Search PubMed⌕ Search

Biomedical subjects

D G Nocera

Publications and source records attributed to D G Nocera.

7 recordsLinked to original sources
PubMed2006

Spin waves in the frustrated kagomé lattice antiferromagnet KFe3(OH)6(SO4)2.

The spin wave excitations of the S=5/2 kagomé lattice antiferromagnet KFe3(OH)6(SO4)2 have been measured using high-resolution inelastic neutron scattering. We directly observe a flat mode which corresponds to a lifted "zero energy mode," verifying a fundamental prediction for the kagomé lattice. A simple Heisenberg spin Hamiltonian provides an excellent fit to our spin wave data. The antisymmetric Dzyaloshinskii-Moriya interaction is the primary source of anisotropy and explains the low-temperature magnetization and spin structure.

Journal Article↗
PubMed2001

Hydrogen produced from hydrohalic acid solutions by a two-electron mixed-valence photocatalyst.

Energy conversion cycles are aimed at driving unfavorable, small-molecule activation reactions with a photon harnessed by a transition metal complex. A challenge that has occupied researchers for several decades is to create molecular photocatalysts to promote the production of hydrogen from homogeneous solution. We now report the use of a two-electron mixed-valence dirhodium compound to photocatalyze the reduction of hydrohalic acid to hydrogen. In this cycle, photons break two RhII-X bonds of a LRh0-RhIIX2 core in the presence of a halogen trap to regenerate the active LRh0-Rh0 catalyst, which reacts with hydrohalic acid to produce hydrogen.

Journal Article↗
PubMed2000

Xanthene-bridged cofacial bisporphyrins.

The synthesis and characterization of cofacial bisporphyrins juxtaposed by xanthene-bridged pillars are presented. The one-pot preparation of the xanthene dialdehyde avoids the lengthy bridge synthesis accompanying other cofacial porphyrin systems, thus allowing for the facile preparation of homobimetallic zinc (10), copper (11), and nickel (12) complexes. The cofacial orientation of the two porphyrin macrocycles was confirmed by X-ray crystallography. Structural data are provided for bisporphyrins 10-12: 10 (C79H82N8OZn2), triclinic, space group P1, a = 11.2671(2) A, b = 14.9809(2) A, c = 20.4852(2) A, alpha = 101.6680(10) degrees, beta = 100.8890(10) degrees, gamma = 101.8060(10) degrees, Z = 2; 11 (C79H82N8OCu2), triclinic, space group P1, a = 11.21410(10) A, b = 14.9539(5) A, c = 20.6915(7) A, alpha = 101.810(2) degrees, beta = 101.044(2) degrees, gamma = 101.722(2) degrees, Z = 2; 12 (C79H82N8ONi2), monoclinic, space group C2/c, a = 24.1671(4) A, b = 10.669 A, c = 50.5080(9) A, beta = 99.553(2) degrees, Z = 8. Exciton interactions between the porphyrin rings are apparent in electronic spectra, consistent with the cofacial superstructure. The combination of structural and spectroscopic data provides a basis for the design of additional metal derivatives for the activation of dioxygen and other small molecules.

Bridged-Ring Compounds↗
PubMed2000

The whole story of the two-electron bond, with the delta bond as a paradigm.

It is shown that the delta bond, as found particularly in the Re(2)(6+) and Mo(2)(4+) cores of hundreds of compounds, provides a paradigm for the behavior of two-electron bonds of all types. By control of the angle of twist around the M-M axis, the strength of the bond can be systematically varied. By means of conventional electronic spectroscopy, nuclear magnetic resonance spectroscopy, and two-photon excitation spectroscopy, the entire picture of the manifold of four states for two electrons bonding two atoms, as first described by Coulson and Fischer in 1949, has been confirmed.

Electrons↗
PubMed1998

Proton-coupled electron transfer.

Proton-coupled electron transfer (PCET) is an important mechanism for charge transfer in a wide variety of systems including biology- and materials-oriented venues. We review several areas where the transfer of an electron and proton is tightly coupled and discuss model systems that can provide an experimental basis for a test of PCET theory. In a PCET reaction, the electron and proton may transfer consecutively (ET/PT) or concertedly (ETPT). The distinction between these processes is formulated, and rate-constant expressions for the two reaction channels are presented. Methods for the evaluation of these rate constants are discussed that are based on dielectric continuum theory. Electron donor hydrogen-bonded-interface electron acceptor systems displaying PCET reactivity are presented, and the rate-constant expressions corresponding to the ETPT and ET/PT channels for several model reaction complexes are evaluated.

Electron Transport↗