Thiols water-soluble

HSCH2CH(0H)CH(0H)CH2SH. a useful water soluble reagent for preserving thiols in the reduced state, and for reducing disulphides quantitatively to dithiols. 

Potassium carbonate (anhydrous). Has a moderate efficiency and capacity, forming the dihydrate. Suitable for an initial drying of alcohols, bases, esters, ketones and nitriles by shaking with them, then filtering off. Also suitable for salting out water-soluble alcohols, amines and ketones. Unsuitable for acids, phenols, thiols and other acidic substances. 

The degradation of carbon tetrachloride to COj by a Pseudomonas sp. (Criddle et al. 1990), although a substantial part of the label was retained in nonvolatile water-soluble residues (Lewis and Crawford 1995). The nature of this was revealed by isolation of adducts with cysteine and N,N -dimethylethylenediamine in which intermediates formally equivalent to COCI2 and CSCI2 were trapped, presumably formed by reaction of the substrate with water and a thiol, respectively. Further consideration of these reactions is given in Chapter 7, Part 3. 

Fig. 13 Top Mechanism of NO release proposed for 3-furoxancarbonitrile derivatives. Middle Thiol induction of NO release from Fx 40. Bottom NO-releasing carbonitrile-Fxs and water-soluble-Fxs...

Dithiothreitol (DTT) and dithioerythritol (DTE) are the trans and cis isomers of the compound 2,3-dihydroxy-1,4-dithiolbutane. The reducing potential of these versatile reagents was first described by Cleland in 1964. Due to their low redox potential (—0.33 V) they are able to reduce virtually all accessible biological disulfides and maintain free thiols in solution despite the presence of oxygen. The compounds are fully water-soluble with very little of the offensive odor of the 2-mercaptoethanol they were meant to replace. Since Cleland s original report, literally thousands of references have cited the use of mainly DTT for the reduction of cystine and other forms of disulfides. 

A common choice of crosslinker for this type of reaction is sulfo-SMCC, which has been used extensively for antibody conjugation (Chapter 20, Section 1.1). A better option for dendrimer conjugation is to use a similar crosslinker design, but one that contains a hydrophilic PEG spacer arm to promote dendrimer hydrophilicity after modification. Derivatization of an amine-dendrimer with a NHS-PEG-maleimide can create an intermediate that is coated with water-soluble PEG spacers. This modification helps to mask any potential for nonspecific interactions that the PAMAM surface may have, while providing terminal thiol-reactive maleimides for coupling ligands (Figure 7.10). 

Figure 9.60 Many different thiol-containing linkers can be used to prepare water-soluble QDs. The monothiol compounds suffer from the deficiency of being easily oxidized or displaced off the surface, thus creating holes for potential nonspecific binding. The dithiol linkers are superior in this regard, as they form highly stable dative bonds with the semiconductor metal surface that do not get displaced. The PEG-based linkers are especially effective at creating a biocompatible surface for conjugation with biomolecules.

This gap in our knowledge is now closed, as the first paper on the uncatalyzed outer-sphere oxidation of an aliphatic thiol was recently published (12).This work selected thioglycolic acid (TGA, mercaptoacetic acid, HSCH2CO2H) as a representative thiol because of its high water solubility, low vapor pressure, and simple structure. The oxidant was [IrCle]2-, a well-characterized one-electron oxidant that frequently reacts through an outer-sphere mechanism. As is typical of such... 

GSTs contain a site that accommodates GSH ("GSH binding domain") [31], where the proton of the GSH s thiol group is abstracted, promoting the nucleophilic conjugation of the thiolate to electrophilic substrates. The resulting adducts become more water-soluble and are then eliminated by a phase II detoxification mechanism. 

A catalytic example of C-S bond breakage in benzothiophene has been reported by Bianchini [47], A catalytic desulfurisation was not yet achieved at the time as this is thermodynamically not feasible at such mild temperatures because of the relative stability of metal sulfides formed. Bianchini used a water-soluble catalyst in a two-phase system of heptane-methanol/water mixtures in which the product 2-ethylthiophenol is extracted into the basic aqueous layer containing NaOH. Figure 2.43 gives the reaction scheme and the catalyst. The 16-electron species Na(sulfos)RhH is suggested to be the catalyst. Note that a hydrodesulfurisation has not yet been achieved in this reaction because a thiol is the product. Under more forcing conditions the formation of H2S has been observed for various systems. 

It is the thiol grouping that acts as a nucleophile, attacking the epoxide function of the toxin (see Box 6.6). In this way, the toxin becomes irreversibly bound to glutathione, and the additional polar functionalities in the adduct mean that the product becomes water soluble. The glutathione-toxin adduct can thus be excreted from the body. 

MPA, a small thiol. Is a useful additive because it s a water-soluble reducing agent and does not have a strong stench. (Adapted from Tam et ah, 2001)... 

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