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941.
Christopher H. Cullen G. Joseph Ray Christina M. Szabo 《Magnetic resonance in chemistry : MRC》2013,51(11):705-713
The performance of three quantitative NMR methods was compared in terms of short‐term and long‐term precision and accuracy, robustness, linear range, and general applicability. The Internal Reference method employs a reference material co‐dissolved with sample; the External Reference method employs a reference material contained in a separate solution; and the third method, known as Electronic REference To access In vivo Concentrations (ERETIC), employs an externally calibrated digital reference peak. The Internal Reference method results were the most precise and remained stable within 0.1% for at least 4 weeks. The results from the External Reference and ERETIC methods were practically equivalent to each other during this time. These methods exhibited small differences relative to the standard set by the Internal Reference method and slightly lower precision, establishing them as practical alternatives to the Internal Reference method. In contrast to the Internal Reference method, the External Reference and ERETIC methods possess several advantages that address peak overlap, flexibility of calibration, and duration of applicability. The study was designed such that each spectrum contained the information needed to compare the three methods while all other variables were kept constant. Applicability of pulse width compensation is addressed. ERETIC software compensation and minor adjustments to 90° pulse width were concluded to be unnecessary for this system. Although each of the methods was applied here to specifically calculate and compare chemical purity values, this evaluation applies generally to absolute quantitation by NMR. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
942.
A. David Baker Mark D. Baker Christopher R. H. Hanusa 《Journal of mathematical chemistry》2011,49(6):1192-1198
Building on work of Tyagi (Progr Theor Phys 114(3):517–521, 2005), we present expressions for calculating the corner ion, edge-center ion, and face-center ion Madelung constants for bulk
sodium chloride crystals. 相似文献
943.
A method for fabricating infrared‐transmitting waveguides that yields low optical losses and strong confinement of light is presented. The method minimises the number of fabrication steps by exploiting the photosensitivity of arsenic trisulfide glass, using it both as a photoresist and as a waveguiding material. Controlled annealing/remelting of the waveguides minimises scattering due to fluctuations in refractive index at the interface between the waveguide and the surrounding medium, allowing low losses to be realised. Bends and Y‐splitter structures have been realised, as well as the longest As2S3 serpentine planar waveguides yet reported. 相似文献
944.
Anna‐Marie Zorn Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2012,50(12):2366-2377
In the present study, n‐butyl acrylate macromonomer (BAMM) (Mn = 1900 g mol?1; PDI = 1.96) has been synthesized via a high‐temperature polymerization process. Subsequently, the olefinic termini of the BAMM have been transformed into a diol via a dihydroxylation process using KMnO4 as an oxidizing agent. The OH‐terminated macroinitiator pBA(OH)2 has subsequently been employed for the ring‐opening polymerization (ROP) of ε‐caprolactone via various catalytic systems, that is, organo‐(1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene), metal (tin(II) 2‐ethylhexanoate), and enzymatic catalysis (Novozym® 435). The obtained pBA‐b‐pCL block copolymers and the initiation efficiency of the BAMM macroinitiator have been investigated via size exclusion chromatography (SEC), electrospray ionization–mass spectrometry (ESI‐MS) hyphenated with SEC and liquid chromatography at the critical conditions of both poly(ε‐caprolactone) (pCL) and pBA. The in vitro enzyme catalysis (eROP) approach proved to be the most efficient catalysis system due to minor transesterification side reactions during the polymerization process. However, side reactions such as transesterifications occur in each catalytic system and—while they cannot be suppressed—they can be minimized. The species generated during the eROP process include the desired block copolymer pBA‐b‐pCL as main species as well as pCL homopolymer and residual macroinitiator pBA(OH)2. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
945.
Dawud H. Tan Chunfeng Zhou Christopher J. Ellison Satish Kumar Christopher W. Macosko Frank S. Bates 《ournal of non Newtonian Fluid Mechanics》2010,165(15-16):892-900
Both melt viscosity (ηo) and elasticity (correlated here with the longest melt relaxation time λ1) were found to control the diameter distribution of meltblown fibers. Fibers were formed by melt blowing binary polystyrene (PS) blends containing widely differing component molecular weights using a custom-built laboratory apparatus. Varying the concentration and molecular weight of a high molecular weight PS provided independent control over ηo and λ1. These rheological parameters influence the average diameter (dav) and the distribution of diameters (coefficient of variation, CV) of meltblown fibers in different ways. Increasing ηo leads to an increase in dav but has little impact on CV. On the other hand, increasing λ1 beyond a threshold value reduces CV while simultaneously increasing dav. A one-dimensional slender-jet theoretical model with both upper convected Maxwell and Phan–Thien and Tanner constitutive equations was developed to investigate the influence of viscoelasticity and processing parameters on the properties of meltblown fibers. This model predicts a strong dependence of fiber diameter on the air shear stress and variations in fiber diameter with viscoelasticity that are in qualitative agreement with the experimental results. We believe these results suggest that carefully controlling the viscoelastic profile of polymers used in melt blowing is a viable approach for producing nanofibers with narrow fiber diameter distributions using current commercial equipment. 相似文献
946.
947.
Christopher Sørum Nebojša Simić Eirik Sundby Bård Helge Hoff 《Magnetic resonance in chemistry : MRC》2010,48(3):244-248
Chemical shift assignment of seven N‐substituted 6‐(4‐methoxyphenyl)‐7H‐pyrrolo[2, 3‐d]pyrimidin‐4‐amines, six of which are fluorinated, have been performed based on 1H, 13C, 19F, and 2D COSY, HMBC and HSQC experiments. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
948.
Andrew L. Korich Amanda R. Walker Christopher Hincke Caitlin Stevens Peter M. Iovine 《Journal of polymer science. Part A, Polymer chemistry》2010,48(24):5767-5774
Boronic acid end‐functionalized polycaprolactone (PCL) polymers were synthesized by ring‐opening polymerization using a pinacol boronate ester‐containing (Bpin) initiator. The polymerization provides access to boron‐terminated polymers (i.e. Bpin‐PCL‐OH) with narrow molecular weight distributions (PDI = 1.09). Postsynthetic manipulation of the polymer's terminal hydroxyl group by copper‐catalyzed azide‐alkyne cycloaddition chemistry provides a series of bis end‐functionalized polymers with significant structural diversity at the termini. Deprotection of the boronate ester end group was accomplished with an acidic solid phase DOWEX resin. The boronate ester deprotection methodology does not result in hydrolysis of the polymeric backbone. The boronic acid‐tipped polymers were converted into star polymer assemblies using thermal dehydration and ligand‐facilitated trimerization. Thermal dehydration of (HO)2B‐PCL‐OAc to the corresponding boroxine‐based star polymer assembly was inefficient and lead to degradation products. Ligand‐facilitated trimerization using either pyridine or 7‐azaindole as the Lewis base was efficient and mild. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
949.
950.