Showing papers in "Chemistry-an Asian Journal in 2006"
TL;DR: It was found that the crystal faces of silver nanoparticles play an essential role in determining the catalytic oxidation properties.
Abstract: Metal nanoparticles with different shapes have different crystallographic faces. It is therefore of interest to study the effect of the shape of metal nanoparticles on their catalytic activity in various organic and inorganic reactions. Truncated triangular silver nanoplates with well-defined planes were synthesized by a simple solvothermal approach. The activity of these truncated triangular silver nanoparticles was compared with that of cubic and near-spherical silver nanoparticles in the oxidation of styrene in colloidal solution. It was found that the crystal faces of silver nanoparticles play an essential role in determining the catalytic oxidation properties. The silver nanocubes had the {100} crystal faces as the basal plane, whereas truncated triangular nanoplates and near-spherical nanoparticles predominantly exposed the most-stable {111} crystal faces. As a result, the rate of the reaction over the nanocubes was more than 14 times higher than that on nanoplates and four times higher than that on near-spherical nanoparticles.
353 citations
TL;DR: This Focus Review aims to shed light on how effectively multiphase organic reactions can be conducted with microchannel reactors by providing examples of recent remarkable studies, which have been grouped on the basis of the phases involved.
Abstract: "Miniaturization" is one of the most important aspects in today's technology. Organic chemistry is no exception. The search for highly effective, controllable, environmentally friendly methods for preparing products is of prime importance. The development of multiphase organic reactions in microchannel reactors has gained significant importance in recent years to allow novel reactivity, and has led to many fruitful results that are not attainable in conventional reactors. This Focus Review aims to shed light on how effectively multiphase organic reactions can be conducted with microchannel reactors by providing examples of recent remarkable studies, which have been grouped on the basis of the phases involved.
221 citations
TL;DR: Recent advances in the applications of this class of shape-persistent oligomers in the promoted synthesis of macrocycles, design of new nonring receptors, supramolecular self-assembly, molecular encapsulation, and reaction acceleration, are highlighted in this Focus Review.
Abstract: With an increasing number of folding and helical structures available, chemists have begun to pay greater attention to the functions of this family of structurally unique oligomers. Hydrogen-bonding-mediated aromatic oligoamide foldamers have the features of good structural predictability, synthetic facility, and structural modification, which make them very promising as scaffolds or platforms for supramolecular chemistry. Recent advances in the applications of this class of shape-persistent oligomers in the promoted synthesis of macrocycles, design of new nonring receptors, supramolecular self-assembly, molecular encapsulation, and reaction acceleration, are highlighted in this Focus Review.
167 citations
TL;DR: Unlike the well-known diphosphine-1,2-diamine-Ru(II)-catalyzed hydrogenation that proceeds in a basic alcohol, this reaction takes place under slightly acidic conditions, creating new opportunities for asymmetric hydrogenation.
Abstract: Chiral arene-N-tosylethylenediamine-Ru(II) complexes can be made to effect both asymmetric transfer hydrogenation and asymmetric hydrogenation of simple ketones through a slight functional modification and by switching reaction conditions. [Ru(OSO2CF3){(S,S)-TsNCH(C6H5)CH(C6H5)NH2}(eta(6)-p-cymene)] catalyzes the asymmetric hydrogenation of acetophenone in methanol to afford (S)-1-phenylethanol with 96% ee in 100% yield. Like the transfer hydrogenation catalyzed by similar Ru catalysts with basic 2-propanol or a formic acid/triethylamine mixture, this hydrogenation proceeds through a metal-ligand bifunctional mechanism. The reduction of the C=O function occurs via an intermediary 18e RuH species in its outer coordination sphere without metal-substrate interaction. The high catalytic efficiency relies on the facile ionization of the Ru triflate complex in methanol. The turnover rate is dependent on hydrogen pressure and medium acidity and basicity. The RuCl analogue can be used as a precatalyst, albeit less effectively. Unlike the well-known diphosphine-1,2-diamine-Ru(II)-catalyzed hydrogenation that proceeds in a basic alcohol, this reaction takes place under slightly acidic conditions, creating new opportunities for asymmetric hydrogenation.
147 citations
TL;DR: Four novel borondipyrromethene and -diindomethene dyes with one or two (dimethylamino)styryl extensions at the chromophore were synthesized and spectroscopically investigated and showed remarkable switching of lipophilicity by protonation.
Abstract: Four novel borondipyrromethene (BDP) and -diindomethene (BDI) dyes with one or two (dimethylamino)styryl extensions at the chromophore were synthesized and spectroscopically investigated. An X-ray crystal structure shows that the extended auxochrome is virtually planar. All dyes thus display intense red/near infrared (NIR) absorption and emission. The (dimethylamino)styryl group induces a charge-transfer character that entails bright solvatochromic fluorescence, which is only quenched with increasing solvent polarity according to the energy-gap law. The dye with an additional dimethylanilino group at the meso position of BDP shows a remarkable switching of lipophilicity by protonation. Two dyes with an 8-hydroxyquinoline ligand at the meso position display quenched emission in the presence of Hg2+ or Al3+ owing to electron transfer from the excited BDP to the complexed receptor. The BDI dye presents a pH indicator with bright fluorescence and extremely low fluorescence anisotropy.
140 citations
TL;DR: Mechanistic studies indicate a monohydride reaction pathway for the homogeneous iron catalyst and high conversion and excellent chemoselectivity are obtained.
Abstract: Iron complexes generated in situ catalyze homogeneously the transfer hydrogenation of aliphatic and aromatic ketones by utilizing 2-propanol as a hydrogen donor in the presence of base. The influence of different reaction parameters on the catalytic activity is investigated in detail by applying a three-component catalyst system composed of an iron salt, 2,2':6',2''-terpyridine, and PPh3. The scope and limitations of the described catalyst is shown in the reduction of 11 different ketones. In most cases, high conversion and excellent chemoselectivity are obtained. Mechanistic studies indicate a monohydride reaction pathway for the homogeneous iron catalyst.
127 citations
TL;DR: This Focus Review describes recent progress in polymerization in the nanochannels of PCPs and demonstrates why this polymerization system is so attractive and promising, from the viewpoints of three essential polymerization processes in PCPs.
Abstract: Inspired by elegant polymerizations in biological systems, polymer synthesis in confined artificial nanospaces is a key challenge in the control of polymer structures and the design of well-defined nanostructures. In this regard, porous coordination polymers (PCPs) have a wide range of advantages, such as regular channel structures, controllable pore size, dynamic and flexible pores, and unique surface potentials and functionality, which can be utilized for precisely controlled polymerization and polymer arrangement. This Focus Review describes recent progress in polymerization in the nanochannels of PCPs and demonstrates why this polymerization system is so attractive and promising, from the viewpoints of three essential polymerization processes in PCPs, that is, monomer arrangement, polymerization methods, and control of polymer structure.
120 citations
TL;DR: This Focus Review highlights the results of experimental and theoretical studies that can contribute to the exploitation of the powerful nature of Pd(II) catalysis.
Abstract: Palladium(II) catalysis allows various aerobic oxidation reactions, but the mechanism of the regeneration of the active catalytic species remains, in many cases, undetermined. In recent years, considerable effort has been directed toward the comprehension of the reaction of dioxygen with hydridopalladium(II) and palladium(0) complexes. This Focus Review highlights the results of these experimental and theoretical studies that can contribute to the exploitation of the powerful nature of Pd(II) catalysis.
113 citations
TL;DR: The pyridine-appended nonchelating bidentate ligands 1 and 2 were complexed with a naked Pd(II) ion for the construction of molecular cage compounds to produce novel structures that are combinations of the M(n)L( n) type frameworks.
Abstract: The pyridine-appended nonchelating bidentate ligands 1,4-bis(3-pyridyl)benzene (1) and 4,4'-bis(3-pyridyl) biphenyl (2) were complexed with a naked Pd(II) ion for the construction of molecular cage compounds. Prior to these experiments, the complexation of the ligands with cis-[Pd(en)(NO3)2] was also examined, because self-assemblies from the cis-protected Pd(II) ion were expected to be simple motifs that constitute the assemblies from naked Pd(II) ion. The structures of the self-assembled compounds resulting from 1 and [Pd(en)(NO3)2] depended on the solvent employed. In aqueous solution, an M2L2 trenchlike compound was obtained. In dimethyl sulfoxide, however, a mixture of the M2L2 trench and an M3L3 macrocycle was found in equilibrium, the dynamic nature of which was confirmed by the concentration-dependent nature of the species. At higher concentration, an M4L4 macrocycle was mostly observed. The complexation of 1 with naked Pd(II) ions was expected to produce novel structures that are combinations of the M(n)L(n) type frameworks. A peculiar tetrahedral M4L8 assembly was obtained quantitatively from 1 and Pd(NO3)2, rather than the smallest possible M3L6 double-walled triangle. Interestingly, the use of Pd(CF3SO3)2 resulted in the sole formation of the latter structure. Thus, the anion is important as a template in the formation of these assemblies. Ligand 2, which contains an extra p-phenylene unit compared to 1, behaved in a similar manner when treated with [Pd(en)(NO3)2], but showed subtle differences with naked Pd(II) ions. With Pd(NO3)2, 2 gave mostly a tetrahedron along with a double-walled triangle. With Pd(CF3SO3)2, this longer ligand formed a double-walled triangle with a negligible amount of tetrahedra. A single discrete assembly of a perfect tetrahedron was obtained from 2 and Pd(II) ions by choosing p-tosylate as a counterion.
109 citations
TL;DR: A series of aminofullerenes that share a common structural motif have been synthesized and subjected to a systematic investigation of structure activity relationship regarding their ability for transient transfection and cytotoxicity, leading to the best reagent being identified, a tetrapiperidinofullerene that can be synthesized in two steps from fullerene, piperazine, and molecular oxygen.
Abstract: A series of aminofullerenes that share a common structural motif have been synthesized and subjected to a systematic investigation of structure activity relationship regarding their ability for transient transfection and cytotoxicity. DNA-binding tests indicated that any water-soluble fullerene-bearing amino group would bind to double-stranded DNA. For these molecules to be effective transfection reagents, however, they require additional structural features. First, the molecule must be capable of producing submicrometer-sized fullerene/DNA aggregates that can be internalized into mammalian cells through endocytosis. Second, the molecule must be capable of releasing DNA as the aggregates are transferred into the cytoplasm. This can be achieved in at least two ways: by loss of the DNA-binding amino groups from the fullerene core, and by transformation of the amino groups to neutral groups such as amides. The screening experiments led us to identify the best reagent, a tetrapiperidinofullerene, that can be synthesized in two steps from fullerene, piperazine, and molecular oxygen, and that is more efficient at transfection than a commonly used lipid-based transfection reagent.
106 citations
TL;DR: A 36-step synthesis was carried out in automated synthesizers to provide a synthetic key intermediate of taxol using a microwave-assisted alkylation reaction to construct the ABC ring system from an AC precursor.
Abstract: A 36-step synthesis was carried out in automated synthesizers to provide a synthetic key intermediate of taxol. A key step involved a microwave-assisted alkylation reaction to construct the ABC ring system from an AC precursor. Subsequent formation of the D ring afforded baccatin III, a well-known precursor of taxol.
TL;DR: The utility of these chemosensors are demonstrated in real-time monitoring of two important biological processes involving nucleoside PP conversion: the apyrase-catalyzed hydrolysis of nucleosid PPs and the glycosyl transfer catalyzed by beta-1,4-galactosyltransferase.
Abstract: Nucleoside pyrophosphate (nucleoside PP) derivatives are widespread in living cells and play pivotal roles in various biological events. We report novel fluorescence chemosensors for nucleoside PPs that make use of coordination chemistry. The chemosensors, which contain two Zn(II)-dipicolylamine units, bind strongly to nucleoside PPs (K(app)>10(6) M(-1)) in aqueous solution and sense them by a dual-emission change. Detailed fluorescence and UV/Vis spectral studies revealed that the emission changes of the chemosensors upon binding to nucleoside PPs can be ascribed to the loss of coordination between Zn(II) and the acridine fluorophore. This is a unique sensing system based on the anion-induced rearrangement of the coordination. Furthermore, we demonstrated the utility of these chemosensors in real-time monitoring of two important biological processes involving nucleoside PP conversion: the apyrase-catalyzed hydrolysis of nucleoside PPs and the glycosyl transfer catalyzed by beta-1,4-galactosyltransferase.
TL;DR: A new method involves the activation of alkenyl and aryl boronates by a catalytic amount of the Cu(I)F-DTBM-segphos complex through transmetalation, generating novel alkenYL and aRYl copper species.
Abstract: A new method for the catalytic enantioselective alkenylation and arylation of aldehydes involves the activation of alkenyl and aryl boronates by a catalytic amount of the Cu(I)F-DTBM-segphos complex through transmetalation, generating novel alkenyl and aryl copper species. These reagents act as the actual nucleophile. A range of aldehydes can be converted into optically active secondary allyl alcohols or diaryl methanols with excellent enantioselectivity. The appropriate choice of additives, depending on the substrate, is critical to ensure high yields of products. These additives possibly modulate the catalyst turnover step from copper alkoxide intermediates generated by the addition of organocopper reagents to aldehydes.
TL;DR: This paper describes a group of around 25 phenylpropiolic acids in which the catemer is the default packing mode and shows that a supporting interaction, in this case a C-H...O hydrogen bond, is the essential condition for the formation of any carboxylic acid catemer.
Abstract: The catemer is an infinite one-dimensional pattern formed by the carboxylic acid group in crystals, and is constituted with O-H...O hydrogen bonds. The catemer is uncommon and may be contrasted with the ubiquitous carboxylic acid dimer, the favored mode of association of this functional group. Both catemers and dimers, however, have two O-H...O hydrogen bonds for each carboxy group, so the reasons for the rarity of the catemer must lie elsewhere. In this paper, we describe a group of around 25 phenylpropiolic acids in which the catemer is the default packing mode. Exceptionally, the particular catemer that is found in this family is of the very rare syn,anti variety. We show that a necessary ingredient in catemer formation is a supportive C-H...O hydrogen bond from a proximal C-H group, which is located on the phenyl ring, ortho to the ethynyl group, and suitably activated by electron withdrawing substituents. When steric factors become noteworthy, alternative patterns are adopted, such as the syn,syn catemer and, in one case, a rare cisoid dimer. When electron-donating groups, either through inductive effect such as methyl or through resonance such as halogens, are present on the phenyl ring, the dimer is formed in all but one case. Polymorphism seems not to be an issue in these carboxylic acids in that no compound would generally crystallize as both a dimer and a catemer. It may be concluded that a supporting interaction, in this case a C-H...O hydrogen bond, is the essential condition for the formation of any carboxylic acid catemer. Catemers are so rare because it is difficult to set up this type of supporting interaction in most carboxylic acids.
TL;DR: The proposed reaction mechanism is based on the kinetics, solvent effect, and redox properties of flavin catalysts and gives the corresponding oxidation products highly efficiently and selectively along with water and molecular nitrogen, which are environmentally benign by-products.
Abstract: Flavin-catalyzed green oxidation of heteroatom compounds such as sulfides and amines with molecular oxygen and even air in the presence of hydrazine monohydrate in a fluorous solvent such as 2,2,2-trifluoroethanol at room temperature gives the corresponding oxidation products highly efficiently and selectively along with water and molecular nitrogen, which are environmentally benign by-products. The proposed reaction mechanism is based on the kinetics, solvent effect, and redox properties of flavin catalysts.
TL;DR: New donor-acceptor materials based on a polynorbornene framework to which both phthalocyanine and C60 electroactive pendant units are randomly attached have been prepared in good yield by ring-opening-metathesis polymerization (ROMP) in the presence of a Grubbs catalyst.
Abstract: New donor-acceptor materi- als based on a polynorbornene frame- work to which both phthalocyanine and C60 electroactive pendant units are randomly attached have been prepared in good yield by ring-opening-metathe- sis polymerization (ROMP) in the presence of a Grubbs catalyst. A struc- turally related phthalocyanine homopo- lymer was also synthesized for compar- ison. A remarkable fluorescence quenching was observed in the homo- polymer and accounts for Pc···Pc inter- actions along the polymeric framework. As expected, the fluorescence quench- ing increases in the case of the polynor- bornenes containing both Pc and C60 units owing to photoinduced electron transfer, which was further confirmed by transient absorption spectroscopy. Finally, preliminary solar cell devices made of one of the copolymers were constructed.
TL;DR: The efficient anion binding of NCPs was attributed to strong hydrogen bonding at the highly polarized NH moieties owing to the electron-deficient C6F5 groups at meso positions as well as the ideally oriented dipole moments and large molecular polarizability.
Abstract: The halide-binding properties of N-confused porphyrin (NCP, 1) and doubly N-confused porphyrins (trans-N2CP (2), cis-N2CP (3)) were examined in CH2Cl2. In the free-base forms, cis-N2CP (3) showed the highest affinity to each anion (Cl-, Br-, I-) with association constants Ka = 7.8x10(3), 1.9x10(3), and 5.8x10(2) M(-1), respectively. As metal complexes, on the other hand, trans-N2CP 2-Cu exhibited the highest affinity to Cl-, Br-, and I- with Ka = 9.0x10(4), 2.7x10(4), and 1.9x10(3) M(-1), respectively. The corresponding Ka values for cis-N2CP 3-Cu and NCP 1-Cu were about 1/10 and 1/2, respectively, of those of 2-Cu. With the help of density functional theory (DFT) calculations and complementary affinity measurements of a series of trisubstituted N-confused porphyrins, the efficient anion binding of NCPs was attributed to strong hydrogen bonding at the highly polarized NH moieties owing to the electron-deficient C6F5 groups at meso positions as well as the ideally oriented dipole moments and large molecular polarizability. The orientation and magnitude of the dipole moments in NCPs were suggested to be important factors in the differentiation of the affinity for anions.
TL;DR: Some phosphaalkene-gold(I) complexes showed catalytic activity for 1,6-enyne cycloisomerization without cocatalysts such as silver hexafluoroantimonate.
Abstract: Mes*-substituted 2,3-dimethyl-1,4-diphosphabuta-1,3-diene, 1,2-diphenyl-3,4-diphosphinidenecyclobutene, 2,2-bis(methylsulfanyl)-1-phosphaethene, and 3,3-diphenyl-1,3-diphosphapropenes (Mes* = 2,4,6-tri-tert-butylphenyl) were employed as P ligands of gold(I) complexes. The (E,E)-2,3-dimethyl-1,4-diphosphabuta-1,3-diene functioned as a P2 ligand for digold(I) complex formation with or without intramolecular Au-Au contact, which depends on the conformation of the 1,3-diphosphabuta-1,3-diene. The 1,2-diphenyl-3,4-diphosphinidenecyclobutene, which has a rigid s-cis P=C-C=P skeleton, afforded the corresponding digold(I) complexes with a slight distortion of the planar diphosphinidenecyclobutene framework and intramolecular Au-Au contact. In the case of the 2,2-bis(methylsulfanyl)-1-phosphaethene, only the phosphorus atom coordinated to gold, and the sulfur atom showed almost no intra- or intermolecular coordination to gold. On the other hand, the 1,3-diphosphapropenes behaved as nonequivalent P2 ligands to afford the corresponding mono- and digold(I) complexes. Some phosphaalkene-gold(I) complexes showed catalytic activity for 1,6-enyne cycloisomerization without cocatalysts such as silver hexafluoroantimonate.
TL;DR: By using a chiral molecular motor as a dopant in a cholesteric liquid-crystalline film, fully reversible control of the reflection color of this film across the entire visible spectrum is possible.
Abstract: By using a chiral molecular motor as a dopant in a cholesteric liquid- crystalline film, fully reversible control of the reflection color of this film across the entire visible spectrum is possible. The large difference in helical twisting power between the two isomeric forms of the motor allows efficient light- and heat-induced switching of the helicity of the cholesteric liquid-crystal superstruc- ture.
TL;DR: This photo-cross-linked microarray format was found to be useful not merely for ligand screening but also to study the structure-activity relationship, that is, the relationship between the structural motif (or pharmacophore) found in small molecules and its binding affinity toward a protein, by taking advantage of the nonselective nature of the photo-Cross-linking process.
Abstract: We have developed a unique photo-cross-linking approach for immobilizing a variety of small molecules in a functional-group-independent manner. Our approach depends on the reactivity of the carbene species generated from trifluoromethylaryldiazirine upon UV irradiation. It was demonstrated in model experiments that the photogenerated carbenes were able to react with every small molecule tested, and they produced multiple conjugates in most cases. It was also found in on-array immobilization experiments that various small molecules were immobilized, and the immobilized small molecules retained their ability to interact with their binding proteins. With this approach, photo-cross-linked microarrays of about 2000 natural products and drugs were constructed. This photo-cross-linked microarray format was found to be useful not merely for ligand screening but also to study the structure-activity relationship, that is, the relationship between the structural motif (or pharmacophore) found in small molecules and its binding affinity toward a protein, by taking advantage of the nonselective nature of the photo-cross-linking process.
TL;DR: In the 1,4-addition of phenylboronic acid to alpha,beta-unsaturated ketones, [Rh(OH)(cod)]2 has a much higher catalytic activity than [Rh (OH)(binap)]2 (cod = 1,5-cyclooctadiene, binap = 2,2'-bis(diphenylphosphanyl)-1,1'-binaphthyl) as discussed by the authors.
Abstract: In the 1,4-addition of phenylboronic acid to alpha,beta-unsaturated ketones, [Rh(OH)(cod)]2 has a much higher catalytic activity than [Rh(OH)(binap)]2 (cod = 1,5-cyclooctadiene, binap = 2,2'-bis(diphenylphosphanyl)-1,1'-binaphthyl). Kinetic studies revealed that the rate-determining transmetalation step in the catalytic cycle has a large rate constant when [Rh(OH)(cod)]2 is used.
TL;DR: A study involving the relatively rare combination of heterogeneous catalysis conducted under microwave conditions is presented, finding that carbon-carbon bond formation can be quickly effected with aryl chloride partners by using a base metal adsorbed in the pores of activated charcoal.
Abstract: A study involving the relatively rare combination of heterogeneous catalysis conducted under microwave conditions is presented. Carbon-carbon bond formation, including Negishi and Suzuki couplings, can be quickly effected with aryl chloride partners by using a base metal (nickel) adsorbed in the pores of activated charcoal. Aminations were also studied, along with cross-couplings of vinyl alanes with benzylic chlorides as a means to stereodefined allylated aromatics. Reaction times for all these processes are typically reduced from several hours to minutes in a microwave reactor.
TL;DR: The structures and electronic properties of the hybrid materials based on high-resolution transmission electron microscopy, electron energy-loss spectroscopy, X-ray and electron diffraction, scanning tunneling microscopy (STM), and field-effect transistor transport measurements are discussed.
Abstract: This review article focuses on the structures and properties of novel hybrid nanocarbon materials, which are created by incorporating atoms and molecules into the hollow spaces of carbon nanotubes (CNTs); thus they are called nanopeapods. After dealing with synthesis procedures, we discuss the structures and electronic properties of the hybrid materials based on high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS), X-ray and electron diffraction, scanning tunneling microscopy (STM), and field-effect transistor transport measurements. Utilization of the low-dimensional nanosized spaces of CNTs to produce novel low-dimensional nanocluster, nanowire, and nanotube materials is also discussed.
TL;DR: This paper has completed its second total synthesis of tetrodotoxin from a synthetic intermediate for 11-deoxytetrodot toxin, which was previously prepared from levoglucosenone as a chiral starting material in this laboratory.
Abstract: Tetrodotoxin, a toxic principal of puffer-fish poisoning, is one of the most famous marine natural products, and has been known as a formidable synthetic target in synthesis owing to its multifunctional structure and unusual chemical properties From the perspective of supplying tetrodotoxin derivatives such as labeled molecules for biochemical research, we have completed our second total synthesis of tetrodotoxin from a synthetic intermediate for 11-deoxytetrodotoxin, which was previously prepared from levoglucosenone as a chiral starting material in this laboratory This paper discloses the details of the total synthesis with special reference to significant influences on the neighboring functional groups found in the installation of guanidine The established route should allow us to prepare the tetrodotoxin-related compounds required for biochemical studies
TL;DR: The synthesis of four new oxo-centered Fe clusters (1 a-c, 2) of the form [Fe(III)3(mu3-O)(CH2=CHCOO)6] with acrylate as the bridging ligand gives rise to potentially intrinsically chiral oxe-centered {M3} trimers that show a tendency to spontaneously resolve upon crystallization.
Abstract: The synthesis of four new oxo-centered Fe clusters (1 a-c, 2) of the form [Fe(III)3(mu3-O)(CH2=CHCOO)6] with acrylate as the bridging ligand gives rise to potentially intrinsically chiral oxo-centered {M3} trimers that show a tendency to spontaneously resolve upon crystallization. For instance, 1 a, [Fe(III)3(mu3-O)(CH2=CHCOO)6-(H2O)3]+, crystallizes in the chiral space group P3(1) as a chloride salt. Crystallization of 1 b, [Fe3(mu3-O)(C2H3CO2)6(H2O)3]NO3 x 4.5 H2O, from aqueous solution followed by recrystallization from acetonitrile also gives rise to spontaneous resolution to yield the homochiral salt [Fe3(mu3-O)(C2H3CO2)6-(H2O)3]NO3 x CH3CN of 1 c (space group P2(1)2(1)2(1)). Furthermore, the reaction of 1 a with hexamolybdate in acetonitrile gives the helical coordination polymer {[(Fe3(mu3-O)L6(H2O))(MoO4)-(Fe3(mu3-O)L6(H2O)2)] x 2 CH3CN x H2O}infinity 2 (L: H2C=CHCOO), which crystallizes in the space group P2(1). The nature of the ligand geometry allows the formation of atropisomers in both the discrete (1 a-c) and linked {Fe3} clusters (2), which is described along with a magnetic analysis of 1 a and 2.
TL;DR: It is proposed that Nd ions doped on TiO2 nanorods to some extent enhance the injection of excited electrons and decrease the recombination rate of the injected electrons.
Abstract: Monodispersed Nd-doped TiO2 nanorods (20 nm x 2 nm) were synthesized by solvothermal methods and characterized by TEM, XRD, and EDS. Application of the nanorods for modifying conventional photoanodes in dye-sensitized solar cells (DSSCs) was investigated. Data show that, after modification, an enhancement of the incident-photon-to-current conversion efficiency (IPCE) in the whole range of visible light was observed and an increase of 33.3% for overall conversion efficiency was achieved. Our mechanistic proposal is that Nd ions doped on TiO2 nanorods to some extent enhance the injection of excited electrons and decrease the recombination rate of the injected electrons.
TL;DR: A novel and robust binaphthyl-based amino acid catalyst was designed and successfully applied to the direct asymmetric aldol reaction, which leads to higher yields and selectivities than the well-known proline catalyst.
Abstract: A novel and robust binaphthyl-based amino acid was designed and successfully applied to the direct asymmetric aldol reaction. In some cases, this catalyst leads to higher yields and selectivities than the well-known proline catalyst. For instance, the direct asymmetric aldol reaction of acetone with 4-nitrobenzaldehyde in the presence of the binaphthyl-based amino acid catalyst proceeded smoothly to give the aldol adduct in 82% yield with 95% ee. This catalyst was also found to catalyze effectively the reactions of cyclic or unsymmetrical ketones to give the corresponding aldol adducts with excellent diastereo- and enantioselectivities.
TL;DR: A protocol that adopts aqueous hydrogen peroxide as a terminal oxidant and [(Me3tacn)(CF3 CO2)2Ru(III)(OH2)]CF3CO2 (1) as a catalyst for oxidation of alkenes, alkynes, and alcohols to organic acids in over 80% yield is presented.
Abstract: A protocol that adopts aqueous hydrogen peroxide as a terminal oxidant and [(Me3tacn)(CF3CO2)2Ru(III)(OH2)]CF3CO2 (1; Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) as a catalyst for oxidation of alkenes, alkynes, and alcohols to organic acids in over 80% yield is presented. For the oxidation of cyclohexene to adipic acid, the loading of 1 can be lowered to 0.1 mol %. On the one-mole scale, the oxidation of cyclohexene, cyclooctene, and 1-octanol with 1 mol % of 1 produced adipic acid (124 g, 85% yield), suberic acid (158 g, 91% yield), and 1-octanoic acid (129 g, 90% yield), respectively. The oxidative C=C bond-cleavage reaction proceeded through the formation of cis- and trans-diol intermediates, which were further oxidized to carboxylic acids via C-C bond cleavage.
TL;DR: An Fe3O4/C nanocomposite was synthesized in a microwave-assisted hydrothermal reaction and exhibits superparamagnetic behavior, and its functional groups were inherited from the starting materials.
Abstract: An Fe3O4/C nanocomposite was synthesized in a microwave-assisted hydrothermal reaction. This green wet-chemical approach is simple, low-cost, and ideal for large-scale production. The resulting composite material was characterized by transmission electron microscopy, powder X-ray diffraction, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller analysis, X-ray photoelectron spectroscopy, vibrating sample magnetometry, and UV/Vis spectroscopy. The product possesses porous structures and exhibits superparamagnetic behavior. Interestingly, its functional groups were inherited from the starting materials. This hydrophilic and biocompatible nanocomposite may find applications in catalysis, separation, adsorption, and bionanotechnology.
TL;DR: The investigation of the biological properties of new derivatives of (+)-panepophenanthrin enabled us to develop new cell-permeable E1 inhibitors, RKTS-80, -81, and -82.
Abstract: The asymmetric total synthesis of (+)-panepophenanthrin, an inhibitor of ubiquitin-activating enzyme (E1), has been accomplished using catalytic asymmetric alpha aminoxylation of 1,4-cyclohexanedione monoethylene ketal as a key step, followed by several diastereoselective reactions The biomimetic Diels-Alder reaction of a monomer precursor was found to proceed efficiently in water The investigation of the biological properties of new derivatives of (+)-panepophenanthrin enabled us to develop new cell-permeable E1 inhibitors, RKTS-80, -81, and -82