Synthesis of molecular Tweezers Based on thiosemi-Carbazide and their Anion Recognition Properties 

Abstract

Two novel molecular receptors based on thiosemicarbazide,compound 3a(1,3-bis(o-tolueneoxoacetylthio-semicarbazideacyl) benzene) and compound 3b(1,3-bis(p-tolueneoxoacetylthio-semicarbazideacyl)benzene),have been designed and synthesized under solid-liquid phase transfer catalysis conditions.The binding properties for anions such as F-,AcO-,Cl-,Br-and I-in DMSO have been examined by UV-Vis and 1H NMR spectroscopy.The results show a high selectivity for F-and AcO-,however,no obvious interaction was found for Cl-,Br-,and I-.The 1H NMR combined with Job curves indicates that a 1∶1 stoichiometry complex is formed between the receptors and the anions through hydrogen bonding interactions.In view of these results,the influences of the number of NH binding points and steric effect on binding properties were discussed.The receptor compound 3b can form much more hydrogen-bonding interactions due to the presence of many NH binding points,with larger association constant(Ks) than that of thiourea receptor.Compared compound 3a with 3b,large steric effect prevent the combination between compound 3a and anions.In terms of F-and AcO-,association constant of compound 3a and 3b followed the same tendency Ks(F-)Ks(AcO-),owing to the better fit of size and shape between the receptors and F-.