Self-assembly of a charge-neutral molecular square

Complexation of cadmium(II) by the ditopic (bis-tridentate) thiocarbazone ligand 1,5-bis(6-methyl-2-pyridylmethylene) thiocarbonohydrazide, H2L1, results in the self-assembly of a charge-neutral 2 x 2 molecular grid, [Cd-4(L-1)(4)], comprising four metals and four ligands in an interlocked cyclic array. The solid-state structure of this tetramer has been established by X-ray crystallography and in solution by H-1 NMR spectroscopy. The presence of lower molecular weight oligomers was identified by both NMR and ESI-MS.

Mechanical properties of interfacial films formed by lysozyme self-assembly at the air-water interface

We present the first characterization of the mechanical properties of lysozyme films formed by self-assembly at the air-water interface using the Cambridge interfacial tensiometer (CIT), an apparatus capable of subjecting protein films to a much higher level of extensional strain than traditional dilatational techniques. CIT analysis, which is insensitive to surface pressure, provides a direct measure of the extensional stress-strain behavior of an interfacial film without the need to assume a mechanical model (e.g., viscoelastic), and without requiring difficult-to-test assumptions regarding low-strain material linearity. This testing method has revealed that the bulk solution pH from which assembly of an interfacial lysozyme film occurs influences the mechanical properties of the film more significantly than is suggested by the observed differences in elastic moduli or surface pressure. We have also identified a previously undescribed pH dependency in the effect of solution ionic strength on the mechanical strength of the lysozyme films formed at the air-water interface. Increasing solution ionic strength was found to increase lysozyme film strength when assembly occurred at pH 7, but it caused a decrease in film strength at pH 11, close to the pI of lysozyme. This result is discussed in terms of the significant contribution made to protein film strength by both electrostatic interactions and the hydrophobic effect. Washout experiments to remove protein from the bulk phase have shown that a small percentage of the interfacially adsorbed lysozyme molecules are reversibly adsorbed. Finally, the washout tests have probed the role played by additional adsorption to the fresh interface formed by the application of a large strain to the lysozyme film and have suggested the movement of reversibly bound lysozyme molecules from a subinterfacial layer to the interface.

Supra-assembly of siliceous vesicles

We report a new approach to produce macroporous (110 nm in diameter) ordered siliceous foams (MOSF) by using block copolymers as templates in the absence of any organic cosolvent. The fine three-dimensional honeycomb structure of MOSF was determined by electron tomography. A formation mechanism of MOSF that spans from the atomic to macroscopic scale is proposed, which involves the cooperative self-assembly of unilamellar vesicles followed by the supra-assembly of vesicles. The fusion of soft vesicles finally leads to MOSF with well-ordered and defined honeycomb structures.