Derivatives of GdAAZTA Conjugated to Amino Acids: A Multinuclear and Multifrequency NMR Study

The GdAAZTA (AAZTA = 6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid) complex represents a platform of great interest for the design of innovative MRI probes due to its remarkable magnetic properties, thermodynamic stability, kinetic inertness, and high chemical versatility. Here, we detail the synthesis and characterization of new derivatives functionalized with four amino acids with different molecular weights and charges: l-serine, l-cysteine, l-lysine, and l-glutamic acid. The main reason for conjugating these moieties to the ligand AAZTA is the in-depth study of the chemical properties in aqueous solution of model compounds that mimic complex structures based on polypeptide fragments used in molecular imaging applications. The analysis of the 1H NMR spectra of the corresponding Eu(III)-complexes indicates the presence of a single isomeric species in solution, and measurements of the luminescence lifetimes show that functionalization with amino acid residues maintains the hydration state of the parent complex unaltered (q = 2). The relaxometric properties of the Gd(III) chelates were analyzed by multinuclear and multifrequency NMR techniques to evaluate the molecular parameters that determine their performance as MRI probes. The relaxivity values of all of the novel chelates are higher than that of GdAAZTA over the entire range of applied magnetic fields because of the slower rotational dynamics. Data obtained in reconstituted human serum indicate the occurrence of weak interactions with the proteins, which result in larger relaxivity values at the typical imaging fields. Finally, all of the new complexes are characterized by excellent chemical stability in biological matrices over time, by the absence of transmetallation processes, or the formation of ternary complexes with oxyanions of biological relevance. In particular, the kinetic stability of the new complexes, measured by monitoring the release of Gd3+ in the presence of a large excess of Zn2+, is ca. two orders of magnitude higher than that of the clinical MRI contrast agent GdDTPA

Long-term performance of milled zerovalent iron particles for in situ groundwater remediation

International audienceThe nanoscale zerovalent iron (nZVI) particles are widely used with high success in removal/degradation of a variety of environmental contaminants under laboratory conditions. However, high production costs, mobility of nZVI particles limited to a maximum of a few meters due to the rapid aggregation of primary particles, and limited effectiveness of the iron surface to serve as an electron donor for longer period due to fast depletion of nZVI particles after side reaction with groundwater constituents were main technical obstacles for rising the full potential of this technology

Long-term performance of milled zerovalent iron particles for in situ groundwater remediation

International audienceThe nanoscale zerovalent iron (nZVI) particles are widely used with high success in removal/degradation of a variety of environmental contaminants under laboratory conditions. However, high production costs, mobility of nZVI particles limited to a maximum of a few meters due to the rapid aggregation of primary particles, and limited effectiveness of the iron surface to serve as an electron donor for longer period due to fast depletion of nZVI particles after side reaction with groundwater constituents were main technical obstacles for rising the full potential of this technology

Long-term performance of milled zerovalent iron particles for in situ groundwater remediation

International audienceThe nanoscale zerovalent iron (nZVI) particles are widely used with high success in removal/degradation of a variety of environmental contaminants under laboratory conditions. However, high production costs, mobility of nZVI particles limited to a maximum of a few meters due to the rapid aggregation of primary particles, and limited effectiveness of the iron surface to serve as an electron donor for longer period due to fast depletion of nZVI particles after side reaction with groundwater constituents were main technical obstacles for rising the full potential of this technology

Effect of field site hydrogeochemical conditions on the corrosion of milled zerovalent iron particles and their dechlorination efficiency

International audienceMilled zerovalent iron (milled ZVI) particles have been recognized as a promising agent for groundwater remediation because of (1) their high reactivity with chlorinated aliphatic hydrocarbons, organochlorine pesticides, organic dyes, and a number of inorganic contaminants, and (2) a possible greater persistance than the more extensively investigated nanoscale zerovalent iron. We have used laboratory-scale batch degradation experiments to investigate the effect that hydrogeochemical conditions have on the corrosion of milled ZVI and on its ability to degrade trichloroethene (TCE). The observed pseudo first-order degradation rate constants indicated that the degradation of TCE by milled ZVI is affected by groundwater chemistry. The apparent corrosion rates of milled ZVI particles were of the same order of magnitude for hydrogeochemical conditions representative for two contaminated field sites (133–140 mmol kg− 1 day− 1, indicating a milled ZVI life-time of 128–135 days). Sulfate enhances milled ZVI reactivity by removing passivating iron oxides and hydroxides from the Fe0 surface, thus increasing the number of reactive sites available. The organic matter content of 1.69% in the aquifer material tends to suppress the formation of iron corrosion precipitates. Results from scanning electron microscopy, X-ray diffraction, and iron K-edge X-ray adsorption spectroscopy suggest that the corrosion mechanisms involve the partial dissolution of particles followed by the formation and surface precipitation of magnetite and/or maghemite. Numerical corrosion modeling revealed that fitting iron corrosion rates and hydrogen inhibitory terms to hydrogen and pH measurements in batch reactors can reduce the life-time of milled ZVI particles by a factor of 1.2 to 1.7