The interactions between oppositely charged surfactant/polymer mixtures have been studied using neutron reflectometry with supplementary surface tension measurements. The cationic surfactant dodecyl trimethylammonium bromide (C12TAB)/anionic polyelectrolyte sodium poly(styrene sulfonate) (NaPSS) system is compared with a system containing anionic sodium dodecyl sulfate (SDS) and cationic poly(vinyl pyridinium chloride) (PVPmCl). The PVPmCl/SDS mixture has been studied both with and without added electrolyte. Neutron reflection shows that for both systems, the surface consists of a mixture of polyelectrolyte and surfactant over a range of surfactant concentrations from above the critical micelle concentration (CMC) to CMC/100 for polymer concentrations between 10 and 140 ppm. In the lower surfactant concentration range, the amount of surfactant adsorbed approximately corresponds to a surfactant monolayer (area per molecule ∼ 35−45 Å 2 for SDS in the presence of 0.1 M NaCl, 35−60 Å2 without NaCl, and 50−60 Å2 for C12TAB with 0.1 M NaBr). However, at higher concentrations and in the presence of electrolyte, this increases to an amount approximately corresponding to three adsorbed layers (area per molecule = 12 Å2 for SDS and 17−20 Å2 for C12TAB). This increase is not observed for PVPmCl/SDS in the absence of 0.1 M NaCl. The structure of the higher concentration layer is a sandwich structure with an outer surfactant layer and a submerged polymer/micellar (spheres or rods) or polymer/defective bilayer. The surface tension and neutron results can be interpreted qualitatively in terms of three species in the system, a surface active complex PSS, a bilayer complex , which can only adsorb on a preformed PSS layer, and a bulk solution complex PSM. PSS is adsorbed at very low concentrations of surfactant, possibly even before any PSM is formed in the bulk solution. At high concentrations, there are two effects. There may be adsorption of complexes to the layer of PSS already at the surface. However, the formation of is in competition with the formation of PSM. If the latter is dominant, there is no secondary adsorption of , as is the case for PVPmCl/SDS in the absence of electrolyte, and the surface tension may increase very sharply with surfactant concentation at the point where the formation of PSM in the bulk solution is complete. If there is secondary adsorption of PSM or PSS, as for NaPSS/C12TAB with or without electrolyte and PVPmCl/SDS with electrolyte, the surface tension should show a more modest increase at this concentration.

The compound [Cu(II)(2)(D(1))(H(2)O)(2)](ClO(4))(4) (D(1) = dinucleating ligand with two tris(2-pyridylmethyl)amine units covalently linked in their 5-pyridyl positions by a -CH(2)CH(2)- bridge) selectively promotes cleavage of DNA on oligonucleotide strands that extend from the 3' side of frayed duplex structures at a site two residues displaced from the junction. The minimal requirements for reaction include a guanine in the n (i.e. first unpaired) position of the 3' overhang adjacent to the cleavage site and an adenine in the n position on the 5' overhang. Recognition and strand scission are independent of the nucleobase at the cleavage site. The necessary presence of both a reductant and dioxygen indicates that the intermediate responsible for cleavage is produced by the activation of dioxygen by a copper(I) form of the dinuclear complex. The lack of sensitivity to radical quenching agents and the high level of site selectivity in scission suggest a mechanism that does not involve a diffusible radical species. The multiple metal center exhibits a synergy to promote efficient cleavage as compared to the action of a mononuclear analogue [Cu(II)(TMPA)(H(2)O)](ClO(4))(2) (TMPA = tris(2-pyridylmethyl)amine) and [Cu(OP)(2)](2+) (OP = 1,10-phenanthroline) at equivalent copper ion concentrations. The dinuclear complex, [Cu(II)(2)(D(1))(H(2)O)(2)](ClO(4))(4), is even capable of mediating efficient specific strand scission at concentrations where [Cu(OP)(2)](2+) does not detectably modify DNA. The unique coordination and reactivity properties of [Cu(II)(2)(D(1))(H(2)O)(2)](ClO(4))(4) are critical for its efficiency and site selectivity since an analogue, [Cu(II)(2)(DO)(Cl(2))](ClO(4))(2), where DO is a dinucleating ligand very similar to D(1), but with a -CH(2)OCH(2)- bridge, exhibits only nonselective cleavage of DNA. The differences in the reactivity of these two complexes with DNA and their previously established interaction with dioxygen suggest that specific strand scission is a function of the orientation of a reactive intermediate.

A trinuclear copper complex, [Cu(3)(II)(L)(H(2)O)(3)(NO(3))(2)](NO(3))(4).5H(2)O (1) (L = 2,2',2' '-tris(dipicolylamino)triethylamine), with pyridyl and alkylamine coordination exhibits a remarkable ability to promote specific strand scission at junctions between single- and double-stranded DNA. Strand scission occurs on the 3' overhang at the junction of a hairpin or frayed duplex structure and is not dependent on the identity of the base at which cleavage occurs. Target recognition minimally requires a purine at the first unpaired position and a guanine at the second unpaired position on the 5' strand. Incorporation of the necessary recognition elements into an otherwise unreactive junction resulted in specific strand scission at that new target and helped to confirm the predictive nature of this complex. Selective strand scission requires both a reductant and dioxygen, suggesting activation of O(2) by the reduced form of 1. The reaction utilizing the trinuclear complex does not appear to involve a diffusible radical species as suggested by its high specificity of target oxidation and its lack of sensitivity to radical quenching agents. Comparisons between the trinuclear copper complex, mononuclear analogues of 1, and [Cu(OP)(2)](2+) (OP = 1,10-phenanthroline) indicate that recognition and reactivity described in this report are dependent on the multiple metal ions within the same complex which together support its unique activity.