Muon-spin relaxation investigation of magnetic bistability in a crystalline organic radical compound

We present the results of a muon-spin relaxation ($\mu^{+}$SR) investigation of the crystalline organic radical compound 4-(2-benzimidazolyl)-1,2,3,5-dithiadiazolyl (HbimDTDA), in which we demonstrate the hysteretic magnetic switching of the system that takes place at $T = 274 \pm 11\,\mathrm{K}$ caused by a structural phase transition. Muon-site analysis using electronic structure calculations suggests a range of candidate muon stopping sites. The sites are numerous and similar in energy but, significantly, differ between the two structural phases of the material. Despite the difference in the sites, the muon remains a faithful probe of the transition, revealing a dynamically-fluctuating magnetically disordered state in the low-temperature structural phase. In contrast, in the high temperature phase the relaxation is caused by static nuclear moments, with rapid electronic dynamics being motionally narrowed from the muon spectra

Genetic Testing for Early Detection of Individuals at Risk of Coronary Heart Disease and Monitoring Response to Therapy: Challenges and Promises

Coronary heart disease (CHD) often presents suddenly with little warning. Traditional risk factors are inadequate to identify the asymptomatic high-risk individuals. Early identification of patients with subclinical coronary artery disease using noninvasive imaging modalities would allow the early adoption of aggressive preventative interventions. Currently, it is impractical to screen the entire population with noninvasive coronary imaging tools. The use of relatively simple and inexpensive genetic markers of increased CHD risk can identify a population subgroup in which benefit of atherosclerotic imaging modalities would be increased despite nominal cost and radiation exposure. Additionally, genetic markers are fixed and need only be measured once in a patient’s lifetime, can help guide therapy selection, and may be of utility in family counseling

Multi-ancestry GWAS of the electrocardiographic PR interval identifies 202 loci underlying cardiac conduction

The electrocardiographic PR interval reflects atrioventricular conduction, and is associated with conduction abnormalities, pacemaker implantation, atrial fibrillation (AF), and cardiovascular mortality. Here we report a multi-ancestry (N=293,051) genome-wide association meta-analysis for the PR interval, discovering 202 loci of which 141 have not previously been reported. Variants at identified loci increase the percentage of heritability explained, from 33.5% to 62.6%. We observe enrichment for cardiac muscle developmental/contractile and cytoskeletal genes, highlighting key regulation processes for atrioventricular conduction. Additionally, 8 loci not previously reported harbor genes underlying inherited arrhythmic syndromes and/or cardiomyopathies suggesting a role for these genes in cardiovascular pathology in the general population. We show that polygenic predisposition to PR interval duration is an endophenotype for cardiovascular disease, including distal conduction disease, AF, and atrioventricular pre-excitation. These findings advance our understanding of the polygenic basis of cardiac conduction, and the genetic relationship between PR interval duration and cardiovascular disease. On the electrocardiogram, the PR interval reflects conduction from the atria to ventricles and also serves as risk indicator of cardiovascular morbidity and mortality. Here, the authors perform genome-wide meta-analyses for PR interval in multiple ancestries and identify 141 previously unreported genetic loci.Peer reviewe

The trans-ancestral genomic architecture of glycemic traits

Glycemic traits are used to diagnose and monitor type 2 diabetes and cardiometabolic health. To date, most genetic studies of glycemic traits have focused on individuals of European ancestry. Here we aggregated genome-wide association studies comprising up to 281,416 individuals without diabetes (30% non-European ancestry) for whom fasting glucose, 2-h glucose after an oral glucose challenge, glycated hemoglobin and fasting insulin data were available. Trans-ancestry and single-ancestry meta-analyses identified 242 loci (99 novel; P < 5 x 10(-8)), 80% of which had no significant evidence of between-ancestry heterogeneity. Analyses restricted to individuals of European ancestry with equivalent sample size would have led to 24 fewer new loci. Compared with single-ancestry analyses, equivalent-sized trans-ancestry fine-mapping reduced the number of estimated variants in 99% credible sets by a median of 37.5%. Genomic-feature, gene-expression and gene-set analyses revealed distinct biological signatures for each trait, highlighting different underlying biological pathways. Our results increase our understanding of diabetes pathophysiology by using trans-ancestry studies for improved power and resolution. A trans-ancestry meta-analysis of GWAS of glycemic traits in up to 281,416 individuals identifies 99 novel loci, of which one quarter was found due to the multi-ancestry approach, which also improves fine-mapping of credible variant sets.Peer reviewe

Models of classroom assessment for course-based research experiences

Course-based research pedagogy involves positioning students as contributors to authentic research projects as part of an engaging educational experience that promotes their learning and persistence in science. To develop a model for assessing and grading students engaged in this type of learning experience, the assessment aims and practices of a community of experienced course-based research instructors were collected and analyzed. This approach defines four aims of course-based research assessment—(1) Assessing Laboratory Work and Scientific Thinking; (2) Evaluating Mastery of Concepts, Quantitative Thinking and Skills; (3) Appraising Forms of Scientific Communication; and (4) Metacognition of Learning—along with a set of practices for each aim. These aims and practices of assessment were then integrated with previously developed models of course-based research instruction to reveal an assessment program in which instructors provide extensive feedback to support productive student engagement in research while grading those aspects of research that are necessary for the student to succeed. Assessment conducted in this way delicately balances the need to facilitate students’ ongoing research with the requirement of a final grade without undercutting the important aims of a CRE education

McConnell I mechanism promotes ferromagnetic interactions between p-stacked Ni(II)-thiazyl complexes

The coordination complex of Ni(hfac)2 (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato) and the 4-(benzoxazol-20-yl)-1,2,3,5-dithiadiazolyl (boaDTDA) neutral radical p-stacks in a one-dimensional ''staircase'' arrangement. This particular packing aligns regions of a and b spin densities on neighbouring NiII(hfac)2(boaDTDA) molecules. This complex exemplifies a McConnell I type mechanism, giving rise to intermolecular ferromagnetic exchange observed for the first time between metal-thiazyl complexes

Manipulating the crystal packing of pyDTDA radical ligand coordination complexes with Mn(II) and Ni(II)

The synthesis of 4′-CN, 5′-CN and 5′-Br substituted pyDTDA neutral radical bidentate ligands is reported (pyDTDA = 4-(2′-pyridyl)-1,2,3,5-dithiadiazolyl). The Ni(hfac)2 and Mn(hfac)2 coordination complexes of both cyano substituted ligands, and the Mn(hfac)2 coordination complex of the bromo substituted ligand, have been prepared and the crystal packing of these is compared (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). Unlike the previously reported Mn(hfac)2(pyDTDA), the Mn(hfac)2(4′-CN-pyDTDA) complex does not form dimers in the solid-state making it possible to measure the magnetic coupling between the unpaired electrons on the coordinated Mn(II) ion and the unpaired electron on the radical ligand by SQUID magnetometry; J/kB = −74(1) K, using H = −2J{SMn*SRad} and gav. = 2.01

[TDNQ][CoCp*2] and [TDNQ]3[CoCp2]2; Radical Anions of a 1,2,5-Thiadiazolo-naphthoquinone

The first crystal structure of a quinone[1,2,5]thiadiazole radical anion is presented. Reduction of naphtha [2,3- c][1,2,5]thiadiazole-4,9-dione (TDNQ) with outersphere electron transfer agents, decamethylcobaltocene (CoCp*2) and cobaltocene (CoCp2), by slow mixing of solutions, generates two species: [TDNQ][CoCp*2] and [TDNQ]3[CoCp2]2, respectively. The [TDNQ][CoCp*2] is soluble in a wide variety of organic solvents, whereas [TDNQ]3[CoCp2]2 is generally insoluble. The radical anion oxidation state, TDNQ*--, in [TDNQ][CoCp*2] is confirmed by lengthened C O bond distances in the (solvated) crystal structure, as compared to neutral TDNQ, shifting of the ν(C O) stretch in the IR absorption spectrum, and the presence of a solution electron paramagnetic resonance (EPR) signal. In the [TDNQ]3[CoCp2]2 species, copacking of single-molecule radical anions, TDNQ*--, and bimolecular radical anion units, (TDNQ)2 *--, with cobaltocenium cations is observed. The magnetic measurements highlight the presence of dominating antiferromagnetic interactions between TDNQ*-- and (TDNQ)2 *-- spins in this cobaltocene salt

Trinuclear Mn(II) complex with paramagnetic bridging 1,2,3-dithiazolyl ligands

The first metal coordination complex of a radical ligand based on the 1,2,3-dithiazolyl heterocycle is reported. 6,7-Dimethyl- 1,4-dioxo-naphtho[2,3-d][1,2,3]dithiazolyl acts as a bridging ligand in the volatile trinuclear Mn(hfac)2-Rad-Mn(hfac)2-Rad-Mn(hfac)2 complex (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). The Mn(II) and radical ligand spins are coupled anti-ferromagnetically (AF) resulting in an ST = 13/2 spin ground state

High-spin supramolecular pair of Mn(II)/thiazyl radical complexes

TheMn(hfac)2 complex of the paramagnetic 4-(benzoxazol-20-yl)-1,2,3,5-dithiadiazolyl ligand is reported (hfac = 1,1,1,5,5,5- hexafluoroacetylacetonato-). The Mn(II) and radical ligand spins are coupled antiferromagnetically (AF) in the coordination complex. Short sulfur–oxygen contacts between molecules provide an efficient pathway for AF coupling between the radical ligand of one molecule and the Mn(II) of a neighbouring molecule, resulting in a large total spin ground state (ST = 4) for a pair of molecules