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by Keyword: Dielectric spectroscopy


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Valenti, S., Diaz, A., Romanini, M., del Valle, L. J., Puiggalí, J., Tamarit, J. L., Macovez, R., (2019). Amorphous binary dispersions of chloramphenicol in enantiomeric pure and racemic poly-lactic acid: Morphology, molecular relaxations, and controlled drug release International Journal of Pharmaceutics 568, 118565

We characterize amorphous solid dispersions (ASDs) of the Chloramphenicol antibiotic in two biodegradable polylactic acid polymers, namely a commercial sample of enantiomeric pure PLLA and a home-synthesized PDLLA copolymer, investigating in particular the effect of polylactic acid in stabilizing the amorphous form of the drug and controlling its release (e.g. for antitumoral purposes). Broadband dielectric spectroscopy and differential scanning calorimetry are employed to study the homogeneity, glass transition temperature and relaxation dynamics of solvent-casted ASD membranes with different drug concentrations. We observe improved physical stability of the ASDs with respect to the pure drug, as well as a plasticizing effect of the antibiotic on the polymer, well described by the Gordon-Taylor equation. The release of the active pharmaceutical ingredient from the films in a simulated body fluid is studied by UV/vis spectroscopy at two different drug concentrations (5 and 20% in weight). The amount of released drug is found to be proportional to the square root of time, with proportionality constant that is almost the same in both dispersions, despite the fact that the relaxation time and thus the viscosity of the two samples differ by four orders of magnitude at body temperature. Since the drug release kinetics does not display a significant dependence on the drug content in the carrier, it may be expected to remain roughly constant during longer release times.

Keywords: Amorphous drug, Controlled liberation, Dielectric spectroscopy, Molecular mobility, Plasticizer, Polymer enantiomerism


Cuervo, A., Dans, P. D., Carrascosa, J. L., Orozco, M., Gomila, G., Fumagalli, L., (2014). Direct measurement of the dielectric polarization properties of DNA Proceedings of the National Academy of Sciences of the United States of America 111, (35), E3624-E3630

The electric polarizability of DNA, represented by the dielectric constant, is a key intrinsic property that modulates DNA interaction with effector proteins. Surprisingly, it has so far remained unknown owing to the lack of experimental tools able to access it. Here, we experimentally resolved it by detecting the ultraweak polarization forces of DNA inside single T7 bacteriophages particles using electrostatic force microscopy. In contrast to the common assumption of low-polarizable behavior like proteins (εr ~ 2–4), we found that the DNA dielectric constant is ~ 8, considerably higher than the value of ~ 3 found for capsid proteins. State-of-the-art molecular dynamic simulations confirm the experimental findings, which result in sensibly decreased DNA interaction free energy than normally predicted by Poisson–Boltzmann methods. Our findings reveal a property at the basis of DNA structure and functions that is needed for realistic theoretical descriptions, and illustrate the synergetic power of scanning probe microscopy and theoretical computation techniques.

Keywords: Atomic force microscopy, Atomistic simulations, DNA packaging, DNA-ligand binding, Poisson-Boltzmann equation, capsid protein, DNA, double stranded DNA, amino acid composition, article, atomic force microscopy, bacteriophage, bacteriophage T7, dielectric constant, dipole, DNA binding, DNA packaging, DNA structure, electron microscopy, ligand binding, nonhuman, polarization, priority journal, protein analysis, protein DNA interaction, scanning probe microscopy, static electricity, virion, virus capsid, virus particle, atomic force microscopy, atomistic simulations, DNA packaging, DNA-ligand binding, Poisson-Boltzmann equation, Bacteriophage T7, Capsid, Cations, Dielectric Spectroscopy, DNA, DNA, Viral, DNA-Binding Proteins, Electrochemical Techniques, Ligands, Microscopy, Atomic Force, Models, Chemical, Nuclear Proteins