Sequence-dependent interactions of cationic naphthalimides and polynucleotides

The binding interactions of three naphthalimide derivatives with heteropoly nucleic acids have been evaluated using fluorescence, absorption and circular dichroism spectroscopies. Mono- and bifunctionalized naphthalimides exhibit sequence-dependent variations in their affinity toward DNA. The heteropoly nucleic acids, [Poly(dA-dT)]2 and [Poly(dG-dC)]2, as well as calf thymus (CT) DNA, were used to understand the factors that govern binding strength and selectivity. Sequence selectivity was addressed by determining the binding constants as a function of polynucleotide composition according to the noncooperative McGhee-von Hippel binding model. Binding affinities toward [poly(dA-dT)](2) were the largest for spermine-substituted naphthalimides (Kb = 2-6 x 10(6) M(-1)). The association constants for complex formation between the cationic naphthalimides and [poly(dG-dC)]2 or CT DNA (58% A-T content) were 2-500 times smaller, depending on the naphthalimide-polynucleotide pair. The binding modes were also assessed using a combination of induced circular dichroism and salt effects to determine whether the naphthalimides associate with DNA through intercalative, electrostatic or groove-binding. The results show that the monofunctionalized spermine and pyridinium-substituted naphthalimides associate with DNA through electrostatic interactions. In contrast, intercalative interactions are predominant in the complex formed between the bifunctionalized spermine compound and all of the polynucleotides.     

Development of Novel Substrates for Surface-enhanced Raman and Surface-enhanced Hyper Raman Spectroscopy

Since its discovery two decades ago, surface-enhanced Raman scattering (SERS) has been explored extensively as a useful technique in the study of molecular behaviors at interfaces and in chemical and biochemical analysis. At solid-liquid interface, SERS has been practiced mainly in aqueous solution on either aggregated metal colloids or roughened metal electrodes. However, both aggregated metal colloids and roughened electrodes have their own problems as SERS substrates. One of the intriguing questions in exploring SERS application in chemistry is that can SERS-activity be gained and regulated from the dispersed metal nanoparticles immobilized on a SERS-inactive smooth electrode surface. The very essence of this question is to explore the effect on SERS-activity when the main features of two conventional SERS-surfaces, namely metal colloids and electrode, are combined. Same question can also be asked for the nonlinear three-photon surface-enhanced hyper Raman scattering (SEHRS).     

Surface-enhanced Raman spectroscopic study of DNA and 6-mercapto-1-hexanol interactions using large area mapping

The emergence of 2D SERS substrates with large areas of hot spots has enabled data to be gathered at large scale. This work presents a statistical tool for analysing large amounts of SERS data by utilizing a peak-fitting model in a specific spectral range. By analysing the distributions of Raman intensities and peak positions it is possible to directly inspect the interplay between DNA and 6-mercapto-1-hexanol on gold covered nanopillars. It is demonstrated that optimised functionalization parameters can be extracted from the Raman spectra directly. Using the peak-fitting approach it is possible to avoid miss-interpretation of intensity histograms, where contamination might contribute with an enhanced background and not a peak.     

Raman and Surface-enhanced Raman Scattering of Chlorophenols

Raman spectrum is a powerful analytical tool for determining the chemical information of compounds. In this study, we obtained analytical results of chlorophenols(CPs) molecules including 4-chlorophenol(4-CP), 2,6-dich- lorophenol(2,6-DCP) and 2,4,6-trichlorophenol(2,4,6-TCP) on the surface of Ag dendrites by surface-enhanced Raman scattering(SERS) spectra. SEM images indicate that the SERS substrate of Ag dendrites is composed of a large number of polygonal nanocrystallites, which self-assembled into a 3D hierarchical structure. It was found that there were distinct differences for those three molecules from Raman and SERS spectra. This indicates that SERS could be a new tool of detection technique regarding trace amounts of CPs.     

Surface-enhanced Raman study of organic sulfides adsorbed on silver

The surface-enhanced Raman scatterings of dimethyl sulfide, diethyl sulfide and dimethyl disulfide have been investigated in silver sol. The dimethyl disulfide molecule decomposes on silver to the corresponding mercaptide implying facile cleavage of its S---S bond. The C---S bond in dialkyl monosulfide appears not to cleave on silver. For diethyl sulfide, the C₂ conformation seems to be favorable on silver than other conformations.     

Surface-enhanced Raman scattering study of the anthraquinone red pigment carminic acid

FT-Raman and surface-enhanced Raman scattering (SERS) spectroscopy were applied in the vibrational characterization and study of the adsorption and acidity behaviour of the highly fluorescent anthraquinone red pigment carminic acid (CA) on Ag nanoparticles prepared by chemical reduction with citrate and hydroxylamine. The SERS spectra were obtained at several pHs and excitation wavelengths and on Ag nanoparticles prepared by two different methods: chemical reduction with citrate and hydroxylamine in order to find the best experimental conditions for the vibrational study and detection of CA. Three CA forms can be identified on the metal surface, corresponding to the mono-, di- and tri-anionic CA species, whose relative intensity in the SERS spectra can markedly vary depending on the chemical properties of the offered surface and the excitation wavelength. This study could be very helpful for researchers trying to apply surface-enhanced techniques in the detection of small amounts of anthraquinone molecules, both under a cultural heritage and under a biological point of view.     

Surface-enhanced Raman spectroscopy of DNA

We report a method for obtaining highly reproducible surface-enhanced Raman spectroscopy (SERS) of single and double-stranded thiolated DNA oligomers. Following a protocol that relaxes the DNA into an extended conformation, SERS spectra of DNA oligonucleotides are found to be extremely similar, strongly dominated by the Stokes modes of adenine. A spectral correlation function analysis useful for assessing reproducibility and for quantifying the highly complex changes corresponding to modifications in molecular conformation of the adsorbate molecules is introduced. This approach is used to monitor the interaction of DNA with cisplatin, a chemotherapy agent in widespread use.     

Cu2+ and AMP complexation of enlarged tripodal polyamines

The synthesis, characterization, Cu2+ coordination and interaction with AMP of three tripodal polyamines are reported. The polyamines are based on the structure of the tetraamine (tren) which has been enlarged with three propylamino functionalities (), with a further anthrylmethyl fragment at one of its terminal primary nitrogens () or with naphthylmethyl fragments at its three ends (). The protonation constants of all three polyamines show that at pH 6, all six primary and secondary nitrogen atoms in the arms are protonated. The interaction with Cu2+ and AMP (adenosine-5'-monophosphate) has been studied by potentiometric, UV-Vis, ESI-MS spectroscopy and NMR techniques. pH-Metric, NMR and ESI/MS techniques indicate that and form with AMP adducts of 1:1, 2:1 and 3:1 AMP:L stoichiometries in water. This is one of the first examples for the formation of such complexes in aqueous solution. Formation of ternary complexes between , , , Cu2+ and AMP is observed. Paramagnetic NMR techniques have been used to obtain structural information on the binding mode of AMP to the Cu2+- binuclear complexes.     

Surface-enhanced Raman Scattering of Self-assembled Superstructures

Surface-enhanced Raman scattering(SERS) is a molecular specific spectroscopic technique that amplifies the Raman signal of absorbed molecules for up to 10¹⁰times. Over the past decades, SERS substrates experienced rapid growth, resulting in excellent development for SERS analysis. Because the surface plasmonic resonance coupling between individual materials can form a "hotspot" region to maximize the Raman signal, among many substrate construction strategies, self-assembly attracts more attention in constructing superstructures with strong, uniform and stable SERS activity. In addition, a number of plasmon-free nanomaterials with appropriate superstructures samely show enhanced SERS activity, which is primarily attributed to the formation of the optical resonator. This review aims to provide a scientific synopsis on the progress of self-assembled superstructures for SERS and ignite new dis˗ coveries in the SERS platform, as well as SERS applications in various fields.     

Surface-enhanced Raman spectroscopy of half-mustard agent

The detection and identification of chemical warfare agents is an important analytical goal. Herein, it is demonstrated that 2-chloroethyl ethyl sulfide (half-mustard, CEES) can be successfully analysed using surface-enhanced Raman spectroscopy (SERS). A critical component in this detection system is the fabrication of a robust, yet highly enhancing, sensor surface. Recent advances in substrate fabrication and in the fundamental understanding of the SERS phenomenon enable the development of improved substrates for practical SERS applications.     

Surface-enhanced Raman spectrometry of chlorinated pesticides

The utility of surface-enhanced Raman scattering (SERS) spectrometry for trace determination of various chlorinated pesticides including chlordan, carbophenothion, bromophos, methyl chloropyrifos, dichloran, linuron, and 1-hydroxychlordene is described. Silver-coated substrates consisting of submicron spheres on solid surfaces were used as SERS-active media. The detection limits for these pesticides are at nanogram levels. The sensitivity and spectral selectivity of this technique for toxic chemical agents are discussed. The results indicate that SERS shows promise for the determination of an important class of chlorinated pesticides.     

Surface-enhanced Raman spectroscopy and density functional theory study on 4,4'-bipyridine molecule

The molecular geometry and vibrational frequencies of 4,4'-bipyridine (BPE) in the ground state were calculated using density functional theory (DFT) methods (B3LYP) with 6-31++G(d,p) basis set. The optimized geometric bond lengths and bond angles are obtained by DFT employing the hybrid of Beckes non-local three parameter exchange and correlation functional and Lee-Yang-Parr correlation functional. Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman) and near-infrared surface-enhanced Raman scattering (NIR-SERS) spectra of BPE on the silver foil substrate have been recorded. All FT-IR, FT-Raman and NIR-SERS band were assigned on the basis of the B3LYP/6-31++G(d,p) method. The vibrational frequencies obtained by DFT(3LYP) are in good agreement with observed results. The NIR-SERS of BPE excited by 1064nm laser line is little difference with that excited by visible laser line. This phenomenon is result to the increase of the contribution of CHEM enhancement effect. Surface selection rules derived from the electromagnetic enhancement model were employed to infer the orientations of BPE on the silver foil substrate surface. Some vibrational frequency which are sensitive to the planar or non-planar structure of BPE, and to the dihedral angle were concluded.     

对氨基苯硫酚分子的表面增强拉曼光谱及等离激元光催化反应

对氨基苯硫酚(PATP)是表面增强拉曼光谱(SERS)研究中最重要的探针分子之一. PATP吸附体系具有非常特征且异常强的SERS信号, 但人们对其SERS信号的理解仍存在较大争议. 本文结合文献, 总结了我们为了理解PATP分子异常的SERS光谱所开展的系统的理论和实验工作. 首先介绍PATP的SERS增强机理方面开展的理论工作, 研究表明PATP分子的异常SERS信号不是来自PATP分子本身, 而是来自其表面催化偶联反应产物二巯基偶氮苯(DMAB). 通过实验和DMAB合成两个方面, 验证了DMAB是异常SERS信号的根源. 其次总结了各种实验条件对PATP转化为DMAB的影响, 并从实验和理论两个角度探讨PATP的表面催化偶联反应机理. 最后, 通过对PATP体系的SERS和等离激元增强化学反应的总结, 展望表面等离激元增强化学反应的未来发展方向.     

Surface-enhanced Raman scattering study of the adsorption of croconate violet on colloidal silver particles

Very stable silver particle suspension has been synthesized for use in surface-enhanced Raman scattering (SERS) spectroscopy with near-infrared exciting radiation. Such citrate-stabilized silver particles were obtained through a suitable control of the nucleation and growth process during the synthesis. The SERS spectra of the bis(dicyanomethylene) croconate dianion or croconate violet (CrocV) were obtained, with excitation in the near-infrared and in the visible region. The differences in the spectral patterns were correlated with a pre-resonance Raman effect of the adsorbate. The vibrational frequencies of CrocV isolated and interacting with silver surface were obtained through theoretical calculations using DFT method that together the surface selection rules allowed to perform the vibrational assignment of the SERS spectra and to infer the adsorption geometry.     

Surface-enhanced Raman spectra of rhodamine 19 octadecylamide

Surface-enhanced Raman scattering (SERS) of the cationic and the neutral form of rhodamine 19 octadecylamide (R19OA) has been studied in the silver citrate colloid using NIR excitation at 1064 nm. Cationic molecules readily adsorb onto negatively charged silver nanoparticles through a positively charged xanthene part of the molecules resulting in surface enhancement of Raman scattering. Due to a lack of the positive charge in molecular structure, SERS spectrum of neutral molecules is not observed. Nevertheless, a broad band appearing at 1240 cm^?1 in the spectrum of the cationic form indicates conversion of the cationic into the neutral species occurring close to the silver surface. The observed band most likely arises from a vibration of the ring formed in the molecular structure after conversion, but before complete desorption of the neutral molecules from the metal surface. Upon addition of HCl and NaOH in the silver sol, equilibrium is shifted toward the cationic and the neutral form of R19OA, respectively, followed by corresponding changes in the Raman spectrum. In addition, FT-SERS spectra of two rhodamine dyes, rhodamine 19 (R19) and rhodamine 6G (R6G), that are structurally related to R19OA, have been studied under the same experimental conditions for comparison.     

Surface-enhanced Raman scattering study of the kinetics of self-assembly of carboxylate-terminated n-alkanethiols on silver

Adsorption of 11-mercaptoundecanoic acid (MUA) on silver from methanol and aqueous solutions was monitored in situ by surface-enhanced Raman scattering (SRES) spectroscopy. While adsorption of MUA from methanol is a one-step formation of a thiol-bound monolayer, SERS spectra reveal that monolayer formation from aqueous solution involves interactions of both carboxylate and thiol groups of MUA with the silver surface. Several Raman scattering bands, including the ν(C-S), ν(s)(COO(-)), and ν(C-C), were used to investigate the evolution of the structure of adsorbed MUA on silver surfaces. The time-dependent profiles of these bands for assembly from aqueous solution indicate a multistep process, which is initiated by the binding of both carboxylate and thiol groups to silver, producing a mixture of gauche and trans conformations. In a subsequent step, the COO-Ag interactions are displaced by stronger S-Ag bonds, leading to ordering of the resulting monolayer with formation of a complete SAM with all-trans conformations. The results also showed that the adsorption process depended strongly on the solution pH and surface potential of the metal. These factors can significantly affect the participation and displacement of -COO(-) during self-assembly of MUA from aqueous solution.     

Surface-enhanced Raman scattering detection of cholinesterase inhibitors

A new sensitive surface-enhanced Raman scattering (SERS) assay for detection of cholinesterase inhibitors such as organophosphorous pesticides using silver colloidal nanoparticles was developed and optimized. Acetylcholinesterase (AChE) mediated the hydrolysis of acetylthiocholine to produce thiocholine, which interacted with the silver nanoparticles to give a specific SERS spectrum. Variation in enzyme activity due to inhibition was measured from changes in intensity of a characteristic peak (772 cm⁻¹) of the SERS spectrum that was directly correlated with the concentration of produced thiocholine. The method was demonstrated for the detection of paraoxon as reference AChE inhibitor. Limit of detection of paraoxon for 5 min incubation at 25 °C was 1.8 × 10⁻⁸ M. This assay can be utilized for the detection of trace amounts of any AChE inhibitor.     

Surface-enhanced Raman scattering detection of lysophosphatidic acid

Surface-enhanced Raman scattering using silver nanoparticles was applied to detect various forms of lysophosphatidic acid (LPA) to examine its potential application as an alternative to current detection methods of LPA as biomarkers of ovarian cancer. Enhancement of the Raman modes of the molecule, especially those related to the acyl chain within the 800–1300 cm⁻¹ region, was observed. In particular, the C–C vibration mode of the gauche-bonded chain around 1100 cm⁻¹ was enhanced to allow the discrimination of two similar LPA molecules. Given the molecular selectivity of this technique, the detection of LPA using SERS may eliminate the need for partial purification of samples prior to analysis in cancer screening.     

对巯基苯甲酸的表面增强拉曼光谱

应用表面增强拉曼光谱研究了吸附于粗糙银电极表面的对巯基苯甲酸。对巯基苯甲酸以去质子的形式通过巯基端进行吸附,表面Ag-S键的形成及羧基的结构改变直接影响苯环的电子结构。羧基的振动谱峰均对其质子化较为敏感,其峰强度随pH值的变化表明吸附态对巯基苯甲酸的pKa约为5．9。铜离子可与吸附对巯基苯甲酸形成表面络合物,配位反应与羧基的质子化反应密切相关。     

乐果涂膜表面增强拉曼光谱研究

通过蒸发乐果饱和水溶液在磁控溅射银膜上形成乐果涂膜,利用表面增强拉曼光谱(SERS)技术研究了乐果涂膜的分子振动特性,并与乐果固体拉曼谱进行比较。研究结果表明,乐果晶体结构长程有序性的破坏造成涂膜SERS体系中υ(P—S)和υ(PS)振动峰的展宽和蓝移,水解引起乐果δ(SPOC)和δs(COPOC)振动模式强度降低,OC—N键中的O原子和N原子以及水解质子化的O在银表面吸附造成υ(OC—N)、υ(OC)、δ(N—H)、υ(CN)、δ(C—N—C)、δ(OPO)和υ(P—O)等振动模式显著增强。这为利用SERS技术研究乐果溶液以及乐果在植物体、食品中的残留提供了实验和理论依据。