Self-assembly asymmetrical

In parallel to the emerging interest for asymmetric organocatalysis seen in recent years, the potential development of supramolecular chirality for the construction of asymmetric self-assembling organocatalytic systems is evident. Moreover, the control over the entire space that surrounds a guest allows in theory fine construction of chiral nano-reactors with the ultimate goal of mimicking nature s efficiency and the selectivity observed in enzymes. 

Figure 5.30. Asymmetric self-assembled monolayer used for nonlinear optics...

Messina MT, Metrangolo P, Resnati G (2000) Resolution of racemic perfluorocar-bons through self-assembly driven by donor-acceptor intermolecular recognition. In Ramachandran PV (ed) Asymmetric fluoro-organic chemistry synthesis, applications, and future directions. ACS symposium series 746. American Chemical Society, Washington DC, p 239... 

Fujima, T., Frusawa, H., Minamikawa, H., Ito, K. and Shimizu, T. (2006) Elastic precursor of the transformation from glycolipid nanotube to vesicle, Journal of Physics Condensed Matter, 18, 3089—3096. Kameta, N., Minamikawa, H., Masuda, M., Mizuno, G. and Shimizu, T. (2008) Controllable biomolecule release from self-assembled organic nanotubes with asymmetric surfaces pH and temperature dependence. Soft Matter, 4 (8), 1681-1688. Weiss R.G. and Terech P. (eds.) (2006) Molecular Gels Materials with Self-Assembled Fibrillar Networks, Springer, Dordrecht. 

The self-assembly of a chiral Ti catalyst can be achieved by using the achiral precursor Ti(OPr )4 and two different chiral diol components, (R)-BINOL and (R,R)-TADDOL, in a molar ratio of 1 1 1. The components of less basic (R)-BINOL and the relatively more basic (R,R)-TADDOL assemble with Ti(OPr )4 in a molar ratio of 1 1 1, yielding chiral titanium catalyst 118 in the reaction system. In the asymmetric catalysis of the carbonyl-ene reaction, 118 is not only the most enantioselective catalyst but also the most stable and the exclusively formed species in the reaction system. 

Terpyridine moieties have been introduced as a terminal unit of macromolecules. In a subsequent procedure the two-step self-assembly process based on Rum/Run chemistry was used for polymers end-capped with the 2,2/ 6/,2 -terpyridine ligand. More precisely, the terpyridine-functionalized polymers were complexed with RUCI3 to selectively form a mono-complex. In a further step, this mono-complex was reacted under reducing conditions with other uncomplexed 2,2/ 6/,2/-terpyridine-terminated polymer blocks in order to form an asymmetrical AB ruthenium(II) frzs-complex. 

The self-assembly of block polymers, in the bulk, thin film and solution states, produces uniformly sized nanostructured patterns that are very useful for nanofabrication. Optimal utilization of these nanoscopic patterns requires complete spatial and orientational control of the microdomains. However, the microdomains in the bulk state normally have grain sizes in the submicron range and have random orientations. In block copolymer thin films, the natural domain orientations are generally not desirable for nanofabrication. In particular, for composition-asymmetric cylindrical thin films, experimental... 

Fig. 6 Illustration of surface energy effects on the self-assembly of thin films of volume symmetric diblock copolymer (a). Sections b and c show surface-parallel block domains orientation that occur when one block preferentially wets the substrate. Symmetric wetting (b) occurs when the substrate and free surface favor interactions with one block B, which is more hydrophobic. Asymmetric wetting (c) occurs when blocks A and B are favored by the substrate and free surface, respectively. For some systems, a neutral substrate surface energy, which favors neither block, results in a self-assembled domains oriented perpendicular to the film plane (d). Lo is the equilibrium length-scale of pattern formation in the diblock system...

Crystallization and reactivity in two-dimensional (2D) and 3D crystals provide a simple route for mirror-symmetry breaking. Of particular importance are the processes of the self assembly of non-chiral molecules or a racemate that undergo fast racemization prior to crystallization, into a single crystal or small number of enantiomorphous crystals of the same handedness. Such spontaneous asymmetric transformation processes are particularly efficient in systems where the nucleation of the crystals is a slow event in comparison to the sequential step of crystal growth (Havinga, 1954 Penzien and Schmidt, 1969 Kirstein et al, 2000 Ribo et al 2001 Lauceri et al, 2002 De Feyter et al, 2001). The chiral crystals of quartz, which are composed from non-chiral Si02 molecules is an exemplary system that displays such phenomenon. 

Weis, M., Waloch, C., Seiche, W. and Breit, B. (2006) Self-assembly of bidentate ligands for combinatorial homogeneous catalysis Asymmetric rhodium-catalyzed hydrogenation. J. Am. Chem. Soc.. 128. 4188-4189. 

Do , Do = PAHAt, P(OR)2 Scheme 2.8 Self-assembly of chiral monodentate to chiral bidentate ligands through complementa hydrogen-bonding on the basis of an A-T base pair analogue for combinatorial asymmetric catalysis. 

Figure 8.9 Results of palladium-catalyzed asymmetric allylic alkylation of 1,3-di phenyl al lyl acetate and dimethyl malonate upon applying a ligand library of self-assembled bidentate ligands. The ligands a-i on the x-axis are defined in Figure 8.8. 

J. Am. Chem. Soc., 126. 4494. (i) Takacs, J.M., Chaiseeda, K. and Moteki, S.A. (2006) Rhodium-catalyzed asymmetric hydrogenation using self-assembled chiral bidentate ligands. Pure Appl. Chem., 78, 501. (j) Duckmanton, P.A., Blake, A.J. and Love, f.B. (2005) Palladium and rhodium ureaphosphine complexes Exploring structural and catalytic consequences of anion binding. Inorg. Chem., 44, 7708-7710. 

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