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101.
Ashish Kumar Yahya E. Jad Ayman El-Faham Beatriz G. de la Torre Fernando Albericio 《Tetrahedron letters》2017,58(30):2986-2988
Herein, we report the use of γ-valerolactone (GVL) and N-formylmorpholine (NFM) as DMF substitutes in polystyrene based SPPS. The solubility of selected amino acids and coupling reagents were studied in GVL and NFM, followed by their use in the successful synthesis of Aib-enkephalin pentapeptide (H-Tyr-Aib-Aib-Phe-Leu-NH2) and Aib-ACP decapeptide (H-Val-Gln-Aib-Aib-Ile-Asp-Tyr-Ile-Asn-Gly-NH2). 相似文献
102.
Vapor–liquid equilibria (VLE) data at 100 kPa have been determinated for the ternary system cyclohexane + cyclohexene + morpholine and two constituent binary systems cyclohexane + morpholine and cyclohexene + morpholine. The thermodynamic consistency of experimental data has been verified. Both binary systems deviate moderately from ideality without the presence of an azeotrope. The VLE data have been well correlated using local composition models (Wilson, NRTL and UNIQUAC) and have been also predicted with the original UNIFAC. 相似文献
103.
104.
Éder José dos Santos Amanda Beatriz Herrmann Charyane Satie Sato Tatiane Andrade Maranhão Adilson José Curtius 《Microchemical Journal》2010,96(1):27-216
Mercury and lead were determined in an extraction solution applied to compact fluorescent lamps by axial view inductively coupled plasma optical emission spectrometry (ICP OES). The solution contained 50% v/v HNO3 and 10% v/v H2O2. The compact fluorescent lamps were treated by removing the socket and breaking the rest of the lamp inside the solution, followed by placing the mixture in an ultrasonic bath for 1 h. The mixture was filtrated in a coarse paper filter and the resulting extraction slurry was analyzed. The determination of Pb in the slurry required calibration by the analyte addition technique, while for Hg, external calibration was adequate. The quantification limits (10 s, n = 7), for Hg (194.164 nm) and Pb (220.353 nm) were, respectively, 10 and 30 µg per lamp. Analysis of spiked samples demonstrated reasonable accuracy of the method, with recoveries in the range from 99 to 120% for Hg and from 91 to 107% for Pb. Fifteen analyzed samples showed Hg masses per lamp in the range from 1.6 to 27 mg, and six samples were above the limit allowed by the European Community that is 5 mg per compact lamp. The values for Pb were between 0.07 and 0.75 mg per lamp. By filtrating the slurry in a membrane filter, and analyzing the resulting solution, it was found that all Hg was extracted to the liquid phase of the slurry, while a fraction of about 40% m/v of Pb is retained in the solid particles. The lamp cover glass, after extraction of the phosphor layer, was also analyzed for Hg and Pb. The concentration of Hg in the glass is quite low; however, the Pb content is high. 相似文献
105.
Hesham A. Habib Beatriz Gil-Hernández Khalid Abu-Shandi Joaquín Sanchiz Christoph Janiak 《Polyhedron》2010
Hydrothermal synthesis with MCl2 (M = Fe, Cu, and Zn) and disodium 5-ammonium-1-hydroxypentylidene-1,1-bisphosphonate, (Na+)2[+H3N(CH2)4C(OH)(PO32−)(PO3H−)] (Na2HAC5OHP2) or sodium 3-ammonium-1-hydroxypropylidene-1,1-bisphosphonate hydrate, Na+[+H3N(CH2)2C(OH)(PO3H–)(PO3H–)]·H2O (NaH2PAM·H2O) the sodium salt of pamidronic acid, H3PAM) yielded the one-dimensional (1D) iron, molecular copper and two-dimensional (2D) zinc compounds 1D-{[Fe(μ3-η5-HAC5OHP2)]·H2O}, 1, [Cu(η2-H2AC5OHP2)2], 2, 2D-{[Zn2(μ5-η7-AC5OHP2)Cl], 3, and 2D-{[Zn(μ2-η3-H2PAM)2], 4, respectively. The bisphosphonate ligand bridges (μn) between 2–5 metal atoms and uses 2–7 oxygen donor atoms towards metal coordination (ηn). The zwitterionic nature of the now bis- or tetrakis-deprotonated ammonium–bisphosphonate is retained in the metal complexes. From the reaction of NiCl2 and Na2HAC5OHP2 the zwitterionic 5-ammonium-1-hydroxypentylidene-1-phosphonic acid, +H3N(CH2)4CH(OH)PO3H−, 5 was obtained as a product of the ligand P–C bond hydrolysis. Adjacent strands, molecules or layers in 1–4, respectively are organized through the Coulomb attraction between the positive ammonium group and the negative phosphonate groups, supported by hydrogen-bonding. Each protic H atom on the C–OH, NH3+ and –PO3H− group is involved in charge-assisted hydrogen-bonding. The ammonium-pentylidene groups act as hydrophobic separators between the hydrophilic units with the polar M{C(OH)(PO3)2} and {NH3} units. Bond valence sum calculations support the Fe(II) oxidation state in 1, which was experimentally determined from a quantitative polarographic Fe(II)/Fe(III) speciation analysis as well as a temperature variable magnetic study. 相似文献
106.
Beatriz Jurado-Sánchez Evaristo Ballesteros Mercedes Gallego 《Analytical and bioanalytical chemistry》2010,396(5):1929-1937
Humans are exposed to endogenous or exogenous formation of aromatic amines (AAs) and N-nitrosamines (NAms), which are considered to be potent carcinogens. The objective of this study was to monitor AAs and NAms
in human urine to obtain a way to assess exposure. However, while NAms can be directly detected in urine samples, AAs require
hydrolysis to convert their conjugates into free amines. A semiautomatic flow-base method is proposed for the simultaneous
determination of aliphatic and aromatic NAms, anilines and chloroanilines in human urine in one analytical run. Conjugated
AAs are released from urine by on-line microwave-assisted acid hydrolysis without degradation of NAms; all amines were then
preconcentrated using solid-phase extraction. Separation/determinations are carried out by gas chromatography and mass spectrometry
operating in selected ion monitoring mode. The method is fast (∼15 min for 25 mL of sample) and provides low limits of detection
(from 2 to 26 ng/L) with good precision (relative standard deviation within and between days less than 7%). Finally, the proposed
method was successfully applied to check AAs and NAms in the human urine of exposed and unexposed researchers. The kinetics
of amine excretion in the urine of the researchers exposed is calculated after termination of the exposure and shows half-life
times between 1.3 and 2.1 h, and that the dosage absorbed was eliminated within 6 h after exposure. 相似文献
107.
The carbamoylating agents carbamoyl azides and carbamoyl cyanides (aka cyanoformamides) react with hydroxylamine in different ways, leading in the first case to N-hydroxyureas and, in the case of carbamoyl cyanides, to carbamoyl amidoxime derivatives. The synthetic procedure developed for the latter type of compound, which represents an interesting precursor for heterocyclic structures, allowed the highly efficient preparation of a wide selection of examples. The Z configuration of the double bond in the amidoxime moiety was proposed on the basis of comparison between experimental and calculated (13)C and (15)N NMR chemical shift values for the isopropyl and benzyl derivatives. 相似文献
108.
A completely automated flow-injection system was developed for the monitoring of biosorption studies of Cu(II) ion on vegetable waste by-products. The system employed flow-through Cu(II)-selective electrodes, of epoxy-resin-CuS/Ag2S heterogeneous crystalline type, and computer controlled pumps and valves for the flow operation. Computer automation was done through a specially devised virtual instrument, which commanded and periodically calibrated the system, allowing for the monitoring of Cu(II) ions between 0.6 and 6530 mg L−1 at a typical frequency of 15 h−1. Grape stalk wastes were used as biosorbent to remove Cu(II) ions in a fixed-bed column with a sorption capacity of 5.46 mg g−1, obtained by the developed flow system, while the reference determination performed by FAAS technique supplied a comparable value of 5.41 mg g−1. 相似文献
109.
Martín Egozcue Luis Fuentes García Wing-Keung Wong Ričardas Zitikis 《Central European Journal of Mathematics》2011,9(6):1288-1297
We show that Grüss-type probabilistic inequalities for covariances can be considerably sharpened when the underlying random
variables are quadrant dependent in expectation (QDE). The herein established covariance bounds not only sharpen the classical
Grüss inequality but also improve upon recently derived Grüss-type bounds under the assumption of quadrant dependency (QD),
which is stronger than QDE. We illustrate our general results with examples based on specially devised bivariate distributions
that are QDE but not QD. Such results play important roles in decision making under uncertainty, and particularly in areas
such as economics, finance, and insurance. 相似文献
110.
We show that a detector acquires a Berry phase due to its motion in spacetime. The phase is different in the inertial and accelerated case as a direct consequence of the Unruh effect. We exploit this fact to design a novel method to measure the Unruh effect. Surprisingly, the effect is detectable for accelerations 10(9) times smaller than previous proposals sustained only for times of nanoseconds. 相似文献