Protonated Co(III) Complexes with Ethylenediaminetetraacetic and S-Proline-N-Mono-3-propionic Acids. Crystal Structures of (H3O)[Co(HEdta)(CN)] · H2O and [Co(Promp)(HPromp)] · H2O

Abstract

Complex compounds in so-called acid form contain hydrogen atoms that are liberated as protons on dissolution. Different cases of localization of such mobile H atoms can be observed in crystals. It is not infrequent that crystallization water molecules undergo protonation to give oxonium ion, either individual or associated with different number of water molecules. Such compounds include crystals with complex anionsand [ Co ( Cdta )] -[1-4]. Protonation of coordinated acetate ion takes place in the [ Co ( en ) 2 ( CH 3 CO 2 )( CH 3 CO 2 H )]( ClO 4 ) 2 · H 2 O crystals: the acetate ions of two complex cations are bonded by a short hydrogen bond [5]. A similar situation is observed in the [Co ( H 3 Cdta )( CN ) 2 ] complexes [6] with coordinated acetate groups and in the [ Co ( Dtmp )( HAla )] HgCl 4 crystals with propionate groups of both ligands [7]. In crystals of [Co(HEddda)] · 2 H 2 O [8] and [ Co ( H 2 Eddp )( HEddp )] Br 2 · 4 H 2 O [9], the carboxylate group of one of the coordinated propionate chains is also protonated, but is bound by a short hydrogen bond with water molecule. 1 Some complexes were supposed to have protonated crystallization water molecules, rather than pro-1 The above-indicated ligands (written in abbreviated form as Gly, Ala, Dtmp, Ida, Edda, Eddp, Eddda, Cdta) are anions of amiacids, respectively; en is ethylenediamine. Another abbreviated forms used in the text will be interpreted further on.tonated carboxyl groups of six-membered cycles [10][11][12].The validity of such a supposition will be discussed below.In continuation of our previous X-ray diffraction studies of the acid Co(III) complexes with aminopropionate six-membered cycles [7-9], we investigated the structures of a complex with S -proline-N -mono-3-propionic acid ( H 2 Promp ). The structures of only two metal complexes (copper(II)) with this ligand have been reported recently [13,14].In all the above cases, protonated carboxyl group remains coordinated by the metal atom. However, as a result of protonation of the Co(III) complex with hexadentate ethylenediaminetetraacetic acid ( H 4 Edta ), one of the acetate branches of the ligand does not participate in coordination [15]. This fact is explained by sufficient strains in the [ Co ( Edta )] -ion arising due to involvement of the ligand atoms in five conjugated fivemembered metal cycles [16,17]. In this case, the greatest distortions are exhibited by aminoacetate cycles of G type, which are almost coplanar to the ethylenediamine cycle. It is exactly one of these cycles that is cleaved on protonation and on coordination of additional monodentate ligands. Therefore, it was of interest to study the mode of protonation of the [Co(Edta)X] complexes, which are less strained, since one acetate group is noncoordinated. For this purpose we selected a complex with cyanide ion as the additional X ligand stable toward aquation. Abstract -Crystal structures of [Co(Promp)(Hpromp)] · H 2 O ( I ) (where Promp and Hpromp are deprotonated and monoprotonated anions of S -proline-N -mono-3-pro...

Proposal and confirmation of N‐(2‐carboxyethyl)proline as a human endogenous metabolite

“…Whether or not it can serve as a surrogate biomarker for oxidative stress is yet to be investigated. While detection of this compound in any biological matrices has not been previously reported to our knowledge, it is noteworthy that this compound was previously reported (PubChem CID 13343632; InChIKey YMZVLADYOVAGRS‐UHFFFAOYSA‐N; SMILES C1CC(N(C1)CCC(=O)O)C(=O)O) and used in nonbiological studies of cobalt coordination chemistry 23,24 . Our results here for the first time revealed N ‐(2‐carboxyethyl)proline as a human endogenous metabolite.…”

“…InChIKey YMZVLADYOVAGRS-UHFFFAOYSA-N; SMILES C1CC(N (C1)CCC(=O)O)C(=O)O) and used in nonbiological studies of cobalt coordination chemistry. 23,24 Our results here for the first time revealed N-(2-carboxyethyl)proline as a human endogenous metabolite. As feces contains a significant portion of this metabolite, one may naturally wonder if this metabolite is possibly biosynthesized by gut microbes and then absorbed into circulation.…”