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To achieve rapid intraparticle diffusion when metal-organic frameworks are used as adsorbents and/or catalysts, it is preferable to reduce their crystal size and improve their monodispersity. The s...

Electrospraying is an electrochemical technique in which fine droplets are generated in the balance of electrostatic repulsion and surface tension. In this paper, we applied electrospray in the liquid phase in a new reactor system in which positively and negatively charged fine droplets collided with each other between two electrospray nozzles submerged in a solvent. When the hydrolysis of alkylchlorosilanes was carried out using this reactor, not only did the reaction rates increase, but also, the product distribution changed: the kinetically favored cyclotrimer was predominantly formed over the thermodynamically favored cyclotetramer. The yield of cyclotrimer increased with an increase in the voltage between the needles. Since the droplet size decreases with an increase in the applied voltage, the result suggests that the formed cyclotrimer could diffuse into the solvent before it was converted to the thermodynamically favored cyclotetramer.

Thermodynamics of the formation of coordination polymers (CPs) or metal-organic frameworks (MOFs) has not been focused on, whereas many CPs or MOFs have been synthesized in a solution. With a view of separating Nd3+ and Dy3+ in an aqueous solution, we demonstrate that crystallization of the CPs of Nd3+ and Dy3+ based on dibutyl phosphoric acid (Hdbp) can be thermodynamically described; crystallization yields of [Ln(dbp)3] (Ln = Nd or Dy) complex are predicted well using a simple calculation, which takes the apparent solubility products (Kspa) for [Ln(dbp)3] and the acid dissociation constant of Hdbp into account. The Kspa values of [Nd(dbp)3] and [Dy(dbp)3] are experimentally determined to be (1.3 ± 0.1) × 10-14 and (2.9 ± 0.4) × 10-18 M4, respectively, at 20 °C. The ratio of these Kspa values, that is, ca. 4500, is significantly larger than the ratio of the solubility products for inorganic salts of Nd3+ and Dy3+. Therefore, Nd3+ and Dy3+ are selectively crystallized in an aqueous solution via the formation of CPs. Under optimized conditions, Dy3+ crystallization is preferable, whereas Nd3+ remains in the solution phase, where the ratio of the Dy molar content to the total metal content (i.e., Nd + Dy) in the crystal is higher than 0.9. The use of acids, such as HCl or HNO3, has no practical impact on the separation in an aqueous solution.

Geometries of benzene complexes with C6F5X, C6H5X, and CF3X (X is I, Br, Cl, and F) were optimized, and their interaction energies were evaluated. The CCSD(T) interaction energies at the basis set limit (Eint) of C6F5X (X is I, Br, Cl, and F) with benzene were -3.24, -2.88, -2.31, and -0.92 kcal mol(-1). Eint of C6H5X (X is I, Br, and Cl) with benzene were -2.31, -1.97, and -1.48 kcal mol(-1). The fluorination of halobenzenes slightly enhances the attraction. Eint of CF3X (X is I, Br, Cl, and F) with benzene (-3.11, -2.74, -2.22, and -0.71 kcal mol(-1)) were very close to Eint of corresponding C6F5X with benzene. In contrast to the halogen bond of iodine and bromine with pyridine (n-type halogen bond acceptor) where the main cause of the attraction is the electrostatic interactions, that of halogen bond with benzene (p-type acceptor) is dispersion interaction. In the halogen bonds with p-type acceptors (halogen-π interactions), the electrostatic interactions and induction interactions are small. The overall orbital-orbital interactions are repulsive. The directionality of halogen bonds with p-type acceptors is very weak, owing to the weak electrostatic interactions, in contrast to the strong directionality of the halogen bonds with n-type acceptors and hydrogen bonds.

The increasing demand for neodymium (Nd)-magnets containing dysprosium (Dy) has necessitated the recovery of Nd and Dy from magnet scraps to ensure their supply. Thus, it is required to develop an environmentally friendly method for separating Nd3+ and Dy3+. Herein, we show that the formation of coordination polymers based on di(2-ethylhexyl) phosphoric acid (HDEHP) enables the fractional precipitation of Nd and Dy in ethanol–water solution because the solubility of the Dy coordination polymer is significantly lower than that of the Nd coordination polymer owing to coordination preference. The separation performance was found to be better in HNO3 than in HCl media. The characterization of the solid and liquid phases obtained from the Nd3+ and Dy3+ precipitation systems suggested that Nd3+– NO 3 - association inhibits the formation of Nd coordination polymers. The partial replacement of dehp− in the Nd coordination polymer by NO 3 - may weaken the binding strength of the framework, resulting in higher solubility. In addition, the formation of Nd(NO3)2+ in solution may shift the equilibrium against the precipitation reaction. However, when Nd3+ and Dy3+ coexist, Nd3+ precipitation is not accompanied by the replacement of dehp− by NO 3 - in the solid phase. This may be attributed to the incorporation of Nd3+ into the framework of the Dy coordination polymer. We conclude that the formation of Nd(NO3)2+ shifts the solution equilibrium and plays an important role in enhancing the separation performance in HNO3 than in HCl when Nd3+ and Dy3+ coexist.

Size selected synthesis of gold nanoparticle (AuNP) was carried out by use of an ultra-fine liquid droplet as a reaction field. The ultra-fine liquid droplets were generated by electrospraying in a liquid medium. The electrospraying in the liquid medium had a great advantage over the conventional electrospraying in the air. The size of electrosprayed liquid droplets can be varied with the supplied electric voltage beyond the range of the electrospraying in the air. When the AuNPs synthesis through the chemical reduction of Au3+ was carried out by use of this electrospraying in the liquid medium for the mixing of Au3+ solution and the reducing agent solution, the size of AuNPs was controlled by the supplied electric voltage. Two types of reaction field equipped with a single and double electrospray nozzles were designed to be demonstrated.

An exchange between lanthanide ions (Ln) in a solution and coordinated yttrium ions (Y) takes place in a coordination polymer (CP) formed by Y and di-(2-ethylhexyl) phosphoric acid (Hdehp). Through this cation exchange, Ln is adsorbed on the CP depending on the coordination power with Hdehp. Accordingly, the Ln with the larger atomic number is more preferably adsorbed into the CP. This adsorption is affected by the concentration of H,  H C , in the solution. For example, at  H C =10 M, Y is replaced directly by the incoming Ln with a 1:1 stoichiometry. In a limited higher  H C region, the CP becomes a gel and the Ln/Y exchange is enhanced therein.

In this paper the exchange of lanthanide(III) ions (Ln(3+)) between a solution and a coordination polymer (CP) of di(2-ethylhexyl)phosphoric acid (Hdehp), [Ln(dehp)3], is studied. Kinetic and selectivity studies suggest that a polymeric network of [Ln(dehp)3] has different characteristics than the corresponding monomeric complex. The reaction rate is remarkably slow and requires over 600 h to reach in nearly equilibrium, and this can be explained by the polymeric crystalline structure and high valency of Ln(3+). The affinity of the exchange reaction reaches a maximum with the Ln(3+) possessing an ionic radius 7% smaller than that of the central Ln(3+), therefore, the affinity of the [Ln(dehp)3] is tunable based on the choice of the central metal ion. Such unique affinity, which differs from the monomeric complex, can be explained by two factors: the coordination preference and steric strain caused by the polymeric structure. The latter likely becomes predominant for Ln(3+) exchange when the ionic radius of the ion in solution is smaller than the original Ln(3+) by more than 7%. Structural studies suggest that the incoming Ln(3+) forms a new phase though an exchange reaction, and this could plausibly cause the structural strain.

In alcohol–water binary mixtures, microheterogeneous clustering creates a non-ideal mixture. This molecular clustering in the binary mixture is controlled by relativity in the intermolecular interaction energies. This relativity-controlled clustering is inherent to the liquid state, irrespective of whether the solution is aqueous or non-aqueous. The vapor–liquid equilibrium for alcohol–water binary mixtures which represents non-ideality is correlated to relativity-controlled clustering. This paper was reviewed on the basis of our reported results, and presented at the 2012 EMLG/JMLG Annual Meeting in Eger.

It is shown that fuzzy search and data mining techniques of supersecondary structure homology for subunits of proteins using conformational code patterns of α-helix-type (3β5α4β) and β-sheet-type (6α4β4β) fragments can be used to extract correlations between fragments of MHC class I molecules and the light chain of immunoglobulins. The new method of conformational pattern analysis with fuzzy search of structural code homology reflects well the shape of main chain rather than secondary structure in comparison with the DSSP method. Further, the data mining technique using the combination of h- and s-fragment patterns can quantify the supersecondary structure homology between any subunits of proteins with different amino acid sequences. Characteristic fragment patterns (string "shhshss"), which were sandwiched between two identical amino acid sequences His and Pro, were found in light chains of various types of immunogloblins, α-chain and β-2 microglobulin of MHC class I and α-chain and β-chain of MHC class II, but not in heavy chains of Fab immunoglobulin fragments and T cell receptors (TCR). Leukocyte immunoglobulin-like receptors (LILR) are related by the conformational fragment (string "shhshss") to β-2 microglobulins as a type of pair forms (string "sohsss"). Further, human IgM rheumatoid factor, one of the immunogloblins, did not strongly exhibit the conformational fragment pattern. Nonclassic MHC class I molecules CD1D, MIC-A, and MIC-B, which have functions to activate NKT, NK, and T cells, did not also clearly show the patterns. These code-driven mining techniques can be utilized as a metadata-generating tool for systems biology to elucidate the biological function of such conformational fragments of MHC I and II molecules, which come in contact with various signal ligands on the surface of T cells and natural killer cells.

Solvation of perfluorooctanoic acid (PFOA) in methanol–water mixed solvents was investigated by means of the mass spectrometric analyses of clusters in the solutions. The observed clusters were composed of PFOA, methanol, and water molecules. The molecular composition of the clusters showed that PFOA was preferentially solvated by methanol in the methanol–water mixed solvents, and that the ratio of methanol molecules in the PFOA solvation sphere was beyond 0.6 at the bulk methanol mole fraction (xMeOH) = 0.045. The microscopic environment of PFOA was almost occupied by the methanol from such lower xMeOH (xMeOH ≥ 0.045), and hence the ratio of methanol in the PFOA solvation sphere did not change at xMeOH ≥ 0.045 as much as the bulk xMeOH. This preferential solvation of PFOA by methanol suggested a potential overestimation on the dissociation constant (pKa) of PFOA extrapolated from a Yasuda–Shedlovsky plot.

The geometries and interaction energies of complexes of pyridine with C(6)F(5)X, C(6)H(5)X (X = I, Br, Cl, F and H) and R(F)I (R(F) = CF(3), C(2)F(5) and C(3)F(7)) have been studied by ab initio molecular orbital calculations. The CCSD(T) interaction energies (E(int)) for the C(6)F(5)X-pyridine (X = I, Br, Cl, F and H) complexes at the basis set limit were estimated to be -5.59, -4.06, -2.78, -0.19 and -4.37 kcal mol(-1) , respectively, whereas the E(int) values for the C(6)H(5)X-pyridine (X = I, Br, Cl and H) complexes were estimated to be -3.27, -2.17, -1.23 and -1.78 kcal mol(-1), respectively. Electrostatic interactions are the cause of the halogen dependence of the interaction energies and the enhancement of the attraction by the fluorine atoms in C(6)F(5)X. The values of E(int) estimated for the R(F)I-pyridine (R(F) = CF(3), C(2)F(5) and C(3)F(7)) complexes (-5.14, -5.38 and -5.44 kcal mol(-1), respectively) are close to that for the C(6)F(5)I-pyridine complex. Electrostatic interactions are the major source of the attraction in the strong halogen bond although induction and dispersion interactions also contribute to the attraction. Short-range (charge-transfer) interactions do not contribute significantly to the attraction. The magnitude of the directionality of the halogen bond correlates with the magnitude of the attraction. Electrostatic interactions are mainly responsible for the directionality of the halogen bond. The directionality of halogen bonds involving iodine and bromine is high, whereas that of chlorine is low and that of fluorine is negligible. The directionality of the halogen bonds in the C(6)F(5)I- and C(2)F(5)I-pyridine complexes is higher than that in the hydrogen bonds in the water dimer and water-formaldehyde complex. The calculations suggest that the C-I and C-Br halogen bonds play an important role in controlling the structures of molecular assemblies, that the C-Cl bonds play a less important role and that C-F bonds have a negligible impact.

We showed that there is a close relation between evaporation properties and cluster-level structures in alcohol–water binary mixtures, on the basis of the mass spectrometric analyses of clusters generated through fragmentation of liquid droplets. The azeotropy for alcohol (ethanol, 1-propanol or 1-butanol)–water mixtures is caused by the change of the evaporation properties attributed to the cluster-level structures in the mixtures. When the hydrogen-bonding network of water molecules is stable at the cluster level in the water-rich mixtures, the alcohol molecules included in the water-rich clusters are evaporated primarily. On the other hand, when the alcohol self-association clusters are formed with an increase of the alcohol concentration in the mixtures, evaporation of the water existing around the alcohol self-association clusters is increased.

Against a backdrop of increasing demand, the recovery of neodymium (Nd) and especially dysprosium (Dy) from manufacturing scraps and used magnets has necessitated the development of Nd/Dy separation technologies. To this end, we suggest a simple and environmentally friendly separation method by fractional precipitation of coordination polymers (CPs)—extended complexes of metal ions and organic ligands. With the di(2-ethylhexyl) phosphoric acid ligand functioning as a precipitant, Dy was exclusively precipitated as a CP due to its precipitation equilibrium that is considerably different from that of Nd.

The present protocol is applied to the synthesis of the naturally occurring aromatase inhibitor (VII).

溶液中の微視的構造に関する情報を得るために，液滴を真空チャンバー内でクラスターレベルに断片化し，その質量スペクトルを測定する分析技術を開発した．これにより水と有機化合物，及び電解質との相互作用によって形成されたクラスター構造とこれら水溶液の物性との関係を研究した．水－有機化合物系では，水－アルコール混合溶液のクラスター構造と，粘度，相分離特性，選択的溶媒和などの溶液の物性との関係を明らかにした．また，アルコール自己会合クラスターの生成が水によって促進されるのは，溶液中で生じる分子間相互作用の相対的関係によることを明らかにした．電解質水溶液系では，硝酸，硫酸，酢酸水溶液のクラスター構造を解析し，酸性度との関係を明らかにした．更に，水中の酢酸が水酸化ナトリウムにより中和され塩を生成する過程をクラスターレベルで観測した．

Molecular clustering in the liquid state is controlled by the relativity of interaction energies. This means that the clustering is strongly promoted by the coexistence of relatively weakly interacting molecules in the solution. This relativity-controlled clustering was observed for 1-pentanol clustering through the mass spectrometry for clusters isolated from liquid droplets via adiabatic expansion in a vacuum chamber. The 1-pentanol clustering through hydrogen-bonding interaction was significantly promoted by the mixing with water, methanol, acetonitrile or dichloromethane, but it was not promoted by the mixing with 1-propanol or 1, 2-dichloroethane. This solvent effect on the 1-pentanol clustering is explained by the relativity of the 1-pentanol–1-pentanol interaction energy to the 1-pentanol–solvent interaction energy. Thermodynamic analysis on this solvent-induced clustering also supports that the clustering controlled by the relativity of interaction energy is inherent in the liquid state.

We have studied the cluster structure of 1-butyl-3-methylimidazolium halide, bmimX (X = Cl, Br, I), in methanol solution by means of an electrospray mass spectrometer, which is specially designed for analysis of clusters isolated from solution. In positive ion mode experiments, the ratio of solvated bmim(+), bmim(+)(MeOH)(n) and ion-pair clusters, bmim(bmim(+)X(-))(m) was dependent on the counter anion. As for bmimCl solutions, few solvated bmim(+) clusters were observed, and the ion-pair clusters were clearly observed. On the other hand, bmimBr and bmimI with large anions, the solvated bmim(+) clusters increased obviously, and the ion-pair clusters were in turn remarkably decreased. In negative ion-mode experiments, the solvation for Br(-) by the methanol is found to be the most prominent among those for Cl(-), Br(-), and I(-). These results were reasonably explained in consideration of the balance between ion-solvent and ion-counterion interactions.

The microscopic structures in ethanol–water binary mixtures were examined by analyzing the mass spectra of clusters generated through fragmentation of liquid droplets. From the effects of temperature and mixing ratios on the cluster structures, we have demonstrated that the ethanol–water binary mixtures have microscopic phase separation at the cluster level in wide mixing ratios: 10 vol.%

Determination was made of the microscopic structures of binary mixtures of water and amphiphile (propyleneglycol-monomethylether (MPG) or propyleneglycol-monopropylether (PPG)) based on the NMR relaxation time (T1) of water and mass spectra of clusters isolated from solutions. The ratio of hydrating to non-hydrating water was derived from T1 and indicated water in MPG-water mixtures to be present more easily in the amphiphile hydration layer than in PPG-water mixtures. Hydrogen-bonded self-association clusters of MPG and PPG could be found in the aqueous solutions by mass spectrometry, the data from which showed MPG self-association clusters to undergo hydrogen bonding with water more readily than PPG self-association clusters. The results of NMR and mass spectrometry were found to be closely correlated. Microscopic structures and intermolecular interactions in aqueous solutions were accurately clarified.

Poly-[N-vinylcaprolactam] (PVCAP) and its related compounds are specific polymeric compounds for inhibiting hydrate formation. To clarify the inhibition mechanism of these compounds on hydrate nucleation at the molecular level, we measured the mass spectra of clusters generated from the fragmentation of liquid droplets including N-methylcaprolactam (NMCAP; functional group of PVCAP). By comparing the mass spectra of clusters of the solutions--pure D2O, tetrahydrofuran (THF)-D2O, NMCAP-D2O, and THF-NMCAP-D2O--it was found that the interaction of NMCAP with D2O was much stronger than that of THF with D2O. The relative intensity ratio of D+(NMCAP)m(D2O)n clusters to all the clusters observed for the NMCAP-D2O (1:250) mixed solution was 0.45. On the other hand, the relative intensity ratio of D+(THF)1(D2O)n clusters to all the clusters observed for the THF-D2O (1:17) mixed solution was 0.15. In the case of the THF-NMCAP-D2O three-component mixed solution, the NMCAP-D2O interaction was more predominant than the THF-D2O interaction, even at a lower NMCAP concentration. NMCAP reduces free mobile water molecules around NMCAP, but THF does not. This correlates with the facts that THF forms its hydrate below the freezing point and that PVCAP works as an inhibitor of gas hydrates.

The neutralization of CH 3 COOH by NaOH in water has been studied by the mass spectrometric analysis of clusters generated via fragmentation of liquid droplets. In water, CH 3 COOH molecules form self-association clusters at higher acid concentrations like the molar ratio of CH 3 COOH:H 2 O=1:10. At these concentrations, the neutralization takes place via interaction between the CH 3 COOH clusters and NaOH to afford Na + (CH 3 COOH) a (CH 3 COONa) b clusters. Furthermore, Na + is preferentially solvated by CH 3 COOH in water to form Na + (CH 3 COOH) α clusters. In consideration with these cluster structure, the reaction mechanism in solution can be realized more precisely.

The relationship between liquid-liquid phase separation and microheterogeneity in water-primary alcohol mixtures was examined by analysing the mass spectra of clusters generated through the fragmentation of liquid droplets. By comparing the cluster structures of water-ethanol, -1-propanol, and -1-butanol binary mixtures at various alcohol concentrations, we discovered differences in the molecular clusters that control phase separation. We also studied the role of water in alcohol self-association. Alcohol self-association is promoted in the presence of a small amount of water (ca. 10 approximately 20 wt%), in which the water-water hydrogen-bonding network is weak and does not contribute to alcohol self-association. We have demonstrated that alcohol self-association is also promoted by non-ideal mixing with other alcohols. The self-association of alcohol molecules complements the loss of stabilization energy caused by the relatively weak coexisting interactions. This complementary relationship among intermolecular interactions is an inherent property of solutions, and plays a key role in the phase separation process.

Microscopic structures of 1-butanol (1-BuOH)–water mixtures in the presence and absence of salts are studied through the mass spectrometric analysis of clusters generated from the fragmentation of liquid droplets. The analysis of cluster structures provides information on the phase separation of 1-BuOH–water mixtures from the microscopic viewpoint. In a saturated solution of 1-BuOH in water, 1-BuOH exists as hydrated 1-BuOH clusters and self-associated 1-BuOH clusters. With further addition of 1-BuOH, a 1-BuOH rich phase is generated. When the salt (LiCl, NaCl, MgCl2, etc.) coexists in the 1-BuOH–water mixtures, the cation is preferentially solvated by the 1-BuOH to form M +(1-BuOH) m or M 2+(1-BuOH) m clusters: M + = Li+, Na+, Mg2+ = Mg2+, etc., m = 1, 2, 3, ... Since the formation of M +(1-BuOH) m corresponds to an increase of the self-associated 1-BuOH clusters in water, the presence of the salt induces the phase separation at lower 1-BuOH concentrations.

Molecular clusters formed by fragmentation of liquid droplets of alcohol (methanol or n-butanol)-acetonitrile mixtures have been detected and analyzed by means of a specially designed mass spectrometer. In the methanol-acetonitrile mixture, methanol clusters retain a sizable magnitude through most of the composition range, whereas acetonitrile clusters decrease in intensity upon increasing the concentration of methanol. Hydrogen bonding among methanol molecules controls the clustering. On the other hand, in n-butanol-acetonitrile mixtures, self-association of n-butanol through hydrogen bonding is remarkably promoted by the mixing with acetonitrile. With decreasing the acetonitrile contents, however, n-butanol self-associated clusters disintegrate completely. The interaction among n-butanol molecules changes from hydrogen bonding to dispersive, depending on the mixing ratio. When phenol is added as a solute to these binary mixtures, the solvation of phenol is found to be controlled by the solvent molecular clustering.

The cluster structures observed by means of mass spectrometry for binary mixtures-tert-bulyl alcohol (TBA)-H 2 O and tetrahydrofuran (THF)-D 2 O-with varying mixing ratios exhibit striking contrast, even though both TBA andTHF are miscible with water at any mixing ratio. In the TBA-H 2 O mixtures at TBA mole fractions of (X T B A ) ≤ 0.01-0.025, some of the H 2 O molecules in the H 2 O clusters are replaced by TBA molecules. For 0.01-0.025 ≤ X T B A ≤ 0.2-0.3, the self-aggregation of TBA forms dominant cluster structures, and the hydrogen-bonded water clusters are disintegrated with increasing X T B A . This TBA self-aggregation is reduced with further increasing TBA at X T B A ≥ 0.3. However, in the THF-D 2 O mixtures, THF molecules have a weak additional interaction with D 2 O clusters, and the self-aggregation of THF is not promoted in the THF-D 2 O mixtures. The D 2 O clusters still exist, even at a THF mole fraction of X T H F = 0.3. On the basis of the observed cluster structure, the mechanism for the mixing between water and the organic solvent and the controlling factors in the self-aggregation are proposed.

The effect of metal ions on the molecular clustering of cytidine in aqueous solution was studied by mass spectrometric analysis of clusters isolated from liquid droplets, and two types of cytidine ...

Mass spectrometric study on cluster structure of solutions of lithium halides (LiX = LiBr and LiI) in acetonitrile is reported. Solvated ions Li+(CH3CN)n, X−(CH3CN)n, and salt clusters Li+(LiX)m(CH3CN)n and X−(LiX)m(CH3CN)n, were observed in the spectra. The mechanism of cluster formation is discussed in terms of a competition between solvation interactions and electrostatic interactions. This helps to explain the differences between clustering in methanol and acetonitrile, since the latter one has much larger dipole moment than the former one. Therefore appearance of solvated clusters, including the solvated salt clusters, is more favourable in methanol solutions' spectra.

Mass spectrometric study on the cluster structure of methanol solutions containing lithium halides (LiX = LiCl, LiBr, and LiI) is reported. Solvated ions: Li+(CH3OH)n and X-(CH3OH)k, and salt clusters: Li+(Li+X-)s(CH3OH)m and X-(Li+X-)p(CH3OH)r, were observed in the mass spectra. The number of methanol molecules around Li+, especially in Li+(Li+X-)s(CH3OH)m clusters, increased when changing the anions from Cl- to I-, which suggested that there was a complementary relation between a Li+−CH3OH interaction and a Li+−X- interaction. In the case of X- = I-, the Li+−CH3OH interaction was enhanced in comparing with the case of X- = Cl-, because a Li+−I- interaction is weaker than a Li+−Cl- interaction. This observed complementary relation is a kind of intrinsic property of a liquid phase. Furthermore, mass distribution of the solvated ions and the salt clusters had correlations with physicochemical properties such as solvation energies and molar conductivities.

The microscopic environments around a cation and its counterion were experimentally studied for methanol solutions of CsCl, LiCl, LiI, and LiClO4 through mass spectrometric analysis of clusters gen...

A part of microscopic structure in aqueous HNO3, and H2SO4 solutions was directly observed as ionic clusters isolated from these aqueous solutions by means of a specially designed electrospray mass spectrometer. The difference in the hydration structure for these acids was partially visualized on the basis of the molecular composition in the observed ionic clusters. For aqueous HNO3 solutions, the protonated water clusters, H+(H2O)n: n = 1, 2, 3 ..., which have similar mass distribution to the inherent water clusters, were observed predominantly. This is in good agreement with microscopic picture that the protons released from HNO3 are hopping and delocalized among water clusters. Such a cluster structure was independent of the HNO3 concentrations of [HNO3] < 1 mol/dm3. On the other hand, for aqueous H2SO4 solution, cluster structure was drastically changed with varying H2SO4 concentration. For diluted H2SO4 solution, clusters that consisted of only water molecules were mainly observed. This means that t...

Oxidative polymerization of phenols using horseradish peroxidase (HRP) in aqueous organic solvents (1,4-dioxane-water and methanol-water), which is an attractive pathway for synthesis of a new class of polyphenols withoutuse of toxic formaldehyde, was remarkably influenced by the water content. The present study is focused on the self-association of m-cresol in such a solvent to understand the effect of solvent on its polymerization. The change of the molecular weight of the polymer with varying the water content was found to be related to the molecular clustering in the solution, observed through the difference UV absorption spectroscopy and the mass spectrometry for clusters. In mixed solvents of 1,4-dioxane and aqueous 0. 1 M phosphate buffer (pH 7), number-average molecular weight had a maximum at the aqueous buffer content of 50 vol %, whereas in methanol-aqueous buffer mixtures, the molecular weight had a small maximum at 20 vol % aqueous buffer content and gradually decreased with increase of the aqueous buffer content. As for the m-cresol clustering, the effect of the water content was also in significant contrast between the above aqueous organic solvent systems. The m-cresol clusters were not formed in 1,4-dioxane, but its clustering was remarkably promoted by an increase of the water content. On the other hand, the m-cresol clusters were formed favorably in methanol and were readily hydrated with increase of the water content in the solution. These effects of the water content on the clustering are related to the enzymatic polymerization. The polymer would be obtained in high yields when the m-cresol clusters were formed in the solution; however, the hydration of the m-cresol cluster would restrain the polymerization.

The microscopic structures of acetonitrile-water and DMSO-water binary mixed solvents and their influence on the solvation for solutes (some alcohols and phenol) have been studied on the basis of the cluster structures observed through a specially designed mass spectrometer. In acetonitrile-water mixtures, the water clusters were observed at water mole fractions: Xw > 0.2; on the other hand, in DMSO-water mixtures, the water clusters were observed only at much higher water mole fractions: Xw > 0.93. In the mixing processes, the water clusters were stabilized in the acetonitrile-water mixtures, whereas the DMSO clusters were stabilized in the DMSO-water mixtures. It is demonstrated that these microscopic structures directly affect the solvation for alcohols and phenol in these binary mixed solvents.

Density functional theory (DFT) B3LYP calculations characterize the structure and stability of the clusters of tropylium ion (Tr+) coordinated by methanol molecules Tr+(MeOH)n with n=1–7. Methanol molecules are bound together through strong O–H⋯O type hydrogen bonds, resulting in a cyclic structure when n≥3, and the methanol cluster thus formed coordinates to Tr+ through weak C–H⋯O type hydrogen bonds. Thus, the formation of the Tr+(MeOH)n clusters is mediated by two kinds of hydrogen bonds. Calculated distances of the O–H⋯O hydrogen bonds lie in the range 1.570–1.991 A (1.712 A in average) while those of the C–H⋯O hydrogen bonds lie in the range 2.083–2.319 A (2.160 A in average). Mass spectroscopic experiments demonstrated that Tr+(MeOH)4 is a dominant, magic-numbered species and that Tr+(MeOH)3 and Tr+(MeOH)5 are minor [Chemical Communication, (2001) in press]. The experimental result is analyzed from the viewpoint of energetics. The specific size effect on the stability of Tr+(MeOH)n is a direct consequence of the stability of the (MeOH)n fragment itself.

Coordination polymers can be attractive ion exchange materials because of their crystallinity and semi-flexibility, which are rather opposing properties, and play integral and synergistic roles in introducing unique ion-exchange behavior. In this paper, Ln(3+)/Ce(3+) exchange (Ln(3+) = Nd(3+), Gd(3+), Dy(3+), or Lu(3+)) in a coordination polymer, [Ce(dehp)3], based on di(2-ethylhexyl)phosphoric acid (Hdehp) is studied by distribution coefficient measurements, ion-exchange isotherms, Kielland plot analysis, and morphology observation. The ion-exchange selectivity is in the order Nd(3+)Gd(3+)Dy(3+)Lu(3+) when a small amount of Ln(3+) is loaded, but Lu(3+) ≈ Nd(3+)Gd(3+) ≈ Dy(3+) for a high loading ratio. The Kielland plot suggests that a steric effect is involved in the reactions, which becomes stronger in the order of Nd(3+)/Ce(3+)Gd(3+)/Ce(3+)Dy(3+)/Ce(3+)Lu(3+)/Ce(3+) for exchange systems. This trend is attributable to the differences in the ionic sizes between an incoming Ln(3+) and original Ce(3+). Scanning electron microscopy observations reveal the generation of a new phase via the Ln(3+)/Ce(3+) exchange. Such a phenomena results from solid-solid transformation, rather than dissolution-recrystallization. The small steric strain in the Nd(3+)/Ce(3+) system leads to the formation of a Nd(3+)-and-Ce(3+) solid-solution, whereas the morphological change is possibly restrained by the strong strain caused by loaded Ln(3+) with an ionic size significantly smaller than the original Ce(3+).

The self-associations of butan-1-ol, butan-2-ol, and 2-methylpropan-2-ol ( tert-butanol) in the pure liquid state and in carbon tetrachloride solutions have been studied mainly through near-infrared spectroscopic observation at various temperatures. A new analysis assuming a successive association process for the alcohol molecules was applied to the sharp band around 1410 nm (the first-overtone band of the OH stretching vibration mode attributed to free OH monomer and partly to OH polymer); it became clear that the mean association number for each alcohol increases with increasing concentration and decreases with increasing temperature. Comparisons of the association numbers at various constant temperatures for the three kinds of alcohols show that the association abilities are on the order butan-1-ol > butan-2-ol > 2-methylpropan-2-ol.

Small-angle X-ray scattering measurements of water droplets in a mist were carried out using the BL15XU beamline at SPring-8. The diameter of the water droplets generated by ultrasonic atomization was found to be ≥ 50 nm and had no distribution in the range under 50 nm, as predicted. The study also showed how difficult it is to measure the small-angle scattering of low-density materials, such as liquid droplets in a mist.

Acid–base interactions were investigated by mass spectrometry of clusters isolated from solutions containing a carboxylic acid (propionic, butyric or hexanoic acid), an aromatic base (pyridine or pyrazine) and a solvent (water, acetonitrile or propionitrile). In water, self-aggregation of the carboxylic acid molecules due to hydrophobic interaction to form carboxylic acid clusters, such as (butyric acid)n, was prominent, and acid–base interaction proceeded between the carboxylic acid clusters and the basic molecules. In acetonitrile, the acid–base interaction was sensitive to the relative strength of the base. When pyridine (relatively strong base) was used as a base, clustering proceeded through the formation of a polarized acid–base complex, (acid)δ-(base)δ+. However, when pyrazine (relatively weak base) was used as a base, self-aggregation of the acid molecules became favorable. In propionitrile, such clusters were not observed because each molecule was separated by individual solvation. This solvent effect is related to the solvation structure, which determines the balance between the self-aggregation of the acid molecules and the formation of the polarized acid–base complex. It has also been demonstrated that the balance of the above intermolecular interactions is also dependent on the size of the alkyl group of the carboxylic acid. The results of the mass spectrometry partially show the microscopic view for the effect of solvent, pKa and the size of the alkyl group on the acid–base interaction in solution.

The solvent effect on the acid–base interaction between acetic acid and pyridine has been studied by the mass spectrometric analysis of clusters isolated from liquid droplets. The clusters resulting from the acetic acid–pyridine, acid–base, interaction in water are quite different from those in acetonitrile solvent. In water (acetic acid∶pyridine∶water = 1∶1∶10) the acid–base interaction occurs through the intercluster interaction between acetic acid and pyridine clusters. On the other hand, in acetonitrile (acetic acid∶pyridine∶acetonitrile = 1∶1∶10), the acid–base interaction proceeds through an intermonomer interaction between an acetic acid molecule and pyridine molecule, and the clusters are produced through the aggregation of a polar (acetic acid)δ–(pyridine)δ+ complex. This solvent effect is mainly attributed to the cluster structure of acetic acid and pyridine in water and acetonitrile solvent.

We here report a comparative experimental and theoretical study of dipole-bound electron attachment on four polar hydrogen-bonded dimers containing one water molecule (water-water, ammonia-water, phenol-water and pyridine-water). When the water molecule is the proton acceptor in the neutral complex, with a trans-linear hydrogen bond (water-water and phenol-water), it is shown that the equilibrium geometry of the dipole-bound anion tends to a cis-linear hydrogen bond for which the total dipole moment is larger. On the contrary, when the water molecule is the proton donor to a nitrogen atom (ammonia-water and pyridine-water), dipole-bound electron attachment does not lead to subsequent modifications of the complex geometry.

Very-low-energy electron attachment to homogeneous and mixed pyridine, phenol and cyclohexanol dimers is studied by means of collisions with laser-excited Rydberg atoms and several new dipole-bound anions are observed. The corresponding structures and binding energies of their neutral parents are determined by model calculations of the intermolecular interactions between these polar closed-shell molecules. In the case of the phenol–pyridine dimer, a valence negative ion is observed. The geometry of its neutral parent is obtained from both abinitio and model calculations.

Molecular self-assembling systems derived from the clustering of acid and base molecules have been investigated by mass spectrometric analysis of clusters isolated from liquid droplets. N–H···N and O–H···N hydrogen-bonded acid–base systems were compared. When heteroaromatic N–H···N hydrogen-bonding acid–base systems, such as 7-azaindole dimer, the indole–quinoline pair, etc. were used as acid–base pairs, the clusters composed of equimolar acid and base molecules were generated. This means that the hydrogen-bonding acid–base complex, N–H···N, behaves like a single molecule in cluster formation. On the other hand, clustering of the aromatic O–H···N hydrogen-bonding systems, such as phenol–pyridine, phenol–pyrazine, etc., was controlled by the acid–base interaction determined by the pKa values, giving a multilayer structure for a relatively strong acid–base pair and a monolayer structure for a relatively weak acid–base pair. Molecular self-assembling systems containing hydrogen-bond donor and acceptor molecules have been systematically described here.