Identification of a copper(I) intermediate in the conversion of 1-aminocyclopropane carboxylic acid (ACC) into ethylene by Cu(II)-ACC complexes and hydrogen peroxide

Several Cu(II) complexes with ACC (=1-aminocyclopropane carboxylic acid) or AIB (=aminoisobutyric acid) were prepared using 2,2'-bipyridine, 1,10-phenanthroline, and 2-picolylamine ligands: [Cu(2,2'-bipyridine)(ACC)(H2O)](ClO4) (1a), [Cu(1,10-phenanthroline)(ACC)](ClO4) (2a), [Cu(2-picolylamine)(ACC)](ClO4) (3a), and [Cu(2,2'-bipyridine)(AIB)(H2O)](ClO4) (1b). All of the complexes were characterized by X-ray diffraction analysis. The Cu(II)-ACC complexes are able to convert the bound ACC moiety into ethylene in the presence of hydrogen peroxide, in an "ACC-oxidase-like" activity. A few equivalents of base are necessary to deprotonate H2O2 for optimum activity. The presence of dioxygen lowers the yield of ACC conversion into ethylene by the copper(II) complexes. During the course of the reaction of Cu(II)-ACC complexes with H2O2, brown species (EPR silent and lambda max approximately 435 nm) were detected and characterized as being the Cu(I)-ACC complexes that are obtained upon reduction of the corresponding Cu(II) complexes by the deprotonated form of hydrogen peroxide. The geometry of the Cu(I) species was optimized by DFT calculations that reveal a change from square-planar to tetrahedral geometry upon reduction of the copper ion, in accordance with the observed nonreversibility of the redox process. In situ prepared Cu(I)-ACC complexes were also reacted with hydrogen peroxide, and a high level of ethylene formation was obtained. We propose Cu(I)-OOH as a possible active species for the conversion of ACC into ethylene, the structure of which was examined by DFT calculation.     

Control of heme peptide activity by using phase transition polymers modified with inhibitors

Catalytic activity of a heme peptide (HP) modified-electrode for H(2)O(2) reduction was controlled by use of poly(N-isopropylacrylamide) modified with an inhibitory moiety, imidazole group. The polymers inhibited the catalytic activity below their lower critical solution temperature (LCST) where the polymers were dissolved and did not inhibit the activity above the LCST where the polymers were precipitated. A polymer with a longer side chain connecting with the imidazole group was more inhibitory than a polymer with a shorter side chain at temperatures below the LCST. Formation constants of dissolved HP-imidazole complexes were evaluated by spectroscopic means, and it was found that the polymers were more inhibitory than the corresponding monomers.     

Croissamide,a proline-rich cyclic peptide with an N-prenylated tryptophan from a marine cyanobacterium Symploca sp.

Croissamide, a proline-rich cyclic peptide that contains an N-prenylated tryptophan, was isolated from a marine cyanobacterium Symploca sp. Its gross structure was determined by spectroscopic analyses, and the absolute configuration was established based on chiral HPLC analyses of acid hydrolysates.     

Attempted reduction of 1,2,3-thiadiazole-4-carboxylates with samarium/iodine in methanol. Unexpected ring enlargement to 1,2,5-trithiepan-4,6-dicarboxylates

When stirred with powdered samarium and iodine in methanol at ice-cold temperature, ethyl 1,2,3-thiadiazole-4-carboxylate 5 underwent unusual reduction involving the dimeric ring enlargement with a sulfur addition, giving dimethyl 1,2,5-trithiepan-4,6-dicarboxylates 7a,b as a cis/trans-isomeric mixture in acceptable yield. The 1,2,3-thiadiazole ring of 5 proved to resist reduction by ordinary reducing agents, where the only choice in most cases was either recovery of the unchanged substrate or decomposition to an intractable mixture of unidentified products and tar.     

Sorption and desorption experiments using stable cesium: considerations for radiocesium retention by fresh plant residues in Fukushima forest soils

Journal of Radioanalytical and Nuclear Chemistry - We conducted sorption experiments with stable cesium (133Cs) solution in different organic matter samples, aiming to understand the sorption of...     

Ruthenium Complexes Bearing Axially Chiral Bipyridyls: The Mismatched Diastereomer Showed Red Circularly Polarized Phosphorescence

Ruthenium^II complexes bearing three axially chiral bipyridyl ligands were synthesized as a new family of chiral complex dyes, and Δ-(S)- and Λ-(S)-diastereomers were obtained. The X-ray crystal structure analyses, spectroscopy, and DFT calculations suggested that all the bipyridyls maintained chirality in both the ground and excited states, and the Δ-(S)- and Λ-(S)-isomers are the matched (more relaxed) and mismatched (more constrained) pairs, respectively. The mismatched Λ-(S)-isomer exhibited red circularly polarized phosphorescence (CPP) both in solution and in the solid state. The solution state CPP is the most intense of ruthenium complexes, while the solid state CPP is the first example of them. It is supposed that, for the Λ-(S)-isomer, the six cumulative CH/π interactions suppress further distortion in the T₁ state.     

A novel partitioning process for treatment of high level liquid waste using macroporous silica-based adsorbents

To separate the long-life and significant fission product elements from high level liquid waste (HLLW), a novel partitioning process for the treatment of HLLW has been studied experimentally based on column separation technique using macroporous silica-based adsorbents. This process consists of (1) Cs and Rb are removed by the first separation column packed with (calix[4] + dodecanol)/SiO₂–P adsorbent; (2) Sr and Ba are eluted out by the second separation column packed with (DtBuCH18C6 + dodecanol)/SiO₂–P adsorbent; (3) Pd is partitioned by the third separation column packed with MOTDGA–TOA/SiO₂–P adsorbent; (4) Ru, Rh and Mo can be separated by the fourth separation column packed with TODGA/SiO₂–P adsorbent; (5) Am is separated from RE by the fifth column is packed with isobutyl-BTP/SiO₂–P adsorbent. The experimental results indicated that this partitioning process is essentially feasible.     

Structural changes in the molecular sheets along (hk0) planes derived from cellulose Iβ by molecular dynamics simulations

We studied the stability of molecular sheets with four cellotetraoses in an aqueous environment by molecular dynamics simulation to identify the molecular details of first structure as one of the possibilities in the course of crystallization of cellulose I. After simulation, the molecular sheets formed by van der Waals forces along the (11?0) and (110) crystal plane did not change their structures in an aqueous environment, whereas the other ones formed by hydrogen bonds along the (100) and (200) crystal plane changed into a van der Waals associated molecular sheet, similar to the former. These simulated molecular sheets formed by van der Waals forces were structurally stable in water because of their hydrophilic exterior and hydrophobic interior. Therefore, if the molecular sheet structures are formed in the real system, the sheets formed by van der Waals forces are probably the initial structure of crystallization. A close analysis indicated that these sheets could be classified into two groups in terms of the hydrogen bonding networks, camber angle, and main and side chain conformations. One group was the molecular sheets corresponding to the (110) after simulation. This sheet is probably rigid because intramolecular hydrogen bonds of the chains in the sheet are highly developed. The other group was the molecular sheets corresponding to (200), (100), and (11?0) crystal plane: the chains in these sheets seemed to be rather flexible due to their moderately developed intramolecular hydrogen bonds.