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91.
Perkin S Chai L Kampf N Raviv U Briscoe W Dunlop I Titmuss S Seo M Kumacheva E Klein J 《Langmuir : the ACS journal of surfaces and colloids》2006,22(14):6142-6152
We have measured normal and lateral interactions across a range of different liquids between mica surfaces using a surface force balance (SFB). The mica surfaces were prepared either by melt cutting using Pt wire and standard procedures in our laboratories or by tearing sheets (that had not been exposed to Pt) off from a freshly cleaved sheet of mica. AFM micrographs revealed the substantial absence of Pt nanoparticles on the melt cut and torn-off mica surfaces. Normal-force versus surface-separation (D) profiles and shear force versus D measurements for purified water (no added salt), for concentrated aqueous NaCl solutions, and for cyclohexane revealed that in all cases the behavior of the highly confined liquids between melt-cut and between torn-off mica sheets was identical within experimental scatter. These results demonstrate directly that interactions measured between melt-cut mica surfaces as routinely prepared using established procedures in our laboratories and in other laboratories are free of the effect of any Pt contamination. 相似文献
92.
Alexey V. Varlamov Ekaterina V. Boltukhina Fedor I. Zubkov Eugenia V. Nikitina Konstantin F. Turchin 《Journal of heterocyclic chemistry》2006,43(6):1479-1495
93.
Villaverde-de-Sáa E Quintana JB Rodil R Ferrero-Refojos R Rubí E Cela R 《Analytical and bioanalytical chemistry》2012,402(1):509-518
Perfluorinated compounds (PFCs) have been used for over 40 years in different commercial and industrial applications mainly
as surfactants and surface protectors and have become an important class of marine emerging pollutants. This study presents
the development and validation of a new analytical method to determine the simultaneous presence of eight PFCs in different
kinds of mollusks using matrix solid-phase dispersion (MSPD) followed by liquid chromatography–tandem mass spectrometry (LC-MS/MS).
Simplicity of the analytical procedure, low volume of solvent and quantity of sample required, low global price, and integration
of extraction and clean-up into a single step, are the most important advantages of the developed methodology. Solvent, solid
support (dispersing agent), clean-up sorbent, and their amounts were optimized by means of an experimental design. In the
final method, 0.5 g of sample are dispersed with 0.2 g of diatomaceous earth and transferred into a polypropylene syringe
containing 4 g of silica as clean-up sorbent. Then, analytes are eluted with 20 mL of acetonitrile. The extract is finally
concentrated to a final volume of 0.5 mL in methanol, avoiding extract dryness in order to prevent evaporation losses and
injected in the LC-MS/MS. The combination of this MSPD protocol with LC-MS/MS afforded detection limits from 0.05 to 0.3 ng g−1. Also, a good linearity was established for the eight PFCs in the range from limit of quantification (LOQ) to 500 ng mL−1 with R
2 > 0.9917. The recovery of the method was studied with three types of spiked mollusk and was in the 64–126% range. Moreover,
a mussel sample was spiked and aged for more than 1 month and analyzed by the developed method and a reference method, ion-pair
extraction, for comparison, producing both methods statistically equal concentration values. The method was finally applied
to the determination of PFCs in different kinds of mollusks revealing concentrations up to 8.3 ng g−1 for perfluoroundecanoic acid. 相似文献
94.
We present an automated microfluidic (MF) approach for the systematic and rapid investigation of carbon dioxide (CO(2)) mass transfer and solubility in physical solvents. Uniformly sized bubbles of CO(2) with lengths exceeding the width of the microchannel (plugs) were isothermally generated in a co-flowing physical solvent within a gas-impermeable, silicon-based MF platform that is compatible with a wide range of solvents, temperatures and pressures. We dynamically determined the volume reduction of the plugs from images that were accommodated within a single field of view, six different downstream locations of the microchannel at any given flow condition. Evaluating plug sizes in real time allowed our automated strategy to suitably select inlet pressures and solvent flow rates such that otherwise dynamically self-selecting parameters (e.g., the plug size, the solvent segment size, and the plug velocity) could be either kept constant or systematically altered. Specifically, if a constant slug length was imposed, the volumetric dissolution rate of CO(2) could be deduced from the measured rate of plug shrinkage. The solubility of CO(2) in the physical solvent was obtained from a comparison between the terminal and the initial plug sizes. Solubility data were acquired every 5 min and were within 2-5% accuracy as compared to literature data. A parameter space consisting of the plug length, solvent slug length and plug velocity at the microchannel inlet was established for different CO(2)-solvent pairs with high and low gas solubilities. In a case study, we selected the gas-liquid pair CO(2)-dimethyl carbonate (DMC) and volumetric mass transfer coefficients 4-30 s(-1) (translating into mass transfer times between 0.25 s and 0.03 s), and Henry's constants, within the range of 6-12 MPa. 相似文献
95.
The molecular shape of proteinogenic glutamic acid has been determined for the first time. Vaporization of the solid amino acid by laser ablation in combination with Fourier transform microwave spectroscopy made possible the detection of five different structures in a supersonic jet. These structures have been identified through their rotational and (14)N quadrupole coupling constants. All conformers show hydrogen bonds linking the amino and alpha carboxylic group through N-H···O═C (type I) or N···H-O (type II) interactions. In three of them there are additional hydrogen bonds established between the amino group and the carboxylic group in the gamma position. Entropic effects related to the side chain have been found to be significant in determining the most populated conformations. 相似文献
96.
Depending on the synthetic conditions, five heterometallic Mn(III)Fe(II) polynuclear compounds with the same ratio of constituents, 2[Mn(acacen)](+)/[Fe(CN)(5)NO](2-), of different nuclearity and dimensionality (0D, 1D, 2D) were isolated. A [Mn(acacen)MeOH](2)[Fe(CN)(5)NO]·1.5MeOH, 1 complex has been prepared by reaction of Mn(III)/Schiff base (SB) complex, [Mn(acacen)Cl] (H(2)acacen is N,N'-ethylenebis(acetylacetoneimine)) with sodium nitroprusside (NP). Single crystal X-ray diffraction analyses reveal that crystallization of 1 from coordinating or non-coordinating solvents results in different coordination polynuclear materials: from C(2)H(5)OH [{Mn(acacen)H(2)O}(2)Fe(CN)(5)NO]·C(2)H(5)OH, 2, a trinuclear complex is formed; from CH(3)CN [{Mn(acacen)H(2)O}(4)Fe(CN)(5)NO][Fe(CN)(5)NO]·4CH(3)CN, an ionic compound with a pentanuclear bimetallic cation is formed 3; from i-C(3)H(7)OH [{Mn(acacen)}(2)(i-PrOH)Fe(CN)(5)NO](n), a coordination chain polymer 4 is formed; from toluene [{Mn(acacen)}(2)Fe(CN)(5)NO](n), a layered network 5 is formed. As the magnetic measurements show, for all compounds the weak interaction between Mn(III)S = 2 spins through the NP bridge is antiferromagnetic and exhibits no significant photoactivity. 相似文献
97.
Examining metal nanoparticle surface chemistry using hollow-core, photonic-crystal, fiber-assisted SERS 总被引:1,自引:0,他引:1
In this Letter, we demonstrate the efficacy of hollow core photonic crystal fibers (HCPCFs) as a surface-enhanced Raman spectroscopy (SERS) platform for investigating the ligand exchange process on the surface of gold nanoparticles. Raman measurements carried out using this platform show the capability to monitor minute amounts of surface ligands on gold nanoparticles used as an SERS substrate. The SERS signal from an HCPCF exhibits a tenfold enhancement compared to that in a direct sampling scheme using a cuvette. Using exchange of cytotoxic cetyltrimethylammonium bromide with α-methoxy-ω-mercaptopoly(ethylene glycol) on the surface of gold nanorods as an exemplary system, we show the feasibility of using HCPCF SERS to monitor the change in surface chemistry of nanoparticles. 相似文献
98.
Yung Yang Noelia Rosales-Conrado Vanesa Guillén-Casla María Eugenia León-González Luis Vicente Pérez-Arribas Luis María Polo-Díez 《Chromatographia》2012,75(23-24):1365-1375
A heart-cut two-dimensional high-performance liquid chromatography method for enantiomeric determination of salbutamol, salmeterol and atenolol in urine is presented. It involves the use of two separations in a liquid chromatography?Cliquid chromatography achiral?Cchiral coupling. Target compounds were previously separated in a primary column (Kinetex? HILIC, 2.6???m, 150?×?2.1?mm I.D.) with a mixture of MeOH:ACN:ammonium acetate buffer (5?mM, pH 6) 90:5:5 (v/v/v) as mobile phase at a flow rate of 0.40?mL?min?1. Enantiomeric separation was carried out by transferring peak of each compound through a switching valve to a vancomycin chiral column (Chirobiotic? V, 2.6???m, 150?×?2.1?mm I.D.) using MeOH:ammonium acetate buffer (2?mM, pH 4) 97:3 (v/v) as mobile phase at a flow rate of 0.50?mL?min?1. Ultraviolet detection was done at 227?nm. The method was applied to determine target analytes in urine samples after enzymatic hydrolysis with ??-glucuronidase from Helix pomatia, followed by a solid-phase extraction procedure using Isolute? HCX mixed-mode cartridges. Extraction recoveries ranged from 82 to 90?% in urine samples. Detection limits were 0.091?C0.095???g for each enantiomer of atenolol and between 0.058 and 0.076 and 0.18?C0.14???g for enantiomers of salbutamol and salmeterol, respectively (3?mL of urine). Linearity ranges were between 0.5 and 10???g?mL?1. Intraday and interday reproducibilities of enantiomeric ratio and enantiomeric fraction, expressed as relative standard deviation, were between 1.9 and 9.0?%. The optimized method was successfully applied to the analysis of urine samples obtained from excretion studies in volunteers and in freeze-dried urine samples, containing urinary components with MW?<?10,000 and components with MW?>?10,000, spiked with different amounts of studied drugs. 相似文献
99.
Parolo ME Avena MJ Pettinari GR Baschini MT 《Journal of colloid and interface science》2012,368(1):420-426
The adsorption of tetracycline (TC) on montmorillonite was studied as a function of pH and Ca(2+) concentration using a batch technique complemented with X-ray diffraction and transmission electron microscopy. In the absence of Ca(2+), TC adsorption was high at low pH and decreased as the pH increased. In the presence of Ca(2+), at least two different adsorption processes took place in the studied systems, i.e., cation exchange and Ca-bridging. Cation exchange was the prevailing process at pH<5, and thus, TC adsorption decreased by increasing total Ca(2+) concentration. On the contrary, Ca-bridging was the prevailing process at pH>5, and thus, TC adsorption increased by increasing Ca(2+) concentration. The pH 5 represents an isoadsorption pH where both adsorption processes compensate each other. TC adsorption became independent of Ca(2+) concentration at this pH. For TC adsorption on Ca(2+)-montmorillonite in 0.01 M NaCl experiments, the ratio adsorbed TC/retained Ca(2+) was close to 1 in the pH range of 5-9, indicating an important participation of Ca(2+) in the binding of TC to montmorillonite. X-ray diffraction and transmission electron microscopy showed that TC adsorption induced intercalation between montmorillonite layers forming a multiphase system with stacking of layers with and without intercalated TC. 相似文献
100.
Synthesis,solid-state photophysical properties and electropolymerization of novel diazulenyl ethenes
Eugenia Andreea Dragu Simona Nica Matei Raicopol Adriana Baran Dan-Florin Anghel Bogdan Cojocaru Laszlo Tarko Alexandru C. Razus 《Tetrahedron letters》2012,53(21):2611-2614
The novel 1,2-di(azulen-1-yl)cyclopent-1-ene 3 was conveniently synthesized via a two-step procedure involving Vilsmeier–Haack acylation of azulene with N,N,N′,N′-tetraethylglutaramide (TEGA) and POCl3, followed by an intramolecular McMurry coupling of the resulting diketone. In contrast with the previously reported (E)-1,2-di(azulen-1-yl)ethene that shows negligible fluorescence in the solid state, alkene 3 displays fluorescence emission from the S2 excited state of the azulene moieties. This compound easily polymerizes upon electrochemical oxidation, leading to the formation of a conducting polymer film at the electrode surface. 相似文献