Neutron Reflectivity Study of the Complexation of DNA with Lipids and Surfactants at the Surface of Water

Abstract

Complexation of lipids and surfactants with short DNA fragments at the air-water interface has been studied by neutron reflectivity. Complexation with zwitterionic lipids occurs in the presence of divalent cations, and ion specificity has been demonstrated (binding is less effective with Ba2+ than with Mg2+ or Ca2+). One and two DNA layers have been observed for dilute and more compact lipid monolayers, respectively. Two DNA layers have also been found with the soluble cationic surfactant dodecyltrimethylammonium bromide (DTAB), except close to the precipitation boundary. This result is opposite to that found in ellipsometry where very thick layers are found in this region. It is possible that the ellipsometry signal is due to highly hydrated bulk complexes adsorbing at the surface, not seen by neutrons because of unfavorable contrast conditions. Long DNA was found to be less keen to form surface complexes than short DNA fragments.

A comparative study on intrinsic fluorescence of BSA and lysozyme proteins in presence of different divalent ions from their solution and thin film conformations

“…Probably, the delicate variation in interaction between the positively charged lysozyme with the divalent cations modifies ion-dependent quenching efficiency. Our results clearly indicated that among these three different divalent cations the effect of protein-ion interaction is maximal for Ca 2+ ions and matches the results obtained from other studies [47][48][49]…”

“…Probably, the delicate variation in interaction between the positively charged lysozyme with the divalent cations modifies ion‐dependent quenching efficiency. Our results clearly indicated that among these three different divalent cations the effect of protein–ion interaction is maximal for Ca 2+ ions and matches the results obtained from other studies in which enhanced interactions were found between biomolecules in the presence of Ca 2+ ions. Studies on such protein–ion interactions therefore imply that protein conformation is modified depending on specific physicochemical conditions.…”

“…Ba 2+ ions are ≈0.72, 1.00 and 1.35 Å [43] , and the electron affinity values of Mg 2+ , Ca 2+ and Ba 2+ ions are ≈ 1.31, 1.0, 0.89 kJ/mol, respectively. [44][45][46] However, interaction between biomolecules in the presence of these three cations varies [47][48][49] and the effect was found to be stronger for Ca 2+ ions and weaker for Ba 2+ ions. [47][48][49] The nature of the hydrated ions may effectively modify interaction in this case.…”

“…[44][45][46] However, interaction between biomolecules in the presence of these three cations varies [47][48][49] and the effect was found to be stronger for Ca 2+ ions and weaker for Ba 2+ ions. [47][48][49] The nature of the hydrated ions may effectively modify interaction in this case. It is well established that lysozyme contains six tryptophan residues (tryptophan 28, 62, 63, 108, 111 and 123) while BSA contains two tryptophan residues (tryptophan 134 and 212) and, among these, surface tryptophan will interact more strongly with solvent ions.…”

Complexes of surfactants with oppositely charged polymers at surfaces and in bulk

“…Although in many cases the layers consist of a surfactant monolayer coupled to a very thin polymer layer lying flat beneath, more complex situations can be encountered. For instance, structures comprising two DNA layers have been found with the soluble cationic surfactant DTAB, except close to the precipitation boundary, where only one DNA layer remains [42]. This result is opposite to that found in ellipsometry where very thick layers are found in this region [40].…”