Selective complexation of α-amino acids and simple peptides via their carboxylate groups

Abstract

The complexation of anions of selected α-amino acids (alanine, valine, proline, tyrosine) and small peptides (L-alanyl-L-alanine, L-alanyl-L-alanyl-L-alanine, and L-alanyl-L-alanyl-L-alanyl-L-alanine) by the dinuclear nickel(II) complex [LNi2(μ-Cl)]+ (1), where (L)2− represents a 24-membered binucleating hexamine-dithiophenolato ligand, has been investigated. The following complexes were prepared, isolated as perchlorate or tetraphenylborate salts, and characterized by UV/Vis, IR, and CD spectroscopy: [LNi2(μ-L-alaninato)]+ (2), [LNi2(μ-L-valinato)]+ (3), [LNi2(μ-L-prolinato)]+ (4), [LNi2(μ-L-tyrosinato)]+ (5a), [LNi2(μ-D-tyrosinato)]+ (5b), [LNi2(μ-L,D-tyrosinato)]+ (5c), [LNi2(μ-L-alanyl-L-alaninato)]+ (6), [LNi2(μ-(L-alanyl)2-L-alaninato)]+ (7), [LNi2(μ-(L-alanyl)3-L-alaninato)]+ (8). Compounds 4, 5a and 6 were additionally identified by X-ray crystallography. In contrast to unsupported amino carboxylate complexes which typically contain five membered NO chelate rings, the [LNi2]2+ fragment selectively binds the α-amino acids and peptides via μ1,3-bridging carboxylato groups. Coordination of the carboxylato coligands in this way confers dissymmetry on the complexes. The CD spectra of the syn,syn-bridged structures are significantly different from those of the NO chelates, and can distinguish between the two coordination modes. The encapsulation of the peptides increases their solubility in the solvent system MeOH–MeCN by up to two orders of magnitude. This is discussed in terms of the absence of intermolecular hydrogen bonding interactions as indicated in the X-ray structure of 6.

Structural and Biochemical Insights into Dimethylsulfoniopropionate Cleavage by Cofactor-Bound DddK from the Prolific Marine Bacterium Pelagibacter

“…The UV–vis spectrum of apo-DddK in the presence of Ni­(II) shows weak absorption bands at 375 nm (272 M –1 cm –1 ), 610 nm (72 M –1 cm –1 ), 945 nm (102 M –1 cm –1 ), and 1020 nm (105 M –1 cm –1 ), indicating the formation of a Ni­(II) complex with an octahedral coordination (Figure S6). A shoulder near 300 nm (∼860 M –1 cm –1 ) was observed that can be attributed to tyrosinate-Ni­(II) interaction, given a Ni­(II)-phenolate chromophore has been shown to exhibit bands between 200 and 400 nm and a Ni­(II)-thiolate species has an absorption feature at 315 nm. , In contrast, intense LMCT transitions due to Ni­(II)-phenolate that appear between 400 and 600 nm (ε > 900 M –1 cm –1 ) , were not present. Interestingly, in the diacrylate-bound Ni­(II)-DddK structure, Tyr 64 does not participate as a metal ligand (Figure D).…”

Synthesis and Characterisation of Luminescent [CrIII2L(μ‐carboxylato)]3+ Complexes with High‐Spin S=3 Ground States (L=N6S2 donor ligand)

“…The doubly deprotonated form, L 2− , is an effective dinucleating ligand that readily forms bioctahedral complexes of the type [M 2 L( μ ‐L′)] + with various first‐row transition metal ions (M=Mn 2+ , Fe 2+ , Co 2+ , Co 3+ , Ni 2+ , Figure 1 ). [38] Several co‐ligands such as L′=Cl − , OH − , [39] HS − , [40] and RCO 2 − ,[ 41 , 42 , 43 , 44 , 45 , 46 ] to name just a few, can be accommodated between the divalent metal ions. Complexes of this kind offer the opportunity to investigate intramolecular magnetic super‐exchange interaction as a function of the electronic configuration of the metal ions and the type of the coligand.…”