Formation of an Imino‐Stabilized Cyclic Tin(II) Cation from an Amino(imino)stannylene

The novel amino(imino)stannylene 1 was prepared by conversion of HNIPr (NIPr=bis(2,6‐diisopropylphenyl)imidazolin‐2‐imino) with one equivalent of Lappert’s tin reagent (Sn[N(SiMe₃)₂]₂). Treatment of 1 with DMAP (4‐dimethylaminopyridine) yields its Lewis acid–base adduct 2 . The reaction of 1 with one equivalent of trimethylsilyl azide results in replacement of the amino group at the tin center by an N₃ substituent with concomitant elimination of N(SiMe₃)₃ to afford dimeric [N₃SnNIPr]₂ ( 3 ). Remarkably, the reaction of 1 with B(C₆F₅)₃ produces the novel tin(II) monocation 4 ⁺[MeB(C₆F₅)₃]^? comprising a four‐membered stannacycle through methyl‐abstraction from the trimethylsilyl group.     

Effect of chain architecture on the phase transition of star and cyclic poly(N‐isopropylacrylamide) in water

The heat‐induced phase transition of aqueous solutions of Poly(N‐isopropylacrylamide) (PNIPAM) in water is examined for a four‐arm PNIPAM star (s‐PNIPAM), a cyclic PNIPAM (c‐PNIPAM), and their linear counterparts (l‐PNIPAM) in the case of polymers (1.0 g L^?1) of 12,700 g mol^?1 < M_n < 14,700 g mol^?1. Investigations by turbidity, high‐sensitivity differential scanning calorimetry (HS‐DSC), and light scattering (LS) indicate that the polymer architecture has a strong effect on the cloud point (T_c: decrease for s‐PNIPAM; increase for c‐PNIPAM), the phase transition enthalpy change (ΔH decrease for s‐PNIPAM and c‐PNIPAM), and the hydrodynamic radius of the aggregates formed above T_c (R_H: c‐PNIPAM < s‐PNIPAM < l‐PNIPAM). The properties of s‐PNIPAM are compared with those of previously reported PNIPAM star polymers (3 to 52 arms). The overall observations are described in terms of the arm molecular weight and the local chain density in the vicinity of the core of the star, by analogy with the model developed for PNIPAM brushes on nanoparticles or planar surfaces. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2059–2068.     

Extrinsic two dimensional excitons and their high density effects in BiI3 single crystals

Sharp absorption lines near the fundamental edge caused by planar stacking faults in BiI₃ crystals have been investigated on absorption and luminescence spectra. Under high excitation-photon densities these lines show peak-shift and line broadening. The high density effects on the exciton bound at the defects shows a two-dimensional feature of the exciton motion.     

Enantiomer-selective radical cyclopolymerization of rac-2,4-pentanediyl dimethacrylate using a ruthenium-mediated chiral atom transfer radical polymerization initiating system

The enantiomer-selective radical polymerization of rac-2,4-pentanediyl dimethacrylate, an equimolar mixture of (2S,4S)-2,4-pentanediyl dimethacrylate (SS- 1 ) and (2R,4R)-2,4-pentanediyl dimethacrylate (RR- 1 ), was carried out with a chiral atom transfer radical polymerization initiating system consisting of methyl 2-bromoisobutyrate ( 3 ), dichlorotris(triphenylphosphine)ruthenium [RuCl₂(PPh₃)₃], and a chiral additive in anisole at 60 °C. When (S)-1,1′-bi-2-naphthol ( a-3 ) was used as the chiral additive, the recovered monomer was enriched in SS- 1 , and the enantiomeric excess was 16.9% at a 22.6% monomer conversion. The specific rotation ([α]₄₃₅, c 0.3, CHCl₃) of the resulting polymer was +40.3° at a 22.6% monomer conversion. For the copolymerization of SS- 1 and RR- 1 with 3 /RuCl₂(PPh₃)₃/ a-3 in anisole at 60 °C, the monomer reactivity ratio for RR- 1 (r_R) was determined to be 4.94, and that for SS- 1 (r_S) was 0.27. For the homopolymerizations of SS- 1 and RR- 1 with 3 /RuCl₂(PPh₃)₃/ a-3 in anisole at 60 °C, the polymerization rate of RR- 1 was considerably faster than that of SS- 1 , and the rate constants for the homopolymerizations were determined to be k_SS = 2.0 × 10⁻³ h⁻¹ and k_RR = 8.2 × 10⁻³ h⁻¹, respectively. With the values of k_SS, k_RR, r_R, and r_S, the relative ratio k_SS/k_RR/k_SR/k_RS was determined to be 1.2:4.9:4.5:1, which indicated that both the growing end of SS- 1 and that of RR- 1 preferentially reacted with RR- 1 . © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4563–4569, 2004     

Evaluating Optical Quality of a Bifocal Soft Contact Lens in Near Vision Using a Shack–Hartmann Wavefront Aberrometer

To assess optical characteristics of bifocal soft contact lenses (BCLs) in use, we measured wavefront aberrations of human eyes, of eyes with a monofocal soft contact lens (MCL), and of eyes with a BCL. Modulation transfer functions (MTFs), Strehl ratios, and simulated images for far and near vision were produced with the measured aberrations. High order aberrations of subject 1 were significantly smaller than those of subject 2 (t-test, P = 0.001). We found that wearing the BCL improved the optical quality of an eye in subject 1, expressed as the horizontal MTF from 2 to 48 cycles per degree (cpd) for near vision and the Strehl ratio (t-test, P = 0.009 for Strehl ratio). But we did not find the same effect in subject 2. This difference may be due to the difference in the aberrations of the eyes of the two subjects.     

Voltammetric study of the transfer of polyammonium ions at nitrobenzene / water interface.

The transfer of polyammonium ions, poly[(dimethylimino)-1,6-hexanediyl] (n = 140, n being the degree of polymerization) ion and poly[(dimethylimino)(2-oxo-1,2-ethanediyl)imino-alpha,omega-alkanediylimino(1-oxo-1,2-ethanediyl)(dimethylimino)-alpha',omega'-alkanediyl] ([-N+ (CH3)2CH2CONH(CH2)x NHCOCH2N+ (CH3)2(CH2)y-]n, x = 2, 3, 4, or 6, y = 3 or 6, and n = 30-130) ions, at a polarizable nitrobenzene / water interface has been studied by normal pulse voltammetry and cyclic voltammetry. Despite the polydispersity of the preparations, by normal pulse voltammetry, an S-shaped current-potential curve with a well-defined limiting current, and, by cyclic voltammetry, a pair of anodic and cathodic peak currents due to the transfer of polyammonium ions across the interface were observed within the potential window. The voltammetric behavior is described. Also, the effect of ion-pair formation of the polyammonium ions with supporting electrolyte anions in nitrobenzene- and water-phases on the half-wave or midpoint potential of the ion-transfer, and the relation between the structure of the polyammonium ions and the transfer potentials are discussed.     

Voltammetric study of the transfer of fluoride ion at the nitrobenzene / water interface assisted by tetraphenylantimony.

The transfer of F- ion assisted by an organometallic complex cation tetraphenylantimony (TPhSb+) across the polarized nitrobenzene / water (NB / W) interface has been studied by means of ion-transfer voltammetry. A well-defined voltammetric wave was observed within the potential window at the NB / W interface when tetraphenylantimony tetrakis(4-chlorophenyl) borate and F- ion were present in NB and W, respectively. The voltammogram can be interpreted as being due to the reversible transfer of F- ion assisted by the formation of the TPhSbF complex through the coordination of F- to Sb atom in NB. The formal formation constant of TPhSbF in NB has been determined to be 10(1.95 +/- 0.2 M(-1). No voltammetric wave due to the TPhSb(+)-assisted transfer of other anions such as Cl-, Br, I-, NO3-, CH3COO- and H2PO4(-) ions has been observed within the potential window.     

Halogen-free water-immiscible ionic liquids based on tetraoctylammonium cation and dodecylsulfate and dodecylbenzenesulfonate anions, and their application as chelate extraction solvent.

The tetraoctylammonium cation forms water-immiscible room temperature ionic liquids with dodecylsulfate and dodecylbenzenesulfonate anions. The ionic liquids are halogen-free and can be considered environmentally friendly solvents. At 25 degrees C, the solubilities of water in tetraoctylammonium dodecylsulfate and tetraoctylammonium dodecylbenzenesulfonate were 2.8 and 4.0%, respectively, and the densities were 0.92 and 0.93 g cm(-3). The ionic liquids formed stable interfaces with water at 25 degrees C. The possible use of tetraoctylammonium dodecylsulfate as chelate extraction solvent was evaluated by using 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione as extractant. Tetraoctylammonium dodecylsulfate showed high extraction performance for divalent transition metal cations.