Self cooperative assembly

Gimzewski J K, Modesti S and Schlittler R R 1994 Cooperative self-assembly of Au atoms and Cgg on Au(110) surfaoes Phys Rev. Lett. 72 1036-9... 

The value of EM for a cooperative self-assembled structure provides a measure of the monomer concentration at which trivial polymeric structures start to compete, and therefore EM represents the upper limit of the concentration range within which the cooperative structure is stable (Scheme 2). The lower limit of this range is called the critical self-assembly concentration (csac) and is determined by the stoichiometry of the assembly and the strength of the non-covalent binding interactions weaker interactions and larger numbers of components raise the csac and narrow the stability window of the assembly (8). Theoretical treatments of the thermodynamics of the self-assembly process have been reported by Hunter (8), Sanders (9), and Mandolini (10). The value of EM is lowered by enthalpic contributions associated with... 

The aniline-zinc porphyrin interaction has also been exploited to form dimers. Hunter (60) reported the dimerization of porphyrins functionalized at one meso position with ortho or meta aniline groups (47, 48, Fig. 15). Both compounds showed concentration-dependent H NMR spectra with large upfield shifts for the aniline protons. The dimerization constants are 160 and 1080 M-1 respectively for 47 and 48, and these values are an order of magnitude higher than the association constants of simple reference complexes (K — 10 and 130 M 1 respectively), which is indicative of cooperative self-assembly. The complexa-tion-induced changes in chemical shift were used to obtain three-dimensional structures of the dimers. 

Time-resolved in situ Small Angle Neutron Scattering (SANS) investigations have provided direct experimental evidence for the initial steps in the formation of the SBA-15 mesoporous material, prepared using the non-ionic tri-block copolymer Pluronic 123 and TEOS as silica precursor. Upon time, three steps take place during the cooperative self-assembly of the Pluronic micelles and the silica species. First, the hydrolysis of TEOS is completed, without modifications of the Pluronic spherical micelles. Then, when silica species begin to interact with the micelles, a transformation from spherical to cylindrical micelles takes place before the precipitation of the ordered SBA-15 material. Lastly, the precipitation occurs and hybrid cylindrical micelles assemble into the two-dimensional hexagonal structure of SBA-15. 

Cooperative Self-Assembly into Chiral Columns... 

Taylor, P. N. Anderson, H. L. Cooperative self-assembly of double-strand conjugated porphyrin ladders./. Am. Chem. Soc. 1999,121, 11538-11545. 

Many other examples of outwardly complex molecular structures, whose salient architectural features appear to self-assemble from their constituent building blocks, have been documented [16]. The formation of the DNA double helix from its constituent chains is perhaps the quintessential example, whilst the perfect reconstitution of the intact tobacco mosaic virus from its constituent RNA and protein monomers also exhibits all the hallmarks of a cooperative self-assembly process [17]. The same is true of ribonuclease. Reconstitution of this enzyme in the presence of mercaptoethanol, to allow reversible exchange of the four disulfide bridges, proceeds smoothly to generate eventually only the active conformation from many possible isomeric states [18], In each of these cases, the thermodynamic stability of the product is vital in directing its synthesis. These syntheses could therefore be termed product-directed. 

Formation Mechanism of Mesostructure Liquid-crystal Template and Cooperative Self-assembly... 

However, there are different ways to describe the details of the cooperative self-assembly of the surfactant and the silicate species. The two mechanisms proposed by Davis[61,66] and Stucky[8] are most noteworthy. 

The synthesis of mesoporous silica films typically begins with the preparation of precursor solutions. These solutions contain a silica source (typically an alkoxide, although chloride and colloidal precursors can be used), a surfactant molecule used to template the mesostructure, an acid or base catalyst, and solvents. The nanoscale structure is then formed by a cooperative self-assembly of monomeric or partially... 

The chemistry involved in the formation of mesoporous silica thin films is qualitatively well understood. However, specific reaction mechanisms of the individual steps are still debated. In addition, owing to the complexity of the sol-gel reaction pathways and cooperative self-assembly, full kinetic models have not been developed. From the time of mixing, hydrolysis reactions, condensation reactions, protonation and deprotonation, dynamic exchange with solution nucleophiles, complexation with solution ions and surfactants, and self-assembly, all occur in parallel and are discussed here. Although the sol-gel reactions involved may be acid or base catalyzed, mesoporous silica film formation is carried out under acidic conditions, as silica species are metastable and the relative rates of hydrolysis and condensation reactions lead to interconnected structures as opposed to the stable sols produced at higher pH. Silicon alkoxides are the primary silica source (tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, etc.) and are abbreviated TMOS, TEOS, and TPOS, respectively. Starting from the alkoxide, Si(OR)4, in ROH and H2O solution, some of the general reactions are ... 

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