Aromatic Ring Systems Research Articles

Evolution properties of cellulose- and lignin-derived pyrolysis tars after interacting with coal chars

The reforming characteristics of biomass volatiles on anthracite chars were investigated by comparing the structural evolution of tars derived from cellulose and lignin as the major biomass components. In a two-stage quartz reactor, the pyrolysis volatiles of cellulose and lignin were produced in the first stage and then reformed in the second stage with or without the presence of anthracite chars between 600 and 900°C. The results show that the presence of anthracite chars enhanced the destruction of volatiles of both feedstocks. Furthermore, the tar yields of lignin showed a slower decreasing trend with temperature than those of cellulose, suggesting that the lignin volatiles were more refractory to be reformed. The lignin tars had higher molecular weights and contained higher percentage of compounds with large aromatic ring systems (≥3 fused benzene rings) than cellulose tars in the studied temperature range. Compositional analysis revealed that tars of both feedstocks experienced the transition from phenolic compounds to polycyclic aromatic hydrocarbons with increasing temperature. The surface areas of anthracite chars were reduced because of coke deposition after interacting with the volatiles of both feedstocks below 800°C, above which the net gasification of chars took place.

Asymmetric Hydrogenation of Azaindoles: Chemo- and Enantioselective Reduction of Fused Aromatic Ring Systems Consisting of Two Heteroarenes.

High enantioselectivity was achieved for the hydrogenation of azaindoles by using the chiral catalyst, which was prepared from [Ru(η(3) -methallyl)2 (cod)] and a trans-chelating bis(phosphine) ligand (PhTRAP). The dearomative reaction exclusively occurred on the five-membered ring, thus giving the corresponding azaindolines with up to 97:3 enantiomer ratio.

Asymmetric Hydrogenation of Azaindoles: Chemo‐ and Enantioselective Reduction of Fused Aromatic Ring Systems Consisting of Two Heteroarenes

AbstractHigh enantioselectivity was achieved for the hydrogenation of azaindoles by using the chiral catalyst, which was prepared from [Ru(η3‐methallyl)2(cod)] and a trans‐chelating bis(phosphine) ligand (PhTRAP). The dearomative reaction exclusively occurred on the five‐membered ring, thus giving the corresponding azaindolines with up to 97:3 enantiomer ratio.

Synthesis, Characterization, and Electronic Structures of Porphyrins Fused with Polycyclic Aromatic Ring Systems

A series of porphyrins fused with acenaphthylene, phenanthroline, and benzofluoranthene polycyclic aromatic rings were prepared by means of a 3+1 porphyrin synthesis approach and subsequent retro-Diels-Alder reaction of bicyclo[2.2.2]octadiene-fused precursors. Analysis of the magnetic circular dichroism spectra and the results of time-dependent DFT calculations are used to identify the reasons for the trends observed in the wavelengths and relative intensities of the Q bands of the products. Michl's perimeter model is used as a conceptual framework to explain the changes in the relative energies of the frontier π-molecular orbitals.

Gold-Catalyzed Cyclization of Furan-Ynes bearing a Propargyl Carbonate Group: Intramolecular Diels-Alder Reaction with In Situ Generated Allenes.

Gold-catalyzed cyclization of various furan-ynes with a propargyl carbonate or ester moiety results in the formation of a series of polycyclic aromatic ring systems. The reactions can be rationalized through a tandem gold-catalyzed 3,3-rearrangement of the propargyl carboxylate moiety in furan-yne substrates to form an allenic intermediate, which is followed by an intramolecular Diels-Alder reaction of furan and subsequent ring-opening of the oxa-bridged cycloadduct. It was found that the steric and electronic properties of phosphine ligands on the gold catalyst had a significant impact on the reaction outcome. In the case of 1,5-furan-yne, the cleavage of the oxa-bridge in the cycloadduct with concomitant 1,2-migration of the R(1) group occurs to furnish anthracen-1(2H)-ones bearing a quaternary carbon center. For 1,4-furan-yne, a facile aromatization of the cycloadduct takes place to give 9-oxygenated anthracene derivatives.

Effects of volatile–char interactions on char during pyrolysis of rice husk at mild temperatures

In order to understand the sensitivity of volatile–char interactions to mild temperatures (600–800°C), in-situ rice husk char was prepared from fast pyrolysis (>103Ks−1) on a fixed-bed reactor. Retention of K in char, changes in char structure and char reactivity were determined. The results showed that volatile–char interactions did not cause obvious effect on the char yield but showed an inhibitory effect on char reactivity. The inhibition began only above 650°C and intensified with temperature rise, but kept almost unchanged at 700–800°C. Char structure and retention of K have a combined effect on char reactivity. The decreased reactivity was caused by additional volatilization of K from char matrix and transformation of relatively smaller aromatic ring systems to large ring systems (>6 benzene rings) above 650°C.

Fluorescence Probe for Detecting CCG Trinucleotide Repeat DNA Expansion and Slip-Out.

Trinucleotide repeat expansion in genomic DNA causes severe neurodegenerative diseases. Fluorescence probes that bind to trinucleotide repeats have potential as diagnostic tools of trinucleotide repeat disorders. Here, we report a novel tricyclic ligand that binds to CCG trinucleotide repeat DNA. The expansion of the aromatic ring system of the 2-amino-1,8-naphthyridine chromophore from the bicyclic to the tricyclic improved the binding ability to the CCG/CCG motif without losing the selectivity and emissive character. The fluorescence sensitively decreased in response to binding to the CCG trinucleotide repeat. The degree of quenching depended on the number of CCG repeats. In addition, the fluorescence detection was applicable to CCG slip-out DNA.

Influence of the chelator structures on the stability of Re and Tc tricarbonyl complexes with iminodiacetic acid tridentate ligands: a computational study.

The development of novel radiopharmaceuticals for nuclear medicine based on M(CO)3 (M = Tc, Re) complexes has attracted great attention. The versatility of this core and the easy production of the fac-[M(CO)3(H2O)3](+) precursor could explain this interest. The main characteristics of these tricarbonyl complexes are the high substitution stability of the three CO ligands and the corresponding lability of the coordinated water molecules, yielding, via easy exchange of a variety of bi- and tridentate ligands, complexes xof very high kinetic stability. Here, a computational study of different tricarbonyl complexes of Re(I) and Tc(I) was performed using density functional theory. The solvent effect was simulated using the polarizable continuum model. These structures were used as a starting point to investigate the relative stabilities of tricarbonyl complexes with various tridentate ligands. These complexes included an iminodiacetic acid unit for tridentate coordination to the fac-[M(CO)3](+) moiety (M = Re, Tc), an aromatic ring system bearing a functional group (-NO2, -NH2, and -Cl) as a linking site model, and a tethering moiety (a methylene, ethylene, propylene butylene, or pentylene bridge) between the linking and coordinating sites. The optimized complexes showed geometries comparable to those inferred from X-ray data. In general, the Re complexes were more stable than the corresponding Tc complexes. Furthermore, using NH2 as the functional group, a medium length carbon chain, and ortho substitution increased complex stability. All of the bonds involving the metal center presented a closed shell interaction with dative or covalent character, and the strength of these bonds decreased in the sequence Tc-CO > Tc-O > Tc-N.

An advanced biomass gasification technology with integrated catalytic hot gas cleaning. Part III: Effects of inorganic species in char on the reforming of tars from wood and agricultural wastes

Char is used directly as a catalyst for the catalytic reforming of tar during gasification. Experiments have been carried out to examine the effects of inorganics in char as a catalyst for the catalytic reforming of tar during the gasification of mallee wood, corn stalk and wheat straw in a pilot plant. The char catalyst was prepared from the pyrolysis of mallee wood at a fast heating rate. The catalytic activities of char and acid-washed char for tar reforming were compared under otherwise identical gasification conditions. For all biomass feedstocks tested for gasification, the tar contents in product gas could be drastically reduced by the catalyst, reaching a tar concentration level well below 100mg/Nm3. The acid-washed char also showed profound activity for tar reforming although its catalytic activity was definitely lower than the raw char. Both catalysts could effectively reform the aromatic ring systems (especially large aromatic ring systems with three or more fused benzene rings) in tars as is revealed using UV-fluorescence spectroscopy. The char itself was also partially gasified. After being used as a catalyst, the condensation of the aromatic rings and the accumulation of inorganic species led to drastic changes in char reactivity with O2 at 400°C. The inorganic species in char tended to enhance the formation of H2 and CO during the reforming reactions in the catalytic reactor.

Extended Aromatic and Heteroaromatic Ring Systems in the Chalcone-Flavanone Molecular Switch Scaffold.

Previous work on the o-hydroxychalcone/flavanone molecular switching scaffold showed that simple substitutions alter the pH range in which rapid interconversion occurs. Herein, more impactful structural modifications were performed via alteration of the characteristic phenyl rings to alternative aromatic systems. It was determined that the scaffold was still viable after these changes and that the range of accessible midpoint pH values was markedly increased. To further explore the switch's scope, scaffolds able to have multiple switching events were also investigated.

Crystal structures of organoplatinum complexes containing alkyl-eugenoxyacetate and p-chloro-aniline.

In the title complexes, trans-di-chlorido-(4-chloro-aniline-κN){3-meth-oxy-4-meth-oxy-carbonyl-meth-oxy-1-[(2,3-η)-prop-2-en-1-yl]benzene}-platinum(II) 0.1-hydrate, [PtCl2(C6H6ClN)(C13H16O4)]·0.1H2O, (I), and trans-di-chlorido-(4-chloro-aniline-κN){4-eth-oxy-carbonyl-meth-oxy-3-meth-oxy-1-[(2,3-η)-prop-2-en-1-yl]benzene}-platinum(II), [PtCl2(C6H6ClN)(C14H18O4)], (II), the Pt(II) metal atom displays a slightly distorted square-planar coordination geometry defined by the aniline N atom, two chloride anions (trans-positioned) and one ethyl-enic double bond. The least-squares planes through the two aromatic ring systems make an angle of 47.3 (3)° for (I) and 38.6 (2)° for (II). Both structures show disorder for the PtCl2 fragment, in the case of (I) even further extended towards the CH2-CH=CH2 ligand. An intra-molecular C-H⋯Cl hydrogen bond occurs in (I). In the crystal packing of (I), which is dominated by N-H⋯O and C-H⋯Cl inter-actions, a partially occupied water mol-ecule is observed on a twofold rotation axis with a refined site occupancy of 0.10 (1). A C-H⋯π inter-action is also present. In (II), inversion dimers form chains along the b-axis direction by N-H⋯O hydrogen bonds.

Assessment of neurotoxic effects of tri-cresyl phosphates (TCPs) and cresyl saligenin phosphate (CBDP) using a combination of in vitro techniques

Environmental exposures to tri-cresyl phosphates (TCPs) and the possible formation of toxic metabolites (e.g. cresyl saligenin phosphate; CBDP) may cause a variety of neurotoxic effects in humans. As reported for other organophosphorus compounds (OPs), the inhibition of acetylcholine esterase (AChE) has also been proposed as the underlying mechanism for TCP neurotoxicity. The ortho-isomer, ToCP and its metabolite CBDP are also known to affect neuropathy target esterase (NTE) leading to organophosphate-induced delayed neuropathy (OPIDN). Recently, in vitro testing has led to the identification of other molecular targets and alternative mechanisms of ToCP toxicity. The metabolite CBDP and other isomers, as well as commercial mixtures have not been tested for such additional modes of actions. Accordingly, the present study investigates alterations of neurobiological correlates of central nervous processes using different in vitro techniques. The three symmetric TCP isomers – ToCP, TpCP, and TmCP – that contain a methyl group at the ortho-, para-, or meta-position of the aromatic ring system, respectively, together with a commercial TCP mixture, and CBDP were all tested using concentrations not exceeding their cytotoxic concentrations. Isolated cortical neurons were kept in culture for 6days followed by 24h incubation with different concentrations of the test compounds. Thus, all endpoints were assessed after 7days in vitro (DIV 7), at which time cell viability, neurite microstructure, and the function of glutamate receptors and voltage-gated calcium cannels (VGCC) were measured. While the cytotoxic potential of the TCP isomers and their mixture were comparable (IC50≥80μM), CBDP was more cytotoxic (IC50: 15μM) to primary cortical neurons. In contrast, CBDP (up to 10μM) did not compromise the microstructure of neurites. Ten μM of ToCP significantly reduced the size and complexity of neurite networks, but neither TmCP and TpCP nor the mixture affected this second endpoint of neurotoxicity assessment. TCPs and their mixture significantly reduced the Ca2+ influx in response to glutamate and KCl stimulation in concentrations of 10μM. Only ToCP showed a specific effect on glutamate receptors with 100nM reducing the evoked Ca2+ influx. The effects of CBDP on the provoked Ca2+ influx were much weaker than those observed for TCPs. These results confirmed that ToCP has a unique mode of action on glutamate receptors that are not observed with the metabolite CBDP and the other symmetric TCP isomers. In addition, the TmCP isomer seems to have the lowest potency with respect to inducing neurotoxic effects. CBDP did not affect the neurospecific endpoints investigated in this study. Therefore, the specific affinity of CBDP for NTE and the reported general cytotoxicity might be the most relevant modes of action of this toxic metabolite in the context of ToCP-induced neurotoxicity, including OPIDN.

Importance of hydrogen and bio-oil inlet temperature during the hydrotreatment of bio-oil

This paper reports the effects of hydrogen and bio-oil inlet temperature on the coke formation and product distribution during the hydrotreatment of bio-oil. A bench scale continuous hydrotreatment fixed-bed reactor set-up was used with pre-sulphided NiMo/γ-Al2O3 as the catalyst. The temperature of hot fluidised sand bath in which the hydrotreatment reactor was immersed was set at 390°C while the pressure at the reactor exit was kept at around 70bar. An LHSV of 1h−1 (on the basis of organics in the bio-oil feed) was used. Our results show that the presence of hot hydrogen in the injection point of bio-oil to the reactor reduced the coke formation and reactor blockage for prolonged catalyst activity. This was due to the enhanced cracking and minimised polymerisation of bio-oil fragments when hot hydrogen was used to heat and activate the catalyst at the injection point. Moreover, lighter products with less coking propensity and smaller aromatic ring systems were formed when the injection point was maintained at a higher temperature with the use of hot hydrogen. These results indicate that the coke formation during hydrotreatment is at least partly because of the slow heating up of the bio-oil and the resulting bond breakage not being matched by the supply of active hydrogen from the catalyst.

DFT analysis and spectral characteristics of Celecoxib a potent COX-2 inhibitor

Extensive quantum mechanical studies are carried out on Celecoxib (CXB), a new generation drug to understand the vibrational and electronic spectral characteristics of the molecule. The vibrational frequencies of CXB are computed by HF and B3LYP methods with 6-311++G (d, p) basis set. The theoretical scaled vibrational frequencies have been assigned and they agreed satisfactorily with experimental FT-IR and Raman frequencies. The theoretical maximum wavelength of absorption of CXB are calculated in water and ethanol by TD-DFT method and these values are compared with experimentally determined λmax values. The spectral and Natural bonds orbital (NBO) analysis in conjunction with spectral data established the presence of intra molecular interactions such as mesomeric, hyperconjugative and steric effects in CXB. The electron density at various positions and reactivity descriptors of CXB indicate that the compound functions as a nucleophile and establish that aromatic ring system present in the molecule is the site of drug action. Electronic distribution and HOMO – LUMO energy values of CXB are discussed in terms of intra-molecular interactions. Computed values of Mulliken charges and thermodynamic properties of CXB are reported.

Phthalocyanines as Molecular Scaffolds to Block Disease-Associated Protein Aggregation.

The aggregation of proteins into toxic conformations plays a critical role in the development of different neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and Creutzfled-Jakob's disease (CJD). These disorders share a common pathological mechanism that involves the formation of aggregated protein species including toxic oligomers and amyloid fibrils. The aggregation of alpha-synuclein (αS) in PD and the amyloid beta peptide (Aβ) and tau protein in AD results in neuronal death and disease onset. In the case of CJD, the misfolding of the physiological prion protein (PrP) induces a chain reaction that results in accumulation of particles that elicit brain damage. Currently, there is no preventive therapy for these diseases and the available therapeutic approaches are based on the treatment of the symptoms rather than the underlying causes of the disease. Accordingly, the aggregation pathway of these proteins represents a useful target for therapeutic intervention. Therefore, understanding the mechanism of amyloid formation and its inhibition is of high clinical importance. The design of small molecules that efficiently inhibit the aggregation process and/or neutralize its associated toxicity constitutes a promising tool for the development of therapeutic strategies against these disorders. In this accounts, we discuss current knowledge on the anti-amyloid activity of phthalocyanines and their potential use as drug candidates in neurodegeneration. These tetrapyrrolic compounds modulate the amyloid assembly of αS, tau, Aβ, and the PrP in vitro, and protect cells from the toxic effects of amyloid aggregates. In addition, in scrapie-infected mice, these compounds showed important prophylactic antiscrapie properties. The structural basis for the inhibitory effect of phthalocyanines on amyloid filament assembly relies on specific π-π interactions between the aromatic ring system of these molecules and aromatic residues in the amyloidogenic proteins. Analysis of the structure-activity relationship in phthalocyanines revealed that their anti-amyloid activity is highly dependent on the type of metal ion coordinated to the tetrapyrrolic system but is not sensitive to the number of peripheral charged substituents. The tendency of phthalocyanines to oligomerize (self-association) via aromatic-aromatic stacking interactions correlates precisely with their binding capabilities to target proteins and, more importantly, determines their efficiency as anti-amyloid agents. The ability to block different types of disease-associated protein aggregation raises the possibility that these cyclic tetrapyrrole compounds have a common mechanism of action to impair the formation of a variety of pathological aggregates. Because the structural and molecular basis for the anti-amyloid effects of these molecules is starting to emerge, combined efforts from the fields of structural, cellular, and animal biology will result critical for the rational design and discovery of new drugs for the treatment of amyloid related neurological disorders.

H‐bonding and stacking interactions between chloroquine and temozolomide

The interactions between temozolomide and chloroquine were examined via Dispersion‐Corrected Density Functional Theory and MP2 methods. Chloroquine was considered in both its lowest energy structure and in a local minimum where its aromatic system and secondary amine group are free to interact directly with temozolomide. The accessibility of these two components to intermolecular interaction makes the lowest energy dimer of this local monomer minimum competitive in total energy with that involving chloroquine's most stable monomer geometry. In either case, the most stable heterodimer places the aromatic ring systems of the two molecules parallel and directly above one another in a stacked geometry. Most of the local minima are also characterized by a stacked geometry as well. Comparison between B3LYP and B3LYP‐D binding energies confirms dispersion is a primary factor in stabilizing these structures. © 2016 Wiley Periodicals, Inc.

Effects of temperature on the hydrotreatment behaviour of pyrolysis bio-oil and coke formation in a continuous hydrotreatment reactor

In this study, we investigated the effects of temperature on the hydrotreatment behaviour of bio-oil from the pyrolysis of mallee wood with a special focus on coke formation. The experiments were carried out in a continuous hydrotreatment reactor with pre-sulphided NiMo/γ-Al2O3 as the main catalyst over a nominal temperature range from 375 to 450°C while the outlet pressure was set at 70bar. GC-MS, TGA, UV-Fluorescence spectroscopy, elemental analysis and FT-Raman spectroscopy were used to characterise the reaction products and spent catalyst. While an upstream Pd/C catalyst bed had some effects of stabilising bio-oil, it was insufficient to ensure long-term operation under all conditions. Aromatic ring growth and polymerisation could take place continuously even under the overall dominating hydrotreatment/hydrocracking conditions. Temperature drastically affected the hydrotreatment product quality and coke formation. Increasing temperature favours the polymerisation for the formation of coke. At high temperature (e.g. 450°C), the coke formation could be so severe that the reactor was blocked before the heavy liquid could reach the end of the reactor. The coke formed mainly from heavy liquid showed very different properties (different aromatic ring systems) from the coke formed mainly from the light species.

The spectrometric characterization of lipids extracted from lignite samples from various coal basins

Lipids were extracted from seven different lignite samples and subsequently characterized using spectrometric methods. Excitation–emission matrix (EEM) or total luminescence spectrometry was here used for the first time to study lipids extracted from lignites more extensively. Spectrometric characterization showed that lipids differ from each other depending on the origin of the lignite in which they occur. EEM spectra can be used as fingerprints not only for distinguishing between lipids but also lignites. Lipids contain fluorophores, which participate in the total fluorescence of lignites; some of these also participate in the fluorescence of humic substances. The typical maxima (260–275/370–440nm) of EEM lipid spectra lie within the A′ region, which can be ascribed to aromatic ring systems and steroids. Lipids from South Moravian lignite also contain maxima in the H (255/305nm) and V (430/475nm) regions, in contrast to other samples. The first could be related to single aromatic systems and substituents such as carboxyl and carbonyl and the latter is probably the result of intramolecular charge-transfer states.

Decomposition of DNA Nucleobases by Laser Irradiation of Gold Nanoparticles Monitored by Surface-Enhanced Raman Scattering

Different approaches have been proposed to treat cancer cells using gold nanoparticles (AuNPs) in combination with radiation ranging from infrared lasers to high-energy ion beams. Here we study the decomposition of the DNA/RNA nucleobases thymine (T) and uracil (U) and the well-known radiosensitizer 5-bromouracil (BrU) in close vicinity to AuNPs, which are irradiated with a nanosecond pulsed laser (532 nm) matching the surface plasmon resonance of the AuNPs. The induced damage of nucleobases is analyzed by UV–vis absorption spectroscopy and surface-enhanced Raman scattering (SERS). A clear DNA damage is observed upon laser irradiation. SERS spectra indicate the fragmentation of the aromatic ring system of T and U as the dominant form of damage, whereas with BrU mainly the cleavage of the Br–C bond and formation of Br– ions is observed. This is accompanied by a partial transformation of BrU into U. The observed damage is at least partly ascribed to the intermediate formation of low-energy electrons from th...

{4,5-Dimethoxy-2-[(2,3-η)-2-prop-2-en-1-yl]phenyl-κC1}(8-hydroxyquinolinato-κN,O)platinum(II)

The crystal structure of the organoplatinum(II) title complex, [Pt(C9H6NO)(C11H13O2)] or [Pt(methyleugenol)(8-hydroxyquinolinato)], has been determined in order to verify the coordination environment of the PtIIcation, which was found to be square-planar with the N and O atoms of the quinolinate ligandcisandtrans, respectively, with respect to the ethylenic double bond. The least-squares planes through the two aromatic ring systems make an angle of 39.87 (10)°. In the crystal, chains are formed parallel to [100] sustained by C—H...O hydrogen bonds. Parallel chains further interactviaC—H...O and C—H...π contacts. The complex shows interesting activity on four human cancer cell lines with IC50values between 1.92 and 4.86 µM.