One step synthesis of 14-alkyl- or aryl-14H-dibenzo[a,j]xanthenes using sodium hydrogen sulfate as catalyst

A simple and environmentally benign procedure for the synthesis of 14-alkyl- or aryl-14H-dibenzo[a,j]xanthenes is described through a one-pot condensation of 2-naphthol with aryl or alkyl aldehydes in the presence of sodium hydrogen sulfate as a catalyst under solvent-free conditions.     

Design of Furan-Based Acceptors for Organic Photovoltaics

We explore a series of furan-based non-fullerene acceptors and report their optoelectronic properties, solid-state packing, photodegradation mechanism and application in photovoltaic devices. Incorporating furan building blocks leads to the expected enhanced backbone planarity, reduced band gap and red-shifted absorption of these acceptors. Still, their position in the molecule is critical for stability and device performance. We found that the photodegradation of these acceptors originates from two distinct pathways: electrocyclic photoisomerization and Diels–Alder cycloaddition of singlet oxygen. These mechanisms are of general significance to most non-fullerene acceptors, and the photostability depends strongly on the molecular structure. Placement of furans next to the acceptor termini leads to better photostability, well-balanced hole/electron transport, and significantly improved device performance. Methylfuran as the linker offers the best photostability and power conversion efficiency (>14 %), outperforming all furan-based acceptors reported to date and all indacenodithiophene-based acceptors. Our findings show the possibility of photostable furan-based alternatives to the currently omnipresent thiophene-based photovoltaic materials.     

Study of the Effects of N Fertilization and Plant Density on the Essential Oil Composition and Yield of Cuminum cyminum L. Seeds by HS–SME

Headspace-solvent microextraction (HS–SME) with sample ultrasound irradiation was successfully used for the study of the influence of nitrogen fertilization and plant density on the essential oil yield and composition of cumin (Cuminum cyminum L.) seeds. The components were collected into a single microdrop of n-heptadecane and directly injected into a GC–MS injection port for analysis. A simplex method was used for fast optimization of the extraction parameters. The experiments were executed as split-plot based on randomized complete block design. Nitrogen fertilization as the main factor (in four levels) and plant density as subsidiary factor (in three levels) were applied. It was shown that the total GC peak areas of the HS–SME extract, is proportional to the essential oil yield of the cumin seeds obtained by a hydrodistillation method. Furthermore, similar trends in the concentrations of cuminaldehyde and most other volatile components were obtained by the two methods.     

Acetaldehyde oxidation at elevated pressure

A detailed chemical kinetic model for oxidation of CH₃CHO at intermediate to high temperature and elevated pressure has been developed and evaluated by comparing predictions to novel high-pressure flow reactor experiments as well as shock tube ignition delay measurements and jet-stirred reactor data from literature. The flow reactor experiments were conducted with a slightly lean CH₃CHO/O₂ mixture highly diluted in N₂ at 600–900 K and pressures of 25 and 100 bar. At the highest pressure, the oxidation of CH₃CHO was in the NTC regime, controlled to a large extent by the thermal stability and reactions of peroxide species such as HO₂, CH₃OO, and CH₃C(O)OO. Model predictions were generally in good agreement with the experimental data, even though the predicted temperature for onset of reaction was overpredicted at 100 bar. This discrepancy was attributed mainly to uncertainties in the CH₃C(O)OO reaction subset. Predictions of ignition delays in shock tubes and species profiles in JSR experiments were also satisfactory. At temperatures above the NTC regime, acetaldehyde ignition and oxidation is affected mainly by the competition between dissociation of CH₃CHO and reaction with the radical pool, and by reactions in the methane subset.     

ACE-Inhibitory and Antioxidant Activities of Peptide Fragments Obtained from Tomato Processing By-Products Fermented Using <Emphasis Type="Italic">Bacillus subtilis</Emphasis>: Effect of Amino Acid Composition and Peptides Molecular Mass Distribution

The effects of amino acid composition and peptide molecular mass on ACE-inhibitory and antioxidant activities of protein fragments obtained from tomato waste fermented using Bacillus subtilis were evaluated. The addition of B. subtilis increased the relative amounts of aromatic and positively-charged amino acids which have been described to influence the biological activities of peptide fragments. IC₅₀ values of hydrolysates for ACE-inhibitory and 2, 2′-diphenyl-1-picrylhydrazyl (DPPH) scavenging activities were found to be 1.5 and 8.2 mg/mL, respectively. Size-exclusion chromatography (SEC) pattern of the hydrolysate indicated the breakdown of parent proteins to smaller peptides with molecular weights mainly below 1400 Da. MALDI-TOF mass spectrometry analysis revealed that the highest ACE-inhibitory activity was due to peptides showing molecular mass range 500–800 Da, while the most active antioxidant peptides were found to be mainly at the two different peptide weight ranges 500–800 Da and 1200–1500 Da.     

Synthesis of 2-mercaptobenzothiazole/magnetic nanoparticles modified multi-walled carbon nanotubes for simultaneous solid-phase microextraction of cadmium and lead

This study describes the successful sequential modification of multi-walled carbon nanotube (MWCNT) by Fe₃O₄ magnetic nanoparticles and 2-mercaptobenzothiazole (MBT) followed by its application as a novel sorbent for simultaneous magnetic solid phase microextraction of lead and cadmium. Fourier transform infrared spectroscopy and scanning electron microscopy were employed to confirm the chemical surface modification of the MWCNT. The ions retained on the 2-MBT/magnetic nanoparticles modified MWCNTs were eluted with 1.0 mL of nitric acid (0.8 mol L^?1) in methanol solution and determined by the flame atomic absorption spectrometry. All parameters affecting the extraction condition were thoroughly investigated and optimised. Under the optimised condition preconcentration factor of 150.0, enhancement factors of 149.0 and 149.2 and limits of detection of 0.21 and 0.01 µg L^?1 were achieved for lead and cadmium, respectively. Using the prepared magnetic nanocomposite, the possible interference of other common ions associated with lead and cadmium determination was effectively avoided and the method was successfully applied to the simultaneous determination of the target ions in various environmental water samples.     

Ultrasonic assistance syntheses of new nano-sized lead(II) coordination polymers: motifs for PbO preparation

Nanoparticles of two new coordination polymers, [Pb(5,5′-dm-2,2′-bpy)Cl₂] _n (1) and [Pb(5,5′-dm-2,2′-bpy)Br₂] _n (2), {5,5′-dm-2,2′-bpy = 5,5′-dimethyl-2,2′-bipyridine}, have been synthesized by ultrasonic assistance at different concentrations and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. Metal oxide nanoparticles were prepared from thermal decomposition of compounds 1 and 2 at 600 °C under air atmosphere. Scanning electron microscopy images of the residue which are obtained from calcination of compounds 1, 2 show the formation of lead(II) oxide nanoparticles with an average diameter of about 80 and 90 nm for compounds 1 and 2, respectively.     

Experimental and theoretical studies of diethyl 2-(<Emphasis Type="Italic">ter</Emphasis>-butylimino)-2,5-dihydro-5-oxo-1-phenyl-1H-pyrrole-3,4-dicarboxylate using DFT calculations

In this study, diethyl 2-(ter-butylimino)-2,5-dihydro-5-oxo-1-phenyl-1H-pyrrole-3,4-dicarboxylate compound 1 is synthesized and characterized by FT-IR, ¹H and ¹³C NMR spectroscopy. The DFT calculations are carried out for compound 1 by B3LYP and PBE1PBE methods. The bond lengths, bond angles, dihedral angles, charge density on the atoms of 1 are calculated. A comparison of the DFT calculations indicate that the B3LYP method with the 6-311G++(d,p) basis set can give accurate results. The ¹³C NMR and ¹H NMR chemical shifts of 1 are calculated and compared with the available experimental data on the molecules. The nuclear independent chemical shift (NICS) calculations are utilized for the pyrrole ring in compound 1.     

The sensitive capillary electrophoretic‐LIF method for simultaneous determination of curcuminoids in turmeric by enhancing fluorescence intensities of molecules upon inclusion into (2‐hydroxypropyl)‐β‐cyclodextrin

Curcuminoids have received great attention in the past decades due to their health benefit properties. The aim of this study is to develop a very simple, rapid, and sensitive capillary zone electrophoresis technique coupled with a laser induced fluorescence detector (LIF) for the simultaneous determination of three major curcuminoids of turmeric, namely, curcumin, demethoxy curcumin (DMC), and bisdemethoxy curcumin (BDMC). Background electrolyte was selected as borate at pH 9.6 and (2‐hydroxypropyl)‐β‐cyclodextrin (2‐HP‐β‐CD) was added to prevent rapid alkali degradation of curcuminoids in buffer and to increase fluorescence intensities of molecules. With the addition of 2‐HP‐β‐CD to the separation electrolyte, the fluorescence signal intensities of curcuminoids were enhanced considerably by 30, 40, and 54 fold for curcumin, DMC, and BDMC, respectively. The three curcuminoids of turmeric were fully separated and quantified in less than 4.5 min. The repeatability of the peak areas of curcuminoids for intra‐day and inter‐day experiments was in the satisfactory range of 2.26 and 2.55%, respectively. The LOD and LOQ values for the developed method were equal to or less than 0.081 and 0.270 μg/mL, respectively, for all curcuminoids. The developed method was successfully applied to find curcuminoids amount in turmeric samples and herbal supplements.     

Notes on random vibration of a vehicle model and other discrete systems possessing repeated natural frequencies

In this study, we investigate random vibration of vehicle model exhibiting repeated natural frequencies. It is shown that the cross-correlations have crucial effect, and their neglect may lead to considerable error in the evaluation of mean-square values of the response. In addition, we revisit some discrete systems with coinciding natural frequencies.