Aromatic Ring Systems Research Articles

Study on the effect of inherent AAEM on char structure evolution during coal pyrolysis by in-situ Raman and TG

Inherent minerals, especially alkali and alkaline earth metals (AAEM), are reactive constituents that interact with organic matter during pyrolysis and have significant effects on thermal characteristics and carbon structure evolution of char. The pyrolysis of raw and leached coal samples was conducted by using thermogravimetric analyzer and in-situ Raman system to explore the effects of content and chemical form of AAEM on pyrolysis characteristics and carbon structure evolution of single char particle. The water-soluble and ion-exchangeable AAEM promoted continuous breaking/reforming of bonds between alkyl substitutional groups and aromatic ring systems, resulting in the delay of volatiles release and orderly evolution of carbon structure during pyrolysis. The effects of water-soluble AAEM was more severe, because the divalent alkaline earth metal bonds to carbon was much more stable than the monovalent alkali metal for the inherent AAEM participated in the polycondensation reaction. Besides, the ion-exchangeable AAEM inhibited the generation of cross-linked structures more effectively than water-soluble AAEM, because ion-exchangeable AAEM existed in the form of AAEM-carboxylates and delayed the thermal decomposition. Moreover, the inherent AAEM promoted the miniaturization of carbon crystal structure in the carbon matrix, forming char with disordered carbon structure.

The structural characteristics of waste tire chars at different pyrolysis temperatures

Pyrolysis was a promising technology to achieve waste tire (WT) dispose and utilization. However, large quantities of low quality waste tire chars (WTCs) would remain after pyrolysis and they could be employed to various applications. Further understanding the structural characteristics of WTCs at different pyrolysis temperatures would benefit to guide their utilizations. Herein, pyrolysis experiments were systematically conducted at 400 °C, 600 °C, 800 °C, and 1000 °C respectively to collect WTCs, whose structural characteristics were detailed analyzed. It was found that higher temperature can promote decrease of large and small aromatic ring systems, alkyl-aryl C-C bonds, defects with ordered arrangements of carbon skeleton structure. Pyrolysis can significantly promote pores formation, higher temperature would promote formation of micropores, while mesopores+macropores destroy before 600 °C and then gradually form. Higher temperature can promote decomposition of pyrrolic nitrogen and sulfur bridge with enrichment of oxidised nitrogen and sulphone bridge. Higher temperature would assist in generation of pyridinic nitrogen before 800 °C and quaternary nitrogen before 600 °C.

Hyperactivity and Seizure Induced by Tricresyl Phosphate Are Isomer Specific and Not Linked to Phenyl Valerate-Neuropathy Target Esterase Activity Inhibition in Zebrafish.

Environmental exposure to tricresyl phosphate (TCP) may lead to severe neurotoxic effects, including organophosphate (OP)-induced delayed neuropathy. TCP has three symmetric isomers, distinguished by the methyl group position on the aromatic ring system. One of these isomers, tri-ortho-cresyl phosphate (ToCP), has been reported for years as a neuropathic OP, targeting neuropathic target esterase (NTE/PNPLA6), but its mode of toxic action had not been fully elucidated. Zebrafish eleuthero-embryo and larva were used to characterize the differential action of the TCP isomers. The symmetric isomers inhibited phenyl valerate (PV)-NTE enzymatic activity in vivo with different IC50, while no effect was observed on acetylcholinesterase activity. Moreover, the locomotor behavior was also affected by tri-para-cresyl phosphate and tri-meta-cresyl phosphate, only ToCP exposure led to locomotor hyperactivity lasting several hours, associated with defects in the postural control system and an impaired phototactic response, as revealed by the visual motor response test. The electric field pulse motor response test demonstrated that a seizure-like, multiple C-bend-spaghetti phenotype may be significantly induced by ToCP only, independently of any inhibition of PV-NTE activity. Eleuthero-embryos exposed to picrotoxin, a known gamma-aminobutyric acid type-A receptor inhibitor, exhibited similar adverse outcomes to ToCP exposure. Thus, our results demonstrated that the TCP mode of toxic action was isomer specific and not initially related to modulation of PV-NTE activity. Furthermore, it was suggested that the molecular events involved were linked to an impairment of the balance between excitation and inhibition in neuronal circuits.

Effect of the conjugation pathway on the electronic structures of p–π* conjugated polymers with fused borepin units

Borepin, an aromatic ring system with tricoordinate boron, was incorporated into p–π* conjugated polymers. The polymers exhibited characteristic optical responses upon the addition of cyanide anions in solution.

Chemistry of porphyrins in fossil plants and animals.

Porphyrins are macrocyclic tetrapyrrole derivatives that are widely distributed in nature. They are often complexed with a metal ion located in the center of the ring system and may be modified by various substituents including additional rings, or by ring opening, which leads to a plethora of different functions. Due to their extended conjugated aromatic ring system, porphyrins absorb light in the visible range and therefore show characteristic colors. Well-known natural porphyrins include the red-colored heme present in hemoglobin, which is responsible for blood oxygen transport, and the chlorophylls in some bacteria and in plants which are utilized for photosynthesis. Porphyrins are mostly lipophilic pigments that display relatively high chemical stability. Therefore, they can even survive hundreds of millions of years. The present review article provides an overview of natural porphyrins, their chemical structures, and properties. A special focus is put on porphyrins discovered in the fossil record. Examples will be highlighted, and information on their chemical analysis will be provided. We anticipate that the development of novel analytical methods with increased sensitivity will prompt new discoveries of porphyrins in fossils.

Influence of cooling rate on structure and combustion reactivity of char during char preparation process

Different chars with various cooling rates were obtained in the novel concentrating photothermal reactor to investigate the influence of cooling rate on the structure and combustion reactivity of char. The chars were prepared at 900°C with holding time of 10s, 30s and 120s, respectively. Subsequently, the cold (ex-situ) chars were prepared from the hot (in-situ) chars by controlling different cooling rates of 180°C/s (fast cooling rate), 30°C/s (sub-fast cooling rate), 6.8°C/s (moderate cooling rate) and 1.3°C/s (slow cooling rate). The ex-situ chars were then employed for the combustion in 30%O2/70%CO2 atmosphere at 900°C for 180s. For comparison, the in-situ char was conducted by instantaneously switching the reaction atmosphere. For the chars with holding time of 10s, the mass fraction of in-situ char was higher than the char yield of ex-situ char, and the char yield was decreased with the decrease of cooling rate. The char yield with slow cooling rate was decreased by 11.16% than that with fast cooling rate. The maximum and average mass loss rate of char in O2/CO2 was decreased as the cooling rate decreased. Reduced influence of cooling rate on the aromatic ring systems of char with holding time of 30s and its reactivity was displayed, while almost no difference of those with holding time of 120s was illustrated. The reactivity was closely related to the chemical structure of the char, but no positive correlation was found between the combustion reactivity and the specific surface area of char. The residues proportion of volatile components was the decisive factor of char reactivity.

Preparation of a novel chromatographic material and its application for spectroscopic characterization of aromatics in crude oil

Petroleum analysis presents many unique challenges as a result of the chemical complexity of petroleum composition. In the present work a novel chromatographic material has been developed and utilized to separate crude oils. A total number of 13 fractions have been collected using different solvent mixtures with increasing proportions of chloroform. UV and IR spectroscopy has been employed to show that the size of the aromatic ring system increases and the extent of molecular branching decreases with elution gradient. This observation suggests that intermolecular non-covalent π-π interactions between the material and the sample molecules are critical to the separation. This novel method for sequencing petroleum molecules based on the size of the aromatic ring systems has been applied to the 2D off-line analysis of crude oil samples. The 2D on-line separation (NPLC × NPLC) has been simulated by 2D off-line separation. A total number of 38 fractions have been obtained with two SPE columns based on the molecular branching and the aromatic ring system size. The chemical information obtained in this study of North Sea crude oil is complementary to standard SARA analysis. The material supports a potential solution to overcome the challenges of tandem NPLC and has demonstrated a new approach to the separation of crude oils into discrete compound classes.

Recent Advances in the Reactions of Cyclic Carbynes.

The acyclic organic alkynes and carbyne bonds exhibit linear shapes. Metallabenzynes and metallapentalynes are six- or five-membered metallacycles containing carbynes, whose carbine-carbon bond angles are less than 180°. Such distortion results in considerable ring strain, resulting in the unprecedented reactivity compared with acyclic carbynes. Meanwhile, the aromaticity of these metallacycles would stabilize the ring system. The fascinating combination of ring strain and aromaticity would lead to interesting reactivities. This mini review summarized recent findings on the reactivity of the metal–carbon triple bonds and the aromatic ring system. In the case of metallabenzynes, aromaticity would prevail over ring strain. The reactions are similar to those of organic aromatics, especially in electrophilic reactions. Meanwhile, fragmentation of metallacarbynes might be observed via migratory insertion if the aromaticity of metallacarbynes is strongly affected. In the case of metallapentalynes, the extremely small bond angle would result in high reactivity of the carbyne moiety, which would undergo typical reactions for organic alkynes, including interaction with coinage metal complexes, electrophilic reactions, nucleophilic reactions and cycloaddition reactions, whereas the strong aromaticity ensured the integrity of the bicyclic framework of metallapentalynes throughout all reported reaction conditions.

Volatile-char interactions during biomass pyrolysis: Effect of char preparation temperature

In this study, the effect of char preparation temperature on the interactions between cellulose volatiles and acid-washed sawdust char was investigated experimentally on a fixed-bed pyrolysis system. The results indicated that significant volatile-char interactions did exist at the pyrolysis temperature of 500 °C as evidenced by the great changes in the composition and distribution of pyrolysis products. The oxygen-containing functional groups as well as the aromatic ring systems in the char both acted as active sites during the volatile-char interactions. The changes in chemical structure of biochar caused by the different preparation temperatures would notably affect the final products of cellulose pyrolysis. Meanwhile, the acid-washed sawdust char was still found to participate in the reaction process, lower temperature chars would have higher reactivities, and an obvious weight loss of char was also observed after interactions. In addition, volatile-char interactions significantly increased the yields of non-condensable gases, especially those of CO and CO2, while decreased the yield of condensable vapors. The introduction of biochar into cellulose pyrolysis could promote the ring scission of pyranoses as well as the decarbonylation/decarboxylation and dehydration reactions, thus caused the yields of anhydrosugars and monoaromatic compounds decreased and the yields of light ketones and acids increased.

The DNA damage-sensing NER repair factor XPC-RAD23B does not recognize bulky DNA lesions with a missing nucleotide opposite the lesion

The Nucleotide Excision Repair (NER) mechanism removes a wide spectrum of structurally different lesions that critically depend on the binding of the DNA damage sensing NER factor XPC-RAD23B (XPC) to the lesions. The bulky mutagenic benzo[a]pyrene diol epoxide metabolite-derived cis- and trans-B[a]P-dG lesions (G*) adopt base-displaced intercalative (cis) or minor groove (trans) conformations in fully paired DNA duplexes with the canonical C opposite G* (G*:C duplexes). While XPC has a high affinity for binding to these DNA lesions in fully complementary double-stranded DNA, we show here that deleting only the C in the complementary strand opposite the lesion G* embedded in 50-mer duplexes, fully abrogates XPC binding. Accurate values of XPC dissociation constants (KD) were determined by employing an excess of unmodified DNA as a competitor; this approach eliminated the binding and accumulation of multiple XPC molecules to the same DNA duplexes, a phenomenon that prevented the accurate estimation of XPC binding affinities in previous studies. Surprisingly, a detailed comparison of XPC dissociation constants KD of unmodified and lesion-containing G*:Del complexes, showed that the KD values were −2.5–3.6 times greater in the case of G*:Del than in the unmodified G:Del and fully base-paired G:C duplexes. The origins of this unexpected XPC lesion avoidance effect is attributed to the intercalation of the bulky, planar B[a]P aromatic ring system between adjacent DNA bases that thermodynamically stabilize the G*:Del duplexes. The strong lesion-base stacking interactions associated with the absence of the partner base, prevent the DNA structural distortions needed for the binding of the BHD2 and BHD3 β−hairpins of XPC to the deletion duplexes, thus accounting for the loss of XPC binding and the known NER-resistance of G*:Del duplexes.

Abstract LB-236: Design, synthesis, and assessment of anticancer properties of pyrazolopyrimidine derivatives as Glycogen Synthase Kinase-3β inhibitors

Abstract Glycogen synthase kinase-3β (GSK-3β) is a serine/threonine kinase with a crucial role in several key cellular functions including tumor cell proliferation and survival. Yet, GSK-3β has emerged as an attractive target for the development of anti-cancer agents. Several small-molecule have been developed as GSK-3β inhibitors. Amongst, several pyrazolopyrimidines based ATP-competitive inhibitors were identified as promising GSK-3β inhibitors. In this work, several pyrazolo[3,4-d]pyrimidine derivatives were designed, synthesized and assessed for their potential anticancer activity. The new compounds are categorized under two templates, Template A and Template B. In these templates two different linkers with varying lengths and electronic properties were used to link additional aromatic ring systems to the core pyrazolopyrimidine scaffold. The aromatic ring systems were designed with different electronic and bonding properties to test their GSK-3β inhibitory activity and consequently their anticancer properties. All compounds under investigation showed GSK-3β inhibitory properties with IC50's ranging from 0.17- 1.01 µM compared to Tideglusib (standard GSK-3β inhibitor) which showed IC50 of 0.22 µM. Furthermore, the compounds were tested for their potential cytotoxicity against two breast cancer cells (MCF-7 and MDA-MB-231) and lung cancer cells (A549). Only one compound from Template B which possesses the longer hydrazide linker and 2,3-dihydroxy phenyl aromatic ring (compound 27), showed considerable cytotoxic effects against MCF-7, MDA-MB-231 and A549 cells (IC50's of 2.4, 2.4 and 2.3 µM, respectively). Compounds 21, 24, 25 and 26 showed weaker cytotoxic effects against cell lines under investigation (IC50's ranged from 29 to 93 µM). DNA content flow-cytometry analysis was undertaken to evaluate the potential effects of compound 27 on the cell cycle distribution of cell lines under investigation. Compound 27 induced significant antiproliferative effect and accumulation of cells in G0/G1-phase after 24 h of exposure. Longer exposure (48 h) to compound 27 resulted in cell cycle arrest in G2/M-phase. Additional assessment for programmed/non-programed cell death using annexin-V/FITC and acridine orange staining coupled with flow-cytometric analysis showed the ability of compound 27 to induce apoptosis as well as autophagy in all cells under investigation. In conclusion, compound 27 represents a promising GSK-3β inhibitor with potential anticancer properties via the induction of cell cycle arrest with subsequent cellular stress and induction of apoptosis and autophagy. Citation Format: Ahmed T. Negmeldin, Mohammed K. AbdElhameid, Dalia Y. Alsaeedy, Fatiha Hammed, Rasha M. Allam, Walid El-Sayed, Ahmed M. Al-Abd. Design, synthesis, and assessment of anticancer properties of pyrazolopyrimidine derivatives as Glycogen Synthase Kinase-3β inhibitors [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-236.

A Sec14-like phosphatidylinositol transfer protein paralog defines a novel class of heme-binding proteins.

Yeast Sfh5 is an unusual member of the Sec14-like phosphatidylinositol transfer protein (PITP) family. Whereas PITPs are defined by their abilities to transfer phosphatidylinositol between membranes in vitro, and to stimulate phosphoinositide signaling in vivo, Sfh5 does not exhibit these activities. Rather, Sfh5 is a redox-active penta-coordinate high spin FeIII hemoprotein with an unusual heme-binding arrangement that involves a co-axial tyrosine/histidine coordination strategy and a complex electronic structure connecting the open shell iron d-orbitals with three aromatic ring systems. That Sfh5 is not a PITP is supported by demonstrations that heme is not a readily exchangeable ligand, and that phosphatidylinositol-exchange activity is resuscitated in heme binding-deficient Sfh5 mutants. The collective data identify Sfh5 as the prototype of a new class of fungal hemoproteins, and emphasize the versatility of the Sec14-fold as scaffold for translating the binding of chemically distinct ligands to the control of diverse sets of cellular activities.

PI by NMR: Probing CH–π Interactions in Protein–Ligand Complexes by NMR Spectroscopy

AbstractWhile CH–π interactions with target proteins are crucial determinants for the affinity of arguably every drug molecule, no method exists to directly measure the strength of individual CH–π interactions in drug–protein complexes. Herein, we present a fast and reliable methodology called PI (π interactions) by NMR, which can differentiate the strength of protein–ligand CH–π interactions in solution. By combining selective amino‐acid side‐chain labeling with 1H‐13C NMR, we are able to identify specific protein protons of side‐chains engaged in CH–π interactions with aromatic ring systems of a ligand, based solely on 1H chemical‐shift values of the interacting protein aromatic ring protons. The information encoded in the chemical shifts induced by such interactions serves as a proxy for the strength of each individual CH–π interaction. PI by NMR changes the paradigm by which chemists can optimize the potency of drug candidates: direct determination of individual π interactions rather than averaged measures of all interactions.

PI by NMR: Probing CH-π Interactions in Protein-Ligand Complexes by NMR Spectroscopy.

While CH–π interactions with target proteins are crucial determinants for the affinity of arguably every drug molecule, no method exists to directly measure the strength of individual CH–π interactions in drug–protein complexes. Herein, we present a fast and reliable methodology called PI (π interactions) by NMR, which can differentiate the strength of protein–ligand CH–π interactions in solution. By combining selective amino‐acid side‐chain labeling with 1H‐13C NMR, we are able to identify specific protein protons of side‐chains engaged in CH–π interactions with aromatic ring systems of a ligand, based solely on 1H chemical‐shift values of the interacting protein aromatic ring protons. The information encoded in the chemical shifts induced by such interactions serves as a proxy for the strength of each individual CH–π interaction. PI by NMR changes the paradigm by which chemists can optimize the potency of drug candidates: direct determination of individual π interactions rather than averaged measures of all interactions.

SYNTHESIS, CHARACTERISATION AND ANTIMICROBIAL STUDIES OF MIXED LIGANDS METAL (II) COMPLEXES OF SULFAMETHOXAZOLE AND N,N- DONORS HETEROCYCLES

Two mixed ligands of sulfamethoxazole (SMX) with N,N donor heterocycles: 1,10-phenanthroline (phen) and 2,2′-bipyridine (bipy) metal complexes having the composition [M(SMX)(phen)X].nH2O and [M(SMX)(bipy)X].nH2O (where M = Zn(II) , Co(II) , Fe (II), Mn (II),Cu(II) ; X = SO4/Cl2) have been synthesised and characterised by physicochemical methods based on their solubility , metal analysis, infrared and UV-Visible techniques. Infrared spectra data showed SMX as a bidentate ligand coordinating to the metals through the N atom of the sulfonamide group ((3195-3030cm-1) and oxygen atom of the sulfonyl moiety (1158-1103 cm-1) while the heterocycles also bonded as bidentate ligands through their diimine nitrogen atoms (1606-1423 cm-1). The electronic spectra data indicated that all the metal(II) complexes were monomeric and octahedral. The in-vitro antimicrobial studies of these complexes and their ligands against environmental strains of microorganisms: Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Aspergillus niger and Candida albicans showed that SMX-phen metal complexes [M(SMX)(phen)X].nH2O are better heterocycle with zone of inhibition in the range 28-10mm to combine with SMX for the enhancement of its antimicrobial spectrum this may be due to their more extensive aromatic ring system which gave better lipophilicity, hence aided cell membrane penetration and promoted hostile intracellular interactions leading to death of microoganisms.

Cannabinoid as Potential Aromatase Inhibitor Through Molecular Modeling and Screening for Anti-Cancer Activity

Inhibition of aromatase (CYTP450), a key enzyme in the estrogen biosynthesis, could result in regression of estrogen-dependent tumors and even prevent the promotion of breast cancer. The present research has been designed for searching a potent chemical moiety from natural sources to inhibit aromatase enzyme, the overfunctionality of which causes the breast cancer. Cannabis sativa contains a very much promising group of cannabinoids with more than 66 compounds with reported anticancer property and for the search of a target specific potent aromatase inhibitor, 61 cannabinoids from C. sativa were selected. The Structures Data File (SDF) of these ligand molecules were subjected to docking studies at the binding site of aromatase X-ray crystallographic structure based on lower resolution of the protein crystal structure and higher docking accuracy, predicted by calculating the correlation between experimental activities and Glide dock scores and compared with the standard aromatase ligand androstenedione and aromatase inhibitor fadrozole with existing drug for breast cancer treatment. The best docked pose of each ligand was selected on the basis of the highest dock score related to the binding free energies of the internal dataset compounds as compared to their observed activities. Apart from the hydrogen bond formation with the oxygen present on the aromatic ring system, the other parts of the molecules are stabilized by hydrophobic interactions with non-polar amino acid residues (Ile133, Phe134, Phe221, Trp224, Ile305, Ala306, Ala307, Val369, Val370, Leu372, Val373, Met374 and Leu477). From the screening results of the cannabinoid analogs, 21 out of 61 were found to have an acceptable docking score in comparison to the standards, androstenedione and fadrozole. The pharmacokinetic filters like absorption, distribution, metabolism and excretion and toxicity (ADMET) property determination were applied to select drug-like compounds. Among them three compounds were found to reveal the most promising drug like activity, which were cannabidiorcol (CN 17, CBD-C1), cannabitriol (CN 43, CBT) and cannabiripsol (CN 55, CBR). The ani-cancer activity of the target compounds was performed against brine shrimp lethality biassay, where cannabidiorcol exhibited significant LC50 value of 0.348 ±0.002 μg/ml (R² = 0.9853) which is almost similar to vincristine sulfate (LC50 = 0.316±0.003 μg/ml, R² = 0.9882). Compound cannabitriol also showed promisimg cytotoxicity 0.650±0.004 μg/ml (R² = 0.9882) in comparison to the reference standard. But cannabiripsol demostrated relatively weaker activity 12.95±1.234 μg/ml (R²=0.9897). It can be concluded that the lead compounds may be developed as potent aromatase inhibitor performing their further biological evaluation.
 Dhaka Univ. J. Pharm. Sci. 19(1): 47-58, 2020 (June)

New insights into transformation pathways of a mixture of cytostatic drugs using Polyester-TiO2 films: Identification of intermediates and toxicity assessment

The photocatalytic activity of two bio-based polymer photocatalysts [poly(ethylene terephthalate)-TiO2 (PET-TiO2) and poly(L-lactic acid)-graphene oxide-TiO2 (PLLA-GO-TiO2)] towards Tamoxifen (TAM), Cyclophosphamide (CP), Cytarabine (CYT) and 5-Fluorouracil (5-FLU) removal was explored and compared. The highest photocatalytic activity for the degradation of the cytostatic drugs was accomplished by PET-TiO2. Among the contaminants, TAM was the most easily removed, requiring 90 min for complete elimination, while CP showed the highest resistance to photocatalysis, not being completely removed after 6 h. Liquid chromatography coupled with high-resolution mass spectrometry analysis was employed for the identification of several transformation products (TPs) and potential pathways were proposed. A total of seventy (70) TPs including thirty-four (34) novel ones detected in AOPs were identified. The ecotoxicity of the mixture of the cytostatic drugs and TPs formed during the photocatalytic treatment was evaluated using Daphnia magna assay and was associated with the occurrence of specific TPs during the treatment process. The follow-up ECOSAR (Ecological Structure Activity Relationship) analysis further elucidated that only minor chemical transformations, such as the hydroxylation or the oxidative opening of an aromatic ring system, could hamper the adverse effects of cytostatic drugs in aquatic species. Such a comparative study on the mixture toxicity of cytostatics and their TPs is presented for the first time.

Sulfur self-doped char with high specific capacitance derived from waste tire: Effects of pyrolysis temperature

Preparation of sulfur self-doped char derived from waste tire (WT) was realized via two successively processes of pyrolysis and activation treatment. WT was firstly pyrolyzed at 400 °C, 600 °C, 800 °C, and 1000 °C to collect waste tire chars (WTCs) and they were subsequently activated at 800 °C with potassium ferrate (K2FeO4). The specific capacitance of activated waste tire chars at different pyrolysis temperatures (AWTCs-x-800) decreased from 92.60 F/g to 54.05 F/g at 1 A/g with pyrolysis temperature rising from 400 °C to 1000 °C. As for AWTCs-x-800, higher pyrolysis temperature promoted pore-forming process before 800 °C, and higher pyrolysis temperature enlarged pores after 800 °C. Increase of pyrolysis temperature promoted decomposition of alkyl–aryl CC bonds, transformation of relative small to large aromatic ring system, ordered arrangement of carbon atoms. Besides, it was found that sulfur doping content dominated in specific capacitance performance before 800 °C while surface area dominated after 800 °C. The large surface area and high S 2p3/2 (-C-S-C-, sulphide bridge) content were beneficial for the larger specific capacitance while more S 2p5/2 (-C-SOx-C- (x = 2–4, sulphone bridge) had the negative effect. Pyrolysis mainly affected sulfur doping properties, lower pyrolysis temperature promoted sulfur enrichment and S 2p3/2 generation. Activation promoted surface area improvement and sulfur conversion, higher pyrolysis temperature promoted surface area improvement and sulfur release before 800 °C while the promotion effects weakened after 800 °C, and sulfur transformation of S 2p3/2 converting to S 2p5/2 strengthened at higher pyrolysis temperature.

Understand the Specific Regio- and Enantioselectivity of Fluostatin Conjugation in the Post-Biosynthesis.

Fluostatins, benzofluorene-containing aromatic polyketides in the atypical angucycline family, conjugate into dimeric and even trimeric compounds in the post-biosynthesis. The formation of the C–C bond involves a non-enzymatic stereospecific coupling reaction. In this work, the unusual regio- and enantioselectivities were rationalized by density functional theory calculations with the M06-2X (SMD, water)/6–311 + G(d,p)//6–31G(d) method. These DFT calculations reproduce the lowest energy C1-(R)-C10′-(S) coupling pathway observed in a nonenzymatic reaction. Bonding of the reactive carbon atoms (C1 and C10′) of the two reactant molecules maximizes the HOMO–LUMO interactions and Fukui function involving the highest occupied molecular orbital (HOMO) of nucleophile p-QM and lowest unoccupied molecular orbital (LUMO) of electrophile FST2− anion. In particular, the significant π–π stacking interactions of the low-energy pre-reaction state are retained in the lowest energy pathway for C–C coupling. The distortion/interaction–activation strain analysis indicates that the transition state (TScp-I) of the lowest energy pathway involves the highest stabilizing interactions and small distortion among all possible C–C coupling reactions. One of the two chiral centers generated in this step is lost upon aromatization of the phenol ring in the final difluostatin products. Thus, the π–π stacking interactions between the fluostatin 6-5-6 aromatic ring system play a critical role in the stereoselectivity of the nonenzymatic fluostatin conjugation.

MOF-derived hybrid nanoarchitectured carbons for gas discrimination of volatile aromatic hydrocarbons

Two-dimensional layered graphene nanosheets are very interesting with regard to molecular sensing and vapor discrimination between aromatic hydrocarbons and their aliphatic analogues. However, graphene oxide (GO) suffers from stacking due to strong van der Waals forces between the adjacent nanosheets, thus reducing the surface area of exposure and limiting molecular ion transport in porous electrodes. Mixing GO with nanoporous carbon polyhedra derived from zeolitic imidazolate framework-8 (ZIF-8) generates a 3D continuous framework of hybrid nanoarchitectured hollow carbon macropores coated with reduced GO (rGO). This 3D hollow graphitic carbon framework (HGCF) synergistically combines π-rich-electron nanospaces with a high surface area and a large hierarchical pore volume, both of which are particularly beneficial as porous electrodes for selective detection of hazardous aromatic hydrocarbon vapors over their aliphatic analogues because of reinforced noncovalent π–π interactions with a π-conjugation system of aromatic rings. A designed quartz crystal microbalance (QCM) nanosensor coated with an HGCF heterostructure clearly shows the high impact of π-rich-electrons in graphene as sensing antennae on the molecular discrimination of vaporized toxic aromatic hydrocarbons as compared to carbon polyhedron shapes derived from the ZIF-8 of low sp2-graphitized carbon content.