Deuterium NMR as a structural probe for micelle-associated carbohydrates: D-mannose.

Abstract

Residual quadrupole splittings for deuterons on perdeuterated a-and (3-D-mannose oriented in a potassium laurate liquid crystal have been measured. Multiple quantum two-dimensional NMR spectroscopy at high magnetic field is used to gain sufficient resolution to assign splittings to specific sites within these molecules. The assigned splittings are interpreted in terms of molecular geometries and preferred orientations of the molecules relative to the surface of the potassium laurate micelles that make up the liquid crystalline phase.The three-dimensional structures of complex carbohydrates and constituent sugars have become a topic of considerable interest over the last several years. It is now recognized that these molecules play central roles in cellular biology as structural components, as protective layers, as cell surface receptors, and as antigenic determinants (1, 2). Yet these molecules are among the least well characterized of biological macromolecules. Recent advances in high-resolution NMR, mass spectrometry, and diffraction studies (2-6) are providing new primary and secondary structural features, but progress toward an understanding of long-range folding in solution or the nature of membrane surface interactions is slow. Improved analytical methods capable of providing such information would be extremely valuable.Deuterium NMR has shown substantial promise as a probe of structural properties of both large and small molecules. This derives from the fact that this spin one nucleus displays both magnetic field-nuclear magnetic moment interactions and electric field gradient-nuclear quadrupole moment interactions. The former are defined in the laboratory frame by the application of a magnetic field. The latter are defined in the molecular frame by the distribution of electrons in chemical bonds, for example, a deuterium-carbon bond. In ordered systems, the manner in which the two interactions combine depends on the orientation of the bond relative to a molecular frame and on an order parameter matrix describing ordering of the molecule relative to the magnetic field. The interactions lead to two observable transitions for each site. At high field, for an axially symmetric bond in an axially ordered system, these transitions are split by 3e2qQ AVQ = 4h (1 -3 cos2)Sz. [1] e2qQ/h is a constant for a given bond type (170 kHz for deuterium bound to aliphatic carbons), 6 is the angle between the bond and averaging axis, and Sz is an order parameter (7). It is clear that information concerning orientation of molecular bonds or molecular order can be extracted from observation of deuterium spectra.Most applications of deuterium spectroscopy to date have used a known molecular geometry to extract order parameters. In a few liquid crystal studies, molecular geometries have been deduced (8)(9)(10)(11) Approximately 15 mg of mannose in 0.04 ml of H20 was added to 1.5 ml of this phase. The sample in a 10 mm NMR tube was placed in an 11.7-T superconducting magnet and allowed to equilibrate at 318 K for -1 hr...

Molecular Conformations in the Pentasaccharide LNF-1 Derived from NMR Spectroscopy and Molecular Dynamics Simulations

“…Already during the 1980s, Prestegard and co-workers were exploring orientational and conformational preferences of mono- and disaccharides in membranelike environments using either potassium laurate micelle systems or the more bilayerlike cesium perfluorooctanoate micelles. − In particular, NMR deuterium quadrupolar splittings of labeled carbohydrates were used to interpret experimental observations; both molecular orientation and conformation were adjusted in the search procedure. For organic molecules in general and carbohydrates in particular, RDCs are a source of additional NMR observables that add knowledge about various conformational processes occurring in solution. − …”

Protein Backbone 15N Relaxation Rates as a Tool for the Diagnosis of Structure Quality

“…This has been successfully achieved using liquid crystals formed by bicelles (2), bacteriophages (9, 10), or purple membranes (11) as the orienting medium. Although the mechanism of molecular alignment in the liquid crystal solutions is still under debate, it has been proposed that, in the case of micelles and neutral bicelles, the alignment force can be of steric origin (12,13). Other types of mechanism cannot be ruled out, since there is evidence of the influence of electrostatic interactions when using charged bicelles (14).…”

Preparation and structural characterization of poly-mannose synthesized by phosphoric acid catalyzation under microwave irradiation

“…74, 4.93, 5.08, 5.15, 5.19, and 5.26 ppm, respectively. Therefore, the H-1/C-1 signal at 4.74/103.0 ppm indicated that the residues should be assigned to (1 → 3)-linked ␤-d-mannopyranosyl (Patra et al, 2013;Prestegard, Miner, & Tyrell, 1983). However, the anomeric chemical shifts of H-1/C-1 at 5.08/104.6, 5.15/104.8, and 5.19/96.6 ppm should be assigned to (1 → 3)-linked ␣-d-mannopyranose residues (Cui, 2005;Ližičárová, Matulová, Machová, & Capek, 2007;Takahashi, Kudoh, Okawa, & Shibata, 2012).…”