Tuning the Structure and Properties of N-doped Positively Charged Polycyclic Aromatic Hydrocarbons

A detailed study of the geometry, aromatic character, electronic and magnetic properties for a series of positively charged N-doped polycyclic aromatic hydrocarbons (PAHs) was performed. Magnetic properties of the examined molecules were analyzed by means of the magnetically induced current density calculated using the diamagnetic-zero version of the continuous transformation of origin of current density (CTOCD-DZ) method. The comparative study of the local aromaticity of the studied molecules was performed using several different indices: energy effect (ef), harmonic oscillator model of aromaticity (HOMA) index, six centre delocalization index (SCI) and nucleus independent chemical shifts (NICS). The presence of N-atoms in the inner rings was found to cause a planarity distortion in the studied N-doped systems. The geometric changes and charged nature of the studied N-doped systems do not significantly influence the current density and the local aromaticity distribution in comparison with the corresponding parent benzenoid hydrocarbons. The present study demonstrates how quantum chemical calculations can be used for rational design of novel PAHs and for fine tuning of their properties.     

Isolation of oxidative degradation products of atorvastatin with supercritical fluid chromatography

The isolation of four oxidative degradation products of atorvastatin using preparative high‐performance liquid chromatography applying at least two chromatographic steps is known from the literature. In this paper it is shown that the same four impurities could be isolated from similarly prepared mixtures in only one step using supercritical fluid chromatography. The methods for separation were developed and optimized. The preparation of the mixtures was altered in such a way as to enhance the concentration of desired impurities. Appropriate solvents were applied for collection of separated impurities in order to prevent degradation. The structures of the isolated impurities were confirmed and their purity determined. The preparative supercritical fluid chromatography has proven to be superior to preparative HPLC regarding achieved purity of standards applying fewer chromatographic as well as isolation steps. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis of novel amphiphilic spin probes with the paramagnetic doxyl group in the polar region

The use of ESR and specially designed spin probes has led to major breakthroughs in understanding the complexity of biological membranes. Research has been focused mainly on molecular events within the lipid bilayer, and few probes have been designed for studying events in the extracellular space near the membrane surface. We have prepared a series of amphiphilic spin probes in which an ethylene glycol type hydrophilic spacer was introduced between a hydrophobic anchor and the doxyl group, placing the latter above the membrane in the extracellular space. Furthermore, the 2pπ orbital, containing the unpaired electron of the nitroxide group, would be orientated perpendicular to the membrane surface, making it more useful for ESR investigations of structural and dynamic properties close to the membrane surface in different situations of the cell life.     

Thermal Pretreatment of Harvest Residues and Their Use in Anaerobic Co-digestion with Dairy Cow Manure

Several batch experiments were conducted on the anaerobic co-digestion of dairy cow manure (DCM) with three harvest residues (HR) (soybean straw, sunflower stalks, and corn stover). The influence of thermal pretreatment of HR on biogas production was investigated, where the HR were thermally pretreated at two different temperatures: T = 121 °C and T = 175 °C, during t = 30 and t = 90 min, respectively. All anaerobic co-digestion batch experiments were performed simultaneously under thermophilic regime, at T = 55 °C. Biogas and methane yields were significantly improved in experiments performed with corn stover thermally pretreated at 175 °C for 30 min (491.37 cm³/g VS and 306.96 cm³/g VS, respectively), if compared to experiments performed with untreated corn stover. The highest VS and COD removal rates were also observed in the same group of experiments and were 34.5 and 50.1%, respectively. The highest biogas and methane yields with soybean straw (418.93 cm³/g VS and 261.44 cm³/g VS, respectively) were obtained when soybean straw pretreated at 121 °C during 90 min. The highest biogas and methane yields with sunflower stalk (393.28 cm³/g VS and 245.02 cm³/g VS, respectively) were obtained when sunflower stalk was pretreated at 121 °C during 90 min.     

Electronic structure study of thermal intraconversions of some dicyclopenta-fused polycyclic aromatic compounds

The electronic structure of dicyclopenta[de,mn]anthracene (P1), dicyclopenta[ de,kl]anthracene (P2), and dicyclopenta[jk,mn]phenanthrene (P3) and their mutual isomerization processes are investigated using density functional theory. Two mechanisms for the thermal intraconversion of P1 to P2 were found. The first mechanism occurs via ethynylaceanthrylene (I0), and the second involves a 1,2-hydrogen shift. It is supposed that I0 is initially formed during the flash vacuum pyrolysis experiments, eventually rearranging to P2 on high temperatures. The energetics of the latter mechanism also indicate that P1 isomerizes to P2. The mechanism for a transformation of P2 to P3 is based on a ring contraction/ring conversion process and requires extremely high temperatures. Our investigation is in accord with the experimental results: unsuccessful synthesis of P1, stability of P2 at high temperature, and formation of P3 under extreme temperature regime.     

Relating Total π-Electron Energy and Resonance Energy of Benzenoid Molecules with Kekulé- and Clar-Structure-Based Parameters

Within classes of isomeric benzenoid hydrocarbons various Kekulé- and Clar-structure-based parameters (Kekulé structure count, Clar cover count, Herndon number, Zhang–Zhang polynomial) are all mutually correlated. This explains why both the total π-electron energy (E), the Dewar resonance energy (DRE), and the topological resonance energy (TRE) are well correlated with all these parameters. Nevertheless, there exists an optimal value of the variable of the Zhang–Zhang polynomial for which it yields the best results. This optimal value is negative-valued for E, around zero for TRE, and positive-valued for DRE. A somewhat surprising result is that TRE and DRE considerably differ in their dependence on Kekulé- and Clar-structure-based parameters.     

Titrimetrische Bestimmung von Zink mit Äthylendiamintetraessigsäure in Gegenwart von Palladium(II)

Zusammenfassung Komplexometrische Methoden zur Bestimmung von Zink in Gegenwart von Palladium(II) wurden ausgearbeitet. Dabei wird Palladium(II) mit Kaliumcyanid getarnt und der Zinkgehalt entweder bei p_H 5,8 oder nach Demaskierung mit Chloralhydrat bei p_H 10 mit ÄDTA gegen Methylthymolblau titriert. Diese Zinkbestimmung läßt sich auch in Anwesenheit einer Mischung von Palladium(II), Kupfer(II), Nickel und Kobalt(II) durchführen.

---

Summary Complexometric methods have been developed for determining zinc in the presence of palladium(II). In these procedures, Pa(II) is masked with potassium cyanide and the zinc content is titrated either at p_H 5.8 or after demasking with chloralhydrate is titrated with EDTA at p_H 10 in the presence of methylthymol blue. This zinc determination may also be conducted in the presence of a mixture of palladium(II), copper(II), nickel(II),and cobalt(II).

     

Influence of structural and interfacial properties of microemulsion eluent on chromatographic separation of simvastatin and its impurities

In order to calculate the structural and compositional characteristics of microemulsions, used as eluents in the investigation of HPLC separation of simvastatin and its six impurities, predictive molecular thermodynamic approach is developed. For calculating fundamental interfacial properties of microemulsions, from pure component properties, the lattice fluid self-consistent field theory (SCF), in conjunction with new classical thermodynamic expressions, was applied. Calculation of predicted radii (PR), area per surfactant (ApS) and film thickness (FT), as well as is interfacial tension and bending moment enabled better understanding of separation of such a complex mixture. The microemulsion, which contained 1% (w/w) of diisopropyl ether, 2% (w/w) of sodium dodecyl sulphate (SDS), 6.6% (w/w) of co-surfactant such as n-butanol and 90.4% (w/w) of aqueous 25 mM disodium phosphate pH 7.0 enabled appropriate chromatographic separation between investigated compounds. It has been proved that this microemulsion had the smallest droplet radii and film thickness, which enabled optimal separation. Also the interfacial tension is the smallest, so the free energy change associated with dispersing the drops favoured a large number of small droplets. Hydrophobic interactions between solutes and stationary phase, as well as the microstructural characteristics of microemulsion eluents had a significant influence on chromatographic behavior of simvastatin and its six impurities.