Temperature Effects on Threshold Counterion Concentration to Induce Aggregation of fd Virus

Abstract

We seek to determine the mechanism of like-charge attraction by measuring the temperature dependence of critical divalent counterion concentration (${\mathrm{C}}_{\mathrm{c}}$) for the aggregation of fd viruses. We find that an increase in temperature causes ${\mathrm{C}}_{\mathrm{c}}$ to decrease, primarily due to a decrease in the dielectric constant ($\epsilon$) of the solvent. At a constant $\epsilon$, ${\mathrm{C}}_{\mathrm{c}}$ is found to increase as the temperature increases. The effects of $T$ and $\epsilon$ on ${\mathrm{C}}_{\mathrm{c}}$ can be combined to that of one parameter: Bjerrum length ($l_B$). ${\mathrm{C}}_{\mathrm{c}}$ decreases exponentially as $l_B$ increases, suggesting that entropic effect of counterions plays an important role at the onset of bundle formation.

12 pages, 3 figures