Immobilization of chiral ligands on polymer fibers by electron beam induced grafting and applications in enantioselective catalysis

[reaction: see text] Styrenic TADDOL and L-prolinol-derived monomers were immobilized on polyethylene fibers by electron beam induced preirradiation grafting using styrene as comonomer. The polymer-supported chiral ligands were utilized as catalysts in the asymmetric addition of diethylzinc to benzaldehyde. Fiber-bound titanium TADDOLate gave a quantitative conversion of benzaldehyde to 1-phenylpropan-1-ol in a 97:3 S/R enantiomeric ratio. The catalyst was successfully regenerated and employed in subsequent reactions with retention of high enantioselectivities.     

Analysis of the ν2 + ν3 band of 12CH4 and 13CH4

The ν₂ + ν₃ bands of ¹²CH₄ and ¹³CH₄ occurring in the region 4400–4650 cm^?1 have been studied from spectra recorded with a high-resolution Fourier transform spectrometer (resolution better than 0.01 cm^?1). Champion's Hamiltonian expansion, Canad. J. Phys.55, 1802 (1977), is applied to the problem of the two interacting F₁ and F₂ vibrational sublevels of this type of a band. As the P branch of ν₂ + ν₃ is strongly overlapped by neighboring bands, a combination-difference method, adapted to tetrahedral XY₄ molecules has been developed to help assignments of lines. A fit of 700 transitions has been performed using 13 new effective constants in the case of ¹²CH₄. In the case of ¹³CH₄, 532 transitions have been fit to 18 constants. The known parameters, relative to the vibrational ground state and the ν₃ state for both methanes, and the ν₂ state for ¹²CH₄ were fixed throughout. Most of the perturbed levels, up to J′ = 12, are well reproduced and the general agreement between experimental and calculated transitions is satisfactory with standard deviations of 0.047 cm^?1 (¹²CH₄) and 0.041 cm^?1 (¹³CH₄). The results (order of magnitude of obtained (ν₂ + ν₃) parameters and comparison of observed and computed intensities) indicate that the ν₂ + ν₃ band is perturbed by many other bands.     

A colorimetric probe for ascorbic acid based on copper-gold nanoparticles in electrospun nylon

We report on a colorimetric probe based on copper-gold alloy nanoparticles (NPs). The probe is capable of selectively detecting ascorbic acid (AA) as a result of the distance-dependent colour change of the nanoparticles immobilized in an electrospun nylon-6 nanofiber. The resulting white nanofibres undergo a colour change to blue as a result of the aggregation of the NPs induced by AA in the pH range 2–7. The probe is selective for AA even in the presence of dopamine, uric acid, saccharides, amino acids and certain organic acids. It covers the 1.76 x10^?2 mg L^?1 to 1.76 x10⁵ mg L^?1 concentration range, and exhibits a limit of detection of 1.76 x10^?2 mg L^?1 based on visual detection. Its application was demonstrated by the determination of ascorbic acid in fruit juices, urine, serum, and vitamin C tablets.