Biomedical subjects

Felipe M Correia

Publications and source records attributed to Felipe M Correia.

2 recordsLinked to original sources

PubMed2004

Colloid stability of lipid/polyelectrolyte decorated latex.

The colloid stability of supramolecular assemblies composed of the synthetic cationic lipid dioctadecyldimethylammonium bromide (DODAB) on carboxymethyl cellulose (CMC) supported on polystyrene amidine (PSA) microspheres was evaluated via turbidimetry kinetics, dynamic light scattering for particle sizing, zeta-potential analysis, and determination of DODAB adsorption on CMC-covered particles. At 0.1 g L(-1) CMC and 2 x 10(11) PSA particles/mL, CMC did not induce significant particle flocculation, and a vast majority of CMC-covered single particles were present in the dispersion so that this was the condition chosen for determining DODAB concentration (C) effects on particle size and zeta potentials. At 0.35 mM DODAB, charge neutralization, maximal size, and visible precipitation indicated extensive flocculation and minimal colloid stability for the DODAB/CMC/PSA assembly. At 0.1 g L(-1) CMC, isotherms of high affinity for DODAB adsorption on CMC-covered particles presented a plateau at a limiting adsorption of 700 x 10(17) DODAB molecules adsorbed per square meter PSA which was well above bilayer deposition on a smooth particle surface. The polyelectrolyte layer on hydrophobic particles was swelled and fluffy (ca. 11-nm hydrodynamic thickness), and maximal adsorption of DODAB lipid onto this layer produced a compressed composite cationic film with 20 mV of zeta potential and about 10-nm mean thickness. The assembly of cationic lipid/CMC layer/polymeric particle was stable only well above charge neutralization of the polyelectrolyte by the cationic lipid, at relatively large lipid concentrations (at and above 1 mM DODAB) with charge neutralization leading to extensive particle aggregation.

Adsorption↗

PubMed2003

Nucleotide conformational change induced by cationic bilayers.

The effects of cetyltrimethylammonium bromide (CTAB) micelles and dioctadecyldimethylammonium bromide (DODAB) bilayers on molecular conformation of 2'-deoxyadenosine 5'-monophosphate (dAMP) were evaluated from circular dichroism spectroscopy (CD) and molecular modeling of dAMP conformations of minimal energy upon varying torsion angles for the glycosidic bond (t(1)) for four different conditions of dielectric constant of the medium (E) and negative charge on the phosphate moiety (C), namely, E80_C2, E80_C0, E1_C2, and E1_C0. Upon decreasing medium polarity, a decreased intensity of the negative band over the 190-210 nm region for the dAMP CD spectrum was observed. Upon increasing relative proportion dAMP: DODAB, an increased intensity of the positive band over the 210-230 nm region plus a red shift were obtained that could be attributed to an increased nitrogenous base stacking, similar to A stacking in poly(A). Concomitant base stacking and insertion in the cationic aggregates were observed for DODAB bilayers but not for CTAB micelles. Thereby, the nucleotide extended, anti conformation in pure water typical for nucleotides in DNA was forced by the cationic bilayer to become syn. dAMP conformational modeling upon simultaneous changes in the nucleotide environment (from water to a hydrocarbon phase) and in the charge on phosphate moiety (-2 to zero) allowed to simulate dAMP conformation in the cationic bilayer/dAMP complex. Modeling confirmed the dAMP anti-to-syn conformational change experimentally characterized from CD spectroscopy. This nucleotide conformational change would possibly be at the root of DNA denaturation upon complexation with cationic lipids.

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