Experimental and computational studies of the macrocyclic effect of an auxiliary ligand on electron and proton transfers within ternary copper(II)-histidine complexes.

The dissociation of [Cu(II)(L)His](*2+) complexes [L = diethylenetriamine (dien) or 1,4,7-triazacyclononane (9-aneN(3))] bears a strong resemblance to the previously reported behavior of [Cu(II)(L)GGH](*2+) complexes. We have used low-energy collision-induced dissociation experiments and density functional theory (DFT) calculations at the B3LYP/6-31+G(d) level to study the macrocyclic effect of the auxiliary ligands on the formation of His(*+) from prototypical [Cu(II)(L)His](*2+) systems. DFT revealed that the relative energy barriers of the same electron-transfer (ET) dissociation pathways of [Cu(II)(9-aneN(3))His](*2+) and [Cu(II)(dien)His](*2+) are very similar, with the ET reactions of [Cu(II)(9-aneN(3))His](*2+) leading to the generation of two distinct His(*+) species; in contrast, the proton transfer (PT) dissociation pathways of [Cu(II)(9-aneN(3))His](*2+) and [Cu(II)(dien)His](*2+) differ considerably.

Dissociation of the N-C(alpha) bond and competitive formation of the [z(n) - H](+) and [c(n) + 2H](+) product ions in radical peptide ions containing tyrosine and tryptophan: the influence of proton affinities on product formation.

Dissociations at the N-C(alpha) bond of tryptophan and tyrosine residues are the prevalent pathways in the fragmentations of radical cations of tripeptides that contain such as residues. This process involves a proton transfer from the beta-carbon of the tryptophan or tyrosine residue to the carbonyl oxygen of the amide group, followed by cleavage of the N-C(alpha) bond, generating low-lying proton-bound dimers that dissociate to give each an ionic and a neutral product. Formation of the [z(n) - H](*+) or [c(n) + 2H](+) ion is a competition between the two incipient fragments for the proton in a dissociating proton-bound dimer.

Catalytic oxidation of H2 by N2O in the gas phase: O-atom transport with atomic metal cations.

Twenty-five atomic cations, M (+), that lie within the thermodynamic window for O-atom transport catalysis of the oxidation of hydrogen by nitrous oxide, have been checked for catalytic activity at room temperature with kinetic measurements using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Only 4 of these 25 atomic cations were seen to be catalytic: Fe (+), Os (+), Ir (+), and Pt (+). Two of these, Ir (+) and Pt (+), are efficient catalysts, while Fe (+) and Os (+) are not.

Gas-phase ionic syntheses of amino acids: beta versus alpha.

Both theoretical and experimental studies are reported for the gas-phase reactions of protonated hydroxylamine with acetic and propanoic acids which yield protonated glycine and alanine, GlyH+ and AlaH+, respectively. The key step for these reactions is an insertion of the amino group into a C-H bond. For the formation of AlaH+, the reaction barrier for insertion into a Cbeta-H bond is ca.

Radical-cationic gaseous amino acids: a theoretical study.

Three major forms of gaseous radical-cationic amino acids (RCAAs), keto (COOH), enolic (C(OH)OH), and zwitterionic (COO(-)), as well as their tautomers, are examined for aliphatic Ala(.+), Pro(.+), and Ser(.

Water-catalyzed hydrolysis of the radical cation of ketene in the gas phase: theory and experiment.

Both theoretical and experimental investigations are reported for the gas-phase hydrolysis of the radical cation of ketene, H(2)CCO(*+). Density functional theory (DFT) with the B3LYP/6-311++G(d,p) method indicates that a second water molecule is required as a catalyst for the addition of water across the C=O bond in H(2)CCO(*+) by eliminating the activation barrier for the conversion of [H(2)CCO.H(2)O](*+) to [H(2)CC(OH)(2)](*+).

Gaseous bradykinin and its singly, doubly, and triply protonated forms: a first-principles study.

The conformers of gaseous bradykinin, BK, (Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)) and its protonated forms, [BK + H](+), [BK + 2H](2+), and [BK + 3H](3+), were examined theoretically using a combination of the Merck molecular force field, Hartree-Fock, and density functional theory. Neutral BK, [BK + H](+), and [BK + 2H](2+) exist in zwitterionic forms that are stabilized by internal solvation and have compact structures; [BK + 3H](3+) differs by the absence of a salt bridge and adopts an elongated form. The common structural feature in all four BK species is a beta-turn in the Ser(6)-Pro(7)-Phe(8)-Arg(9) sequence.

O-atom transport catalysis by atomic cations in the gas phase: reduction of N2O by CO.

Atomic cations (26), M+, have been shown to lie within a thermodynamic window for O-atom transport catalysis of the reduction of N2O by CO and have been checked for catalytic activity at room temperature with kinetic measurements using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Only 10 of these 26 atomic cations were seen to be catalytic: Ca+, Fe+, Ge+, Sr+, Ba+, Os+, Ir+, Pt+, Eu+, and Yb+. The remaining 16 cations that lie in the thermodynamic window (Cr+, Mn+, Co+, Ni+, Cu+, Se+, Mo+, Ru+, Rh+, Sn+, Te+, Re+, Pb+, Bi+, Tm+, and Lu+) react too slowly at room temperature either in the formation of MO+ or in its reduction by CO.

Existence of doubly charged lead monohydrate: experimental evidence and theoretical examination.

Despite reports to the contrary, doubly charged lead monohydrate is a stable species against both proton and charge transfers. [Pb(H(2)O)](2+) has been observed as a minor product in the ligand-exchange reaction of [Pb(CH(3)CN)](2+) with H(2)O after collisional activation. Density functional theory has been used to examine reaction profiles of [Pb(H(2)O)(n)](2+) where n = 1, 2, and 3.

Theoretical study of the amazing firefly bioluminescence: the formation and structures of the light emitters.

Reaction mechanisms for the formation of the keto-form of oxyluciferin (OxyLH(2)) from the luciferin of fireflies via a dioxetanone intermediate are predicted using the B3LYP/6-31G theoretical method. The ring opening of a model dioxetanone and the decarboxylation proceed in one step via a singlet diradical transition structure with an activation barrier of 18.1 and an exothermicity of 90.

Regioselective silylation of sugars through palladium nanoparticle-catalyzed silane alcoholysis.

Palladium(0)-catalyzed silane alcoholysis was applied to sugars for the first time using tert-butyldimethylsilane (TBDMS-H) and Ph(3)SiH as the silanes. The catalyst is a colloidal solution of Pd(0) generated in situ from PdX(2) (X = Cl(-), OAc(-)) and TBDMS-H in N,N-dimethylacetamide. The colloid has been characterized by dynamic light scattering and transmission electron microscopy and consists of catalytically highly active nanoparticles of approximately 2 nm diameter.