H/T exchange

Equilibrium acidities are usually determined by titration, either with indicators of known plCa [24] or by following the extent of dissociation spectroscopically (e.g. by UV-spectroscopy [35]). Kinetic acidities, i.e. the rates of deprotonation of acids, can be determined by measuring rates of racemization[36] or rates of H-D or H-T exchange [37, 38], by chemical relaxation experiments (e.g. T-jump method [35, 39]), or by H NMR (line broadening and saturation recovery [40]). 

Eaborn and Singh22 have reported rate constants for H-T exchange in tri(4-substituted phenyl)-tritio-germanes, (4 — XPn GeT, with methoxide ion in methanol at 20, 30 and 40 °C (set CR1, Table 4). The data were correlated with the LDRT equation which has the form of equation 13 ... 

Akhter S, Nath SK, Tse CM, et al. Squalamine, a novel cationic steroid, specifically inhibits the brush-border Na-t/H-t exchanger isoform NHE3. Am J Physiol 1999 276(1 Pt 1) C136. 

Nieuwland R, Siffert W, Akkerman JW. Effect of epinephrine on the regulation of Na+/H-t- exchange in human platelets. Biochim Biophys Acta 1993 1148 185-190... 

Figure 21. Effect of calcium on H-T exchange of trypsin DFP trypsin in 0.1 M tris-Ci, pH 7.0, 4 0.1 M...

Thus, cyclobutane-Toj (x < 5) has been obtained from the reaction of cyclobutene with excess T2 over R black, that promotes extensive H/T exchange in addition to the saturation of the double bond (8). 

Huguenin, R, New experience in the Ir-catalyzed H/T-exchange reaction using Crabtree s catalyst. Presentation at the RC Tritec Workshop, Teufen, Switzerland, June 18-19, 2007. 

FIgur 7.4 If film transfer coefficients difier significantly, then nonvertical h t transfer is necessary to achieve the minimum area. (Reprinted from Linnhoff and Ahmad, Cost Optimum Heat Exchanger Networks I. Minimum Energy and Capital Using Simple Models for Capital Cost," Computers Chem. Engg., 7 729, 1990 with permission from Elsevier Science, Ltd.)... 

Pollard et al., 1992] Pollard, T. D., Goldberg, I., and Schwarz, W. H. Nucleotide exchange, structure, and mechanical properties of filaments assembled from ATP-actin and ADP-actin. J. Biol. Chem. 267 (1992) 20339-20345... 

FIG. 23-3 Temperature and composition profiles, a) Oxidation of SOp with intercooling and two cold shots, (h) Phosgene from GO and Gfi, activated carbon in 2-in tubes, water cooled, (c) Gumene from benzene and propylene, phosphoric acid on < uartz, with four quench zones, 260°G. (d) Mild thermal cracking of a heavy oil in a tubular furnace, hack pressure of 250 psig and sever heat fluxes, Btu/(fr-h), T in °F. (e) Vertical ammonia svi,ithesizer at 300 atm, with five cold shots and an internal exchanger. (/) Vertical methanol svi,ithesizer at 300 atm, Gr O -ZnO catalyst, with six cold shots totaling 10 to 20 percent of the fresh feed. To convert psi to kPa, multiply by 6.895 atm to kPa, multiply by 101.3. 

We adopt the nomenclature introduced by Hawthorne and Davis [1], in which compressor, heater, turbine and heat exchanger are denoted by C, H, T and X, respectively, and subscripts R and I indicate internally reversible and irreversible processes. For the open cycle, the heater is replaced by a burner, B. Thus, for example, [CBTX]i indicates an open irreversible regenerative cycle. Later in this book, we shall in addition, use subscripts... 

McDowell and Stirling194 studied electronic effects upon the reactivity of aryl vinyl sulfones towards amines. Rate constants for t-butylamine addition in ethanol at 25 °C were well correlated by the Hammett equation, with p = 1.59. Comparison of this with p values for H-D exchange mentioned above191 suggested considerable carbanionic character in the transition state, perhaps in a concerted mechanism. Rates of addition of amines to alkenyl, allenyl and alkynyl p-tolyl sulfones have also been measured195. 

Rotzinger then evaluated and H t as a function of the distance between the two reactant metal centers. He used the Fuoss equation to calculate the ion-pairing equilibrium constant to form the precursor complex at these internuclear distances. Assembly of these data then allowed the calculation of the self-exchange rate constants as a function of the internuclear distance in the transition state, the maximum rate being taken as the actual rate. 

Fig. 11.26. Negative-ion ESI spectrum of the ohgonucleotide dTio in the presence of imidazole and piperidine. Here, H /Na exchange is not completely suppressed. By courtesy of T. Kruger, University of Heidelberg.

Table 11.2 Average rate constants and number of amide hydrogens in each rate group for H/D exchange of ras-CDP under different Mg concentrations. Measurements were made in 100 mM KCI/50 mM HEPES, 90% D2O, apparent pH of 7.4, T = 21.5 + 0.5 °C. The final [ras-GDP]tot in H/D exchange media was 1.5 pM. EDTA was used to control [Mg +] in solution.

Powell, K.D. Wales, T.E. Fitzgerald, M.C. Thermodynamic stability measurements on multimeric proteins using a new H/D exchange-and matrix-assisted laser desorption/ ionization (MALDl) mass spectrometry-based method. Protein Sci. 2002, 11, 841-851. 

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