Noncovalent Modulation of Chemoselectivity in the Gas Phase Leads to a Switchover in Reaction Type from Heterolytic to Homolytic to Electrocyclic Cleavage

In the gas phase, thermal activation of supramolecular assemblies such as host–guest complexes leads commonly to noncovalent dissociation into the individual components. Chemical reactions, for example of encapsulated guest molecules, are only found in exceptional cases. As observed by mass spectrometry, when 1-amino-methyl-2,3-diazabicyclo[2.2.2]oct-2-ene (DBOA) is complexed by the macrocycle β-cyclodextrin, its protonated complex undergoes collision-induced dissociation into its components, the conventional reaction pathway. Inside the macrocyclic cavity of cucurbit[7]uril (CB7), a competitive chemical reaction of monoprotonated DBOA takes place upon thermal activation, namely a stepwise homolytic covalent bond cleavage with the elimination of N₂, while the doubly protonated CB7⋅DBOA complex undergoes an inner-phase elimination of ethylene, a concerted, electrocyclic ring-opening reaction. These chemical reaction pathways stand in contrast to the gas-phase chemistry of uncomplexed monoprotonated DBOA, for which an elimination of NH₃ predominates upon collision-induced activation, as a heterolytic bond cleavage reaction. The combined results, which can be rationalized in terms of organic-chemical reaction mechanisms and density-function theoretical calculations, demonstrate that chemical reactions in the gas phase can be steered chemoselectively through noncovalent interactions.     

Negative binomial multiplicity distributions in high energy hadron collisions

We examine the 2⁺⁺ gluonium spectrum in the framework of the Gauss-Weierstrass and Finite Energy QCD sum rules. The results of our analysis support the interpretation of the θ(1710) as a tensor glueball, but they also suggest the existence of at least another state with a massM?2 GeV and a width of about 200 MeV.     

Synthesis of complex oligosaccharides by using a mutated (1,3)-beta-D-glucan endohydrolase from barley

Complex oligosaccharides with newly formed (1,3)-beta-glycosidic linkages were obtained in good to excellent yields when substituted or unsubstituted alpha-laminaribiosyl fluorides, acting as donors, were condensed onto mono- and disaccharide beta-D-hexopyranoside acceptors by using a (1,3)-beta-D-glycosynthase. These linear and branched (1,3)-beta-linked oligosaccharides could prove to be important in a range of medical, pharmaceutical, and agricultural applications. Furthermore, the observation that the (1,3)-beta-D-glucan glycosynthase accommodates (1,3)-, (1,4),- and (1,6)-beta-oligosaccharides in its acceptor subsites suggests novel, yet unexpected physiological roles for the wild type (1,3)-beta-D-glucan endohydrolase from higher plants.