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1.
Pu Duan Bo Zhi Luke Coburn Christy L. Haynes Klaus Schmidt-Rohr 《Magnetic resonance in chemistry : MRC》2020,58(11):1130-1138
The composition of fluorescent polymer nanoparticles, commonly referred to as carbon dots, synthesized by microwave-assisted reaction of citric acid and ethylenediamine was investigated by 13C, 13C{1H}, 1H─13C, 13C{14N}, and 15N solid-state nuclear magnetic resonance (NMR) experiments. 13C NMR with spectral editing provided no evidence for significant condensed aromatic or diamondoid carbon phases. 15N NMR showed that the nanoparticle matrix has been polymerized by amide and some imide formation. Five small, resolved 13C NMR peaks, including an unusual ═CH signal at 84 ppm (1H chemical shift of 5.8 ppm) and ═CN2 at 155 ppm, and two distinctive 15N NMR resonances near 80 and 160 ppm proved the presence of 5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]pyridine-7-carboxylic acid (IPCA) or its derivatives. This molecular fluorophore with conjugated double bonds, formed by a double cyclization reaction of citric acid and ethylenediamine as first shown by Y. Song, B. Yang, and coworkers in 2015, accounts for the fluorescence of the carbon dots. Cross-peaks in a 1H─13C HETCOR spectrum with brief 1H spin diffusion proved that IPCA is finely dispersed in the polyamide matrix. From quantitative 13C and 15N NMR spectra, a high concentration (18 ± 2 wt%) of IPCA in the carbon dots was determined. A pronounced gradient in 13C chemical-shift perturbations and peak widths, with the broadest lines near the COO group of IPCA, indicated at least partial transformation of the carboxylic acid of IPCA by amide or ester formation. 相似文献
2.
The effect of low-energy ion bombardment on CD4/O2 and CF3X (X=F, Cl, Br) plasma etching has been assessed by applying controlled rf bias voltages on polystyrene (PS) and polymethylmethacrylate (PMMA) samples. In both cases ion bombardment has been found to have a chemical effect. In the case of CF4/O2 discharges, ion bombardment has been found to change the relative etching efficiency of different mixtures. In the case of CF3X plasmas, ion bombardment has been found to alter PMMA and PS etch rates in a different way. In particular, the ratios between CF4 and CF3X (X=Cl, Br) etch rates of PS have been found to decrease with increasing bias voltage. This effect has been tentatively attributed to an ion bombardment-induced enhancement of the reaction between the aromatic ring and halogen molecules formed in CF3Cl and CF3Br discharges. 相似文献
3.
In a previous communication from this laboratory it was reported that benzotriazole reacts with both picryl chloride and picryl fluoride to give 1-picrylbenzotriazole exclusive of any 2-picrylbenzotriazole (3). As an extension of this study we have examined the reactions of benzo[1,2-d:4,5-d′]bistriazole (I) and benzo[1,2-d:4,5-d′]bistriazole-4,8-dione (II) with picryl fluoride. 相似文献
4.
Betty W. Harris Jannie L. Singleton Michael D. Coburn 《Journal of heterocyclic chemistry》1973,10(2):167-171
The condensation of various aminopyrimidines with picryl chloride and picryl fluoride has been investigated as part of our continuing effort in the field of picrylamino-substituted heterocycles. Most of the aminopyrimidines that can tautomerize reacted with picryl fluoride to form picryl derivatives of their imino forms, but they gave picrylamino derivatives when they condensed with picryl chloride. 相似文献
5.
A number of mesoionic thiazolo[3,2-a ]pyrimidine-5,7-diones, isoconjugate mesoionic analogs of xanthinc, were prepared by the condensation of 2-alkylaminothiazoles with bis(2,4,6-trichloro-phenyl)malonate esters. The ground state molecular properties and reactions of these compounds were found to be consistent with predictions based upon previous SCF molecular orbital treatments of the π-systems of these analogs. 相似文献
6.
Treatment of 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one ( 1 ) with picryl fluoride (PkF) in 1-methyl-2-pyrrolidinone (NMP) gave a mixture of a monopicryl and a dipicryl derivative of 1 in a ratio of 2 :1 , respectively, regardless of the initial concentrations of 1 and PkF. The products were identified as 5-nitro-2-picryl-2,4-dihydro-3H-1,2,4-triazol-3-one ( 2 ) by X-ray crystallography and 5-nitro-2,4-dipicryl-2,4-dihydro-3H-1,2,4-triazol-3-one ( 4 ) by 15N labeling experiments. 相似文献
7.
M. D. Coburn G. A. Buntain B. W. Harris M. A. Hiskey K.-Y. Lee D. G. Ott 《Journal of heterocyclic chemistry》1991,28(8):2049-2050
A new synthesis for the title compound that gives an 80% overall yield was developed. Treatment of triaminoguanidine monohydrochloride ( 1 ) with 2,4-pentanedione ( 2 ) gave 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine ( 3 ) in 80–85% yield. Oxidation of 3 with nitric oxide or nitrogen dioxide to 3,6-bis(3,5-dimethyylpyrazol-1-yl)-1,2,4,5-tetrazine ( 4 ) followed by ammonolysis of 4 gave 3,6-diamino-1,2,4,5-tetrazine ( 5 ) in guantitatively yields. 相似文献
8.
The cytolysin is a novel, two-peptide lytic toxin produced by some strains of Enterococcus faecalis. It is toxic in animal models of enterococcal infection, and associated with acutely terminal outcome in human infection. The cytolysin exerts activity against a broad spectrum of cell types including a wide range of gram positive bacteria, eukaryotic cells such as human, bovine and horse erythrocytes, retinal cells, polymorphonuclear leukocytes, and human intestinal epithelial cells. The cytolysin likely originated as a bacteriocin involved with niche control in the complex microbial ecologies associated with eukaryotic hosts. However, additional anti-eukaryotic activities may have been selected for as enterococci adapted to eukaryotic cell predation in water or soil ecologies. Cytolytic activity requires two unique peptides that possess modifications characteristic of the lantibiotic bacteriocins, and these peptides are broadly similar in size to most cationic eukaryotic defensins. Expression of the cytolysin is tightly controlled by a novel mode of gene regulation in which the smaller peptide signals high-level expression of the cytolysin gene cluster. This complex regulation of cytolysin expression may have evolved to balance defense against eukaryotic predators with stealth. 相似文献
9.
Let T f be a Toeplitz operator on the Segal–Bargmann space or the standard weighted Bergman space over a bounded symmetric domain \({\Omega \subset {\bf C}^n}\) with possibly unbounded symbol f. Combining recent results in Bauer et al. (J. Funct. Anal. 259:57–78, 2010), Bauer et al. (J. reine angew. Math. doi: 10.1515/crelle-2015-0016), Issa (Integr. Equ. Oper. Theory 70:569–582, 2011) we show that in the case of uniformly continuous symbols f with respect to the Euclidean metric on C n and the Bergman metric on \({\Omega}\), respectively, the operator T f is bounded if and only if f is bounded. Moreover, T f is compact if and only if f vanishes at the boundary of \({\Omega.}\) This observation substantially extends a result in Coburn (Indiana Univ. Math. J. 23:433–439, 1973). 相似文献
10.
R. A. Coburn 《Journal of heterocyclic chemistry》1971,8(6):881-887
Thirty mesoionic analogs of purin-6-one, -2-one and -2,6-dione have been formulated based upon reported simple monocyclie mesoionic systems and factors influencing their stability. lluckel molecular orbital calculations were performed for these structures employing the ω, ω′ -technique and the variation of resonance integrals with bond orders. The results provide predictions concerning the properties and stability of the analogs, assist the determination of reasonable synthetic goals, and serve as input for more sophisticated theoretical treatments. 相似文献