Haruo Nakayama

Separate determinations of the surface excesses of surface-active ions and of gegenions at the air-solution interface

Abstract The physical meaning of the slope of surface tension vs. the logarithm of the concentration under various conditions has been analyzed thermodynamically. The surface excesses (concentrations) of surface-active ions and of gegenions at the air-solution interface have been determined from the graphs of ( 1 ) the surface tension vs. the concentration of surface-active ions under the condition of a definite concentration of gegenions, and of ( 2 ) the surface tension vs. the concentration of the gegenions under the condition of a definite concentration of surface-active ions. The surface concentrations at the air-solution interface of aqueous solutions of perfluoro-octanoic acid, potassium perfluoro-octanoate, and barium perfluoro-octanoate were Γ C 7 F 15 COO- = 4.0, Γ H+ = 1.8; Γ C 7 F 15 COO- = 3.9, Γ K+ = 2.0; Γ C 7 F 15 COO- = 3.3-2.8, Γ Ba++ = 1.0-0.9. in 10 −10 mole/cm. 2 below, but near, the CMC. The surface excesses determined from the graphs of the ordinary surface tension vs. the concentration of surface-active agent were 5.8, 5.9, and 4.3-3.7 in 10 −10 mole/cm. 2 . These values were of course equal to the respective summation of the surface excesses of surface-active ions and of gegenions within experimental error. The fact that the surface concentration of gegenions is about one half that of surface-active ions is noteworthy.

Efficient energy transfer in Langmuir–Blodgett films containing J-aggregated antenna cyanine dye

Abstract The light-harvesting function of the J-aggregate of the cyanine dye, N,N′-dioctadecyloxacyanine (Cy), in Langmuir–Blodgett (LB) monolayers containing the amphiphilic perylene derivative (Pe) as an energy acceptor was examined by varying the Cy:Pe molar ratio from 10:1 to 2000:1. A characteristic J-band considerably red-shifted from the corresponding monomer absorption band of Cy was intensely observed in the absorption spectra of the mixed Cy LB monolayers with Pe with the molar mixing ratios Cy:Pe=200:1, 500:1, 1000:1, and 2000:1. Although the contents of Pe in the mixed LB monolayers are such small fractions, the emission from excited Pe induced by energy transfer (ET) from photo-excited Cy was observed clearly. The highest sensitized emission intensity of Pe was observed on the mixed LB monolayer with the molar mixing ratio Cy:Pe=50:1 in which all excited energies of Cy were transferred to Pe. In this molar ratio, however, the ET from monomer or dimer Cy to Pe seemed to be dominant, and the antenna effect of Cy in this state is as low as ca. 50. In contrast, the antenna effect of J-aggregated Cy estimated for the mixed LB monolayers with low Pe ratios (Cy:Pe=500:1, 1000:1, and 2000:1) was such that ca. 250 molecules of Cy would harvest light for excitation of one Pe molecule. This can be attributed to the high rate of exciton migration in the J-aggregates, by which ET probability was increased.

Supercooling and enthalpy of mixing of aqueous solutions of tetrabutylammonium (or isopentylammonium) chloride subjected to different thermal treatments

Abstract In order to observe more directly the structural organization of water molecules around an apolar molecule in an aqueous solution, supercooling phenomena and enthalpies of mixing with various solvents have been examined using aqueous solutions of tetrabutylammonium (or isopentylammonium) chloride subjected to different thermal treatments. Solution I was kept at a temperature only one degree higher than its dissolution temperature, at which a hydrate crystal phase was completely dissolved. The temperature of solution II was raised to 80°C. The supercooling temperatures of solution I were found to be rather higher than those of solution II: 10–15°C for (n-C4H9)4NCl and about 20°C for (i-C5H11)4NCl, regardless of the concentrations of these salts. The differences of the enthalpies of mixing between solution I and solution II in the same solvent ΔHI – ΔHII were determined. It was found that, (1) for solvents such as acetone, tetrahydrofuran, and 1,4-dioxane, ΔHI – ΔHII values were about 10 kJ per mole of (n-C4H9)4NCl which contained 49 moles of water (i.e. the mole fraction of a sample solution was 0.02), and (2) when the solvents were alcohols (methanol and ethanol), the ΔHI – ΔHII value became rather small and in the case of water the ΔHI – ΔHII value became even smaller (1.1 kJ mol−1). It is concluded that the difference in the stability of water networks between solutions I and II is 0.204 kJ per mole of water, which corresponds to about 3.4% of the enthalpy of fusion of ice I.

The effect of simple anions on the formation of poly(tetraisopentylammonium acrylate) hydrates

Abstract In order to know the effect of simple anions on the formation of a poly(tetraisopentyl-ammonium acrylate) ((i-C 5 H 11 ) 4 NPA) hydrate, a thermal analytic method using a differential scanning calorimeter was applied to (a) aqueous solutions of (i-C 5 H 11 ) 4 NPA whose PA anion is partially replaced with simple anions like Cl − and C 2 H 5 COO − , (i-C 5 H 11 ) 4 N[PA] 1 − x Cl x and (i-C 5 H 11 ) 4 N[PA] 1 − x [C 2 H 5 COO] x ( x = 0−1.0), and to (b) aqueous solutions of (i-C 5 H 11 ) 4 NPA containing either NaCl or C 2 H 5 COONa. It was found that when Cl − ion coexisted with the PA anion, two kinds of hydrates, i.e. (i-C 5 H 11 ) 4 NPA hydrate and (i-C 5 H 11 ) 4 NCl hydrate, were formed separately, and a solid solution phase containing both (i-C 5 H 11 ) 4 NPA hydrate and (i-C 5 H 11 ) 4 NCl hydrate was not detected. In addition, in the (i-C 5 H 11 ) 4 NPA + NaCl systems, the amount of (i-C 5 H 11 ) 4 NCl hydrate increased and the PA anion was gradually expelled from the hydrate phase on increasing the amount of NaCl. The behavior of the C 2 H 5 COO − ion was almost the same as that of the Cl − ion.

The formation of clathrate-like hydrates of tetrabutylammonium halogenated carboxylates

The solid-liquid phase diagrams of binary mixtures of tetrabutylammonium halogenated carboxylates with water were examined in order to confirm the formation of clathrate-like hydrates. It was found that, among thirteen carboxylates examined, four carboxylates having CH2FCOO−, CHF2COO−, CF3COO−, and CH2ClCOO−, formed a hydrate with hydration numbers around 30 and seven carboxylates having CHCl2COO−, CCl3COO−, CH2BrCOO−, CHBr2COO−, CBr3COO−, CH3CHClCOO−, and CH3CHBrCOO− formed a hydrate with hydration numbers around 23. The latter hydrate has not been reported earlier. The melting points of these newly found hydrates were fairly high: they lie between 10 and 16°C. The effect of Cl and Br atoms attached to the carbon atom of theα-position of a carboxylate anion both on the type of hydrate formed and on its stability was greatly different from that of a CH3 group attached to the same position of the carboxylate anion.

The Study of Water Structure in Aqueous Solutions of Butoxyethanol by Enthalpy of Mixing Measurements

In order to confirm the existence of regions I and II in aqueous solutions of butoxyethanol(BE), the concentration and temperature dependences of enthalpies of mixing of aqueous BE solutions with some organic solvents were measured. It has been found that the increments of apparent enthalpies of mixing per mole of water with respect to the mole fraction of BE change irregularly at a certain concentration. This concentration nearly corresponds to the reported boundary between regions I and II. Although similar behavior has also been observed in aqueous solutions of iso-butoxyethanol, aqueous solutions oftert-butoxyethanol have shown no anomalous behaviors.

Direct observation of hydrophobic interactions in aqueous solutions of organic compounds by supercooling and enthalpies of mixing

Supercooling temperatures and enthalpies of mixing with some solvents have been examined for two kinds of solutions subjected to different thermal treatments (solutions I and II) of tetrahydrofuran (THF), isopropyl alcohol (2-PrOH), and ethyleneglycol butylether (BE), and ethyleneglycol isobutylether (i-BE) in order to observe more directly the structural organization of water molecules around a nonpolar molecule in an aqueous solution. For THF and 2-PrOH solutions, supercooling temperatures of solution I were found to be 2–3 degrees higher than those of solution II, and differences ΔHI-ΔHII were found to be about 3 kJ mol−1. It has been concluded that these results directly reflect the difference in the stability of hydrogen-bonded water networks in an aqueous solution.

Studies on the hydrophobic hydration by the measurements of supercooling temperature and enthalpies of mixing

Abstract In order to observe, more directly, the structural organization of water molecules around a nonpolar molecule in an aqueous solution, supercooling temperatures and enthalpies of mixing with some organic solvents were measured using two kinds of aqueous solutions (solution I and II) of tetrabutylammonium chloride. Solution I was prepared by melting a hydrate solid formed from the ammonium salt and water, and by keeping its temperature only 1° higher than its dissolution temperature; solution II was prepared by adding urea into solution I at the same temperature by keeping the molar ratio of urea to water as 1 : 49. Supercooling temperatures of solution I were found to be about 20° higher than those of solution II. The differences in enthalpies of mixing between solution I and solution II, ΔH I – ΔH II , were found to be about 0.17 kJ/mol of water regardless of the kind of solvents. It has been concluded that these directly reflect the difference in the stability of hydrogen-bonded water networks around a butyl chain of the ammonium cation in aqueous solutions.

The confirmation of the formation of clathrate-like hydrates of poly(tetrabutylammonium ethenesulfonate) and of poly(tetraisopentylammonium ethenesulfonate)

A thermal method using differential scanning calorimeter has been applied to aqueous solutions of a series of poly(tetraalkylammonium ethenesulfonates) (R4NPES). It was found that only the salts withR=n-C4H9 andR=i-C5H11 could form stable hydrates having large hydration numbers. The melting point and hydration numbers of these two hydrates were 12.0°C and 30±1 for the (n-C4H9)4NPES hydrate and 16.0°C and 53±2 for the (i-C5H11)4NPES hydrate, respectively. It was concluded that these hydrates were clathrate-like essentially similar to such hydrates as (n-C4H9)4NF·30H2O and (i-C5H11)4NF·40H2O.ZusammenfassungUnter Einsatz eines Differential-Scanning-Kalorimeters wurde eine thermoanalytische Methode an wäßrigen Lösungen einer Reihe von Poly(tetraalkylammoniumethensulfonat)-en (R4NPES) angewendet. Man fand, daß nur die Salze mitR=n-C4H9 undR=i-C5H11 stabile Hydrate mit hoher Hydratationszahl bilden können. Der Schmelzpunkt und die Hydratationszahl für diese beiden Hydrate beträgt 12.0°C und 30±1 für (n-C4H9)4NPES Hydrat und 16.0°C und 53±2 für (i-C5H11)4NPES Hydrat. Man zog die Schlußfolgerung, daß diese Hydrate klathratähnliche Verbindungen, ähnlich wie solche Hydrate wie (n-C4H9)4NF30H2O und (n-C5H11)4NF·40H2O sind.

The Effect of Car Boxy Late Anions on the Formation of Clathrate Hydrates Of Tetrabutylammcnium Carboxylates

The solid-liquid phase diagrams of binary mixtures of water with tetrabutylammonium carboxylate having an unsaturated alkyl group in the carboxylate anion ((n-C4H9)4NOOCR; R=C2H3-C9H17) were examined in order to confirm the formation of clathrate-like hydrates. The results are summarized as follows:(1) the formation of a clathrate-like hydrate is newly confirmed for all the 13 carboxylates examined; (2) these hydrates are classified into three groups I, II, and III on the basis of the hydration numbers; (3) the group I hydrates, which are formed by the carboxylates with R=C2 and R=C3, have hydration numbers around 30 and are the most stable hydrates among those examined in this study; (4) the group II hydrates, with hydration numbers around 39, are formed by all the carboxylates with R=C4 and C5 including sorbate and are less stable than the group I hydrates; (5) the group III hydrates, with hydration numbers around 30 like the group I hydrates, are formed by carboxylates with long alkyl chains such as 2-octenoate and 2-decenoate and are generally unstable.