Synthesis and Characterization of Symmetrically versus Unsymmetrically Proton-Bridged Hexa-Iron Clusters

Syntheses and magnetic and structural characterization of hexa-iron complexes of derivatized salicylaldoximes are discussed. Complexation of Fe(BF4)2·6H2O with each ligand (H2 L1 and H4 L2) in a methanolic-pyridine solution resulted in hexa-iron compounds (C1 and C2, respectively), which each contain two near-parallel metal triangles of [Fe3-μ3-O], linked by six fluoride bridges and stabilized by a hydrogen-bonded proton between the μ3-O groups. Within each metal triangle of C2, Fe(III) ions are connected via the amine "straps" of (H4 L2-2H). Variable-temperature magnetic susceptibility and Mössbauer data of C1 and C2 indicate the presence of dominant antiferromagnetic interactions between the high-spin (S = 5/2) Fe(III) centers. For C1, two quadrupole doublets are observed at room temperature and 5 K, consistent with structural data from which discrete but disordered [Fe3-μ3-O] and [Fe3-μ3-OH] species were inferred. For C2, a single sharp quadrupole doublet with splitting intermediate between those determined for C1 was observed, consistent with the symmetric [Fe3-μ3-O···H···μ3-O-Fe3] species inferred crystallographically from the very short μ3-O···μ3-O separation. The differences in the physical properties of the complexes, as seen in the Mössbauer, X-ray, and magnetic data, are attributed to the conformational flexibility imparted by the nature of the linkages between the closely related ligands

[Fe(µ2-OH)6]3− Linked Fe3O Triads: Mössbauer Evidence for Trigonal µ3-O2− or µ3-OH− Groups in Bridged versus Unbridged Complexes

The syntheses, coordination chemistry, and Mössbauer spectroscopy of hepta-iron(III) complexes using derivatised salicylaldoxime ligands from two categories; namely, ‘single-headed’ (H2L) and ‘double-headed’ (H4L) salicylaldoximes are described. All compounds presented here share a [Fe3-µ3-O] core in which the iron(III) ions are µ3-hydroxo-bridged in the complex C1 and µ3-oxo-bridged in C2 and C3. Each compound consists of 2 × [Fe3-µ3-O] triads that are linked via a central [Fe(µ2-OH)6]3− ion. In addition to the charge balance and microanalytical evidence, Mössbauer measurements support the fact that the triads in C1 are µ3-OH bridged and are µ3-O bridged in C2 and C3

Ketamine Response.

<p>Beta1 (14Hz– 20Hz) SPD differences from the pre-injection period to the post-injection period for left hemispheric hippocampal bodies (HB) and parahippocampal gyri (PHG) exposed to various concentrations of ketamine (A). High frequency PDs computed from an average of beta1 (14Hz– 20Hz) and gamma (30Hz– 40Hz) SPD differences from the pre-injection period to the post-injection period for left hemispheric hippocampal bodies (HB) and parahippocampal gyri (PHG) exposed to 1nM ketamine compared to sham injection (B). Significant differences are indicated (p < .05).</p

Repeated Exposure: Glutamate.

Gamma (30Hz– 40Hz) power within the left parahippocampal gyrus for trials involving surface injections of 10−8 to 10−6 M glutamate as a function of trial order, or implicitly, time.</p

Null Hippocampal Effect: Ketamine.

Non-parametric correlation between delta (1.5Hz– 4Hz) SPD differences from the pre-injection period to the post-injection period and molar concentration of ketamine for the left hippocampal body. No significant correlation was identified (p>.05).</p

Glutamate Response in a Darkened Environment.

Beta2 (20Hz– 30Hz) PDs for periods of pre- and post-injection for right (dark) and left (light) parahippocampal gyri exposed to 1 mL surface injections of 100 nM glutamate (A) and water (B). A significant difference from pre-to-post-injection periods for the left parahippocampal gyrus was revealed (p < .05).</p

When Is the Brain Dead? Living-Like Electrophysiological Responses and Photon Emissions from Applications of Neurotransmitters in Fixed Post-Mortem Human Brains

<div><p>The structure of the post-mortem human brain can be preserved by immersing the organ within a fixative solution. Once the brain is perfused, cellular and histological features are maintained over extended periods of time. However, functions of the human brain are not assumed to be preserved beyond death and subsequent chemical fixation. Here we present a series of experiments which, together, refute this assumption. Instead, we suggest that chemical preservation of brain structure results in some retained functional capacity. Patterns similar to the living condition were elicited by chemical and electrical probes within coronal and sagittal sections of human temporal lobe structures that had been maintained in ethanol-formalin-acetic acid. This was inferred by a reliable modulation of frequency-dependent microvolt fluctuations. These weak microvolt fluctuations were enhanced by receptor-specific agonists and their precursors (i.e., nicotine, 5-HTP, and L-glutamic acid) as well as attenuated by receptor-antagonists (i.e., ketamine). Surface injections of 10 nM nicotine enhanced theta power within the right parahippocampal gyrus without any effect upon the ipsilateral hippocampus. Glutamate-induced high-frequency power densities within the left parahippocampal gyrus were correlated with increased photon counts over the surface of the tissue. Heschl’s gyrus, a transverse convexity on which the primary auditory cortex is tonotopically represented, retained frequency-discrimination capacities in response to sweeps of weak (2μV) square-wave electrical pulses between 20 Hz and 20 kHz. Together, these results suggest that portions of the post-mortem human brain may retain latent capacities to respond with potential life-like and virtual properties.</p></div