Spontaneous Self-assembly Process Research Articles

A chiral spherical molecular assembly held together by 60 hydrogen bonds

Spontaneous self-assembly processes that lead to discretespherical molecular structures are common in nature. Sphericalviruses1 (such ashepatitis B) and fullerenes2 are well-known examples inwhich non-covalent and covalent forces,respectively, direct the assembly of smaller subunits intolarger superstructures. A common feature of theseshell-like architectures is their ability to encapsulateneutral and/or charged guests whose size, shape and chemicalexteriors complement those of the host's innersurface3,4. Their interiors can often beregarded as a new phase of matter5, capable of controlling the flowof reactants, transients and products, and of catalysingreactions of both chemical and biological relevance. Suchproperties have inspired the recent emergence ofmonomolecular5,6,7 and supramolecular dimeric molecularcapsules8,9, many of which have been basedon the head-to-head alignment of bowl-shapedpolyaromatic macrocycles such as calix[4]arenes5,7,9. But true structural mimicry offrameworks akin to viruses and fullerenes, which are based onthe self-assembly of n > 3 subunits,and where surface curvature is supplied by edge sharing of regularpolygons, has remained elusive. Here we present anexample of such a system: a chiral spherical molecular assemblyheld together by 60 hydrogen bonds (1) (Fig. 1). We demonstrate the ability of 1, which consists of six calix[4]resorcinarenes 2 and eight water molecules, to self-assemble and maintain its structure in apolar media and to encapsulate guest species within a well-defined cavity that possesses an internal volume of about 1,375 A3. Single crystal X-ray analysis shows that its topology resembles that of a spherical virus1 and conforms to the structure of a snub cube, one of the 13 Archimedean solids10.

Synthesis of a Chiral Alkyl-Bridged Bis(catecholamide) Ligand for the Self-Assembly of Enantiomerically Pure Helicates

The chiral bis(catechol) ligand 4 can be synthesized starting with 1,2-bis(2,3-dimethoxyphenyl)ethane (1) and S-1-phenylethyl isocyanate (2). An enantiomerically pure binuclear triple-stranded helicate 5 is formed in a spontaneous self-assembly process from ligand 4 and titanium(IV) ions in the presence of potassium carbonate.

Self-Assembly of a Macrocyclic Dinuclear Pd(II)–Phosphine Complex

Abstract Reaction of a diphosphine ligand, bis[4-[2-(diphenylphosphino)ethyl]phenyl] ether (1) with Na2PdCl4 gave a macrocyclic dinuclear complex [PdCl2(μ-1)]2 (2) in a 58% isolated yield. The formation of 2 appears to result from a spontaneous self-assembly process under thermodynamic control, and thus, no special technique such as a high-dilution method was needed.

Molecular helicity in inorganic complexes: The crystal and molecular structure of 2,6-diacetylpyridine bis(6-chloro-2-pyridylhydrazone) silver(I) hexafluorophosphate dimer

The crystal and molecular structure of the complex [Ag 2L 1 2][PF 6] 2 [L 1 = 2,6- diacetylpyridine bis(6-chloro-2-pyridylhydrazone)] have been determined. The cation is binuclear with each silver in a distorted four-coordinate environment, showing weak interactions with a fifth ligand and with a short Ag—Ag distance of 3.142 Å. The two equivalent ligands are wrapped around the binuclear core in a double-helical array. This is stabilized by π-stacking interactions between parallel pyridyl rings. The double-helical array is generated in a spontaneous self-assembly process which is dictated by the relative acceptor properties of the silver(I) ion and the donor properties of the ligand.

Intermolecular interactions in collagen self-assembly as revealed by Fourier transform infrared spectroscopy.

When a solution of collagen molecules, at neutral pH and moderate ionic strength, is warmed from 4 degrees to 30 degrees C, a spontaneous self-assembly process takes place in which native-type collagen fibers are produced. Events occurring during thermally induced fibrillogenesis process can be monitored, in aqueous media and in real time, by Fourier transform infrared spectroscopic techniques. Tentative assignments of observed spectral bands are given.