【作者】 李占龙；

【导师】 里佐威； 彭慰先；

【作者基本信息】 吉林大学 ， 光学， 2009， 博士

【摘要】 β-胡萝卜素在光合作用中有采集,转移,淬灭单线态氧等功能;有双键结构的共轭多稀类分子在可见和紫外光谱区含有几个电子吸收带,因此它又是共振拉曼光谱研究的理想样品之一;在医学领域β-胡萝卜素又是一种有效预防癌症的天然生物大分子,近年来已从分子水平,细胞和基因等不同的途径阐述了抗癌机理和效果;同时它具有半导体特性使之成为一种重要的光电材料。因此对其研究具有重要的理论研究意义又有光明的应用前景。多稀类分子的性质,功能与其分子结构有极大的关系,尤其是这种链状大分子结构有序性与分子的性质,功能密切相关。因此研究结构有序性以及结构有序性对分子性质和功能的影响是倍受国内外研究人员重视的课题。大量分子结构信息反映在谱峰的峰强上而不单是反映在谱峰的所在位置上。对于分子光谱的研究,我们不应只满足于谱峰位置的测定与分析上,而应着手于谱峰强度的测定与分析上,这样才能真正打开分子光谱学的研究大门。拉曼散射截面作为分子散射入射光能力的一个重要的参数,它不仅与激发光的波长和分子结构有关,还与分子所处的环境有关。本文针对多稀类分子分子结构有序性对拉曼散射截面的影响进行研究,主要包括以下几个内容:第一章:介绍拉曼散射及相关效应研究的历史和现状,相关概念和技术,以及本论文的选题背景、研究内容和研究意义。第二章:对和本文相关的光散射理论加以针对性的描述和概括,包括极化率、诱导偶极矩的概念、拉曼散射经典、半经典理论和量子理论,以及分子间相互作用理论和模型。第三章:对液芯光纤自发拉曼散射技术（LCOF-RS）、液芯光纤内共振拉曼散射技术（LCOF-RRS）两种技术方法的特点加以了概括。第四章:实验.主要介绍实验的步骤,方法和实验仪器。第五章:（1）将!-胡萝卜素溶解在不同的溶剂中,利用可见吸收和拉曼光谱,分析了分子的有序性和拉曼散射截面的变化。只是采用共振增强效应,无法获得满意的解释,我们尝试了一种新的电子-声子偶合的CC相干振动模型对其进行试探性的解释。（2）将液芯光纤和共振拉曼联合,发挥两种技术的优点。获得了低浓度下极性溶剂——水中(10^-6—10^-10M)!-胡萝卜素拉曼散射截面变化规律。给出低浓度下的!-胡萝卜素的分子有序性和散射截面之间的定性关系,采用电子-声子相干振动给出了理论解释。（3）利用LCOF—RRS技术对!-胡萝卜素分子在非极性溶剂——二硫化碳中低浓度下(10^-5-10^-11M),拉曼散射截面的变化规律及分子结构有序性。在更低浓度下(10^-7-10^-11mol/L)随着浓度的降低!-胡萝卜素拉曼频移(1520 cm^-1)发生红移、线宽变窄,该研究结论是相干振动的最有利的证据。第六章:论文总结,对本论文的所做工作进行总结,指出文章的优点与不足,对本课题进行展望。本论文的研究主要是研究了β-胡萝卜素的结构有序性同拉曼光谱的散射截面（强度）的定性关系,随有序性提高拉曼散射截面变大。β-胡萝卜素的溶剂效应可以方便地模拟其在不同的蛋白质环境下的频移特性,具有方便快捷的特点,采用完全的共振拉曼无法解释其散射截面的增强,而由于分子结构有序性的增加,引起CC相干振动具有不可忽视的作用。在不同的溶剂中拉曼散射截面发生如此大的变化,可以想象其在不同的蛋白质环境中也同样表现不同的散射截面,这很可能与β-胡萝卜素分子在光和作用或淬灭单线态氧的过程有关,需要进一步的研究和探讨。我们利用液芯光纤的光放大作用,进行了极低浓度下的拉曼散射截面的测试,显示了在低浓度下拉曼散射截面突然增大的特性,利用拉曼频移表征了分子的结构有序性,弥补了在很低浓度下难以获得电子吸收光谱的缺陷。在很低的浓度下获得共振拉曼散射,展示了共振拉曼在分子结构分析中具有红外吸收无法比拟的优势,在多稀分子中的分析、鉴别、检测中具有实际应用价值,特别是对分子工程学、分子生物学、分子医学、纳米材料等提供了一可行的测试研究手段,丰富了拉曼散射的研究内容、研究深度和广度,对于单分子的研究具有一定的借鉴价值。更多还原

【Abstract】 The study of biomolecules promotes the development of life science, medicine and chemistry etc.The non-biological application of biomolecules is a challenging research,and is strongly potential. Recently,biomolecules have been applied to catalyzer,molecular identification,optical memory and molecular lead etc.The study of bimolecules promotes the progress of the experimental and theoretical research for molecular interaction,resonance Raman effect,surface enhancement Raman scattering.β-carotene molecule has the function of collecting optical energy,energy transfer,effective singlet oxygen quencher and free radical trap.We know that molecule structure has closely related with the property and function of molecule.Especially the molecular chain structural order of this kind of long chain conjugated polyene effects on the property and function of molecule. Moreover effect of the optimized order of polyene on the optical property is focused by the researcher.But recent years the progress is slow for scare research method,for example the polyene molecular chain structural order study of the extremely low concentration is not found on the papers.The study to the molecular chain structural order is urgent by the needs of biological science and material science.Raman cross section（RCS） is an important parameter which can shows the molecular microscopic property as well as the Raman shift and the line width.It relates not only to the incident frequency and the structure of a scattered molecule but also to the environment where the scattered molecules are located.Furthermore,it indicates the light-scattering capacity of a particular molecule and the distribution of electric cloud. The paper calculated the Raman cress section ofβ-carotene on different molecular environment and at the same time the chain structural order is studied by the Raman spectra and absorbing spectra.1 The RCSs ofβ-carotene in different solvents and the molecular chain structural order.Under 514.5nm excitation laser the twe basic characteristic Raman line are1520cm^-1,1150cm^-1,which originate,respectively,from carbon-carbon single and double-bond stretching vibration of the conjugated backbone. The cyclohexane line 1444cm^-1 is regard as internal standard,shown in fig.1.Fig.1 Resonance Raman spectra ofβ-carotene in aqueous solution at 10^-5M concentration1 CS₂ 2 C₆H₆ 3 CH₃OH 4 C₂H₅OH 5 CCL₄ Table 1 The relative RCS for C=C and C-C stretching modes of aqueousβ-Carotene at 10^-5M at different solventsThe relative RCS for C=C and C-C stretching modes of aqueousβ-carotene at different solvents were computed.Table 1 shows the relative RCS of aqueousβ-carotene at solvents,in the paper the relative RCS ofβ-carotene is 5.1*10⁷ in benzene.From the relative RCS we can find that the absolute RCSs for C=C and C-C stretching mode ofβ-carotene is larger than general RCS(10^-30 cm² molecule^-1Sr^-1)for about 10⁶～10⁷ times. Figure 2 and Figure 3 show that the intensity of Raman is increasing linearly with the increase of the solvents.The slope of Figure 2 is a little steeper than Figure 3.It can be seen the Raman bands of C=C stretching is more sensitive to around environment than C-C stretching. Figure 4 and Figure 5 show the relative RCSs ofβ-Carotene increase With the increase of the solvents refractive index,especially the relative RCS ofβ-Carotene in CS₂ is the largest.Figure 6 show the absorbing spectra ofβ-Carotene in different solvent.With the increase of solvents refractive index the wavelength peak shift red,indicating that the molecules chain become extension.ExtendedЛ-electron giving a strong electron-phonon coupling bring CC coherent vibration,meaning a large RCS.The increasing factor to the RCS is about 10～10².Fig.2 Relative Raman intensity of C=C(1520cm^-1) inβ-Carotene and Refractive index of solventsFig.3 Relative Raman intensity of C-C(1150cm^-1)inβ-Carotene and Refractive index of solvents Fig.4 Relative RCSs for C=C(1520 cm^-1) stretching mode of aqueousβ-Carotene in solventsFig.5 Relative RCSs for C-C(1150 cm^-1) stretching mode of aqueousβ-Carotene in solventsFig.6β-Carotene absorption spectra in solvents2 The study of RCSs and molecular chain structural order in polar solvent （water）at low concentrationUsing Teflon-AF2400 liquid optical fiber,RCSs for C=C and C-C stretching modes ofβ-carotene in aqueous solution at low concentrations(10^-6-10^-10 M) were determined by measuring Raman intensity.It was unexpected that the RCS increased rapidly with the decrease of concentration at extremely low concentration range(10^-8-10^-10 M),larger than general RCS (10^-30cm²molecule^-1Sr^-1) for 10⁹ times.Fig.7 shows the dependence of the changing tendency of RCS for C=C and C-C stretching mode of aqueousβ -Carotene on the concentration.Each point on the curve is the value of the RCSs at various concentrations.The molecular chain tended to become extension with the concentration decreasing,Despite the fact that the tendency is not very clearly.Fig.7 The relative changing tendency of RCS for C=C stretching mode ofβ-Carotene in aqueous solution with the decreasing concentration. The solid dots are the RCS values of 1520cm^-1 band versus various concentrations.The inset is corresponding to C-C stretching mode (1155cm^-1).3 The study on RCS and molecular chain structural order in nonpolar solvent（CS₂） at low concentration.RCS for C=C and C-C stretching modes ofβ-carotene in aqueous solution at low concentrations(10^-6-10^-11 M) were determined by measuring Raman intensity.It was unexpected that the RCS increased rapidly with the decrease of concentration at extremely low concentration range (10^-8-10^-11M),which is larger than general RCS(10^-30cm²molecule^-1Sr^-1) for 10¹⁰ times.We fit the RCS ofβ-carotene and the concentration according to the data on Table 2:σ_R（C）=A exp（-C/B）+D Where A B D is fitted parameter;C isthe concentration ofβ-carotene.To the C=C stretching mode,A=38838,B=1.9E-10,D=287,the correlation factor is R²=0.995;To the C-C stretching mode,A=1869,B=2.0E-9,D=36 the correlation factor is R²=0.986.The dot is the experimental data,and the solid line is fitted line.From the figure8 and figure9,you can see that the tendency of RCS of C-C stretching mode forβ-carotene is the same as one of the C=C stretching mode.With the concentration decreasing the Raman line shift red,shown in figure10.The band line width become narrow,which is attributed to the CC coherent from the electon-phonon coupling.In the nonpolar solventsβ-carotene Raman band shift red is clearer than that one in polar solvents,which means that the chain structural order ofβ-carotene in nonpolar solvents is better than that one in polar solvents.We give experimental evidence of the changes in the structure of the molecular backbone induced by the solvents.Table2 RCS ofβ-carotene at different concentration Fig.8 The relative changing tendency of RCS for C=C stretching mode ofβ-Carotene in aqueous solution with the decreasing concentration.Fig.9 The relative changing tendency of RCS for C-C stretching mode ofβ-Carotene in aqueous solution with the decreasing concentration.Fig.10 The Raman shift in different concentrationThe study of RCS forβ-carotene in different solvents can supply a emulating environment where the subject,especially biological samples exist,which is a potentially powerful analytical tool for life sciences, medicine and biological environment.Resonance about RCS of biomolecules at extremely low concentrations supplies experimental data and theoretical basis for the microscope mechanism of molecular interaction, which is helpful to know the natures of electron-phonon coupling. These researches are not only basic research,but also applicable one. All the studies will be beneficial to the bioanalytical and biomedical application,surface chemistry etc.更多还原