PubMed · 3405538
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J C Welch. 1988-08-10. Chelation therapy.. https://pubmed.ncbi.nlm.nih.gov/3405538/
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A heterotrinuclear lanthanide complex has been prepared which contains two terbium ions in DO3A-derived binding sites and a single ytterbium ion in a DTPA-like site. The luminescence properties of the system have been investigated, showing that the terbium remains in a seven-coordinate binding site throughout the synthesis, while the ytterbium occupies the eight-coordinate site. Pumping the 488 nm absorption band of the terbium ion results in energy transfer to ytterbium with emission at 980 nm.
Iron chelates such as ethylenediamine-N,N'-bis(2-hydroxyphenyl)acetic acid (EDDHA) and their analogues are the most efficient soil fertilizers to treat iron chlorosis in plants growing in calcareous soils. EDDHA, EDDH4MA (ethylenediamine-N,N'-bis(2-hydroxy-4-methylphenyl)acetic acid), and EDDCHA (ethylenediamine-N,N'-bis(2-hydroxy-5-carboxyphenyl)acetic acid) are allowed by the European directive, but also EDDHSA (ethylenediamine-N,N'-bis(2-hydroxy-5-sulfonylphenyl)acetic acid) and EDDH5MA (ethylenediamine-N,N'-bis(2-hydroxy-5-methylphenyl)acetic acid) are present in several commercial iron chelates. In this study, these chelating agents as well as p,p-EDDHA (ethylenediamine-N,N'-bis(4-hydroxyphenyl)acetic acid) and EDDMtxA (ethylenediamine-N,N'-bis(2-metoxyphenyl)acetic acid) have been obtained following a new synthetic pathway. Their chemical behavior has been studied to predict the effect of the substituents in the benzene ring on their efficacy as iron fertilizers for soils above pH 7. The purity of the chelating agents has been determined using a novel methodology through spectrophotometric titration at 480 nm with Fe(3+) as titrant to evaluate the inorganic impurities. The protonation constants were determined by both spectrophotometric and potentiometric methods, and Ca(2+) and Mg(2+) stability constants were determined from potentiometric titrations. To establish the Fe(3+) and Cu(2+) stability constants, a new spectrophotometric method has been developed, and the results were compared with those reported in the literature for EDDHA and EDDHMA and their meso- and rac-isomers. pM values have been also determined to provide a comparable basis to establish the relative chelating ability of these ligands. The purity obtained for the ligands is higher than 87% in all cases and is comparable with that obtained by (1)H NMR. No significant differences have been found among ligands when their protonation and stability constants were compared. As expected, no Fe(3+) complexation was observed for p,p-EDDHA and EDDMtxA. The presence of sulfonium groups in EDDHSA produces an increase in acidity that affects their protonation and stability constants, although the pFe values suggest that EDDHSA could be also effective to correct iron chlorosis in plants.
meso-2,3-Dimercaptosuccinic acid ( meso-DMSA) is an effective chelating agent for the treatment of lead poisoning. We have developed a capillary electrophoresis (CE) method to monitor the urinary excretion of meso-DMSA in human beings. The urine sample was directly injected for analysis in CE without the requirement of solid-phase extraction (SPE). The meso-DMSA was detected in 20 mM borate buffer (pH 8.3) using a 60-cm length bare fused-silica capillary (75-microm ID, 52.5-cm effective length). The meso-DMSA can be extensively biotransformed during metabolism, and no meso-DMSA in urine samples was found in our studies. Any metabolized meso-DMSA can be successfully converted to free meso-DMSA by chemical reduction with dithiothreitol (DTT). In addition, samples were also treated with ethylenediaminetetraacetic acid (EDTA) to transchelate any meso-DMSA that is coordinated with metal ions present in the urine samples. The total amount of meso-DMSA present as these chemical forms was quantified after chemical reduction and addition of EDTA. The detection limit of meso-DMSA was about 50 microM, the RSD of peak area and migration time of meso-DMSA were 4-8% and less than 1%, respectively.