C. Cerrillos

Compaction and decompaction of DNA induced by the cationic surfactant CTAB.

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.

UV photolytic degradation of butyltin chlorides in water

Abstract The UV degradation of tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) chlorides in water was studied. TBT in water is photodegraded to inorganic tin, via DBT and MBT as intermediates. Results are also presented concerning the photodegradation of TBT, DBT and MBT in different atmospheric gases, and they indicate that the surrounding environment influences the rate of photodegradation of these compounds.

UV-photoassisted degradation of phenyltin(IV) chlorides in water

The UV degradation of triphenyltin (TPT), diphenyltin (DPT) and monophenyltin (MPT) chlorides in water was studied. The UV-photoassisted degradation of TPT in water takes place by sequential dephenylation via DPT and MPT. Results are also presented concerning the photodegradation of TPT and DPT in different atmospheric gases. The chemical nature of the surrounding atmosphere seems to affect the photodegradation rate of the TPT species, but not that of DPT.

Photocatalytic Reduction and Removal of Uranium From a Uranium- EDTA Solution

Abstract The removal, from aqueous solution, of uranyl ions by adsorption in the absence and presence of the chelant EDTA, and the photocatalytic removal by reduction of uranium from U:EDTA solutions is reported. Uranyl (UO22+) adsorption at pH6 approaches saturation at about 40 ppm UO2(NO3)2. Adsorption is negligible at pH 2, and increases to a maximum at pH = 7-8, then declines at pH 10. The increased adsorption is consistent with a progressively higher deprotonation of TiO2 surface sites, whereas the decrease at pH 10 corresponds to partial conversion of positive uranyl specie, UO22+, to a negatively charged hydroxy complex, UO2(OH)3-. Added EDTA competes for uranyl with the surface sites, and a monotonic diminution of adsorbed uranium is observed with increasing EDTA level. At 1:1 U:EDTA ratio, the adsorbed metal increases monotonically from zero at pH 2 to a maximum at pH 10 (more basic conditions were not explored), a result reflective of the stability of the U:EDTA complex. Under illumination in the absence of dissolved oxygen, the uranium (VI) in solution (free and complexed) decreases indicating a reductive process for the metal. The apparent first order rate constant for disappearance is observed to decrease with increasing pH, i.e. the rate constant is maximum at pH 2 and smallest at pH 10. Centrifugation of catalyst and exposure of supernatant for 24 h to air results in regaining the original uranyl (VI) concentration at pH near 2 and 5; in contrast, one day exposure to air provides no reoxidation of supernatants at pH 7 or 10. These results indicate that uranyl is photocatalytically reduced to a lower, positive oxidation state to form a positive specie which adsorbs appreciably only under neutral/ basic conditions, above the isoelectric point of TiO2.

Degradation of n-Butyl tin Chlorides in Waters. A Comparative Assessment of the Process by Photo-assisted and Chemical- treatment Methods

Abstract The degradation of aqueous n-butyl tin by several selected advanced oxidation technologies (AOTs) was studied and comparisons made between the processes. UV-photolytic and TiO2-photoassisted oxidation and treatment with chemical oxidants (hydrogen peroxide, hypochlorite) were thus evaluated in terms of their action upon n-butyltin chlorides in water.

UV photolytic degradation of phenylmercury compounds in water-acetonitrile (1:1) media

Abstract The photochemical degration of diphenylmercury and monophenylmercury compounds in water—acetonitrile (1:1) media in an air-equilibrated atmosphere was studied. The photoprocess involves sequential dephenylation to inorganic forms of mercury, with the subsequent formation of several organic products, most of them pollutants. The ecological impact of this photoprocess is emphasized.

Degradation of Phenylmercury Compounds by Heterogeneous Photocatalysis Over α-Fe2O3

Abstract We report here on the degradation of diphenylmercury and monophenylmercury chloride in air-equilibrated aqueous solutions by heterogeneous photocatalysis over α-Fe2O3. Photocatalysis proceeded via sequential de-phenylation leaving inorganic mercury. GC-MS analysis of the products revealed that photocatalytic degradation involved hydroxylation of the phenyl rings. Mechanistic features and photocatalytic activity were also studied and are reported upon.