scholarly journals N.m.r. and molecular-modelling studies of the solution conformation of heparin

1993 ◽  
Vol 293 (3) ◽  
pp. 849-858 ◽  
Author(s):  
B Mulloy ◽  
M J Forster ◽  
C Jones ◽  
D B Davies
Keyword(s):  
Molecular Modelling ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Conformational Energy Calculations ◽  
Molecular Modelling Studies ◽  
Modelling Studies ◽  
Modelling Techniques ◽  
Nuclear Overhauser

The solution conformations of heparin and de-N-sulphated, re-N-acetylated heparin have been determined by a combination of n.m.r. spectroscopic and molecular-modelling techniques. The 1H- and 13C-n.m.r. spectra of these polysaccharides have been assigned. Observed 1H-1H nuclear Overhauser enhancements (n.O.e.s) have been simulated using the program NOEMOL [Forster, Jones and Mulloy (1989) J. Mol. Graph. 7, 196-201] for molecular models derived from conformational-energy calculations; correlation times for the simulations were chosen to fit experimentally determined 13C spin-lattice relaxation times. In order to achieve good agreement between calculated and observed 1H-1H n.O.e.s it was necessary to assume that the reorientational motion of the polysaccharide molecules was not isotropic, but was that of a symmetric top. The resulting model of heparin in solution is similar to that determined in the fibrous state by X-ray-diffraction techniques [Nieduszynski, Gardner and Atkins (1977) Am. Chem. Soc. Symp. Ser. 48, 73-80].

The conformational equilibrium in [13C-1-methyl]-cis-1,4-dimethylcyclohexane

1980 ◽  
Vol 58 (23) ◽  
pp. 2709-2713 ◽  
Author(s):  
Harold Booth ◽  
Jeremy Ramsey Everett
Keyword(s):  
Conformational Equilibrium ◽  
Chemical Shifts ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Nuclear Overhauser ◽  
In Cis ◽  
C Nmr

The conformational equilibrium in [13C-1-methyl]-cis-1,4-dimethylcyclohexane has been assessed by (a) direct integration of signals due to equatorial and axial methyl carbons in the 13C nmr spectrum at 172 K and (b) by measurement of the 13C chemical shifts of C-1 and C-4 in the spectrum at 300 K. It is concluded that a 13C isotope effect on the position of the degenerate equilibrium in cis-1,4-dimethylcyclohexane is either nonexistent, or is too small to be detected by methods of analyses employed. The 13C nmr data incidental to the study (chemical shifts, coupling constants, spin–lattice relaxation times, nuclear Overhauser enhancements, and 1-bond isotope shifts) are recorded for the title compound and its trans-isomer.

Further justification for the exo-anomeric effect. Conformational analysis based on nuclear magnetic resonance spectroscopy of oligosaccharides

1982 ◽  
Vol 60 (1) ◽  
pp. 44-57 ◽  
Author(s):  
Henning Thøgersen ◽  
Raymond U. Lemieux ◽  
Klaus Bock ◽  
Bernd Meyer
Keyword(s):  
Hard Sphere ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Resonance Spectroscopy ◽  
Anomeric Effect ◽  
Spin Lattice ◽  
H Nmr ◽  
Nmr Study ◽  
Nuclear Overhauser

Hard-sphere (HS) calculations predict three conformers for the branched B human blood group antigenic determinant (α LFuc(1 → 2)[α DGal(1 → 3)]βDGal) and two conformers for the linear tetrasaccharide (αLRha(1 → 2)αLRha(1 → 3)αLRha(1 → 3)βDGlcNAc), which constitutes a part of the repeating unit of the Shigellaflexneri O-antigen, which differ in conformational energy by less than 0.7 and 0.2 kcal/mol, respectively. However, a detailed 1H nmr study of specific interunit deshielding effects, quantitative treatment of spin-lattice relaxation times, and nuclear Overhauser enhancements requires that only one of the conformers thus predicted be, in fact, conformationally preferred in solution. These conformers are those predicted by hard-sphere exo-anomeric (HSEA) calculations.

1H–1H internuclear distance measurements in carbohydrates: proton transient nuclear Overhauser enhancement and spin-lattice relaxation in (13C)- and (2H)-substituted compounds

1990 ◽  
Vol 68 (12) ◽  
pp. 2171-2182 ◽  
Author(s):  
Paul C. Kline ◽  
Anthony S. Serianni ◽  
Shaw-Guang Huang ◽  
Michael Hayes ◽  
Robert Barker
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Lattice Relaxation ◽  
Substitution Effects ◽  
Distance Measurements ◽  
Spin Lattice ◽  
Nuclear Overhauser Enhancement ◽  
Nuclear Overhauser

Proton transient nuclear Overhauser enhancement (TnOe) and spin-lattice relaxation times (T1) have been used to evaluate the conformations of several monosaccharides and disaccharides containing (13C) and (2H) substitution. Absolute 1H–1H internuclear distances were determined by TnOe and DESERT (deuterium substitution effects on relaxation times) experiments on conformationally rigid methyl β-D-galactopyranoside and α- and β-D-xyloses, respectively. The DESERT method was extended to examine O-glycoside conformation in two blood-group disaccharides that were prepared enzymically with (13C) and (or) (2H) substitution. Preferred disaccharide conformations deduced from these distance measurements are compared to those determined from 13C–13C and 13C–1H spin coupling constants, theoretical calculations, and crystallographic studies. Keywords: TnOe, DESERT, carbohydrate conformation.

Measurement, employing 1H and 13C spin-lattice relaxation times, of the temperature dependence of the correlation time for rotational reorientation (τR)of diamagnetic transition-metal Bis- and Tris-acetylacetonate complexes

1977 ◽  
Vol 30 (5) ◽  
pp. 943 ◽  
Author(s):  
DM Doddrell ◽  
MR Bendall ◽  
AJ O'Connor ◽  
DT Pegg
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Carbon Nucleus ◽  
Methyl Carbon ◽  
Spin Lattice ◽  
Barrier Energy ◽  
Complex Spin ◽  
Nuclear Overhauser ◽  
Acetyl Acetonate

1H and 13C nuclear relaxation times for the ligand positions of Pd(acac)2 and Co(acac)3 (acac = acetyl-acetonate) have been measured as a function of temperature. Nuclear Overhauser enhancement factors are used to demonstrate that except for the methyl carbon nucleus internuclear dipolar interactions dominate the relaxation times. Consequently TR can be extracted from the data. It is found that TR for a 0.05 M solution in CDCl3 varies with temperature (T) as TR = 3.92x10-13exp(1.38x103/T) (Co) TR = 4.42x10-13exp(1.20x103/T) (Pd) Activation energies for rotational reorientation calculated from the data are found to be 9-10 kJ mol-1 for both complexes. There appears to be a slight concentration dependence of ER, ER being about 12 kJ mol-1 for a 0.2 M solution of the palladium complex. Spin internal reorientation affects the T1 value of the CH3 carbon of Pd(acac)2, with T1 getting shorter as the temperature is raised. A simple single-axis model of rotational reorientation in solution is presented whereby it can be shown that ER is the average barrier energy encountered by a molecule during a single angular reorientation.

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