Supramolecular complementary components

Kotera M, Lehn JM, Vigneron JP. Design and synthesis of complementary components for the formation of self-assembled supramolecular rigid rods. Tetrahedron 1995 51 1953-1972. 

Self-Organization of Supramolecular Liquid Crystalline Polymers from Complementary Components. If two (or more) complementary units e or 3 are grafted on a template T, mixing Te m with the complementary T3m may lead to the hetero-self-assembly of a linear or cross-linked, main-chain supramolecular copolymer species (Te m, Tsw), whose existence is conditioned by the molecular recognition-directed association between the e and a groups. 

Figure 39 represents schematically such a process in the case of two-site (ditopic) complementary components Te 2 and Ts2. The resulting supramolecular polymeric material ((Te 2, T32) may present liquid-crystalline properties if suitable chains are grafted onto the components. One may note that the mixed site species e Tsrepre-... 

It is reasonable to assume that the complementary units form the expected triply hydrogen bonded pairs, so that the entirely different behaviour of the pure compounds and of the 1 1 mixtures may be attributed to the spontaneous association of the complementary components into a polymolecular entity based on hydrogen bonding. The overall process may then be described as the self-assembly of a supramolecular liquid-crystalline polymer based on molecular recognition (Figure 40). The resulting species (TP2, TU2) is represented schematically by structure 174. 

These results illustrate how extended supramolecular-polymolecular entities build up through molecular recognition directed polyassociation of complementary components. They also show that molecular chirality is transduced into supramolecular helicity, which is expressed at the level of the material on nanometric and micrometric scales, amounting to a sort of size amplification of chirality. 

The mixed sites species TPU would represent a self-complementary component capable of homo-self-assembly into a (TPU) supramolecular entity. 

Triaminopyrimidine and barbituric acid derivatives are complementary components presenting the required features, since they should be able to form two arrays of three hydrogen bonds with each other. However, as pointed out above, based solely on hydrogen bonding recognition, their association could yield either a linear or a macrocyclic supramolecular structure (Section 9.4.2 Figure 37). 

Nonlinear optical (NLO) properties are usually considered to depend on the intrinsic features of the molecule and on the arrangement of a material. An intermediate level of complexity should also be taken into account, that of the formation of well-defined supermolecules, resulting from the association of two or more complementary components held together by a specific array of intermolecular interactions (1). Such intermolecular bonding may yield more or less pronounced NLO effects in a variety of supramolecular species (2). Thus, three levels of nonlinear optical properties may be distinguished the molecule, the supermolecule and the material. The molecular and supramolecular levels involve respectively - intramolecular effects and structures, -... 

Molecular recognition processes rest on selective intermolecular interactions between complementary components. They may affect the properties of the system at the molecular, the supramolecular and the material levels by respectively 1) perturbing the electronic and optical properties of the components 2) generating supramolecular species 3) inducing organization in condensed phase. All three effects are of importance with respect to the NLO properties of the material and its constituents. 

One of the most classic examples of chiral expression in thermotropic liquid crystals is that of the stereospecific formation of helical fibres by di-astereomers of tartaric acid derivatised either with uracil or 2,6-diacylamino pyridine (Fig. 9) [88]. Upon mixing the complementary components, which are not liquid crystals in their pure state, mesophases form which exist over very broad temperature ranges, whose magnitude depend on whether the tartaric acid core is either d, l or meso [89]. Electron microscopy studies of samples deposited from chloroform solutions showed that aggregates formed by combination of the meso compounds gave no discernable texture, while those formed by combinations of the d or l components produced fibres of a determined handedness [90]. The observation of these fibres and their dimensions makes it possible that the structural hypothesis drawn schematically in Fig. 9 is valid. This example shows elegantly the transfer of chirality from the molecular to the supramolecular level in the nanometer to micrometer regime. 

Fig. 7. Formation of main-chain supramolecular polymers by polyassociation of complementary components. R and Rj represent different subunits fitted with recognition groups a variety of such groups may be used. Cross-linking components may also be introduced. The process is instructed, dynamic, and combinatorial.

In the realm of supramolecular synthesis, the construction of rack, ladder, and grid architectures represents a particular case of self-assembly, which relies on the three basic levels of operation of a programmed supramolecular system recognition (selective interaction of complementary components) orientation (building up the stmcture through the con ect spatial disposition of the components) and termination, that is, the formation of the desired discrete supramolecular entity. "... 

In the field of self-assembly of molecular components to generate defined structures which can be used as molecular devices, structural and functional information must be contained at the molecular level. The approach described in 1993 in Lehn s group was to use two complementary components a mesa 5,15-diuracil-substituted porphyrin and an alkyl triaminopyrimidine.- The interaction between the hydrogen-bonded sites of both components led in large part to a bis-porphyrin supramolecular cage structure 6 as evidenced by proton NMR and fluorescence and electrospray mass spectroscopy as well as by vapour phase osmometry (Figure 7). 

Mesophases and liquid crystalline polymers of supramolecular nature have been generated from complementary components, amounting to macroscopic expression of molecular recognition (Figure 3) [23,24]. 

Figure 17 Schematic representation of the formation of side-chain supramolecular polymers from a covalent polymer bearing recognition groups, that bind complementary components, and of the constituting subunits. Dynamic diversity may be generated by scrambling of lateral components containing different residues R.

Figure 6. Formation of supramolecular main-chain polymers by poly association of complementary components.

Figure 10 Schematic representation of (top) a self-assembled rigid rod supramolecular system from two rigid complementary components and (bottom) a self-assembled mixed system from a rigid unit and a complementary flexible one.

Fouquey, C. Lehn, J.-M. Levelut, A.-M. Molecular recognition directed self-assembly of supramolecular liquid crystalline polymers from complementary chiral components. Adv. Mater. 1990, 2, 254-257. 

Gulikkrzywicki T, Fouquey C, Lehn JM. Electron-microscopic study of supramolecular liquid-crystalline polymers formed by molecular-recognition-directed self-assembly from complementary chiral components. Proc Natl Acad Sci USA 1993 90 163-167. 

The photophysical and photochemical features of supramolecular entities form a vast area of investigation into processes occurring at the level of intermolecular organization. They may depend on recognition events and then occur only if the correct selective binding of the complementary active components takes place, as illustrated for a two-component case in Figure 17. 

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