Inductive Effects on the Acid Dissociation Constants of Mercaptans<sup>1</sup>

Kreevoy, Maurice M.; Harper, Edwin T.; Duvall, Richard E.; Wilgus, H. S.; Ditsch, Leroy T.

doi:10.1021/ja01503a037

Cited by 123 publications

(66 citation statements)

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“…1. 20 ####fr is the least square function that need to be optimized#### fr=function(par,ph,Rph){ R0=par[1] alpha=par [2] pka1=par [3] pka2=par [4] sum(((R0+alpha*R0*10^(ph-pka1))/(1+10^(ph-pka1)*(1+10^(ph-pka2)))-Rph)^2) } ####################################################################### # ############# # pka.fit is the function to fit the parameters # # par is a vector of the initial guess for the parameters R0,alpha, pka1 and pka2 # # ph is the experimental value for ph # # Rph is the experimental value for Rph # # Returning values are fitted parameters, fitted Rph and MSE # ####################################################################### # ############# pka.fit=function(par,ph,Rph){ res=optim(par, fr, ph=ph, Rph=Rph) R0.f=res$par[1] alpha.f=res$par [2] pka1.f=res$pa [3] pka2.f=res$par [4] Rph.f=(R0.f+alpha.f*R0.f*10^(ph-pka1.f))/(1+10^(ph-pka1.f)*(1+10^(ph-pka2.f))) MSE=sum((Rph.f-Rph)^2) return(list(R0.f=R0.f,alpha.f=alpha.f,pka1.f=pka1.f,pka2.f=pka2.f,Rph.f=Rph.f, MSE=MSE))}…”

Section: A1mentioning

confidence: 99%

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Evaluation of Thiol Raman Activities and pK_a Values Using Internally Referenced Raman-Based pH Titration

Suwandaratne

Siriwardana

et al. 2016

Anal. Chem.

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Section: A1mentioning

confidence: 99%

“…Therefore, thiols can be treated with alkali metal hydroxides to obtain thiolates as shown in equation 1. 4.…”

Section: Introduction To Thiolsmentioning

confidence: 99%

Evaluation of Thiol Raman Activities and pK_a Values Using Internally Referenced Raman-Based pH Titration

Suwandaratne

Siriwardana

et al. 2016

Anal. Chem.

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“…The rate constants were calculated from eq. [19] where the slope is determined from a plot l/(mLcdcd -mLti,) versus time in seconds; mLcdcd is the number of millilitres of titrating base necessary to neutralize the quenching acid and mLti, is the number of millilitres of base necessary to titrate the aliquot of quenched reaction solution.…”

Section: Kineticsmentioning

confidence: 99%

The influence of the changing of P=O to P=S and P—O—R to P—S—R on the reactivity of phosphinate esters under alkaline hydrolysis conditions

Cook¹,

Farah²,

Ghawi³

et al. 1986

Can. J. Chem.

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ROBERT D. COOK, SELIM FARAH, LABIB GHAWI, ADNAN ITANI, and JUBRAIL RAHIL. Can. J. Chem. 64, 1630 (1986). Alkyl dialkylphosphinates, thionates, thioates, and dithioates have been studied under alkaline hydrolysis conditions in 60% DME -H20 and pure H20. Substitution of S for 0 in the phosphoryl group has only a small rate retarding effect, typically less than a factor of 10. The effect of the similar replacement in the leaving group, however, can lead to rate increases greater than a factor of 100. Activation parameters were determined and the AS* values range from -19 to -49 eu for the bimolecular reactions. The more negative values are for the esters with higher sulfur content and/or sterically large substituents. The results are discussed in terms of a pathway involving a pentacoordinate intermediate. 1630 (1986). Operant dans un melange ? i 60% de DME/eau ainsi que dans de I'eau pure, on a CtudiC les dialkylphosphinates, les thionates, les thioates et les dithioates d'alkyles dans des conditions d'hydrolyse alcaline. La substitution du S par un 0 dans le groupement phosphoryle provoque un faible ralentissement de la vitesse de la reaction et le rapport des deux vitesses est plus petit que 10. Toutefois, si I'on effectue un remplacement semblable dans le groupement nucleofuge, la vitesse de la reaction est augmentke par un facteur de plus de 100. On a determine les param6tres d'activation et, pour les reactions bimolCculaires, les valeurs des AS* varient de -19 i -49 ue. Les valeurs les plus negatives sont liees aux esters comportant le plus grand nombre d'atomes de soufre et/ou les substituants les plus encombrants d'un point de vue sterique. On discute des resultats en fonction d'une voie reactionnelle impliquant un intermkdiaire pentacoordonne.[Traduit par la revue]

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“…This corresponds to a six-fold difference in nucleophilic reactivity constants. The pK a of benzenethiol is 6.6 (45), while that of benzeneselenol is 4.6 (35). The pK a of benzenethiol is low enough such that proton transfer no longer becomes a rate-limiting factor, and the difference in nucleophilicity of the two atoms is rather small when this condition is met.…”

mentioning

confidence: 99%

Selenocysteine in Thiol/Disulfide-Like Exchange Reactions

Hondal

Marino

Gladyshev

2013

Antioxidants & Redox Signaling

153

119

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Significance: Among trace elements used as cofactors in enzymes, selenium is unique in that it is incorporated into proteins co-translationally in the form of an amino acid, selenocysteine (Sec). Sec differs from cysteine (Cys) by only one atom (selenium versus sulfur), yet this switch dramatically influences important aspects of enzyme reactivity. Recent Advances: The main focus of this review is an updated and critical discussion on how Sec might be used to accelerate thiol/disulfide-like exchange reactions in natural selenoenzymes, compared with their Cys-containing homologs. Critical Issues: We discuss in detail three major aspects associated with thiol/ disulfide exchange reactions: (i) nucleophilicity of the attacking thiolate (or selenolate); (ii) electrophilicity of the center sulfur (or selenium) atom; and (iii) stability of the leaving group (sulfur or selenium). In all these cases, we analyze the benefits that selenium might provide in these types of reactions. Future Directions: It is the biological thiol oxidoreductase-like function that benefits from the use of Sec, since Sec functions to chemically accelerate the rate of these reactions. We review various hypotheses that could help explain why Sec is used in enzymes, particularly with regard to competitive chemical advantages provided by the presence of the selenium atom in enzymes. Ultimately, these chemical advantages must be connected to biological functions of Sec.

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Inductive Effects on the Acid Dissociation Constants of Mercaptans¹

Cited by 123 publications

References 0 publications

Evaluation of Thiol Raman Activities and pK_a Values Using Internally Referenced Raman-Based pH Titration

Evaluation of Thiol Raman Activities and pK_a Values Using Internally Referenced Raman-Based pH Titration

The influence of the changing of P=O to P=S and P—O—R to P—S—R on the reactivity of phosphinate esters under alkaline hydrolysis conditions

Selenocysteine in Thiol/Disulfide-Like Exchange Reactions

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Inductive Effects on the Acid Dissociation Constants of Mercaptans1

Cited by 123 publications

References 0 publications

Evaluation of Thiol Raman Activities and pKa Values Using Internally Referenced Raman-Based pH Titration

Evaluation of Thiol Raman Activities and pKa Values Using Internally Referenced Raman-Based pH Titration

The influence of the changing of P=O to P=S and P—O—R to P—S—R on the reactivity of phosphinate esters under alkaline hydrolysis conditions

Selenocysteine in Thiol/Disulfide-Like Exchange Reactions

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Product

Resources

About

Inductive Effects on the Acid Dissociation Constants of Mercaptans¹

Evaluation of Thiol Raman Activities and pK_a Values Using Internally Referenced Raman-Based pH Titration

Evaluation of Thiol Raman Activities and pK_a Values Using Internally Referenced Raman-Based pH Titration