Complexation of DNA with positive spheres: phase diagram of charge inversion and reentrant condensation

The phase diagram of a water solution of DNA and oppositely charged spherical macroions is studied. DNA winds around spheres to form beads-on-a-string complexes resembling the chromatin 10 nm fiber. At small enough concentration of spheres these "artificial chromatin" complexes are negative, while at large enough concentrations of spheres the charge of DNA is inverted by the adsorbed spheres. Charges of complexes stabilize their solutions. In the plane of concentrations of DNA and spheres the phases with positive and negative complexes are separated by another phase, which contains the condensate of neutral DNA-spheres complexes. Thus when the concentration of spheres grows, DNA-spheres complexes experience condensation and resolubilization (or reentrant condensation). Phenomenological theory of the phase diagram of reentrant condensation and charge inversion is suggested. Parameters of this theory are calculated by microscopic theory. It is shown that an important part of the effect of a monovalent salt on the phase diagram can be described by the nontrivial renormalization of the effective linear charge density of DNA wound around a sphere, due to the Onsager-Manning condensation. We argue that our phenomenological phase diagram or reentrant condensation is generic to a large class of strongly asymmetric electrolytes. Possible implication of these results for the natural chromatin are discussed.Comment: Many corrections to text. SUbmitted to J. Chem. Phy

Herd behaviour in Southeast Asian stock markets — An empirical investigation

This study examines herd behaviour in four Southeast Asian stock markets, namely Indonesia, the Philippines, Malaysia, and Vietnam. Empirical results indicate that except for the Philippines, herding exists in the other three markets. Stronger evidence of herding has been detected in these markets when the market is up. When the market is down, it is only the Malaysian market that exhibits significant herding. The study further investigates herding by dividing the entire sample period into two sub-periods: pre-crisis and during economic crisis. We find strong evidence of the existence of herding in Indonesia and Malaysia in both sub-periods. However, the findings are mixed when we additionally examine herding in up and down market scenarios during the two sub-periods by using modified models

Study on Fructooligosaccharide (Fos) Production By Enzyme Pectinex Ultra Sp-l Immobilzed On Alginate

Fructooligosaccharide (FOS) is a new alternative sweetener with its characteristics such as low energy and safety for people with diabetes. Pectinex Ultra SP-L which has fructosyltransferase, catalyzes the reaction to produce short chain fructooligosaccharides. The research was conducted to enhance the high FOS content in process of FOS production by immobilized enzyme. Results achieved by Empirical planning Design Expert 7.0 - central composite method (CCD) identified at optimum conditions for process of immobilized enzyme with alginate 3.3 (%), ratio of enzyme: alginate was 0.79 (w/w), CaCl2 3.75 (%). Efficiency of loading protein reached 73.32 (%). Reaction conditions: 60 (oC), shaking velocity 90 (rpm), the initial sucrose concentrations of 50 (%), pH 5.75. When produced in 20 (h), the reaction obtained the highest level of FOS with column reaction system. The FOS for producted by immobilized enzyme achieved 47.87 (%), of which 1-kestose obtained 37.06 (%), the remaining was 10.81 (%) including nystose and fructofuranosylnystose. Efficiency of producing FOS by using immobilized enzyme compared to the free enzyme was high up to 89.49 (%)

Screening of a charged particle by multivalent counterions in salty water: Giant charge inversion

Screening of a macroion such as a charged solid particle, a charged membrane, double helix DNA or actin by multivalent counterions is considered. Small colloidal particles, charged micelles, short or long polyelectrolytes can play the role of multivalent counterions. Due to strong lateral repulsion at the surface of macroion such multivalent counterions form a strongly correlated liquid, with the short range order resembling that of a Wigner crystal. These correlations create additional binding of multivalent counterions to the macroion surface with binding energy larger than $k_BT$. As a result even for a moderate concentration of multivalent counterions in the solution, their total charge at the surface of macroion exceeds the bare macroion charge in absolute value. Therefore, the net charge of the macroion inverts its sign. In the presence of a high concentration of monovalent salt the absolute value of inverted charge can be larger than the bare one. This giant inversion of charge can be observed by electrophoresis or by direct counting of multivalent counterions.Comment: 17 pages, 9 figures. Many corrections. Accepted to J. Chem. Phy

A model of inversion of DNA charge by a positive polymer: fractionization of the polymer charge

Charge inversion of a DNA double helix by an oppositely charged flexible polyelectrolyte (PE) is considered. We assume that, in the neutral state of the DNA-PE complex, each of the DNA charges is locally compensated by a PE charge. When an additional PE molecule is adsorbed by DNA, its charge gets fractionized into monomer charges of defects (tails and arches) on the background of the perfectly neutralized DNA. These charges spread all over the DNA eliminating the self-energy of PE. This fractionization mechanism leads to a substantial inversion of the DNA charge, a phenomenon which is widely used for gene delivery.Comment: 4 pages, 2 figures. Improved figures and various corrections to tex