Selective complexation of N-alkylpyridinium salts: Binding of NAD+ in water.
A new class of receptor mols. is presented that is highly selective for N-alkylpyridinium ions and electron-poor aroms. Its key feature is the combination of a well pre-organized mol. clip with an electron-rich inner cavity and strategically placed, flanking bis-phosphonate mono-ester anions. This shape and arrangement of binding sites attracts predominantly flat electron-poor aroms. in water, binds them mainly by p-cation, p-p, CH-p, and hydrophobic interactions, and leads to their highly efficient desolvation. NAD+ and NADP, the important cofactors of many redox enzymes, are recognized by the new receptor mol., which embraces the catalytically active nicotinamide site and the adenine unit. Even nucleosides such as adenosine are likewise drawn into the clip's cavity. Complex formation and structures were examd. by one- and two-dimensional NMR spectroscopy, Job plot analyses, and isothermal titrn. micro-calorimetric (ITC) measurements, as well as quantum chem. calcns. of 1H NMR shifts. The new receptor mol. is a promising tool for controlling enzymic oxidn. processes and for DNA chem.
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