Molecular recognition of nucleotides by a calix[4]arene derivative with two alkyl guanidinium groups at the air–water interface

Abstract

Monolayers of 5,11,17,23-tetra-tert-butyl-25,27-bis(2-guanidinoethoxy)-26,28-dihydroxy calix[4]arene hydrochloride (BGC) on the surface of pure water and of aqueous subphases containing 5′-AMP⁻ and 5′-GMP²⁻ were studied by film balance measurements and relaxation experiments. LB films deposited from the monolayers on the three kinds of subphases were investigated by ultraviolet visible spectra (UV), circular dichroism spectra (CD), Fourier transform infrared spectra (FT-IR) and X-ray photoelectron spectra (XPS). All the results indicate that BGC can form stable monolayers on these different subphases. Moreover, BGC can effectively bind with 5′-AMP⁻ and 5′-GMP²⁻ dissolved in the subphase by complementary hydrogen bonding and electrostatic interactions in 1∶1 and 2∶1 molar ratios, respectively. Two intermolecular interaction patterns are proposed and the binding constants are estimated to be 1 ± 0.5 × 10⁶ and 6 ± 1 × 10⁵ M⁻¹, respectively.