A series of bis(alpha-iminopyridine)metal complexes featuring the first-row transition ions (Cr, Mn, Fe, Co, Ni, and Zn) is presented. It is shown that these ligands are redox noninnocent and their paramagnetic pi radical monoanionic forms can exist in coordination complexes. Based on spectroscopic and structural characterizations, the neutral complexes are best described as possessing a divalent metal center and two monoanionic pi radicals of the alpha-iminopyridine. The neutral M(L*)2 compounds undergo ligand-centered, one-electron oxidations generating a second series, [(L(x))2M(THF)][B(ArF)4] [where L(x) represents either the neutral alpha-iminopyridine (L)0 and/or its reduced pi radical anion (L*)-]. The cationic series comprise mostly mixed-valent complexes, wherein the two ligands have formally different redox states, (L)0 and (L*)-, and the two ligands may be electronically linked by the bridging metal atom. Experimentally, the cationic Fe and Co complexes exhibit Robin-Day Class III behavior (fully delocalized), whereas the cationic Zn, Cr, and Mn complexes belong to Class I (localized) as shown by X-ray crystallography and UV-vis spectroscopy. The delocalization versus localization of the ligand radical is determined only by the nature of the metal linker. The cationic nickel complex is exceptional in this series in that it does not exhibit any ligand mixed valency. Instead, its electronic structure is consistent with two neutral ligands (L)0 and a monovalent metal center or [(L)2Ni(THF)][B(ArF)4]. Finally, an unusual spin equilibrium for Fe(II), between high spin and intermediate spin (S(Fe) = 2 S(Fe) = 1), is described for the complex [(L*)(L)Fe(THF)][B(ArF)4], which consequently is characterized by the overall spin equilibrium (S(tot) = 3/2 S(tot) = 1/2). The two different spin states for Fe(II) have been characterized using variable temperature X-ray crystallography, EPR spectroscopy, zero-field and applied-field Mossbauer spectroscopy, and magnetic susceptibility measurements. Complementary DFT studies of all the complexes have been performed, and the calculations support the proposed electronic structures.

Neutral bis(alpha-iminopyridine)metal complexes of the first-row transition ions (Cr, Mn, Fe, Co, Ni, Zn) and their monocationic analogues: mixed valency involving a redox noninnocent ligand system.

Dysfunctional interactions of metal ions, especially Cu, Zn, and Fe, with the amyloid-beta (A beta) peptide are hypothesized to play an important role in the etiology of Alzheimer's disease (AD). In addition to direct effects on A beta aggregation, both Cu and Fe catalyze the generation of reactive oxygen species (ROS) in the brain further contributing to neurodegeneration. Disruption of these aberrant metal-peptide interactions via chelation therapy holds considerable promise as a therapeutic strategy to combat this presently incurable disease. To this end, we developed two multifunctional carbohydrate-containing compounds N,N'-bis[(5-beta-D-glucopyranosyloxy-2-hydroxy)benzyl]-N,N'-dimethyl-ethane-1,2-diamine (H2GL1) and N,N'-bis[(5-beta-D-glucopyranosyloxy-3-tert-butyl-2-hydroxy)benzyl]-N,N'-dimethyl-ethane-1,2-diamine (H2GL2) for brain-directed metal chelation and redistribution. Acidity constants were determined by potentiometry aided by UV-vis and 1H NMR measurements to identify the protonation sites of H2GL1,2. Intramolecular H bonding between the amine nitrogen atoms and the H atoms of the hydroxyl groups was determined to have an important stabilizing effect in solution for the H2GL1 and H2GL2 species. Both H2GL1 and H2GL2 were found to have significant antioxidant capacity on the basis of an in vitro antioxidant assay. The neutral metal complexes CuGL1, NiGL1, CuGL2, and NiGL2 were synthesized and fully characterized. A square-planar arrangement of the tetradentate ligand around CuGL2 and NiGL2 was determined by X-ray crystallography with the sugar moieties remaining pendant. The coordination properties of H2GL1,2 were also investigated by potentiometry, and as expected, both ligands displayed a higher affinity for Cu2+ over Zn2+ with H2GL1 displaying better coordinating ability at physiological pH. Both H2GL1 and H2GL2 were found to reduce Zn2+- and Cu2+- induced Abeta1-40 aggregation in vitro, further demonstrating the potential of these multifunctional agents as AD therapeutics.

Synthesis, Characterization, and Metal Coordinating Ability of Multifunctional Carbohydrate-Containing Compounds for Alzheimer's Therapy

The aggregation of alpha-synuclein (AS) is a critical step in the etiology of Parkinson’s disease (PD). A central, unresolved question in the pathophysiology of PD relates to the role of AS-metal interactions in amyloid fibril formation and neurodegeneration. Our previous works established a hierarchy in alpha-synuclein-metal ion interactions, where Cu(II) binds specifically to the protein and triggers its aggregation under conditions that might be relevant for the development of PD. Two independent, non-interacting copper-binding sites were identified at the N-terminal region of AS, with significant difference in their affinities for the metal ion. In this work we have solved unknown details related to the structural binding specificity and aggregation enhancement mediated by Cu(II). The high-resolution structural characterization of the highest affinity N-terminus AS-Cu(II) complex is reported here. Through the measurement of AS aggregation kinetics we proved conclusively that the copper-enhanced AS amy...

Bioinorganic chemistry of Parkinson's disease: Structural determinants for the copper-mediated amyloid formation of Alpha-Synuclein.

Typically, microbial methane production occurs under oxygen-free conditions and abiotic methane production occurs under harsh conditions. Here, the authors show methane production from organosulphur compounds under ambient conditions, suggesting a role for these compounds in methane formation in the environment.

/pdf/abiotic-methanogenesis-from-organosulphur-compounds-under-3fga3fq66r.pdf

Abiotic methanogenesis from organosulphur compounds under ambient conditions

Structural Studies of the Alzheimer's Amyloid Precursor Protein Copper-binding Domain Reveal How it Binds Copper Ions

Herein we describe an integrated approach — Molecular Sophe — for determination of the molecular structure of redox active cofactors in metalloproteins from an analysis of their high-resolution EPR spectra. Molecular Sophe involves the computer simulation of continuous-wave and orientation-selective pulsed EPR and electron nuclear double resonance(ENDOR) spectra. As aids to the correct analysis of these spectra, calculation of energy level diagrams, transition roadmaps, and transition surfaces can also be performed. This approach, based on molecularstructure, promises to revolutionize the three-dimensional molecular (geometric and electronic) characterization of paramagnetic materials using a combination of high-resolution EPR spectroscopy and quantum chemistry calculations.

Molecular Sophe, an integrated approach to the structural characterization of metalloproteins, The next generation of computer simulation software

The XSophe-Sophe-XeprView computer simulation software suite provides scientists with an easy-to-use research tool for the analysis of isotropic, randomly orientated and single crystal continuous wave electron paramagnetic resonance (CW EPR) spectra. XSophe provides an X Windows graphical user interface to the Sophe programme allowing; the creation of multiple input files, the local and remote execution of Sophe and display of Sophelog (output from Sophe) and input parameters/files. Sophe is a sophisticated computer simulation software programme with a number of innovative technologies including; the Sophe partition and interpolation schemes, a field segmentation algorithm, the mosaic misorientation line width model, parallelisation (OpcnMP — for SGI computers running the lrix operating system) and spectral optimisation. In conjunction with the SOPHE partition scheme and the field segmentation algorithm, the SOPHE interpolation scheme and mosaic misorientation linewidth model greatly increase the speed of simulations for most spin systems. The output of CW EPR spectra (1D and 2D) from the Sophe programme can be visualised in conjunction with the experimental spectrum in XeprView or Xepr. Energy level diagrams, transition roadmaps and transition surfaces aid the interpretation of complicated randomly orientated EPR spectra and can he viewed with a netscape browser and an OpenInventor scene graph viewer.

XSophe — Sophe — XeprView

Herein we provide a description of the XSophe-Sophe-XeprView and Molecular Sophe computer simulation software suites for the analysis of continuous wave (CW) and pulsed EPR spectra. While the XSophe-Sophe-XeprView computer simulation software suite employs a traditional structural approach through calculation of the spin Hamiltonian parameters which are then compared with other compounds or parameters obtained from computational chemistry calculations, Molecular Sophe utlizes an integrated molecular structure approach. Both computer simulation suites are completely general, employ matrix diagonalization, the mosaic misorientation linewidth model and provide additional tools (calculation of energy level diagrams, transition roadmaps and transition surfaces) aiding scientists in their analysis of complex CW or pulsed EPR spectra. Molecular Sophe enables the computer simulation of continuous wave and orientation selective pulsed EPR and electron nuclear double resonance (ENDOR) spectra. The molecular structure approach employed within Molecular Sophe, promises to revolutionize the 3-dimensional molecular (geometric and electronic) characterization of paramagnetic species using a combination of high resolution EPR spectroscopy and quantum chemistry calculations.

XSophe – Sophe – XeprView and Molecular Sophe: Computer Simulation Software Suites for the Analysis of Continuous Wave and Pulsed EPR and ENDOR Spectra

XSophe: An integrated molecular approach to the analysis of continuous wave and pulsed EPR spectra from metalloprotein

XSophe-Sophe-XeprView. A computer simulation software suite (v. 1.1.3) for the analysis of continuous wave EPR spectra.

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