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81.
82.
George M. Frame 《Analytical and bioanalytical chemistry》1997,357(6):714-722
Weight percents of PCB congeners in Aroclors 1221, 1016, 1242, 1254, 1260, and 1262 were determined by separately averaging resolved peaks quantified against standards of all 209 congeners in 9 HRGC-ECD and 9 HRGC-MS systems. A separate pair of systems provided nearly complete profiles of Aroclors 1232 and 1248. The tabulated values lack sufficient accuracy to qualify the Aroclors as secondary standards for comprehensive, quantitative, congener-specific analyses, but they provide more complete and accurate semi-quantitative characterizations of congener distributions for a larger number of Aroclors than prior publications. 相似文献
83.
Yang J Gitlin I Krishnamurthy VM Vazquez JA Costello CE Whitesides GM 《Journal of the American Chemical Society》2003,125(41):12392-12393
Proteins are functional biopolymers; viewed as molecules, they are also monodisperse polyamides with chemically reactive side chains. This paper describes the use of proteins as starting materials for the synthesis of monodisperse polymers with nonbiological functionalities attached to the side chains. It demonstrates the complete derivatization of amine groups (lysine side chains and N-termini) on three different proteins by addition of activated carboxylate reagents in aqueous solutions containing sodium dedecyl sulfate (SDS), under denaturing conditions. Several different acylating reagents were used to generate derivatized proteins; the resulting compounds constitute a new class of monodisperse, semisynthetic polymers, having the potential for wide variation in the structure of the backbone and of the side chains. Modification of lysozyme on a gram scale demonstrated that the method can generate useful quantities of material. 相似文献
84.
On December 10, 1998, the 102nd anniversary of Alfred Nobels death, in Stockholms Konserthus (Concert Hall), Swedens King Carl XVI Gustav awarded one half of the 1998 Nobel Prize in Chemistry (3,800,000 kronor, about $489,000) to Professor John A. Pople, 73, of Northwestern University, Evanston, Illinois for his development of computational methods in quantum chemistry.The remaining half of the prize, the ne plus ultra of chemistry, was awarded to Professor Walter Kohn, 75, of the University of California, Santa Barbara for his development of the density-functional theory [1–9]. Because of health problems in his family, Kohn was unable to attend the ceremony but presented his Nobel lecture in Stockholm on January 28, 1999. According to the Royal Swedish Academy of Sciences: The laureates have each made pioneering contributions in developing methods that can be used for theoretical studies of the properties of molecules and the chemical processes in which they are involved [7]. 相似文献
85.
Anthony Fratiello George A. Vidulich Clifford Cheng Vicki Kubo 《Journal of solution chemistry》1972,1(5):433-444
A competitive solvation study of Al(ClO4)3, Ga(ClO4)3, In(ClO4)3, UO2(ClO4)2, and UO2(NO3)2 in water-acetone-dimethylsulfoxide (DMSO) and water-acetone-hexamethylphosphoramide (HMPT) mixtures has been carried out by direct H1 and P31 nuclear magnetic resonance (NMR) techniques. At low temperature, proton and ligand exchange are slow enough in these systems to permit the observation of signals for bulk and coordinated molecules of water and the organic bases (DMSO and HMPT). Both DMSO and HMPT compete effectively with water for coordination sites in the Al3+, Ga3+, and In3+ systems, with steric effects dominating the HMPT results. Both Al3+ and In3+ are able to bind a maximum of two to three HMPT molecules, for example. In contrast, UO2+ is solvated selectively by the organic molecules to the allowed maximum of 4 molecules per cation. H1 and P31 NMR spectral results support the formation of only the mono-, tri-, and tetra-HMPT solvation complexes. 相似文献
86.
The NMR chemical shifts of alkali and thallium(I) salts with various monovalent anions have been measured in N-methylformamide solution. Lithium-7 chemical shifts are virtually concentration and counter-ion independent, presumably due to an absence of direct cation-anion interactions. The sodium-23, potassium-39 and cesium-133 chemical shifts of the salts studied depend on the anion and vary linearly with the concentration. The observed behavior can be accounted for by the formation of collisional ion pairs. On the other hand, the thallium-205 chemical shifts of thallium(I) nitrate and perchlorate were anion-dependent and varied non-linearly with the salt concentration. These results are indicative of contact ion pair formation; formation constants were calculated to be 2.6±0.4 M
–1
for TlNO
3
and 1.7±0.5 M
–1
for TlClO
4
. The cesium-133 NMR spectra of several mixed electrolyte systems also have been measured in N-methylformamide solution. The133Cs chemical shifts also change linearly with the concentrations of the salts added to 0.10 M CsI/NMF solutions. The influence of the anions on the chemical shifts is the same as that observed for cesium salts alone. 相似文献
87.
Ligia Bicudo de Almeida Marilene De Vuono Camargo Penteado George Britton Peter Uebelhart Murat Acemoglu Conrad Hans Eugster 《Helvetica chimica acta》1988,71(1):31-32
The 5,6:5′,6′-diepoxy-5,6:5′,6;-tetrahydro-β,β-carotene, isolated from tubers of a white-fleshed variety of sweet potato (Ipomoea batatas LAM .) has been assigned the (5R,6S,5′R,6′S)-chirality on the basis of its HPLC, UV/VIS, and CD data. 相似文献
88.
Using laser-induced fluorescence of ozone (to measure the rate of disappearance of O32) and NO2 titration (to determine O atom concentrations), we have determined bimolecular rate constants for the deactivation by O(3P atoms) of ozone in excited stretching and bending modes. These experiments do not distinguish between deactivation by (a) the exchange of vibrational and translational energy or (b) the chemical reaction O3 + O → 2O2. If the non-reactive pathway (a) is assumed to dominate, then O(3P) is 150 times more effective than O2 in deactivating O23. If chemical reaction (b) is dominant, the bimolecular rate constant for O23 + O(3P) is larger by a factor of 150–1500 than that for ground-state ozone. 相似文献
89.
George S Nangia A Lam CK Mak TC Nicoud JF 《Chemical communications (Cambridge, England)》2004,(10):1202-1203
Crystalline nitrodiphenyl ureas adopt the N-H...O tape alpha-network only when stabilization accrues from the I...O(2)N or C[triple bond]C-H...O(2)N synthon, otherwise the ureanitro motif is preferred; soft, weak interactions can direct polar self-assembly in strong N-HO hydrogen-bonded crystals. 相似文献
90.
Tsutsumi T Amakura Y Nakamura M Brown DJ Clark GC Sasaki K Toyoda M Maitani T 《The Analyst》2003,128(5):486-492
The chemical-activated luciferase expression (CALUX) assay is a reporter gene assay that detects dioxin-like compounds based on their ability to activate the aryl hydrocarbon receptor (AhR) and thus expression of the reporter gene. In this paper, the CALUX assay was examined for its application in the screening of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dioxin-like PCBs) in retail fish. The sample extracts were cleaned up on a sulfuric acid-silica gel column followed by an activated carbon column, and the AhR activity of the separated PCDD/F and dioxin-like PCB fractions was determined using the assay. The quantitative limit for 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) was 0.98 pg ml(-1) (0.19 pg assay(-1) in the standard curve, corresponding to 0.16 pg g(-1) of CALUX-based toxic equivalency (2,3,7,8-TCDD equivalents) in the tested sample. Recovery tests in which dioxins were added to fish samples resulted in acceptable recoveries (77-117%). The CALUX assay performed well in the analysis of dioxins in fish samples and a comparative study revealed a strong correlation between the CALUX assay and high-resolution gas chromatography-high-resolution mass spectrometry analysis for the determination of PCDD/Fs (r = 0.89) and dioxin-like PCBs (r = 0.91) in retail fish (n = 22). These data revealed that the CALUX assay would be a useful screening method for PCDD/Fs and dioxin-like PCBs in retail fish. 相似文献