Calix[4]pyrrole based scrupulous probe for track on of tryptophan: Host-guest interaction, in silico modeling and molecular docking insights

Abstract

• Novel aromatic calix[4]pyrrole, i.e. ABCP is synthesized by microwave as well as conventional method. • Synthesized ABCP is selective towards tryptophan in comparison to other amino-acids which is very well supported by absorption and computational studies i.e, the host–guest interaction analysis. • Insilico method favors the complexation with Tryptophan via H-bonding and π-π interaction. The natural Bonding Orbital analysis and other molecular properties support the charge transfer from tryptophan to ABCP via n1(O123) → σ*(N11-H61). The TDDFT support the charge transfer from HOMO-17 → LUMO, HOMO-11 → LUMO + 3, HOMO-3 → LUMO, and HOMO → LUMO + 4 transition with 17 nm blue shift. Interaction of a novel calix[4]pyrrole bearing carboxylic acid functionality (ABCP) has been investigated towards amino acids in methanol. The ABCP-Tryptophan complex produces a blue shift in absorption spectra based on charge transfer mediated recognition. Additionally, the density functional theory calculations could substantiate possible mechanism for the 1:1 binding of Tryptophan with ABCP theoretically. Moreover, other parameters such as stability, softness, hardness and chemical potential have been calculated to know about the binding behaviour of ABCP as host and Tryptophan as guest. The Natural Bond Orbital and TDDFT calculation facilitates to understand the proper binding mechanism in reference to experimental results.