Reactive Sulfur Species:  Hydrolysis of Hypothiocyanite To Give Thiocarbamate-<i>S</i>-oxide

Wang, Xiaoguang; Lemma, Kelemu; Ashby, Michael T.

doi:10.1021/ja0770532

Cited by 19 publications

(23 citation statements)

References 20 publications

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“…The final absorbance is considerably below the initial value, consistent with the sum of reactions 10 and 11. Trace B in Figure 4 shows that there is no observable absorbance change when the reaction is performed with a twofold excess of thiosulfate; this can be understood if S 2 O 3 and Tropaeolin O as the indicator (as suggested by Nagy et al) 32 showed quite small absorbance changes at 550 nm, which suggests that the hydrolysis of ClS 2 O 3 − is base-catalyzed. On the basis of the assumption that the hydrolysis of ClS 2 O 3 − at pH 4.1 obeys first-order kinetics, the integrated rate law can be derived, which leads to eq 14 as an expression of the time dependence of the absorbance.…”

Section: ■ Results and Discussionmentioning

confidence: 78%

Oxidations at Sulfur Centers by Aqueous Hypochlorous Acid and Hypochlorite: Cl⁺ Versus O Atom Transfer

Xie

Stanbury

2017

Inorg. Chem.

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Sulfur-containing compounds are known to be susceptible to oxidation by aqueous HOCl, but the factors affecting the rates of these reactions are not well-established. Here we report on the kinetics of oxidation of thiosulfate, thiourea, thioglycolate, (methylthio)acetate, tetrathionate, dithiodiglycolate, and dithiodipropionate at 25 °C and 0.4 M ionic strength. These reactions obey the general rate law -d[OCl]/dt = (k[OCl] + k[HOCl])[substrate] with some exceptions: tetrathionate and the two disulfides undergo rate-limiting hydrolysis at high pH, and dithiodiglycolate has an additional term in the rate law that is second order in [substrate]. The reactions of HOCl are believed to have a Cl transfer mechanism, and in the case of thiosulfate the rate of hydrolysis of the ClSO intermediate was determined. In the case of thiourea evidence was obtained for thiourea monoxide as a long-lived product. It is shown that sulfite and species with terminal sulfur atoms have k values in the vicinity of 1 × 10 M s, while SCN and thioethers react somewhat more slowly; tetrathionate, trithionate, and disulfides react much more slowly. Comparison of the rate constants with those for oxidation of these sulfur substrates by HO and [Pt(CN)Cl] shows that HOCl reacts a few orders of magnitude more rapidly than [Pt(CN)Cl] and ∼9 orders of magnitude more rapidly than HO. Many of the k values are leveled by the high electrophilicity of HOCl. It is proposed that the k values correspond to oxygen-atom transfer mechanisms, as supported by LFERS (linear free energy relationships) relating these rate constants to those for reactions of HO and [Pt(CN)Cl].

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Section: ■ Results and Discussionmentioning

confidence: 78%

Oxidations at Sulfur Centers by Aqueous Hypochlorous Acid and Hypochlorite: Cl⁺ Versus O Atom Transfer

Xie

Stanbury

2017

Inorg. Chem.

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“…Similarly, we have discovered a corresponding less-reactive derivative of OSCN -, thiocarbamate-S-oxide [H 2 NC(=O)-S-O -] (Nagy et al, 2007c). Thiocarbamate-S-oxide, which is formed by the hydrolysis of OSCN -, is one of the chemical species formed during the redox cascade that results in the decomposition of OSCN - (Nagy et al, 2007c). Recently, we have learned that H 2 NC(=O)-S-O -reacts with thiols via a mechanism that is analogous to the one that is observed for OSCN -, albeit with slower kinetics (unpublished observations).…”

Section: The Antimicrobial Depletion Modelmentioning

confidence: 97%

“…Thus, complementing HOCl is taurine chloroamine (TauCl), a less reactive (Carr et al, 2001) and more selective (Peskin and Winterbourn, 2006) electrophilic chlorinating agent that may play a role in host defense in the oral cavity (Woldring, 1955;Mainnemare et al, 2004). Similarly, we have discovered a corresponding less-reactive derivative of OSCN -, thiocarbamate-S-oxide [H 2 NC(=O)-S-O -] (Nagy et al, 2007c). Thiocarbamate-S-oxide, which is formed by the hydrolysis of OSCN -, is one of the chemical species formed during the redox cascade that results in the decomposition of OSCN - (Nagy et al, 2007c).…”

Section: The Antimicrobial Depletion Modelmentioning

confidence: 99%

Inorganic Chemistry of Defensive Peroxidases in the Human Oral Cavity

Ashby

2008

J Dent Res

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The innate host response system is comprised of various mechanisms for orchestrating host response to microbial infection of the oral cavity. The heterogeneity of the oral cavity and the associated microenvironments that are produced give rise to different chemistries that affect the innate defense system. One focus of this review is on how these spatial differences influence the two major defensive peroxidases of the oral cavity, salivary peroxidase (SPO) and myeloperoxidase (MPO). With hydrogen peroxide (H2O2) as an oxidant, the defensive peroxidases use inorganic ions to produce antimicrobials that are generally more effective than H2O2 itself. The concentrations of the inorganic substrates are different in saliva vs. gingival crevicular fluid (GCF). Thus, in the supragingival regime, SPO and MPO work in unison for the exclusive production of hypothiocyanite (OSCN−, a reactive inorganic species), which constantly bathes nascent plaques. In contrast, MPO is introduced to the GCF during inflammatory response, and in that environment it is capable of producing hypochlorite (OCl−), a chemically more powerful oxidant that is implicated in host tissue damage. A second focus of this review is on inter-person variation that may contribute to different peroxidase function. Many of these differences are attributed to dietary or smoking practices that alter the concentrations of relevant inorganic species in the oral cavity ( e.g.: fluoride, F−; cyanide, CN−; cyanate, OCN−; thiocyanate, SCN−; and nitrate, NO3−). Because of the complexity of the host and microflora biology and the associated chemistry, it is difficult to establish the significance of the human peroxidase systems during the pathogenesis of oral diseases. The problem is particularly complex with respect to the gingival sulcus and periodontal pockets (where the very different defensive stratagems of GCF and saliva co-mingle). Despite this complexity, intriguing in vitro and in vivo studies are reviewed here that reveal the interplay between peroxidase function and associated inorganic chemistry.

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“…It is therefore rather amazing—and in many ways very fortunate—that the field of inorganic RSS over the years has developed its own dynamic, fuelled by three parallel developments: (a) the stream of ten prominent publications on inorganic RSS by Michael Ashby and his colleagues between 2004 and 2010, all with a title commencing with “Reactive Sulfur Species” and focussed on inorganic RSS [46,72,73,74,75,76,77,78,79,80,81], (b) The eruption of H 2 S research, accompanied by the suspicion that H 2 S is probably not really the signalling molecule one had previously thought, but that there is a case of mistaken identity, involving an entire series of inorganic polysulfides (H 2 S x ), which clearly belong to the realm of inorganic RSS, (c) the issue of the lost electron, i.e., the rather curious situation that many interactions involving thiols and radicals, for instance in the field of S-nitrosothiols, do not add up when it comes to electrons, hence questioning if RSS are really predominantly electrophilic compounds, such as sulfenic acids, or rather radical species. We will now consider the inorganic side of sulfide species in more detail.…”

Section: What Are Rss?mentioning

confidence: 99%

The Reactive Sulfur Species Concept: 15 Years On

et al. 2017

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Fifteen years ago, in 2001, the concept of “Reactive Sulfur Species” or RSS was advocated as a working hypothesis. Since then various organic as well as inorganic RSS have attracted considerable interest and stimulated many new and often unexpected avenues in research and product development. During this time, it has become apparent that molecules with sulfur-containing functional groups are not just the passive “victims” of oxidative stress or simple conveyors of signals in cells, but can also be stressors in their own right, with pivotal roles in cellular function and homeostasis. Many “exotic” sulfur-based compounds, often of natural origin, have entered the fray in the context of nutrition, ageing, chemoprevention and therapy. In parallel, the field of inorganic RSS has come to the forefront of research, with short-lived yet metabolically important intermediates, such as various sulfur-nitrogen species and polysulfides (Sx2−), playing important roles. Between 2003 and 2005 several breath-taking discoveries emerged characterising unusual sulfur redox states in biology, and since then the truly unique role of sulfur-dependent redox systems has become apparent. Following these discoveries, over the last decade a “hunt” and, more recently, mining for such modifications has begun—and still continues—often in conjunction with new, innovative and complex labelling and analytical methods to capture the (entire) sulfur “redoxome”. A key distinction for RSS is that, unlike oxygen or nitrogen, sulfur not only forms a plethora of specific reactive species, but sulfur also targets itself, as sulfur containing molecules, i.e., peptides, proteins and enzymes, preferentially react with RSS. Not surprisingly, today this sulfur-centred redox signalling and control inside the living cell is a burning issue, which has moved on from the predominantly thiol/disulfide biochemistry of the past to a complex labyrinth of interacting signalling and control pathways which involve various sulfur oxidation states, sulfur species and reactions. RSS are omnipresent and, in some instances, are even considered as the true bearers of redox control, perhaps being more important than the Reactive Oxygen Species (ROS) or Reactive Nitrogen Species (RNS) which for decades have dominated the redox field. In other(s) words, in 2017, sulfur redox is “on the rise”, and the idea of RSS resonates throughout the Life Sciences. Still, the RSS story isn’t over yet. Many RSS are at the heart of “mistaken identities” which urgently require clarification and may even provide the foundations for further scientific revolutions in the years to come. In light of these developments, it is therefore the perfect time to revisit the original hypotheses, to select highlights in the field and to question and eventually update our concept of “Reactive Sulfur Species”.

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Reactive Sulfur Species: Hydrolysis of Hypothiocyanite To Give Thiocarbamate-S-oxide

Cited by 19 publications

References 20 publications

Oxidations at Sulfur Centers by Aqueous Hypochlorous Acid and Hypochlorite: Cl⁺ Versus O Atom Transfer

Oxidations at Sulfur Centers by Aqueous Hypochlorous Acid and Hypochlorite: Cl⁺ Versus O Atom Transfer

Inorganic Chemistry of Defensive Peroxidases in the Human Oral Cavity

The Reactive Sulfur Species Concept: 15 Years On

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Reactive Sulfur Species: Hydrolysis of Hypothiocyanite To Give Thiocarbamate-S-oxide

Cited by 19 publications

References 20 publications

Oxidations at Sulfur Centers by Aqueous Hypochlorous Acid and Hypochlorite: Cl+ Versus O Atom Transfer

Oxidations at Sulfur Centers by Aqueous Hypochlorous Acid and Hypochlorite: Cl+ Versus O Atom Transfer

Inorganic Chemistry of Defensive Peroxidases in the Human Oral Cavity

The Reactive Sulfur Species Concept: 15 Years On

Contact Info

Product

Resources

About

Oxidations at Sulfur Centers by Aqueous Hypochlorous Acid and Hypochlorite: Cl⁺ Versus O Atom Transfer

Oxidations at Sulfur Centers by Aqueous Hypochlorous Acid and Hypochlorite: Cl⁺ Versus O Atom Transfer