Charge-tagging

Another example of the data provided by our approach is shown in Fig. 4, which tracks the platinum-catalyzed redistribution of two silanes [16], one charge-tagged with a phosphonium group. This demonstrates the ability of the technique to monitor air-sensitive reactions in non-routine solvents in this case, fluorobenzene. The temperature of the reaction was increased from room temperature to reflux at 20 min the catalyst used was Karstedt s catalyst, Pt[(H2C = CHMe2Si)20]2(Fig.5). 

Ruthenium-based metathesis reactions have also been subject to a number of ESl-MS studies. We note that these systems have been studied extensively in the gas phase by Chen however, this work is beyond the scope of our review. Chen also pioneered the study of these systems in the condensed-phase using a charge-tagged substrate (see Section 1.1.3) [69],... 

Fig. 12. Cationic norbornene as a charged-tag for detection by ESI-MS of ruthenium species involved in ring-opening metathesis polymerization (69].

Ruthenium-catalyzed hydroformylation of alkenes was also studied using charged tags [84]. A unique permanently-charged version of a self-assembling bidentate ligand (Fig. 15) was synthesized to study the catalytic mechanism. 

Scheme 15. Observation of charge-tagged compiexes generated in reaction of charged-tagged acetyie [85].

Eberiin has reported a charge-tagged acetate iigand as a probe for mass spectrometry [85]. Nickei, copper, and paiiadium compiexes of this iigand have been synthesized and characterized by ESi-MS (Scheme 15). Also, catalytic activity of a charged-tagged... 

A palladium-catalyzed system in which charged tags were used was recently reported by Schade et al. This study also includes examples of the use of charged quaternary ammonium-tagged substrates for studying Zn, Mg and In systems by ESI-MS and described some true reaction-monitoring experiments (vide infra) [86],... 

A key example of the usefulness of charged tags in probing reaction mechanisms is found in our study of the esterification of alcohols and carboxylic acids [90] reportedly catalyzed by dis-tannoxanes [91]. A permanently-charged pyridinium group was... 

Fig. 17. ESI(+)-MS ofthe charge tagged chromium tricarhonyl complex in methanol (m/z 457). A small amount of free ligand is also observed (m/z 321).

Fig. 25. Hydrodehalogenation progress observed by (+)-MS with intensities over time of all key species bearing the charged tag (Ar=[C6H4CH2PPh3r L=PPh3).The intensities of the palladium-containing intermediates have been multiplied by 100. Inset plot demonstrating the first order kinetics.

Figure 1. Chemical structures of common matrices for the MALDl analysis of DMA, proteins and charge-tagged DNA molecules.

Figure 4. Principle of the GOOD assay. CT synibolises the charge-tag, N" a DNA base and N a quartemary ammonium.

Charge tagging The amino functionality of the synthesised primers was used for attaching a positive charge tag (6-trimethylammoniumhexyryl-N-hydroxy-succinimidylester) according to Gut et al. [17] and Bartlett-Jones et al. [16]. The primers were dissolved in 1 % TE-buffer to 5(X) pmol/pl. 30 pi of this solution were mixed with 1.5 pi 2 M triethylammoniumhydrogencarbonate (pH 8,0) and 24 pi fresh 1% 6-trimethylammoniumhexyryl-N-hydroxy-succinintidylester solution. This... 

Prison, G. van der Rest, G. Turecek, F. Besson, T. Lemaire, J. Maitre, P Chamot-Rooke, J. Structure of electron-capture dissociation fragments from charge-tagged peptides probed by tunable infrared multiple photon dissociation. J. Am. Chem. Soc. 2008, 130, 14916-14917. 

Table 2.3 Oxysterol Content of Rodent Brain and Human Cerebrospinal Fluid as Determined by Charge Tagging and LC-ESI-MS"... 

When analysis is performed on ion-trap instruments, this ion can be selected and subjected to further fragmentation. The resulting MS spectra are rich in structural information (Figure 2.15). The MS/MS spectra on tandem quadrupole or Q-TOF instruments are effectively a composite of MS2 and MS3 spectra recorded on an ion trap. Using our charge-tagging methodology, we have profiled the oxysterol content of adult, newborn, and... 

Figure 2.12 Charge tagging with the GP reagent to an oxysterol. Oxidation of an oxysterol with a 3p-hydroxy-5-ene function (e.g., 24S,25-epoxycholesterol, C -3p-ol-24S,25-epoxide) to the analogous sterol with a 3-oxo-4-ene function (24S,25-epoxycholest-4-en-3-one, C -24S,25-epoxy-3-one) followed by derivatization with GP reagent.

Steroidomics Steroidomics is profiling the free sterol content of cerebrospinal fluid by a combination of charge tagging and liquid chromatography-tandem mass spectrometry. 

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