The use of arrays of oriented hydrogen bonds to form supramolecular devices
A group of simple amide receptors were synthesised to investigate the effect varying the number/type of hydrogen bond donors or in preorganisation has on host/guest binding abilities. Proton NMR titrations revealed preorganised nitrogen atoms could reduce the size of the binding cleft increasing the selectivity for the smaller anions and binding affinities were increased by the addition of additional hydrogen bond donors, increasing the size of the binding cleft and the presence of sulphonamide groups. A number of receptors were also investigated as colorimetric sensors and visual colour changes were observed with the addition of guest, however further investigations revealed these could be due to deprotonation of the receptor. A fluorescent cation was also synthesised which proton NMR titrations proved had increasing binding affinities. Fluorescence titrations showed the addition of guest increased the fluorescence intensity suggesting it could possibility be used for calculating the concentration of chloride in serum samples. Cyclotrimeric receptors containing three urea/thiourea moieties were successfully synthesised by a one-pot cyclotrimerisation. However they proved to be very insoluble preventing purification and investigations of their binding ability. The presence of TBA nitrate proved to have a templating effect in the synthesis of the thiourea cyclotrimer but not the urea cyclotrimer. A step-wise cyclotrimerisation was not possible due to the lack of solubility of the products from step-one for the urea receptor and step-two for the thiourea. However Proton NMR titrations of these receptors revealed the urea/thiourea hydrogen bond donors formed stronger interactions with anionic guests than the previous amide receptors. Finally a number of substrates containing alkene moieties and bis-urea/thiourea receptors were synthesised in the hope of templating cycloaddition photochemical reactions forcing the formation of head-to-head photodimers. Unfortunately cycloaddition photochemical reactions were unsuccessful due to the lack of solubility of both the receptors and substrates preventing any investigations being carried out.