20-Nanogold Au20(Td) and Low-Energy Hollow Cages: Void Reactivity

peer reviewe

On the N3O2- paradigm

A survey of the existing experimental and theoretical data on the trinitrogen dioxide anion N3O2- that manifests a controversy as to the number of isomers and their chemical structures is presented. To resolve the controversy, new computational studies are performed at the MP2/aug-cc-pVTZ computational level. Two hitherto unknown isomers are predicted, one with singlet and one with triplet spin multiplicity. The singlet isomer, structurally characterized as N-2 center dot[ONO](-), is the most stable among all known isomers and accounts for fragmentation patterns observed in the recent dissociative photodetachment experiments. (C) 2007 Elsevier B.V. All rights reserved

The gold-ammonia bonding patterns of neutral and charged complexes Au m 0+/-1-(NH3)n. I. Bonding and charge alternation.

The gold-ammonia bonding patterns of the complexes which are formed between the ammonia clusters (NH/sub 3/)/sub 1<or=n<or=3/ and gold clusters of different sizes that range from one gold atom to the tri-, tetra-, and 20-nanogold clusters are governed by two basic and fundamentally different ingredients: the anchoring Au-N bond and the nonconventional N-H ... Au hydrogen bond. The latter resembles, by all features, a conventional hydrogen bond and is formed between a typical conventional proton donor N-H group and the gold cluster that behaves as a nonconventional proton acceptor. We provide strong computational evidence that the gold-ammonia bonding patterns exhibit distinct characteristics as the Z charge state of the gold cluster varies within Z=0,+/-1. The analysis of these bonding patterns and their effects on the N-H ... N H-bonded ammonia clusters are the subject of this paper

Charge distribution in 3'-deoxythymidine-fullerene: Mass spectrometry, laser excitation, and computational studies

Electrospray ionization of the donor-spacer-acceptor model system 3'-imino[60]fulleryl-3'-deoxythymidine molecule (FdT) produces deprotonated negatively charged species (dFdT). In this paper, we investigate where the negative charge is localized and whether its location can be manipulated. The fragmentation of dFdT is studied experimentally by mass spectrometry using both collisional and photoactivation. Besides fragmentation, photoexcitation of anions stored in an ion trap leads to electron photodetachment. The competition between the two channels is studied as a function of the excitation wavelength. Starting from the neutral parents, two families of dFdT molecules are computationally identified. Deprotonation takes place on the 3'-deoxythymidine (dT) subunit, either on the thymine at N3 or on the deoxyribose residue at O5'. Deprotonation in N3 leads to negatively charged molecules with an extended geometry and the excess charge largely localized on the dT. The O5'-deprotonation leads to lower-energy folded conformers stabilized by an additional bond (C-O or C-H) with the nearby C-60-N acceptor part, and the negative charge is mostly localized on the fullerene. The calculated electron detachment energies are higher for the extended N3dFdT conformers than for the O5'dFdT ones. Multiphoton photodetachment experiments at 1064 nm indicate the negative charge to be on the C-60 unit. No indication for a photoinduced charge transfer was found. In MS beside the C-60 anion a C60NH, - fragment is observed, which implies a double intramolecular H transfer. The computed energy of the corresponding dFdT, stabilized by two H-C-60 bonds, is intermediate between N3 and O5' deprotonated molecules