Low temperature ionic conductor: ionic liquid incorporated within a metal–organic framework

Ionic liquids (ILs) show promise as safe electrolytes for electrochemical devices. However, the conductivity of ILs decreases markedly at low temperatures because of strong interactions arising between the component ions. Metal–organic frameworks (MOFs) are appropriate microporous host materials that can control the dynamics of ILs via the nanosizing of ILs and tunable interactions of MOFs with the guest ILs. Here, for the first time, we report on the ionic conductivity of an IL incorporated within a MOF. The system studied consisted of EMI-TFSA (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide) and ZIF-8 (Zn(MeIM)₂, H(MeIM) = 2-methylimidazole) as the IL and the MOF, respectively. While the ionic conductivity of bulk EMI-TFSA showed a sharp decrease arising from freezing, the EMI-TFSA@ZIF-8 showed no marked decrease because there was no phase transition. The ionic conductivity of EMI-TFSA@ZIF-8 was higher than that of bulk EMI-TFSA below 250 K. This result points towards a novel method by which to design electrolytes for electrochemical devices such as batteries that can operate at low temperatures.     

Chemical constituents in the leaves of Vateria indica

Comprehensive re-investigation of the chemical constituents in the leaves of Vateria indica (Dipterocarpaceae) resulted in the isolation of a novel resveratrol dimeric dimer having a C(2)-symmetric structure, vateriaphenol F (1), and two new O-glucosides of resveratrol oligomers, vateriosides A (2) (resveratrol dimer) and B (4) (resveratrol tetramer), along with a new natural compound (3) and 33 known compounds including 26 resveratrol derivatives. The absolute structures were elucidated by spectroscopic analysis, including two dimensional NMR and circular dichroism (CD) spectra.     

Synthesis and photocatalytic activity of mesoporous SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>

Mesoporous SiO₂–TiO₂ was synthesized by the sol–gel method using Si(OC₂H₅)₄, Ti(OC₂H₅)₄, and stearyltrimethylammonium chloride. By using acetylacetone as the capping agent of Ti(OC₂H₅)₄, homogeneous SiO₂–TiO₂ composite was obtained. Spherical mesoporous SiO₂–TiO₂ was also synthesized by the sol–gel method using W/O emulsion under microwave irradiation. The specific surface area of these mesoporous SiO₂–TiO₂ materials decreased when the Ti/Si molar ratio was higher than 0.1, which indicated that Ti was homogeneously distributed in mesoporous SiO₂ matrix at Ti/Si ≦ 0.1. The photocatalytic activity of mesoporous SiO₂–TiO₂ materials was investigated by the degradation of methylene-blue in water under UV light irradiation. Mesoporous SiO₂–TiO₂ was effective for the adsorption–decomposition of methylene-blue.     

Automated determination of venlafaxine in human plasma by on‐line SPE‐LC‐MS/MS. Application to a bioequivalence study

A new automated SPE‐LC‐ESI‐MS/MS method was developed and validated to quantify venlafaxine in human plasma using fluoxetine as an internal standard. The analytes were automatically extracted from plasma by C18 SPE cartridges, separated on a C8 RP column and analyzed by MS in the multiple reaction‐monitoring (MRM) mode. The method has a chromatographic run time of 4.0 min and a linear calibration curve over the range of 0.25–200 ng/mL (r >0.997). The between‐run precisions, based on the percent RSD for replicate quality controls (0.75; 80, and 200 ng/mL), were < 8.5% for all concentrations. The between‐run accuracies, based on the percent relative error, were < 4.0%. This method was successfully employed in a bioequivalence study of two venlafaxine capsule formulations (test formulation from Eurofarma (Brazil) and Efexor XR, reference formulation, from Wyeth‐Whitehall, Brazil) in 48 healthy volunteers of both sexes who received a single 150 mg dose of each formulation. More than 3000 samples were analyzed eliminating the analyst's exposure to hazardous organic solvents normally employed in off‐line liquid–liquid extractions. The 90% confidence interval (CI) of the individual ratio geometric mean for Test/Reference was 91.6–103.4% for AUC_{0–48 h} and 102.2–112.6% for C_max. Since both 90% CI for AUC_{0–48 h} and C_max were included in the 80–125% interval proposed by the US Food and Drug Administration (FDA) and the Brazilian National Health Surveillance Agency (ANVISA), the test formulation was considered bioequivalent to Efexor XR according to both the rate and extent of absorption.     

Characterization of host-guest complexes of cucurbit[n]uril (n = 6, 7) by electrospray ionization mass spectrometry

When an intramolecular cavity exists in a molecule, it can trap another chemical species to form a host-guest complex. We examine the formation of such an inclusion complex with cucurbit[n]uril (CBn, n = 6, 7) as the host to trap alkali metal or ammonium ions as the guest, by electrospray ionization mass spectrometry (ESI-MS). The results show that the inclusion complexes are formed between the three-dimensional cylinder of CBn hosts and the guest cations. Selectivity of the complex formation is dependent both on (1) ion-dipole interactions between the cylindrical portal of the CBn hosts and the guest cations and (2) the hydrophobic interactions at the inner cavity of CBn.     

Electron-transfer fluorescence quenching of aromatic hydrocarbons by europium and ytterbium ions in acetonitrile

To make the effects of molecular size on photoinduced electron-transfer (ET) reactions clear, the ET fluorescence quenching of aromatic hydrocarbons by trivalent lanthanide ions M3+ (europium ion Eu3+ and ytterbium ion Yb3+) and the following ET reactions such as the geminate and free radical recombination were studied in acetonitrile. The rate constant k(q) of fluorescence quenching, the yields of free radical (phi(R)) and fluorescer triplet (phi(T)) in fluorescence quenching, and the rate constant k(rec) of free radical recombination were measured. Upon analysis of the free energy dependence of k(q), phi(R), phi(T), and k(rec), it was found that the switchover of the fluorescence quenching mechanism occurs at deltaG(fet) = -1.4 to -1.6 eV: When deltaG(fet) < -1.6 eV, the fluorescence quenching by M3+ is induced by a long-distance ET yielding the geminate radical ion pairs. When deltaG(fet) > -1.4 eV, it is induced by an exciplex formation. The exciplex dissociates rapidly to yield either the fluorescer triplet or the geminate radical ion pairs. The large shift of switchover deltaG(fet) from -0.5 eV for aromatic quenchers to -1.4 to -1.6 eV for lanthanide ions is almost attributed to the difference in the molecular size of the quenchers. Furthermore, it was substantiated that the free energy dependence of ET rates for the geminate and free radical recombination is satisfactorily interpreted within the limits of the Marcus theory.     

Constituents of Holothuroidea, 18. Isolation and structure of biologically active disialo- and trisialo-gangliosides from the sea cucumber Cucumaria echinata

Three new disialo- and trisialo-gangliosides, CEG-6 (6), CEG-8 (8), and CEG-9 (9), were obtained, together with one known ganglioside, HLG-3 (7), from the lipid fraction of the chloroform/methanol extract of the sea cucumber Cucumaria echinata. The structures of the new gangliosides were determined on the basis of chemical and spectroscopic evidence to be 1-O-[alpha-L-fucopyranosyl-(1-->11)-(N-glycolyl-alpha-D-neuraminosyl)-(2-->4)-(N-acetyl-alpha-D-neuraminosyl)-(2-->6)-beta-D-glucopyranosyl]-ceramide (6) and 1-O-[(N-glycolyl-D-neuraminosyl)-(2-->11)-(N-glycolyl-D-neuraminosyl)-(2-->4)-(N-acetyl-D-neuraminosyl)-(2-->6)-D-glucopyranosyl]-ceramide (8, 9). The ceramide moieties of each compound were composed of an homogeneous sphingosine or phytosphingosine base and heterogeneous 2-hydroxy or nonhydroxylated fatty acid units. These gangliosides showed neuritogenic activity toward the rat pheochromocytoma cell line PC-12 in the presence of nerve growth factor.     

Biologically active glycosides from asteroidea, 42. Isolation and structure of a new biologically active ganglioside molecular species from the starfish Asterina pectinifera

A ganglioside molecular species GP-3 (1) has been obtained from the water-soluble lipid fraction of the chloroform/methanol extract of the starfish Asterina pectinifera. The structure of the ganglioside has been determined on the basis of chemical and spectroscopic evidence. Compound 1 represents new ganglioside molecular species possessing two moles of sialic acids at the inner part of the sugar moiety. Partial hydrolysis by hot water and an enzymatic hydrolysis by means of endoglycoceramidase (EGCase) have proved useful for structure elucidation of the complex oligosaccharide moiety. Moreover, 1 exhibits neuritogenic activity toward the rat pheochromocytoma cell line, PC-12 cells, in the presence of nerve growth factor (NGF).     

Synthesis of a one-dimensional metal-dimer assembled system with interdimer interaction, M2(dtp)4 (M = Ni, Pd; dtp = dithiopropionato)

A metal-dimer assembled system, M(2)(dtp)(4) (M = Ni, Pd; dtp = dithiopropionate, C(2)H(5)CS(2-)), was synthesized and analyzed by the X-ray single-crystal diffraction method, UV-vis-near-IR spectra of solutions, solid-state diffuse reflectance spectroscopies, and electrical conductivity measurements. The structures exhibit one-dimensional metal-dimer chains of M(2)(dtp)(4) with moderate interdimer contact. These complexes are semiconducting or insulating, which is consistent with the fully filled d(z)2 band of M(II)(d(8)). Interdimer metal-metal distances were 3.644(2) Angstroms in Ni(2)(dtp)(4) and 3.428(2) Angstroms in Pd(2)(dtp)(4), each of which is marginally longer than twice the van der Waals radius of the metal. Interdimer charge-transfer transitions were nevertheless observed in diffuse reflectance spectra. The origin of this transition is considered to be due to an overlap of two adjacent d(sigma) orbitals, which spread out more than the d(z)2 orbital because of the antibonding d(sigma) character of the M(d(z)2)-M(d(z)2). The Ni(2)(dtp)(4) exhibited an interdimer charge-transfer band at a relatively low energy region, which is derived from the Coulomb repulsion of the 3d(sigma) orbital of Ni.