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31.
A paradigm shift in rate determining step from single electron transfer between phenylsulfinylacetic acids and iron(III) polypyridyl complexes to nucleophilic attack of water to the produced sulfoxide radical cation: a non‐linear Hammett
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Perumal Subramaniam Jebamoney Janet Sylvia Jaba Rose Rajasingh Jeevi Esther Rathinakumari 《Journal of Physical Organic Chemistry》2016,29(10):496-504
Mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAAs) by iron(III) polypyridyl complexes in aqueous acetonitrile medium has been investigated spectrophotometrically. An initial intermediate formation between PSAA and [Fe(NN)3]3+ is confirmed from the observed Michaelis–Menten kinetics and fractional order dependence on PSAA. Significant rate retardation with concentration of [Fe(NN)3]3+ is rationalized on the basis of coordination of a water molecule at the carbon atom adjacent to the ring nitrogen of the metal polypyridyl complexes by nucleophilic attack at higher concentrations. Electron‐withdrawing and electron‐releasing substituents in PSAA facilitate the reaction and Hammett correlation gives an upward ‘V’ shaped curve. The apparent upward curvature is rationalized based on the change in the rate determining step from electron transfer to nucleophilic attack, by changing the substituents from electron‐releasing to electron‐withdrawing groups. Electron‐releasing substituents in PSAA accelerate the electron transfer from PSAA to the complex and also stabilize the intermediate through resonance interaction leading to negative reaction constants (ρ). Conversely, electron‐withdrawing groups, while retarding the electron transfer exert an accelerating effect on the nucleophilic attack of H2O which leading to low magnitude of ρ+ compared to high ρ? values of electron‐releasing groups. Marcus theory is applied, and a fair agreement is seen with the experimental values. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Casey A. Dougherty Joseph C. Furgal Dr. Mallory A. van Dongen Prof. Theodore Goodson III Prof. Mark M. Banaszak Holl Dr. Janet Manono Prof. Stassi DiMaggio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4638-4645
Fluorescent dyes are commonly conjugated to nanomaterials for imaging applications using stochastic synthesis conditions that result in a Poisson distribution of dye/particle ratios and therefore a broad range of photophysical and biodistribution properties. We report the isolation and characterization of generation 5 poly(amidoamine) (G5 PAMAM) dendrimer samples containing 1, 2, 3, and 4 fluorescein (FC) or 6‐carboxytetramethylrhodamine succinimidyl ester (TAMRA) dyes per polymer particle. For the fluorescein case, this was achieved by stochastically functionalizing dendrimer with a cyclooctyne “click” ligand, separation into sample containing precisely defined “click” ligand/particle ratios using reverse‐phase high performance liquid chromatography (RP‐HPLC), followed by reaction with excess azide‐functionalized fluorescein dye. For the TAMRA samples, stochastically functionalized dendrimer was directly separated into precise dye/particle ratios using RP‐HPLC. These materials were characterized using 1H and 19F NMR spectroscopy, RP‐HPLC, UV/Vis and fluorescence spectroscopy, lifetime measurements, and MALDI. 相似文献
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Jizhong Zhou Anthony V. Palumbo Janet M. Strong 《Applied biochemistry and biotechnology》1999,80(3):243-253
Two bacterial communities (NO92 and GBS) capable of degrading carbon tetrachloride (CT) were enriched from in-house CT-contaminated
water. These communities are able to degrade CT in the presence of toluene. To characterize the community structure and diversity,
one enrichment (NO92) was subjected to 16S ribosomal RNA (rRNA) gene-based molecular analysis. The 16S rRNA genes were amplified
from the bulk genomic community DNA and cloned into plasmid vectors. Unique 16S rRNA gene clones, i.e., phylotypes, were detected
by four tetrameric restriction enzymes. Together, 123 16S rRNA gene clones were obtained; thirty-one showed different restriction
fragment length polymorphism (RFLP) patterns. About 73% of the clones belong to two dominant RFLP patterns. Phylogenetic analysis
based on the partial 16S rRNA gene sequences of 10 major phylotypes showed that all the phylotypes that were sequenced were
affiliated with the high G+C Gram-positive bacteria. Whereas seven of the phylotypes (∼80% of the clones) were closely related
to Rhodococcus, the other three (∼5% of the clones) were related to Curtobacterium. These results suggest that this CT-degrading community is diverse but is predominated by closely related bacterial groups. 相似文献
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There is a class of data compression techniques that involve replacing repeating strings by pointers to previous occurrences of those strings. In order to implement these techniques, it would be useful to have an index which can quickly locate repeats within a fixed window of the text seen so far. One such index is the directed acyclic word graph (DAWG). An algorithm is presented which constructs the DAWG for a fixed window of k letters moving from left to right along the input text. It is shown that this algorithm has worst case behavior proportional to nk, where n is the length of the input text and k is the size of the window. This bound is the best possible for a window moving through the DAWG and also for a window moving through the suffix tree, a functionally related structure. The average case for the algorithm is analyzed under the assumption that input strings are random texts constructed from a fixed alphabet where each letter has equal probability. The resulting upper bound is O(nlogk). 相似文献
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Ernesto C. Tuazon Pilar Martin Sara M. Aschmann Janet Arey Roger Atkinson 《国际化学动力学杂志》2011,43(11):631-638
Rate constants for the reactions of 2‐methoxy‐6‐(trifluoromethyl)pyridine, diethylamine, and 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol with OH radicals have been measured at 298 ± 2 K using a relative rate method. The measured rate constants (cm3 molecule?1 s?1) are (1.54 ± 0.21) × 10?12 for 2‐methoxy‐6‐(trifluoromethyl)pyridine, (1.19 ± 0.25) × 10?10 for diethylamine, and (1.76 ± 0.38) × 10?12 for 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol, where the indicated errors are the estimated overall uncertainties including those in the rate constants for the reference compounds. No reaction of 2‐methoxy‐6‐(trifluoromethyl)pyridine with gaseous nitric acid was observed, and an upper limit to the rate constant for the reaction of 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol with O3 of <7 × 10? 20 cm3 molecule?1 s?1 was determined. Using a 12‐h average daytime OH radical concentration of 2 × 106 molecule cm?3, the lifetimes of the volatile organic compounds studied here with respect to reaction with OH radicals are 7.5 days for 2‐methoxy‐6‐(trifluoromethyl)pyridine, 1.2 h for diethylamine, and 6.6 days for 1,1,3,3,3‐pentamethyldisiloxan‐1‐ol. Likely reaction mechanisms are discussed. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 631–638, 2011 相似文献
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