Chiral Recognition of Amino Acids Using CC2 Porous Organic Cages

Enantiomers have the same physical properties but different chemical properties due to the difference in the orientation of groups in space and thus Chiral discrimination is quite necessary, as an enantiomer of drug can have lethal effects. In this study, we used the CC2 cage for chiral discrimination of amino acids using density functional theory. The results indicated the physisorption of amino acids in the central cavity of the cage. Among the four selected amino acids, proline showed maximum interactions with the cage and maximum chiral discrimination energy is also observed in the case of proline that is 2.78 kcal/mol. Quantum theory of atoms in molecules and noncovalent interaction index analyses showed that the S enantiomer in each case has maximum interactions. The charge transfer between the analyte and surface is further studied through natural bond orbital analysis. It showed sensitivity of cage for both enantiomers, but a more pronounced effect is seen for S enantiomers. In frontier molecular orbital analysis, the least E_H-L gap is observed in the case of R proline with a maximum charge transfer of -0.24 e^-. Electron density difference analysis is carried out to analyze the pattern of the charge distribution. The partial density of state analysis is computed to understand the contribution of each enantiomer in overall density of the complexes. Our results show that S-CC2 porous organic cages have a good ability to differentiate between two enantiomers. S-CC2 porous organic cages efficiently differentiated the S enantiomer from the R enantiomers of selected amino acids.

High-Pressure Crystallization and Thermodynamic Stability Study on the Resolution of High-Density Enantiomers from Low-Density Racemates

High-pressure recrystallization could be the cheapest clean method of resolving enantiomers from the racemates defying Wallach's rule. We have investigated the effect of pressure on sodium tartrate monohydrate (NaTa·H₂O), a notorious exception from Wallach's rule: both racemic polymorphs α-dl-NaTa·H₂O and β-dl-NaTa·H₂O are less dense than the enantiomers. According to the mobile-equilibrium principle, such high-density enantiomorphs should spontaneously separate under high pressures. The pressure dependence of the Gibbs free energy explains the preferential crystallization of mixed enantiomers of NaTa·H₂O.

Spontaneous resolution, whence and whither: from enantiomorphic solids to chiral liquid crystals, monolayers and macro- and supra-molecular polymers and assemblies

One of the great challenges in stereochemistry is the explanation of why some molecules resolve spontaneously while others do not. In this critical review the recent advances in the creation of chiral systems from achiral and racemic compounds in three-, two- and one-dimensional systems are discussed. There are some groups of molecules in some systems that do tend to display conglomerates, which may suggest that there are enantiophobic and enantiophilic molecules whose assembly is guided by the structural and thermodynamic properties of the systems in question.