UV absorption spectra of methyl-substituted hydroxy-cyclohexadienyl radicals in the gas phase

UV absorption spectra of five methyl-substituted hydroxy-cyclohexadienyl radicals, formed by the addition of the hydroxyl radical (OH) to toluene (methyl benzene), o-, m- and p-xylene (1,2-, 1,3- and 1,4-dimethyl benzene, respectively) and mesitylene (1,3,5-trimethylbenzene), have been determined at 298 K, 1 atm pressure (N-2 + O-2), and the corresponding absolute absorption cross-sections measured, using laser flash photolysis and time-resolved UV absorption detection. As observed for other cyclohexadienyl-type radicals, a strong absorption band is present in the 260-340 nm spectral region, with maximum cross-sections in the range (0.9-2.2) x 10(-17) cm(2) molecule(-1). The shape of the band varies significantly from one radical to the next for the series of aromatic precursors investigated. The nature and yields of hydroxylated ring-retaining oxidation products, identified in previous studies of the OH-initiated oxidation of aromatic hydrocarbons, and the results of theoretical density functional theory (DFT) calculations indicate that one or more possible isomers of the various OH-adducts may contribute to the observed spectra. Isomers where the OH-group is ortho- (or both ortho- and ipso-) to a substituent methyl-group are likely to be the most abundant but other isomers may also be formed to a significant extent. Nonetheless, the present study provides absorption spectra of the adduct radicals formed from the gas phase addition of OH to the aromatic hydrocarbons considered, near room temperature and I atm pressure. (c) 2005 Elsevier B.V. All rights reserved.

Extraction and coordination studies of the unexplored bifunctional ligand carbamoyl methyl sulfoxide (CMSO) with uranium(VI) and cerium(III) nitrates. Synthesis and structures of [UO2(NO3)(2)((PhSOCH2CONBu2)-Bu-i)] and [Ce(NO3)(3)(PhSOCH2CONBu2)(2)]

The bifunctional carbamoyl methyl sulfoxide ligands, PhCH2SOCH2CONHPh (L-1), PhCH2SOCH2CONHCH2Ph (L-2), (PhSOCH2CONPr2)-Pr-i (L-3), PhSOCH2CONBu2 (L-4), (PhSOCH2CONBu2)-Bu-i (L-5) and PhSOCH2CON(C8H17)(2) (L-6) have been synthesized and characterized by spectroscopic methods. The selected coordination chemistry of L-1, L-3, L-4 and L-5 with [UO2(NO3)(2)] and [Ce(NO3)(3)] has been evaluated. The structures of the compounds [UO2(NO3)(2)((PhSOCH2CONBu2)-Bu-i)] (10) and [Ce(NO3)(3)(PhSOCH2CONBu2)(2)] (12) have been determined by single crystal X-ray diffraction methods. Preliminary extraction studies of ligand L-6 with U(VI), Pu(IV) and Am(III) in tracer level showed an appreciable extraction for U(VI) and Pu(IV) in up to 10 M HNO3 but not for Am(III). Thermal studies on compounds 8 and 10 in air revealed that the ligands can be destroyed completely on incineration. The electron spray mass spectra of compounds 8 and 10 in acetone show that extensive ligand distribution reactions occur in solution to give a mixture of products with ligand to metal ratios of 1 : 1 and 2 : 1. However, 10 retains its solid state structure in CH2Cl2.

Synthesis and characterization of carbamoyl methyl pyrazole(CMPz) compounds of palladium(II) chloride: the crystal and molecular structure of [PdCl2{(C3H3N2CH2CONBu2)-Bu-i}(2)]

Carbamoyl methyl pyrazole compound of palladium(II) chloride of the type [PdCl2L2] (where L = C5H7N2CH2CON(C4H9)(2), C5H7N2CH2CON((C4H9)-C-i)(2), C3H3N2CH2CON(C4H9)(2), or C3H3N2CH2CON((C4H9)-C-i)(2)) has been synthesized and characterized by IR and H-1 NMR spectroscopy. The structure of the compound [PdCl2{(C3H3N2CH2CONBu2}2)-Bu-i] has been determined by single crystal X-ray diffraction and shows that the ligands are bonded through the soft pyrazolyl nitrogen atom to the palladium(II) chloride in a trans disposition. (c) 2007 Elsevier B.V. All rights reserved.

Interactions of an anionic surfactant with poly(oxyalkylene) copolymers in aqueous solution

The interactions of sodium dodecyl sulfate (SDS) with poly(ethylene oxide)/poly(alkylene oxide) (E/A) block copolymers are explored in this study: With respect to the specific compositional characteristics of the copolymer, introduction of SDS can induce fundamentally different effects to the self-assembly behavior of E/A copolymer solutions. In the case of the E18B10-SDS system (E = poly(ethylene oxide) and B = poly(butylene oxide)) development of large surfactant-polymer aggregates was observed. In the case of B20E610-SDS, B12E227B12-SDS, E40B10E40-SDS, E19P43E19-SDS (P = poly(propylene oxide)), the formation of smaller particles compared to pure polymeric micelles points to micellar suppression induced by the ionic surfactant. This effect can be ascribed to a physical binding between the hydrophobic block of unassociated macromolecules and the non-polar tail of the surfactant. Analysis of critical micelle concentrations (cmc*) of polymer-surfactant aqueous solutions within the framework of regular solution theory for binary surfactants revealed negative deviations from ideal behavior for E40B10E40-SDS and E19P43E19-SDS, but positive deviations for E18B10-SDS. Ultrasonic studies performed for the E19P43E19-SDS system enabled the identification of three distinct regions, corresponding to three main steps of the complexation; SDS absorption to the hydrophobic backbone of polymer, development of polymer-surfactant complexes and gradual breakdown of the mixed aggregates. (C) 2008 Elsevier Inc. All rights reserved.

Syntheses, characterization and X-ray crystal structures of Ni(II) complexes of tridentate monocondensed and tetradentate dicondensed Schiff bases

Two octahedral complexes [Ni(HL1)(2)](ClO4)(2) (1) and [Ni(HL2)(2)](ClO4)(2) (2) and a square planar complex [Ni(HL3)]ClO4 (3) have been prepared, where [HL1 = 3-(2-amino-ethylimino)-butan-2-one oxime, HL2 = 3-(2-amino-propylimino)butan-2-one oxime] and H2L3 = 3-[2-(3-hydroxy-1-methyl-but-2-enylideneamino)-1-methyl-ethylimino]-buta n-2-one oxime. All the complexes have been characterized by elemental analyses, spectral studies and room temperature magnetic moment measurements. The molecular structures of all three compounds were elucidated on the basis of X-ray crystallography: complexes 1 and 2 are seen to be the met isomers. (C) 2008 Elsevier Ltd. All rights reserved.

Effect of sequence distribution on the morphology, crystallization, melting, and biodegradation of poly(epsilon-caprolactone-co-epsilon-caprolactam) copolymers

Two types of poly(epsilon-caprolactone (CLo)-co-poly(epsilon-caprolactam (CLa)) copolymers were prepared by catalyzed hydrolytic ring-opening polymerization. Both cyclic comonomers were added simultaneously in the reaction medium for the First type or materials where copolymers have a random distribution of counits, as evidenced by H-1 and C-13 NMR. For the second type of copolymers, the cyclic comonomers were added sequentially, yielding diblock poly(ester-amides). The materials were characterized by differential scanning calorimetry (DSC), wide- and small-angle X-ray scattering (WAXS and SAXS), and transmission and scanning electron microscopies (TEM and SEM). Their biodegradation in compost was also studied. All copolymers were found to be miscible by the absence of structure in the melt. TEM revealed that all samples exhibited a crystalline lamellar morphology. DSC and WAXS showed that in a wide composition range (CLo contents from 6 to 55%) only the CLa units were capable of crystallization in the random copolymers. The block copolymer samples only experience a small reduction of crystallization and melting temperature with composition, and this was attributed to a dilution effect caused by the miscible noncrystalline CLo units. The comparison between block and random copolymers provided a unique opportunity to distinguish the dilution effect of the CLo units on the crystallization and melting of the polyamide phase from the chemical composition effect in the random copolymers case, where the CLa sequences are interrupted statistically by the CLo units, making the crystallization of the polyamide strongly composition dependent. Finally, the enzymatic degradation of the copolymers in composted soil indicate a synergistic behavior where much faster degradation was obtained for random copolymers witha CLo content larger than 30% than for neat PCL.

Self-nucleation and crystallization kinetics of double crystalline poly(p-dioxanone)-b-poly(epsilon-caprolactone) diblock copolymers

The crystallization kinetics of each constituent of poly(p-dioxanone)-b-poly(epsilon-caprolactone) diblock copolymers (PPDX-b-PCL) has been determined in a wide composition range by differential scanning calorimetry and compared to that of the equivalent homopolymers. Spherulitic growth rates were also measured by polarized optical microscopy while atomic force microscopy was employed to reveal the morphology of one selected diblock copolymer. It was found that crystallization drives structure formation and both components form lamellae within mixed spherulitic superstructures. The overall isothermal crystallization kinetics of the PPDX block at high temperatures, where the PCL is molten, was determined by accelerating the kinetics through a previous self-nucleation procedure. The application of the Lauritzen and Ho. man theory to overall growth rate data yielded successful results for PPDX and the diblock copolymers. The theory was applied to isothermal overall crystallization of previously self-nucleated PPDX ( where growth should be the dominant factor if self-nucleation was effective) and the energetic parameters obtained were perfectly matched with those obtained from spherulitic growth rate data of neat PPDX. A quantitative estimate of the increase in the energy barrier for crystallization of the PPDX block, caused by the covalently bonded molten PCL as compared to homo-PPDX, was thus determined. This energy increase can dramatically reduce the crystallization rate of the PPDX block as compared to homo-PPDX. In the case of the PCL block, both the crystallization kinetics and the self-nucleation results indicate that the PPDX is able to nucleate the PCL within the copolymers and heterogeneous nucleation is always present regardless of composition. Finally, preliminary results on hydrolytic degradation showed that the presence of relatively small amounts of PCL within PPDX-bPCL copolymers substantially retards hydrolytic degradation of the material in comparison to homo-PPDX. This increased resistance to hydrolysis is a complex function of composition and its knowledge may allow future prediction of the lifetime of the material for biomedical applications.

Nanostructure formation in poly(gamma-benzyl-L-glutamate)-poly(ethylene glycol)-poly(gamma-benzyl-L-glutamate) triblock copolymers in the solid state

The morphology in the solid state of a series of triblock copolymers comprising a poly(ethylene glycol) (PEG) midblock and symmetric poly(gamma-benzyl-L-glutamate) (PBLG) end blocks has been studied using X-ray scattering and microscopy techniques. Transmission electron microscopy (TEM) on samples selectively stained with uranyl acetate provided clear assignment of morphologies for as-cast and annealed samples. The thickness of both PEG and PBLG domains was in good agreement with calculations based on the conformations of the respective chains, allowing for the crystal or amorphous state of PEG and the a-helical or P-sheet structure of the PBLG. Atomic force microscopy provided complementary information on surface morphology for several samples that was in good agreement with the structure observed by TEM. A morphology diagram was constructed. Cylindrical structures were observed for ordered samples with low f(PBLG), whereas at higher f(PLBG) there was evidence for broken lamellar and "hockey puck" nanostructures. Regular lamellae were observed for intermediate compositions.

Chiral poly(aromatic amide ester) dendrimers bearing an amino acid derived C-3-symmetric core: synthesis and properties

The effect of hyperbranched macromolecular architectures (dendrimers) upon chirality has received significant attention in recent years in the light of the proposal of amplification of chirality. In particular, several studies have been carried out on the chiroptical properties of dendrimers that contain a chiral core and achiral branches in order to determine if the chirality of the central core can be transmitted to the distal. region of the macromolecule. In addition to interest of a pure academic nature, the presence of such chiral conformational order would be extremely useful in the development of asymmetric catalysts. In this paper, a novel class of chiral dendrimers is described - these perfect hyperbranched macromolecules have been prepared by a convergent route by the coupling of a chiral central core based upon tris(2-aminoethyl)amine and poly(aromatic amide ester) dendritic branches. The chiral properties of these dendrimers have been investigated by detailed optical rotation studies and circular dichroism analysis; the results of these studies are described herein. (C) Wiley-VCH Verlag GmbH Co.

A stereocontrolled total synthesis of methyl (+/-)-O-methylpodocarpate

A stereocontrolled total synthesis of methyl (+/-)-O-methyl podocarpate (4) has been successfully accomplished using the trans-fused diester 21 as a key intermediate. Intramolecular Michael reaction of the enone-diester 18 afforded the cis-fused keto-diester 19 in high yield which was stereoselectively converted into 21 via the enone 20. (C) 2003 Elsevier Science Ltd. All rights reserved.

DNA cleavage and antitumour activity of platinum(II) and copper(II) compounds derived from 4-methyl-2-N-(2-pyridylmethyl)aminophenol: spectroscopic, electrochemical and biological investigation

The reaction of the redox-active ligand, Hpyramol (4-methyl-2-N-(2-pyridylmethyl)aminophenol) with K2PtCl4 yields monofunctional square-planar [Pt(pyrimol)Cl], PtL-Cl, which was structurally characterised by single-crystal X-ray diffraction and NMR spectroscopy. This compound unexpectedly cleaves supercoiled double-stranded DNA stoichiometrically and oxidatively, in a non-specific manner without any external reductant added, under physiological conditions. Spectro-electrochemical investigations of PtL-Cl were carried out in comparison with the analogue CuL-Cl as a reference compound. The results support a phenolate oxidation, generating a phenoxyl radical responsible for the ligand-based DNA cleavage property of the title compounds. Time-dependent in vitro cytotoxicity assays were performed with both PtL-Cl and CuL-Cl in various cancer cell lines. The compound CuL-Cl overcomes cisplatin-resistance in ovarian carcinoma and mouse leukaemia cell lines, with additional activity in some other cells. The platinum analogue, PtL-Cl also inhibits cell-proliferation selectively. Additionally, cellular-uptake studies performed for both compounds in ovarian carcinoma cell lines showed that significant amounts of Pt and Cu were accumulated in the A2780 and A2780R cancer cells. The conformational and structural changes induced by PtL-Cl and CuL-Cl on calf thymus DNA and phi X174 supercoiled phage DNA at ambient conditions were followed by electrophoretic mobility assay and circular dichroism spectroscopy. The compounds induce extensive DNA degradation and unwinding, along with formation of a monoadduct at the DNA minor groove. Thus, hybrid effects of metal-centre variation, multiple DNA-binding modes and ligand-based redox activity towards cancer cell-growth inhibition have been demonstrated. Finally, reactions of PtL-Cl with DNA model bases (9-Ethylguanine and 5'-GMP) followed by NMR and MS showed slow binding at Guanine-N7 and for the double stranded self complimentary oligonucleotide d(GTCGAC)(2) in the minor groove.

Trinuclear Cu(II) complexes containing peripheral ketonic oxygen bridges and a mu(3)-OH core: steric influence on their structures and existence

Two tridentate Schiff bases, HL1(6-amino-3-methyl-1-phenyl-4-azahex-2-en-1-one), and HL2 (6-atnino-3,6-dimethyl-1-phenyl-4-azahex-2-en-1-one) on reaction with Cu(II) perchlorate in the presence of triethyl amine yielded two new trinuclear copper(II) complexes, [(CuL1)(3)(mu(3)-OH)](ClO4)(2) (1) and [(CuL2)(3)(mu(3)-OH)](ClO4)(2) center dot 0.75H(2)O (2), whereas another tridentate ligand HL3 (7-amino-3-methyl-1-phenyl-4-azahept-2-en-1-one) underwent hydrolysis under the same reaction conditions to result in the formation of a mononuclear complex, [Cu(bn)(pn)ClO4] (3) [where bn = 1-benzoylacetonate and pn = 1,3-propanediamine]. All three complexes have been characterized by X-ray crystallography. For both 1 and 2 the cationic part is trinuclear with a [Cu3OH] core held by three carbonyl oxygen bridges between each pair of copper(II) atoms. The structure of 3 is a monomer with a chelating 1,3-propanediamine and a benzoyl acetone moiety. Magnetic measurements of I and 2 have been performed in the 2-300 K temperature range. The experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = -J(S1S2 + S2S3 + S1S3), yielding as best fit parameters: J = -25.6 cm(-1), g = 2.21 for 1 and J = 11.2 cm(-1), g = 2.10 for 2. The EPR spectra at low temperature could be indicative of spin frustration in complex 1. (C) 2006 Elsevier Ltd. All rights reserved.

Stereoselective syntheses of (+/-)-komaroviquinone and (+/-)-faveline methyl ether through intramolecular Heck reaction

An efficient, flexible, and stereoselective convergent route for constructing the trans-10-hydroxy1,1-dimethyloctahydrodibenzo[a,d]cyclohepten-7-ones (5a-c) was achieved via intramolecular Heck reaction. This strategy has been successfully implemented for the syntheses of (+/-)-komaroviquinone (3) through (+/-)-coulterone dimethyl ether (5c) and (+/-)-faveline methyl ether (1a).

One-pot synthesis and characterization of soluble poly(aryl ether-ketone)s having pendant carboxyl groups

Aromatic poly(ether-ketone)s having pendant carboxyl groups have been obtained by direct, one-pot, Friedel-Crafts copolycondensation of 4,4'-diphenoxybenzophenone with a mixture of terephthaloyl chloride (TC) and trimellitic anhydride acid chloride (TAAC), over a wide range of TAAC/TC molar ratios, in the presence of anhydrous aluminum chloride. The syntheses were performed as precipitation-polycondensations, and the polymers were obtained in particulate form. Besides globular particles of polymer, small quantities of elongated, needlelike particles were observed when the mole ratio TAAC/TC was less than 1. Use of X-ray microdiffraction with synchrotron radiation has revealed that the needlelike material consists of a cyclic compound containing 10 phenylene units, i.e., the crystals are of a [2 + 2] macrocyclic dimer. The polymers obtained are soluble in strong acids and in mixtures of methanesulfonic acid or trifluoroacetic acid with chlorinated hydrocarbons. The molecular structures of the polymers were confirmed by H-1 and C-13 NMR spectroscopy. Reaction of TAAC with 4,4'-diphenoxybenzophenone produced mainly meta-orientation of the resulting ketone linkages. The size of the polymer particles, their molecular weights, and the melting behavior of the products obtained depend on the TAAC/TC ratio used. Ortho-keto acid residues, formed during reaction of anhydride groups of TAAC with 4,4'-diphenoxybenzophenone, exhibit ring-chain tautomerism. A carboxyl-containing aromatic polyketone derived from p-terphenyl, and thus having with no ether linkages in the main chain, was prepared by analogous chemistry, and functional derivatives of carboxy-substituted polyketones were also obtained and characterized.

Formation of crystalline macrocyclic phases during electrophilic precipitation-polycondensation syntheses of poly(arylene ether ketone)s

Elongated crystalline particles formed as by-products during poly(arylene ether ketone) synthesis by electrophilic precipitation-polycondensation of 4,4'-diphenoxybenzophenone with terephthaloyl chloride or isophthaloyl chloride, thought previously to be polymer-whiskers, have now been identified as macrocyclic phases. Single crystal X-ray analysis of the needle-like particles formed in the reaction with terephthaloyl chloride, using the microdiffraction technique with synchrotron radiation, revealed that they consist of a macrocylic compound containing ten phenylene units, i.e. the [2 + 2] cyclic dimer. An analogous structure has also been demonstrated for the corresponding macrocycle derived from the reaction of 4,4-diphenoxybenzophenone with isophthaloyl chloride. Chloroform extraction of the products of the two polycondensations dissolved the macrocyclic material (but not the linear polymer), and analysis of the extracts by MALDI-TOF mass spectrometry demonstrated the presence in both cases of homologous families of macrocyclic products. Higher yields of macrocycles were obtained under pseudo-high dilution conditions, enabling the [2 + 2] cyclodimers from reactions of 4,4'-diphenoxybenzophenone with both terephthaloyl and isophthaloyl chloride to be isolated as pure compounds and fully characterised. (C) 2003 Published by Elsevier Ltd.