Cooperative binding of sodium myristate to amylose

Abstract

The binding of sodium myristate to amylose has been studied by a surface tension method. Surface tensions of myristate solutions were compared with those of systems containing amylose. Slow adsorption of amylose-myristate complex at the air-water interface has rendered possible the use of surface tension for estimating mean activities of sodium myristate in the presence of amylose and the construction of a binding isotherm. Information has also been gained on the "surface activity" of complexes. Comparison of the isotherm with optical rotation studies has revealed that a relatively low level of binding can fully induce a conformational transition in the amylose to a helical state. Moreover, this state remains unaffected by the subsequent binding at free myristate approaching the critical micelle concentration. Optical rotation studies together with measurements of surface activity of the complex provide supportive evidence for more than one type of binding process. A cooperative mode of binding is inferred for low free myristate with selective binding to the helical conformer. The cooperative constants and saturation binding for this mode, estimated on linear Ising theory, conform to a model of interrupted but extensive end-to-end packing of extended myristate molecules in the cavity of an amylose helix with six residues per turn. The secondary binding is also cooperative, reflecting lateral hydrophobic attraction between adsorbed myristate molecules and free energies of binding approaching that of micellization.

Affinity capillary electrophoretic studies of complexation between dextrin oligomers and polyiodides

“…In more general terms, this approach also adds to a series of techniques used previously to probe the amylose conformation in solutions and its versatility to complex with a variety of other molecules: 13 C-NMR spectrometry [13], circular dichroism [14], viscometry [8], calorimetry [15], potentiometry [16], and surface tension measurements [17]. In describing the complexation phenomena between the amylose oligomers and various pharmaceuticals [18], we have recently demonstrated the value of this electrophoretic approach: (i) it provides ªoligomer-specific informationº, for which the bulk measurements are not informative; (ii) capillary zone electrophoresis (CZE) is inherently a sensitive technique, necessitating only minute quantities of studied materials; and (iii) CZE overcomes any potential problems with a limited solubility of amylose and its complexes that may complicate less sensitive bulk measurements.…”

Supramolecular Inclusion Complexation of Amylose with Photoreactive Dyes

“…It is suggested that a cooperative binding is the complexation process between amylose and guest molecules,19,20 implying the possibility of conformational change (induced by guest) in amylose due to the complexation. Some studies of this aspect have been made by surface tension and viscosity measurements of surfactants.18, 20 In this paper, we make a systematic assessment of complexation behavior of amylose with photoreactive dyes having a stilbazolium chromophore, based on spectroscopic studies of UV-vis, fluorescence, and circular dichroism (CD) in various compositions of DMSO-H20 mixtures. Molecules with this chromophore have the largest secondorder polarizabilities21 such that nonlinear optical materials based on this chromophore have been studied in recent years.22,23 A potential benefit of inclusion formation of photoreactive dyes is to induce photo-and thermal stability to the dyes through chemical rigidization and shielding of the guest molecules by host, amylose.24 (15) Ring, S. G.; L'Anson, K. J.; Morris, V. J. Macromolecules 1985, 18, 182.…”

Complexation between Amylodextrin Oligomers and Selected Pharmaceuticals Measured through Capillary Electrophoresis

“…Various methods have been employed to explore the conformation of amylose in aqueous solutions: 13 C NMR, 21,29 circular dichroism, 30 viscosity 18 and potentiometric 27 measurements, calorimetry, 31 spectrophotometry, 17,20 use of a fluorescent probe, 32 and surface tension measurements. 26 While X-ray data have clearly shown amylose featuring strictly helical forms in its crystalline state, 1 the situation in aqueous solutions is somewhat nebulous. The three forms that were suggested 18,20 to describe the conformation of amylose in aqueous solutions include a helix, an extended helix, and a random coil.…”