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121.
122.
An algebraic method that includes Gibbs minimization for performing phase equilibrium calculations for any number of components or phases 总被引:1,自引:0,他引:1
Gustavo A. Iglesias-Silva Adrin Bonilla-Petriciolet Philip T. Eubank James C. Holste Kenneth R. Hall 《Fluid Phase Equilibria》2003,210(2):229-245
The most widely used technique for performing phase equilibria calculations is the K-value method (equality of chemical potentials). This paper proposes a more efficient algorithm to achieve the results that includes Gibbs minimization when we know the number of phases. Using the orthogonal derivatives, the tangent plane equation and mass balances, it is possible to reduce the Gibbs minimization procedure to the task of finding the solution of a system of non-linear equations. Such an operation is easier and faster than finding tangents or areas, and appears to converge as fast as the K-value method. Examples illustrate application of the new technique to two and three phases in equilibrium for binary and ternary mixtures. 相似文献
123.
John Philip Tarburton Cynthia S. Day Victor W. Day Iraj Tavaniepour Norman H. Cromwell 《Journal of heterocyclic chemistry》1986,23(2):433-441
Solid-state structures have been determined for cis- and trans-1-cyclohexyl-2-phenyl-3-(p-toluyl)aziridines using single-crystal X-ray diffraction techniques. The cis isomer crystallizes in the centrosymmetric monoclinic space group P21/c (No. 14), with a = 18.669(3)Å, b = 5.709(1)Å, c = 17.412(2)Å, β = 96.29(1)° and Z = 4; the trans isomer crystallizes in the noncentrosymmetric orthorhombic space group Pna21 (No. 33), with a = 17.089(2)Å, b = 18.729(3)Å, c = 5.749(1)Å and Z = 4. Full-matrix least-squares refinement of the structural parameters led to the following final agreement factors: R1 (unweighted, based on F) = 0.040 and R2 (weighted, based on F) = 0.054 for the 2592 independent reflections of the cis isomer having 2θMoK¯α <55° and I>3σ1, and R1 = 0.033 and R2 = 0.031 for the 1504 independent reflections of the trans isomer having 2θMoK¯α <55° and I>3σ1. The statistically significant differences that exist between the two isomers for two bond lengths and ten bond angles (p < 0.05) appear to be the direct result of the p-toluyl group orientation with respect to the cyclohexyl and phenyl substituents. In the cis isomer it is anti with respect to the N-cyclohexyl group and cis with respect to the phenyl group, whereas in the trans isomer it is syn with respect to the N-cyclohexyl and trans with respect to the phenyl group. Three-ring to carbonyl hyperconjugation is correlated with stereoelectronic interactions in the trans isomer. Bonding, determined by X-ray and nmr studies, is discussed for the three-membered aziridine ring proper; while bonding, determined by X-ray studies, is discussed for substituents of the aziridine ring. These aziridinyl ketone compounds are of importance as potential mammalian DNA alkylating anti-tumor agents in solid-state solid-state systems. To date only a trans isomer has demonstrated this biological activity in tumor-bearing rats. 相似文献
124.
Kirmaier C Bautista JA Laible PD Hanson DK Holten D 《The journal of physical chemistry. B》2005,109(50):24160-24172
Subpicosecond transient absorption studies are reported for a set of Rhodobacter (R.) capsulatus bacterial photosynthetic reaction centers (RCs) designed to probe the origins of the unidirectionality of charge separation via one of two electron transport chains in the native pigment-protein complex. All of the RCs have been engineered to contain a heterodimeric primary electron donor (D) consisting of a bacteriochlorophyll (BChl) and a bacteriopheophytin (BPh). The BPh component of the M heterodimer (Mhd) or L heterodimer (Lhd) is introduced by substituting a Leu for His M200 or His L173, respectively. Previous work on primary charge separation in heterodimer mutants has not included the Lhd RC from R. capsulatus, which we report for the first time. The Lhd and Mhd RCs are used as controls against which we assess RCs that combine the heterodimer mutations with a second mutation (His substituted for Leu at M212) that results in replacement of the native L-side BPh acceptor with a BChl (beta). The transient absorption spectra reveal clear evidence for charge separation to the normally inactive M-side BPh acceptor (H(M)) in Lhd-beta RCs to form D+H(M)- with a yield of approximately 6%. This state also forms in Mhd-beta RCs but with about one-quarter the yield. In both RCs, deactivation to the ground state is the predominant pathway of D decay, as it is in the Mhd and Lhd single mutants. Analysis of the results indicates an upper limit ofV2L/V2m < or = 4 for the contribution of the electronic coupling elements to the relative rates of electron transfer to the L versus M sides of the wild-type RC. In comparison to the L/M rate ratio (kL/kM) approximately 30 for wild-type RCs, our findings indicate that electronic factors contribute approximately 35% at most to directionality with the other 65% deriving from energetic considerations, which includes differences in free energies, reorganization energies, and contributions of one- and two-step mechanisms on the two sides of the RC. 相似文献
125.
Huang F Switek KA Zakharov LN Fronczek FR Slebodnick C Lam M Golen JA Bryant WS Mason PE Rheingold AL Ashraf-Khorassani M Gibson HW 《The Journal of organic chemistry》2005,70(8):3231-3241
Four new bis(m-phenylene)-32-crown-10-based cryptands with different third bridges were prepared. Their complexes with paraquat derivatives were studied by proton NMR spectroscopy, mass spectrometry, and X-ray analysis. It was found that these cryptands bind paraquat derivatives very strongly. Specifically, a diester cryptand with a pyridyl nitrogen atom located at a site occupied by either water or a PF(6) anion in analogous complexes exhibited the highest association constant K(a) = 5.0 x 10(6) M(-1) in acetone with paraquat, 9000 times greater than the crown ether system. X-ray structures of this and analogous complexes demonstrate that improved complexation with this host is a consequence of preorganization, adequate ring size for occupation by the guest, and the proper location of the pyridyl N-atom for binding to the beta-pyridinium hydrogens of the paraquat guests. This readily accessible cryptand is one of the most powerful hosts reported for paraquats. 相似文献
126.
Reppert PM Morgan FD Lesmes DP Jouniaux L 《Journal of colloid and interface science》2001,234(1):194-203
An experimental apparatus and data acquisition system was constructed to measure the streaming potential coupling coefficients as a function of frequency. The purpose of the experiments was to measure, for the first time, the real and imaginary portion of streaming potentials. In addition, the measured frequency range was extended beyond any previous measurements. Frequency-dependent streaming potential experiments were conducted on one glass capillary and two porous glass filters. The sample pore diameters ranged from 1 mm to 34 μm. Two frequency-dependent models (Packard and Pride) were compared to the data. Both Pride's and Packard's models have a good fit to the experimental data in the low- and intermediate-frequency regime. In the high-frequency regime, the data fit the theory after being corrected for capacitance effects of the experimental setup. Pride's generalized model appears to have the ability to more accurately estimate pore sizes in the porous medium samples. Packard's model has one unknown model parameter while Pride's model has four unknown model parameters, two of which can be independently determined experimentally. Pride's additional parameters may allow for a determination of permeability. Copyright 2001 Academic Press. 相似文献
127.
Alkyl, aromatic, benzylic and benzoyl halides have been successfully coupled in good yields using lithium wire suspended in tetrahydrofuran and ultrasound. 相似文献
128.
The title compounds may be made from bis(phenylthio) acetals and aldehydes by routes involving PhS migration. 相似文献
129.
We find all torsion-free, spherically symmetric, vacuum solutions to the theory of gravity recently proposed by Hehl, Ne'eman, Nitsch, and von der Heyde. There are three classes of solutions: (A) the Schwarzschild metrics with arbitrary mass,M, and arbitrary cosmological constant, ; (B) the Nariai-Bertotti metrics with arbitrary positive cosmological constant, ; and (C) the conformally flat metrics whose conformai factor is 2/
2 where is a function of only the time coordinate , and the radial coordinate, and satisfies the wave equation in these variables. Hence there is no Birkhoff theorem for this theory. In fact, solutions (C) include some asymptotically flat but nonstationary solutions. On the other hand, solutions (A) include a gravitational confinement potential, as was sought by Hehl et al., since when <0, the weak field limit of the Schwarzschild metric becomes a harmonic oscillator potential. We also discuss the relationship of this theory to the Eddington theory, the Lichnerowicz-Kilmister-Newman-Yang theory, the Nordström theory and the Einstein theory with a cosmological constant. 相似文献
130.
Abstract— The triplet state characteristics (spectrum, lifetime and quantum yield) for four dye sensi tisers [methylene blue (MB), erythrosin (ER), haematoporphyrin (HP) and riboflavin (RF)] were determined in methanol by laser flash photolysis and singlet oxygen yields (0.60 to 0.48) from time-resolved measurements of the 1270 nm near infrared emission. The reaction of singlet oxygen with four long chain unsaturated phenyl esters [oleate (18: 1), linoleate (18: 2), linolenate (18: 3) and arachidonate (20: 4)] was followed quantitatively using the singlet oxygen luminescence technique and also, after continuous420–700 nm irradiation, by HPLC and other analysis of the isomeric product monohydroperoxides. The overall quantum yield of photooxidation (∼10-2 ) was shown to be consistent with the observed singlet oxygen quenching constants(2–12 times 104 dm3 mol-1 s-1 ) for the four esters studied and the singlet oxygen lifetime in methanol (τ∼ 9 μs). The isomer product distribution was interpreted in terms of a dual singlet oxygen and radical mechanism, the radical contribution increasing with sensitiser in the order ER = MB < HP ≪ RF, but also showing some dependence on substrate unsaturation. Evidence is presented for singlet oxygen quenching by MB and RF ( kO = 1.6 and 6.0 times 107 dm3 mol-1 s-1 ) and for the accelerated photobleaching of the dye sensitisers in the presence of the unsaturated esters. 相似文献