PubMed · 4522450
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D E Dorman. 1973-12-31. Long range C-H coupling in conformational analysis.. https://doi.org/10.1111/j.1749-6632.1973.tb15316.x
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Many common, biologically important polysaccharides contain pyranose rings made of five carbon atoms and one oxygen atom. They occur in a variety of cellular structures, where they are often subjected to considerable tensile stress. The polysaccharides are thought to respond to this stress by elastic deformation, but the underlying molecular rearrangements allowing such a response remain poorly understood. It is typically assumed, however, that the pyranose ring structure is inelastic and locked into a chair-like conformation. Here we describe single-molecule force measurements on individual polysaccharides that identify the pyranose rings as the structural unit controlling the molecule's elasticity. In particular, we find that the enthalpic component of the polymer elasticity of amylose, dextran and pullulan is eliminated once their pyranose rings are cleaved. We interpret these observations as indicating that the elasticity of the three polysaccharides results from a force-induced elongation of the ring structure and a final transition from a chair-like to a boat-like conformation. We expect that the force-induced deformation of pyranose rings reported here plays an important role in accommodating mechanical stresses and modulating ligand binding in biological systems.
A combination of affinity chromatography and chemometrics is demonstrated to provide information on drug analytes and on biomacromolecules forming stationary phases, which is of relevance to molecular pharmacology and to rational drug design. The approach can also be applied to elucidate the molecular mechanism of enantioseparation on natural biopolymer stationary phases. Affinity high-performance liquid chromatographic data, which were determined on silica-based human serum albumin, alpha1-acid glycoprotein, keratin, collagen, melanin and amylose tris(3,5-dimethylphenylcarbamate) stationary phases, are discussed. Quantitative structure-retention relationships (QSRRs) derived for test series of drug analytes are interpreted in terms of structural requirements of specific binding sites on biomacromolecules. A means to quantify the differences in drug-biomacromolecule binding among the members of analyte families is demonstrated based on hydrophobicity and structural descriptors from molecular modeling. Chemometric processing of appropriately designed sets of affinity chromatographic data may increase the speed and efficiency of a search for new drugs, providing at the same time a chance to reduce the number of in vivo screenings. It can also be of help in rational selection of chiral columns for specific analytical separations.
The purpose of this work was to monitor and quantify water transport and dimensional changes occurring in the early stages of hydration in cross-linked amylose (CLA) matrices using image analysis technique. Samples were prepared by direct compression of CLA-6 powder to obtain matrices of 0.17 cm thickness and 1.295 cm in diameter. A surface gel layer was formed quasiinstantaneously. The gel expansion was then constrained and the material continuity caused the outer gel layer to be in a state of biaxial compression and the internal core in a state of biaxial tension. A diffusion front preceded the gel-glass interface even in the early stages of hydration. A delayed stress-release occurred through a radial expansion of the tablet interior. This relaxation coincided with the time at which the axial diffusion fronts met. The dimensional changes had a marked impact on the kinetics of water uptake in CLA-6 tablets in early stages of hydration.