Molecular recognition in aqueous solution: Supramolecular complexation and catalysis

Abstract

One of the ways to study molecular recognition involves the use of designed polymolecular entities ("supramolecular complexes") and assemblies formed between two or more chemical species and held together by intermolecular forces, i.e., the noncovalent bonds (I). This fascinating and dynamic research area is recognized worldwide as an important intellectual and technological frontier in chemistry. For more than 150 years, organic chemists were predominantly concerned with the nature of the covalent bond in organic molecules. Today, the nature of the noncovalent bond has advanced to the center of interest in organic chemistry. For their pioneering studies in molecular recognition, Charles J. Pedersen, Jean-Marie Lehn, and Donald J. Cram were awarded the 1987 Nobel Prize in Chemistry (13).Biochemical phenomena have provided inspiration for much of the current work in chemical molecular recognition. The fascinating properties of enzymes, antibodies, membranes and their receptors, carriers, and channels rest on the controlled and efficient use of weak intermolecular interactions. Selective recognition and material transport, high catalytic activity, the fast conductance of electrical impulses from the brain to the nerve terminals, or replicationprocesses all rely on the reversible formation of complexes and assemblies held together by noncovalent bonding.Studies of recognition and catalysis in designed supramolecular complexes may provide answers on a microscopic level to important open questions in biological sciences. However, the maior motivation for these investigations is the strong desirero generate a full understandini of weak noncovalen~ interactions in ground state and transition stace com~lexes. With such understandine. we shall not onlv he ahleato design synthetic systems with-fascinating prope;ties observed in natural svstems hut also to create novel oreanic chemistry of great interest to both academia and ind&ry. New molecular electronic devices for information and energy storage and transfer, new generations of homogeneous solution catalysts, receptors, and molecular sensors with unprecedented sensitivity, new separation techniques, new polymers and mesophases with fascinating electro-optical properties, and new tools for the mapping of the human genom and for investigating the origin of protein folding are only a few examples for the technological perspectives generated by the fundamental research in molecular recognition.During the past decade, cyclophanes with apolar cavities have been increasingly recognized as a versatile class of synthetic receptors for supramolecular complexation and catalysis (4-16). This account on cyclophane research from our laboratories outlines the basic design criteria for this major class of synthetic receptors ("hosts"). Their potential for forming specific and strong inclusion complexes with ueutral oreanic substrates Yeuests") both in aoueous and organic colutions is demonstrated. he progress in the development of opticallv active cvclo~hane hosts for chiral molecmade...

Synthesis and Characterization of the Inclusion Complex of Dicationic Ionic Liquid and β-Cyclodextrin

“…Inclusion complexes (ICs), particularly those leading to supramolecular self-assemblies, have been attracting much attention as they serve as models for understanding molecular recognition and as precursors for designing novel nanomaterials for electronics and biological applications [ 1 – 4 ]. An example of supramolecular self-assembly is host-guest inclusion complexes made of cyclodextrins (CDs) and guest molecules.…”

Photoinduced electron transfer reactions oftrans-stilbene surfactants in Langmuir-Blodgett assemblies and phospholipid bilayers

“…For bis(6S4E) PC and (4S6E, 4S4~) PC, the spectra resemble those of the same PC's in diluted aqueous solutions with DPPC as the "host." The results with the bis(4S6E) the "H" aggregate or dimer is evidently closely related to apolar association of other aromatic chromophores in aqueous media (Dewey et al 1978;Diederich 1990;Smithrud et al 1990) and may exert important control over the type of assembly formed by these aromatic-functionalized amphiphiles. While the "H" aggregate clearly represents an energy minimum or at least a favored aggregate, our studies with the phospholipids, and to some extent the LB assemblies, suggest that packing forces can in some cases lead to the formation of different aggregates having quite different photophysical properties which may be of interest in tuning the behavior of extended arrays of these chromophores.…”

On the dimerization of unsubstituted α,ω-diphenylpolyenes at low concentrations in inert solvents

“…The highly complex forces governing the establishment of supramolecular assemblies make the painstaking work of Whitten and coworkers toward elucidating the photophysics behind the aggregation of α,ω‐diphenylpolyenes (DPPs) in surfactant assemblies worth especial praise. These authors examined the UV–Vis spectral properties of multilayered fatty acid derivatives of the DPPs t ‐stilbene, diphenylbutadiene ( DPB ), and diphenylhexatriene ( DPH ), constructed by using the Langmuir–Blodgett technique, and ascribed the spectral properties of the derivatives to “H” aggregates.…”