Colorimetric determination of acidity constant using a paper-based microfluidic analytical device

Acid dissociation constant is an important chemical characteristic of organic and inorganic compounds and it affects both chemical properties and biological activities of the molecules. Herein, a very simple, fast and cost-effective method based on microfluidic technology has been reported for colorimetric determination of acidity constants. The designed device works based on pH-metric titration of colorful indicators followed by colorimetric measurements by a smart phone mobile device or a flatbed scanner. So, it does not need sophisticated instrumentation and is accomplished in a very short time (about 1 min). All titration steps are transferred on a star-like designed µPAD device: (1) spotting 0.3 µL buffers of different pHs at the end of the channels (reaction zones), (2) spotting a 30 µL portion of the indicator on the center of µPAD followed by movement of indicator solution toward the reaction zone by capillary action of the paper. The measured color change of the indicators at the reaction zone is fitted to the Henderson–Hasselbalch equation, through which acidity constants are calculated. The performance of the device was evaluated by measuring acidity constant of 4 indicators including bromothymol blue, bromocresol green, bromocresol purple and phenolphthalein. A very close agreement was achieved between those measured by the suggested device here and the previously reported values. The reproducibility of this method was lower than 5% for relative standard deviation of three replicate measurements.     

Preparation and characterization of curcumin loaded gold/graphene oxide nanocomposite for potential breast cancer therapy

Research on Chemical Intermediates - Graphene oxide (GO) and gold/graphene oxide (Au/GO) nanocomposites were fabricated through a facile chemical route and their application as excellent...     

Polarizability of the Si<Subscript>60</Subscript>H<Subscript>60</Subscript> Derivatives Containing Epoxide Moieties (Si<Subscript>60</Subscript>H<Subscript>60−2n</Subscript>O<Subscript>n</Subscript> with n up to 30): A DFT Study

We have applied density functional theory calculations to study polarizability of the Si₆₀H₆₀ derivatives with epoxide moieties (Si₆₀H_60?2nO_n with n up to 30). The results show that mean polarizability, α, of oxygen-containing silicon fullerene derivatives is higher than that of Si₆₀H₆₀. The mean polarizabilities of the isomers slightly depend on the positional relationship of the epoxide moieties, and are determined mainly by the number of epoxide moieties. Mean polarizabilities of Si₆₀H_60?2nO_n linearly increase with n, and are characterized by the depression of polarizability. The formula describing the mean polarizability as a function of the number of epoxide groups has been obtained, which may be important for the design of silicon-containing nanostructures with regulated polar parameters.     

Binuclear paddle-wheel platinum(II) and platinum(III) complexes containing 4-methyl-4H-1,2,4-triazole-3-thiol ligand: Synthesis,X-ray studies,and spectroscopic characterization

The complex [Pt₂(μ-mtrzt)₄(mtrzt)₂] (1) was synthesized from the reaction of a mixture of 4-methyl-4H-1,2,4-triazole-3-thiol (Hmtrzt) and ethylenediamine (en) with K₂PtCl₄ in CH₃OH/H₂O (2:1) as solvent. The complex [Pt₂(μ-mtrzt)₄] (2) was synthesized by the same procedure as described for preparation of complex 1 but in the absence of ethylenediamine. Both complexes were characterized by elemental analysis, IR,¹H NMR,¹³C{¹H}NMR, UV-Vis, as well as luminescence spectroscopy and their structures were analyzed by single-crystal X-ray diffraction method. The X-ray structure determinations show that complexes of 1 and 2 have binuclear structures in a paddle-wheel fashion with Pt-Pt distances of 2.6628(7) and 2.7977(16)Å, respectively. In complex 1, each platinum(III) atom has a distorted octahedral coordination geometry with the sulfur atom and the second platinum subunit in axial positions and two nitrogen and two sulfur atoms in equatorial positions. Also, in complex 2, each platinum(II) atom has a distorted square-pyramidal coordination geometry with the second platinum subunit in axial position and two nitrogen and two sulfur atoms in equatorial positions. In addition, intermolecular C?H···N and C?H···S hydrogen bonds in 1 and 2 as well as intermolecular anagostic C?H···Pt and C?H···π interactions in 2 are effective in the stabilization of the crystal packing of these complexes.     

DFT and MP2 Calculations on Tautomers and Water-Assisted Proton Transfer on 1,2,5-Oxadiazol-4,3-diamine

In this work a detailed quantum-chemical comparison of the relative stability of six tautomers of 1,2,5-oxadiazol-4,3-diamine studied in the gas phase and solution. Theoretical calculations are carried out by the density functional theory (DFT/B3LYP) and MP2 methods using the standard 311++G(d,p) basis set. The results indicate that A is the most stable form in the gas phase and also is the predominant tautomer in solution at the DFT and MP2 methods. The transition states of proton transfer reaction are calculated. The variation of dipole moments and charges on atoms are studied in various solvent. Specific solvent effects with addition of one water molecule near the electrophilic centers of tautomer investigated. Also the transition state of proton transfer assisted by a water molecule was investigated.     

Synthesis of 3-(quinolin-2-yl)indolizines through iodine-mediated sp3C–H functionalization of azaarenes

An efficient approach toward C–H bond activation using iodine-mediated sp³C–H bond functionalization for the synthesis of dialkyl 3-(quinolin-2-yl)indolizine-1,2-dicarboxylates and dialkyl 3-(quinolin-2-yl)pyrrolo[2,1-a]isoquinoline-1,2-dicarboxylates through 1,3-dipolar cycloaddition reaction of nitrogen ylides with acetylenic esters is described.     

Heteropolyacid immobilized on polymer/magnetic zeolite nanocomposite as a new and recyclable catalyst for the selective oxidation of alcohols

A new magnetic oxidation catalyst was prepared using immobilization of tungstophosphoric acid on poly(N-vinylimidazole) entrapped magnetic nanozeolite and characterized by FTIR, TGA, XRD, SEM, TEM, EDX, VSM, and ICP-OES. The resulting heterogeneous catalyst displays high catalytic performance for selective oxidation of alcohols compared to the other catalysts. The catalyst could be reused eight times without any loss of catalytic activity.     

Second-order standard addition for deconvolution and quantification of fatty acids of fish oil using GC-MS

In the present work two second-order calibration methods, generalized rank annihilation method (GRAM) and multivariate curve resolution-alternating least square (MCR-ALS) have been applied on standard addition data matrices obtained by gas chromatography-mass spectrometry (GC-MS) to characterize and quantify four unsaturated fatty acids cis-9-hexadecenoic acid (C16:1ω7c), cis-9-octadecenoic acid (C18:1ω9c), cis-11-eicosenoic acid (C20:1ω9) and cis-13-docosenoic acid (C22:1ω9) in fish oil considering matrix interferences. With these methods, the area does not need to be directly measured and predictions are more accurate. Because of non-trilinear conditions of GC-MS data matrices, at first MCR-ALS and GRAM have been used on uncorrected data matrices. In comparison to MCR-ALS, biased and imprecise concentrations (%R.S.D. = 27.3) were obtained using GRAM without correcting the retention time-shift. As trilinearity is the essential requirement for implementing GRAM, the data need to be corrected. Multivariate rank alignment objectively corrects the run-to-run retention time variations between sample GC-MS data matrix and a standard addition GC-MS data matrix. Then, two second-order algorithms have been compared with each other. The above algorithms provided similar mean predictions, pure concentrations and spectral profiles. The results validated using standard mass spectra of target compounds. In addition, some of the quantification results were compared with the concentration values obtained using the selected mass chromatograms. As in the case of strong peak-overlap and the matrix effect, the classical univariate method of determination of the area of the peaks of the analytes will fail, the “second-order advantage” has solved this problem successfully.     

Indirect determination of free cyanide in water and industrial waste water by flow injection-atomic absorption spectrometry

A simple and rapid flow injection system is proposed for indirect determination of cyanide by flame atomic absorption spectrometry. It consists of a microcolumn of immobilized salen (N,N′-bis(salicylidene)ethylenediamine) on sodium dodecyl sulfate (SDS)-coated alumina saturated with silver ion and a carrier of dilute solution of sodium hydroxide (10⁻⁵ mol L⁻¹). The micro-column was located between the injection valve and nebulizer of atomic absorption spectrometry. Injection of 250 μL of aqueous cyanide standard or sample solution at pH range of 9–11 cause elution of silver as silver cyanide complexes, which was then measured by flame atomic absorption spectrometry. The absorbance was proportional to the concentration of cyanide in the sample. The graph of absorbance (as peak height) vs. cyanide concentration was linear over the concentration range of 0.1–10 mg L⁻¹ of cyanide, and the detection limit was 0.06 mg L⁻¹. The relative standard deviation at 1 and 3 mg L⁻¹ of cyanide concentration were 4.1 and 4.7%, respectively. The method was successfully applied to determination of cyanide in water and industrial waste waters, and the accuracy was examined through independent analysis by accepted method of pyridine-barbituric acid.