Fabrication of birefringent anisotropic model materials

Widely different techniques have been employed in the fabrication of transparent, birefringent, anisotropic model materials. Some of the techniques reported in the technical literature are briefly reviewed. A simple method of fabricating large plates of arbitrary layup is described.     

A class of zero-birefrngent polymers

A class of photoelastically insensitive materials consisting of a blend of rigid and flexible polyesters is described. The mechanical and optical response of these polymers is viscoelastic in character. For a wide range of the compositions, the birefringence changes from positive to negative under constant load or constant displacement. The influence of composition, time under load, and principal stress difference on the birefringence is studied. Isochromatic-fringe development in a diametrally loaded disk shows that a major region of the stressed body becomes optically insensitive after a reasonable period of time under load and remains insensitive for a time sufficiently large for associated photoelastic operations. A typical operating-time band is presented during which the optical response of a model characterized by the fringe order per unit thickness is reasonably small. It appears that this class of photoelastically insensitive materials can be employed to produce composite models with glass-fiber reinforcements. Compared to other zero-birefringent polymers, the present material has the advantage of easier processing (casting and curing), improved adhesion to glass fibers and closer matching of the refractive index with that of glass.     

High visible light-driven photocatalytic activity of large surface area Cu doped SnO<Subscript>2</Subscript> nanorods synthesized by novel one-step microwave irradiation method

The paper investigates the structural, optical and photocatalytic activity of large surface area single crystalline copper (Cu) doped SnO₂ nanorods (NRs) synthesized by a novel one-step microwave irradiation method. Powder X-ray diffraction (XRD) analysis confirms that both pure and Cu doped SnO₂ are tetragonal rutile type structure (space group P42/mnm) formed during the microwave process within 10 min without any post annealing treatment. Transmission electron microscopy (TEM) reveals that the as synthesized Cu doped SnO₂ samples exhibited rod-like shape and the length was less than 80 nm and diameter was about few nanometers. Typical selected-area electron diffraction (SAED) pattern indicates that, the growth direction of Cu–SnO₂ nanorod is along [110] direction. The variety of phonon interaction in the pure and Cu doped SnO₂ is observed by Raman spectroscopy. Electron paramagnetic resonance and X-ray photoelectron spectroscopy (XPS) confirms that the presence of copper and tin as Cu²⁺ and Sn⁴⁺ in state, respectively. The photocatalytic activity was monitored via the degradation of methylene blue (MB) and Rhodamine B (RhB) dyes and the Cu–SnO₂ showed better photocatalytic activity than that of pure SnO₂. This could be attributed to the effective electron–hole separation by surface modification.     

Free radical-mediated aryl amination: convergent two- and three-component couplings to chiral 2,3-disubstituted indolines

5-exo-trig Cyclization of an aryl radical to the nitrogen of an azomethine is used as the key annulating step in a modular preparation of 2,3-cis- and trans-disubstituted indolines. The precursors are readily prepared by phase-transfer-catalyzed Michael addition of a glycine Schiff base to a variety of acceptors. When the more reactive alkylidene malonate Michael acceptors are implemented, a one-pot three-component coupling is possible. The net result is a convergent [3 + 2] coupling strategy for the construction of highly functionalized indolines, a substructure occurring in numerous biologically active natural products.     

Ruthenium and enzyme-catalyzed dynamic kinetic resolution of alcohols

Ruthenium acts as a good catalyst for the racemization reaction of secondary alcohols and amines. Ruthenium-catalyzed racemization is coupled with enzymatic kinetic resolution to prepare chiral compounds in 100% theoretical yield. Ten ruthenium complexes (1–10) act as a good catalyst the for racemization reaction and are also compatible with DKR process. Two other ruthenium complexes [RuCl₂(PPh₃)₃] and [Cp^*RuCl(COD)] are active for racemization reaction but their successful compatibility with DKR has not yet been reported. Ru/γ-Al₂O₃ and Ru–HAP are the heterogeneous catalysts used for the racemization reaction. They have also not been employed for DKR process. Polymer supported ruthenium is employed as a reusable racemization catalyst for aerobic DKR of alcohols.