Experimental and theoretical studies of rate coefficients for the reaction O(3P)+CH3OH at high temperatures

Rate coefficients of the reaction O((3)P) + CH(3)OH in the temperature range of 835-1777 K were determined using a diaphragmless shock tube. O atoms were generated by photolysis of SO(2) with a KrF excimer laser at 248 nm or an ArF excimer laser at 193 nm; their concentrations were monitored via atomic resonance absorption excited by emission from a microwave-discharged mixture of O(2) and He. The rate coefficients determined for the temperature range can be represented by the Arrhenius equation, k(T) = (2.29 +/- 0.18) x 10(-10) exp[-(4210 +/- 100)T] cm(3) molecule(-1) s(-1); unless otherwise noted, all the listed errors represent one standard deviation in fitting. Combination of these and previous data at lower temperature shows a non-Arrhenius behavior described as the three-parameter equation, k(T) = (2.74 +/- 0.07) x 10(-18)T(2.25 +/- 0.13) exp[-(1500 +/- 90)T] cm(3)molecule(-1) s(-1). Theoretical calculations at the Becke-3-Lee-Yang-Parr (B3LYP)6-311 + G(3df,2p) level locate three transition states. Based on the energies computed with coupled clusters singles, doubles (triples) [CCSD(T)]/6-311 + G(3df,2p)B3LYP6-311 + G(3df,2p), the rate coefficients predicted with canonical variational transition state theory with small curvature tunneling corrections agree satisfactorily with the experimental observations. The branching ratios of two accessible reaction channels forming OH + CH(2)OH (1a) and OH + CH(3)O (1b) are predicted to vary strongly with temperature. At 300 K, reaction (1a) dominates, whereas reaction (1b) becomes more important than reaction (1a) above 1700 K.     

Dual room-temperature fluorescent and phosphorescent emission in 8-quinolinolate osmium(II) carbonyl complexes: rationalization and generalization of intersystem crossing dynamics

A new series of quinolinolate osmium carbonyl complexes were synthesized and characterized by spectroscopic methods. Single-crystal X-ray diffraction studies indicate that these complexes consist of an octahedral ligand arrangement with one chelating quinolinolate, one tfa or halide ligand, and three mutually orthogonal terminal CO ligands. Variation of the substituents on quinolinolate ligands imposes obvious electronic or structural effects, while changing the tfa ligand to an electron-donating iodide slightly increases the charge density on the central osmium atom. These Os(II) complexes show salient dual emissions consisting of fluorescence and phosphorescence, the spectral properties and relaxation dynamics of which have been studied comprehensively. The results, in combination with the theoretical approaches, lead us to propose that the emission mainly originates from the quinolinolate pi pi* state. Both experimental and theoretical approaches generalize various types of intersystem crossing versus those of the tris(quinolinolate) iridium Ir(Q)3, and their relative efficiencies were accessed on the basis of the associated frontier orbital configurations. Our results suggest that [1d(pi)pi* absolute value(H(so))3 pi pi*] (or [3d(pi)pi* absolute value(H(so))1 pi pi*]) in combination with a smaller deltaE(S1-T1) gap (i.e., increasing the MLCT (d(pi)pi*) character) is the main driving force to induce the ultrafast S1 --> T1 intersystem crossing in the third-row transition metal complexes, giving the strong phosphorescent emission.     

Speciation of bound and free metals evaluated for lobster digestive gland extracts

A simple method is described for the speciation of metalions in biological extracts with a short desalting gel-filtration column. The system was optimized for the eluent and gel type to provide accurate free metal ion levels and minimum processing times. The four separation media studied were Sephadex G25, Bio-Gel P-6DG, controlled pore glass CPG40, and Fractogel HW40F. The best medium was the Fractogel HW40F because it was not compressible and allowed a pump to be used to obtain uniform flow rates. The eluent was 0.10 M ammonium acetate/0.01 M citric acid adjusted to pH 7.0. This eluent minimized ion/gel interactions and gave a lower salt content relative to other possible eluents. The separation time was 10 min per sample per metal ion of interest. The detection limits relative to the mass of wet tissue for the column/flame spectrometer system were 0.80 μg g^?1, 0.80 μg g^?1, and 1.6 μg g^?1 for zinc, cadmium and copper, respectively. The method is evaluated for a lobster digestive gland extract; the methodology should be applicable to other systems containing nonlabile metal species.     

Multiple hydrogen bonds tuning guest/host excited-state proton transfer reaction: its application in molecular recognition

A molecular recognition concept exploiting multiple-hydrogen-bond fine-tuned excited-state proton-transfer (ESPT) was conveyed using 3,4,5,6-tetrahydrobis(pyrido[3,2-g]indolo)[2,3-a:3',2'-j]acridine (1a). The catalytic type 1a/carboxylic acids hydrogen-bonding (HB) complexes undergo ultrafast ESPT, resulting in an anomalously large Stokes shifted tautomer emission (lambdamax approximately 600 nm). Albeit forming a quadruple HB complex, ESPT is prohibited in the noncatalytic-type 1a/urea complexes (lambdamax approximately 430 nm). The HB configuration tuning ESPT properties lead to a feasible design for sensing multiple-HB-site analytes of biological interest.     

Performance improvement of electrochromic display devices employing micro-size precipitates of tungsten oxide

In this paper, we studied the effect of micro-size WO₃ precipitates on the electrochromic characteristics based on aging test. The electrochromic mechanism can be effectively investigated by a solid-state TaN/WO₃/ITO capacitor. The experimental results reveal that WO₃ electrochromic devices with optimized aging time of 4 days exhibit a higher optical contrast and longer retention time, which is mainly attributed to the formation of micro-size WO₃ precipitates during aging process. The performance improvement using micro-size WO₃ precipitates has the potential in future large-area window or energy efficient display applications.