Synthesis and polymerization of a new nitrogen‐containing bis‐ortho‐diynylarene monomer

This study focuses on the preparation, characterization, and optical properties of new bis(3,4‐diphenylethynylphenyl)phenylamine. This is the first nitrogen‐containing bis‐ortho‐diynylarene (BODA) monomer having a nitrogen atom as the spacer group. BODA monomers are usually prepared from common bisphenols, thereby providing great synthetic versatility and the opportunity to develop a wide array of novel polyarylene thermosets by varying the aromatic spacer group. The new bis(3,4‐bisphenylethynylphenyl)phenylamine was synthesized in five steps. This compound emits an intense blue color (λ = 438 nm) upon irradiation by UV light and may be suitable for use as an emitting layer in electroluminescent devices. Bis‐(3,4‐bisphenylethynylphenyl)phenylamine and its polymer have photoluminescence quantum yields 34 and 38%, respectively, and long excited‐state lifetimes of 3.2 and 3.6 ns, respectively. The structure of the monomer and its polymer were characterized using spectroscopic techniques including Ultraviolet–visible Spectrophotometer, Photoluminescence Spectrophotometer, Fourier Transform infrared spectroscopy, and Gel Permeation Chromatography. The polymerizations were studied by Differential Scanning Calorimeter. The amount of weight loss and the thermostability of the nitrogen‐containing polymer were determined from thermogravimetric analysis. The electrical conductivity of neat HCl‐doped BODA‐derived polymer film was measured according to the standard four‐point probe technique. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6988–6996, 2006     

Practical syntheses of [1,3,5]‐triazine dendritic molecules on solid supports

A practical and divergent synthesis of supported [1,3,5]‐triazine dendritic molecules on Wang resin, PEGA resin, SynPhase? Lanterns, and silica gel is described. The alkylamine linkers used allow derivatization with functionality for both synthetic (e.g., supported reagent and scavenger activity) and chemical biology applications. The use of supported intermediates allows differentiation of symmetric linkers without the need for protecting group chemistry. The synthetic route uses inexpensive, readily available starting materials in a straightforward and scaleable strategy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2248–2259, 2006     

On the multi-attribute stopping problem with general value functions

We examine a sequential selection problem in which a single option must be selected. Each option's value is a function of its attributes, whose precise values can be ascertained at a given cost. We prove the optimality of a threshold stopping rule for a general class of objective functions.     

Investigation by EPR and ENDOR spectroscopy of the novel 4Fe ferredoxin fromPyrococcus furiosus

The hyperthermophilic archaeonPyrococcus furiosus contains a four-Fe ferredoxin (Pf- Fd) that differs from most other 4Fe-Fd’s in that its [Fe₄S₄] cluster is anchored to protein by only three cysteinyl residues.Pf- Fd also is of interest because in its reduced form, [Fe₄S₄]⁺, the cluster exhibits bothS = 1/2 andS = 3/2 spin states. Addition of excess cyanide ion converts the cluster exclusively to anS = 1/2 state (g₁ = 2.09, g₂ = 1.95, g₃ = 1.92), however dialysis restores the EPR signal of native reduced protein indicating that the cluster is not irreversibly altered by cyanide. Both the native protein and protein in the presence of excess cyanide ion (Pf- Fd 4Fe-CN) were investigated here using the techniques of electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy. In particular,Pf- Fd 4Fe-CN was investigated using¹³CN^? and C¹⁵N^? ligands.¹³C and¹⁵N ENDOR indicated that a single cyanide ion bound directly, with the cluster showing an unusually small contact interaction (a_iso(¹³C)～ ?3 MHz, a_iso(¹⁵N) ～ 0). This is in contrast to cyanide bound to monomeric low-spin Fe(III)-containing proteins such as transferrin and myoglobin, for which the¹³C hyperfine coupling has a large isotropic component (a_iso(¹³C) ≈ ?30 MHz). This small contact interaction is not due to low spin density of Fe, as⁵⁷Fe ENDOR of the singly and triply labeledPf- Fd 4FeCN isotopologs, [⁵⁷FeFe₃S₄]⁺ and [Fe⁵⁷Fe₃S₄]⁺, show hyperfine coupling characteristic for [Fe₄S₄]⁺ clusters, particularly for the Fe to which cyanide binds. Thus, the low spin density on¹³C is not due to low spin density on the Fe ion to which it binds. Further theoretical work is needed to explain the contrast between the strong electronic effect of cyanide ion binding with the low spin density on the ligand.     

Radiative characteristics of pulsed power driven Z-pinch aluminumplasmas

In this paper, we study the dynamics of a massive aluminum Z-pinch plasma load and evaluate its performance as a soft X-ray radiator. A radiation hydrodynamic model self-consistently driven by a circuit describes the dynamics. Comparisons are made for the K- and L-shell soft X-ray emission as a function of the ionization dynamic model. The ionization dynamic models are represented by: 1) a time-dependent nonequilibrium (NEQ) model, 2) a collisional radiative equilibrium (CRE) model, and 3) a local thermodynamic equilibrium (LTE) model. For all three scenarios the radiation is treated 1) in the free streaming optically thin approximation where the plasma is treated as a volume emitter and 2) in the optically thick regime where the opacity for the lines and continuum is self-consistently calculated online and the radiation is transported through the plasma. Each simulation is carried out independently to determine the sensitivity of the implosion dynamics to the ionization and radiation model, i.e., how the ionization dynamic model affects the radiative yield and emission spectra. Results are presented for the L- and K-shell radiation yields and emission spectra as a function of photon energy from 10 eV to 10 keV. Also, departure coefficients from LTE are presented for selected levels and ionization stages