Synthesis, characterisation and photochemistry of PtIV pyridyl azido acetato complexes

PtII azido complexes [Pt(bpy)(N3)2] (1), [Pt(phen)(N3)2] (2) and trans-[Pt(N3)2(py)2] (3) incorporating the bidentate diimine ligands 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen) or the monodentate pyridine (py) respectively, have been synthesised from their chlorido precursors and characterised by X-ray crystallography; complex 3 shows significant deviation from square-planar geometry (N3–Pt–N3 angle 146.7°) as a result of steric congestion at the Pt centre. The novel PtIV complexes trans, cis-[Pt(bpy)(OAc)2(N3)2] (4), trans, cis-[Pt(phen)(OAc)2(N3)2] (5), trans, trans, trans-[Pt(OAc)2(N3)2(py)2] (6), were obtained from 1–3via oxidation with H2O2 in acetic acid followed by reaction of the intermediate with acetic anhydride. Complexes 4–6 exhibit interesting structural and photochemical properties that were studied by X-ray, NMR and UV-vis spectroscopy and TD-DFT (time-dependent density functional theory). These PtIV complexes exhibit greater absorption at longer wavelengths (ε = 9756 M−1 cm−1 at 315 nm for 4; ε = 796 M−1 cm−1 at 352 nm for 5; ε = 16900 M−1 cm−1 at 307 nm for 6, in aqueous solution) than previously reported PtIV azide complexes, due to the presence of aromatic amines, and 4–6 undergo photoactivation with both UVA (365 nm) and visible green light (514 nm). The UV-vis spectra of complexes 4–6 were calculated using TD-DFT; the nature of the transitions contributing to the UV-vis bands provide insight into the mechanism of production of the observed photoproducts. The UV-vis spectra of 1–3 were also simulated by computational methods and comparison between PtII and PtIV electronic and structural properties allowed further elucidation of the photochemistry of 4–6

Synthesis, two-dimensional (HNMR)-H-1 spectrum, and DNA binding studies of 2,2 '-bipyrudine-2-pyridinecarboxylato-platinum (II) nitrate

A complex of formula [Pt (a-n) (bpy)] NO3 (where a-n is 2 - pyridinecarboxylate anion and bpy is 2,2'-bipyridine) was prepared, its structure was established by 2D COSY spectral method; and it binds to calf thymus DNA nonintercalative noncovalent mode of binding

Binding properties and conformational change of human growth hormone upon interaction with Fe3+

Binding properties and conformational change of human growth hormone (hGH) upon interaction with Fe3+ were investigated at 27 °C in NaCl solution, 50 mM, by calorimetry and spectroscopy. UV spectroscopy indicates that thermal denaturation of hGH is an irreversible process and is accompanied by aggregation. At an optimum concentration of iron thermal denaturation of hGH becomes reversible. Results from equilibrium dialysis and isothermal titration calorimetry indicate a set of four binding sites on hGH for Fe3+. Interaction of three iron ions with hGH prevents irreversibility and aggregation. Differential scanning calorimetry confirms the UV spectroscopic finding. Domain analysis by DSC shows that in the presence of iron, there are at least two main transitions corresponding with the two groups of helices. Deconvolution of the main transitions provides two sub-transitions each, the first pair is similar, but the second pair is considerably different in the enthalpy change of unfolding. Interaction of iron ions with hGH prevents aggregation by an effect on the hydrophobicity and provides information about its structure and thermal denaturation. © 2005 Elsevier B.V. All rights reserved