Heterochiral recognition

Schematic representation of [Ru(phen)3] (4.4) showing Ti-stacking interactions between bidentate phenanthroline ligands, giving rise to dimers in solution. 

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We have published a theoretical study of peptide model dimers in what homo-vs. heterochiral recognition is concerned for For-Gly-NH2, For-Ala-NH2, and four of their fluoro substituted derivatives using DFT methods (B3LYP/6-31+G and B3LYP/6-311+G ) [27]. This is related to the work of Kojo and Tanaka [129], and Kojo et al. [130] that experimentally studies the cocrystallization of asparagine with other aminoacid. 

VI. Interlude. Molecular clips Capable of Enantiomeric Self-Recognition, Heterochiral Recognition, and Self-Sorting... 

Gut. D. Rudi, A. Kopilov, J. Goldberg. I. Kol. M. Pairing of propellers Dimerization of octahedral ruthe-nium(II) and osmium(II) complexes of eilatin via n-n stacking featuring heterochiral recognition. J. Am. Chem. 

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). 

J. Paul, I. Hearn, and B. J. Howard, Chiral recognition in a single molecule A study of homo and heterochiral butan 2,3, diol by Fourier transform microwave spectroscopy. Mol. Phys. 105, 825 839 (2007). 

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... 

The neutral, homochiral complex (SS,SS-9) is formed by stirring two equivalents of (4S,4, S)-7 with Zn(OAc)2 (Figure 9.5). Zn(OAc)2 serves a dual role in the readion, simultaneously delivering the metal center and the required base. When a racemic mixture of box ligands [i.e., one equivalent each of (4S,4 S)-7 and (4R,4 R)-7] is combined with Zn(OAc)2, three complexes could form, the homochiral complexes SS,SS)- and RR,RR)-9 (i.e., chiral self-recognition) and the heterochiral complex SS,RR)- (i.e., chiral self-discrimination). The tetrahedral coordination geometry strongly favors self-discrimination only the heterochiral complex SS,RR)- is... 

To simplify the problem, let us consider the case of self-recognition (homo vs. heterochiral) why is it so difficult to predict (or explain) the sign of the interaction The stability of the complex is the sum of a series of terms relating both enantiomers steric, electronic, and orbital effects. These effects are transmitted either through... 

Only two articles considered the effect of solvation on the chiral recognition. The first one, already discussed in the previous section, checks the effect of water as solvent in the relative stability of a dimer of a-aminoalcohols [32]. While in the gas phase, one of the heterochiral dimers is always the more stable one, the inclusion of the water solvation effect provides, as the most stable configuration, a homochiral one in three of the four systems studied. 

From the abundance ratio, the enantiodifferentiation energy of the clusters is obtained, having found seven cases in which the heterochiral complexes are more stable than the corresponding homochiral, while only four cases of the homochiral complex are more stable. A chiral recognition of between —1.8 kJ mol-1 and +2.3 kJ mol 1 has been found depending on the metallic center. 

A theoretical study of the chiral recognition of the bis(amino(phenyl)methanol) chromium(O) complexes and chiral discrimination of the dimers of amino(phenyl) methanol linked by HB has been carried out by means of a DFT method, the B3LYP/6-31+G. The results (Fig. 3.24) show that in the chromium complexes, the homochiral one is preferred over the heterochiral one, while the opposite... 

Z. Su et al., Chiral self-recognition Direct spectroscopic detection of the homochiral and heterochiral dimers of propylene oxide in the gas phase. J. Am. Chem. Soc. 128, 17126-17131 (2006)... 

As observed for the molecular clips reported above, the chiral scaffold is pivotal in promoting homo- or heterochiral self-discrimination. Amide hydrogen bonds were implemented on helicene chiral scaffolds as well, but in this case dimerization of the monomers was characterized by homochiral enantioselective self-recognition, that is self-association between molecules with the same helicity (Fig. 17B) [44], These species dimerized in solution with association constants of 207 M 1 by means of four non-covalent bonding interactions and, in combination with the peculiar helical shape of the monomers, forms only homochiral dimers. 

Chiral recognition techniques have been used in photoinduced electron transfer reactions and the differential formation of homochiral against heterochiral exciplexes. In the systems studied excited states of lanthanide complexes are quenched by transition metal complexes. The complexes with trigonal dihedral (D3) symmetry which can exist as enantiomers with either left handed (a) or right-handed (A) configurational chirality are chosen. The system consists of a mixture of racemic lanthanide complex and optically resolved... 

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