Supramolecular trimers, formation

Phthalocyanines and porphyrins are often used as model compounds for the manipulation (guest molecule) of surface-supported supramolecular two-dimensional arrays both in UHV and in solution. Spillmann et al. reported that zinc(II) 5,15-bis(3-cyanophcnyl)-10,20-bis 3,5-di(/c/7-bu(yl )phcnylj porphyrin, 2, molecules predominantly formed a hexagonal pattern by trimer formation, when 0.5-0.7 MLs of 2 was deposited on Ag(l 11) especially, 2 forms a characteristic nanostructure on Ag(l 11) at low coverage [163], As reported by Yokoyama et al., it is suggested that the molecular assembly is driven by both van der Waals and dipole-dipole interactions involving the polar 3-cyanophenyl residues [79], After further deposition of C60... 

A host-guest molecular recognition process of L-tryptophan, with the above various triangular, bowl-shaped Cp Rh-nucleobase/nucleoside/nucleotide cyclic trimer molecular receptors, was also detected in a gas phase by electrospray ionization mass spectrometry.In this case, the supramolecular complex formation was found to occur predominately via non-covalent tt-tt interactions non-covalent hydrophobic forces apparently being weak or nonexistent. Trp-Met-Asp-Phe tetrapeptide with the trimeric-rhodium host [Cp Rh(2 -deoxyadenosine)]3[OTf]3 also formed a host-guest complex in water that is detected in the gas phase. 

Triphenylenes provided with nonionic di(ethylene oxide) side-chains (25f)132 134 or with ionic alkyl chains (25g)135 form supramolecular polymers in water.136 The arene—arene interactions of the aromatic cores allow for the formation of columnar micelles . At low concentrations the columns are relatively short, and the solutions are isotropic. At higher concentrations the longer columns interact and lyotropic mesophases are formed.133 Computer simulations showed that in the isotropic solution the polymerization of the discotics is driven by solute-solute attraction and follows the theory of isodesmic linear aggregation the association constants for dimerization, trimerization, and etc., are equal and the DP of the column thus can easily be tuned by concentration and temperature.137 138 At higher concentrations the sizes of the columns are influenced by their neighbors, the columns align, and the DP rises rapidly. 

Self-assembly through secondary bonds results in the formation of discrete supermoiecules (dimers, trimers, tetramers) or supramolecular polymeric arrays, both in purely inorganic systemsand in organometallic compounds. They are frequently found in derivatives... 

These considerations should be bom in mind when interpreting the self-assembly of numerous molecules which contain both donor and acceptor binding sites, with formation of dimeric, trimeric, or tetrameric supermolecules or polymeric supramolecular arrays. That some chemical classes of compound can exist both as mono-... 

Although trimers are quite rare, a more preferred type of supramolecular association in solvated alkali metal hydrocarbyls is the formation of tetramers in the solid state. Typical examples of cyclic tetramers are the sodium o-xylyl derivative [Na(o-xylyl)(tmeda)]4, 41, and the diphenylmethyl complex [NaCHPh2(tmeda)]4, 42 [41], The tetrameric THF adduct of -butylethynyllithium, 35, forms a heterocubane... 

Supramolecular discotic liquid crystals may be generated via the initial formation of disk-like supermolecules. Thus, the tautomerism-induced self-assembly of three units of the lactam-lactim form of disubstituted derivatives of phthalhydrazide yields a disk-like trimeric supermolecule (Figure 3). Thereafter, these disks self-organize into a thermotropic, columnar discotic mesophase [13]. 

The most used approaches for the construction of multiporphyrin systems are the self-assembly methods. For example, electrostatic assembly is an easy and widely used method based on the interaction of oppositely charged porphyrins for preparation of more complex systems [1-12]. Self-assembly of porphyrins are also possible by coordination of nucleophihc groups to the central metal ion or using compounds having two nucleophihc sites to coordinate two metalloporphyrins [13-22]. These methods have been used not only for the preparation of porphyrin dimers and trimers, but also for the formation of larger supramolecular networks. Despite the apparent simphcity of the preparation methods of multiporphyrin materials by self-assembly, they generally are less stable as compared to covalently bond... 

Similarly P-P, meso-meso, P-P triply linked dimers were obtained by Diederich and CO workers. They showed that such dimers led to weU-organized self-assembled networks on silver surfaces [162, 163]. Similar self-organized networks were observed for hybrid Ceo-triply linked dimer assemblies [162, 163]. Hybrid assemblies between single-walled carbon nanotubes (SWNTs) and triply linked trimers were also investigated and allowed the formation of stable supramolecular carbon nanotubes-porphyrin complexes [164]. 

The distinctive features of the Oosawa mechanism, in particular the large DP of the supramolecular polymer, emerge upon detailed consideration of the model. The formation and the growth of the basic helical nucleus of four units (Fig. 24) is characterized by the fact that the addition of the fourth (and successive) unit(s) involves a larger number of bonds per unit, and a larger binding constant (Kh) relative to the constant K of the linear sequence. Thus, in analogy with Eq. (13), the concentration of incipient helical trimers may be written as... 

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