Effect of Pyridyl Donors in the Chelation of Aluminum(III), Gallium(III), and Indium(III)

Abstract

A new preparation of N,N'-bis(2-pyridylmethyl)ethylenediamine-N,N'-diacetic acid (H(2)bped) is reported, and its properties of complexation with Al(III), Ga(III), In(III), and Co(III) are investigated. The molecular structure of the cobalt(III) complex [Co(bped)]PF(6).CH(3)CN.H(2)O (C(20)H(25)CoF(6)N(5)O(5)P) has been solved by X-ray methods; the complex crystallizes in the triclinic space group P&onemacr;, with a = 10.611(2) Å, b = 12.720(2) Å, c = 9.868(1) Å, alpha = 102.70(1) degrees, beta =93.60(1) degrees, gamma = 106.96(1) degrees, and Z = 2. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.041 (R(w) = 0.038) for 4312 reflections with I > 3sigma(I). The Co(III) ion is coordinated in a distorted octahedral geometry with an N(4)O(2) donor atom set. The carboxylato oxygen atoms are coordinated trans, while the pyridyl nitrogen atoms are coordinated cis. The largest distortion from octahedral geometry is the N(pyridyl)-Co-N(pyridyl) angle of 107 degrees. Complex formation constants have been measured at 25 degrees C (&mgr; = 0.16 M (NaCl)). log K([M(bped)](+)) (log K([M(bped)(OH)])): M = Al, 10.85 (6.37); M = Ga, 19.89 (15.62); M = In, 22.6 (15.44). A protonated complex was also detected, [Ga(Hbped)](2+), log K = 21.79. The order of stability is In(III) > Ga(III) > Al(III) for the binary species, [M(bped)](+). The solution structures of the complexes have been probed in multinuclear NMR ((1)H, (13)C, (27)Al) studies, and these solution structures are compared with the solid state structure of the cobalt(III) complex. The complexes [In(bped)](+) and [In(bped)(OH)] are proposed to contain 7-coordinate In(III) with water and hydroxide completing the respective coordination spheres. The gallium complexes are proposed to be 6-coordinate: the [Ga(Hbped)](2+) complex contains a nondeprotonated carboxylic acid group which is not coordinated, and [Ga(bped)(OH)] contains a coordinated hydroxide which displaces a carboxylato donor. The [Al(bped)(OH)] complex may be 5-coordinate on the basis of its downfield (27)Al NMR chemical shift, 54 ppm.

A Manganese Alternative to Gadolinium for MRI Contrast

“…Prior NMR studies have demonstrated that metal complexes of acyclic pyridyl- N containing chelates exhibit a lesser degree of fluxionality in solution than those formed by analogous chelates featuring acetate- O donors instead. 40 We rationalized that this effect will boost kinetic inertness. We also rationalized that the trans -1,2-cyclohexanediamine linkage and pyridyl- N donor combine could provide sufficient lipophilic character to promote hepatic uptake, and thus partial non-renal clearance of the resultant anionic Mn complex.…”

RuIII Complexes of Edta and Dtpa Polyaminocarboxylate Analogues and Their Use as Nitric Oxide Scavengers

“…The structural formulation fits the general trend (vide supra) in that the Ru III center exhibits a higher affinity for N donors over O-donors (acid groups) under the complexation conditions employed. This trend is further borne out with compound 16 (Scheme 4), synthesized from 15, [43] which was concluded to have four N atoms bound based on the characterization data. The effect of substituting one edta N atom for a pyridyl moiety was also investigated as shown in Scheme 5.…”

“…All solvents (anhydrous grade) were obtained from Aldrich and used as supplied. K 2 [RuCl 5 (OH 2 )], [50] ({3-[bis(carboxymethyl)amino]propyl}(carboxymethyl)amino)acetic acid (3), [41] N,NЈ-bis(2-pyridylmethyl)-ethylenediamine-N,NЈ-diacetic acid (15), [43] methyl 6-(hydroxymethyl)pyridine-2-carboxylate (17), [44] 6-(hydroxymethyl)pyridine-2-carbaldehyde (21), [45] iminodiacetic acid di-tert-butyl ester, [46] 2,6-bis(bromomethyl)pyridine hydrogen bromide (25), [48] and N-(hydroxyethyl)iminodiacetic acid di-tert-butyl ester [49] were pre-pared according to literature procedures. 1 H NMR and 13 C NMR spectra were recorded with a Bruker Avance 300 with chemical shifts referenced to SiMe 4 .…”

“…The symmetric ligand 15, exhibiting two pendant pyridyl groups for metal binding, was synthesized by a literature method (Scheme 4). [43] Edta ligand analogues, where one N atom of edta is replaced by a pyridyl N atom (19,23), were prepared by multi-step synthetic routes as shown in Scheme 5. Reaction of methanesulfonyl chloride with methyl 6-(hydroxymethyl)pyridine-2-carboxylate [44] (17) afforded compound 18 in near quantitative yield.…”

On the Antibacterial Activity of Azacarboxylate Ligands: Lowered Metal Ion Affinities for Bis‐amide Derivatives of EDTA do not mean Reduced Activity

“…The first protonation values are lower for AmGly 2 and AmPy 2 fragment due to the weakly electron‐withdrawing effect that the amide groups exert on the neighbouring amines. Assignment of subsequent protonation events to either pyridines or carboxylates in AmPy 2 on the basis of pH‐potentiometry alone is not realistic due to the small differences in the protonation constants between each functional group …”