title: High affinity crown ether complexes in water: thermodynamic analysis, evidence of crystallography and binding of NAD+.
abstract: Improving traditional crown ether to the water-soluble and high binding ability host molecule is critical to our efforts to model or mimic biological supramolecular systems. In this paper, we converted two traditional crown ethers, 1,5-dinaphtho-32-crown-8 and 1,5-dinaphtho-38-crown-10, into the water-soluble tetrasulfonated 1,5-dinaphtho-32-crown-8 and tetrasulfonated 1,5-dinaphtho-38-crown-10, evaluated their complexation with three dicationic bipyridiniums in aqueous solution by microcalorimetric titration, UV-vis, and NMR experiments, and then determined the crystal structures of three tetrasulfonatocrown ether-bipyridinium complexes. The equilibrium association constants of tetrasulfonated 1,5-dinaphtho-32-crown-8 with these bipyridiniums reach up to 10(7) M(-1), while those of tetrasulfonated 1,5-dinaphtho-38-crown-10 are just in the range of 10(5) M(-1) order of magnitude. The thermodynamic data obtained show that the complexation of two tetrasulfonatocrown ethers with dicationic bipyridiniums is absolutely enthalpy-driven in water with an accompanying little entropic gain, and each monocationic pyridinium moiety in guest molecules can provide about -10 to -15 kJ·mol(-1) enthalpy contribution irrespective of the size of ether crowns. Moreover, we also investigated the recognition capability of the two water-soluble crown ethers with NAD(+) and NADH by microcalorimetric titration and NMR experiments, indicating that tetrasulfonated 1,5-dinaphtho-32-crown-8 shows exclusive selectivity to NAD(+). The water-solubility and high affinity of this system as well as the flexible and non-preorganized characteristic of these crown ethers make it suitable to serve as a model for mimicking biological systems.
authors.affiliation: Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People's Republic of China.
authors.forename: Ling
authors.initials: L
authors.lastname: Chen
authors.forename: Heng-Yi
authors.initials: HY
authors.lastname: Zhang
authors.forename: Yu
authors.initials: Y
authors.lastname: Liu
mesh_terms: D043844:Crown Ethers / Q000737:chemistry*; D003461:Crystallography; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009243:NAD / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D012995:Solubility; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D043844:Crown Ethers; D014867:Water; D009243:NAD