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Stefan-Van Staden R.-I.,Romanian National Institute for Research for Electrochemistry and Condensed Matter
New Journal of Chemistry | Year: 2010

Enantioselective, potentiometric membrane electrodes based on [5,6]fullerene-C70 and diethyl (1,2-methanofullerene-C 70)-71,71-dicarboxylate were proposed for the enantioanalysis of d-histidine in pharmaceutical compounds. Molecular modelling calculations were performed to support the experimental results. Electronic structures, as well as molecular interactions, have been investigated using Hartree-Fock theory, 3-21G(*) basis set. Stability and feasibility of all the generated structures were supported by their respective energy minima and fundamental frequencies. Molecular modelling calculations were in good agreement with the performances (e.g., response characteristics, enantioselectivity, recovery tests) of the proposed electrodes. © 2010 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique. Source


Stefan-van Staden R.-I.,Romanian National Institute for Research for Electrochemistry and Condensed Matter
Talanta | Year: 2010

Two enantioselective, potentiometric membrane electrodes based on [5,6]fullerene-C70 (1) and diethyl (1,2-methanofullerene C70)-71-71-dicarboxylate (2) immobilized in carbon paste, were designed for the enantioanalysis of R-deprenyl. The electrodes exhibited near-Nernstian slopes: 57.90 (1) and 59.00 mV/decade of concentration (2), respectively with low limits of detection 5.9 × 10-11 (1) and 9.6 × 10-11 mol/L (2), respectively. The linear concentration ranges are between 10-10 and 10-4 mol/L (1) and between 10-9 and 10-4 mol/L (2), respectively. The different characteristics involved in the molecular interaction between R-deprenyl and C70 fullerenes were explained, namely (i) the stability of each molecule and (ii) the explanation of the molecular mechanism of interaction, using restricted Hartree-Fock theory, 3-21G(*) RHF-basis set. Furthermore, two intermolecular forces of interactions confer the stability of the electrodes; electrostatic interaction and moderate hydrogen bond interaction. Stability and feasibility of all the generated structures involved in this analysis were supported by their respective fundamental frequencies and energy minima. R-deprenyl can be recovered with average recoveries higher than 99.10% (RSD < 0.03%) from synthetic mixtures between R- and S-deprenyl. The high selectivity and enantioselectivity made possible the enantioanalysis of R-deprenyl in its pharmaceutical formulations. © 2010 Elsevier B.V. All rights reserved. Source


Stefan-van Staden R.-I.,Polytechnic University of Bucharest | Gugoasa L.A.,Polytechnic University of Bucharest | Calenic B.,Romanian National Institute for Research for Electrochemistry and Condensed Matter | Legler J.,VU University Amsterdam
Scientific reports | Year: 2014

Stochastic microsensors based on diamond paste and three types of electroactive materials (maltodextrin (MD), α-cyclodextrin (α-CD) and 5,10,15,20-tetraphenyl-21H,23H porphyrin (P)) were developed for the assay of estradiol (E2), testosterone (T2) and dihydrotestosterone (DHT) in children's saliva. The main advantage of utilization of such tools is the possibility to identify and quantify all three hormones within minutes in small volumes of childen's saliva. The limits of quantification obtained for DHT, T2, and E2 (1 fmol/L for DHT, 1 pmol/L for T2, and 66 fmol/L for E2) determined using the proposed tools allows the utilization of these new methods with high reliability for the screening of saliva samples from children. This new method proposed for the assay of the three hormones overcomes the limitations (regarding limits of determination) of ELISA method which is the standard method used in clinical laboratories for the assay of DHT, T2, and E2 in saliva samples. The main feature of its utilization for children's saliva is to identify earlier problems related to early puberty and obesity. Source


Stefan-van Staden R.-I.,Romanian National Institute for Research for Electrochemistry and Condensed Matter
Electrochimica Acta | Year: 2010

Enantioselective, potentiometric membrane electrodes based on (1,2-methanofullerene C60)-61-carboxylic acid, diethyl (1,2-methanofullerene C60)-61-61-dicarboxylate and tert-butyl (1,2-methanofullerene C60)-61-carboxylic acid were proposed for the enantioanalysis of S-deprenyl in pharmaceutical compounds. Molecular modeling calculations were performed to prove the reliability of the proposed electrodes. The different characteristics involved in this analysis were explained, namely (i) the stability of each molecule using total energy, hardness and dipole moment, and (ii) the explanation of the mechanism of interaction using intermolecular forces (moderate hydrogen bond interactions), atomic charges and electrostatic potential. Electronic structures as well as molecular interaction have been investigated using Hartree-Fock theory, 3-21G(*) basis set. Stability and feasibility of all the generated structures were supported by their respective energy minima and fundamental frequencies. © 2009 Elsevier Ltd. All rights reserved. Source


Tsioupi D.A.,University of Cyprus | Stefan-van Staden R.-I.,Romanian National Institute for Research for Electrochemistry and Condensed Matter | Kapnissi-Christodoulou C.P.,University of Cyprus
Electrophoresis | Year: 2013

This review article provides an overview of the recent advances in enantioanalysis by use of electrophoretic techniques. Due to the big number of publications in the subject mentioned above, this article is focused on chiral method developments and applications published from 2008 until 2011, and it demonstrates chiral selectors used in CE. Numerous chiral selectors have been used over the years, and these include the cyclic and the linear oligo- and polysaccharides, the branched polysaccharides, the polymeric and monomeric surfactants, the macrocyclic and other antibiotics, and the crown ethers. Different dual-selector systems are also presented in this article, and the results are compared with those obtained by use of a single chiral selector. Finally, several pharmaceutical and biomedical applications based on chiral recognition are summarized. © 2012. Source

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