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The kinetics and mechanism for the unimolecular decomposition of o-nitrotoluene (o-CH3C6H4NO2) have been studied computationally at the G2M(RCC, MP2)//B3LYP/6-311G(d, p) level of theory in conjunction with rate constant predictions with RRKM and TST calculations. The results of the calculations reveal 10 decomposition channels for o-nitrotoluene and its six isomeric intermediates, among them four channels give major products: CH3C6H4 + NO2, C6H4C(H)ON (anthranil) + H2O, CH3C6H4O (o-methyl phenoxy) + NO, and C6H4C(H2)NO + OH. The predicted rate constants in the 500−2000 K temperature range indicate that anthranil production, taking place initially by intramolecular H-abstraction from the CH3 group by NO2 followed by five-membered ring formation and dehydration, dominates at temperatures below 1000 K, whereas NO2 elimination becomes predominant above 1100 K and CH3C6H4O formation by the nitro−nitrite isomerization/decomposition process accounts for only 5−11% of the total product yield in the middle temperature range 800−1300 K. The branching ratio for CH2C6H4NO formation by the decomposition process of CH2C6H4N(O)OH is negligible. The predicted high-pressure-limit rate constants with the rate expression of 4.10 × 1017 exp[−37000/T] s-1 for the NO2 elimination channel and 9.09 × 1012 exp[−25800/T] s-1 for the H2O elimination channel generally agree reasonably with available experimental data. The predicted high-pressure-limit rate constants for the NO and OH elimination channels are represented as 1.49 × 1014 exp[−30000/T] and 1.31 × 1015 exp[−38000/T] s-1, respectively. [ABSTRACT FROM AUTHOR]

Mammalian myosin filaments are helically ordered only at higher temperatures (> 20 °C) and become progressively more disordered as the temperature is decreased. It had previously been suggested that this was a consequence of the dependence of the hydrolytic step of myosin ATPase on temperature and the requirement that hydrolysis products (e.g., ADP·P[sub i]) be bound at the active site. An alternative hypothesis is that temperature directly affects the conformation of the myosin heads and that they need to be in a particular conformation for helical order in the filament. To discriminate between these two hypotheses, we have studied the effect of temperature on the helical order of myosin heads in rabbit psoas muscle in the presence of nonhydrolyzable ligands. The muscle fibers were overstretched to nonoverlap such that myosin affinity for nucleotides was not influenced by the interaction of myosin with the thin filament. We show that with bound ADP·vanadate, which mimics the transition state between ATP and hydrolysis products, or with the ATP analogues AMP-PNP or ADP·BeF[sub x] the myosin filaments are substantially ordered at higher temperatures but are reversibly disordered by cooling. These results reinforce recent studies in solution showing that temperature as well as ligand influence the equilibrium between multiple myosin conformations [Málnási-Csizmadia, A., Pearson, D. S., Kovács, M., Woolley, R. J., Geeves, M. A., and Bagshaw, C. R. (2001) Biochemistry 40, 12727-12737; Málnási-Csizmadia, A., Woolley, R. J., and Bagshaw, C. R. (2000) Biochemistry 39, 16135-16146; Urbanke, C., and Wray, J. (2001) Biochem. J. 358, 165-173] and indicate that helical order requires the myosin heads to be in the closed conformation. Our results suggest that most of the heads in the closed conformation are ordered, and that order is not produced in a separate step. Hence, helical order can be used as a signature... [ABSTRACT FROM AUTHOR]

Formation dynamics of free and neutral donor bound excitons (FX and D0X) in a high quality ZnO single crystal are studied by means of time-resolved photoluminescence (TRPL) at various temperatures. At low-temperatures, FX and D0X formation times are determined to be ~5 and ~10 ps, respectively, by fitting the rise process with the Boltzmann sigmoidal function. Temporal information of FX- and D0X-longitudinal optical (LO) phonon coupling is also acquired by measuring TRPL spectra of the first-order LO phonon-assisted FX and D0X transitions. In particular, interesting time evolution of luminescence intensity in the Fano resonance region due to the configuration interaction of exciton--impurity--phonon is explored. [ABSTRACT FROM AUTHOR]

Examines silicone [poly(dimethylsiloxane)s PDMS] hydrolysis over a wide range of soil moisture levels. Information on the widespread use of silicone polymers [poly(dimethylsiloxane)s PDMS] and its entry into soils through the disposal of sewage sludge. Details on the fate of this polymer in a variety of soil environments; What are silicone polymers.

In this work, we present the coating regulations of Fe3O4nanoparticles (NPs) by the reverse microemulsionmethodto obtain the Fe3O4@SiO2core/shellNPs. The regulation produces the core/shell NPs with a single coreand with different shell thicknesses, and it especially can be appliedto different sizes Fe3O4NPs and avoid the formationof core-free silica particles. Our results reveal that the silicacoating parameters suitable for Fe3O4NPs withcertain size are not definitely applicable to that with other sizes,and the match of the number of Fe3O4NPs withaqueous domain is essential. We found that the small aqueous domainis suitable to coat ultrathin silica shell, while the large aqueousdomain is indispensable for coating thicker shells. To avoid the formationof core-free silica particles, the thick silica shell can be achievedby increasing the content of either TEOS through the equivalentlyfractionated drops or ammonia with a decreased one-off TEOS. The ligandexchange between the intermediate processes of the silica coatingis evidenced. Our results provide not only a strategy for synthesizinguniform Fe3O4@SiO2core/shell NPswith controlled shell thickness, but also a regulation that can beapplied to preparation other core–shell NPs. [ABSTRACT FROM AUTHOR]