Lithium cationization, mass spectrometry

Z. Zhou, S. Ogden and J.A. Leary, Linkage position determination in oligosaccharides mass spectrometry (MS/MS) study of lithium-cationized carbohydrates, J. Org. Chem., 55 (1990) 5444-5446. 

The study of the interactions between organic compounds and aUtali-metal cations, in the gas phase, is related to many topics such as ion solvation, catalysis and molecular recognition. Furthermore, mass spectrometry has been used for the analyses of organolithium compounds and supramolecular assemblies that contain lithium cations. Alkali cationization is an important ionization technique, implemented for the analyses of a wide range of organic compounds. Finally, gas-phase studies are also useful for the quantitative determination of lithium cation affinity. The interaction between lithium cation and organic substances is thus related to different aspects of gas-phase chemistry and mass spectrometry. 

The same group studied the lithium cation basicities of a series of compounds of the general formula R R R PO, i.e. phosphine oxides, phosphinates, phosphonates and phosphates, by using Fourier Transform Ion Cyclotron Resonance (FTTCR) mass spectrometry. A summary of their results is shown in Figure 4. The effect of methyl substitution on LCA as well as the correlation between LCA and PA was also investigated by Taft, Yanez and coworkers on a series of methyldiazoles with an FTICR mass spectrometer. They showed that methyl substituent effects on Li binding energies are practically additive. 

Carbohydrates show a considerable affinity toward alkali cations, which are frequently used for their mass spectral analyses. Lithium cation exhibits specific affinity toward glucose, as has been detected by electrospray ionization mass spectrometry. The experimental results were found to be consistent with the ab initio theoretical calculations and confirm the following order of stability of the M+-glucose complexes [gl-Li] > [gl-Na]+ > [gl-K]+4 . 

Hofmeister GE, Zhou Z, Leary JA. Linkage position determination in lithium-cationized disaccharides tandem mass spectrometry and semiempirical calculations. J Am Chem Soc. 1991 113 5964-70. 

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