Methyl formate, HCOOCH 3 , is a well-known interstellar molecule prominent in the spectra of hot molecular cores. The current view of its formation is that it occurs in the gas phase from precursor methanol, which is synthesized on the surfaces of grain mantles during a previous colder era and evaporates while temperatures increase during the process of high-mass star formation. The specific reaction sequence thought to form methyl formate, the ion-molecule reaction between protonated methanol and formaldehyde followed by dissociative recombination of the protonated ion [HCO(H)OCH 3 ] + , has not been studied in detail in the laboratory. We present here the results of both a quantum chemical study of the ion-molecule reaction between [CH 3 OH 2 ] + and H 2 CO as well as new experimental work on the system. In addition, we report theoretical and experimental studies for a variety of other possible gas-phase reactions leading to ion precursors of methyl formate. The studied chemical processes leading to methyl formate are included in a chemical model of hot cores. Our results show that none of these gas-phase processes produces enough methyl formate to explain its observed abundance.

Hydrogen/deuterium exchange in reactions of H3O(+)(H2O)n and NH4(+)(H2O)n (1 < or = n < or = 30) with D2O has been studied experimentally at center-of-mass collisions energies of < or = 0.2 eV. For a given cluster size, the cross-sections for H3O(+)(H2O)n and NH4(+)(H2O)n are similar, indicating a structural resemblance and energetics of binding. For protonated pure water clusters, H3O(+)(H2O)n, reacting with D2O the main H/D exchange mechanism is found to be proton catalyzed. In addition the H/D scrambling becomes close to statistically randomized for the larger clusters. For NH4(+)(H2O)n clusters reacting with D2O, the main mechanism is a D2O/H2O swap reaction. The lifetimes of H3O(+)(H2O)n clusters have been estimated using RRKM theory and a plateau in lifetime vs. cluster size is found already at n = 10.

In order to reach a deeper insight into the reaction mechanism of the zeolite catalyzed methanol to hydrocarbons reaction (MTH), the proposed reaction intermediates, i.e., a series of multiply methyl-substituted benzenium ions has been generated in the gas phase by chemical ionization. The fragmentations of the corresponding long-lived (metastable) ions have been investigated. While expulsion of H 2 dominates for the lower homologues, elimination of methane dominates for the higher homologues, accompanied by increasing amounts CH 3 . Loss of larger fragments relevant to the MTH-reaction, in particular ethene, propene and even butene, is also observed in minor amounts. This latter finding is consistent with a proposed reaction cycle in the MTH reaction known as the paring mechanism, and the feasibility of this mechanism has thus been demonstrated. The metastable gasphase ions studied here are considerably more energetic than those residing in a zeolite catalyst, but they were found to decompose with markedly higher selectivity towards alkenes as compared to those activated by collision-induced dissociation (CID).

Rituximab, a chimeric murine/human monoclonal anti-CD20 antibody, was licensed for the treatment of B-cell lymphoma and has also shown efficacy against autoimmune diseases such as immune thrombocytopenic purpura (ITP). It is relatively safe; however, about 1-20% of patients were reported to have developed rituximab-induced serum sickness, which is more common among patients with autoimmune conditions than among those with hematologic malignancies. Here we describe a pediatric patient with steroid-dependent chronic ITP who presented with arthralgia and fever ten days after the second infusion of rituximab (on day 10), and presented with malaise and maculopapular rash on day 21. Oral prednisolone was started and his symptoms resolved. He had an elevated level of human anti-chimeric antibody (HACA) on day 27; thereafter, the HACA level slowly decreased. To our knowledge, among pediatric patients who received rituximab for chronic ITP, this is the sixth documented case of serum sickness and the only one who manifested an elevated level of HACA. Rituximab is a beneficial treatment option against chronic ITP; however, the risk of serum sickness should be considered. Steroid, usually used for the treatment of serum sickness, may prevent the development of severe serum sickness when administered during and after rituximab treatment.

We report the unimolecular decomposition following collisional activation of protonated mono-, di- and trimethylbenzenes as a function of collision energy. The resulting energy-resolved mass spectra are then used for the quality control of high-level quantum chemical models of the respective potential energy surfaces. Distinction is made between direct dissociation products (CH(4) or H(2)) and indirect products (alkenes), since formation of the latter requires extensive rearrangement of the molecular skeleton. Very good consistency was found between model and experiment. The models thereby provide a solid foundation for discussing the reaction mechanisms of the industrial methanol-to-hydrocarbon process. The losses of CH(4), C(2)H(4) and C(3)H(6) from mesitylenium ions have been studied by (13)C and (2)H labelling and the alkene losses were found to occur via irreversible isomerisation pathways.