Structures and Encapsulation Motifs of Functional Molecules Probed by Laser Spectroscopic and Theoretical Methods

Ryoji Kusaka,Yoshiya Inokuchi,Takayuki Ebata,Sotiris S Xantheas

doi:10.3390/s100403519

Abstract

We report laser spectroscopic and computational studies of host/guest hydration interactions between functional molecules (hosts) and water (guest) in supersonic jets. The examined hosts include dibenzo-18-crown-6-ether (DB18C6), benzo-18-crown-6-ether (B18C6) and calix[4]arene (C4A). The gaseous complexes between the functional molecular hosts and water are generated under jet-cooled conditions. Various laser spectroscopic methods are applied for these species: the electronic spectra are observed by laser-induced fluorescence (LIF), mass-selected resonance enhanced multiphoton ionization (REMPI) and ultraviolet-ultraviolet hole-burning (UV-UV HB) spectroscopy, whereas the vibrational spectra for each individual species are observed by infrared-ultraviolet double resonance (IR-UV DR) spectroscopy. The obained results are analyzed by first principles electronic structure calculations. We discuss the conformations of the host molecules, the structures of the complexes, and key interactions forming the specific complexes.

Highlights

Crown ethers and calixarenes are known as functional molecules, which can encapsulate various neutral and ionic species within their cavities
DB18C6-(H2O)n complexes, because they do exhibit IR bands of OH stretching vibrations of water molecule(s), which will be described in later section
Water containing complexes of DB18C6, B18C6, and C4A were generated in supersonic jets and their structures determined by various laser spectroscopic methods with the aid of quantum chemical calculations

Summary

Introduction

Crown ethers and calixarenes are known as functional molecules, which can encapsulate various neutral and ionic species within their cavities. They act as host molecules to encapsulate guest species in their cavities through non-covalent interactions, such as hydrogen(H)-bond and/or van der Waals (vdW) forces. One of the important aspects of these host/guest molecular systems is their selectivity in the encapsulation of guest species. There are two important factors controlling the selectivity: the size and the flexibility of the host cavity. If the size of the cavity of the host molecule matches that of the guest species, the host shows an efficient selectivity for the encapsulation of the particular species. The 18-crown-6-ether (18C6) forms an exceptionally stable 1:1 complex with K+ [6,7]

Methods

Results

Conclusion