The Experts below are selected from a list of 198 Experts worldwide ranked by ideXlab platform
Nahid Sarlak - One of the best experts on this subject based on the ideXlab platform.
-
Design of an Optical Nanosensor for Determination of Trace Amounts of Thiourea and Cyanide
Advances in Phytonanotechnology, 2019Co-Authors: Nahid Sarlak, Zeynab Sameri, Reza Pourrahim, Keyvan ShaabaniAbstract:Abstract The characterization of an optical absorption-based one-shot sensor is described for the determination of thiourea and cyanide ions based on the immobilization of new nanocomposite of MWCNT-graft-poly(citric acid)/Au on a Triacetylcellulose membrane. MWCNT-g-PCA/Au is covalently bonded to a transparent Triacetylcellulose film. Thiourea and cyanide ions react with the immobilized nanocomposite and cause a decrease in the absorbance of the film at 300 nm. The response time of sensing phase is within 5 min depending on the concentration of thiourea and cyanide. This sensing phase has a linear range of 40–250 and 250–1000 mg L− 1 for thiourea with a limit of detection of 11 mg L− 1 at a wavelength of 300 nm. This sensing phase has a linear range of 0.1–200 mg L− 1 for CN− ions with a limit of detection of 0.08 mg L− 1 at a wavelength of 300 nm. The nanosensor was successfully applied for the determination of thiourea and cyanide in tap and spring water.
-
Catalytic determination of traces of Rh(III) using an optode based on immobilization of methyl violet on a Triacetylcellulose membrane
Sensors and Actuators B-chemical, 2011Co-Authors: Nahid Sarlak, M. AnizadehAbstract:Abstract The characterization of an optical sensor membrane is described for determination of rhodium. The optode sensing reagent is methyl violet which is immobilized on Triacetylcellulose membrane. It has been found that oxidation of methyl violet with periodate is very slow. Presence of trace amount of Rh(III) catalyzes the reaction and causes a significant increase in the reaction rate. The reaction of periodate with the immobilized methyl violet in the presence of rhodium in acidic media causes a decrease in the absorbance of the film at 594 nm which is directly proportional to the concentration of rhodium. This sensing phase has a linear range of 1–110 μg mL−1 for Rh(III) ions. The one-shot sensor can readily be fully regenerated with methyl violet solution, and the color is fully reversible.
-
Design and characteristics of a sulfide and sulfite optode based on immobilization of methyl violet on a Triacetylcellulose membrane
Sensors and Actuators B: Chemical, 2007Co-Authors: Abbas Afkhami, Nahid SarlakAbstract:Abstract The characterization of an optical sensor membrane is described for the determination of sulfite and sulfide ions based on the immobilization of methyl violet on a Triacetylcellulose membrane. Methyl violet is covalently bonded to a transparent Triacetylcellulose film. The absorbance of the membranes decreased by increasing sulfite and sulfide concentration. This optode has a linear range of 0.375–8.75 mmol L−1 (30–700 μg mL−1) and 0.156–18.75 mmol L−1 (5–600 μg mL−1) for sulfite and sulfide ions, respectively, at 598 nm. The response time of optode is within 0–3 min depending on the concentration of sulfite and sulfide ions. The sensor can readily be regenerated with water. The sensor could be fully regenerated, and the color is fully reversible. The sensor was successfully used to the determination of sulfide in water and determination of sulfite in water and fruit juice samples.
-
A novel cyanide sensing phase based on immobilization of methyl violet on a Triacetylcellulose membrane
Sensors and Actuators B-chemical, 2007Co-Authors: Abbas Afkhami, Nahid SarlakAbstract:Abstract The characterization of an optical absorption based one-shot sensor membrane is described for the determination of cyanide ion based on the immobilization of methyl violet on a Triacetylcellulose membrane. Methyl violet is covalently bonded to a transparent Triacetylcellulose film. Cyanide ion reacts with the immobilized methyl violet and causes a decrease in the absorbance of the film at 598 nm. The response time of sensing phase is within 8–12 min depending on the concentration of CN − ions. This sensing phase has a linear range of 3.8–95 mmol L −1 (100–2500 μg mL −1 ) for CN − ions with a limit of detection of 2.4 mmol L −1 (63 μg mL −1 ) at a wavelength of 598 nm. The one-shot sensor can readily be fully regenerated with methyl violet solution, and the color is fully reversible.
Abbas Afkhami - One of the best experts on this subject based on the ideXlab platform.
-
Kinetic Determination of Trace Amounts of Nitrite Using an Optical Chemical Sensor
CLEAN - Soil Air Water, 2012Co-Authors: Abbas Afkhami, Tayyebeh Madrakian, Seyyed Bahman AleseyyedAbstract:An optical chemical sensor (optode) is proposed for the kinetic determination of nitrite ion. The optode was fabricated by the immobilization of methyl violet on a Triacetylcellulose polymeric membrane. Methyl violet is covalently bonded to a transparent Triacetylcellulose film. By immersion of the sensor into an acidic nitrite solution, the absorbance of the sensor at 596 nm decreases with time that is due to the reaction of nitrite with the immobilized methyl violet. A fixed time method of 15 min was used to monitor the reaction. The linear range for the determination of nitrite was 0.20–8.00 µg mL−1 and the limit of detection was 0.08 µg mL−1. The optodes were one-shot, they had durability more than 2 months and were easily prepared. The optode was successfully applied to the determination of nitrite ion in spring water and sewage samples.
-
Design and characteristics of a sulfide and sulfite optode based on immobilization of methyl violet on a Triacetylcellulose membrane
Sensors and Actuators B: Chemical, 2007Co-Authors: Abbas Afkhami, Nahid SarlakAbstract:Abstract The characterization of an optical sensor membrane is described for the determination of sulfite and sulfide ions based on the immobilization of methyl violet on a Triacetylcellulose membrane. Methyl violet is covalently bonded to a transparent Triacetylcellulose film. The absorbance of the membranes decreased by increasing sulfite and sulfide concentration. This optode has a linear range of 0.375–8.75 mmol L−1 (30–700 μg mL−1) and 0.156–18.75 mmol L−1 (5–600 μg mL−1) for sulfite and sulfide ions, respectively, at 598 nm. The response time of optode is within 0–3 min depending on the concentration of sulfite and sulfide ions. The sensor can readily be regenerated with water. The sensor could be fully regenerated, and the color is fully reversible. The sensor was successfully used to the determination of sulfide in water and determination of sulfite in water and fruit juice samples.
-
A novel cyanide sensing phase based on immobilization of methyl violet on a Triacetylcellulose membrane
Sensors and Actuators B-chemical, 2007Co-Authors: Abbas Afkhami, Nahid SarlakAbstract:Abstract The characterization of an optical absorption based one-shot sensor membrane is described for the determination of cyanide ion based on the immobilization of methyl violet on a Triacetylcellulose membrane. Methyl violet is covalently bonded to a transparent Triacetylcellulose film. Cyanide ion reacts with the immobilized methyl violet and causes a decrease in the absorbance of the film at 598 nm. The response time of sensing phase is within 8–12 min depending on the concentration of CN − ions. This sensing phase has a linear range of 3.8–95 mmol L −1 (100–2500 μg mL −1 ) for CN − ions with a limit of detection of 2.4 mmol L −1 (63 μg mL −1 ) at a wavelength of 598 nm. The one-shot sensor can readily be fully regenerated with methyl violet solution, and the color is fully reversible.
Ulf Berg - One of the best experts on this subject based on the ideXlab platform.
-
Stereochemical variations on the colchicine motif. Peracid oxidation of thiocolchicone. Synthesis, conformation and inhibition of microtubule assembly
Organic & biomolecular chemistry, 2004Co-Authors: Ulf Berg, Håkan Bladh, Konstantinos MpamposAbstract:When 7-oxodesacetamidothiocolchicine (1) was treated with various peroxides in order to afford a Baeyer–Villiger rearrangement, a complex mixture of products was formed, which included the sulfoxide, (2) and sulfone, (3). When peracetic acid was used two additional products were formed; a C-ring lactone (4) and a ring-contracted allocolchicine derivative (5). The sulfoxide (2) was semi-preparatively resolved into enantiomers by chromatography on microcrystalline Triacetylcellulose. Rotational barriers around the A–C pivot bond of 2, 4 and 5 were determined by dynamic 1H NMR analysis. The compounds 2, 3, 4 and 7a exhibit moderate inhibition of tubulin polymerization, according to in vitro turbidity studies, whereas 5 was inactive.
-
Synthesis and Chiroptical Properties of Methanocycloocta[b]indoles
The Journal of organic chemistry, 2000Co-Authors: Eugenius Butkus, Ulf Berg, And Julė Malinauskienė, Jan SandströmAbstract:The synthesis of chiral methanocyclocta[b]indoles, the fused structures obtained from enantiomeric bicyclo[3.3.1]nonanones via Fisher indolization reaction, is reported. The starting optically active bicyclo[3.3.1]nonane-2,6-dione (1) was obtained by a chiral HPLC enantiomer separation on a swollen microcrystalline Triacetylcellulose column and by the enzymatic resolution of the racemic dione. The circular dichroism (CD) spectra of the chiral structures 4, 5, and 7 were recorded, and the absolute configuration for the indole compounds was assigned. The theoretical calculations of the CD spectrum of diindole 4 reproduce the 1Bb couplet at 229 nm but predict wrong signs for the 1La and 1Lb bands using standard polarization directions. The CD spectrum of indole ketone 5 is reproduced correctly.
-
Enantiomer separation and absolute configuration of densely functionalized 2-oxatricyclo[4.3.1.03,8]decanes by CD spectroscopy and chemical correlation
Tetrahedron: Asymmetry, 2000Co-Authors: Eugenijus Butkus, Ulf Berg, Albinas Zilinskas, Rytis Kubilius, Sigitas StončiusAbstract:Abstract Enantiomer separation by HPLC on a swollen microcrystalline Triacetylcellulose column of highly substituted 2-oxatricyclo[4.3.1.0 3,8 ]decane (2-oxaprotoadamantane) structures afforded enantiomers of this molecule. Application of the octant rule to the carbonyl chromophore to establish the absolute configuration of the enantiomers did not lead to an unequivocal conclusion. The enantioselective synthesis of 4-bromo-3-methoxy-oxaprotoadamantanone was performed from homochiral (+)-(1 S ,5 S )-bicyclo[3.3.1]nonane-2,6-dione thus permitting the assignment of the (1 R ,3 S ,4 S ,6 R ,8 R )-configuration to the title structures.
-
Chromatographic enantiomer separation and absolute configuration of spiro[benzo-1,3-dioxole-2,9′-bicyclo[3.3.1]nonan]-2′-one and the corresponding diastereomeric hydroxy acetals
Journal of the Chemical Society Perkin Transactions 2, 1998Co-Authors: Eugenius Butkus, Ulf Berg, Arvydas Stoncius, Audrius RimkusAbstract:The enantiomers of spiro[benzo-1,3-dioxole-2,9′-bicyclo[3.3.1]nonan]-2′-one 2 and the corresponding diastereomeric exo-2′- and endo-2′-hydroxy acetals 3a,b obtained from this monoacetal were resolved by HPLC on a swollen microcrystalline Triacetylcellulose column. The absolute configuration of the enantiomers of 2 and 3a,b was assigned based on the signs of the Cotton effect and employing the octant rules for the carbonyl and the aromatic chromophores. The low intensity of the band at 290 nm in the CD spectrum of monoacetal 2 was accounted for by the interaction of the carbonyl and aromatic chromophores.
-
Chromatographic Separation and Absolute Configuration of Chiral Methyl 2-Oxobicyclo[3.2.1]octane-6-carboxylate
Mendeleev Communications, 1995Co-Authors: Eugenius Butkus, Ulf Berg, Arvydas Stoncius, Albinas ZilinskasAbstract:Enantiomer separation of methyl exo -2-oxobicyclo[3.2.1]octane-6-carboxylate 2 has been achieved by liquid chromatography on swollen microcrystalline Triacetylcellulose and the absolute configuration of (−)- 2 and ( + )- 2 assigned using circular dichroism spectra.
Afsaneh Safavi - One of the best experts on this subject based on the ideXlab platform.
-
Design of an optical sensor for indirect determination of isoniazid.
Spectrochimica acta. Part A Molecular and biomolecular spectroscopy, 2007Co-Authors: Afsaneh Safavi, Mozhgan BagheriAbstract:The characterization of an optical sensor membrane is described for indirect determination of isoniazid. The sensing membrane was consisted of immobilized 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT) on a Triacetylcellulose membrane. The procedure is based on the reaction of Fe(III) with isoniazid in the presence of PDT. Fe(III) is reduced by isoniazid to Fe(II) which forms a complex with PDT. The complex shows an absorption maximum at 558 nm. By measuring the absorbance of the complex at this wavelength, isoniazid can be determined in the range of 0.62–6.15 μg mL−1. This method was applied to the determination of isoniazid in pharmaceutical formulation and enabled the determination of isoniazid in microgram quantities.
-
Development of an optode membrane for high pH values.
Spectrochimica acta. Part A Molecular and biomolecular spectroscopy, 2006Co-Authors: Afsaneh Safavi, Marzieh SadeghiAbstract:Abstract The development of an optical pH sensor for high pH values is described based on the immobilization of Aniline Blue on an optically transparent Triacetylcellulose membrane. The membrane is useful for repetitive and reversible pH measurements in the pH range of 8.8–13. The relative standard deviation is about 1.6% and 2% for seven measurements of the maximum change at 579 nm from pH 9 to 10.8 and from pH 11.1 to 12.8, respectively. Other advantages of the sensor include rapid equilibration time, long term stability, reversibility, high sensitivity, freedom from interference of other cations and ease of fabrication.
-
design and characteristics of a mercury ii optode based on immobilization of dithizone on a Triacetylcellulose membrane
Sensors and Actuators B-chemical, 2004Co-Authors: Afsaneh Safavi, Mozhgan BagheriAbstract:Abstract The development of an optical sensor based on immobilization of dithizone on a Triacetylcellulose membrane is described. This optode has a linear range of 0.15–1.94 μg ml−1 (0.75–9.7 μM) of Hg2+ ions with a limit of detection of 20 ng ml−1 (0.1 μM). The response time of optode was within 6–9 min depending on the concentration of Hg2+ ions. The selectivity of optode to Hg2+ ions in universal buffer is good, with Cu2+ ions as the main interference. The sensor can readily be regenerated with potassium iodide solution. The optode is fully reversible.
-
Novel optical pH sensor for high and low pH values
Sensors and Actuators B-chemical, 2003Co-Authors: Afsaneh Safavi, Mozhgan BagheriAbstract:Abstract The development of an optical pH sensor based on immobilization of mixture of two dyes on a Triacetylcellulose membrane is described. The sensor has a useful pH range at low and high pH values, where glass electrodes show acidic and alkaline errors, respectively. Application of a back-propagation artificial neural network (ANN) model extends the measuring range of the proposed optode to the whole pH range. The results show very good agreement between true and predicted pH values. The response of the sensor is reversible and reproducible (R.S.D. less than 2%).
-
Optical sensor for high pH values
Analytica Chimica Acta, 1998Co-Authors: Afsaneh Safavi, H. AbdollahiAbstract:Abstract A new optical pH sensor for high pH values has been developed by covalently immobilizing Thiazole Yellow on an optically transparent Triacetylcellulose membrane, which had been previously hydrolyzed. The advantageous features of the sensor include (a) the ability to respond at high pH values (12.0–13.5), where glass electrodes show an alkaline error, (b) a rapid equilibration time, (c) high reproducibility, (d) long term stability, (e) high sensitivity and (f) ease of fabrication.
Albrecht Mannschreck - One of the best experts on this subject based on the ideXlab platform.
-
Axially chiral 2‐(dialkylamino)benzamides. Barriers to rotations, determined by NMR and by racemization (neighboring rotor substituents on arene systems, part 3)
Recueil des Travaux Chimiques des Pays-Bas, 2010Co-Authors: C. Kiefl, H. Zinner, T. Burgemeister, Albrecht MannschreckAbstract:The title compounds (Scheme 1, Y = NMe2) were investigated by variable-temperature NMR and/or by racemization of enantiomers enriched by liquid chromatography on microcrystalline Triacetylcellulose. For several reasons, a dialkylamino and a dimethylcarbamoyl group were used, for the first time, as neighboring rotor substituents on a benzene ring. Barriers to rotations about their aryl-nitrogen and/or aryl-carbon bonds were determined and assigned (Table I). Correlated or uncorrelated motions of these groups are possible for amides 11 and 19 bearing in their 3-positions tert-butyl substituents which hinder the aryl-nitrogen rotation. Uncorrelated rotations have been found for amide 15 (Figure 2) and thioamide 8 which have the less voluminous bromine atom in their 3-position.
-
Separation and Thermal Racemization of the Enantiomers of Spiro[cyclohexadiene-dihydroacridines]
Monatshefte für Chemie Chemical Monthly, 2000Co-Authors: Thomas Zimmermann, Nikola Pustet, Albrecht MannschreckAbstract:The enantiomers of substituted spiro[cyclohexadiene-dihydroacridines] were separated by enantioselective liquid chromatography with the sorbent/solvent systems Triacetylcellulose/methanol, tris-(3,5-dimethylphenylcarbamoyl)-cellulose/silica gel (Chiralcel OD^TM)/ n -heptane/2-propanol, and (+)-poly-(trityl methacrylate)/silica gel/ n -heptane/2-propanol. Interconversion barriers of the enantiomers were determined for a series of derivatives by thermal racemization. Electrocyclic ring opening/ring closure in terms of the Woodward-Hoffmann rules is discussed for the enantiomerization mechanism; the interconversion of the enantiomers by enolization is ruled out by deuterium exchange experiments.
-
The Enantiomers of Spiro(cyclohexadiene-indolines) and their Thermal Racemization
Monatshefte für Chemie Chemical Monthly, 1999Co-Authors: Thomas Zimmermann, Nikola Pustet, Albrecht MannschreckAbstract:The separation of the enantiomers of substituted spiro(cyclohexadiene-indolines) was performed by enantioselective liquid chromatography with the sorbent/solvent systems Triacetylcellulose/methanol, Triacetylcellulose/ethanol/water, and (+)-poly(trityl methacrylate)/SiO_2/ n -hexane/isopropanol. The interconversion barriers of the enantiomers were determined for a series of derivatives by thermal racemization. A mechanism for the thermal ring opening/ring closure is discussed in terms of the Woodward - Hoffmann rules. Die Enantiomeren von substituierten Spiro(cyclohexadien-indolinen) wurden durch enantioselektive Flüssigkeitschromatographie mit den Solvent/Sorbens-Systemen Triacetylcellulose/Methanol, Triacetylcellulose/Ethanol/Wasser und (+)-Poly(tritylmethacrylat)/SiO_2/n-Hexan/Isopropanol getrennt. Aus thermischen Racemisierungen wurden die Barrieren der Enantiomerisierung für eine Reihe von Derivaten bestimmt. Ein Mechanismus der thermischen Ringöffnung und des Ringschlusses wird auf der Grundlage der Woodward - Hoffmann -Regeln diskutiert.
-
The Enantiomers of Spiro(cyclohexadiene-indolines) and their Thermal Racemization
Monatshefte für Chemie Chemical Monthly, 1999Co-Authors: Thomas Zimmermann, Nikola Pustet, Albrecht MannschreckAbstract:The separation of the enantiomers of substituted spiro(cyclohexadiene-indolines) was performed by enantioselective liquid chromatography with the sorbent/solvent systems Triacetylcellulose/methanol, Triacetylcellulose/ethanol/water, and (+)-poly(trityl methacrylate)/SiO2/n-hexane/isopropanol. The interconversion barriers of the enantiomers were determined for a series of derivatives by thermal racemization. A mechanism for the thermal ring opening/ring closure is discussed in terms of the Woodward-Hoffmann rules.
