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[MIS12-05] Chiral Bias in Chiral Crystallization Induced by Circularly Polarized Laser Trapping of Silver Nanoparticles in Sodium Chlorate Solution
Keywords:chiral crystallization, laser-induced crystallization, circularly polarized light, metal nanoparticle, localized surface plasmon
A CW CPL green laser (532 nm, 940±5 mW, ellipticity ›93%) was focused onto the air-liquid interface of the undersaturated NaClO3 solution containing AgNPs by using a 60× objective lens (NA = 0.9) equipped on an inverted polarized light microscope. We repeated crystallization and chirality identification of the NaClO3 crystal 100 times and 100 times by using l- and r-CPL, respectively. The number of the resulting enantiomorphs was counted.
As the result of the laser irradiation, crystallization occured from the focal spot. The crystallization using l-CPL(r-CPL) yielded l-enantiomorph 42(65) times and d-enanitomorph 58(35) times, respectively, indicating that the d-(l-)enantiomorph was dominant over the l-(d-)enantiomorph. Namely, the “dominant” enantiomorph can be switchable by switching the handedness of incident CPL, i.e. the chiral bias is enantioselective. In total, the “dominant” enantiomorph crystallized 123 times out of 200 crystallization. This chiral bias is statistically significant because the number of the “dominant” enantiomorph deviates 99% interval of the binomial distribution B(n,p) = B(200,0.5), where n is the number of trials and p is the probability that the “dominant” enantiomorph crystallizes out (Figure 1). This deviation demonstrates that the probability p is more than 0.5, i.e. the probability of the occurrence of each enantiomorph is no longer equal.
We found that the crystallization of NaClO3 chiral crystal can be induced by the irradiation of tightly focused CPL laser (532 nm) at the interface between air and NaClO3 solution containing AgNPs. We also found that this crystallization method can cause a statistically-significant chiral bias in the probability of crystallization of both of the enantiomorphs. Moreover, the “dominant” enantiomorph is found to be switchable by changing the handedness of CPL. Our results may provide implications for the origin of biohomochirality.
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