Control of the morphology of linear and cyclic PS-b-PI block copolymer micelles via PS addition

We have studied the effect of polystyrene (PS) homopolymer addition on the morphology of self-assembled block copolymer micelles made from linear or cyclic poly(styrene-b-isoprene), PS-b-PI, in a selective solvent for the PI block (heptane). Both copolymers have the same composition: the degree of polymerization is 290 for the PS block, and 110 for the PI block, and we focused on the influence of the addition of small amounts of PS homopolymer on the micellar morphology. For the copolymer concentrations considered, the linear copolymer self-organizes into spherical micelles while the cyclic copolymer forms cylindrical micelles. PS and PI chains constitute the core and the corona of these micelles, respectively, due to the different affinity of the blocks for heptane. Consequently, the PS homopolymer added is "solubilized" into the micellar core. Dynamic light scattering (DLS) data combined with atomic force microscopy (AFM) results show that the addition of PS homopolymer induces a drastic change in the micellar organization. Indeed, a morphological transition, from spheres to cylinders for the linear copolymer, and from cylinders to vesicles for the cyclic copolymer, is observed. These results highlight the fact that a small incorporation of PS homopolymer is clearly sufficient to modify the morphology (size and shape) of the micelles. This approach could be a key parameter for the design/control of micelles for specific applications in nanotechnology.     

Analysis of serotonin in brain microdialysates using capillary electrophoresis and native laser-induced fluorescence detection

Serotonin or 5-hydroxytryptamine (5-HT) is a major neurotransmitter in the central nervous system. In this work, a method for analyzing 5-HT in brain microdialysis samples using a commercially available capillary electrophoresis (CE) system has been developed. A pH-mediated in-capillary preconcentration of samples was performed, and after separation by capillary zone electrophoresis, native fluorescence of 5-HT was detected by a 266 nm solid-state laser. The separation conditions for the analysis of 5-HT in standard solutions and microdialysates have been optimized, and this method has been validated on both pharmacological and analytical bases. Separation of 5-HT was performed using a 80 mmol/L citrate buffer, pH 2.5, containing 20 mmol/L hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and +30 kV voltage. The detection limit was 2.5 x 10(-10) mol/L. This method allows the in vivo brain monitoring of 5-HT using a simple, accurate CE measurement in underivatized microdialysis samples.     

Theoretical investigation of the proton affinities of benzazoles in the gas phase and in solution

The ground‐state equilibrium geometries of benzothiazole, benzoxazole, and benzimidazole were optimized at the density functional theory (DFT)/6‐31G** level of theory. Proton affinities on each of the possible sites in the studied series of compounds have been calculated at the DFT/6‐31G**/6‐311++G** level. The results indicate clearly that N‐site protonation is strongly favored over X‐site protonation (X = NH, O, S) for the series studied. Correlation of the computed proton affinities to the energy (E_HOMO) of the highest occupied MO in the gas phase and in solution has been explored and discussed. A comprehensive investigation of the effect of solvent on the process of protonation of the studied compounds has been performed. Different dielectric continuum models (i.e., Onsager, PCM, and IPCM) have been tested; their performance and range of applicability are reported and discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Molecular tectonics. Selective exchange of cations in porous anionic hydrogen-bonded networks built from derivatives of tetraphenylborate

Tetraphenylmethanes with multiple hydrogen-bonding sites are known to associate to form robust porous supramolecular networks. Analogous anionic networks can be built from the corresponding tetraphenylborates. Crystallization of the tetraphenylphosphonium salt of tetraphenylborate 2 produces an anionic network in which 74% of the volume is available for including cations and neutral guests. Other salts of anion 2 with diverse cations crystallize consistently to form the same network, whereas a neutral analogue of anion 2, tetraphenylmethane 1, produces an uncharged network that is far less open. Cations can be exchanged in single crystals of salts of tetraphenylborate 2 with retention of crystallinity and with selectivities similar to those observed in typical zeolites. Together, these observations provide new strategies for making ordered molecular materials by design, and they reveal that constructing such materials from charged subunits offers special advantages.     

Vibrational spectra and structure of CH3Cl:NO complex: IR matrix isolation and DFT study

Infrared spectra of the CH(3)Cl:NO complex isolated in solid neon have been investigated. Most of the vibrational modes of the complex have been detected. The weak interaction between NO and CH(3)Cl in CH(3)Cl:NO is responsible for small shifts of the vibrational mode frequencies of both CH(3)Cl and NO molecules. The measured shifts range between -3.2 and + 3.8 cm(-1). On the basis of DFT calculations, different geometries have been explored for the complex, and it has been shown that the most stable structure is of C(1) symmetry. The calculated frequency shifts match well the experimental data.     

Polyelectrolyte multilayers and degradable polymer layers as multicompartment films

Polyelectrolyte multilayers are now a well established concept with numerous potential applications in particular as biomaterial coatings. To timely control the biological activity of cells in contact with a substrate, multicompartment films made of different polyelectrolyte multilayers deposited sequentially on the solid substrate constitute a promising new approach. In a first paper (Langmuir 2004, 20, 7298) we showed that such multicompartment films can be designed by alternating exponentially growing polyelectrolyte multilayers acting as reservoirs and linearly growing ones acting as barriers. In the present study, we first demonstrate however that these barriers composed of synthetic polyelectrolytes are not degraded despite the presence of phagocytic cells. We propose an alternative approach where exponentially growing poly(L-lysine)/hyaluronic acid (PLL/HA) multilayers, used as reservoirs, are alternated with biodegradable polymer layers consisting in poly(lactic-co-glycolic acid) (PLGA) and acting as barriers for PLL chains that diffuse within the PLL/HA reservoirs. We first show that these PLGA layers can be deposited alternatively with PLL/HA multilayers leading to polyelectrolyte multilayer/hydrolyzable polymeric layer films and acting as a reservoirs/barriers system. Bone marrow cells seeded on these films ending by a PLL/HA reservoir rapidly degrade it and internalize the PLL chains confined in this reservoir. Then the cells degraded locally the PLGA barrier and internalize the PLL localized in a lower (PLL/HA) compartment after 5 days of seeding. By changing the thickness of the PLGA layer, we hope to be able to tune the time delay of degradation. Such mixed architectures made of polyelectrolyte multilayers and hydrolyzable polymeric layers could act as coatings allowing us to induce a time scheduled cascade of biological activities. We are currently working on the use of comparable films with compartments filled by proteins or peptides and in which the degradation of the barriers results from a hydrolysis over tunable time scales.     

Studies on Fused Azoles: Synthesis of Several Polyfunctionally Substituted Fused Azoles

The synthesis of several new polyfunctionally substituted fused pyrazoles via reaction of 5‐amino‐3‐methylthio‐1H‐pyrazole‐4‐carboxylate ( 2 ) with different reagents is described.     

Electrophoreted Zn-TiO2-ZnO nanocomposite coating films for photocatalytic degradation of 2-chlorophenol

TiO₂-ZnO nano-powders with different TiO₂/ZnO ratios have been synthesized by hydrothermal method. Nanocomposite coating films consisting of TiO₂-ZnO and Zn with thickness of 20 μm have been electrophoreted on steel plates by rapid plating from a ZnO-based alkaline bath. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis were used to investigate the structure, the size distribution, and the composition of prepared nano-powders and plated materials. The effect of the operating parameters such as powder contents, pH and current density on the electrophoresis process has been investigated and optimum conditions of coating process were determined. Corrosion properties of plated samples have been studied by salt spray test. The catalytic activity of the prepared nanocomposite Zn-TiO₂-ZnO films for the photocatalytic degradation of 2-chlorophenol (2-CP) was measured.     

Conversion of iminoacyl quinolinylpalladium (II) complexes into novel oxo‐pyrrolo[3,4‐b] quinolines via depalladation reactions

Oxidative addition reactions of quinolines 1a , b with Pd(dba)₂ in the presence of PPh₃ (1:2) in acetone gave dinuclear palladium complexes [Pd(C,N‐2‐C₉ H₄N‐CHO‐3‐R‐6)Cl(PPh₃)]₂ [(R = H ( 2a ), R = OMe ( 2b ), which were reacted with isocyanide XyNC (Xy = 2,6‐Me₂C₆H₃) to give novel iminoacyl quinolinylpalladium complexes 3a , b in good yields (81 and 77%). Cyclopalladated complexes 3a , b were also obtained in low yields (39 and 33.5%) via one‐pot reaction of 1a , b with isonitrile XyNC:Pd(dba)₂ (4:1). The reaction of 3a , b with Tl(TfO) (TfO = triflate, CF₃SO₃) in the presence of H₂O or EtOH causes depalladation reactions of complexes to provide the corresponding organic compounds 4a , b , 5a , b and 6a , b in yields of 41, 27 and 18 ? 19%, respectively. The products were characterized by satisfactory elemental analyses and spectral studies (IR, ¹H, ¹³C and ³¹P NMR). The crystal structures 2a , 3a and 3b were determined by X‐ray diffraction studies. Copyright © 2008 John Wiley & Sons, Ltd.     

Nano-sized Co(II)-8-hydroxyquinolate complex thin film via surface layer-by-layer chemical deposition method: Optimized factors and optical properties

An extensive study was performed and reported for evaluation and optimization of the factors affecting thin film formation of nano-sized Co(II)-8-hydroxyquinolate complex by surface layer-by-layer chemical deposition method. The formation of uniform thin films of nano-crystalline metal complex is heavily dependent on several important factors. Variation in metal and ligand concentrations (1:1–1:3) was found to show insignificant contribution to the molar stoichiometric ratio of the synthesized thin film of nano-sized Co(II)-8-hydroxyquinolate. The number of dipping cycles (2–50) was characterized by strong influence on the thin film thickness. The dependence of the immersion time (2–50 s) was proved to influence the crystal growth and homogeneity of the thin film. The role of pH of metal and ligand solutions was identified by strong contribution in development and formation of deposited Co(II)-8-hydroxyquinolate complex thin film. Finally, the role of solvent on the thin film formation was also studied and evaluated. Metal analysis, SEM, EI-MS, FT-IR and TGA were applied as monitoring techniques of these factors. The optical properties of Co(II)-8-hydroxyquinolate complex were also studied and the complex thin films were characterized by the highest optical transition from π–π* or n, π* states with energy gap in the UV-range at 3.13 eV. The lowest optical transition resulted from d–d transition or metal centered transition with energy 1.5 eV while, the optical transition at 2.35 eV is the contribution of metal ligand or ligand metal transition. In the light of the optical measurement, Co(II)-8-hydroxyquinolate complex can be considered as an organic semiconductor with the potential applications in the design of organic light-emitting diodes (OLEMs).