrabutylammonium iodide as model compound. Desai et al. [12] reported an electrospray microdevice with an integrated particle filter on silicon nitride. 

Wigger, M., Nawrocki, J. P., Watson, C. H., Eyler, J. R. und Benner, S. A., Assessing enzyme substrate specificity using combinatorial libraries and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Rapid Commun. Mass Spectrom. 1997, II, 1749-1752. 

C.J. Zea, N.L. Pohl, Kinetic and substrate binding analysis of phosphorylase b via electrospray ionization mass spectrometry a model for chemical proteomics of... 

Zhang T, Zhu Y, Gunaratna C. Rapid and quantitative determination of metabolites from multiple cytochrome P450 probe substrates by gradient liquid chromatography-electrospray ionization-ion trap mass spectrometry. J Chromatogr B Analyt Technol Biomed Life Sci 2002 780 371-379. 

Law KP (2010) Laser desorption/ionization mass spectrometry on nanostructured semiconductor substrates DIOS (TM) and QuickMass (TM). Int J Mass Spectrom 290 72-84 Law KP, Larkin JR (2011) Recent advances in SALDI-MS techniques and their chemical and bioanalytical applications. Anal Bioanal Chem 399 2597-2622 Lewis WG, Shen Z, Finn MG, Siuzdak G (2003) Desorption/ionization on silicon (DIOS) mass spectrometry background and applications. Int J Mass Spectrom 226 107-116 Li Q, Alonso R, Renner SA, Winefordner JD, Powell DH (2005) Desorption/ionization on porous silicon mass spectrometry studies on pentose-borate complexes. Anal Chem 77 4503-4508 Lin Z, Zhang S, Zhao M, Yang C, Chen D, Zhang X (2008) Rapid screening of clenbuterol in urine samples by desorption electrospray ionization tandem mass spectrometry. Rapid Commun Mass Spectrom 22 1882-1888... 

In the last decade, mass spectrometry has developed at a tremendous rate. This expansion has been driven by the growing knowledge of ionization methods at atmospheric pressure (API), mainly electrospray ionization (ESI) [1], which makes the investigation of liquid solutions possible by mass spectrometry. ESI is used for ionic species in solution, and this ionization method opened up the access to the direct investigation of chemical reactions in solution via mass spectrometry. In principle, ESI make possible the detection and study not only of reaction substrates and products, but even short-lived reaction intermediates as they are present in solution, providing new insights into the mechanism of several studied reactions. 

Ricci and coworkers [64] studied oxazoline moiety fused with a cyclopenta[P]thio-phene as ligands on the copper-catalyzed enantioselective addition of Et2Zn to chalcone. The structure of the active Cu species was determined by ESI-MS. Evans and coworkers [65] studied C2-symmetric copper(II) complexes as chiral Lewis acids. The catalyst-substrate species were probed using electrospray ionization mass spectrometry. Comelles and coworkers studied Cu(II)-catalyzed Michael additions of P-dicarbonyl compounds to 2-butenone in neutral media [66]. ESI-MS studies suggested that copper enolates of the a-dicarbonyl formed in situ are the active nucleophilic species. Schwarz and coworkers investigated by ESI-MS iron enolates formed in solutions of iron(III) salts and [3-ketoesters [67]. Studying the mechanism of palladium complex-catalyzed enantioselective Mannich-type reactions, Fujii and coworkers characterized a novel binuclear palladium enolate complex as intermediate by ESI-MS [68]. 

Electrospray ionization works especially well for mass spectrometry of proteins, carbohydrates, and nucleic acids. ESI mass spectrometry has been used to study protein molecular weights and sequence, enzyme-substrate complexes, antibody-antigen binding, drug-receptor interactions, and DNA oligonucleotide sequence, as well as simply for small molecules that cannot be ionized by electron impact. 

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