We prepare iron(II) and iron(III) complexes with polydentate ligands that contain quinols, which can act as electron proton transfer mediators. Although the iron(II) complex with N-(2,5-dihydroxybenzyl)-N,N ',N '-tris(2-pyridinylmethyl)-1,2-ethanediamine (H(2)qp(1)) is inactive as an electrocatalyst, iron complexes with N,N '-bis(2,5-dihydroxybenzyl)-N,N '-bis(2-pyridinylmethyl)-1,2-ethanediamine (H4qp2) and N-(2,5-dihydroxybenzyl)-N,N '-bis(2-pyridinylmethyl)-1,2-ethanediamine (H(2)qp(3)) were found to be much more active and more selective for water production than a previously reported cobalt-H(2)qp(1) electrocatalyst while operating at low overpotentials. The catalysts with H(2)qp(3) can enter the catalytic cycle as either Fe(II) or Fe(III) species; entering the cycle through Fe(III) lowers the effective overpotential. On the basis of their TOF0 values, the successful iron-quinol complexes are better electrocatalysts for oxygen reduction than previously reported iron-porphyrin compounds, with the Fe(III)-H(2)qp(3) arguably being the best homogeneous electrocatalyst for this reaction. With iron, the quinol-for-phenol substitution shifts the product selectivity from H2O2 to water with little impact on the overpotential, but unlike cobalt, this substitution also greatly improves the activity, as assessed by TOFmax, by hastening the protonation and oxygen binding steps. The addition of a second quinol further enhances the activity and selectivity for water but modestly increases the effective overpotential.

In the current work, we demonstrate ligand design concepts that significantly improve the superoxide dismutase (SOD) activity of a zinc complex; the catalysis is enhanced when two quinol groups are present in the polydentate ligand. We investigate the mechanism through which the quinols influence the catalysis and determine the impact of entirely removing a chelating group from the original hexadentate ligand. Our results suggest that SOD mimicry with these compounds requires a ligand that coordinates Zn(II) strongly in both its oxidized and reduced forms and that the activity proceeds through Zn(II)-semiquinone complexes. The complex with two quinols displays greatly enhanced catalytic ability, with the activity improving by as much as 450% over a related complex with a single quinol. In the reduced form of the diquinol complex, one quinol appears to coordinate to the zinc much more weakly than the other. We believe that superoxide can more readily displace this portion of the ligand, facilitating its coordination to the metal center and thereby hastening the SOD reactivity. Despite the presence of two redox-active groups that may communicate through intramolecular hydrogen bonding and redox tautomerism, only one quinol undergoes two-electron oxidation to a para-quinone during the catalysis. After the formation of the para-quinone, the remaining quinol deprotonates and binds tightly to the metal, ensuring that the complex remains intact in its oxidized state, thereby maintaining its catalytic ability. The Zn(II) complex with the diquinol ligand is highly unusual for a SOD mimic in that it performs more efficiently in phosphate solution.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Several gallium(III) salts, most notably GaCl3, were found to serve as mild catalysts for the deformylation of aldehydes to alkenes by H2O2 and base, demonstrating that redox-active transition metals are not strictly required for this sort of reactivity. The identities of the counteranion and solvent strongly influence both the extent of the activity and the incidence of side-products. Although the catalysis has thus far been modest (similar to 3 turnovers), these turnovers occur in under 20 min at 20 degrees C; the reactivity compares well to that promoted by transition metal peroxo complexes, which require much more time to stoichiometrically convert aldehydes to alkenes and often substantial amounts of ketone side-products.

In vivo MR spectroscopy is a non -invasive methodology that provides information about the biochemistry of tissues. It is available as a “push-button” application on state-of-the-art clinical MR scanners. MR spectroscopy has been used to study various brain diseases including tumors, stroke, trauma, degenerative disorders, epilepsy/seizures, inborn errors, neuropsychiatric disorders, and others. The purpose of this review is to provide an overview of MR spectroscopy findings in the pediatric population and its clinical use.

BACKGROUND AND PURPOSE:Many patients with dementia may have comorbid or misdiagnosed normal pressure hydrocephalus, a treatable neurologic disorder. The callosal angle is a validated biomarker for normal pressure hydrocephalus with 93% diagnostic accuracy. Our purpose was to develop and evaluate an algorithm for automatically computing callosal angles from MR images of the brain. MATERIALS AND METHODS:This article reports the results of analyzing callosal angles from 1856 subjects with 5264 MR images from the Open Access Series of Imaging Studies and the Alzheimer's Disease Neuroimaging Initiative databases. Measurement variability was examined between 2 neuroradiologists (n = 50) and between manual and automatic measurements (n = 281); from differences in simulated head orientation; and from real-world changes in patients with multiple examinations (n = 906). We evaluated the effectiveness of the automatic callosal angle to differentiate normal pressure hydrocephalus from Alzheimer disease in a simulated cohort. RESULTS:The algorithm identified that 12.4% of subjects from these carefully screened cohorts had callosal angles of <90°, a published threshold for possible normal pressure hydrocephalus. The intraclass correlation coefficient was 0.97 for agreement between neuroradiologists and 0.90 for agreement between manual and automatic measurement. The method was robust to different head orientations. The median coefficient of variation for repeat examinations was 4.2% (Q1 = 3.1%, Q3 = 5.8%). The simulated classification of normal pressure hydrocephalus versus Alzheimer using the automatic callosal angle had an accuracy, sensitivity, and specificity of 0.87 each. CONCLUSIONS:In even the most pristine research databases, analyses of the callosal angle indicate that some patients may have normal pressure hydrocephalus. The automatic callosal angle measurement can rapidly and objectively screen for normal pressure hydrocephalus in patients who would otherwise be misdiagnosed.

Previously prepared Mn(II)- and quinol-containing magnetic resonance imaging (MRI) contrast agent sensors for H2O2 relied on linear polydentate ligands to keep the redox-activatable quinols in close proximity to the manganese. Although these provide positive T1-weighted relaxivity responses to H2O2 that result from oxidation of the quinol groups to p-quinones, these reactions weaken the binding affinity of the ligands, promoting dissociation of Mn(II) from the contrast agent in aqueous solution. Here, we report a new ligand, 1,8-bis(2,5-dihydroxybenzyl)-1,4,8,11-tetraazacyclotetradecane, that consists of two quinols covalently tethered to a cyclam macrocycle. The macrocycle provides stronger thermodynamic and kinetic barriers for metal-ion dissociation in both the reduced and oxidized forms of the ligand. The Mn(II) complex reacts with H2O2 to produce a more highly aquated Mn(II) species that exhibits a 130% greater r1, quadrupling the percentile response of our next best sensor. With a large excess of H2O2, there is a noticeable induction period before quinol oxidation and r1 enhancement occurs. Further investigation reveals that, under such conditions, catalase activity initially outcompetes ligand oxidation, with the latter occurring only after most of the H2O2 has been depleted.

Purpose: To evaluate six cerebral arterial segmentation algorithms in a set of patients with a wide range of hemodynamic characteristics to determine real-world performance. Approach: Time-of-flight magnetic resonance angiograms were acquired from 33 subjects: normal controls (N = 11), sickle cell disease (N = 11), and non-sickle anemia (N = 11) using a 3 Tesla Philips Achieva scanner. Six segmentation algorithms were tested: (1) Otsu's method, (2) K-means, (3) region growing, (4) active contours, (5) minimum cost path, and (6) U-net machine learning. Segmentation algorithms were tested with two region-selection methods: global, which selects the entire volume; and local, which iteratively tracks the arteries. Five slices were manually segmented from each patient by two readers. Agreement between manual and automatic segmentation was measured using Matthew's correlation coefficient (MCC). Results: Median algorithm segmentation times ranged from 0.1 to 172.9 s for a single angiogram versus 10 h for manual segmentation. Algorithms had inferior performance to interobserver vessel-based (p < 0.0001, MCC = 0.65) and voxel-based (p < 0.0001, MCC = 0.73) measurements. There were significant differences between algorithms (p < 0.0001) and between patients (p < 0.0042). Post-hoc analyses indicated (1) local minimum cost path performed best with vessel-based (p = 0.0261, MCC = 0.50) and voxel-based (p = 0.0131, MCC = 0.66) analyses; and (2) higher vessel-based performance in non-sickle anemia (p = 0.0002) and lower voxel-based performance in sickle cell (p = 0.0422) compared with normal controls. All reported MCCs are medians. Conclusions: The best-performing algorithm (local minimum cost path, voxel-based) had 9.59% worse performance than inter-observer agreement but was 3 orders of magnitude faster. Automatic segmentation was non-inferior in patients with sickle cell disease and superior in non-sickle anemia. (C) 2021 Society of Photo-Optical Instrumentation Engineers (SPIE)