Junya Kohno

Abstract Guanine (G) molecules form a stable tetramer with a metal ion called a G-quartet. We observed G-quartets by using atmospheric pressure droplet Infrared-laser ablation mass spectrometry, which enables us to analyze the abundance of chemical species in solutions. We estimated the association constants of Gn and M+ (M+ = Li+, Na+, and K+) from the intensities of G1–5H+ and G1–4M+ in the obtained mass spectra. The larger association constants of G4 than those of Gn (n ≠ 4) indicate the stability of G-quartets.

© 2019 The Royal Society of Chemistry. An S-S bond containing maleimide-conjugated closo-dodecaborate (SSMID) was synthesised for identification of albumin binding sites. Three Lys residues, Lys221, Lys413 and Lys431, were identified as SSMID modification sites in addition to Cys34 in bovin serum albumin (BSA). Fluorescent-labelled MID-BSA was found to be accumulated in the cytosol of HeLa cells.

Dynamic properties of the metastable interface between two miscible solutions are investigated by the collision of two droplets. A clear interface is observed between the two colliding droplets. The interface moves in the colliding droplet toward the side where the original droplet has a lower surface tension. The interface is set to the middle of the colliding droplet by controlling the surface tension of the droplets to observe the chemical reactions at the droplet interface by cavity-enhanced Raman spectroscopy. This study provides a foundation for further research on the initial process of the chemical reactions of two miscible solutions.

X-ray free-electron lasers (XFELs) have opened new opportunities for time-resolved X-ray crystallography. Here a nanosecond optical-pump XFEL-probe device developed for time-resolved serial femtosecond crystallography (TR-SFX) studies of photo-induced reactions in proteins at the SPring-8 Angstrom Compact free-electron LAser (SACLA) is reported. The optical-fiber-based system is a good choice for a quick setup in a limited beam time and allows pump illumination from two directions to achieve high excitation efficiency of protein microcrystals. Two types of injectors are used: one for extruding highly viscous samples such as lipidic cubic phase (LCP) and the other for pulsed liquid droplets. Under standard sample flow conditions from the viscous-sample injector, delay times from nanoseconds to tens of milliseconds are accessible, typical time scales required to study large protein conformational changes. A first demonstration of a TR-SFX experiment on bacteriorhodopsin in bicelle using a setup with a droplet-type injector is also presented.

Materials work in multicomponent forms. A wide range of compositions must be tested to obtain-the optimum composition for a specific application. We propose optimization using a series of small levitated single particles. We describe a tandem-trap apparatus for merging liquid droplets and analyzing the merged droplets and/or dried particles that are produced from the merged droplets under levitation conditions. Droplet merging was confirmed by Raman spectroscopic studies of the levitated particles. The tandem-trap apparatus enables the synthesis of a particle and spectroscopic investigation of its properties. This provides a basis for future investigation of the properties of levitated single particles.

A liquid-droplet injector has been developed that delivers pristine microcrystals to an X-ray irradiation area for conducting serial femtosecond crystallography (SFX) with an X-ray free-electron laser (XFEL). By finely tuning the pulsed liquid droplets in time and space, a high hit rate of the XFEL pulses to microcrystals in the droplets was achieved for measurements using 5 mm tetragonal lysozyme crystals, which produced 4265 indexable diffraction images in about 30 min. The structure was determined at a resolution of 2.3 angstrom from < 0.3 mg of protein. With further improvements such as reduction of the droplet size, liquid droplets have considerable potential as a crystal carrier for SFX with low sample consumption.

Gas-phase isolation of bovine serum albumin (BSA) from aqueous solutions is performed by IR laser ablation of a droplet beam. Multiply charged BSA ions (positive and negative) were produced by the IR laser irradiation onto a droplet beam of aqueous BSA solutions with various pH values prepared by addition of hydrochloric acid or sodium hydroxide to the solution. The isolation mechanism was discussed based on the charge state of the isolated BSA ions. A nanodroplet model explains the gas-phase charge distribution of the BSA ions. This study provides a fundamental basis for further studies of a wide variety of biomolecules in the gas phase isolated directly from solution.

The collisional reaction of droplets is observed by time-resolved fluorescence spectroscopy. Colliding droplets of the reactant solutions are irradiated with a pulsed laser, and the resulting fluorescence spectra and images of the colliding droplets are observed as a function of the elapsed time from the collision. The amidation reaction of dansyl chloride with isopropylamine is observed through fluorescence enhancement on a microsecond time scale. The present method enables us to measure the early stages of reactions in solutions.

Many important Chemical reactions are induced by mixing two solutions. This paper presents a new way to measure rates of rapid chemical reactions induced by mixing two reactant solutions using a liquid droplet collision. The coloring reaction of phenolphthalein (H2PP) by a reaction with NaOH is investigated: kinetically. Liquid droplets Of H2PP/ethanol and NaOH/H2O solutions are made to collide, Which induces a reaction that transforms H2PP into a deprotonated form,(PP2-). The concentration of PP2- is evaluated from the RGB values of pixels in the colored droplet images, and is measured as a function of the elapsed time from the collision. The obtained rate constant is (2.2 +/- 0.7) X 10(3) M-1 s(-1), which is the rate constant for the rate-determining step of the coloring reaction of H2PP. This method was shown to be applicable to determine rate constants of rapid chemical reactions between two solutions.

Processes involved between colliding droplets were investigated using simultaneous analysis of spectra and images of Raman-scattered light emitted by irradiation with a pulsed laser. This enabled spatially and temporally resolved Raman spectra of the colliding droplets to be obtained. Colliding droplets of ethanol and water produce a characteristic protrusion from the contact point to the antipode of the water droplet in the course of interaction. From its Raman spectrum, the protrusion is seen to be composed of water. This result supports our surface-tension release model previously proposed to describe the mechanism of protrusion formation because the protrusion is the result of positive interference of a capillary wave propagating over the surface of the water droplet in this model.

Collision processes of liquid droplets were observed to study the dynamics of molecules in solution with an apparatus which allows us to observe the collision sequence stroboscopically with time resolution of similar to 1 mu s. The collision sequences of water-water and ethanol-water droplets were observed by production of droplets through piezo-driven nozzles. Formation of characteristic protrusion was traced in the collision of ethanol and water droplets. A model mechanism of protrusion in these systems is proposed based on the observed behavior indicating release deformation of surface tension that propagates as a capillary wave on the droplet surface. (C) 2013 Elsevier B. V. All rights reserved.

Molecules exhibit their intrinsic properties in their isolated forms. Investigations of isolated large biomolecules require an understanding of the detailed mechanisms for their emergence in the gas phase because these properties may depend on the isolation process. In this study, we apply droplet-beam laser-ablation mass spectrometry to isolate protein molecules in the gas phase by IR-laser ablation of aqueous protein solutions, and we discuss the isolation mechanism. Multiply charged hydrated lysozyme clusters were produced by irradiation of the IR laser onto a droplet beam of aqueous lysozyme solutions with various pH values prepared by addition of sodium hydroxide to the solution. The ions produced in the gas phase show significantly low abundance and have a lower number of charges on them than those in the aqueous solutions, which we explained using a nanodroplet model. This study gives quantitative support for the nanodroplet model, which will serve as a fundamental basis for further studies of biomolecules in the gas phase. © 2012 American Chemical Society.

Scanning cavity-enhanced droplet spectroscopy (S-CEDS) has been developed to obtain Raman spectra of liquid media with high sensitivity. Cavity-enhanced Raman spectra of a water droplet are measured by irradiation of a laser with nine different wavelengths. Each of the spectra consists of a series of intense and narrow peaks resulting from the cavity-enhancement conditions, and the envelope of their peak apexes displays a stimulated Raman spectrum of liquid water. A series of continuous Raman spectra of liquid water is obtained by scanning the laser wavelength, which dissolves the discreteness of each spectrum. S-CEDS provides a novel method to obtain stimulated Raman spectra of liquid media keeping their continuous spectral shapes. (C) 2012 Elsevier B. V. All rights reserved.

We describe a novel method to trap biomolecular ions in the gas phase produced by an IR-laser ablation of a droplet beam The IR-laser ablation is performed in an Ion trap so that the product ions are readily trapped with high efficiency The ions are thermalized in collisions with the ambient water molecules which are simultaneously produced with the ions by the IR-laser ablation

Droplet-beam laser-ablation mass-spectrometry was applied for a study of the UV-laser induced proton-transfer reaction of protonated lysozyme hydrated clusters in the gas phase. Protonated lysozyme hydrated clusters were produced by irradiation of an IR laser onto a droplet-beam of an aqueous solution of lysozyme and were subsequently irradiated by a UV laser. It is found that H(+) and H(3)O(+) are produced through photodissociation of protonated lysozyme hydrated clusters. The mechanism of the proton-transfer reaction is discussed. (c) 2008 Elsevier B.V. All rights reserved.

Ions, OH (H2O)(n), were produced from a liquid beam of pure water by irradiation of a Mid- and a Near-IR lasers resonant to the fundamental and the forth harmonic of the OH vibration of the liquid water, respectively. The ions were composed of two components originating from the liquid beam surface and the inside, which liberated the ions into the gas phase at 0.2 and 1.7 +/- 0.2 mu s, respectively, after the Near-IR excitation. The Near-IR excitation created an ion pair (H+ center dot center dot center dot OH) in the course of non-equilibrium disintegration of the liquid beam induced by the Mid-IR excitation. (c) 2008 Elsevier B.V. All rights reserved.

Ions, OH-(H2O)(n), were found to be ejected from a liquid beam of water under irradiation of Mid- and Near-IR lasers resonant to the fundamental and the fourth harmonic (nu(OH) = 4) of the OH-stretching mode of liquid water, respectively. Dependence of the ion intensity on a delay time between the two lasers reveals that locally preheated water by the Mid-IR laser helps ejecting OH-(H2O), to a vacuum through an ion pair (H+center dot center dot center dot OH-) created by the Near-IR laser.

A liquid beam of water was irradiated with an IR-laser resonant to the OH stretching mode of liquid water. Hydrated hydonium ions, H3O+(H2O)(n), and hydroxyl ions, OH-(H2O)(n), were ejected to the gas phase. Dependences of the ion intensity on the power and the frequency of the IR laser show that an ion-pair state, (H+...OH-), was produced by vibrational four-photon excitation of a water molecule in the liquid water and was subsequently separately ejected to the gas phase. The four-photon excitation proceeds in a particular local structure, where the water molecule weakly interacts with the neighboring ones. (c) 2005 Elsevier B.V. All rights reserved.

A liquid beam of aqueous solutions of arginine (AH), its hydrochloric acid salt (AH(2)Cl) and its sodium salt (ANa) was irradiated with a pulsed IR laser at 3509 cm(-1) (2.85 mu m). Positive and negative ions ejected to the gas phase were mass analyzed. From the AH(2)Cl and the ANa aqueous solutions, the pre-existing ions in the solution were ejected directly to the gas phase. From the AH solution, on the other hand, both a protonated arginine ion, AH(2)(+) and an argininate ion, A(-) were observed in the gas phase. Production of these ions is accounted for the four-photon excitation of water molecules in the solution. (c) 2005 Elsevier B.V. All rights reserved.

Droplet beam-laser ablation mass spectrometry has been developed for studies of molecules in a liquid after isolating them in the gas phase. A liquid droplet of an aqueous solution of NaI was introduced into a vacuum chamber, and its velocity and shape were obtained from stroboscopic images and a diffraction pattern of visible and UV lasers, respectively. The ions produced by irradiation of a UV laser onto the liquid droplet were almost identical to those produced from a liquid beam. The mechanism of ion formation is explained by the Coulomb-ejection model employed for ion ejection from the liquid beam. (c) 2005 Elsevier B.V. All rights reserved.

Hydration structures in the vicinity of solute arginine molecules have been investigated by measuring the mass spectra of protonated arginine-water cluster ions ejected from a liquid beam of an arginine aqueous solution by IR-laser ablation. It is revealed that an arginine aggregate is less hydrated than an arginine monomer, because of a smaller dipole moment, and that an arginine monomer is less hydrated in a concentrated arginine solution, because of formation of a hydrophobic hydration structure of water around an arginine aggregate in the solution. (c) 2005 Elsevier B.V. All rights reserved.

In this account, we describe the dynamics of reactions induced by multiphoton excitation of solute and solvent molecules in solutions, studied by means of a liquid beam (a continuous liquid flow in a vacuum) combined with mass spectrometry. Unique reaction intermediates and products are found to be produced and ejected into the gas phase by multiphoton excitation of the molecules in the liquid beam. The reaction dynamics were elucidated by observing the reaction intermediates and products ejected into the gas phase. In particular, we refer to reactions via UV multiphoton excitation of solute molecules, such as ketal formation of phenyl ketones and reduction by solvated electrons, and those via IR multiphoton excitation of solvent molecules, such as formation of internally hot and cold molecules/clusters in the gas phase.

A continuous liquid flow of water in a vacuum (a liquid beam) was irradiated with a pulsed IR laser at 2.96 mum that is resonant to an OH stretching mode of liquid water. Neutral species ejected from the liquid beam were detected directly by a Daly detector without ionization. The flight-time distribution was found to show neutral species having high and low velocities, which are attributable to water clusters ejected from the surface and inside of the liquid beam, respectively. The flight-time distribution expressed by a Maxwellian velocity distribution reveals that the clusters are ejected by explosion of the liquid beam after absorption of the IR laser. This ejection scheme is supported by the presence of a delayed ejection of clusters, which is considered to originate from the inside of the liquid beam into the gas phase.

A continuous liquid flow of an aqueous solution of phenol (Phe) in a vacuum (a liquid beam) was irradiated with an IR laser at 2,85 pm, which is resonant to the vibrational absorption band of the liquid water. The Phe (H2O)(N), ejected from the liquid beam surface into the gas phase, was ionized by a UV laser at 270 nm into hydrated phenol cluster ions, Phe(+) (H2O)(n) (n = 0-30), and analyzed by a time-of-flight mass spectrometer. The velocity distributions of the product cluster ions were derived from the spatial distributions measured at different elapsed times after the IR laser irradiation. The results and the analysis show that dense neutral clusters are ejected from surface regions locally heated by the intense IR laser.

Gold nanoparticles with an average diameter of similar to20 nm were prepared in water by laser ablation at 1064 nm against a gold metal plate in it. The gold nanoparticles thus prepared in water and those mixed with an aqueous solution of sodium dodecyl sulfate (SDS) were irradiated with an intense pulsed laser at 532 nm. The products in the solution were examined by transmission electron microscopy (TEM) and optical absorption spectroscopy. The TEM images of the products revealed that gold nanonetworks and much smaller gold nanoparticles were produced selectively by a proper choice of the laser fluence and the SDS concentration. The optical absorption spectra measured simultaneously showed that the gold nanonetworks have an optical absorption in the wavelength longer than 600 nm which is assignable to longitudinal plasma oscillation of the gold nanonetworks, while the smaller gold nanoparticles (clusters) have an absorption band in the visible to the UV region. Taking advantage of those characteristic absorption bands, we constructed a two-dimensional mapping which illustrates the formation of the gold nanonetworks and the smaller nanoparticles as functions of the laser fluence and the SDS concentration.

Platinum nanoparticles were produced by laser ablation of a platinum metal plate in an aqueous solution of sodium dodecyl sulfate (SDS). The absorption spectrum of the platinum nanoparticles was essentially the same as that of platinum nanoparticles chemically prepared in a solution. The size distribution of the nanoparticles thus produced was measured to be in the range of 1-7 nm in diameter by an electron microscope. The abundance of the nanoparticles changes with the concentration of SDS in the solution. Stable platinum nanoparticles were found to be produced by this method even in pure water.

A continuous liquid flow of an aqueous solution of phenol (Ph) in a vacuum (a liquid beam) was irradiated with a pulsed IR laser at 3 mum, which was resonant to the OH-stretching vibration of the solvent water molecules. Phenol molecules ejected from the liquid beam were selectively ionized at about 0.5 mm above it by a pulsed UV laser (270-280 nm). The photoions thus produced were extracted in a pulsed electric field with a given residence time after the photoionization for mass analysis. It was shown that photoions, Ph+, were solvated into Ph+(H2O)(n) in a dense cloud of water vapor ejected from the liquid beam by IR irradiation. (C) 2002 Elsevier Science B.V. All rights reserved.

A continuous liquid flow in a vacuum (a liquid beam) of an aqueous solution of adenine salt containing hydrochloric acid or sodium hydroxide was irradiated with an intense pulsed IR laser at 3 pm, which is resonant to a vibrational mode related to the OH stretch vibration of H2O. Neutral species isolated into the vacuum were ionized by a pulsed UV laser at 270 nm, and the product ions were mass-analyzed by a time-of-flight mass spectrometer. It is found that AH(2)(2+) (.) 2Cl(-) and [A-iH](i-) (.) iNa(+) (i = 1-3) are isolated in the vacuum from the aqueous acidic and alkaline solutions, respectively, under irradiation of the IR laser, and undergo four-photon ionization involving decomposition and proton transfer of the intermediate species under irradiation of the UV laser.