Proton and multinuclear N.M.R. studies of cyclogentiotetraose peracetate-alkali cation complexation.
Complexation of alkali cation picrates with cyclogentiotetraose peracetate (CGD4Ac) have been studied by 1H-N.M.R. spectroscopy in acetone d6 and nitromethane d3. We determined the stability constants directly from the observed change of the chemical shifts of H-4 and H-6 pro S protons of CGD4Ac at constant ligand concentration with increasing amounts of alkali salt. The stability constants have also been determined by multinuclear n.m.r. spectroscopies, from the observed change of the chemical shifts of Lithium-7, Sodium-23, Potassium-39, Rubidium-87 and Cesium-133 at constant alkali salt concentration with increasing amount of CGD4Ac. The stabilities of the complexes varied in the order Cs+ greater than Rb+ greater than K+ greater than Na+ greater than Li+. The complexation of CGD4Ac with Cs+ induced conformational change, the gg conformer being predominant at the complexed state. In most cases the cationic exchanges between the free and complexed sites were rapid. However in the CsPic-CGD4Ac-Acetone system the exchange was slow enough to observe below 288 K two 133Cs+ resonances.
Bonas
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Centre de Recherches sur les Macromolécules Végétales, Grenoble, France.
Vignon
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MR
D002241:Carbohydrates / Q000737:chemistry; D002412:Cations; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008672:Metals, Alkali / Q000737:chemistry*; D015394:Molecular Structure; D009844:Oligosaccharides / Q000737:chemistry*; D010851:Picrates / Q000737:chemistry*; D011522:Protons; D013816:Thermodynamics
D002241:Carbohydrates; D002412:Cations; D008024:Ligands; D008672:Metals, Alkali; D009844:Oligosaccharides; D010851:Picrates; D011522:Protons; C069626:cyclogentiotetraose peracetate