A co-crystal of polyoxometalates exhibiting single-molecule magnet behavior: the structural origin of a large magnetic anisotropy

A polyoxometalate-based {Mn(III)(3)Mn(IV)} single-molecule magnet exhibits a large axial anisotropy (D = -0.86 cm(-1)) resulting from a near-parallel alignment of Jahn-Teller axes. Its rigorous three-fold symmetry (i.e. rhombicity E→ 0) and increased intercluster separation via co-crystallization effectively hamper quantum tunnelling of the magnetization.     

Elastic “hard” fibers. I.

Elastic “hard” fibers may be prepared from a number of semicrystalline polymers, notably polypropylene, poly-3-methylbutene-1, and polyoxymethylene. These materials show typically a high degree of length recovery from large extensions, a marked, more-or-less recoverable reduction of apparent density on stretching, and the generation of very large amounts of accessible volume and surface area on stretching. Wide- and low-angle X-ray and electron-microscopic observations indicate that the morphological basis for these properties lies in an array of closely packed lamellae of which the normals lie predominantly parallel to the fiber extrusion direction. It is the tilting and splaying apart of the lamellar network which creates the internal volume and surface area on stretching. The long-range elasticity is believed to be distinctly nonrubberlike, as reflected in an insensitivity of mechanical properties to low temperatures, and to arise from bending of the lamellae. This unusual class of materials provides a significant link between macroscopic properties and a particular morphological structure.     

Fermi Resonance In the Infrared Spectra of endo,anti-Tetracyclo[5.2.1.02,6.03,5]dec-8-en-10-one and endo,anti-Tetracyclo[5.2.1.02,6.03,5]decan-10-one

We have uncovered strong Fermi resonance coupling^2–4 in endo, anti-tetracyclo[5.2.1.0^2,6.0^3,5]dec-8-en-10-one (I) and the related tetracyclodecan-10-one (II).     

Euclidean perspective on the unfolding of azurin: angular correlations

The geometrical model introduced previously by the authors has been extended quantitatively to document changes in angular correlations between and among residues as azurin unfolds. In the early stages of denaturation, these changes are found to be more pronounced than changes in the spatial displacement of residues, a result that is also found for residues acting in concert, viz., α-helices, β-sheet residues and residues in ‘turning regions.’ Our analysis leads to a picture of the large-scale motion of the polypeptide chain as azurin denatures. Flanking a central ‘ribbon’ of residues whose orientation remains essentially invariant, we find that in the early stages of unfolding, left- and right-hand ‘wings’ adjacent to this stationary scaffolding pivot counterclockwise, while smaller regions on opposing ends of the β-barrel pivot clockwise. As spatial constraints characterising the native state are further relaxed, our calculations show that some regions reverse their orientational motion, reflecting the enhanced flexibility of the polypeptide chain in the denatured state.     

Locally (-1,1) Rings

If M is a finitely-generated module over a commutative noetherian ring, then it is well-known that the ideal-theoretic assassin and the ideal-theoretic support of M satisfy the following two conditions: (CD supp(M) and ass(M) have the same minimal elements ; (C2) supp(M) has only finitely-many minimal elements. The purpose of this note is to consider a sufficient condition on a noncommutative ring, generalizing the commutative case, for analogous results to hold for the torsion-theoretic assassin and the torsion-theore-tic support of suitable left R-modules M. Since the order in the lattice of torsion theories over the category R-mod of left R-modules is the reverse of the order in the lattice of left ideals of R, we would expect to substitute “maximal” for “minimal” in the above conditions. Also, noetherianness should be replaced by its torsion-theoretic counterpart, semi-noetherianness.     

Groups 5 and 6 terminal hydrazido(2-) complexes: N(β) substituent effects on ligand-to-metal charge-transfer energies and oxidation states

Brightly colored terminal hydrazido(2-) (dme)MCl(3)(NNR(2)) (dme = 1,2-dimethoxyethane; M = Nb, Ta; R = alkyl, aryl) or (MeCN)WCl(4)(NNR(2)) complexes have been synthesized and characterized. Perturbing the electronic environment of the β (NR(2)) nitrogen affects the energy of the lowest-energy charge-transfer (CT) transition in these complexes. For group 5 complexes, increasing the energy of the N(β) lone pair decreases the ligand-to-metal CT (LMCT) energy, except for electron-rich niobium dialkylhydrazides, which pyramidalize N(β) in order to reduce the overlap between the Nb═N(α) π bond and the N(β) lone pair. For W complexes, increasing the energy of N(β) eventually leads to reduction from formally [W(VI)≡N-NR(2)] with a hydrazido(2-) ligand to [W(IV)═N═NR(2)] with a neutral 1,1-diazene ligand. The photophysical properties of these complexes highlight the potential redox noninnocence of hydrazido ligands, which could lead to ligand- and/or metal-based redox chemistry in early transition metal derivatives.     

Outer-sphere contributions to the electronic structure of type zero copper proteins

Bioinorganic canon states that active-site thiolate coordination promotes rapid electron transfer (ET) to and from type 1 copper proteins. In recent work, we have found that copper ET sites in proteins also can be constructed without thiolate ligation (called "type zero" sites). Here we report multifrequency electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), and nuclear magnetic resonance (NMR) spectroscopic data together with density functional theory (DFT) and spectroscopy-oriented configuration interaction (SORCI) calculations for type zero Pseudomonas aeruginosa azurin variants. Wild-type (type 1) and type zero copper centers experience virtually identical ligand fields. Moreover, O-donor covalency is enhanced in type zero centers relative that in the C112D (type 2) protein. At the same time, N-donor covalency is reduced in a similar fashion to type 1 centers. QM/MM and SORCI calculations show that the electronic structures of type zero and type 2 are intimately linked to the orientation and coordination mode of the carboxylate ligand, which in turn is influenced by outer-sphere hydrogen bonding.     

Seismo-acoustic ray model benchmarking against experimental tank data

Acoustic predictions of the recently developed traceo ray model, which accounts for bottom shear properties, are benchmarked against tank experimental data from the EPEE-1 and EPEE-2 (Elastic Parabolic Equation Experiment) experiments. Both experiments are representative of signal propagation in a Pekeris-like shallow-water waveguide over a non-flat isotropic elastic bottom, where significant interaction of the signal with the bottom can be expected. The benchmarks show, in particular, that the ray model can be as accurate as a parabolic approximation model benchmarked in similar conditions. The results of benchmarking are important, on one side, as a preliminary experimental validation of the model and, on the other side, demonstrates the reliability of the ray approach for seismo-acoustic applications.     

Continuous Maps on Aronszajn Trees

Assuming $\diamondsuit$ : Whenever B is a totally imperfect set of real numbers, there is special Aronszajn tree with no continuous order preserving map into B.