engleski

Protonation of some Supramolecular Compounds Based on Pyridine Subunits

It is a common knowledge that neutral organic bases and superbases possess a number of advantageous properties compared to their inorganic counterparts. They exhibit higher solubility in most organic solvents, low sensitivity to moisture and CO2, and very good stability at low temperatures. Therefore, they can be used in mild chemical conditions [1]. Various structural and electronic motifs have been used in tailoring strong and ultrastrong bases. Molecular suprastructures containing pyridine building fragments are very good candidates for strong and ultrastrong bases, bounding the proton inside the macrocycle in a bifurcated manner [2]. In the present work we considered protonation of macrocyclic systems with three (1, 2) and four (3) pyridine subunits.Gas phase molecular structures and gas phase proton affinities as well as gas phase basicities were calculated by the B3LYP/6-311+G(2df, p)//B3LYP/6-31G(d) method. It is found that supramolecules 1, 2 and 3 have high proton affinities of 290.3 kcal mol-1, 294.4 kcal mol-1 and 284.7 kcal mol-1, respectively, and corresponding superbasicities of 283.5 kcal mol-1, 285, 5 kcal mol-1 and 278.9 kcal mol-1, respectively. The reason behind are strong bifurcated intramolecular bond in conjugate acids. Subsequent calculations on the complexation of small cations and dications reveal some binding principle, which might be useful for understanding cation affinities of biosystems. [1] H. Oediger, F. Möller, K. Eiter, Synthesis 1972, 591- 598. [2] I. Despotović, B. Kovačević, Z. B. Maksić, Org. Lett. 2007, 9, 1101- 1104.

Protonation; Supramolecular Compounds; Pyridine

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