Accelerating Surface Photoreactions Using MoS2-FeS2 Nanoadsorbents: Photoreduction of Cr(VI) to Cr(III) and Photodegradation of Methylene Blue.

Nanocubic MoS2-FeS2, as a photocatalyst, was synthesized with high catalytic active edges and high specific surface areas with the capability of absorbing visible light. The results showed that the photocatalytic efficiency of nanocubic MoS2-FeS2 for adsorption/degradation of methylene blue (MB) as well as the reduction of Cr(VI) was high. The adsorption process was found to follow a kinetic model of a pseudo-second-order kind (Qe.cal = 464 mg g-1) along with an isotherm described by the Langmuir model with Qe.cal = 340 mg g-1. The photodegradation process was achieved by holes. It was found that the photodegradation rate constant of MB by MoS2-FeS2 (0.203 min-1) was about 22 times higher than that of MoS2 (0.0091 min-1). The percent apparent quantum yield for photoreduction of Cr(VI) to Cr(III) using MoS2-FeS2 (5.7%) was about 33 times higher than utilizing MoS2 (0.1709%). Therefore, the synergistically prolonged visible-light harvesting as well as the photocarrier diffusion length proved that MoS2-FeS2 nanotubes can effectively be utilized in environmental pollutant's remediation.

A novel selective and sensitive multinanozyme colorimetric method for glutathione detection by using an indamine polymer.

A sensitive and selective novel multinanozyme colorimetric method for glutathione (GSH) detection was developed. MnO2-nanozymes can catalyze the oxidation reaction of 3, 3՛-diaminobenzidine (DAB) and produce a brown indamine polymer. In the presence of GSH, this reaction slowly proceeds. When Au-nanozymes was used as peroxidase mimic along with MnO2-nanozymes, the analytical signal and selectivity (particularly, over Cys and AA) were significantly improved for GSH detection. Therefore, this novel multinanozyme system was further developed through optimization for the colorimetric detection of GSH. The calibration curve presented two wide linear range from 0.05 to 0.19 and 0.19-11.35 mg L̶ 1 with a very low detection limit of 0.02 mg L̶ 1 (5 nM) for GSH. The developed method was employed for human serum analysis without any dilution and any deproteinization.

A field-applicable colorimetric assay for notorious explosive triacetone triperoxide through nanozyme-catalyzed irreversible oxidation of 3, 3'-diaminobenzidine.

A field-applicable colorimetric assay for fast detection of notorious explosive triacetone triperoxide (TATP) has been developed through the selective irreversible oxidation of 3, 3'-diaminobenzidine by hydrogen peroxide (HP) liberated during the acidic hydrolysis/degradation of TATP in the presence of MnO2 nanozymes. The generated HP was detected by probing the absorbance of the product (indamine polymer) of the 3, 3'-diaminobenzidine (DAB) oxidation reaction at 460.0 nm. The UV-Vis measurements provided a linear range from 1.57 to 10.50 mg L-1 TATP with a detection limit of 0.34 mg L-1. The oxidation of DAB cannot proceed by molecular oxygen, thus it is selectively oxidized by H2O2; this prevents false-positive results from laundry detergents (containing O2-releasing substances). Moreover, a naked-eye field test was developed, and a fast spot test analyzing time of 5 s was achieved. The selectivity of the assay was checked by analyzing some synthetic samples prepared with a laundry detergent as camouflage. The results of the developed assay revealed quantitative recoveries for TATP whereas the standard nanozyme-based method showed significant false-positive results. Graphical abstract.

A three-dimensional origami microfluidic device for paper chromatography: Application to quantification of Tartrazine and Indigo carmine in food samples.

Herein, we report three-dimensional paper chromatography (3D-PC) as a micro-chromatographic platform. The method was based on applying the origami microfluidic device for separation, coupled by colorimetric methods for simultaneous determination. The microfluidic device fabrication was a facile printing approach. Two azo food dyes, Tartrazine (E102) and Indigo carmine (E132), were selected as a model analyte, while carbonate-bicarbonate buffer was used as the mobile phase. Our micro-chromatographic device is associated with two big advantages including needing very small volume of mobile phase ( ~12 µL) and ultrafast separation time (~35 s). Under the optimal conditions, the method provided acceptable linear ranges of 0. 0 g L1-18.0 g L1 (R2 = 0.997) for E102 and 0.070 g L1-10.0 g L1 for E132 and the limits of detection (3σ/slope) were evaluated as 0.620 and 0.060 g L1, respectively. The proposed method was successfully applied in the separation and quantification of these dyes in commercial food products such as jelly, candy, and four kinds of drink samples without any sample preparation prior to analysis. The mean recovery values for the real sample analysis were in the range of 100.14%-102.38% for E132 and E102 respectively. The inter-device relative standard deviations were in the ranges of 1.5%-11.8%. In total, our chromatographic µPAD is small (1.0 cm × 1.0 cm × 0.5 cm), portable, inexpensive, no need of specialized user, requires low volumes of sample (0.5 µL), and can perform separation using 12 µL of aqueous mobile phase in very short time.

Electrochemical sensing of hydrogen peroxide using a glassy carbon electrode modified with multiwalled carbon nanotubes and zein nanoparticle composites: application to HepG2 cancer cell detection.

A nanobiocomposite was prepared from multiwalled carbon nanotubes and zein nanoparticles. It was dispersed in water/ethanol and drop cast onto a glassy carbon electrode. The modified electrode can be used for electroreduction of H2O2 (typically at a working potential of -0.71 V vs. Ag/AgCl). The electrochemical properties of the electrode were investigated by cyclic voltammetry, linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Response to H2O2 is linear in the 0.049 to 22 µM concentration range, and the detection limit is 35 nM at pH 7.0. The sensor was successfully utilized for the measurement of H2O2 in a synthetic urine sample, and for monitoring the release of H2O2 from human dermal fibroblasts and human hepatocellular carcinoma cells. Graphical abstractSchematic representation of a novel metal- and enzyme-free electrochemical nanosensor. A glassy carbon electrode was modified with a nanocomposite prepared from multiwalled carbon nanotubes and zein nanoparticles. It was applied to the identification of liver cancer cells via sensing of H2O2 and has a very low detection limit.

Specification of Zwitterionic or Non-Zwitterionic Structures of Amphoteric Compounds by Using Ionic Liquids.

Some imidazolium-based ionic liquids were used to determine zwitterionic or non-zwitterionic structures of glycine and p-amino benzoic acid, as model amphoteric compounds, in their corresponding isoelectric point. To do this, the partitioning behaviors of both compounds between the ionic liquid and aqueous phase at different pH values were investigated. The results revealed that due to having different pH-dependent chemical structures, each compound showed different partitioning behavior. This observation was considered as a basis for introducing a green technique for understanding the real chemical structures (species), i.e. zwitterionic or non-zwitterionic structures of amphoteric compounds such as amino acids in the aqueous solutions. This study revealed the existence of a non-zwitterionic (neutral) structure for p-amino benzoic acid and a zwitterionic structure for glycine in their corresponding isoelectric points.

Simultaneous determination of captopril and hydrochlorothiazide by using a carbon ionic liquid electrode modified with copper hydroxide nanoparticles.

A carbon electrode modified with the ionic liquid octylpyridinium hexafluorophosphate and copper hydroxide nanoparticles was employed in an electrochemical assay for simultaneous determination of captopril (CPT) and hydrochlorothiazide (HCT). The electrode showed two well-defined oxidation peaks for CPT (at 0.22 V) and HCT (at 0.73 V, both vs. Ag/AgCl) at pH 8.0 using square wave voltammetry. Calibration plots are linear in the concentration ranges of 0.7-70 µM (CPT) and 3-600 µM (HCT), with detection limits of 12 and 60 nM, respectively. The electrode was repeatedly applied to simultaneous determination of CPT and HCT in pharmaceutical formulation without showing any fouling. Graphical abstract Application of carbon ionic liquid electrode (CILE) modified with Cu(OH)2 nanoparticles (Cu(OH)2NP/CILE) for the simultaneous determination of captopril (CPT) and hydrochlorothiazide (HCT) in pharmaceutical formulation is presented.

Gas-assisted dispersive liquid-phase microextraction using ionic liquid as extracting solvent for spectrophotometric speciation of copper.

Gas-assisted dispersive liquid-phase microextraction (GA-DLPME) has been developed for preconcentration and spectrophotometric determination of copper ion in different water samples. The ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate and argon gas, respectively, were used as the extracting solvent and disperser. The procedure was based on direct reduction of Cu(II) to Cu(I) by hydroxylamine hydrochloride, followed by extracting Cu(I) into ionic liquid phase by using neocuproine as the chelating agent. Several experimental variables that affected the GA-DLPME efficiency were investigated and optimized. Under the optimum experimental conditions (IL volume, 50µL; pH, 6.0; acetate buffer, 1.5molL(-1); reducing agent concentration, 0.2molL(-1); NC concentration, 120µgmL(-1); Ar gas bubbling time, 6min; argon flow rate, 1Lmin(-1); NaCl concentration, 6% w/w; and centrifugation time, 3min), the calibration graph was linear over the concentration range of 0.30-2.00µgmL(-1) copper ion with a limit of detection of 0.07µgmL(-1). Relative standard deviation for five replicate determinations of 1.0µgmL(-1) copper ion was found to be 3.9%. The developed method was successfully applied to determination of both Cu(I) and Cu(II) species in water samples.

Highly sensitive colorimetric determination of amoxicillin in pharmaceutical formulations based on induced aggregation of gold nanoparticles.

A novel, simple and highly sensitive colorimetric method is developed for determination of Amoxicillin (AMX). The system is based on aggregation of citrate-capped gold nanoparticles (AuNP) in acetate buffer (pH=4.5) in the presence of the degradation product of Amoxicillin (DPAMX). It was found that the color of gold nanoparticles changed from red to purple and the intensity of surface plasmon resonance (SPR) peak of AuNPs decreased. A new absorption band was appeared in the wavelength range of 600-700nm upon addition of DPAMX. The absorbance ratio at the wavelength of 660 and 525nm (A660/A525) was chosen as the analytical signal indirectly related to AMX concentration. The linearity of the calibration graph was found over the concentration range of 0.3-4.5µM AMX with a correlation coefficient of 0.9967. Under the optimum experimental conditions, the detection limit was found to be 0.15µM. The applicability of the method was successfully demonstrated by analysis of AMX in pharmaceutical formulations including capsules and oral suspensions.

Building optimal regression tree by ant colony system-genetic algorithm: application to modeling of melting points.

The classification and regression trees (CART) possess the advantage of being able to handle large data sets and yield readily interpretable models. A conventional method of building a regression tree is recursive partitioning, which results in a good but not optimal tree. Ant colony system (ACS), which is a meta-heuristic algorithm and derived from the observation of real ants, can be used to overcome this problem. The purpose of this study was to explore the use of CART and its combination with ACS for modeling of melting points of a large variety of chemical compounds. Genetic algorithm (GA) operators (e.g., cross averring and mutation operators) were combined with ACS algorithm to select the best solution model. In addition, at each terminal node of the resulted tree, variable selection was done by ACS-GA algorithm to build an appropriate partial least squares (PLS) model. To test the ability of the resulted tree, a set of approximately 4173 structures and their melting points were used (3000 compounds as training set and 1173 as validation set). Further, an external test set containing of 277 drugs was used to validate the prediction ability of the tree. Comparison of the results obtained from both trees showed that the tree constructed by ACS-GA algorithm performs better than that produced by recursive partitioning procedure.

Determination of amylose in Iranian rice by multivariate calibration of the surface plasmon resonance spectra of silver nanoparticles.

A simple and non-separative analytical method for selective determination of amylose in Iranian rice has been developed. It was based on the reduction of silver ions by amylose and production of Ag nanoparticles, which exhibit surface plasmon resonance (SPR) spectra in the ultraviolet/visible region. The formation of Ag nanoparticles in the presence of amylose was monitored by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The experimental conditions were optimized to obtain the highest yield for nanoparticle formation. Partial least square (PLS) regression as an efficient multivariate spectral calibration method was employed to make a connection between the SPR spectra of the generated Ag nanoparticles and the amylose content (AC) of the rice starch. The number of PLS latent variables was optimized by leave-one-out cross-validation utilizing prediction residual error sum of square (PRESS). The proposed model exhibited a high ability for prediction of amylose concentration in both standard starch samples and real rice samples prepared from different regions of Iran. The relative errors of prediction were almost lower than ±5% for different real samples and the detection limit was 3.23 weight percent of amylose in rice. In comparison to the reference method (Juliano method), the proposed method is simpler and does not need tedious sample preprocessing steps.

Partitioning of acidic, basic and neutral amino acids into imidazolium-based ionic liquids.

In this paper, partitioning behaviors of typical neutral (Alanine), acidic (Glutamic acid) and basic (Lysine) amino acids into imidazolium-based ionic liquids [C(4)mim][PF(6)], [C(6)mim][PF(6)], [C(8)mim][PF(6)], [C(6)mim][BF(4)] and [C(8)mim][BF(4)] as extracting solvents were examined. [C(6)mim][BF(4)] showed the best efficiency for partitioning of amino acids. The partition coefficients of amino acids in ionic liquids were found to depend strongly on pH of the aqueous solution, amino acid and ionic liquid chemical structures. Different chemical forms of amino acids in aqueous solutions were pH dependent, so the pH value of the aqueous phase was a determining factor for extraction of amino acids into ionic liquid phase. Both water content of ionic liquids and charge densities of their anionic and cationic parts were important factors for partitioning of cationic and anionic forms of amino acids into ionic liquid phase. Extracted amino acids were back extracted into phosphate buffer solutions adjusted on appropriate pH values. The results showed that ionic liquids could be used as suitable modifiers on the stationary phase of an HPLC column for efficient separation of acidic, basic, and neutral amino acids.

Novel PVC-membrane potentiometric sensors based on a recently synthesized sulfur-containing macrocyclic diamide for Cd2+ ion. Application to flow-injection potentiometry.

A new sulfur-containing macrocyclic diamide, 1,15-diaza-3,4,12,13-dibenzo-5,11-dithia-8-oxa-1,15-(2,6-pyrido)cyclooctadecan-2,14-dione, L, was synthesized, characterized and used as an active component for fabrication of PVC-based polymeric membrane (PME), coated graphite (CGE) and coated silver wire electrodes (CWE) for sensing Cd(2+) ion. The electrodes exhibited linear Nernstian responses to Cd(2+) ion in the concentration range of 3.3 x 10(-6) to 3.3 x 10(-1)M (for PME, LOD=1.2 x 10(-6)M), 2.0 x 10(-7) to 3.3 x 10(-1)M (for CWE, LOD=1.3 x 10(-7)M) and 1.6 x 10(-8) to 1.3 x 10(-1)M (for CGE, LOD=1.0 x 10(-8)M). The CGE was used as a proper detection system in flow-injection potentiometry (FIP) with a linear Nernstian range of 3.2 x 10(-8) to 1.4 x 10(-1)M (LOD=1.3 x 10(-8)M). The optimum pH range was 3.5-7.6. The electrodes revealed fairly good discriminating ability towards Cd(2+) in comparison with a large number of alkali, alkaline earth, transition and heavy metal ions. The electrodes found to be chemically inert, showing a fast response time of <5s, and could be used practically over a period of about 2-3 months. The practical utility of the proposed system has also been reported.

An efficient variable selection method based on the use of external memory in ant colony optimization. Application to QSAR/QSPR studies.

A novel approach for the use of external memory in ant colony optimization strategy for solving descriptor selection problem in quantitative structure-activity/property relationship studies is described. In this approach, several ant colony system algorithms are run to build an external memory containing a number of elite ants. In the next step, all of the elite ants in the external memory are allowed to update the pheromones. Then the external memory is emptied and the updated pheromones are used again, by several ant colony system algorithms to build a new external memory. These steps are iteratively run for certain number of iterations. At the end, the memory will be containing several top solutions to the problem. The proposed approach was applied to solving variable selection problem in quantitative structure-activity/property relationship studies of rate constants of o-methylation of 36 phenol derivatives and activities of 31 antifilarial antimycin compounds, for which the obtained results revealed that both the speed and the solution quality are improved compared to conventional ant colony system algorithms.

Extraction and high performance liquid chromatographic determination of 3-indole butyric acid in pea plants by using imidazolium-based ionic liquids as extractant.

In this paper, imidazolium-based ionic liquids [C(4)mim][PF(6)], [C(6)mim][PF(6)], [C(8)mim][PF(6)], [C(6)mim][BF(4)] and [C(8)mim][BF(4)] were tested as extracting solvents for removal of 3-indole butyric acid (IBA) from aqueous media with subsequent determination using HPLC. Percent extraction of IBA was strongly affected by pH of aqueous phases and the chemical structures of ionic liquids (ILs). Extraction of IBA was quantitative in the pH values lower than pK(a) of IBA. Considering both extraction and stripping efficiencies of IBA, [C(4)mim][PF(6)] was found to act more efficient than other studied ILs. Capacity of [C(4)mim][PF(6)] was 17.6x10(-4)mmol IBA per 1.0 mL of IL. Ionic strength of aqueous phase and temperature had shown no serious effects on extraction efficiency of IBA. A preconcentration factor of 100 and a relative standard deviation of 1.16% were obtained. It was found that ionic liquid phase was reusable almost five times for extraction/stripping purposes. 3-Indole acetic acid showed interferential effect in the extraction step. In order to assess the applicability of the method, extraction and stripping of IBA from pea plants and some other samples were studied.

A comparative study between PCR and PLS in simultaneous spectrophotometric determination of diphenylamine, aniline, and phenol: Effect of wavelength selection.

Partial least squares (PLS) and principal component regression (PCR) have received considerable attention in the chemometrics for multicomponent analysis where superiority of one over another is a challenging problem yet. Considering the effect of wavelength selection, a comparison was made between PCR and PLS methods by application those to simultaneous spectrophotometric determination of diphenylamine (DPA), a compound from the third European Union list of priority pollutants, and its environmentally related products aniline and phenol. The UV absorbance spectra of the methanolic solutions of the analytes were measured in the concentration ranges of 1.0-10.0 microg mL(-1) and then subjected to PCR and PLS. The models refinement procedure and validation was performed by cross-validation. A modified changeable size moving windows strategy, where optimized the intervals between the sensors in a selected windows, was also proposed to select the more informative spectral regions for each of the analytes. It was found that wavelength selection improved the quality of predictions for both regression methods whereas more reliable results were obtained by removing of the highly collinear neighboring wavelengths. The resultant data explained that PLS produced more or less better results when whole spectral data were used but in the case of selected wavelength regions both methods produced similar results and no comments could be given about the superiority of one against another. The major difference was obtaining the higher number of factors for PCR, which is not a significant problem.

Genetic algorithm applied to the selection of factors in principal component-artificial neural networks: application to QSAR study of calcium channel antagonist activity of 1,4-dihydropyridines (nifedipine analogous).

A QSAR algorithm, principal component-genetic algorithm-artificial neural network (PC-GA-ANN), has been applied to a set of newly synthesized calcium channel blockers, which are of special interest because of their role in cardiac diseases. A data set of 124 1,4-dihydropyridines bearing different ester substituents at the C-3 and C-5 positions of the dihydropyridine ring and nitroimidazolyl, phenylimidazolyl, and methylsulfonylimidazolyl groups at the C-4 position with known Ca(2+) channel binding affinities was employed in this study. Ten different sets of descriptors (837 descriptors) were calculated for each molecule. The principal component analysis was used to compress the descriptor groups into principal components. The most significant descriptors of each set were selected and used as input for the ANN. The genetic algorithm (GA) was used for the selection of the best set of extracted principal components. A feed forward artificial neural network with a back-propagation of error algorithm was used to process the nonlinear relationship between the selected principal components and biological activity of the dihydropyridines. A comparison between PC-GA-ANN and routine PC-ANN shows that the first model yields better prediction ability.

A study of the photo-degradation kinetics of nifedipine by multivariate curve resolution analysis.

A multivariate curve resolution method based on the combination of Kubista approach and iterative target transformation method of Gemperline has been proposed. This method is a soft model and need no information about the spectrum of the product and mechanism of the reaction. The method was used to study the degradation kinetics of nifedipin, 1,4-dihydro-2,6-dimethyl-4-(2-nitrophenyl)-3,5-pyridine dicarboxilic acid dimethyl ester, upon exposure to the light of a 40 W tungsten lamp. The spectra of the nifedipine, collected at different lighting times, were subjected to the factor analysis and two chemical components were detected in the reaction system. Pure spectra of the components involved and their concentration profiles were obtained. The results revealed that the photodecomposition kinetics of nifedipine is zero-order at the beginning of the reaction. However, when the reaction preceded more than 50%, the kinetics of reaction changed to a first-order manner. The rate constants for the zero-order and first order regions were estimated as regions (4.96+/-0.13) x 10(-9) M(-1) s(-1) and (6.22+/-0.10) x 10(-5) s(-1), respectively.

Quantitative structure-activity relationship study of recently synthesized 1,4-dihydropyridine calcium channel antagonists. Application of the Hansch analysis method.

The Hansch analysis method was applied to a series of recently synthesized nifedipine analogues containing nitroimidazolyl, phenylimidazolyl, and methylsulphonylimidazolyl groups at the C-4 position and different ester substituents at C-3 and C-5 positions of the dihydropyridine ring. Hydrophobic, electronic, inductive, and resonance substituent constants were used. The effect of these parameters on the biological activity of 1,4-dihydropyridines (calcium channel antagonist activity in Guinea-pig ileal cells, log (1/IC50)) was determined by multiple linear regression analysis. Linear and quadratic relationships were obtained between the activity and these parameters. It was found that both electronic and hydrophobic interactions occur between the nifedipine analogues and the receptor.