A principle of virtual work for combined electrostatic and mechanical loading of materials

The equations governing mechanics and electrostatics are formulated for a system in which the material deformations and electrostatic polarizations are arbitrary. A mechanical/electrostatic energy balance is formulated for this situation in terms of the electric enthalpy, in which the electric potential and the electric field are the independent variables, and charge and electric displacement, respectively, are the conjugate thermodynamic forces. This energy statement is presented in the form of a principle of virtual work (PVW), in which external virtual work is equated to internal virtual work. The resulting expression involves an internal material virtual work in which (1) material polarization is work-conjugate to increments of electric field, and (2) a combination of Cauchy stress, Maxwell stress and a product of polarization and electric field is work-conjugate to increments of strain. This PVW is valid for all material types, including those that are conservative and those that are dissipative. Such a virtual work expression is the basis for a rigorous formulation of a finite element method for problems involving the deformation and electrostatic charging of materials, including electroactive polymers and switchable ferroelectrics. The internal virtual work expression is used to develop the structure of conservative constitutive laws governing, for example, electroactive elastomers and piezoelectric materials, thereby determining the form of the Maxwell or electrostatic stress. It is shown that the Maxwell or electrostatic stress has a form fully constrained by the constitutive law and cannot be chosen independently of it. The structure of constitutive laws for dissipative materials, such as viscoelastic electroactive polymers and switchable ferroelectrics, is similarly determined, and it is shown that the Maxwell or electrostatic stress for these materials is identical to that for a material having the same conservative response when the dissipative processes in the material are shut off. The form of the internal virtual work is used further to develop the structure of dissipative constitutive laws controlled by rearrangement of material internal variables.     

Proposal of a two-qutrit contextuality test free of the finite precision and compatibility loopholes

It has been argued that any test of quantum contextuality is nullified by the fact that perfect orthogonality and perfect compatibility cannot be achieved in finite precision experiments. We introduce experimentally testable two-qutrit violations of inequalities for noncontextual theories in which compatibility is guaranteed by the fact that measurements are performed on separated qutrits. The inequalities are inspired by the basic building block of the Kochen-Specker proof of quantum contextuality for a qutrit, despite the fact that their proof is completely independent of it.     

Highly stable redox-active molecular layers by covalent grafting to conductive diamond

We demonstrate a modular "click"-based functionalization scheme that allows inexpensive conductive diamond samples to serve as an ultrastable platform for surface-tethered electrochemically active molecules stable out to ～1.3 V vs Ag/AgCl. We have cycled surface-tethered Ru(tpy)(2) to this potential more than 1 million times with little or no degradation in propylene carbonate and only slightly reduced stability in water and acetonitrile.     

The CO Photodissociation and Recombination Dynamics of the W172Y/F282T Ligand Channel Mutant of Rhodobacter sphaeroides aa3 Cytochrome c Oxidase

In the ligand channel of the cytochrome c oxidase from Rhodobacter sphaeroides (Rs aa₃) W172 and F282 have been proposed to generate a constriction that may slow ligand access to and from the active site. To explore this issue, the tryptophan and phenylalanine residues in Rs aa₃ were mutated to the less bulky tyrosine and threonine residues, respectively, which occupy these sites in Thermus thermophilus (Tt) ba₃ cytochrome oxidase. The CO photolysis and recombination dynamics of the reduced wild‐type Rs aa₃ and the W172Y/F282T mutant were investigated using time‐resolved optical absorption spectroscopy. The spectral changes associated with the multiple processes are attributed to different conformers. The major CO recombination process (44 μs) in the W172Y/F282T mutant is ~500 times faster than the predominant CO recombination process in the wild‐type enzyme (~23 ms). Classical dynamic simulations of the wild‐type enzyme and double mutant showed significant structural changes at the active site in the mutant, including movement of the heme a₃ ring‐D propionate toward Cu_B and reduced binuclear center cavity volume. These structural changes effectively close the ligand exit pathway from the binuclear center, providing a basis for the faster CO recombination in the double mutant.     

Asymmetric indium-mediated Barbier-type allylation reactions with ketones to form homoallylic alcohol products

We report a general method for the enantioselective allylation of both aromatic and aliphatic ketones under indium-mediated Barbier-type conditions. Using 2 equiv of a commercially available amino alcohol, either (1S,2R)-(+)-2-amino-1,2-diphenylethanol ((+)-1) or (1R,2S)-(−)-2-amino-1,2-diphenylethanol ((−)-1) as the chiral auxiliary, good yields and enantioselectivities were achieved. To our knowledge, the enantioselectivities reported herein are the highest obtained for the indium-mediated allylations of ketones, specifically the homoallylic alcohol product obtained from the addition to α,α,α-trifluoroacetophenone provided 80% enantiomeric excess.     

Highly enantioselective hydroformylation of aryl alkenes with diazaphospholane ligands

Asymmetric, rhodium-catalyzed hydroformylation of terminal and internal aryl alkenes with diazaphospholane ligands is reported. Under partially optimized reaction conditions, high enantioselectivity (>90% ee) and regioselectivities (up to 65:1 alpha:beta) are obtained for most substrates. For terminal alkenes, both enantioselectivity and regioselectivity are proportional to the carbon monoxide partial pressure, but independent of hydrogen pressure. Hydroformylation of para-substituted styrene derivatives gives the highest regioselectivity for substrates bearing electron-withdrawing substituents. A Hammett analysis produces a positive linear correlation for regioselectivity.     

Solvent dependence of the solid‐state structures of salicylaldiminate magnesium amide complexes

There are challenges in using magnesium coordination complexes as reagents owing to their tendency to adopt varying aggregation states in solution and thus impacting the reactivity of the complexes. Many magnesium complexes are prone to ligand redistribution via Schlenk equilibrium due to the ionic character within the metal–ligand interactions. The role of the supporting ligand is often crucial for providing stability to the heteroleptic complex. Strategies to minimize ligand redistribution in alkaline earth metal complexes could include using a supporting ligand with tunable sterics and electronics to influence the degree of association to the metal atom. Magnesium bis(hexamethyldisilazide) was reacted with salicylaldimines [¹L = N‐(2,6‐diisopropylphenyl)salicylaldimine and ²L = 3,5‐di‐tert‐butyl‐N‐(2,6‐diisopropylphenyl)salicylaldimine] in either nondonor (toluene) or donor solvents [tetrahydrofuran (THF) or pyridine]. The structures of the magnesium complexes were studied in the solid state via X‐ray diffraction. In the nondonor solvent, i.e. toluene, the heteroleptic complex bis{μ‐2‐[(2,6‐diisopropylphenyl)iminomethyl]phenolato}‐κ³N,O:O;κ³O:N,O‐bis[(hexamethyldisilazido‐κN)magnesium(II)], [Mg₂(C₁₉H₂₂NO)₂(C₆H₁₈NSi₂)₂] or [¹LMgN(SiMe₃)₂]₂, (1), was favored, while in the donor solvent, i.e. pyridine (pyr), the formation of the homoleptic complex {2,4‐di‐tert‐butyl‐6‐[(2,6‐diisopropylphenyl)iminomethyl]phenolato‐κ²N,O}bis(pyridine‐κN)magnesium(II) toluene monosolvate, [Mg(C₂₇H₃₈NO)₂(C₅H₅N)₂]·C₅H₅N or [{²L₂Mg₂(pyr)₂}·pyr], (2), predominated. Heteroleptic complex (1) was crystallized from toluene, while homoleptic complexes (2) and the previously reported [¹L₂Mg·THF] [Quinque et al. (2011). Eur. J. Inorg. Chem. pp. 3321–3326] were crystallized from pyridine and THF, respectively. These studies support solvent‐dependent ligand redistribution in solution. In‐situ¹H NMR experiments were carried out to further probe the solution behavior of these systems.