Noncovalent association phenomena of 2,5-dihydroxybenzoic acid with cyclic and linear oligosaccharides. A matrix-assisted laser desorption/ionization time-of-flight mass spectrometric and X-ray crystallographic study.

D-Glucose and 19 glucose derivatives were investigated by positive and negative ion matrix assisted laser desorption/ionization time-of-flight mass spectrometry using 2,5-dihydroxybenzoic acid (DHB) as the matrix. The set of substrates includes oligomers of amylose and cellulose, native alpha-, beta-, and gamma-cyclodextrin, and chemically modified beta- and gamma-cyclodextrins. These analytes were chosen to modulate molecular weight, polarity, and capability of establishing noncovalent interactions with guest molecules. In the negative-ion mode, the DHB matrix gave rise to charged multicomponent adducts of type [M + DHB - H]- (M = oligosaccharide) selectively for those analytes matching the following conditions: (i) underivatized chemical structure and (ii) number of glucose units > or = 4. In the positive-ion polarity, only some amylose and cellulose derivatives and methylated beta-cyclodextrins provided small amount of cationized adducts with the matrix of type [M + DHB + X]+ (X = Na or K), along with ubiquitous [M + X]+ ions. The results are discussed by taking into account analyte-matrix association phenomena, such as hydrogen bond and inclusion phenomena, as a function of the molecular structure of the analyte. The conclusions derived by mass spectrometric data are compared with the X-ray diffraction data obtained on a single crystal of the 1:1 alpha-cyclodextrin - DHB noncovalent adduct.