Three-bond Couplings not Involving Hydrogen

Schwalbe and co-workers have measured /c ca and VnNHa couplings in unfolded ubiquitin. The authors have found that the measured carbon-carbon couplings which are related to the torsion angles are small with a mean value of 0.85 0.2 Hz, This means that individual amino acids of the unfolded ubiquitin sample have both positive and negative torsion angles. The authors also observed that the measured proton-proton couplings fit in well with the predicted values, which supports the model of local conformational preferences in the denatured polypeptide chain. 

The Jcc couplings of several bis- C-labelled derivatives of famesyl and geranylgeranyl have been measured in a variety of solvents by Zahn et al Since the measured coupling value does not depend on the solvent type it proves that the prenyl chain exists in all the solvents in an extended conformation. 

The carbon-carbon one- and three-bond couplings have been determined for cis and trans cinnamic acids by Hanai et al  

Long-range C-N couplings have been reported by Lycka et al for the product of the coupling of benzenediazonium chloride with 1,3-dihydroxy-naphthalene and benzenediazonium chloride with 1,5-dihydroxynaphthalene. 

Ding has measured cp and Vhp couplings in the fructose-1,6-diphosphate anion. 

The new empirical Karplus relationships for Vccy Vncy proteins have been obtained by Bax and co-workers. ° The couplings required to parametrize these relationships have been measured for ubiquitin and the third IgG-binding domain of protein G. The experimental Karplus curves have been confirmed by the DFT calculations including an unusual phase shift which causes the maximum Vccy - ncy couplings to occur for dihedral angles slightly smaller than 180°. The new Karplus curves permit determination of rotamer populations for the Xi torsion angles. 

The effects of mutations on the motions of side-chains in the B1 domain of peptostreptococcal protein L and in a pair of point mutants of the domain, F22I and A20V, have been investigated by Millet et a/. by the aid of methyl H spin relaxation rates and three-bond Cy-C(O), C -N and C -C6 couplings. It is noteworthy that the measurements of the relaxation rates provide information on a picosecond-nanosecond time scale, whereas J couplings span a wide range of time-scales. 

Vcp couplings are a valuable source of information on the geometry of a double CC bond Vcp(frani)(16 Hz or larger) Vcp(ns)(6-10 Hz). This relationship has been applied by Panarina et to establish the structure of diethyl-2- 

A spectral characteristics, which also included Vcp couplings, has been obtained for three new C-bonded cyclotriphosphazenes, [N3P3(2-thienyl)6], [N3P3(3-thienyl)6] and [N3P3(3,3 -bithienyl-2,2 -ylene)3], the first examples of non-spiro and trispirocyclotriphosphazene derivatives composed of thiophene and 3,3 -dithiophene substituents, respectively.  

The Vcp couplings have been measured by Marinic et al for diethyl 2- and 8-quinolylmethylphosphonates and their palladium(II) dihalide complexes, trans-[PdL2X2], X = Cl, Br in the ligands additionally the C-P couplings across four and five bonds have been observed. 

---

Electronic couphngs between pairs of the three different T1 centers have also been calculated. These centers are connected pairwise by 13 covalent and 2 hydrogen bonds, resulting in an electronic decay coupling factor of 1.7 x lO. However, in spite of this relatively short distance, intramolecular ET between these sites is not expected. The high-potential TIC is, as mentioned above, most likely in the reduced state even in the resting (as isolated) enzyme and thus not involved in ET at all. The driving force for TIA to TIB ET is very low or even... 

---