FE-FET

Figure 4. Isotopic mass-balance for measured 6 Fe values of ferric ( ) and ferrous ( ) Fe in solution as a function of Fe(II)/FeT ratios. Although the initial Fe isotope compositions of the fluids have 6 Fe values of 0%o (shown hy dotted mixing line), the lighter Fe isotopes are portioned into the ferrous species following attaimnent of isotopic equilihrium. The triangles (A) represent the calculated isotopic mass balance of the different solutions. Fractionations noted are measured values based on data for equimolar and higher Fe(II)/total Fe ratio experiments. (A) and (D) are for experiments with zero Cl at 22 and 0°C, respectively. (B) and (E) are experiments done with at 11 mM Cl at 22 and 0°C, respectively. (C) and (F) are experiments done with 111 mM Cl at 22 and 0°C, respectively. Modifled from Welch et al. (2003).

The situation is different for solvolysis reactions in most other solvents, where the intermolecular interactions between ions at an ion pair are stronger than the compensating interactions with solvent that develop when the ion pair separates to free ions. This favors the observation of racemization during solvolysis. There are numerous reports from studies on solvolysis in solvents with relatively low dielectric constant such as acetic acid, of polarimetric rate constants (fe , s ) for racemization of chiral substrates that greatly exceed the titrimetric rate constant (fet, s ) for formation of acid from the solvolysis reaction. ... 

Electrode reactions can be classified into two groups one in which an electron transfer takes place across the electrode interface, such as ferric-ferrous redox reaction (Fet, + e = Fe ) and the other in which an ion transfer takes place across the electrode interface, such as iron dissolution-deposition reaction (Fe M = FeVq). Since electrons are Fermi particles in contrast to ions that obey the Boltzmann statistics as described in Chap. 1, the reaction kinetics of the two groups differ in their electrode reactions. 

The transformation has been followed up by XRD, Mbssbauer spectroscopy, EXAFS and colorimetry. It can be monitored more conveniently, however, by the acid oxalate extraction method in which residual ferrihydrite is dissolved and the crystalline product left intact (Schwertmann Fischer, 1966). The extent of transformation at any time is given as the ratio FOo/Fet where Fe is the oxalate soluble iron (i. e. the unconverted ferrihydrite) and Fet is the total iron in the system. A plot of log (FCo/Fet) against time of aging at 100 °C is linear over 90-95 % of the reaction... 

All of our P450CAM molecular wires bind in the active-site channel, as established by the Ru-Fe heme distances (< 22.1 A) determined by fluorescence energy transfer (FET), crystallographic analyses, and competition experiments with the natural substrate (camphor). Imidazole-terminated... 

The phase relations in the ternary Fe-Cr-S system are influenced by the extended ternary monosulfide solid solution series of the binary endmembers Fet XS and Crj JCS (see Fig. 11). This series increases rapidly with increasing temperatures... 

The pH of minimum solubility of Fe(OH)2s or solution pH of zero net charge can be obtained by differentiating Equation 2.47 and setting the derivative of FeT with respect to OH" equal to zero. Therefore,... 

The time of flight (TOF) method has been described in Section 8.4.1. The FET mobility, FE, is obtained from the characteristic of a field effect transistor constructed with the conjugated polymer as the conduction channel see below. With source-drain voltages larger than the gate voltage the source-drain current, Jsd, saturates and is given by ... 

Iron-platinum alloy nanoparticles are very promising candidates for future data storage systems. They become available by simultaneous reduction of platinum acetylacetonate and the decomposition of Fe(CO)5 in oleic acid and oleyl amine.The composition of FexPti x can be varied between X = 0.48 and x = 0.7. The particles exhibit disordered fee structure. They are superparamagnetic at room temperature. Aimealing at 550-600 °C transforms the fee structure into a face-centered tetragonal (fet) one. These have been shown to be suited for storage devices owing to their room temperature coercivity. The exact transition temperature depends on the stoichiometry. 

The equilibrium constant for eqn. (100) varies with change in solvent composition and this variation is calculated from the acidity function. The effect of this variation in equilibrium constant on the measured value of fe, is used to calculate a Bronsted exponent. The rate coefficient for detritiation kT is related to fe, by a primary isotope effect (assuming mechanism (99) applies) and therefore a plot of log, 0 feT against H +... 

Trimethoxybenzene, like azulene, is particularly interesting because the equilibrium with the conjugate acid (in this case a benzenonium ion) can be observed in acidic solution and pK values for a series of benzenonium ions formed by protonation of hydroxy- and meth.oxy-benzenes have been measured [32]. The rates of detritiation in acidic solution for several of these derivatives have also been measured [27(c)]. The rate coefficient for detritiation (scheme (104)) is given by feT = fe,/(l + k i/k2) and the reverse rate obtained by combining this with the equilibrium constant for protonation of the aromatic molecule will be ferev = k l/(l + k, /k2). Hence the values of ftT and ferev are somewhat different from the rate coefficients kY and k 1 for protonation of the aromatic molecule and deprotonation of the benzenonium ion, respectively. For trimethoxybenzene the value k, /k2 - 16 has been measured [28], Experimental values of kT extrapolated to dilute solution from measurements in strong acid for several aromatic substrates are collected in Table 10 [27(c)]. The values of log 0 kT and log 0 ferev for these substrates are plotted in Fig. 9... 

When other metals (M) substitute for Fe in the structure of an Fe oxide the mole ratio of substitution is given by Mt/(Mt + Fet)(mol/mol), where Mt and Fet (t = total) are expressed in mol. Fe and other metals present at the surface of the iron oxide or in separate phases must be determined separately to correct the extent of substitution. Ferrihydrite as a separate phase can be selectively dissolved an with acid oxalate solution (see p. 50). This treatment also dissolves any separate Mn or Cr oxides. Alternatively, a short extraction (30 min, 25 °C) with 0.4 M HCl removes adsorbed surface species this method is useful if the solubility of the substituting ion in acid oxalate solution is not known or if the iron oxide under consideration (for example magnetite) is soluble in acid oxalate solution. The total Fet and Mt have then to be corrected for the oxalate soluble Fe and M. 

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