Chemical derivatization approach

In the chemical derivatization approach one introduces a pendent long alkyl or alkoxy group to increase solubility. 

The straightforward approach to de novo sequencing sometimes fails, for example, due to the low quality tandem mass spectra. Often it is not caused by the equipment settings or operator s capabilities, but just by unfavorable fragmentation pattern of a given peptide. Among possible approaches to solve such issues is chemical derivatization of peptides. 

Two different techniques have been developed for MIP production, namely the covalent and the non-covalent approaches. The covalent way is based on the chemical derivatization of the template with molecules containing polymerizable groups using reversible covalent bonds. Different chemical reactions can be ap-... 

Preston et al. [698,699] have described novel approaches to 15N-isotope dilution determination of ammonium and of free amino acids in natural waters, incorporating chemical derivatization and conventional GC-MS analysis. 

Another approach combines the mass spectrometric derivatization approach with chemical amplification (Reiner et al., 1997, 1998). In this instrument, H02 and R02 are converted to OH through the reactions in the chemical amplifier approach discussed below, and the OH is then converted to H2S04 by reaction with S02 and measured by chemical ionization mass spectrometry using NO, (HN03) clusters as described earlier. In this case, the use of isotopically labeled S02 is not necessary, since the ambient H2S04 concentration is much smaller than that of the peroxy radicals. 

Isolation of the feeding factor for M. sexta was a far more difficult task. Whereas 2-tridecanone is a simple, stable molecule soluble in organic solvents, the feeding factor is water soluble, occurs at trace levels in plant tissue, and is easily hydrolyzed under mild alkaline or acidic conditions with subsequent loss of biological activity. The isolation of such a compound was a formidable obstacle requiring a departure from the more classical approach of hydrolysis or chemical derivatization followed by isolation of the lipophilic product. The necessity that pure substance be isolated with retention of biological activity required some basic research in modem separation techniques to develop a suitably mild isolation strategy. 

Synthetic chemists can play a vital role by designing chemical approaches for processing of important nonlinear materials. Two specific examples presented here are (a) Soluble precursor route and (b) Chemical derivatization for improving solubility. 

Interesting approaches to affect intestinal absorption include drug physicochemical modification by either chemical derivatization or the use of delivery agents, low molecular weight peptide-like compounds that form a complex with the permeant. Generally, the transport of... 

Other approaches attempted to overcome the obstacle of poor GI absorption of macromolecules include the use of enzyme intestinal inhibitors, chemical derivatization, prodrugs,... 

Chemical derivatization of an analyte is performed to improve the selectivity and sensitivity of that analyte. There are two approaches to the use of derivatizing agents in HPLC. Precolumn derivatization, which is performed before the analytes are separated, is most commonly used for small molecules such as amino acids, whereas postcolumn derivatization, which is performed after the separation but before the analytes reach the detector, is often used for larger molecules such as peptides. 

Chemical derivatization of the capillary wall has also been used to alter the properties of the interface. Derivatization using trichlorovinylsilane followed by copolymerization with polyacrylamide is one approach. Another effective reagent is (o -methacryloxypropyl)trimethoxysilane, followed by cross-linking the surface-bound methacryl groups with polyacrylamide. 

Other strategies, such as on-line H/D exchange LC/-MS/MS and chemical derivatization, were well-established approaches for characterization of small... 

D. Q. Liu and C. E. C. A. Hop, Strategies for characterization of drug metabolites using liquid chromatography-tandem mass spectrometry in conjunction with chemical derivatization and on-line H/D exchange approaches,/. Pharm. Biomed. Anal. 37 (2005), 1-18. 

Figure 34. Schematic illustration of the occlusion electrosynthesis approach for the preparation of M-Ti02 (M = metal) composite films and subsequent chemical derivatization to yield the metal hexacyanoferrate (MHCF)-Ti02 counterparts. Refer to the text for further details.

It is clear that the use of mPC-CE and lA-CE afford a powerful approach for preconcentration and on-line sample eleanup of antilyte mixtures prior to separation by CE. While these techniques continue to be refined, they overcome the current limitations of poor CLOD in conventional CE. Finally, the use of these devices as microreactors affords enhanced chemical derivatization or enzymatic reactions a lower analyte concentrations than is currently possible by conventional solution chemistries. 

In order to enhance or modify the chemical selectivity of an SERS substrate, it is possible to chemically derivatize the metal surface. For example, covalent bonding of a hydrocarbon to a silver island film should selectively adsorb nonpolar analytes from an aqueous solution. The general approach is shown schematically in Figure 13.24 for the case of metal ions detected by a surface-bound complexing agent (47). Field enhancement is provided by the substrate, while adsorption selectivity results from the chemistry of the derivatized... 

In general, natural products contain either only one useful chromophore or none at all. For this reason the selection of suitable chromophore(s) to be introduced into the substrate by chemical derivatization is an important issue when it comes to the determination of AC by CD. With the so-called monochromophoric approach, applicable mainly to rigid substrates, two identical chromophores are introduced in a one-step reaction, usually by acylating the primary or secondary hydroxyl or amino groups. In such cases the exciton coupling provides an intense CD and allows for uncomplicated AC assignments.9,11... 

When tackling a complex chemical problem in many areas of chemistry, it is advisable to adopt a variety of methodologies, both chemical and instrumental, in combination, rather than relying on a single approach in attempting to solve the problem. In this context, the utilization of infrared spectroscopy in conjunction with chemical derivatization methods has proven to be a fruitful marriage in the solution of many chemical problems in the past. This is particularly true in the case of humic substances—the utility of infrared spectroscopy has been expanded considerably when used in conjunction with chemical derivatization as will be discussed later. 

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