脯氨酸雷射捕陷結晶化於溶液中之研究

Abstract

雷射捕捉促使分子聚集化最近引起大家的重視，特別是它所引起更進一步的分子聚集化現象:結晶化，我們稱之為“雷射捕陷結晶化”。第一次成功示範出雷射捕陷結晶化，是在過飽和的甘氨酸重水溶液中，利用一道近紅外光的雷射聚焦在空氣與液體介面上。透過這項新穎的方法，可以達到空間及時間上控制的結晶化，還可能控制結晶的晶形結構。甚至在未飽和溶液中，光壓(雷射捕捉)可提高局部的溶液濃度至過飽和，使結晶化成功。這項新穎的結晶化被嘗試應用在許多化合物上，但並不是每一個化合物都能成功，而且它的機制尚未明瞭。 在這研究中，我們探討雷射捕陷結晶化動力學與其機制，基於研究與觀察脯氨酸雷射捕陷結晶化於不同的溶劑中。首先我們發現脯氨酸於重水中，雷射捕陷結晶化不易成功。藉由檢驗不一樣的溶劑至乙醇(EtOD)，我們最終成功地首次示範出脯氨酸的雷捕陷結晶化並且在結晶化前發現了其高濃度液滴的形成。高濃度液滴是一種液態/液態的相分離，藉由觀察它的形成使我們得以進一步探究在光壓下分子聚集的機制與原理。最後，根據觀察到雷射捕陷所引發的現象，我們將討論許多因素(溶劑的性質，溶質與溶劑分子的作用力與雷射引發局部溶液環境的改變)對於雷射捕陷結晶化和高密度液滴形成造成的影響，這些將助於我們對於雷射捕陷聚集化和結晶化有更深的認識。

Photon pressure induced well-ordered molecular assembly formation technique, which has developed in our group and named as “laser trapping crystallization”, is quite unique and high potential method since its spatiotemporal controllability of crystallization. Meanwhile crystallization under laser trapping is not always successful and its mechanism has not been clarified. In this work, we studied laser trapping crystallization of a natural amino acid L-proline to clarify its crystallization dynamics and mechanism under laser trapping condition. Laser trapping crystallization of L-proline in different solvents was examined by focusing a trapping laser to the air/solution interface. We observed obvious difference of crystallization behavior depending on the solvent. We found that the laser trapping crystallization of proline in deuterated water (D2O) is difficult. Meanwhile in deuterated ethanol (EtOD), we succeeded the laser trapping crystallization. Crystallization of proline in EtOD is very similar to previously reported laser trapping crystallization of glycine. Microscopic characterization of formed crystals indicates we successfully formed proline crystal by laser trapping. In addition to crystallization, we observed locally induced liquid-liquid phase separation of proline in EtOD prior to the crystal formation, namely dense liquid droplet formation, as well as glycine in D2O solution. Detailed observation of droplet formation dynamics enabled us to understand droplet formation dynamics and propose its mechanism. Observed results indicate the dense droplet formation is indispensable process for laser trapping crystallization of proline in EtOD and laser trapping assembly formation, i.e. both crystallization and droplet formation, is dominated by complex contribution of various factors such as solvent characteristics, interactions between solvent and solute or solutes, and laser-induced local environment change around focal spot.