Micellar and surface properties of a poly(methyl methacrylate)-block-poly(N-isopropylacrylamide) copolymer in aqueous solution

Critical micelle concentrations (cmc) of aqueous solutions of poly(methyl methacrylate)-block-poly(N-isopropylacrylamide) were determined at several temperatures by surface tensiometry. Below the lower critical solution temperature (LCST), the low Delta(mic) H-0 determined can be assigned to the PMMA block being tightly coiled in the dispersed molecular state, so that the unfavorable interactions of hydrophobic entities with water are minimized. Above the LCST the cmc value was found to increase; an anomalous behavior that can be directly related to the micelle-globule transition of the hydrophilic block. Interestingly, above the LCST the surface tension of relatively concentrated solutions was found to depend weakly on temperature not following the usual strong decrease with temperature expected for aqueous solutions. (C) 2007 Elsevier Inc. All rights reserved.

Two new Ni-II complexes with mu(1.5)-dicyanamide as bridging ligand

One 3D and one 2D mu(1,5)-dicyanamide bridged Ni-II complexes having molecular formula [Ni(L1)(dca)(2)] (1) and [Ni-2(L-2)(2)(dca)(4)] (.) 0.5H(2)O (2) (L1 = 4-(2-aminoethyl)-morpholine, L2 = 1-(2-aminoethyl)-piperidine and dca = dicyanamide dianion) have been synthesized. X-ray single crystal analyses and low temperature magnetic measurements were used to characterize the complexes. Complex 1 represents a 3D structure where each metal ion is chelated by morpholine ligand (L1) and connected by four mu(1,5)-dca. Whereas complex 2 shows an undulated 2D structure with grid of (4,4) topology having two crystallographically independent Ni-II centers in similar octahedral environment where each metal center is chelated by one piperidine ligand (L2) and coordinated by four mu(1,5)-dca. Magnetic measurements of both the complexes indicate weak antiferromagnetic interactions through the mu-(1,5)-dca bridging ligands. (c) 2004 Elsevier B.V. All rights reserved.

Water-soluble, unimolecular containers based on amphiphilic multiarm star block copolymers

A new class of water-soluble, amphiphilic star block copolymers with a large number of arms was prepared by sequential atom transfer radical polymerization (ATRP) of n-butyl methacrylate (BMA) and poly( ethylene glycol) methyl ether methacrylate (PEGMA). As the macroinitiator for the ATRP, a 2-bromoisobutyric acid functionalized fourth-generation hyperbranched polyester (Boltorn H40) was used, which allowed the preparation of star polymers that contained on average 20 diblock copolymer arms. The synthetic concept was validated by AFM experiments, which allowed direct visualization of single molecules of the multiarm star block copolymers. DSC and SAXS experiments on bulk samples suggested a microphase-separated structure, in agreement with the core-shell architecture of the polymers. SAXS experiments on aqueous solutions indicated that the star block copolymers can be regarded as unimolecular micelles composed of a PBMA core and a diffuse PPEGMA corona. The ability of the polymers to encapsulate and release hydrophobic guests was evaluated using H-1 NMR spectroscopy. In dilute aqueous solution, these polymers act as unimolecular containers that can be loaded with up to 27 wt % hydrophobic guest molecules.

Synthesis, crystal structure, magnetic behavior and thermal property of three polynuclear complexes: [M(dca)(2)(H2O)2](n)center dot(hmt)(n) [M = Mn(II), Co(II)] and [Co(dca)(2)(bpds)](n) [dca, dicyanamide; hint, hexamethylenetetramine; bpds, 4,4 '-bipyridyl disulfide]

Three mu(1.5)-dicyanamide bridged Mn(II) and Co(II) complexes having molecular formula [Mn(dca)(2)(H2O)(2)](n)center dot(hmt)(n) (1), [Co(dca)(2) (H2O)(2)](n)center dot(hmt)(n) (2) and [Co(dca)(2)(bpds)](n) (3) [dca = dicyanamide; hmt = hexamethylenetetramine; bpds = 4,4'-bipyridyl disulfide] have been synthesized and characterized by single crystal X-ray diffraction study, low temperature (300-2 K) magnetic measurement and thermal behavior. The X-ray diffraction analysis of 1 and 2 reveals that they are isostructural, comprising of 1D coordination polymers [M(dca)(2)(H2O)(2)](n) [M = Mn(II), Co(II) for 1 and 2. respectively] with uncoordinated hmt molecules located among the chains. The [M(dca)(2)(H2O)(2)](n) chains and the lattice hint molecules are connected through H-bonds resulting in a 3D supramolecular architecture. The octahedral N4O2 chromophore surrounding the metal ion forms via two trans located water oxygens and four nitrogens from four nitrile dca. Complex 3 is a 1D chain formed by two mu(1.5)-dca and one bridging bpds. The octahedral N-6 coordination sphere surrounding the cobalt ions comprises four nitrogens from dca and two from bpds. Low temperature magnetic study indicates small antiferromagnetic coupling for all the complexes. Best fit parameters for 1: J = -0.17 cm(-1), g = -2.03 with R = 6.1 x 10(-4), for 2, J = -0.50 cm(-1), and for 3, J = -0.95 cm(-1). (c) 2005 Elsevier B.V. All rights reserved.

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.

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).

Thermo-responsive poly(methyl methacrylate)-block-poly(N-isopropylacrylamide) block copolymers synthesized by RAFT polymerization: micellization and gelation

RAFT polymerization was used to prepare PMMA-b-PNIPAM copolymers. Two different chain transfer agents, tBDB and MCPDB, were used to mediate the sequential polymerizations. Micellar solutions and gels were prepared from the resulting copolymers in aqueous solution. When heated above T-c of PNIPAM (about 31 degrees C), DLS revealed that PNIPAM coronas collapsed, resulting in aggregation of the original micelles. The micellar gels underwent syneresis above T-c as water was expelled from the ordered gel structure, the lattice periodicity of which was determined by SANS. A large decrease in lattice spacing was observed above T-c. The gel became more viscoelastic at high temperature, as revealed by shear rheometry which showed a large increase in G".

Relationship between sublethal injury and microbial inactivation by the combination of high hydrostatic pressure and citral or tert-butyl hydroquinone

The aim was to investigate (i) the occurrence of sublethal injury in Listeria monocytogenes, Escherichia coli, and Saccharomyces cerevisiae after high hydrostatic pressure (HHP) treatment as a function of the treatment medium pH and composition and (ii) the relationship between the occurrence of sublethal injury and the inactivating effect of a combination of HHP and two antimicrobial compounds, tert-butyl hydroquinone (TBHQ) and citral. The three microorganisms showed a high proportion of sublethally injured cells (up to 99.99% of the surviving population) after HHP. In E. coli and L. monocytogenes, the extent of inactivation and sublethal injury depended on the pH and the composition of the treatment medium, whereas in S. cerevisiae, inactivation and sublethal injury were independent of medium pH or composition under the conditions tested. TBHQ alone was not lethal to E. coli or L. monocytogenes but acted synergistically with HHP and 24-h refrigeration, resulting in a viability decrease of >5 log(10) cycles of both organisms. The antimicrobial effect of citral depended on the microorganism and the treatment medium pH. Acting alone for 24 h under refrigeration, 1,000 ppm of citral caused a reduction of 5 log(10) cycles of E. coli at pH 7.0 and almost 3 log(10) cycles of L. monocytogenes at pH 4.0. The combination of citral and HHP also showed a synergistic effect. Our results have confirmed that the detection of sublethal injury after HHP may contribute to the identification of those treatment conditions under which HHP may act synergistically with other preserving processes.

Glycol methyl ether and glycol amine substituted titanocenes as antitumor agents

6-[4-(2-Methoxyethoxy)phenyl]fulvene (3a) and 6-(4-[2-(di-methylamino)ethoxy]phenyl)fulvene (3b) were prepared as starting materials for the synthesis of three dofferent classes of titanocenes, which are ansa-titanocenes, diarylmethyl-substituted titanicenes and benzyl-substituted titanocenes and benyzyl-subtituted titanocenes. Because the synthetic possibilities seem to be limited, only ansa-titanocene {1,2-bis(cyclopentadienyl)-1,2-bis[4-(2-methoxyethoxy)phenyl]ethanediyl}titanium dichloride (4a) and benzyl-substituted titanocene bis-{[4-(2-methoxyethoxy)benzyl]cyclopentadienyl}titantium(IV) dichloride (6a) were obtained and characterised. The change in the substitution pattern f the phenyl moiety from an oxygen atom to a nitrogen atom had such a big influence on the reaction that not one compound of the threee titanocene classes could be synthesised, and it was also not possible to obtain diarylmethyl-substituted titanocenes with the use of either of the fulvenes. When benzyl-substituted titanocene 6a was tested agianst pig kidney cells (LLC-PK), an antiproliferative effect that result in an IC50 value of 43 mu m, was observed. This IC50 value is in the lower range of the cytotoxicities evaluated for titanocenes up to now. ansa-Titanocene 4a surprisingly showed, when tested on the same cell line, a proliferative effect together with a fast rate of hydrolysis.

Miscibility studies in poly(methyl vinyl ether)/hydroxypropylcellulose binary system in aqueous solutions and solid state

The phase separation behaviour in aqueous mixtures of poly(methyl vinyl ether) and hydroxypropylcellulose has been studied by cloud points method and viscometric measurements. The miscibility of these blends in solid state has been assessed by infrared spectroscopy; methanol vapours sorption experiments and scanning electron microscopy. The values of Gibbs energy of mixing of the polymers and their blends with methanol as well as between each other were calculated. It was found that in solid state the polymers can interact with methanol very well but the polymer-polymer interactions are unfavourable. Although in aqueous solutions the polymers exhibit some intermolecular interactions their solid blends are not completely miscible. (C) 2005 Elsevier Ltd. All rights reserved.

Temperature-responsive water-soluble copolymers based on 2-hydroxyethyl acrylate and butyl acrylate

Amphiphilic copolymers have been synthesised by free radical copolymerisation of 2-hydroxyethyl acrylate with butyl acrylate, the reactivity ratios of which indicate practically equal reactivity. The copolymers containing less than 30 mol-% of BA were soluble in water and exhibited a LCST in aqueous solutions. It was found that the interaction between these copolymers and poly(acrylic acid) in aqueous solutions resulted in the formation of interpolymer complexes stabilised by hydrogen bonds and hydrophobic interactions. This interaction was significantly affected by solution I pH and led to modification of the temperature-responsive behaviour of the copolymers.

Novel temperature-responsive water-soluble copolymers based on 2-hydroxyethylacrylate and vinyl butyl ether and their interactions with poly(carboxylic acids)

Novel water-soluble amphiphilic copolymers have been synthesized by free radical copolymerization of 2-hydroxyethylacrylate with vinyl butyl ether. In water these copolymers exhibit lower critical solution temperature, which depends on the content of hydrophobic vinyl butyl ether units. The interaction between these copolymers and poly(acrylic acid) or poly(methacrylic acid) in aqueous solutions results in formation of interpolymer complexes stabilized by hydrogen bonds and hydrophobic interactions. An increase in hydrophobicity of the copolymers leads to the enhancement of their complex formation ability with respect to poly(acrylic acid) and poly(methacrylic acid). Poly(methacrylic acid) forms stronger complexes with the copolymers when compared with poly(acrylic acid). The complexes exhibit dual sensitivity to pH- and temperature and this property may be easily adjusted regulating the strength of interaction. (c) 2005 Wiley Periodicals, Inc.

Characterisation of blends based on hydroxyethylcellulose and maleic acid-alt-methyl vinyl ether

Hydrophilic polymeric films based on blends of hydroxyethylcellulose and maleic acid-co-methyl vinyl ether were produced by casting from aqueous solutions. The physicochemical properties of the blends have been assessed using Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, dielectric spectroscopy, etc. The pristine films exhibit complete miscibility due to the formation of intermacromolecular hydrogen bonding. The thermal treatment of the blend films leads to cross-linking via intermacromolecular esterification and anhydride formation. The cross-linked materials are able to swell in water and their swelling degree can be easily controlled by temperature and thermal treatment time. The formation of the crosslinks is apparent in the dynamic properties of the blends as observed through the mechanical relaxation and dielectric relaxation spectra. The dielectric characteristics of the material are influenced by the effects of change in the local structure of the blend on the ionic conduction processes and the rate of dipolar relaxation. Separation of these processes is attempted using the dielectric modulus method. Significant deviations from a simple additive rule of mixing on the activation energy are observed consistent with hydrogen bonding and crosslinking of the matrix. This paper indicates a method for the creation of films with good mechanical and physical characteristics by exposing the blends to a relatively mild thermal treatment.

Mucoadhesive interactions of amphiphilic cationic copolymers based on [2-(methacryloyloxy)ethyl]trimethylammonium chloride

Three series of water-soluble cationic copolymers have been synthesised by free-radical copolymerisation of [2-(methacryloyloxy)ethyl]-trimethylammonium chloride (MADQUAT) with methyl acrylate (MA), butyl acrylate (BA) and butyl methacrylate (BMA). The interactions between these copolymers and porcine stomach mucin have been studied in aqueous solutions using dynamic light scattering, zeta-potential measurements, turbidimetric titration and transmission electron microscopy (TEM). It was demonstrated that mixing aqueous dispersions of mucin with solutions of the cationic copolymers results in significant changes in size distribution and zeta-potential of its particles. It was found that an increase in the content of hydrophobic groups in copolymers leads to more efficient adsorption of macromolecules on the surface of mucin particles, which evidences the importance of hydrophobic effects in mucoadhesion. The efficiency of mucoadhesive interactions was found to be significantly dependent on pH, which affects the surface charge and aggregation stability of mucin. (C) 2007 Elsevier B.V. All rights reserved.