藉由雷射捕陷技術控制環糊精的結晶化現象:調整雷射能量與偏振

Abstract

我們利用雷射捕陷藉由調控雷射能量以及雷射極性控制 β-環糊精的多晶型態。我們利用線性或圓性偏振之連續式 1064 nm 雷射聚焦於 β-環糊精/重水溶液的液氣介面。藉由此方法可以在焦點上或周圍產生單一的塊狀結晶或多片的片狀結晶。我們在配製不同初始濃度的 β-環糊精/重水溶液進行雷射捕陷時發現了在控制多晶上的影響。當飽和度低於 0.28時，可以產生片狀結晶;在飽和度大於 0.56時，可以產生塊狀結晶，但是無法從雷射能量及雷射極性的控制產生影響。然而，在飽和度等於 0.45 時，我們發現在使用線性雷射時容易產出塊狀結晶，在圓性偏振時容易產出片狀結晶。另一方面，我們也發現在提高雷射能量時，可以提高塊狀結晶產出的機率，反之亦可提高片狀結晶產出的機率。另一方面，我們也推 測在形成結晶前已經在焦點周圍形成團簇的高濃度區域。為了證明此推測，我們利用共軛焦顯微鏡測量硫代黃素及 γ-環糊精包合物的激發二聚體的螢光強度。藉由雷射捕陷下，激發二聚體的螢光強度在焦點及焦點附近確實上升。這也代表著雷射捕陷增加激發二聚體的形成並且將此交互作用拓展到焦點外。其調整雷射能量與極性控制多晶現象之機制將會利用分子在團簇內的排列進一步的說明。

We present laser trapping-controlled crystal polymorphism of β-cyclodextrin (β-CD) by tuning laser power and polarization. A linearly- or a circularly-polarized continuous-wave laser beam of 1064 nm was tightly focused at a surface layer of β-CD/D2O solutions. Laser trapping consistently provided either single block- or some plate-like crystals at/around the laser focus. Initial concentration of mother solutions considerably exerted an influence on the polymorphism. In the case of supersaturation value (SS) of less than 0.28, plate-like crystals were consistently generated, while single block-like crystal formation was observed upon SS more than 0.56, independent of laser power and polarization. When the SS was set to 0.45, linearly- and circularly- polarized laser irradiation preferentially caused the block- and plate-like crystal formation, respectively. Moreover, the probability of the block- like crystal formation was increased with the input laser power. On the other hand, it was also that the highly concentrated domain of CD liquid-like clusters was formed prior to crystal nucleation. In order to examine the concentration distribution of the cluster domain, we measured fluorescence intensity of the excimer of the inclusion compound, Thioflavin T (ThT)/γ-CD in D2O, around the focal position by using a confocal microscope. The fluorescence intensity of the excimer at/around the laser focus was increased with the laser irradiation. This means that laser trapping increases local concentration of γ-CD, which enhances the excimer formation, at the laser focus, from which the association is extended to the outside the laser focus resulting in the formation of a highly concentration domain. The dynamics and mechanism of laser power and polarization-dependent polymorphism of CDs are discussed in terms of the orientation of CD molecules in the cluster domain depending on laser power and polarization.