NMR studies of hydrogen bonds

Because of the ability to identify all individual C, N, and H atoms in the NMR spectra of proteins via isotopic labeling and multi-dimensional NMR techniques [31], NMR has become the key technique for investigation of biomolecular struc- 

---

J.W. Traer, G.R. Goward, Solid-state NMR studies of hydrogen bonding networks and proton transport pathways based on anion and cation dynamics, Magn. Reson. Chem. 45 (2007) S135-S143. 

Fu W, Sun P (2011) Solid state NMR study of hydrogen bonding, miscibility, and dyntimics in multiphase polymer systems. Front Chem China 6173-189 Gaisford S (2005) Stability assessment of pharmaceuticals and biopharmaceuticals by isothermtd calorimetry. Curr Pharm Biotechnol 6 181-191... 

Alkylated bases in DMSO NMR study of hydrogen bonding 136... 

The complex [Ru(tpy)Cl3] binds to DNA, and is active as a cytostatic in L1210 leukemia cells. Its activity lies between those of cisplatin and carboplatin. Model complexes [Ru(tpy)L(H20)] + in which L = 9-ethylguanine or 9-methylhypoxanthine, have been prepared and characterized using NMR spectroscopy. " Proton NMR spectroscopy has been applied to a study of hydrogen bonding between 2, 3 -isopropylidine adenosine and [Ru(tpy)2] derivatives bearing a thymine group. 

In this paper we report for the first time our studies of hydrogen bonding in the imidazole-carboxylate system, a common motif in enzyme active sites. The H solid state NMR data of polymorphic crystalline histidines were taken on a Chemagnetic... 

NMR other aspects Two other aspects of the H NMR spectrum of hydrogen bonded aggregates are useful in determining structure. Variable-temperature NMR can reveal dynamic processes that are fast (or slow) on the NMR time scale at room temperature [51]. Nuclear Overhauser effect (nOe) studies can be used to determine relative proximity of the hydrogen bonded protons and the diastereotopic methylene protons [40,43,46]. H NMR competition studies where two different hubs (for example, Hub(M)3 and Flex(M)3) compete for only three equivalents of CA allows direct assessment of the relative stability of the competing aggregates [45,55]. 

Bachovchin, W.W. (2001) Contributions of NMR spectroscopy to the study of hydrogen bonds in serine protease active sites, Magn. Resort Chem. 39, S199-S213. 

Nearly all of the compounds were synthesized photochemically, which imposes a nuihber of quite strict limitations on larger-scale preparations of these compounds. The primary, or at least the initial, identification of these compounds has been via IR spectroscopy. (The sole exception has been Cp Re(CO)(C2H4)2 which was tentatively identified by NMR [18]). In most cases, characterization of the metal carbonyl moiety via v(C-O) IR bands is definitive, particularly if library spectra are available from liquid noble gas [23] or matrix isolation experiments [4]. This is because these bands are sharp and intense, and the C-O stretching vibrations are largely uncoupled from other vibrations of the molecule. Furthermore, the precise wavenumber of the bands are extremely sensitive to the oxidation state of the metal center as illustrated, for example, by Kazarian et al. in their study of hydrogen bonding to metal centers [25]. 

The study by Klinger and Rathke established the formation of radical Co(CO)4, which is involved in the equilibrium. Their observation was based on high-pressure NMR studies of hydrogen transfer and related dynamic process in 0x0 catalysis.They have determined the Co-Co and Co-H bond-dissociation enthalpies (19 and 59 kcal mol respectively), which have been previously obtained by Ziegler and Folga (148 and 283 kj mol ,... 

Foces-Foces, C., Echevarria, A., Jagerovic, N., Alkorta, L, Elguero, J., Langer, U., Klein, O., Minguet-Bonvehi, M. Limbach, H-. (2001) A Solid-State NMR, X-ray Diffraction, and ab Initio Computational Study of Hydrogen-Bond Structure and Dynamics of Pyrazole-4-Carboxylic Add Chains, J. Am. Chem. Soc. Vol. 123 7898-7906. 

The entropy value of gaseous HCl is a sum of contributions from the various transitions summarized in Table 4. Independent calculations based on the spectroscopic data of H Cl and H Cl separately, show the entropy of HCl at 298 K to be 186.686 and 187.372 J/(mol K) (44.619 and 44.783 cal/(mol K), respectively. The low temperature (rhombic) phase is ferroelectric (6). SoHd hydrogen chloride consists of hydrogen-bonded molecular crystals consisting of zigzag chains having an angle of 93.5° (6). Proton nmr studies at low temperatures have also shown the existence of a dimer (HC1)2 (7). 

Levy (Chapter 6) has also explored the use of supercomputers to study detailed properties of biological macromolecule that are only Indirectly accessible to experiment, with particular emphasis on solvent effects and on the Interplay between computer simulations and experimental techniques such as NMR, X-ray structures, and vltratlonal spectra. The chapter by Jorgensen (Chapter 12) summarizes recent work on the kinetics of simple reactions In solutions. This kind of calculation provides examples of how simulations can address questions that are hard to address experimentally. For example Jorgensen s simulations predicted the existence of an Intermediate for the reaction of chloride Ion with methyl chloride In DMF which had not been anticipated experimentally, and they Indicate that the weaker solvation of the transition state as compared to reactants for this reaction In aqueous solution Is not due to a decrease In the number of hydrogen bonds, but rather due to a weakening of the hydrogen bonds. 

---