Biophysical tools to assess the interaction of PF4 with polyanions

SummaryThe antigen in heparin-induced thrombocytopenia (HIT) is expressed on platelet factor 4 (PF4) when PF4 complexes with polyanions. In recent years, biophysical tools (e. g. circular dichroism spectroscopy, atomic force microscopy, isothermal titration calorimetry, x-ray crystallography, electron microscopy) have gained an important role to complement immunological and functional assays for better understanding the interaction of heparin with PF4. This allowed identification of those features that make PF4 immunogenic (e. g. a certain conformational change induced by the polyanion, a threshold energy of the complexes, the existence of multimeric complexes, a certain number of bonds formed by PF4 with the polyanion) and to characterize the morphology and thermal stability of complexes formed by the protein with polyanions. These findings and methods can now be applied to test new drugs for their potential to induce the HIT-like adverse drug effect by preclinical in vitro testing. The methods and techniques applied to characterize the antigen in HIT may also be helpful to better understand the mechanisms underlying other antibody-mediated disorders in thrombosis and hemostasis (e. g. acquired hemophilia, thrombotic thrombocytopenic purpura). Furthermore, understanding the mechanisms making the endogenous protein PF4 immunogenic may help to understand the mechanisms underlying other autoimmune disorders.

Coordination Assemblies of CoII, NiII, ZnII, and CuII with 3,3′,4,4′-Biphenyltetracarboxylic Acid and Three Positional Isomeric Ligands

Eight different complexes with three positional isomeric dipyridyl ligands (3,3′-Hbpt, 3,4′-Hbpt, and 4,4′-Hbpt) (here, 3,3′-Hbpt = 1H-3,5-bis(3-pyridyl)-1,2,4-triazole, 3,4′-Hbpt = 1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole, and 4,4′-Hbpt = 1H-3,5-bis(4-pyridyl)-1,2,4-triazole), as well as 3,3′,4,4′-biphenyltetracarboxylic acid (H4bptc), namely, {[M(bptc)0.5(3,3′-Hbpt)(H2O)2]·H2O}n (M = Co (1), M = Ni (2)), {[Zn2(bptc)(3,3′-Hbpt)2]·3H2O}n (3), [Co(bptc)0.5(3,4′-Hbpt)(H2O)]n (4), [Ni(bptc)0.5(3,4′-Hbpt)2(H2O)2]n (5), {[Cu(bptc)0.5(3,4′-Hbpt)(H2O)]·H2O}n (6), and {[M(bptc)0.5(4,4′-Hbpt)2(H2O)]·4H2O}n (M = Co (7), and Ni (8)) were synthesised and characterised by single-crystal X-ray diffraction. The crystallographic analysis demonstrates that bptc influences the MII (M = Co, Ni, Cu, and Zn) ions to form 2D layers, which are further connected via the isomeric bpt connectors, leading to many types of coordination polymers, such as 2D layers(for 1–3, 5), 3D four-connected nets with a short Schläfli symbol of (64.82) (for 4, 6), and 3D four-connected nets with a short Schläfli symbol of (64.82)(5.63.72)0.5 (for 7–8). This work demonstrates that the isomeric effects of the bpt ligands influence the construction of these frameworks. The thermal stability of complexes 1–6 was investigated.