Amide protons, exchange reaction

It is useful to note that lanthanides act as catalysts in some biochemical reactions like (i) depolymerization of RNA [14], (ii) cleavage of yeast tRNA [15], (iii) cleavage of phosphate group [14] from ATP in presence of Ce3+, (iv) increase in amide proton exchange in aspartyl-phenylalanine [16]. 

Noda et al. [ 168] reported the details of Bronsted acid-based ionic liquids consisting of a monoprotonic acid and an organic base, in particular solid bis(trifluorometha-nesulfonyl)amide (HTFSI) and solid imidazole (Im) mixed at various molar ratios to form liquid fractions. Studies of the conductivity, H NMR chemical shift, selfdiffusion coefficient, and electrochemical polarization results indicated that, for the Im excess compositions, the proton conductivity increased with an increasing Im molar fraction, with rapid proton-exchange reactions taking place between the protonated Im cation and Im. Proton conduction was found to occur via a combination of Grotthuss- and vehicle-type mechanisms. Recently, Nakamoto [169] reported the... 

Electrochemically induced cyclization of linear bromoamides in ionic liquids at room temperature has been reported to yield 3-lactams [66]. The proton exchange reaction between amide substrates 82 and electrochemically generated carbene 83 led to the generation of a carbanion that underwent cyclization to 3-lactam 84 via C3-C4 bond formation (Scheme 3.31). 

Alkynyl anions are more stable = 22) than the more saturated alkyl or alkenyl anions (p/Tj = 40-45). They may be obtained directly from terminal acetylenes by treatment with strong base, e.g. sodium amide (pA, of NH 35). Frequently magnesium acetylides are made in proton-metal exchange reactions with more reactive Grignard reagents. Copper and mercury acetylides are formed directly from the corresponding metal acetates and acetylenes under neutral conditions (G.E. Coates, 1977 R.P. Houghton, 1979). 

A variety of protonic and Lewis acids initiate the cationic polymerization of lactams [Bertalan et al., 1988a,b Kubisa, 1996 Kubisa and Penczek, 1999 Puffr and Sebenda, 1986 Sebenda, 1988]. The reaction follows the mechanism of acid-catalyzed nucleophilic substitution reactions of amides. More specibcally, polymerization follows an activated monomer mechanism. Initiation occurs by nucleophilic attack of monomer on protonated (activated) monomer (XXIV) to form an ammonium salt (XXV) that subsequently undergoes proton exchange with monomer to yield XXVI and protonated monomer. The conversion of XXIV to XXV involves several steps—attachment of nitrogen to C+, proton transfer from... 

Owing to the high affinity of the NH2- ion for the proton, potassium amide is an exceptionally effective catalyst of hydrogen exchange reactions in organic compounds. As was noted above, it can be used to extend the range in which the acidity of substances, including hydrocarbons (and even to saturated hydrocarbons), can be studied. 

The protection factor, pi, for the amide proton of residue i is given by the ratio of the rate constants fejnt,i and fe0bs,i f°r the intrinsic chemical exchange and the respective observed exchange reactions for residue i as follows ... 

Figure 14.5. HX reveals a temperature-dependent transition in mobility, (a) Arrhenius plot for the oxidation of protonated (circles) or deuterated (squares) benzyl alcohol by htADH. The discontinuity at 30 °C indicates a transition in activation energy for the reaction, (b) Weighted averaged HX rate constant ( HX(wA)) fot peptides from htADH plotted versus 1 /T show/s discontinuities at 30 °C in five peptides. The w/eighted averaged kHX is defined as (A(ti + 6(t2 + Ck )/NH where NH is the total number of amide hydrogens in the peptide, and A, B, and C are the number of amide hydrogens exchanging with rate...

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