Platinum dioxide cation: easy to generate experimentally but difficult to describe theoretically.

A formal platinum(V) dioxide cation [Pt,O2](+) can be generated in the gas phase by successive oxidation of Pt(+) with N2O. The ion's reactivity is in keeping with the dioxide structure OPtO(+), rather than with [Pt,O2](+) isomers having intact O-O bonds, e.g., the dioxygen complex Pt(O2)(+) and peroxo species PtOO(+). Inter alia due to the high ionization energy of the neutral counterpart (11.2 eV), the [Pt,O2](+) cation is a rather aggressive reagent toward oxidizable neutrals. [Pt,O2](+) is even capable of activating inert substrates such as H2, CO, and CH4. Further, a sequence for the catalytic conversion CO + N(2)O --> CO2 + N2 is described with a turnover number of >100 for the catalytically active species PtOn(+) (n = 0-2). As a consequence of the high reactivity, however, the observed selectivities with most substrates are rather poor. For example, the reaction of PtO2(+) with ethane gives rise to 10 different product channels. In an attempt to analyze the structural features and different minima of the [Pt,O2](+) system, extensive ab initio studies are performed. While correlated ab initio methods describe the system reasonably well, density functional theory turns out to be much less accurate in terms of both structural and energetic descriptions.

Analysis of CD8 T cell reactivity to cytomegalovirus using protein-spanning pools of overlapping pentadecapeptides.

The frequencies of human cytomegalovirus (HCMV) protein-specific CD8 T cells, identified by the presence of intracellular IFN-gamma, were measured by flow cytometry following stimulation of freshly isolated peripheral blood mononuclear cells (PBMC) with comprehensive peptide pools. These pools spanned the entire amino acid sequences of the HCMV pp65 and major immediate early (IE-1) proteins and consisted of 15-amino acid peptides with at least nine overlaps between neighboring peptides. As a result all potential CD8 T cell epitopes contained in these proteins were provided by the complete pools and, therefore, unlike with single epitopes, testing was independent of donor HLA type. Individual stimulating peptides from the same pools were identified in parallel experiments. Thus we found that our results with the complete pools using PBMC from 26 healthy HCMV-seropositive donors were 100% sensitive and specific with respect to predicting the presence of recognized epitopes in the respective proteins. In addition, cells from 15 renal transplant patients were tested with complete pools alone. While our results confirmed our previous contention that HCMV IE-1 is an important CD8 T cell target, the technical improvement we made in order to address this question has clearly wider implications. Similar pools may be applied to examine the role of proteins from other pathogens, in autoimmune disease or following vaccination.