On some global well-posedness and asymptotic results for quasilinear parabolic equations

We prove that the quasilinear parabolic initial-boundary value problem (1.1) below is globally well-posed in a class of high order Sobolev solutions, and that these solutions possess compact, regular attractors ast+.     

Synthesis and Structural Studies of Platinum Complexes Containing Monodentate, Bridging, and Chelating Formamidine Ligands

The reactions of K(2)PtCl(4) with N,N'-diphenylformamidine (HDPhF) and N,N'-di-p-tolylformamidine (HDTolF) produce the trans square-planar compounds PtCl(2)(HDPhF)(2), 1a, and PtCl(2)(HDTolF)(2), 1b. Compound 1a crystallizes as yellow parallelepipeds in the space group P2(1)/c with two independent molecules in the asymmetric unit and unit cell dimensions a = 23.427(7) ?, b = 16.677(6) ?, c = 12.980(4) ?, and beta = 96.10(2) degrees. These compounds are soluble in common organic solvents and have been used as starting materials for the preparation of diplatinum compounds. Treatment of 1a and 1b with NaOMe and the halide abstraction reagent TlPF(6) produces the compounds Pt(2)(&mgr;-DArF)(2)(eta(2)-DArF)(2), Ar = Ph (2a) and Tol (2b), respectively. Compound 2a crystallizes as yellow rods in the space group P&onemacr; with unit cell dimensions a = 12.296(3) ?, b = 12.310(4) ?, c = 15.374(4) ?, alpha = 90.75(2) degrees, beta = 91.02(2) degrees, and gamma = 110.20(2) degrees. Compound 2b crystallizes with a molecule of THF, as yellow rods in the space group P2(1)/c with a = 17.883(3) ?, b = 14.517(3) ?, c = 22.581(3) ?, and beta = 98.17(1) degrees. These compounds contain two cis bridging formamidinato ligands and two formamidinato ligands that are chelated to separate Pt centers. Upon heating, they further react to give the tetrabridged compounds Pt(2)(&mgr;-DArF)(4), Ar = Ph (3a), Tol (3b). Compound 3a crystallizes as orange cubes in the cubic space group I432 with a = 19.671(1) ?. On going from the bis-bridged, bis-chelate structure in 2a to the tetrabridged structure in 3a, the metal-metal separation decreases from 2.910(1) to 2.649(1) ?. Both 2band 3b have been oxidized to give the Pt(II)-Pt(III) compound Pt(2)(&mgr;-DTolF)(4)(PF(6)), 4. Compound 4 crystallizes as cubes in the tetragonal space group P4/ncc with a = 14.392(1) ? and c = 14.436(1) ?. The Pt-Pt distance in 4 is 2.5304(6) ?.     

Electrofugal Fragmentation of Alkylcobalamin Derivatives Using Cob(I)Alamin and Heptamethyl Cob (I)yrinate as Catalysts

The cob (I)alamin- ( 1(I) ) and the heptamethyl cob(I)ynnate- ( 2(I) ) catalyzed transformation of an epoxide to the corresponding saturated hydrocarbon 3→4→5 is examined (see Schemes 1 and 3–5). Under the reaction conditions, the epoxyalkyl acetate 3 is opened by the catalysts with formation of appropriate (b?-hydroxyalkyl)-corrinoid derivatives ( 13 , 14 , 17 , 18 , see Schemes 12 and 14). Triggered by a transfer of electrons to the Co-corrin-π system, the Co, C-bond of the intermediates is broken, generating the alkenyl acetate 4 (cf. Schemes 12 and 14) following an electrofugal fragmentation (cf. Schemes 2 and 12). The double bond of 4 is also attacked by the catalysts, leading to the corresponding alkylcorrinoids ( 15 , 19 , see Schemes 12 and 14) which in turn are reduced by electrons from metallic zinc, the electron source in the system, inducing a reductive cleavage of the Co, C-bond with production of the saturated monoacetate 5 (see Schemes 2, 5 and 12). In the cascade of steps involved, the transfer of electrons to the intermediate alkylcorrinoids ( 13–15 , 17–19 , see Schemes 12 and 14) is shown to be rate-limiting. Comparing the two catalytic species 1(I) and 2(I) , it is shown that the ribonucleotide loop protects intermediate alkylcobalamins to some extent from an attack by electrons. The protective function of the ribonucleotide side-chain is shown to be present in alkylcobalamins existing in the base-on form (cf. Chap. 4 and see Scheme 14).     

Chiral hydroperoxides as oxygen source in the catalytic stereoselective epoxidation of allylic alcohols by sandwich-type polyoxometalates: control of enantioselectivity through a metal-coordinated template

The epoxidation of allylic alcohols is shown to be efficiently and selectively catalyzed by the oxidatively resistant sandwich-type polyoxometalates, POMs, namely [WZnM(2)(ZnW(9)O(34))(2)](q)(-) [M = OV(IV), Mn(II), Ru(III), Fe(III), Pd(II), Pt(II), Zn(II); q = 10-12], with organic hydroperoxides as oxygen source. Conspicuous is the fact that the nature of the transition metal M in the central ring of polyoxometalate affects significantly the reactivity, chemoselectivity, regioselectivity, and stereoselectivity of the allylic alcohol epoxidation. For the first time, it is demonstrated that the oxovanadium(IV)-substituted POM, namely [ZnW(VO)(2)(ZnW(9)O(34))(2)](12-), is a highly chemoselective, regioselective, and also stereoselective catalyst for the clean epoxidation of allylic alcohols. A high enantioselectivity (er values up to 95:5) has been achieved with [ZnW(VO)(2)(ZnW(9)O(34))(2)](12)(-) and the sterically demanding TADOOL-derived hydroperoxide TADOOH as regenerative chiral oxygen source. Thus, a POM-catalyzed asymmetric epoxidation of excellent catalytic efficiency (up to 42 000 TON) has been made available for the development of sustainable oxidation processes. The high reactivity and selectivity of this unprecedented oxygen-transfer process are mechanistically rationalized in terms of a peroxy-type vanadium(V) template.     

On the regiochemistry of the methylphenylcyclopropenone dimer. A reinvestigation

The regiochemistry of the previously reported dimer of methyhlphenylcyclopropenone is corrected through analysis of the long-range ¹H, ¹³C correlated (COLOC) 2D nmr spectrum.     

Anionic graft polymerization of methyl methacrylate on starch and dextrin

The anionic graft polymerization of methyl methacrylate on the potassium alkoxide derivative of starch or dextrin in DMSO was studied. The effects of monomer and alkoxide concentrations as well as temperature were investigated. The yield of graft polymer increased with increasing alkoxide concentration. With increasing monomer concentration and with increasing temperature the extent of homopolymer formation increased. The composition of the graft polymers was found to depend on the reaction conditions. Graft polymers having about 10–40% poly(methyl methacrylate) were obtained. There were quantitative differences in yield of isolated graft polymer between starch and dextrin and these were ascribed to differences in the solubility properties of the carbohydrates. Evidence on the structure of the graft polymers and on the mechanism of the graft polymerization was obtained from acid hydrolysis of the graft polymers and determination of the molecular weights of the cleaved side chains.     

Structure and reactivity of xanthocorrinoids. Part V. Formation of trans-diol derivatives of 5,6-dihydrocobyrinic acid from xanthocorrinoids under acidic conditions

On treatment with H₂SO₄/MeOH, epimerization of hexamethyl cis-5,6-dihydroxycobyrinate c,8-lactam ( 3 ) takes place quantitatively at C(6), yielding the corresponding trans-diol 4 . The corresponding lactone 7 , whose structure has been established by X-ray analysis, is obtained from xanthocorrinoids 5 and 6 under similar conditions.     

Fiber optic multi-channel protein detector for use in preparative continuous annular chromatography

On-line coupling continuous-flow liquid membrane extraction (CFLME) with HPLC, a novel automatic system was developed for the determination of sulfonylurea herbicides in water. After an automatic trace-enrichment process by CFLME, which is the combination of continuous flow liquid-liquid extraction and support liquid membrane (SLM) extraction, the target analytes were concentrated in 50 microl of 0.2 M Na2CO3-NaHCO3 (pH 10.0) buffer. The concentrated sample solutions were injected directly onto a C18 analytical column with a valve, and detected at 240 nm with a diode array detector. Metsulfuron methyl (MSM), and DPX-A 7881 were baseline separated with a mobile phase consisting of methanol and 67 mM KH2PO4-Na2HPO4 (pH 5.91) buffer (45+55, v+v) at a flow-rate of 1.0 ml min(-1). With an enrichment time of 10 min and enrichment sample volume of 20 ml, the enrichment factors and detection limits are 100 and 0.05 microg l(-1) for MSM, and 96 and 0.1 microg l(-1) for DPX-A 7881, respectively. The linear range and precision (RSD) are 0.1-50 microg l(-1) and 7.0% for MSM, and 0.2-50 microg l(-1) and 9.2% for DPX-A 7881, respectively. This proposed method was applied to determine MSM and DPX-A 7881 in seawater, tap water, and bottled mineral water with spiked recoveries in the range of 83-95% for MSM and 88-100% for DPX-A 7881, respectively.