Decay kinetics of the green emission in tungstates and molybdates

Luminescence characteristics of a number of undoped and variously doped PbWO₄ crystals were studied at 0.4–400 K by the time-resolved spectroscopy and compared with those of ZnWO₄,CdWO₄ and PbMoO₄ crystals. Two types of green emission centres are detected in PbWO₄ crystals. The centres of the first type are responsible for the low-temperature 2.3–2.4 eV emission observed under excitation around 3.90–3.95 eV. The structure and parameters of their relaxed excited states were determined. It was concluded that the origin of defects responsible for the green emission of the first type could vary for different crystals. The centres of the second type with the emission around 2.5 eV appear in crystals containing oxygen vacancies after the thermal destruction of Pb⁺-WO₃ centres at T>180 K. Decomposition of the exciton and various defect-related states was also studied, and activation energies of this process were calculated.     

Dynamic polarization of lipid bilayers as a special case in the electrochemistry of liquid/liquid interfaces

Dynamically obtained current/voltage curves of bilayer lipid membranes partitioning a solution of lipophilic ions are compared with the results of the type expected in a voltammetry experiment involving ionic transport across a liquid/liquid interface. Lipophilic ions yielding “voltammograms” analogous to reversible and irreversible voltammograms (in conventional electrochemical systems) are reported. Also reported are examples of ions which yield what may be analogous to a masked response, a phenomenon known in the literature of liquid/liquid interfaces. Although the behavior of the two systems is similar, there exist differences in the interpretation of the voltammograms and suggestions are offered for an energetic and mechanistic interpretation of the membrane voltammogram.     

PT Symmetry in Quantum Field Theory

The Hamiltonian H specifies the energy levels and the time evolution of a quantum theory. It is an axiom of quantum mechanics that H be Hermitian. The Hermiticity of H guarantees that the energy spectrum is real and that the time evolution is unitary (probability preserving). In this talk we investigate an alternative formulation of quantum mechanics in which the mathematical requirement of Hermiticity is replaced by the more physically transparent condition of space-time reflection (PT) symmetry. We show that if the PT symmetry of a Hamiltonian H is not broken, then the spectrum of H is real. Examples of PT-symmetric non-Hermitian Hamiltonians are H=p ²+ix ³ and H=p ²-x ⁴. The crucial question is whether PT-symmetric Hamiltonians specify physically acceptable quantum theories in which the norms of states are positive and the time evolution is unitary. The answer is that a Hamiltonian that has an unbroken PT symmetry also possesses a physical symmetry that we call C. Using C, we show how to construct an inner product whose associated norm is positive definite. The result is a new class of fully consistent complex quantum theories. Observables exhibit CPT symmetry, probabilities are positive, and the dynamics is governed by unitary time evolution.     

Effects of ground-state correlations on 2νββ decay rates and limitations of the QRPA approach

Half-lives of the 2νββ decay are calculated in the proton-neutron QRPA for⁷⁶Ge,⁸²Se,¹⁰⁰Mo,^128,130Te,¹³⁶Xe and¹⁵⁰Nd. The strength of the particle-particle interaction, which plays a decisive role for a reliable evaluation of the half-lives, is determined from a QRPA calculation of singleβ ⁺ decays. The 2ν decay rates calculated with the interaction strength fitted in this way are strongly suppressed and found to be consistent with the existing experimental data. Effects of the ground-state correlations on the suppression are investigated. On the other hand, the present calculation indicates limitations of the QRPA approach.     

Poly(ε-caprolactone) macroligands with β-diketonate binding sites: synthesis and coordination chemistry

Dibenzoylmethane (dbm) initiators with one and two alcohol sites were used to generate dbm end-functionalized and dbm-centered poly(ε-caprolactone) macroligands (dbmPCL and dbmPCL₂) with low polydispersities (∼1.1). Chelation of polymeric ligands to metal ions (Eu³⁺, Fe³⁺, Ni²⁺ and Cu²⁺) produced metal-centered star polymers, which were characterized by UV-vis and fluorescence spectroscopy, as well as gel permeation chromatography.     

Role for bound water and CH-pi aromatic interactions in photosynthetic electron transfer

Photosystem I (PSI) is one of two photosynthetic reaction centers present in plants, algae, and cyanobacteria and catalyzes the reduction of ferredoxin and the oxidation of cytochrome c or plastocyanin. The PSI primary chlorophyll donor, which is oxidized in the primary electron-transfer events, is a heterodimer of chl a and a' called P700. It has been suggested that protein relaxation accompanies light-induced electron transfer in this reaction center (Dashdorj, N.; Xu, W.; Martinsson, P.; Chitnis, P. R.; Savikhin, S. Biophys. J. 2004, 86, 3121. Kim, S.; Sacksteder, C. A.; Bixby, K. A.; Barry, B. A. Biochemistry 2001, 40, 15384). To investigate the details of electron transfer and relaxation events in PSI, we have employed several experimental approaches. First, we report a pH-dependent viscosity effect on P700+ reduction; this result suggests a role for proton transfer in the PSI electron-transfer reactions. Second, we find that changes in hydration alter the rate of P700+ reduction and the interactions of P700 with the protein environment. This result suggests a role for bound water in electron transfer to P700+. Third, we present evidence that deuteration of the tyrosine aromatic side chain perturbs the vibrational spectrum, associated with P700+ reduction. We attribute this result to a linkage between CH-pi interactions and electron transfer to P700+.