Search

The density functional calculations are used to investigate the catalytic role of [Cu.sup.+2] ions in the peptide bond formation. The free energy barrier formed during intracomplex condensation is lowered by the interaction of glycines with [Cu.sup.+2] and the water molecules present.

A study of the coordination of Cu(super 2+) is conducted by glyoxilic acid oxime, the oxime analogue of glycine amino acid and its deprotonated species. Calculations suggest a different global minimum structure for Cu(super 2+) interacting with glyoxillic acid oxime rather than with glycine.

A detailed analysis of the gas-phase binding chemistry between Co(super +) and Co(super 2+) cations and glycine, the simplest amino acid is presented. The most stable structure of Co(super +)-glycine is bidentate, the ground electronic state being (super 3)A while the ground electronic state for Co(super 2+) is (super 4)A.

The effect of counterpoise correction on the geometries and vibrational frequencies of fifteen hydrogen-bonded systems was analyzed at the B3LYP and MP2 levels of theory, using the popular 6-31++G(d,p) set. The counterpoise correction increases the H-bond distance, decreases the intermolecular stretching frequency and decreases the red-shift of the donor H-X frequency.

An investigation of the ionization process of the lowest four conformers of glycine is presented. Attention is given to the intramolecular proton-transfer process of the second conformer in the ground and first excited states of glycine radical cation.

The characteristics of the process of hydrogen or proton transfer in neutral and single positive ions of salicylic acid, o-hydroxybenzaldehyde, and salicylaldimine were investigated using the B3LYP density functional method. Single-point computations at the CCSD(T) level were also conducted. For neutral systems, the reaction corresponds to a proton transfer process coupled with an electronic transfer, which leads to a compound with nonzwitterionic character. A similar behavior is seen for ionized pi radical cations.

The metal-glycine bonding in the biologically significant Cu(super +) and Cu(super 2+) pair has been investigated. To this end, the structure and vibrational frequencies for various coordination modes of Cu(super +) and Cu(super 2+) to glycine were determined using the hybrid three-parameter B3LYP density functional theory. Results show that glycine acquires an essential radical property that alters the relative metal affinities of the different basic sites, which favors the interaction of the metal cation with the carbon dioxide group compared with other coordinations.

The adsorption of 11 amino acids (Gly, Leu, Met, Phe, Ser, Cys, Glu, Gln, Arg, Lys, and His) on the TiO2(110) rutile surface is investigated adopting a theoretical approach, using the PBE-D2* functional as implemented in the periodic VASP code. The adsorption of the amino acids is considered in their canonical, deprotonated and zwitterionic forms. For all cases, the most stable adsorption mode adopts a bidentate (O,O) binding with surface undercoordinated Ti atoms, in agreement with previous experimental and computational studies using glycine as a test case. Such a binding mode is possible due to the surface morphology, because the Ti–Ti distances match very well with the carboxylic O–O distance. The most stable adsorption states are the deprotonated and the zwitterionic ones, the canonical one lying significantly above in energy. The relative stability between the deprotonated and the zwitterionic states results in a delicate trade-off among dative interactions (O, N, and S atoms of the amino acids with Ti atoms of the surface), H-bond interactions, dispersive forces and, to a lesser extent, steric hindrance of the amino acidic lateral chains. Finally, the difference in the amino acid adsorption between the (110) rutile and the (101) anatase surfaces is discussed both from the energetic and surface morphological standpoints, highlighting the larger reactivity of the rutile polymorph in adsorbing and deprotonating the amino acids compared with the anatase one. [ABSTRACT FROM AUTHOR]

DFT and CASSCF methods are used for examining the [2+2] photocycloaddition reaction of 2(5H)-furanone to ethylene and acetylene. Although reaction through the triplet state of olefins is disregarded due to the short lifetime of these species, the studies have shown that sensitization of ethylene triplet state has occurred at typical synthetic conditions, thus leading to photochemical addition to the lactone.

A study is conducted to analyze the binding of first-row transition metal monocations (Sc-Cu) to N7 of guanine and N7 to N3 of adenine nucleobases. The result from analysis show that differences between guanine and adenine arise from Pauli repulsion and deformation terms.

The effects of oxidation, protonation and metal cationization with Cu(super +) and Cu(super 2+) on the strength of the N-glycosidic bond in 2'-deoxyguanosine are studied by using quantum chemical calculations. The analysis has shown that these changes might not only influence the hydrolysis mechanism of the N-glycosidic bond but also affect other properties such as N9-C1' chemical shielding tensors.

The ground and low-lying states of Cu(super 2+)-H2O is studied by using different density functional and post-Hartree-Fock methods. CCSD(T) results indicate that Cu(super 2+)-H2O has C2v symmetry and that the ground electronic state is a (super 2)S(sub 1) state.

The gas-phase reactivity of Ni(super +1) (urea) was investigated by means of mass spectrometry techniques and density functional calculations. Calculations showed that the most stable Ni(super +1) - urea complex had the Ni(super +1) cation interacting with the oxygen, with the computed binding energy being 66.3 kcal/mol.

The collinear reaction of Fe+ (4F) and Fe+ (6D) with H2 leading to FeH+ and H has been studied at the configuration interaction (CI) level of theory, using a relativistic pseudopotential approach. The 6D electronic state of Fe+ reacts with H2 through a very large energy barrier that slightly exceeds the endothermicity of the reaction. The 4F electronic state appears to be much more reactive than the 6D state, in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The electronic states of FeH+ dissociating into Fe+ (6D) and H (2S) have been studied at the restricted open Hartree–Fock (ROHF) and configuration interaction (CI) level of theory, using a pseudopotential approach and considering or not relativistic effects. The ground state appears to be a 5Δ at the ROHF level but inclusion of correlation effects leads to a 5Π ground state. Nevertheless both states exhibit in all cases a near degeneracy. The calculated D0 is about 90% of the experimental value at the CI level whereas ROHF calculations account only for about 25% of the experimental dissociation energy. [ABSTRACT FROM AUTHOR]

Mass spectrometry and B3LYP density functional calculations are used to examine the reaction mechanism between Ni+ and glycine in the gas phase. Calculation optimized the most stable ground-state structure to be a bidentate, eta (super 2)-N, O, one in which the Ni+ cation interacts with the nitrogen atom and the carbonyl oxygen.

The electronic state of FeH dissociating into Fe (5D) and H (2S) have been studied at the restricted open Hartree–Fock (ROHF) and configuration interaction (CI) level of theory, using a relativistic pseudo-potential approach and including or not f functions in the basis set. The relative energies and spectroscopic properties obtained by us are in very good agreement with the experimental results found in the literature. In particular this work provides a new theoretical confirmation of a 4Δ electronic ground state for FeH. The effect of including or not f functions in the basis set is discussed. [ABSTRACT FROM AUTHOR]

Using periodic DFT-D2 methods, atomistic simulations of interstellar H adsorption and H2 formation on a (010) Fe-containing olivine surface are presented. At variance with the (010) Mg2SiO4 surface and key to these processes are the large Fe/H interaction energies, suggesting that olivine surfaces are good reservoirs of H atoms for subsequent recombination to form H2. [ABSTRACT FROM AUTHOR]