A previously proposed [Sutcliffe and Tennyson, Int. J. Quantum Chem. 29 , 183 (1991)] body-fixed Hamiltonian is applied to AB2 systems in Radau coordinates with the x-axis embedded along the bisector of the angle. It is shown that by using a discrete variable representation for the angular coordinate it is possible to avoid singular regions of the Hamiltonian. A two-step variational procedure is used to obtain rotationally excited states of the system. The results of test calculations H2S and D2S with J = 0, 1, 5, and 10 are discussed along with computer-usage characteristics. 相似文献
The reductive half‐reaction of morphinone reductase involves a hydride transfer from enzyme‐bound β‐nicotinamide adenine dinucleotide (NADH) to a flavin mononucleotide (FMN). We have previously demonstrated that this step proceeds via a quantum mechanical tunnelling mechanism. Herein, we probe the effect of the solvent on the active site chemistry. The pKa of the reduced FMN N1 is 7.4±0.7, based on the pH‐dependence of the FMN midpoint potential. We rule out that protonation of the reduced FMN N1 is coupled to the preceding H‐transfer as both the rate and temperature‐dependence of the reaction are insensitive to changes in solution pH above and below this pKa. Further, the solvent kinetic isotope effect is ～1.0 and both the 1° and 2° KIEs are insensitive to solution pH. The effect of the solvent’s dielectric constant is investigated and the rate of H‐transfer is found to be unaffected by changes in the dielectric constant between ～60 and 80. We suggest that, while there is crystallographic evidence for some water in the active site, the putative promoting motion involved in the H‐tunnelling reaction is insensitive to such changes. 相似文献
Putting the squeeze on : Hydrostatic pressure causes a shortening of the charge‐transfer bond in the binary complex of morphinone reductase and NADH4 (see diagram). Molecular dynamics simulations suggest that pressure reduces the average reaction barrier width by restricting the conformational space available to the flavin mononucleotide and NADH within the active site. The apparent rate of catalysis increases with pressure.
Experimental results are reported for the response of an initially turbulent boundary layer (Reθ≈1700) to a favourable pressure gradient with a peak value of K≡(−υ/ρU3E) dp/dx equal to 4.4×10-6. In the near-wall region of the boundary layer (y/δ<0.1) the turbulence intensity u′ scales roughly with the free-stream velocity UE until close to the location where K is a maximum whereas in the outer region u′ remains essentially frozen. Once the pressure gradient is relaxed, the turbulence level increases throughout the boundary
layer until K falls to zero when the near wall u′ levels show a significant decrease. The intermittency γ is the clearest indicator of a fundamental change in the turbulence
structure: once K exceeds 3×10-6, the value of γ in the immediate vicinity of the wall γs falls rapidly from unity, reaches zero at the location where K again falls below 3×10-6 and then rises back to unity. Although γ is practically zero throughout the boundary layer in the vicinity of γs=0, the turbulence level remains high. The explanation for what appears to be a contradiction is that the turbulent frequencies
are too low to induce turbulent mixing. The mean velocity profile changes shape abruptly where K exceeds 3×10-6. Values for the skin friction coefficient, based upon hot-film measurements, peak at the same location as K and fall to a minimum close to the location where K drops back to zero.
Received: 28 January 1998/Accepted: 8 April 1998 相似文献
3-Acetoxy-1-oxaphenalene4 (Ia) is conveniently prepared from naphthalene-1,8-carbalactone5 (IIa) by hydrolysis, condensation of the resulting hydroxy compound with chloroacetic acid and cyclisation of the resulting di-acid. Combined hydrolysis and reduction of (Ia) using alkaline potassium or sodium borohydride gives 2,3-dihydro-1-oxaphenalen-3-ol which may be converted into the 3-chloro-compound from which 1-oxaphenalene (Ib) is obtained by de-hydrochlorination.4相似文献
The use of high-pressure gas jets in the laser-drilling process has significant influence on the melt ejection mechanism. These jets are highly unstable and this directly relates to the gas pressure and the geometry of the hole being drilled. The evolution of gas-dynamic instabilities during the laser-drilling process was investigated numerically. A minimum length nozzle (MLN) with a 300 μm throat diameter was modelled at various gas pressures, with the gas jet impinging on a range of simulated holes with different aspect ratios. The simulations predict the formation of surface pressure fluctuations that have a broad spectrum due to both the turbulent nature of the jet and the blunt shock oscillation on the surface. The surface pressure variations and the blunt shock oscillation govern the gas dynamic conditions inside the hole, which strongly influence the melt ejection phenomena during the laser-drilling process. 相似文献
