Copper–Oxygen Dynamics in the Tyrosinase Mechanism

The dinuclear copper enzyme, tyrosinase, activates O₂ to form a (μ‐η²:η²‐peroxido)dicopper(II) species, which hydroxylates phenols to catechols. However, the exact mechanism of phenolase reaction in the catalytic site of tyrosinase is still under debate. We herein report the near atomic resolution X‐ray crystal structures of the active tyrosinases with substrate l ‐tyrosine. At their catalytic sites, CuA moved toward l ‐tyrosine (CuA1 → CuA2), whose phenol oxygen directly coordinates to CuA2, involving the movement of CuB (CuB1 → CuB2). The crystal structures and spectroscopic analyses of the dioxygen‐bound tyrosinases demonstrated that the peroxide ligand rotated, spontaneously weakening its O?O bond. Thus, the copper migration induced by the substrate‐binding is accompanied by rearrangement of the bound peroxide species so as to provide one of the peroxide oxygen atoms with access to the phenol substrate's ? carbon atom.     

Distinguishing hepatic hemangiomas from metastatic tumors using T1 mapping on gadoxetic-acid-enhanced MRI

Objective

The objective was to evaluate the usefulness of T1 mapping in distinguishing hepatic hemangiomas from metastatic tumors on gadoxetic-acid-enhanced magnetic resonance imaging.

Methods

We examined 20 hemangiomas in 14 patients and 21 metastatic tumors in 11 patients. We performed T1 mapping using the double-flip angle method before and after the injection of gadoxetic acid. Quantitative evaluation was carried out using the pre- and post-contrast enhancement ratios (CERs), and qualitative evaluation was conducted to evaluate the added value of T1 mapping using receiver operating characteristics analysis.

Results

The mean CERs of metastatic tumors at 70 s, 240 s and 20 min after the injection of gadoxetic acid were 1.54 (95% confidence interval: 1.37–1.71), 1.47 (1.34–1.6) and 1.30 (1.19–1.41); those of hemangiomas were 3.36 (2.41–4.31), 3.06 (2.44–3.68) and 2.20 (2.02–2.38), respectively. The mean CERs of hemangiomas were significantly higher than those of metastatic tumors (P< .05). When the mean CER cutoff value 20 min after the injection was set at 1.6, the diagnostic sensitivity of hepatic hemangiomas was 100%. There was no added value observed statistically in the qualitative evaluation of T1 mapping (P> .05).

Conclusion

It is valuable to evaluate quantitatively T1 mapping 20 min after hepatobiliary phase acquisition in the case of difficulty in distinguishing hepatic hemangiomas from metastatic tumors qualitatively.     

Synthesis of a water-soluble molecular tweezer and a recognition study in an aqueous media

Synthesis of a 1,10-diphenanthryl all-trans fused perhydrophenanthrene derivative and a recognition study in an aqueous media were carried out. A water-soluble derivative recognized certain benzene derivatives with 10⁴-10⁵ M⁻¹ of binding constant.     

Determination of vanadium in heavy oils by atomic absorption spectrometry using a graphite furnace coated with tungsten.

A simple and rapid method was established for the direct determination of vanadium in an oil sample using the tungsten-coated graphite-furnace AAS. The interference of the sulfur compound could be suppressed by choosing the ashing temperature. If the sulfur concentration in the sample is diluted to 1.0 wt% or less, the interference can be suppressed. This proposed method should make important contributions to the quality control of petroleum refineries.     

Alignment behavior for novel triphenylene compounds possessing fluoroalkylated side chains on modified substrates

The alignment behavior of the triphenylene compounds possessing fluoroalkylated side chains was investigated for the hexagonal columnar (Col_h) mesophase on the polyimide-, cetyltrimethylammonium bromide (CTAB)-, and indium-SnO₂ (ITO)-coated glass substrates by polarizing optical microscopy. It was found that 2,3,6,7,10,11-hexakis(1H,1H,2H,2H,3H,3H-perfluoroheptyloxy)- and 2,3,6,7,10,11-hexakis(1H,1H,2H,2H,3H,3H-perfluorononyloxy)-triphenylenes exhibit a spontaneous homeotropic alignment on these substrates, in contrast to the non-uniformity of alignment of Col_h phase in the corresponding hydrocarbon mesogens. On the other hand, it was also found that 4,4,4-trifluorobutyloxy, 4,4,5,5,5-pentafluoropentyloxy and 4,4,5,5,6,6,6-heptafluorohexyloxy derivatives do not show such a spontaneous homeotropic alignment on these substrates. These results indicate that the spontaneous homeotropic alignment of the Col_h phase could be easily attained by the introduction of an appropriate number and length of the fluoromethylene chains in the peripheral parts of discogens.     

Total‐reflection X‐ray diffraction study of friction‐transferred poly(tetrafluoroethylene) film

The orientational structure of the friction‐transferred poly(tetrafluoroethylene) (PTFE) film, which consists of highly oriented polymer strands, was evaluated with energy‐dispersive total‐reflection X‐ray diffractometry. In the film, each PTFE molecule is oriented along the friction direction, and PTFE crystallites have a preferred orientation with respect to the substrate surface. The orientational distribution of the chain direction was quantitatively evaluated. The half‐width of the distribution was determined to be about 3°. The dependence of the orientational distribution on temperature is discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 432–438, 2001     

Separation of rhodium and iridium by anion-exchange thin-layer chromatography

Ohne Zusammenfassung

---

Spectro photometric determination of thallium(I) and dimethylthallium compounds in small concentrations

     

Aqueous two-phase extraction of nickel dimethylglyoximato complex and its application to spectrophotometric determination of nickel in stainless steel

A polyethylene glycol (PEG)-based aqueous two-phase system has been established for the extraction of Ni-dimethylglyoximato complex. Appropriate amounts of PEG solution and solid (NH₄)₂SO₄ were added to the Ni-dimethylglyoximato complex which had been formed in the presence of sodium tartrate and K₂S₂O₈ at pH 12 in a separatory funnel and shaken vigorously for about 1 min. The mixture was allowed to stand for 10 min and then the absorbance of the extracted complex in the upper PEG-rich phase was measured at 470 nm. Beer's law was obeyed over the range of 0.26-2.1 ppm Ni. The proposed extraction method has been applied to the determination of Ni in steel. A steel sample was decomposed with an appropriate acid mixture. An aliquot of the sample solution was taken, treated with H₃PO₄ and most of the iron and copper were removed by hydroxide precipitation using solid BaCO₃ to control the pH of the sample solution in advance of the extraction of Ni. The analytical results obtained for Ni in steel certified reference material JSS 650-10 (The Japan Iron and Steel Federation), BCS 323 (Bureau of Analysed Samples Ltd.) and NIST SRM 361 and 362 (National Institute of Standards and Technology) were in good agreement with certified values.     

Synthesis of potent CXCR4 inhibitors possessing low cytotoxicity and improved biostability based on T140 derivatives

A peptidic CXCR4 antagonist T140 efficiently blocks the entry of T cell line-tropic strains of HIV-1 (X4-HIV-1) into target cells. In this study, a series of T140 derivatives, replacing the basic amino acid residues with Glu (D-Glu) and/or L-citrulline (Cit), were synthesized in order to reduce non-specific binding and cytotoxicity. Among them, TE14011 ([Cit6, D-Glu8]-T140 with the C-terminal amide) exhibited strong anti-HIV activity and low cytotoxicity. TE14011 was found to be stable in mouse serum, but unstable in rat liver homogenate due to the deletion of the N-terminal Arg1-Arg2-L-3-(2-naphthyl)alanine (Nal)3 residues from the parent peptide. N-Terminal acetylation of TE14011 led to the development of a novel lead compound, Ac-TE 14011, which possesses a high selectivity index as well as increased stability in serum and liver homogenate.     

Photochemical (2 + 2) cycloaddition of and thermal decomposition to n-methylacridone and acetone: chemiluminescence as a probe of possible formation of 1,2-dioxetanes

Irradiation of N-methylacridone (NMA) in an acetone solution at ?78°C in the argon atmosphere afforded light emission (φ_CL: 10^?6 - 10^?8 einstein/mol) upon warming-up to room temperature. The final products were NMA acetone exclusively.