Thiosulfate utilization

It seems worth mentioning that sulfur disproportionation of elemental sulfur is performed only by the thiosulfate-utilizing species of Chlorobiaceae (see Oil. In the absence of CO and under strictly anaerobic conditions in the light, these organisms form sulfide and thiosulfate simultaneously as long as sulfide is flushed out with an inert gas. The stoichiometry of this reaction is ... 

In Chlorobium limicola . thiosulfatophilum cytochrome c-SSl serves as electron acceptor of thiosulfate oxidation, before the electrons flow to oxidized bacteriochlorophyll via a soluble small cytochrome c-SSS and a membrane-bound cytochrome (2). The absence of cytochrome c-SSl in the non-thiosulfate-utilizing Chlorobiaceae might be one explanation why these organisms cannot use thiosulfate (4). 

Many municipal water sources are chlorinated and contain sufficiently high levels of chlorine so as to be toxic to aquatic life. Chlorine can be removed by passing the water through activated charcoal filters or through the use of sodium thiosulfate metered into the incoming water. Municipal water is usually not used in aquaculture operations that utilize large quantities of water, either continuously or periodically, because of the initial high cost of the water and the cost of pretreatment to remove chlorine. 

Nitrogen nucleophiles used to diplace the 3 -acetoxy group include substituted pyridines, quinolines, pyrimidines, triazoles, pyrazoles, azide, and even aniline and methylaniline if the pH is controlled at 7.5. Sulfur nucleophiles include aLkylthiols, thiosulfate, thio and dithio acids, carbamates and carbonates, thioureas, thioamides, and most importandy, from a biological viewpoint, heterocycHc thiols. The yields of the displacement reactions vary widely. Two general approaches for improving 3 -acetoxy displacement have been reported. One approach involves initial, or in situ conversion of the acetoxy moiety to a more facile leaving group. The other approach utilizes Lewis or Brmnsted acid activation (87). 

This is typically accompHshed by cooling the titration solution with ice, determining the blank, and titrating rapidly. Another method utilizes deterrnination of the total peroxide and peracid content by use of a ceric sulfate titration to measure hydrogen peroxide followed by a iodide/thiosulfate titration to measure total active oxygen (60). 

A method to circumvent the problem of chalcogen excess in the solid is to employ low oxidation state precursors in solution, so that the above collateral reactions will not be in favor thermodynamically. Complexation strategies have been used for this purpose [1, 2]. The most established procedure utilizes thiosulfate or selenosulfate ions in aqueous alkaline solutions, as sulfur and selenium precursors, respectively (there is no analogue telluro-complex). The mechanism of deposition in such solutions has been demonstrated primarily from the viewpoint of chemical rather than electrochemical processes (see Sect. 3.3.1). Facts about the (electro)chemistry of thiosulfate will be addressed in following sections for sulfide compounds (mainly CdS). Well documented is the specific redox and solution chemistry involved in the formulation of selenosulfate plating baths and related deposition results [11, 12]. It is convenient to consider some elements of this chemistry in the present section. 

Other substrates which can be utilized as reducing agents by various photosynthetic bacteria are hydrogen, isopropanol, thiosulfate, and selenium/ ... 

The amount of hypochlorite ion present in bleach can be determined by an oxidation-reduction titration. In this experiment, an iodine-thiosulfate titration will be utilized. The iodide ion is oxidized to form iodine, I2. This iodine is then titrated with a solution of sodium thiosulfate of known concentration. Three steps are involved ... 

HCN is a systemic poison toxicity is due to inhibition of cytochrome oxidase, which prevents cellular utilization of oxygen. Inhibition of the terminal step of electron transport in cells of the brain results in loss of consciousness, respiratory arrest, and ultimately, death. Stimulation of the chemoreceptors of the carotid and aortic bodies produces a brief period of hyperpnea cardiac irregularities may also occur. The biochemical mechanisms of cyanide action are the same for all mammalian species. HCN is metabolized by the enzyme rhodanese which catalyzes the transfer of sulfur from thiosulfate to cyanide to yield the relatively nontoxic thiocyanate. 

Sodium thiosulfate is a common reducing agent. It reduces iodine to iodide anion forming sodium tetrathionate. This reaction is utilized in the so-called iodometric titration ... 

A reaction that is ordinarily of minor consequence in the animal body but which may be enhanced by a deficiency of sulfite oxidase is the reductive coupling of two molecules of sulfite to form thiosulfate (Eq. 24-45, step e). Several organic hydrodisulfide derivatives such as thiocysteine, thioglutathione, and thiotaurine occur in animals in small amounts. Another biosynthetic pathway, outlined in Eq. 24-47 converts sulfite and PEP into coenzyme M (Fig. 15-22)475/475a This cofactor is needed not only for methane formation (Fig. 15-2) but also for utilization of alkenes by soil bacteria.4751 ... 

SULFUR (In Biological Systems). Sulfur, in some form, is required by all living organisms. It is utilized in various oxidation stales, including sulfide, elemental sulfur, sulfite, sulfate, and thiosulfate by lower forms and in organic combinations by all. The more important sulfur-containing organic compounds include the amino acids (cysteine, cystine, and methionine, which are components of proteins) the vitamins thiamine and... 

While sulfide is toxic to cytochrome (c) oxidase the most important enzyme of the respiratoiy chain, at concentrations in the tens of pM, thiosulfate is not Thus, the animal has produced a soluble and excretable detoxification product and protected animal respiration. This thiosulfate still contains large amounts of energy and can serve as a substrate for bacterial chemoautotrophic metabolism. The bacterial endosymbionts can utilize the thiosulfate along with sulfide to fix CO2 (5Q) and supply the host s nutritional needs. 

Anoxypnotobacteria utilize mainly sulfide, thiosulfate or elemental sulfur as photosynthetic electron donors. The ability to use sulfite or tetrathionate is restricted to only a few species (4.23). 

If phototrophic bacteria can utilize externally offered elemental sulfur as sole electron source, they will oxidize it directly to sulfate without the formation of any other sulfur intermediate (27.291. If only thiosulfate is available, Anoxyphotobacteria have two possibilities to metabolize it ... 

For Chromatium vinosum it has been reported that the utilization of thiosulfate is influenced by the pH of the medium. At pH 73 thiosulfate is cleaved into elemental sulfur and sulfite, while at pH 6.25 it is oxidized to tetrathionate which cannot be further metabolized (30). 

In agreement with the statements of Trueper (1) one can say that principally different dissimilatory sulfur metabolic pathways exist in Anoxyphotobacteria for the oxidation of sulfite to sulfate (via APS or directly), the utilization of thiosulfate (splitting or formation of tetrathionate), and the oxidation of sulfide or elemental sulfur (by a "reverse" siroheme sulfite reductase or other mechanisms). 

The configurations of the cis and trans forms of dinitro-bis(ethylenediamine)cobalt(III) ion were established by Werner,4 who resolved the cis form into its optical antipodes. The cis and trans isomers may also be distinguished chemically by utilization of the fact that a warm aqueous 3 % solution of the cis form yields precipitates when treated with concentrated solutions of potassium chromate, ammonium oxalate, or sodium thiosulfate a warm 10% solution of the trans form gives no precipitate with any of these reagents.3... 

The cyanide antidote kit contains amyl nitrate, sodium nitrate, and sodium thiosulfate. Nitrates convert hemoglobin to methemoglobin, which in turn competes for cyanide with the mitochondrial oxidase complex. Amyl nitrate pearls, administered by inhalation, can be utilized as a first aid measure when intravenous (IV) access is impossible or will be delayed. If IV access is available, IV sodium nitrate is preferred, followed by sodium thiosulfate. Sodium thiosulfate reacts with cyanide to form nontoxic thiocyanate, which is then excreted into the urine. 

After the initial therapy of methemoglobin inducers, the cyanide has to be converted to thiocyanate which is eliminated in urine. This enzymatic detoxification of cyanide is facilitated by a sulfur donor like sodium thiosulfate. The mechanism of this reaction was discussed earlier under elimination of cyanide. High tissue oxygen markedly potentiates the effects of this reaction. In cases where methemoglobin formation is not desirable, sodium thiosulfate together with oxygen alone is sufficient. The utility of... 

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