@article {2460,
	title = {Hydrophobicity/Hydrophilicity of 1-Butyl-2,3-dimethyl and 1-Ethyl-3-methylimodazolium Ions: Toward Characterization of Room Temperature Ionic Liquids},
	journal = {Journal of Physical Chemistry B},
	volume = {113},
	number = {44},
	year = {2009},
	note = {ISI Document Delivery No.: 510QMTimes Cited: 2Cited Reference Count: 52Kato, Hitoshi Miki, Kumiko Mukai, Tomohiro Nishikawa, Keiko Koga, Yoshikata},
	month = {Nov},
	pages = {14754-14760},
	type = {Article},
	abstract = {We continue to experimentally characterize the constituent ions of room temperature ionic liquids in terms of their interactions with H2O. By using the so-called 1-propanol probing methodology, we experimentally index the relative hydrophobicity/hydrophilicity of a test ion. In this paper, we examine 1-butyl-2,3 dimethylimidazolium (abbreviated as [C(4)C(1)mim](+)) and 1-ethyl-3-methylimidazolium ([C(2)mim](+)). We found that [C(4)C(1)mim](+) dissociates completely in dilute aqueous solution less than 0.006 mol fraction, and hence, its hydrophobicity/hydrophilicity could be determined. The results indicate that [C(4)C(1)mim](+) is highly amphiphilic with much stronger hydrophobicity and hydrophilicity than normal ions. Our earlier similar studies indicated the same conclusion for such typical constituent ions as 1-butyl-3-methylimidazolium ([C(4)mim](+)) PF6-, CF3SO3-, and N(SO2CF3)(2)(-). Hence, we suggest that the constituent ions of room temperature ionic liquids that we have studied so far are all amphiphiles with much stronger hydrophobicity and hydrophilicity than normal ions. We found, furthermore, that the hydrophobicity and hydrophilicity of [C(4)C(1)mim](+) are stronger than those for [C(4)mim](+). A possible reason for higher hydrpohilicity is discussed in terms of strong acidic character of H on the C(2) of the imidazolium ring, which tends to attract the delocalized positive charge toward itself oil forming a hydrogen bond to H2O. On replacing it with CH3 in [C(4)C(1)mim](+), the lack of acidic H enhances the positive charge in the vicinity of N-C-N in the ring that interacts with the surrounding H2O strongly to an induced dipole of O of the H2O. For [C(2)mim](+), we found it does not dissociate completely, even in dilute aqueous solution, and hence, we could not characterize it within the present methodology.},
	keywords = {1-BUTYL-3-METHYLIMIDAZOLIUM BROMIDE, AGGREGATION BEHAVIOR, ALKYL CHAIN-LENGTH, APPROACH, AQUEOUS-SOLUTIONS, HOFMEISTER SERIES, MIXING SCHEMES, MOLECULAR-ORGANIZATION, partial molar enthalpy, PHYSICOCHEMICAL PROPERTIES, THERMODYNAMIC},
	isbn = {1520-6106},
	url = {<Go to ISI>://000271105600027},
	author = {Kato, H. and Miki, K. and Mukai, T. and Nishikawa, K. and Koga,Yoshikata}
}
@article {2123,
	title = {Chemical Potentials in Aqueous Solutions of Some Ionic Liquids with the 1-Ethyl-3-methylimidazolium Cation},
	journal = {Journal of Physical Chemistry B},
	volume = {112},
	number = {42},
	year = {2008},
	note = {ISI Document Delivery No.: 361AWTimes Cited: 3Cited Reference Count: 33Kato, Hitoshi Nishikawa, Keiko Murai, Hiromi Morita, Takeshi Koga, Yoshikata},
	month = {Oct},
	pages = {13344-13348},
	type = {Article},
	abstract = {We determined the vapor pressures of aqueous solutions of 1-ethyl-3-methylimidazolium ([C(2)mim])-based ionic liquids (IL) with counteranions, tetrafluoroborate (BF4-), trifluoromethanesulfonate (OTF-), and iodide (I-) Because in literature the evidence is accumulating and pointing to the fact that ionic liquid ions do not dissociate in aqueous media for the most of the concentration range, we analyzed the vapor pressure data on the basis of binary mixture, and the excess chemical potentials of each component were calculated. From these, the intermolecular interactions in terms of excess chemical potential and hence the concentration fluctuations were evaluated. Though any further discussion into the mixing schemes of the mixture awaits the excess partial molar enthalpy and hence the excess partial molar entropy data, the net interaction in terms of excess chemical potential indicates that the affinity of each IL is ranked in the descending order [C2mim]l > [C(2)mim]OTF > [C(2)mim]BF4. This is consistent with our earlier findings that [C(2)mim](+) is modestly amphiphilic with almost equal hydrophobicity and hydrophilicity, I- is a hydrophile, and OTF- is amphiphilic, and BF4- is believed to be strongly hydrophobic.},
	keywords = {1-BUTYL-3-METHYLIMIDAZOLIUM, ACETONITRILE, AGGREGATION BEHAVIOR, ENTHALPY-ENTROPY COMPENSATION, MIXING SCHEMES, MOLECULAR-ORGANIZATION, SYSTEMS, TETRAFLUOROBORATE, TETRAFLUOROBORATE PLUS WATER, THERMODYNAMIC APPROACH, VAPOR-PRESSURE MEASUREMENT},
	isbn = {1520-6106},
	url = {<Go to ISI>://000260100900026},
	author = {Kato, H. and Nishikawa, K. and Murai, H. and Morita, T. and Koga,Yoshikata}
}
@article {2302,
	title = {Experimental determination of the third derivative of G. I. Enthalpic interaction},
	journal = {Journal of Chemical Physics},
	volume = {129},
	number = {21},
	year = {2008},
	note = {ISI Document Delivery No.: 379XWTimes Cited: 2Cited Reference Count: 19Westh, Peter Inaba, Akira Koga, Yoshikata},
	month = {Dec},
	pages = {4},
	type = {Article},
	abstract = {The solute (i)-solute interaction in terms of enthalpy, H-i-i(E)=N(partial derivative H-2(E)/partial derivative n(i)(2))=(1-x(i))(partial derivative H-2(E)/partial derivative n(i)partial derivative x(i)), the third derivative of G, was experimentally determined using a Thermal Activity Monitor isothermal titration calorimeter for aqueous solutions of 2-butoxyethanol (BE) and 1-propanol (1P). This was done using both calorimetric reference and sample vessels actively. We simultaneously titrate small and exactly equal amounts of solute i (=BE or 1P) into both cells which contain the binary mixtures at an average mole fraction, x(i), which differs by a small amount Delta x(i). The appropriate amount of titrant delta n(i) was chosen so that the quotient (delta H-E/delta n(i)) can be approximated as (partial derivative H-E/partial derivative n(i)), and so that the scatter of the results is reasonable. delta H-E is the thermal response from an individual cell on titration, and we measure directly the difference in the thermal response between the two cells, Delta(delta H-E). The resulting quotient, Delta(delta H-E)/delta n(i)/Delta x(i), can be approximated as (partial derivative H-2(E)/partial derivative n(i)partial derivative x(i)) and hence provides a direct experimental avenue for the enthalpy interaction function. We varied the value of Delta x(i) to seek its appropriate size. Since H-E contains the first derivative of G with respect to T, the result is the third derivative quantity. Thus we present here a third derivative quantity directly determined experimentally for the first time.},
	keywords = {AQUEOUS-SOLUTIONS, calorimetry, DYNAMICS, enthalpy, fluctuations, H2O, HOFMEISTER SERIES, LIQUID MIXTURES, MOLECULAR-ORGANIZATION, organic compounds, SOLVATION, WATER},
	isbn = {0021-9606},
	url = {<Go to ISI>://000261430900001},
	author = {Westh, P. and Inaba, A. and Koga,Yoshikata}
}
@article {2129,
	title = {Mixing schemes in a urea-H2O system: A differential approach in solution thermodynamics},
	journal = {Journal of Physical Chemistry B},
	volume = {112},
	number = {36},
	year = {2008},
	note = {ISI Document Delivery No.: 345EVTimes Cited: 5Cited Reference Count: 29Koga, Yoshikata Miyazaki, Yuji Nagano, Yatsuhisa Inaba, Akira},
	month = {Sep},
	pages = {11341-11346},
	type = {Article},
	abstract = {The excess partial molar enthalpies of urea (UR), H-UR(E), were experimentally determined in UR-H2O at 25 degrees C. The H-UR(E) data were determined accurately and in small increments in the mole fraction of UR, X-UR, up to X-UR approximate to 0.22. Hence it was possible to evaluate one more X-UR-derivative graphically Without resorting to any fitting function, and the model-fi-ee UR-UR enthalpic interaction, H{\textquoteright}U{\textquoteright}-R-uR, was calculated. Using previous data for the excess chemical potential, mu(E)(UR), the entropy analogue, S-UR(E)-UR. was also calculated. The X-UR-dependences of both H-UR(E)-UR and S-UR(E)-UR indicate that there is a boundary at X-UR approximate to 0.09 at which the aggregation nature of urea changes. Front the results of our earlier works, we suggest that a few UR molecules aggregate at X-UR approximate to 0.09, while the integrity of H2O is retained at least up to X-UR approximate to 0.20. Together with the findings from our previous studies, we suggest that in the concentration range X-UR < 0.22, UR or its aggregate form hydrogen bonds to the H2O network, reducing the degree of fluctuation characteristic to liquid H2O. However, up to at least X-UR = 0.20 the hydrogen bond network remains intact. Above X-UR approximate to 0.22, the integrity of H2O is likely be lost. Thus, in discussing the effect of urea on H2O and in relating it to the Structure and function of biopolymers in aqueous solutions, the concentration region in question must be specified.},
	keywords = {25-DEGREES-C, AQUEOUS UREA, DYNAMICS, ENTHALPIES, H2O, LIQUID WATER, MOLECULAR-ORGANIZATION, NUCLEAR-MAGNETIC-RESONANCE, POTASSIUM, WATER-STRUCTURE},
	isbn = {1520-6106},
	url = {<Go to ISI>://000258979800023},
	author = {Koga,Yoshikata and Miyazaki, Y. and Nagano, Y. and Inaba, A.}
}
@article {1227,
	title = {Hydration number of glycine in aqueous solution: An experimental estimate},
	journal = {Journal of Chemical Physics},
	volume = {123},
	number = {23},
	year = {2005},
	note = {ISI Document Delivery No.: 996ADTimes Cited: 6Cited Reference Count: 31},
	month = {Dec},
	pages = {6},
	type = {Article},
	abstract = {An experimental estimate of hydration number, N-H, of glycine in aqueous solution is given by using the calorimetric methodology developed by us earlier, which is briefly reviewed. We found N-H to be 7 +/- 0.6 for glycine presumably in the zwitter ion form, 10 +/- 1 for sodium glycinate, and 5 +/- 0.4 for glycine hydrochloride. Both glycine and sodium glycinate seem to work purely as a hydration center without altering the nature of the bulk H2O away from the hydration shell. Glycine hydrochloride, in addition to the role of hydration center, seems also to act as a typical hydrophilic species such as polyols, urea, or polyethylene glycols. Hence, the effect of the latter on H2O is of a long range, like other hydrophilic species. (c) 2005 American Institute of Physics.},
	keywords = {25-DEGREES-C, fluctuations, H2O, INTRAMOLECULAR PROTON-TRANSFER, MIXING SCHEMES, MOLECULAR-ORGANIZATION, NONELECTROLYTES, PARTIAL MOLAR ENTHALPIES, TAUTOMERIZATION, WATER},
	isbn = {0021-9606},
	url = {<Go to ISI>://000234145900026},
	author = {Parsons, M. T. and Koga,Yoshikata}
}
@article {1201,
	title = {Hydrophobicity vs hydrophilicity: Effects of poly(ethylene glycol) and tert-butyl alcohol on H2O as probed by 1-propanol},
	journal = {Journal of Physical Chemistry B},
	volume = {109},
	number = {41},
	year = {2005},
	note = {ISI Document Delivery No.: 974SQTimes Cited: 8Cited Reference Count: 33},
	month = {Oct},
	pages = {19536-19541},
	type = {Article},
	abstract = {The enthalpic interaction between 1-propanol (IP) molecules, H-1P- 1P(E), was evaluated in 1P-poly(ethleneglycol) (PEG)-H2O and 1P-tert-butyl alcohol (TBA)-H2O ternary mixtures. The model-free and experimentally accessible quantity, H-1P-1p(E), indicates the effect of an additional 1P on the actual enthalpic situation of 1P in the mixture. It was shown earlier that the composition dependence of H-1P-1P(E) reflects the process how 1P modifies H2O. This H-1P-1P(E) pattern changes in the presence of a third component, PEG or TBA. The effects of PEG or TBA on the molecular organization of H2O were elucidated from these induced changes. Together with previous similar studies for the effects of methanol (ME), 2-propanol (2P), ethylene glycol (EG), and glycerol (Gly), we suggest a method and hence a possible scaling for sorting out hydrophobicity vs hydrophilicity of these alcohols by the changes induced to the loci of the maxima in H-1P-1P(E). We show that hydrophilicity scales with the number of oxygen, regardless of whether O is the ether -O- or the hydroxyl -OH. Hydrophobicity also scales with the number of carbon atoms for alcohols without a methyl group. For those with methyl groups, the hydrophobicity seems proportional to the total number of carbon with a different proportionality factor from those without methyl group.},
	keywords = {25-DEGREES-C, ALKANE-MONO-OLS, AQUEOUS-SOLUTIONS, EXCESS CHEMICAL-POTENTIALS, GLYCEROL, HOFMEISTER SERIES, MIXING SCHEMES, MOLECULAR-ORGANIZATION, PARTIAL MOLAR ENTHALPIES, THERMODYNAMIC APPROACH},
	isbn = {1520-6106},
	url = {<Go to ISI>://000232612100072},
	author = {Miki, K. and Westh, P. and Koga,Yoshikata}
}
@article {901,
	title = {Mixing schemes in ionic liquid-H2O systems: A thermodynamic study},
	journal = {Journal of Physical Chemistry B},
	volume = {108},
	number = {50},
	year = {2004},
	note = {ISI Document Delivery No.: 879CXTimes Cited: 78Cited Reference Count: 33},
	month = {Dec},
	pages = {19451-19457},
	type = {Article},
	abstract = {We studied the hydration characteristics of room-temperature ionic liquids (IL). We experimentally determined the excess chemical potentials, mu(i)(E), the excess partial molar enthalpies, H-i(E), and the excess partial molar entropies S-i(E) in IL-H2O systems at 25 degreesC. The ionic liquids studied were 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4) and the iodide ([bmim]l). From these data, the excess (integral) molar enthalpy and entropy, H-m(E) and S-m(E), and the IL-IL enthalpic interaction, H-IL-IL(E), were calculated. Using these thermodynamic data, we deduced the mixing schemes, or the "solution structures", of IL-H2O systems. At infinite dilution IL dissociates in H2O, but the subsequent hydration is much weaker than for NaCl. As the concentration of IL increases, [bmim]l ions and the counteranions begin to attract each other up to a threshold mole fraction, x(IL) = 0.015 for [bmim]BF4 and 0.013 for [bmim]l. At still higher mole fractions, IL ions start to organize themselves, directly or in an H2O-Mediated manner. Eventually for x(IL) > 0.5-0.6, IL molecules form clusters of their own kind, as in their pure states. We show tha HI-L-IL, a third derivative of G, provided finer details than H-i(E) and S-i(E) second derivatives, which in turn gave more detailed information than H-m(E) and S-m(E), first derivative quantities.},
	keywords = {25-DEGREES-C, AQUEOUS SODIUM-CHLORIDE, ENTHALPIES, GLYCEROL, H2O, METHANOL, MIXTURES, MOLECULAR-ORGANIZATION, SOLVENTS, WATER},
	isbn = {1520-6106},
	url = {<Go to ISI>://000225695100058},
	author = {Katayanagi, H. and Nishikawa, K. and Shimozaki, H. and Miki, K. and Westh, P. and Koga,Yoshikata}
}
@article {709,
	title = {Excess chemical potentials and partial molar enthalpies in aqueous 1,2-and 1,3-propanediols at 25 degrees C},
	journal = {Journal of Solution Chemistry},
	volume = {32},
	number = {2},
	year = {2003},
	note = {ISI Document Delivery No.: 661CMTimes Cited: 4Cited Reference Count: 24},
	month = {Feb},
	pages = {137-153},
	type = {Article},
	abstract = {Excess chemical potentials and excess partial molar enthalpies of 1,2- and 1,3-propanediols ( abbreviated as 12P and 13P), mu(i)(E), and H-i(E) ( i = 12P or 13P) were determined in the respective binary aqueous solutions at 25degreesC. For both systems, the values of mu(i)(E) are almost zero, within +/-0.4 kJ-mol(-1). However, the excess partial molar enthalpies, H-i(E) show a sharp mole fraction dependence in the water-rich region. Thus, the systems are highly nonideal, in spite of almost zero mu(i)(E). Namely, the enthalpy-entropy compensation is almost complete. From the slopes of the HE i against the respective mole fraction x(i) we obtain the enthalpic interaction functions between solutes, H-i-i(E), ( i = 12P or 13P). Using these quantities and comparing them with the equivalent quantities for binary aqueous solutions of 1-propanol ( 1P), 2-propanol (2P), glycerol (Gly), and dimethyl sulfoxide ( DMSO), we conclude that there are three composition regions in each of which mixing schemes are qualitatively different. Mixing Schemes II and III, operative in the intermediate and the solute-rich regions, seem similar in all the binary aqueous solutions mentioned above. Mixing Scheme I in the water-rich region is different from solute to solute. 12P shows a behavior similar to that of DMSO, which is somewhat different from typical hydrophobic solute, 1P or 2P. 13P, on the other hand, is less hydrophobic than 12P, and shows a behavior closer to glycerol, which shows hydrophilic behavior.},
	keywords = {2-and 1, 3-propanediols, ALCOHOL, chemical potentials, ENERGIES, ENTHALPIES, ENTROPIES, H2O, interaction functions, MIXING SCHEMES, mixing schemes in aqueous 1, MOLECULAR-ORGANIZATION, NONELECTROLYTES, partial molar, TERT-BUTANOL MIXTURES, VOLUMES, WATER-RICH REGION},
	isbn = {0095-9782},
	url = {<Go to ISI>://000181873700003},
	author = {Parsons, M. T. and Lau, F. W. and Yee, E. G. M. and Koga,Yoshikata}
}
@article {421,
	title = {Mixing schemes in ternary aqueous solutions - Thermodynamic approach},
	journal = {Journal of Thermal Analysis and Calorimetry},
	volume = {69},
	number = {3},
	year = {2002},
	note = {ISI Document Delivery No.: 604BRTimes Cited: 8Cited Reference Count: 282nd International Symposium on the New Frontiers of Thermal Studies of MaterialsNOV 25-27, 2001SUZUKAKEDAI, JAPAN},
	pages = {705-716},
	type = {Proceedings Paper},
	abstract = {The enthalpic interaction functions introduced by us earlier were evaluated in some ternary aqueous solutions. They are determined purely experimentally without resorting to any model system. From them, the pair interaction coefficients based on the virial expansion were evaluated, which will serve for a future theoretical development based on the McMillan-Mayer theory of solution. Secondly, our new methodology of using the mole fraction dependence of the enthalpic interaction function as a probe to elucidate the effect of a third component on the molecular organization is introduced. The conclusions for selected third components in ternary aqueous 1-propanol are reviewed.},
	keywords = {25-DEGREES-C, effect of selected solutes on the molecular organization of H2O, enthalpic interaction functions, ENTROPIES, EXCESS CHEMICAL-POTENTIALS, H2O, MOLECULAR-ORGANIZATION, pair interaction coefficients, PARTIAL MOLAR ENTHALPIES, ternary aqueous solutions, TERT-BUTANOL, TETRAMETHYL UREA, the, VOLUMES, WATER},
	isbn = {1418-2874},
	url = {<Go to ISI>://000178596200002},
	author = {Koga,Yoshikata}
}
