Crystal structures, solution properties and ribonuclease activity of copper() complexes of a binucleating, bis-pyridyl ligand (N,NЈ-bis(2-pyridylmethyl)-1,3-diaminopropan-2-ol, L) have been investigated. The single-crystal X-ray structure of the mononuclear complex [CuL(ClO 4 ) 2 ] (1) shows distorted octahedral geometry around the metal ion, with the four nitrogens of the ligand in the equatorial plane of copper(). A µ-alkoxo-bridged dinuclear complex is formed in the presence of a two-fold metal excess. Despite the symmetrical ligand, the two metal ions in [Cu 2 (LH Ϫ1 )(DPP)(ClO 4 )(CH 3 OH)]ClO 4 (2, DPP = diphenyl phosphate) have distinct, distorted octahedral (Cu1) and square pyramidal (Cu2) geometry. Beside the alkoxo-oxygen, the phosphate group of DPP also bridges the two metal centers in 2 in a µ-1,3-bridging mode. The complexes formed in aqueous solution are likely to have analogous structures to 1 and 2. The dinuclear [Cu 2 (LH Ϫ1 )(OH)] complex efficiently promotes the hydrolysis/transesterification of both activated (2-hydroxypropyl p-nitrophenyl phosphate, hpnp) and non-activated, biological phosphodiesters (uridine-2Ј,3Ј-cyclic-monophosphate, cUMP and uridylyl-(3Ј,5Ј)-uridine, UpU). For example, a 2 mM solution of the dinuclear complex provides 5 orders of magnitude acceleration in the hydrolysis of cUMP. The proposed mechanisms include double Lewis-acid activation with intramolecular general base catalysis.

For many, especially complex, systems, modern spectroscopic measurements can be generated as large experimental data sets in matrix form. We report a new algorithm for the application of matrix rank analysis to extract significant experimental information from these large matrixes. The algorithm may be used to detect and remove erroneous rows and/or columns from the matrixes and to monitor the most significant experimental information along the rows and/or columns of the data sets. A new method for determining the number of absorbing species and a new concept for the treatment of experimental errors are presented. The algorithm is illustrated on real experimental examples.

The solution chemical properties, superoxide dismutase and catecholase activity of the copper(ii)-Ac-His-His-Gly-His-OH (hhgh) complexes were studied to identify functional and structural models of copper-containing oxidases. The solution speciation was determined in the pH range 3-11 by two independent methods (potentiometry and pH-dependent EPR measurements). The results obtained by the two methods agree very well with each other and show the formation of differently protonated CuH(x)L complexes (where x= 2 ,1, 0, -1, -2, -3) in aqueous solution. The spectroscopic (UV-Vis, CD, EPR) data indicate that the coordination of the imidazole rings is a determinant factor in all these complexes. Amide coordinated complexes are dominant only above pH 8. This offers excellent possibilities for structural/functional modelling of copper(ii) containing metalloenzymes. Indeed, the {3N(im)} coordinated CuL species (pH = 6-7) has efficient superoxide dismutase-like activity. The {3N(im),OH(-)} coordinated CuH(-1)L possesses outstanding activity to catalyze the oxidation of 3,5-di-tert-butylcatechol (H(2)dtbc) by dioxygen in 86 wt% methanol-water, providing the first example that copper(ii)-peptide complexes are able to mimic copper containing oxidases.

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Time differential perturbed angular correlation (TDPAC) of γ-rays spectroscopy has been applied in chemistry and biochemistry for decades. Herein we aim to present a comprehensive review of chemical and biochemical applications of TDPAC spectroscopy conducted at ISOLDE over the past 15 years, including elucidation of metal site structure and dynamics in proteins and model systems. β-NMR spectroscopy is well established in nuclear physics, solid state physics, and materials science, but only a limited number of applications in chemistry have appeared. Current endeavors at ISOLDE advancing applications of β-NMR towards chemistry and biochemistry are presented, including the first experiment on 31Mg2+ in an ionic liquid solution. Both techniques require the production of radioisotopes combined with advanced spectroscopic instrumentation present at ISOLDE.

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A de novo designed dodecapeptide (HS), inspired by the metal binding loops of metal-responsive transcriptional activators, was synthesized. The aim was to create a model system for structurally promiscuous and intrinsically unstructured proteins, and explore the effect of metal ions on their structure and dynamics. The interaction with Cd(II) was investigated by UV, synchrotron radiation CD, (1)H NMR, and perturbed angular correlation (PAC) of γ-rays spectroscopy, pH-potentiometry, and molecular modelling. The peptide mainly displays characteristics of random coil in the CD spectra, and the molecular dynamics simulations demonstrate that it is unstructured with transient and varying helical content. The spectroscopic studies revealed the formation of loop structures with the coordination of the two Cys-thiolates close to each end of the HS peptide, in the presence of one equivalent of Cd(II) per ligand. The imidazole moiety from histidine is also bound to Cd(II) at neutral pH and above. In the presence of 0.5 equivalent of Cd(II) per HS metal bridged structures with e.g. CdS(2)N(2) and possibly CdS(4) coordination geometries are formed above pH ~6. In an equilibrium of several co-existing species the peptide is exchanging between a number of structures also in its metal ion bound state(s), as indicated by NMR and PAC data.

Designed metal ion binding peptides offer a variety of applications in both basic science as model systems of more complex metalloproteins, and in biotechnology, e.g. in bioremediation of toxic metal ions, biomining or as artificial enzymes. In this work a peptide (HS: Ac-SCHGDQGSDCSI-NH2) has been specifically designed for binding of both Zn(II) and Hg(II), i.e. metal ions with different preferences in terms of coordination number, coordination geometry, and to some extent ligand composition. It is demonstrated that HS accommodates both metal ions, and the first coordination sphere, metal ion exchange between peptides, and speciation are characterized as a function of pH using UV-absorption-, synchrotron radiation CD-, (1)H-NMR-, and PAC-spectroscopy as well as potentiometry. Hg(II) binds to the peptide with very high affinity in a {HgS2} coordination geometry, bringing together the two cysteinates close to each end of the peptide in a loop structure. Despite the high affinity, Hg(II) is kinetically labile, exchanging between peptides on the subsecond timescale, as indicated by line broadening in (1)H-NMR. The Zn(II)-HS system displays more complex speciation, involving monomeric species with coordinating cysteinates, histidine, and a solvent water molecule, as well as HS-Zn(II)-HS complexes. In summary, the HS peptide displays conformational flexibility, contains many typical metal ion binding groups, and is able to accommodate metal ions with different structural and ligand preferences with high affinity. As such, the HS peptide may be a scaffold offering binding of a variety of metal ions, and potentially serve for metal ion sequestration in biotechnological applications.