Magnetic Resonance in Chemistry

Alemany, Lawrence B.

doi: 10.1002/mrc.3988pmid: 23893374

New information has been obtained from very‐high‐resolution 13C NMR studies of a series of long‐chain n‐alkanes. These compounds are fundamentally important in the petroleum industry and are essential to the life of some plants, flowers, and insects. At least partial resolution of the ten different 13C NMR signals of n‐C20H42 is observed at 11.7 T for solutions in C6D6 or C6D5CD3. A 13C T1 inversion‐recovery experiment provides much more detailed information than in previous studies of long‐chain n‐alkanes, demonstrates a steady increase in the relaxation times of the ten different carbons proceeding from the middle to the end of the chain because of segmental motion, and thus confirms the assignments for the interior carbons. In contrast, there is significant overlap for the signals for C‐7 and the more interior carbons in a solution of n‐C16 or longer chain alkanes in CDCl3. Not only are the chemical shifts sensitive to the solvent used, but also the relative chemical shifts change. Signals for the interior carbons of the odd‐number alkanes in CDCl3 are better resolved than in the spectra of their even‐number counterparts. Some mixed aromatic solvent systems give increased dispersion of the cluster of C‐6 through C‐10 signals of n‐C20H42, n‐C21H44, and n‐C22H46. However, none of the solvents used could even partially resolve the C‐10 and C‐11 signals of n‐C21H44 or n‐C22H46 at 11.7 T, which may result from a different distribution of conformers for n‐C21H44 or n‐C22H46 than for n‐C20H42 and shorter n‐alkanes. Copyright © 2013 John Wiley & Sons, Ltd.

Bolebrukh, O. N.; Sinyavsky, N. Ya.; Dobosz, B.; Korneva, I. P.; Krzyminiewski, R.; Ostafin, M.; Nogaj, B.

doi: 10.1002/mrc.3990pmid: 23925857

Asymmetry parameters of the electric field gradient tensor at 75As nuclei were determined for chalcogenide glassy semiconductors (CGS) of the Ge‐As‐Se system by comparing the experimental and simulated 75As nuclear quadrupole resonance nutation interferograms. The electric field gradient asymmetry in CGS was analyzed, and it is believed that a structural change in these glassy semiconductors takes place at r¯ = 2.425. Electron paramagnetic resonance spectra of the Ge‐As‐Se system were obtained for the first time. A comparison was made between the results of analysis of the Ge‐As‐Se system by nuclear quadrupole resonance and electron paramagnetic resonance methods, and this allowed us to make the supposition that a structural phase transition occurs at r¯ = 2.4 from two‐dimensional to three‐dimensional CGS structure. Copyright © 2013 John Wiley & Sons, Ltd.

Kraikin, Vladimir A.; Fatykhov, Akhnef A.; Sakhipova, Il'nara I.; Sedova, Elvira A.; Egorov, Aleksandr E.; Salazkin, Sergey N.

doi: 10.1002/mrc.3991pmid: 23921970

1H and 13С NMR spectral assignments have been provided for low‐molecular reference monomers, poly(diphenyleneoxidephthalide) and periodic copoly(arylenephthalide) derivatives such as AB, ABB, and ABBB (where A = terphenylenephthalide and B = diphenyleneoxidephthalide) using 1H‐1H COSY, 1H‐13C HSQC and HMBC NMR techniques. Distinctive 13C NMR chemical shifts of a main chain have been observed containing fragments of similar structures and lateral phthalate groups being part of various diads. Copyright © 2013 John Wiley & Sons, Ltd.

Radula‐Janik, Klaudia; Kupka, Teobald; Ejsmont, Krzysztof; Daszkiewicz, Zdzislaw; Sauer, Stephan P. A.

doi: 10.1002/mrc.3992pmid: 23922027

Structures of selected 3,6‐dihalogeno‐N‐alkyl carbazole derivatives were calculated at the B3LYP/6‐311++G(3df,2pd) level of theory, and their 13C nuclear magnetic resonance (NMR) isotropic shieldings were predicted using density functional theory (DFT). The model compounds contained 9H, N‐methyl and N‐ethyl derivatives. The relativistic effect of Br and I atoms on nuclear shieldings was modeled using the spin–orbit zeroth‐order regular approximation (ZORA) method. Significant heavy atom shielding effects for the carbon atom directly bonded with Br and I were observed (~−10 and ~−30 ppm while the other carbon shifts were practically unaffected). The decreasing electronegativity of the halogen substituent (F, Cl, Br, and I) was reflected in both nonrelativistic and relativistic NMR results as decreased values of chemical shifts of carbon atoms attached to halogen (C3 and C6) leading to a strong sensitivity to halogen atom type at 3 and 6 positions of the carbazole ring. The predicted NMR data correctly reproduce the available experimental data for unsubstituted N‐alkylcarbazoles. Copyright © 2013 John Wiley & Sons, Ltd.

Voronov, Vladimir K.; Ushakov, Igor А.; Grishmanovskii, Dmitrii S.; Cherkasov, Vladimir K.

doi: 10.1002/mrc.3993pmid: 23940079

High‐resolution NMR spectra of 3,6‐di‐tert‐butylquinone were recorded and analyzed for the first time in a wide range of temperatures. The spectra were transformed by paramagnetic additives of cobalt, nickel, and copper complexes synthesized on the basis of metal semiquinolates. Chloroform, dimethylsulfoxide, toluene, and acetone were used as solvents. It was shown that the spectra changed by paramagnetic additives can contain valuable information on the nature of a superfine interaction in paramagnetic complexes and on peculiarities of intramolecular dynamics inherent in these compounds. Copyright © 2013 John Wiley & Sons, Ltd.

D'Aléo, Anthony; Dumont, Elise; Maury, Olivier; Giraud, Nicolas

doi: 10.1002/mrc.3994pmid: 23955873

We present a method for fitting curves acquired by chemical shift titration experiments, in the frame of a three‐step complexation mechanism. To that end, we have implemented a fitting procedure, based on a nonlinear least squares fitting method, that determines the best fitting curve using a “coarse grid search” approach and provides distributions for the different parameters of the complexation model that are compatible with the experimental precision. The resulting analysis protocol is first described and validated on a theoretical data set. We show its ability to converge to the true parameter values of the simulated reaction scheme and to evaluate complexation constants together with multidimensional uncertainties. Then, we apply this protocol to the study of the supramolecular interactions, in aqueous solution, between a lanthanide complex and three different model molecules, using NMR titration experiments. We show that within the uncertainty that can be evaluated from the parameter distributions generated during our analysis, the affinities between the lanthanide derivative and each model molecule can be discriminated, and we propose values for the corresponding thermodynamic constants. Copyright © 2013 John Wiley & Sons, Ltd.

Cobas, C.; Seoane, F.; Vaz, E.; Bernstein, M. A.; Dominguez, S.; Pérez, M.; Sýkora, S.

doi: 10.1002/mrc.3995pmid: 24038382

A novel data‐evaluation procedure for the automatic atom to peak or multiplet assignment of 1H‐NMR spectra of small molecules has been developed using a fast and robust expert system. The applicability and reliability of the method are demonstrated by comparison of a manually assigned database of 1H‐NMR spectra with the assignments produced by the automatic procedure. The results of this analysis show an excellent success ratio, indicating that this new algorithm can have a major impact as a time saving tool for the organic chemist. A new graphical feature used to illustrate both the stability and quality of the elementary assignments is also introduced. Copyright © 2013 John Wiley & Sons, Ltd.

Schmieder, Peter; Nitschke, Felix; Steup, Martin; Mallow, Keven; Specker, Edgar

doi: 10.1002/mrc.3996pmid: 23913630

Phosphorylation and dephosphorylation of starch and glycogen are important for their physicochemical properties and also their physiological functions. It is therefore desirable to reliably determine the phosphorylation sites. Heteronuclear multidimensional NMR‐spectroscopy is in principle a straightforward analytical approach even for complex carbohydrate molecules. With heterogeneous samples from natural sources, however, the task becomes more difficult because a full assignment of the resonances of the carbohydrates is impossible to obtain. Here, we show that the combination of heteronuclear 1H,13C and 1H,13C,31P techniques and information derived from spectra of a set of reference compounds can lead to an unambiguous determination of the phosphorylation sites even in heterogeneous samples. Copyright © 2013 John Wiley & Sons, Ltd.

Jaźwiński, Jarosław; Sadlej, Agnieszka

doi: 10.1002/mrc.3997pmid: 23943201

The complexation of rhodium(II) tetraacetate, tetrakistrifluoroaceate and tetrakisoctanoate with a set of diamines (ethane‐1,diamine, propane‐1,3‐diamine and nonane‐1,9‐diamine) and their N,N′‐dimethyl and N,N,N′,N′‐tetramethyl derivatives in chloroform solution has been investigated by 1H and 13C NMR spectroscopy and density functional theory (DFT) modelling. A combination of two bifunctional reagents, diamines and rhodium(II) tetracarboxylates, yielded insoluble coordination polymers as main products of complexation and various adducts in the solution, being in equilibrium with insoluble material. All diamines initially formed the 2 : 1 (blue), (1 : 1)n oligomeric (red) and 1 : 2 (red) axial adducts in solution, depending on the reagents' molar ratio. Adducts of primary and secondary diamines decomposed in the presence of ligand excess, the former via unstable equatorial complexes. The complexation of secondary diamines slowed down the inversion at nitrogen atoms in NH(CH3) functional groups and resulted in the formation of nitrogenous stereogenic centres, detectable by NMR. Axial adducts of tertiary diamines appeared to be relatively stable. The presence of long aliphatic chains in molecules (adducts of nonane‐1,9‐diamines or rhodium(II) tetrakisoctanoate) increased adduct solubility. Hypothetical structures of the equatorial adduct of rhodium(II) tetraacetate with ethane‐1,2‐diamine and their NMR parameters were explored by means of DFT calculations. Copyright © 2013 John Wiley & Sons, Ltd.

Usta, Keziban; Ozen Karakus, Ozlem; Usta, Ayhan; Deligoz, Hasalettin

doi: 10.1002/mrc.3998pmid: 23950032

A macrocyclic azocalix(4)arene (1) based ester derivative was synthesized. The single crystals of azocalix(4)arene were produced by slow evaporation of concentrated ethyl acetate solutions. These single crystals were exposed to 60Co gamma rays with a dose rate of 0.980 kGy h‐1 for 48 and 72 h to produce a stable free radical. Electron paramagnetic resonance (EPR) measurements were performed in three mutually perpendicular planes of the single crystal in the magnetic field, in addition, temperature dependence of the EPR signal was studied between 120 K and 450 K. The spectra were found to be temperature and angular dependent. Analysis based on the spectra recorded showed that a free radical was formed by fission of a C–H bond. This radical is described as •CaHCbH3 The averages of the principal values of the hyperfine parameters and g‐factor are: g = 2.0034, AHa = 1.28 mT, AH1=H2 = 1.00 mT, and AH3 = 0.49 mT. Copyright © 2013 John Wiley & Sons, Ltd.