Ring System Research Articles

Primordial dust rings, hidden dust mass, and the first generation of planetesimals in gravitationally unstable protoplanetary disks

We study a new mechanism of dust accumulation and planetesimal formation in a gravitationally unstable disk with suppressed magnetorotational instability and we compare it with the classical dead zone in a layered disk model. We used numerical hydrodynamics simulations in the thin-disk limit ( FEOSAD code) to model the formation and long-term evolution of gravitationally unstable disks, including dust dynamics and growth. We found that in gravitationally unstable disks with a radially varying strength of gravitational instability (GI), an inner region (of several astronomical units) of low mass and angular momentum transport is formed. This region is characterized by a low effective value for the $ GI $ parameter, often used to describe the efficiency of mass transport by GI in young protoplanetary disks. The inner region is also similar in terms of characteristics to the dead zone in the layered disk model. As the disk forms and evolves, the GI-induced dead zone accumulates a massive dust ring, which is susceptible to the development of the streaming instability. The model and observationally inferred dust masses and radii may differ significantly in gravitationally unstable disks with massive inner dust rings. The early occurrence of the GI-induced dust ring, followed by the development of the streaming instability suggest that this mechanism may be behind the formation of the first generation of planetesimals in the inner terrestrial zone of the disk. The proposed mechanism, however, crucially depends on the susceptibility of the disk to gravitational instability and requires the magnetorotational instability to be suppressed.

Hyperlanins A and B, Two Highly Rearranged Meroterpenoids from Hypericum lancasteri

Comprehensive SummaryHyperlanins A (1) and B (2), two highly rearranged polycyclic polyprenylated acylphloroglucinol (PPAP)‐related meroterpenoids based on different new carbon skeletons, were isolated from Hypericum lancasteri. Compound 1 incorporates an unprecedented 5/6/7/5 ring system featuring a 3,13‐dioxatetracyclo[9.2.1.12,5.01,8]pentadecane core. Compound 2 possesses a unique compact 6/6/5/6/6/5/6 ring system with a caged tetracyclo[6.2.1.13,8.05,11]dodecane motif. Their structures were established by spectroscopic data, X‐ray diffraction, and computational approaches. Both compounds showed anti‐inflammatory activity in vitro. Compounds 1 and 2 could decrease the lipopolysaccharide (LPS)‐/nigericin‐induced IL‐1β release in THP‐1 cells. Both compounds also showed inhibition in hypoxia‐inducible factor‐1α (HIF‐1α) pathway luciferase reporter assay.

N-Oxide-to-Carbon Transmutations of Azaarene N-Oxides.

Reactions that change the identity of an atom within a ring system are emerging as valuable tools for the site-selective editing of molecular structures. Herein, we describe the expansion of an underdeveloped transformation that directly converts azaarene-derived N-oxides to all-carbon arenes. This ring transmutation exhibits good functional group tolerance and replaces the N-oxide moiety with either unsubstituted, substituted, or isotopically labeled carbon atoms in a single laboratory operation.

Piston ring and cylinder liner scuffing analysis in dual-fuel low-speed engines considering liner deformation and tribofilm evolution

The piston ring and cylinder liner (PRCL) system in larger-bore low-speed marine engines frequently experiences scuffing failures, which significantly decrease the engine reliability. To understand this failure mechanism, a scuffing failure model subjected to the PRCL system was developed considering multidisciplinary coupling effects that integrate asperity contact, hydrodynamic lubrication, tribochemistry reactions, thermal effects, friction, and surface wear. The impacts of large-scale deformation and gas-combustion mode on the scuffing performances of the PRCL system were examined. The key findings indicate that the larger-scale liner deformation can markedly reduce oil film thickness and exacerbate local asperity contact, influencing the evolution of the tribofilm by increasing the removal process. Under gas-combustion mode, the oil film thickness is even lower, and the asperity contact pressure further increases due to a more starved lubrication state and higher combustion temperature. This leads to tribofilm breakdown and severe wear near the ring opening area, which are aligning with the full-scale experimental results with scuffing failure.

Synthesis and Biological Properties of Fluorescent Strigolactone Mimics Derived from 1,8-Naphthalimide.

Strigolactones (SLs) have potential to be used in sustainable agriculture to mitigate various stresses that plants have to deal with. The natural SLs, as well as the synthetic analogs, are difficult to obtain in sufficient amounts for practical applications. At the same time, fluorescent SLs would be useful for the mechanistic understanding of their effects based on bio-imaging or spectroscopic techniques. In this study, new fluorescent SL mimics containing a substituted 1,8-naphthalimide ring system connected through an ether link to a bioactive furan-2-one moiety were prepared. The structural, spectroscopic, and biological activity of the new SL mimics on phytopathogens were investigated and compared with previously synthetized fluorescent SL mimics. The chemical group at the C-6 position of the naphthalimide ring influences the fluorescence parameters. All SL mimics showed effects similar to GR24 on phytopathogens, indicating their suitability for practical applications. The pattern of the biological activity depended on the fungal species, SL mimic and concentration, and hyphal order. This dependence is probably related to the specificity of each fungal receptor-SL mimic interaction, which will have to be analyzed in-depth. Based on the biological properties and spectroscopic particularities, one SL mimic could be a good candidate for microscopic and spectroscopic investigations.

New α-Glucosidase Inhibitors from the Whole Plant of Hypericum beanii Based on Ligand Fishing and Molecular Networking Analysis.

In this work, a new rapid and targeted method for screening α-glucosidase inhibitors from Hypericum beanii was developed and verified. Ten new polycyclic polyprenylated acylphloroglucinols (PPAPs), hyperlagarol A-J (1-10), and nine known PPAPs (11-19) were obtained from H. beanii. Their structures were identified by using comprehensive analyses involving mass spectrometry, ultraviolet spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, and electron capture dissociation calculations. 1 and 2 are two new rare 2,3-seco-spirocyclic PPAPs, 3 and 4 are two novel 12,13-seco-spirocyclic PPAPs, 5 and 6 are two novel spirocyclic PPAPs, 7 and 8 are two new unusual spirocyclic PPAPs with complex bridged ring systems, and 9 and 10 are two novel nonspirocyclic PPAPs. α-GC inhibitory activities of all isolated compounds were tested. Most of them displayed inhibitory activities against α-glucosidase, with the IC50 values ranging from 6.85 ± 0.65 to 112.5 ± 9.03 μM. Moreover, the inhibitory type and mechanism of the active compounds were further analyzed using kinetic studies and molecular docking.

Saturn's F ring is intermittently shepherded by Prometheus.

One of the stranger planetary rings is Saturn's narrow, clumpy F ring, lying just outside the main rings, in a region disturbed by chaotic orbital dynamics. We show that the F ring has a stable "true core" that dominates its mass and is confined into discontinuous short arcs of particles larger than a few millimeters in radius. The more obvious micron-size particles seen in images, outlining and obscuring the true core, contribute only a small fraction of its mass. We found that these arcs of large particles orbit Saturn in a specific corotational resonance with the nearby 100-kilometer diameter ringmoon Prometheus, which stabilizes the F ring material and allows it to persist within the disturbed region for decades or longer. Toward the end of the observing period, a small chaotic glitch in the orbit of Prometheus temporarily disrupted the confinement, but the arcs seem to be able to adapt.

Synthesis of Stereodefined Polysubstituted Bicyclo[1.1.0]butanes.

We report a highly diastereoselective synthesis of polysubstituted bicyclobutanes possessing up to three stereodefined quaternary centers and five substituents. Our strategy involves a diastereoselective carbometalation of cyclopropenes followed by a cyclization to furnish the bicyclobutane ring system. This straightforward approach allows for the incorporation of a diverse range of substituents and functional groups, notably without the need for electron-withdrawing functionalities.

Piroxicam analogue metal complexes: Synthesis, crystal structures, molecular modeling and biological studies

In recent decades, metal‐based drugs have gained considerable attention all over the world because of their enhanced therapeutic potential. The piroxicam analogue, that is, 2‐Benzyl‐4‐hydroxy‐1,1‐dioxo‐1,2‐dihydro‐1λ6‐benzo [e][1,2] thiazine‐3‐carboxylic acid pyridin‐2‐yl amide 1 was synthesized and coupled with Mn (II), Co (II), Ni (II), Cu (II) and Zn (II) metal ions to isolate complexes 2–6. The N,O‐bidentate chelator coordinated with the metal center via pyridyl nitrogen and amide oxygen atoms by forming six‐membered ring system. Several analytical techniques like UV–Vis, FT‐IR, 1H NMR, magnetic susceptibility, and elemental analysis were performed to confirm the syntheses of the octahedral complexes. The conductance measurement was employed to determine the non‐electrolytic nature of the complexes. The molecular structures of manganese (II) 2, cobalt (II) 3, and zinc (II) 6, complexes were confirmed by single beam X‐ray crystallography revealing the monoclinic crystal system with P21/c space group. The crystallographic data was utilized to carry out the DFT studies, which were found in line with the experimental data. The antioxidant (DPPH, FRAP) and antibacterial activities were performed to determine the therapeutic potential of these synthesized compounds. These studies indicated that understudied compounds have potential as therapeutic agents and they may be used as drug candidates in the future. The in‐silico studies also aligned with the in‐vitro potential of the targeted compounds.

Divergent Synthesis of Scabrolide A and Havellockate via an exo-exo-endo Radical Cascade.

Here we report a concise and divergent synthesis of scabrolide A and havellockate, representative members of polycyclic marine natural product furano(nor)cembranoids. The synthesis features a highly efficient exo-exo-endo radical cascade. Through the generation of two rings, three C-C bonds, and three contiguous stereocenters in one step, this remarkable transformation not only assembles the bowl-shaped, common 6-5-5 fused ring system from simple building blocks but also precisely installs the functionalities at desired positions and sets the stage for further divergent preparation of both target molecules. Further studies reveal that the robust and unusual 6-endo radical addition in the cascade is likely facilitated by the rigidity of the substrate.

Carbon–nitrogen transmutation in polycyclic arenol skeletons to access N-heteroarenes

Developing skeletal editing tools is not a trivial task, and realizing the corresponding single-atom transmutation in a ring system without altering the ring size is even more challenging. Here, we introduce a skeletal editing strategy that enables polycyclic arenols, a highly prevalent motif in bioactive molecules, to be readily converted into N-heteroarenes through carbon–nitrogen transmutation. The reaction features selective nitrogen insertion into the C–C bond of the arenol frameworks by azidative dearomatization and aryl migration, followed by ring-opening, and ring-closing (ANRORC) to achieve carbon-to-nitrogen transmutation in the aromatic framework of the arenol. Using widely available arenols as N-heteroarene precursors, this alternative approach allows the streamlined assembly of complex polycyclic heteroaromatics with broad functional group tolerance. Finally, pertinent transformations of the products, including synthesis complex biheteroarene skeletons, were conducted and exhibited significant potential in materials chemistry.

Anti-inflammatory discovery of sesquiterpenoids and a jasmonic acid derivative from Artemisia stolonifera

Eleven previously undescribed sesquiterpenoids (8−18), one undescribed jasmonic acid derivative (35) and 28 known compounds were isolated from the leaves of Artemisia stolonifera. Undescribed compounds with their absolute configurations were determined by extensive spectroscopic analysis, single-crystal X-ray diffraction and ECD calculation. Compound 8 was identified as a rare sesquiterpenoid featuring a rearranged 5/8 bicyclic ring system, whereas compound 17 was found to be an unprecedented monocyclic sesquiterpenoid with methyl rearrangement. Evaluation of biological activity showed that compounds 1−5 and 7 displayed cytotoxicity against six tumor cells. In the meantime, compounds 11, 12, 18 and 35 exhibited inhibitory effects against LPS-stimulated NO production in RAW 264.7 macrophage cells and reduced the transcription of IL-6 and IL-1β in a dose-dependent manner at 25, 50 and 100 μM. Moreover, the anti-inflammatory-based network pharmacology and molecular docking analyses revealed potential target proteins of 11, 12, 18 and 35.

Phosphorus–nitrogen compounds: part 75—design, synthesis, stereogenic and conformational properties of chiral dispiro(N/N)cyclotriphosphazenes: structural analysis and photophysical and bioactivity studies

Multiheterocyclic inorganic–organic hybrid phosphazenes have robust inorganic ring systems with the stabilities of the phosphorus nitrogen skeleton and many different substituents bonded to the P atoms. In present study, unsymmetrical dispirocyclotriphosphazenes were prepared due to their potential to depict steric hindrance and electronic rearrangement in creating permanent chirality for certain conformational and configurational isomers. These isomers may have an effect on DNA bindings and activitiy against selected fungi and bacteria, remarkably. Herein, tetrachlorocyclotriphosphazenes (1 and 2) were reacted with 9-ethyl-N-methyl-3-carbazolyl-1,2-diaminoethane (3), 9-ethyl-N-ethyl-3-carbazolyl-1,2-diaminoethane (4) and 9-ethyl-N-methyl-3-carbazolyl-1,3-diaminopropane (5) to give the new unsymmetrical cis/trans-dispirocyclotriphosphazenes, [(ClBz/BzSpiro-6)R1(N3P3)(CzSpiro-n)R2]Cl2 (Cz: Carbazolyl; R1:Me R2:Me or Et; n = 5 or 6; trans 6a–11a and cis 6b–11b). Characterizations, chiralities, and photophysical and biological properties of the new compounds were examined. The molecular and crystal structures of cis-6b, cis-7b, trans-9a, cis-9b, trans-10a and cis-10b were determined by single crystal X-ray crystallography. The chiralities of these compounds with unsymmetrical spiro-architectures were confirmed by X-ray crystallography. These results were further proven by 31P NMR data recorded with the addition of a chiral solvent (CSA). Additionally, circular dichroism (CD) spectra also supported the results. Photophysical measurements indicate that these compounds show emission with lifetimes of approximately 5.6–5.9 ns. In addition, the bioactivities of some isomers were found to be different and quite high against some bacterial and yeast strains. Trans-8a was very active against B. cereus (MBC = 78.1 µM), while cis-6b, trans-9a and cis-9b were very active against the pathogenic yeast C. albicans (MFC = 156.3 µM).Graphical abstract

Crystal structure characterization, Hirshfeld surface analysis, and DFT calculation studies of 1-(6-amino-5-nitronaphthalen-2-yl)ethanone

The title compound, C12H10N2O3, was obtained by the deacetylation reaction of 1-(6-amino-5-nitronaphthalen-2-yl)ethanone in a concentrated sulfuric acid methanol solution. The molecule comprises a naphthalene ring system bearing an acetyl group (C-3), an amino group (C-7), and a nitro group (C-8). In the crystal, the molecules are assembled into a two-dimensional network by N...H/H...N and O...H/H...O hydrogen-bonding interactions. n–π and π–π stacking interactions are the dominant interactions in the three-dimensional crystal packing. Hirshfeld surface analysis indicates that the most important contributions are from O...H/H...O (34.9%), H...H (33.7%), and C...H/H...C (11.0%) contacts. The energies of the frontier molecular orbitals were computed using density functional theory (DFT) calculations at the B3LYP-D3BJ/def2-TZVP level of theory and the LUMO–HOMO energy gap of the molecule is 3.765 eV.

Forming localized dust concentrations in a dust ring: DM Tau case study

Context. Previous high-angular-resolution 225 GHz (~1.3 mm) continuum observations of the transitional disk DM Tau have resolved an outer ring at 20–120 au radii that is weakly azimuthally asymmetric. Aims. We aim to examine dust growth and filtration in the outer ring of DM Tau. Methods. We performed ~0″.06 (~8.7 au) resolution Karl G. Jansky Very Large Array (JVLA) 40–48 GHz (~7 mm; Q band) continuum observations, along with complementary observations at lower frequencies. In addition, we analyzed the archival JVLA observations undertaken since 2010. Results. Intriguingly, the Q band image resolved the azimuthally highly asymmetric, knotty dust emission sources close to the inner edge of the outer ring. Fitting the 8–700 GHz spectral energy distribution (SED) with two dust components indicates that the maximum grain size (amax) in these knotty dust emission sources is likely ≳300 µm, whereas it is ≳50 µm in the rest of the ring. These results may be explained by a trapping of inwardly migrating “grown” dust close to the ring inner edge. The exact mechanism for developing the azimuthal asymmetry has not yet been identified, which may be due to planet-disk interaction that might also be responsible for the creation of the dust cavity and pressure bump. Otherwise, it may be due to the fluid instabilities and vortex formation as a result of shear motions. Finally, we remark that the asymmetries in DM Tau are difficult to diagnose from the ≳225 GHz observations, owing to a high optical depth at the ring. In other words, the apparent symmetric or asymmetric morphology of the transitional disks may be related to the optical depths of those disks at the observing frequency.

Metalla‐Carbaporphyrinoids Consisting of an Acyclic N‐Confused Tetrapyrrole Analogue Served as Stable Near‐Infrared‐II Dyes

AbstractWe present herein the synthesis of novel pseudo‐metalla‐carbaporphyrinoid species (1M: M=Pd and Pt) achieved through the inner coordination of palladium(II) and platinum(II) with an acyclic N‐confused tetrapyrrin analogue. Despite their tetrapyrrole frameworks being small, akin to well‐known porphyrins, these species exhibit an unusually narrow HOMO–LUMO gap, resulting in an unprecedentedly low‐energy absorption in the second near‐infrared (NIR‐II) region. Density functional theory (DFT) calculations revealed unique dπ‐pπ‐conjugated electronic structures involving the metal dπ‐ligand pπ hybridized molecular orbitals of 1M. Magnetic circular dichroism (MCD) spectroscopy confirmed distinct electronic structures. Remarkably, the complexes feature an open‐metal coordination site in the peripheral NN dipyrrin site, forming hetero‐metal complexes (1Pd‐BF2 and 1Pt‐BF2) through boron difluoride complexation. The resulting hetero metalla‐carbaporphyrinoid species displayed further redshifted NIR‐II absorption, highly efficient photothermal conversion efficiencies (η; 62–65 %), and exceptional photostability. Despite the challenges associated with the theoretical and experimental assessment of dπ‐pπ‐conjugated metalla‐aromaticity in relatively larger (more than 18π electrons) polycyclic ring systems, these organometallic planar tetrapyrrole systems could serve as potential molecular platforms for aromaticity‐relevant NIR‐II dyes.

Metalla-Carbaporphyrinoids Consisting of an Acyclic N-Confused Tetrapyrrole Analogue Served as Stable Near-Infrared-II Dyes.

We present herein the synthesis of novel pseudo-metalla-carbaporphyrinoid species (1M: M=Pd and Pt) achieved through the inner coordination of palladium(II) and platinum(II) with an acyclic N-confused tetrapyrrin analogue. Despite their tetrapyrrole frameworks being small, akin to well-known porphyrins, these species exhibit an unusually narrow HOMO-LUMO gap, resulting in an unprecedentedly low-energy absorption in the second near-infrared (NIR-II) region. Density functional theory (DFT) calculations revealed unique dπ-pπ-conjugated electronic structures involving the metal dπ-ligand pπ hybridized molecular orbitals of 1M. Magnetic circular dichroism (MCD) spectroscopy confirmed distinct electronic structures. Remarkably, the complexes feature an open-metal coordination site in the peripheral NN dipyrrin site, forming hetero-metal complexes (1Pd-BF2 and 1Pt-BF2) through boron difluoride complexation. The resulting hetero metalla-carbaporphyrinoid species displayed further redshifted NIR-II absorption, highly efficient photothermal conversion efficiencies (η; 62-65 %), and exceptional photostability. Despite the challenges associated with the theoretical and experimental assessment of dπ-pπ-conjugated metalla-aromaticity in relatively larger (more than 18π electrons) polycyclic ring systems, these organometallic planar tetrapyrrole systems could serve as potential molecular platforms for aromaticity-relevant NIR-II dyes.

4-(1H-2,3-Dihydro-naphtho-[1,8-de][1,3,2]di-aza-borinin-2-yl)-1-ethylpyridin-1-ium iodide.

The title compound, C17H17BN3I, is a type of di-aza-borinane featuring substitution at the 1, 2, and 3 positions of the nitro-gen-boron six-membered heterocycle. The organic mol-ecule has a planar structure, the dihedral angle between the pyridyl ring and the fused ring system being 3.46 (4)°. In the crystal, mol-ecules are stacked in a head-to-tail manner. The iodide ion makes close contacts with three organic mol-ecules and supports the alternating stack.

4-(1H-2,3-Dihydronaphtho-[1,8-de][1,3,2]di-aza-borinin-2-yl)-1-ethylpyridin-1-ium iodide monohydrate.

The cation of the title hydrated salt, C17H17BN3 +·I-·H2O, is a di-aza-borinane featuring substitution at the 1, 2, and 3 positions in the nitro-gen-boron six-membered heterocycle. The cation is approximately planar with a dihedral angle between the pyridyl ring and the di-aza-borinane ring system of 5.40 (5)°. In the crystal, the cations stack along [100] in an alternating head-to-tail manner, while the iodide ion and water mol-ecule form one-dimensional hydrogen-bonded chains beside the cation stack. The cation stacks and I--water chains are crosslinked by N-H⋯I and N-H⋯O hydrogen bonds.

Synthesis and characterization of new heterocycles containing the 1,2,3-triazole ring system

The unexpected (E)-1,4-bis(5-methyl-1-(4-nitrophenyl)-1H-1,2,3-triazol-4-yl)but‑2-ene-1,4‑dione was produced in 89 % yield from the reaction of 2‑bromo-1-(5-methyl-1-(4-nitrophenyl)-1H-1,2,3-triazol-4-yl)ethan-1-one and sodium benzenesulfinate dihydrate in boiling ethanol. The reaction of the synthesized symmetrical 2-butene-1,4‑dione and 1,2-phenylenediamine in acetic acid afforded 2-(5-methyl-1-(4-nitrophenyl)-1H-1,2,3-triazol-4-yl)-1H-benzo[d]imidazole in 68 % yield. 2,3-Dibromopropan-1-one was synthesized in 82 % from bromination of the corresponding chalcone under acidic conditions. Treatment of dibromoketone and benzylamine or phosphonic dihydrazide in ethanol in the presence of a basic catalyst unexpectedly afforded 2‑bromo-3-ethoxyketone in reasonable yield. The reactivity of hydrazonoyl chloride towards 5-methyl- and 5‑chloro-1,2,3-triazol-4-carbohydrazides was also investigated to afford the corresponding bis-hydrazone and the unanticipated tris-hydrazone.