The Study of Intramolecular Rate Processes by Dynamic Nuclear Magnetic Resonance

In Search of the Weak, Six‐Membered Intramolecular Hydrogen Bond in the Solution and Solid States of Guanidinobenzimidazole

“…The rates were determined at more than one temperature near the coalescence region to minimize error. [37,38] Only cases simple enough to model with a two-states-related-by-one-rate process were determined. For example, there were situations in which H4 and H7 were unequally broadened by a moderate hydrogen-atom exchange at N1; such a situation was deemed beyond the scope of this study.…”

“…Isochronous NH and CH methine signals in CDCl 3 made line shape analysis [37,38] with these peaks unreliable (see Figure 5); however, line shape analysis of the iPr CH 3 1 H NMR signals allowed determination of the N10C11 rotational barrier, ‡ ∆G ϭ 12.7Ϯ0.3, 13.0Ϯ0.1, and 13.5Ϯ0.2 kcal/mol for 2b at 8.8 and 0.4 mm and 2c at 5.7 mm, respectively. Another estimate of the stability of S(6) in 2 was available with the comparison of the N10C11 rotation rate in 2b with the analogous rotation rate in 4 (rate of iPr exchange).…”

Structural and Dynamic Information on Ligand Binding

“…When scalar couplings change as a result of the exchange process the density operator formalism must be used [2][3][4][5][6]; the review by Bain [6] contains a useful comparison of the McConnell and density operator approaches. For the present illustrative purposes, we will simply present the result for a two-site exchange of an isolated spin (i.e.…”

“…1 It is important to begin this ligand titration at concentrations much less than that of the protein (approximately 0.1-0.2 molar equivalents), to make a number of additions at <1 molar equivalent and to continue until at least 5 molar equivalents of ligand have been added. 2 After each addition of ligand, a spectrum is acquired; a simple 1D 1 H spectrum will provide preliminary information about both ligand and protein resonances, while a 1 H-15 N HSQC spectrum will provide more detailed information about a labelled protein (cf. Figure 7.2).…”

“…It is of course possible to do the inverse experiment, adding protein progressively to a ligand solution, but this is much more difficult to do satisfactorily and is best avoided if at all possible 2. In order to minimise the number of manipulations of the sample and the likelihood of systematic errors (e.g.…”