96 research outputs found
Rod-like Polyelectrolytes in Presence of Monovalent Salt
We investigate the properties of rigid polyelectrolyte solutions in presence
of monovalent salt. The free energy within the Debye-H\"uckel-Bjerrum (DHBj)
theory [M. E.
Fisher and Y. Levin, {\it Phys. Rev. Lett.} 71, 3826 (1993)] is constructed.
It is found that at thermodynamic equilibrium the polyelectrolyte solution
consists of clusters composed of one polyion and various counterions. The
distribution of the cluster densities is determined by finding the minimum of
the Helmholtz free energy. The osmotic pressure and the average charge of the
cluster are found and their dependence on Manning parameter is
elucidated. A good agreement with the experimental results is obtained.Comment: 11 pages, Revtex (using twocolumn style), 15 figures and postscript
file. Submitted to Macromomelecule
Amphiphile Adsorption on Rigid Polyelectrolytes
A theory is presented which quantitatively accounts for the cooperative
adsorption of cationic surfactants to anionic polyelectrolytes. For high salt
concentration we find that the critical adsorption concentration (CAC) is a
bilinear function of the polyion monomer and salt concentrations, with the
coefficients dependent only on the type of surfactant used. The results
presented in the paper might be useful for designing more efficient gene
delivery systems
Polyelectrolyte Solutions with Multivalent Salts
We investigate the thermodynamic properties of a polyelectrolyte solution in
a presence of {\it multivalent} salts. The polyions are modeled as rigid
cylinders with the charge distributed uniformly along the major axis. The
solution, besides the polyions, contain monovalent and divalent counterions as
well as monovalent coions. The strong electrostatic attraction existing between
the polyions and the counterions results in formation of clusters consisting of
one polyion and a number of associated monovalent and divalent counterions. The
theory presented in the paper allows us to explicitly construct the Helmholtz
free energy of a polyelectrolyte solution. The characteristic cluster size, as
well as any other thermodynamic property can then be determined by an
appropriate operation on the free energy
Flexible Polyelectrolytes with Monovalent Salt
We present a model for describing flexible polyelectrolytes in a good solvent
a nd in the presence of monovalent salt . The molecule composed by monomers
is characterized by the end to end distanc e and the
number of associated counterions . At high tem peratures the polyelectrolyte
behaves as a neutral polymer (). Dec reasing the temperature, the
macromolecule changes from this extended configurat ion() to a
stretched form (). At even lower temp eratures, above the
Manning condensation threshold, the polyelectrolyte collapse s (). Our results show good agreement with simulations
Charge inversion in DNA-amphiphile complexes: Possible application to gene therapy
We study a complex formation between the DNA and cationic amphiphilic
molecules. As the amphiphile is added to the solution containing DNA, a
cooperative binding of surfactants to the DNA molecules is found. This binding
transition occurs at specific density of amphiphile, which is strongly
dependent on the concentration of the salt and on the hydrophobicity of the
surfactant molecules. We find that for amphiphiles which are sufficiently
hydrophobic, a charge neutralization, or even charge inversion of the complex
is possible. This is of particular importance in applications to gene therapy,
for which the functional delivery of specific base sequence into living cells
remains an outstanding problem. The charge inversion could, in principle, allow
the DNA-surfactant complexes to approach negatively charged cell membranes
permitting the transfection to take place.Comment: Latex, 5 figure
Complexation of DNA with Cationic Surfactant
Transfection of an anionic polynucleotide through a negatively charged
membrane is an important problem in genetic engineering. The direct association
of cationic surfactant to DNA decreases the effective negative charge of the
nucleic acid, allowing the DNA-surfactant complex to approach a negatively
charged membrane. The paper develops a theory for solutions composed of
polyelectrolyte, salt, and ionic surfactant. The theoretical predictions are
compared with the experimental measurements.Comment: 9 pages, 3 figure
Complex Formation Between Polyelectrolytes and Ionic Surfactants
The interaction between polyelectrolyte and ionic surfactant is of great
importance in different areas of chemistry and biology. In this paper we
present a theory of polyelectrolyte ionic-surfactant solutions. The new theory
successfully explains the cooperative transition observed experimentally, in
which the condensed counterions are replaced by ionic-surfactants. The
transition is found to occur at surfactant densities much lower than those for
a similar transition in non-ionic polymer-surfactant solutions. Possible
application of DNA surfactant complex formation to polynucleotide delivery
systems is also mentioned.Comment: 5 pages, latex, 3 figure
Criticality in polar fluids
A model of polar fluid is studied theoretically. The interaction potential,
in addition to dipole-dipole term, possesses a dispersion contribution of the
van der Waals-London form. It is found that when the dispersion force is
comparable to dipole-dipole interaction, the fluid separates into coexisting
liquid and gas phases. The calculated critical parameters are in excellent
agreement with Monte Carlo simulations. When the strength of dispersion
attraction is bellow critical, no phase separation is found.Comment: 5 pages, 2 figures, references modifie
Genome-Wide Analysis in Brazilian Xavante Indians Reveals Low Degree of Admixture
Characterization of population genetic variation and structure can be used as tools for research in human genetics and population isolates are of great interest. the aim of the present study was to characterize the genetic structure of Xavante Indians and compare it with other populations. the Xavante, an indigenous population living in Brazilian Central Plateau, is one of the largest native groups in Brazil. A subset of 53 unrelated subjects was selected from the initial sample of 300 Xavante Indians. Using 86,197 markers, Xavante were compared with all populations of HapMap Phase III and HGDP-CEPH projects and with a Southeast Brazilian population sample to establish its population structure. Principal Components Analysis showed that the Xavante Indians are concentrated in the Amerindian axis near other populations of known Amerindian ancestry such as Karitiana, Pima, Surui and Maya and a low degree of genetic admixture was observed. This is consistent with the historical records of bottlenecks experience and cultural isolation. By calculating pair-wise F-st statistics we characterized the genetic differentiation between Xavante Indians and representative populations of the HapMap and from HGDP-CEPH project. We found that the genetic differentiation between Xavante Indians and populations of Ameridian, Asian, European, and African ancestry increased progressively. Our results indicate that the Xavante is a population that remained genetically isolated over the past decades and can offer advantages for genome-wide mapping studies of inherited disorders.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento CientÃfico e Tecnológico (CNPq)INCT- Obesidade e DiabetesUniversidade Federal de São Paulo, Disciplina Endocrinol, Escola Paulista Med, São Paulo, BrazilUniv São Paulo, Sch Med, Lab Genet & Mol Cardiol, Inst Heart, São Paulo, BrazilUniv São Paulo, Fac Med Ribeirao Preto, Dept Social Med, Ribeirao Preto, BrazilUniversidade Federal de São Paulo, Disciplina Endocrinol, Escola Paulista Med, São Paulo, BrazilWeb of Scienc
Genome-Wide Analysis in Brazilian Xavante Indians Reveals Low Degree of Admixture
Characterization of population genetic variation and structure can be used as tools for research in human genetics and population isolates are of great interest. The aim of the present study was to characterize the genetic structure of Xavante Indians and compare it with other populations. The Xavante, an indigenous population living in Brazilian Central Plateau, is one of the largest native groups in Brazil. A subset of 53 unrelated subjects was selected from the initial sample of 300 Xavante Indians. Using 86,197 markers, Xavante were compared with all populations of HapMap Phase III and HGDP-CEPH projects and with a Southeast Brazilian population sample to establish its population structure. Principal Components Analysis showed that the Xavante Indians are concentrated in the Amerindian axis near other populations of known Amerindian ancestry such as Karitiana, Pima, Surui and Maya and a low degree of genetic admixture was observed. This is consistent with the historical records of bottlenecks experience and cultural isolation. By calculating pair-wise F-st statistics we characterized the genetic differentiation between Xavante Indians and representative populations of the HapMap and from HGDP-CEPH project. We found that the genetic differentiation between Xavante Indians and populations of Ameridian, Asian, European, and African ancestry increased progressively. Our results indicate that the Xavante is a population that remained genetically isolated over the past decades and can offer advantages for genome-wide mapping studies of inherited disorders.Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (Fapesp)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)INCT Obesidade e DiabetesINCT- Obesidade e Diabete
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