New holomorphically closed subalgebras of C∗C^*-algebras of hyperbolic groups

We construct dense, unconditional subalgebras of the reduced group $C^*$-algebra of a word-hyperbolic group, which are closed under holomorphic functional calculus and possess many bounded traces. Applications to the cyclic cohomology of group $C^*$-algebras and to delocalized $L^2$-invariants of negatively curved manifolds are given

Bond cleavage reactions in the tripeptide trialanine upon free electron capture

In the present study we performed dissociative electron attachment (DEA) measurements with the tripeptide trialanine, C9H17N3O4, utilizing a crossed electron-molecular beam experiment with high electron energy resolution (100 meV). Anion efficiency yields as a function of the incident electron energy are obtained for the most abundant anions up to electron energies of 4 eV. Quantum chemical calculations are performed to determine the thermochemical thresholds for the anions observed in the measurements. There is no evidence of a molecular anion with lifetime of mass spectrometric timescales. The dehydrogenated closed shell anion (M-H) is one of the fragment anions observed for which the calculations show that H-loss is energetically possible from carboxyl, as well as amide groups. In contrast to the dipeptide dialanine and monomer alanine the cleavage of the N-C [alpha] bond in the peptide chain is already possible by attachment of electrons at 0 eV.(VLID)1020375Accepted versio

NCO-, a key fragment upon dissociative electron attachment and electron transfer to pyrimidine bases: site selectivity for a slow decay process

We report gas phase studies on NCO- fragment formation from the nucleobases thymine and uracil and their N-site methylated derivatives upon dissociative electron attachment (DEA) and through electron transfer in potassium collisions. For comparison, the NCO- production in metastable decay of the nucleobases after deprotonation in matrix assisted laser desorption/ionization (MALDI) is also reported. We show that the delayed fragmentation of the dehydrogenated closed-shell anion into NCO- upon DEA proceeds few microseconds after the electron attachment process, indicating a rather slow unimolecular decomposition. Utilizing partially methylated thymine, we demonstrate that the remarkable site selectivity of the initial hydrogen loss as a function of the electron energy is preserved in the prompt as well as the metastable NCO- formation in DEA. Site selectivity in the NCO- yield is also pronounced after deprotonation in MALDI, though distinctly different from that observed in DEA. This is discussed in terms of the different electronic states subjected to metastable decay in these experiments. In potassium collisions with 1- and 3-methylthymine and 1- and 3-methyluracil, the dominant fragment is the NCO- ion and the branching ratios as a function of the collision energy show evidence of extraordinary site-selectivity in the reactions yielding its formation.(VLID)1020364Accepted versio

N-site de-methylation in pyrimidine bases as studied by low energy electrons and ab initio calculations

Electron transfer and dissociative electron attachment to 3-methyluracil (3meU) and 1-methylthymine (1meT) yielding anion formation have been investigated in atom-molecule collision and electron attachment experiments, respectively. The former has been studied in the collision energy range 14-100 eV whereas the latter in the 0-15 eV incident electron energy range. In the present studies, emphasis is given to the reaction channel resulting in the loss of the methyl group from the N-sites with the extra charge located on the pyrimidine ring. This particular reaction channel has neither been approached in the context of dissociative electron attachment nor in atom-molecule collisions yet. Quantum chemical calculations have been performed in order to provide some insight into the dissociation mechanism involved along the N-CH3 bond reaction coordinate. The calculations provide support to the threshold value derived from the electron transfer measurements, allowing for a better understanding of the role of the potassium cation as a stabilising agent in the collision complex. The present comparative study gives insight into the dynamics of the decaying transient anion and more precisely into the competition between dissociation and auto-detachment. © 2013 the Owner Societies.DA and FFS acknowledge the Portuguese Foundation for Science and Technology (FCT-MEC) for post-graduate and post-doctoral scholarships SFRH/BD/61645/2009 and SFRH/BPD/68979/2010, respectively. DA acknowledges the valuable discussions with Dr Rodrigo Antunes and Eng. Gonçalo Martins. PL-V, FFS and DA acknowledge the strategic grant PEst-OE/FIS/UI0068/2011 and PTDC/FIS/ATO/1832/2012. PL-V and GG acknowledge the support from the Portuguese-Spanish joint collaboration through the bilateral Project HP 2006-0042. This work also forms part of EU/ESF COST Actions The Chemical Cosmos CM0805 and Nanoscale Insights into Ion Beam Cancer Therapy (Nano-IBCT) MP1002. This work was partially supported by the Fonds zur Förderung der wissenschaftlichen Forschung (FWF, P22665), Wien.Peer Reviewe

A K-theoretic Selberg trace formula

Let G be a semisimple Lie group and Γ a uniform lattice in G. The Selberg trace formula is an equality arising from computing in two different ways the traces of convolution operators on the Hilbert space L2( Γ∖G) associated to test functions f ∈ Cc(G). In this paper we present a cohomological interpretation of the trace formula involving the K-theory of the maximal group C∗-algebras of G and Γ. As an application, we exploit the role of group C∗-algebras as recipients of “higher indices” of elliptic differential operators and we obtain the index theoretic version of the Selberg trace formula developed by Barbasch and Moscovici from ours