The effect of ionising radiation on poly(methyl methacrylate) used in intraocular lenses

Gamma radiation is increasingly being used to sterilise intraocular lenses (IOLs) made from poly(methyl methacrylate) (PMMA). In this study, samples of PMMA used in the fabrication of IOLs were exposed to irradiation doses typically used for their sterilisation. The effect of this treatment on the polymer was analysed by size-exclusion chromatography (SEC), UV-visible and infrared spectroscopy and scanning electron microscopy (SEM). The PMMA was found to have undergone chain scission, decarboxylation and colour change following the irradiation.     

High-performance liquid chromatography of coenzyme Q-related compounds and its application to biological materials

A convenient and precise method for the separation and determination of coenzyme Q (CoQ)-related compounds (CoQ homologues, plastoquinone-9, ubichromenol-9, etc.) was developed using high-performance liquid chromatography (HPLC). All compounds tested were separated using a reverse-phase column with a suitable mobile phase and detected at a wavelength of 275 nm. CoQ extracts in plasma and erythrocytes were purified by thin-layer chromatography prior to HPLC analysis, but such purification was not necessary when determining CoQ in urine and tissues. Hydroquinone forms of CoQ existing in animal tissues were oxidized to the corresponding quinone forms with potassium hexacyanoferrate(III). This HPLC method was applied satisfactorily to the determination of the contents of CoQ homologues in human and animal samples. CoQ10 was the only homologue detected in human samples, and CoQ8, CoQ9 and CoQ10 were native homologues of CoQ in rat tissues. Ubichromenol-9 and plastoquinone-9 were not detected in these samples.     

New catalytic cycle for couplings of aldehydes with organochromium reagents

[reaction: see text] A new catalytic cycle has been developed to effect all three subgroups of Cr-mediated couplings, i.e., (1) Ni/Cr-mediated alkenylation, alkynylation, and arylation, (2) Co/Cr-mediated 2-haloallylation, alkylation, and propargylation, and (3) Cr-mediated allylation. In the presence of chiral sulfonamide ligands, good asymmetric inductions can be achieved for some of the Ni/Cr-mediated alkenylation, Co/Cr-mediated 2-haloallylation and propargylation, and Cr-mediated allylation.     

Surprisingly efficient catalytic Cr-mediated coupling reactions

[reaction: see text] With use of 1 mol % of Cr catalyst 5, surprisingly efficient Cr-mediated couplings of aldehydes with various types of nucleophiles have been realized. The catalyst set of Cr catalyst 5 and Ni catalyst 4 is used for alkenylation, alkynylation, and arylation, whereas the catalyst set of Cr catalyst 5 and CoPc (cobalt phthalocyanine) is used for 2-haloallylation, alkylation, and propargylation. Only the Cr catalyst 5 is required for allylation. The reaction rates in DME and THF have been found significantly faster than that in MeCN.     

The effect of humidity on thermal process of zinc acetate

The thermal decomposition of zinc acetate dihydrate Zn(CH₃CO₂)₂·2H₂O in some humidity-controlled atmospheres has been successfully investigated by novel thermal analyses, which are sample-controlled thermogravimetry (SCTG), thermogravimety combined with evolved gas analysis using mass spectrometry (TG–MS) and simultaneous measurement of differential scanning calorimetry and X-ray diffractometry (XRD–DSC). The thermal processes of anhydrous zinc acetate in dry gas atmosphere by conventional linear heating experiment initiated with the sublimation around 180 °C, followed by the fusion and the decomposition over 250 °C. SCTG was useful to interpret clearly the successive reaction because the high-temperature parallel decompositions were effectively inhibited. The thermal behavior changed dramatically by introducing water vapor in the atmosphere and the thermal process was quite different from that in dry gas atmosphere. Zinc oxide (ZnO) was formed only in a humidity-controlled atmosphere, and could be easily synthesized at temperatures below 300 °C. XRD–DSC equipped with a humidity generator revealed directly the crystalline change from Zn(CH₃CO₂)₂ to ZnO. A detailed thermal process of Zn(CH₃CO₂)₂·2H₂O and the effect of water vapor are discussed.     

Synthesis of poly (ethylene oxide)-b-polysilane by anionic polymerization of masked disilenes using a macroinitiator method

Poly(ethylene oxide-)-poly(1, 1-dimethyl-2, 2-dihexyldisilene) block copolymers (PEO-b-PMHS) were synthesized by the anionic polymerization of masked disilenes initiated with the potassium alkoxide of poly(ethylene glycol). The block copolymer self-assembled into polymer micelles in water accompanied by a transition in the polysilane conformation.     

Medicinal foodstuffs. XVII. Fenugreek seed. (3): structures of new furostanol-type steroid saponins, trigoneosides Xa, Xb, XIb, XIIa, XIIb, and XIIIa, from the seeds of Egyptian Trigonellafoenum-graecum L

Six new furostanol-type steroid saponins called trigoneosides Xa, Xb, XIb, XIIa, XIIb, and XIIIa were isolated from the seeds of Egyptian Trigonella foenum-graecum L. (Leguminosae) together with six known furostanol-type steroid saponins: trigoneosides Ia, Ib, and Va, glycoside D, trigonelloside C, and compound C. The structures of trigoneosides Xa, Xb, Xlb, XIIa, Xllb, and XIIIa were determined on the basis of chemical and physicochemical evidence as 26-O-beta-D-glucopyranosyl-(25S)-5alpha-furostane-2alpha+ ++,3beta,22xi,26-tetraol 3-O-alpha-L-rhamnopyranosyl(1-->2)-,beta-D-glucopyranoside, 26-O-beta-D-glucopyranosyl-(25R)-5alpha-furostane-2 alpha,beta,22xi,26tetraol 3-O-alpha-L-rhamnopyranosyl(l -->2)-beta-D-glucopyranoside, 26-O-beta-D-glucopyranosyl-(25R)-5alpha-furostane2alpha++ +,beta,22xi,26-tetraol 3-O-beta-D-xylopyranosyl(l -->4)-beta-D-glucopyranoside, 26-O-beta-D-glucopyranosyl-(25S)-furost-4-ene-3beta,22xi,26- triol 3-O-Ca-L-rhamnopyranosyl(1-->2)-beta-D-glucopyranoside, 26-O-beta-D-glucopyranosyl-(25R)-furost-4-ene-3beta,22xi+ ++,26-triol 3-O-alpha-L-rhamnopyranosyl(1-->2)-beta-D-glucopyranoside, and 26-O-beta-D-glucopyranosyl(25S)-furost-5-ene-3beta,22xi,26-t riol 3-O-alpha-L-rhamnopyranosyl(1-->2)-beta-D-glucopyranosyl (1-->3)-beta-D-glucopyranosyl(1--4)]-beta-D-glucopyranoside, respectively.     

Isolation,chemical characterization and structure of ansamitocin,a new antitumor ansamycin antibiotic

In this paper we report the isolation, chemical characterization and structural elucidation of Ansamitocin, a new antitumor antibiotic obtained from Nocardia No. C-15003 (N-1). Ansamitocin P-3, P-3' and P-4 with molecular formulae C₃₂H₄₃ClN₂O₉, C₃₂H₄₃ClN₂O₉ and C₃₃H₄₅ClN₂O₉, respectively, were identified as novel antibiotics. Their UV spectra resemble that of maytansine obtained from a plant source. Analysis of the PMR spectrum and spin-decoup studies of P-3 demonstrated that its skeletal structure was the same as that of maytansine. Reductive cleavage of each antibiotic gave maytansinol (P-0). Alkali hydrolysis of P-3, P-3' and P-4 gave isobutyric, butyric and isovaleric acids, respectively. P-3, P-3' and P-4 were concluded to be the isobutyrate, butyrate and isovalerate ester of maytansinol at C-3, respectively. An antitumor plant product, maytanacine, and its semisynthetic derivative, maytansinol propionate, were also produced by the same strain.