engleski

Shaking Ureido and Carboxylic Hands – Calixarenes Uniting

Covering many application areas such as sensing, extraction, self-assembly, transport, and catalysis, investigations in anion receptor chemistry are very important. Calixarenes functionalized with (thio)urea as hydrogen-bond donating groups can serve as classical anion receptors, but also as building blocks for molecular containers and, more recently, as selective binders and transporters of different biochemically relevant species. Recently, we have prepared two p-tert-butylcalix[4]arene derivatives bearing urea moieties , determined their pKa values and investigated their complexation with several anions (Cl–, HSO4–, H2PO4 –, benzoate, and hydrogen pyrophosphate) in acetonitrile. Macrocycle 2 is better anion binder than 1 due to more urea groups present in its structure and lower pKa values. Complexes of 1:2 and 2:1 stoichiometry (as receptor:anion) were observed with H2PO4 – and hydrogen pyrophosphate, respectively. Compound 1 was also designed as ion-pair receptor, so cooperative effect of binding of Na+ on the complexation of several anions with 1 was thermodynamically quantified. Herein, the thermodynamics of acetate binding with 1 and 2 was characterized using 1H NMR, UV-Vis, and ITC. Relatively high values of stability constants of the corresponding complexes (log β11 > 4) were determined and the formation of 12AcO– complex was detected. These results motivated the research of possible capsule formation between ureido-calix[4]arene derivatives and diacetatocalix[4]arenes via hydrogen bonding between the urea and carboxylate moieties. Indeed, the uniting of the two types of calixarenes into very stable (especially for 2) complexes was observed using the above methods as well as DOSY and conductometry. Tertiary amide groups in carboxylic calix[4]arene 4 lowered the affinity for its handshake with calixarene 2 in comparison to 1.

anion receptors ; calixarene ; calorimetry ; NMR ; spectrophotometry

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