Phase Transformations and Structural Developments in the Radular Teeth of Cryptochiton Stelleri

During mineralization, the hard outer magnetite‐containing shell of the radular teeth of Cryptochiton stelleri undergoes four distinct stages of structural and phase transformations: (i) the formation of a crystalline α‐chitin organic matrix that forms the structural framework of the non‐mineralized teeth, (ii) the templated synthesis of ferrihydrite crystal aggregates along these organic fibers, (iii) subsequent solid state phase transformation from ferrihydrite to magnetite, and (iv) progressive magnetite crystal growth to form continuous parallel rods within the mature teeth. The underlying α‐chitin organic matrix appears to influence magnetite crystal aggregate density and the diameter and curvature of the resulting rods, both of which likely play critical roles in determining the local mechanical properties of the mature radular teeth.     

Cationic Polymerization of Tetrahydrofuran with Fuming Sulfuric Acid Initiator: Effects of Superacid Salts and Aromatic Compounds on Mn and Yield of the Polymer

Bulk polymerization of tetrahydrofuran was studied to find a facile method for the preparation of polytetramethyleneglycol having molecular weight more than 1000 initiated by fuming sulfuric acid as a main component at -5 to 0°C. Superacid salts, being soluble in tetrahydrofuran, showed excellent activity for increasing the molecular weight. The polymerization initiated by fuming sulfuric acid in combination with sodium trifluoromethane sulfonate was examined under several conditions. It was also found that a mixture of fuming sulfuric acid and an aromatic compound such as benzenesulfonic acid, benzene, and xylene, contributed to an increase in the molecular weight of polymer.     

Vinyl Polymerization by Metal Complexes. XXXI. Initiation by Chitosan-Copper(II) Complex

The polymerization of methyl methacrylate and acrylonitrile can be initiated by the chitosan-copper(II) complex and its monomeric form, glucosamine-copper(II) complex, in the presence of carbon tetrachloride. The chitosan complex system was found to be more active for initiating the polymerization of methyl methacrylate than acrylonitrile at neutral pH. On the other hand, the glucosamine complex system showed no activity at neutral pH region, but had high activity at higher pH, because of the reducing endgroup of the glucosamine. Formation of the copper(II) complexes was studied by pH titration and visible spectroscopy. The relationship between complex formation and the activity for initiating the polymerization is discussed.     

Contracted helix to stretched helix Rearrangement of an aromatic polyacetylene prepared in n‐hexane with [Rh(norbornadiene)Cl]2‐triethylamine catalyst

p‐n‐Heptylphenylacetylene (pHepPA) was stereoregularly polymerized in n‐hexane at 25 °C using [Rh(nbd)Cl]₂ catalyst (nbd: norbornadiene) and NEt₃, affording the purple‐red Poly( R ) in 97% yield. A 80 °C heat treatment transformed Poly( R ) to the black Poly( B ). The Poly( R ) X‐ray diffraction (XRD) pattern revealed a hexagonal crystal structure comprising contracted cis‐cisoid helices [ ^Hexa Poly( R ) ^CC ]. The 80 °C heat treatment generated two tetragonal crystals: ^Tetra Poly( B ) ^CC containing contracted cis‐cisoid helices and ^Tetra Poly( B ) ^CT containing stretched cis‐transoid helices. The helical diameters before and after heat treatment were estimated using XRD and were consistent with molecular mechanics calculations (MMFF94 force field method). When heated at 80 °C in the solid phase, the λ_max in the diffuse reflective UV–vis spectra of ^Hexa Poly( R ) ^CC shifted from 482 to 560 nm. Additionally, an endothermic transition occurred in the ^Hexa Poly( R ) ^CC differential scanning calorimetric trace at ～80 °C. Therefore, these data corroborated the assertion that ^Hexa Poly( R ) ^CC thermally converted to ^Tetra Poly( B ) ^CC and ^Tetra Poly( B ) ^CT . © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5177–5183     

Stereoselective approach to potential scaffold of A-nor B-aromatic OSW-1 analogues via [4+2] cycloaddition of o-quinodimethane

A-nor B-aromatic steroidal skeleton was efficiently constructed by means of o-quinodimethane chemistry with exclusive stereoselectivity. The benzocyclobutene substrate for generation of the o-quinodimethane intermediate and subsequent [4+2] cycloaddition could be synthesized via (E)-selective Julia–Kocienski olefination and diastereoselective Grignard addition reactions. The synthesized tricyclic steroid-like compound with a trans-diol substructure would be utilized for divergent syntheses of potentially antitumor OSW-1 analogues with the truncated steroidal aglycone.     

Laser-Induced Diffraction Rings from an Absorbing Solution

We observed multiple diffraction rings of a cw Ar⁺ laser beam from a nitrobenzene solution of saturable absorber BDN (bis-(4-dimethylaminodithiobenzil)-nickel) caused by the spatial self-phase modulation at low incident optical intensities. We obtained 37 rings for a 200-μm thick sample at an optical intensity of 38 W/mm². The refractive-index change Δ;n and effective nonlinear refractive index n₂ were determined from the number of observed rings and by the z-scan technique. We obtained large values of Δ;n∼0.1 and n₂ = -2.9×;10^-5 cm²/W. This large nonlinearity is attributed to a thermal effect resulting from linear absorption.