Green complexation for heavy metals removal from wastewater by Keggin-polyoxometalates enhanced ultrafiltration.

The presence of heavy metals in wastewater has become a serious issue and a global concern for the environment and public health with rapid progress of modern textile industry. To minimize the health risks of heavy metals their complexation to a chelating agent constitute a promising process using membrane separation. We highlight for the first time the use of Keggin type-polyoxometalates (PW12) as complexing agent to eliminate heavy metals from synthetic textile wastewater. Indeed, filtration experiments were performed through the ultrafiltration organic regenerated cellulose membrane (3KDa). Effects of pressure (1-2.5 bar), PW12 concentration (10-50 mg·L-1), salt concentration (10-4-2 M) and pH value (2-12) on cadmium (Cd) and copper (Cu) removal were regularly explored. Experimental data showed that the addition of PW12 improves metal removal efficiency (up to 90%). The addition of NaCl salt significantly decreases the metals retention to 42%. The retention drop is probably due to the competition between Na+ and metals on complexation same negative sites of the PW12 and to the electric double-layer compressing. 24 full factorial design has been used to evaluate the most influencing parameters. The results obtained revealed that the maximum metal retention was 99% for both Cd and Cu.

Electrochemical and theoretical investigations of the role of the appended base on the reduction of protons by [Fe2(CO)4(κ2-PNP(R)(µ-S(CH2)3S] (PNP(R) ={Ph2PCH2}2NR, R=Me, Ph).

The behavior of [Fe(2)(CO)(4)(κ(2)-PNP(R))(µ-pdt)] (PNP(R) =(Ph(2)PCH(2))(2)NR, R=Me (1), Ph (2); pdt=S(CH(2))(3)S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP(R) appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF(3)SO(3)H or CH(3)SO(3)H; the cation with a bridging hydride ligand, 1 µH(+) (R=Me) or 2 µH(+) (R=Ph) is obtained rapidly. Only 1 µH(+) can be protonated at the nitrogen atom of the PNP chelate by HBF(4)·Et(2)O or CF(3)SO(3)H, which results in a positive shift of the proton reduction by approximately 0.15 V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η(2)-H(2) species in the Fe(I)Fe(II) state. When R=Ph, the bridging hydride cation 2 µH(+) cannot be protonated at the amine function by HBF(4)·Et(2)O or CF(3)SO(3)H, and protonation at the N atom of the one-electron reduced analogue is also less favored than that of a S atom of the partially de-coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2 µH(+). The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 (k(obs) ≈4-7 s(-1)) because of the slow intramolecular proton migration and H(2) release steps identified by the theoretical study.

Biophysical properties of cationic lipophosphoramidates: Vesicle morphology, bilayer hydration and dynamics.

Cationic lipids are used to deliver genetic material to living cells. Their proper biophysical characterization is needed in order to design and control this process. In the present work we characterize some properties of recently synthetized cationic lipophosphoramidates. The studied compounds share the same structure of their hydrophobic backbone, but differ in their hydrophilic cationic headgroup, which is formed by a trimethylammonium, a trimethylarsonium or a dicationic moiety. Dynamic light scattering and cryo-transmission electron microscopy proves that the studied lipophosphoramidates create stable unilamellar vesicles. Fluorescence of polarity probe, Laurdan, analyzed using time-dependent fluorescence shift method (TDFS) and generalized polarization (GP) gives important information about the phase, hydration and dynamics of the lipophosphoramidate bilayers. While all of the compounds produced lipid bilayers that were sufficiently fluid for their potential application in gene therapy, their polarity/hydration and mobility was lower than for the standard cationic lipid - DOTAP. Mixing cationic lipophosphoramidates with DOPC helps to reduce this difference. The structure of the cationic headgroup has an important and complex influence on bilayer hydration and mobility. Both TDFS and GP methods are suitable for the characterization of cationic amphiphiles and can be used for screening of the newly synthesized compounds.

Physicochemical properties of cationic lipophosphoramidates with an arsonium head group and various lipid chains: A structure-activity approach.

We studied the physicochemical properties of some cationic lipophosphoramidates used as gene vectors in an attempt to better understand the link between the nature of the hydrophobic chain and both physico-chemical properties and transfection efficiency. These compounds have an arsonium head group and various chain lengths and unsaturation numbers. The synthesis of cationic phospholipids with oleic (Guenin et al., 2000 [1]; Floch et al., 2000 [2]) or linoleic (Fraix et al., 2011 [3]; Le Gall et al., 2010 [4]) chains has already been reported by our group and their efficiency as gene carriers has been demonstrated. Four new compounds were synthesized which incorporated either C14:0, C18:0, C20:4 or C20:5 chains. The membrane fluidity was studied by fluorescence anisotropy measurements. The fusion of liposomes and lipoplexes with membrane models was studied by Förster Resonant Energy Transfer. Finally, DNA condensation was studied and the lipoplexes were tested in vitro to quantify their transfection efficiency. From the results obtained on these cationic lipophosphoramidates series, we show that aliphatic chain length and unsaturation number have an important influence on liposomes physicochemical properties and transfection efficiency. However there is no direct link between fluidity and fusion efficiency or between fluidity and DNA condensation. Nevertheless, it seems that for best transfection efficiency the compounds need to combine the properties of fluidity, fusion efficiency and DNA condensation efficiency. This was the case for the C18:1 and C18:2 compounds.