Heterogeneous aquacatalytic highly selective organic transformations are what may be considered ideal chemical processes of the next generation, where the advantages of both aqueous- and heterogeneous-switching are combined in one system to meet green sustainable chemical requirements. Heterogeneous aquacatalytic asymmetric reactions were achieved with palladium complexes of homochiral phosphine ligands which were immobilized onto amphiphilic polystyrene–poly(ethylene glycol) (PS–PEG) resin beads via chemical bonding. The catalyst was recovered by simple filtration and was reused without any loss of catalytic activity and stereoselectivity. In particular, a novel chiral P,N-ligand, (3R,9aS)-2-aryl-3-[2-(diphenylphosphino)phenyl]tetrahydro-1H-imidazo[1,5-a]indole-1-one, was designed and prepared on PS–PEG to realize palladium-catalyzed π-allylic substitution of both cyclic and acyclic substrates with carbon, nitrogen, and oxygen nucleophiles in water with enantioselectivity of up to 99% ee.
Catalytic asymmetric organic molecular transformations, including carbon–carbon, carbon–nitrogen, and carbon–oxygen bond-forming reactions, were performed in water under heterogeneous conditions with amphiphilic polymer-supported chiral palladium complexes with high stereoselectivity (up to 99% ee).
The present account describes the summary of the recent developments to the design of helical self-assemblies of linear π-conjugated molecules, particularly of oligo(p-phenylenevinylenes) (OPVs) and oligo(p-phenyleneethynylenes) (OPEs). The design strategy involves functionalization of π-conjugated backbones with achiral and chiral alkoxy side chains and hydroxymethyl end groups. Self-organization of these molecules in nonpolar hydrocarbon solvents resulted in a variety of supramolecular architectures such as tapes, helices, vesicles, and tubules. These supramolecular structures eventually lead to the formation of entangled networks resulting in gelation of solvents. It has been observed that OPVs in nonpolar solvents prefer to form supramolecular tapes whereas the corresponding OPEs form nano- to microsized vesicles and bundled fibers. Attachment of chiral motifs to OPVs and OPEs resulted in the formation of helical structures with a preferred handedness. The “sergeants and soldiers” co-assembly approach to chirality induction and amplification is efficient in these systems in the gel state. These results highlight the importance of the subtle difference in the strength of π–π interaction in gel forming linear π-systems to the creation of hierarchical architectures with different size and shape, particularly helical structures.
Self-assembly of oligo(p-phenylenevinylene)s (OPVs) and oligo(p-phenyleneethynylene)s (OPEs) leads to helical supramolecular structures of different size and shape. Nature of the end functional groups, the side chains, and the π-conjugated backbone strongly influences upon the self-assembly processes.
The mechanism of cyanide oxidation by ferrate in water is discussed using DFT computations in the framework of the polarizable continuum model. The reactivity of three oxidants, nonprotonated, monoprotonated, and diprotonated ferrates is evaluated. This reaction is initiated by a direct attack of an oxo group of ferrate to the carbon atom of cyanide, followed by an H-atom transfer from cyanide to another oxo group to lead to an intermediate having cyanate (NCO−) as a ligand. The produced cyanate is oxidized by an oxo ligand of ferrate and exogenous oxygen molecule to CO2 and NO2−. The initial C–O bond formation is found to be the rate-determining step in this reaction. The activation energy for the C–O bond formation is 51.9 kJ mol−1 for nonprotonated ferrate, 44.4 kJ mol−1 for monoprotonated ferrate, and 41.4 kJ mol−1 for diprotonated ferrate, which indicates that the oxidizing power of the three oxidants is in the order of nonprotonated ferrate < monoprotonated ferrate < diprotonated ferrate. The general energy profile for cyanide oxidation by ferrate is downhill toward the product direction after the C–O bond formation, so cyanide is readily converted to the final products in water. The reaction kinetics of this reaction are analyzed from the calculated energy profile and experimentally determined pKa values.
The mechanism of cyanide oxidation by ferrate in water is discussed using DFT computations. The reaction is initiated by a direct attack of an oxo group of ferrate to the carbon atom of cyanide, followed by an H-atom transfer from cyanide to another oxo group to form an intermediate having cyanate (NCO−). The produced cyanate is oxidized by an oxo ligand of ferrate and exogenous oxygen molecule to CO2 and NO2−.
The purpose of this paper is to examine the effect of six different mixing rules on the calculated transport properties including viscosities and thermal conductivities of some binary and ternary gas mixtures. These properties are calculated using pair potential energies of the systems obtained from the inversion procedure. The Chapman–Enskog theory and Schreiber’s method are employed to calculate viscosity and thermal conductivity of different mixtures, respectively. Different mixing rules do not behave the same in predicting the two aforementioned properties. The Fit (MADAR-2) mixing rule gives rise to more acceptable viscosity values, while the Halgren-HHG rule stands over other mixing rules in predicting thermal conductivity. It is found that, when the mixture components are similar in size, different mixing rules often do not change the errors in calculated properties more than ±1%. However, as the size similarity decreases, the effect of applied mixing rules becomes more important. In this case, different mixing rules are able to change the errors in calculations at most ±3.5%. The collision diameters (σ) of our studied mixture components, vary from 2.641 Å for He, to 5.26 Å for R125. The energy scaling parameters (ε) of mixture components range from 10.956 K for He to 475.76 K for C4H10.
In order to investigate static quantum isotope effects on the stability of proton-transferred structures, we defined an effective quantal potential energy hypersurface (EQPES), which includes mass-dependent quantum effects. We demonstrated the difference between the ordinary potential energy surface and EQPES of the double well potential as a simple example. The minimum energy path on EQPES describes the zero-point energy-corrected structures and tunneling motion, which is characterized as a classically forbidden motion. We also performed the EQPES analysis of model proton-transfer reactions in DNA base pairs. It was found that the double proton-transferred structure of an adenine–thymine (AT) pair is quantum mechanically unstable and that of a guanine–cytosine (GC) pair is stable within a least uncertainty regime. In order to investigate dynamic quantum isotope effects on the stability of the proton-transferred structures, we performed quantal cumulant dynamics (QCD) simulations of the GC pair. Results show that the proton-transferred structure of the protonated isotopomer is dynamically unstable though the EQPES analysis predicts its stability. It is relevant to include dynamic effects in the investigation of the quantum isotope effects on geometric stability of systems with a small energy gap between global and metastable structures.
Selective oxidation under visible light is attractive for application in environment-benign societies. Oxidative dehydrogenation of ethanol proceeds over mesoporous V-doped TiO2 under visible light in clear contrast to ethanol dehydrogenation over crystalline TiO2 doped or undoped with V and inactive mesoporous TiO2. The red-ox states of VIV and VIII were detected using X-ray spectroscopies. In this paper, kinetic measurements of each catalytic step and X-ray spectroscopic monitoring under catalytic reaction conditions are correlated. The ethanol conversion to acetaldehyde in the absence of O2 was monitored under visible light coupled with reduction of VIV to VIII species based on V Kβ5,2 emission and V Kβ5,2-selecting X-ray absorption fine structure spectra. The oxidative dehydrogenation of dissociatively adsorbed ethoxyl species proceeded in O2 under visible light with formation rates 38% of steady photo-catalysis in ethanol + O2. The acetaldehyde desorption step by H subtraction from ethoxyl species on VIII was found to be rate-limiting. The origin of oxidative dehydrogenation over mesoporous V–TiO2 was suggested to be coordinatively unsaturated VIII species specifically activating O2 molecules. Further, a poisoning effect of product water was demonstrated to block the active V sites. UV light illumination was found to be effective to re-activate the mesoporous V–TiO2 catalyst.
The yields of IO radical from the reaction of CH3I with Cl atom in the presence of O2 were determined as functions of total pressure from 5 to 250 Torr of N2 diluent and temperature over the range of 278 to 328 K using cavity ring-down spectroscopy. The yields are pressure and temperature dependent. The rate constants and product branching ratios of the reaction of CH2I radical with O2 were investigated. We determined a rate constant of (1.28±0.22)×10−12 cm3 molecule−1 s−1 at 298 K (2σ uncertainty) for this reaction. Theoretical calculations were performed to determine energetics of the reactions of CH2I + O2 and CH2Br + O2. The present results suggest that non-negligible IO radicals will be formed from the reactions of CH3I/CH2I2 + OH/Cl/NO3 at atmospheric conditions.
It has been well-known that fatty acids occurring in the royal jelly of honeybees are effective towards autonomic imbalance, perimenopausal symptoms, osteoporosis, and other conditions. These pharmacological effects of royal jelly similar to those caused by the hormone estrogen are thought to appear due to the interaction of the fatty acids of royal jelly with an estrogen receptor inside the human body. Although the structure of several major fatty acids present in royal jelly has been determined experimentally, no direct evidence of the interaction of these fatty acids with the estrogen receptor have been reported yet. In this study, we therefore give an insight into the interaction of fatty acids with the human estrogen receptor β by quantum mechanical (QM), ONIOM, and molecular dynamics (MD) methods using a model active site.
The behavior of a recent kinetics mechanism for the reduction reaction of NO by CO on the surface of a series of percolation clusters is studied by means of Monte Carlo simulations using experimental rate constant values from the literature. The structural sensitivity of the reaction is observed through the production curves and phase diagrams. The kinetics phase transitions and the relation between production and the mean number of nearest neighbors of the cluster’s active site, the temperature and the pressure of the gas-phase components are analyzed.
Mono- and dihydrated clusters of guanosine (Gs) and 2′-deoxyguanosine (2′-dGs) are formed by laser desorption combined with supersonic-jet cooling, and their electronic spectra are obtained by resonant two-photon ionization spectroscopy. The electronic spectra of these hydrated clusters appear to be composed of multiple structural isomers. Possible hydration structures are investigated based on comparison with the result for 9-methylguanine (9MG) and computational studies. The dihydrated cluster of Gs is found to exhibit absorption bands which are significantly shifted with respect to those of 2′-dGs and 9MG. The observation suggests the existence of specific dihydrate structures involving the 2′-hydroxy group of Gs.
It has been found that the J-aggregates of thiacarbocyanine self-assembled in solution spontaneously transform into H-aggregates. The transformation mechanism was found to be solvent-mediated phase transformation that proceeds through dissolution of the J-aggregates and subsequent aggregation into H-aggregates.
Ruthenium complexes containing a tridentate N-ethyl-N,N-bis(2-pyridylmethyl)amine (N,N-bis(2-pyridylmethyl)ethylamine: bpea) ligand having two different types of nitrogen donors, one an amine and the other pyridine rings connected with flexible CH2-arms, were synthesized and characterized. A trichlororuthenium isomeric pair of fac- and mer-[RuCl3(bpea)] was synthesized from RuCl3·nH2O in a H2O–C2H5OH solution. A reaction of fac-[RuCl3(bpea)] in an C2H5OH–H2O–CH3CN solution under refluxing conditions afforded a triacetonitrile complex, fac-[Ru(CH3CN)3(bpea)](PF6)2. Four nitrosylruthenium complexes, trans(NO, py), cis(NO, Cl), fac-[RuCl2(NO)(bpea)]PF6, trans(NO, OH), cis(NO, NO2), mer-[Ru(NO2)(OH)(NO)(bpea)]PF6, trans(NO, OCH3), cis(NO, Cl), mer-[RuCl(OCH3)(NO)(bpea)]PF6 and trans(NO, OH), cis(NO, Cl), mer-[RuCl(OH)(NO)(bpea)]PF6, were synthesized and characterized by X-ray crystallography. The bpea of three nitrosylruthenium complexes bearing an electron-donating ligand such as hydroxo or methoxo as an ancillary ligand coordinated in a meridional fashion.
Two [Co2(L)2(μ-CO3)(μ-OH)2] complexes (L: N-methyliminodiacetato, or 1,4,7-triazacyclononane) were prepared and characterized. In each complex, the dihedral angle between Co–Oμ-OH–O′μ-OH and Co′–Oμ-OH–O′μ-OH planes was ca. 160° and the μ-CO32− plane was perpendicular to each Co–Oμ-OH–μ-O′μ-OH plane. 13C NMR signals of μ-CO32− in these complexes appeared at ca. 170 ppm.
We have studied antibacterial activities of model peptides based on Pleurocidin (Ple). In this study, to investigate the effect of the C-terminal portion of these model peptides on antibacterial activity, we synthesized several short peptides which are devoid of the C-terminal four and more amino acid residues from the corresponding model peptides and examined their biological activities and behaviors against lipid and cell membranes. Removal of the C-terminal four residues resulted in maintained antibacterial activity and reduction of hemolytic activity.
Five new polyoxygenated steroids 1–5 have been isolated from a Formosan soft coral Sinularia facile. The structures of new metabolites were elucidated on the basis of extensive spectroscopic analysis and cytotoxic activity of 1–5 against the proliferation of a limited panel of cancer cell lines was measured. Metabolite 4 has been shown to exhibit weak cytotoxicity against Hep G2, Hep G3B, MDA-MB-231, and Ca9-22 cancer cell lines.
Highly stereoselective intramolecular Diels–Alder (IMDA) reaction of decatrienoates has been achieved by using a more sterically hindered ester group, i.e., t-butoxycarbonyl, or electron-withdrawing hetero substituents, i.e., chloro and phenylsulfonyl, as terminal activating groups. A remarkable olefin isomerization of the Diels–Alder cycloadduct bearing a phenylsulfonyl group occurred upon heating it for a few hours and it was found that the isomerization can be catalyzed by Brønsted acid.
A series of titanate pyrochlore Ln2Ti2O7 (Ln = Eu–Lu) was prepared by a polymerized complex method and evaluated as a photocatalyst for water splitting reaction. All the Ln2Ti2O7, except for Tb2Ti2O7, demonstrated evolution of H2 and O2 in a stoichiometric ratio from pure water under UV-light irradiation. The photocatalytic activities of the Ln2Ti2O7 were significantly enhanced by the addition of excess Ln (5%) in the preparation procedure. As for the Ln2Ti2O7 containing small Ln3+ (Ln = Dy–Lu), the enhanced photocatalytic activity can be explained by the suppression of impurity phase formation, rutile titanium oxide (TiO2), which formed in the stoichiometric preparation at high temperature. It was also found that the addition of excess Ln increased the surface area of these materials, which certainly contributed to the enhanced photocatalytic activity. In the case of Gd2Ti2O7, the photocatalytic activity was remarkably improved by the addition of excess Gd, in spite of the fact that no impurity phase formed even in the stoichiometric preparation. Scanning electron microscopy (SEM) and pore size distribution analysis revealed that the addition of excess amount of Gd made the Gd2Ti2O7 material porous, which is undoubtedly one of the major factors enhancing the photocatalytic activity.
Benzo[1,2-b:4,3-b′]dithiophene/triphenylamine copolymers P-2eh (with no methyl substituents) and P-Me and P-2Me (with methyl substituents at triphenylamine sites) were synthesized by Stille coupling reactions. In the ground state, the methyl substituents at the ortho positions to the BDT unit on the triphenylamine (TPA) moiety in P-Me and P-2Me caused twisting of the polymer structure and clearly limited conjugation of the polymer backbones. However, in their excited states, all of these copolymers were shown to have planar structures, and almost the same emission maxima were observed. This result indicates that, in the excited states, π-conjugation of the polymer backbone results in the adoption of a more stable planar structure rather than the twisted structure observed in the ground state. The maximum EL efficiencies of devices based on P-Me and P-2Me were about three times higher than that of P-2eh due to restricted π-stacking/aggregation of the conjugated copolymers in the solid state and improvements in thermal and electrochemical stability.
Polyaniline (PANI)-intercalated MoO3 ((PANI)xMoO3), which is a conventional layered organic/MoO3 hybrid, as a gas sensor has a resistance drift problem, which should be solved in order to realize practical applicable gas sensing devices. In this analytical study, XPS studies reveal that the resistance drift is caused by adsorbing and desorbing oxygen molecules from the atmosphere. The adsorption of enough oxygen molecules by annealing in air at a higher temperature than operating temperature can reduce the resistance drift phenomena.