Fragmentation deconvolution

Registration of a metastable ion in the spectrum is rather useful, as it confirms realization of a certain fragmentation reaction. The fragmentation schemes are considered to be true if corresponding metastable peaks are detected. On the other hand, metastable peaks deteriorate spectral resolution. Depending on the amount of energy released, the forms of the metastable peaks may be quite different. These peaks are eliminated from the spectra as part of the computer deconvolution process. 

Next, custom software is used to interrogate the deconvoluted data set to identify the protein s mass and the intensity of the peak, determine any potential modification above a user-defined intensity threshold and, if there is a hit, calculate the mass and the relative conjugation of the fragment. In fact, the percent conjugation is used as a measure of relative affinities of the fragment hits. Since the library is mass encoded (all compounds in a well have a unique mass), the calculated mass of any hits are queried into a database to identify their structures. 

Table I. Deconvolution of the Principal, pH-Dependent Endotherm for CBH I and Its Core Fragment...

Figure 7.5 Deconvoluted, zero charge state mass spectrum demonstrating a hit from a DCL-targeting metallo-[3-lactamase (Bell). The dominant peak corresponds to anrora A kinase linked to extender 23, which is in turn linked to fragment 24 to give 25 (dynamic hit ). Reprinted from Reference 27, with permission from Elsevier, Copyright (2008).

This is illustrated in Fig. 2.4, where the deconvolution of differential pulse voltammograms at the glassy carbon electrode in the ethanol extract from two commercial inks are shown. Samples were taken from paper fragments of 0.10 mg immersed for 10 min in a 50 50 (v/v) ethanol 0.50 M aqueous acetate buffer (pH 4.85) solution. 

The resulting very sharp peaks are then released onto the short fast column 2. The modulator actually collects eluent from column 1 every few seconds (generally 2-9 s), and so an individual chromatographic peak is actually sliced into many fragments. Figure 15.5 demonstrates how two overlapping peaks are effectively deconvoluted into two interleaved series of pulses. 

One other approach is direct-inlet MS. A prerequisite for mass analysis is ionisation, a process that critically influences the sensitivity and selectivity of the experiment. Electron impact ionisation (El) causes considerable fragmentation. Because of overlapping fragment and parent ions, the molecular information is difficult to deconvolute, and little chemical information can be extracted. 

Generation of xanthyl cation from 2-(9-xanthyl)ethanol [87] is an extended Grob fragmentation. The intervening chain of separating the terminal donor groups may also incorporate heteroatoms, as shown in the deconvolution of a decalindione monoxime tosylate [88]. 

Figure 25. Deconvolution of various types of fragmentation from the ion signal in the case of K4 [23].

Figure 7.14 Deconvoluted ESI mass spectra from an equimolar mixture of 19 thiols

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