Thiols chemical structure

Amenates acylated at the exocydic nitrogen are stable as solid compounds but decompose in aqueous solutions releasing NO. This decomposition depends on the pH and most importantly on their chemical structure [147, 152]. The proposed mechanism of NO-release is shown in Scheme 6.24. It is related to that postulated for sydnonimines. The main difference is that here 5-substituted amenates 128 are able to react with water to form acyclic nitroso semicarbazides 129 directly without needing enzymatic cleavage, and these intermediates release NO by an oxidative or thiol mediated mechanism that is not fully understood [153]. 

In general, EC reactions are typically observed according to the following general rank order (by relative ease of oxidation) o,p-quinol and o,p-aminophenol > tertiary amine > m-quinol rv phenol rv arylamine > secondary amine thiol > thioether primary amines, aliphatic alcohols. (HDVs) each redox active metabolite are obtained from the response across adjacent EC-Array sensors. These data are a reflection of the kinetic and thermodynamic components of electron transfer reactions. Since chemical structure is a critical determinant of an analyte s redox behavior, the intrinsic generation of an HDV with EC-Array provides qualitative information for each species. 

Moutsopoulos et al. [165, 166] reported that anti-Ro (SSA) positive Greek rheumatoid arthritis patients experienced a significantly high frequency of side effects from D-penicillamine. Despite their dissimilar chemical structures, the thiol compounds, sodium aurothiomalate and D-penicillamine, have remarkably similar clinical effects, and this similarity extends to the incidence and type of adverse effects [138,167]. Several investigators have noted the association between prior gold nephropathy and D-penicillamine. Billingsley and Stevens reported the significant correlation of D-peni-cillamine-induced proteinuria to a previous history of... 

A wide variety of photoinitiators have been investigated for polymerization of different monomers, such as acrylates, epoxides, vinyl ethers, and thiol-ene monomers. From this point of view, the D-rc-D or A-rc-A chromophores are favored sensitizers if they are combined with a coinitiator [269, 563], The sensitizer excited by TPA can be either oxidized (route A) or reduced (route B) by the coinitiator, depending on the chemical structure of the coinitiator (Fig. 3.64). 

FIGURE 19.1 Chemical structures of nerve agents the nerve agents sarin (GB), soman (GD), and cyclosarin (GF) lose fluorine subsequent to binding to cholinesterase. The agents tabun (GA), VX, and Russian VX lose CN, and the thiol groups, respectively. 

Product stability and performance can be affected by exposure to several oxidative sources, including oxygen, free radicals, UV radiation, oxidative enzymes, catabolic oxidation, and chemical oxidation. Many antioxidants are also good UV absorbers due to their conjugated chemical structure. Typical antioxidants found in cosmetic products are flavonoids, polyphenols, carotenoids, thiols, tocopherol (vitamin E) and ascorbic acid (vitamin C) [71,72], According to Black [73], a combination of antioxidants from different classes is more effective than a single antioxidant due to an antioxidant cascade mechanism. 

Oxidation mechanisms for drug substances depend on the chemical structure of the drug and the presence of reactive oxygen species or other oxidants. Catechols such as methyl-dopa180 and epinephrine181 are readily oxidized to quinones, as shown in Scheme 45. 5-Aminosalicylic acid undergoes oxidation and forms quinoneimine,182 which is further degraded to polymeric compounds (Scheme 46).183 Ethanolamines such as procaterol are oxidized to formyl compounds (Scheme 47),184 whereas thiols such as 6-mercaptopurine,185... 

Figure 2 Chemical structures of the commercially available phosphoramidite and solid support used for the preparation of thiol-oligonucleotides.

After the observation that PTU Inhibited the peripheral delodinatlon of T4 (68,74), attempts to relate delodinase Inhibitory activity to structural parameters were undertaken (74). These studies emphasized the need for tautomerizatlon to a thiol form and for the presence of a polar hydrogen on the nitrogen adjacent to the sulfur-bearing carbon. A study of the relation of chemical structure to 5 -D-l Inhibitory activity related to similar studies of structural requirements for TPO Inhibition could prove fruitful In the design of Improved antithyroid drugs. 

Fig. 20. Oligosaccharide-mediated nuclear transport of glyco-QDs. (A) Chemical structures of neoglycoconjugates. (B) Synthesis of glyco-QDs by thiol exchange reaction. (C) Confocal fluorescence images (top panels) and differential interference contact (lower panels) of digitonin-permeabilized HeLa cells incubated with glyco-QDs. (D) Digitalized fluorescence intensity of different QDs in the nucleus. Adapted from Ref 204. (See Color Plate 42.)...

Ligands A, B, and C have similar chemical structures. They all carry an end thiol functional group (for attaching onto a gold surface of a QCM device), an alkane chain (to form the well-packed SAM ), and a triethylene glycol linker (to prevent nonspecific adsorption ). The resulting 1 1 mixed SAMs... 

Figure 12 chemical structure of (a) amine and (b) thiol reactive PEG-PLA copolymers. From Tessmar, J. Mikos, A. Gbpferich,... 

In order to covalently link a dye to either a nucleic acid or polypeptide it is necessary to derivatize the fluorophore with a functional group that is reactive towards specific functional groups that occur naturally in these biomolecules or that have been introduced in their synthesis. As we have seen, despite their different chemical structures both nucleic acids and proteins are almost always conjugated to fluorophore derivatives containing functional groups that react primarily with either amines or thiols. We shall now briefly describe the chemical properties of these functional groups. 

ToF-SIMS is routinely applied to the characterization of competitive thiol adsorption and mixed self-assembled layers [73-75]. Mixed monolayers of alkyl sulfides (and dialkyl disulfides) were first investigated with SIMS by Offord et al. in a detailed multitechnique study [76]. The authors concluded that the adsorption is thermodynamically driven for sulfides (longer chains preferred) and kinetically driven for disulfides (no preference). In parallel, the usefulness of ToF-SIMS to determine the chemical structure and composition of mixed layers of alkanethiols was demonstrated [77]. 

The efficiency of the flow-through reducing electrode is limited by a number of factors, including diffusion coefficient, eluent pH, applied potential and very importantly the chemical structure of the disulfide. Figure 5.5 shows that the sensitivity towards GSSG is less than ca 2% that of GSH. As only amperometric electrodes were used it should be expected that <5% of the disulfide might be reduced at the first electrode and then <5% of the thiol(s) produced would be detected at the second. Since two thiol molecules are formed from one disulfide it is to be expected that the detector sensitivity to disulfides would be <10% that of... 

Introductory chapters give information on basic electrochemistry and HPLC-ED, and on the specialised area of HPLC-ED of thiols. The major portion of the book is devoted to summary details of over 400 published HPLC-ED methods that are discussed in a standard format (column, eluent, internal standard, ED conditions, extraction procedure, limit of quantitation, etc.). These data are not always available via published abstracts and, wherever possible, sufficient information is given for the reader to decide whether a particular approach is worth pursuing. Chemical structures are given for most analytes and internal standards to ensure unambiguous identification and to illustrate possible electroactive moieties. Problems and pitfalls, and alternative techniques when appropriate, are emphasised throughout. Literature coverage is comprehensive up to the end of 2003. 

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