A tridentate ligand, pyphos (6-diphenylphosphino-2-pyridonato), was utilized to prepare tetrametal complexes since this ligand has unique coordinating sites comprised of three different elements, i.e., phosphorus, nitrogen, and oxygen, in almost linear fashion. By using pyphos ligand, linearly aligned tetrametal complexes of group 10 metals [Mo2M2(pyphos)4X2n] (M = Pt and Pd; n = 0, 1, and 2) were prepared, and for group 9 metals, [Mo2M2(pyphos)4(RNC)4X2n]2+ (M = Ir and Rh; n = 0 and 1). Fully metal-to-metal bonded complexes were obtained by reduction of MII to MI for group 10 metals and by oxidation of MI to MII for group 9 metals. Both reactions afforded complexes having unique M–Mo≡Mo–M skeletons, i.e., metalla-2-butyne. Structural and chemical properties were systematically investigated for M0 (M = Pt and Pd) and MI (M = Ir and Rh). Thus, oxidative reactions of Pd0 complexes [Mo2Pd2(pyphos)4] and IrI complexes [Mo2Ir2(pyphos)4(RNC)4]2+ with RX or X2 were studied and unique 1,4-addition reaction was demonstrated. Dichromium complexes analogous to dimolybdenum complexes were prepared and axial donation of PtMe2 moiety significantly elongated the Cr–Cr bond, due to the dative bonding interaction between CrII and PtII units.
Addition of two metals to the quadruply-bonded Mo2 core resulted in the formation of fully metal-to-metal bonded tetrametal fragments, M-Mo≡Mo-M, metalla-2-butyne, where the new triple bond at Mo-Mo moiety has a (π2δ) component.
The rational design of small-molecule chiral catalysts is an important subject in the development of practical organic syntheses. We have designed primary ammonium salt catalysts for enantioselective cycloaddition reactions with α-substituted acroleins such as α-(acyloxy)acroleins and α-diacylaminoacroleins. Ammonium salts of an aliphatic triamine derived from H–L-Phe–L-Leu–N(CH2CH2)2 successfully promote the Diels–Alder reaction of α-(acyloxy)acroleins and α-(N,N-diacylamino)acroleins, and the [2 + 2] cycloaddition reaction of α-(acyloxy)acroleins with high enantioselectivity. An ammonium salt of a C2-symmetric aromatic diamine, 1,1′-binaphthyl-2,2′-diamine, with a superacid is also an efficient catalyst and shows high activity and enantioselectivity for the Diels–Alder reaction of cyclic dienes with α-(acyloxy)acroleins.
This account describes rational design of primary ammonium salt catalysts for enantioselective cycloaddition reactions with α-(acyloxy)acroleins and α-diacylaminoacroleins. The flexible asymmetric environment created using the chiral primary ammonium salts would be essential for the high-level induction of the enantioselectivity.
A series of lanthanoid trigermanides of Pr, Nd, and Tm has been prepared by high-pressure (3–5 GPa) and high-temperature (1200 °C) reactions. TmGe3 crystallizes in an orthorhombic unit cell (Cmcm, No. 63) with a = 3.990(1) Å, b = 20.488(5) Å, c = 3.8794(8) Å, and V = 317.2(1) Å3. It is isotypic with the DyGe3 structure composed of Ge zig-zag chains and Tm situated between double square Ge-meshes. PrGe3.36 crystallizes in an orthorhombic unit cell (Cmmm, No. 65) with a = 4.062(4) Å, b = 21.43(3) Å, c = 4.212(6) Å, and V = 366.6(8) Å3. The structure is principally the same to the DyGe3 structure but contains an additional Ge site. The site is partially occupied, and is situated on the square mesh. Each Ge atom in the site is coordinated by five Ge atoms in the chain and in the mesh. NdGe3.25 is isotypic with PrGe3.36 and has lattice constants of a = 4.073(1) Å, b = 20.961(6) Å, c = 4.254(1) Å, and V = 363.2(2) Å3. The magnetic susceptibilities of PrGe3.36 and NdGe3.25 follow the Curie–Weiss law with the effective magnetic moments μeff = 3.60 and 3.57 μB, respectively, implying the oxidation states of Pr and Nd are 3+.
We have prepared three new binary germanides, PrGe3.36, NdGe3.25, and TmGe3 using high-pressure (≥3 GPa) and high-temperature (1200 °C) reactions. TmGe3 is isotypic with DyGe3 having a double square Ge-mesh structure. The Pr and Nd germanides contain additional Ge atoms in the interlayer region.
Structural specificity including dynamic behavior and stable conformations in the bulk phase of diethylmethylammonium trifluoromethanesulfonate [dema][TfOH], which is assumed to be a prominent ionic liquid electrolyte for non-humidified intermediate temperature fuel cells, have been investigated by 1H NMR, IR spectroscopic analyses, and molecular dynamics (MD) simulation. It is found that an N–H proton in [dema][TfOH] is an exchangeable mobile proton which can be substituted by D2O, and free rotation around the N–C bond in the ethyl side chain of the ammonium cation is retarded by ionic interactions between the cations and anions, therefore the methylene protons in the ethyl side chain are unisochronous. In addition, the rotational barrier of this N–C bond was observed to be 71 kJ mol−1, comparable to the barrier height of the amide N–C bond (which is well-known to have partial double bond character) from temperature-dependent NMR experiments by monitoring the peak-shape changes of methylene protons in the ethyl side chain of the ammonium cation. The bulk-phase structure of [dema][TfOH] was calculated by MD simulations on the basis of the OPLS-AA force field, and the evaluated structure was consistent with those of experimental results. Thus, IR spectrum frequency of the N–H proton, and the 1H NMR chemical shift values could be rationally assigned on the basis of the theoretically evaluated structures in the bulk phase.
A series of tetrakis(alkylthio)tetraselenafulvalene compounds (TTCn-TSeF, n = 1–15) were prepared by a one-step reaction between dialkyl disulfide and tetralithiated TSeF. Molecular properties (redox potentials and optical absorptions in solution) and solid-state properties (thermal behaviors, electric conductivities, and molecular and crystal structures for n = 1 and 10) were studied. TTCn-TSeF compounds are weak electron donor molecules and characterized by small on-site Coulomb repulsion. TTC1-TSeF has a high-dimensional conduction network owing to the presence of high-dimensional heteroatomic contacts, “Atomic-Wire Effect.” The π-moieties of TTC10-TSeF were fastened by the alkyl chains (“Fastener Effect”) to form π-columns and there are a variety of short heteroatomic contacts resulting in two-dimensional electronic structure. Electrical conductivity exhibited peculiar enhancement for n = 1 and 7 ≤ n ≤ 14 owing to the presence of high-dimensional conduction paths. These compounds may manifest high carrier mobility, and are good candidates for the field-effect transistor channel based on the advantageous features: low dark conductivity, low donor ability, on-site Coulomb repulsion energy, high-dimensional π-electron structure, and high solubility in organic solvents.
In this work the 50% effective inhibition concentration after 48 h (log(1/EC50)) of 39 substituted benzenes to the algae Scenedesmus obliquus was predicted by quantitative structure–toxicity relationship (QSTR) approaches. Descriptors which appeared in the best model are; highest occupied molecular orbital, molecular weight, lowest unoccupied molecular orbital, chemical potential, zero point energy, and hardness parameters. These descriptors were obtained from density functional theory (DFT) calculation at B3LYP level together with 6-31G* basis set. Results of this modeling provide the statistics of R = 0.91, F = 19, and SE = 0.30 for training set and R = 0.91, F = 18, and SE = 0.34 for test set. Also the average error and average absolute error in the prediction of log(1/EC50) are −0.00041 and 0.198 for training set and for prediction set are −0.056 and 0.217, respectively. Moreover, the credibility of the model was tested by cross-validation and Y-scrambling, the results of these tests indicated the reliability of the model. The results of this investigation show that it was possible to predict the molecular toxicity of organic compounds from their DFT-calculated molecular descriptors.
A competitive reaction theory in which flexibility is given to the orders of reaction has been established. As a result of an analysis based on this novel theory, the stoichiometric coefficients of the reactions between superoxide dismutase (SOD) and superoxide radicals (O2−•), between xanthine oxidase (XOD) and O2−•, and between 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and O2−• have all been estimated to be 1:1. Furthermore, the hitherto unknown second-order rate constant for the reaction between XOD and O2−• has been estimated to be 1.4 × 106 or ca. 8.0 × 105 M−1 s−1. It is considered that the presence of the SOD-like activity possessed by XOD itself is one of the causes of the puzzling fact reported that the amount of O2−• observed in a xanthine–XOD system is smaller than the anticipated amount by one order of magnitude. In addition, this SOD-like activity of XOD may cause researchers to underestimate the rate constant for the reaction between O2−• and a spin-trapping agent when the spontaneous dismutation of O2−• in the presence of XOD was used as a competitor against the spin-trapping reaction for O2−•.
Reaction of a series of dodecadentate ligands (H4L), 1,4,8,11-tetrakis(salicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane and its substituted derivatives, with copper(II) salts afforded dinuclear copper(II) complexes, [Cu2L], which were characterized by IR and UV–vis–NIR spectroscopy, and temperature dependence of magnetic susceptibilities (4.5–300 K). Single-crystal X-ray crystallography of these complexes revealed that each copper(II) ion is bound by the chelating of the two Schiff-base pendant arms outside the central tetraazacyclotetradecane ring forming a distorted square plane with an intramolecular Cu–Cu distance of 8.692(2)–8.949(2) Å. In accordance with the crystal structures, the magnetic interaction between the two copper(II) atoms is very weak. In the case of 1,4,8,11-tetrakis(3-methoxysalicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane (H4tmsaec), a hexanuclear complex with a crystallographic inversion center, [Cu6(O2CCH3)8(tmsaec)], was isolated. In the asymmetric unit, one copper atom is bonded to one pendant arm and two copper atoms are bound to another pendant arm with the methoxy group of the Schiff-base moiety with the Cu–Cu distance of 3.096(1) Å, giving a novel system containing monodentate, bidentate, and bridging acetate ions in the same molecule. Magnetic susceptibility data shows that a weak antiferromagnetic interaction is operating between the closest two copper atoms.
Artificial prosthetic groups tethering a polyamine moiety at the terminal of two peripheral heme–propionate side chains as a molecular interface were inserted into apocytochrome b562 to provide positively charged reconstituted hemoproteins, which exhibit a strong binding with double-stranded DNA.
N-Alkyl-4,4′-bipyridiniums [4,4′-bpy-N-(CH2)nOAr]+(Cl−) (n = 6 and 10, Ar = C6H3-3,5-t-Bu2, C6H3-3,5-(OMe)2, and C6H2-2,4,6-Me3), having the cationic bipyridinium group and a long hydrophobic alkyl chain, were prepared from the reaction of 4,4′-bipyridine with the corresponding alkyl chlorides. The amphiphilic compounds in water form micelles which encapsulate added pyrene in the hydrophobic core. Addition of α-cyclodextrin to the micellar solution converts a part of the aggregated amphiphilic molecules to their pseudorotaxane with α-cyclodextrin. Formation of the pseudorotaxanes is favored at lower temperature, as is observed by temperature dependent change of the absorption spectra.
The one-pot synthesis of 2-arylquinoline with arylamines, arylaldehyde, and 1,1-diethoxyethane were studied using a catalytic amount ytterbium triflate. Various 2-arylquinolines showed fluorescence properties and the fluorescence was quenched by introducing the nitro group into aryl moiety of 2-arylquinolines.
Crystal structures of two vancomycin complexes with phosphate and N-acetyl–D-Ala (AcDA) were determined. Each complex involves two crystallographically independent vancomycin molecules (V1 and V2) in the asymmetric unit, which form a usually observed back-to-back arranged vancomycin dimer V1–V2 with two disaccharide chains packed in a head-to-head manner, but only one of the two ligand-binding sites is occupied. Comparison of the published crystal structures of low-affinity (small in molecular size) ligand complexes of vancomycin with high-affinity (large) ligand complexes reveals that when the high-affinity ligand binds, three structural factors (hydrogen-bonding interactions between the two peptide-backbones and hydrophobic intra-dimer sugar–ring and ring (face)–ring (edge) interactions) work to enhance the stabilization of the back-to-back dimer-interface, an important factor that is believed to promote antibacterial activity. It has also been revealed, by examining the high-affinity ligand complexes (including N-acetyl–D-Ala–D-Ala), that sugar–ligand interaction could cause different affinities of the two halves of the dimer; this is a factor responsible for the failure of the ligand binding to V1 in the AcDA complex. Possible scenarios for the formation of vancomycin complexes with low-affinity as well as high-affinity ligands are presented.
In 50% (v/v) DMF– and DMA–H2O mixed solvents, salt effects on the solvolysis reaction rates of aliphatic halides and related compounds (RX) have been examined for further exploring. Compared with previous results obtained in other organic solvent systems, such as 50% (v/v) acetone–, 1,4-dioxane–, or sulfolane–H2O, no exceptional behavior was observed in the “pseudo” first-order rate constants (k/s−1) of all the typical SN1 and SN2 substrates by the addition of alkali metal and alkaline earth metal perchlorates or many kinds of tetraalkylammonium salts in 50% (v/v) DMF– and DMA–H2O mixed solvents. The detailed examination of Δlog(k/s−1)/Δ[LiClO4] for 1-adamantyl bromide vs. the contents of organic solvents (CH3CN, DMA, and DMSO) suggested that the observed different salt effects were caused by the different solvation abilities of the solvents toward the leaving-group anion as well as the metal cation. As a new highlight in the present paper, we were able to demonstrate a proportionality or correlation between the LiClO4 effects in the solvolysis rates and the carbocation stabilities expressed by the Gibbs free energy values (ΔGo) of RX in the gas phase. Based on the Raman spectra of DMA–H2O and DMA–D2O as well as DMF–D2O mixed solvents, we discuss the distortion of the bulk water structure.
Tetravalent hafnium ion conducting solid electrolytes with a NASICON-type structure, HfNbP3−xVxO12 and Hf1−y/4NbP3−yWyO12, were developed by partially replacing the P5+ site in a HfNb(PO4)3 solid with larger V5+ or W6+ ions. Although the Hf4+ ion conductivity monotonically increased with increasing V content in the HfNbP3−xVxO12 solids, the electronic conduction appeared to be due to the valence change of V5+. In contrast, the Hf1−y/4NbP3−yWyO12 series maintained a high ionic transference number, above 0.995 for single-phase NASICON-type samples (y ≤ 0.15). The optimum lattice volume for Hf4+ conduction was determined to be 1.482 nm3, which was obtained for samples with x = 0.1 or y = 0.05. The Hf395/400NbP2.95W0.05O12 solid, which contains the higher valence W6+ ion rather than the V5+ ion, showed the highest conductivity of 2.8 × 10−4 S cm−1 at 600 °C, approximately 2.5 times that of HfNb(PO4)3.
The synthesis, crystal structure, and conducting properties of two new BEDT-TTF charge-transfer salts containing tris(oxalato)germanate(IV) anions are described. (BEDT-TTF)5[Ge(C2O4)3]2 (1) crystallizes in the monoclinic space group C2, a = 23.0994(11) Å, b = 11.0200(5) Å, c = 19.5455(9) Å, β = 117.628(4)°, V = 4408.1(4) Å3, T = 120(2) K, Z = 2, R1 = 0.0659 [F2 > 2σ(F2)]. Compound 2 (BEDT-TTF)7[(Ge(C2O4)3]2·0.87CH2Cl2·0.09H2O crystallizes in the monoclinic space group C2/c, a = 37.081(2) Å, b = 11.5449(7) Å, c = 28.6415(13) Å, β = 93.7767(9)°, V = 12234.8(12) Å3, T = 293(2) K, Z = 4, R1 = 0.0834 [F2 > 2σ(F2)]. Electrical resistivity measurements show that 1 and 2 are both semiconductors.
A bifunctional siloxane cage, where double four-membered ring (D4R) silicate was capped with alkoxyvinylsilyl groups, was synthesized as a novel building block for the formation of inorganic–organic microporous solids in order to show its usefulness for synthesizing silica-based nanomaterials with unique structures and properties. The nanobuilding blocks were connected to each other either by hydrolysis and condensation of alkoxysilyl groups to form Si–O–Si linkages or by hydrosilylation of vinyl groups with hydrogen-terminated D4R (H8Si8O12), which was used as a linking agent, to form Si–CH2CH2–Si linkages. Xerogel obtained by hydrosilylation showed a significant increase in the surface area upon removal of alkoxy groups by post treatment. The molecular design of bifunctionally-silylated D4R units provides a new approach to the formation of microporous networks with uniform distribution of reactive groups that allow post-modification.