Search results for "analytical"
showing 10 items of 9586 documents
Suitability of 1-hexyl-3-methylimidazolium ionic liquids for the analysis of pharmaceutical formulations containing tricyclic antidepressants
2018
Abstract The reversed-phase chromatographic behaviour of six tricyclic antidepressants (amitryptiline, clomipramine, doxepin, imipramine, nortryptiline and maprotiline) was examined in this work with acetonitrile-water mobile phases, in the absence and presence of the ionic liquids 1-hexyl-3-methylimidazolium chloride and 1-hexyl-3-methylimidazolium tetrafluoroborate, which have interesting features for the separation of basic compounds, in terms of peak shape combined with reduced retention. Tricyclic antidepressants are low polarity drugs that strongly associate to the alkyl chains of conventional stationary phases. They are also positively charged in the usual working pH range (2–8) in r…
Micelles of the chiral biocompatible surfactant (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide (DMEB): molecular dynamics …
2017
Rationale The study of self-assembly process of surfactant molecules in gas phase is of actually interest for several theoretical and technological reasons related to their possible exploitation as drug carriers, protein shields and cleaning agents in gas phase. Methods Stability and fragmentation patterns of singly and multiply charged (either positively or negatively) aggregates of the surfactant (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl) dimethyl ammonium bromide (DMEB) in gas phase have been studied by ion mobility mass spectrometry and tandem mass spectrometry. Molecular dynamics (MD) simulations of positively and negatively singly and multiply charged DMEB aggregates have been …
Keyhole limpet haemocyanin: negative staining in the presence of trehalose
1995
Abstract Samples of unpurified and purified haemocyanin from the giant keyhole limpet Megathura crenulata have been studied by transmission electron microscopy (TEM) using mixtures of trehalose with the negative stains, uranyl acetate and ammonium molybdate. Trehalose is a known protein preservative during air and freeze drying, UV irradiation and high temperatures, and therefore offers the possibility of protecting proteins during the drying of negatively-stained specimens and their subsequent electron microscopical study. Evidence is presented that trehalose possesses satisfactory stability within the electron beam during conventional room temperature, negative-staining studies. The combi…
Enhanced organic mass fraction and decreased hygroscopicity of cloud condensation nuclei (CCN) during new particle formation events
2010
In a forested near-urban location in central Germany, the CCN efficiency of particles smaller than 100 nm decreases significantly during periods of new particle formation. This results in an increase of average activation diameters, ranging from 5 to 8% at supersaturations of 0.33% and 0.74%, respectively. At the same time, the organic mass fraction in the sub-100-nm size range increases from approximately 2/3 to 3/4. This provides evidence that secondary organic aerosol (SOA) components are involved in the growth of new particles to larger sizes, and that the reduced CCN efficiency of small particles is caused by the low hygroscopicity of the condensing material. The observed dependence of…
Expression, purification, crystallization and preliminary X-ray analysis of strictosidine glucosidase, an enzyme initiating biosynthetic pathways to …
2005
Abstract Strictosidine β- d -glucosidase, a plant enzyme initiating biosynthetic pathways to about 2000 monoterpenoid indole alkaloids with an extremely large number of various carbon skeletons, has been functionally expressed in Escherichia coli and purified to homogeneity in mg scale. Crystals suitable for X-ray analysis were found by robot-mediated screening. Using the hanging-drop technique, optimum conditions were 0.3 M ammonium sulfate, 0.1 M sodium acetate, pH 4.6 and PEG 4000 (10%) as precipitant buffer. The crystals of strictosidine glucosidase belong to the space group P 42 1 2 with unit cell dimensions of a =157.63, c =103.59 A and diffract X-rays to 2.48-A resolution.
Human sweat odour conjugates in human milk, colostrum and amniotic fluid
2012
International audience; Using ultra performance liquid chromatography-mass spectrometry we identified for the first time glutamine-N-alpha-conjugates of the fatty acids (E)/(Z)-3-methylhex-2-enoic acid and (R)/(S)-3-hydroxy-3-methylhexanoic acid as well as cysteinylglycine-S-conjugates of (R)/(S)-3-methyl-3-sulphanylhexan-1-ol and (R)/(S)-3-sulphanylhexan-1-ol as constituents of human milk and colostrum. The glutamine-N-alpha-conjugates were detected also in human amniotic fluids. The mean values of glutamine-N-alpha-conjugate of (R)/(S)-3-hydroxy-3-methylhexanoic acid were highest in colostrums with a range of <0.1-382 mu g/kg, followed by the mature human milk with values from <0.1 to 39.…
Determination of barbiturates in urine by micellar liquid chromatography and direct injection of sample.
2000
Abstract A liquid chromatographic procedure for the determination of six barbiturates (barbital, diallyl barbituric acid, phenobarbital, butabarbital, amobarbital and pentobarbital) in urine samples is described. The proposed system uses a Spherisorb octadecyl-silane ODS-2 C 18 analytical column and a guard column of similar characteristics. The UV detector was set at 240 nm. A study to select adequate composition of the micellar mobile phase for the separation of these compounds in urine samples is performed. Maximum resolution was achieved with a 0.07 M sodium dodecylsulphate-0.3% propanol at pH 7.4 eluent. Limits of detection at 240 nm were ranged between 0.13 μg ml −1 for diallyl barbit…
Short-range order and luminescence in amorphous silicon oxynitride
2000
Abstract Using Si 2p core-level X-ray photoelectron spectroscopy, we found that the short-range order in amorphous silicon oxynitride (a-SiOxNy) can be quantitatively described by a random bonding model. Results also show that the second and even further neighbours of the Si in the network affect the chemical shifts of the X-ray photoelectron spectra. Cathodoluminescence and photoluminescence of a-SiOxNy with different compositions are also measured. A red band with energies of 1.8–1.9 eV, a blue band with an energy of 2.7 eV and ultraviolet bands with energies of 13.1, 3.4–3.6, 4.4–4.7 and 5.4eV were observed. The 1.8–1.9 eV band is attributed to the O and N atoms with an unpaired electron…
Amplified Spontaneous Emission Properties of Solution Processed CsPbBr3 Perovskite Thin Films
2017
Metal halide perovskites are currently emerging as highly promising optoelectronic materials. It has been recently demonstrated that fully inorganic solution processed CsPbBr3 perovskite thin films show good electroluminescence properties combined with high thermal stability. In this work, we investigate in details the amplified spontaneous emission (ASE) properties of CsPbBr3 perovskite thin films, as a function of the temperature and the trap density, modified by changing the CsBr-PbBr2 precursor concentration. ASE is observed in samples from both CsBr-rich solution (low trap density) and equimolar solution (higher trap density), up to about 150 K, with a minimum threshold of 26 and 29 mu…
Concentration dependence of amplified spontaneous emission in two oligo-(p-phenylenevinylene) derivatives
2005
Amplified spontaneous emission sASEd in optically pumped polystyrene sPSd films doped with two different oligo-sp-phenylenevinylened derivatives sOPVsd, with three s3-OPVd and five s5-OPVd monomer units is reported. It is observed that there is a maximum content of oligomer s25 wt. % for 3-OPV and 20 wt. % for 5-OPVd that can be introduced in the films, due to degradation sin 3-OPVd and ASE quenching sin 5-OPVd. Optimal concentrations swith minimum pump-intensity thresholds for the observation of ASEd of 15 wt. % and 9 wt. % are measured for the trimer and the pentamer, respectively. The concentration dependence of the ASE threshold is discussed in terms of the optical absorption spectra. G…