【作者】 王鲁宁；

【导师】 许东； 张光辉；

【作者基本信息】 山东大学 ， 材料学， 2013， 硕士

【摘要】 L-精氨酸磷酸晶体(LAP)是山东大学国际上首创的,获得国内外高度认可的一种非线性光学晶体材料。该晶体于1988年获得国家技术发明奖一等奖。LAP晶体具有优异的性能：在紫外区具有良好的透过性,有效非线性光学系数约为KDP晶体的2-3.5倍,并可以实现高达90%以上的高转化率。除此之外,LAP晶体在与不同类型能量作用过程中均体现出特异现象。首先,研究人员发现,LAP晶体在对相应波段激光有较强吸收的情况下,依然表现出极高的激光损伤阈值：在脉冲宽度为1ns、波长为1053nm下,激光损伤阈值可达到63GW/cm2,高出KDP晶体约半个数量级；第二,LAP晶体具有低的受激布里渊散射(SBS)阈值和高SBS反射率,其反射率远高于石英玻璃；最后,LAP晶体特殊的分子结构基团使其与热能作用过程中体现出热释电性能。这些异常现象成为困扰科研人员多年的谜团。阐释LAP晶体与能量作用的过程、能量存储的机理、特殊现象出现的原因等将具有重要意义。我们通过分析LAP晶体结构,并运用新型手段表征LAP晶体与能量作用过程后认识到,LAP晶体这些特殊性能可能与其分子构象以及分子间作用力易变性具有关系。在解决、验证这一机理中我们通过文献调研发现,无脊椎动物体内存在一种高能化合物——磷酸精氨酸(PA),其与LAP晶体具有相似的化学组成。生物科学研究表明,L-精氨酸和磷酸分子可以结合生物能(来自于生物体内糖、ATP等的水解)合成PA,并将大量能量存储于磷酸—胍基特殊相互作用(亦即“高能磷酸键”)中；另一方面,PA作为“磷源”和“能量库”,可以为生物体其他过程(例如ADP→ATP转化)提供磷酸基团以及能量。PA的能量存储以及释放过程中,分子构象以及L-精氨酸与磷酸分子之间作用力发生改变。综合考察L-精氨酸和磷酸分子在晶体以及生物体内与能量的相互作用,我们认为,LAP晶体与能量的作用可能和PA储能过程具有相似性：同PA储能过程类似,LAP晶体在各种不同形式能量(激光、热能、磁场)作用下,发生分子基团的激发以及构象的改变,从而导致原子间距离、分子间(尤其是L-精氨酸胍基与磷酸分子之间)相互作用发生变化,实现能量的存储,并使得晶体呈现出各种特殊现象。这一猜想从全新角度为揭示LAP晶体特殊性能提供了研究思路和研究方法。为验证以上猜想,证明LAP晶体构象以及分子间作用力的易变性,本论文进行了如下工作：1.分子手性与分子构象联系紧密。基于L-精氨酸的手性性质,’运用分子手性表征手段,如圆二色谱、分子比旋光度,探索了L-精氨酸磷酸水溶液在温度变化下,L-精氨酸手性性质的改变。研究发现,随温度升高,L-精氨酸磷酸水溶液圆二色谱强度呈现规律性下降,光谱出现一正的"cotton"效应,峰值大约出现在207nm处。同时,L-精氨酸水溶液为右旋,随温度升高,L精氨酸水溶液比旋光度亦逐渐降低。2.借助于分子模拟,深入探讨了L-精氨酸手性性质发生改变的本质原因。分子模拟利用Gaussian Hyperchem等软件进行,采用从头算法以及分子力场等多种方法,模拟了L-精氨酸在水溶液环境下,随温度升高可能出现的手性性质的改变,同时探讨了这一过程中分子构象的迁移。模拟结果证明,L-精氨酸在温度升高下,圆二色谱强度以及分子比旋光度均出现规律性下降,与实验测试相符合；L-精氨酸构象出现“折叠式”与“伸展式”之间的迁移转化。3.运用二维红外光谱表征了升温过程中LAP晶体分子基团之间可能出现的分子间作用力情况。为探索LAP晶体与生物PA之间的关系,研究重点放在了L-精氨酸胍基与磷酸基团之间,目标红外波段为1700cm-1～1000cm-1以及1400cm-1～600cm-1。研究发现,在升温过程中,磷酸基团对温度变化较为敏感,其与晶体热释电性能可能有关；L-精氨酸胍基与磷酸基团之间并不存在明显的证据表明二者之间具有分子间作用。4.运用紫外光谱、分子模拟等探索了L-精氨酸磷酸水溶液中可能存在的分子间作用力。紫外光谱测试波段为220-300nm之间。实验发现,随磷酸加入量的增加,L-精氨酸水溶液在这一区间的紫外光谱可以分为三个不同的波段范围,并分别出现不同的变化趋势。接下来对三个不同紫外波段进行了基团归属与定义,探讨了发生变化的可能原因。5.合成并生长了新型L-精氨酸盐非线性光学晶体——L-精氨酸双对硝基苯酚晶体(LAPP).运用显微结晶法研究了该晶体生长的合适化学条件。运用XRD研究了晶体结构,发现该晶体为单斜晶系,空间群P21,a=7.8669(5)A,b=10.3764(2)A,c=13.8301(2)A。同时测试了该晶体的红外光谱、紫外/可见光/近红外透过性能、热稳定性能,实验发现,LAPP晶体红外光谱主要产生于硝基、羰基、苯基团以及水分子等,其透过截止波段大约在500nm。LAPP晶体非线性倍频性能测试表明,其倍频强度与尿素晶体相当,并且可以实现相位匹配。更多还原

【Abstract】 As an outstanding nonlinear optical (NLO) crystal, L-arginine phosphate monohydrate crystal (LAP) is initially created and developed by Shandong University. This crystal has been awarded "1st Award of National Technology Invention" in1988because of its excellent properties:A. Wonderful transparency property in ultraviolet (UV) band; B. High nonlinear optical efficiency, which is2-3.5times higher compared with KDP crystal; C. High conversion rate, about90%, especially for the deuterated LAP crystal (DLAP).In addition, researchers have found several abnormal phenomenons when LAP crystal is reacted with different forms of energy, such as laser, heat and magnetic field. Firstly, LAP crystal has extremely high laser damage threshold. When radiated with a beam of laser with wavelength1053nm and pulse width1ns, LAP crystal can reach as high as63GW/cm2without getting damaged. Secondly, scientists have discovered that LAP crystal has low SBS threshold and high SBS reflection, which is much higher compared with fused silica. Finally, molecules with special conformations enable LAP crystal a pyroelectrical property. These issues still remain enigmatic while the solution of which will has significant meanings. Via novel characterization methods and analysis of crystalline structure of LAP, we believe these special phenomenons of LAP crystal may have relations with its molecular conformations and inter-molecular forces.Recently we have found that Phosphate Arginine (PA), which has similar chemical composition with LAP crystal and serves as a key biological substance in energy storage and conversion, is widely existed in the body of invertebrate animals. Biological scientific research has shown that, after combining biological energy, L-arginine and phosphate acid can react and transfer to be PA. In this process, large amount of energy is stored in a special phosphate-guanidine group interaction (the so-called "high-energy phosphate bond"). In another aspect, acting as the "phosphate source" and "energy source", PA can provide phosphate group and energy for other biological functions. During the energy storage and conversion process of PA, transformation of molecular conformation of L-arginine as well as the interaction between phosphate and guanidine group has important functions. Noticing that PA and LAP crystal have similar chemical composition, we believe that the reaction between LAP crystal and high energy may has something in common with the energy conversion process of PA, such as that the molecular conformation of L-arginine may get changed when LAP crystal reacts with laser, heat etc. To test this hypothesis, we have conducted the following experiments:1. Circular Dichorism (CD) spectrum and specific rotation test on the aqueous solution of L-arginine and phosphate acid with temperature rises. Tests show that:A. L-arginine has a positive "Cotton" effect with the peak locating at207nm. B. When temperature rises, the intensity of the CD spectrum as well as the value of specific rotation of the aqueous solution decrease.2. Molecular simulation on the chirality property of L-arginine based on Molecular Mechanics and ab inito. In this part, we have calculated the CD spectrum and the specific rotations of L-arginine aqueous solution with software including Gaussian and Hyperchem. Simulation shows that:A. the CD spectrum of L-arginine aqueous solution has one peak locating at around212nm. B. With temperature rising, the intensity of CD spectrum and specific rotations decrease, which is the same with experimental results. Calculation shows that the molecular conformation of L-arginine changes beween "extended way" and "partly folded way".3. Investigation on the molecular interaction in LAP crystal employing two-dimensional infrared spectrum. Research focus is located at the guanidine and phosphate acid group. Correspondingly, the wavenumber should be1700cm-1～1000cm-1and1400cm-1～600cm-1, respectively. Research shows that with temperature rising, phosphate group changes intensively while no obvious evidence observed for the interaction between guanidine group and phosphate acid.4. Investigation of possible molecular interaction between L-arginine and phosphate acid in aqueous solution utilizing ultraviolet spectrum and molecular simulation. Research focus locates between220nm and300nm. Research shows that the waveband of220-300nm can be divided into three different parts while different phenomenon occur in each band. The assignments of the absorptions in these three bands are further researched.5. Discovery of a new NLO crystal——L-arginine4-nitrophenolate4-nitrophenol dehydrate crystal (LAPP). The optimal growth condition of the crystal is investigated. XRD is used to characterize the crystalline structure and shows that the crystal belongs to the monoclinic crystallographic system with space group P21, a=7.8669(5) A, b=10.3764(2) A, c=13.8301(2) A. The thermal stability, IR and UV/Vis/NIR spectrum are tested, which show that the cutting wavelength of LAPP crystal is around500nm. NLO characterization shows that LAPP crystal has a similar NLO efficiency with urea and is phase matchable.更多还原