A bis(η-cyclopentadienyl)cobalt complex of a bis-dithiolene: a chemical analogue of the metal centres of the DMSO reductase family of molybdenum and tungsten enzymes, in particular ferredoxin aldehyde oxidoreductase

The synthesis is described of a bis-ene-1,2-dithiolate pro-ligand, designed to model the stereochemical situation in the cofactor of the tungsten enzyme ferredoxin aldehyde oxidoreductase from Pyrococcus furiosus. Each masked ene-1,2-dithiolate unit is mounted on a pyrano[2,3-b]tetrahydroquinoxaline tricycle, comparable to the pyrano[2,3-g]tetrahydropteridines found in all molybdoenzymes and tungsten analogues. Hydrolytic release of the bis-ligand was confirmed by its entrapment as a double (η⁵-C₅H₅)Co complex.     

Measurement of elastic nonlinearity using remote laser ultrasonics and CHeap Optical Transducers and dual frequency surface acoustic waves

A nonlinear ultrasonic technique for evaluating material elastic nonlinearity has been developed. It measures the phase modulation of a high frequency (82MHz) surface acoustic wave interacting with a low frequency (1MHz) high amplitude stress inducing surface acoustic wave. A new breed of optical transducers has been developed and used for the generation and detection of the high frequency wave. The CHeap Optical Transducer (CHOT) is an ultrasonic transducer system, optically activated and read by a laser. We show that CHOTs offer advantages over alternative transducers. CHOTs and nonlinear ultrasonics have great potential for aerospace applications. Results measuring changes in ultrasonic velocity corresponding to different stress states of the sample are presented on fused silica and aluminium.     

New routes to high nuclearity cages: a fluoride-based hexaicosametallic manganese cage

The reaction of MnF3 with benzotriazole (BTAH) in hot MeOH gives the Mn(III) complex [Mn26O16(OH)10(OMe)6(F)10(BTA)20(BTAH)2(MeOH)13(H2O)] which displays hysteresis and temperature-independent magnetisation relaxation at low temperature.     

Magnetic and optical studies on an S = 6 ground-state cluster [Cr12O9(OH)3(O2CCMe3)15]: determination of,and the relationship between,single-ion and cluster spin Hamiltonian parameters

The dodecametallic Cr(III) cluster [Cr(12)O(9)(OH)(3)(O(2)CCMe(3))(15)] has a ground spin state of S = 6 characterized by the spin Hamiltonian parameters g(ZZ)() = 1.965, g(XX)() = g(YY)() = 1.960, D(S=)()(6) = +0.088 cm(-)(1), and E(S=)()(6) = 0 (where D and E are the axial and rhombic zero-field splitting parameters, respectively) as determined by multifrequency EPR spectroscopy and magnetization studies. Micro-SQUID magnetization studies reveal steps due to the fine structure of the ground state, with the spacing between the steps in excellent agreement with the D(S=)()(6) value determined by EPR. Analysis of high-resolution optical data (MCD) allows us to determine the single-ion g values and D value (= -1.035 cm(-)(1)) of the constituent Cr(III) ions directly. A vector coupling analysis demonstrates that the cluster ZFS is almost entirely due to the single-ion component. Thus, the relative orientations of the local and cluster magnetic axes can lead to a cluster ZFS of opposite sign to the single-ion value, even when this is the only significant contribution.     

Patterns of phoneme perception errors by listeners with cochlear implants as a function of overall speech perception ability

Many studies have noted great variability in speech perception ability among postlingually deafened adults with cochlear implants. This study examined phoneme misperceptions for 30 cochlear implant listeners using either the Nucleus-22 or Clarion version 1.2 device to examine whether listeners with better overall speech perception differed qualitatively from poorer listeners in their perception of vowel and consonant features. In the first analysis, simple regressions were used to predict the mean percent-correct scores for consonants and vowels for the better group of listeners from those of the poorer group. A strong relationship between the two groups was found for consonant identification, and a weak, nonsignificant relationship was found for vowel identification. In the second analysis, it was found that less information was transmitted for consonant and vowel features to the poorer listeners than to the better listeners; however, the pattern of information transmission was similar across groups. Taken together, results suggest that the performance difference between the two groups is primarily quantitative. The results underscore the importance of examining individuals' perception of individual phoneme features when attempting to relate speech perception to other predictor variables.     

Regularized matched-mode processing for source localization

This paper develops a new approach to matched-mode processing (MMP) for ocean acoustic source localization. MMP consists of decomposing far-field acoustic data measured at an array of sensors to obtain the excitations of the propagating modes, then matching these with modeled replica excitations computed for a grid of possible source locations. However, modal decomposition can be ill-posed and unstable if the sensor array does not provide an adequate spatial sampling of the acoustic field (i.e., the problem is underdetermined). For such cases, standard decomposition methods yield minimum-norm solutions that are biased towards zero. Although these methods provide a mathematical solution (i.e., a stable solution that fits the data), they may not represent the most physically meaningful solution. The new approach of regularized matched-mode processing (RMMP) carries out an independent modal decomposition prior to comparison with the replica excitations for each grid point, using the replica itself as the a priori estimate in a regularized inversion. For grid points at or near the source location, this should provide a more physically meaningful decomposition; at other points, the procedure provides a stable inversion. In this paper, RMMP is compared to standard MMP and matched-field processing for a series of realistic synthetic test cases, including a variety of noise levels and sensor array configurations, as well as the effects of environmental mismatch.     

Synthesis, structure and redox properties of bis(cyclopentadienyl)dithiolene complexes of molybdenum and tungsten

The compounds [Cp(2)M(S(2)C(2)(H)R)] (M = Mo or W; R = phenyl, pyridin-2-yl, pyridin-3-yl, pyridin-4-yl or quinoxalin-2-yl) and [Cp(2)Mo(S(2)C(2)(Me)(pyridin-2-yl)] have been prepared by a facile and general route for the synthesis of dithiolene complexes, viz. the reaction of [Cp(2)MCl(2)] (M = Mo or W) with the dithiolene pro-ligand generated by reacting the corresponding 4-(R)-1,3-dithiol-2-one with CsOH. These Mo compounds were reported previously (Hsu et al., Inorg. Chem. 1996, 35, 4743); however, the preparative method employed herein is more versatile and generates the compounds in good yield and all of the W compounds are new. Electrochemical investigations have shown that each compound undergoes a diffusion controlled one-electron oxidation (OX(I)) and a one-electron reduction (RED(I)) process; each redox change occurs at a more positive potential for a Mo compound than for its W counterpart. The mono-cations generated by chemical or electrochemical oxidation are stable and the structures of both components of the [Cp(2)Mo(S(2)C(2)(H)R)](+)/[Cp(2)Mo(S(2)C(2)(H)R)] (R = Ph or pyridin-3-yl) redox couples have been determined by X-ray crystallography. For each redox related pair, the changes in the Mo-S, S-C and C-C bond lengths of the {MoSCCS} moiety are generally consistent with OX(I) involving the loss of an electron from a π-orbital that is Mo-S and C-S antibonding and C-C bonding in character. These results have been interpreted successfully within the framework provided by DFT calculations accomplished for [Cp(2)M(S(2)C(2)(H)Ph)](n) (M = Mo or W; n = +1, 0 or -1). The HOMO of the neutral compounds is derived mainly from the dithiolene π(3) orbital (65%); therefore, OX(I) is essentially a dithiolene-based process. The similarity of the potentials for OX(I) (ca. 30 mV) for analogous Mo and W compounds is consistent with this interpretation and the EPR spectra of each of the Mo cations show that the unpaired electron is coupled to the dithiolene proton but relatively weakly to (95,97)Mo. The DFT calculations indicate that the unpaired electron is more localised on the metal in the mono-anions than in the mono-cations. In agreement with this, the EPR spectrum of each of the Mo-containing mono-anions manifests a larger (95,97)Mo coupling (A(iso)) than observed for the corresponding mono-cation and RED(I) for a W compound is significantly (ca. 300 mV) more negative than that of its Mo counterpart. [Cp(2)W(S(2)C(2)(H)(quinoxalin-2-yl))] is anomalous; RED(I) occurs at a potential ca. 230 mV more positive than expected from that of its Mo counterpart and the EPR spectrum of the mono-anion is typical of an organic radical. DFT calculations indicate that these properties arise because the electron is added to a quinoxalin-2-yl π-orbital.