Ethylene diamine complexes with metal ions

Mn2+, D.F.P.-ase is further activated by cysteine, histidine, thiolhistidine, and serine, histamine and 2 2 -dipyridyl. Reagents reacting with metal ions, SH groups and carbonyl groups inhibit D.F.P.-ase activity. Work is proceeding on the further elucidation of such mechanisms.1 In a somewhat similar connexion attention is called to the fact that the non-enzymic hydrolysis of D.F.P. is accelerated by heavy metals and their complexes, in particular by copper chelates of ethylene diamine, o-phenanthroline, 2 2 -dipyridyl and histidine.2... 

The recovery of proteins from their complexes with metals has been greatly facilitated by the introduction of ion-exchange desalting, and of the complexones such as ethylene diamine-tetra-acetic acid (EDTA), which remove the metals as non-ionised complexes. The use of specific precipitants for effecting separations covers a large field in Biochemistry, and some examples from protein chemistry are given below to illustrate the possibilities of this method. 

Heavy metal ions, in particular copper, inhibit enzyme activity in the urease. In the case of waters containing heavy metals, e.g. bathing water treated with copper, add 0.1 % EOT A (ethylene diamine tetraacetic acid) to complex the metal ions. 

This dye fluoresces after binding Pb+2 and Ca+2 lead is considered an interferant to the determination of calcium by this approach. However, by complexing the divalent lead ion with the heavy metal chelator TPEN (N,N,N ,N -tetrakis(2-pyridylmethyl)ethylene-diamine) prior to the addition of the fluo-3, the fluorescent... 

Vickery and Vickery [9] have investigated the interference by aluminium and iron in the ion-selective electrode method for the determination of fluoride in plant extracts. They demonstrated that plant ashes may contain sufficient of these two elements to seriously interfere in the determination of fluoride when using the fluoride-selective electrode. In the presence of these metals, the known additions method gives erroneous results, as did that involving the attempted formation of complexes with ethylene diamine tetraacetic acid (disodium salt) or 1,2-cyclohexylenedinitrilotetraacetic acid. 

The treatment of complex ion equilibria in solution is analogous to the treatment of weak acids. One of the best known chelators is the well-known EDTA (ethylene diamine tetraacetic acid). The metal stability constants for EDTA are very high, which indicates strong complexes. Various other compounds are available with high metal-stability constants for agricultural or environmental uses. Some of the more important ones are DPTA (diethylene triamine pentaacetic acid), CyDTA (cyclohexane diamine tetraacetic acid), EDDA [ethylene diamine di (0-hydroxyphenyl acetic acid], or Chel-138. 

The Cu ion reacts with [OH] to form [CuOH] ", which exhibits a pH-depen-dent absorption with = 300 nm. Copper(III) complexes with NHj, ethylene-diamine and various amino acids are characterized by pulse radiolysis . The [Cu(EDTA)] (EDTA = ethylenediaminetetraacetate) and [Cu(NTA)] (NTA = nitrilotriacetate) ions are oxidized to the corresponding Chj(III) species by [OH] Cu(lII) rearranges and then metal-ligand intramolecular electron transfer yields some Cud) species. ... 

The most effective catalysts were found to be the 1 1 copper complexes with a,a -dipyridyl, L-histidine, o-phenanthroline, imidazole, and ethylene-diamine. Because of the apparent requirement that the metal be incompletely coordinated, it was suggested that the reactive positions of the metal are those occupied by water or hydroxide ion. Three such species have been reported by Fowkes et al. (9) from a study of aqueous equilibria involving the 1 1 dipyridyl chelate, according to the following reaction scheme ... 

---