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Potential oscillations that occur during galvanostatic formic acid oxidation on a Pt electrode are investigated by time-resolved surface-enhanced infrared absorption spectroscopy (SEIRAS). Temporal potential oscillations allowed carbon monoxide (CO) and formate to adsorb on the surface and change their coverages synchronously.

The absorption process of bisphenol A (BPA) in a number of poly(acrylate) thin films, such as poly(2-methoxyethyl acrylate) (PMEA), poly(ethyl acrylate) (PEA), poly(n-butyl methacrylate) (PBMA), and poly(methyl methacrylate) (PMMA), has been investigated by quartz crystal microbalance (QCM) and infrared reflection absorption spectroscopy (IRRAS) measurements. Both QCM and IRRAS measurements show that the BPA molecules absorb in PMEA, PEA, and PBMA thin films but not in PMMA thin film. The differences in the BPA absorption behavior are mainly attributed to the difference in the glass transition temperature ([T.sub.g]) between these polymers. This absorption behavior also depends on the BPA concentration and polymer film thickness. Furthermore, IRRAS characterization demonstrates that the hydrogen bonding is formed between the hydroxyl group in BPA and the carbonyl group in the poly(acrylate) thin films. BPA molecule absorbed in these polymer thin films can be removed by ethanol rinse treatment. By optimizing experimental conditions for the QCM electrode modified by PMEA thin film, detection limitation of ~1 ppb for BPA can be realized by the in situ QCM measurement. This method is expected to be a sensitive in situ detection way for trace BPA in the environmental study.

Results of a study revealed that the second harmonic (SH) intensity at gold electrodes modified with self-assembled monolayers (SAMs) of two novel molecules, which have trans-ferrocenyl-nitrophenyl ethylene and thiol groups as the second harmonic generation and surface-attached groups, was dependent on the oxidation state of the ferrocene group. The SH intensity rose when the ferrocene moiety of the SAMs was oxidized to the ferricenium cation. The molecular orientation change in each SAM upon reduction/oxidation of the ferrocene moiety was also studied by Fourier transform infrared reflection.

An electrochemical quartz crystal microbalance (EQCM) and in situ electrochemical scanning tunneling microscopy (STM) were used to study the adsorption and electrochemical reduction of PdCl(sub 4)(super 2-) on an Au(111) electrode in H2SO4 solution containing PdCl(sub 4)(super 2-). The palladium deposition was found to proceed with an epitaxial layer-by-layer growth mode. The adlayer of PdCl(sub 4)(super 2-) was found to be on the deposited palladium layer.

The electro-oxidation of methanol on platinum by in-situ surface enhanced infrared absorption spectroscopy with the Kretschmann ATR configuration is explained. It is found that formate should be included as a reactive intermediate in the non-CO path in the reaction of the methanol electro-oxidation.

Ground state molecular vibration coupling to low energy electronic ruthenium(III,II) porphyrin dimer transition is examined.

The four different oxidation states of a monocarbonyl trinuclear ruthenium complex Ru3(mu-O)(mu-CH3COO)6(CO)(pyridine)2 (compound 1) are measured by the in-situ Fourier transform infrared reflection absorption spectroscopy with a thin layer cell. The complex 1 exhibit electrochemically reversible sequential one-electron steps with net charges from -1 to +2 in acetonitrile. Partial decomposition occurs in the +1 and +2 potential region. In 1 the d-pi(Ru)-p-pi(mu3-O) molecular orbital is delocalized and the Ru(II)-CO state is localized.

Accurate quantification of miRNA expression level is essential to the study of its biology, and many cutting-edge technologies have been developed to accommodate this need. Yet most of them were designed primarily for the "regular" RNAs such as animal miRNAs and may overlook the fact that plant miRNAs and many other small noncoding RNAs are 2'-O-methylated at the 3' end nucleotide. According to our experimental data and previous reports, this structural variation is detrimental to the effectiveness of the commonly used enzymatic labeling methods, leading to strongly biased results (∼24-fold difference). Herein, we demonstrate that our Stacking-Hybridized Universal Tag (SHUT) microarray assay is well suited for unbiased profiling of both normal and methylated small RNA species. The detected signals of small RNAs with 2'-hydroxyl and 2'-O-methyl 3' ends are highly consistent (no significant difference at α = 0.01 level). For specificity, the presented method edges over others by its unique ability to discriminate single-base difference at or near the 5' end. Notably, as compared to many delicate techniques, this enzyme-free and label-free approach requires much less reagent and manipulation, benefiting the SHUT-based applications with more efficient workflow and highly reproducible results. [ABSTRACT FROM AUTHOR]

The synthesis and assembly of nanomaterials from molecular components are receiving a great deal of attention because of expectations in a wide variety of applications such as molecular devices and sensors. Transition-metal complexes and clusters are eminent candidates for the molecular building blocks because of their versatile physical and chemical properties. Because of the availability of precise ligand control in the ruthenium clusters, molecular switching properties are highly expected for the functional layers. These unique electrochemically controlled surface reactions are more convenient and efficient than conventional ligand exchange reactions in solution.

Guest-promoted modulation of the electronic states in metal-organic frameworks (MOFs) has brought about a new field of interdisciplinary research, including host-guest chemistry and solid-state physics. Although there are dozens of studies on guest-promoted enhancement of the electrical conductivity properties, including stoichiometry, conductive carriers and structure-property relationships have been scarcely studied in detail. Herein, we studied the effects of continuous and controlled bromine vapor doping on structural, optical, thermoelectric, and semiconducting properties of Cu[Cu(pdt) 2 ] (pdt = 2,3-pyrazinedithiolate) as a function of bromine stoichiometry. We demonstrated that the same material could act as both p- and n-type semiconductors by tuning the stoichiometry of Br doped in Br x @Cu[Cu(pdt) 2 ], and a change in the charge-carrier type from holes in pristine MOF to electrons upon bromine vapor doping was observed. Bromine molecules acted as an oxidant, causing the selective oxidation of [Cu II (pdt) 2 ] in the host framework. In addition, a redox hopping pathway between the partially oxidized Cu II /Cu III center contributed to the enhancement of the electrical conductivity of the MOF.

This paper reviews the dispersion of complex refractive indices for representative intense vibrational bands of organic liquids in the absolute scale. Conspicuous variations in both real and imaginary refractive indices over the intense bands are precisely determined as a function of infrared wavenumber by attenuated total reflection infrared absorption measurement. The accurate spectral data offer an excellent reference to calibrate the absolute infrared intensities by various quantum chemical calculations, and thus, critical comparison between the present experiment and computation was reported to clarify the general accuracy of the quantum chemical calculations. The precise data of the dispersion will be utilized to clarify their impact on the analysis of vibrational spectroscopy of interfaces in the subsequent paper.

Sharp and intense vibrational bands are characterized with conspicuous dispersion of complex refractive indices. Based on the quantitative data of dispersion in the preceding paper, this paper clarifies the influence of the dispersion on the sum frequency generation (SFG) spectroscopy. As a consequence of the large dispersion, the lineshapes of SFG spectra could be influenced by the frequency dependence of the Fresnel factor as well as the nonlinear susceptibility. This paper argues the relative importance of the two factors in general cases and provides a useful criterion to evaluate their importance. The effect of Fresnel dispersion becomes significant when the SFG spectrum involves a sharp and intense vibrational band as well as a large non-resonant background susceptibility, typically in some solid-liquid interfaces. A possible way to correct the effect of Fresnel dispersion is suggested using the heterodyne measurement.

The pulmonary surfactant monolayer is indispensable for the respiratory system. Recently, it was reported that some unsaturated lipids of the pulmonary surfactants are oxidized by low-level ozone in ambient air. However, the molecular-level understanding of the reaction mechanism is still limited due to technical difficulties. We applied heterodyne-detected sum frequency generation (HD-SFG) spectroscopy to probe the reaction process of an unsaturated phospholipid monolayer (1-palmitoyl-2-oleoyl-glycero-3-phosphocholine, POPC), which is one of the major lipids in the pulmonary surfactant, under low-level ozone (30 ± 5 ppb). The HD-SFG spectroscopy realized the accurate peak assignments of the spectra and the identification of molecular species with high sensitivity, which were impossible with previous measurements. The time-resolved spectra indicated that the C═C moiety in the unsaturated alkyl chain is selectively oxidized by ozone with a time constant of 22 ± 3 min by first-order reaction kinetics. Furthermore, it was revealed for the first time that the reaction product of the POPC monolayer under low-level ozone is not the carboxylic form but the aldehyde form based on the vibrational spectroscopy results. The present study has deepened our molecular-level understanding of the oxidation mechanism of unsaturated lipids that are widely found in many biological systems.

In the present study, we investigated the surface reorganization behaviors and adsorption conformations of fibrinogen on the surface of polyrotaxanes containing different amounts of α-cyclodextrin (α-CD) by using surface-sensitive vibrational spectroscopy sum frequency generation (SFG). For comparison, behaviors of the surface restructuring and fibrinogen adsorption on the random copolymers containing similar terminal groups were also investigated. It was found that larger amounts of BMA moieties of polyrotaxanes form ordered surface structures after immersion in water for 48 h. Furthermore, the polyrotaxane surfaces exhibit a much higher capability of fibrinogen adsorption than the random copolymer surfaces. The water-induced surface restructuring of the polyrotaxane films slightly affects the adsorption structure of the fibrinogen molecules.

Sum frequency generation (SFG) vibrational spectroscopy was employed to investigate the surface structures of polyelectrolyte multilayers (PEMs) constructed by sequentially alternating adsorption of poly(diallyldimethylammonium chloride) (PDDA) and poly(styrenesulfonate) (PSS). It was found that the surface structures and surface charge density of the as-deposited PEMs of PDDA/PSS significantly depend on the concentration of sodium chloride (NaCl) present in the polyelectrolyte solutions. Furthermore, it was found that the surface structure of the as-deposited PEMs is in a metastable state and will reach the equilibrium state by diffusion of the polyelectrolyte chain after an aging process, resulting in a polyelectrolyte mixture on the PEM surfaces.

Ambient ozone is a common pollutant in the atmosphere that has an extremely high oxidative ability, can dramatically change the structure and functionality of biomolecules, and is harmful to public health. However, the knowledge about the influence of low-level ozone is still very limited at a molecular level. In the present study, the monolayer of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC, 16:0-18:1 PC) as well as its binary mixed monolayer with 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC, 16:0 PC), which are widely found in many biological systems, have been systematically investigated in a low-level ozone environment (20 ± 10 ppb), by π-A isotherm, sum frequency generation (SFG) vibrational spectroscopy, and atomic force microscopy (AFM). Our results demonstrate that the POPC monolayer is unstable and the C═C moieties in the oleyl chain are selectively oxidized by the low-level ozone. The oxidized lipids from POPC initially remain and reorientate the hydrophilic portion to the water surface and gradually dissolve into the aqueous solution. One should take great caution when using unsaturated lipid molecules to avoid their possible oxidation in the ambient environment. The present study expands and deepens our insights into the oxidation mechanism of unsaturated lipids at a molecular level.

Polyrotaxanes, such as supramolecular assemblies with methylated α-cyclodextrins (α-CDs) as host molecules noncovalently threaded on the linear polymer backbone, are promising materials for biomedical applications because they allow adsorbed proteins possessing a high surface flexibility as well as control of the cellular morphology and adhesion. To provide a general design principle for biomedical materials, we examined the surface reorganization behaviors and adsorption conformations of fibrinogen on the polyrotaxane surfaces with comparison to several random copolymers by sum frequency generation (SFG) vibrational spectroscopy. We showed that the polyrotaxane (OMe-PRX-PMB) with methylated α-CDs as the host molecule exhibited unique surface structures in an aqueous environment. The hydrophobic interaction between the methoxy groups of the methylated α-CD molecules and methyl groups of the n-butyl methacrylate (BMA) side chains may dominate the surface restructuring behavior of the OMe-PRX-PMB. The orientation analysis revealed that the orientation of the fibrinogen adsorbed on the OMe-PRX-PMB surface is close to a single distribution, which is different from the adsorption behaviors of fibrinogen on other polyrotaxane or random copolymer surfaces.

The formation and structure of isotopically asymmetric supported bilayer membranes (SBMs) has been investigated using sum frequency generation (SFG) vibrational spectroscopy supplemented by reflection absorption infrared spectroscopy (RAIRS). The bilayers were composed of a proximal and distal leaflet of the phospholipid dipalmitoyl phosphatidylethanolamine (DPPE) supported on a gold surface. The proximal leaflet was chemically tethered to the gold via an 11-mercapto-undecanoic acid (MUA) self-assembled monolayer (SAM) that had been chemically modified to produce an activated succinimidyl ester headgroup using N-hydroxysuccinimide (NHS) and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC). The activation of the MUA and the tethering of the DPPE were monitored and confirmed using SFG and RAIRS. The distal leaflet of the bilayer was added using either vesicle fusion (VF) or Langmuir-Blodgett (LB) deposition. To gain insight into the structure of each layer of the SBM perdeuterated DPPE (d-DPPE) and MUA (d-MUA) were used to create SBMs with a layer that was isotopically distinguishable from the rest. The polar orientation and conformational ordering of the lipids was determined using SFG. It was found that the tethering of the proximal lipid leaflet resulted in an increase in the conformational order of the MUA SAM. Furthermore, by careful analysis and comparison of spectra recorded in both the C-H (2800-3000 cm(-1)) and C-D (2000-2300 cm(-1)) stretching regions it was concluded that a better ordered and more biologically relevant lipid bilayer was formed when the distal leaflet was added using LB deposition. On the other hand the SFG spectra of the SBMs in which the distal leaflet was added by VF showed little evidence of conformational ordering on the time scale of minutes, suggesting the presence of an incomplete monolayer or of multilayer formation.

The preparation and properties of a new cyano complex containing the Ru3(μ3-O) core, [Ru3(μ3-O)(μ-CH3COO)6(py)2(CN)] (1; py = pyridine), are reported. Complex 1 in CH2Cl2 showed intense absorption bands at 244, 334, and 662 nm, corresponding to a π-π* transition of the ligand, cluster-to-ligand charge transfer, and intracluster transitions, respectively. The cyclic voltammogram of 1 in 0.1 M (n-Bu)4NPF6-CH2Cl2 showed redox waves for the processes Ru3(II,II,III)/Ru3(II,III,III), Ru3(II,III,III)/Ru3(III,III,III), and Ru3(III,III,III)/Ru3(III,III,IV) at E1/2 = -1.49, -0.26, and +1.03 V vs Ag/AgCl, respectively. The first two redox potentials are more negative by ca. 0.2 V in comparison with the corresponding potentials of [Ru3(μ3-O)(μ-CH3COO)6(py)3](+). This is in sharp contrast to the positive shifts of the corresponding waves of [Ru3(II,III,III)(μ3-O)(μ-CH3COO)6(py)2(CO)]. Density functional theory (DFT) calculations of [Ru3(II,III,III)(μ3-O)(μ-CH3COO)6(py)3], [Ru3(II,III,III)(μ3-O)(μ-CH3COO)6(py)2(CN)](-), and [Ru3(II,III,III)(μ3-O)(μ-CH3COO)6(py)2(CO)] showed that the positive charge of the ruthenium is delocalized over the triruthenium cores of the first two and is localized as Ru(II)(CO){Ru(III)(py)}2 in the CO complex. The calculations explain the difference in the π interactions of the two ligands with the triruthenium cores.

The monolayer structures and conformational ordering of cationic surfactants including the biodegradable quaternary ammonium molecules have been systematically characterized by π-A isotherm, surface potential, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and sum frequency generation (SFG) vibrational spectroscopy. It was found that the monolayer of the typical dialkyl dimethylammonium on the water surface was less densely packed along with many conformational gauche defects. The packing density and ordering of these monolayers were improved as halide ions were added to the subphase. A similar condensation effect was also observed when amide or ester groups are present in the alkyl tails of the surfactant. These results are discussed on the basis of the repulsive electrostatic interactions between the terminal ammonium moieties, the hydrogen bonding between the functional groups in the alkyl chains, as well as the flexibility of the alkyl chains in these surfactants. The present study is crucial to understanding the relationship between the interfacial structures and the functionalities of the biodegradable quaternary ammonium surfactants.

A new μ-oxo-bis(μ-acetato)diruthenium(III) complex bearing two pyridyl disulfide ligands {[Ru2(μ-O)(μ-OAc)2(bpy)2(L(py-SS))2](PF6)2 (OAc = CH3CO2(-), bpy = 2,2'-bipyridine, L(py-SS) = (C5H4N)CH2NHC(O)(CH2)4CH(CH2)2SS) (1)} has been synthesized to prepare self-assembled monolayers (SAMs) on the Au(111) electrode surface. The SAMs have been characterized by contact-angle measurements, reflection-absorption surface infrared spectroscopy, cyclic voltammetry, and reductive desorption experiments. The SAMs exhibited proton-coupled electron transfer (PCET) reactions when the electrochemistry was studied in aqueous electrolyte solution (0.1 M NaClO4 with Britton-Robinson buffer to adjust the solution pH). The potential-pH plot (Pourbaix diagram) in the pH range from 1 to 12 has established that the dinuclear ruthenium moiety was involved in the interfacial PCET processes with four distinct redox states: Ru(III)Ru(III)(μ-O), Ru(II)Ru(III)(μ-OH), Ru(II)Ru(II)(μ-OH), and Ru(II)Ru(II)(μ-OH2). We also demonstrated that the interfacial redox processes were modulated by the addition of Lewis acids such as BF3 or Al(3+) to the electrolyte media, in which the externally added Lewis acids interacted with μ-O of the dinuclear moiety within the SAMs.

π-A isotherms, atomic force microscopy (AFM), and sum frequency generation (SFG) vibrational spectroscopy are employed to investigate the molecular structure and lateral interactions in mixed monolayers of dioctadecyldimethylammonium chloride (DOAC) and stearyl alcohol (SA) at air/water and air/solid interfaces. To avoid possible interference between the two molecules in the SFG spectroscopic measurements, perprotonated DOAC and perdeuterated SA (dSA) were used. The thermodynamic analyses for the π-A isotherms show that DOAC is miscible with dSA. SFG observations reveal that DOAC molecules become conformationally ordered as dSA molecules are introduced into the monolayer. AFM observations demonstrate coexistence of DOAC-rich and dSA-rich domains in the mixed monolayer with ratios different from their initial composition in the subphase. The present study suggests that DOAC molecules in the mixed monolayer are condensed by mixing with dSA in which the repulsive interactions between positively charged head groups of the DOAC molecules are largely reduced along with an increase of van der Waals interactions with dSA.

Herein, we report the influence of the position and the solution environment around surface-bound redox-active moieties on their redox reaction. The study was made possible by using rigid norbornylogous bridges, which possess anthraquinone (AQ) moieties. An L-shaped norbornylogous bridge (L-NB) and straight-shaped norbornylogous bridge (S-NB) were used to situate AQ moieties at well-defined position and environments above a mixed alkanethiol self-assembled monolayer (SAM) on Au (111) surfaces. Sum frequency generation (SFG) vibrational spectroscopy was employed to evaluate the interaction between the S-NB and L-NB with diluent molecules in the mixed SAMs. The SFG measurements demonstrated that hydrogen-bonding interactions were formed between AQ moieties of L-NB and diluent molecules terminated by hydroxyl group within a suitable separation. The SFG observations provided information about the relative position of the AQ moieties in each SAM, which significantly affects the thermodynamics and the kinetics of the electron transfer on the electrode/solution interface. The rate constant (k(et)) of the electron transfer between the AQ moiety and the gold surface and the apparent formal potential (E(0')) were studied using cyclic voltammetry (CV), alternating current voltammetry (ACV), and electrochemical impedance spectroscopy (EIS). It was found that the k(et) increases and E(0') shifts to more anodic values as the distance between the AQ moiety and the surface of the diluent was increased, for both methyl and hydroxyl terminated diluent. These results are discussed in relation to H-bonding interactions with water surrounding the AQ moieties.

Sum frequency generation (SFG) vibrational spectroscopy is employed to investigate the reversible, photoinduced spiro→merocyanine isomerization of a self-assembled monolayer, the result of attachment of nitrospiropyran to a gold surface using a dithiolane anchoring group. The attachment of these molecular "alligator clips" to spiropyran molecules provide an easily accessible method to self-assemble a robust monolayer of spiropyran on a gold surface, which allows photoswitching of the spiropyran units. Probing the symmetric and antisymmetric stretching modes of the nitro group allows the determination of the structural orientation of the charged moiety with respect to the surface normal as well as the isomerization rates under photoinduced switching conditions. The photoisomerization of the spiropyran SAM on the gold surface is much faster than the rates of switching spiropyrans in a solid crystalline form, and the rate of thermal relaxation of the opened to closed form in this study is found to be on the same time scale as the relaxation of spiropyran when present in solutions with polar solvents.