197Au Mössbauer Study of Bimetallic Nanoparticles Prepared by Sonochemical Technique

Mössbauer measurements with circularly polarized radiation were performed on a nanocrystalline, disordered Fe₄₈Al₅₂ alloy. The analysis of the data for various polarization states resulted in the characterization of the hyperfine magnetic field distribution and the dependence of the average z-component of hyperfine field on the chemical environment. An increasing number of Al in the first coordination shell causes not only a decrease of magnetic moments but also introduces noncollinearity.     

Speciation of small molecules and inorganic ions in salmon egg cell cytoplasm by surfactant-mediated HPLC/ICP-MS.

The speciation of diverse elements in salmon egg cell cytoplasm was performed by a surfactant-mediated HPLC/ICP-MS hyphenated system. In the present experiment, an ODS column coated with CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate), which is a zwitterionic bile acid derivative, was employed as a surfactant-mediated separation column, and ICP-MS was used as an element-selective detector. The present surfactant-mediated HPLC allowed us to separate large and small molecules within 10 min; large molecules, such as proteins, were eluted within 2.5 min, while small molecules were eluted after 2.5 min, but within 10 min. In the present experiment, Fe, Cu, and Zn in egg cell cytoplasm were observed mostly in species with large molecular weights, indicating that these elements are contained as metalloproteins or metalloenzymes in egg cell cytoplasm. On the contrary, it was found that P, S, Mo, and halogens in egg cell cytoplasm were contained as small molecules or inorganic ions. The major species of P in egg cell cytoplasm was identified as the phosphate ion (PO4(3-)). Molybdenum, Cl, and Br in egg cell cytoplasm were molybdate (MoO4(2-), chloride (Cl-), and bromide (Br-) ions, respectively.     

Dual modification of a triple-stranded β-helix nanotube with Ru and Re metal complexes to promote photocatalytic reduction of CO2

We have constructed a robust β-helical nanotube from the component proteins of bacteriophage T4 and modified this nanotube with Ru(II)(bpy)(3) and Re(I)(bpy)(CO)(3)Cl complexes. The photocatalytic system arranged on the tube catalyzes the reduction of CO(2) with higher reactivity than that of the mixture of the monomeric forms.     

Proposed reaction mechanisms for selenium UV photolysis vapor generation by computational methods

The production of volatile analyte species by UV photolysis in the presence of low-molecular-weight organic acids as an alternative to chemical vapor generation has been of recent interest. The mechanism of this process is not well understood. Proposed mechanisms often involve photolytic cleavage of the organic acid as the initial step. Evidence suggests that this may not be the dominant route for UV photolysis vapor generation. In this work computational methods were applied to determine a possible alternative mechanism in the absence of free-radical production. The proposed mechanism specifically focused on selenium vapor generation. An energetically favored mechanism was found for UV photolysis of inorganic selenium in the presence of formic and acetic acids which is consistent with previously reported experimental results.     

Azurin–Poly(N‐isopropylacrylamide) Conjugates by Site‐Directed Mutagenesis and their Thermosensitive Behavior in Electron‐Transfer Processes

Searching for “intelligence” : Azurin–PNIPAM conjugates were prepared by site‐directed mutagenesis followed by protein reconstitution by using imidazole‐conjugated poly(N‐isopropylacrylamides). The polymer‐bound imidazole acts as a ligand in the active site of the blue copper protein azurin. The bioconjugates showed thermosensitive behavior in electron‐transfer processes with reduced cytochrome c.

     

A Versatile Co(bisalen) Unit for Homogeneous and Heterogeneous Cooperative Catalysis in the Hydrolytic Kinetic Resolution of Epoxides

Bisalen—very cooperative : A novel styryl‐substituted, unsymmetrical bisalen is shown to be a versatile precursor to both soluble and insoluble cooperative catalysts for the hydrolytic kinetic resolution of epoxides. The unique bisalen motif ensures all catalysts derived from it have the necessary molecular‐level ligand pairing needed for cooperative bimetallic catalytic reactions (see scheme).

     

Macrocyclic Cyclooctene-Supported AlCl–Salen Catalysts for Conjugated Addition Reactions: Effect of Linker and Support Structure on Catalysis

AlCl–salen (salen=N,N′-bis(salicylidene)ethylenediamine dianion) catalysts supported onto macrocyclic oligomeric cyclooctene through linkers of varying length and flexibility have been developed to demonstrate the importance of support architecture on catalyst activity. The role played by the support and the linkers in dictating catalyst activity was found to vary for reactions with contrasting mechanisms, such as the bimetallic cyanide and the monometallic indole addition reactions. While the flexible support significantly enhanced the cyanide addition reaction, most likely by improving salen–salen interactions in the transition state, it lowered the reaction rate for the monometallic indole reaction. For both reactions, significant increase in catalytic activity was observed for catalysts with the longest linkers. The effect of the flexible macrocyclic support on catalysis was further exemplified by the enhanced activity of the supported catalyst in comparison with its unsupported analogue for the conjugate addition of tetrazoles, which is known to be catalyzed by dimeric μ-oxo–salen catalysts. Our studies with the cyclooctene supported AlCl–salen catalysts provides significant insights for rationally designing highly efficient AlCl–salen catalysts for a diverse set of reactions.     

Conformational specificity in photoinduced intramolecular 1,7-hydrogen abstraction of homonaphthoquinones with a spiro-linked dibenzocycloheptene ring

[reaction: see text] Irradiation of homonaphthoquinones with spiro-linked dibenzocycloheptene rings brings about the Norrish type II reaction to give polycyclic alcohols via a stereospecific 1,7-hydrogen abstraction of the less stable twist-boat conformer.     

Stereoselective syntheses of lycopodium alkaloids, (±)-fawcettimine and (±)-8-deoxyserratinine

Lycopodium alkaloids, (±)-fawcettimine (1) and (±)-8-deoxyserratinine (3) were stereoselectively synthesized through the stereoselective Diels-Alder reaction and the regioselective aldol condensation reaction of the dialdehyde (8).     

Optical resolution by preferential crystallization of (RS)-2-benzoylamino-2-benzyl-3-hydroxypropanoic acid and its use in synthesizing optically active 2-amino-2-methyl-3-phenylpropanoic acid

To synthesize optically active 2-amino-2-methyl-3-phenylpropanoic acid (1), (RS)-2-benzoylamino-2-benzyl-3-hydroxypropanoic acid [(RS)-2] was first optically resolved using cinchonidine as a resolving agent to yield optically pure (S)- and (R)-2 in yields of about 70%, based on half of the starting amount of (RS)-2. Next, the racemic structure of (RS)-2 was examined based on melting point, solubility, IR spectrum, and binary and ternary phase diagrams, with the aim of optical resolution by preferential crystallization of (RS)-2. Results indicated that the (RS)-2 exists as a conglomerate at room temperature, although it forms a racemic compound at the melting point. The optical resolution by preferential crystallization yielded (S)- and (R)-2 with optical purities of about 90%, which were fully purified by recrystallization. After O-tosylation of (S)- and (R)-2, reduction by zinc powder and sodium iodide gave (R)- and (S)-1, respectively.