不同受限状态下链硫醇的非线性光学响应

以和频(SFG)振动光谱技术探测了正十二硫醇(DDT)在不同受限状态下的分子振动信号,包括金属基底上的自组装单层(SAM)分子,放置在二氧化硅基底上的表面DDT化的金纳米粒子以及金纳米粒子的甲苯溶液.在三种状态下都探测到了来自于DDT分子的振动光谱,振动光谱的区别提供了在不同受限态下DDT分子的结构信息.在金属基底上DDT分子排列规整,放置在二氧化硅基底上的金纳米粒子表面的DDT分子具有一定的柔性,在空气-甲苯溶液界面金纳米粒子表面的DDT分子高度无序.此外,光谱实验显示,金纳米粒子表面的分子振动信号产生了局域场增强的效应,相对于金基底上的自组装单层分子而言,增强系数为102-103,取决于光谱的偏振组合.     

建立在硫醇分子电化学替换组装基础上的纳米粒子区域化组装

利用金基底电位变化时硫醇自组装膜的吸脱附性质, 通过改变基底电位和组装溶液, 用电化学方法在金基底上实现了传统自组装技术难以实现的硫醇分子的替换组装; 通过金基底的分区化设计, 用控制电位的组装技术在基底的不同微区内制备了不同末端官能团的硫醇及其衍生物自组装膜; 并在此基础上实现了纳米粒子的区域化组装.     

水/油界面上自组装金纳米粒子单层薄膜

采用界面自组装的方法制备了金纳米粒子单层薄膜。该方法克服了传统制备金纳米粒子薄膜需要引入第三种助剂的缺点,仅用金溶胶和另外一种疏水溶剂通过简单的混合,就可得到金纳米粒子单层薄膜。通过调节疏水溶剂的极性,可以调节组成金膜中金纳米粒子的数密度,即纳米粒子的间距。     

金电极表面上硫醇自组装的影响因素研究进展

本文综述了金表面上硫醇自组装的影响因素研究进展,包含表面预处理、电位控制、外加超声、微波和磁场、金属离子欠电位沉积和组装方式等几个方面。通过金表面上硫醇自组装影响因素的总结探讨,对硫醇单层的快速可控与重现构建具有重要的指导意义。     

利用和频振动光谱研究空气/短链脂肪酸界面的分子取向

利用和频振动光谱(SFG-VS)方法检测了5种短链脂肪酸分子(乙酸、丙酸、正丁酸、正戊酸及正己酸)在空气/纯液体界面的结构, 得到了3种偏振组合(ssp, ppp, sps)下的和频振动光谱. 通过偏振选择定则对各个谱峰进行了指认和分析, 同时计算出空气/纯脂肪酸液体界面上脂肪酸分子的甲基取向角. 对比发现, 从丙酸到己酸, 分子甲基基团的界面取向角随碳链的增长略有增大. 并对其机理进行了分析.     

氟化单元封端的不同聚合度PBMA甲苯溶液气/液界面结构

采用ATRP技术合成具有不同聚合度的末端连接甲基丙烯酸全氟辛基乙酯(FMA)单元的聚甲基丙烯酸丁酯(PBMAm-ec-PFMAn).利用和频振动光谱(SFG)和表面张力测定技术研究了各种氟化聚合物溶液的气/液界面结构.发现PBMAm-ec-PFMAn甲苯溶液的表面活性及其气/液界面的结构与两种结构单元数密切相关.当PFMA聚合度(n)大约为4和6时,聚合物溶液的表面张力随着PBMA聚合度的增加从21增加到25mN/m(该值与PBMA均聚物溶液相同).SFG的研究结果表明PBMA段较长时溶液表面被PBMA所占据.PBMA段较短时,PFMA组分吸附在溶液表面,排列比较有序且紧密堆积.当PBMA末端只有1个FMA单元时,其甲苯溶液的表面张力随PBMA段长稍有增加(从22增加到23mN/m),其值介于21与25mN/m之间.研究表明当PBMA段较短时,可能聚合物中的氟化组分吸附在溶液表面,但其排列的有序性较差.随着PBMA聚合度的增加,氟化组分与PBMA组分可能同时占据在溶液表面,这时其表面张力大约为23mN/m.     

新型偶氮苯硫醇衍生物自组装膜的制备与结构表征

自组装单分子膜(ＳＡＭｓ)是近年来引起广泛注意的一种稳定的、二维有序的、致密的有机超薄膜体系,由于其优越的性能,在润滑、吸附、防腐、电化学及微电子等领域中显示出广阔的应用前景[1～4].自组装单分子膜是使用含有各种活性官能团(如-ＣＯＯＨ,-ＳＨ,-Ｓ-Ｓ-,-ＯＨ,-ＣＮ等)的分子,以化学键的形式与相应的基底(如Ａｕ,Ａｇ,Ｃｕ,Ｐｔ,Ｓｉ,Ｍｉｃａ等)相互作用从而自发地形成自组装膜.根据不同的研究或应用目的合理设计组装分子的结构及基底表面,从而得到具有所需功能的自组装单分子膜是近年来界面科学和材料科学等领域研究的热点之一.…     

聚合物-纳米金在油水界面的自组装及有序结构的构筑

聚合物-纳米金复合物既具有金纳米粒子的光、电及催化性能,又具有聚合物的可加工性及对外界的刺激响应性,因此已成为高分子科学及材料科学研究的热点。本文主要介绍了我们实验室在聚合物-纳米金在油水界面的自组装及有序结构的构筑研究方面的相关工作:(1)利用界面聚合的方法制备侧链接枝亲水性金纳米粒子的聚苯乙烯及杂化聚合物在水溶液中的自组装;(2)亲水性金纳米粒子及疏水性聚合物(或疏水性磁性纳米粒子)在油水界面的自组装研究;(3)利用金纳米粒子为交联点制备具有温度响应性聚合物微凝胶的研究。     

水/正己烷界面上超声波介导组装金纳米粒子薄膜用作SERS基底

本文以高能量的超声波作用于溶胶/疏水溶剂两相体系, 使溶胶相中的纳米颗粒先被加速吸附到乳液油滴的小表面. 随着乳液油滴向上转移, 在界面处破乳, 纳米颗粒就被释放到水/油界面上来, 形成自组装纳米薄膜. 尽管这种组装机制尚不完全清楚(如超声波是否确实如预期那样可以提高纳米粒子的动能), 但这种方法不需要预先对纳米粒子表面疏水修饰, 也不需向体系中添加表面活性有机小分子或电解质等诱导剂, 可快速有效制备表面“洁净”的纳米粒子薄膜, 并可用作高活性SERS基底.     

新型偶氮苯硫醇衍生物自组装膜的制备与结构表征

Self Assembled Monolayers(SAMs) of a series of mercapto contained azobenzene derivatives with the structure of CnH2n+1AzoO(CH 2)mSH (where n =4,6,8,10,12; with m =3,5 respectively) were prepared and characterized. Wettability measurement of water on the SAMs demonstrates that molecular packing density in the monolayers increases while the alkyl chain in the molecules is lengthened. Both the n and m values have similar contribution to the wetting property of SAMs. The RA IR spectra reveal that the alkyl chains in the SAMs tilt away dramatically from the surface normal direction with the increase in their length. However, the orientation of azobenzene moiety is found to be influenced slightly by the alkyl chain length, which is due to the tenderness of the molecule.     

二价阳离子诱导细胞膜融合的和频光谱研究（英文）

细胞膜融合是一种重要的基础生物学过程,细胞的很多生物学功能都涉及到细胞膜的融合.二价阳离子可以通过与带负电磷脂的结合诱导磷脂膜的融合,然而,其详细的分子学机制目前还不太清楚.本文应用表/界面敏感的和频振动光谱结合动态光散射实验研究了磷脂分子层对二价金属离子(如Ca²⁺和Mg²⁺)暴露的响应.动态光散射实验测量的粒度分布结果显示Ca²⁺可以诱导囊泡间融合,而Mg²⁺的介导却不能导致磷脂膜的融合.为了应用和频光谱研究磷脂分子不同基团对金属离子的响应,本文设计了十八烷基三氯硅烷自组装单分子层/磷脂单分子层组成的混合模型膜系统进行和频振动光谱实验.实验发现,相比于Mg²⁺,Ca²⁺与磷脂头部基团PO₂^-有更强烈地相互作用,会更容易诱导细胞膜融合.和频光谱实验还显示,虽然两种金属阳离子没有与磷脂中C=O基团直接连接.但是Ca²⁺/Mg²⁺-PO₂^-...     

Methanol Perturbing Modeling Cell Membranes Investigated using Linear and Nonlinear Vibrational Spectroscopy (cited: 3)

Cell membranes play a crucial role in many biological functions of cells. A small change in the composition of cell membranes can strongly influence the functions of membrane-associated proteins, such as ion and water channels, and thus mediate the chemical andphysical balance in cells. Such composition change could originate from the introduction of short-chain alcohols, or other anesthetics into membranes. In this work, we have applied sum frequency generation vibrational spectroscopy (SFG-VS), supplemented by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), to investigate interaction between methanol and 1,2-dimyristoyl-d54-sn-glycero-3-phosphocholine (d54-DMPC) lipid bilayers. Lipid's hydrocarbon interior is deuterated while its head group is hydrogenated. At the same time, CH₃ symmetric stretch from methanol and lipid head amine group has different frequency, thus we can distinguish the behaviors of methanol, lipid head amine group, and lipid hydrocarbon interior. Based on the spectral feature of the bending mode of the water molecules replaced by methanol, we determined that the methanol molecules are intercalated into the region between amine and phosphate groups at the lipid hydrophilic head. The dipole of CH₃ groups of methanol and lipid head, and the water O-H all adopt the same orientation directions. The introduction of methanol into the lipid hydrophilic head group can strongly perturb the entire length of the alkyl chains, resulting that the signals of CD₃ and CD₃ groups from both leaflets can not cancel each other.     

和频与差频振动光谱实验构型的分析模拟

实验构型分析是定量分析和频振动光谱的基础.变换实验构型,不仅要考虑某一振动模式信号强度的大小,还要考虑不同构型下的信号检测效率.现有的和频振动光谱实验构型分析主要考虑前者.本文探讨实验构型分析中所涉及的信号检测效率问题,模拟在共向式和频(差频)及对射式和频(差频)振动光谱实验中选取何种实验构型对采集信号光更加合理有效.利用相干光学过程能量守恒和动量守恒原理,分析了入射角及入射光频率等因素对信号出射角的影响,并模拟了信号出射角与入射角及入射光频率的关系,得到了可选的入射角组合最多、出射角随入射光频率变化最小的实验构型.结果表明,和频振动光谱采取共向式实验构型,差频振动光谱采取对射式实验构型,有利于信号采集,进而有利于用实验构型分析方法对和频(差频)振动光谱进行定量研究.     

Absolute Orientation of Molecules with Competing Hydrophilic Head Groups at the Air/Water Interface Probed with Sum Frequency Generation Vibrational Spectroscopy

The constructive or destructive spectral interference between the molecular groups oriented up and down at the interface in the sum-frequency generation （SFG） spectra provides a direct measurement of the absolute orientation of these molecular groups. This simple approach can be employed to interrogate absolute molecular orientations other than using the complex absolute phase measurement in the SFG studies. We used the -CN group in the p-cyanophenol （PCP） molecule as the internal phase standard, and we measured the phases of the SFG fields of the -CN groups in the 3,5-dimethyl-4-hydroxy-benzonitrile （35DMHBN） and 2,6-dimethyl-4-hydroxy-benzonitrile （26DMHBN） at the air/water interface by measuring the SFG spectra of the aqueous surfaces of the mixtures of the PCP, 35DMHBN, and 26DMHBN solutions. The results showed that the 35DMHBN had its -CN group pointing into the aqueous phase; while the 26DMHBN, similar to the PCP, had its -CN group pointing away from the aqueous phase. The tilt angles of the -CN group for both the 35DMHBN and 26DMHBN molecules at the air/water interface were around 25°-45° from the interface normal. These results provided insights on the understanding of the detailed balance of the competing factors, such as solvation of the polar head groups, hydrogen bonding and hydrophobic effects, etc., on influencing the absolute molecular orientation at the air/water interface.     

有序分子系统的线性与非线性光谱学的简化描述

A simplified formulation for treating the linear and nonlinear spectroscopy of ordered molecular systems is presented,in order to help experimentalists to have an explicit physical picture and quantitative tool on using linear and nonlinear spectroscopy to study molecules in ordered molecular systems. This formulation is expended from our recent quantitative orientational and polarization treatment on second-order nonlinear spectroscopic techniques in interface studies,namely,the Second Harmonic Generation（SHG）and Sum Frequency Generation-Vibrational Polarization Spectroscopy（SFG-VPS）. The key to this formulation is to simplify the effective linear or nonlinear molecular susceptibility and construct the general orientational functional with a clear approach to calculate the orientational and intensity parameters from the experimental parameters,which determines the orientational and polarization behavior of the general orientational functional in a particular experimental configuration. Also discussed are the advantages of coherent spectroscopic techniques over incoherent ones for the accurate measurement of orientation and ordering of ordered molecular system.     

Sum Frequency Generation Vibrational Spectra of Perovskite Nanocrystals at the Single-Nanocrystal and Ensemble Levels

Determination of molecular structures of organic-inorganic hybrid perovskite (OIHP) nanocrystals at the single-nanocrystal and ensemble levels is essential to understanding the mechanisms responsible for their size-dependent optoelectronic properties and the nanocrystal assembling process, but its detection is still a bit challenging. In this study, we demonstrate that femtosecond sum frequency generation (SFG) vibrational spectroscopy can provide a highly sensitive tool for probing the molecular structures of nanocrystals with a size comparable to the Bohr diameter (~10 nm) at the single-nanocrystal level. The SFG signals are monitored using the spectral features of the phenyl group in (R-MBA)PbBr₃ and (R-MBA)₂PbI₄ nanocrystals (MBA: methyl-benzyl-ammonium). It is found that the SFG spectra exhibit a strong resonant peak at 3067±3 cm^-1 (ν₂ mode) and a weak shoulder peak at 3045±4 cm^-1 (ν_7a mode) at the ensemble level, whereas a peak of the ν₂ mode and a peak at 3025±3 cm^-1 (ν_20b mode) at the single-nanocrystal level. The nanocrystals at the single-nanocrystal level tend to lie down on the surface, but stand up as the ensemble number and the averaged sizes increase. This finding may provide valuable information on the structural origins for size-dependent photo-physical properties and photoluminescence blinking dynamics in nanocrystals.     

Characterization of Formation Kinetics of Self-Assembled Thiol Monolayers on Gold by Electrochemical Impedance Spectroscopy

Interest in the properties of organized monolayers has grown enormously in recent years because these monolayers can provide a means to control the interface at a molecular level1. The self-assemblies of alkanethiols and their derivatives were probably the most intensively studied due to their stability, well-packed structure, ease in preparation, and flexibility in designing the tail group2. The adsorption kinetics of thiol monolayer has been studied by using several techniques, including con…     

和频振动光谱(SFG-VS)研究超铺展三甲基硅烷表面活性剂在空气/水界面的振动光谱和吸附

The C-H stretch vibrational spectra of the trisiloxane superspreading surfactant Silwet L-77((CH3)3Si-O-Si(CH3)(C3H6)(OCH2CH2)7-8OCH3)-O-Si(CH3)3) at the air/water interface are measured with the surface Sum Frequency Generation Vibrational Spectroscopy (SFG-VS). The spectra are dominated with the features from the –Si-CH3 groups around 2905 cm-1 (symmetric stretch or SS mode) and 2957 cm-1 (mostly the asymmetric stretch or AS mode), and with the weak but apparent contribution from the -O-CH2- groups around 2880 cm-1 (symmetric stretch or SS mode). Comparison of the polarization dependent SFG spectra below and above the critical aggregate or micelle concentration (CAC) indicates that the molecular orientation of the C¡H related molecular groups remained unchanged at different surface densities of the Silwet L-77 surfactant. The SFG-VS adsorption isotherm suggested that there was no sign of Silwet L-77 bilayer structure formation at the air/water interface. The Gibbs adsorption free energy of the Silwet surfactant to the air/water interface is -42.2±0.8kJ/mol, indicating the unusually strong adsorption ability of the Silwet L-77 superspreading surfactant     

A Highly Sensitive Femtosecond Time-Resolved Sum Frequency Generation Vibrational Spectroscopy System with Simultaneous Measurement of Multiple Polarization Combinations

Characterization of real-time and ultrafast motions of the complex molecules at surface and interface is critical to understand how interfacial molecules function. It requires to develop surface-sensitive, fast-identification, and time-resolved techniques. In this study, we employ several key technical procedures and successfully develop a highly sensitive femtosecond time-resolved sum frequency generation vibrational spectroscopy (SFG-VS) system. This system is able to measure the spectra with two polarization combinations (ssp and ppp, or psp and ssp) simultaneously. It takes less than several seconds to collect one spectrum. To the best of our knowledge, it is the fastest speed of collecting SFG spectra reported by now. Using the time-resolved measurement, ultrafast vibrational dynamics of the N-H mode of α-helical peptide at water interface is determined. It is found that the membrane environment does not affect the N-H vibrational relaxation dynamics. It is expected that the time-resolved SFG system will play a vital role in the deep understanding of the dynamics and interaction of the complex molecules at surface and interface. Our method may also provide an important technical proposal for the people who plan to develop time-resolved SFG systems with simultaneous measurement of multiple polarization combinations.