Photophysical behavior of some aromatic poly(1,3,4-oxadiazole-ether)s derivatives.

The change in electronic absorption and emission spectra of two fluorinated poly(1,3,4-oxadiazole-ether)s in neat and binary solvent mixtures has been studied. The optical properties, absorption and photoluminescence of these polymers were investigated in solution and in solid state. The results were discussed as a function of solvent nature, excitation wavelength and local solvent composition, X2. The Catalan solvent scale was used for describing the solvatochromic shifts of the absorption and emission bands. The following binary solvent mixtures were used: chloroform-N,N'-dimethylformamide (CHCl3-DMF), chloroform-dimethyl sulfoxide (CHCl3-DMSO), and dimethylformamide-dimethyl sulfoxide (DMF-DMSO) and the influence of their composition on the absorption and emission maxima has been analyzed. The preferential solvation parameters such as local mole fraction (X2(L)), excess function (δs2) and preferential solvation constant (KPS) were determined.

Solvatochromic effects in the UV/vis absorption spectra of some pyridazinium ylides.

Solvatochromic behavior of some carbanion monosubstituted and disubstituted pyridazinium ylides was studied experimentally in various polar and nonpolar solvents. Different solvent parameters, such as microscopic solvent polarity, E(T)(30), the Kamlet-Taft and the Catalan parameters have been used for describing the solute-solvent interactions and solvatochromic shifts of the visible intramolecular charge transfer (ICT) absorption band of pyridazinium ylides. It is found that the solute hydrogen bond donating ability and dipolarity/polarizability play an important role in the description of the pronounced solvatochromism in the studied solutions. The Catalan solvent scales are found to be the most suitable for describing the solvatochromic shifts.

Citric-acid-coated magnetite nanoparticles for biological applications.

Water-based magnetic fluids, generally intended for biomedical applications, often have various coating molecules that make them stable and compatible with biological liquids. Magnetic fluids containing iron oxide particles have been prepared by a co-precipitation method, using citric acid as stabilizer. The magnetic particles of the magnetic fluids were obtained by chemical precipitation from ferric (FeCl(3)) and ferrous salts (FeSO(4) or FeCl(2)) in alkali medium (ammonia hydroxide). Citric acid was used to stabilize the magnetic-particle suspension. Physical tests were performed in order to determine various microstructural and rheological features. Transmission electron microscopy was the main investigation method for assessing the magnetic-particle size. The dimensional distribution of the magnetic-particle physical diameter was analyzed using the box-plot statistical method while infrared absorption spectra were used to study the colloidal particle structure. The magnetic-fluid density (picnometric method), viscosity (capillary method) and surface tension (stalagmometric method) were measured using standard methods.

Highly stable C(60)/poly(vinylpyrrolidone) charge-transfer complexes afford new predictions for biological applications of underivatized fullerenes.

The equilibrium constants for complexation of C(60) with poly(vinylpyrrolidone) (PVP) in water have been determined by UV-visible spectroscopy. The magnitude of the equilibrium constants was found to describe the formation of a charge-transfer (CT) saturated 1:1 complex for [PVP] = 2.62-5.25 x 10(-2) M (K = 1331.3 M(-1)), and a contact-pairs complex for [PVP] = 7.0-12.25 x 10(-2) M (K = 20.64 x 10(-2) M(-1)). These results indicate that the binding affinity of C(60) for drug receptors, base pairs in double-stranded DNA, or AT-rich segments of its minor groove to form CT complexes is limited by the strong coordination in the C(60)/PVP-saturated CT complex or envelopment by the polymer ligand in the contact CT complex.

Dissolution studies of microencapsulated 4-sulphonamidophenoxyacetic acid: effect of preparative variables on dissolution.

Ethylcellulose-walled microcapsules of 4-sulphonamidophenoxyacetic acid were prepared and their in vitro dissolution characteristics were investigated. Different release kinetics must be applied according to the respective average particle size and wall content values of the microcapsule fractions. The 'dissolution model' appears to fit better with small thin-walled microcapsules whereas, for larger thicker-walled microcapsules, Higuchi-type kinetics seem to describe the release of the major part of the drug more adequately.