Separation of cannabinoids on three different mixed‐mode columns containing carbon/nanodiamond/amine‐polymer superficially porous particles

Three mixed‐mode high‐performance liquid chromatography columns packed with superficially porous carbon/nanodiamond/amine‐polymer particles were used to separate mixtures of cannabinoids. Columns evaluated included: (i) reversed phase (C₁₈), weak anion exchange, 4.6 × 33 mm, 3.6 μm, and 4.6 × 100 mm, 3.6 μm, (ii) reversed phase, strong anion exchange (quaternary amine), 4.6×33 mm, 3.6 μm, and (iii) hydrophilic interaction liquid chromatography, 4.6 × 150 mm, 3.6 μm. Different selectivities were achieved under various mobile phase and stationary phase conditions. Efficiencies and peak capacities were as high as 54 000 N/m and 56, respectively. The reversed phase mixed‐mode column (C₁₈) retained tetrahydrocannabinolic acid strongly under acidic conditions and weakly under basic conditions. Tetrahydrocannabinolic acid was retained strongly on the reversed phase, strong anion exchange mixed‐mode column under basic polar organic mobile phase conditions. The hydrophilic interaction liquid chromatography column retained polar cannabinoids better than the (more) neutral ones under basic conditions. A longer reversed phase (C₁₈) mixed‐mode column (4.6 × 100 mm) showed better resolution for analytes (and a contaminant) than a shorter column. Fast separations were achieved in less than 5 min and sometimes 2 min. A real world sample (bubble hash extract) was also analyzed by gradient elution.     

Solvent,substituent, and dimerization effects on the ring-opening mechanisms of monosilacyclopropylidenoids: a theoretical study

Density functional theory and ab initio computations elucidated the ring-opening of substituted (R = –CF₃, –CN, –CH₃, –H, –NH₂, –OCH₃, –OH, –SiH₃) 1-bromo–1-lithiosilirane 1 and 2-bromo–2-lithiosilirane 2 to LiBr complexes of 2-silaallene and 1-silaallene, respectively. Formally, two competitive pathways can be considered. The ring-opening reaction can take place through a concerted manner via TS3. Alternatively, the reaction may proceed in a stepwise fashion with the intermediacy of a free silacyclopropylidene–LiBr complex 7. In both cases, the position of the substituents determines the kinetic of the reactions. The structures with an electron-donating group are generally unstable, whereas the silacyclopropylidenoids bearing electron-withdrawing substituents are particularly stable species. Here, we propose the ring-opening of 5a–h to corresponding LiBr complexes of 2-silaallenes can proceed in both concerted and stepwise mechanism except for –H, –CH₃, and –SiH₃. The obtained activation energies for the ring-openings of 5a–h to related 2-silaallenes are too high for a reaction at room temperature with up to 61.4 kcal/mol. In contrast, the activation energy barriers for the isomerization of 6a–h to the LiBr complexes of 1-silaallenes was determined to be relatively low at the B3LYP/6-31+G(d,p), M06/6-31+G(d,p), and MP2/6-31+G(d,p) levels. Moreover, we have also investigated the solvent effect on the unsubstituted models using both implicit and explicit solvation models. The energy barriers of the solvated models are found to be slightly higher than the results of gas phase calculations. Additionally, the ring-opening of dimer 6 (6–Dim) is also calculated for the ring-opening mechanism with the energy barrier of 3.7 kcal/mol at B3LYP/6-31+G(d,p) level of theory.     

Maximum loss and maximum gain of spectrally negative Lévy processes

The joint distribution of the maximum loss and the maximum gain is obtained for a spectrally negative Lévy process until the passage time of a given level. Their marginal distributions up to an independent exponential time are also provided. The existing formulas for Brownian motion with drift are recovered using the particular scale functions.     

Synthesis of carrageenan coated silver nanoparticles by an easy green method and their characterization and antimicrobial activities

The aim of the present work was to synthesize carrageenan coated silver nanoparticles (CA–AgNPs) using carrageenan as reducing and stabilizing agent. For this purpose, 10 mL of 0.35% (w/v) carrageenan solution was mixed with 10 mL AgNO₃ solution at different concentrations (1, 5 and 10 mM), and the resulting mixture was stirred at 100 °C at high speed for 2 h. The formation of CA–AgNPs was proven with the surface plasmon peaks observed at approximately 420 nm. The sizes and zeta potentials of CA–AgNPs were determined by Zeta-Sizer. Negative zeta potentials of CA–AgNPs indicated that the obtained AgNPs were stable. With scanning electron microscope (SEM) and transmission electron microscope analysis, it was seen that CA–AgNPs have spherical structure. According to the energy dispersion spectrometer analysis based on SEM images, it was observed that the samples were elementally composed of carbon, oxygen, sulfur, potassium and silver. The chemical structures of CA–AgNPs were determined by Fourier transform infrared spectroscopy, and it was proved that the carbonyl and OH groups of carrageenan were involved in formation and stabilizing of AgNPs, respectively. According to thermal gravimetric analysis, it has been observed that CA–AgNPs were thermally more stable than pure carrageenan. Antibacterial activity of CA–AgNPs against gram-positive and gram-negative bacteria was investigated with agar well diffusion and liquid test. It has been observed that CA–AgNPs synthesized with 1 mM AgNO₃ did not have an antibacterial activity on Escherichia coli and Staphylococcus aureus. Inhibition zones of varying diameters were observed in the 5 mM and 10 mM S-AgNPs groups. The synthesized CA–AgNPs (5 and 10 mM) have the capacity to be used in wound dressing materials or topical agents applied to burns and wounds due to their antibacterial effects and stability.

     

Effect of Membrane Preparation Methods on the Release of Theophylline through CA Membranes at In-Vitro Conditions

In this study the effect of the membrane preparation methods on the release of theophylline through cellulose acetate (CA) membranes was studied at in vitro conditions. CA/acetone binary and CA/acetone/water ternary systems were used as casting solutions and poly(ethylene glycol) (PEG) was used as the pore forming, plasticizing agent in the study. Membranes were characterized by FTIR, SEM, and DSC analysis. It was determined that pH, temperature and drug concentration affected the release of theophylline. A decrease in pH, increase in temperature and drug concentration increased the permeated amount of theophylline through the membranes. In addition, receiver solution circulation at a capillary blood rate increased the permeation of theophylline. As a result of the study, it was concluded that the release of theophylline could be controlled for a prolonged period of time and modified CA membranes prepared in the study could be as an advisable membrane material for potential release of theophylline at transdermal conditions.     

Determination of Tetracyclines in Milk,Eggs and Honey Using in-situ Ionic Liquid Based Dispersive Liquid–Liquid Microextraction

In this study, in-situ ionic liquid based dispersive liquid?liquid microextraction method for enrichment of tetracyclines before liquid chromatographic analysis has been improved. A 1-benzyl-3- methylimidazolium chloride was used as an ionic liquid. To increase extraction efficiency, some optimization parameters (amount of ammonium hexafluorophoshate, extraction time, centrifugation time, ratio of ionic liquid/salt) were investigated. At optimized conditions, enrichment factors of four tetracycline antibiotics (tetracycline, chlortetracycline, methacycline, doxycycline) were between 25 and 98. The residues of tetracyclines were not found in the studied real samples. For the accuracy of the method, the concentration of 50 and 250 μg/L of standard tetracycline mixture solutions were spiked to the blank real milk, honey and egg samples and the percentage recoveries were obtained in the range of 75.8–109.7%.     

Thermal decomposition kinetics of polypyrrole and its star shaped copolymer

Thermal behavior of 2,4,6-tris(4-(1H-pyrrol-1-yl)phenoxy)-1,3,5-triazine monomer, polypyrrole, and their star shaped copolymer, were investigated using TG and DTA methods. It was found that Tria melts at 517 K and after than it starts to decompose. Decomposition proceeded in two stages which were corresponding to removal of branched groups and remaining core structure degradation, respectively. Polypyrrole and copolymer showed similar thermal behaviors. These compounds decomposed in three stages which are removal of solvent, removal of dopant anion and rest of structure decomposition. The calculation of activation energies of all reactions were realized using model-free (KAS and FWO) methods. The graphs were prepared which show the alteration of activation energy with decomposition ratio. Thermal analysis results showed that dopant anion and solvent removal activation energy values for copolymer are lower than polypyrrole. Star shaped loose-packed novel structure greatly facilitates solvent and dopant anion removal from copolymer. It can be concluded also that thermal analysis can be used as predict package structure of conducting polymers.