Proton transfer is not rate-limiting in buffer-induced non-enzymic glucation of hemoglobin

1988 ◽  
Vol 110 (24) ◽  
pp. 8265-8266 ◽  
Author(s):  
Herminia. Gil ◽  
Julio F. Mata-Segreda ◽  
Richard L. Schowen
Keyword(s):  
Proton Transfer ◽  
Rate Limiting

scholarly journals Study of Kinetics, Equilibrium and the Influence of Steric Effects on Proton-Transfer in the Reactions of 2, 2, 4- and 2, 6- Substituted Anilines with 2-Phenoxy-3,5-dinitropyridine in DMSO

2010 ◽  
Vol 7 (1) ◽  
pp. 253-259 ◽  
Author(s):  
Basim H. Asghar
Keyword(s):  
Proton Transfer ◽  
Steric Effect ◽  
Nucleophilic Attack ◽  
Steric Effects ◽  
Substituted Anilines ◽  
Phenoxy Group ◽  
Kinetics Studies ◽  
Zwitterionic Intermediate ◽  
Rate Limiting ◽  
Step Mechanism

Kinetic and equilibrium results for the reactions of 2-phenoxy-3,5-dinitropyridine (1), with a series of 2, 2, 4- and 2, 6- substituted anilines (2a-f), in the presence of DABCO in DMSO are reported. The reactions yield the 2-anilino derivatives (5), without the accumulation of intermediates. Kinetics studies are compatible with a two-step mechanism involving initial nucleophilic attack by amine at the ring carbon substituted by phenoxy group followed by either base-catalyzed or uncatalyzed conversion to the product. The base-catalyzed pathway is likely to involve rate-limiting proton-transfer from the zwitterionic intermediate to base. This work indicates a steric effect to proton transfer in reactions involving 2, 6-disubstituted anilines. The results were compared with those for reactions of 1, 3, 5-trinitrobenzene with anilines.

ChemInform Abstract: CATALYSIS OF TRANSIMINATION BY RATE-LIMITING PROTON TRANSFER TO BUFFER BASES

1980 ◽  
Vol 11 (21) ◽  
Author(s):  
H. FISCHER ◽  
F. X. DECANDIS ◽  
S. D. OGDEN ◽  
W. P. JENCKS
Keyword(s):  
Proton Transfer ◽  
Rate Limiting

scholarly journals Atomically manipulated proton transfer energizes water oxidation on silicon carbide photoanodes

2018 ◽  
Vol 6 (47) ◽  
pp. 24358-24366 ◽  
Author(s):  
Hao Li ◽  
Huan Shang ◽  
Yuchen Shi ◽  
Rositsa Yakimova ◽  
Mikael Syväjärvi ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Electron Transfer ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Proton Coupled Electron Transfer ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Preferential exposure of Si-face of SiC will mechanistically shift the rate limiting step of water oxidation from sluggish proton-coupled electron transfer on C-face to a more energy-favorable electron transfer.

Concerted rate-limiting proton transfer to sulfur with nucleophilic attack at phosphorus — A new proposed mechanism for hydrolytic decomposition of the P=S pesticide, Diazinon, in moderately acidic sulfuric acid media

2007 ◽  
Vol 85 (6) ◽  
pp. 421-431 ◽  
Author(s):  
Doreen Churchill ◽  
Julian M Dust ◽  
Erwin Buncel
Keyword(s):  
Proton Transfer ◽  
Organophosphorus Pesticide ◽  
Nucleophilic Attack ◽  
Acid Media ◽  
Hydronium Ion ◽  
Neutral Aqueous Solution ◽  
Region Product ◽  
Rate Limiting ◽  
Hydrolysis Of ◽  
Acid Region

We report herein the first kinetic study of a P=S containing organophosphorus pesticide, Diazinon (1), in the moderately concentrated acid region. Product analyses (31P NMR) show that reaction occurs only at the P centre. The rate-acidity profile (kobs vs. molarity of H2SO4) appears as a curve in which the initial slight downward trace (molarity = 1 to ca. 5) is followed by sharper upward curve (molarity ca. 5 to 14). Using treatments involving the excess acidity (X) method, the A-1 and A-2 mechanistic possibilities were found to be inoperative over the full acidity range. A novel mechanism is proposed for the higher acidity (X ca. 2–6) region. This mechanism involves proton transfer to P=S from hydronium ion with concomitant proton transfer from water, which effectively delivers hydroxide to the P centre in a variant of the A-SE2 process. A putative A-2 mechanism in this region is supplanted by the proposed A-SE2 variant where the cyclic array results in proton transfer being efficiently coupled with nucleophilic attack involving water. This constitutes the first report of rate-limiting proton transfer at the P=S functionality in acid hydrolysis of this class of organophosphorus neutroxins. A 600 000-fold acceleration in the decomposition of Diazinon is associated with the change of medium from neutral aqueous solution to the most acidic medium studied (X ca. 6). Key words: phosphorothioate ester hydrolysis, acid catalysis, rate-limiting proton transfer at P=S, excess acidity analysis, new A-SE2 variant mechanism.

Base-catalyzed formation of spiro adduct from N-methyl-N-(2,4,6-trinitrophenyl)glycinamide, the smiles rearrangement of the amide in methanol

1988 ◽  
Vol 53 (3) ◽  
pp. 601-618 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Makky M. M. Hassanien ◽  
Vojeslav Štěrba
Keyword(s):  
Proton Transfer ◽  
Equilibrium Constant ◽  
Ammonium Salt ◽  
Aliphatic Amine ◽  
Reaction Pathway ◽  
Smiles Rearrangement ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Kinetics Of

The reaction of N-methyl-N-(2,4,6-trinitrophenyl)glycinamide (Ic with methoxide in methanol produces the spiro adduct IIc(A). In methanolic acetate buffers, the equilibrium is rapidly established between the spiro adduct IIc(A) and the dipolar ion of 2-methylamino-N-(2,4,6-trinitrophenyl)acetamide (IIIc(Z)). The equilibrium constant of the reaction IIIc(Z) ⇆ IIc(A) + H+ is by eight orders of magnitude greater than that of the analogous cyclization of 2-methylamino-N-methyl-N-(2,4,6-trinitrophenyl)acetamide to the spiro adduct. In chloracetate buffers, the dipolar ion is protonated to give 2-methylammonium-N-(2,4,6-trinitrohenyl)acetamide IIIc(K). The kinetics of the reversible reaction IIIc(Z) ⇆ IIc(A) + H+ has been studied in acetate buffers, aliphatic amine – ammonium salt buffers, and methoxide solutions. In all cases, the rate-limiting step was the proton transfer with half-lives in milliseconds. In more basic methanolic buffers (pH > 10) the rate-limiting step consists in the formation of spiro adduct from the zwiterion IIIc(Z) resulting from the protonation of the anion IIIc(A). n acetate buffers, the second reaction pathway via the cation IIIc(K) is predominant.

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