Chiral resolution of a racemic macrocyclic complex by recognition of one enantiomer over the other: structures and DFT calculations

Abstract

The enantiopure agents d- and l-leucine, selectively bind RR and SS enantiomers from a racemate [Ni(alpha-rac-L)](2+) to give {[Ni(RR-L)(d-HLeu)](ClO(4))(2)}(n) (Delta-) and {[Ni(SS-L)(l-HLeu)](ClO(4))(2)}(n) (Lambda-), respectively, and leave the corresponding uninteracted SS and RR enantiomers of [Ni(alpha-SS-L)](ClO(4))(2) (S-) and [Ni(alpha-RR-L)](ClO(4))(2) (R-). Occasionally, a few crystals of {[Ni(RR-L)(l-HLeu)](ClO(4))(2)}(n) (Delta-) and {[Ni(SS-L)(d-HLeu)](ClO(4))(2)}(n) (Lambda-) were found to have accreted with the crystals of Lambda-/R-, and Delta-/S-, respectively (the yields are less than 2%). The results of X-ray crystal structural analysis reveal that Delta- and Lambda-, S- and R-, and Delta- and Lambda- are enantiomers, in which Delta- and Delta- possess 1D right-handed helical chains, while Lambda- and Lambda- exhibit a motif of 1D left-handed helical chains. The results of DFT calculations reveal that the single-point energies of [Ni(RR-L)(d-HLeu)](2+)/[Ni(SS-L)(l-HLeu)](2+) in Delta-/Lambda- are 582 kJ mol(-1) lower than those of [Ni(RR-L)(l-HLeu)](2+)/[Ni(SS-L)(d-HLeu)](2+) in Delta-/Lambda-, demonstrating the favorable stereo-coordination environments of [Ni(alpha-RR-L)](2+) and [Ni(alpha-SS-L)](2+) towards d and l-HLeu, respectively.

Enantiomeric discrimination of leucine enantiomers by nanotubular cyclic peptides: DFT and ONIOM calculation of the absorption spectra of guested enantiomers

“…However, the mechanism for most separations is still unknown in detail, so it is of particular significance to get an insight into this topic. In continuum with our preceding study on physicochemical properties of cyclic peptides [23,24,[41][42][43], in this work we report the ability of various nanotubular cyclo alanines in potential separation of leucine enantiomers by using DFT calculations. In addition, the possibility of using UV absorption spectra of enantiomers interacting with cyclic peptide as a tool for discriminating of the enantiomers is investigated using ONIOM method which stands for ''Our own N-layered Integrated molecular Orbital and molecular Mechanics'' calculations.…”

“…We concluded that the most favorable complex is formed between CycAla9 and enantiomers of lactic acid. The enantiomeric separation of amino acids especially for leucine has been reported [42]. However, the mechanism for most separations is still unknown in detail, so it is of particular significance to get an insight into this topic.…”

Crystal Structures and Spectroscopic and Theoretical Properties of Pentacoordinate Nickel(II) Complexes Containing Tris(pyrazolyl)borate and Quinolinate Ligands

“…All calculations were performed with the unrestricted (U)B3LYP35 functional and a generic basis set def2‐SVP36 for all atoms by using the Gaussian 09W software 37. The B3LYP functional has been reported to be highly reliable for these types of calculations 11,38,39. The obtained energies are shown in the Supporting Information.…”

Heterochiral or Homochiral Self‐Assembly: Mercury(II), Cadmium(II), and Spontaneous Resolution of Silver(I) Complexes Derived from a Racemic Bis(pyridyl) Ligand

“…Spontaneous resolution, which often yields a conglomerate comprised of equal amount of enantiomers with opposite chirality, is a rare phenomenon and has become an increasingly important area of research for the importance of enantiopure substances to biological processes and the pharmaceutical industry . Since Louis Pasteur's discovery of spontaneous resolution, discrimination in the solid state has received much attention and many examples of conglomerate crystallizations have been reported . Although various intelligence of crystal engineering approaches indicate that the formation of conglomerates is determined by the laws of physics under specific conditions, these laws are not yet fully understood.…”