Remarkable spectator ligand effect on the rate constant of ligand substitution of (aqua)ruthenium(II) complexes

The influence of two different di(1-pyrazolyl)alkane ligands on the rate constant of aqua ligand substitution of ruthenium(II) complexes with the formula [Ru(H2O)(L2)(tpmm)]2+ (L2 = di(1-pyrazolyl)methane (DPMet) or 2,2-di(1-pyrazolyl)propane (DPPro)) was investigated. A 9.4 x 10(5)-fold increase in the rate constant of ligand substitution at pH = 6.86 was observed when DPMet was replaced with DPPro. This remarkable increase was unexpected, considering that these bidentate ligands appear quite similar. To help lend insight into this dramatic spectator ligand effect, the activation parameters for the ligand substitution reactions were determined, and single-crystal X-ray data were collected on the structurally analogous (chloro)ruthenium(II) complexes, [Ru(Cl)(L2)(tpmm)]+. These results are discussed in the context of a heteroscorpionate effect exerted by the DPPro ligand.     

Structure of human apolactoferrin at 2.0 A resolution. Refinement and analysis of ligand-induced conformational change. addendum

The coordinates and structure factors have now been deposited with the Protein Data Bank for the high-resolution structure described in the paper by Jameson, Anderson, Norris, Thomas & Baker [Acta Cryst. (1998). D54, 1319-1335]. The PDB reference code for this structure is 1cb6.     

Modification of spin crossover behavior through solvent assisted formation and solvent inclusion in a triply interpenetrating three-dimensional network

The 3D coordination polymer [Fe(4ditz)3](PF6)2.solv consists of three interpenetrating infinite networks. There are cavities between iron atoms of different networks, which are partly filled with solvent molecules. With a change of the solvent used during synthesis from methanol to ethanol, the magnetic behavior of the materials changes. Both show an abrupt two-step spin crossover from low spin (S = 0) to high spin (S = 2) with the methanolate curve lying 7 K higher and showing a small hysteresis. Single crystal and powder diffraction studies show that they both have the same structure, but in powder form, the methanolate slowly loses methanol to finally leave about 0.075 MeOH/Fe. In comparison, the bigger ethanol remains at 0.25 EtOH/Fe. These results, in conjunction with thermodynamic data, strongly suggest that the differences in magnetic behavior are largely entropic in nature. Possible reasons for this are discussed.     

Optimal Control of First-Order Hamilton–Jacobi Equations with Linearly Bounded Hamiltonian

We consider the optimal control of solutions of first order Hamilton–Jacobi equations, where the Hamiltonian is convex with linear growth. This models the problem of steering the propagation of a front by constructing an obstacle. We prove existence of minimizers to this optimization problem as in a relaxed setting and characterize the minimizers as weak solutions to a mean field game type system of coupled partial differential equations. Furthermore, we prove existence and partial uniqueness of weak solutions to the PDE system. An interpretation in terms of mean field games is also discussed.     

Partial spin crossover behaviour in a dinuclear iron(II) triple helicate

Reported herein are the synthesis, structural, magnetic and M?ssbauer spectroscopic characterisation of a dinuclear Fe(II) triple helicate complex [Fe(2)(L)(3)](ClO(4))(4).xH(2)O (x = 1-4), 1(H(2)O), where L is a bis-bidentate imidazolimine ligand. Low temperature structural analysis (150 K) and M?ssbauer spectroscopy (4.5 K) are consistent with one of the Fe(II) centres within the helicate being in the low spin (LS) state with the other being in the high-spin (HS) state resulting in a [LS:HS] species. However, M?ssbauer spectroscopy (295 K) and variable temperature magnetic susceptibility measurements (4.5-300 K) reveal that 1(H(2)O) undergoes a reversible single step spin crossover at one Fe(II) centre at higher temperatures resulting in a [HS:HS] species. Indeed, the T(1/2)(SCO) values at this Fe(II) centre also vary as the degree of hydration, x, within 1(H(2)O) changes from 1 to 4 and are centred between ca. 210 K-265 K, respectively. The dehydration/hydration cycle is reversible and the fully hydrated phase of 1(H(2)O) may be recovered on exposure to water vapour. This magnetic behaviour is in contrast to that observed in the related compound [Fe(2)(L)(3)](ClO(4))(4)·2MeCN, 1(MeCN), whereby fully reversible SCO was observed at each Fe(II) centre to give [LS:LS] species at low temperature and [HS:HS] species at higher temperatures. Reasons for this differing behaviour between 1(H(2)O) and 1(MeCN) are discussed.     

Iron, cysteine and Parkinson’s disease

Abstract  

A short review of the role of cysteine and iron in the progression of Parkinson’s disease is presented. The complex chemistry of cysteine and iron and its interactions are discussed and put into the context of oxidative stress during neurodegeneration.