Koichi Fumino

A potentiodynamic study of the lead electrode in sulphuric acid solution

Cyclic voltammetry has been used to study the electrochemical redox behaviour of the Pb/PbOn(1,2)/PbSO4 system on the lead electrode in aqueous H2SO4 solutions. The anodic and the cathodic polarization behaviour has been investigated under the various conditions by changing the potential region, sweeping rate, and concentration of an electrolyte. The mutual electrochemical behaviour of Pb/PbOn(1,2)/PbSO4 is discussed in detail.

NMR studies on dynamic behavior of water molecule in aqueous denaturant solutions at 25 °C: Effects of guanidine hydrochloride, urea and alkylated ureas

Abstract The spin-lattice relaxation times (T1) of the 17O nucleus of a water molecule in guanidine hydrochloride, urea, and alkylated ureas at 25 °C were measured by NMR spectroscopy. Urea has no significant effect on the water structure. Also, guanidine hydrochloride as a stronger denaturant than urea does not perturb the water structure similar to urea. The change in the dynamic structure (BR) of water was proportional to the carbon number of the alkyl chain of the alkylated urea. Compared to the results of alcohols and tetraalkylammonium solution, it is clear that the contribution of one carbon of the alkyl chain to the water structure is independent of the type of solute. The BR of urea and its alkylated substances show a good correlation with the concentration of denaturation midpoints obtained on sperm whale myoglobin and cytochrome c. Because the water structure is not perturbed by urea and guanidine hydrochloride, these results indicate that the effect of hydrophobic hydration of denaturants becomes important for the denaturation of a protein with increasing hydrophobicity of the denaturants.

Controlling the Subtle Energy Balance in Protic Ionic Liquids: Dispersion Forces Compete with Hydrogen Bonds**

The properties of ionic liquids are determined by the energy-balance between Coulomb-interaction, hydrogen-bonding, and dispersion forces. Out of a set of protic ionic liquids (PILs), including trialkylammonium cations and methylsulfonate and triflate anions we could detect the transfer from hydrogen-bonding to dispersion-dominated interaction between cation and anion in the PIL [(C6 H13 )3 NH][CF3 SO3 ]. The characteristic vibrational features for both ion-pair species can be detected and assigned in the far-infrared spectra. Our approach gives direct access to the relative strength of hydrogen-bonding and dispersion forces in a Coulomb-dominated system. Dispersion-corrected density functional theory (DFT) calculations support the experimental findings. The dispersion forces could be quantified to contribute about 2.3 kJ mol(-1) per additional methylene group in the alkyl chains of the ammonium cation.

Spectroscopic Evidence for Clusters of Like-Charged Ions in Ionic Liquids Stabilized by Cooperative Hydrogen Bonding.

Abstract Direct spectroscopic evidence for hydrogen‐bonded clusters of like‐charged ions is reported for ionic liquids. The measured infrared O−H vibrational bands of the hydroxyethyl groups in the cations can be assigned to the dispersion‐corrected DFT calculated frequencies of linear and cyclic clusters. Compensating the like‐charge Coulomb repulsion, these cationic clusters can range up to cyclic tetramers resembling molecular clusters of water and alcohols. These ionic clusters are mainly present at low temperature and show strong cooperative effects in hydrogen bonding. DFT‐D3 calculations of the pure multiply charged clusters suggest that the attractive hydrogen bonds can compete with repulsive Coulomb forces.

Non‐Ideal Mixing Behaviour of Hydrogen Bonding in Mixtures of Protic Ionic Liquids

Ionic liquids (ILs) attract interest in science and technology as a result of their unique properties. Binary and ternary mixtures of ILs significantly increase the number of possible cation/anion combinations, resulting in targeted physical and chemical properties. In this work, we study the mixing behaviour of two protic ILs: triethyl ammonium methylsulfonate [Et3 NH][CH3 SO3 ] and triethylammonium triflate [Et3 NH][CF3 SO3 ]. We find a characteristic deviation from ideal mixing by means of low-frequency infrared spectroscopy. By using molecular dynamics simulations, we explain this behaviour as being the result of different strengths of anion/cation hydrogen bonding. This non-ideality of non-random H-bond mixing is also reflected in macroscopic properties such as the viscosity. Mixing suitable ILs may, thus, result in new ILs with targeted physical properties.

NMR studies on dynamic behavior of water molecules in tetraalkylammonium bromide-D2O solutions at 5–25°C+☆

Abstract The spin-lattice relaxation times (T 1 ) of D and 17 O nuclei of D 2 O molecules in tetraalkylammonium bromides (R 4 NBr; R=Me, Et, Pr, Bu), dilute aqueous solutions were measured at the concentration of 0.2 to 1.0 mol/kg and at the temperature of 5 to 25 °C. The relative spin-lattice relaxation rate, R 1 /R 1 0 (R 1 =1/T 1 ) at 25 °C increased linearly with increasing concentration of tetraalkylammonium bromide solutions. But, it varied nonlinearly against the concentration below 20 °C and the deviation increased with decreasing temperature. The dynamic hydration number (n DHN ) of D and 17 O nuclei of a D 2 O molecule in the hydration sphere of tetraalkylammonium ions had good correlation with the molecular size, except for the Bu 4 N + ion. The deviation of n DHN of Bu 4 N + ion at low temperature reflected the caging effect due to the association through hydrogen bonding among water molecules as the association increases at lower temperature. It was suggested that the rotational anisotropy ( τ + D / τ + 170 ) of water molecules can be used as a new indicator to classify three types of hydration; negative, positive, and hydrophobic hydrations.

NMR Studies on Dynamic Structure of Hydrated Water Molecules in Alcohol-D2 O Solutions

Abstract The spin-lattice relaxation times (T 1 ) of D and 17 O nuclei of coordinated D 2 O molecules in n -ROH (R= Me, Et, Pr and Bu) dilute aqueous solutions in the concentration range of 0.2 and 1.0 mol kg −1 ( 0.004 - 0.02 molar fraction ) at 25°C were measured by NMR spectroscopy. The relaxation rates (R 1 =1/T 1 ) of D and 17 O nuclei increased linearly with the concentration. B 1 (i=D or 17 O) is defined by R 1 =R 1 0 (1 + B 1 m ), where R 1 and R 1 0 are spin-lattice relaxation rates of the D 2 O molecule at concentration m (mol kg −1 ) and that of pure D 2 O. B 1 increases with the size of the alkyl group of n -ROH. T 1 in alcohol/water solutions were interpreted with bulk and coordinated water. Positive and molecular size dependent B 1 , values are caused by the hydrophobic hydration of the alkyl group. The dynamic hydration number of alcohol solution had good correlation with partial molar volume quantitatively through solute-solvent interactions.

Pressure effects on the spin-lattice relaxation rates of D and 17O nuclei for heavy water molecules in alkali bromide aqueous solutions

Abstract The spin-lattice relaxation rates (R1) of D and 17O nuclei of heavy water (D2O) in alkali bromide (LiBr, NaBr, KBr, CsBr) aqueous solutions were measured in the range of 01–300 MPa at 1.0 molkg−1 and 30°C by NMR. The R1 value decreases with pressure up to 300MPa. In this pressure range, the R1/R1° value (R1° is R1 of these nuclei for pure water) is in the following order : LiBr>NaBr>1>KBr>CsBr.

Pressure effect on the spin-lattice relaxation rates of D and 17O nuclei for heavy water molecules in MgCl2 and CaCl2 aqueous solutions

Abstract The spin-lattice relaxation rates ( R 1 ) of D and 17 O nuclei of heavy water (D 2 O) in MgCl 2 and CaCl 2 aqueous solutions were measured in the range of 0.1–300 MPa and 0–1.0 mol kg −1 at 25 °C by NMR. With solution concentration, R 1 varies quadratically at 0.1–200 MPa and linearly at 250 and 300 MPa, respectively. Moreover, it decreases with increasing pressure and is at each pressure in this order: MgCl 2 >CaCl 2 >pure D 2 O. The rotational correlation times (τ) for the D 2 O molecule coordinated to Mg 2+ and Ca 2+ estimated from R 1 increase with increasing pressure, and at each pressure they have this order: Mg 2+ >Ca 2+ >pure D 2 O.

Temperature and pressure effects on the spin-lattice relaxation rates of D nucleus for heavy water molecules in alkali bromide aqueous solutions

Abstract In order to elucidate the pressure effect on the rotational motion of the D2O molecule coordinated to alkali metal ion, the spin-lattice relaxation rates (R1) of D nucleus of D2O in alkali bromide (LiBr, NaBr, KBr, CsBr) aqueous solutions were measured in the range of 0.1–300 MPa, 0–1.0 molkg−1 and 10–50°C by NMR. R1 value varies linearly with solution concentration even under high pressure at each temperature, so that it can be expressed as a weighted sum of the limiting spin-lattice relaxation rates in infinite dilution based on two-state model. Moreover, R1 value decreases with increasing pressure and temperature and is at each pressure and temperature in this order : LiBr > NaBr > KBr > CsBr. The rotational correlation times (τ), which is estimated from R1 value of D2O molecule, coordinated to alkali metal ions decrease with increasing pressure and temperature and at each pressure and temperature they have this order : Li+ > Na+ > K+ > Cs+. This order also holds for the pressure dependence of τ and the temperature dependence of τ.