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Upon crystallization from mixtures containing indole and isoquinoline, intermolecular compounds of 1:1 molecular ratio have been isolated as crystals. This crystallisation process, i.e., molecules→clusters→nucleus was studied in a specially designed mass spectrometer. From the mass spectrometric analysis of clusters isolated from liquid droplets containing indole, isoquinoline and acetonitrile, clusters composed of equimolecular indole and isoquinoline, i.e. (indole) n (isoquinoline) n : n=1, 2, 3,..., were observed as prominent species. This suggested that the hydrogen-bonded complex of indole and isoquinoline works as a unit species for the nucleation of the intermolecular compounds.

Clusters, ensemble of atoms and/or molecules with less number enough to form stable bulk, are thought to play important roles in various phenomena such as, crystallization, phase separation, chemical reactions, etc. Several techniques to produce clusters have been developed and studies in this field are becoming active. Two new methods to produce clusters and the investigations on their characteristics are described in this paper. One is the characteristics of clusters formed from liquid (solution), and the other is the formation and the stabilization of clusters on the surface and their structural investigation.

[structure: see text] As a halogen-free anion for an imidazolium room temperature ionic liquid, the use of a camphorsulfonate causes an increase in the number of free (naked) imidazolium cations, which produces an effective endo/exo stereoselective Diels-Alder reaction.

The CCSD(T) level interaction energies at the basis set limit (E(int)) were calculated for 33 halogen bonded pyridine complexes with substituted iodobenzenes. The CCSD(T) level electron correlation correction substantially decreases the magnitude of attraction in comparison with the MP2. The E(int) for the pyridine complexes with mono substituted iodobenzenes varies from -3.14 to -4.42 kcal mol(-1), depending on the substituent. The electron-withdrawing substituents such as NO2 enhance the attraction, while the effects of electron-donating substituents reduce. The additivity of the substituent effects is observed for the E(int) of the pyridine complexes with multiple substituted iodobenzenes. The electrostatic interactions are mainly responsible for the substituent effects on the magnitude of the attraction in the halogen-bonded complexes. The electrostatic energy depends significantly on the substituent. They have a strong correlation with the E(int). On the other hand the effects of the substituent on the dispersion energy are small, however the dispersion does contribute greatly to the attraction.

Molecular clusters generated from vacuum adiabatic expansion of liquid droplets including acid and base molecules provide an insight into molecular self-assembly through non-covalent interactions. The mass spectrometric analysis for the resulting clusters indicates a systematic structure change which is dependent on the acid–base interaction: a multilayer stacking structure for relatively strong acid–base pairs (phenol–pyridine, phenol–N,N-dimethylaniline, etc.), and a monolayer structure for relatively weak acid–base pairs (phenol–pyrazine, cyclohexanol–pyridine, etc.). As another viewpoint, mass spectrometry of the molecular clusters composed of acid and base molecules can be presented as a new method to characterise the acid–base interaction.

Solvent effects on acid–base interactions between phenol and pyridine have been observed via mass spectrometry of solutions containing phenol, pyridine and water, alcohol and nitrile solvents. In the solvents having sufficiently long alkyl chains to solvate phenol and pyridine, such as propan-1-ol and propionitrile, the phenol–pyridine interaction was limited to the inter-unimolecular interactions. However, in the solvents having short alkyl chains such as methanol and acetonitrile, and in water, clustering between phenol and pyridine was observed as a result of inter-cluster interactions. The phenol molecules also formed clusters in methanol and acetonitrile, but not in propan-1-ol or propiontrile. This indicates that the observed clusters are controlled by the solvation structure depending on the solvent alkyl-chain length.

Experimental evidence for the preferential solvation of phenol in a mixed solvent of acetonitrile and water has been obtained by mass spectrometric analysis of the clusters isolated from liquid droplets by the adiabatic expansion. The effect of temperature on the formation of phenol–hydrate clusters, (C6H5OH)(H2O)n : n= 1,2,3, …, showed that phenol molecules are solbated preferentially by acetonitrile molecules at xw(water mole fraction) < 0.85, the phenol–hydrate clusters were hardly observed at temperatures lower than 50 °C but appeared at higher temperatures. On the contrary, at xw 0.85, hydrate formation became preferable at lower temperatures. The observed temperature effect confirmed microscopically inhomogeneous clustering of the solvent and solute molecules in the mixtures. A. similar temperature effect was also observed in the emission spectra of 2-naphthol in the same mixtures.

Preferential solvation of Na+ by N,N-dimethylformamide (DMF) in a DMF−water binary mixture is observed at the cluster level through mass spectrometry. Since DMF is highly electron donating, the Na+−DMF interaction is more favorable than the DMF−H2O interaction. The observed clusters in a DMF−water mixture with and without NaCl, show that once a DMF molecule interacts with Na+, the DMF molecule hardly forms a hydrogen bond with a water molecule or cluster.

Ethanol, acetonitrile, acetone etc. are miscible with water at any mixing ratio; however, the mixtures are not homogeneous in view of the molecular level owing to the hydrogen-bonding interaction between water molecules and the hydrophobic interaction between water and organic solvent molecules. Through these interactions, molecular clusters are easy to be formed in the aqueous organic solvents. The clustering structure of the aqueous organic solvents influences the microscopic environment of substrates in these solvents and controls various chemical reactions such as the hydrolysis of tert-butyl chloride (SN1 reaction).This review will focus on the solvent effects studied in terms of the molecular clusters which reflect the microscopic environment around the substrates. Furthermore, it will be described that the fluctuation of solvent molecules in the solvation cluster is another important factor to trigger a chemical reaction.

We have studied the salt effect on the clustering of a nucleoside (cytidine) in water by means of an electrospray mass spectrometer, which is specially designed for the analysis of clusters isolate...

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

Ethanol, acetonitrile, acetone etc. are miscible with water at any mixing ratio; however, the mixtures are not homogeneous in view of the molecular level owing to the hydrogen-bonding interaction between water molecules and the hydrophobic interaction between water and organic solvent molecules. Through these interactions, molecular clusters are easy to be formed in the aqueous organic solvents. The clustering structure of the aqueous organic solvents influences the microscopic environment of substrates in these solvents and controls various chemical reactions such as the hydrolysis of tert-butyl chloride (SN1 reaction).This review will focus on the solvent effects studied in terms of the molecular clusters which reflect the microscopic environment around the substrates. Furthermore, it will be described that the fluctuation of solvent molecules in the solvation cluster is another important factor to trigger a chemical reaction.

In acetonitrile–water mixtures, dynamical processes of hydrophobic substrates, such as deprotonation of excited-state 2-naphthol and hydrolysis of tert-butyl chloride, hardly occur at water mole fractions (xw) less than 0.8. In contrast, the reaction rates increased markedly with increasing xw for xw > 0.8. These results were correlated with properties which reflect the solvent clustering conditions, such as partial vapour pressure and IR absorption of acetonitrile–water mixtures. IR absorption of water molecules due to the antisymmetric O—H stretching vibration showed a step-wise change of the absorption peak position suggesting the presence of four different solvent structures in the regions 0 < xw < 0.2, 0.2 < xw < 0.5, 0.5 < xw < 0.8 and 0.8 < xw < 1.0. Mass spectrometric analyses of liquid fragments of acetonitrile–water mixtures and the solutions with phenol, benzyl alcohol and 2-n-butoxyethanol showed clustering conditions characteristic of the water mole fractions in the mixtures. In 0.8 < xw < 1.0 the hydrate clusters of phenol and benzyl alcohol increased very quickly with increasing xw. In xw < 0.8, the signals of the hydrate clusters of the solutes were very weak, while the acetonitrile hydrates increased with decreasing xw. The observed mass spectral change with varying xw is discussed in relation to the structure of acetonitrile–water solutions and its effect on the dynamical processes of hydrophobic substrates.

High-frequency (2.4 MHz) ultrasonic irradiation to an ethanol-water mixture can induce the generation of ethanol-rich mist droplets at lower temperatures. Two groups of droplets in micrometer- and nanometer-sized were observed in the mist generated by the ultrasonic atomization. Nanosized droplets were considered to be ethanol-rich droplets which cause ethanol condensation.

Nucleation processes of alkali metal chlorides (MCl) in methanol were studied by specially designed electrospray ionization mass spectrometry at the cluster level. From solutions of LiCl, NaCl, KCl and RbCl, the M+ (MCl)n clusters with n = 4, 13 and 22 were observed prominently as magic number clusters. These clusters correspond to a square-planar 3 x 3 x 1, cubic 3 x 3 x 3, and cuboid 3 x 3 x 5 structure, respectively. On the other hand, from the solution of CsCl, the Cs+ (CsCl)n clusters were almost monotonically decreased with an increase in the cluster size n, without showing any magic number species. This has a good correlation with the difference in the crystalline structures. When nucleation occurs in the condensed phase, the difference in the crystalline structure will be realised at the cluster level. Moreover, it was demonstrated that the mass distributions of K+ (KCl)n and Cl-(KCl)n' clusters look very similar. When these inter-cluster interactions take place efficiently, the crystal growth will be accelerated rapidly.

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Raman scattering and mass spectra of n-propanol and p-dioxane mixtures have been measured in order to study diluted effects on n-propanol. The results of both high frequency Raman spectra and mass spectra show the rapid decrease of clusters of hydrogen bonded molecules with decreasing n-propanol mole fractions ( x np ). In the low frequency Raman spectra, line shapes were analyzed using the mode coupling theory. It is found that the minimum frequency of the imaginary part of dynamic susceptibility, ω min , becomes lower with decreasing x np . These concentration dependencies suggest a strong relation between the slow structural relaxation and the network structure of molecules in n-propanol.

We have studied the interaction between metal ions and the metal ion-binding motif in hammerhead ribozymes, as well as the functions of the metal ion at the motif, with heteronuclear NMR spectroscopy. In this study, we employed model RNA systems which mimic the metal ion-binding motif and the altered motif. In Co(NH3)6(III) titrations, we observed large 1H and 31P chemical shift perturbations for the motif and found that outer-sphere complexation of Co(NH3)6(III) is possible for this motif. From the reinvestigation of our previous 15N chemical shift data for Cd(II) binding, in comparison with those of organometallic compounds, we conclude that Cd(II) can form an inner-sphere complex with the nucleobase in the motif. Therefore, the A9/G10.1 site was found to accept both inner-sphere and outer-sphere complexations. The Mg(II) titration for a slightly different motif from the A9/G10.1 site (G10.1-C11.1 to A10.1-U11.1) revealed that its affinity to Mg(II) was drastically reduced, although the ribozyme with this altered motif is known to retain enzymatic activities. This observation suggests that the metal ion at these motifs is not a catalytic center of hammerhead ribozymes.

We have studied the microscopic solvent structure of dimethyl sulfoxide-water mixtures and its influence on the solvation structure of solute from a clustering point of View, by means of a specially designed mass spectrometric system. It was observed that the propensity to the cluster formation is nonlinearly dependent on the solvent composition, exhibiting the existence of a critical value of mixing ratios where drastic changes in the microscopic solvent structure occur. It was also demonstrated that in such a solvent mixture the solvation structure of solutes such as 2-butanol, cyclopentanol, cyclohexanol, and phenol is greatly related to the microscopic solvent structures, implying that solute species interact with already established solvent clusters, rather than with individual solvent molecules.

Fluorescence quenching by molecular oxygen is a serious problem for fluorometric analysis and the lifetime measurement of fluorescent compounds in many fields. Compound detectability is reduced and the lifetime shortened by quenching. Deoxygenation is the most effective means for eliminating quenching. Various methods, suitable for liquid samples, have been used for the deoxygenation and include nitrogen (1, 2) or argon (3) purging, evacuation (4), freeze-pump-thaw cycles (5), ultrasonification (6), chemical scavenging (7, 8), and the use of permeable membranes (9-11). However, they require much time and are rather tedious. Here, the authors report a simple and efficient method for alleviating fluorescence quenching by oxygen, through the addition of small amounts of solid carbon dioxide (CO{sub 2}) to solutions of fluorescent compounds and by sealing off the solution vessels.

Metal-ion clusters involving alkaline earth metal and perchlorate ions, and N,N-dimethylformamide (DMF) have been studied by electrospray ionization mass spectrometry (ESI-MS). Three types of metal...

The mass spectrometric analyses of clusters in solutions composed of hydrophobic 1-alkyl-3-methylimidazolium hexafluorophosphates and various polar organic solvents demonstrate that the Coulomb-dip...

The complex formation of alkali metal ion (Li+ or Na+) with 18-crown-6 in an acetone–water mixed solvent was studied by means of the specially designed mass spectrometer. The Li+–18-crown-6 complex...

The preferential solvation and the coordination characterizing metal ions (Mg2+ and Zn2+) in solution, which control the microscopic environments around the metal ions, were directly observed through the mass spectrometric analysis of clusters isolated from liquid droplets.

We have first observed clusters for solvated tropylium ions (Tr+(ROH)n) which were isolated from ROH–CH3CN (1∶1 by vol.; R = Me, Et, and Prn) solutions by using a specially designed mass spectrometer and found the clear-cut essential features concerning the solvation structure around Tr+.

C 60 aggregates generated by sublimation were characterised using scanning mobility particle sizer (SMPS) and cavity ring-down (CRD) spectroscopy. Sublimation under dried nitrogen atmosphere resulted in aggregates with a mode diameter ranging from 30 to 60 nm. The authors found the size reduction of the aggregates upon humidification of the carrier gas. CRD spectroscopy enabled on-line monitoring of C 60 structure that composed particles and showed no chemical modification of the sublimation product in the presence of water molecules. The authors concluded that the heat balance was modified in the presence of water, thereby the size of the aggregates was reduced.

The acid-base interaction could be visualized in the mass spectra of clusters isolated from solutions. The butyric acid-pyridine acid-base system in acetonitrile afforded clusters in which (butyric acid)1(pyridine)1 complex behaves like an unit species; on the contrary, the butyric acid-pyrazine system afforded clusters in which butyric acid clusters, (butyric acid)n, hold main structure. This clear difference is reasonably related with the relatively strong and weak acid-base interactions.

The preferential association of 7-azaindole (Az) dimer was observed by the mass spectrometric analysis of clusters isolated from liquid droplets containing Az and acetonitrile. In the mass spectrum, the peaks corresponding to the even-numbered Az clusters, (Az)2,4,6,8···, were observed much more prominently than those neighboring odd-numbered Az clusters, (Az)3,5,7,9···.

C2 formation from C1, as the simplest growing process of carbon clusters, can be observed from the time-resolved emission spectra of C2(the Swan bands) generated by the laser vaporization of graphite.

The laser-power dependence on the formation of carbon clusters through the laser vaporization of graphite confirms the direct vaporization of carbon clusters from the graphite.

A graphite sample has been irradiated with a YAG laser under an argon atmosphere. The emission due to the C2(d 3Πg→ a 3Πu) Swan band was observed with a decay time 20 times the intrinsic lifetime of C2(d 3Πg). In the presence of benzene, which reacts with C1, the observed decay time of the C2 Swan band decreased with increasing benzene around the graphite. Furthermore, the reaction products between benzene and C1 or C2 were identified and their distribution varied remarkably with benzene concentration. From these results, the simplest growth process of carbon clusters, 2C1→ C2, was confirmed experimentally. Comparing the emission spectra from the irradiated graphite surface under an argon atmosphere and under vacuum, the collisional relaxation of C1 with argon was found to be indispensable to the growth process.

Carbon-cluster positive ions C+n have been produced by laser vaporization of a graphite target by using three wavelengths (1064, 532 and 266 nm). When the graphite target was placed between the acceleration electrodes of a time-of-flight mass spectrometer and irradiated, the mass distribution of C+n immediately after the laser vaporization was recorded as a mass spectrum. C+n with n= 1, 3, 5, 7 and 11 atoms were produced predominantly, and their distribution was found to be dependent on the laser power and its wavelength. When the laser power was not too high, the logarithm of the concentration of carbon-cluster ions is linearly dependent on the logarithm of the laser power density. This logarithmic relation is well explained by the mechanism that C+n with 1 ⩽n⩽ 20 is vaporized directly from the graphite through conversion of the multiphoton energy into thermal energy. Furthermore, contributions of photoelectronic excitation to the formation of carbon clusters become important for 266 nm laser irradiation.

Line broadening of NMR signals of solvent components induced by a paramagnetic chromium complex has been measured at varying temperatures to reveal the energetics for preferential solvation of the complex by a component of a mixture of an organic solvent (acetonitrile or acetone) and water. At water mole fractions lower than 0.8, [Cr(SCN)6]3– is preferentially solvated by the organic solvent molecules, mostly owing to lowering of the enthalpy of the organic solvent in the solvation layer compared to that of the bulk solution. However, at water mole fractions higher than 0.8, the population of water molecules in the solvation layer increases markedly because of the increase in entropy. Such thermodynamic properties of the solvation are correlated with the microscopic structure of mixed solvents. In contrast, in an acetonitrile (or aceteone)–benzene mixture, no preferential solvation was observed for Cr(acac)3.

Irradiation of anthraquinone-2-sulfonate (AQS) in the presence of 2-propanol (0.08 M) in aqueous acetonitrile solution with nitrogen laser (337 nm) gave AQS radical anion (AQS/sup .-/) in a yield depending very much on water content, the highest yield being obtained in the solution of 40-60 vol% water content. This is attributable to exponential increase with water concentration of the decay rate of triplet AQS and of the deprotonation rate of AQSH/sup ./ resulting from hydrogen abstraction of triplet AQS from 2-propanol. The dependence of these rates on water concentration was treated satisfactorily with Perrin's equation to give an average value of 3.3 A for the radius of the solvation sphere surrounding triplet AQS and AQSH/sup ./ in which a water molecule must exist to quench triplet AQS and to accept a proton from AQSH/sup ./, respectively. Laser exciation and continuous irradiation gave apparently different pK/sub a/ values of AQSH/sup ./. The meaning of this observation was also discussed

The exchange of lanthanide(III) ions (Ln(3+)) between a solution and a coordination polymer (CP) formed by cerium(III) or samarium(III) ion and an organophosphorous ligand has been studied. The CPs exhibit distinctive Ln(3+) affinity that varies with a small change in its framework, depending on the central Ln(3+).

Eosin Y sensitized efficiently the reduction of duroquinone and anthraquinone-2-sulfonate to their persistent radical anions in aqueous 2-propanol in the presence of triethanolamine.

2-propanol acted as an efficient reductant in sodium anthraquinone-2-sulfonate sensitized reduction of methyl viologen in aqueous 2-propanol.