4-membered Ring Research Articles

Inhibition mechanism of electric field on polycyclic aromatic hydrocarbon formation during n-decane pyrolysis: A ReaxFF MD and DFT study

Polycyclic aromatic hydrocarbon (PAH) is the soot precursor in hydrocarbon fuel pyrolysis process, which results in serious combustion and environmental issues. This work investigated the process of n-decane pyrolysis and PAHs formation under electric field using ReaxFF molecular dynamics and density functional theory (DFT) method. The results demonstrated that the electric field increased the decomposition reaction rate constant (k) from 5.15 × 109 s−1 to 9.01 × 109 s−1 and decreased the reaction activation energy (Ea) from 59.47 to 54.79 kcal/mol of n-decane pyrolysis at 0.20 V/Å. DFT calculation validated that the enthalpy change (ΔH) of bonds cracking was decreased and the polarization of n-decane was enhanced by electric field. A priority selective effect was performed on the initial cracking path and validated by the potential energy surfaces (PES). With products distribution statistics, C2 precursors of ring formation were decreased by the field, resulting in the inhibition of largest molecular size growth. The development of the largest molecule structure revealed clearly that the 5-member ring was unstable and the growth of 6-member ring was inhibited under electric field. This work supplies the n-decane pyrolysis and PAH formation mechanism modified by electric field, which provides a wide application in fuel clean combustion and environmental pollution researches.

A Chemical Strategy toward Novel Brain-Penetrant EZH2 Inhibitors.

Aberrant gene-silencing through dysregulation of polycomb protein activity has emerged as an important oncogenic mechanism in cancer, implicating polycomb proteins as important therapeutic targets. Recently, an inhibitor targeting EZH2, the methyltransferase component of PRC2, received U.S. Food and Drug Administration approval following promising clinical responses in cancer patients. However, the current array of EZH2 inhibitors have poor brain penetrance, limiting their use in patients with central nervous system malignancies, a number of which have been shown to be sensitive to EZH2 inhibition. To address this need, we have identified a chemical strategy, based on computational modeling of pyridone-containing EZH2 inhibitor scaffolds, to minimize P-glycoprotein activity, and here we report the first brain-penetrant EZH2 inhibitor, TDI-6118 (compound 5). Additionally, in the course of our attempts to optimize this compound, we discovered TDI-11904 (compound 21), a novel, highly potent, and peripherally active EZH2 inhibitor based on a 7 member ring structure.

Three-dimensional tetrahexcarbon: Stability and properties

Although cyclobutene consisting of 4-membered rings of C atoms is highly unstable, one- and two-dimensional (1D, 2D) carbon allotropes, called tetrahexcarbon (th-C) consisting of 4- and 6- membered rings, have been reported recently, which shows novel properties with prominent applications in nano-electronics, optoelectronics, and nano-mechanics. Going beyond the studies of 1D and 2D tetrahexcarbon, in this study we propose a 3D-tetrahexcarbon structure (3D th-C12), which shows dynamical, mechanical, and thermal stability. Different from the mixed sp2-sp3 features in 1D and 2D tetrahexcarbon structures, all the C atoms are 4-coordinated in the 3D tetrahexcarbon. Moreover, different from the metallic and highly ductile 2D tetrahexcarbon sheet, the 3D tetrahexcarbon is brittle with high hardness, and it is semiconducting with an indirect bandgap of 3.92 eV at HSE06 level, exhibiting anisotropic elasticity, good optical absorption in visible and UV regions, strong phonon inelastic scattering. This study expands the tetrahexcarbon family with additional new features.

Density functional modeling of structural and electronic properties of amorphous high temperature oxides

Ab initio molecular dynamics modeling in the NPT ensemble is used to obtain amorphous states by melting SiO2, ZrO2 and HfO2 crystals. A wide range of melt stabilization temperatures are used. Two types of SiO2 amorphous states are obtained. For melt temperatures below 4500 K, a perfect silica glass is obtained without any point defects. For melt temperatures above 4500 K, silica point defects such as threefold coordinated oxygen atoms, edge-sharing SiO4-tetrahedra, and others together with a wide range of Si-O-Si rings including 3-, and 4-membered rings appear. When the temperature of the melt exceeds the ZrO2 and HfO2 crystal melting point by 100 – 400 K, a sharp drop in the density of amorphous states is observed, accompanied by a decrease in atomic coordination, but this does not lead to the formation of defect states in the depth of the band gap of hafnium and zirconium dioxides.

Improvement of the photostability of cycloalkylamine-7-sulfonyl-2,1,3-benzoxadiazole-based fluorescent dyes by replacing the dimethylamino substituent with cyclic amino rings

Replacing the dimethylamino substituent of a fluorescent probe with 3- and 4-membered cyclic amine rings led to significantly enhanced photostability.

Synthesis of Aerogel with Graphene and Significance with Aerospace Industry

The Primarily focus on Graphene Aerogel, its synthesis and structural integrity together with high electrical conduction. Graphene could be a new nanocarbon that has, single-, bi- or few- layers of carbon atoms forming membered rings. Mechanically powerful and electrically semiconductive graphene aerogels will be produced by either essential drying or freeze of gel precursors integration from the reduction of graphene substance with L-ascorbic acid. In distinction to ways in which utilize physical cross-links between GO, this approach provides valency carbon bonding between the graphene sheets. The graphene aerogels put together possess large surface areas and pore volumes, creating those materials to a feasible possibility to be used in energy repository, catalysis, and sensing applications. We've additionally showcased some applications for Graphene Aerogel such as their electrical conductivities, Lithium-ion batteries and electrical phenomenon devices, Supercapacitors and photocatalysis.

SYNTHESIS AND BIOLOGICAL ACTIVITY OF NEW COMPOUNDS OF FIVE AND SIX MEMBERED RINGS INCORPORATING TO COUMARIN DERIVATIVES

SYNTHESIS AND BIOLOGICAL ACTIVITY OF NEW COMPOUNDS OF FIVE AND SIX MEMBERED RINGS INCORPORATING TO COUMARIN DERIVATIVES

Chemisorption-Induced Formation of Biphenylene Dimer on Ag(111).

We report an example that demonstrates the clear interdependence between surface-supported reactions and molecular-adsorption configurations. Two biphenyl-based molecules with two and four bromine substituents, i.e., 2,2'-dibromobiphenyl (DBBP) and 2,2',6,6'-tetrabromo-1,1'-biphenyl (TBBP), show completely different reaction pathways on a Ag(111) surface, leading to the selective formation of dibenzo[e,l]pyrene and biphenylene dimer, respectively. By combining low-temperature scanning tunneling microscopy, synchrotron radiation photoemission spectroscopy, and density functional theory calculations, we unravel the underlying reaction mechanism. After debromination, a biradical biphenyl can be stabilized by surface Ag adatoms, while a four-radical biphenyl undergoes spontaneous intramolecular annulation due to its extreme instability on Ag(111). Such different chemisorption-induced precursor states between DBBP and TBBP consequently lead to different reaction pathways after further annealing. In addition, using bond-resolving scanning tunneling microscopy and scanning tunneling spectroscopy, we determine with atomic precision the bond-length alternation of the biphenylene dimer product, which contains 4-, 6-, and 8-membered rings. The 4-membered ring units turn out to be radialene structures.

Regiodivergent synthesis of vinyl trifluoromethansulfonates γ/δ lactones: Via 1,6 addition/intramolecular one-pot annulation of 1,4-dihidropyridines derivated from pyridinyl propenones

We report a novel intramolecular 1,6 oxa-Michael addition on substituted dihydropyridines to obtain 5 and 6 member ring lactones in an one-pot reaction starting from activated pyridinyl propenones, without organic catalysis or presence of bulky groups in the Michael acceptor. A marked dependence on the regioselectivity of ring closure was found, dependent on the propenone used.

Antibacterial, spectroscopic and X-ray crystallography of newly prepared heterocyclic thiourea dianion platinum(II) complexes with tertiary phosphine ligands

Treatment of one molar equivalent of [PtCl2(diphos)] (diphos = dppe, dppp, dppb or dppf) or [PtCl2(PPh3)2] with one molar equivalent of (H2CPPT) in the presence of Et3N afforded the new heterocyclic thiourea dianion complexes [Pt(κ2-CPPT)(diphos)] and [Pt(κ2-CPPT)(PPh3)2] (1–5). The synthesized complexes were characterized by FT-IR, 1H NMR and 31P-{1H} NMR spectroscopy. Moreover, X-ray single crystal structure determination for complexes [Pt(κ2-CPPT)(dppe)] (1) and [Pt(κ2-CPPT)(dppb)] (3) showed a four membered ring structure with the Pt(II) ion being central and adopting a slightly distorted square planar geometry. Furthermore, the X-ray structures showed that the sulfur atom is trans to the phosphine ligand with the shortest Pt-P bond, compared to the nitrogen atom that is trans to the other Pt-P bond. Interestingly, the obtained complexes, apart from previously synthesized ones, showed one isomer formation only. This behavior is probably due to the inductive effect for both of the heteroatoms and the chlorine atom on the pyridyl group. Generally, the prepared complexes showed similar behavior to their analogous non-substituted thiourea dianion complexes, with no observable effect of the heteroatom on the overall structure. Furthermore, antibacterial activities were tested against three pathogenic bacterial species; among the four tested complexes, complexes 4 and 2 showed high activity values.

Novel base-free dianion complexes of Pt(II) and Pd(II) derived from heterocyclic thiourea and tertiary phosphine ligands

Treatment of one molar equivalent of [M(HCPPT)2] (M=Pd, Pt; H2CPPT = 1-(5-chloropyridin-2-yl)-3-phenylthiourea) with one molar equivalent of κ2-diphos (diphos = dppe, dppp, dppb, and dppf) or two molar equivalent of κ1-phos afforded eight heterocyclic thiourea dianion complexes (1–8). The spectroscopic data analysis showed clear AX splitting pattern, which indicates that the two coordinated phosphorus atoms are non-equivalent. Meaning that, the metal's center is attached to both S,N donor atoms in a chelating fashion. In addition, the splitting system show a good resemblance to the previously synthesized thiourea dianion complexes. Furthermore, the reaction is believed to undergo a square planar substitution mechanism at which five coordinate intermediate is formed. Generally, the reported complexes (1–8) are believed to resemble their analogues thiourea dianion complexes at which a four membered ring structure is formed with Pt(II) or Pd(II) being centered, adopting a square planar geometry. Four of the synthesized complexes (1–4) were tested against Salmonella typhimurium and Bacillus subtilis bacteria at which complexes 4 and 2 showed highest activity values.

Influence of Al location on formation of silver clusters in mordenite

Formation of zeolite supported Ag 0 clusters depends on a combination of thermodynamically stable atomic configurations, charge balance considerations, and mobility of species on the surface and within pores. Periodic density functional theory (DFT) calculations were performed to evaluate how the location of Al in the mordenite (MOR) framework and humidity control Ag 0 nanocluster formation. Four Al framework sites were studied (T1-T4) and the Al positions in the framework were identified by the shifts in the differential Al⋯Al pair distribution function (PDF). Furthermore, structural information about the Ag 0 nanoclusters, such as dangling bonds, can be identified by Ag⋯Ag PDF data. For Ag 0 formation in vacuum MOR structures with a Si:Al ratio of 5:1 with Al in the T1 position resulted in the most framework flexibility and the lowest Ag 0 nanocluster charge, indicating the best result for formation of charge neutral nanoclusters. When water is present, Al in the T3 and T4 positions results in the formation of the smallest average Ag 0 nanoclusters plus greater expansion of the O-T-O bond angle than in vacuum, indicating easier diffusion of the Ag 0 nanoclusters to the surface. The presence of Al in 4-membered rings and in pairs indicates favorable MOR structures for formation of single Ag atoms, despite the existence of synthesis challenges. Therefore, Al in the T2 position is the least favorable for Ag 0 nanocluster formation in both vacuum and in the presence of water. Al in the T1, T3, and T4 positions provides beneficial effects through framework flexibility and changes in nanocluster size or charge that can be leveraged for design of zeolites for formation of metallic nanoclusters. • Differential pair distribution functions identified Al locations in mordenite. • Al position alters framework flexibility and charge of Ag clusters. • Al in the T3 and T4 positions forms several smaller Ag cluster in water. • Location of Al in mordenite influences the type and size of Ag clusters formed.

Synthesis of silicate and alumina pillared MWW zeolite as ethane dehydroaromatization catalyst

Pillared MWW zeolites were prepared with polymeric hydroxyl-aluminum Keggin-Al13 cations and tetraethylorthosilicate as pillaring agents to investigate catalyst acidity and interlayer structure impact on ethane dehydroaromatization. The intercalation effect of the pillars causes the MWW zeolite to be stretched between the layers, which cause the 12 member ring (MR) pocket structure to be exposed to outside surface. The modification method can effectively generate the micropore and mesopore MWW zeolite composite, MCM-36. The introduction of silica columns and alumina columns led to the overall decrease of acidity and the increase of weak and Lewis acid of pillared MWW zeolites, respectively. Although the strong Brönsted acid sites of MWW play major effect on catalyzing aromatization of ethylene generated by the dehydrogenation of ethane to aromatics, the modification decreases the cracking of ethylene oligomers. The 12-MR pockets exposed on the pillared MWW zeolite can provide more reaction sites for xylene generation.

Co-Crystalline ZSM-5/ZSM-11 Nanostructures for Alkylation of Benzene with Ethanol

The interzeolite transformation approach has been used extensively for the quick synthesis of zeolites at a lower cost. Herein, an interzeolite transformation method for the quick synthesis of co-crystalline ZSM-5/ZSM-11 (CDM-5) nanoaggregates has been developed by precisely controlling the synthesis parameters and using 1,6-hexamethylenediamine as an organic structure-directing agent. In contrast, the irregular CDM-5 zeolite block obtained from an amorphous aluminosilicate gel takes a longer crystallization time using the conventional method. Combined with the related results of characterization, UV-Raman spectra show that double 6-membered rings in the parent USY zeolite framework are broken, and an ordered aluminosilicate aggregate species (OAAS) containing 4-membered rings (4Rs) are formed during the interzeolite transformation. HRTEM and SEM images demonstrate that the block OAAS is dissolved into amorphous nanoparticles, followed by converting into CDM-5 nanoaggregates. These results reveal that an OAAS is essential for the synthesis of CDM-5 nanoaggregates via the interzeolite transformation method. In addition, the CDM-5 nanoaggregate catalyst exhibits superior stability and resistance to carbon deposition in the alkylation reaction of benzene with ethanol compared with the irregular block CDM-5 catalyst.

One-step ion-exchange from Na-SSZ-13 to Cu-SSZ-13 for NH3-SCR by adjusting the pH value of Cu-exchange solution: The effect of H+ ions on activity and hydrothermal stability

A one-step ion-exchange method is developed to prepare high-performance Cu-SSZ-13 from Na-SSZ-13, by adjusting pH values of Cu salt solution during Cu-exchange. The H + concentration has a significant influence on the Cu loading and distribution. In the absence of H + , the Cu 2+ can only exchange the Na + in 8 member rings (8-MR) as Cu(OH) + , due to the steric hindrance of Na + ions located in 6 member rings (6-MR). When H + is present, it is found to compete with Cu 2+ to exchange the Na + and to occupy the exchange sites in Na-SSZ-13. The Cu 2+ ions take a priority over H + to occupy the neighboring Al sites in 6-MR, while H + takes precedence over Cu 2+ to occupy ion-exchange sites in 8-MR, causing that Cu 2+ coordinated to 6-MR is dominant in Cu-SSZ-13 via one-step method. The H + concentration affects the overall catalytic activity and hydrothermal stability by controlling the Cu 2+ loading and distribution. • High-performance Cu-SSZ-13 is prepared via one-step ion-exchange from Na-SSZ-13. • The H + competes with Cu 2+ ions to exchange the Na + ions in Na-SSZ-13 during Cu-exchange. • The chemistry of the competition between H + and Cu 2+ ions are revealed. • The H + concentration affects the Cu 2+ loading and distribution in Cu-SSZ-13. • The H + concentration determines the activity and HTA stability of prepared catalysts.

Molecular dynamics simulation of evolution of nanostructures and functional groups in glassy carbon under pyrolysis

With the continued and sustained growth of the field of carbon MEMS (C-MEMS) in several application areas, there is a corresponding increased and renewed interest in understanding the exact molecular structure of the ensuing glassy carbon (GC) material and, therefore, potential to engineer some of its key characteristics. Associated with that interest, the effects of key process parameters like temperature ramping, holding and cooling times on carbonization, the final nanostructures and – importantly – on the nature and distribution of functional groups remain to be of significant research importance to the GC community. While recent in-situ imaging approaches during the synthesis process have opened up opportunities for better understanding of these nanostructures, the 2D nature of the approaches, however, had introduced significant barriers. In this paper, therefore, we present a simulation-based approach using reactive molecular dynamics (MD) where we model the synthesis process and investigate in detail (i) the intermediate and final stages of carbonization with particular focus on GC nanostructures and (ii) formation of functional groups and the processes and parameters that drive their evolution. Our simulation captured the pyrolysis-driven synthesis process where the polymer structure degraded followed by increased carbonization and formation of flakes of 3-, 4-, membered carbon rings that further grew into graphene-type 6-member carbon rings as well as 5- and 7-member rings. These eventually evolved into a complex multi-layer 3D nanostructure consisting of connected but distinct zones of (a) dominant cage-like tubular components and (b) long chains of flat graphene-like parts rich with functional groups. Taken together, the MD simulations demonstrate that (i) holding time at the maximum temperature has the most significant effect in the formation of complex cage-like 3D nanostructures with stacked layers, (ii) the closed cage-like zones have crystallite diameter (La) in the range of 3.2 Å - 9.5 Å with clear and well-defined curved and stacked graphene-like sheets of stacking thickness (Lc) = 3.0 Å - 3.3 Å, (iii) carbonyl, ether, epoxide, hydroxyl, and alkyne groups form predominately on the edges of flat components of GC where abundant non-6 membered rings, dangling bonds, long sp carbon chains, and intermediate structures exist, and to a lesser extent on edges of vacancy defects inside cage-like zones.

Controlling liquid hydrocarbon composition in valorization of plastic waste via tuning zeolite framework and SiO2/Al2O3 ratio

Abundance of plastic waste has become threat to the mankind and aquatic life and thus needs to be recycled or converted into value added products. Liquefaction of waste plastics via catalytic cracking is one the efficient routes towards plastic waste management. Concerning this, in present study, conversion of polymer mixture containing polypropylene, low-density polyethylene and high-density polyethylene (PP, LDPE and HDPE) was done for the production of gasoline and diesel range hydrocarbons using two-step cracking approach. MWW and MFI (12 and 10 member ring structures respectively) type zeolites having different pore structure and acidity were used for catalytic cracking of polymer feed at 350 °C. Investigations revealed that MWW type zeolite having two independent pore channels selectively provides gasoline range of hydrocarbons (C7–C12, 99.12%) in polymer cracking reaction as compared to MFI type which results in C13–C20 range of hydrocarbons (73.19%). Hydrocarbon compositions were confirmed from GC-MS, 1H, 13C NMR and FT-IR techniques. In activity results it was observed that acidity of zeolites affects the liquid yield and hydrocarbon distribution as analysed by using zeolites of two different SiO2/Al2O3 (SAR) ratio (30 and 55) which directs that zeolite (MFI/MWW) with lower SAR (30) having higher acidity results in higher yield of fuel range liquid hydrocarbons as compared to higher SAR (55) zeolite. Characterization studies such as XRD, N2-physisorption, NH3-TPD, FE-SEM and EDX were performed to check the physiochemical properties of zeolite and correlated with the activity. Overall, the present investigation provides detailed comparative study on plastic degradation using MFI and MWW type zeolites resulting into different range of liquid hydrocarbons.

Impact of planet mesh phasing on the vibration of three-dimensional planetary/epicyclic gears

This work analytically derives rules for how planet mesh phasing impacts the vibration of planetary/epicyclic gears. A key quantity is defined that depends on the mesh frequency harmonic number, ring gear tooth number, and total number of planets. This quantity dictates, for each harmonic of mesh frequency, which central member (sun, carrier, and ring) motions are present or absent, which force and moment components can be transmitted from the central members to their surrounding components, which modes are present in the response at the given harmonic, and which modes can experience resonance in the given harmonic. Neither the derivation nor the mesh phasing rules depend on a planetary gear model; only cyclic symmetry and periodicity of the response at the mesh frequency are required. The mesh phasing rules apply to spur/helical planetary gears where each component has six, three-dimensional rigid-body degrees of freedom. They apply to systems with high-speed, gyroscopic effects and those where rotational effects are neglected. Dynamic simulations using a finite element/contact mechanics model and an analytical model confirm the mesh phasing rules. Use of these mesh phasing rules for design and troubleshooting offers significant benefits to reduce vibration of planetary gears.

Regioselective C-H arylation of imidazoles employing macrocyclic palladium(II) complex of organoselenium ligand

In this report we have presented synthesis of a new air stable bidentate selenium ligand (L1) by the reaction of 1,8-bis(2-(chloromethyl)phenoxy)octane with sodium salt of diphenyl diselenide. The reaction of bidentate selenium ligand (L1) with Pd(CH3CN)2Cl2 in acetonitrile under reflux conditions resulted nineteen membered ring macrocyclic palladium(II) complex. The structure of ligand precursors, ligand, and macrocyclic palladium(II) complex were authenticated by using 1H, 13C{1H} NMR spectroscopy and elemental analysis. The repeated attempts to obtain single crystals of macrocyclic palladium(II) complex were unsuccessful probably due to long flexible aliphatic chain in the molecule. The air and moisture stable, thermally robust macrocyclic palladium(II) complex was employed as catalyst to catalyze the regioselective arylation reaction of imidazole derivatives. The reaction works efficiently without any need of inert atmosphere. The current protocol works under mild reaction conditions with exclusive C-5 regioselectivity. Excellent yields (~73–95%) were obtained by using only 1.5 mol% of C1, with wide range of derivatives and large functional group tolerance. Homogeneous nature of catalysis process was confirmed with the help of mercury and triphenylphosphine poisoning tests. Further, the catalyst can be reused with significant loss (22%) in the efficiency.

Diagonally Compressed TNAZ - A DFT Treatment

TNAZ is an insensitive explosive material having a 4-membered azetidine ring system which has three nitro groups substituted, one of them is a nitramine type. In the present density functional treatise at the level of B3LYP/6-311++G(d,p), the 4-membered ring of TNAZ is compressed diagonally either along the X- or Y-axis direction. Various properties (including energies, quantum chemical and spectral etc.) in the perturbed systems have been searched and discussed.