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.

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.

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.

A prominent current hypothesis is that impaired metal ion homeostasis may contribute to Alzheimer's disease (AD). We elucidate the interaction of Cu with wild-type (WT) Aβ and the genetic variants A2T and A2V which display increasing pathogenicity as A2T