A free-energy perturbation method based on Monte Carlo simulations using quantum mechanical calculations (QM/MC/FEP method): application to highly solvent-dependent reactions

This study describes the framework of the quantum mechanical (QM)/Monte Carlo (MC)/free‐energy perturbation (FEP) method, a FEP method based on MC simulations using quantum chemical calculations. Because a series of structures generated by interpolating internal coordinates between transition state and reactant did not produce smooth free‐energy profiles, we used structures from the intrinsic reaction coordinate calculations. This method was first applied to the Diels–Alder reaction between methyl vinyl ketone and cyclopentadiene and produced ΔG values of 20.1 and 21.4 kcal mol^?1 in aqueous and methanol solutions, respectively. They are very consistent with the experimentally observed values. The other two applications were the free‐energy surfaces for the Cope elimination of N,N‐dimethyl‐3‐phenylbutan‐2‐amine oxide in aqueous, dimethyl sulfoxide, and tetrahydrofuran solutions, and the Kemp decarboxylation of 6‐hydroxybenzo‐isoxazole‐3‐carboxylic acid in aqueous, dimethyl sulfoxide, and CH₃CN solutions. The calculated activation free energies differed by less than 1.8 kcal mol^?1 from the experimental values for these reactions. Although we used droplet models for the QM/MC/FEP simulations, the calculated results for three reactions are very close to the experimental data. It was confirmed that most of the interactions between the solute and solvents can be described using small numbers of solvent molecules. This is because a few solvent molecules can produce large portions of the solute–solvent interaction energies at the reaction centers. When we confirmed the dependency on the droplet sizes of solvents, the QM/MC/FEP for a large droplet with 106 water molecules produced a ΔG value similar to the experimental values, as well as that for a small droplet with 34 molecules. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

New determination methods of halides and cyanide ions by electrospray ionization mass spectrometry based on ternary complex formation

Determination methods of halide ions (X(-) = F(-), Cl(-), Br(-) and I(-)) by electrospray ionization mass spectrometry (ESIMS) were developed, where negative ions of the ternary complexes of group-13 elements, nitrilotriacetic acid (NTA), and halides were measured. In particular, these halides were simultaneously determined by measuring [InX(nta)](-), and the limits of detection (LODs) were 1.1 μmol dm(-3) for F(-), 0.32 μmol dm(-3) for Cl(-), 3.8 nmol dm(-3) for Br(-), and 1.6 nmol dm(-3) for I(-), respectively. This approach was extended to the determination of CN(-), where the ternary complex of Cu(II), CN(-) and 4-(2-pyridylazo)resorcinol (PAR), i.e., [(63)Cu(II)(CN)(par)](-) (m/z 302) was measured. The LOD for CN(-) was 20 nmol dm(-3).     

Anion conductive block poly(arylene ether)s: synthesis, properties, and application in alkaline fuel cells

Anion conductive aromatic multiblock copolymers, poly(arylene ether)s containing quaternized ammonio-substituted fluorene groups, were synthesized via block copolycondensation of fluorene-containing (later hydrophilic) oligomers and linear hydrophobic oligomers, chloromethylation, quaternization, and ion-exchange reactions. The ammonio groups were selectively introduced onto the fluorene-containing units. The quaternized multiblock copolymers (QPEs) produced ductile, transparent membranes. A well-controlled multiblock structure was responsible for the developed hydrophobic/hydrophilic phase separation and interconnected ion transporting pathway, as confirmed by scanning transmission electron microscopic (STEM) observation. The ionomer membranes showed considerably higher hydroxide ion conductivities, up to 144 mS/cm at 80 °C, than those of existing anion conductive ionomer membranes. The durabilities of the QPE membranes were evaluated under severe, accelerated-aging conditions, and minor degradation was recognized by (1)H NMR spectra. The QPE membrane retained high conductivity in hot water at 80 °C for 5000 h. A noble metal-free direct hydrazine fuel cell was operated with the QPE membrane at 80 °C. The maximum power density, 297 mW/cm(2), was achieved at a current density of 826 mA/cm(2).     

Catalytic asymmetric allylation of 3,4-dihydroisoquinolines and its application to the synthesis of isoquinoline alkaloids

A catalytic asymmetric allylation of 3,4-dihydroisoquinoline was carried out with allyltrimethoxylsilane-Cu as the nucleophile in the presence of DTBM-SEGPHOS as the chiral ligand to afford corresponding chiral 1-allyltetrahydroisoquinoline derivatives in good yield and stereoselectivity. The allyl adduct thus obtained was applied to the synthesis of several isoquinoline alkaloids such as crispine A and homolaudanosine. The reaction was further used for the synthesis of the isoquinoline moiety of schulzeine A.     

Two-photon excitation of confined biexcitons in CuCl quantum dots

We have studied direct creation processes of confined biexcitons in CuCl quantum dots by polarization-dependent resonant two-photon excitation spectroscopy. The two-photon absorption band for the lowest state of the biexciton (total angular momentum J=0) which appears on the lower energy side of confined exciton band was identified from the analysis of the polarization dependence of the photoluminescence excitation spectrum of the biexciton. Furthermore, the two-photon excitation process for the excited state of the biexciton (J=2) was also found with polarization dependence different from the J=0 biexciton state.     

STM imaging of a model surface of Ru(4,4′-dicarboxy-2,2′-bipyridine)2(NCS)2 dye-sensitized TiO2 photoelectrodes

A TiO₂(1 1 0)-(1 × 1) surface was prepared in an ultra-high vacuum, transported in laboratory air, and observed with a scanning tunneling microscope (STM) operated in a vacuum of 10⁻⁴ Pa. Empty state images showed atomically flat terraces separated by single-height steps, on which 5-fold-coordinated surface Ti atoms were observed as spots arranged in a rectangular lattice. The Ru(4,4′-dicarboxy-2,2′-bipyridine)₂(NCS)₂ (N3) dye was adsorbed on the TiO₂ surface by immersing the TiO₂ wafer into an acetonitrile solution of the dye. In the empty state images, individual N3 molecules were observed as oval particles protruding by 0.6 nm from the TiO₂ surface. The oval shape elongated to the [1  0] directions was attributed to electron tunneling from tip to unoccupied states localized at the two carboxyl groups bound to the TiO₂ surface.