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Soret equilibrium

This reaction occurs thermally in toluene at 30°C with an equilibrium constant (K) equal to 1.5 (13). Both bis(phosphine) and (carbonyl)phosphine Soret bands are present in the active catalyst solutions (see Decarbonylation Procedure), together with the unassigned, and likely critical, band at 420 nm. This could be due to some species giving rise to, or resulting from, a RuII + RCO reaction this is equivalent, of course, to a (Ru H-COR) acyl or a RuIII(C0)R (carbonyl)alkyl species, and the final elimination reaction after loss of CO could be written as ... [Pg.248]

The spectrum in the Soret region, indicative of the c-type center of the enzyme, immediately following the reduction is not identical to that obtained when the enzyme is fully reduced under steady-state/equilibrium conditions. This suggests that the reduced c-type cytochrome center formed under the conditions of the pulse radiolysis experiment retained the His/His coordination. [Pg.179]

Since compound II has a Soret peak at 420 nm and the oxycomplex 416 nm, the equilibrated solution of compound II, H2O2, and compound III should exhibit an intermediate absorption peak. The existence of such an equilibrium has been established with HRP (22) and was also observed with lignin peroxidase (Cai, D., and Tien, M., unpublished results 23). Wariishi and Gold (25) recently proposed the existence of a new enzyme intermediate when compound in is formed in the presence of H2O2. They referred to this intermediate as compound III and suggested it to be a complex between compound III and H2O2. The existence of such an intermediate was based primarily on the Soret spectral properties where a 419 nm maximum was observed. In contrast, we see no evidence for existence of such a complex. The observed 419 nm absorbance maximun can be best explained by the existence of both compounds II and III in solution. [Pg.182]

The interaction of the tetracationic [M(4-TRPyP)]" species with calf thymus DNA was studied by UV-Vis and luminescence spectroscopy (168, 169, 240). Dramatic changes were observed in the absorption and emission spectra, as shown in Fig. 25, indicating that the interaction occurs in two steps. When the relative concentration of DNA is low, the Soret band decreases steeply while the luminescence increases a bit, consistent with the predominance of the electrostatic interaction mode. Nevertheless, as the relative concentration of DNA increases, the Soret band shifts to the red and there is a large enhancement of fluorescence, consistent with an intercalation mode. The equilibrium constants for both processes was determined as ti = 1.5 x 10 and7t2 = 2.5 x Zn(4-TRPyP) also in-... [Pg.409]

The apparent discrepancy between the RFQ and stopped-flow experiments was recently ascribed to differences in pH between the two studies. The pH influences the pre-equilibrium concentrations between Cpd I (Soret maximum at 367 nm) and the Y 96 radical intermediate (Soret maximum at 406 nm) ... [Pg.6571]

Vogelsang, R., Hoheisel, C., Paolini, O.V., and Ciccitti, G. Soret coefficient of isotropic Lennard-Jones mixtures and Ar-Kr system as determined by equilibrium molecural dynamics simulations. Phys. Rev. A, 1987, 36, No. 8, p. 3964-3974. [Pg.140]

Perronace, A., Ciccotti, G., Leroy, F., Fuchs A.H.,and Rousseau, B. Soret coefficient for liquid argon-krypton mixtures via equilibrium and nonequilibrium molecular dynamics A comparison with experiments. Phys. Rev. E, 2002, 66, p. 031201 1-15. [Pg.140]

The rapid temperature change of the electrode perturbs the equilibrium at the electrode-solution interface and causes a change in the potential of the electrode measured with respect to a reference electrode. The change in the open-circuit potential, A t, and its relaxation with time are used to obtain kinetic information about the electrode reaction. A number of different phenomena come into play to cause the potential shift with temperature (e.g., temperature dependence of the double-layer capacitance and the Soret potential arising from the temperature gradient between the electrode and the bulk electrolyte), but the response can be treated by a general master equation (40) ... [Pg.327]

Denbigh 2 Drickamer and collaborators/ Wirtz, Wirtz and Hiby/ and Prigogine and co-workers have written numerous papers containing molecular interpretations of the heat of transport and the related Soret coefficient in liquids. These have proceeded on the basis of special assumptions concerning the molecular structure of the liquid and the mechanism of the diffusion process, and have assumed the validity of the equilibrium statisticaL mechanical distribution in the nonequilibrium case. In the present paper we remove the special assumptions and show from general statistical mechanics that the heat of transport consists not only of an equilibrium term but also a term which arises from the nonequilibrium perturbation to the distribution function. In the special case of a regular solution, the expression for the equilibrium... [Pg.1]

In general a substrate shifts the equilibrium to the high spin form of cytochrome P450 which can be easily followed by the spectral blue shift of the Soret band from 420 to 390 nm . This explains why the spectral dissociation constant, K, calculated for this conversion agrees with the K i of the monooxygenase reaction . [Pg.82]

CD can be used to monitor the phenomenon of heme isomerism in heme proteins. " The isomerism, discovered by LaMar and co-workers, results from the presence of two forms of myoglobin which differ by 180° in the heme orientation about the a, y-methine carbon axis. The two isomers are present in a 9 1 ratio at equilibrium in carbonmonoxymyo-globin (MbCO) but are in a 1 1 ratio in a sample freshly reconstituted from apomyoglobin and heme. Freshly reconstituted MbCO has a Soret CD band with only about half the amplitude of the native form, " suggesting that the minor isomer (at equilibrium) has only a weak Soret CD spectrum. The major form has a strong positive Soret CD band, whereas the minor form has a weakly negative Soret CD band. These results and the CD of the heme undecapeptide from cytochrome indicate that the origin of the Soret CD band must be more complex than proposed by Hsu and Woody, ... [Pg.58]

Figures 14 and 15 show the spectra acquired with each excitation line. As was explained in the previous chapter (see [18] in this volume), under Soret band excitation (i.e., 416 nm), the totally symmetric lines (1/2, v, and 1 4) are strongly enhanced, whereas excitation at 532 nm (Q band) provides strong enhancement of nontotally symmetric modes (r,o, vn, and 1, 9). In Figs. 14 and 15 the spectrum of the equilibrium deoxy species is presented along with that of the 7 nsec photoproduct, and it is immediately obvious that all of the features associated with the heme macrocycle... Figures 14 and 15 show the spectra acquired with each excitation line. As was explained in the previous chapter (see [18] in this volume), under Soret band excitation (i.e., 416 nm), the totally symmetric lines (1/2, v, and 1 4) are strongly enhanced, whereas excitation at 532 nm (Q band) provides strong enhancement of nontotally symmetric modes (r,o, vn, and 1, 9). In Figs. 14 and 15 the spectrum of the equilibrium deoxy species is presented along with that of the 7 nsec photoproduct, and it is immediately obvious that all of the features associated with the heme macrocycle...
Balaban et al. suggested that there was preferential tetramer 35 formation from meso-2-aminopyrimidinyl zinc porphyrin in dry toluene at millimolar concentrations. The Soret band shows temperature-dependent equilibrium between the monomer and its associated species. The associated enthalpy... [Pg.72]

Expressions (4.514), (4.515) are known as phenomenological equations of linear irreversible or non-equilibrium thermodynamics [1-5, 120, 130, 185-187], in this case for diffusion and heat fluxes, which represent the linearity postulate of this theory flows (ja, q) are proportional to driving forces (yp,T g) (irreversible thermodynamics studied also other phenomena, like chemical reactions, see, e.g. below (4.489)). Terms with phenomenological coefficients Lgp, Lgq, Lqg, Lqq, correspond to the transport phenomena of diffusion, Soret effect or thermodiffusion, Dtifour effect, heat conduction respectively, discussed more thoroughly below. [Pg.259]

We now consider the phenomena of thermal diffusion, Soret effect and Dufour effect in a specific system. We consider an isotropic system consisting of two components 1 and 2. The concentration and temperature are non-uniform in the system. The pressure is supposed to be different at all points in the system so that mechanical equilibrium is rapidly established. There are no viscous forces and we shall neglect the viscous phenomena. Furthermore we assume that no chemical reactions are occurring. Since the system is non-uniform, local quantities have to be considered. [Pg.84]


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See also in sourсe #XX -- [ Pg.7 ]




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