A multifaceted study on the interaction of the cationic surfactant CTAB with calf thymus DNA was carried out by using different techniques. The measurements were done at different molar ratios X = [CTAB]/[DNA]. Results show the conformational change that DNA suffers due to the interaction with surfactant molecules at low molar ratios: the condensation of the polynucleotide, from an extended coil state to a globular state. The effect observed at the higher molar ratios is worth noting: the decondensation of DNA, that is, the transition from a compact state to a more extended conformation. Experimental data obtained confirm that this latter state is not exactly the same as that found in the absence of the surfactant. Attractive interactions between different parts of the molecule by ion correlation effects are the driving force to produce both the compaction and decompaction events. Results also show the importance of choosing both a proper system for the study and the most seeming measuring technique to use. The study demonstrates that, in some cases, the use of several techniques is desirable in obtaining reliable and accurate results.

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The photoassisted degradation of n-butyltin chlorides in air-equilibrated aqueous TiO2 suspension has been studied. Several factors affecting the degradation rate, such as the extent of adsorption on the surface of catalyst particles and the effect of pH values, were examined. Particular interest is focused on the TiO2-assisted photodegradation of n-butyltin species. The simultaneous photodeposition of tin oxides/metallic tin on the TiO2 surfaces is also addressed as a route to form surface-complexed semiconductors. A mechanism consisting of interfacial trapping of a photogenerated electron−hole pair can explain the observed photoassisted degradation of n-butyltin species and the simultaneous photodeposition of tin onto the TiO2 surface. The results are compared with those, previously reported, on the photolytic degradation of these species in water.

An Electrochemical Scanning Tunneling Microscopy (EC-STM) study of the adsorption of adenine on Au(111) electrodes was undertaken in the pH range between 1 and 7, aiming at achieving a deeper knowledge on the structure and organization of adenine chemisorbed on gold, and at confirming previous conclusions obtained from combined electrochemical and insitu IR spectroscopy measurements. This study confirms that chemisorption of adenine induces the lifting of the Au(111) surface reconstruction. Furthermore, the 4% excess gold atoms of the reconstructed surface which are expelled during lifting of the reconstruction do not diffuse away from the reconstruction rows. We observe, in contrast, the formation of nanometric islands arranged forming chains along the directions previously followed by the reconstruction solitons. Chemisorbed adenine adlayers consist of short chains of adenine molecules roughly aligned along the three main crystallographic directions of the substrate and stabilized by  stacking. These chains tend to align parallel to each other, forming very small domains and yielding an adlayer with a very short-range order. The same adlayer structure is observed at all the studied pH values. The STM results also confirm that, in very acidic media, and at low potentials, adenine adsorbs very weakly on the reconstructed Au(111) surface.

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The photoassisted degradation of phenyltin(IV) chlorides in air-equilibrated aqueous TiO2 suspension has been studied. The stability of the triphenyltin(IV) derivative in aqueous solutions at different pH values and the extent of adsorption of tri-and diphenyltin(IV) chloride species were examined. Particular interest is focused on the TiO2-assisted photodegradation of phenyltin species. Detailed surface analyses of the catalyst particles by IR and of the liquid medium by GC-MS are reported. A mechanism consisting of interfacial trapping of a photogenerated electron-hole pair can explain the TiO2-photoassisted degradation of phenyltin species. The results are compared with those previously reported on the photolytic degradation of theses species in water and with those of n-butyltin species (photolytic and TiO2-photoassisted). Our results allow that this is not a photocatalysis system but a photoassisted one in the presence of TiO2.

Small N-(2-mercaptopropionyl)glycine gold nanoparticles (AuNPs) of 1.6 nm core size were synthesized. The mode of binding and the effect of ethanol on DNA conformational changes induced by AuNPs nanoparticles were studied in detail by means of fluorescence and circular dichroism (CD) spectroscopy, zeta potential, dynamic light scattering (DLS), viscometric, and atomic force microscopy (AFM) methods. The measurements were done at different molar ratios R = C AuNPs /C DNA and at different ethanol content. Both spectroscopic and structural techniques revealed that the binding of AuNPs with DNA grooves largely prevailed up to 30% EtOH (v/v). For higher ethanol levels (from 40% to 65% EtOH (v/v)), all methods concurred by showing that AuNPs were able to induce DNA strand elongation, which preceded formation of the AuNPs/DNA groove complex. Moreover, under suitable R values and ethanol content, the CD spectra, DLS, and AFM experiments revealed that AuNPs nanoparticles induced the formation of a rather compact AuNPs/DNA complex. The results suggested that this form is a coiled DNA structure stabilized by AuNPs interconnections.

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