Abstract:The kinetics and mechanisms of the reactions of aluminium(III) with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) have been investigated in aqueous solution at 25°C and ionic strength 0.5 mol dm" 3 NaC104. Al 3+ reacts with the HUDTPA" and H3DTPA 2 with rate constants of 2.06(±0.35) and 19.3(±1.6) respectively while Al(OH) 2+ reacts with H3DTPA 2 with a rate constant of 1.34(±0.20) χ 10 3 dm 3 mol" 1 s" 1 . The outersphere association constant for reaction of Al 3+ with H… Show more
“…The reagents DHAB and calcein mainly exist as the no-charged (p K a1 = 8.20, p K a2 = 11.6) 23 and −4 form (p K a4 = 5.5, p K a5 = 10.8), , respectively, at pH 7.5. Although there are many reports about Al complex formation kinetics with various ligands, − the kinetics are very complicated, and all of the factors involving the formation processes, such as the numbers of atoms participating in the chelate ring and the rigidity of the ligand, have yet completely elucidated. 5 Formation reaction curve of Al 3+ −dhab complex in a batch solution.…”
The contamination of metal ions from reagents used frequently restricts the practical detection limit of the metal ion, which itself is a source of contamination. We have found a novel solution to this problem, a chemical-suppressing method of contaminant metal ions on a reversed-phase HPLC for Al3+ with a detection limit of 7.6 x 10(-11) mol dm(-3) (2.1 ng dm(-3)) by only adding a certain agent into all stock solutions without any preconcentration or purification steps. This technique decreases the concentration of the contaminant Al3+ originating from the reagents by more than 1 order of magnitude using selective derivatization of sample Al3+ ions to a powerful fluorescent complex at a metastable state in the precolumn chelation processes. Meanwhile, the contaminant Al3+ remains as a nonfluorescent complex with a blocking reagent in order to suppress the contamination. This selective derivatization is achieved by the accumulation of several complexation processes based on the difference of formation, dissociation, and ligand-exchange kinetics and the thermodynamics between the derivatizing reagent, the 4',5'-geometorical isomer of calcein, and the blocking reagent, o,o'-dihydroxyazobenzene. This simple and smart HPLC system was validated through recovery tests of environmental and biological samples.
“…The reagents DHAB and calcein mainly exist as the no-charged (p K a1 = 8.20, p K a2 = 11.6) 23 and −4 form (p K a4 = 5.5, p K a5 = 10.8), , respectively, at pH 7.5. Although there are many reports about Al complex formation kinetics with various ligands, − the kinetics are very complicated, and all of the factors involving the formation processes, such as the numbers of atoms participating in the chelate ring and the rigidity of the ligand, have yet completely elucidated. 5 Formation reaction curve of Al 3+ −dhab complex in a batch solution.…”
The contamination of metal ions from reagents used frequently restricts the practical detection limit of the metal ion, which itself is a source of contamination. We have found a novel solution to this problem, a chemical-suppressing method of contaminant metal ions on a reversed-phase HPLC for Al3+ with a detection limit of 7.6 x 10(-11) mol dm(-3) (2.1 ng dm(-3)) by only adding a certain agent into all stock solutions without any preconcentration or purification steps. This technique decreases the concentration of the contaminant Al3+ originating from the reagents by more than 1 order of magnitude using selective derivatization of sample Al3+ ions to a powerful fluorescent complex at a metastable state in the precolumn chelation processes. Meanwhile, the contaminant Al3+ remains as a nonfluorescent complex with a blocking reagent in order to suppress the contamination. This selective derivatization is achieved by the accumulation of several complexation processes based on the difference of formation, dissociation, and ligand-exchange kinetics and the thermodynamics between the derivatizing reagent, the 4',5'-geometorical isomer of calcein, and the blocking reagent, o,o'-dihydroxyazobenzene. This simple and smart HPLC system was validated through recovery tests of environmental and biological samples.
“…A reduced charge on the deprotonated small Al 3+ may be responsible for the increased water exchange rate. Limited kinetic data are available for Al 3+ reactions (formation and dissociation) in aqueous medium. ,− This is due to the fact that (1) stability of aluminum complexes is relatively low in strongly acidic medium (2) Al(H 2 O) 6 3+ hydrolyzes at lower acidity or higher pH, and (3) there is a lack of specific UV/vis absorbance to monitor the progress of the reactions. However, it has been proposed that Al(H 2 O) 6 3+ and Al(H 2 O) 5 (OH) 2+ react via an I d mechanism with the latter being more reactive. − …”
“…Due to the sluggish nature of Al 3+ , the rates of complexation of aluminum with linear polyaminocarboxylates (such as EDTA and DTPA) have been rather slow with second-order rate constants (M –1 s –1 ) as 4.73 and 21.5 for H 3 EDTA – and H 2 EDTA 2– , respectively, and 2.06 and 19.3 for H 4 DTPA – and H 3 DTPA 2– , respectively . Both Al(H 2 O) 6 3+ and Al(H 2 O) 5 (OH) 2+ were identified as reactive forms for various protonated forms of the ligands.…”
The clinical applications of positron emission tomography (PET) imaging pharmaceuticals have increased tremendously over the past several years since the approval of fluorine-fluorodeoxyglucose (F-FDG) by the Food and Drug Administration (FDA). Numerous F-labeled target-specific potential imaging pharmaceuticals, based on small and large molecules, have been evaluated in preclinical and clinical settings.F-labeling of organic moieties involves the introduction of the radioisotope by C-F bond formation via a nucleophilic or an electrophilic substitution reaction. However, biomolecules, such as peptides, proteins, and oligonucleotides, cannot be radiolabeled via a C-F bond formation as these reactions involve harsh conditions, including organic solvents, high temperature, and nonphysiological conditions. Several approaches, including F-labeled prosthetic groups, silicon, boron, and aluminum fluoride acceptor chemistry, and click chemistry have been developed, in the past, forF labeling of biomolecules. Linear and macrocyclic polyaminocarboxylates and their analogs and derivatives form thermodynamically stable and kinetically inert aluminum chelates. Hence, macrocyclic polyaminocarboxylates have been used for conjugation with biomolecules, such as folate, peptides, affibodies, and protein fragments, followed by F-AlF chelation, and evaluation of their targeting abilities in preclinical and clinical environments. The goal of this report is to provide an overview of theF radiochemistry and F-labeling methodologies for small molecules and target-specific biomolecules, a comprehensive review of coordination chemistry of Al, F-AlF labeling of peptide and protein conjugates, and evaluation ofF-labeled biomolecule conjugates as potential imaging pharmaceuticals.
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