Synthesis, structure, and optical-limiting properties of heterobimetallic [M(3)CuS(4)] cuboidal clusters (M = Mo or W) with terminal phosphine ligands.

Cubane-type clusters of formula [Mo(3)CuS(4)Cl(4)(dmpe)(3)](PF(6)) (4), [Mo(3)CuS(4)Br(4)(dmpe)(3)](PF(6)) (5), and [W(3)CuS(4)Br(4)(dmpe)(3)](PF(6)) (6) have been prepared by reacting the incomplete cuboidal trimers [Mo(3)S(4)Cl(3)(dmpe)(3)](PF(6)) (1), [Mo(3)S(4)Br(3)(dmpe)(3)](PF(6)) (2), and [W(3)S(4)Br(3)(dmpe)(3)](PF(6)) (3), respectively, with CuX (X = Cl or Br) or the mononuclear copper complex [Cu(CH(3)CN)(4)](+) in THF. The reaction takes place without global changes in the metal oxidation states, and compounds 4-6 with a [M(3)CuS(4)](5+) core possess 16 e(-) for metal-metal bonding. X-ray structural analysis of 4-6 revealed an effective C(3v) symmetry for the M(3)Cu unit with the M-M distances being statistically the same for M = Mo or W. However, the M-Cu distance is 0.04 and 0.1 A longer than the M-M bond length for Mo and W, respectively. There is no significant structural rearrangement of the ligand-metal bonding in proceeding from [M(3)S(4)X(3)(dmpe)(3)](+) to [M(3)CuS(4)X(4)(dmpe)(3)](+). The cyclic voltammograms of the [Mo(3)CuS(4)] cubane clusters show one quasi-reversible reduction process at E(1/2) = -0.31 V for 4 and at E(1/2) = -0.23 V for 5 and one irreversible reduction at -0.69 and -0.58 V for 4 and 5, respectively. The tungsten cluster 6 shows a unique quasi-reversible reduction wave at E(1/2) = -0.71 V. The incorporation of copper into the incomplete [M(3)S(4)] cuboidal complexes produces a decrease of the reduction potential for both molybdenum and tungsten. Absorption spectra of 1-6 are broadly similar; replacing Mo by W in proceeding from 2 to 3 or from 5 to 6 and replacing Br by Cl in proceeding from 2 to 1 or from 5 to 4 results in a blue shift of the three UV-visible absorption bands. All six clusters exhibit optical limiting, as measured by the Z-scan technique at 523 nm using 40 ns pulses. The power-limiting mechanism remains obscure, but under the conditions employed, threshold-limiting fluence decreases on replacing W by Mo on proceeding from 3 to 2 or 6 to 5 and on proceeding from tetranuclear cluster (4-6) to trinuclear precursor (1-3, respectively). For all six clusters, values of the excited-state cross section sigma(eff) are larger than those of the corresponding ground-state cross section sigma(0); i.e., all clusters are efficient optical limiters.

Intermittent electromechanical dissociation as an unusual sign of prosthetic valve thrombosis in a patient with prosthetic fibrous ingrowth.

We describe the echocardiographic features of an unusual hemodynamic phenomenon of intermittent electromechanical dissociation during regular sinus tachycardia in a patient with prosthetic mitral valve thrombosis. Thrombolysis with a solution of recombinant tissue-type plasminogen activator resulted in the disappearance of electromechanical dissociation and was effective in stabilizing the patient's condition. The later discovery of panus covering the valve ring after the lysis of clots confirmed surgery as the definitive treatment.

Effect of chill and freezing temperatures on survival of Vibrio parahaemolyticus inoculated in homogenates of oyster meat.

Survival of Vibrio parahaemolyticus was determined in oyster meat homogenates at various temperatures. (4 degrees C, 0 degrees C, -18 degrees C and -24 degrees C) and bacterial levels (10(2), 10(4), 10(5) and 10(7) ml-1). In all cases, the numbers of V. parahaemolyticus were a logarithmic function of log time. This study indicates that high numbers of V. parahaemolyticus can be inactivated at low temperatures. The time of total inactivation depends on the initial number of micro-organisms and incubation temperature. It is possible to use this information to determine the storage time necessary to reduce V. parahaemolyticus hazards in fish.

Preservation of the amputated canine hind limb by extracorporeal perfusion.

The hind limbs of six dogs were reimplanted immediately after amputation. Another nine were conserved by extracorporeal circulation for 24 h, and then examined histologically. A further six were conserved by the same method and then reimplanted after 24 h. Conservation by extracorporeal circulation maintained the limbs in good condition. Less than 5% of the muscle fibres showed abnormality when examined, and the lesions were reversible.