Abstract
By using various techniques (pH-potentiometry, UV-Visible spectrophotometry, 1H and 17O-NMR, EPR, ESI-MS), first time in the literature, solution equilibrium study has been performed on complexes of dipeptide and tripeptide hydroxamic acids—AlaAlaNHOH, AlaAlaN(Me)OH, AlaGlyGlyNHOH, and AlaGlyGlyN(Me)OH—with 4d metals: the essential Mo(VI) and two half-sandwich type cations, [(η6-p-cym)Ru(H2O)3]2+ as well as [(η5-Cp*)Rh(H2O)3]2+, the latter two having potential importance in cancer therapy. The tripeptide derivatives have also been studied with some biologically important 3d metals, such as Fe(III), Ni(II), Cu(II), and Zn(II), in order to compare these new results with the corresponding previously obtained ones on dipeptide hydroxamic acids. Based on the outcomes, the effects of the type of metal ions, the coordination number, the number and types of donor atoms, and their relative positions to each other on the complexation have been evaluated in the present work. We hope that these collected results might be used when a new peptide-based hydroxamic acid molecule is planned with some purpose, e.g., to develop a potential metalloenzyme inhibitor.
Highlights
Hydroxamic acids containing one or more weak acidic function(s) -C(O)N(R)OH (R = H in primary, alkyl or aryl moiety in secondary derivatives) [1,2] are an important class of organic molecules with a huge number of biological activities, including the well-known, crucial role of the hydroxamate-based natural siderophores in the microbial iron uptake [3] or antifungal, antimalarial, metalloenzyme inhibitory effects [4,5]
As a continuation of our previous solution equilibrium work in this subject, in the present work, we have investigated the interaction of dipeptide and tripeptide hydroxamic acids, AlaAlaNHOH, AlaAlaN(Me)OH, AlaGlyGlyNHOH, and AlaGlyGlyN(Me)OH
Literature data could be found for the investigated dipeptide derivatives only in the presence of KCl, and those are in perfect agreement with the corresponding ones in Table 1 [19,20]
Summary
Some derivatives may behave as NO donors under certain conditions [6]. In some part, these diverse and important effects depend on the significant H-bonding ability [7]. The most typical coordination mode of a hydroxamate function involves chelation via deprotonated hydroxyl and carbonyl oxygen atoms providing a five-membered (O,O). Chelate, which can be hydroxamato, if the function is mono-deprotonated, and hydroximato, if it is doubly-deprotonated. The latter type of chelate can only be formed with primary derivatives.
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