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Purpose This study aimed to investigate the recovery of physical function, muscle mass, and quality of life (QOL) in allogeneic hematopoietic stem cell transplantation (allo-HSCT) patients 1 year after the procedure. Methods A total of 71 patients who underwent allo-HSCT at our institution between February 2010 and June 2020, for whom a physical therapy assessment could be performed before allo-HSCT, at discharge, and 1 year after allo-HSCT, were included. Exercise therapy during hospitalization was provided individually by a physical therapist, and exercise was self-administered after discharge. Results One year after allo-HSCT, handgrip strength and results of the 6-minute walk test (6 MWT) recovered to pre-HSCT levels. Muscle mass 1 year after allo-HSCT showed slight improvement after discharge from the hospital but did not reach the pre-HSCT level. All subscales of QOL, 1 year after allo-HSCT, recovered to pre-HSCT levels, but only two of the eight subscales recovered to the national norm of 50. Multivariate analysis revealed factors associated with the recovery of physical function and QOL, including improved hemoglobin levels, albumin levels, and adherence to exercise therapy. In contrast, factors that negatively affected recovery were steroid administration and pre-HSCT intensity conditioning. Conclusion The results suggest that continued exercise therapy may contribute to the recovery of muscle strength, endurance, and QOL 1 year after allo-HSCT.

In this work, the thermodynamic properties of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide/primary alcohol (methanol to 1-nonanol) mixtures were studied. The densities, viscosities, and electrical conductivities of the mixtures were determined for a range of compositions up to the solubility limit of the alcohol in the ionic liquid at room temperature. From these data, excess molar volumes and viscosity deviations were calculated. The changes in the structure of the ionic liquid upon addition of the primary alcohols are discussed. We also considered the relationship between the macroscopic properties observed in the present study and the Raman spectral changes reported in our previous study. We explained the behavior of the systems at the molecular level, especially at lower alcohol concentrations, by a concept where the alcohols occupy spaces formed inside the nanoheterogeneous structure of the ionic liquid.

The high-pressure (HP) phase transition and conformational change of n-octane (hereafter abbreviation as n-C8) up to 15.3 GPa were studied using Raman spectroscopy to investigate the relationship between the HP phase state and the alkyl chain length of n-alkanes. The Raman spectral analysis of n-C8 indicated that the liquid-solid transition (solidification) occurs at ∼0.9 GPa and that the corresponding transition pressure of n-alkanes depends on their density. Further pressurization at ∼4 GPa increased the population of the gauche conformer, while the solid (order)-amorphous transition occurred at ∼6 GPa along with a change in the full width at half maximum of the ruby R1 fluorescence line. The comparison of our findings with previously reported results suggested that the even-odd effect in the HP phase transition after solidification of n-alkanes appears between n-C7 and n-C8 as their HP phase transition up to ∼15 GPa was different.

We report biocompatible materials for cryostorage of unstable proteins such as cancer-related enzyme

We investigated the stability of the liquid phase of 1-butyl-3-methylimidazolium iodide (hereafter abbreviated as [C4mim][I]) up to 16.7 GPa at room temperature. We observed a peculiar phase transition behavior in the [C4mim][I] sample. In particular, a glassy state was formed at ∼1.3 GPa; however, the reddish-brown precipitate was formed probably due to concentrated I3- or I2- species that were formed above 12 GPa; [C4mim][I] showed a pressure-induced partial crystallization from the glassy state. We concluded that the conformation of [C4mim]+ is essential in iterative modulation to control the environmental formation of iodide precipitate.

The anomalous phase behaviors of ionic liquids (ILs) were examined under low temperature (LT) and high pressure (HP). Under LT condition, crystal polymorphs and multiple crystallization pathways could be found for protic IL ethylammonium nitrate ([EAN][NO3]). For 1-ethyl-3-methylimidazolium nitrate ([C2mim][NO3]), an aprotic IL, simple LT-crystallization behavior was observed. However, HP conditions produced complicated phase behaviors. The HP-inherent conformer of the C2mim+ cation governed the crystallization pathways. In the liquid state, a variety of complicated phase transitions were influenced by multiple passible non-equilibrium degree factors: charge (scalar), dipole moment (vector), conformations (topology), and proton (transfer/network). The non-equilibrium degrees of protic and aprotic ILs were described by various solid phases both at LT and HP.

In this study, ionic liquids (ILs) properties of rubbers and resins dissolution and absorption were investigated, and direct and indirect potential contamination possibilities were proposed. From the trial of the direct immersion of various rubbers and resins in ILs, it was confirmed that most of the materials are dissolved in ILs resulting in contamination, with the exception of silicone rubber. On top of that, indirect contamination possibility during distillation under reduced pressure (vacuum treatment) was investigated. Following the application of vacuum to ILs, we observed a new absorption peak appear in the ultraviolet-visible spectra of various ILs in the range of 350 to 450 nm. The cause of new peak was investigated from several aspects and finally determined to result from the absorption of one or more volatilized compounds from the chloroprene rubber cap of the glass vacuum vessel, even though the IL was not in direct contact with the cap. Interestingly, although CO2 absorbed in ILs can be desorbed by the application of a vacuum, this compound could not be removed from the ILs simply by vacuum treatment conversely. These results indicate ILs contamination could be occurred through direct and indirect contact with rubbers and resins. Therefore, we need to be careful in dealing with ILs. It also follows that silicone materials should be used in conjunction with ILs where possible to avoid contamination, even in cases where the IL is not in direct contact with the material.

Short alanine (Ala) oligopeptides in aqueous solution adopt polyproline II [PPII; (φ, ψ) = (−60°, 150°)] and extended β conformations [(φ, ψ) = (−150°, 150°)], whose conformers are related to the denatured state of proteins. In this study, we investigated pressure-induced conformational changes of penta- and hexa-alanines (Ala5 and Ala6, respectively) in aqueous solutions using Fourier-transform infrared (FTIR) spectroscopy. A remarkable observation was that two peaks at 1620 and 1690 cm−1 in Ala6 assigned to the intermolecular β-sheets were generated with increasing pressure. These peaks were not observed in Ala5. Our analyses of absorbance changes and frequency shifts further suggested that pressure was responsible for the PPII → β conformational change of Ala5, and the PPII → intermolecular β-sheet structure of Ala6, respectively. These results indicated a differing conformational stability of Ala5 under high pressure as compared with Ala6.

The glass-forming concentration and the cooling effect of aqueous DMSO solutions at various concentrations X (mol%DMSO) on protein state were investigated using Raman spectroscopy and Fourier-transform infrared (FTIR) spectroscopy along with differential thermal analysis (DTA) to obtain fundamental information on storage of recombinant protein at cryogenic temperature. DTA and Raman spectral measurements showed that the aqueous DMSO solutions with lysozyme formed the glassy state at X = 15–60. Activity and structural stability of lysozyme in aqueous DMSO solutions before and after cooling exhibited small change up to X = 0–30. Thus, the DMSO concentration at X = 15–30 was found to be a suitable condition for lysozyme storage at cryogenic temperature. The cryopreservation ability of aqueous DMSO solutions for lysozyme was observed to be strongly associated with the glassy solution structure that inhibits protein unfolding and aggregation. The present findings may serve as basic information regarding the appropriate experimental conditions for DMSO solutions to be employed as a suitable cryoprotectant for various recombinant proteins.

We conducted high-pressure Raman spectroscopy measurements on a series of 1-alkyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([Pyr1n][TFSI], n = 3, 4, 6 and 8) homologues that have different alkyl chain lengths, n, at room temperature. The results showed that all [Pyr1n][TFSI] samples formed a glassy state in which the glass transition pressure (pg) slightly increased with an increase in n. This tendency is similar to prior results of high-pressure glass formation of [Cnmim][TFSI], although the pgs for [Pyr1n][TFSI] are larger than those for [Cnmim][TFSI] with corresponding n by ∼0.5 GPa. We discuss the local structural changes occurring in [Pyr1n][TFSI] in view of the conformational changes of the Pyr+1n cation and TFSI− anion.

Amyloid aggregates containing a high content of β-sheet structure are one of several water-insoluble protein aggregates. In this study, we assessed the use of aqueous ionic liquid (IL) solutions as part of a simple preservation/refolding technique for amyloid aggregates. We investigated the dissolution and refolding of cryopreserved bovine insulin amyloid in concentrated aqueous solutions (X = 20 mol%IL) of six different ionic liquids: three 1-butyl-3-methylimidazolium-based ILs ([bmim][X]; X = SCN, NO3, or Cl), 1-ethyl-3-methylimidazolium nitrate ([emim][NO3]), ethylammonium nitrate (EAN), and propylammonium nitrate (PAN). Dimethyl sulfoxide (DMSO) was used as the reference standard for spectroscopy. The six ILs all exhibited the ability to dissolve insulin amyloid, with imidazolium-based ILs exhibiting increased dissolution capacity compared with ammonium-based ILs or DMSO. Remarkably, >80% of the secondary structure of the folded insulin monomer was recovered from insulin amyloid dissolved in aqueous IL solutions following cryopreservation and IL removal by dialysis. These results indicate that concentrated aqueous IL solutions have potential as a new and simple agent for the dissolution, cryopreservation, and refolding of amyloid aggregates.

The effect of adding ethylammonium nitrate (EAN), which is an ionic liquid (IL), on the aggregate formation of α-synuclein (α-Syn) in aqueous solution has been investigated. FTIR and Raman spectroscopy were used to investigate changes in the secondary structure of α-Syn and in the states of water molecules and EAN. The results presented here show that the addition of EAN to α-Syn causes the formation of an intermolecular β-sheet structure in the following manner: native disordered state → polyproline II (PPII)-helix → intermolecular β-sheet (α-Syn amyloid-like aggregates: α-SynA). Although cations and anions of EAN play roles in masking the charged side chains and PPII-helix-forming ability involved in the formation of α-SynA, water molecules are not directly related to its formation. We conclude that EAN-induced α-Syn amyloid-like aggregates form at hydrophobic associations in the middle of the molecules after masking the charged side chains at the N- and C-terminals of α-Syn.

Amyloid aggregates are composed of protein fibrils with a dominant β-sheet structure, are water-insoluble, and are involved in the pathogenesis of many neurodegenerative diseases. Development of pharmaceuticals to treat these diseases and the design of recovery agents for amyloid-type inclusion bodies require the successful suppression and dissolution of such aggregates. Since ionic liquids (ILs) are composed of both a cation and anion and are known to suppress protein aggregation and to dissolve water-insoluble compounds such as cellulose; they may also have potential use as suppression/dissolution agents for amyloid aggregates. In the following review, we present the suppression and dissolution effects of ILs on amyloid aggregates so far reported. The protein–IL affinity (the ability of ILs to interact with amyloid proteins) was found to be the biochemical basis for ILs’ suppression of amyloid formation, and the hydrogen-bonding basicity of ILs might be the basis for their ability to dissolve amyloid aggregates. These findings present the potential of ILs to serve as novel pharmaceuticals to treat neurodegenerative diseases and as recovery agents for various amyloid aggregates.

The high-pressure (HP) crystal polymorph of a fluorinated ionic liquid (fIL) was determined using X-ray diffraction and Raman spectroscopy. The irreversible crystal polymorph of 1-butyl-3-methylimidazolium perfluorobutanesulfonate ([C4mim][PFBS]) was observed upon compression and decompression using X-ray diffraction. Conformational variance/invariance of [C4mim]+ and [PFBS]− in the Raman spectra corresponded to the HP crystal polymorph. By the degrees of freedom of the conformations and their conformational flexibilities, the conformational variance was switched at the specific pressure for a volume contraction under HP, at which point the crystal system changed. The HP crystal polymorph was entirely different from the low-temperature crystal polymorph.

Understanding the helical formation of proteins in concentrated aqueous solutions of alkylammonium-based ionic liquids (RAN-ILs) forming the glassy state is necessary to devise the guidelines for the design of ILs for use in protein cryopreservation. To reveal the effect of the alkyl-chain length of cation on the helix forming ability of RAN-ILs, helix formation in five model proteins (ribonuclease A, β-lactoglobulin, ubiquitin, α-lactalbumin, and cytochrome c ) with different secondary structure contents in the solutions of three RAN-ILs, namely methylammonium nitrate (MAN), ethylammonium nitrate (EAN), and propylammonium nitrate (PAN) were investigated over a wide concentration range X (mol%IL) using optical spectroscopy. Overall, although the addition of RAN-ILs to proteins caused protein unfolding, condensed solutions with EAN and PAN ( X > 10) induced helical formation, which was disrupted by the tertiary structure of proteins, except for ubiquitin and α-lactalbumin. In contrast, aqueous MAN solutions did not induce the non-native helical structure of the five model proteins throughout the studied concentration range, X . The difference in the helix-forming ability between MAN and the other two RAN-ILs was dependent on the low polarity of the solutions. Moreover, although EAN and PAN have helix-forming abilities, these abilities were dependent on protein species. The present finding is that the consideration of solution polarity and dependence of protein species is related to the guidelines for the design of RAN-ILs for the cryopreservation of proteins such as recombinant proteins.

In pure ethylammonium nitrate (EAN), which is a protic ionic liquid (pIL), multiple crystallization pathways are extracted by simultaneous X-ray diffraction and differential scanning calorimetry measurements. Multiple pathways for crystallization are selected by minimum temperatures in a pure EAN crystal. In an EAN – water system, phase equilibria are determined precisely by in situ observations made by using simultaneous measurements. Electrochemical instabilities induced by proton transfer are observed at 70 x 2 O [ Chem. Phys . 475 (2016) 119.]. Complicated phase diagrams indicate water-mediated anomalies as a crossover point from pIL-dominant to water-dominant regions.

The conformational stability of 1-alkyl-3-methylimidazolium tetrafluoroborate ([Cnmim][BF4], n = 3-8) under high pressure was investigated using Raman spectroscopy to reveal the preferential role of the alkyl-chain length (n) in high-pressure glass transition. To evaluate this, we determined the intensity ratio (r) and differences in the partial molar volume (ΔVtrans→gauche) between the whole trans and gauche conformers of the [Cnmim] cation using Raman intensities. Interestingly, both values were classified into a two alkyl-chain length region at the border of n = 5. The coulombic interaction (cation-anion interaction) for the conformational stability is the predominant factor below n = 5 (the cation-head portion: alkyl carbon number C 5). In combination with the conformational preference of the [Cnmim] cation under a high-pressure glassy state, the alkyl chain displays a preferential role, i.e., an increase in the gauche conformer of [Cnmim][BF4] adjusts to avoid crystallization (the conformational adjustment effect). In the presence of the coulombic interaction, the preferential role of the flexible alkyl chain is an important key to elucidate the mechanism of the complicated high-pressure phase transition behavior of ionic liquids.

Recently, the presence of cavities in ionic liquids (ILs), which affects the solubility of solute molecules such as CO2, has been demonstrated. With the aim of gaining more insight into the interactions between the IL and guest water molecules, the changes experienced upon addition of water molecules to an IL have been monitored by Raman spectroscopy. This study focuses on how the difference in the nanoheterogeneous structures of two ILs, 1-butyl-3-methylimidazolium iodide (abbreviated as [bmim][I]) and 1-butyl-3-methylimidazolium tetrafluoroborate (abbreviated as [bmim][BF4]) influences the local structure of water embedded in the ILs. The evolution of local water clusters formed in the ILs is compared. Then, the connections between microscopic and macroscopic properties were reviewed.

We have investigated the structure and activity of chicken egg-white lysozyme in aqueous solutions of two typical ionic liquids, 1-butyl-3-methylimidazolium chloride and ethylammonium nitrate, at cryogenic temperature. An increase in structural disorder due to the unfolding and a decrease in the α-helical structure of lysozyme were noticeable upon glass formation. However, a decrease in the structural stability after cooling was less than that before cooling. The secondary and tertiary structures showed good reversibility upon cooling to 77 K and then reverting back to ambient temperature. We discussed an influence of a cooling upon the structure in aqueous ionic liquid solutions.

Electrochemical impedance spectroscopy was used to evaluate protic ionic liquid (pIL)-water mixtures in the temperature range of −35–25 °C. The pIL used in this study was ethylammonium nitrate (EAN). At room temperature, the resonant mode of conductivity was observed in the high frequency region. The anomalous conductivity disappeared once solidification occurred at low temperatures. The kinetic pH of the EAN-water system was investigated at a fixed temperature. Rhythmic pH oscillations in the EAN-H 2 O mixtures were induced at 70 x 2 O. The electrochemical instabilities in a EAN-water mixture are caused in an intermediate state between pIL and bulk water. From the ab initio calculations, it was observed that the dipole moment of the EAN-water complex shows a discrete jump at around 85 mol% H 2 O. Water-mediated hydrogen bonding network drastically changes at the crossover concentration.

Non-crystal formation of ice is investigated by simultaneous X-ray diffraction and differential scanning calorimetry measurements upon cooling to -100 °C. At room temperature, size-tunable water confinement (≈20 Å size) in a room-temperature ionic liquid (RTIL, 1-butyl-3-methylimidazolium nitrate, [C4 mim][NO3 ]) exists in a water-rich region (70-90 mol % D2 O). The confined water (water pocket) is characterized by almost monodispersive size distribution. In [C4 mim][NO3 ]-x mol % D2 O (70x94), the absence of sharp Bragg reflections and a distinct exothermal peak indicate that crystallization/cold crystallization both of [C4 mim][NO3 ] and D2 O is suppressed, even upon slow cooling and heating.

Helix formation in β-lactoglobulin (β-LG) and α-synuclein (α-Syn) was investigated in aqueous solutions of ethylammonium halides (EAX; X = Cl, Br, or I) at different concentrations using vibrational spectroscopy. It was found that EABr and EAI induced helix formation in both proteins; however, no helix-promoting ability was observed for EACl. Notably, particularly enhanced helix formation was detected in EAI. Moreover, no intermolecular β-sheet development (i.e., amyloid-like aggregation) was noted for either β-LG or α-Syn at any EAX concentration.

The solid states of crystalline and amorphous phases and their mixtures in room-temperature ionic liquids (RTILs) were distinguished both at low-temperature (LT) and high-pressure (HP) by X-ray diffraction. Various solidifications of the RTILs were investigated using three cations. These were 1-butyl-3-methylimidazolium, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium and N-2-methoxyethyl-N-methylpyrrolidinium. The common anions were nitrate, tetrafluoroborate, hexafluorophosphate, [PF6]−, trifluoromethanesulfonate, and bis(trifluoromethanesulfonyl)imide. The solid states of the RTILs depended on the cation-anion combinations. Crystal polymorph formation, cold crystallization on heating, and decompression crystallization on pressure reduction derived from competition among the molecular orientational order, degrees of freedom of cation conformers, and molecular packing efficiency in addition to the anion effect. In [PF6]−-based RTILs, complex phase behaviors were observed both at LT and HP.

The dynamic and static properties of mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and alcohols with various alkyl chain lengths were investigated. For alcohol concentrations of 20 mol% or less, where the alcohol/ionic liquid system maintains a nano-heterogeneous structure, the self-diffusion coefficient and the chemical shift of anions and cations in the alcohol/[BMIM][BF4] system were not dependent on the alkyl chain length of the alcohol, but were almost coincident with each other when comparing the same solvent concentration. This indicates that the solution structure of pure [BMIM][BF4] was almost maintained in the alcohol/ionic liquid system. Moreover, alcohol having short alkyl chain length and water moved clearly faster than the IL, but the movement of alcohol having long alkyl chain length moved close to that of the IL suggesting that the alcohols may not be able to move significantly in the IL.

We investigated the optical absorption and photoconductivity of iodine-excess ionic liquids (ILs) based on 1-alkyl-3-methyl imidazolium iodide ([Cnmim][I]; n = 3, 4, and 6). The iodide concentration m was 2 ≦ m ≦ 8, which was determined by the molar fraction [Cnmim]+ : [Im]− = 1 : m. By adding iodine, an absorption edge shifted from 282 nm in the UV region to around 600 nm in the visible-light region. The optical bandgaps Eo decreased gradually from 2.3 eV to 1.9 eV with increasing m from 2 to 8. The alkyl-side chain lengths of the cations have little effect on the Eo. This experimental result was confirmed by ab initio molecular orbital calculations. The effects were reflected in the photoconductivity of the ILs, as expected. [C4mim][Im] exhibited greater photo-induced electron generation compared with [C3mim][Im] and [C6mim][Im]. The photoconductivity in both [C3mim][Im] and [C6mim][Im] increased slightly with increasing m. The trend of photoconductivity in [C4mim][Im] exhibited an N-shaped form. The highest photoconductivity 1.6 was observed in [C4mim][I8].

We investigated the stability of the liquid phase of a series of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Cnmim][TFSI]) homologues with different alkyl chain lengths for 3 ≤ n ≤ 10 at room temperature. We found that all [Cnmim][TFSI] samples (n = 3–10) formed a glassy state when pressure was applied. Intriguingly, the glass transition pressure (pg) slightly increases up to n = 5, reaches a plateau at n ≧ 8, and increases again at n = 10. This is completely different from the high-pressure glass formation of [Cnmim][BF4], where the pg decreases as n increases. We discussed the local structural changes occurring in [Cnmim][TFSI] in view of the conformational changes of the cation and anion, and small-angle X-ray scattering data. It seems that [Cnmim][TFSI] is resistant to external pressure and retains its local liquid structure by conformational adjustments of the cation and anion.

Using the congo red assay and Fourier transform infrared spectroscopy, we have investigated the suppression of bovine insulin amyloid formation by the addition of 1-butyl-3-methylimidazolium thiocyanate ([bmim][SCN]), ethylammonium nitrate ([EAN][NO3]), and propylammonium nitrate ([PAN][NO3]) ionic liquids (ILs). The results of our investigations showed that the three studied ILs strongly inhibit the formation of insulin amyloid. Furthermore, the condensed solutions containing [EAN][NO3] and [PAN][NO3] demonstrated a higher protectant ability for the structure of monomeric insulin rather than that of [bmim][SCN]. To investigate the mechanism underlying the suppression ability of ILs, the interaction site of ILs and amino acid residues in insulin was determined. The affinity between ILs and specific amino acid residues in insulin was found to be the main cause for the suppression of insulin amyloid formation. The present finding is that ILs can be potentially used as the suppression agent of insulin amyloi...

Room-temperature ionic liquids (RTILs) can extract hidden information about water. Various types of hydrogen bonds of water are detected clearly in the liquid, glass, and crystal states. In addition to hydrogen bonding in water, balancing among charge (scalar), dipole (vector), and coordination number (topology) contribute to heterogeneous structure on the multiple scales in RTILs–water systems. The water-mediated hierarchical structure in the liquid is connected to macroscopic properties such as AC impedance, p H oscillations, density, and differential scanning calorimetry trace as a function of water concentration. Nanoscale water confinement was observed inside the RTILs, and the size and distribution of confined water were tuned by water concentration and temperature. The loosely packed confinement plays an important role in the engineering of next generation novel nanoheterogeneous materials. High-pressure crystal polymorphs were identified in pure RTILs by X-ray diffraction and Raman spectroscopy. By further compression, amorphous appeared partially in the deformed crystalline.

The phase behavior of 1-ethyl-3-methylimidazolium nitrate ([emim][NO 3 ]) was investigated at 298 K under high pressures, reaching 8.6 GPa, by Raman spectroscopy. This compound was found to crystallize at 0.4 GPa. The crystalline state of [emim][NO 3 ] seems to undergo, at least, three more phase changes under the present experimental conditions. The conformational isomerism of the [emim] + cation between planar and nonplanar forms was also investigated. Remarkably, these crystals showed drastic conformational changes upon phase changes, concomitant with the appearance of a new Raman peak attributable to the planar [emim] + cation. This behavior contrasts markedly with previous results obtained for 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF 4 ]), which showed pressure-induced amorphization at 2.8 GPa.

Aqueous ionic liquid (IL) solutions form a glassy state at 77 K over a wide concentration of ILs. They have potential as novel cryopreservation/refolding solvents for proteins. However, even if proteins in glass-forming concentrations of ILs are preserved at 77 K, the recovery of activity and the structure of the proteins after cryopreservation are still unclear. To achieve high recovery of protein activity and structure by removal of ILs after cryopreservation at 77 K, we studied the recovery of activity and structural stability after cryopreservation of bovine heart cytochrome c in aqueous solutions with ILs, including ethylammonium nitrate (EAN) and 1-butyl-3-methylimidazolium thiocyanate ([bmim][SCN]) over wide IL concentrations using UV-vis, Fourier transform infrared (FTIR), and circular dichroism (CD) spectroscopy. On the whole, although the addition of both ILs induced a decrease of activity and unfolding of the secondary structure of cytochrome c before and after cooling to 77 K, EAN, a weak denaturant, showed a reduction in protein damage (decrease of activity and unfolding of secondary structure) during the reheating process from 77 K (protection ability). In contrast, [bmim][SCN], a strong denaturant, did not have this protective ability. A remarkable result is that although the addition of both ILs caused cytochrome c denaturation,90% of activity and structure after cryopreservation (X10 mol %IL) was recovered after the removal of both ILs by dialysis. These recoveries after the removal of ILs are slightly higher than the results for dimethyl disulfide (DMSO), another cryoprotectant. The present results indicate that concentrated aqueous IL solutions have potential as one-pot (i.e., solubilization/preservation/refolding) solvents for proteins, which easily aggregate after purification, with comparable results to DMSO.

We have investigated structural changes of myoglobin and cytochrome c, which are helical-rich proteins, in aqueous 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) solutions by Fourier transform infrared and circular dichroism spectroscopy. At low [bmim][Cl] concentrations {X (mol% IL) 10), myoglobin aggregates whereas cytochrome c refolds its α-helical structure. The tertiary structures of both proteins are disrupted over the entire range of studied [bmim][Cl] concentrations. Our results suggest that, in aqueous solutions at high [bmim][Cl] concentrations, the differences in structural transitions between myoglobin and cytochrome c might be due to the difference in hydration between these proteins.

The kinetics of small-angle X-ray scattering (SAXS) was assessed in the room temperature ionic liquid (RTIL)–x mol% H2O system, where the RTIL is N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate, [DEME][BF4]. During equilibration of a non-equilibrium state, the largest time evolution of SAXS was observed at approximately 90 mol% H2O. Above 85 mol% (x c), the SAXS intensity increased gradually for 24 h. For the larger q region, the prepeak and principal peak in X-ray diffraction patterns have no time dependence in the water-rich region (70–91 mol%). The long time relaxation process observed in SAXS was related to the outstanding pH oscillations at 90–95 mol% over several days in the [DEME][BF4]–water system. The x c for nonequilibrium anomalies is related to the equilibrated crossover concentration from 65–85 mol% (from SAXS) to 85–95 mol% (for the prepeak in X-ray diffraction) in the [DEME][BF4]–H2O system. Inside [DEME][BF4], the dynamic and static properties of hydrogen bonding of water changed drastically at x c.

We have used Raman spectroscopy to investigate the high-pressure phase behavior of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), a representative ionic liquid, at pressures up to ~7.5 GPa. We have also studied how increasing pressure leads to conformational changes in the [bmim]+ cation. We have found that liquid [bmim][BF4] undergoes pressure-induced solidification (freezing) into a superpressed (metastable) state at 2.5 GPa; another structural change probably occurs at ~6 GPa. Remarkably, conformational changes in the [bmim]+ cation between trans and gauche conformers are concordant with the metastable structural changes of [bmim][BF4]. As the pressure is increased from ambient, the fraction of gauche conformers increases, but the gauche fraction decreases above the solidification pressure (2.5 GPa), and slope of the gauche/trans ratio changes again above 6 GPa. We interpret these results in terms of the fragility of the ionic liquid.

We present a study on the effects of deuterated water on the conformational equilibria of the imidazolium cation in aqueous mixtures of imidazolium-based ionic liquids at room temperature. We provide spectroscopic evidence that the conformational dynamics of the imidazolium cation in D2O are directly related to the H/D exchange reaction of the C–H group at position 2 on the imidazolium ring. The relation is supported by comparing Raman spectra obtained from solutions prepared with H2O and D2O.

We have investigated the relationship between protein size and the structural modification in concentrated aqueous solutions of ionic liquids (ILs) 1-alkyl-3-methylimidazolium nitrate ([C n mim][NO 3 ] ( n = 2, 4)). Proteins with the radii of gyration ( R g ) above ∼20 A form amorphous aggregates in an aqueous [C 4 mim][NO 3 ] solution at X (mol% IL) = 20, whereas those with R g values below ∼20 A assume partial globular states. Remarkably, a decrease in the alkyl-chain length causes an increase in the protein size at which protein aggregation occurs. Concentrated [C n mim][NO 3 ] ( n = 2, 4) solutions might control a boundary between the protein aggregation and partial globular states.

The pH oscillations related to the protonation/deprotonation process in a room temperature ionic liquid (RTIL)–water system were observed at fixed temperatures. The RTIL was hydrophilic N , N -diethyl- N -methyl- N -2-methoxyethyl ammonium tetrafluoroborate ([DEME][BF 4 ]). The rhythmic oscillations of pH were observed only at a water concentration of approximately 90 mol%, where the equilibrated pH value was approximately 3. In contrast, in the water-poor region from 6 to 10 mol% H 2 O, the pH was almost constant at approximately 8 within the investigated timeframe. The acid–base properties of the [DEME][BF 4 ]–water mixture are related to particular aggregations in the liquid phase.

We have used single-crystal X-ray structural analysis and Raman spectroscopy to study the crystalline structure and conformational properties of a quaternary ammonium ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium iodide ([DEME][I]). At 296 K the crystal structure of [DEME][I] was determined to be monoclinic (P21/a, Z = 8) with a = 13.216 (5), b = 12.842 (3), c = 14.417 (6), β = 104.10 (3)°, and V = 2373.1 (15) A3. With results from X-ray diffraction measurements and density functional theory calculations, we have identified two folded forms: Gauche−-Gauche−–gauche−-gauche−-trans and Gauche+-Gauche+–gauche+-gauche+-trans conformers, having intramolecular attractive N+⋯O− interactions of [DEME]+ in the single-crystal state. In the liquid state, [DEME]+ exists in equilibrium between folded and (non-interacting) extended forms.