Structure Of Tar Research Articles

Catalytic influence of iron oxide (Fe2O3) on coal pyrolysis and char combustion at various temperatures

The conversion of coal into cleaner energy forms is essential for achieving sustainable development. This study investigates the role of Fe2O3 as a catalyst in enhancing the efficiency of coal pyrolysis and char combustion. A fixed-bed tube furnace (TF) was selected for pyrolysis, and a Thermogravimetric Analyzer coupled with Fourier Transform Infrared Spectroscopy (TG-FTIR) was used for combustion analysis. The produced syngas and tar were characterized using Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC/MS). Our results show higher volatile release volume (VRV) from coal with catalyst compared with without catalyst and the rise with temperature within the 600–1000 ℃ range. Although hydrogen production decreased with the addition of the catalyst, at 1000 ℃, the catalyst's impact was negligible. The catalyst notably facilitated the breakdown of heavy aromatic rings in tar, eliminating triple-bond aromatic structures. In contrast, tar from raw coal exhibited a 20% yield of such structures. Scanning Electron Microscopy (SEM) revealed a cubic structure of Fe2O3 in char, with an increased surface area compared to raw coal char (338.75 m2/g vs. 313.51 m2/g). TG-FTIR analysis indicated a lower activation energy for catalysts with char combustion. Overall, Fe2O3 improves tar structure, increases char surface area, and lowers activation energy.

Solid Phase Synthesis and TAR RNA-Binding Activity of Nucleopeptides Containing Nucleobases Linked to the Side Chains via 1,4-Linked-1,2,3-triazole.

Nucleopeptides (NPs) represent synthetic polymers created by attaching nucleobases to the side chains of amino acid residues within peptides. These compounds amalgamate the characteristics of peptides and nucleic acids, showcasing a unique ability to recognize RNA structures. In this study, we present the design and synthesis of Fmoc-protected nucleobase amino acids (1,4-TzlNBAs) and a new class of NPs, where canonical nucleobases are affixed to the side chain of L-homoalanine (Hal) through a 1,4-linked-1,2,3-triazole (HalTzl). Fmoc-protected 1,4-TzlNBAs suitable for HalTzl synthesis were obtained via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) conjugation of Fmoc-L-azidohomoalanine (Fmoc-Aha) and N1- or N9-propargylated nucleobases or their derivatives. Following this, two trinucleopeptides, HalTzlAAA and HalTzlAGA, and the hexanucleopeptide HalTzlTCCCAG, designed to complement bulge and outer loop structures of TAR (trans-activation response element) RNA HIV-1, were synthesized using the classical solid-phase peptide synthesis (SPPS) protocol. The binding between HalTzls and fluorescently labeled 5'-(FAM(6))-TAR UCU and UUU mutant was characterized using circular dichroism (CD) and fluorescence spectroscopy. CD results confirmed the binding of HalTzls to TAR RNA, which was evident by a decrease in ellipticity band intensity around 265 nm during complexation. CD thermal denaturation studies indicated a relatively modest effect of complexation on the stability of TAR RNA structure. The binding of HalTzls at an equimolar ratio only marginally increased the melting temperature (Tm) of the TAR RNA structure, with an increment of less than 2 °C in most cases. Fluorescence spectroscopy revealed that HalTzlAAA and HalTzlAGA, complementary to UUU or UCU bulges, respectively, exhibited disparate affinities for the TAR RNA structure (with Kd ≈ 30 and 256 µM, respectively). Hexamer HalTzlTCCCAG, binding to the outer loop of TARUCU, demonstrated a moderate affinity with Kd ≈ 38 µM. This study demonstrates that newly designed HalTzls effectively bind the TAR RNA structure, presenting a potential new class of RNA binders and may be a promising scaffold for the development of a new class of antiviral drugs.

Infrared Spectrum and Principal Component Analysis of Heavy Tar Cut by Different Fractions from Tar-Rich Coal.

The composition and content of heavy tar vary significantly depending on the pyrolysis conditions and separation methods. This study aimed to effectively identify the main components and content of heavy coal tar and provide a theoretical basis for its subsequent utilization. To achieve this, simulated distillation and infrared spectrum analysis of heavy coal tar were conducted with a focus on understanding the impact of simulated distillation on the composition and structure of tar. The results showed that the fraction content in the tar underwent significant changes after simulated distillation at different temperatures. Specifically, the content of light oil decreased from 4.3 to 0.1%, while the asphalt content increased from 77.6 to 90.6%. Infrared spectrum and peak fitting revealed that the distilled coal tars exhibited similar characteristic peaks in regions associated with hydroxyl, aliphatic hydrocarbon, oxygen-containing functional group, and aromatic hydrocarbon structure. Based on the infrared spectrum of heavy coal tar, principal component analysis was conducted on different fractions. When using two principal components, the cumulative value reached 96.93%. It was found that PC1 displayed strong peak signals around 749 and 687 cm-1, while PC2 exhibited strong peak signals near 2356 and 1143 cm-1.

STUDY OF COAL TAR PITCH MORPHOLOGY AND STRUCTURE

The morphology and structure of the mesophase in the series: coal tar pitch (CTP) - α-fraction of CTP - carbonised α-fraction after heating to 1200 °C, were studied by scanning electron microscopy, X-ray phase and X-ray structural analysis. The X-ray structural parameters were determined: longitudinal and transverse dimensions of the lamellae and the thickness of packages, the distance between the lamellae and the number of lamellae in the formed packages. It is shown that the two-dimensional structures of carbon mesophase are ordered into three-dimensional packages during the formation of semi-coke under CTP heating. It is established that the carbon structure of CTP and its α-fraction is represented by the turbostratic and graphite-like phases. The sizes of the packages formed by the lamellae during structuring in the transverse direction in the studied samples are of the order of 18-25 Å, in the longitudinal direction 46-63 Å, the average distance between the lamellae in the studied samples is 3.46-3.52 Å.

Study of Coal Tar Pitch Morphology and Structure

Study of Coal Tar Pitch Morphology and Structure

Effects of variable amounts of volatiles in corncob on microwave co-pyrolysis of low-rank coal and corncob

Crop waste-assisted microwave pyrolysis of low-rank coal (LRC) can provide sufficient hydrogen for thermal decomposition reactions of LRC, which can change the pyrolysis reactions and product characteristics. To reveal the effect of crop waste as a hydrogen supply on the microwave pyrolysis of LRC, the temperature-rise characteristics, product distribution, and product characteristics of microwave co-pyrolysis of LRC and corncob (CR) with different amounts of volatiles were investigated in detail, and the crystal and chemical structures of char and tar were analyzed. The results showed that the volatiles in CR promoted the production of tar and inhibited the generation of pyrolysis gas within a certain range during microwave co-pyrolysis; however, the volatiles had the opposite effect beyond this range. With an increase in volatiles in CR, the yields of char and pyrolysis water gradually decreased and increased, respectively. CR with low amounts of volatiles at high final pyrolysis temperatures increased the specific surface area and total pore volume of the char obtained by microwave co-pyrolysis and improved the aromaticity and graphitization of char and the ordered structure of the crystal structure in char. Additionally, the formation of aromatic structures in the tar was promoted, and the contents of oxygen-containing functional groups and aliphatic hydrocarbons in the tar were reduced. The fraction of light oil in the tar increased by 18.49%, indicating that the lightness and stability of the tar significantly increased. These findings have provided a theoretical basis for microwave co-pyrolysis of LRC and crop wastes, as well as experimental evidence for regulating its product characteristics.

Improved CPD model coupled with lattice vacancy evolution

The development of CFD (Computational Fluid Dynamics) technology needs more extensive process adaptability of coal pyrolysis models. Some modified CPD (Chemical Percolation Devolatilization) models may have extended the application, but problems still exist: this paper presents further improvements and experimental verification. On the one hand, the improvements cover the integration of cross-linking process with the lattice structure, as well as an updating of the kinetic calculation; i.e., creating directed graphs Gchar and Gtar for modeling char and tar structures, counting node/edge properties for producing macroscopic lattice features, solving traditional DAEM (Distribution Activation Energy Model) for calculating bridge kinetic processes, and tracking the influence of evaporation on the lattice network vacancy. On the other hand, the verification shows that the proposed model can reasonably predict the pyrolysis data of Ill6 and Zap coal under both fast and slow conditions simultaneously. In order to save computational cost and facilitate practical application, an ANN (Artificial Neural Network) is trained. At last, some future work includes optimization of kinetic parameters and modeling of real lattices.

Evaluation of tar from the microwave co-pyrolysis of low-rank coal and corncob using orthogonal-test-based grey relational analysis (GRA)

Tar is a potential alternative to crude oil and can be produced through the pyrolysis technology of low-rank coal. However, the low H/C ratio of coal leads to unsatisfactory tar yield and quality. The use of corncob as a hydrogen donor to assist the microwave pyrolysis of low-rank coal through orthogonal-test-based grey relational analysis was investigated. The yield, structure, and component of tar under the optimum conditions were discussed. Results showed that pyrolysis time had the most obvious effect on tar yield, followed by corncob particle size, microwave power, and corncob additive amount, but the difference was small. The maximum tar yield of 8.85% was achieved under the following conditions: microwave power of 700 W, pyrolysis time of 30 min, corncob particle size of 0.420–0.841 mm, and corncob additive amount of 30%. The positive synergistic effect resulted in increased tar yield and decreased long-chain carbon structure and heteroatom organics in tar, thereby producing “lighter” and more “valuable” tar. This positive synergistic effect was due to the H free radicals and reactive oxygen-containing groups produced from corncob cracking.

Role of conformational heterogeneity in ligand recognition by viral RNA molecules.

Ribonucleic acid (RNA) molecules are known to undergo conformational changes in response to various environmental stimuli including temperature, pH, and ligands. In particular, viral RNA molecules are a key example of conformationally adapting molecules that have evolved to switch between many functional conformations. The transactivation response element (TAR) RNA from the type-1 human immunodeficiency virus (HIV-1) is a viral RNA molecule that is being increasingly explored as a potential therapeutic target due to its role in the viral replication process. In this work, we have studied the dynamics in TAR RNA in apo and liganded states by performing explicit-solvent molecular dynamics (MD) simulations initiated with 27 distinct structures. We determined that the TAR RNA structure is significantly stabilized on ligand binding with especially decreased fluctuations in its two helices. This rigidity is further coupled with the decreased flipping of bulge nucleotides, which were observed to flip more frequently in the absence of ligands. We found that initially-distinct structures of TAR RNA converged to similar conformations on removing ligands. We also report that conformational dynamics in unliganded TAR structures leads to the formation of binding pockets capable of accommodating ligands of various sizes.

Viral RNA structure analysis using DMS-MaPseq.

RNA structure is critically important to RNA viruses in every part of the replication cycle. RNA structure is also utilized by DNA viruses in order to regulate gene expression and interact with host factors. Advances in next-generation sequencing have greatly enhanced the utility of chemical probing in order to analyze RNA structure. This review will cover some recent viral RNA structural studies using chemical probing and next-generation sequencing as well as the advantages of dimethyl sulfate (DMS)-mutational profiling and sequencing (MaPseq). DMS-MaPseq is a robust assay that can easily modify RNA in vitro, in cell and in virion. A detailed protocol for whole-genome DMS-MaPseq from cells transfected with HIV-1 and the structure of TAR as determined by DMS-MaPseq is presented. DMS-MaPseq has the ability to answer a variety of integral questions about viral RNA, including how they change in different environments and when interacting with different host factors.

GEOMETRIC AND ELECTRONIC STRUCTURE OF HEAVY HIGHLY VISCOUS OIL COMPONENTS

Physical-chemical and structural-rheological properties of the oil disperse system are determined by the structure, size and composition of the complex structures resulting from the association of paraffins and tarry asphaltene components. Therefore, data about hydrocarbon composition, especially the structure of paraffins, tars and asphaltenes, required to choose recovery method in the extraction, field treatment, transportation and processing of heavy oils. In article parameters of the geometric and electronic structure of the tars and asphaltenes model molecules to determine reactivity indexes and, consequently, the possibility of a new oil dispersed system formation were calculated. Based on the density functional method B3LYP/6-311+G(d,p), quantum chemical calculations of the electronic structure and geometry of model tar molecules are given in the work. It was found that the number of benzene rings does not have a significant impact on the geometric and electronic structure of hydrocarbon fragments. The heteroatoms N, S and -OH functional group have a significant influence on the characteristics of model molecules. The nitrogen atom significantly increases the molecule dipole moment, compared to the sulfur and hydroxyl group, and the greatest change in geometric and electronic structure is observed in the presence of a sulfur atom. To choose recovery method in the heavy hydrocarbon crude treatment, the elemental composition is quite important, since it is heteroatoms in multi-core systems with condensed nuclei that affect the reactivity indices and provides generation of a free radical form and creation of a new oil dispersion system.

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.

HIV-1 Tat interactions with cellular 7SK and viral TAR RNAs identifies dual structural mimicry

The HIV Tat protein competes with the 7SK:HEXIM interaction to hijack pTEFb from 7SK snRNP and recruit it to the TAR motif on stalled viral transcripts. Here we solve structures of 7SK stemloop-1 and TAR in complex with Tat’s RNA binding domain (RBD) to gain insights into this process. We find that 7SK is peppered with arginine sandwich motifs (ASM)—three classical and one with a pseudo configuration. Despite having similar RBDs, the presence of an additional arginine, R52, confers Tat the ability to remodel the pseudo configuration, required for HEXIM binding, into a classical sandwich, thus displacing HEXIM. Tat also uses R52 to remodel the TAR bulge into an ASM whose structure is identical to that of the remodeled ASM in 7SK. Together, our structures reveal a dual structural mimicry wherein viral Tat and TAR have co-opted structural motifs present in cellular HEXIM and 7SK for productive transcription of its genome.

Structure of HIV-1 TAR in complex with a lab-evolved protein provides insight into RNA recognition and synthesis of a constrained peptide that impairs transcription

Structure of HIV-1 TAR in complex with a lab-evolved protein provides insight into RNA recognition and synthesis of a constrained peptide that impairs transcription

Conformational Dynamics of the HIV-1 Trans-Activation Response Element RNA Hairpin Bound to a Lab-Evolved Peptide

We report microsecond-length classical molecular dynamics simulations of a lab-evolved peptide bound to the HIV-1 trans-activation response element (TAR) RNA hairpin. An essential 5′-structure in all HIV-1 mRNAs, TAR interacts with HIV-1 Tat to promote HIV-1 genome transcription, and is considered a promising therapeutic target. Using yeast display, a U1A-derived TAR binding protein (TBP) was selected that binds TAR with subnanomolar affinity and extraordinarily high specificity over the native U1A U1hpII target, thereby preventing Tat-dependent transcription in vitro. A co-crystal structure of TBP in complex with TAR reveals the basis for its unprecedented affinity and specificity. The complex exhibits a Watson-Crick C30-G34 base pair in the six-nucleotide apical loop. From chemical modification experiments and sequence conservation, this base pair has been posited as a prerequisite for Tat binding. We investigated the role of a short TBP peptide - responsible for the preponderance of TAR readout - in stabilizing the observed TAR structure using molecular dynamics simulations of TAR in the apo state and in complex with the full TBP protein and the short TBP peptide. To define discrete conformational states, we performed principal component analysis and clustered trajectories based on the resulting principal components. We observed that the apical loop C30-G34 base pair and a major groove U23-A27-U38 base triple are stable features of peptide-bound TAR on the microsecond timescale. In agreement with NMR studies of free TAR, dissolution of the major groove base triple occurs in trajectories of the apo state. The occupancy of contacts between the protein and the TAR major groove is greater for the arginine residues whose mutation to alanine has a greater impact on the binding affinity, as measured by isothermal calorimetry.

Событие рассказывания в романе Т. Майн Рида «Морской волчонок, или Путешествие на дне трюма»

Событие рассказывания в романе Т. Майн Рида «Морской волчонок, или Путешествие на дне трюма»

Effects of H2O and CO2 on the homogeneous conversion and heterogeneous reforming of biomass tar over biochar

The effects of H2O and CO2 reforming agents on the homogeneous conversion and heterogeneous reforming of biomass tar were studied in the presence of a biochar catalyst to better understand the transformation pathway between tar and biochar. Catalysis was performed in a two-stage fluidized bed/fixed bed reactor while Raman analysis and Gas Chromatograph-Mass Spectrometry were used to investigate biochar and tar characteristics. The results show temperatures of 700–900 °C are required for the homogeneous transformation of tar in the presence of H2O/CO2, which especially affect polycyclic aromatic hydrocarbons. The tar homogeneous reforming effect of 15 vol.% H2O is significantly higher than that of 29 vol.% CO2. During heterogeneous reforming of tar over biochar at 800 °C, the tar yield decreases in varying degrees with the H2O and CO2 concentration increasing. H2O and CO2 not only directly affect the tar transformation on biochar, but also indirectly influence the reforming of tar through changing the structure of biochar catalyst. The formation of additional oxygen-containing functional groups and transformation of small aromatic rings to larger aromatic rings in the biochar structure are promoted with the concentration of H2O and CO2 increasing. Under a H2O/CO2 atmosphere, a higher degree of aromatic ring heterogeneous reforming occurs over biochar than for non-aromatic tar components. Heterogeneous reforming reactivity of tar is promoted by the biomass tar structure (e.g the substituents, large aromatic ring size and five-carbon ring structures) over biochar under H2O/CO2 atmospheres. Further increasing H2O and CO2 concentration enhances this effect.

Aquathermolysis of Natural Bitumen under Supercritical Conditions in the Presence of Ferrospheres

The influence of a catalytic additive – magnetic ferrospheres – on the product composition of cracking of natural bitumen from Ashal'chinskoe oilfield (4.6 wt % of fractions with IBP 200 °C) was studied. The reaction was achieved in an autoclave in the presence of a hydrogen donor (water). The addition of 10 wt % of ferrospheres was shown to favor the tar destruction and to increase the yield of light boiling fractions. The coke formation was decelerated during bitumen aquathermolysis under supercritical conditions. In aquathermolysis with ferrospheres at 500 °C, the yield of fractions IBP 360 °C increase by 12.5 %, while gas and coke yields decreased by 14.4 and 3.9 wt %, respectively, against the yields during bitumen cracking. The data on structure and group analysis of tars and asphaltenes indicate considerable destruction of the alkyl and naphthene species during aquathermolysis. Application of aquathermolysis allows heavy hydrocarbon feedstock to be processed using inexpensive and effective additives to improve considerably the conversion ratio.

Insights into HIV-1 proviral transcription from integrative structure and dynamics of the Tat:AFF4:P-TEFb:TAR complex.

HIV-1 Tat hijacks the human superelongation complex (SEC) to promote proviral transcription. Here we report the 5.9 Å structure of HIV-1 TAR in complex with HIV-1 Tat and human AFF4, CDK9, and CycT1. The TAR central loop contacts the CycT1 Tat-TAR recognition motif (TRM) and the second Tat Zn2+-binding loop. Hydrogen-deuterium exchange (HDX) shows that AFF4 helix 2 is stabilized in the TAR complex despite not touching the RNA, explaining how it enhances TAR binding to the SEC 50-fold. RNA SHAPE and SAXS data were used to help model the extended (Tat Arginine-Rich Motif) ARM, which enters the TAR major groove between the bulge and the central loop. The structure and functional assays collectively support an integrative structure and a bipartite binding model, wherein the TAR central loop engages the CycT1 TRM and compact core of Tat, while the TAR major groove interacts with the extended Tat ARM.

Synthesis and in Vitro Screening of New Series of 2,6-Dipeptidyl-anthraquinones: Influence of Side Chain Length on HIV-1 Nucleocapsid Inhibitors.

2,6-Dipeptidyl-anthraquinones are a promising class of nucleic acid-binding compounds that act as NC inhibitors in vitro. We designed, synthesized, and tested new series of 2,6-disubstituted-anthraquinones, which are able to bind viral nucleic acid substrates of NC. We demonstrate here that these novel derivatives interact preferentially with noncanonical structures of TAR and cTAR, stabilize their dynamics, and interfere with NC chaperone activity.