Transfer chemical potentials

Transfer chemical potentials solvation metal ions, 2,298 Transferrins, 2, 772 6, 669... 

Solubilities in the water-1-octanol system (262) provide a link between solubilities and transfer chemical potentials on the one hand and distribution coefficients and possibilities of crossing membranes... 

Fig. 10. Transfer chemical potentials for tris(maltolato)gallium(III) and tris(maltolato)indium(III) to methanol-water mixtures at 298.2 K (data from Ref (236)).

Figure 1 Transfer chemical potentials for selected iron complexes from water into aqueous methanol (on the molar scale, at 298 K). Ligand abbreviations not appearing in the list at the end of this chapter are acac = acetylacetonate (2,4-pentanedionate) dmpp = l,2-dimethyl-3-hydroxy-4-pyridinonate, the anion from (24) malt = maltolate (2-methyl-3-hydroxy-4-pyranonate, the anion from (233)).

Solubilities, in water, ethanol, and ethanol-water mixtures, have been reported for [Fe(phen)3]-(0104)2, [Fe(phen)3]2[Fe(CN)6], and [Fe(phen)3][Fe(phen)(CN)4]. Solubilities of salts of several iron(II) iiimine complexes have been measured in a range of binary aqueous solvent mixtures in order to estimate transfer chemical potentials and thus obtain quantitative data on solvation and an overall picture of how solvation is affected by the nature of the ligand and the nature of the mixed solvent medium. Table 8 acts as an index of reports of such data published since 1986 earlier data may be tracked through the references cited below Table 8, and through the review of the overall pattern for iron(II) and iron(III) complexes (cf. Figure 1 in Section 5.4.1.7 above) published recently. ... 

Transfer chemical potentials for the low-spin amine-diimine complexes [Fe(tsba)2] " with tsba = (8 were estimated from the solubilities of their perchlorate salts, in methanol-water mixtures.Solubility and transfer chemical potential data are also available for [Fe(Me2bsb)3] " " in several nonaqueous solvents. One of the main purposes in determining transfer chemical potentials for these iron(II)-diimine complexes is to enable dissection of reactivity trends into initial state and transition state components for base hydrolysis (see next section) in binary aqueous solvent mixtures. Systems for which this has been achieved are indicated in Table 8. 

Numbers given in the body of this table indicate the references in which measured solubilities and derived transfer chemical potentials are reported an asterisk indicates that the transfer chemical potentials have been used in Initial state-transition state analyses of reactivity trends for base hydrolysis. tsb = (89) with X = H or Me. (75 ) = (75) with quinolyl in place of pyridyl. Bcage = (78) with X = F or OBu (also analogues with Ph, Ph in place of Me, Me and X = OBu", and with -CH2CH2CH2CH2- in place of Me, Me (i.e., cyclohexyl moieties) and X = F). 

The structure of [Fe(MeCOCOCHCOMe)3] has been determined/ of [Fe(acac)]3 redetermined at 20K (Fe—0=1.977 to 2.004A).Iron(III) forms mainly 1 1 and 1 3 complexes with acetylacetone and with benzoylacetone in DMF their reduction has been monitored electrochem-ically. " Solubilities, and derived transfer chemical potentials, of [Fe(acac)3] in various binary aqueous solvent mixtures give a measure of preferential solvation. Rate constants have been determined, at 283 K, for formation of 2,4-octanedione and 2,4-nonanedione complexes of iron(III). ... 

EXAFS studies on tris-maltolatoiron(III) in the solid state and in solution, and on [Fe(Ll)3] hydrate, pave the way for detailed investigation of the hydration of complexes of this type in aqueous media.Solubilities and transfer chemical potentials have been determined for tris-maltolatoiron(III) in methanol-water, and for tris-etiwlmaltolatoiron(III) in alcohol-water mixtures and in isobutanol, 1-hexanol, and 1-octanol. Solubility maxima in mixed solvents, indicating synergic solvation, is relevant to trans-membrane transport of complexes of this type. Solubilities of tris-ethylmaltolatoiron(III) and of [Fe(Ll)3] have been determined in aqueous salt solutions (alkali halides NH4 and NR4 bromides). ... 

The solvation of clathrochelate iron(II) cyclohexanedione-1,2-dihydrazonate in methanol-water mixtures was studied in research reported in Ref. 184. The comparison of transfer chemical potentials (Fig. 41) illustrates the greater preference of the larger and more hydrophobic [Fe(cxcage)]-+ cation for methanol in a series of cage complexes. However, these complexes appear to exhibit somewhat less hydrophobic behaviour than their nonmacrocyclic analogs. 

Cobalt(II,III) sepulchrates have been used in the chemical education [415] and considerable number of the chemical and physicochemical studies as efficient quencher of the phosphorescence [416] and electronic excited states [417, 418], as a reductant in kinetic studies of redox reactions [419, 420], as a model for study of magnetodynamic [421], solvent [422] and pressure [423] effects on the outer-sphere electron-transfer reactions. Transfer chemical potentials (from solubility measurements) [424], electrochemical reduction potentials [425] and ligand-field parameters [426] for cobalt sepulchrates have been calculated. Solvent effect on Co chemical shift of cobalt(III) ion encapsulated in the sepulchrate cavity [427]... 

Limiting rate constants for loss of pyrazine or of piperidine from their respective pentacyanoferrate(II) derivatives are affected to only a very small extent by the acetone content of binary aqueous mixtures.Probably here, as in the earlier case of the 4-cyanopyridine complex in aqueous alcohols, " this minor effect on rate constants conceals large but almost equal effects on the initial and transition states. This proved impossible to assess, due to the authors failure to find salts of appropriate solubility for the requisite measurements and transfer chemical potential derivations. It may be that the recently characterized transition metal(II) salts could lead to an answer. 

Figure 5.1 Initial state (is) and transition state (ts) transfer chemical potential variations for solvolysis of trans- Coipy)4,C in aqueous methanol. Kinetic data are from Ref. 209, solubility data from Ref. 210 (is) values were obtained by using 8 , x°(Cl") values interpolated from Ref. 202. Transfer chemical potentials for Rb" and for Ba " (also from Ref. 202) are shown for comparison. All values are on the molar scale, at 298.2 K.

In principle, the transfer chemical potentials recently published for [Fe(bipy)3f and [Fe(phen)3] for transfer from water into methanol-water mixtures should be valuable in the interpretation of solvent effects on reactivities of these cations, but unfortunately the authors derivations are unreliable. There are errors in calculating solubility products and transfer chemical potentials for the salts studied the transfer chemical potentials for the perchlorate anion are ignored (a serious error in methanol-rich mixtures) and there are transcription or printing errors in their published Table 3 for methanol contents of above 44.7%. Acceptable transfer chemical potentials for the [Fe(phen)3] cation, for these and other mixed aqueous solvent media, are available from van Meter and Neumann. ... 

There are marked divergences between transfer chemical potential trends according to the Wells and TATB assumptions, and the conclusions... 

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