Novel bifunctional organocatalysts, which possess a thiourea moiety and an amino group, were designed and synthesized. We discovered that bifunctional thiourea bearing a tertiary amino group significantly accelerated several nucleophilic addition reactions of active methylene compounds to electron-deficient double bonds. In these reactions, the double hydrogen-bonding activation of electrophiles bearing nitro, imide, and carbamate groups by the thiourea moiety and simultaneous deprotonation of nucleophiles by the dimethylamino group of bifunctional thiourea proved to play a crucial role for enhancing both reaction rate and enantioselectivity. We have demonstrated the utility of PEG-bound thiourea as a homogeneous catalyst. Although the reaction rate was somewhat decreased with PEG-bound thiourea, immobilization to a PEG support proved to facilitate the recovery and reuse of thiourea catalyst without affecting the chemical yield and enantioselectivity. A newly designed thiourea catalyst provided sufficient activation of organoboronic acids to facilitate the enantioselective Petasis transformation of quinolines even at low temperatures. A high degree of stereocontrol was achieved in the reaction of various quinolines and organoboronic acids by using a combination of H2O and NaHCO3 as additives.
Bifunctional thiourea catalysts were designed and synthesized. Catalyst having an amino group accelerated several nucleophilic additions of active methylene compounds and catalyst having a chelating functionality provided sufficient activation of organoboronic acids to facilitate the Petasis transformation of quinolines.
To elucidate the structural requirements for the endotoxic and antagonistic activities of lipid A derivatives, we have focused on the effects of the acyl moieties and acidic groups at the 1- and 4′-positions in the present study. We have synthesized new analogues corresponding to Rubrivivax gelatinosus lipid A, which has a characteristic symmetrical distribution of its acyl groups on its two glucosamine residues with shorter acyl groups (decanoyl groups (C10) and lauryl groups (C12)) than Escherichia coli lipid A’s. Carboxymethyl (CM) analogues in which one of the phosphates was replaced with a CM group were also synthesized with a different distribution of acyl groups. Biological tests revealed that the acyl group distribution in the lipid A analogue, strongly affected its bioactivity. The synthetic Ru. gelatinosus type lipid A showed potent antagonistic activity against LPS, whereas its 1-O-carboxymethyl analogue showed weak endotoxic activity. These results demonstrate that when lipid A has shorter (C10 and C12) hexa-acyl groups, its bioactivity is more easily affected by small structural differences, such as differences in acidic groups or acyl group distribution, and that they can change bioactivity from endotoxic to agonistic or vice versa at this structural boundary for the bioactivity.
To elucidate the structural requirements for immunologically active lipid A derivatives, we synthesized Rubrivivax gelatinosus lipid A and its new analogues focusing on the effects of acyl moieties and acidic groups at 1-position, with an affinity separation method.
We theoretically analyzed the geometrical isotope effect and kinetic isotope effect for R–H(D)···R type proton (deuteron) transfer on the intramolecular hydrogen bond of (Z)-1,3-pentadiene (R=CH2), 3-imino-1-propen-1-amine (R=NH), and malonaldehyde (R=O) by using Hartree–Fock (HF) and second-order Møller–Plesset (MP2) levels of a multi-component molecular orbital (MC_MO) method to treat the quantum effects of nuclei. As the protonic and deuteronic basis functions, our proposed exponent values of 24.1725 and 35.6214 for the single protonic and deuteronic Gaussian-type functions were employed, respectively. In the case of R=NH and O, the calculated R5–D6 and R1···D6 bond lengths are shorter and longer than those of the R5–H6 and R1···H6 bonds due to the anharmonicity of the potential. The charge densities around the deuteron for all R=CH2, NH, and O cases are larger than those around the proton because the deuteron is more localized than the proton. The ratio of rate constant (kaH⁄kaD) obtained by MP2 level theory of the MC_MO method is estimated as 10.16, which is in reasonable agreement with the experimental result (12.2). For the systematic analysis of the intramolecular proton (deuteron)-transfer reaction, we also estimated the kaH⁄kaD of R=NH and O.
The π-current density induced in a polycyclic π-system is strongly dependent on molecular geometry, so that information on main aromatic pathways cannot be extracted straightforwardly from the π-current density. Using our graph theory of aromaticity and ring-current diamagnetism, we re-interpreted the π-current densities and aromatic stabilization energies of porphyrins consistently and found that main pathways of π-electron circulation along the macroscopic ring are not those of aromatic stabilization. Four five-site circuits instead proved to be the main origin of aromaticity in porphyrins. In general, currents are induced in all possible circuits in a π-system. Superposition of all these circuit currents gives rise to the apparent bifurcation of the π-current across each pyrrolic unit. Local π-currents induced in pyrrolic rings represent those induced in the corresponding five-site circuits.
We observed the IR-induced reaction of C2H5OH on MoO3 using a pulsed and tunable infrared free electron laser (IR-FEL). The IR-FEL-induced reaction showed wavelength dependency and requires light stronger than a certain threshold level. The C2H5OH was converted mainly to C2H4 only when the MoO3 was irradiated with focused IR-FEL at 967 and 814 cm−1 corresponding to Mo=O stretching modes, whereas IR light at 1200 cm−1 induced no reaction. The origin of this IR-FEL-induced reaction is discussed.
Electron spin–lattice relaxation times (T1e) of a unique nonionic amphiphilic compound, (poly(oxyethylene) hydrogenated castor oil, HCO) in aqueous dispersions, were investigated by electron paramagnetic resonance (EPR) and saturation recovery (SR) spectroscopies. The spin probes, 5-doxylstearic acid (5-DSA) and 3β-doxyl-5α-cholestane (CHL), were used to obtain T1e values for the head group region in the HCO membrane. Analysis of SR signals from both probes showed that the T1e value (≈5 μs at 20 °C) indicates relatively faster relaxation behavior in the region than that of 12-DSA. No abrupt change (such as phase transition) of the relaxation time was observed in the temperature region studied. Thus, the present T1e results indicate relative flexibility for both probe moieties in the membrane throughout the temperatures studied.
The hydrogen adsorption properties and uptake capacities of three-dimensional microporous materials of lantern-type dinuclear M(BDC)(DABCO)1⁄2 (M=CoII, CuII, and ZnII; BDC = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane; Co(BDC)(DABCO)1⁄2 (1), Cu(BDC)(DABCO)1⁄2 (2), Zn(BDC)(DABCO)1⁄2 (3)) were investigated at various temperatures of 77–333 K and pressures up to 10 MPa using a PCT automatic measuring system (Sievert-type apparatus). The results indicated that uptake to 4.11, 2.70, and 3.17 wt % of hydrogen can be stored on 1, 2, and 3, respectively, at 77 K. The amounts of hydrogen are adsorbed by all complexes at around room temperature (293 K) and high-pressures are much lower (<0.5 wt %). Adsorption isotherms at around room temperature show a linear uptake relationship; all of them follow the Henry’s law. By measuring nitrogen gas adsorption/desorption, all complexes exhibit approximately Type-I isotherms according to the IUPAC classification and possess BET surface areas in the range of 1165 (for 3) to 1595 m2 g−1 (for 1). Further, the thermal stability of all complexes is high, in the range of about 500 K (for 3) to 600 K (for 1). These complexes were synthesized and characterized by X-ray powder diffraction pattern, TG/DTA, FT-IR, surface area analysis, and hydrogen adsorption measurements.
Hydroxamate-type siderophores like desferrioxamine B (DFO) are the most common siderophores ubiquitously found in the environment. These naturally occurring chelating substances have the potential to enhance the solubility and mobility of actinides by forming soluble complexes. The unknown interaction between curium(III) and aqueous DFO species is the subject of this paper. The reactions between soluble species of curium(III) and DFO were studied at trace curium(III) concentrations (3×10−7 M) in 0.1 M NaClO4 using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Three Cm3+–DFO species, MpHqLr, could be identified from the luminescence spectra, CmH2DFO2+, CmHDFO+, and CmDFO, having emission maxima at 599, 611, and 614 nm, respectively. The large formation constants, logβ121=31.62±0.23, logβ111=25.70±0.17, and logβ101=16.80±0.40, compared to those of other chelating agents illustrate the unique complexation properties of hydroxamate-type siderophores. An indirect excitation mechanism for the curium(III) luminescence was observed in the presence of the DFO molecules.
A new preparation of 2-(hydroxymethyl)chromones was developed via the new regio-selective six-membered cyclization of 1-[o-(tert-butyldimethylsiloxy)phenyl]but-2-yn-1-ones by a three-step treatment with 1) diethylamine (activation of the γ-position), 2) KF-18-crown-6 (deprotection), and 3) silica-gel (cyclization). A naturally occurring chiral hydroxymethylfurochromone, (−)-umtatin, was synthesized starting from chiral (R)-(−)-2-isopropenyl-4,6-dimethoxy-2,3-dihydrobenzofuran, and the absolute structure was determined to R.
A series of intramolecular charge-transfer compounds comprised of 1-alkyl-3,3-dimethyl-2-methyleneindoline (In, donor, n = alkyl chain length; 1–8, 10, 14, 16, 18, 20, and 22) and 7,8,8-tricyanoquinodimethane (=2-(4′-cyanomethylene-2′,5′-cyclohexadienylidene)malononitrile (3CNQ), acceptor) moieties linked through a π-bond, In–3CNQ were prepared, and their structures are discussed. The melting points of the In–3CNQ solids decreased with increasing alkyl chain length until reaching a minimum point (95 °C) at n=18, and then began to gradually increase, indicating self-aggregation of the alkyl chains. The In–3CNQ derivatives with long alkyl chains (n≥6) produced supercooled liquids displaying conspicuous color changes after melting. Diverse molecular packing patterns were observed in the crystal structures. Most In–3CNQ derivatives formed face-to-face and/or side-by-side dimeric motifs to cancel net dipole moments. I20–3CNQ formed a two-dimensional bilayer structure by π-stacking and self-assembly of the alkyl chains. Two types of molecular conformation, which significantly affect the electronic structures, were observed to be dependent on the alkyl chain length. A parameter to evaluate the degree of intramolecular charge transfer, namely bond length ratio, was proposed; it exhibited good agreement with solvatochromic shifts and molecular orbital calculations.
In the presence of a nickel(0) catalyst, cyclobutanones reacted with diynes to produce bicyclic eight-membered ring ketones. Cyclobutanones acted as a C4 unit in the formal [4+2+2]-type annulation reaction, which proceeded through a ring-expansion of a spirocyclic seven-membered oxanickelacycle to a nine-membered nickelacycle via β-carbon elimination. A similar annulation reaction was also examined with enynes.
Photochemical reaction of 4-hydroxycoumarin with 3,4-dihydro-2H-pyran gave 4-hydroxy-3-(oxan-3-yl)coumarin whose formation was explained by considering a hydrogen shift and successive keto–enol isomerization from a head–tail biradical intermediate (A). The reaction mechanism was confirmed by molecular orbital analysis to be induced by intermolecular hydrogen bonding between the 4-OH and pyran oxygen at the transition state.
Alkylation, i.e., isopropylation, s-butylation, and t-butylation, of naphthalene (NP) was examined over one-dimensional twelve-membered (12-MR) zeolites: H-mordenite (MOR), SSZ-24 (AFI), SSZ-55 (ATS), and SSZ-42 (IFR) in order to elucidate how zeolite structure and alkylating agent play roles in the shape-selective catalysis. The β,β-selectivities (for β,β-dialkylnaphthalene (2,6- and 2,7-dialkylnaphthalenes, β,β-DAN)) and the 2,6-selectivities (for 2,6-DAN) were varied with the types of zeolite and of alkylating agent. MOR and AFI gave high β,β-selectivities by using alkylating agents, propene, 1-butene, and 2-methylpropene. However, the β,β-selectivities were changed over ATS and IFR at 250 °C: 40% for the isopropylation, 80% for the s-butylation, and almost 100% for the t-butylation. The 2,6-selectivities in the isopropylation were as high as 60% over MOR and 50% over AFI at 250 °C; however, they were less than 20% over ATS and IFR. The selectivities increased by using bulky alkylating agents over these one-dimensional zeolites: selective formation of 2,6-DAN occurred in the s-butylation and t-butylation. The different features among zeolites are explained by the zeolite channel and the bulkiness of alkylating agent. MOR and AFI with straight channels gave smaller reaction spaces than ATS and IFR with corrugated channels. Bulky alkylating agent also enhances the discrimination of the isomers, particularly between 2,6- and 2,7-DAN. The β,β- and 2,6-selectivities are synergetically governed by the zeolite channel and the bulkiness of alkylating agents.
Based on our past work on the successfully fabricating giant liposomes, it is necessary to systematically study the capsules’ permeability. In this paper, fluorescence recovery after photo-bleaching (FRAP) experiment was carried out by confocal laser scanning microscope (CLSM) in order to quantify the 6-carboxyfluorescein (6-CF) molecules passing through capsules’ wall. The results showed that the diffusion coefficient of the pure multilayered polyelectrolyte (PE) capsules was similar to the one of partly the lipid-coated PE capsules. The diffusion coefficient for completely coated PE capsules catalyzed selectively by phospholipase A2 is similar to that of partly coated PE capsules.
The cesium ion-exchange behavior of sodium difluorotetrasilicate (Na-TSM) and sodium taeniolite (Na-TAE) was investigated in the presence of alkaline-earth metal ions. When Na-TSM was exchanged beforehand with alkaline-earth metal ions, the amount of ion-exchanged Cs+ decreased slightly compared to untreated Na-TSM. In contrast, when Cs+-TSM was used very little ion exchange occurred with alkaline-earth metal ions. The interlayer spacing of Na-TSM contracted during the ion-exchange reaction with Cs+ because interlayer water molecules were displaced. For the alkaline-earth metal ion exchange, interlayer water molecules were retained. Thus, the Cs+ exchange occurred on Na-TSM that was exchanged beforehand with alkaline-earth metal ions. The Cs+ exchange was superior to that observed for alkaline-earth metal ions in the mixed solutions. In contrast, the ion-exchange reaction occurred under all conditions examined with Na-TAE. In particular, even Cs+ exchange was observed on Na-TAE that was exchanged beforehand with alkaline-earth metal ions. Furthermore, alkaline-earth metal ions exchange was observed on Cs+-TAE.