Gelation of micellar solutions of diblock-copoly (oxyethylene/oxybutylene) in aqueous K2SO4. An investigation of excluded volume effects

The micellization and gelation properties of oxyethylene/oxybutylene diblock copolymers E₄₀B₁₀ and E₄₁B₈ in aqueous K₂SO₄ solutions were investigated. The thermodynamic and hydrodynamic volumes of the micelles in salt solutions of various concentrations up to 0.4 mol dm^?3 were determined by static and dynamic light scattering, respectively. The related changes in the gelation behavior of concentrated micellar solutions of the copolymers were explained as thermodynamic (excluded) volume effects. The thermodynamic volumes of micelles measured in moderately concentrated solution were used successfully to predict the critical gel concentrations of concentrated solutions. ©1995 John Wiley & Sons, Inc.     

An unusual synthesis of 2,3-dihydrophosphindole 1-oxides

A very simple route to dimeric phosphole oxides is reported as is the pyrolytic decomposition of these phosphorus-bridged dimers. Like similar dimeric phosphole sulfides, these phosphole oxide dimers readily eliminate the bridging phosphorus grouping upon strong heating but, unlike the analogous sulfides, hydrogen transfer to give a 2,3-dihydrophosphindole 1-oxide rather than hydrogen elimination to give the fully unsaturated phosphindole oxide occurs. This hydrogen transfer is shown to be non-stereospecific and some mechanistic implications of this are briefly discussed.     

Synthesis and characterization of N-carbazole end-capped oligofluorene-thiophenes

A series of novel N-carbazole end-capped oligofluorene-thiophenes with one, two, three, and four thiophene rings were synthesized using either palladium catalyzed cross-coupling reaction or nickel-catalyzed reductive dimerization. All the oligomers have been characterized by ¹H, ¹³C NMR, FTIR, UV-vis, PL spectroscopy and mass spectrometry. It has been demonstrated that the optical, thermal, and electrochemical properties of these materials can be tuned by varying the conjugation length of the oligothiophene segment. The terminal carbazole and fluorene moieties of the resulting materials are beneficial for their morphology, conjugation length, and solubility. These bright fluorescent, thermally and electrochemically stable compounds have potential applications as light-emitting and hole-transporting layers in organic light-emitting devices.     

Synthesis, optical, electrochemical, and thermal properties of α,α′-bis(9,9-bis-n-hexylfluorenyl)-substituted oligothiophenes

A series of new α,α′-bis(9,9-bis-n-hexylfluorenyl)-substituted oligothiophenes with 2-, 4-, and 6-thiophene rings have been synthesized via a nickel-catalyzed reductive dimerization and their optical, electrochemical, and thermal properties investigated. The fluorene substituents have shown electronic interactions with the oligothiophene chains, enhanced the solubility of these materials and stabilized the radical cation and dication by blocking the reactive α-positions of the thiophene moieties. The absorption, fluorescence, electrochemical, and thermal properties of these materials can be tuned by varying the conjugation length of the oligothiophene segment.     

Theoretical study of modes of adsorption of water dimer on H-ZSM-5 and H-Faujasite zeolites

Modes of adsorption of water dimer on H-ZSM-5 and H-Faujasite (H-FAU) zeolites have been investigated by a quantum embedded cluster approach, using the hybrid B3LYP density functional theory. The results indicate that there are two possible adsorption pathways, namely the stepwise process where only one water binds strongly to the (-O)3-Al-O(H) tetrahedral unit while the other weakly binds to the zeolite framework and the concerted process where both water molecules form a large ring of hydrogen-bonding network with the Br?nsted proton and an oxygen framework. With inclusion of the effects of the Madelung potential from the extended zeolite framework, for adsorption on H-ZSM-5 zeolite, both the neutral and ion-pair complexes exist with adsorption energies of -15.13 and -14.73 kcal/mol, respectively. For adsorption on the H-FAU, only the ion-pair complex exists with the adsorption energy of -14.63 kcal/mol. Our results indicate that adsorption properties depend not only on the acidity of the Br?nsted acidic site but also on the topology of the zeolite framework, such as on the spatial confinement effects which lead to very different adsorption structures for the ion-pair complexes in H-ZSM-5 and H-FAU, even though their adsorption energies are quite similar. Our calculated vibrational spectra for these ion-pair complexes support previous experimental IR interpretations.     

Synthesis and characterization of N-carbazole end-capped oligofluorenes

A series of N-carbazole end-capped oligofluorenes (CF_n, n = 1-3) were synthesized. The 9-position of the carbazole moiety was attached to the terminal ends of the oligofluorene cores using an Ullmann coupling reaction. These molecules exhibit red shifts in absorption and photoluminescence spectra with respect to the number of fluorene units and excellent electrochemical reversibility. They were found to be potential blue light-emitting or hole-transporting materials for organic light-emitting diodes (OLEDs).     

Theoretical investigation of novel carbazole-fluorene based D-π-A conjugated organic dyes as dye-sensitizer in dye-sensitized solar cells (DSCs)

The ground state structure and frontier molecular orbital of newly synthesized carbazole-fluorene based D-π-A organic dyes, CFP1A, CFP2A, CFP1CA, and CFP2CA, were theoretically investigated using density functional theory (DFT) at B3LYP/6-31G(d,p) level. These dye molecules have been constructed based on carbazole-fluorene as the electron-donating moiety while introducing benzene units as π-spacer connected to different anchor groups, such as acrylic acid and cyanoacrylic acid, as acceptors. The electronic vertical excitation energies and absorption wavelength were carried out using time-dependent DFT (TD-DFT). Furthermore, the adsorptions of phenylacrylic acid and phenylcyanoacrylic acid on the TiO(2) anatase (101) surface were carried out by means of quantum-chemical periodic calculations employing periodic PBE functional with DNP basis set. The results promise that anchor dyes with strong withdrawing CN group have easier injected electron to the conduction band of semiconductor implying that CFP1CA and CFP2CA show better performance among four dyes. Additionally, the intramolecular charge transfers (ICT) from electron donor group to anchoring group of CFP1CA and CFP2CA have shown better performance. The calculated results provide the efficiency trend of our new dyes as CFP1CA ≈ CFP2CA > CFP1A ≈ CFP2A which are excellently agree with experimental observation.     

Enhanced gentamicin loading and release of PLGA and PLHMGA microspheres by varying the formulation parameters

The purpose of this study was to develop a suitable formulation for gentamicin sulfate (GS) that gives a sustained release of the drug. Therefore this drug was loaded into poly(D,L-lactide-co-glycolide) (PLGA) and poly(lactic-co-hydroxymethyl glycolic acid) (PLHMGA) microspheres. The effects of various formulation parameters (ethanol, surfactant, osmotic value of the external phase, polymer type and concentration) on particle characteristics (size, loading and release) were investigated. The GS loaded microspheres were prepared using a double emulsion evaporation technique. The results demonstrate that neither ethanol nor surfactants had beneficial effects on the drug loading efficiency (around 4-10%). However, an increase in buffer concentration (and thus osmotic pressure) of the external phase resulted in a substantial increase of GS-loading (from 10 to 28%). Further, an increase of concentration of PLGA in DCM from 10% to 15/20% caused a 4-time increase of the drug loading. The best formulation identified in this study had a loading efficiency of around 70% resulting in PLGA microspheres with a 6% (w/w) loading. The particles showed a burst release of the drug depending on their porosity, followed by a phase of 35 days where hardly any release occurred. The drug was then slowly released for around 25 days likely due to degradation of the microspheres. The drug loading efficiency of GS in PLHMGA was not significantly different from PLGA microspheres (64%). The release of GS from PLHMGA microspheres was faster than that of PLGA because the degradation rate of PLHMGA is more rapid than PLGA. This study shows that prolonged release of gentamicin can be obtained by loading this drug into microspheres made of biodegradable aliphatic polyesters.     

Arginine conjugates of metallo-supramolecular cylinders prescribe helicity and enhance DNA junction binding and cellular activity

The conjugation of arginine residues at the ends of a metallo-supramolecular triple-helical cylinder enables absolute control over the helicity of the cylinder core, and boosts the DNA junction recognition by the complexes and their activity against a cancer cell line.