Gadolinium(III) complexes have been widely utilised as magnetic resonance imaging (MRI) contrast agents for decades. In recent years however, concerns have developed about their toxicity, believed to derive from demetallation of the complexes in vivo, and the relatively large quantities of compound required for a successful scan. Recent efforts have sought to enhance the relaxivity of trivalent gadolinium complexes without sacrificing their stability. This review aims to examine the strategic design of ligands synthesised for this purpose, provide an overview of recent successes in gadolinium-based contrast agent development and assess the requirements for clinical translation.
Hoctapa is an extremely versatile acyclic chelator for a wide variety of medicinally relevant metal ions, forming complexes of both high thermodynamic and kinetic stability. This work reports a significantly simplified 3 step high yield straightforward synthesis of Hoctapa directly from EDDA. Crystals of the octa-protonated form of the ligand [Hoctapa] as its tetrachloride salt, and of the mixed lanthanum-sodium salt of [La(octapa)] were isolated and characterized by X-ray diffraction. All eight protonation constants for the ligand were determined through combined potentiometric-spectrophotometric titrations and in batch experiments using UV spectrophotometry and H NMR spectroscopy. Synthesis, characterisation and solution equilibria studies are presented for complexes [Ln(octapa)] (Ln = lanthanide element) with Sm(iii), Dy(iii), and Yb(iii) (each of which have radiopharmaceutical applications). Complex formation equilibria studies provided evidence of Ln(Hoctapa), [Ln(octapa)] and [Ln(octapa)(OH)] species in solution, and their stability constants were evaluated by pH-potentiometric competition titrations using [ttha] as a competing ligand, and by UV-vis spectrophotometric measurements. The high stability constants of the [Ln(octapa)] complexes with Sm(iii), Dy(iii), and Yb(iii) (log K = 20.10(2), log K = 20.14(3) and log K = 19.90(1)) are similar to the published values for other lanthanides and consequently these initial investigations confirm Hoctapa as a valuable ligand for Sm(iii), Dy(iii), Yb(iii) and other Ln for application in diagnostic and therapeutic nuclear medicine.
A novel probe based on an exendin-4-dota(ga) conjugate, GdEx, is presented. GdEx accumulates in the pancreas, allowing organ-specific contrast enhancement which is reduced in mouse models where pancreatic β-cells are depleted.
In this work additives have been incorporated in the paste materials to improve the capacity and the life of the lead-acid battery. The battery's capacity is improved by additives that permanently increase the porosity of the positive active material and therefore the acid supply in the positive plate. Another material that has intrinsic conductivity was also added to permanently enhance the conductivity of the positive paste body. Antimony grids have historically given long service life at the cost of high water loss catalyzed by deposition of antimony on the negative active material, which has precluded their use in maintenance-free batteries. To combat the negative effects of antimony alloys, antimony-absorbing agents were dispersed into the negative active material to preferentially absorb and irreversibly bind the antimony ions, thereby protecting the active material. In this work we have evaluated the use of these performance-improving additives in Valve Regulated Lead Acid (VRLA) batteries. This paper is the first of a two part series; where the additives are evaluated in the Absorbed Glass Mat (AGM) type of VRLA battery where the electrolyte is immobilized in a non-woven glass mat material.The results suggest a significant improvement in battery performance through enhanced acid supply and diffusion in the positive electrode. An organic porosity additive (ES-100) and an inorganic porosity additive (ES-60) have shown an increase in active material utilization, and therefore discharge capacity, of 29% and 38% respectively at the "c" or one hour rate over similarly built additive-free Control cells. A performance advantage imparted by the porosity additives appears to be maintained throughout the life of the cells. One antimony control additive (ESA-4) appears to be showing a benefit over additive-free cells in preventing the deposition of antimony on the negative active material as evidenced by the notably altered behavior of the negative electrode. Pasting trials in a small batch mixer suggest that all of the additives are compatible with production-scale paste mixing operations used in lead-acid battery manufacturing.
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