Anaminopolycarboxylic acid (sometimes abbreviatedAPCA) is achemical compound containing one or morenitrogen atoms connected throughcarbon atoms to two or morecarboxyl groups. Aminopolycarboxylates that havelost acidic protons form strongcomplexes withmetal ions. This property makes aminopolycarboxylic acids useful complexone in a wide variety of chemical, medical, and environmental applications.[1]
The parent of this family of ligands is theamino acidglycine, H2NCH2COOH, in which the amino group, NH2, is separated from the carboxyl group, COOH by a single methylene group, CH2. When the carboxyl group is deprotonated the glycinate ion can function as a bidentateligand, binding the metal centre through the nitrogen and one of two carboxylate oxygen atoms, to formchelate complexes of metal ions.[2]
Replacement of a hydrogen atom on the nitrogen of glycine by another acetate residue, –CH2COOH givesiminodiacetic acid, IDA, which is a tridentate ligand. Further substitution givesnitrilotriacetic acid, NTA, which is a tetradentate ligand.[3] These compounds can be described as aminopolycarboxylates. Related ligands can be derived from other amino acids other than glycine, notablyaspartic acid.
Higher density is achieved by linking two or more glycinate or IDA units together.EDTA contains two IDA units with the nitrogen atoms linked by two methylene groups and is hexadentate.DTPA has two CH2CH2 bridges linking three nitrogen atoms and is octadentate. TTHA[1] has ten potential donor atoms.
Thechelating properties of aminopolycarboxylates can be engineered by varying the groups linking the nitrogen atoms so as to increase selectivity for a particular metal ion. The number of carbon atoms between the nitrogen and carboxyl group can also be varied and substituents can be placed on these carbon atoms. Altogether this allows for a vast range of possibilities.Fura-2 combines two functionalities: it has high selectivity forcalcium overmagnesium and it has a substituent which makes the complexfluorescent when it binds calcium. This reagent provides a means of determining the calcium content in intra-cellular fluid. Details concerning applications of the following examples can be found in the individual articles and/or reference. The aminopolycarboxylatenicotianamine is widespread in plants, where it is used to transport iron.
 |  |  |  |
| glycinate | IDA[1] | NTA[3] | EDDA[3] |
 | )disuccinic_acid_200.svg) |  |  |
| EDTA | EDDS | DTPA[1] | EGTA |
 |  |  | |
| BAPTA | NOTA[1] | DOTA[1] | |
 |  | ||
| Nicotianamine[4] | EDDHA |