【作者】 杨燕；

【导师】 杜新贞；

【作者基本信息】 西北师范大学 ， 分析化学， 2008， 硕士

【摘要】 荧光探针技术由于具有方法多样、灵敏度高、设备依赖性小等优点,成为人们研究超分子物理与化学问题的有力手段。相比于以往的荧光探针,基于激发态分子内质子转移(ESIPT)的有机分子具有荧光量子产率高、Stokes位移较大和光稳定性好等优点,成为化学、生物学领域的新一代荧光探针,被广泛应用于检测胶束、环糊精、蛋白质分子等微观环境方面。水杨酸衍生物是研究ESIPT反应的重要模型分子。在氢键性环境中,水杨酸酯因形成基态分子间氢键和分子内氢键而呈现出双重荧光。基于分子内氢键的ESIPT荧光位于可见光区,而基于分子间氢键的荧光则位于紫外光区,其相对强度对所处微环境有依赖性。水杨酸酯可作为荧光探针,定性地表征微观环境的氢键特性。环糊精(CDs)的疏水空腔,可选择性包合与其尺寸大小相匹配的分子。由于环糊精的内腔尺寸和疏水性会影响被包合客体分子的光化学和光物理性质,通过和环糊精作用可以探测ESIPT光化学过程。本论文工作主要包括以下两方面内容:第一部分以长链的水杨酸-2′-乙基己基酯(EHS)和短链的水杨酸甲酯(MS)为例,研究了水杨酸酯在不同性质溶剂中的双重荧光光谱。结果表明,水杨酸酯的双重荧光与其能否和溶剂形成氢键,以及形成氢键的能力强弱有很大的关系。随着溶剂形成氢键能力的增强,长、短波长荧光比值(Ia/Ib)显著减小,水杨酸酯分子在溶液中更倾向于形成分子间氢键,且短波长荧光会随溶剂极性的减小发生蓝移。水杨酸酯可作为荧光探针,定性地表征微观环境(氢键及极性)的特性。第二部分研究了不同类型环糊精及环糊精衍生物对EHS和MS双重荧光光谱的影响,具体内容如下:(1)考察了α-CD、β-CD和γ-CD对EHS双重荧光的影响,通过比较客体分子与CDs空腔的大小推测了包合物的结构,认为在α-CD和β-CD与EHS形成的包合物中,主-客体浓度比例不同时,分别生成1:1型、2:1型包合物;在所研究的浓度范围内,γ-CD与EHS只生成1:1型络合物,空腔尺寸是影响EHS与三种环糊精包合作用的主要因素。(2)考察了β-CD及不同取代度甲基修饰β-CD对EHS双重荧光光谱的影响,讨论了四种β-CD与EHS形成的超分子体系中的包合模式和氢键作用,以及EHS的识别能力。结果表明,EHS在β-CD、DM-β-CD、HDM-β-CD和HTM-β-CD溶液中都会出现ESIPT双重荧光,生成主-客体包合物。与β-CD相比,甲基的引入一方面可以增加空间位阻,另一方面降低了环糊精空腔的极性,取代基的个数和位置是影响空间位阻的重要因素。以EHS作为双重荧光探针,不仅可以对甲基的位置而且可以对甲基的个数进行识别。(3)采用荧光光谱法研究β-CD、M-β-CD和HP-β-CD对MS的包合作用,测定了包合物的稳定常数,并对比了三种β-CD对短链MS和长链EHS双重荧光的影响,从包合模式的角度解释了光谱的不同变化。结果表明,MS的双重荧光与所处微环境的氢键性质密切相关,β-CD取代基的大小会导致空腔口处的极性和空间位阻不同,相应改变了分子间氢键相互作用。当MS、EHS分子进入β-CD空腔时会引起其基态互变异构体之间平衡的移动,但包合模式的不同会导致光谱的不同变化。包合物稳定常数测定表明,三种β-CD对MS包合能力的大小为M-β-CD>HP-β-CD>β-CD。更多还原

【Abstract】 The fluorescence probe technique is an attractive means for investigating supramolecular physical and chemical problems due to its variety, high sensitivity and low dependence on equipment. Compared to former fluorescence probes, a new family of fluorescence probes based on excited state intramolecular proton transfer (ESIPT) has been widely used to probe the microenvironments of micellar media, cyclodextrins and proteins because of their photophysical characteristics such as intense fluorescence, large Stokes shifts and significant photostability.Salicylates are typical molecules with ESIPT reaction. In hydrogen-bonding environment, salicylates exhibit dual fluorescence from the ground-state intermolecular and the intramolecular hydrogen-bonding forms. The ESIPT fluorescence from intramolecular hydrogen bonding form appears in the visible region, while the fluorescence from the intermolecular hydrogen bonding appears in the UV region, which is dependent on microenvironment around salicylates. Thus salicylates can be used as a fluorescence probe to qualitatively characterize the microenvironment of the hydrogen bonds.The hydrophobic cavities of cyclodextrins (CDs) are capable of incorporating guest molecules with a suitable size. As the size and hydrophobicity of cyclodextrin cavity could affect the photochemical and photophysical properties of incorporated guest molecules, CDs can be used as a host to detect the photochemical process of ESIPT.This thesis consists of two parts:Part 1 mainly describes the dual fluorescence of 2′-ethylhexyl (EHS) salicylate and methyl salicylate(MS) in various solvents. The results obtained indicate that salicylate shows very different dual fluorescence in solvents with different H-bonding ability. The intensity ratio of long wavelength emission to short wavelength emission (Ia/Ib) markedly decreases with increasing H-bonding ability of the solvent and the short wavelength emission blue-shifts with decreasing solvent polarity. Salicylates can be used for fluorescence probe to detect the hydrogen bonding effect and polarity of microenvironment.In Part 2, the influences of CDs and its derivatives on the dual fluorescence of EHS and MS were studied.(1) Dual fluorescence of EHS was examined in aqueous solution containingα-CD,β-CD andγ-CD. A detailed comparison of molecular structures and sizes provides the geometry of inclusion complexes. EHS was found to form the 1:1 inclusion complexes withα-CD,β-CD in aqueous solution at its lower concentration. Higher concentration of EHS is needed for the formation of the 1:2 cage-type inclusion complexes. The formation of 1:1γ-CD-EHS was examined. The cavity size is primary factor in inclusion processes.(2) Dual fluorescence of EHS was examined in aqueous solution containing natural and methylatedβ-CDs. The geometry of inclusion complexes, the hydrogen bonding effect in supramolecular inclusion and the recognition of EHS were discussed. The results show that EHS forms host-guest inclusion complexes inβ-CD, DM-β-CD, HDM-β-CD and HTM-β-CD solution and all complexes exhibit dual fluorescence. On the one hand, the methyl substitution would result in the steric hindrance. On the other hand, the methyl substitution would reduce the polarity of CD cavity. Effect of number and position of methyl substituents on the steric hindrance was important. As a novel ESIPT fluorescence probe, EHS depends on the number and the position of the methyl substituent.(3) Dual fluorescence of MS was examined in aqueous solution containingβ-CD, methylated-β-cyclodextrin(M-β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and compared with that of EHS. It was found that dual fluorescence of MS closely correlate with the hydrogen bonding property of its surrounding microenvironment. The sizes of substituents at the rim ofβ-CD result in different polarity and steric hindrance at the cavity opening. The intermolecular hydrogen bonding interaction of MS changes in the presence of differentβ-CDs accordingly. When MS and EHS are bound toβ-CDs, their ground state equilibria shift but different geometry of inclusion complexes leads to different dual fluorescence. The formation constants indicate that the binding strength ofβ-CD and its derivatives to MS is in the order M-β-CD>HP-β-CD>β-CD.更多还原