Continuing studies based on measurements of the nuclear spin relaxation rates running via the SC2 mechanism (scalar relaxation of the second kind), we present in this work the results obtained for three bromo compounds: CBrCl3, (CH3)3CBr, and CBr4. A careful separation of saturation-recovery curves, measured for signals of (13)C nuclei at 7.05 and 11.7 T on two components, has provided the longitudinal SC2 relaxation rates of carbon signals in (79)Br and (81)Br containing isotopomers of the investigated compounds. These data have enabled experimental determination of spin-spin coupling constants and relaxation rates of quadrupole bromine nuclei, both types of parameters being hardly accessible by direct measurements. Investigation of the relaxation behavior of these molecules, being of similar size and shape, has provided quite different practical and interpretational problems which are likely to be encountered in relaxation studies of many other carbon-bromine systems. In order to evaluate the quality of the obtained experimental results, advanced theoretical calculations of the indirect (1)J((13)C,(79)Br) coupling constants, magnetic shielding of carbon nuclei, and quadrupole coupling constants of bromines in the investigated compounds have been performed and compared with the experimental values. Relatively small divergences between experiment and theory have been found. The contributions of the relativistic effects to the values of the discussed parameters have been tentatively estimated.

H NMR and C NMR spectra of uracil, thymine, 5-hydroxymethyluracil, 5,6-dihydrouracil, and 5,6-dihydrothymine in DMSO-d solutions have been measured. Additionally, molecular structures as well as NMR parameters of these compounds and their various solvates have been calculated using DFT B3LYP/6-311++G(2d,p) PCM(DMSO) method. The analysis of the chemical shift data for these compounds has shown that, indeed, in DMSO solutions they occur as equilibrium mixtures of free molecules and solvates in which solute and solvent molecules are joined by NH···O or OH···O hydrogen bonds. The populations of particular species present in the solutions have been estimated. Moreover, it has been found that 5,6-dihydrothymine exists in DMSO solution preferentially in conformation with the methyl group occupying the pseudoequatorial position. This finding is based on the molecular energy calculations and remains in full agreement with the interpretation of NMR data and theoretical calculations of NMR parameters.

Continuing studies based on measurements of the nuclear spin relaxation rates running via the SC2 mechanism (scalar relaxation of the second kind), we present in this work the results obtained for three molecules: 9-bromotriptycene, 1,3,5-tribromobenzene, and 1-(2-bromoethynyl)-4-ethynylbenzene in which C-Br bond and one of C-H bonds are collinear. Separation of saturation-recovery or inversion-recovery curves of (13)C NMR signals of bromine-bonded carbons in the investigated compounds on two components has provided the longitudinal SC2 relaxation rates of these carbons in (79)Br- and (81)Br-containing isotopomers. These data have enabled experimental determination of the bromine-carbon spin-spin coupling constants and relaxation rates of quadrupole bromine nuclei, hardly accessible by direct measurements. At the same time the rotational diffusion parameters describing the reorientation of the C-Br vectors have been determined for the investigated molecules on the basis of the dipolar relaxation of protonated carbons. These diffusion parameters are crucial for interpretation of the bromine relaxation rates. The values of the indirect (1)J((13)C,(79)Br) coupling constants, magnetic shielding of carbon nuclei and quadrupole coupling constants of bromines, determined for the investigated compounds, have been compared with the results of the theoretical calculations which take into account relativistic effects. The origin of some divergences between the results obtained by different methods has been discussed.

Orotic acid, a biologically important compound, can exist in aqueous solutions in several ionic and tautomeric forms. Interpretation of the experimental (13)C NMR chemical shifts of this compound based on the results of energy and magnetic shielding calculations performed by DFT B3LYP/6-311++G(2d,p)/PCM method has shown that in water solutions the diketo tautomers are the dominant structural forms of this acid and its anions. For neutral molecules the anti conformation is preferable, monoanion occurs as the conventional carboxylate anion, whereas the orotic dianion exists in two tautomeric forms in the proportion of ca. 4:1. It has been found that the experimental (13)C NMR chemical shifts can be reproduced well by the results of DFT calculations, although for the orotate monoanion some small but characteristic divergences can be noticed. Similar divergences have been also observed for a few other aromatic carboxylates. It seems that the specific solute-solvent interactions occurring in our systems can be the cause of this inconsistency. To support this hypothesis, a simple and effective method of including the specific hydration into the theoretical calculations has been proposed.

The practical utility of the method of retrieving the relaxation rate of a quadrupole nucleus via the scalar relaxation of the second kind (SC2) of an I = 1/2 spin nucleus has been considered once again. The study was motivated by the fact that such data are frequently very useful in investigations of reorientational movements of molecules in solutions. At the same time, the parameters describing spin-spin and quadrupolar couplings, necessary in such studies, have become relatively easily accessible owing to a remarkable progress in theoretical methods. It was shown that even in the case of small N-C coupling constants ((1)J = 7-8 Hz) the classical method of approaching SC2 relaxation effects by measurements of the longitudinal relaxation rates in the rotating frame, although somewhat tedious, can yield acceptably accurate results. The whole procedure has been successfully applied in the investigation of molecular movements of N-methylpyridone (1) and 1,3-dimethyluracil (2) in acetone solution.

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A range of inborn metabolic diseases result in abnormal accumulation of acylglycines in body fluids. Therefore, detection of these metabolites is important for diagnostic purposes. 1 H and 13 C NMR spectroscopies have successfully been applied for both qualitative and quantitative determinations of various acylglycines in urine samples from patients suffering from metabolic diseases connected with excretion of these compounds. Various acylglycines were identified in test urine samples from 15 patients suffering from five different metabolic diseases, providing information which could be crucial for their diagnoses. The paper reports complete 1 H and 13 C NMR data of 11 acylglycines, which is essential for this type of NMR analysis of body fluids. NMR spectroscopy has been proven effective in determining the presence as well as the levels of acylglycines in urine. The proposed method is rapid, simple and requires minimal sample treatment.

The longitudinal relaxation times of (13)C nuclei and NOE enhancement factors for 2-bromopyridine (1), 6-bromo-9-methylpurine (2), 3,5-dibromopyridine (3), 2,4-dibromopyrimidine (4), and 2,4,6-tribromopyrimidine (5) have been measured at 25 °C and B0 = 11.7 T. The most important contributions to the overall relaxation rates of nonbrominated carbons, i.e., the relaxation rates due to the (13)C-(1)H dipolar interactions and the shielding anisotropy mechanism, have been separated out. For 3 and 5, additionally, the T2,Q((14)N) values have been established from (14)N NMR line widths. All of these data have been used to determine rotational diffusion tensors for the investigated molecules. The measured saturation recovery curves of brominated carbons have been decomposed into two components to yield relaxation times, which after proper corrections provided parameters characterizing the scalar relaxation of the second kind for (13)C nuclei of (79)Br- and (81)Br-bonded carbons. These parameters and theoretically calculated quadrupole coupling constants for bromine nuclei have allowed the values of one-bond (13)C-(79)Br spin-spin coupling constants to be calculated. Independently, the coupling constants and magnetic shielding constants of the carbon nuclei have been calculated theoretically using the nonrelativistic and relativistic DFT methods F/6-311++G(2d,p)/PCM and so-ZORA/F/TZ2P/COSMO (F = BHandH or B3LYP), respectively. The agreement between the experimental and theoretical values of these parameters is remarkably dependent on the theoretical method used.