Couplings Through Hydrogen Bonds

Recently detected couplings across hydrogen bonds have become an object of great interest. Theoretical studies on this topic have been performed by Del Bene et al., who analysed the parameters which determine N-N and 0-0 couplings, across X-H - X hydrogen bonds,and considered to what extent the bonding at the nitrogens influences Comprehensive ab 

A coupling of 8.5 Hz has been measured by Claramunt et in 6-aminofulvene-l-aldimine, which represents an example of a new class of compounds exhibiting couplings across the hydrogen bond. No significant effect was observed when protium was replaced by deuterium. 

Both increased and decreased couplings have been observed by Li et 

Kainosho and co-workers have studied temperature dependence of couplings in N-selectively enriched DNA oligomers. The authors observed a significant decrease of the coupling value with the rise of the temperature. 

Several other interesting couplings measured in protein and nucleic acids are listed in Table 7. 

The Vhh couplings in six H-X-Y-H systems (ethane, methylamine, methanol, hydrazine, hydroxyloamine and hydrogen peroxide) and Jhh couplings in four systems H-X H Y-H, [HjN H NHj] + (two arrangements), HOH NH3 and H0H 0H2 have been calculated theoretically by Alkorta and Elguero in a search of relationship between vicinal H-H and supramolecular couplings. 

The positive signs of reduced two-bond spin-spin couplings Xx,y across X-H-Y hydrogen bonds have been predicted by Del Bene and Elguero for complexes stabilized by C-H-N, N-H-N, O-H-N, F-H-N, C-H-O, O-H-O, F-H-O and C-H-F hydrogen bonds. 

Correlation between hydrogen-bond stability and J-coupling through a hydrogen bond has been studied theoretically by Kawahara et The relationship has been found to be dependent on the type of the nucleus forming the H-bond the linear correlation has been observed in N-H O/N type or 0-H N type H-bonded complexes, but not in 0 H 0 type H-bonded complexes. 

A thorough theoretical investigation of the spin-spin coupling mechanism across a H-bond in proteins, N-H - 0 = C, has been performed by Cremer and co-workers. ° An analysis of the data obtained for the protein ubiquitin has shown that there are simple relationships between the spin-spin couplings associated with the H bond in proteins and the geometrical features of these bonds. In particular, the authors emphasized the importance of the and Jhn couplings as descriptors of the H-bond. 

The Dn/Hn isotope effect on Vnc and Jnc couplings as well as on N, and Ha chemical shifts in the small globular protein ubiquitin has been studied by Jaravine et They have found that amide deuteration induces a very slight weakening of 0.03 + 0.03 Hz for the couplings, whereas the Jnc couplings 

---

Within the Hush formalism of electron transfer [129], the electronic coupling through hydrogen bond interfaces may be deduced from the intensity of a mixed-valence transition between juxtaposed donor-acceptor pairs. We highlight the only such detailed study in this section. Curtis and coworkers have studied a collection of hydrogen-bonded mixed-valence adducts formed between ruthenium(II) electron-donor and ruthenium(III) electron-acceptor complexes in solution [130]. Using acetonitrile or nitromethane as a solvent, hydrogen-bonded assemblies of the type [(tpy)(bpy)Ru (CN)]2, (en)2Ru (bpy) 5+ 45 (bpy = 2,2 -bipyridine, tpy = 2, 6", 2 -terpyridine, en = ethylenediamine) and [(bpy)2Ru (CN)2]2, (en)2Ru (bpy) +... 

Observation of spin-spin couplings through hydrogen bonds... 

The Vc N and Vc n scalar couplings have been used by Grzesiek and co-workers " for the quantification of H/D isotope effects on protein hydrogen-bonds. The authors have used the values of the Vc n couplings through hydrogen bond as a measure of the acceptor-donor distanee. Their results indicate that protein is destabilized upon deuterium exchange. 

Coupling to a mineral surface requires the presence of active hydroxyls on the substrate. The coupling reaction is a multi-step process that proceeds from a state of physisorption through hydrogen bond formation to actual covalent bond formation through condensation of surface hydroxyls with silanols ... 

Figure 4.13 The transition state for CO + OH coupling to form COOH on the Pt(lll) surface. The transition state is stabilized in the aqueous model system through hydrogen bonding between the hydroxyl species and a nearby water molecule [Janik and Neurock, 2006].

The behaviour of ternary systems consisting of two polymers and a solvent depends largely on the nature of interactions between components (1-4). Two types of limiting behaviour can be observed. The first one occurs in non-polar systems, where polymer-polymer interactions are very low. In such systems a liquid-liquid phase separation is usually observed each liquid phase contains almost the total quantity of one polymer species. The second type of behaviour often occurs in aqueous polymer solutions. The polar or ionic water-soluble polymers can interact to form macromolecular aggregates, occasionally insoluble, called "polymer complexes". Examples are polyanion-polycation couples stabilized through electrostatic interactions, or polyacid-polybase couples stabilized through hydrogen bonds. 

Blake, P.R., Lee, B., Summers, M.F., Adams, M.WW., Park, J.B., Zhou, Z.H. and Bax, A. (1992) Quantitative measurement of small through-hydrogen-bond and through space 1H-113Cd and 1H-199Hg J-couplings in metal-substituted rubredoxin from Pyrococcus Juriosus.J. Biomol. NMR, 2, 527—233. 

When the NMR spectrum of A is recorded in a non-polar solvent (CCI4 or n-hexane), a triplet-quadruplet substructure superimposed in a comb-like pattern on the primary doublet-triplet main structure (Fig. 7) appears. Such a triplet-quadruplet secondary pattern implies the existence in solution of an intermolecular (P... P) coupling, probably through hydrogen bonds as it is the case for N3P3C14[HN— (CH2)3—NH]33). This assumption is supported by the fact that the secondary structure disappears in highly polar solvents. 

---