A “Catch‐and‐Release” Protocol for Alkyne‐Tagged Molecules Based on a Resin‐Bound Cobalt Complex for Peptide Enrichment in Aqueous Media

The development of new and mild protocols for the specific enrichment of biomolecules is of significant interest from the perspective of chemical biology. A cobalt–phosphine complex immobilised on a solid‐phase resin has been found to selectively bind to a propargyl carbamate tag, that is, “catch”, under dilute aqueous conditions (pH 7) at 4 °C. Upon acidic treatment of the resulting resin‐bound alkyne–cobalt complex, the Nicholas reaction was induced to “release” the alkyne‐tagged molecule from the resin as a free amine. Model studies revealed that selective enrichment of the alkyne‐tagged molecule could be achieved with high efficiency at 4 °C. The proof‐of‐concept was applied to an alkyne‐tagged amino acid and dipeptide. Studies using an alkyne‐tagged dipeptide proved that this protocol is compatible with various amino acids bearing a range of functionalities in the side‐chain. In addition, selective enrichment and detection of an amine derived from the “catch and release” of an alkyne‐tagged dipeptide in the presence of various peptides has been accomplished under highly dilute conditions, as determined by mass spectrometry.     

The comparison of two clean-up procedures, multifunctional column and immunoaffinity column, for HPLC determination of ochratoxin A in cereals, raisins and green coffee beans

To evaluate a clean-up method of detecting ochratoxin A (OTA) by HPLC, the performances of two different clean-up columns, an immunoaffinity column and a multifuntional column were compared in an inter-laboratory study. As samples, un-contaminated wheat, corn grits, green coffee beans and naturally contaminated raisins were used. The recovery test was performed at two different concentrations of OTA (0.5 and 5.0 μg/kg) except for naturally contaminated raisins. Using the immunoaffinity column, the recovery rates, and relative standard deviations for repeatability (R.S.D._r) and reproducibility (R.S.D._R) for wheat, corn grits and green coffee beans ranged 59.0-85.8, 4.2-7.8 and 22.9-29.2%, respectively. For naturally contaminated raisins, recovery, R.S.D._r and R.S.D._R were 84.1, 1.8 and 5.1%, respectively. Using the multifunctional column, the recovery rates, R.S.D._r and R.S.D._R for wheat, corn grits and green coffee beans ranged 80.8-185.0, 0.7-6.9 and 15.2-33.9%, respectively. For naturally contaminated raisins, the recovery, R.S.D._r and R.S.D._R were 128.7, 1.1 and 3.7%, respectively. The results suggest that a multifunctional column could be used to detect OTA in wheat and corn grits at a concentration as low as 0.5 μg/kg; however, it was difficult to detect OTA in green coffee beans and raisins at such a low level. Although an immunoaffinity column could be used for all the test samples in this study from a low level to a high level, the recovery rates were lower than with a multifunctional column.     

Channel-dependent conformations of single-strand polymers in organic networks composed of tetrapodal adamantanes with N-heterocyclic moieties

Three tetrapodal adamantanes bearing imidazole (1), benzimidazole (2), and phenylimidazole (3) moieties were designed and synthesized. The co-crystallization of polyethylene glycol (PEG) and tetrapodal molecules provided polymer-inclusion organic crystals (1a–3a). Single crystal X-ray analysis revealed that organic networks possessing various channels were produced by CH/N and CH/π interactions. The PEG chain had zigzag, kink-type, and helical conformations.     

Visible‐Light‐Induced Photoredox Catalysis with a Tetracerium‐Containing Silicotungstate

The development of visible‐light‐induced photocatalysts for chemoselective functional group transformations has received considerable attention. Polyoxometalates (POMs) are potential materials for efficient photocatalysts because their properties can be precisely tuned by changing their constituent elements and structures and by the introduction of additional metal cations. Furthermore, they are thermally and oxidatively more stable than the frequently utilized organometallic complexes. The visible‐light‐responsive tetranuclear cerium(III)‐containing silicotungstate TBA₆[{Ce(H₂O)}₂{Ce(CH₃CN)}₂(μ₄‐O)(γ‐SiW₁₀O₃₆)₂] (CePOM; TBA=tetra‐n‐butylammonium) has now been synthesized; when CePOM was irradiated with visible light (λ>400 nm), a unique intramolecular Ce^III‐to‐POM(W^VI) charge transfer was observed. With CePOM, the photocatalytic oxidative dehydrogenation of primary and secondary amines as well as the α‐cyanation of tertiary amines smoothly proceeded in the presence of O₂ (1 atm) as the sole oxidant.     

Solvent-free asymmetric conjugate addition of malonates to enones using a diaminomethylenemalononitrile organocatalyst

Diaminomethylenemalononitrile organocatalyst 1 efficiently promotes the asymmetric conjugate addition of malonates to α,β-unsaturated ketones to afford the corresponding addition products in high to excellent yields with up to 98% ee.     

Development of novel magnetic nano-carriers for high-performance affinity purification

We developed novel magnetic nano-carriers around 180 nm in diameter for affinity purification. Prepared magnetic nano-carriers possessed uniform core/shell/shell nano-structure composed of 40 nm magnetite particles/poly(styrene-co-glycidyl methacrylate (GMA))/polyGMA, which was constructed by admicellar polymerization. By utilizing relatively large 40 nm magnetite particles with large magnetization, the magnetic nano-carriers could show good response to permanent magnet. Thanks to uniform polymer shell with high physical/chemical stability, the magnetic nano-carriers could disperse in a wide range of organic solvent without disruption of core/shell structure and could immobilize various kinds of drugs. We examined affinity purification using our prepared magnetic nano-carriers with anti-cancer agent methotrexate (MTX) as ligand. Our magnetic nano-carriers showed higher performance compared to commercially available magnetic beads in terms of purification efficiency of target including extent of non-specific binding protein.     

Direct asymmetric aldol reactions catalyzed by l-proline-2,4,6-trinitroanilide

Direct aldol reactions of several aromatic aldehydes with ketones using l-proline-2,4,6-trinitroanilide catalyst 2d were conducted. Under optimized conditions, high enantioselectivity (99% ee), regioselectivity (up to 95:5), and diastereoselectivity (up to 98:2) were achieved.     

Development of Mössbauer diffractometer by using nuclear resonant scattering at SPring-8 BL11XU

A Mössbauer diffractometer has been developed by using ⁵⁷Fe nuclear resonant scattering apparatus at SPring-8 BL11XU in order to obtain a crystal-site-selective Mössbauer spectrum. A ??-2?? goniometer was newly installed between the nuclear monochromator and a detector. From a single crystal Fe₃ O ₄ mounted on the goniometer, the 111, 222, and 220 reflected γ-rays were used to collect the diffraction spectra at room temperature. The intensity ratio of the two subspectra, corresponding to A- and B-site Fe ions, changes notably according to the reflection index. The diffraction spectrum is composed of a major absorption spectrum and a minor emission spectrum. The former is given by the γ-ray due to the electron scattering and nuclear absorption, whereas the latter is given by the γ-ray due to the nuclear resonant scattering. Interference effects between these two γ-rays are also seen as line broadenings, asymmetric line shapes, and slope of the base lines. These features can be successfully expressed by a Fano function. We consider that the emission spectrum due to the nuclear resonant scattering represents crystal-site-selective Mössbauer spectrum.     

Identification of a chemical substructure that is immobilized to ferrite nanoparticles (FP)

Despite the wide utility of ferrite nanoparticles (FP), a methodology to conjugate heterologous molecules to FP is still limited and characterization of small molecule-conjugated FP is not well known. Here, we describe what kinds of proteins and amino acids are selectively immobilized onto FP when FP is synthesized in the presence of these molecules. Two-dimentional gel electrophoresis (2D SDS-PAGE) showed that proteins with low pI value were selectively bound to FP. Quantitative analyses using HPLC suggested that L-aspartic acid (Asp) and L-cysteine (Cys) were bound to FP selectively among natural amino acids examined. Additional analysis of compounds-conjugated FP revealed that selective binding of Asp to FP was attributed with its molecular structure. It was found that the substructure of amino acid-bound to FP specifically was composed of a defined chelation of two carboxyl groups separated by two carbon atoms as deduced from FT-IR measurement. Thus, we concluded that molecules possessing two carboxyl groups separated by two carbons were bound to FP spontaneously and selectively, which might enable the attachment of free functional groups onto the FP surface if their molecules have functional groups other than carboxyl groups. The resulting complex might be applicable as a chemical tag to immobilize various molecules onto FP.     

One-pot synthesis of cyclic triamides with a triangular cavity from trans-stilbene and diphenylacetylene monomers

Base-promoted self-condensation reactions of trans-stilbene and diphenylacetylene monomers bearing 4-alkylamino and 4'-methoxycarbonyl groups were investigated. Reactions of N-propyl monomers under pseudohigh-dilution conditions (a THF solution of monomer was added dropwise to a THF solution of LiHMDS) afforded the corresponding cyclic triamides in good yields. X-ray crystallographic analysis showed that these cyclic triamides possessed an almost equilateral triangle structure with a cavity surrounded by tilted benzene rings.