Marysilvia Ferreira

Cooperativity of phospholipid reorganization upon interaction of dipyridamole with surface monolayers on water.

Results from various surface sensitive characterization techniques suggest a model for the interaction of the piperidinopyrimidine dipyridamole (DIP)--known as a vasodilator and inhibitor of P-glycoprotein associated multidrug resistance of tumor cells--with phospholipid monolayers in which the drug is peripherally associated with the membrane, binding (up to) five phospholipids at a time. These multiple interactions are responsible for a very strong association of the drug with the lipid monolayer even at exceedingly low concentrations (approximately 0.2 mol%). Electrostatic interactions and hydrogen bonding are likely involved in the binding of DIP to DPPC. Cooperative effects among the lipids are invoked to explain the macroscopically measurable changes of lipid monolayer properties even when only one out of 100 DPPC molecules is directly associated with a DIP molecule. A reversal of the observed changes upon drug association with the membrane as the DIP concentration surpasses a threshold concentration (c(crit)approximately 0.5 mol%) may be explained by cooperativity in a different context, the self-aggregation of drug molecules. With its implications for the interaction of DIP with phospholipid films, this work provides a first approach to the explanation of the high sensitivity of cell membranes to piperidinopyrimidine drugs on a molecular level.

The effects of water absorption on an ester vinyl resin system

Derakene is a vinyl ester resin largely employed as matrix for polymeric based composite systems. In this work, the performance of such polymeric system was evaluated considering the effect of hygrothermal aging. The mechanical and thermal properties were examined for the processed material before and after ageing in water at 60 oC for a maximum period of 64 days. Both analyses indicated the occurrence of post cure of the system after 16 days due to exposition at 60 oC in water, which was also confirmed by analyses in samples with post cure treatment. Moreover, it was observed plasticizing of resin after 36 and 64 days of ageing. Micro structural and fracture surface analyses were carried out in order to characterize the samples. The appearance of surface voids was also observed.

Ionic desorption in valence- and core- excited polymers: poly(vinyl chloride) and poly(vinylidene chloride)

Photon stimulated ion desorption (PSID) studies have been performed in poly(vinyl chloride) (PVC) and poly(vinylidene chloride) (PVDC) using synchrotron radiation, covering from valence to core electron (Cl 2p and C 1s) energy ranges. Data acquisition was performed at the TGM beam line from the Brazilian Synchrotron Light Source (LNLS), operating in a multi-bunch mode and using a time-of-flight mass spectrometer (TOF-MS). A new pulsed system developed uses as a trigger for the TOF-MS experiments the pulsed extraction high voltage applied to the sample. Ionic desorption from PVC and PVDC shows strong selectivity in the formation of chlorine ions around the Cl 2p-edge while very similar fragmentation patterns are observed for the other energies studied.

Mesoscopic patterns in POMA spin-coated films: A systematic study

The surface morphology of poly(o-methoxy aniline) (POMA) films produced by spin coating was systematically studied using Atomic Force Microscopy (AFM). Initial solution concentrations, rotation speeds and relative humidity affected the final film structure and thickness. Particularly interesting is the unexpected appearance, at solution concentrations of 2% or higher, of regular patterns composed of characteristic nanometer sized holes. These patterns were caused by phase separation.

Propriedades Mecânicas de Epóxis Utilizadas no Recobrimento Interno de Oleodutos e Gasodutos

Mechanical properties of epoxy based coating materials suitable for in-situ internal application in gas/oil pipelines were studied. Coatings were applied on carbon steel substrates submitted to two different surface preparation procedures (ST3 and SA2½) and the effect from surface treatment on coating adhesion, impact, hardness and wear was evaluated. It was found that adhesion failure occurs through distinct mechanisms depending on coating material and surface preparation. Wear occurs mostly by abrasive mechanism, although adhesive wear was found to be significant in some cases also depending on material and surface. Microhardness, as expected, was found to be a coating property not unaffected by surface treatment.

Electron transfer between adjacent layers in self-assembled films

Abstract A simple model of electron transfer is adapted to explain fluorescence quenching in self-assembled films of poly(p-phenylene vinylene) (PPV) alternating with poly(thiophene acetic acid) (PTAA). Quenching is caused by a photo-induced electron transfer between the excited PPV (donor, D) and the PTAA (acceptor, A). The electron-transfer process can be mediated by insertion of electronically inert spacing bilayers between the D and A layers. As the number of bilayers is increased, the fluorescence is gradually recovered which is explained theoretically by assuming that the electron-transfer rate can be described as k=Z exp (−βr) where r is the distance between D and A.