Thiosulfate formation constants with

Exciting developments have occurred in the coordination chemistry of the alkali metals during the last few years that have completely rejuvenated what appeared to be a largely predictable and worked-out area of chemistry. Conventional beliefs had reinforced the predominant impression of very weak coordinating ability, and had rationalized this in terms of the relatively large size and low charge of the cations M+. On this view, stability of coordination complexes should diminish in the sequence Li>Na>K>Rb> Cs, and this is frequently observed, though the reverse sequence is also known for the formation constants of, for example, the weak complexes with sulfate, peroxosulfate, thiosulfate and the hexacyanoferrates in aqueous solutions. 

Using the same general formula that we used for K, we can examine constants for the formation of complex ions and determine what woulcfbe the best substance to use as a film fixer in other words, what substance can remove a large number of silver ions from the unexposed portion of the film. We use the symbol Kf for the formation constant of a complex ion. We know that thiosulfate ions are combined with silver ions to form the Ag(S203) 23- complex ... 

X 10 eq. and [tryptamine] =4.8 x 10 M. If the k was not influenced, the shift of the equilibrium implies an increase m k. This is consistent with the primary salt effect. On the other hand, a cationic poly electrolyte, DE, was rather insensitive to A, as was the case with an anionic polyelectrolyte, polyacrylate, in the bromoacetate-thiosulfate reaction (see Figure 2). The complex formation of indole acetate with propylchloride-quaternized polyvinylpyridine [C3PVP], C4PVP and benzylchloride-quatemized polyvinylpyridine [BzPVP], which is a reaction between oppositely charged species, was hindered by potassium chloride, calcium chloride, and DE, as was observed for the urea conversion. The formation constant A was decreased from 98 M for C4PVP to about 20 M by addition of 3 x 10 eq. 1 of DE,... 

Two papers dealing with the trans-[Os(OH)204] oxidation of thiosulfate have appeared. The mechanism involves intermediate complex formation shown in equation (12) with a formation constant of 6.12 at... 

To determine the equilibrium constant of foe system, identical one-liter glass bulbs are filled with 3.20 g of HI and maintained at a certain temperature. Each bulb is periodically opened and analyzed for iodine formation by titration with sodium thiosulfate, Na O ... 

We can now make sensible guesses as to the order of rate constant for water replacement from coordination complexes of the metals tabulated. (With the formation of fused rings these relationships may no longer apply. Consider, for example, the slow reactions of metal ions with porphyrine derivatives (20) or with tetrasulfonated phthalocyanine, where the rate determining step in the incorporation of metal ion is the dissociation of the pyrrole N-H bond (164).) The reason for many earlier (mostly qualitative) observations on the behavior of complex ions can now be understood. The relative reaction rates of cations with the anion of thenoyltrifluoroacetone (113) and metal-aqua water exchange data from NMR studies (69) are much as expected. The rapid exchange of CN " with Hg(CN)4 2 or Zn(CN)4-2 or the very slow Hg(CN)+, Hg+2 isotopic exchange can be understood, when the dissociative rate constants are estimated. Reactions of the type M+a + L b = ML+(a "b) can be justifiably assumed rapid in the proposed mechanisms for the redox reactions of iron(III) with iodide (47) or thiosulfate (93) ions or when copper(II) reacts with cyanide ions (9). Finally relations between kinetic and thermodynamic parameters are shown by a variety of complex ions since the dissociation rate constant dominates the thermodynamic stability constant of the complex (127). A recently observed linear relation between the rate constant for dissociation of nickel complexes with a variety of pyridine bases and the acidity constant of the base arises from the constancy of the formation rate constant for these complexes (87). 

To give an idea of the possible magnitude of K, we can cite some extreme values it can acquire for example, from 10 120 (as in the gas-phase decomposition of N2 to atomic nitrogen) to 10+79 (as in the formation of an Ag complex with six thiosulfate ligands). In aqueous solutions the most common values for K are in the range 10-3° to 10+3° (e.g., solubility products, complex formation, dissociation constants, etc.). The magnitude of K signifies the extent of a reaction. 

Table II summarizes the sources and key properties of isolated HiPIPs, almost all of which have been isolated from photosynthetic organisms, and there has been extensive speculation on their involvement in respiratory electron transport chains (18, 21, 91-93, 95, 96, 102-105). Evidence in support of such a hypothesis has recently emerged from studies of a partially reconstructed reaction center (RC) complex from Rhodoferax fermentans (93, 95). The kinetics of photo-induced electron transfer from HiPIP to the reaction center suggested the formation of a HiPIP-RC complex with a dissociation constant of 2.5 fx,M. In vivo and in vitro studies by Schoepp et al. (94) similarly have demonstrated that the only high-redox-potential electron transfer component in the soluble fraction of Rhodocyclus gelatinosus TG-9 that could serve as the immediate electron transfer donor to the reaction-center-bound C3d ochrome was a HiPIP. In vitro experiments have shown HiPIP to be an electron donor to the Chromatium reaction center (106). Fukumori and Yamanaka (107) also reported that Chromatium vinosum HiPIP is an efficient electron acceptor for a thiosulfate-oxidizing enzyme isolated from that organism.

The mechanism of the oxidation of sulfide sulfur to sulfate is probably much more complex than a simple fixation of oxygen. Fromageot and Royer (51) have presented the hypothesis that the oxidation of hydrogen sulfide to sulfate involves formation of thiosulfate as intermediary. They base this hypothesis on the constant presence of thiosulfate in the urine of higher animals, and also on the ease with which hydrogen sulfide is oxidized to thiosulfate by inorganic catalysts in the presence of air (106). 

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