Using Low-Field NMR To Infer the Physical Properties of Glassy Oligosaccharide/Water Mixtures (original) (raw)
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Journal of Magnetic Resonance, 2004
A series of mathematical functions has been used to fit the proton free-induction decays (FIDs) of concentrated carbohydratewater samples. For the solid protons, these functions included a sinc function, as well as the Fourier transforms of single and multiple Pake functions multiplied by a Gaussian broadening. The NMR signal from the mobile protons is described by an exponential function. It is found that in most cases the sinc function gives a satisfactory result and provides valuable information about the second moment M 2 and the ratio of solid to mobile protons (f s =f m ). A good indication for using the sinc function is the presence of a beat in the FID. For high temperatures this approach breaks down, and a biexponential fit is more appropriate. If a clear dipolar splitting is observable in the NMR spectra, the Pake function (or a multiple Pake fit) should be used. In this case information about M 2 and f s =f m can also be obtained.
2003
A 2D-HSQC-carbon selective/proton selective-constant time COSY, 2D-HSQC-(sel C, sel H)-CT COSY experiment, which is applicable to uniformly 13 C isotopically enriched samples (U-13 C) of oligosaccharides or oligonucleotides is proposed for the measurement of proton-proton RDC in crowded regions of 2D-spectra. In addition, a heteronuclear constant time-COSY experiment, 13 C-13 C CT-COSY, is proposed for the measurement of one bond carbon-carbon RDC in these molecules. These two methods provide an extension, to U-13 C molecules, of the original homonuclear constant time-COSY experiment proposed by for saccharides. The combination of a number of these RDC with NOE data may provide the method of choice to study oligosaccharide conformation in the free and receptor-bound state.
1H NMR relaxation studies of protein–polysaccharide mixtures
International Journal of Biological Macromolecules, 2008
NMR water proton relaxation was used to characterize the structure of plant proteins and plant protein-polysaccharide mixtures in aqueous solutions. The method is based on the mobility determination of the water molecules in the biopolymer environment in solutions through relaxation time measurements. Differences of conformation between pea globulin and alpha gliadin seem to control the water molecules mobility in their environment. As deduced from the study of complexes, the electrostatic interactions may also play a major role in the water molecule motions. The phase separation induced under specific conditions seems to promote the translational diffusion of structured water molecules whereas the rotational motion was more restricted.
Carbohydrate Research, 1999
Relatively few details are known about the conformational preferences of hydroxyl groups in carbohydrates in water solution, though these would be informative about solvation and H-bonding. We show that highly concentrated solutions of sucrose and trehalose exhibit surprisingly well-resolved 1 H NMR spectra in a deuterium oxide -water solvent mixture at subzero temperatures. Measurement conditions are suitable to extract nearly all homonuclear and, for the first time, heteronuclear coupling constants of OH groups of carbohydrates in their natural abundance. For 2,3 J HO,C coupling constants new, powerful variants of HETLOC and HECADE techniques were applied. The present data do not support the presence of persistent H-bonds in these two cryogenic disaccharides.
NMR analysis of carbohydrates with model-free spectral densities: the dispersion range revisited
Glycoconjugate journal, 1997
Over the past decade molecular mechanics and molecular dynamics studies have demonstrated considerable flexibility for carbohydrates. In order to interpret the corresponding NMR parameters, which correspond to a time-averaged or 'virtual' conformer, it is necessary to simulate the experimental data using the averaged geometrical representation obtained with molecular modelling methods. This structural information can be transformed into theoretical NMR data using empirical Karplus-type equations for the scalar coupling constants and the appropriate formalism for the relaxation parameters. In the case of relaxation data, the 'model-free' spectral densities have been widely used in order to account for the internal motions in sugars. Several studies have been conducted with truncated model-free spectral densities based on the assumption that internal motion is very fast with respect to overall tumbling. In this report we present experimental and theoretical evidence th...
Magnetic Resonance in Chemistry, 1998
The tetrasaccharide lacto-N-neotetraose b-D-Galp-(1 ] 4)-b-D-GlcpNAc-(1 ] 3)-b-D-Galp-(1 ] 4)-D-Glcp was dissolved in a dilute mixture of dimyristoyl-and dihexanoylphosphatidylcholine in deuterium oxide and 1J(C,H) spinÈspin coupling constants were measured in an isotropic solution at 25 ¡C. On raising the temperature to 38 ¡C, an ordering of the system occurs which permits determination of dipolar couplings. An energy minimized molecular mechanics model was generated showing that the molecule is anisotropic and can be treated as a cylinder. A Ðt of the expression for the carbonÈproton dipolar couplings in a uniaxial molecule in a uniaxial liquid crystal revealed good agreement with experimental data, emphasizing the future potential of the method in studies of carbohydrate conformation.
NMR analysis of compositional heterogeneity in polysaccharides
Pure and Applied Chemistry, 2017
Many copolysaccharides are compositionally heterogeneous, and the composition determined by the usual analytical or spectroscopic methods provides only an average value. For some polysaccharides, the NMR data contain copolymer sequence information, such as diad, triad, and tetrad sequence intensities. In such cases, it is possible to estimate the extent of compositional heterogeneity through NMR. Two general types of methodologies can be used: perturbed Markovian and discrete component approaches. The theoretical bases for these approaches are reviewed in this work, and three examples are shown of the application of these NMR methodologies to copolysaccharides.