Synthesis and supramolecular properties of molecular tweezers and clips substituted by dendrimer and sulphate groups
Molecular recognition and self-organization are key processes for the construction of high organized molecular systems resulting from the association of two or more molecules. This supramolecules are formed due to weak, but highly specific, intermolecular interactions such as hydrogen bonds, salt bridges, arene-arene interactions as well as the less specific van der Waals interactions or dispersion forces. The main topic of this work has been the synthesis of tweezers and clips soluble in water and study of their supramolecular properties by means of binding experiments with electron-poor guest molecules (e.g. N-methylnicotinamide iodide, Kosower salt, caffeine). In order to achieve water solubility, different substituents in the central spacer unit of those receptors have been used. The use of triethyleneglycol monomethylether-based dendrimer of first generation did not lead to the desired water solubility and the binding properties of these new receptors are comparable to those known receptors substituted by acetoxy groups. The use of polyglycerol dendrimers of high generations (3 or higher) make the molecular clips with naphthalene sidewalls soluble in water, whereas the use of lower generations of this kind of dendrimer only makes the mentioned clips soluble in methanol. The binding properties in methanol of these new glycerol substituted clips are significantly enhanced in comparison to those of the dimethoxy substituted clip, which shows no significant binding properties with any common guest. Finally anionic sulphate groups were successfully attached to molecular clips with both naphthalene and anthracene sidewalls. The new sulphate substituted molecular clips are good soluble in water and, in order to minimize hydrophobic interactions with water molecules, they form very stable self-aggregates in water which has been found to be due to the non-classical hydrophobic effect. The self-aggregation is overruled when a suitable electron-withdrawing guest is added into a clip solution. Especially worth of mention is the supramolecular complex of nicotinamide adenine dinucleotide, NAD+, known cofactor in many enzymatic reactions, with the anthracene sulphate clip. This supramolecule has been studied by means of 1H NMR and fluorescent titrations.