4-membered Ring Research Articles

ReaxFF molecular dynamics study on pyrolysis of bicyclic compounds for aviation fuel

In this paper, we investigate the initial fuel pyrolysis of four bicyclic compounds, which are potential alternative jet fuels, using ReaxFF force field based molecular dynamics (MD) simulations. These fuels can be separated into two categories, (a) cyclic alkanes attached through a 4-membered ring and (b) cyclic alkanes attached through a single C–C bond. We use a systematic procedure to investigate the reaction chemistry of all these fuel molecules. Global Arrhenius parameters, such as activation energies and pre-exponential factors, are calculated and used to analyze the overall decomposition kinetics of the fuels. The bicyclic fuels have a faster or comparable decomposition rate compared to some existing jet-fuels, such as JP-10. These fuels decompose through two main reaction classes. One pathway is the cleavage of the central bond leading to the formation of two cyclic radicals or species. Second class of reactions involves ring opening leading to the formation of small alkene molecules. The importance of these reactions in fuel decomposition process is found to be highly temperature dependent. This work demonstrates that ReaxFF can be used to investigate pyrolysis and combustion chemistry of existing or future fuels and to potentially contribute to the development of their chemical kinetic models without any a priori input and chemical intuition.

DFT and experimental studies on Rh(III)-catalyzed dual directing-groups-assisted [3+2] annulation and ring-opening of N‑aryloxyacetamides with 1-(phenylethynyl)cycloalkanol

A density functional theory (DFT) has been conducted to elucidate the mechanism of N-aryloxyacetamides reacting with 1-(phenylethynyl)cyclobutanol and 1-(phenylethynyl)cyclopentanol under rhodium (III) catalysis. The impact of substrates with different ring numbers on the reaction mechanism has been discussed in detail. When the ring number exceeds 4, 1-(phenylethynyl)cycloalkanol simply conducts [3+2] annulation like the general reaction between N-aryloxyacetamides and alkyne. When the ring number is equal to 4, 1-(phenylethynyl)cyclobutanol undergoes cascade [3+2] annulation and ring-opening reaction via rhodium (III) catalysis. The results show that the ring-opening or not in 1-(phenylethynyl)cycloalkanol depends on ring members and the 4-membered ring is the critical structure for its high ring strain and steric hindrance.

Synthesis of Nonionic Surfactants Containing Five Membered Ring: Application as Corrosion Inhibitor of Carbon Steel in 0.5 M H2SO4 Solution

Synthesis of Nonionic Surfactants Containing Five Membered Ring: Application as Corrosion Inhibitor of Carbon Steel in 0.5 M H2SO4 Solution

Impact of Organic Templates on the Selective Formation of Zeolite Oligomers.

Zeolites are essential materials to industry due to their adsorption and catalytic properties. The best current approach to prepare a targeted zeolite still relies on trial and error's synthetic procedures since a rational understanding of the impact of synthesis variables on the final structures is still missing. To discern the role of a variety of organic templates, we perform simulations of the early stages of condensation of silica oligomers by combining DFT, Brønsted-Evans-Polanyi relationships and kinetic Monte Carlo simulations. We investigate an extended reaction path mechanism including 258 equilibrium reactions and 242 chemical species up to silica octamers, comparing the computed concentrations of Si oligomers with 29 SI NMR experimental data. The effect of the templating agent is linked to the modification of the intramolecular H-bond network in the growing oligomer, which produces higher concentration of 4-membered ring intermediates, precursors of the key double-four ring building blocks present on more than 39 known zeolite topologies.

Glycans to improve efficacy and solubility of protein aggregation inhibitors.

Glycans to improve efficacy and solubility of protein aggregation inhibitors.

N-H⋯X interactions stabilize intra-residue C5 hydrogen bonded conformations in heterocyclic α-amino acid derivatives.

Nature makes extensive and elaborate use of hydrogen bonding to assemble and stabilize biomolecular structures. The shapes of peptides and proteins rely significantly on N–H⋯O Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C interactions, which are the linchpins of turns, sheets and helices. The C5 H-bond, in which a single residue provides both donor and acceptor, is generally considered too weak to force the backbone to adopt extended structures. Exploiting the synergy between gas phase (experimental and quantum chemistry) and solution spectroscopies to decipher IR spectroscopic data, this work demonstrates that the extended C5-based conformation in 4-membered ring heterocyclic α-amino acid derivatives is significantly stabilized by the formation of an N–H⋯X H-bond. In this synergic system the strength of the C5 interaction remains constant while the N–H⋯X H-bond strength, and thereby the support provided by it, varies with the heteroatom.

An Unsymmetric Imino-Phosphanamidinate Ligand and its Y(III) Complex: Synthesis, Characterization, and Catalytic Hydroboration of Carbonyl Compounds.

An imino-phosphanamide ligand, [NHIiPr2Me2P(Ph)NH-2,6-iPr2C6H3] (LH), containing two different N-substituents was prepared by the direct reaction of the lithium salt of N-heterocyclic imine (NHI) with phenylchloro-2,6-diisopropylphenyl phosphanamine, PhP(Cl)NH-2,6-iPr2-C6H3. Reaction of LH with Y(N(SiMe3)2)3 afforded the heteroleptic complex, [{L}Y(N(SiMe3)2)2] (1), by elimination of HN(SiMe3)2. Compound 1 was characterized by multinuclear NMR and X-ray crystallography. In the complex, the Y(III) center was found to be tetracoordinate in a distorted tetrahedral geometry. The ligand, imino-phosphanamidinate, [L]-, functions in a chelating manner, and its coordination to Y(III) results in a distorted 4-membered YPN2 ring. As a proof of principle of its activity, 1 was used as a precatalyst for the hydroboration of various aldehydes and ketones using HBpin as the hydrogen source. The hydroboration reaction was rapid and clean even with low catalyst loadings (0.01-0.1 mol %). In addition, a very good functional group tolerance was observed in these reactions.

Designing of Heterocyclic Compounds as Promising VEGFR2 Tyrosine Kinase Inhibitors: An In silico Analysis

Cancer is the most dangerous disease a human race battle with. Due to which, it is necessity of medicinal chemist to evaluate possible scenario to fight against this disease. The heterocyclic compounds have shown to possess intrinsic diversity and several physicochemical properties. Thus, investigation of newer and potential compounds for their activity to resist several malignancies. The present study aims to derivatize four different heterocyclic compounds. The number of members present in the ring has importance in heterocyclic compounds. Thus, the six-member ring containing pyrimidine, six-member ring fused with five-member ring in indole, bi-penta membered ring containing thiadiazole, and one six-member and a penta membered ring containing triazoles have been used in the present study. In search of potential anticancer drugs, several molecules were evaluated and checked for their potency to interact with a cancer target enzyme Vascular endothelial growth factor receptor 2 (VEGFR2). This study involves detailed in-silico analysis of several compounds and indicates compounds having the potential ability to resist these enzymes and hence the anticancer agent.

Silicene Growth through Island Migration and Coalescence

Silicene, the Si based counterpart to graphene is predicted to demonstrate similar desirable features to graphene, possessing a Dirac cone in the band-structure and Fermi velocities comparable to graphene. It has also been predicted to demonstrate several exotic properties such as the quantum spin Hall effect, chiral superconductivity and giant magnetoresistance. It has the added benefit of being easy to integrate into current industrial device engineering processes. Silicene monolayers have been grown on Ag (111) and Ir (111) substrates and recently a working field-effect transistor has been demonstrated at room temperature. While it is possible to characterize the final monolayer structure, it is impossible to probe experimentally the evolving atomic structure during growth.We perform massively-parallel molecular dynamics (MD) simulations to study long time monolayer silicene growth on an Ir (111) surface. We observe an intricate multi-stage growth process driven by atomic and cluster migration on the surface. Initial growth involves formation of sub-nanometer clusters via adatom surface diffusion. Subsequently, these clusters rearrange spontaneously with each additional Si atom, forming clusters containing 4–7 member rings. Growth of each cluster through adatom adhesion is accompanied by the formation of larger islands through cluster migration and coalescence. Coalescence of smaller, more mobile islands into larger clusters is aided by the internal rearrangement of rings within each cluster. This flexibility, both of clusters and their constituent atoms, allows the impinging clusters to reorient after first contact and form a more perfect union. We also report on the effect of temperature and flux on the growth process and the final nanostructure. Our study provides atomistic insights into the early stage growth mechanisms of silicene which can be significant for controlled synthesis of its 2D monolayers. Reference: Cherukara, M. J., Narayanan, B., Chan, H., & Sankaranarayanan, S. K. (2017). Silicene growth through island migration and coalescence. Nanoscale, 9(29), 10186-10192. Figure 1

Biological Importance of Oxazoles

ing five and six member rings having hetero atoms such as N, O, S, P, Si and B etc. Many heterocyclic compounds are employed in the treatment of infectious diseases due to their specific antimicrobial activity. Heterocyclic compounds have attracted the attention of medicinal chemists because of having broad spectrum of pharmacological activities and hence it continues to yield new therapeutic agents. One such medicinal important heterocyclic nucleus is oxadiazole moiety. Oxazole is the parent compound for a vast class of heterocyclic aromatic organic compounds. These are azoles with an oxygen and a nitrogen separated by one carbon Oxazoles are aromatic compounds but less so than the thiazoles. Oxazole is a weak base

LEVELS OF POLYCYCLIC AROMATIC HYDROCARBONS (PAHs) IN FISH SAMPLES FROM DIFFERENT PROCESSING METHODS

Fish is easily contaminated from water prone to water pollution. In this study, the levels of polycyclic aromatic hydrocarbons (PAHs) in fish samples processed, using three methods and marketed in Makurdi, Benue state, were determined. The samples were coded as SF (Smoked Fish), SD (Sundried) and FD (fried) fish samples. PAHs in the samples were quantified, using gas chromatography – mass spectrometer (GC-MS). The Ʃ16PAH concentrations were in the range of 0.2- 10.0 mg/kg. Both LPAHs/HPAHs and the binary diagnostic ratios of PAHs indicated pyrogenic and petrogenic sources Ʃ16PAH and their dominant PAH ring-types were separately computed for each sample. The six-membered ring PAHs in smoked fish was 32.07% (with Bezo(ghi)perylene as most dominant). High levels of six member ring PAHs (Dibenz(a,h) anthracene) were also found in Sundried fish and fried fish contain Dibenz(a,h) anthracene. Generally, the PAHs concentrations in the samples, pointed more at pyrogenic than the petrogenic source. With exception of the five and six membered rings, estimated PAH levels were within the NAFDAC permissible limits.

Synthesis of new benzo[f]chromene-based heterocycles targeting anti-proliferative activity

In this article β-enaminonitrile 1 undergoes intramolecular cyclocondensation reaction under acidic conditions to generate novel chromeno[2,3-b]azet-9-one derivative 2 in good yield. Ring expansion of the four membered ring of the azet-2(1H)-one derivative 2 to six and/or seven membered rings was achieved via reaction of compound 2 with different nitrogen nucleophiles. A new series of benzochromeneone, benzochromenopyrimidine, and benzo[f]coumarin derivatives were prepared via reaction of β-enaminonitrile 1 with different C-electrophiles. The structures of the products have been affirmed on the basis of analytical and spectral data. The anti-proliferative activity of the newly synthesized compounds against two human epithelial cell lines; liver (HepG2) and breast (MCF-7) in addition to normal fibroblasts (WI-38) was investigated. Derivatives 4 and 10 had significant and selective anti-proliferative activity against liver and breast cancer cell lines without harming normal fibroblasts.

Hierarchical Ti-Beta zeolites with uniform intracrystalline mesopores hydrothermally synthesized via interzeolite transformation for oxidative desulfurization

Precisely designing and constructing metallosilicate zeolite with abundant and uniform intracrystalline mesopore is urgently desired, bearing the merits of boosting accessibility of active sites and of improving diffusion properties for organics in the process of catalytic reactions. Herein, hierarchical Ti-Beta zeolite with uniform intracrystalline mesopore (ca. 3.4 nm) is hydrothermally synthesized via interzeolite transformation of siliceous FAU zeolite, which is not capable to be achieved using amorphous silica sources. The crystallization process is thoroughly explored via series of characterization methods, obeying liquid crystallization mechanism. Additionally, the assembly of hierarchical Ti-Beta zeolite is nourished by the primary structural units (mainly 4-membered ring) resulting from the degraded silicate species of FAU zeolite. This burgeoning hierarchical Ti-Beta zeolite shows extraordinary catalytic performances in terms of both active site-based turnover frequency and weight-based space-time-yield for oxidative desulfurization of model oil, far beyond than conventional fluoride-mediated Ti-Beta and microporous Ti-Beta prepared by this developed strategy without addition of CTAB, which is attributed to its excellent diffusion properties and undemanding contact of active sites with reaction substrates. This work provides a span-new guidance for designing hierarchical metallosilicates with uniform mesopore from the standpoint of employing exotic primary structural units derived from the degradation of crystallized siliceous zeolites.

Emerging Nickel Catalysis in Heck Reactions: Recent Developments

AbstractThe synthetic application of nickel catalysts in Heck‐coupling reactions is quite prominent and noticeable of late in organic synthesis. It shows great interest over the other transition metal catalysts due to its unique characteristic that prepares them more significantly applicable in different fields of synthetic application. The usefulness of nickel‐catalysts relies in the fact that they are abundant in nature, relatively less precious and environment friendly. Nickel plays pivotal role in different kind of Heck reactions known such as intramolecular‐, intermolecular‐, reductive‐Heck type reaction producing mainly carbocycles and hetero cycles of biological significance. Carbocyclization or hetero‐cyclization reaction occurred under optimized reaction conditions developed and come up with the formation of various structural building blocks of naturally occurring compounds. Via reductive Heck cyclization large membered ring of carbo‐ or hetero‐cyclic system was formed which performed key role as building blocks in pharmaceutical synthesis and bioactive molecule formation. Intermolecular Heck type reactions were comparatively more explored. Silyl‐Heck, carbonyl‐Heck, and other miscellaneous type reactions were covered up through nickel‐catalyzed intermolecular Heck reaction. Asymmetric versions of Heck‐ coupling reactions are also reported to proceed even with unactivated alkenes, offering molecules having quaternary stereogenic center in a regio‐ and enantioselective manner. This manuscript intends to cover these entire concepts.magnified image

1-Hydroxydodecylidene-1,1-diphosphonic acid flotation of bastnäsite: Performance and mechanism

To separate and enrich rare-earth elements (REE) minerals from their ores through flotation process has become an attracting topic for REE’s strategic position. In the present investigation, the floatability of bastnäsite [(Ce,La)CO3F] was explored by using 1-hydroxydodecylidene-1,1-diphosphonic acid (HDDPA) as a collector. The micro-flotation results showed that bastnäsite displayed an eminent floatability under pH 7.0–10.0, and HDDPA realized an efficient separation of bastnäsite from calcite at pH around 8.0. Zeta potential and solution chemistry inferred that at pH 7.5–9.3, HDDPA3− anions were glad to replace the CO32- ions of Ce(Ⅲ) carbonates in/on bastnäsite interface, resulting in a high flotation recovery of bastnäsite. With increasing OH- concentration, the competition ability of OH- against HDDPA anion intensified, gradually the surface Ce(III) hydroxide species increased, and the floatability of bastnäsite reduced. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) recommended that the surface Ce(III) of bastnäsite interacted with the O atoms of HDDPA’s OP(O)O group to generate a four membered ring configuration, which hydrophobized bastnäsite particles.

Unveiling the local structure of 2-mercaptobenzothiazole intercalated in (Zn2Al) layered double hydroxides

The structure and composition of a zinc‑aluminum layered double hydroxide (Zn2Al LDH) with the intercalated 2-mercaptobenzothiazole corrosion inhibitor (a.k.a. benzo[d]thiazole-2-thiol) are interpreted by means of atomistic molecular dynamics (MD) simulations. The results concerning the proportion of intercalated 2-mercaptobenzothiazole and water species in the Zn2Al LDH interlayer were correlated with experimental X-ray diffraction (XRD) and thermogravimetric analysis (TGA) data of samples obtained at pH 8.5, 10 and 11.5. While the sample synthesized at the lowest pH is almost free of contaminants, the sample obtained at the highest pH is contaminated by a small fraction of a material with intercalated OH−. The comparison of the calculated and XRD interlayer distances suggests that the most stable structure has a ratio of ~4.5 water molecules per intercalated organic species, which is higher than the ratio of ~2 typically reported in the literature. The distribution of molecules in the LDH interlayer consists of a layer of water near the hydroxides, a second layer grown over the first layer, with the 2-mercaptobenzothiazole species adopting conformations with the sulfur of the thioamide group facing the hydroxide/water layers and the 6-member ring oriented towards the middle of the interlayer. Different structural analyses were done to explain the equilibria between the different species in the interlayer space, and their molecular interactions with the LDH metal hydroxide layers.

Study of Aqueous Am(III)-Aliphatic Dicarboxylate Complexes: Coordination Mode-Dependent Optical Property and Stability Changes.

The thermodynamics of Am(III) complex formation in natural groundwater systems is one of the major topics of research in the field of high-level radioactive waste management. In this study, we investigate the absorption and luminescence properties of aqueous Am(III) complexes with a series of aliphatic dicarboxylates in order to learn the thermodynamic complexation behaviors in relation to binding geometries. The formation of Am(III) complexes with these carboxylate ligands induced distinct red shifts in the absorption spectra, which enabled chemical speciation. The formation constants determined by deconvolution of the absorption spectra showed a linear decrease for the three ligands (oxalate (Ox), malonate (Mal), and succinate (Suc)) and a mild decrease for the remaining ligands (glutarate (Glu) and adipate (Adi)). Time-resolved laser fluorescence spectroscopy (TRLFS) was used to obtain information about the aqua ligand, which indirectly indicated the bidentate bindings of these dicarboxylate ligands. A complementary attenuated total reflectance Fourier transform infrared (ATR-FTIR) study on Eu(III), which is a nonradioactive analogue of Am(III) ion, showed that the coordination modes differ depending on the alkyl chain length. Ox and Mal bind to Am(III) via side-on bidentate bindings with two carboxylate groups, resulting in the formation of stable 5- and 6-membered ring structures, respectively. On the other hand, Suc, Glu, and Adi form end-on bidentate bindings with a single carboxylate group, resulting in a 4-membered ring structure. Density functional theory calculations provided details about the bonding properties and supported the experimentally proposed coordination geometries. This study demonstrates that coordination mode-dependent changes in optical properties occur along with thermodynamic stability changes in Am(III)-dicarboxylate complexes.

Three tetragonal superhard sp3 carbon allotropes

Four tetragonal anisotropic superhard carbon phases, T-C8, T-C12, T-C20 and T-C28 were generated by RG2 program, T-C8 has been reported and named bct-Carbon. The calculated relative enthalpy, elastic constants and phonon dispersion spectra show that these structures are stable. Their lattice failure modes are mainly tensile. Thermodynamic stability, thermal performance and hardness are all in the order T-C20 >T-C8>T-C12>T-C28, which is contrary to the proportion of the four membered ring in the corresponding structure, suggesting that strained four-membered ring is detrimental to the stability and mechanical properties of carbon phases. Among them, T-C20 with hardness of 90.8 GPa is more stable than bct-Carbon and graphite under 20 GPa, suggesting that it is likely to be transformed by cold compressed graphite.

Investigation and Assessment of Polycyclic Aromatic Hydrocarbons Concentrations in Sediments at Drainage Discharge Points into the Mangrove Stretch of New Calabar River, Port Harcourt, Nigeria

Sediment samples were collected from surface of sediments from parts of the mangrove wetlands of the New Calabar River at points of effluents discharge. The samples were treated according to standard procedures and analyzed for the concentrations of polycyclic aromatic hydrocarbons (PAHs). The results showed the presence of ten PAHs at Iwofe Jetty and Police Post stations and eleven PAHs at the Minipiti station. The summation of the total PAHs in the stations showed 23.440, 33.694 and 51.094 mg/Kg in sediments from Iwofe Jetty, Minipiti and Police Post stations respectively. Pyrene was the most abundant PAH in sediment from Iwofe station, Dibenzo (a,h) anthracene was the most abundant PAH at the Minipiti Station and acenaphthylene was the most abundant PAH at the Police Post Station. The categorization of the PAHs classes showed that the high molecular weight PAHs (HMW PAHS) were more abundant than the low molecular weight (PAHs) in all the stations examined, although, at the Police Post station, the values were very close. The 4-membered rings were more abundant in sediments from Iwofe Jetty station. The 4 and 5-membered rings were more abundant at the Minipiti station and the 2-3 membered rings were dominant at the police Post station. The 6-membered rings were the least abundant or undetected in all the stations. Source and origin diagnosis showed that LMW/ HMW PAHs as pyrogenic in all the stations, An/(An+Phe) ratio revealed pyrogenic sources of PAHs, Fl/(Fl+Pyr) analysis in all the stations indicated petrogenic origin of PAHs, BaA/ (BaA+Chr) evaluation in all the stations revealed pyrogenic sources of PAHs. The mixed sources of PAHs in the wetlands drainage discharge points calls for concern and therefore, efforts should be geared to identify the points at which they were introduced into the effluents and be adequately controlled to prevent harm to the environment.

Toward Efficient Synthesis of Chiral Zeolites: A Rational Strategy for Fluoride-Free Synthesis of STW-Type Zeolite.

The STW-type zeolite is attractive for developing novel enantioselective syntheses/separation of chiral compounds because it is the only chiral zeolitic microporous material whose enantioenriched synthesis has been achieved. In addition to the conventional industries in which zeolites are used, STW should have diverse industrial applications in the pharmaceutical and food industries. However, the toxic and caustic fluoride required for synthesizing STW severely hinders its commercialization by mass production. Herein, we report the first example of fluoride-free STW synthesis, in which the two roles of fluoride-formation of a zeolitic framework rich in tetravalent T-atoms and promotion of double 4-membered ring unit formation-were substituted by dry gel conversion and Ge addition, respectively. The STW obtained was highly crystalline, with a similar micropore volume and thermal stability as those of original fluoride-based STW. Our approach is promising not only for the fluoride-free synthesis of enantiomeric STW but also for general fluoride-free syntheses.