Parity violating energetic difference and enantiomorphous crystalsp-caveats; reinvestigation of tyrosine crystallization.

The present article challenges reports claiming to have demonstrated the Parity Violating Energetic Difference (PVED) between enantiomorphous D- and L-crystals. Apart from PVED, the presence of minute quantities and differing profiles of impurities incorporated during their different history of preparation will affect the physical properties of D- and L-crystals. These impurities are anticipated to play a much greater role in affecting crystallization behavior than PVED.

Homochiral oligopeptides by chiral amplification within two-dimensional crystalline self-assemblies at the air-water interface; relevance to biomolecular handedness.

A possible role that might have been played by ordered clusters at interfaces for the generation of homochiral oligopeptides under prebiotic conditions has been probed by a catalyzed polymerization of amphiphilic activated alpha-amino acids, in racemic and chiral non-racemic forms, which had self-assembled into two-dimensional (2D) ordered crystallites at the air-aqueous solution interface. As model systems we studied N(epsilon)-stearoyl-lysine thioethyl ester (C(18)-TE-Lys), gamma-stearyl-glutamic thioethyl ester (C(18)-TE-Glu), N(alpha)-carboxyanhydride of gamma-stearyl-glutamic acid (C(18)-Glu NCA) and gamma-stearyl-glutamic thioacid (C(18)-thio-Glu). According to in-situ grazing incidence X-ray diffraction measurements on the water surface, (R,S)-C(18)-TE-Lys, (R,S)-C(18)-TE-Glu, and (R,S)-C(18)-Glu-NCA amphiphiles self-assembled into ordered racemic 2D crystallites.

Oligopeptides with homochiral sequences generated from racemic precursors that spontaneously separate into enantiomorphous two-dimensional crystalline domains on water surface.

The feasibility of generating oligopeptides with homochiral sequence via lattice-controlled polymerization of racemic mixtures of precursor molecules that undergo spontaneous segregation into two-dimensional (2-D) enantiomorphous domains at the air-aqueous solution interface was analyzed. For model systems, we studied the polymerization reaction within 2-D crystalline domains of mixtures of (R,S)-N(epsilon)-stearoyl-thio-lysine with approximately 10% (R,S)-N(epsilon)-stearoyl-lysine, and (R,S)-N(alpha)-carboxyanhydride of N(epsilon)-stearoyl-lysine. According to in situ grazing incidence X-ray diffraction (GIXD) measurements at the air-water interface, the molecules form 2-D crystallites packing by translation symmetry only.

Chiral amplification of oligopeptides in two-dimensional crystalline self-assemblies on water.

Differences in the two-dimensional packing arrangements of racemic and enantiomeric crystalline self-assemblies on the water surface of amphiphilic activated analogs of lysine and glutamic acid have been used to prepare oligopeptides of homochiral sequence and oligopeptides of single handedness from chiral nonracemic mixtures. The crystalline structures on the water surface were determined by grazing incidence x-ray diffraction and the diastereomeric composition of the oligopeptides by matrix-assisted laser desorption time-of-flight mass spectrometry with enantio-labeling. These results suggest that reactivity of ordered clusters at interfaces might have played a role in the generation of early homochiral biopolymers.