Synthesis Of Cucurbituril And The Complexation With Benzidine

Cucurbit[n]uril is a novel macrocyclic host with an exceptional capacity to encapsulate other molecules or ions within its hollow core, which was synthesized from acidic condensations of glycoluril with formaldehyde. As a new receptor in supramolecular chemistry it demonstrates molecular recognition with high specificity, better selectivity and easily synthesized than now most recognized hosts such as crown ethers, cyclodextrins and cailxarenes. In the past decade cucurbituril has become a new star molecule with emphasis on the study of host-guest molecular recognition and assembly to supramolecular structure. Based on our study of supramolecular chemistry of cyclodextrins and cailxarenes, we initiated the research cucurbit[n]uril system. In this article, we described the synthesis of several cucurbiturils and their derivatives and the results of complexation of cucurbituril with benzidine, especially complexation of cucurbit[7]uril and benzidine, and the possibility of using CB[7] to treat waste water containing aryl amines.1. Synthesis and Characterization of Cucurbit[n]uril and ItsDerivativesFour cucurbit[n]uril(n=5-8) and decamethylcucurbituril homologue were synthesized by the reactions of formaldehyde with glycoluril, or dimethylglycoluril, which were prepared previously from the reaction of glyoxal, diacetyl with urea. Another cucurbituril derivatives was synthesized by cucurbit[6]uril. All the products have been characterized by IR and ¹H NMR spectrum. The results showed that there three important factors to influence the yield: that is concentration of the acid,concentration of reactant and reaction temperature. Their UV and FU spectrum were determined, in which the maximum absorption of UV is recorded, but fluorescence emission is not been detected.2. Complexation of cucurbituril for benzidineComplexation of cucurbituril and benzidine in the acidic aqueous solution has been studied by using UV and FU spectrum. The recognition effect of the hollow size of cucurbituril for benzidine has been compared, in which CB[7] showed stronger complexation for benzidine, with the depression of the UV absorption and enhancement of fluorescence emission of benzidine remarkably. The effect of other cucurbituril is weak. CB[7] is the best choice to recognize benzidine.3. Recognition study of CB[7] for benzidineComplexation of CB[7] with benzidine is investigated thoroughly in the solution system of 0.2mol/L NaCl and 0.lmol/L HC1. The association constant of CB[7] for benzidine was determined using UV spectrum. According to the experimental results, complexation of CB[7] with benzidine is quite stable. The association constant is 3.45 X 10⁴L/mol in 25 ℃. It has been found that CB[7] can enhance fluorescence intensity remarkably. When the molecular ratio of 5:1, i.e. the concentration of CB[7] is 4X10^-4 mol/L, the fluorescence intensity of benzidine can be increased more than six times. Complexation is also studied with cyclic voltammetry. Finally, the possibility of using CB[7] treating waste water containing aryl amines was analyzed briefly using UV spectrum. The salts such as NaCl KCl MgCl₂ CaCl₂, and temperature influence the complexation. It has been found that excessive salts can decrease the solubility of CB[7] and make benzidine disengage from the cavity of CB[7].