高分子学会九州支部講演会
講演題目：Polymer-surfactant interactions: bulk and interfaces
Manipulation of DNA by surfactant.
講師 : Bjön Lindman 教授 1， Maria da Graça Miguel 教授 2

1Chair Professor, Division of Physical Chemistry 1, Department of Chemistry andChemical Engineering, Lund University
2Department of Chemistry, University of Coimbra, 3004-535 Coimbra
場 所：九州大学 理学部 化学第3講義室（理学部2号棟2階2275室）
日 時：6 月 4 日 (月)13:00-15:00

Ionic surfactants generally associate with all classes of polymers-ionic and nonionic,hydrophilic and hydrophobic- but the association behaviour and the effect onmacroscopic properties, like rheology, are very different. On the basis of a review ofpolymer-surfactant association in bulk, the behaviour of these mixed systems on solid
surfaces are discussed. In particular, we consider the adsorption of mixtures ofpolyelectrolytes and oppositely charged surfactants on polar and nonpolar surfaces. It isfound that, depending on concentration, an ionic surfactant can either induce additional
polyion adsorption or induce desorption. Kinetic control of adsorption and, in particular,desorption is typical. Important consequences of this include increased adsorption onrinsing and path dependent adsorbed layers.
The interaction between DNA and cationic surfactant is strong and leads in bulk
solution to cooperative binding and to condensation of DNA from an extended to acompact conformation. It also leads to an associative phase separation with aconcentrated DNA-surfactant phase in equilibrium with a dilute solution. Phase
diagrams are found to depend strongly on surfactant and also on DNA conformation.
The difference in phase diagrams between single- and double-stranded DNA show therole of hydrophobic interactions in surfactant binding. Particles formed from
DNA-surfactant solutions have different sizes and shapes depending on thestoichiometry. The particles, as well as the macroscopic phases formed, have a regularinternal structure as demonstrated by small angle X-ray diffraction and cryogenictransmission electron microscopy. There is typically a 5-10 nm periodicity and themajor structures formed are lamellar and reversed or normal hexagonal, structure
formed mainly determined by the surfactant chemical structure. By controlled mixing ofsolutions of DNA and surfactant, globular transparent gel-like particles can be formed.
By chemical cross-linking of DNA, macroscopic gels can be prepared. These gels arevery useful in studying DNA-cosolute interactions from simple volumetricmeasurements. Thus, on addition of a simple electrolytes, polycations or cationicsurfactants, the gels shrink; this effect is reversible as reswelling occurs as theDNA-cosolute association is eliminated. Regarding the covalent gels, denaturation ofcross-linked DNA gels has been induced by changes in temperature. This process,studied by fluorescence using ethidium bromide, appears to be reversible when aheating/cooling cycle was performed. The swelling behaviour on addition of different
cosolutes, such as metal ions, polyamines, charged proteins and surfactants wasinvestigated for different DNA gel samples, which include long and short ds-DNA andlong and short ss-DNA. The DNA molecular weight has only a slight effect on thedeswelling curves, while conformation shows a more pronounced one. In general, single
stranded DNA gels exhibits a larger collapse, in the presence of cations, than double
stranded does. This has been attributed to differences in linear charge density, chain
flexibility and hydrophobicity. In the presence of surfactants with different chain
lengths, the swelling behaviour displayed by ss-DNA can be interpreted in terms of aninterplay between hydrophobic and electrostatic interactions, the latter being relatedwith polymer flexibility. Increasing hydrophobicity of the network leads to a decreased
critical aggregation concentration (cac) for the surfactant/gel complex, due to thestrengthened hydrophobic attractive force between the surfactant ions and the gel chain.
The swelling of DNA gels appears to be reversible and this process does not depend on
the DNA conformation. No macroscopic separation of collapsed and swollen region isobserved at intermediate degrees of binding for ds-DNA gels, whereas a dense
surfactant-rich surface phase (skin) is found to co-exist with a swollen core network for
ss-DNA gels with ﾟ >0.5. One explanation to this difference is the large deformationenergy required for the compression of the very stiff ds-DNA chains.

For further information, please contact Masahiko Annaka,
Dept. of Chem. Kyushu Univ.
Phone: 092-882-6520,
E-mail: annaka-scc@mbox.nc.kyushu-u.ac.jp