Charge Inversion by Monovalent Hydroxide Ions.

The interaction between the hydroxide ion (OH) and the headgroup of a model cationic lipid (DPTAP, 1,2-dipalmitoyl-3-trimethylammonium-propane chloride) was investigated for different concentrations of NaOH solutions by using sum-frequency vibrational spectroscopy. The OH signal (3000-3700 cm) of the interfacial water under the Langmuir monolayer of DPTAP decreased with increasing NaOH concentration, due to screening of the surface charge by OH counterions. Surprisingly, after reaching a minimum at 5 mM NaOH, the OH signal steadily increased.

Effect of pH and salt on the protonation state of fatty aniline investigated by sum-frequency vibrational spectroscopy.

Langmuir monolayers of fatty aniline (C16-aniline) were investigated using sum-frequency vibrational spectroscopy at various pH levels and NaCl concentrations. To analyze the sum-frequency generation (SFG) spectra of aniline, a multi-peak Lorentzian model, in accordance with the theory of SFG for a charged interface, was applied. First, SFG spectra of C16-aniline from pH 2 to 6 at a constant ionic strength of 10 mM (where the phase of the complex potential of the dc-induced signal was suppressed to a few degrees) were fitted with the above-mentioned method.

Activation Energy of Ion Desorption at Ionic Liquid/Pt Electrode Interfaces: A Sum-Frequency Generation Vibrational Spectroscopic Study.

Electrolyte/electrode interfaces of room-temperature ionic liquids (RTILs) exhibit hysteretic responses to different applied potentials owing to the differences in the ion adsorption/desorption processes; the ion desorption requires excess potential, which reflects the activation energy of ion desorption. Thus far, the contributions of the ion adsorption energy and the activation barrier for ion desorption toward the ion-dependent excess potential have not been quantified. Herein, we report on our infrared-visible sum-frequency generation vibrational spectroscopy study of the hysteretic responses of the anion adsorption/desorption at Pt electrode interfaces using neat, binary, and diluted RTILs composed of 1-butyl-3-methylimidazolium cations ([Cmim]) and bis(trifluoromethanesulfonyl)amide ([TFSA]) and trifluoromethanesulfonate ([OTf]) anions.

Sensitive Detection of Biomolecular Adsorption by a Low-Density Surfactant Layer Using Sum-Frequency Vibrational Spectroscopy.

Small molecules or proteins interact with a biomembrane in various ways for molecular recognition, structure stabilization, and transmembrane signaling. In this study, 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP), having a choline group, was used to investigate this interaction by using sum-frequency vibrational spectroscopy. The sum-frequency spectrum characteristic of a neat monolayer changed to that of a bare air/water interface at a larger molecular area of the DPTAP molecules due to local laser heating.

Systematic investigation of coupling between symmetric and antisymmetric stretches of D2O in CHCl3 by 2D IR.

The coupling between the symmetric (νs) and antisymmetric (νa) OD stretch modes of monomeric D2O in CHCl3 is investigated using polarization-dependent two-dimensional infrared (2D IR) spectroscopy supported by numerical 2D IR simulations based on the exciton-band theory. The relationship between the local modes' and the exciton states' parameters is systematically studied, including center frequencies, diagonal anharmonicities, coupling, and off-diagonal anharmonicity. The mean coupling between νs and νa is accurately evaluated to be -49.

Sum-Frequency Vibrational Spectroscopic Study of the Cation-π Interaction: Amine and Guanidine.

The cation-π interaction is an interaction between a positively charged cation and π electrons in an aromatic group of a molecule. It is considered to play key roles in signal transduction, stabilization of the protein structure, enzyme catalysis in biology, and wet adhesion and biomolecular condensation. In this study, octadecylguanidine hydrochloride (ODG) and octadecylamine (ODA) having guanidine and amine headgroups, respectively, are found to interact with π molecules (phenol or indole) as investigated by sum-frequency vibrational spectroscopy.

Characterization of Noise in a Single-Molecule Fluorescence Signal.

Single-molecule fluorescence experiments allow monitoring of the structural change and dynamics of a single biomolecule in real time using dye molecules attached to the molecule. Often, the molecules are immobilized on the surface to observe a longer molecular dynamics, yet the finite photon budget available from an individual dye molecule before photobleaching sets the limit to the relatively poor signal-to-noise level. To increase the accuracy of these single-molecule experiments, it is necessary to study the cause of noise in the fluorescence signal from the single molecules.

Recovery of Fatty Acid Monolayers by Salts Investigated by Sum-Frequency Generation Spectroscopy.

Langmuir monolayers consisting of fatty acids with relatively short alkyl chains (CHCOOH (pentadecanoic acid), CHCOOH (palmitic acid), and CHCOOH (heptadecanoic acid)) are stable at a neutral pH (pH ≈ 6) but become unstable at a high pH (pH ≈ 11). Further addition of a small amount of divalent salt in subphase water was found to recover the monolayer at a high pH because binding of the divalent cations to the carboxylic headgroups renders the molecule more stable against dissolution in subphase water. This revival of the monolayer was observed via a pressure-area isotherm measurement and sum-frequency generation spectrum in the CH and OH ranges.

Kinetics of DNA looping by Anabaena sensory rhodopsin transducer (ASRT) by using DNA cyclization assay.

DNA cyclization assay together with single-molecule FRET was employed to monitor protein-mediated bending of a short dsDNA (~ 100 bp). This method provides a simple and easy way to monitor the structural change of DNA in real-time without necessitating prior knowledge of the molecular structures for the optimal dye-labeling. This assay was applied to study how Anabaena sensory rhodopsin transducer (ASRT) facilitates loop formation of DNA as a possible mechanism for gene regulation.

Structure of Electric Double Layer under Cationic Langmuir Monolayer: Charge Condensation Effect.

Langmuir monolayers consisting of mixtures of 1-hexadecanol (HD) and 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP) (having quaternary amine headgroup) at different molar ratios were prepared to investigate the effect of the surface charge density on the structure of an electric double layer. The fatty alcohol molecules worked as passive spacers to widen the distance between the amine groups in the monolayer, to vary the surface charge density of the monolayer, and these mixture monolayer systems were probed by surface-sensitive sum-frequency vibrational spectroscopy. A strong sum-frequency signal in the OH range for a pure DPTAP monolayer (with a surface charge density of ∼0.

Reply to the 'Comment on "Bi-layering at ionic liquid surfaces: a sum-frequency generation vibrational spectroscopy- and molecular dynamics simulation-based study"' by M. Deutsch, O. M. Magnussen, J. Haddad, D. Pontoni, B. M. Murphy and B. M. Ocko, , 2021, DOI.

In our recent paper titled "Bi-layering at ionic liquid surfaces: a sum-frequency generation vibrational spectroscopy- and molecular dynamics simulation-based study" co-authored by T. Iwahashi, T. Ishiyama, Y.

Bi-layering at ionic liquid surfaces: a sum-frequency generation vibrational spectroscopy- and molecular dynamics simulation-based study.

Room-temperature ionic liquids (RTILs) are being increasingly employed as novel solvents in several fields, including chemical engineering, electrochemistry, and synthetic chemistry. To further increase their usage potential, a better understanding of the structure of their surface layer is essential. Bi-layering at the surfaces of RTILs consisting of 1-alkyl-3-methylimidazolium ([Cmim]; n = 4, 6, 8, 10, and 12) cations and bis(trifluoromethanesulfonyl)amide ([TFSA]) anions was demonstrated via infrared-visible sum-frequency generation (IV-SFG) vibrational spectroscopy and molecular dynamics (MD) simulations.

The Effect of Epoxy Polymer Addition in Sn-Ag-Cu and Sn-Bi Solder Joints.

To analyze the reinforcement effect of adding polymer to solder paste, epoxies were mixed with two currently available Sn-3.0Ag-0.5Cu (wt.

Suppression of the Growth of Intermetallic Compound Layers with the Addition of Graphene Nano-Sheets to an Epoxy Sn⁻Ag⁻Cu Solder on a Cu Substrate.

This study investigated the suppression of the growth of the intermetallic compound (IMC) layer that forms between epoxy solder joints and the substrate in electronic packaging by adding graphene nano-sheets (GNSs) to 96.5Sn⁻3.0Ag⁻0.

Concentration Dependence of Ion Pairing in Imidazolium-Based Ionic Liquid Solutions.

Infrared vibrational spectroscopy was used to probe concentration-dependent ion pair dissociation of imidazolium-based ionic liquids with three different halide anions (I , Br , and Cl ) in deuterated chloroform. Dissociation of the ion pairs at low concentrations of ionic liquids was found to be the easiest for ionic liquid with Cl anion, the most electronegative anion among the three investigated. This anomalous trend of ion pair dissociation was explained in terms of varying interaction strength between the solvent (CDCl ) and the anions investigated.

Rotation and translation dynamics of coumarin 153 in choline chloride-based deep eutectic solvents.

The equilibrium and dynamic solvation responses of coumarin 153 (C153) in a range of deep eutectic solvents (DESs) based on choline chloride with either urea (molar ratio 1:2, ChCl:U), glycerol (1:2, ChCl:G), ethylene glycol (1:2, ChCl:E), or malonic acid (1:1, ChCl:Mal) were investigated using both steady-state and time-resolved fluorescence emission spectroscopy at room temperature (298 K). From steady-state fluorescence data, "red-edge effects" were observed in all the DESs studied, attributed to spatial heterogeneity of the DES matrix. Time-resolved Stokes shifts were used to quantify dynamic solvation with the solvation response function in DES found to be a biexponential function of time, which were used to obtain average solvation times (⟨ ⟩) which are generally faster in DES than in ionic liquids of comparable viscosity.

Binding of trivalent ions on fatty acid Langmuir monolayer: Fe versus La.

Langmuir monolayers consisting of fatty acid molecules were prepared on solutions of FeCl and LaCl to investigate adsorption of trivalent metal ions on carboxylic headgroups by using sum-frequency vibrational spectroscopy. Fe ions bound to the fatty acid headgroups only in the form of hydroxide complexes (Fe(OH) ), and sum-frequency intensity of water stretch modes increased markedly upon adsorption of ion hydroxide. On the other hand, La ions bound to the charged anionic headgroup as bare trivalent ions.

Change of hydrogen bonding structure in ionic liquid mixtures by anion type.

Ionic liquid mixtures have gained attention as a way of tuning material properties continuously with composition changes. For some mixture systems, physicochemical properties such as excess molar volume have been found to be significantly different from the value expected by linear interpolation, but the origin of this deviation is not well understood yet. The microstructure of the mixture, which can range from an ideal mixture of two initial consisting ionic liquids to a different structure from those of pure materials, has been suggested as the origin of the observed deviation.

Turn-on and Turn-off Fluorescent Probes for Carbon Monoxide Detection and Blood Carboxyhemoglobin Determination.

Water-soluble, carbazole-based two-photon excitable fluorescent probes MPVC-I ("turn-on") and MPVC-II ("turn-off") are rationally designed and synthesized for the selective monitoring of carbon monoxide (CO). Both probes can effectively measure carboxyhemoglobin (HbCO) in the blood of the animals exposed to a CO dose as low as 100 ppm for 10 min. The palladium catalyzed azidocarbonylation reaction was optimized to improve the sensing efficiency.

RecA filament maintains structural integrity using ATP-driven internal dynamics.

At the core of homologous DNA repair, RecA catalyzes the strand exchange reaction. This process is initiated by a RecA loading protein, which nucleates clusters of RecA proteins on single-stranded DNA. Each cluster grows to cover the single-stranded DNA but may leave 1- to 2-nucleotide (nt) gaps between the clusters due to three different structural phases of the nucleoprotein filaments.

Salt Promotes Protonation of Amine Groups at Air/Water Interface.

Interfacial water reorientation caused by charged Langmuir monolayers consisting of primary fatty amine (ODA) and cationic lipid having quaternary amine headgroup (DPTAP) were investigated by interface-selective vibrational sum-frequency generation spectroscopy. For DPTAP monolayer, initially large sum-frequency intensity from interfacial water OH band decreased steadily by increasing monovalent salt (NaCl, NaI) concentration due to counterion adsorption. On the other hand, ODA/water exhibited significantly smaller sum-frequency intensity than DPTAP/water, implying only small portion of protonated amine group (-NH) initially existed.

Observation of isolated ionic liquid cations and water molecules in an inert solvent.

1-Octyl-3-methyl imidazolium halides ([OMIM]I and [OMIM]Cl) were loaded on top of CCl, and an in situ inclusion process was monitored from the CCl phase as time elapses by infrared absorption spectroscopy. Absorption from the bands corresponding to the C(2)-H and C(4,5)-H stretch modes in the imidazolium cation was reduced significantly compared to the bulk IL spectra. This indicates that (1) the [OMIM] cation exists in CCl as a monomer, dissociated from the anion and other cations, and (2) hydrogen bonding between the anion and the cation increases the dipole strength of the CH moieties in the imidazolium ring.

Raman Spectroscopic Study on Alkyl Chain Conformation in 1-Butyl-3-methylimidazolium Ionic Liquids and their Aqueous Mixtures.

Ionic liquids of 1-butyl-3-methylimidazolium ([BMIM]) cation with different anions (Cl , Br , I , and BF ), and their aqueous mixtures were investigated by using Raman spectroscopy and dispersion-included density functional theory (DFT). The characteristic Raman bands at 600 and 624 cm for two isomers of the butyl chain in the imidazolium cation showed significant changes in intensity for different anions as well as in aqueous solutions. The area ratio of these two bands followed the order I >Br >Cl >BF (in terms of the anion X in [BMIM]X), indicating that the butyl chain of [BMIM]I tends to adopt the trans conformation.

Origin of the Instability of Octadecylamine Langmuir Monolayer at Low pH.

It has been reported that an octadecylamine (ODA) Langmuir monolayer becomes unstable at low pH values with no measurable surface pressure at around pH 3.5, suggesting significant dissolution of the ODA molecule into the subphase solution (Albrecht, Colloids Surf. A 2006, 284-285, 166-174).