Hydrogen atom abstraction from Piperazine by hydroxyl radical: a theoretical investigation

Dual level of quantum mechanical calculations have been carried out for hydrogen abstraction from Piperazine [HN(CH₂CH₂)₂NH] initiated by OH radical. Geometry optimisation and frequency calculations of all species involved in the titled reaction have been performed at M06-2X/6-31+G(d,p) level of theory. For the accuracy in the thermochemistry and kinetics data, single-point energy calculations have been further carried out at coupled cluster CCSD(T) method along with 6-311G(d,p) basis set. An energy profile diagram for the reaction has been plotted along with pre-reactive and post-reactive complexes at entrance and exit channels. Intrinsic reaction coordinates (IRCs) calculations have been performed for identification of real transition states that connect it via reactant to product. Our result shows that the H-atom abstraction takes place from the C–H position of Piperazine. The rate constant is calculated using canonical transition state theory (CTST) is found to be 2.86 × 10^?10 cm³ molecule^?1 s^?1 which is in good agreement with the reported experimental rate constant (2.38 ± 0.28) × 10^?10 cm³ molecule^?1 s^?1 at 298 K. We have also reported rate constant for the temperature range 300–500 K. Using group-balance isodesmic reaction, the standard enthalpies of formation for Piperazine and product radicals generated by hydrogen abstraction are reported. The branching ratios for both reaction channel (i.e. H-abstraction from –CH₂ and –NH position of Piperazine) are found to be 93% and 7%, respectively. The calculated atmospheric life time of Piperazine is found to be 0.97 hour.     

Application of PMR Spectroscopy in Pharmaceutical Analysis Assay of Piperazine

A new method, involving the application of PMR spectroscopy for the assay of piperazine anhydrous, hydrate and its salts is described. The PMR spectrum of piperazine in D₂o has a well-defined singlet system for the piperazine ring protons which is chosen for the quantitative measurement. The principal of the method involves comparing the integral of this signal to that of the sharp singlet (positioned at 0.00 ppm) of trimethyl silyl propane sulfonate sodium salt which is used as PMR reference and internal standard.

The proposed method which is simple and rapid gives results of high degree of accuracy and percision when applied to the assay of pure piperazine anhydrous, hydrate and dihydrochloride samples. An average recovery percent of 100.24 ± 0.89 was obtained. The method was used for the analysis of piperazine hydrate in syrup and effervecent granules. The average recovery percent of the added piperazine was 99.64 ± 0.75. In addition the PMR spectrum obtained helps in confirming the identity and purity of the drug or its salts.     

SPECTROPHOTOMETRIC DETERMINATION OF ZINC IN PHARMACEUTICAL SAMPLES USING DI-2-PYRIDYL KETONE SALICYLOYLHYDRAZONE

ABSTRACT

A highly sensitive procedure for spectrophotometric determination of zinc has been developed. At pH 4.5, in 50% (V/V) ethanol-water medium and in the presence of di-2-pyridyl ketone salicyloylhydrazone (DPKSH), zinc forms a yellow complex which has maximum absorption at 376 nm The molar absorptivity is 4.82×10⁴ L mol^?1 cm^?1. The detection limit of this method is 62.1 nM for Zn(II).

The method has been applied to the spectrophotometric determination of zinc in pharmaceutical formulations and the results comply with those obtained by AAS. The proposed method is simple, rapid and accurate.     

UV-Spectroscopic Determination of Mixtures of Tetramethrin and Piperonyl Butoxide in Pharmaceutical Formulations

Abstract

A simple rapid and accurate UV-spectroscopic method have been developed for determination of tetramethrin in presence of piperonyl butoxide, which are present in Licid^R, a newly introduced pharmaceutical drug in Egypt used as antilice, and antiscopis. The method is applicable in the concentration range of 1–12 μg.ml^?1 and 1–50 μg.ml^?1 for tetramethrin and piperonylbutoxide respectively. Average recoveries for tetramethrin and piperonyl butoxide in Licid^R spray and Licid^R lotion are 98.14 ± 0.3 – 103.88 ± 1.88 (Tetra), 103.78 ± 1.23 (piperonyl) and 100.62 ± 0.89 – 100.94 ± 1.10 (Tetra), 102.38 ± 1.02 (piperonyl) for the spray and lotion, respectively.     

(2R,5S)-N-间氟苄基-2,5-二甲基哌嗪的合成

以(2R,5S)-2,5-二甲基哌嗪为原料,经过成盐,单取代反应,用D-酉石酸对光学异构体的手性拆分,用氢氧化钠游离,最终合成(2R,5S)-N-间氟苄基-2,5-二甲基哌嗪,反应总收率为83％.该物质的合成未见文献报道,目标化合物用1H NMR,IR进行结构表征.     

Crystal Structure and Interaction of 6-Amino Coumarin with Nitrite Ion for Its Selective Fluorescence Detection

ABSTRACT

6-Amino coumarin has been established as an efficient nitrite ion selective fluorescent sensor. The developed method shows linearity up to 1.6 × 10^?6 mol L^?1 of nitrite ion concentration. Interference from other common anions is almost negligible. The reagent shows strong binding affinity towards nitrite ion as evident from its binding constant value (5.8 × 10⁴), estimated by Stern-Volmer method. Some real samples were analyzed. Single crystal X-ray structure of the reagent is reported. Preliminary computational studies on the molecular level interaction between the reagent and nitrite ion were performed by density functional theory (DFT, B3LYP) method.     

Facile synthesis of labile gold nanodiscs by the Turkevich method

The Turkevich method has been the preferred one for synthesis of gold nanoparticles (AuNPs), owing to its apparent simplicity and facility of replacing the citrate ions on the particle surface by molecules exhibiting different functionalities. Using the most common procedure labile spherical nanoparticles are usually obtained by this method. Here, by using factorial design of experiments, we demonstrated that gold nanodiscs (AuNDs) with short aspect ratio can be generated by the Turkevich method when Au:citrate ratio is 1:1. In comparison with the CTAB capped gold nanorods (AuNR), the citrate stabilized AuNDs exhibited a more labile character, allowing fast ligand exchange reactions and easy functionalization of the nanoparticle surface. In the presence of 4-mercaptopyridine (4-mpy), the surface enhancement Raman scattering effect was 100 and 1000 times higher than the one observed for CTAB-AuNR and spherical AuNPs, respectively, increasing the 4-mpy detection limit to 2.5 × 10^?9 molL^?1.     

Rationally designed non-peptides: Variously substituted piperazine libraries for the discovery of bradykinin antagonists and other G-protein-coupled receptor ligands

Summary Molecular modeling studies of potent decapeptide bradykinin antagonists suggested the de novo design of peptide mimetics based on a 1,2,3,4-tetrasubstituted 1,4-piperazin-6-one scaffold. These de novo-designed antagonists exhibited only modest potency (IC₅₀ 55 M) on a cloned human B₂ receptor and antagonist activity in an in vitro human-cell functional assay. The success of these structures led to the creation of prototype libraries based on variously substituted 1,4-piperazine scaffolds, which allowed a rapid and general search of pharmacophores attached to a piperazine scaffold. The parent piperazinedione structures and fully reduced piperazine libraries differ from recently reported diketopiperazine libraries in the use of diverse nonnatural amino acids, on-resin-submonomer synthesis to provide more diverse N-substituted structures, and the adaptation of simultaneous ring closure and resin cleavage to drive the formation of highly hindered amide bonds. Using this chemistry, a rationally directed non-peptide library of approximately 2500 N,N-disubstituted piperazines and piperazinediones was synthesized and screened for ligand affinity on bradykinin, neurokinin, and opioid receptors. A number of lead structures were identified. Notably, a bradykinin antagonist lead, CP-2458, with good receptor selectivity and antagonist activity in human-cell assays was identified and is undergoing optimization by traditional and combinatorial methods.Abbreviations BK bradykinin - Boc tert-butoxycarbonyl - Cbz carboxybenzyl - DMF dimethylformamide - DMSO dimethylsulfoxide - Fmoc fluorenylmethoxycarbonyl - HBTU O-benzotriazol-l-yl-N,N,N,N-tetramethyluronium hexafluorophosphate - HPLC high-performance liquid chromatography - MALDI-MS matrix assisted laser desorption ionization-mass spectrometry - PyBroP bromo-tris-pyrrolydino-phosphonium hexafluorophosphate - RDDA rationally directed diverse analogs - TFA trifluoroacetic acid     

High-resistivity nickel–zinc ferrites by the citrate precursor method

Nickel–zinc ferrites of different compositions, Ni_1−xZn_xFe₂O₄ with x=0.2, 0.35, 0.5 and 0.6, have been prepared by a precursor method involving citrate precursors of the concerned metals and mixing them in solution state. Resistivity has been studied as a function of composition and sintering temperature. It is observed that NiZn ferrites prepared by this method have resistivity ⩾10⁸ Ω cm which is higher by atleast two orders of magnitude than that reported (⩽10⁶ Ω cm) for ferrites prepared by the conventional ceramic method. This is attributed to better purity as well as better compositional and microstructural control achievable by the citrate method. High resistivity makes these ferrites suitable particularly for high-frequency applications where eddy current losses are required to be low.     

Solid-Phase Extraction Using Polymer-Based Cartridge Modified with 2-(2-benzothiazolylazo)-3-hydroxyphenol for Preconcentration of Uranium(VI) Ions from Water and Real Samples

ABSTRACT

A highly sensitive, selective, and rapid method for the determination of ng mL^?1 level of U(VI) based on the rapid reaction of U(VI) with 2-(2-benzothiazolylazo)-3-hydroxyphenol (BTAHP) and the solid-phase extraction of the colored complex with a reversed-phase polymer-based C18 cartridge was developed. The BTAHP reacted with U(VI) to form a violet complex of molar ratio 2:1 [BTAHP to U(VI)] in the presence of 4.0 M of phosphoric acid solution and Triton X-114 medium. This complex was enriched by the solid-phase extraction with a polymer-based C18 cartridge. The enrichment factor of 200 was achieved. The molar absorptivity of the complex is 2.73 × 10⁶ L mol^?1 cm^?1 at 639 nm in the measured solution. The system obeys Beer's law in the range of 2.0–125 ng mL^?1, whereas the optimum concentration range obtained from Ringbom plot was 8.0–115 ng mL^?1. The relative standard deviation for 10-replicates sample of 100 ng mL^?1 level is 1.05%. The detection and quantification limits are 0.6 and 1.98 ng mL^?1 in the original sample. This method was applied to the determination of uranium(VI) in sea, tap, and waste waters, ore standard reference material, soil and sediment samples with good results comparing to the graphite furnace atomic absorption spectroscopy (GFAAS) method.     

A method of quenching in fusing state under high static pressure used to study quasicrystals

Abstract

In this paper, a new method of quenching in fusing state under high static pressure (MQFSHP), which was developed in the beginning of 1986 by our group^1,2, used to study quasicrystals in alloys has been introduced.     

A multispectrum fitting procedure to deduce molecular line parameters: Application to the 3-0 band of 12 C 16 O

To deduce accurate infrared molecular line parameters (positions at zero pressure, pressure-shifting and pressure-broadening coefficients, collisional narrowing coefficients, and intensities) from rovibrational spectra, an automatic method based upon a multispectrum fitting procedure has been set up, able to treat simultaneously several laboratory Fourier transform spectra. A validation of this method, using absorption spectra of the 3-0 vibrational band of CO around 6 350 cm^-1, already used to measure line intensities and self-broadening coefficients, is presented, and the advantages of the method are pointed out. The self-collisional narrowing of CO was observed and determined for the first time in Fourier transform spectra: β = 0.028±0.004 cm^-1 atm^-1 at about 296 K. Received 21 September 2000 and Received in final form 15 January 2001     

Spectrophotometric Determination of Trace Amounts of Mercury with 3-(2-Thiazolylazo)-2, 6-Diaminopyridine and Gelatine

Abstract

A sensitive method for the determination of trace amounts of mercury by complexation with 3-(2-Thiazolylazo)-2, 6-diaminopyridine (2, 6-TADAP) is described. Hg(II) forms a 1:2 complex with the reagent. Beer's law is obeyed over the range 5–40 μg in the total volume of 10 ml. The molar absorptivity was found to be 1.4 × 10⁴ L mol^?1 cm^?1. This method is simple, rapid and involves no extraction steps whereby the use of gelatine as a solubilizing agent is described.     

A Spectrophotometric Method for the Determination of Buclizine Hydrochloride Using the Charge-Transfer Spectrum of Buclizine-Iodine Complex

Abstract

A simple and sensitive spectrophotometric method is described for the determination of buclizine hydrochloride in bulk and tablets form. The method is based on the formation of charge-transfer complex between buclizine, as n-donor, and iodine, as Δ acceptor, which measured spectrophotometrically at 295 and 355 nm. A Job's plot indicated a 1:1 complex between the drug and iodine and Beer's law was obeyed in a concentration range of 4–30 μg ml^?1. A more detailed investigation of the complex was made with respect to its association constant and the free energy change. The method is simple and sensitive and has been applied successfully to the analysis of laboratory-made tablets without any interference from the tablet excipients. To validate the method, the results obtained were compared statistically with a newly developed uv-derivative spectrophotometric method. The charge-transfer method was favored due to its higher sensitivity, cheap coast and available equipments.     

Effect of pressure on the properties of DH diode lasers in AlxGa1-xAsySb1-y/GaSb system

Abstract

A helium pressure appparatus for diode laser studies up to 1.4 GPa at 77–300 K has been developed. DH lasers with Al_xGa_1-xAs_ySb_1-y active layers (x=0-0.05) lattice-matched to GaSb substrates have been investigated. It has been shown that in lasers with x,y=0 pressure dependences of the threshold current density (J_th) and the average electron lifetime at the threshold (τ) measured at 80 K depend strongly on the quadratic recombination of L^c ₆ electrons, the characteristic coefficient being 1.5×10^?11 cm³s^?1. The pressure-composition equivalence coefficient dx/dP=2.2×10^?10 Pa^?1 has been obtained for the lowest temperatures used.     

Real-time dynamic vocal tract imaging using an accelerated spiral GRE sequence and low rank plus sparse reconstruction

PurposeTo develop a real-time dynamic vocal tract imaging method using an accelerated spiral GRE sequence and low rank plus sparse reconstruction.MethodsSpiral k-space sampling has high data acquisition efficiency and thus is suited for real-time dynamic imaging; further acceleration can be achieved by undersampling k-space and using a model-based reconstruction. Low rank plus sparse reconstruction is a promising method with fast computation and increased robustness to global signal changes and bulk motion, as the images are decomposed into low rank and sparse terms representing different dynamic components. However, the combination with spiral scanning has not been well studied. In this study an accelerated spiral GRE sequence was developed with an optimized low rank plus sparse reconstruction and compared with L1-SPIRiT and XD-GRASP methods. The off-resonance was also corrected using a Chebyshev approximation method to reduce blurring on a frame-by-frame basis.ResultsThe low rank plus sparse reconstruction method is sensitive to the weights of the low rank and sparse terms. The optimized reconstruction showed advantages over other methods with reduced aliasing and improved SNR. With the proposed method, spatial resolution of 1.3*1.3 mm² with 150 mm field-of-view (FOV) and temporal resolution of 30 frames-per-second (fps) was achieved with good image quality. Blurring was reduced using the Chebyshev approximation method.ConclusionThis work studies low rank plus sparse reconstruction using the spiral trajectory and demonstrates a new method for dynamic vocal tract imaging which can benefit studies of speech disorders.     

Rapid determination of ethyl pentanoate in liquor using Fourier transform near-infrared spectroscopy coupled with chemometrics

ABSTRACT

The feasibility of Fourier transform near-infrared spectroscopy for rapid determination of ethyl pentanoate in Chinese liquor was investigated. A total of 108 liquor samples from production line were analyzed with Fourier transform near-infrared transmission spectroscopy. The calibration model for ethyl pentanoate content prediction was established with partial least square, and validated using internal cross validation. In a calibration set (80 samples), the coefficient of determination was 0.958, with the corresponding root mean square error of cross validation 0.020 g L^?1. In a validation set (28 samples), the coefficient of determination was 0.964, with the root mean square errors of prediction 0.023 g L^?1, and the bias value (0.005 g L^?1) for the validation set was less than the bias confidence limits value (0.009 g L^?1), indicating that the resulting near-infrared spectroscopy prediction model has good performance for online rapid determination of ethyl pentanoate in Chinese liquor. The determination of ethyl pentanoate in liquor can be completed in less than 2 min per sample using the near-infrared spectroscopy prediction model. The near-infrared spectroscopy combining chemometrics as a rapid analytical method has a promising application prospect of application in the liquor production field.     

Dispersive liquid–liquid microextraction based on solidification of floating organic drop for separation and preconcentration of malachite green before its determination by flow injection spectrophotometry

ABSTRACT

A simple and fast dispersive liquid–liquid microextraction based on solidification of floating organic drop has been developed for the separation and preconcentration of malachite green in water samples prior to its determination by flow injection spectrophotometry. Sodium lauryl sulfate, an anionic surfactant, was used for the ion-pair formation with malachite green. The factors affecting the ion-pair formation and extraction were optimized. Under the optimized conditions (volume of 1-undecanol as the extraction solvent, 40 μL; the volume of ethanol as the disperser solvent, 100 μL; sodium lauryl sulfate concentration, 7.5 × 10^?7 mol L^?1, and the pH of the sample, ～3.0), the calibration graph was linear over the range of 0.8–25 µg L^?1 with the detection limit of 0.3 µg L^?1 and the preconcentration factor of 750. The relative standard deviation at 7 µg L^?1 (n = 6) was found to be 2.1%. The developed method was successfully applied to the determination of malachite green in river water and fish farming water samples.     

Sensitive Detection of Luteolin Using Thioglycolic Acid–Capped Cadmium Telluride/Cadmium Sulphide Quantum Dots as the Fluorescent Probe

ABSTRACT

A sensitive and simple method for the determination of luteolin (LTL) was developed based on the fluorescence quenching effect of LTL for thioglycolic acid–capped (TGA-capped) CdTe/CdS quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 0.3 to 20.0 µg · mL^?1 with a correlation coefficient of 0.9972, and the detection limit was 7.2 ng · mL^?1. The fluorescence quenching mechanism has been proposed on the basis of electron transfer supported by ultraviolet-visible (UV-Vis) absorption, fluorescence (FL) spectroscopy. The proposed method was successfully applied to the determination of LTL in commercial capsules and human urine samples. It manifested several advantages such as high sensitivity, short analysis time, low cost, and ease of operation.     

Solid-Phase Spectrophotometric Determination of Beryllium at ng mL−1

Abstract

A microdetermination method at ng mL^?1 level for beryllium by solid-phase spectrophotometry was been developed. Chrome Azurol S was used as chromogenic reagent to form a blue complex which was easily and strongly sorbed and concentrated on a dextran-type anion-exchange resin. The resin-phase absorbances at 594- and 800 nm were measured directly. Beryllium could be determined over the 1.5 - 15.0 ng mL^?1 range with a RSD of 2.7 % by using 100 mL of sample solution. The detection limit was 0.21 ng mL^?1. By using only 10 mL of sample solution, the calibration graph was linear over the concentration range 10–85 ng mL^?1, the RSD being 1.2 %. The method was applied to the determination of beryllium in underground and mining waste water samples and in beryl mineral.