Synthesis, structure, and conformational mobility of a vaulted trans-bis(o-aminophenolato)platinum(II) complex

The synthesis, structure, and conformational mobility of a trans-bis(aminophenolato)platinum(II) complex bearing a dodecamethylene bridge, [Pt(L)] (1) [H ₂ L = N,N′-Dimethyl-N,N′-bis(2-hydroxyphenylmethyl)dodecane-1,12-diamine] are described. The 2D NMR and X-ray diffraction analysis revealed that the complex has a “reversed U”-shaped syn conformation in the solution state, which is mainly due to steric congestion of the vaulted structure and hydrogen bonding at the bis[(o-aminomethyl)phenolato] coordination site, while the complex unit is packed in the crystalline state with “Z-shaped” anti-conformation due to highly regulated molecular arrangement by 3D CH-π and hydrogen bonding interactions.     

Advances in Artificial Cell Membrane Systems as a Platform for Reconstituting Ion Channels

An artificial cell membrane that is composed of bilayer lipid membranes (BLMs) with transmembrane proteins incorporated within them represents a well‐defined system for the analysis of membrane proteins, especially ion channel proteins that are major targets for drug design. Because the BLM system has a high compatibility with recently developed cell‐free expression systems, it has attracted attention as a next‐generation drug screening system. However, three issues associated with BLM systems, i. e., their instability, the need for non‐volatile organic solvents and a low efficiency of ion channel incorporation, have limited their use as a drug screening platform. In this personal account, we discuss our recent approaches to address these issues based on microfabrication. We also discuss the potential for using the BLM system combined with cell‐free expression systems as a drug screening system for future personalized medicine.     

Hydrogen absorption property and magnetism of SmFeAl and its hydrides

Magnetic properties of SmFeAl and its hydrides synthesized at 298–673 K under 40 bar hydrogen pressure were investigated by a superconducting quantum interference device (SQUID) from 4.2 to 300 K. SmFeAl and its hydrides have a mictomagnetic transition during the field-cooled process. In both SmFeAl and its hydrides, a shifted magnetic hysteresis cycle towards positive magnetization was observed. But when SmFeAlH_x decomposes completely into SmH_x and Fe–Al alloy, this special transition disappears.     

Preparation,properties and structure of stable ionic dialkylbis(2,2′-bipyridine)cobalt(III) tetraalkylaluminate and related complexes

Two types of dialkylcobalt(III) complexes containing the 2,2′-bipyridine ligand have been isolated as products of the reactions of tris(2,4-pentanedionato)cobalt(III) (Co(acac)₃), 2,2′-bipyridine (bpy), and alkylaluminums in diethyl ether. When high Al/Co ratios (Al/Co > 7) were used, ionic complexes, dialkylbis(2,2′-bipyridine)cobalt(III) tetraalkylaluminates, [CoR₂(bpy)₂][AlR₄] (R = CH₃, C₂H₅) were obtained exclusively. Similar reactions at lower ratios (Al/Co - 1.5–2.0) gave neutral CoR₂(acac)(bpy) (R = CH₃, C₂H₅, n-C₃H₇, i-C₃H₇). These compounds were characterized by IR and NMR spectroscopy as well as by elemental analysis and chemical reactions. Molecular structural analysis of the cationic dimethylcobalt compound confirmed the cis configuration. Stepwise formation of [CoR₂(bpy)₂][AlR₄] from Co(acac)₃ is postulated and the mechanism of the alkylation reaction is discussed.     

Regulation mechanism of spin-orbit coupling in charge-transfer-induced luminescence of imidazopyrazinone derivatives

The spin transition in the reactions of the derivatives of imidazo[1,2-a]pyrazin-3(7H)-one (1H) with a triplet molecular oxygen (3O2) has been investigated by the geometry optimization at the B3LYP/6-31+G(d) level and the evaluation of the electronic matrix elements for spin-orbit coupling (SOC) using the full Pauli-Breit SOC operator. The reductive activation for the 3O2 reaction is affected by the proton activity and solvent polarity of a surrounding reaction field. In a polar aprotic solvent, a base-prompted anionic substrate may react with 3O2 in a stepwise manner through complete electron transfer from the substrate anion to 3O2, while the irreversible concerted 3O2 addition via intersystem crossing may become complete in a less polar solvent. SOC in the thermal decomposition of a resulting peroxide adduct can be controlled by the protonation state of the substrate. There exists an optimal protonation state for the suppression of SOC in the charge-transfer-induced luminescence (CTIL) of the peroxide, which is closely related with the ability of a substituent to donate an electron. This will constitute a necessary condition for the high efficiency of chemi- and bioluminescence.     

Domino double Michael-Claisen cyclizations: a powerful general tool for introducing quaternary stereocenters at C4 of cyclohexane-1,3-diones and total synthesis of diverse families of sterically congested alkaloids

Reactions of substituted acetone derivatives with acrylic acid esters (>200 mol %) in the presence of t-BuOK (200 mol %) in t-BuOH-THF (1:1 by volume) turned out to proceed as a cascade process consisting of the first Michael addition, the second Michael addition, and the last Claisen reaction to afford 4,4-disubstituted cyclohexane-1,3-diones. Only more substituted enolates play the role of a Michael donor in this cascade process, and therefore the ketone took up two alkoxycarbonylethyl groups on the same carbon bearing more substituents. Such intermediates were followed by intramolecular Claisen reactions leading to cyclohexane-1,3-diones bearing quaternary stereogenic centers at C(4), which bears an alkoxycarbonylethyl group and the substituent of the starting acetone derivatives. Thus-obtained 4,4-disubstituted cyclohexane-1,3-diones were successfully employed for total syntheses of intricate alkaloids of biological interest such as (+)-aspidospermidine, (+/-)-galanthamine, (+/-)-lycoramine, and (+/-)-mesembrine, all featuring quaternary stereogenic centers. DFT calculations provided us with clear-cut explanations for the observed chemoselectivity of the cascade process involving ketone-based enolates under thermodynamically controlled conditions.     

High sequence-coverage detection of proteolytic peptides using a bis(terpyridine)ruthenium(II) complex

The use of a bis(terpyridine)ruthenium(ii) complex for peptide labeling (Ru-CO labeling) supplied high intensity peaks in mass spectrometry (MS) analysis that overcame the contribution of protonation or sodiated adduction to peptides. Ru-CO-labeled insulin A- and B-chains were detected simultaneously in comparable peak abundance by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The mass spectra of chymotryptic peptide fragments of Ru-CO-labeled insulin also simultaneously indicated both N-terminal fragment ions, and amino acid sequences were determined easily by matrix-assisted laser desorption/ionization post-source-decay (MALDI-PSD). The sensitivity of detecting Ru-CO-labeled peptide fragment ions was not dependent on the length or the sequences of the peptides. The Ru-CO labeling method was applied to tryptic myoglobin fragments. The method indicated that each fragment ion is detected nearly equal in abundance and enabled the desired fragment ions to be distinguished from matrix clusters or their in-source fragments in lower mass regions. The desired fragment ions can be found in the mass region higher than 670.70 (= Ru-CO). This method provided a high sequence coverage (96%) by peptide mass fingerprinting (PMF). Application of this method to a protein mixture (myoglobin, lysozyme and ubiquitin) successfully achieved high sequence-coverage characterization (>90%) of these proteins simultaneously.     

Synthesis of nitrosylruthenium complexes containing 2,2':6',2"-terpyridine by reactions of alkoxo complexes with acids

Nitrosylruthenium complexes containing 2,2':6',2"-terpyridine (terpy) have been synthesized and characterized. The three alkoxo complexes trans-(NO, OCH3), cis-(Cl, OCH3)-[RuCl(OCH3)(NO)(terpy)]PF6 ([2]PF6), trans-(NO, OC2H5), cis-(Cl, OC2H5)-[RuCl(OC2H5)(NO)(terpy)]PF6 ([3]PF6), and [RuCl(OC3H7)(NO)(terpy)]PF6 ([4]PF6) were synthesized by reactions of trans-(Cl, Cl), cis-(NO, Cl)-[RuCl2(NO)(terpy)]PF6 ([1]PF6) with NaOCH3 in CH3OH, C2H5OH, and C3H7OH, respectively. Reactions of [3]PF6 with an acid such as hydrochloric acid and trifluoromethansulforic acid afford nitrosyl complexes in which the alkoxo ligand is substituted. The geometrical isomer of [1]PF6, trans-(NO, Cl), cis-(Cl, Cl)-[RuCl2(NO)(terpy)]PF6 ([5]PF6), was obtained by the reaction of [3]PF6 in a hydrochloric acid solution. Reaction of [3]PF6 with trifluoromethansulforic acid in CH3CN gave trans-(NO, Cl), cis-(CH3CN, Cl)-[RuCl(CH3CN)(NO)(terpy)]2+ ([6]2+) under refluxing conditions. The structures of [3]PF6, [4]PF6.CH3CN, [5]CF3SO3, and [6](PF6)2 were determined by X-ray crystallograpy.