Molecular recognition chiral

The following sections describe examples of the application of these approaches to the study of chiral molecular recognition in thin film systems, using the battery of techniques outlined above. 

Figure 17 shows the 11/A isotherms of racemic and enantiomeric films of the methyl esters of 7V-stearoyl-serine, -alanine, -tryptophan, and -tyrosine on clean water at 25°C. Although there appears to be little difference between the racemic and enantiomeric forms of the alanine surfactants, the N-stearoyl-tyrosine, -serine, and -tryptophan surfactants show clear enantiomeric discrimination in their WjA curves. This chiral molecular recognition is first evidenced in the lift-off areas of the curves for the racemic versus enantiomeric forms of the films (Table 2). As discussed previously, the lift-off area is the average molecular area at which a surface pressure above 0.1 dyn cm -1 is first registered. The packing order differences in these films, and hence their stereochemical differentiation, are apparently maintained throughout the compression/expansion cycles. 

All of the experiments in pure and mixed SSME systems, as well as in the Af-stearoyltyrosine systems, have one common feature, which seems characteristic of chiral molecular recognition in enantiomeric systems and their mixtures enantiomeric discrimination as reflected by monolayer dynamic and equilibrium properties has only been detected when either the racemic or enantiomeric systems have reverted to a tightly packed, presumably quasi-crystalline surface state. Thus far it has not been possible to detect clear enantiomeric discrimination in any fluid or gaseous monolayer state. 

Kondo, T., Oyama, K., and Yoshida, K., Chiral molecular recognition on formation of a metalloanthocyanins a supramolecular metal complex pigment from blue flowers of Salvia patens, Angew. Chem. Int. Ed. Engl, 40, 894, 2001. 

This study clearly demonstrated the enthalpic basis of chiral molecular recognition by molecularly imprinted polymers. 

Over the years, a range of structurally diverse crown ethers has been prepared and fundamental studies has been conducted on them to understand host-guest interactions in solution and the solid state. This has provided the basis for the growth of supramolecular chemistry, and novel applications for crown ethers are now proliferating in several fields of chemistry and biology. In this section, we present a selection of the new trends that have emerged in the literature in the last decade in the field of ion, ion-pair, and chiral molecular recognition. 

Clavier et al. used the amino acid (L)-valine to synthesise a C-chiral imdazolidinium salt for chiral molecular recognition studies [65]. The synthetic route utilises the C-terminus to form an amide. Subsequent reduction to the diamine and ring closure with trimethyl-orthoformate yields the chiral imdazolidinium salt (see Figure 6.25). 

Morihara K, Takiguchi M, Shimada V (1994) Footprint catalysis 11. Molecular footprint cavities imprinted with chiralamines and their chiral molecular recognition. Bull Chem Soc Jpn 67 1078... 

Pirkle,W. H., Pochapsky,T. C. Chiral molecular recognition in small bimolecular systems a spectroscopic investigation into the nature of diastereomeric complexes,/. Am. Chem. Soc., 1987,109, 5975-5982. 

The chiral molecular recognition of neutral molecules has become an important subject in the fields of analytical, biochemical and pharmaceutical technologies. 

Susan, EB, HC John, FL Stephen and R Daniel (1991). Coghlan and Christopher J. Easton. Chiral molecular recognition A 19F nuclear magnetic resonance study of the diastereoisomer inclusion complexes formed between fluorinated amino acid derivatives and a-cyclodextrin in aqueous solution. Journal of the Chemical Society, Faraday Transactions, 87,2699-2703. 

Lahav, M. Kharitonov, A.B. Willner, I. Imprinting of chiral molecular recognition sites in thin Ti02 films associated with field-effect transistors novel functionalized devices for chiroselective and chirospecific analyses. Chem. Eur. J. 2001, 7, 3992-3997. 

The chiral molecular recognition manifested in copper(II) simple and mixed complexes with biofunctional ligands (amino acids, dipepti s, etc..) was found to be strongly dependent on the formation of weak bonds between side chain residues [21,22], as shown in Figure 2. 

Bearing this in mind, we designed and synthesized a number of P-CD derivatives [27-34] which could i) bind copper(II) forming a multisite recognition system ii) show thermodynamic stereoselectivity in copper(II) ternary complexes iii) perform chiral separation of unmodified amino acid enantiomers. Among the monofunctionalized P-CD derivatives, only those functionalized in position 6 with diamines show chiral molecular recognition [29,32,35-37]. On the contrary, the P-CDs both functionalized in position 3 and those where a triamine was attached to the narrower rim of the toroid do not act as chiral receptors. 2-(aminomethyl)pyridine, histamine and NH3 molecules were used to obtain the three isomers of P-CDs (Figure 3), but only the A,BCD-NH2 molecule, coordinated to the copper(II) ion, is seen to have enatioselective effects on aromatic amino acids [38]. 

Matsumura Y, Maki T, Murakami S, Onomura O (2003) Copper ion-induced activation and asymmetric benzoylation of 1,2-diols kinetic chiral molecular recognition. J Am Chem Soc 125 2052... 

Schug, K.A., Lindner, W. (2005) Chiral molecular recognition for the detection and analysis of enantiomers by mass spectrometric methods. J. Sep. ScL, 28,1932-1955. 

Schug, KA., Erycak, P., Maier, N.M., and Lindner, W. (2005) Measurement of solution phase chiral molecular recognition in the gas phase using electrospray ionization — mass spectrometry. Anal. Chem., Tl, 3660-3670. 

A report out of the Jorgensen laboratory further expanded the scope of copper-catalyzed aza-Henry reactions [50]. This report utilized chiral molecular recognition by combination of a chiral Cu(II) Lewis acid and chiral amine bases (organocatalysts) to catalyze the addition of tertiary nitro compounds (169) to an... 

The dipole pairing model is based on the pair formation of molecules in adjacent layers through the dipole-dipole interaction. Because of the experimental observation (2), pairing must be made between like enantiomers, as shown in Figure 9.14 [32]. Otherwise, anticlinic orientation cannot be formed in the racemic compoimds. Therefore, in this model, chiral molecular recognition is required. The pairing may be dynamic and may occur in optically resolved local enantiomeric domains. 

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