Attachment of alkali cations on beta-D-glucopyranose: matrix-assisted laser desorption/ionization time-of-flight studies and ab initio calculations

In matrix-assisted laser desorption/ionization mass spectrometry, carbohydr ates ionize by attachment of an alkali cation, and the ion yield varies wit h the nature of the cation. In an attempt to contribute to the understandin g of the mechanisms involved, we have conducted matrix-assisted laser desor ption/ionization time-of-flight (MALDI-TOF) experiments on the simple gluco se molecule with the alkali cations Li+, Na+ and K+, and have also performe d ab initio calculations. The calculations show that, for the most stable c arbohydrate-cation geometry, the carbohydrate ring is twisted and the catio n is coordinated to four oxygen atoms. Calculations also show that in these complexes the positions of the three cations are very similar, and the sma ller the cation, the closer it is to the oxygen atoms. Finally, the calcula ted formation enthalpies of the different complexes agree with the experime ntal results obtained for the order of stability of these complexes. Copyri ght (C) 2001 John Wiley & Sons, Ltd.