Highly practical and enantioselective cu-catalyzed conjugate addition of alkylzinc reagents to cyclic enones at ambient temperature

[reaction: see text] A new ligand for Cu-catalyzed enantioselective additions of dialkylzincs to cyclic enones has been developed. In addition to providing good to excellent enantioselectivities with a range of cyclic enones and dialkylzincs, the ligand has several notworthy features: it can be readily prepared in just two steps, is an air-stable crystalline solid, and provides optimal performance at ambient temperature.     

Free volume properties of model fluids and polymers: Shape and connectivity

The Cavity Energetic Sizing Algorithm (CESA) method of in 't Veld (J Phys Chem B 2000, 104, 12028) is extended to characterize the nonspherical nature of free volume. The new technique is introduced with reference to simple model fluids (water, hard spheres, and a Lennard‐Jones fluid) and then applied to polymers of interest to membrane scientists. A set of shape parameters is introduced, characterizing nanopores in terms of surface area, volume, radius of gyration, and span. Results are presented for Lennard‐Jones fluid and hard sphere fluid, and for the high free volume polymers (poly‐trimethyl‐silyl‐propane) poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) and a random copolymer of 2,2‐bis(trifluoromethyl)‐4,5‐difluoro‐1,3‐dioxole (TFE/BDD). PTMSP is observed to have an average free volume cluster span of 1.43 nm, compared to TFE/BDD with an average cluster span of 0.98 nm, consistent with the markedly higher permeability of CO₂ observed in PTMSP. An additional method for measuring free volume is introduced, similar to a method introduced by Greenfield and Theodorou (Macromolecules 1993, 26, 5461; Mol Simul 1997, 19, 329; Macromolecules 1998, 31, 7068; 2001, 34, 8541), which measures free volume relative to a specific probe. The method captures 1–3 times the fractional cavity volume captured by CESA. Free volume measurements are presented for a set of polysulfones with respect to noble gas probes (J Chem Phys 2005, 122, 84906; J Mol Struct 2005, 739, 173). © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44:1385–1393, 2006     

The ligand effect in Ti‐mediated living radical styrene polymerizations initiated by epoxide radical ring opening. 2. Scorpionate and half‐sandwich LTiCl3 complexes

The ligand effect and the reaction conditions for the living radical polymerization of styrene initiated by epoxide radical ring opening was investigated in a series of piano‐stool, Ti(IV) scorpionate and, half‐sandwich metallocenes (LTiCl₃; L = Tp, Cp*, Ind and Cp, where Tp = hydrotris(pyrazol‐1‐ylborato), Cp* = pentamethylcyclopentadienyl, Ind = indenyl and Cp = cyclopentadienyl). The polymerization is mediated by the reversible termination of the growing chains with Ti(III) species derived from Zn reduction of parent Ti(IV) derivatives. A poor performance was observed for TpTiCl₃ because of probable over‐reduction. The strong electron donating effect of Cp* accounts for a strong C? Ti chain end bond and consequently, a living‐like process is observed only at T > 110 °C. However, both Ind and Cp ligands provide a linear dependence of M_n on conversion and narrow polydispersity over a wide range of experimental conditions. Investigation of the effect of temperature and reagent ratios generates an optimum for epoxide/CpTiCl₃/Zn = 1/2/4 at 70–90 °C. On the basis of a combination of steric and electronic properties, the ligands rank as Cp ≥ Ind ? Cp* ? Tp. This trend is different from coordination polymerization, and in conjunction with our previous results on Cp₂TiCl₂, further supports a radical mechanism. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6039–6047, 2005     

Finite element analysis of incompressible material by residual energy balancing

Incompressibility is gradually introduced into the finite elements with the mesh refinement in such a way as to balance it with the residual discretization energy in order to ensure fastest convergence to the incompressible solution with best conditioned stiffness matrix to minimize round-off errors in the computations.     

Interactions of metal‐encapsulated fullerenes with solvents

The present investigation reports on the interaction of M@C₆₀(M = Be, Mg, Ca) with solvents (H₂O, CH₃OH, HF, NH₃) using Density Functional Theory calculations. Our computations reveal that the interaction of the fullerene species increases when endohedral metal atoms are inserted into its cavity. The most profound interaction of the fullerene systems is with water and hydrogen fluoride. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Linearization of analytic isochronous centers from a given commutator

In this paper we propose an algorithmic way to get the change of variables that linearizes an analytic isochronous center from a given commutator. Moreover, we use this method in order to obtain the linearization of some isochronous centers of the existent literature.     

Variational Splines and Paley–Wiener Spaces on Combinatorial Graphs

Notions of interpolating variational splines and Paley–Wiener spaces are introduced on a combinatorial graph G. Both of these definitions explore existence of a combinatorial Laplace operator on G. The existence and uniqueness of interpolating variational splines on a graph is shown. As an application of variational splines, the paper presents a reconstruction algorithm of Paley–Wiener functions on graphs from their uniqueness sets.      

Turning Around a Method of Successive Iterations to Yield Closed-Form Solutions for Vibrating Inhomogeneous Bars

In this study, the method of successive approximations is turned around so as to obtain closed form solutions for vibrating inhomogeneous bars. In particular, the method recently developed by the first author for the homogeneous beams is extended for bars.     

Bulk and shear mechanical loss of titania-doped tantala

We report on the mechanical loss from bulk and shear stresses in thin film, ion beam deposited, titania-doped tantala. The numerical values of these mechanical losses are necessary to fully calculate the Brownian thermal noise in precision optical cavities, including interferometric gravitational wave detectors like LIGO. We found the values from measuring the normal mode mechanical quality factors, Q's, in the frequency range of about 2000-10,000 Hz, of silica disks coated with titania-doped tantala coupled with calculating the elastic energy in shear and bulk stresses in the coating using a finite element model. We fit the results to both a frequency independent and frequency dependent model and find ${?}_{\mathrm{shear}}=(8.3\pm 1.1)\times {10}^{?4}$, ${?}_{\mathrm{bulk}}=(6.6\pm 3.8)\times {10}^{?4}$ with a frequency independent model and ${?}_{\mathrm{shear}}\left(f\right)=(5.0\pm 0.7)\times {10}^{?4}+(5.4\pm 1.1)\times {10}^{?8}f$, ${?}_{\mathrm{bulk}}\left(f\right)=(11\pm 2.8)\times {10}^{?4}?(8.7\pm 4.7)\times {10}^{?8}f$ with a frequency dependent (linear) model. The ratio of these values suggest that modest improvement in the coating thermal noise may be possible in future gravitational wave detector optics made with titania-doped tantala as the high index coating material by optimizing the coating design to take advantage of the two different mechanical loss angles.