Supercritical Carbon Dioxide as a Green Alternative to Achieve Drug Complexation with Cyclodextrins

Cyclodextrins are widely used in pharmaceutics to enhance the bioavailability of many drugs. Conventional drug/cyclodextrin complexation techniques suffer from many drawbacks, such as a high residual content of toxic solvents in the formulations, the degradation of heat labile drugs and the difficulty in controlling the size and morphology of the product particles. These can be overcome by supercritical fluid technology thanks to the outstanding properties of supercritical CO2 (scCO2) such as its mild critical point, its tunable solvent power, and the absence of solvent residue after depressurization. In this work the use of scCO2 as an unconventional medium to achieve the complexation with native and substituted cyclodextrins of over 50 drugs, which belong to different classes, are reviewed. This can be achieved with different approaches such as the “supercritical solvent impregnation” and “particle-formation” techniques. The different techniques are discussed to point out how they affect the complexation mechanism and efficiency, the physical state of the drug as well as the particle size distribution and morphology, which finally condition the release kinetics and drug bioavailability. When applicable, the results obtained for the same drug with various cyclodextrins, or different complexation techniques are compared with those obtained with conventional approaches.

Antimony (V) Adsorption at the Hematite–Water Interface: A Macroscopic and In Situ ATR-FTIR Study

The environmental mobility of antimony (Sb) is largely unexplored in geochemical environments. Iron oxide minerals are considered major sinks for Sb. Among the different oxidation states of Sb, (+) V is found more commonly in a wide redox range. Despite many adsorption studies of Sb (V) with various iron oxide minerals, detailed research on the adsorption mechanism of Sb (V) on hematite using macroscopic, spectroscopic, and surface complexation modeling is rare. Thus, the main objective of our study is to evaluate the surface complexation mechanism of Sb (V) on hematite under a range of solution properties using macroscopic, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic, and surface complexation modeling. The results indicate that the Sb (V) adsorption on hematite was highest at pH 4–6. After pH 6, the adsorption decreased sharply and became negligible above pH 9. The effect of ionic strength was negligible from pH 4 to 6. The spectroscopic results confirmed the presence of inner- and outer-sphere surface complexes at lower pH values, and only outer-sphere-type surface complex at pH 8. Surface complexation models successfully predicted the Sb (V) adsorption envelope. Our research will improve the understanding of Sb (V) mobility in iron-oxide-rich environments.

Feasibility of nanoscale zero-valent iron loaded sediment-based biochar (nZVI-SBC) for simultaneous removal of nitrate and phosphate: high selectivity towards dinitrogen and synergistic mechanism

In the process of water treatment, excessive nitrogen and phosphorus pollutants are of great concern. Therefore, we prepared nanoscale zero-valent iron loaded on sediment-based biochar (nZVI-SBC) to conduct nitrate and phosphate removal at the same time. The characterization demonstrated that nZVI-SBC was successfully synthesized, which had obvious advantages for larger specific surface area and better dispersion compared with pure nZVI. The batch experiments indicated that the best loading ratio of nZVI to SBC and optimum dosage for nitrate and phosphate were 1:1and 2 g·L-1, respectively. Their removal by nZVI-SBC was an acid-driven process. Anoxic environment was more conducive to the reduction of nitrate while the phosphate removal was fond of oxygen environment. 77.78% of nitrate and 99.21% of phosphate have been successfully removed, mainly depending on reduction and complexation mechanism, respectively. Moreover, nZVI-SBC had higher N2 selectivity and produced less ammonium than nZVI. The interaction between nitrate and phosphate was studied to manifest that they had different degrees of inhibition during the removal of the other. Our research indicated that nZVI-SBC has great potential for remediation of nitrogen and phosphorus polluted water.

Unraveling the complexation mechanism of actinide(iii) and lanthanide(iii) with a new tetradentate phenanthroline-derived phosphonate ligand

The separation and complexation mechanisms of actinide(iii) and lanthanide(iii) with a new phenanthroline-derived phosphonate ligand were studied experimentally and theoretically.

Radionuclides distribution and its sorption behavior in the Kara sea bottom sediments surface layer

The sorption characteristics of the Kara sea bottom sediments were investigated. The sediments were collected during scientific expedition of the R/V Akademik Mstislav Keldysh (Cruise AMK-66). The mineral and fraction composition of sediments was determined. It has been found that 137Cs sorbed predominantly by an ion exchange mechanism because of the clay minerals presence in the sediments. At the same time, 243Am and 90Sr sorbed from seawater by the surface complexation mechanism. The sorption kinetics for 243Am was established: about 20 hours, 137Cs: 2 hours, 90Sr: less than an hour. The sorption isotherms shows Cs and Am in experiments on marine and distilled water are described by the Henry equation. The Sr behavior in deionized water is described by the Langmuir equation, in the case of sea water, by the Freundlich equation.