Laser vaporization combined with a supersonic molecular beam was employed to generate and study the Au(C 5 H 5 N) þ complex for the first time. On the basis of the ionization energies (IE) between gold and pyridine, the Au(C 5 H 5 N) þ species is viewed as being a Au þ -C 5 H 5 N species. Photodissociative charge transfer was observed with exclusive C 5 H 5 N þ (pyridine) formation. The photofragmentation spectrum of Au þ -(C 5 H 5 N) was scanned by monitoring the pyridine fragments. A structureless continuum spectrum was observed and the onset of C 5 H 5 N þ appearance indicates the upper limit on the Au þ -C 5 H 5 N bond strength to be 59.6 kcal mol À1 . Ab initio calculations at the MP2 level were employed to optimize the geometries of the gold complexes and binding energies were obtained using CCSD(T) single point calculations. Besides from the C 2v structure observed in Cu þ and Ag þ complexes, the theoretical results yielded a second isomer with C 1 symmetry which is 24 kcal mol À1 less stable in energy than the C 2v isomer.

Free oligosaccharides are abundant macronutrients in milk and involved in prebiotic functions and antiadhesive binding of viruses and pathogenic bacteria to colonocytes. Despite the importance of these oligosaccharides, structural determination of oligosaccharides is challenging, and milk oligosaccharide biosynthetic pathways remain unclear. Oligosaccharide structures are conventionally determined using a combination of chemical reactions, exoglycosidase digestion, nuclear magnetic resonance spectroscopy, and mass spectrometry. Most reported free oligosaccharides are highly abundant and have lactose at the reducing end, and current oligosaccharide biosynthetic pathways in human milk are proposed based on these oligosaccharides. In this study, a new mass spectrometry technique, which can identify linkages, anomericities, and stereoisomers, was applied to determine the structures of free oligosaccharides in human, bovine, and caprine milk. Oligosaccharides that do not follow the current biosynthetic pathways and are not synthesized by any discovered enzymes were found, indicating the existence of undiscovered biosynthetic pathways and enzymes.

A simple method to generate and characterize a pure highly vibrationally excited azulene molecular beam is demonstrated. Azulene molecules initially excited to the S4 state by 266-nm UV photons reach high vibrationally excited levels of the ground electronic state upon rapid internal conversion from the S4 electronically excited state. VUV laser beams at 157 and 118 nm, respectively, are used to characterize the relative concentrations of the highly vibrationally excited azulene and the rotationally and vibrationally cooled azulene in the molecular beam. With a laser intensity of 34 mJ/cm2, 75% of azulene molecules absorb a single 266-nm photon and become highly vibrationally excited molecules. The remaining ground-state azulene molecules absorb two or more UV photons, ending up either as molecular cations, which are repelled out of the beam by an electric field, or as dissociation fragments, which veer off the molecular-beam axis. No azulene without absorption of UV photons is left in the molecular beam. The molecular beam that contains only highly vibrationally excited molecules and carrier gas is useful in various experiments related to the studies of highly vibrationally excited molecules.

Differentiation of stereoisomers that are only dissimilar in the orientation of chemical bonds in space by mass spectrometry remains challenging. Structural determination of carbohydrate by mass spectrometry is difficult, mainly...

Free oligosaccharides are abundant macronutrients in milk and involved in prebiotic functions and antiadhesive binding of pathogenic bacteria to colonocytes. Despite the importance of these oligosaccharides, structural determination of oligosaccharides is challenging, and milk oligosaccharide biosynthetic pathways remain unclear. Oligosaccharide structures are conventionally determined using a combination of chemical reactions, exoglycosidase digestion, nuclear magnetic resonance spectroscopy, and mass spectrometry. Most reported free oligosaccharides are highly abundant and have lactose at the reducing end, and current oligosaccharide biosynthetic pathways in human milk are proposed based on these oligosaccharides. In this study, a new mass spectrometry technique, which can identify linkages, anomericities, and stereoisomers, was applied to determine the structures of free oligosaccharides in human, bovine, and caprine milk. Oligosaccharides that do not follow the current biosynthetic pathways and are not synthesized by any discovered enzymes were found, indicating the existence of undiscovered biosynthetic pathways and enzymes. New biosynthetic pathways were proposed.