Laser trapping-induced crystallization of L-phenylalanine through its high concentration domain formation

Ken-ichi Yuyama, Chi-Shiun Wu, Teruki Sugiyama and Hiroshi Masuhara
We present laser trapping-induced crystallization of L-phenylalanine through high concentration domain formation in H2O and D2O solutions which is achieved by focusing a continuous-wave (CW) near-infrared laser beam at the solution surface. Upon the laser irradiation into the H2O solution, laser trapping of the liquid-like clusters increases local concentration, accompanying laser heating, and a single plate-like crystal is eventually prepared at the focal spot. On the other hand, in the D2O solution, a lot of the monohydrate needle-like crystals are observed not at the focal spot where concentration is high enough to trigger crystal nucleation, but in 0.5–1.5 millimetres range from the focal spot. The dynamics and mechanism of the amazing crystallization behaviour induced by laser trapping are discussed from the viewpoints of concentration increase due to laser heating depending on solvent, large high concentration domain formation by laser trapping of liquid-like clusters, and orientational disorder of molecules/clusters at the domain edge.
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