61 research outputs found
Distance dependence of photoinduced long-range electron transfer in zinc/ruthenium-modified myoglobins
An experimental investigation of the distance dependence of long-range electron transfer in zinc/ruthenium-modified myoglobins has been performed. The modified proteins were prepared by substitution of zinc mesoporphyrin IX diacid (ZnP) for the heme in each of four previously characterized pentaammineruthenium(III) (a_5Ru;a = NH_3) derivatives of sperm whale myoglobin (Mb): a_5Ru(His-48)Mb, a_5Ru(His-12)Mb, a_5Ru(His-116)Mb, a_5Ru(His-81)Mb. Electron transfer from the ZnP triplet excited state (^3ZnP*) to Ru^3+, ^3ZnP*-Ru^3+ → ZnP^+-Ru^2+ (ΔE° ~ 0.8V) was measured by time-resolved transient absorption spectroscopy: rate constants (k_f) are 7.0 × 10^4 (His-48), 1.0 × 10^2 (His-12), 8.9 × 10^1 (His-116), and 8.5 × 10^1 (His-81) s^-1 at 25 °C. Activation enthalpies calculated from the temperature dependences of the electron-transfer rates over the range 5-40 °C are 1.7 ± 1.6 (His-48), 4.7 ± 0.9 (His-12), 5.4 ± 0.4 (His-116), and 5.6 ± 2.5 (His-81) kcal mol^-1. Electron-transfer distances (d = closest ZnP edge to a_5Ru(His) edge; angstroms) were calculated to fall in the following ranges: His-48, 11.8-16.6; His-12, 21.5-22.3; His-116, 19.8-20.4; His-81, 18.8-19.3. The rate-distance equation is k_f = 7.8 × 10^8 exp[-0.9l(d - 3)] s^-1 . The data indicate that the ^3ZnP*-Ru(His-12)^3+ electronic coupling may be enhanced by an intervening tryptophan (Trp-14)
Morphology and Oxygen Sensor Response of Luminescent Ir-Labeled Poly(dimethylsiloxane)/Polystyrene Polymer Blend Films
Polymer films consisting of a linear poly(dimethylsiloxane) end-functionalized with a luminescent Ir(III) complex (Ir−PDMS), blended with polystyrene (PS), function as optical oxygen sensors. The sensor response arises by quenching of the luminescence from the Ir(III) chromophore by oxygen that permeates into the polymer film. The morphology and luminescence oxygen sensor properties of blend films consisting of Ir−PDMS and PS have been characterized by fluorescence microscopy, atomic force microscopy, and scanning electron microscopy. The investigations demonstrate that microscale phase segregation occurs in the films. In blends that contain a relatively small amount of Ir−PDMS in PS (ca. 10 wt %), the Ir−PDMS exists as circular domains, with diameters ranging from 2 to 5 μm, surrounded by the majority PS phase. For larger weight fractions of Ir−PDMS in the blends, the film morphology becomes bicontinuous. A novel epifluorescence microscopy method is applied that allows the construction of Stern−Volmer quenching images that quantify the oxygen sensor response of the blend films with micrometer spatial resolution. These images provide a map of the oxygen permeability of the polymer blend films with a spatial resolution of ca. 1 μm. The results of this investigation show that the micrometer-sized Ir−PMDS domains display a 2−3-fold higher oxygen sensor response compared to the surrounding PS matrix. This result is consistent with the fact that PDMS is considerably more gas permeable compared to PS. The relationship of the microscale morphology of the blends to their performance as macroscale optical oxygen sensors is discussed
The photodecomposition product μ-oxalato-1κ^2O,O′:2κ^2O″,O‴-bis{bis[2-(2-pyridyl)phenyl-κ^2C,N]iridium(III)}–acetone (1/1.974)
An attempt to grow crystals of [Ir(ppy)_2(vacac)], (I), from an acetone-d_6 solution formed instead crystals of [{Ir(ppy)_2}_2(μ-oxalato)] acetone solvate, (II), [Ir_2(C_(11)H_8N)_4(C_2O_4)]·1.974C_3H_6O, where ppy is the phenylÂpyridine anion and vacac is vinÂylacetylÂacetonate. Each Ir^(III) ion in (II) is in a pseudo-octaÂhedral coordination environment, where the pyridine N atoms are trans to each other and the phenÂyl C atoms are trans to the O atoms of the oxalate bridging ligand. There are two crystallographically independent dimer molecules, each lying on an inversion centre. It is suggested that the oxalate ligand is formed in a series of steps initiated by the aldol condensation of acetone with vacac
Distance dependence of photoinduced long-range electron transfer in zinc/ruthenium-modified myoglobins
Morphology and Oxygen Sensor Response of Luminescent Ir-Labeled Poly(dimethylsiloxane)/Polystyrene Polymer Blend Films
The relationship between eruptive activity, flank collapse, and sea level at volcanic islands: A long-term (>1 Ma) record offshore Montserrat, Lesser Antilles
Hole U1395B, drilled southeast of Montserrat during Integrated Ocean Drilling Program Expedition 340, provides a long (>1 Ma) and detailed record of eruptive and mass-wasting events (>130 discrete events). This record can be used to explore the temporal evolution in volcanic activity and landslides at an arc volcano. Analysis of tephra fall and volcaniclastic turbidite deposits in the drill cores reveals three heightened periods of volcanic activity on the island of Montserrat (?930 ka to ?900 ka, ?810 ka to ?760 ka, and ?190 ka to ?120 ka) that coincide with periods of increased volcano instability and mass-wasting. The youngest of these periods marks the peak in activity at the Soufrière Hills volcano. The largest flank collapse of this volcano (?130 ka) occurred towards the end of this period, and two younger landslides also occurred during a period of relatively elevated volcanism. These three landslides represent the only large (>0.3 km3) flank collapses of the Soufrière Hills edifice, and their timing also coincides with periods of rapid sea-level rise (>5 m/ka). Available age data from other island arc volcanoes suggests a general correlation between the timing of large landslides and periods of rapid sea-level rise, but this is not observed for volcanoes in intra-plate ocean settings. We thus infer that rapid sea-level rise may modulate the timing of collapse at island arc volcanoes, but not in larger ocean-island settings
Solvent dependence of ligand to metal charge-transfer oscillator strength: outer-sphere perturbation of the ruthenium(III)-cyanamide bond
Dependence of the Ru(III)-cyanamide chromophore on inner-sphere coordination: comparison of cis-[Ru(bpy)2(pcyd)2]+ and [Ru(NH3)5(pcyd)]2+ complexes
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