Self-recognition

Fig. 32. Hexameric self-assembled supermolecule involving self-recognition (198).

Fig. 33. Self-recognition in the self-assembly of double helixes (9,200).

A particular point of interest included in these hehcal complexes concerns the chirality. The heUcates obtained from the achiral strands are a racemic mixture of left- and right-handed double heUces (Fig. 34) (202). This special mode of recognition where homochiral supramolecular entities, as a consequence of homochiral self-recognition, result from racemic components is known as optical self-resolution (203). It appears in certain cases from racemic solutions or melts (spontaneous resolution) and is often quoted as one of the possible sources of optical resolution in the biological world. On the other hand, the more commonly found process of heterochiral self-recognition gives rise to a racemic supramolecular assembly of enantio pairs (204). 

The diaminopyridodipyrimidinedione 73 has been synthesised as a cytosine-like Tecton designed for self assembly into a helical superstructure. Self recognition occurs in the solid state <96MI02 96CA(125)221771 >. 

The carboxylic acid functionality is not involved in any significant interaction with the gold substrate but rather dominates the pairing interaction between enantiomers. This three-point bonding of each molecule, Au—S, Au—N, and O—H—O, drives the self-recognition preference for homochiral pairs [58]. 

A more subtle example of homochiral preference, which draws attention to the conformational changes in the molecules needed to achieve self-recognition, is that... 

Ando, T. and Davies, T.F., Self-recognition and the role of fetal microchimerism, Best Pract. Res. Clin. Endocrin. Metab., 18, 197, 2004. 

Platek, S.M., Burch, R.L. and Gallup, G.G. (2001) Sex differences in olfactory self-recognition. Physiol. Behav. 73, 635-640. 

Through conspecific chemical recognition, Liolaemus are able to recognize the sex of the sender, and both conspecific and self-recognition are modulated by sea-... 

Fig. 34.1 Self-recognition in three Liolaemus species. Data of L lemniscatus in conspecific and control treatments come from Labra and Niemeyer (2004)...

It is unknown which compounds are involved in Liolaemus communication. However, information available from the chemical composition of the lipidic fraction of the precloacal secretions suggests that individuals, populations and species can be discriminated by the chemical profile of these secretions (Escobar, Escobar, Labra and Niemeyer 2003 Escobar, Labra and Niemeyer 2001). This, in addition to probable chemical differences in the other sources of chemosignals, may allow individual, population and species recognition (Labra et al. 2001). Based on the individual variation observed in the composition of the secretions of L. bellii (Escobar et al. 2001), it is likely that lizards can achieve self-recognition, and also that they can extract detailed information about sender characteristics, as we have seen for L. monticola (Labra 2006). 

Double helixes, self-recognition in the self- assembly of, 16 803 Double-heterojunction (DH) structures, for LEDs, 22 173, 174, 175 Double heterostructure (DH), 14 844 Double heterostructure laser diodes, 14 700 Double hetero structure OLEDs, 22 216 Double-immunodiffusion technique, 9 753-754... 

A. Garcia Fraile, D. G. Morris, A. Garcia Martinez, S. de la Moya Cerero, K. W. Muir, K. S. Ryder, and E. Teso Vilar. Self recognition and hydrogen bonding by polycyclic bridgehead monoalcohols. Org. Biomol. Chem. 1, 700 704 (2003). 

In principle, mass spectrometry is not suitable to differentiate enantiomers. However, mass spectrometry is able to distinguish between diastereomers and has been applied to stereochemical problems in different areas of chemistry. In the field of chiral cluster chemistry, mass spectrometry, sometimes in combination with chiral chromatography, has been extensively applied to studies of proton- and metal-bound clusters, self-recognition processes, cyclodextrin and crown ethers inclusion complexes, carbohydrate complexes, and others. Several excellent reviews on this topic are nowadays available. A survey of the most relevant examples will be given in this section. Most of the studies was based on ion abundance analysis, often coupled with MIKE and CID ion fragmentation on MS " and FT-ICR mass spectrometric instruments, using Cl, MALDI, FAB, and ESI, and atmospheric pressure ionization (API) methods. 

The same CIMS approach has been used for investigating the self-recognition processes in proton-bound tartrate trimers. The trimer chirality effect is consistent with the heterochiral trimers as more stable than the homochiral ones. The reverse is true when the proton in the proton-bound trimers is replaced by hydronium, ammonium ion, or primary aminium ions. " This changeover is... 

Kramer, R. Lehn, J.-M. Marquis-Rigault, A. Self-recognition in heUcate self-assembly Spontaneous formation of helical metal complexes from mixtures of ligands and metal ions. Proc. Natl. Acad. Sci. USA 1993, 90, 5394-5398. 

Scheme 4.2 Self-recognition within mixtnres of bipyridine-based Cn+ donble helicates.

Scheme 4.5 Enantiomeric self-recognition of ( )-ll is triggered by addition of 12.

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