Simultaneous Induction of Axial and Planar Chirality in Arene–Chromium Complexes by Molybdenum‐Catalyzed Enantioselective Ring‐Closing Metathesis

The molybdenum‐catalyzed asymmetric ring‐closing metathesis of the various C_s‐symmetric (π‐arene)chromium substrates provides the corresponding bridged planar‐chiral (π‐arene)chromium complexes in excellent yields with up to >99 % ee. With a bulky and unsymmetrical substituent, such as N‐indolyl or 1‐naphthyl, at the 2‐positions of the η⁶‐1,3‐diisopropenylbenzene ligands, both biaryl‐based axial chirality and π‐arene‐based planar chirality are simultaneously induced in the products. The axial chirality is retained even after the removal of the dicarbonylchromium fragment, and the chiral biaryl/heterobiaryl compounds are obtained with complete retention of the enantiopurity.     

Microchip reversed-phase liquid chromatography with packed column and electrochemical flow cell using polystyrene/poly(dimethylsiloxane)

A microchip pressure-driven liquid chromatography (LC) with a packed column and an electrochemical flow cell has been developed by using polystyrene (PS) and poly(dimethylsiloxane) (PDMS). The cylindrical separation column with packed octadecyl silica particles was fabricated in the PS substrate. The three electrode system (working, reference, and counter electrode) for amperometric detection was fabricated onto the PS substrate, using the Au deposition, photolithography, and chemical etching. The detector flow cell was formed by sealing the electrode system with a PDMS chip containing a channel. In this flow cell, the effect of working electrode width (in the direction of flow) on chromatographic parameters, such as peak width and peak resolution were studied in electrode width ranging 50-5,000 microm. The effect of electrode width on sensitivity (current intensity, current density, and S/N ratio) was also examined. The sensitivity was discussed by simulating the concentration profile generated around the working electrode. The effects of the column packing size and the column size on the separation efficiency were examined. In this study, a good separation of three catechins was successfully achieved and the detection limits for (+)-catechin, epicatechin, and epigallocatechin gallate were 350, 450, and 160 nM, respectively.     

Immunosensor for Detection of the Textile Dye Disperse Orange 1 Based on Non‐conventional Competitive Assay

Textile dyes appear as an important class of compounds that has become a matter of public concern and a serious challenge for scientists and environmentalists due to their large‐scale production and extensive application. In this work, a non‐conventional competitive‐type amperometric immunosensor was successfully developed for detection of the textile dye Disperse Orange 1 (DO1). The DO1 was magnetically captured and separated from the sample solution using magnetic particles (MP) functionalized with the antibody anti‐DO1 and with HRP and gold electrodes were modified with the conjugate DO1‐BSA. Molecules of DO1 immobilized on the electrode surface and DO1 captured by MP compete for antibody binding sites. As a result, the amperometric signal decreases with increasing target DO1 concentration at the capture step, because this decreases, the attachment between the HRP coated MP and the electrode. This strategy allowed us to determine DO1 at the low detection limit of 0.87 ng mL^?1 with great specificity. Also, there were good recoveries for detection of the textile dye in river water samples without the need of sample pre‐treatment. The competitive amperometric immunosensor shows applicability for the determination of small molecules that cannot be determined by conventional competitive or sandwich immunosensors.     

Cobalt-Catalyzed Intramolecular Hydroacylation Involving Cyclopropane Cleavage

A simple cobalt-diphosphine catalyst has been found to efficiently promote intramolecular cyclization of ortho-cyclopropylvinyl- and cyclopropylidenemethyl-substituted benzaldehydes into benzocyclooctadienone and benzocycloheptadienone derivatives, respectively. This ring-opening hydroacylation likely involves aldehyde C−H oxidative addition, olefin insertion, cyclopropane cleavage by β-carbon elimination, and C−C bond-forming reductive elimination, as was supported by mechanistic experiments and DFT calculations.     

Open-loop and closed-loop control of dissociative ionization of ethanol in intense laser fields

The relative yield of the C-O bond breaking with respect to the C-C bond breaking in ethanol cation C2H5OH+ is maximized in intense laser fields (10(13)-10(15) Wcm2) by open-loop and closed-loop optimization procedures. In the open-loop optimization, a train of intense laser pulses are synthesized so that the temporal separation between the first and last pulses becomes 800 fs, and the number and width of the pulses within a train are systematically varied. When the duration of 800 fs is filled with laser fields by increasing the number of pulses or by stretching all pulses in a triple pulse train, the relative yield of the C-O bond breaking becomes significantly large. In the closed-loop optimization using a self-learning algorithm, the four dispersion coefficients or the phases of 128 frequency components of an intense laser pulse are adopted as optimized parameters. From these optimization experiments it is revealed that the yield ratio of the C-O bond breaking is maximized as far as the total duration of the intense laser field reaches as long as approximately 1 ps and that the intermittent disappearance of the laser field within a pulse does not affect the relative yields of the bond breaking pathways.     

Highly regio- and stereoselective hydrometallation reactions of fluorine-containing internal alkynes: Novel approaches to fluoroalkylated alkenes

Hydroalumination, hydrocupration, and hydroboration reactions of various fluorine-containing alkynes were investigated. The alkyne reacted smoothly with 2.0 equiv. of Red-Al at −78 °C to give the hydroaluminated adduct in a highly regio- and stereoselective manner, which was treated with iodine, the corresponding vinyliodide being produced in moderate yield. Hydrocupration of the alkynes also took place, but the resulting vinylmetal reacted with various electrophiles sluggishly. In sharp contrast, the reaction with dicyclohexylborane proceeded smoothly to afford the cis-addition products preferentially, which were subjected to Suzuki-Miyaura cross-coupling reaction, leading to trisubstituted alkenes in high yields.     

Enantio- and diastereoselective hydrogenation via dynamic kinetic resolution by a cationic iridium complex in the synthesis of beta-hydroxy-alpha-amino acid esters

Anti-selective asymmetric hydrogenation of alpha-amino-beta-keto esters via dynamic kinetic resolution under low hydrogen pressure has been achieved by an easily-handled cationic iridium complex with tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BARF) as a counterion.     

Experimental and theoretical evaluation of the charge distribution over the ruthenium and dioxolene framework of [Ru(OAc)(dioxolene)(terpy)] (terpy = 2,2':6',2' '-terpyridine) depending on the substituents

A series of ruthenium complexes [Ru(OAc)(dioxolene)(terpy)] having various substituents on the dioxolene ligand (dioxolene = 3,5-t-Bu2C6H2O2 (1), 4-t-BuC6H3O2 (2), 4-ClC6H3O2 (3), 3,5-Cl2C6H2O2 (4), Cl4C6O2 (5); terpy = 2,2':6'2' '-terpyridine) were prepared. EPR spectra of these complexes in glassy frozen solutions (CH2Cl2:MeOH = 95:5, v/v) at 20 K showed anisotropic signals with g tensor components 2.242 > g1 > 2.104, 2.097 > g2 > 2.042, and 1.951 > g3 > 1.846. An anisotropic value, Deltag = g1 - g3, and an isotropic g value, g = [(g1(2) + g2(2) + g3(2))/3]1/2, increase in the order 1 < 2 < 3 < 4 < 5. The resonance between the Ru(II)(sq) (sq = semiquinone) and Ru(III)(cat) (cat = catecholato) frameworks shifts to the latter with an increase of the number of electron-withdrawing substituents on the dioxolene ligand. DFT calculations of 1, 2, 3, and 5 also support the increase of the Ru spin density (Ru(III) character) with an increase of the number of Cl atoms on the dioxolene ligand. The singly occupied molecular orbitals (SOMOs) of 1 and 5 are very similar to each other and stretch out the Ru-dioxolene frameworks, whereas the lowest unoccupied molecular orbital (LUMO) of 5 is localized on Ru and two oxygen atoms of dioxolene in comparison with that of 1. Electron-withdrawing groups decrease the energy levels of both the SOMO and LUMO. In other words, an increase in the number of Cl atoms in the dioxolene ligand results in an increase of the positive charge on Ru. Successive shifts in the electronic structure between the Ru(II)(sq) and Ru(III)(cat) frameworks caused by the variation of the substituents are compatible with the experimental data.     

Potential energy curve for ring-opening reactions: comparison between broken-symmetry and multireference coupled cluster methods

The spin-unrestricted Hartree-Fock (UHF)-based coupled cluster singles and doubles (UHF-CCSD) and Mukherjee's state-specific multireference CCSD (MkCCSD) methods are applied to four ring-opening reactions. The spin-restricted Hartree-Fock (RHF)-based CCSD (RHF-CCSD) calculations are also performed for comparison. In the case of the UHF-CCSD method, an approximate spin-projection (AP) method is applied to the broken-symmetry (BS) singlet solution to remove the spin contamination effect. For potential energy curves (PECs) of all reactions presented in this study, the results of RHF-CCSD and UHF-CCSD are substantially different from those of MkCCSD, while the results after the AP method (AP-UCCSD) reproduce the MkCCSD results well. It strongly suggests that the spin contamination effect should be removed by the AP correction even at the UHF-CCSD level to predict reliable energetics of these reactions.