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.     

乙腈溶液中银电极的表面增强拉曼光谱研究

利用共焦显微拉曼系统研究了非水体系0.1mol·L^-1LiClO4/CH3CN溶液中,乙腈分子在粗糙银和金电极表面的吸附和解离行为。结果表明非水体系中乙腈可在银、金表面发生还原反应,产物CN^-离子与电极表面作用形成的表面配合物可以较宽的电位区间吸附于电极表面。溶液中的微量水、激光照射以及电极电位均对该反应有较大的影响。通过拉曼谱图的比较,得出乙腈分子解离出的CN^-在金电极表面比在银电极表面有更强的吸附作用。     

表面增强拉曼光谱研究银电极/乙腈界面微量水的吸附行为

利用表面增强拉曼散射技术研究了含微量水的乙腈溶液中银电极 /乙腈界面水分子的吸附行为 ,详细考察了随电极电位的改变及微量水浓度对其的影响 .研究表明 ,银电极双电层中存在多种吸附模式下的水分子结构 .在较正电位下 ,水分子主要与乙腈形成弱的氢键共吸附于电极表面上 ,ν(O— H)伸缩振动出现在3 487cm- 1左右 ,一定范围内增加体相水的浓度对其影响较小 ;在较负电位下 ,随着乙腈解离反应的进行 ,水分子转为与表面配合物 [Ag(CN) n]( n- 1 ) - 作用而共吸附于电极表面 ,其有序性地增加导致 ν(O— H)频率出现在更高的波数 3 5 83 cm- 1 .增加水的浓度加强了界面水分子间的氢键作用 ,致使 ν(O— H)红移 ;在极负电位下 ,水分子发生解离 ,ν(O— H)的振动主要来自 Li OH微晶 ,其波数为 3 665 cm- 1 .随着体相水含量的增加 ,电极表面进一步形成水合 Li OH· H2 O,特征 ν(O— H)的波数为 3 5 63 cm- 1 .     

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.     

碱性体系中金电极表面硫氰根离子的宽带和频光谱研究

本文使用宽带和频光谱研究不同电位下碱性溶液中多晶金电极表面硫氰根离子（SCN^-）的吸附行为. 在-1.1 V ~ 0.2 V（vs. SCE）,C-N伸缩振动的Stark斜率的变化表明,随着电位正移,SCN^-在金电极表面从N端吸附变为S端吸附. 在较正电位下,C-N伸缩振动具有Fano线型. 这是因为金的费米能级随电位的正移而降低,和频过程中金的电子跃迁方式从带内跃迁（sp→sp）变为带间跃迁（d→sp）,造成金基底与表面吸附SCN^-和频信号的相对相位改变. 实验表明,通过研究和频光谱线型随电位的变化可以获取电极表面电子能级相对位置的信息.     

和频光谱研究油酸包覆的Fe3 O4 纳米颗粒

采用红外-可见和频振动光谱研究了表面包覆油酸分子的Fe3O4纳米颗粒, 得到了2种实验构型(构型1: 可见光入射角63°, 红外光入射角55°; 构型2: 可见光入射角45°, 红外光入射角55°)和3种偏振组合(ssp, ppp, sps)下的和频振动光谱, 比较了2种实验构型下和频光谱的特征, 通过偏振分析方法对各个光谱峰进行了归属.     

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^-...     

二乙腈基二硫纶自组装膜修饰金电极对多巴胺的电化学催化作用

将经抛光清洗的金电极置于5mmol·L-1 cis-1,2-二腈基乙烯-1,2-二硫醇钠(简称二腈基二硫纶,Na2mnt)溶液中浸泡24h,制得Na2mnt自组装膜修饰的金电极mnt-SAM/Au,用电化学方法研究了上述修饰电极的电化学性质。结果表明:多巴胺在mnt-SAM/Au修饰电极上的氧化还原可逆性显著变好,峰电流增加;此氧化还原过程受扩散控制,多巴胺在电极上无吸附,电极不受污染。由于多巴胺是生物物质,选用在pH 7.00的磷酸盐介质中检测。在所选定的条件下,多巴胺的浓度在4.0×10-6~2.0×10-4 mol·L-1之间与其相应的峰电流(i/nA)之间呈线性关系。     

Interfacial Water Structure in Langmuir Monolayer and Gibbs Layer Probed by Sum Frequency Generation Vibrational Spectroscopy

Langmuir monolayer and Gibbs layer exhibit surface‐active properties and it can be used as simple model systems to investigate the physicochemical properties of biological membranes. In this report, we presented the OH stretching vibration of H₂O in the 4′′‐n‐pentyl‐4‐cyano‐p‐terphenyl (5CT), nonadecanenitrile (C₁₈CN) Langmuir monolayer and compared them with CH₃CN Gibbs layer at the air/water interface with polarization SFG‐VS. This study demonstrated that the hydrogen bond network is different in the Langmuir monolayer of 5CT, C₁₈CN from CH₃CN Gibbs layer at the air/water interface which showed two different water structures on the different surface layer. The results provided a deeper insight into understanding the hydrogen bond on the interfaces.     

Methanol Adsorption on TiO2 Film Studied by Sum Frequency Generation Vibrational Spectroscopy (cited:2)

A broadband infrared surface sum frequency generation vibrational spectroscopy (SFG-VS) and an in situ UV excitation setup devoted to studying surface photocatalysis have been constructed. With a home-made compact high vacuum cell, organic contaminants on TiO₂ thin lm surface prepared by RF magnetron sputtering were in situ removed under 266 nm irradiation in 10 kPa O₂ atmosphere. We obtained the methanol spectrum in the CH₃ stretching vibration region on TiO₂ surface with changing the methanol pressure at room temperature. Features of both molecular and dissociative methanol, methoxy, adsorbed on this surface were resolved. The CH₃ symmetric stretching vibration frequency and Fermi resonance of molecular methanol is red-shifted by about 6?8 cm^-1 from low to high coverage. Moreover, the recombination of dissociative methanol and H on surfaces in vacuum was also observed. Our results suggest two equilibria exist: between molecular methanol in the gas phase and that on surfaces, and between molecular methanol and dissociative methanol on surfaces.     

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     

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.     

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.     

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.     

Vibrational Spectroscopy of Surface Adsorbates by Sum Frequency Generation (SFG)

The vibrational spectroscopy by way of vibrational sum-frequency generation (VSFG) has been made of formic acid adsorbed on MgO(001) surface and of n-alkyltrichlorosilanes chemisorbed on quartz plates. It was revealed that the species on the MgO surface was formate ion (HCOO⁺) with CH bonds standing vertical to the surface and that the different adsorption sites showed up on repeated cycles of adsorption-desorption processes. The results of chemisorbed films indicated that the g-t and/or g-t-g′ conformational scquences of n-alkyl chains occurred more frequently by the length of alkyl chain and that the surface hydroxyls, which are the sites of chemisorption, are ripped off by pre-exposure of substrate to oxygen plasma.