Development of miniaturized multi-channel high-performance liquid chromatography for high-throughput analysis

We have developed miniaturized multi-channel high-performance liquid chromatography (HPLC) system. With this system, we can simultaneously separate multiple samples, using a single high-pressure gradient pump, a chip-based sample injection unit, a monolithic silica capillary column array, and a multi-channel UV detection unit based on fiber optics. The injection unit has a simplified structure composed of brass housing and a quartz microchip having microchannels and access ports, which enable a direct injection of sample to multi-channel by commercial multichannel micropipette. Moreover, that possesses a function of microvalve, and on-chip definition of sample injection plugs achieved with a cross channel injection method, providing each column of monolithic silica capillary array. The substances in channels were simultaneously detected with UV having multiple cells. Standard samples were analyzed for characterizing newly developed system, and sharp peaks were obtained with reproducibility data of < 0.9% (R.S.D.). Analysis of tryptic digestion of casein was also employed. These results show that the novel multi-channel HPLC system has the benefits for the high-throughput analysis in the post-genomic analysis/combinatorial chemistry.     

A molecular-beam study of the collision dynamics of methane and ethane upon a graphitic monolayer on Pt(111)

Utilizing a supersonic molecular-beam scattering technique, the angular intensity distributions of alkane molecules (CH4 and C2H6) have been measured, which are scattered from a chemically inert and highly oriented monolayer graphite (MG) on Pt(111). A MG which covers the Pt(111) surface with a full monolayer is found to induce a large energy loss of alkanes during collision with the surface by phonon creation due to the large mass ratio of an alkane molecule with respect to MG. Based on the classical cube model, only applicable to the molecules without internal mode excitation, the effective masses of MG of 76 (six atoms of carbon) and Pt(111) of 585 (three atoms of platinum) are determined from rare-gas atom scattering data. Despite the difference in the degree of freedom between CH4 and rare-gas atoms, CH4 scattering is found to be well described by the simple hard-cube model as a result of the high symmetry of the CH4 structure. With the recently developed ellipsoid-washboard model, an extension of the hard-cube model to include some internal mode excitation of impinging molecules in addition to the surface corrugation, it is found that unlike CH4 the cartwheel rotation mode of C2H6 is significantly excited during collision, while the helicopter mode excitation is negligible on a flat MG surface.     

Direct observation of adduct formation of alkyl and aromatic iodides with cl atoms using cavity ring-down spectroscopy

The reactions of Cl atoms with RI (R = n-C3H7, n-C4H9, cyclo-C6H11, C6H5, C6F5, and p-CH3C6H4) have been studied using cavity ring-down spectroscopy at a temperature range of 233-313 K and at 100 Torr total pressure of N2 diluent. Visible absorption spectra of the RI-Cl adducts were recorded at 440-520 nm at 263 K. The yields of the adducts were temperature-dependent. There was no discernible reaction of the adducts in the presence of 100 Torr of O2 at 263 K. Theoretical calculations were performed for C4H9I-Cl and C6H5I-Cl for quantitative explanation of the absorption spectra and the strength of the I-Cl bonds in the charge-transfer complexes. Evidence for the adduct formation following the reaction of Cl with C6H5Br was sought but not found at 440 and 520 nm.     

Photoinduced ionic polymerization. II. Cationic polymerization of α-methylstyrene in the presence of tetracyanobenzene

The dependence of the rate of polymerization on light intensity and the stereoregularity of the polymer was studied to elucidate the propagation and termination mechanisms of the photoinduced cationic polymerization of α-methylstyrene in the presence of tetracyanobenzene in methylene chloride. The rate of polymerization was proportional to the light intensity. The polymer is highly syndiotactic, and the stereoregularity is similar to that of polymers obtained by radiation-induced cationic polymerization. The initiation mechanism was also studied by electron spin resonance, by which the anion radical of tetracyanobenzene formed from a photoexcited complex between α-methylstyrene and tetracyanobenzene was observed. The cation radical of α-methylstyrene, counterpart of the anion radical, is believed to initiate the polymerization.     

Structures of a CO adlayer on a Pt(100) electrode in HClO4 solution studied by in situ STM

We have obtained the first in situ STM atomic images of a CO adlayer on a Pt(100)-(1 x 1) electrode in 0.1 M HClO(4) solution, exhibiting a phase transition from c(6 x 2)-10CO to c(4 x 2)-6CO at E > 0.3 V vs. RHE.     

Changes in electronic structure upon lithium insertion into the A-site deficient perovskite type oxides (Li,La)TiO3

Investigation on variation of the electronic structure accompanying the electrochemical lithium insertion into the perovskite type oxide, (Li,La)TiO3, has been carried out by X-ray absorption spectroscopy (XAS). During the electrochemical lithium insertion, titanium ion reduced its oxidation state from Ti4+ to Ti3+, while La3+ does not contribute to the reduction reaction resulting from Ti K-edge and La L3-edge XAS, respectively. Furthermore, O K-edge XAS showed marked spectral changes with electrochemical lithium insertion, indicating the electronic structure around oxide ion affected by lithium insertion reaction. From the XAS measurement, we have concluded the variation observed in O K-edge XAS was related to the strong interaction with inserted Li ion. To confirm this, first-principles band calculations were performed for the perovskite structure before and after electrochemical lithium insertion. The calculated results showed that the electron originated from inserted Li transferred to neighboring oxide ion locally as well as to Ti ion. This may be due to local neutralization effect of Li to reduce the electrostatic interaction in the crystal.     

Poly(ethylene glycol)-lipase complexes that are highly active and enantioselective in ionic liquids

Lipase-catalyzed alcoholysis between vinyl acetate and 2-phenyl-1-propanol was investigated in dialkylimidazolium-based ionic liquids. Although native lipase powder exhibited very low activity in an ionic liquid, forming a poly(ethylene glycol)(PEG)-lipase complex improved the lipase activity in the ionic liquid. The activity of the PEG-lipase complex was higher in ionic liquids than in common organic solvents (n-hexane, isooctane and dimethylsulfoxide). Fluorescence measurements using 4-aminophthalimide revealed that the ionic liquids were more hydrophilic than the organic solvents used for non-aqueous enzymology. A kinetic study of lipase-catalyzed alcoholysis in an ionic liquid ([Bmim][PF6]) revealed that the Michaelis constant (Km) for 2-phenyl-1-propanol in the ionic liquid was half that in n-hexane, suggesting that the ionic liquid stabilized the enzyme-substrate complex. Finally, we carried out enantioselective alcoholysis of 1-phenylethanol in ionic liquids employing the PEG-lipase complex, and obtained high enantioselectivity, comparable to that in n-hexane.     

Structure and magnetic properties of the two-dimensional ferrimagnet (NEt4)[[Mn(salen)]2Fe(CN)6]: investigation of magnetic anisotropy on a single crystal

The title compound, (NEt(4))[[Mn(salen)](2)Fe(CN)(6)] (1), was synthesized via a 1:1 reaction of [Mn(salen)(H(2)O)]ClO(4) with (NEt(4))(3)[Fe(CN)(6)] in a methanol/ethanol medium (NEt(4)(+) = tetraethylammonium cation, salen(2)(-) = N,N'-ethylenebis(salicylidene)iminate). The two-dimensional layered structure of 1 was revealed by X-ray crystallographic analysis: 1 crystallizes in monoclinic space group P2(1)/c with cell dimensions of a = 12.3660(8) A, b = 15.311(1) A, c = 12.918(1) A, beta = 110.971(4) degrees, Z = 2 and is isostructural to the previously synthesized compound, (NEt(4))[[Mn(5-Clsalen)](2)Fe(CN)(6)] (5-Clsalen(2-) = N,N'-ethylenebis(5-chlorosalicylidene)iminate; Miyasaka, H.; Matsumoto, N.; Re, N.; Gallo, E.; Floriani, C. Inorg. Chem. 1997, 36, 670). The Mn ion is surrounded by an equatorial salen quadridentate ligand and two axial nitrogen atoms from the [Fe(CN)(6)](3-) unit, the four Fe[bond]CN groups of which coordinate to the Mn ions of [Mn(salen)](+) units, forming a two-dimensional network having [[bond]Mn[bond]NC[bond]Fe[bond]CN[bond]](4) cyclic repeating units. The network is spread over the bc-plane of the unit cell, and the layers are stacked along the a-axis. The countercation NEt(4)(+) is located between the layers. Compound 1 is a ferrimagnet with T(c) = 7.7 K and exhibits hysteresis with a remnant magnetization of 13.44 cm(3).mol(-1) (M/N mu(B) = 2.4) at zero field and a coercivity of 1000 Oe when the powder sample was measured at 1.9 K. Magnetic measurements of a direction-arranged single crystal were also carried out. The orientation of the crystallographic axes of a selected single crystal was determined by X-ray analysis, and magnetization was measured when an external field was applied in the a*, b, and c directions. The magnetization in the a* direction increased more easily than those in the b and c directions below the critical temperature. No hysteresis was observed only for the measurement in the a* direction, indicating the presence of strong structural anisotropy with potential anisotropy on Mn(III) ions.     

Tetragonal nanocrystals from the Zr0.5Ce0.5O2 solid solution by hydrothermal method

The formation of tetragonal Zr(0.5)Ce(0.5)O(2) solid solution nanocrystallites of 5 +/- 1 nm size by a hydrothermal method at 120 degrees C for 6 h was confirmed by careful Raman and XRD studies for the first time. It was characterized as the t' '-form with an axial ratio of c/a = 1 but with oxygen ion displacements. The as-prepared sample was hydrous in nature, which is responsible for the lattice expansion. However, most of the water held in the structure can be expelled by heating the sample above 600 degrees C. Above 1050 +/- 50 degrees C the t' '-form of tetragonal Zr(0.5)Ce(0.5)O(2) solid solution dissociates into two phases, cubic phase and the t-form of tetragonal phases.     

Crystal engineering of photochromic diarylethene single crystals

Photochromic performance of diarylethene single crystals was controlled by crystal engineering using non-covalent aromatic-aromatic interactions as the directional intermolecular force. A diarylethene derivative with two pentafluorophenyl groups, 1,2-bis(2-methyl-5-pentafluorophenyl-3-thienyl)perfluorocyclopentene (1a), formed stoichiometric co-crystals with benzene (Bz) and naphthalene (Np) by aryl-perfluoroaryl interactions. Face-to-face pi-stacking interactions between the pentafluorophenyl groups of 1a and the aromatic molecules are responsible for 2:1 and 1:1 stoichiometric compositions in 1a/Bz and 1a/Np co-crystals, respectively. The diarylethene underwent thermally stable and photoreversible photochromic reactions in a homo-crystal of 1a and co-crystals 1a/Bz and 1a/Np. The absorption spectra of the photogenerated closed-ring isomers varied depending on the conformation of the diarylethene molecules packed in the crystals. The diarylethene 1a also formed 1:1 stoichiometric co-crystals with different kinds of diarylethenes, 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene (2a) and 1,2-bis[2-methyl-5-(1-naphthyl)-3-thienyl]perfluorocyclopentene (3a). Both co-crystals 1a/2a and 1a/3a showed photochromism. Although 1a, 2a, and 3a underwent efficient photocyclization reactions in their homo-crystals, highly selective photocyclization reactions of 2a or 3a were observed in the co-crystals. The selective reactions were confirmed by HPLC and X-ray crystallography. Excited energy transfers from 1a to 2a and from 1a to 3a are considered to occur and cause the selective reactions.