An Investigation into the Dissolution Properties of Celecoxib Melt Extrudates: Understanding the Role of Polymer Type and Concentration in Stabilizing Supersaturated Drug Concentrations

In this study, the dissolution properties of celecoxib (CX) solid dispersions manufactured from Eudragit 4155F and polyvinylpyrrolidone (PVP) were evaluated. Hot-melt extrusion (HME) technology was used to prepare amorphous solid dispersions of drug/polymer binary systems at different mass ratios. The drug concentrations achieved from the dissolution of PVP and Eudragit 4155F solid dispersions in phosphate buffer, pH 7.4 (PBS 7.4) were significantly greater than the equilibrium solubility of CX (1.58 µg/mL). The degree of supersaturation increased significantly as the polymer concentration within the solid dispersion increased. The maximum drug concentration achieved by PVP solid dispersions did not significantly exceed the apparent solubility of amorphous CX. The predominant mechanism for achieving supersaturated CX concentrations in PBS 7.4 was attributed to stabilization of amorphous CX during dissolution. Conversely, Eudragit 4155F solid dispersions showed significantly greater supersaturated drug solutions particularly at high polymer concentrations. For example, at a drug/polymer ratio of 1:9, a concentration of 100 µg/mL was achieved after 60 min that was stable (no evidence of drug recrystallization) for up to 72 h. This clearly identifies the potential of Eudragit 4155F to act as a solubilizing agent for CX. These findings were in good agreement with the results from solubility performed using PBS 7.4 in which Eudragit 4155F had been predissolved. In these tests, Eudragit 4155F significantly increased the equilibrium solubility of CX. Solution 1H NMR spectra were used to identify drug/polymer interactions. Deshielding of CX aromatic protons (H-1a and H-1b) containing the sulfonamide group occurred as a result of dissolution of Eudragit 4155F solid dispersions, whereas deshielding of H-1a protons and shielding of H-1b protons occurred as a result of the dissolution of PVP solid dispersions. In principle, it is reasonable to suggest that the different drug/polymer interactions observed give rise to the variation in dissolution observed for the two polymer/drug systems.

Sugar–derived organogels as templates for structured, photoluminescent conjugated polymer-inorganic hybrid materials

Co-assembly of an inorganic–organic hybrid material through the combination of supramolecular organogel self-assembly, phase partitioning of a conjugated polymer (CP) and transcription of an inorganic oxide leads to a hybrid material with structured domains of organogel, CP and silica within tube and rod microstructures.

A multiconfigurational time-dependent Hartree-Fock method for excited electronic states. II. Coulomb interaction effects in single conjugated polymer chains

Conjugated polymers have attracted considerable attention in the last few decades due to their potential for optoelectronic applications. A key step that needs optimisation is charge carrier separation following photoexcitation. To understand better the dynamics of the exciton prior to charge separation, we have performed simulations of the formation and dynamics of localised excitations in single conjugated polymer strands. We use a nonadiabatic molecular dynamics method which allows for the coupled evolution of the nuclear degrees of freedom and of multiconfigurational electronic wavefunctions. We show the relaxation of electron-hole pairs to form excitons and oppositely charged polaron pairs and discuss the modifications to the relaxation process predicted by the inclusion of the Coulomb interaction between the carriers. The issue of charge photogeneration in conjugated polymers in dilute solution is also addressed. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3600404]

Generation of metallosupramolecular polymer gels from multiply functionalized grid-type complexes

A ditopic ligand (1), containing two tridentate bis(acylhydrazone) subunits and bearing both long alkyl chains and hydrogen-bonding groups, has been synthesised. Metal cation binding in the presence of a base leads to hierarchical self-assembly, forming first a neutral [2 x 2] grid-type complex (2) that hierarchically assembles into metallosupramolecular polymer gels in toluene.

Nanosecond optical limiting response of sandwich-type neodymium dyphthalocyanine in a co-polymer host

The nanosecond optical limiting characteristics of sandwich-type neodymium diphthalocyanine in a co-polymer matrix of polymethyl methacrylate (PMMA) and methyl-2-cyanoacrylate have been studied for the first time. The measurements were performed using 9 ns laser pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. The optical limiting performance of neodymium diphthalocyanine in co-polymer host was studied at different linear transmission. Laser damage threshold was also measured for the doped and undoped co-polymer samples. The optical limiting response is attributed to reverse saturable absorption which is due to excited-state absorption.

Peptide mediated formation of hierarchically organized solution and solid state polymer nanostructures

Biologically-inspired peptide sequences have been explored as auxiliaries to mediate self-assembly of synthetic macromolecules into hierarchically organized solution and solid state nanostructures. Peptide sequences inspired by the coiled coil motif and "switch" peptides, which can adopt both amphiphilic alpha-helical and beta-strand conformations, were conjugated to poly(ethylene glycol) (PEG). The solution and solid state self-assembly of these materials was investigated using a variety of spectroscopic, scattering and microscopic techniques. These experiments revealed that the folding and organization properties of the peptide sequences are retained upon conjugation of PEG and that they provide the driving force for the formation of the different nanoscale structures which were observed. The possibility of using defined peptide sequences to direct structure formation of synthetic polymers together with the potential of peptide sequences to induce a specific biological response offers interesting prospects for the development of novel self-assembled and biologically active materials.

A supramolecular polymer based on tweezer-type pi-pi stacking interactions: molecular design for healability and enhanced toughness

An elastomeric, healable, supramolecular polymer blend comprising a chain-folding polyimide and a telechelic polyurethane with pyrenyl end groups is compatibilized by aromatic pi-pi stacking between the pi-electron-deficient diimide groups and the pi-electron-rich pyrenyl units. This interpolymer interaction is the key to forming a tough, healable, elastomeric material. Variable-temperature FTIR analysis of the bulk material also conclusively demonstrates the presence of hydrogen bonding, which complements the pi-pi stacking interactions. Variable-temperature SAXS analysis shows that the healable polymeric blend has a nanophase-separated morphology and that the X-ray contrast between the two types of domain increases with increasing temperature, a feature that is repeatable over several heating and cooling cycles. A fractured sample of this material reproducibly regains more than 95% of the tensile modulus, 91% of the elongation to break, and 77% of the modulus of toughness of the pristine material.

Application of abrupt cut-off models in the analysis of the capacitance spectra of conjugated polymer devices

In this paper, a detailed study of the capacitance spectra obtained from Au/doped-polyaniline/Al structures in the frequency domain (0.05 Hz-10 MHz), and at different temperatures (150-340 K) is carried out. The capacitance spectra behavior in semiconductors can be appropriately described by using abrupt cut-off models, since they assume that the electronic gap states that can follow the ac modulation have response times varying rapidly with a certain abscissa, which is dependent on both temperature and frequency. Two models based on the abrupt cut-off concept, formerly developed to describe inorganic semiconductor devices, have been used to analyze the capacitance spectra of devices based on doped polyaniline (PANI), which is a well-known polymeric semiconductor with innumerous potential technological applications. The application of these models allowed the determination of significant parameters, such as Debye length (approximate to 20 nm), position of bulk Fermi level (approximate to 320 meV) and associated density of states (approximate to 2x10(18) eV(-1) cm(-3)), width of the space charge region (approximate to 70 nm), built-in potential (approximate to 780 meV), and the gap states` distribution.

Zidovudine-Loaded PLA and PLA-PEG Blend Nanoparticles: Influence of Polymer Type on Phagocytic Uptake by Polymorphonuclear Cells

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Application of abrupt cut-off models in the analysis of the capacitance spectra of conjugated polymer devices

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Role of Branching on the Structure of Polymer Brushes Formed from Comb Copolymers

The distinguishing feature of a polymer brush at equilibrium is the stretched configuration of the chains that results from tethering the polymer chains by one end at the solid-fluid interface. The stretched configuration of the chains and the crowded nature of the interfacial layer is the origin of many of the useful properties of polymer brushes: these layers resist compression and aggregation, effectively dissipate shear stresses, and respond reversibly to changes in their solution environment.

Discovery and redescription of type material of Nausithoe simplex (Kirkpatrick, 1890), comb. nov (Cnidaria: Scyphozoa: Coronatae: Nausithoidae) from the North Atlantic

With discovery and examination of type specimens in the Natural History Museum, London, UK, we reassign Stephanoscyphistoma simplex (Kirkpatrick, 1890) to the genus Nausithoe Kolliker, 1853, as Nausithoe simplex, comb. nov., and designate a lectotype for the species. Use of morphometric measurements is considered important in coronate systematics, but key features also include the unique whorl of internal cusps and the shape of these cusps. All previous records of N. simplex must be re-evaluated, taking into consideration the morphology of these internal cusps.

Photo- and electroluminescence in a series of PPV type terpolymers containing fluorene, thiophene and phenylene units

The emissive properties of terpolymers with fluorene, thiophene and phenylene groups, forming alternating PPV type structures, are discussed in terms of their composition, photo- and electroluminescence properties. The fluorene groups were inserted in each phenylene-vinylene and thiophene-vinylene units, and their concentration did not vary, representing 50% of the molar composition. The ratio of thiophene-vinylene/phenylene-vinylene varied in the range 25,50 and 75%. Photo- and electroluminescence properties were strongly dependent on the thiophene-vinylene content and were compared with the fluorene-vinylene-thiophene and fluorene-vinylene-phenylene parent copolymers. (C) 2012 Elsevier B.V. All rights reserved.

Photophysical and photovoltaic properties of a PPV type copolymer containing alternated fluorene and thiophene units

The synthesis and photophysical characterization of a PPV-type copolymer containing a fluorene derivative alternated with thiophene units is presented: poly(9,9'-dioctylfluorene-thiophene) (LAPPS29). Photophysical studies demonstrated that in the solid state only preformed ground state aggregates are responsible for exciton formation. These aggregates are formed with a wide range of size distribution. The emission from isolated segments is quenched either by resonant energy transfer, or by migration processes. Also, the main photovoltaic parameters are discussed in connection with the photophysical behavior.