Chiral (R,R)-tartaric acid and NaBr-doubly modified Raney nickel (TA-MRNi) is a promising heterogeneous catalyst for enantioselective hydrogenation of prochiral β-keto esters. To obtain deeper insights into the factors ruling the enantioselectivity, enantiodifferentiating hydrogenation of substituted ketones was studied over TA-MRNi and NaBr-modified RNi by use of combined individual-competitive hydrogenation techniques. Relative equilibrium adsorption constants of the substrates were estimated to evaluate their relative interaction strength with adsorbed tartaric acid moiety. DFT calculations were also performed to estimate the interaction energy through hydrogen bonding, providing clear support to the kinetic analysis and surface model. It is concluded with the enantioselective hydrogenation of ketones over TA-MRNi that the enantioselectivity increases as the substrate-modifier interaction strength increases: methyl acetoacetate (MAA) > acetylacetone (AA) ≈ 4-hydroxy-2-butanone (HB) > 2-octanone (2O).
Platinum (Pt) is known as one of the most promising electrocatalysts, and nanostructured Pt materials have enhanced its activity due to their abundant catalytically active sites derived from their high surface area. Herein, we synthesize fascinating dendritic Pt nanoparticles (DPNs) by a soft-templating method using hexadecyltrimethylammonium chloride (CTAC) as a pore-forming agent. The dissolved negatively charged Pt precursor (PtCl42−) effectively interact with the surfactant. The particle size of the obtained DPNs is around 20 nm, and the pore walls are composed of Pt nanocrystals. The obtained DPNs show good electrocatalytic activity towards methanol oxidation reaction (MOR) compared to commercial Pt black (PtB), and its stability is also higher than that of PtB.
Lipid-membrane-incorporated symmetrical and unsymmetrical porphyrins were prepared with relatively high concentrations via exchange from cyclodextrins to liposomes. We determined the location of these porphyrins in the lipid membranes from chemical shift changes of the lipid signals in the 1H NMR spectra. Symmetrical tetraphenyl porphyrin accumulates in the hydrophobic core of the lipid membranes. In contrast, several unsymmetrical porphyrins with more polar group(s), such as pyridine and pyridinium moieties, are located close to the liposome surface.
DNA is a very long polymeric molecule that governs the genetic processes in cells, and its structural regulation is critical to their functions. In addition, several uses of DNA as a novel material have also been proposed in nanomaterial science and engineering. In this account, we introduce our efforts to understand the regulatory strategies of chromatins (a very long DNA molecule complexed with and compacted by a large number of histone protein complexes) in crowded cellular environments and in nanoscale confinements, using computer simulations of chromatins. We first show that macromolecular crowding in the cell nucleus has distinguishable influences on chromatins with different compaction densities, suggesting that cellular control of macromolecular crowding may be utilized to control different chromatin domains, called heterochromatin and euchromatin. Then, we also show that chromatins placed in an array of nanoscale posts have different molecular arrangements depending on the dimension of the nanopost arrays: either localized and aligned parallel to the nanoposts or distributed perpendicular to the nanoposts. Our studies suggest that the entropic effects of macromolecular crowding and nanoscale confinement can regulate chromatin structures and arrangements.
Urine is more than 90% water, and can contain more than 3000 metabolites. Consequently, extraction of biomarker candidates from urine for measuring subtle fluctuations in the quantities of metabolites in healthy individuals and cancer patients is very difficult. A variety of technologies, such as liquid chromatography/mass spectrometry (LC/MS), for analysis of urinary metabolites and identification of substances that show fluctuations in cancer patients compared with healthy individuals was used for this purpose. The substances detected by LC/MS were evaluated using machine learning, multivariate analysis to reduce and visualize parameters, and mass spectrometry for structural estimation of metabolites with unknown structures. One of the important biomarker candidates for breast cancer was determined to be 2-amino-4-methyl-1,1-pentanediol by an MS/MS spectrum. A one-dimensional linear discriminant analysis shows that this compound is estimated to be a promising biomarker for breast cancer. Urinary metabolites are found to be biomarkers for breast cancer.
Hydrogel-based water pipes which can capture ionic contaminants are a promising solution for achieving efficient water treatment. However, the fabrication of such unique water pipes as an ion-harvester remains a challenge. In this work, we have fabricated this kind of water pipe through the confined synthesis of coordination frameworks inside a double-network PAAm/PAMPS hydrogel. The hydrogel could trigger the partial decomposition and reduction of K3[Fe(CN)6] upon heating. The released Fe3+/Fe2+ ions could react with the [Fe(CN)6]4−/[Fe(CN)6]3−, finally producing Prussian Blue coordination frameworks inside the hydrogel. The resulting composite exhibited a high capacity for Cs+ ions (397 mg g−1 in 10 minutes) by taking the coupling effect between the cation-selective hydrogel and the coordination frameworks. By shaping this composite into water pipes, Cs+ ions present in the contaminated water could be captured by the pipe wall. The proposed strategy will be useful, providing a potential method for fast treatment of aqueous nuclear waste.
3,3′,5,5′-tetramethoxy azobenzene (TMAB) and amphiphilic azobenzene dendrimers (AGn-azo) bearing triethylene glycol were synthesized and their isomerization behavior investigated. The solvation structures and isomerization behavior of AGn-azo were expected to change with solvent and generation.
Formate dehydrogenase (FDH) is a useful biocatalyst for CO2 reduction to formic acid in a photoredox system consisting of a photosensitizer and an electron carrier. The electron carrier, single-electron reduced 2,2′-bipyridinium salts (2,2′-BP2+s) act as the co-enzyme for FDH in the reaction of CO2 to formic acid. An advantage of 2,2′-BP2+s is the easy change of structural geometry and the various single-electron reduction potentials. For further improvement of CO2 reduction catalytic activity of FDH, various 2,2′-BP2+s were synthesized as effective artificial co-enzymes for FDH. The effect of the structural geometry and the single-electron reduction potential in the single-electron reduced form of 2,2′-BP2+s on the CO2 reduction catalytic activity of FDH was studied by enzymatic kinetic analysis in detail for the first time. Especially, the catalytic efficiency, kcat/Km value of the single-electron reduced 1,1′-ethylene-2,2′-bipyridinium salt was c.a. 126 times larger than that of native co-enzyme, NADH. These results showed that catalytic activity of FDH can be manipulated with complete control by using 2,2′-BP2+ without changing the structure of FDH and has opened a new avenue for the approach of NAD+/NADH redox free system with FDH using an inexpensive small electron carrier molecule.
We present a reparameterization of PM6 (rPM6) for Fe in a similar procedure to that for Mn in our previous work [T. Saito, Y. Takano, Chem. Lett. 2017, 46, 1567]. The performance of the spin unrestricted rPM6 (UrPM6) method has been examined on both energy minimization and transition state (TS) search on the basis of the spin unrestricted density functional theory (UDFT) calculations. For energy minimization, the UrPM6 outperforms the original UPM6 on the basis of the UB3LYP/SVP-optimized geometries. The test set for TS search is comprised of 58 TS structures for oxidation reactions catalyzed by a variety of iron and manganese complexes including active sites of cytochrome P450 and soluble methane monooxygenase as well as their biomimetic complexes. The standard UPM6 method can locate only 21 out of 58 TS structures (36%), whereas an overall success rate is 83% (48 out of 58) by means of UrPM6. Furthermore, the UrPM6-optimized structures can be obtained easily (on the order of several minutes) and 94% of those are found to be utilized for the subsequent refinement by UDFT without any modifications of geometrical parameters.
A series of mono-functionalized polyhedral octasilsesquioxane (POSS) derivatives (R-POSSs) were prepared by corner capping reaction of heptaisobutyl incompletely condensed POSS and their orientationally disordered (OD) phase transition properties studied by DSC, XRD, and solid state NMR analyses. According to DSC analysis, octaisobutyl-POSS (iBu-POSS) showed the highest OD phase transition temperature among R-POSSs, whereas the OD phase transition temperatures decreased with replacing the mono-substituents smaller and larger than the isobutyl unit. The solid state NMR analysis suggests that the OD phase transition was caused by increasing the mobility of the substituent not by rotating the POSS cage. The composite films were prepared by drop-casting of a chloroform solution of PMMA with heptaisobutyl-butyl-POSS (Bu-POSS). No appearance change of films was observed despite the heating and cooling of the films on the hotplate due to the absence of drastic density difference below and above the OD phase transition.
This paper reports that the treatment of Ru/CeO2 with PPh3 and HCHO in 2-methoxyalcohol was an efficient way to generate the catalytically active Ru species for hydroarylation of C-C multiple bonds. A variety of alkenes was applicable toward the title reactions. The solid Ru/CeO2 could be recycled for several times.
The stereoisomerism of propane derivatives with bond rotations is investigated by means of correlation diagrams of stereoisograms, where the diagrams are governed by epimeric RS-stereoisomeric groups formulated as subgroups of stereoisomeric groups. A molecular-symmetry group GCσ for specifying the eight positions of a propane skeleton is obtained as a wreath product with chirality fittingness (C2v[C3v, C∞v]), where bond rotations are taken into consideration. The group GCσ of order 36 is extended to give the corresponding RS-stereoisomeric group of order 72, which characterizes the global symmetry of the propane skeleton. Then the group is further extended to give a stereoisomeric group H of order 288 for treating chiral and achiral proligands (or of order 144 for treating achiral proligands only) by considering epimerizations at the three RS-stereogenic carbon centers (for Ci, i = 1,2,3). The groups H or are useful to investigate thestereoisomerism of propane derivatives. An epimeric RS-stereoisomeric group is selected as a subgroup of H (or ) in order to show the local RS-stereogenicity at a given RS-stereogenic center (Ci), where the element represents an epimerization at the Ci atom. Such an epimeric RS-stereoisomeric group corresponds to a correlation diagram of stereoisograms for showing RS-stereoisomeric relationships at the Ci atom, i.e., enantiomeric, RS-diastereomeric, and holantimeric relationships. Two RS-diastereomers of each pair are pairwise specified by a pair of RS-stereodescriptors of the CIP system.
A novel tris-cyclometalated iridium(III) complex bearing carbazole-based hole-transporting and triarylphosphine oxide-based electron-transporting dendrons was synthesized through a convergent synthetic route, and its facial and meridional isomers were isolated by conventional silica gel chromatography. The facial isomer exhibited sky-blue photoluminescence (PL) from the phosphorescent core even in the neat film state with a relatively high PL quantum yield (ΦPL) of 0.57 because the dendrons efficiently suppress aggregate formation between the cores. The meridional isomer was less emissive (ΦPL; 0.029 in deaerated dichloromethane) but photoisomerized to the facial isomer by UV light irradiation (365 nm) in spite of large steric hindrance between the bulky dendrons. A non-doped organic light-emitting diode (OLED) employing the facial isomer exhibited sky-blue electroluminescence with a higher maximum external quantum efficiency (EQEmax) of 1.6% than that of a comparable device employing a reference complex bearing only hole-transporting dendrons (EQEmax; 0.5%). As lipophilic and apolar tert-butyl groups are placed on the molecular surface, the present dendritic complex is soluble in cyclohexane and insoluble in ethanol. Utilizing this characteristic solubility, non-doped multilayer OLEDs consisting of a stack of hole-transporting layer/emitting layer (the dendritic complex)/electron-transporting layer were fabricated by solution processing. One of the multilayer devices exhibited an improved EQEmax of 5.2%.
New quinoline-based PNN pincer ligands were prepared via Friedländer synthesis and phosphination reaction. The ligation reaction of PNN ligands with FeX2 (X = Cl, OTf) preferentially led to the formation of mono-chelated (PNN)FeX2 and bis-chelated [(PNN)2Fe]2+ complexes depending on phosphorus substituents and X ligands. Molecular structures and electron configurations of the mono-chelated and bis-chelated complexes were determined by X-ray diffraction analysis and NMR measurements.
The biological functions of proteins are strongly related to their conformational transitions. To elucidate the essential dynamics, molecular dynamics (MD) simulation has become a powerful tool. However, it might still be difficult to address the relevant conformational transitions of proteins with the conventional MD (CMD) because the accessible time scales of CMD are far from those of the biological functions. Furthermore, the essential transitions are induced as stochastic processes in the long time scales, i.e. the conformational transitions are regarded as biologically relevant rare events. To reproduce/predict the rare events, we have proposed several enhanced conformational sampling methods. Our strategy to detect the rare events is based on cycles of the following conformational resampling consisting of two steps. (1) Selections of essential initial structures. (2) Restarting of short-time MD simulations from the initial structures. The cycles of conformational resampling increase the transition probabilities, promoting the rare events. In the present article, we review the enhanced conformational sampling methods developed by us, i.e. parallel cascade selection MD (PaCS-MD), fluctuation flooding method (FFM), taboo search algorithm (TBSA), outlier flooding method (OFLOOD), structural dissimilarity sampling (SDS), and self-avoiding conformational sampling (SACS). Furthermore, we introduce representative applications using our methods for several biological systems.
Iron-sulfur proteins are essential in several biological processes, such as electron transfers in photosystems and respiratory chains. The range of redox potentials of these proteins are so wide that many substrates can interact with them. Thus, the redox potentials of the iron-sulfur proteins are crucial to facilitate the process. This study aims to investigate the redox potential of iron-sulfur proteins with [2Fe-2S] core by using two typical exchange-correlation functionals in density functional theory (DFT), i.e., B3LYP and M06, with and without the diffuse function. Since it involves transition metals, several types of spin approximation were also explored, such as high spin (HS), low spin (LS), approximated spin projection (AP), and J coupling parameter (JC) methods. We found that the diffuse function contributes to improving the accuracy. We also found that M06 functional produced more accurate results than B3LYP. The best result is obtained for AP UM06/6-31++G(d,p) with the absolute error of 0.01 V.
Surface coating with sulfobetaine methacrylate (SBMA) containing polymers is a simple method for reducing non-specific protein adsorption and cell adhesion to biomaterials. It has been shown that copolymers of zwitterionic monomers and butyl methacrylate (BMA) could be adsorbed onto hydrophobic substrates in order to provide anti-fouling properties. However, the copolymers of BMA/SBMA dissolved in organic solvents such as DMSO and THF, which is harmful to the host and environment, but not in environmentally friendly solvents, such as methanol and ethanol. Hydroxyethyl methacrylate (HEMA) was introduced in the copolymers in order to enhance the solubility of BMA/SBMA copolymers in methanol and ethanol. The solubility of the copolymers in methanol, ethanol and DMSO were examined. BMA/SBMA/HEMA copolymers in different solvents were coated on polystyrene (PS) plates, and the surface hydrophilicity and anti-fouling capacity were investigated. On the other hand, many studies have pointed out that spheroid formations of stem cells have the abilities to boost functionality and enhance their therapeutic potential. Therefore, the spheroid formation of human adipose-derived stem cells (hASCs) was studied on a plate coated with copolymers. The substrates coated with the copolymers prevented the adhesion of human adipose-derived stem cells (hASCs); moreover, hASCs formed spheroids after 24 hours of culture. In conclusion, the addition of HEMA in the BMA/SBMA copolymers made the copolymers soluble in methanol and ethanol. With the coating of copolymers, cell adhesion was inhibited and the stem cell spheroids were formed on the plate. The copolymers showed a potential for surface modification under an environmentally friendly condition for anti-fouling and stem cell spheroid application.