173 research outputs found
Single-ion and exchange anisotropy effects and multiferroic behavior in high-symmetry tetramer single molecule magnets
We study single-ion and exchange anisotropy effects in equal-spin
tetramer single molecule magnets exhibiting , , ,
, , or ionic point group symmetry. We first write the
group-invariant quadratic single-ion and symmetric anisotropic exchange
Hamiltonians in the appropriate local coordinates. We then rewrite these local
Hamiltonians in the molecular or laboratory representation, along with the
Dzyaloshinskii-Moriay (DM) and isotropic Heisenberg, biquadratic, and
three-center quartic Hamiltonians. Using our exact, compact forms for the
single-ion spin matrix elements, we evaluate the eigenstate energies
analytically to first order in the microscopic anisotropy interactions,
corresponding to the strong exchange limit, and provide tables of simple
formulas for the energies of the lowest four eigenstate manifolds of
ferromagnetic (FM) and anitiferromagnetic (AFM) tetramers with arbitrary .
For AFM tetramers, we illustrate the first-order level-crossing inductions for
, and obtain a preliminary estimate of the microscopic
parameters in a Ni from a fit to magnetization data.
Accurate analytic expressions for the thermodynamics, electron paramagnetic
resonance absorption and inelastic neutron scattering cross-section are given,
allowing for a determination of three of the microscopic anisotropy
interactions from the second excited state manifold of FM tetramers. We also
predict that tetramers with symmetries and should exhibit both
DM interactions and multiferroic states, and illustrate our predictions for
.Comment: 30 pages, 14 figures, submitted to Phys. Rev.
Transfer hydrogenation as a redox process in nucleotides
© 2014 American Chemical Society. Using a combined theoretical and experimental strategy, the heats of hydrogenation of the nucleotide bases uracil, thymine, cytosine, adenine, and guanine have been determined. The most easily hydrogenated base is uracil, followed by thymine and cytosine. Comparison of these hydrogenation enthalpies with those of ketones and aldehydes derived from sugar models indicates the possibility of near-thermoneutral hydrogen transfer between uracil and the sugar phosphate backbone in oligonucleotides. (Figure Presented
Implantable Cardioverter Defibrillator Therapy in Patients with Cardiac Sarcoidosis
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93643/1/j.1540-8167.2012.02350.x.pd
Novel CÎČâCÎł Bond Cleavages of Tryptophan-Containing Peptide Radical Cations
In this study, we observed unprecedented cleavages of the CÎČâCÎł bonds of tryptophan residue side chains in a series of hydrogen-deficient tryptophan-containing peptide radical cations (Mâą+) during low-energy collision-induced dissociation (CID). We used CID experiments and theoretical density functional theory (DFT) calculations to study the mechanism of this bond cleavage, which forms [M â 116]+ ions. The formation of an α-carbon radical intermediate at the tryptophan residue for the subsequent CÎČâCÎł bond cleavage is analogous to that occurring at leucine residues, producing the same product ions; this hypothesis was supported by the identical product ion spectra of [LGGGH â 43]+ and [WGGGH â 116]+, obtained from the CID of [LGGGH]âą+ and [WGGGH]âą+, respectively. Elimination of the neutral 116-Da radical requires inevitable dehydrogenation of the indole nitrogen atom, leaving the radical centered formally on the indole nitrogen atom ([Ind]âą-2), in agreement with the CID data for [WGGGH]âą+ and [W1-CH3GGGH]âą+; replacing the tryptophan residue with a 1-methyltryptophan residue results in a change of the base peak from that arising from a neutral radical loss (116 Da) to that arising from a molecule loss (131 Da), both originating from CÎČâCÎł bond cleavage. Hydrogen atom transfer or proton transfer to the Îł-carbon atom of the tryptophan residue weakens the CÎČâCÎł bond and, therefore, decreases the dissociation energy barrier dramatically
Cardiac magnetic resonance imaging-indeterminate/negative cardiac sarcoidosis revealed by 18F-fluorodeoxyglucose-positron emission tomography: two case reports and a review of the literature
Risk of adverse outcomes associated with cardiac sarcoidosis diagnostic schemes
BackgroundMultiple cardiac sarcoidosis (CS) diagnostic schemes have been published.ObjectivesThis study aims to evaluate the association of different CS diagnostic schemes with adverse outcomes. The diagnostic schemes evaluated were 1993, 2006, and 2017 Japanese criteria and the 2014 Heart Rhythm Society criteria.MethodsData were collected from the Cardiac Sarcoidosis Consortium, an international registry of CS patients. Outcome events were any of the following: all-cause mortality, left ventricular assist device placement, heart transplantation, and appropriate implantable cardioverter-defibrillator therapy. Logistic regression analysis evaluated the association of outcomes with each CS diagnostic scheme.ResultsA total of 587 subjects met the following criteria: 1993 Japanese (n = 310, 52.8%), 2006 Japanese (n = 312, 53.2%), 2014 Heart Rhythm Society (n = 480, 81.8%), and 2017 Japanese (n = 112, 19.1%). Patients who met the 1993 criteria were more likely to experience an event than patients who did not (n = 109 of 310, 35.2% vs n = 59 of 277, 21.3%; OR: 2.00; 95% CI: 1.38-2.90; P P P = 0.18 or OR: 1.51; 95% CI: 0.97-2.33; P = 0.067, respectively).ConclusionsCS patients who met the 1993 and the 2006 criteria had higher odds of adverse clinical outcomes. Future research is needed to prospectively evaluate existing diagnostic schemes and develop new risk models for this complex disease.Cardiolog
Direct Generation of Oxygen-Stabilized Radicals by Hâą Transfer from Transition Metal Hydrides
- âŠ