雷射捕陷控制雙成分溶液的結晶化

Laser trapping-controlled crystallization in two-component solution

岡野和希(Kazuki Okano)

指導教授 ： 杉山輝樹

國立交通大學/理學院/應用化學系所/碩士(2019年)

摘要

在本篇論文中，我們在乙醯胺酚和苯丙胺酸的雙成分溶液裡利用雷射捕陷技術達到結晶化控制。當1064奈米的連續波雷射聚焦在乙醯胺酚和苯丙胺酸莫爾比例1:1溶液的氣液介面上時，乙醯胺酚和苯丙胺酸的共結晶會於40分鐘內出現在雷射焦點。在結晶化的同時我們用拉曼光譜技術對結晶進行定性，而結晶的結構也成功利用X光晶體繞射來測定。有趣的是，除了產生共結晶外，在雷射焦點內也會產生苯丙胺酸的結晶，甚至是當乙醯胺酚和苯丙胺酸莫爾比例1:0.5時也一樣會發生這個現象。由此得知，苯丙胺酸的結晶可以從雙成分溶液中被單獨分離出來；反之，乙醯胺酚的結晶現象則從來沒有在焦點產生出來。
在本篇中控制了雷射能量大小與偏振方向兩個變因，以探究兩者對乙醯胺酚和苯丙胺酸莫爾比例1:0.9的雙成分溶液結晶化產生的影響。當雷射能量從1.3瓦逐漸調低至0.7瓦時，雷射焦點內產生苯丙胺酸的機率也隨著降低了，且在0.7瓦時並不會產生苯丙胺酸的結晶。另一方面，雷射的偏振方向幾乎沒有對共結晶或苯丙胺酸的結晶化機率產生影響。不過相較於圓偏振光，苯丙胺酸的結晶在線偏振光條件下的結晶時間比較短。
結晶化現象的機制推測如下所述。首先，值得一提的是即使起始濃度在未飽和的條件下，所有在焦點產生的結晶大小都會達到數十微米，這個大小是遠大於雷射焦點的範圍，這個是在我們之前雷射捕陷誘發結晶化的實驗中已經發現的現象。在雷射焦點內增加的濃度會向外擴散，偶然間會產生一個由分子團簇所組成的數微米高濃度區域，並傾向於結晶化。在低雷射能量時，溶液中不同團簇間的折射率差異並不大，不會對實驗結果造成明顯的影響，所以兩個分子成分的比例還是維持在與起始濃度相似的條件，進一步的雷射照射產生了共結晶。反之，在高雷射能量時，濃度會上升比較快，在焦點內的團簇會變成更高濃度的集合，其集合會強烈的被雷射能量與偏振方向所影響。由得到的結果來說，跟乙醯胺酚相比，苯丙胺酸的團簇有比較大的折射率，並且會隨著能量變大而有著更大的差異。尤其是苯丙胺酸的團簇會比較容易被線偏振光所捕捉，導致會有比較高機率產生苯丙胺酸的結晶。
這些不常見的現象是藉由雷射捕陷技術才可能在確定的時間與空間內觀察到。在這篇論文中我們的發現將會為闡明雙成分溶液的機制時給予新的視角，並且能讓我們有機會在多成分溶液中分離出想要的結晶。

關鍵字

雷射捕陷 ； 雙成分 ； 共結晶 ； 乙醯胺酚 ； 苯丙胺酸

並列摘要

Laser trapping-controlled crystallization in two-component aqueous solution of acetaminophen (Ace) and L-phenylalanine (L-Phe) is demonstrated. Upon focusing a continuous-wave laser beam of 1064 nm at an air/solution interface of the sample solution with 1:1 molar ratio of each compound, the single co-crystal was generated always at the laser focus within 40 min-irradiation. The resultant crystal was in-situ characterized by Raman micro-spectroscopy, and the crystal structure was successfully determined by single X-ray diffraction. Intriguingly, L-Phe crystal was formed at the laser focus, instead of 1:1 co-crystal, and it was still generated even from two-component solution with Ace/L-Phe = 1/0.5. Thus, pure L-Phe can be selectively extracted from two-component solution as its crystal, although Ace crystal formation has been never observed at the laser focus.
Dependence of laser power and polarization on the crystallization behavior was systematically investigated in two-component solution with Ace/L-Phe = 1/0.9. The formation probability of L-Phe crystal was decreased with the decrease in the laser power, ranging from 1.3 to 0.7 W, and co-crystal was constantly obtained at 0.7 W. On the other hand, the formation probability of co-crystal and L-Phe crystals was almost independent of laser polarization, however, the crystallization time was clearly affected by laser polarization; shorter time for L-Phe crystallization upon linearly-polarized light, compared to that upon circularly-polarized light.
The dynamics and mechanism of the crystallization behavior is proposed as follows. First, it is noteworthy that the size of all crystals generated at laser focus reaches to be a few tens micrometer, which is much larger than the laser focus of 1 micrometer, in spite that initial solution is under unsaturation. Such a phenomenon has been seen on our laser trapping-induced crystallization. The increase in solution concentration achieved at laser focus is extended to the outside of laser focus, eventually forming a highly-concentrated domain consisting of clusters in a few micrometer order prior to nucleation. At low laser power, there is no apparent difference in refractive indices of all clusters existing in solution, so that the component ratio inside the cluster domain is almost same as that in initial solution. Further irradiation into the cluster domain produces co-crystal. While, at high laser power, the large increase in concentration is achieved. The clusters at laser focus eve into more highly-concentrated cluster domain, where the association and orientation are strongly affected by laser power and polarization. Considering the obtained results, L-Phe clusters has a large refractive index compared to Ace ones, and the difference in their refractive indices becomes large as laser power is increased. Especially upon linearly-polarized light, L-Phe clusters are efficiently trapped, resulting in high probability of L-Phe crystal formation.
The observation of such unusual phenomena is made possible by its spatiotemporal controllability of this method. Our findings in this work will give new insights into the elucidation of the dynamics and mechanism of crystallization from two-component solution, and enable us to demonstrate optical filtration from multi-component solution.

並列關鍵字

Laser trapping ； Two-component ； Co-crystal ； Acetaminophen ； L-Phenylalanine

參考文獻

[1] T. Rungsimanon, K. Yuyama, T. Sugiyama, H. Masuhara, N. Tohnai, and M. Miyata, “Control of crystal polymorph of glycine by photon pressure of a focused continuous wave near-infrared laser beam,” J. Phys. Chem. Lett., 3, 599, 2010.

[2] A. Ashkin, “ACCELERATION AND TRAPPING OF PARTICLES BY RADIATION PRESSURE,” Phys. Rev. Lett., 4, 156, 1970.

[3] J. R. Moffit, Y. R. Chemla, S. B. Smith, and C. Bustamante, “Range dependent radiation leakage from thin scattering columns due to multiple small angle scatter,” Annu. Rev. Biochem., 2, 205, 2008.

[4] H. Yoshikawa, T. Matsui, and H. Masuhara, “Reversible assembly of gold nanoparticles confined in an optical microcage,” Phys. Rev. E - Stat. Physics, Plasmas, Fluids, Relat. Interdiscip. Top., 6, 061406, 2004.

[5] K. Sasaki, M. Koshioka, H. Misawa, N. Kitamura, and H. Masuhara, “Laser-scanning micromanipulation and spatial patterning of fine particles,” Jpn. J. Appl. Phys., 5, 907, 1991.