Pseudopolymorph Control of l -Phenylalanine Achieved by Laser Trapping

Chi Shiun Wu, Pei Yun Hsieh, Ken Ichi Yuyama, Hiroshi Masuhara, Sugiyama Teruki*

*Corresponding author for this work

Research output: Contribution to journalArticle

9 Scopus citations


We demonstrate pseudopolymorph control of l-phenylalanine (l-Phe) with laser trapping method by tuning laser power, polarization, and initial solution concentration. When a continuous-wave near-infrared laser beam of 1064 nm was focused at an air/solution interface of l-Phe D2O solutions with different saturation, l-Phe crystallization was always observed within 30 min-irradiation, even from unsaturated solution. Either whisker- or plate-like crystals were generated depending on given conditions, and identified by Raman spectroscopy to be two l-Phe pseudopolymorphs of monohydrate and anhydrous forms, respectively. The absolute control of l-Phe pseudopolymorphism was achieved by changing the initial solution concentration. In unsaturated solution, laser trapping always produced only one anhydrous crystal at the focus, which can never be produced on spontaneous nucleation at ordinary temperatures and pressures, while in supersaturated solution, a number of monohydrate crystals were densely distributed in an area ranging from 500 μm to 1 mm away from the focus. Moreover, in saturated solution, laser power and polarization contributed to the pseudopolymorphism. As laser power was increased, linearly and circularly polarized laser irradiation increased the formation probability of the anhydrous and monohydrate crystals, respectively. The dynamics and mechanism of laser trapping-induced pseudopolymorphism of l-Phe are discussed in view of the formation of a highly concentrated domain consisting of the liquid-like clusters and the stability of the clusters in the domain under electromagnetic field of trapping laser.

Original languageEnglish
Pages (from-to)5417-5425
Number of pages9
JournalCrystal Growth and Design
Issue number9
StatePublished - 5 Sep 2018

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