Search results for "ionic"
showing 10 items of 2016 documents
Use of green alternative solvents in dispersive liquid‐liquid microextraction: A review
2021
Dispersive liquid-liquid microextraction is one of the most widely used microextraction techniques currently in the Analytical Chemistry field, mainly due to its simplicity and rapidity. The operational mode of this approach has been constantly changing since its introduction, adapting to new trends and applications. Most of these changes are related to the nature of the solvent employed for the microextraction. From the classical halogenated solvents (e.g., chloroform or dichloromethane), different alternatives have been proposed in order to obtain safer and non-pollutants microextraction applications. In this sense, low density solvents, such as alkanols, switchable hydrophobicity solvent…
New approach for synthesis of poly(ethylglyoxylate) using Maghnite-H + , an Algerian proton exchanged montmorillonite clay, as an eco-catalyst
2017
International audience; In this works, we have explored a new method for a green synthesis of poly(ethylglyoxylate) (PEtG). This method consists on using a montmorillonite clay called Maghnite-H+ as an eco-catalyst to replace triethylamine which is toxic. Cationic polymerization experiments are performed in bulk conditions at three temperatures (-40 degrees C, 25 degrees C, 80 degrees C) and in THF solutions at room temperature (25 degrees C). At 25 degrees C, an optimum ratio of 5 wt% of catalyst leads to molar masses up to 22000 g/mol in THF solutions. Polymerizations in bulk conditions lead to slightly lower masses than experiments conducted in THF solutions. However, bulk polymerization…
Uncommon perspectives in palladium- and copper-catalysed arylation and heteroarylation of terminal alkynes following Heck or Sonogashira protocols: I…
2013
Abstract Conjugated alkynes are recurring building blocks in natural products and in a wide range of important compounds, such as pharmaceuticals, agrochemicals, or molecular materials. The palladium-catalysed cross-coupling reaction between the sp 2 -hybridized carbon atoms of aryl, heteroaryl, and vinyl halides with the sp -hybridized carbon atoms of terminal alkynes is one of the most important developments in the field of alkyne chemistry over the past 50 years. Room for improvement still exists in these important reactions of direct arylation of terminal alkynes. In this prospect, the present authors have developed several strategies aiming at improving the reactivity, the selectivity,…
Modelling Photoionisations in Tautomeric DNA Nucleobase Derivatives 7H-Adenine and 7H-Guanine: Ultrafast Decay and Photostability
2021
The study of radiation effects in DNA is a multidisciplinary endeavour, connecting the physical, chemical and biological sciences. Despite being mostly filtered by the ozone layer, sunlight radiation is still expected to (photo)ionise DNA in sizeable yields, triggering an electron removal process and the formation of potentially reactive cationic species. In this manuscript, photoionisation decay channels of important DNA tautomeric derivatives, 7H-adenine and 7H-guanine, are characterised with accurate CASSCF/XMS-CASPT2 theoretical methods. These simulation techniques place the onset of ionisation for 7H-adenine and 7H-guanine on average at 8.98 and 8.43 eV, in line with recorded experimen…
F117Hystero-embryoscopic findings in early nonviable pregnancies
2000
Background A high proportion of early pregnancy losses are associated to abnormal embryo development. However, chromosomal analysis of routine curettage samples are of limited value; and histopathological examinations of the embryos are rarely performed in clinical practice. Method A transcervical hystero-embryoscopy was performed prior to the curettage in 31 nonviable first-trimester pregnancies and a control group of 5 early terminations of pregnancy. In the study group, the estimated gestational age according to the ultrasound findings was 6.7 (4–9) menstrual weeks. Direct biopsies of different gestational structures were taken during the endoscopic procedure. Results In nonviable pregna…
Toward Mechanistic Design of Surrogate Buffers for Dissolution Testing of pH-Dependent Drug Delivery Systems
2020
The in vivo dissolution of enteric-coated (EC) products is often overestimated by compendial in vitro dissolution experiments. It is of great interest to mimic the in vivo conditions as closely as possible in vitro in order to predict the in vivo behavior of EC dosage forms. The reason behind this is the overly high buffering capacity of the common compendial buffers compared to the intestinal bicarbonate buffer. However, a bicarbonate-based buffer is technically difficult to handle due to the need for continuous sparging of the media with CO2 to maintain the desired buffer pH. Therefore, bicarbonate buffers are not commonly used in routine practice and a non-volatile alternative is of inte…
Water mites of small boreal forest lakes (Central Finland)
1999
The water mite fauna of 10 small forest lakes in close proximity to each other was studied in 1979–1985. In total approximately 62 species of water mites belonging to 22 genera were detected in the lakes. The most diverse genera were Piona (14 species), Arrenurus (11), Unionicola (4) and Limnesia (4). Widely spread and abundant species were Piona variabilis and Limnesia maculata. Locally abundant were Unionicola crassipes, U. minor, Piona carnea and P. paucipora. Zoogeographically interesting though accidental species were Arrenurus werestschagini, Limnesia polonica, Momonia karelica, Piona gyrophora and Unionicola parvipora. Considerable spatial and seasonal differences were observed in th…
Functionalized halloysite nanotubes for enhanced removal of lead(II) ions from aqueous solutions
2018
In this study, environmental friendly halloysite nanotubes and their amino derivatives were used as adsorbent materials for lead(II) ions. The adsorption ability of both nanomaterials towards Pb2+ ions has been studied in NaClaq, at I = 0.1 mol L−1, in the pH range 3–6. Moreover, the effect of ionic strength on the adsorption process was evaluated at the pH of maximum efficiency of the adsorbent materials. Kinetic and equilibrium experiments were carried out by using the Differential Pulse Anodic Stripping Voltammetry (DP-ASV) technique to check the metal ion concentration in solution after contact with the two adsorbents. Different isotherm and kinetic equations were used to fit the experi…
Equilibrium studies in natural waters: Speciation of phenolic compounds in synthetic seawater at different salinities
1995
Interactions between some phenolic compounds and macro-constituents of synthetic seawater (Na{sup +}, K{sup +}, Ca{sup 2+}, Mg{sup 2+}, Cl{sup {minus}}, and SO{sub 4}{sup 2{minus}}), at 20, 35, and 45 {per_thousand} salinity, have been investigated potentiometrically by using the [H]-glass electrode. The formation constants of phenol, o- and p-cresol, o-a dn p-nitrophenol complexes with sodium, potassium, calcium, and magnesium ions have been determined in the ionic strength range 0 {le} I {le} 1 mol/L. A comparison between the apparent protonation constants of phenols determined in synthetic seawater, and those simulated by a suitable complex formation model, is discussed. The possibility …
HPLC-SEC: a new approach to characterise complex wastewater effluents
2016
ABSTRACTThis work investigates the use of HPLC-SEC to characterise dissolved organic matter (DOM) of complex wastewater effluents. A silica-based column, sodium acetate eluent and multiple detections were employed: UV-254 absorbance for humictype, and tryptophan-like (Ex/Em = 270/355) and tyrosine-like (Ex/Em = 270/310) fluorescence for protein type compounds. Effects of eluent pH, eluent ionic strength and injection volume on separation efficiency were tested. Humic-type and protein-type fractions were clearly differentiated and eluted within and out of calibration range. Eluent ionic strength had the greatest influence on global resolution; the lowest eluent concentration of 0.01 M produc…