1,721,033 research outputs found
Hydration structure of ethanol water solution at low alcohol concentration
No full textThe analysis of the hydration structure of ethanol in water is performed employing both neutron and X-ray scattering data. An abrupt structural change as a function of the molar concentration is evidenced and connected with the water distribution around the ethanol. The change in structure appears to be related to the hydrogen bonds in the system and a small isotope effect may appear on substituting hydrogen with deuterium
Calorimetric and dynamic light scattering investigation of cationic surfactant- DNA complexes
No full textDNA Condensation Induced by Cationic Surfactant: A Viscosimetry and Dynamic Light Scattering Study
No full textPolyion-induced aggregation of lipidic-coated solid polystyrene spheres: The many facets of complex formation in low-density colloidal suspensions
No full textWe have investigated the formation of a cluster phase in low-density colloidal systems formed by charged solid charged particles stuck together by an oppositely charged polyion. In analogy with what we have previously observed in the case of soft charged particles, also in this case the same basic phenomenology occurs, consisting of the presence of the two well-known characteristic phenomena of this class of colloids, that is, reentrant condensation and charge inversion. With the aim of comparing the cluster formation in both soft and solid charged particles, we have, in previous works, employed cationic liposomes (soft particles, lipidic vesicles built up by dioleoyltrimethylammonium propane [DOTAP] lipid) and, in the present work, polystyrene particles (solid particles) covered by the same lipidic bilayer as the one of the soft particles, so that the two classes of particles share electrostatic interactions of the same nature. These charged particle clusters, where the single aggregating particles maintain their integrity without undergoing a structural rearrangement, join to a class of different aggregated structures (lamellar or inverse hexagonal phases) observed as well in the polyion-induced aggregation of oppositely charged mesoscopic particles, in particular, lipidic vesicles. Our results show that the formation of relatively large, equilibrium clusters of particles which maintain their integrity, stuck together by a polyion which acts as an electrostatic glue, is one of the many facets of the complex phenomenology underlying the interactions of charged particles with oppositely charged objects
Thermal stability of DNA in DNA-induced DOTAP liposome aggregates
No full textThe influence on the melting of calf thymus DNA induced by cationic liposomes, commonly used in gene therapy, was studied by means of ultraviolet spectrophotometry and differential scanning calorimetry. Both the two methods reveal that DNA in DNA-induced liposome complexes undergoes a denaturation process at a much higher temperature than free DNA does. The extent of protection strongly depends on the charge ratio R(+/-) of liposome-DNA complexes. In the case of dioleoyl trimethyl ammonium propane (DOTAP) liposomes, the maximum of the stabilization occurs at R(+/-)=0.7, where the DNA is still native up to temperatures higher than 100 degrees C. This protection against denaturation up to higher temperatures might be of importance for bio-technological applications, such as biomolecular separation, antigene sequencing and for drug design purpose
Polyion-Induced Cluster Formation in Different Colloidal Polyparticle Aqueous Suspensions
No full textThe formation of aggregates in polyion-induced charged colloidal particles in aqueous suspension is characterized, under appropriate conditions, by two complementary effects, known as re-entrant condensation and charge inversion, which are considered as proof for the existence of a cluster phase. In this paper, we extend our previous investigation to a set of aqueous colloidal particle suspensions, such as polystyrene spheres, colloidal gold particles, and polylactic acid particles. These systems are characterized by the evolution of the average size of the aggregates and their surface electrical charge (charge inversion) by means of dynamic light-scattering measurements and laser Doppler electrophoretic techniques. The results, together with the previous ones concerning liposome particles, support the notion of a common behavior of this group of complex colloids characterized by short-ranged attractive interactions. The study provides some insights into these structures, which are potentially useful in biotechnological applications, such as multicompartmental carriers in nonviral drug delivery
Study of the ribosome structure of the mesophilic bacterium Escherichia coli by dielectric spectroscopy, fluorescence and microcalorimetry
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