Sensitive determination of atorvastatin in human plasma by dispersive liquid–liquid microextraction and solidification of floating organic drop followed by high‐performance liquid chromatography

A novel and sensitive dispersive liquid–liquid microextraction method based on the solidification of the floating organic drop combined with high‐performance liquid chromatography and ultraviolet detection was used for the determination of atorvastatine in blood serum samples. The chromatographic separation of atorvastatin was carried out using methanol as the mobile phase organic modifier. Various parameters affecting the extraction efficiency were optimized, such as the kind and volume of extraction solvent (1‐undecanol) and disperser solvent (acetonitrile), pH, and the extraction time. The calibration curve was linear in the range of 0.2–6000 μg/L of atorvastatin (r² = 0.995) with a limit of detection of 0.07 μg/L. The relative standard deviation for 100 μg/L of atorvastatin in human plasma was 8.4% (n = 4). The recoveries of plasma samples spiked with atorvastatin were in the range of 98.8–113.8%. The obtained results showed that the proposed method is fast, simple, and reliable for the determination of very low concentrations of atorvastatin in human plasma samples.     

Molecular Complexes of Crown Ethers, Part 5: Complexes of DB18C6 with Some Acceptors

The UV-Visible spectra of DB18C6 as a donor with TCNE (Tetracyanoethylene), and DDQ (2,3-dichloro-5,6-dicyano-1,4- benzoquinone) as acceptors were studied. Charge transfer spectra were obtained for these systems from which it was possible to calculate the formation constant, Kc. The effects of potassium halides were studied. This study shows that in the presence of the anion there is an electron transfer from the anion to the acceptor. This process is enhanced by the presence of the crown ether, CE. The formation of the anion salt with the acceptor, in the presence of the CE, follows the trend F = I > Br > Cl. It is also indicated in this study that the interaction between DB18C6 and the acceptor follow the trend DDQ > TCNE.     

Efficient ecofriendly synthesis of pyrazole acryloyl analogs by amino acid catalysis

An easy and effective green approach of Knoevenagel condensation and arylidene formation with the substrates involves pyrazole-3-carbaldehydes and active methylenes under catalytic action of glycine (the simplest amino acid) in dimethylsulfoxide. These reactions were successfully carried out at room temperature.     

Synthesis of eight-membered hydroquinolines related to alkaloid skeletons via addition of 4-hydroxycoumarin or 4-hydroxypyran-2-one to quinolinium salts

A new one-pot synthesis of hitherto unknown polyheterocyclic systems via tandem C-alkylation and intramolecular O-alkylation of 4-hydroxycoumarin or 4-hydroxypyran-2-one with quinolinium salts in excellent yields (71-89%) is reported. The present approach provides a powerful route into polycyclic structures containing nitrogen and oxygen related to alkaloids.     

Nonstatistical energy flow in the first N–H stretch overtone region of methylamine

Methylamine (CH₃NH₂) molecules, excited to vibrational states lying in the energy window of the first N–H stretch overtone, were studied by room temperature photoacoustic spectroscopy and jet-cooled action spectroscopy. Benefiting from both types of spectra and specifically from the narrowed action spectrum, a multiband structure was revealed. Simulation of the spectral contours allowed retrieving the band origins, band types and transition linewidths. The linewidths indicate that the energy redistribution occurs nonstatistically and that the 2ν₁₀ state (antisymmetric N–H stretch) is relatively longer lived.     

Conformational preference of substituted naphthalenes: 1—Aldehyde derivatives of naphthalene

Long-range proton-proton coupling constants between the aldehyde proton and the ring protons were used to deduce the conformational preference of 1-naphthaldehyde, 2-naphthaldehyde, 2-hydroxy-1-naphthaldehyde, 2-methoxy-1-naphthaldehyde and 1-bromo-2-naphthaldehyde. Molecular orbital calculations at the CNDO/2 and INDO level were used to calculate the stability and the long-range proton-proton couplings of different conformers of 1- and 2-naphthaldehyde. The Z conformer was found to be more stable in 1-naphthaldehyde and the E conformer was more stable in 2-naphthaldehyde.     

The 13C chemical shifts of 2′-hydroxy-substituted N-benzylidene-anilines and some N,N-(o-hydroxy-benzylidene)diamines

¹³C chemical shifts of fourteen substituted 2′-hydroxy-N-benzylidene-anilines and three N,N-(o-hydroxy-benzylidene)-diamines are reported.     

Improved performance of a crystalline silicon solar cell based on ZnO/PS anti-reflection coating layers

A porous silicon (PS) layer was prepared by photoelectrochemical etching (PECE), and a zinc oxide (ZnO) film was deposited on a PS layer using a radio frequency (RF) sputtering system. The surface morphology of the PS and ZnO/PS layers was characterised using scanning electron microscopy (SEM). Nano-pores were produced in the PS layer with an average diameter of 5.7 nm, which increased the porosity to 91%. X-ray diffraction (XRD) of the ZnO/PS layers shows that the ZnO film is highly oriented along the c-axis perpendicular to the PS layer. The average crystallite size of the PS and ZnO/PS layers are 17.06 and 17.94 nm, respectively. The photoluminescence (PL) emission spectra of the ZnO/PS layers present three emission peaks, two peaks located at 387.5 and 605 nm due to the ZnO nanocrystalline film and a third located at 637.5 nm due to nanocrystalline PS. Raman measurements of the ZnO/PS layers were performed at room temperature (RT) and indicate that a high-quality ZnO nanocrystalline film was formed. Optical reflectance for all the layers was obtained using an optical reflectometer. The lowest effective reflectance was obtained for the ZnO/PS layers. The fabrication of crystalline silicon (c-Si) solar cells based on the ZnO/PS anti-reflection coating (ARC) layers was performed. The I–V characteristics of the solar cells were studied under 100 mW/cm² illumination conditions. The ZnO/PS layers were found to be an excellent ARC and to exhibit exceptional light-trapping at wavelengths ranging from 400 to 1000 nm, which led to a high efficiency of the c-Si solar cell of 18.15%. The ZnO/PS ARC layers enhance and increase the efficiency of the c-Si solar cell. In this paper, the fabrication processes of the c-Si solar cell with ZnO/PS ARC layers are an attractive and promising technique to produce high-efficiency and low-cost of c-Si solar cells.     

Vibrational dynamics of pyrrole via frequency-domain spectroscopy

The N-H stretch overtones of pyrrole, a key constituent of biologic building blocks, were studied by room temperature photoacoustic and jet-cooled action spectroscopies to unravel their intramolecular dynamics. Contrary to "isolated" states excited with two and three N-H stretch quanta, the one with four quanta shows strong accidental resonances with two other states involving three quanta of N-H stretch and one quantum of C-H stretch. The inhomogeneously reduced features in the action spectra provide the means for getting insight into the intramolecular interactions and the factors controlling energy flow within pyrrole. The time dependence of the survival probability of the 4ν(1) N-H stretch, deduced from the vibrational Hamiltonian, shows an initial decay in ~0.3 ps with ensuing quantum beats from the N-H-C-H resonance and their decay with a time constant of about 5 ps as a result of weaker coupling to bath states.