Determination of volatile organic compounds in materials from polystyrene intended for contact with food: comparison of HS-GS/MS and SPME-GC/MS techniques.

Background: Plastic materials intended for contact with food sometimes exhibit unfavorable organoleptic properties which is related to the presence of volatile organic compounds. These substances not only worsen organoleptic properties, but can be very harmful to humans health. For the sake of consumer safety, it is necessary to control such materials for the content of substances harmful to health, as well as the possibility of their migration to food.

Solvation of Uracil and Its Derivatives by DMSO: A DFT-Supported H NMR and C NMR Study.

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.

Orotic acid in water solution, a DFT and (13)C NMR spectroscopic study.

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.

Interpretation of the longitudinal (13)C nuclear spin relaxation and chemical shift data for five bromoazaheterocycles supported by nonrelativistic and relativistic DFT calculations.

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.

Scalar relaxation of the second kind. A potential source of information on the dynamics of molecular movements. 4. Molecules with collinear C-H and C-Br bonds.

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.

Scalar relaxation of the second kind. A potential source of information on the dynamics of molecular movements. 3. A (13)C nuclear spin relaxation study of CBrX3 (X = Cl, CH3, Br) molecules.

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.

Detection of acylglycines in urine by 1H and 13C NMR for the diagnosis of inborn metabolic diseases.

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.

Scalar relaxation of the second kind: a potential source of information on the dynamics of molecular movements. 1. Investigation of solution reorientation of N-methylpyridone and 1,3-dimethyluracil using measurements of longitudinal relaxation rates in the rotating frame.

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.