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51.
Corsaro C Spooren J Branca C Leone N Broccio M Kim C Chen SH Stanley HE Mallamace F 《The journal of physical chemistry. B》2008,112(34):10449-10454
Proton nuclear magnetic resonance (1H NMR) experiments have been performed to measure the spin-lattice, T1, and spin-spin, T2, relaxation times of the three functional groups in water/methanol mixtures at different methanol molar fractions (XMeOH=0, 0.04, 0.1, 0.24, 0.5, 1) as a function of temperature in the range 205 K相似文献
52.
In developing countries, subsistence gold mining entails mixing metallic mercury with crushed sediments to extract gold. In this approach, the gold−mercury amalgam is heated to evaporate mercury and obtain gold. Thus, the highly volatile mercury can be absorbed through inhalation, resulting in adverse health effects. Urinalysis can be used to detect mercury, which is excreted in urine and feces, and correlate exposure with toxic effects. The current gold standard analytical methods are based on fluorescence or inductively coupled plasma mass spectrometry methods, but are expensive, time consuming, and are not easily accessible in countries where testing is needed. In this work, we report on a miniature electrochemical sensor that can rapidly detect mercury in urine at levels well below the US Biological Exposure Index (BEI) limit of 50 ppb (μg/L). The sensor is based on a thin-film gold electrode and anodic stripping voltammetry electroanalytical approach. The sensor successfully detected mercury at trace levels in urine, with a limit of detection of ∼15 ppb Hg in the linear range of 20–80 ppb. With the low-cost disposable sensors and portable instrumentation, it is well suited for point-of-care applications. 相似文献
53.
Annese C D'Accolti L Dinoi A Fusco C Gandolfi R Curci R 《Journal of the American Chemical Society》2008,130(4):1197-1204
The challenging hypothesis of a "biphilic" (i.e., electrophilic vs nucleophilic) character for dioxirane reactivity, which envisages that electron-poor alkenes are attacked by dioxiranes in a nucleophilic fashion, could not be sustained experimentally. Rate data, which estimate Hammett "rho" values for the epoxidation of 3- or 4-substituted cinnamonitriles X x Ph-CH=CH-CN, unequivocally allow one to establish that dioxiranes epoxidize electrophilically even alkenes carrying electron-withdrawing groups. The greater propensity of methyl(trifluoromethyl)dioxirane TFDO (1b) to act as an electrophilic oxidant with respect to dimethyldioxirane DDO (1a) parallels the cathode reduction potentials for the two dioxiranes, as measured by cyclic voltammetry. A simple FMO approach for alkene epoxidation is helpful to conceive a likely rationale for the greater oxidizing power of TFDO as compared to DDO. 相似文献
54.
Amorati R Catarzi F Menichetti S Pedulli GF Viglianisi C 《Journal of the American Chemical Society》2008,130(1):237-244
Rotation about the Ar-S bond in ortho-(alkylthio)phenols strongly affects the bond dissociation enthalpy (BDE) and the reactivity of the OH group. Newly synthesized sulfur containing heterocycles 3 and 4, where the -SR group is almost coplanar with the phenolic ring, are characterized by unusually low BDE(O-H) values (79.6 and 79.2 kcal/mol, respectively) and by much higher reactivities toward peroxyl radicals than the ortho-methylthio derivative 1 (82.0 kcal/mol). The importance of the intramolecular hydrogen bond (IHB) in determining the BDE(O-H) was demonstrated by FT-IR experiments, which showed that in heterocycles 3 and 4 the IHB between the phenolic OH group and the S atom is much weaker than that present in 1. Since the IHB can be formed only if the -SR group adopts an out-of-plane geometry, this interaction is possible only in the methylthio derivative 1 and not in 3 and 4. The additive contribution to the phenolic BDE(O-H) of the -SR substituent therefore varies from -3.1 to +2.8 kcal/mol for the in-plane and out-of-plane conformations, respectively. These results may be relevant to understanding the role of the tyrosine-cysteine link in the active site of galactose oxidase, an important enzyme that catalyzes the two-electron aerobic oxidation of primary alcohols to aldehydes. The switching of the ortho -SR substituent between perpendicular and planar conformations may account for the catalytic efficiency of this enzyme. 相似文献
55.
Fattorusso C Stendardo E Appendino G Fattorusso E Luciano P Romano A Taglialatela-Scafati O 《Organic letters》2007,9(12):2377-2380
A nor-caryophyllane derivative, artarborol, has been isolated from wormwood (Artemisia arborescens) and its stereostructure established by using a combination of chemical derivatization, NMR data, molecular modeling, and quantum-mechanical calculations. In particular, comparison of experimental 13C NMR data with a Boltzmann-weighed average of 13C NMR chemical shifts, calculated by ab initio DFT method, supported the stereochemical assignment. 相似文献
56.
57.
Barillari C Taylor J Viner R Essex JW 《Journal of the American Chemical Society》2007,129(9):2577-2587
Water molecules play a crucial role in mediating the interaction between a ligand and a macromolecular receptor. An understanding of the nature and role of each water molecule in the active site of a protein could greatly increase the efficiency of rational drug design approaches: if the propensity of a water molecule for displacement can be determined, then synthetic effort may be most profitably applied to the design of specific ligands with the displacement of this water molecule in mind. In this paper, a thermodynamic analysis of water molecules in the binding sites of six proteins, each complexed with a number of inhibitors, is presented. Two classes of water molecules were identified: those conserved and not displaced by any of the ligands, and those that are displaced by some ligands. The absolute binding free energies of 54 water molecules were calculated using the double decoupling method, with replica exchange thermodynamic integration in Monte Carlo simulations. It was found that conserved water molecules are on average more tightly bound than displaced water molecules. In addition, Bayesian statistics is used to calculate the probability that a particular water molecule may be displaced by an appropriately designed ligand, given the calculated binding free energy of the water molecule. This approach therefore allows the numerical assessment of whether or not a given water molecule should be targeted for displacement as part of a rational drug design strategy. 相似文献
58.
59.
Prof. Francesca Caterina Izzo Matilde Kratter Dr. Austin Nevin Prof. Elisabetta Zendri 《ChemistryOpen》2021,10(9):904-921
Up to 70 % of the oil paintings conserved in collections present metal soaps, which result from the chemical reaction between metal ions present in the painted layers and free fatty acids from the lipidic binders. In recent decades, conservators and conservation scientists have been systematically identifying various and frequent conservation problems that can be linked to the formation of metal soaps. It is also increasingly recognized that metal soap formation may not compromise the integrity of paint so there is a need for careful assessment of the implications of metal soaps for conservation. This review aims to critically assess scientific literature related to commonly adopted analytical techniques for the analysis of metal soaps in oil paintings. A comparison of different analytical methods is provided, highlighting advantages associated with each, as well as limitations identified through the analysis of reference materials and applications to the analysis of samples from historical paintings. 相似文献