Synthesis of novel cyclic sulfilimines, 2-azathiabenzene derivatives

The synthesis and some properties of novel cyclic sulfilimines, 2-methyl-1-aza-2-thianaphthalene and 9-methyl-10-aza-9-thiaphenanthrene are described.     

Organic and organometallic derivatives of dihydrogen-encapsulated [60]fullerene

Regioselective multi-addition reaction of organocopper and amine compounds onto dihydrogen-encapsulated [60]fullerene, H2@C60, produced a variety of organic and organometallic derivatives of H2@C60. The X-ray crystallographic analysis of dihydrogen-encapsulated bucky ferrocene, Fe(H2@C60Ph5)C5H5, showed the presence of the dihydrogen molecule located almost in the center but slightly away from the ferrocene moiety. The 1H NMR chemical shift values for the encapsulated molecular hydrogen indicated that these values are susceptible to the magnetic environment of the inside as well as the outside of the fullerene cage.     

Titanium N-heterocyclic carbene complexes incorporating an imidazolium-linked bis(phenol)

The synthesis and characterization of titanium complexes of the aryloxido-functionalized N-heterocyclic carbene ligand (L) is reported, in which the tridentate L ligand meridionally coordinates to the metal center.     

Substrate phage as a tool to identify novel substrate sequences of proteases

Combinatorial phage peptide libraries have been used to identify the ligands for specific target molecules. These libraries are also useful for identification of the specific substrates of various proteases. A substrate phage library has a random peptide sequence at the N-terminus of the phage coat protein and an additional tag sequence that enables attachment of the phage to an immobile phase. When these libraries are incubated with a specific enzyme, such as a protease, the uncleaved phage is excluded from the solution with tag-binding macromolecules. This provides a novel approach to define substrate specificity. The aim of this review is to summarize recent progress on the application of the substrate phage technique to identify specific substrates of proteolytic enzymes. As an example, some of our own experimental data on the selection and characterization of substrate sequences for thrombin, a serine protease, and membrane type-1 matrix metalloproteinase (MT1-MMP) will be presented. Using this approach, the canonical consensus substrate sequence for thrombin was deduced from the selected clones. As expected from the collagenolytic activity of MT1-MMP, a collagen-like sequence was identified in the case of MT1-MMP. A more selective substrate sequence for MT1-MMP was identified during a substrate phage screen. The delineation of the substrate specificity of proteases will help to elucidate the enzymatic properties and the physiological roles of these enzymes. Comprehensive screening of very large numbers of potential substrate sequences is possible with substrate phage libraries. Thus, this approach allows novel substrate sequences and previously unknown target molecules to be defined.     

Nickel(0)-Catalyzed Three-Component Connection Reaction of Dimethylzinc, 1,3-Dienes, and Carbonyl Compounds

Linear 1:1:1 coupling of dimethylzinc, 1,3-dienes, and carbonyl compounds in this order is facilitated by catalytic amounts of [Ni(acac)(2)] to give (E)-3-hexen-1-ols in good yields under mild conditions [Eq. (a)]. Increasing steric hindrance at the carbonyl group favors formation of the 1:2:1 adduct, and this is the sole product when the carbonyl compound is acetone. acac=acetylacetonate.     

Photoinduced reversible pH change in aqueous solution of azoaromatic poly(carboxylic acid)

To regulate the pH value of an aqueous solution containing polyelectrolyte by photoirradiation, an azoaromatic poly(carboxylic acid), acrylic acid(AA)-p-phenylazoacrylanilide (PAAn) copolymer was synthesized and the photoresponse of the polymer solution was investigated. AA-PAAn copolymer, which takes a compact form in the ordinary state owing to the presence of azoaromatic side chains, is transformed into an extended form when azoaromatic moieties are isomerized by photoirradiation. Thus, the pH value of the solution can be reversible regulated by irradiation and interruption of light through a change in polymer conformation. The range of the pH change was about 0.15. These phenomena can be explained on the basis of polarity change induced by the photoisomerization of azoaromatic side chains.     

Photocatalytic degradation of adenosine triphosphate in an aqueous suspension of TiO<Subscript>2</Subscript>: a HPLC and <Superscript>1</Superscript>H-NMR study

Photocatalytic degradation process of ATP was followed by HPLC and ¹H-NMR measurements. Adenine was one of the major products when the aqueous ATP sample with TiO₂ dispersion was irradiated by UV light (λ = 365 nm) for 90 min. The ¹H-NMR spectra indicated the presence of another product (Z), which likely came from the ribose moiety in ATP. Photocatalytic generation of OH^˙ radicals on TiO₂ surface was concluded to be responsible for degrading ATP. A working hypothesis of the reaction process was proposed to account for the reaction products.     

Determination of cadmium by suction-flow liquid-liquid extraction combined with inductively-coupled plasma atomic emission spectrometry

The flow manifold described permits suction-flow liquid-liquid extraction of cadmium in a discrete aqueous sample as its diethyldithiocarbamate into carbon tetrachloride. The organic extract is fed into the nebulizer of an inductively-coupled plasma atomic emission spectrometer by a peristatic pump. An increase in sensitivity of ca. 250-fold is achieved in comparison with direct aspiration of the aqueous solution. The sampling frequency is 20 h^?1 and the consumption of carbon tetrachloride and 5% (w/v) sodium diethyldithiocarbamate solution are each 0.6 ml min^?1. The 3σ detection limit is 0.4 ng ml^?1 cadmium, and the calibration is linear up to 300 ng ml^?1. The relative standard deviation for 10 replicate measurements is 1.5% for 50 ng ml^?1 cadmium. The flow interferences observed can be decreased or eliminated by the addition of citrate to the buffer solution. Results of analysis of some certified biological reference materials are given.     

Relationship between redox function and protein stability of cytochromes c

Electrochemical, 1H NMR, and optical studies on mesophile Pseudomonas aeruginosa cytochrome c551, its single (F34Y) and quintuple (F7A/V13M/F34Y/E43Y/V78I) mutants, and thermophile Hydrogenobacter thermophilus cytochrome c552 at wide temperature range demonstrated that the stable protein exhibits the low redox potential predominantly due to the enthalpic contribution to the redox reaction. The overall stability of the oxidized form was shown to determine the stability of the Fe-methionine coordination bond, which then directly regulates the redox function.     

[(R)-2-Methyl-1,4,7-triazacyclononane] [1,1,1-tris(aminomethyl)ethane]-cobalt(III) and some Mono[(R)-2-methyl-1,4,7-triazacyclononane]-cobalt(III) Complexes

Summary [(R)-2-Methyl-1,4,7-triazacyclononane][1,1,1-tris(aminomethyl)ethane]cobalt(III) has been prepared and separated into two isomers which show weak Cotton effects in the¹A₁¹T₁ region (d-electron transition) compared with that of bis[(R)-2-methyl-1,4,7-triazacyclononane]cobalt(III). The effect is comparable to that of tetraammine[(R)-1,2-diamino propane]cobalt(III). The circular dichroism spectra of the mono complex change markedly upon addition of sodium sulphate. The chelate rings are more flexible in the mono than in the bis complex. Some other related mono[(R)-2-methyl 1,4,7-triazacyclononane]cobalt(III) and [(R)-2-methyl-1,4,7 triazacyclononane][1,1,1-tris(aminomethyl)ethaneI nickel (II) complexes have also been prepared and characterized.