Biomedical subjects

M J Potrzebowski

Publications and source records attributed to M J Potrzebowski.

9 recordsLinked to original sources

PubMed2005

Distance measurements in disodium ATP hydrates by means of 31P double quantum two-dimensional solid-state NMR spectroscopy.

POST-C7 measurements provide constraints allowing distinguishing crystal lattice organization and establishing intra and/or intermolecular distances between phosphorus atoms of triphosphate chains for different hydrates of disodium ATP salts. Double-quantum efficiency in function of excitation time obtained from series of two-dimensional spectra for POST-C7 experiments was used to set up of buildup curves and semi-quantitative measure of 31P-31P length.

Adenosine Triphosphate↗

PubMed2002

Two-dimensional and variable temperature 31P solid-state NMR studies of single crystals containing symmetrical/unsymmetrical bis[6-O,6-O'-(1,2:3,4-diisopropylidene-alpha-D- galactopyranosyl)thiophosphoryl] dichalcogenides.

The organisation and phase transition of single crystals containing three isostructural bis[6-O,6-O'-(1,2:3,4-diisopropylidene-alpha- D-galactopyranosyl)thiophosphoryl] dichalcogenide derivatives: disulfide 1, diselenide 2 and mixed seleno-sulfide 3, was deduced upon 1D, 2D and variable temperature 31P NMR experiments.

Journal Article↗

PubMed2000

13C high-resolution solid state NMR studies of the structure and dynamics of 1,6:3,4-dianhydro-2-O-tosyl-beta-D-galactopyranose.

13C CP/MAS, dipolar dephasing MAS and theoretical GIAO calculations were employed to assign 13C resonances to the molecular structure of 1,6:3,4-dianhydro-2-O-tosyl-beta-D-galactopyranose 1. From spinning sideband intensities, employing the graphical method of Herzfeld and Berger the 13C delta(ii) parameters for aromatic residue were calculated. The experimental data were compared with computed results obtained by means of the B3PW91 hybrid method and 6-311G (df, p) basis set. The X-ray geometry of 1 with the correlated position of hydrogen atoms was taken as input data for theoretical calculations. As concluded from Cambridge Crystallographic Database (CSD) search, there are two reports describing the X-ray studies of 1 that show the slightly different geometry of the compound under investigation. This work shows that such discrepancies in geometry can generate differences between computed 13C delta(ii) parameters up to 6 ppm. 13C T1 and 1H T1rho relaxation times reveal that 1 is very rigid in crystal lattice. This structure is characterized by extremely long 1H T1rho, found to be in range ca. 200 ms.

Carbohydrate Conformation↗

PubMed2000

X-ray and 13C solid-state NMR studies of N-benzoyl-phenylalanine.

A crystalline sample of N-benzoyl-DL-phenylalanine 1 and a polycrystalline sample of N-benzoyl-L-phenylalanine 2 were studied using 13C high-resolution solid-state NMR spectroscopy. The X-ray structure of the DL form was established. Sample 1 crystallizes in a monoclinic form with a P21/c space group, a=11.338(1) A, b=9.185(1) A, c=14.096(2) A, beta=107.53(3) degrees, V=1400(3) A3, Z=4 and R=0.053. The principal elements of the 13C chemical shift tensors deltaii for 1 and 2, selectively 13C (99%) labeled at the carboxyl groups were calculated. On the basis of 13C (delta)ii analysis the hydrogen bonding pattern for sample 2 was deduced. Enriched samples were used to establish the intermolecular distance between chemically equivalent nuclei for 1 and spatial proximity in heterogeneous domain for 2, employing the ODESSA pulse sequence. The consistence of the complementary approach covering X-ray data, analysis of the 13C (delta)ii parameters and ODESSA results is revealed.

Carbon Isotopes↗

PubMed1998

Comment to 13C-NMR studies of alpha and gamma polymorphs of glycine.

Glycine provided to research laboratories by chemical companies can contain different polymorphs and/or mixture of polymorphs. The alpha- and gamma-glycine differ slightly in 13C shielding parameters and very much in dynamic properties. The isotropic values of chemical shifts for carboxyl groups of alpha- and gamma-glycine are found to be delta(iso) = 176.50 ppm and delta(iso) = 174.60 ppm, respectively. By using cross-polarization contact time equal to 20 ms, the intensity of carboxyl signal arising from gamma-glycine is reduced almost to zero, while that of alpha-glycine is only slightly depleted compared to the intensity of signal recorded at contact time of 1 ms. In contrast, for alpha-form, the 13C T1 relaxation time of carboxyl carbon is five times shorter compared to gamma-form.

Glycine↗

PubMed1998

X-ray and high resolution selenium-77 solid state NMR spectroscopy as complementary probes to structural studies of organophosphorus diselenides.

77Se high resolution solid state NMR spectroscopy was employed to study structural properties of bis(diisopropoxyphosphorothioyl) diselenide 1 and bis(dineopentoxyphosphorothioyl) diselenide 2. The principal elements Tii of 77Se effective dipolar/chemical shift tensor were calculated from spinning sideband intensities employing the WIN-MAS program. The values of anisotropy and asymmetry parameters reflect the distortion of the selenium environment. It was found that the T33 component mostly contributes to changes in the isotropic chemical shifts. 77Se CP/MAS experiments were used to decide the assignment of space group by counting the number of crystallographically unique selenium centers in the unit cell. Crystals of diselenide 1 are triclinic, space group P1 with a = 8.485(3) A, b = 8.508(1) A, c = 8.511(2) A, alpha = 98.835(15) degrees, beta = 111.653(24) degrees, gamma = 93.524(21) degrees, V = 559.5(3) A3, Dc = 1.544(2) g/cm3 and Z = 1. Refinement using 2222 reflections for 157 variables gives R = 0.037. Crystals of diselenide 2 are triclinic, space group P1 with a = 9.1418(8) A, b = 9.1465(8) A, c = 9.9200(9) A, alpha = 74.751(8) degrees, beta = 74.629(7) degrees, gamma = 82.216(7) degrees, V = 769.7(1) A3, Dc = 1.365(2) g/cm3 and Z = 1. Refinement using 3316 reflections for 297 variables gives R = 0.0272.

Humans↗

PubMed1998

Anisotropy of chemical shift and J coupling for P-31 and Se-77 in trimethyl and triphenyl phosphine selenides.

The 31P and 77Se magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments for selenium-77 enriched (70%) trimethylphosphine selenide 1 and triphenylphosphine selenide 2 were carried out in order to determine the nuclear magnetic shielding tensors of both nuclei and to establish values of the phosphorus-selenium indirect spin-spin coupling anisotropy delta J. The m = +1/2 and m = -1/2 subspectra were analysed by the dipolar-splitting-ratio method of Eichele and Wasylischen. For the C(S) molecule 1, delta J was obtained to be +640 +/- 260 Hz from the 31P spectrum and +550 +/- 140 Hz from the 77Se spectrum. Density functional theory (DFT) calculations give a delta J value of about +705 Hz. The value of delta J could not be determined unambiguously by analysis of the 31P spectra for the C1 molecules 2; nevertheless, an estimation of delta J was possible. The principal axis 3 of the phosphorus shielding tensor was determined to be nearly parallel to the PSe bond in 1 and 2. For the selenium shielding of 1, the same orientation was found, whereas in 2, the principal axis 2 of the selenium shielding was found to be oriented nearly along the PSe bond. The experimentally determined phosphorus nuclear magnetic shielding tensors agree well with those calculated by the IGLO method. For those two principal values of the selenium-shielding tensors corresponding to directions nearly perpendicular to the SeP bond, the agreement between calculated and experimental values is satisfactory. For the third one, corresponding to the principal axis close to the SeP bond, the calculated deshielding contributions are distinctly too small for both compounds investigated. Trends observed for the calculated molecular orbital (MO) contributions to the shielding as well as possible reasons for the underestimation of the deshielding contributions along the SeP bond are discussed.

Anisotropy↗

PubMed1994

31P and 15N solid-state nuclear magnetic resonance spectroscopic study of some monophospha-lambda 5-azenes.

31P Cross-polarization magic-angle spinning nuclear magnetic resonance (CP-MAS NMR) spectra of eight monophospha-lambda 5-azenes were measured at room temperature. Three of these compounds, with 2-OH substituents, are in principle capable of taking part in the equilibrium process. However, only the open form, tautomer A, is found in the present study. 15N CP-MAS NMR spectra support the results. The most shielded component of the 31P chemical shift tensor lies in the direction of the P = N bond.

Azo Compounds↗

PubMedDate not supplied

Nucleophilic N1-->N3 rearrangement of 5'-O-trityl-O2,3'-cycloanhydrothymidine.

5'-O-Trityl-O2,3'-cycloanhydrothymidine (1) heated at 150 degrees C in the presence of O,O-diethyl phosphate or O,O-diethyl phosphorothioate anions undergoes rearrangement into N3-isomer (2); its structure was established by both advanced NMR methods and X-ray crystallographic studies. The most probable mechanism of 1-->2 rearrangement relies upon reversibility of glycosidic bond cleavage process.

Crystallography, X-Ray↗