Organization of the interior of molecular capsules by hydrogen bonding

Abstract

The enclosure of functional entities within a protective boundary is an essential feature of biological systems. On a molecular scale, free-standing capsules with an internal volume sufficiently large to house molecular species have been synthesized and studied for more than a decade. These capsules have been prepared by either covalent synthesis or self-assembly, and the internal volumes have ranged from 200 to 1,500 Å 3 . Although biological systems possess a remarkable degree of order within the protective boundaries, to date only steric constraints have been used to order the guests within molecular capsules. In this article we describe the synthesis and characterization of hexameric molecular capsules held together by hydrogen bonding. These capsules possess internal order of the guests brought about by hydrogen bond donors within, but not used by, the framework of the capsule. The basic building blocks of the hexameric capsules are tetrameric macrocycles related to resorcin[4]arenes and pyrogallol[4]arenes. The former contain four 1,3-dihydroxybenzene rings bridged together by -CHR-units, whereas the latter contain four 1,2,3-trihydroxybenzene rings bridged together. We now report the synthesis of related mixed macrocycles, and the main focus is on the macrocycle composed of three 1,2,3-trihydroxybenzene rings and one 1,3-dihydroxybenzene ring bridged together. The mixed macrocycles self-assemble from a mixture of closely related compounds to form the hexameric capsule with internally ordered guests.

Inner Core Structure Responds to Communication between Nanocapsule Walls

“…[4][5][6][7] Despite keen interest in the self-assembly of simple organic building blocks into molecular containers, there is generally little information on the fate of the encapsulated guest molecules. [8][9][10] Although the confined guest matrix within these molecular containers has been regarded as a new phase of matter, [11] a detailed understanding of the interplay and relative orientations of the constituent guest molecules has, until now, been restricted to a few instances of limited complexity. [12,13] We previously described the self-assembly of the pyrogallol [4]arene building block into a globular hexamer, which is stable even in aqueous media.…”

“…[12,13] We previously described the self-assembly of the pyrogallol [4]arene building block into a globular hexamer, which is stable even in aqueous media. [8,14] To date, only capsules composed of C-isobutylpyrogallol [4]arene [8,14,15] and C-propylpyrogallol [4]arene [16] have been structurally authenticated by X-ray single-crystal structure analysis. In these studies, it was not possible to determine any geometrical information relating to the included guest molecules.…”

“…[8,14,16] The assembly is stabilized by a total of 72 hydrogen bonds, of which 48 are intermolecular (eight intermolecular hydrogen bonds per bound macrocycle). In contrast, the self-assembled capsule consisting of six resorcin [4]arene units and eight water molecules in the form of an Archimedean snub cube, [20] which is capable of housing up to eight benzene molecules, utilizes only 60 hydrogen bonds, of which 36 are intermolecular (only 2.6 intermolecular hydrogen bonds per bound entity).…”

Synthesis and characterization of nanoarchitectures from fatty acid derivatives of 2,6-diaminopyridine and 2-aminopyridine

“…Unlike the carbon nanotubes (CNTs), organic nanotubes have excellent dispersibility in water and incorporate guest substance of over 10 nm in size, such as nucleic acids and proteins [15]. The organic nanotubes can provide suitable hollow cylindrical space for biomacromolecules that are at least 10 times larger in dimension as compared to macrocylic molecules used for host-guest study [16]. Because of the confined nanospace, lipid nanotubes (LNTS) have found potential in chemical and biological applications [17][18][19][20][21][22][23], including controlled drug release [19][20][21][22] and artificial chaperoning of denatured protein [23].…”

Vibrational Spectroscopy of Gas Phase Functional Molecules and Their Complexes Cooled in Supersonic Beams

“…The concept of the supramolecule was first proposed by Jean-Marie Lehn, who succeeded in synthesizing cryptand (Lehn, 1995). In the early stage, many studies have been carried out for host-guest complexes of crown ether (Gokel, 1991;Izatt et al, 1969;Pedersen, 1967;Pedersen & Frensdorff, 1972), calixarene (Atwood et al, 2002;Gutsche, 1998;Purse et al, 2005;Thallapally et al, 2005), and cyclodextrin (Brocos et al, 2010;Szejtli, 1988). These studies are extended to larger size systems built by several units, such as protein, Langmuir-Blodgett (LB) film, self assembled monolayer (SAM), and liquid crystal.…”