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41.
Hendrik De Cooman Tim Desmet Freddy Callens Peter Dubruel 《Journal of polymer science. Part A, Polymer chemistry》2012,50(11):2142-2149
Electron paramagnetic resonance (EPR) measurements were performed on poly‐ε‐caprolactone (PCL) films at different stages of the postplasma‐grafting process. PCL films prepared by solvent casting (SC) or electrospinning (ESP) yield very similar EPR spectra after Ar‐plasma treatment and subsequent exposure to air, but the EPR signal is much stronger in the PCL‐ESP films. The free radicals appear to be mainly, and possibly exclusively, oxygen centered. The radicals generated by UV irradiation in PCL‐ESP films were studied in situ with EPR, using a UV‐LED (λ = (285 ± 5) nm). Their EPR spectrum is distinctly different from the plasma‐induced signal, indicative of carbon‐centered radicals, and appears to be independent of the plasma pretreatment. UV‐induced homolytic splitting of (hydro)peroxide bonds was not observed. Both the plasma‐ and UV‐induced radicals decay at room temperature (RT), even in an inert atmosphere. This study demonstrates the potential of electrospun films and UV‐LEDs for the study of plasma‐ and UV‐generated free radicals with EPR in polyesters, and raises questions with respect to the validity of some generally accepted molecular mechanisms underpinning the postplasma grafting technique for polyesters. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
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Daniel Townsend Prof. Dr. Kenneth Shankland Dr. Alex Weymouth-Wilson Dr. Zofia Komsta Dr. Tim Evans Dr. Alexander J. A. Cobb 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(16):3504-3508
A highly enantioselective, organocatalytic, and scalable synthesis of a very unusual cis-decalin-cis-hydrindane tricyclic diterpenoid system has been achieved. Despite the prevalent pharmacological space that the related trans,trans and trans,cis-systems occupy, there have been no reports of an asymmetric synthesis of the cis,cis systems in the literature until now. We demonstrate the flexibility of our approach not only through access to a diverse range of products, all of which are attained in exceptionally high selectivities, but also by showing their easy conversion to the corresponding trans,cis-system and other derivatives. 相似文献
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Dr. Tim Schleif Dr. Jörg Tatchen Julien F. Rowen Frederike Beyer Prof. Dr. Elsa Sanchez-Garcia Prof. Dr. Wolfram Sander 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(46):10452-10458
The Cope rearrangement of selectively deuterated isotopomers of 1,5-dimethylsemibullvalene 2 a and 3,7-dicyano-1,5-dimethylsemibullvalene 2 b were studied in cryogenic matrices. In both semibullvalenes the Cope rearrangement is governed by heavy-atom tunneling. The driving force for the rearrangements is the small difference in the zero-point vibrational energies of the isotopomers. To evaluate the effect of the driving force on the tunneling probability in 2 a and 2 b , two different pairs of isotopomers were studied for each of the semibullvalenes. The reaction rates for the rearrangement of 2 b in cryogenic matrices were found to be smaller than the ones of 2 a under similar conditions, whereas differences in the driving force do not influence the rates. Small curvature tunneling (SCT) calculations suggest that the reduced tunneling rate of 2 b compared to that of 2 a results from a change in the shape of the potential energy barrier. The tunneling probability of the semibullvalenes strongly depends on the matrix environment; however, for 2 a in a qualitatively different way than for 2 b . 相似文献
45.
Rob Turner Sean Robert Wevrett Suzanne Edmunds Marc Brown Robert Atkinson Tim Shea 《Biomedical chromatography : BMC》2019,33(8)
The aim of this investigation was to develop receiver and extraction fluids, and subsequently validate an analytical method to quantify the permeation and penetration of flurbiprofen into human pharynx tissue using a Franz diffusion cell. The solubility and stability of flurbiprofen in a suitable receiver fluid, and a suitable extraction method and fluid to recover and quantitate flurbiprofen from human pharynx tissue, were investigated using high‐performance liquid chromatography (HPLC). The potential interference of human pharynx tissue in the receiver fluid was also investigated. The HPLC analytical method was successfully validated according to current guidelines. The final receiver fluid demonstrated sufficient solubility and stability, and the extraction method and fluid resulted in >95% recovery of flurbiprofen following exposure to human pharynx tissue. The lower limit of quantitation of flurbiprofen was 0.045 μg/mL in both the receiver and extraction fluids. There was no interference of the human pharynx tissue with the HPLC method. This investigation validated an analytical method for quantitating flurbiprofen, and determined a suitable receiver fluid and extraction method and fluid, which can be used to investigate the permeation and penetration of flurbiprofen through human pharynx tissue using the Franz diffusion cell method. 相似文献
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Chelsea Weir Michelle L. Pantoya Gautham Ramachandran Tim Dallas Daniel Prentice Michael Daniels 《Journal of Electrostatics》2013,71(1):77-83
Composite energetic material response to electrical stimuli was investigated and a correlation between electrical conductivity and ignition sensitivity was examined. The composites consisted of micrometer particle aluminum combined with another metal, metal oxide, or fluoropolymer. Of the nine tested mixtures, aluminum (Al) with copper oxide (CuO) was the only mixture to ignite by electrostatic discharge. Under the loose powder conditions of these experiments, the Al–CuO minimum ignition energy (MIE) is 25 mJ and exhibited an electrical conductivity two orders of magnitude higher than the next composite. This study showed a similar trend in MIE for ignition triggered by a discharged spark compared with a thermal hot wire source. 相似文献
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Ming-Sin Cheung Mahon L. Maguire Tim J. Stevens R. William Broadhurst 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2010,202(2):223-233
This paper introduces DANGLE, a new algorithm that employs Bayesian inference to estimate the likelihood of all possible values of the backbone dihedral angles ? and ψ for each residue in a query protein, based on observed chemical shifts and the conformational preferences of each amino acid type. The method provides robust estimates of ? and ψ within realistic boundary ranges, an indication of the degeneracy in the relationship between shift measurements and conformation at each site, and faithful secondary structure state assignments. When a simple degeneracy-based filtering procedure is applied, DANGLE offers an ideal compromise between accuracy and coverage when compared with other shift-based dihedral angle prediction methods. In addition, per residue analysis of shift/structure degeneracy has potential to be a useful new approach for studying the properties of unfolded proteins, with sufficient sensitivity to identify regions of residual structure in the acid denatured state of apomyoglobin. 相似文献