A multitechnique study of structure and dynamics of polyfluorene cast films and the influence on their photoluminescence.

This article describes the microstructure and dynamics in the solid state of polyfluorene-based polymers, poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), a semicrystalline polymer, and poly[(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-{2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene}, a copolymer with mesomorphic phase properties. These structures were determined by wide-angle X-ray scattering (WAXS) measurements. Assuming a packing model for the copolymer structure, where the planes of the phenyl rings are stacked and separated by an average distance of approximately 4.5 A and laterally spaced by about approximately 16 A, we followed the evolution of these distances as a function of temperature using WAXS and associated the changes observed to the polymer relaxation processes identified by dynamical mechanical thermal analysis. Specific molecular motions were studied by solid-state nuclear magnetic resonance. The onset of the side-chain motion at about 213 K (beta-relaxation) produced a small increase in the lateral spacing and in the stacking distance of the phenyl rings in the aggregated structures. Besides, at about 383 K (alpha-relaxation) there occurs a significant increase in the amplitude of the torsion motion in the backbone, producing a greater increase in the stacking distance of the phenyl rings. Similar results were observed in the semicrystalline phase of PFO, but in this case the presence of the crystalline structure affects considerably the overall dynamics, which tends to be more hindered. Put together, our data explain many features of the temperature dependence of the photoluminescence of these two polymers.

Lipid model membranes for drug interaction study.

The present work shows a structural study on the process of incorporation of a hydrophobic drug, Ellipticine (ELPT), into lipid model membranes for drug targeting purpose. The ELPT is an alkaloid that showed an anti-proliferation activity against several types of tumor cells and against the HIV1 virus. We used the zwitterionic lipid dipalmitoyl phosphatidylcholine (DPPC) and four different anionic lipids: cardiolipin (CL), dipalmitoyl phosphatidic acid (DPPA), dipalmitoyl phosphatidylglycerol (DPPG) and dipalmitoyl phosphatidylserine (DPPS), both spread on a Langmuir monolayer and deposited on a solid substrate to mimic a model membrane and study the interaction with the drug ELPT. X-ray reflectivity results pointed toward an increase in drug loading efficiency up to 13.5% mol/mol of ELPT into mixed systems DPPC/CL. This increase in loading efficiency was also accompanied by a slight distortion in the stacking of the bilayers less evidenced after optimization of the molar ratio between the co-lipids. Grazing incidence X-ray diffraction measurements revealed an in-plane lattice distortion due to the presence of hydrocarbon chain backbone ordering in pure systems of DPPC doped with ELPT. The same was not observed in mixed membranes with DPPC/CL and DPPC/DPPA.

Small angle x-ray scattering from lipid-bound myelin basic protein in solution.

The structure of myelin basic protein (MBP), purified from the myelin sheath in both lipid-free (LF-MBP) and lipid-bound (LB-MBP) forms, was investigated in solution by small angle x-ray scattering. The water-soluble LF-MBP, extracted at pH < 3.0 from defatted brain, is the classical preparation of MBP, commonly regarded as an intrinsically unfolded protein. LB-MBP is a lipoprotein-detergent complex extracted from myelin with its native lipidic environment at pH > 7.0. Under all conditions, the scattering from the two protein forms was different, indicating different molecular shapes. For the LB-MBP, well-defined scattering curves were obtained, suggesting that the protein had a unique, compact (but not globular) structure. Furthermore, these data were compatible with earlier results from molecular modeling calculations on the MBP structure which have been refined by us. In contrast, the LF-MBP data were in accordance with the expected open-coil conformation. The results represent the first direct structural information from x-ray scattering measurements on MBP in its native lipidic environment in solution.

Humidity-dependent structural changes in native collagen studied by x-ray diffractometry

X-ray diffractometry was in this work to study structural modifications of powdered native collagen submitted to repeated cycles of gradual drying and hydration. Hysteresis effects known to exist in water sorption isotherms of this fibrous protein were detected in the plots of relative humidity vs integrated intensity of the wide angle X-ray reflections which constitute the main features of the diffraction pattern. A gradual loss of structural material was observed after each drying and rehydration process. An increase in the amorphous regions of the fibrils could also be inferred from the diffraction data. Drying the samples up to a critical degree of hydration (0.12 g H2O per g protein) did not produce a hysteresis loop in the plots of the parameters studied. One-step drying-rehydration cycles did not seem to affect the order of the samples since they repeatedly recovered their original structure.The difference between these results and those of the gradual hydration processes may be attributed to the kinetic properties of biopolymer hydration. The rate o water removal seems to be an important factor in the structural modifications proceduced by the hydration (dehydration) process_

Humidity-dependent structural changes in native collagen studied by X-ray diffractometry.

1. X-ray diffractometry was used in this work to study structural modifications of powdered native collagen submitted to repeated cycles of gradual drying and hydration. 2. Hysteresis effects known to exist in water sorption isotherms of this fibrous protein were detected in the plots of relative humidity vs integrated intensity of the wide angle X-ray reflections which constitute the main features of the diffraction pattern. 3. A gradual loss of structured material was observed after each drying and rehydration process. An increase in the amorphous regions of the fibrils could also be inferred from the diffraction data. 4. Drying the samples up to a critical degree of hydration (0.12 g H2O per g protein) did not produce a hysteresis loop in the plots of the parameters studied. 5. One-step drying-rehydration cycles did not seem to affect the order of the samples since they repeatedly recovered their original structure. The difference between these results and those of the gradual hydration processes may be attributed to the kinetic properties of biopolymer hydration. The rate of water removal seems to be an important factor in the structural modifications produced by the hydration (dehydration) process.

Acetobacter cellulose pellicle as a temporary skin substitute.

A bacterial strain with morphological and biochemical properties close to Acetobacter xylinum has been cultured in nonagitated, inverted sucrose- and yeast water-based medium for the production of thick, smooth, and floating cellulosic pellicles. The cellulose content (greater than 90%, dry weight, depending on the efficiency of water washing) and the beta-D-homopolyglucan nature of these pellicles were assessed by physical, chemical, and enzymatic methods. The apyrogenic bacterial biomass, a minor component of the dried biofilm (BioFill), is inactivated by ethylene dioxide. Once applied on exudating or bloody tissues, this biofilm displays several advantages as a biological dressing, and hence, it is valuable as a temporary skin substitute in the treatment of skin wounds, such as burns, ulcers, grafts, and as an adjuvant in dermal abrasions.