Effect of Chiral and Achiral Perturbations on the Crystallization of 4,4‘-Dimethylchalcone from Ethyl Acetate

Abstract

4,4′-Dimethylchalcone is an achiral molecule that crystallizes from ethyl acetate in the chiral space group P2 1 2 1 2 1 . Herein we report the effect of beta radiolysis and circularly and linearly polarized light on the crystallization of 4,4′-dimethylchalcone from ethyl acetate. Exposure of the evaporating solution to energetic beta particles from a Sr-90 source generated a random distribution of (+) and (-) crystals. Irradiation of the evaporating solution by intense right-or left-circularly polarized light (1064 nm) from a Nd:YAG laser afforded results that were comparable to the results of the beta radiolysis experiments. Linearly polarized light (LPL), on the other hand, had a profound influence on the distribution of crystals, yielding in this instance a large bifurcation of (+) and (-) crystals. A likely cause of this outcome may be due to the optical Kerr effect. The anisotropic polarizability of the chalcone molecule causes a preferential alignment in the direction of the E field when using LPL. This molecular alignment results in a sizable enantiomeric excess. Circularly polarized light does not produce the alignment of the chalcone and thus has no effect on the asymmetric induction. This alignment offers an opportunity for chirally autocatalytic secondary nucleation to occur, which is then able to amplify small initial asymmetry in the number of (+) and (-) crystals. The chirality of the chalcone crystals was determined via their reaction in water with pyridinium tribromide to yield the chiral compound erythro 1,2-dibromo-4,4′-dimethylchalcone, thus allowing the chirality of the crystal to be propagated to molecular chirality.

Strong Enhancement of Nucleation Efficiency of Aqueous Ethylenediamine Sulfate Solutions by Nonphotochemical Laser-Induced Nucleation: Investigations on the Role of Solid Impurities in the Mechanism

“…Non-photochemical laser-induced nucleation (NPLIN) is the phenomenon where crystal nucleation is triggered by using laser irradiation, usually emitted by an unfocused nanosecond pulsed laser, without a photochemical reaction. It has been used to induce the nucleation of several compounds, either organic − or inorganic, − either from metastable supersaturated solutions or from the supercooled state, − resulting in the publication of more than 40 scientific articles since its discovery in 1996 . The phenomenon is attractive from an engineering perspective as it permits to reduce induction times for nucleation ( i.e.…”

Mie-Resonant Nanophotonic-Enhancement of Asymmetry in Sodium Chlorate Chiral Crystallization

“…Since Kagan and Calvin first demonstrated nonzero enantiomeric excess (ee), which is defined by ( C l – C d )/( C l + C d ) × 100 where C l and C d are the concentrations of l - and d -molecules, respectively, in the absolute asymmetric photosynthesis of helicene molecules in a liquid phase using circularly polarized light (CPL) in the 1970s, − researchers have been attempting to control the handedness of chiral molecules using CPL as the source of chirality induction. This scheme is currently known to yield only slight chiral imbalance, which is typically in the range 0.5–2% in ee. , Similarly, statistically significant crystal enantiomeric excess (CEE), defined by ( N l – N d )/( N l + N d ) × 100 where N l and N d are the number of l -crystals and d -crystals, respectively, has never been reported in chiral crystallization induced by CPL pulsed laser beams from a solution. − The fact that CPL yields only a small chiral imbalance has been attributed to the intrinsically weak interaction between chiral materials and CPL, which arises from the large-scale difference between the minimum chiral unit of chiral materials with an angstrom scale and the spiral pitch of CPL with a several 100-nm scale determined by its wavelength …”