Biomedical subjects

F J Solis

Publications and source records attributed to F J Solis.

4 recordsLinked to original sources

PubMed2005

Charge induced pattern formation on surfaces: segregation in cylindrical micelles of cationic-anionic peptide-amphiphiles.

Micelles, vesicles, and films composed of two species of incompatible heterogeneous molecules exhibit full internal segregation of the component species. This macroscopic segregation can be inhibited by oppositely charging the two different molecular species. The degree of compatibility achieved by the charges leads to either fully homogenous mixtures or to local segregation and the possible formation of regular patterns. We investigate the induction of periodic surface patterns by the presence of opposite charges in flat films and cylindrical micelles. In the strong segregation limit the incompatibility between species can be described by a line tension parameter gamma. The size of the patterns formed is of the order of a characteristic size L approximately (gamma/sigma(2))(1/2), where sigma is the surface charge density. The pattern symmetry on flat surfaces is function only of the fraction of area covered by the components, f: lamellar for 0.34<f<0.66 and hexagonal otherwise. In cationic and anionic mixtures aggregated into cylindrical micelles the symmetry and size of the surface charged domains depends also on the radius R of the cylinder. For large radii the patterns are similar to those in the plane, but for small radii only lamellar patterns are formed. At high salt concentration the surface domain size jumps discontinuously to an infinite value, resulting in macroscopic phase segregation.

Anions↗

PubMed2004

A statistical thermodynamic model applied to experimental AFM population and location data is able to quantify DNA-histone binding strength and internucleosomal interaction differences between acetylated and unacetylated nucleosomal arrays.

Imaging of nucleosomal arrays by atomic force microscopy allows a determination of the exact statistical distributions for the numbers of nucleosomes per array and the locations of nucleosomes on the arrays. This precision makes such data an excellent reference for testing models of nucleosome occupation on multisite DNA templates. The approach presented here uses a simple statistical thermodynamic model to calculate theoretical population and positional distributions and compares them to experimental distributions previously determined for 5S rDNA nucleosomal arrays (208-12,172-12). The model considers the possible locations of nucleosomes on the template, and takes as principal parameters an average free energy of interaction between histone octamers and DNA, and an average wrapping length of DNA around the octamers. Analysis of positional statistics shows that it is possible to consider interactions between nucleosomes and positioning effects as perturbations on a random positioning noninteracting model. Analysis of the population statistics is used to determine histone-DNA association constants and to test for differences in the free energies of nucleosome formation with different types of histone octamers, namely acetylated or unacetylated, and different DNA templates, namely 172-12 or 208-12 5S rDNA multisite templates. The results show that the two template DNAs bind histones with similar affinities but histone acetylation weakens the association of histones with both templates. Analysis of locational statistics is used to determine the strength of specific nucleosome positioning tendencies by the DNA templates, and the strength of the interactions between neighboring nucleosomes. The results show only weak positioning tendencies and that unacetylated nucleosomes interact much more strongly with one another than acetylated nucleosomes; in fact acetylation appears to induce a small anticooperative occupation effect between neighboring nucleosomes.

Acetylation↗

PubMed1999

Attractive interactions between rodlike polyelectrolytes: polarization, crystallization, and packing.

We study the attractive interactions between rodlike charged polymers in solution that appear in the presence of multivalence counterions. The counterions condensed to the rods exhibit both a strong transversal polarization and a longitudinal crystalline arrangement. At short distances between the rods, the fraction of condensed counterions increases, and the majority of these occupy the region between the rods, where they minimize their repulsive interactions by arranging themselves into packing structures. The attractive interaction is strongest for multivalent counterions. Our model takes into account the hard-core volume of the condensed counterions, and their angular distribution around the rods. The hard-core constraint strongly suppresses longitudinal charge fluctuations.

Journal Article↗

PubMed1991

Entamoeba histolytica: microtubule movement during mitosis.

The movement of microtubules (MTs) during nuclear division of Entamoeba histolytica was ultrastructurally studied. Regarding this MT movement, five stages of mitosis could be defined: prophase, metaphase, anaphase A, anaphase B, and telophase. In early stages of mitosis, chromatinic material appeared condensed, and MTs were detected in the center of the nucleus. Later, MTs seemed to grow from an electron-dense body located in the center of the nucleus. This body might be the microtubule organizing center, which organized the MTs, first in a lateral way, and later to form the mitotic spindle, which was made of a bundle of MTs joined by their ends. This junction of MTs to themselves could also be observed in cross-sections. The last stage of mitosis was the nuclear separation. Two different morphological types of intranuclear vesicles were also observed, which seemed to have different types of membrane. Both intranuclear vesicles were present during nuclear division, generally in clusters, and located close to the nuclear periphery.

Anaphase↗