Effects of H+ and OH- on H2O as probed by the 1-propanol probing methodology: differential thermodynamic approach.

We applied what we call the "1-propanol (1P) probing methodology" on the effects of H+ and OH- on liquid H2O. We found that H+ is an amphiphile with a modest hydrophobic and an equally modest hydrophilic contribution. Its hydration number is 2 ± 1, suggesting that the equilibrium hydration structure is like the Zundel type (H5O2+). OH-, on the other hand, has a large hydration shell with 12 ± 3 H2O molecules and acts as a hydrophobe-like hydration center. In other words, it forms a hydration shell around itself, but as the probing 1P increases and the available H2O decreases, it exerts its influence over a longer range and reduces the hydrogen-bond probability of bulk H2O away from hydration shells, just as a hydrophobe does to bulk H2O.

Effects of constituent ions of a phosphonium-based ionic liquid on molecular organization of H2O as probed by 1-propanol: tetrabutylphosphonium and trifluoroacetate ions.

Aqueous solutions of tetrabutylphosphonium trifluoroacetate, [P4444]CF3COO, exhibit a liquid-liquid phase transition with a lower critical solution temperature. Herein, we characterized the constituent ions, [P4444](+) and CF3COO(-), in terms of their effects on the molecular organization of H2O on the basis of 1-propanol probing methodology devised by Koga et al. The resulting characterization of the hydrophobicity/hydrophilicity is displayed on a two-dimensional map together with previous results, for a total of four cations and nine anions of typical ionic liquid (IL) constituents. The results indicate that [P4444](+) is the most significant amphiphile with strong hydrophobic and equally strong hydrophilic contributions among the group of constituent cations of ILs studied so far. The hydration number for [P4444](+) was evaluated to be nH = 72, which is three times larger than that of a typical imidazolium-based cation, [C4mim](+). Self-aggregation of [P4444](+) was found to occur in an aqueous solution of [P4444]CF3COO above 0.0080 mole fraction of the IL.

Commonalities and differences among symbiosis islands of three Mesorhizobium loti strains.

To shed light on the breadth of the host range of Mesorhizobium loti strain NZP2037, we determined the sequence of the NZP2037 symbiosis island and compared it with those of strain MAFF303099 and R7A islands. The determined 533 kb sequence of NZP2037 symbiosis island, on which 504 genes were predicted, implied its integration into a phenylalanine-tRNA gene and subsequent genome rearrangement. Comparative analysis revealed that the core regions of the three symbiosis islands consisted of 165 genes. We also identified several NZP2037-specific genes with putative functions in nodulation-related events, suggesting that these genes contribute to broaden the host range of NZP2037.

IscR regulates RNase LS activity by repressing rnlA transcription.

The Escherichia coli endoribonuclease LS was originally identified as a potential antagonist of bacteriophage T4. When the T4 dmd gene is defective, RNase LS cleaves T4 mRNAs and antagonizes T4 reproduction. This RNase also plays an important role in RNA metabolisms in E. coli. rnlA is an essential gene for RNase LS activity, but the transcriptional regulation of this gene remains to be elucidated. An Fe-S cluster protein, IscR, acts as a transcription factor and controls the expression of genes that are necessary for Fe-S cluster biogenesis. Here, we report that overexpression of IscR suppressed RNase LS activity, causing the loss of antagonist activity against phage T4. This suppressive effect did not require the ligation of Fe-S cluster into IscR. beta-Galactosidase reporter assays showed that transcription from an rnlA promoter increased in iscR-deleted cells compared to wild-type cells, and gel-mobility shift assays revealed specific binding of IscR to the rnlA promoter region. RT-PCR analysis demonstrated that endogenous rnlA mRNA was reduced by overexpression of IscR and increased by deletion of iscR. From these results, we conclude that IscR negatively regulates transcription of rnlA and represses RNase LS activity.

Hydrophobicity/hydrophilicity of 1-butyl-2,3-dimethyl and 1-ethyl-3-methylimodazolium ions: toward characterization of room temperature ionic liquids.

We continue to experimentally characterize the constituent ions of room temperature ionic liquids in terms of their interactions with H(2)O. 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](+)), PF(6)(-), CF(3)SO(3)(-), and N(SO(2)CF(3))(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 on forming a hydrogen bond to H(2)O. On replacing it with CH(3) 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 H(2)O strongly to an induced dipole of O of the H(2)O. 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.

Interactions of Na-salts and 1-propanol in 1-propanol-Na-Salt-H2O systems: toward an understanding the Hofmeister series (IV).

The excess chemical potential of 1-propanol (1P), muE1P, was evaluated in ternary 1P-Na-salt(S)-H2O at 25 degrees C. The counter anions of the Na-salts studied are SO42-, F-, Cl-, I-, and ClO4-. The effect of the anion on muE1P follows the Hofmeister ranking, in that the more kosmotropic ions make the muE1P value more positive. We then evaluate the effect of the Na-salt (S) on muE1P, the 1P-S interaction in terms of excess chemical potential, at a semi-infinite dilution. The results indicate that the 1P-S interaction in terms of excess chemical potential is unfavorable (repulsive) for all of the ions studied. The degree of repulsive interaction decreases in the order of the Hofmeister ranking from the kosmotropic to the chaotropic end. Namely, salting-out samples make the excess part of the chemical potential of 1P more unfavorable, while the salting-in counterparts make it less unfavorable. From earlier calorimetric studies on the same ternary systems, the enthalpic 1P-S interaction function, HE 1P-S , was calculated. Hence, the entropy analogue, S1P-S , was also obtained, and a detailed thermodynamic signature of 1P-S interactions became available. This revealed that both HE 1P-S and SE 1P-S decrease from the kosmotropic ion to the middle of the ranking (Cl-), whereupon they turn to increase toward the chaotropic end. Hence, the build up of unfavorable 1P-S interactions in Hofmeister salts (signified by muE1P) relies on a pronounced enthalpy-entropy compensation, which must be accounted for in attempts to understand the molecular mechanisms underpinning Hofmeister effects.

Effect of an "ionic liquid" cation, 1-butyl-3-methylimidazolium, on the molecular organization of H2O.

The excess partial molar enthalpy of 1-propanol (1P), , was measured at 28 degrees C in the ternary mixture of 1P-1-butyl-3-methylimidazolium chloride ([bmim]Cl)-H(2)O in the H(2)O-rich composition range. From these data we evaluated what we call the 1P-1P enthalpic interaction function, . Its changes induced by addition of [bmim]Cl of the pattern of were used as a probe to elucidate the effect of [bmim]Cl on the molecular organization of H(2)O. It was found that the effect of Cl(-) was not conspicuous within this methodology, and the observed dependence is predominantly due to the hydration of [bmim](+). The changes in the x(1P)-dependence of were compared with those brought about by temperature increase, or by the addition of fructose or glycerol. It was found that the effect of [bmim](+) is similar to that of fructose or increased temperature. We speculate that in the H(2)O-rich composition region a number of H(2)O molecules are attracted to the delocalized positive charge of the imidazolium ring and the bulk of H(2)O is influenced in such a manner that the global hydrogen bond probability is reduced.

Hydrophobicity vs hydrophilicity: Effects of poly(ethylene glycol) and tert-butyl alcohol on H2O as probed by 1-propanol.

The enthalpic interaction between 1-propanol (1P) molecules, , was evaluated in 1P-poly(ethylene glycol) (PEG)-H2O and 1P-tert-butyl alcohol (TBA)-H2O ternary mixtures. The model-free and experimentally accessible quantity, , 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 reflects the process how 1P modifies H2O. This 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 . 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.