Free Radical Fragments Research Articles

Molecular reaction dynamics simulation of pyrolysis mechanism of typical bituminous coal via ReaxFF

A reasonable and effective macromolecular model of bituminous coal was established. The molecular dynamics method based on reactive force field (ReaxFF) was used to simulate the pyrolysis process of typical bituminous coal in the range of 1400–2600 K. The distribution of products and evolution of intermediate radicals were analyzed. Calculation results showed that with increase of pyrolysis temperature, yield of char firstly increased and then decreased, while the trend in tar production was opposite. Yield of pyrolysis gas increased monotonously with increasing temperature. The pyrolysis of coal at low temperature mainly experienced primary reaction with formation of tar free radical fragments and small molecular gases. At high temperature, the secondary reaction of tar fragments was remarkable, and char with more content but less quantity and small molecular gas with more content and quantity were produced. The temperature turning point from the primary reaction to the second one was 2000 K. Under the high temperature pyrolysis conditions, C and H in coal gradually migrated into char and tar, while oxygen-containing functional groups were more active, resulting in migration of O to pyrolysis gases. In the secondary reaction stage, comparing chemical properties of the three elements C, H and O, O was the most active, H was the second, and C was the most stable. H2O was firstly released during pyrolysis. NH3 mainly came from secondary reactions during which H2S was consumed and converted into other products. Yield of H2 was the highest, and increased with increasing pyrolysis temperature. A large amount of H2 was generated in secondary reactions, which was mainly from collision of hydrogen radicals generated from pyrolysis and condensation of aromatic structures. Based on ReaxFF simulation results, the weightless activation energy of coal pyrolysis was 39.45 kJ/mol.

Oil shale pyrolysis in a moving bed with internals enhanced by rapid preheating in a heated drop tube

The enhanced oil shale pyrolysis in a moving bed with internals (MBI) by rapid preheating in a drop tube was developed to improve the quality of shale oil through reaction regulation in stages. Initially rapid preheating of oil shale in the upper drop tube endowed the generation of massive free radical fragments and volatile precursors, which would simultaneously restrict the remarkable release of volatiles from particles to minimize the gas-phase secondary reactions. The preheated oil shale subsequently fell into the lower MBI to shape a granular bed with the cocurrent flow of heat and volatiles. In the MBI, the oil shale pyrolysis and volatiles reactions were directed and regulated by matching the flow and temperature fields to realize the selective cracking of heavy fraction in shale oil. The granular bed also served as a filter for the in-situ removal of dust entrained by the volatiles. The shale oil yield reached 83.0% of Fischer Assay oil yield, its light fraction was as high as 89.2 wt% and dust content was as low as 0.6 wt%. The advantages of pyrolysis in the MBI enhanced by rapid preheating were further justified by comparison with other pyrolysis processes.

Effects of Direct Coal Liquefaction Residue Additions on Low-Rank Pulverized Coal during Co-Pyrolysis

This study examined the co-pyrolysis characteristics of low-rank coal (SJC) and direct coal liquefaction residue (DCLR) through thermogravimetric analysis coupled with Fourier transform infrared spectrometry. It also investigated the influences of different mass fractions of DCLR to SJC on the co-pyrolysis characteristics and release regulation of gas phase components. Results showed that with increasing DCLR content, coke yield initially decreased and then increased, but tar and gas yield reversed. Different addition of DCLR changed the composition of the pyrolysis gas in various degrees, and reduced the content of-OH and nitrogen compounds in coke. The H2 content in the gas gradually increased. When 40% DCLR was added, the maximum tar yield was 22.79%, and the maximum H2 yield was 37.12%. At 60% DCLR, the lowest semi-coke yield was 65.01%, and the highest gas yield was 14.65%. The co-pyrolysis of SJC and DCLR can be divided into three stages. The first was the dry degassing stage, during which the adsorbed gas and small-molecule gas were removed on the coal surface at room temperature to 350 °C. The second stage (350 °C–650 °C) was the intense pyrolysis reaction stage, during which a large number of volatiles were obtained. The substantial weight loss rate peak appeared around 450 °C. The weight loss rate of pyrolysis gradually increased with increasing DCLR dosage. The co-pyrolysis of SJC and DCLR was not a simple sum between SJC and DCLR, which indicated a synergistic effect in the co-pyrolysis. The synergistic effect between SJC and DCLR enhances the interaction between free-radical fragments, thereby increasing the yield of pyrolysis tar. The third stage was the shrinkage of semi-coke from 650 °C to the end of the reaction. The polycondensation reaction between free-radical fragments to form solid coke with higher aromaticity, and H2 released.

Preparation and characterization of stable water soluble hybrid nanostructures of hydrophobic compounds by encapsulation into nanoparticles of amphiphilic N-vinylpyrrolidone copolymers of new generation

The conditions for obtaining stable aqueous solutions of prospective pharmaceutical: a lipophilic aminonitroxyl platinum complex, namely, e-amine-d-(4-amino-2, 2, 6, 6-tetramethylpiperidine 1-oxyl)-a, fbis(octanoato)-b, c-dichloroplatinum(IV) (PNC), and a dye zinc tetraphenylporphyrinate (ZnTPP) by means of their solubilization with polymer particles of N-vinylpyrrolidone with dimethacrylate. Aqueous solutions of PNC and ZnTPP encapsulated into polymer particles were investigated by dynamic light scattering, and the temperature dependence of nanostructure sizes was studied. According to transmission electron microscopy, the hybrid nanostructures are core—shell particles, in which the PtIV complex forms small clusters (∼4 nm). It was established by ESR and voltammetric measurements that the free radical fragment of the aminonitroxyl PtIV complex kept its mobility and the same ESR and redox characteristics as the 4-acetylamino-2, 2, 6, 6-tetramethylpiperidine 1-oxyl radical. The obtained results indicate that biocompatible copolymers of N-vinylpyrrolidone are of interests as carriers and delivery tools for ZnTPP and organic PtIV complexes. Hybrid structures of given dimensions and properties can be created on their basis necessary for biomedical applications.

Product Characteristics and Interaction Mechanism in Low-Rank Coal and Coking Coal Co-Pyrolysis Process

The co-pyrolysis characteristics and the interaction with a kind of low-rank coal from SunJiaCha mining area (SJC) and coking coal (Chinese pinyin for coking coal is Jiaomei, JM) from HuangLing were investigated using thermogravimetric Fourier transform infrared (TG-FTIR) analysis and gas chromatography-mass spectrometry (GC-MS). The results revealed a significant synergistic effect of the SJC+JM co-pyrolysis process The addition of JM increased the number of colloids and provided the conditions for the interaction reaction among the pyrolysis products. SJC and JM were used as hydrogen donors, the [H] and free radical fragments from pyrolysis facilitated the hydrogenation reaction. In addition, the composition and structure of the gas were changed due to the synergistic effect, which also substantially decreased the light component in tar substantially.

Investigation of the interaction between vitrinite and inertinite of Xinjiang Wucaiwan coal in pyrolysis by ReaxFF molecular dynamics simulation

The interaction mechanism between vitrinite and inertinite of Xinjiang Wucaiwan coal during coal pyrolysis was investigated via ReaxFF molecular dynamics simulation. The results indicated that the interaction reactions between vitrinite and inertinite of Wucaiwan coal could be divided into three categories: (1) two active hydrogen atoms respectively heated out of the two macromolecular structures and interacted with each other, producing H2; (2) the aliphatic hydrocarbon free radicals, oxygen-containing radicals and other small free radical fragments consisting of cyclic structure that are generated by the cracking of vitrinite macromolecule and interacted with radicals belonging to the inertinite macromolecule and formed new interaction products; (3) residual fragments of the vitrinite and inertinite macromolecules combined with each other and formed a large molecular structure interaction product with more than 40 carbon atoms.

Adhesive antibacterial coatings based on copolymers bearing thiazolium cationic groups and catechol moieties as robust anchors

Herein, we describe a simple approach for the preparation of antibacterial polymeric coatings based on mussel inspired catechol chemistry. A series of statistical copolymers composed of 2-(4-methylthiazol-5-yl)ethyl methacrylate (MTA) and N-(3,4-dihydroxyphenethyl) methacrylamide (DOMA) were synthesized by conventional free radical and reversible addition fragmentation chain transfer (RAFT) polymerizations. Subsequently, the thiazole groups of MTA units were quaternized with methyl and butyl iodide as alkylating agents to provide cationic copolymers with also adhesive anchoring groups of catechol. The copolymers were systematically studied to investigate the effects of composition (MTA/DOMA ratio), molecular weight and alkylating agent on adhesive and antibacterial properties. It was proved that DOMA units play a major role in the adhesion, while the antibacterial activity only decreases slightly with content of DOMA up to 32%. Remarkable, for similar MTA molar equivalent, the copolymers with higher molecular weight exhibit better antimicrobial properties in solution, whereas when they are tethered onto a surface as a coating, the copolymers with lower molecular weight showed enhanced antibacterial performance even against Gram-negative bacteria. These findings confirm that antimicrobial polymers attached onto surfaces behave in a different manner than in solution, and can be more effective as the mobility and accessibility of the cationic groups increase.

Polymer nanoparticles of N-vinylpyrrolidone loaded with an organic aminonitroxyl platinum (iv) complex. Characterization and investigation of their in vitro cytotoxicity

The conditions for obtaining stable aqueous solutions of a lipophilic aminonitroxyl platinum complex, namely, e-amine-d-(4-amino-2,2,6,6-tetramethylpiperidine 1-oxyl)-a, f-bis(octanoato)-b, c-dichloroplatinum(iv), by means of its encapsulation into nanoparticles of copolymers of N-vinylpyrrolidone with triethylene glycol dimethacrylate with various monomer compositions and topologies were found. Aqueous solutions of the complex encapsulated into polymer particles were investigated by dynamic light scattering, the temperature dependence of nanostructure sizes was studied. Transmission electron microscopy established that the hybrid nanostructures are core—shell particles, in which the platinum complex forms small clusters (∼4 nm). The parameters of ESR spectra of aqueous dispersions indicate a high mobility of nitroxyl contained in hybrid nanostructures. Voltammetric measurements demonstrate a similarity of the redox reactions related to the free radical fragment of the aminonitroxyl PtIV complex and of the 4-acetylamino-2,2,6,6-tetramethylpiperidine 1-oxyl radical. Polymer products containing the platinum complex were studied by IR spectroscopy, TGA, and DSC. The cytotoxicity index (IC50) of the free and the encapsulated complex was determined for HeLa tumor cells. The cytotoxicity of the latter (IC50 47–205 nmol L−1) depends on the monomeric composition of the nanoparticles and the incubation time.

Influence of calcium promoter on catalytic pyrolysis characteristics of iron-loaded brown coal in a fixed bed reactor

The Fe–Ca catalysts in catalytic pyrolysis of brown coals were studied to investigate the catalytic activity of the Fe–Ca in a fixed-bed reactor. Experimental results showed the maximum yields of the light aromatic hydrocarbons (LAHs) were 5.90 wt% (0.88 wt% of benzene, toluene and xylene ‘BTX’, 4.10 wt% of phenol and cresol ‘PC’ and 0.92 wt% of naphthalene) when the 1.5% Ca was added into 5% Fe-loaded brown coal. The yields of water and gas significantly reduced, the tar yield gradually increased with increasing heating rate. The characterization results indicated that when calcium promoter was impregnated with iron, Ca2Fe2O5, CaO, Fe2O3 and α-Fe were formed on the surface of the coal char, Ca2Fe2O5 and α-Fe decomposed polyaromatic tar, CaO and Fe2O3 accelerated water gas shift reaction to enhance the H2 yield, the Fe2O3 and Ca2Fe2O5 could be reduced to α-Fe by volatiles (C, CO and H2) under high temperature catalytic pyrolysis. The synergistic effects between iron and calcium improved brown coal pyrolysis and the volatiles such as free radical fragments were further pyrolyzed, indicating that Fe–Ca catalysts inhibited α-Fe deactivation by tar and carbon deposition, thus promoting brown coal pyrolysis and formation of COx, H2 and LAHs.

Effects of quinones and nitroazoles on free-radical fragmentation of glycerol-1-phosphate and 1,2-dimyristoyl-glycero-3-phosphatidyl-glycerol.

Effects of quinones and azoles on the formation of steady-state radiolysis products in aqueous solutions of glycerol-1-phosphate and aqueous dispersions of 1,2-dimyristoyl-glycero-3-phosphatidyl-glycerol has been investigated. The data obtained by LC-MS-ESI and spectrophotometric measurements shows that the compounds having quinoid structures, including the antitumor agent doxorubicin, and azoles having nitro groups effectively inhibit free-radical fragmentation of glycerol-1-phosphate and 1,2-dimyristoyl-glycero-3-phosphatidyl-glycerol, decreasing the radiation-chemical yields of either inorganic phosphate or phosphatidic acid respectively. The observed effects of blocking free-radical processes are believed to be related to the ability of the tested compounds to oxidize α-hydroxyl-containing carbon-centered radicals of starting substrates, which give rise to fragmentation reaction. The possibility of using the discovered properties of quinones, doxorubicin and nitroazoles to provide practical solutions in oncological radiotherapy and pathophysiology is discussed.

ROS-induced lipid transformations without oxygen participation.

This review presents data showing the possibility of novel pathways to be realized for free-radical transformations of glycerophospholipids and sphingolipids. These transformations include the stages of formation and subsequent decay of carbon- and nitrogen-centered radicals of the starting lipids resulting in the accumulation of signal molecules. The presence of a hydroxyl group in the polar component of lipids is a prerequisite for the implementation of these processes. This enables their structural modification and/or destruction to take place with the accumulation of biologically active products such as phosphatidic acid, ceramides, diacylglycerols and acylamides. Sphingolipids containing a free amino group, when interacting with active species of oxygen or chlorine, form aminyl radicals. These lipid radicals undergo further fragmentation, leading to the accumulation of 2-hexadecenal, which has a broad spectrum of biological activity. The presence of an amide group in the structure of sphingolipids determines the possibility of their photodestruction, which also results in the formation of 2-hexadecenal. In contrast with lipid peroxidation, which is inhibited by reducing agents, free-radical fragmentation reactions of hydroxyl-containing lipids involving carbon-centered radicals are blocked by oxidants.

Radical Reactions and Two-Step Kinetics of Sub-Bituminous Coal Liquefaction in Various Solvents

To understand the role of hydrogen donation from solvents to the coal-generated free-radical fragments (coal radicals) in direct coal liquefaction (DCL), a coal with 72.4 wt % carbon was reacted at...

Co-pyrolysis characteristics and synergistic mechanism of low-rank coal and direct liquefaction residue

ABSTRACTIn this study, the co-pyrolysis of low-rank pulverized coal (SJC) and direct liquefaction residue (DCLR) was comparatively examined. The structure and composition of tar and the evolution characteristics of gas during pyrolysis were analyzed through GC-MS, TG-FTIR, and other analytic techniques. Results showed that SJC+DCLR co-pyrolysis exhibited a significant synergistic effect. SJC and DCLR served as hydrogen donors to facilitate the hydrogenation of small molecular free radical fragments through pyrolysis, which increased the tar yield by 5.55%. Aromatic hydrocarbon and phenol contents in tar decreased by 11.88% and 7.94%, respectively, and alkane content increased by 12.25%. H2 content in gas decreased by 19.05%, and CH4 content increased by 19.60%. Co-pyrolysis could be divided into three stages. In the first stage, adsorbed water and CO2 were removed at room temperature to 344.91°C, and the weak chemical bond between SJC and DCLR began to break. In the second stage, SJC and DCLR became pyrolyzed, small molecular free radical fragments were hydrogenated, large amounts of tar and small-molecule gases were produced at 344.91–643.35°C, and synergistic effect was primarily observed. In the third stage, condensation reaction occurred between small molecular free radical fragments at 643.35–845.75°C, thereby producing solid coke and a small amount of gas.

Bond cleavage and reactive radical intermediates in heavy tar thermal cracking

Thermal cracking is an important step of heavy tar processing, in which covalent bonds are initially cleaved to form free radical fragments. The free radical fragments, namely the reactive intermediates, react with each other to form lighter products and coke. Quantity and activity of these reactive radicals determine the products distribution and process operation. Since few studies can be found about the reactive radicals from thermal cracking of heavy tar, we quantify their generation and analyze their activity using two tars provided by ExxonMobil Chemical Company. The tars are heavy fractions of steam cracking of naphtha and heavier hydrocarbon streams. It is found that these heavy tars crack significantly at 350 °C. The reactive radicals generated in 10 min for Tar-1 at 350 and 400 °C are 2.62 and 4.73 mmol/g-tar, respectively, and 1.27 and 3.88 mmol/g-tar, respectively, for Tar-2. The bonds cleaved in 10 min at 400 °C are about 1.50% and 1.30% of total covalent bonds in Tar-1 and Tar-2, respectively, and the bond cleavage activation energies are 31.00 and 38.80 kJ/mol, respectively. The differences in bond cleavage were analyzed from the viewpoint of the composition and structural differences between the two heavy tars, in terms of asphaltene content, aromaticity, and substitutive degree of aromatic ring, for example. The reactive radicals were further categorized into low activity ones and high activity ones and were correlated with stable radicals which have survived the cracking.

P-77 - Effects of azoles on processes involving hydroxyl-containing carbon-centered organic radicals

Free radical fragmentation (FRF) reactions taking place in hydroxyl-containing (HC) biologically relevant substances can make a substantial contribution to the consequences resulting from irradiation of biosystems. HC organic compounds under radiolysis of their aqueous solutions undergo fragmentation that cause damage to carbohydrates, HC lipids and proteins. It has been established earlier that the HC lipids being subjected to radiolysis undergo such fragmentation, giving phosphatidic acid (PA). Accumulation of PA in cancer cells promotes their proliferation. The aforesaid is an important incentive to perform the search for the substances capable of producing an effective regulative action on the probability of FRF reactions occurrence. The object pursued in this study was investigation of the effects produced by azoles on formation of the end products during radiolysis of aqueous solutions of glycerol-1-phosphate (G1F), free radical transformations of that models HC lipids fragmentation. We established ability of nitroazoles to inhibit fragmentation of G1F. This fact open up a new possibility to enhance efficacy of radiation therapy by introducing agents effectively blocking the radiation-induced processes leading to formation of products promoting cancer cell proliferation.

P-35 - Free-radical fragmentation reactions of biomolecules involving C-C, C-O and C-N bond cleavage

Among a wide variety of homolytic transformations taking place in biomolecules, the oxidation processes occurring in the cell membrane lipids have been the most thoroughly studied ones. For such processes to be realized, the presence of oxygen is necessary. At low O2 concentrations the probability of oxidation processes decreases, enabling other types of free-radical reactions to occur in biomolecules. In our studies, a concept is being developed focusing on the important contribution of free-radical fragmentation reactions involving C-C, C-O and C-N bond rupture in organic molecules to the biosystem damage. Such processes can take place without participation of oxygen and may lead not only to destruction and modification of biologically relevant compounds but to accumulation of physiologically active products as well. The reactions resulting in the C-C, C-O or C-N bond ruptures occurring in an organism are known to be catalyzed by lyases. Many of these reactions proceed according to a free-radical mechanism. The report will be focused on discussion of the above-named fragmentation reactions of biomolecules and the possible consequences of their realization in an organism.

Effects of extractable compounds on the structure and pyrolysis behaviours of two Xinjiang coal

The extractable compounds are a very important part of coal and play an important role in the pyrolysis of coal. To further understand the effect of the extracts on the structure and pyrolysis behaviours of coal, Naomaohu (NMH) lignite and Hutubi (HTB) bituminous coal were extracted with pyridine and swollen with its solvent vapor. The pyrolysis process was performed in a fixed-bed reactor. Thermogravimetric analysis (TGA) of the coal samples was carried out on a thermogravimetric (TG) analyser. The pore structure characteristics of the coal samples and their chars obtained from pyrolysis at different temperatures were measured by the mercury intrusion porosimetry (MIP) method. The components of the pyrolysis gas were detected by gas chromatography (GC). It was found that the extraction and swelling processes enlarged the pore size and improved the porosity of the coals to some extent. Compared with the pyrolysis of the raw coal, that of the swollen coal resulted in a higher tar yield owing to the destruction of the cross-linked structure and the variations in the coal structure; the tar yield for the pyrolysis of all the residues decreased significantly, but the gas yield increased, where the volume of the CO gas mainly increased. The NMH residue char obtained from pyrolysis of the residue at different temperatures had a lower proportion of micropores than the HTB residue char. The extractable compounds will be converted to gas-phase (e.g. volatiles) and liquid-phase (e.g. colloids) products during the pyrolysis process, which could stabilise the free radical fragments, form coke in the pore structure of the char and increase the number of new micropores formed.

Effect of sulfur-containing amino acids and peptides on the free-radical fragmentation of biologically active phospho derivatives of glycerol

The effects of sulfur-containing amino acids and peptides (cysteine, N-acetylcysteine (NAC), methionine, methionine sulfoxide (MetO), taurine (Tau), glutathione (GSH, GSSH), cysteinylglycine, and glutamylcysteine) on the free-radical degradation of glycero-1-phosphate and dimiristoyl phosphatidylglycerol with phosphoether bond rupture induced by γ-radiation or the Fe2+(EDTA)(Cu2+)–H2O2–(ascorbate) systems have been studied. In the case of a radiation-initiated process, thiols exert the greatest radioprotective effect in a concentration-dependent manner, and the action of MetO and Tau is neutral. In the case of Cu2+- mediated fragmentation, all of the test compounds with exception of Tau and NAC inhibit the process. The action of the test compounds on the fragmentation mediated by the Fe2+/EDTA–H2O2 (Fe2+–H2O2–ascorbate) systems can be either anti(pro)oxidant or neutral. In this case, all of the thiols other than glutamylcysteine exert an activating effect.

ChemInform Abstract: Transition‐Metal‐Catalyzed C—C and C—X Bond‐Forming Reactions Using Cyclopropanols

AbstractReview: [73 refs.

Effect of histidine-containing dipeptides on the free-radical fragmentation of biologically active phospho derivatives of glycerol

The effects of carnosine, anserine, and glycyl-histidine on the free-radical fragmentation of glycero-1-phosphate and dimiristoyl phosphatidylglycerol induced by γ-radiation or Fe2+(Cu2+)-containing systems have been studied. The histidine-containing dipeptides (HCDs) exert a radioprotector effect on the fragmentation; this effect depends on the concentration of O2 and reaches a maximum in deaerated systems (by a factor of ~1.7). The HCDs can be antior prooxidants under the conditions of the Fe2+(Cu2+)-mediated generation of HO· radicals. Carnosine exhibits protector properties in a dose-dependent manner regardless of the inductor. Carnosine more effectively inhibits Cu2+-induced fragmentation (by a factor of 2–2.5) than the Fe2+-mediated process (by a factor of 1.4).