following solutions tfere prepared for enzymatic assay: (1) PIPES-NaOAc buffer (0.01 M PIPES, 0.2 M NaOAc and 0.01 mM EDTA, pH 6.5). This buffer was prepared according to the literature procedure.19 (2) a-n-Glucosidase: 1.5 mg of solid protein (70 U/mg) was dissolved in 1 mL of PIPES-NaOAc buffer solution and used for assay without dilution. (3) /S-D-Glucosidase: the assay enzyme solution was prepared by dissolving 20 mg of solid protein (4.8 U/mg solid) in 6 mL of PIPES-NaOAc buffer solution. (4) a-D-Mannosidase: 5 mg of solid protein was suspended in 1 mL of 3 M (NH4)2S04 and 0.1 M ZnOAc. (5) a-D-Galactosidase: 5 U of -galactosidase was dissolved in 2.2 mL of PIPES-NaOAc buffer solution. ( 6) 0-D-Galactosidase: 0.5 mg of solid protein (345 U/mg) was dissolved in 1 mL of PIPES-NaOAc buffer solution.General Procedure for Enzyme Assay. For each inhibitor, four or five inhibitor concentrations, ranging from 0 to 3 times K" were used to determine the K¡ value. At each inhibitor concentration, five substrate concentrations were used to obtain a single Lineweaver-Burk plot (Figure 5). The amount of enzyme added in each assay was adjusted so that less than 10% of the (19) Dale, .

Ion trap mass spectrometry has been used to structurally characterize and differentiate positional and stereo isomers of arylglycosides having potential antioxidant properties. The use of the self-ionization (SI) technique has allowed to evidence a strong reactivity of fragment ions produced from dissociations of the molecular ion towards the molecules introduced into the trap. Specific structural effects due to positional isomers and anomers have been also envisaged through the occurrence of bimolecular processes inside the ion trap analyzer. Under self-ionization conditions, even-electron ions are produced. The charge is retained on the sugar moiety, in agreement with its proton affinity higher than that of the substituted phenol moiety. Most of the fragmentation pathways involve elimination of acetic acid that protects the hydroxylic groups of the glycoside. SI also produces adduct ions, likely as covalent species, having higher m/z values than the molecular ion. The reaction site is mainly the double bond present in the pyranosidic ring. Even if some fragment ions have lost the initial stereochemistry, their formation can be related to the structure of the parent neutrals introduced into the cell. Collision-induced dissociation (CID) experiments, carried out on ions formed by ionmolecule reactions, have allowed to obtain further information on gas phase ion structures. The study of mass-selected ion-molecule reactions and their kinetics have evidenced a spectacularly different reactivity of the ion at m/z 111 towards the two anomers 2␣ and 2␤, with the latter showing a much more pronounced reactivity. The approach developed in this work revealed to be an useful tool in structural characterization, as well as in stereo and regiochemical differentiation of arylglycosides. A lot of different organic compounds can exist as isomers, such as regio, stereochemical, and positional isomers. Owing to the specific features of a given isomer, such as reactivity and biological properties, its structural characterization and differentiation is of particular importance. Different chemicophysical methods, such as nuclear magnetic resonance, circular dichroism, X-ray crystallography, and other spectroscopic methods can give useful and complementary information. One of these methods is represented by mass spectrometry (MS) [1,2] that has found more and more applications in isomer characterization and differentiation [3,4], some of them developed in our research groups [5][6][7]. MS offers several advantages over other techniques: speed of analysis, high sensitivity at low picomol level, possibility to carry out gas phase reactions, etc. A large number of investigations concerning stereochemical effects on gas phase reactions occurring in mass spectrometry experiments has been reported recently [8,9]. Different mass spectrometry techniques, such as chemical ionization [10 -12] and self-ionization (SI) [13][14][15][16], can be successfully used. In particular, the SI mode is a suitable approach for obtaining gas phase ion spec...