Six-membered Ring Research Articles

Hybrids Diazine: Recent Advancements in Modern Antimicrobial Therapy

Nowadays, antimicrobial therapies have become a very challenging issue because of a large diversity of reasons such as antimicrobial resistance, over consumption and misuse of antimicrobial agents, etc. A modern, actual and very useful approach in antimicrobial therapy is represented by the use of hybrid drugs, especially combined five and six-membered ring azaheterocycles. In this review, we present an overview of the recent advanced data from the last five years in the field of hybrid diazine compounds with antimicrobial activity. In this respect, we highlight here essential data concerning the synthesis and antimicrobial activity of the main classes of diazine hybrids: pyridazine, pyrimidine, pyrazine, and their fused derivatives.

Unraveling the mechanistic interplay of mediators orchestrating the neuroprotective potential of harmine.

Neurodegenerative diseases (NDDs) encompass a range of conditions characterized by the specific dysfunction and continual decline of neurons, glial cells, and neural networks within the brain and spinal cord. The majority of NDDs exhibit similar underlying causes, including oxidative stress, neuroinflammation, and malfunctioning of mitochondria. Elevated levels of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), alongside decreased expression of brain-derived neurotrophic factor (BDNF) and glutamate transporter subtype 1 (GLT-1), constitute significant factors contributing to the pathogenesis of NDDs. Additionally, the dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) gene has emerged as a significant target for the treatment of NDDs at the preclinical level. It significantly contributes to developmental brain defects, early onset neurodegeneration, neuronal loss, and dementia in Down syndrome. Moreover, an impaired ubiquitin-proteosome system (UPS) also plays a pathological role in NDDs. Malfunctioning of UPS leads to abnormal protein buildup or aggregation of α-synuclein. α-Synuclein is a highly soluble unfolded protein that accumulates in Lewy bodies and Lewy neurites in Parkinson's disease and other synucleinopathies. Recent research highlights the promising potential of natural products in combating NDDs relative to conventional therapies. Alkaloids have emerged as promising candidates in the fight against NDDs. Harmine is a tricyclic β-carboline alkaloid (harmala alkaloid) with one indole nucleus and a six-membered pyrrole ring. It is extracted from Banisteria caapi and Peganum harmala L. and exhibits diverse pharmacological properties, encompassing neuroprotective, antioxidant, anti-inflammatory, antidepressant, etc. Harmine has been reported to mediate its neuroprotective via reducing the level of inflammatory mediators, NADPH oxidase, AChE, BChE and reactive oxygen species (ROS). Whereas, it has been observed to increase the levels of BDNF, GLT-1 and anti-oxidant enzymes, along with protein kinase-A (PKA)-mediated UPS activation. This review aims to discuss the mechanistic interplay of various mediators involved in the neuroprotective effect of harmine.

On Entangled Singlet Pure Diradicals.

This work addresses a class of conjugated hydrocarbons that are expected to be singlet diradicals according to the topological Hückel Hamiltonian while possibly satisfying full on-bond electron pairing. These systems possess two degenerate singly occupied molecular orbitals (SOMOs), but aromaticity brought by properly positioned six-membered rings does prevent Jahn-Teller distortions. Density functional theory (DFT) calculations performed on two emblematic examples confirm the strong bond-length alternation in the closed-shell solutions and the clear spatial symmetry in the open-shell spin-unrestricted determinants, the latter solution always being found to have significantly lower energy. Since the SOMOs are here of different symmetry, the wave function is free from ionic valence-bond component, and spin decontamination of the unrestricted DFT solutions and wave function calculations at the CASSCF-plus-second-order-perturbation level confirm the expected pure diradical character of such molecules. In contrast to disjoint diradicals, the SOMOs of present systems have large amplitudes on neighbor atoms, and we propose to name them entangled pure diradicals, further providing some prescription rules for their design. Additional calculations point out the qualitative contrast between these molecules and the related diradicaloids.

Improving Copper Active Site Speciation on Cu-Ce/SSZ-13 for Ammonia Oxidation via Si/Al Ratio Modulation.

Catalytic oxidation is a promising purification technique for ammonia (NH3) emission. However, high ignition temperatures and NOx peroxide generation limit its effectiveness due to a lack of active sites. Herein, the effects of Si/Al ratio (SAR) modulation on the speciation of copper active sites and the reaction mechanism at different acidic sites were investigated by loading CuO-CeO2 onto SSZ-13 with different SARs (Cu-Ce/SAR15, 20, and 30). Among them, Cu-Ce/SAR20 exhibits the lowest induction temperature (T20 = 180 °C) and the highest nitrogen selectivity (above 95%), attributing to a higher number of Cu2+ exchange sites. In situ IR spectroscopy and isotopic (18O2) transient response experiments indicate that more active Cu2+ in Cu-Ce/SAR20 provides sufficient Lewis acidic sites for NH3 adsorption and favors the stability of Si-OH-Al structures (Brønsted acid sites). NH3 adsorbed at Lewis acidic sites tends to form peroxide byproducts (NOx), while the NH4+ adsorbed at Brønsted acidic sites generates the key intermediate NH4NO2, which decomposes to N2 at high temperatures, thus enhancing nitrogen selectivity. The whole process mainly follows the Mars-van Krevelen (M-K) mechanism, with the Langmuir-Hinshelwood (L-H) mechanism playing a supporting role. Z2Cu2+ coordinates with adjacent Al atoms within the six-membered ring (6MR) and undergoes a slight deformation at high temperatures, facilitating the migration of the lattice oxygen. SAR plays a crucial role in local environmental speciation of reactive Cu2+, where the sufficient isolated Al provided in SAR20 pulls Cu2+ into the eight-membered ring (8MR), allowing it to come into contact with NH3 more readily.

Two Hydroxyfluorooxoborates Achieving Deep-ultraviolet Cutoff Edges and Moderate Birefringence by Assembling Multi-anionic Groups.

Assembling multi-anionic groups is conducive to utilizing respective advantage to achieve the enhancement of optical performance. Two new hydroxyfluorooxoborates, Ama2-Rb2B3O3F4(OH) and K8Cs2B15O14(OH)7F20 ⋅ H2O with [B3O3F4(OH)] six-membered rings were synthesized for the first time. The title compounds exhibit short ultraviolet cutoff edges (<200 nm) and K8Cs2B15O14(OH)7F20 ⋅ H2O possesses a moderate experimental refractive index difference of 0.051@546 nm.

Exploration of pyridine-based self-assembled complexes-An overview

Pyridine is a heterocyclic aromatic compound with a six-membered ring that is essential for the design and synthesis of self-assembled complexes because of its unique electrical characteristics and intrinsic capacity to participate in various non-covalent interactions. Pyridine-based complexes have attracted much interest and are being used in modern science. They are invaluable in various industries due to their adaptability and unique qualities. These compounds function as catalysts in catalysis, quickening chemical reactions and promoting effective procedures. Additionally, they are essential to drug delivery systems because they guarantee the precise and regulated release of medicinal substances, improving treatment outcomes and lowering adverse effects. They are also helpful in biomedical imaging and used as contrast agents to produce detailed and crisp diagnostic images. Moreover, pyridine-based compounds play a crucial role in sensing and detection applications by selectively and sensitively identifying particular molecules or ions. Their versatility and wide range of applications highlight their importance in advancing science and technology. This review provides a comprehensive overview and analysis of the synthesis methods employed in creating a diverse range of novel pyridine-based complexes.

Accelerating Zn2+ kinetics and regulating zinc anode interface for high stable aqueous zinc-ion batteries

Aqueous zinc-ion batteries are promising for large-scale energy storage. However, their practicability and industrialization still face challenges due to the issues such as hydrogen evolution, corrosion, and zinc dendrites, which seriously limit their cycling life. This study introduces a cost-effective and practical solution to enhance the reversibility and cycle life of Zn anodes. It is found that 1, 4-cyclohexanedione can regulate hydrogen bonds to reduce H2O activity and accelerate Zn2+ kinetics. This organic molecule with symmetric carbonyl group and steric hindrance effect from the six-membered ring can mitigate the tip effect to inhibit the zinc dendrite formation. The Zn|| NH4V4O10 cell exhibit a capacity of 135.6 mAh g-1 and 75% capacity retention after 1400 cycles at 4 A g-1. This work demonstrates the significant potential of this multifunctional and low-cost additive to extend the cycle life of the batteries, marking a step forward in their applicability for large-scale energy storage.

Monomer-Recyclable Polyester from CO2 and 1,3-Butadiene.

Synthesis of monomer-recyclable polyesters solely from CO2 and bulk olefins holds great potentials in significantly reducing CO2 emissions and addressing the issue of plastic pollutions. Due to the kinetic disadvantage of direct copolymerization of CO2 and bulk olefins compared to homopolymerization of bulk olefins, considerable research attention has been devoted to synthesis of polyester via the ring-opening polymerization (ROP) of a six-membered disubstituted lactone intermediate, 1,2-ethylidene-6-vinyl-tetrahydro-2H-pyran-2-one (𝜹-L), obtained from telomerization of CO2 and 1,3-butadiene. However, the conjugate olefin on the six-membered ring of 𝜹-L leads to serious Michael addition side reactions. Thus, selective ROP of 𝜹-L, which can precisely control the repeating unit for the production of polyesters potentially amenable to efficient monomer recycling, remains an unresolved challenge. Herein, we report the first example of selective ROP of 𝜹-L using a combination of organobase and N,N'-Bis[3,5-bis(trifluoromethyl)phenyl]urea as the catalytic system. Systematic modifications of the substituent of the urea shows that the presence of electron-deficient 3,5-bis(trifluoromethyl)-phenyl groups is the key to the extraordinary selectivity of ring opening over Michael addition. Efficient monomer recovery of oligo(𝜹-L) was also achieved under mild catalytic conditions. This article is protected by copyright. All rights reserved.

Symmetry Evolution Induced 2D Pt Single Atom Catalyst with High Density for Alkaline Hydrogen Oxidation.

The performance of single-atom catalysts is greatly influenced by the chemical environment surrounding the central atom. Here, a salt-assisted method is employed to transform the tetrahedral coordination structure of zeolitic imidazolate frameworks - 8 (ZIF-8)into a planar square coordination structure without altering the ligands. During the subsequent carbonization process, concurrent with the evaporation of zinc atoms, the structure of the nitrogen and carbon carriers (NC carriers) undergoes a transition from five-membered rings to six-membered rings to preserve the 2D structure. This transition results in the generation of additional defect sites on the 2D-NC substrates. Hence, the Pt single-atom catalysts with planar square coordination symmetries can be precisely prepared via electrodeposition (denoted as 2D-Pt SAC). The Pt loading of 2D-Pt SAC is 0.49 ± 0.03 µg cm-2, higher than that of 3D-Pt SAC (0.37 ± 0.04 µg cm-2). In the context of the hydrogen oxidation reaction electrocatalysis, under an overpotential of 50 mV, these single-atom catalysts with 2D coordination exhibit mass activities of 2396 A gPt -1 (32 times higher than commercial Pt/C catalyst, 2 times higher than 3D-PtNC).

Synthetic Protocols, Structural Activity Relationship, and Biological Activity of Piperazine and its Derivatives.

The versatile basic structure of piperazine allows for the development and production of newer bioactive molecules that can be used to treat a wide range of diseases. Piperazine derivatives are unique and can easily be modified for the desired pharmacological activity. The two opposing nitrogen atoms in a six-membered piperazine ring offer a large polar surface area, relative structural rigidity, and more acceptors and donors of hydrogen bonds. These properties frequently result in greater water solubility, oral bioavailability, and ADME characteristics, as well as improved target affinity and specificity. Various synthetic protocols have been reported for piperazine and its derivatives. In this review, we focused on recently published synthetic protocols for the synthesis of the piperazine and its derivatives. The structure-activity relationship concerning different biological activities of various piperazine-containing drugs was also highlighted to provide a good understanding to researchers for future research on piperazines.

Copper-Catalyzed [2 + 2] Cyclization/Ring Expansion of Ene-Ynamides: Construction of Medium- and Large-Sized Rings.

Catalytic cyclization of enynes is an efficient approach for the preparation of cyclic compounds, and a large variety of four- to six-membered rings could be synthesized using this method. However, it has been rarely employed for the construction of medium- and large-sized rings. Herein, we describe a copper-catalyzed cycloisomerization of ene-ynamides through a [2 + 2] cyclization/electrocyclic ring opening cascade, leading to the atom-economical assembly of indole-fused medium- and large-sized rings in moderate to excellent yields under mild reaction conditions. Importantly, the synthetic utility of this reaction was demonstrated by the convenient synthesis of iprindole.

Synthesis, crystal structure and Hirshfeld surface analysis of 2-[(4-hy-droxy-phen-yl)amino]-5,5-diphenyl-1H-imidazol-4(5H)-one.

In the title mol-ecule, C21H17N3O2, the five-membered ring is slightly ruffled and dihedral angles between the pendant six-membered rings and the central, five-membered ring vary between 50.78 (4) and 86.78 (10)°. The exocyclic nitro-gen lone pair is involved in conjugated π bonding to the five-membered ring. In the crystal, a layered structure is generated by O-H⋯N and N-H⋯O hydrogen bonds plus C-H⋯π(ring) and weak π-stacking inter-actions.

Reactivity of a Linear 2-Germapropadiene with Acids, Ketones, and Amines.

The reactivity of an isolable 2-germapropadiene with acids, ketones, and amines was investigated. The reactions of 2-germapropagiene 1 with hydrogen chloride and acetic acid afforded the corresponding dichlorogermane (2) and diacetoxygermane (3), respectively, indicating that the central germanium atom of 1 is electrophilic. The reaction of 1 with benzaldehyde proceeds via a formal [2+2] cycloaddition to afford the corresponding spiro compound (4). Moreover, 1 reacts smoothly with acetone to furnish germane 5, which contains a six-membered ring involving two acetone molecules. Furthermore, 1 undergoes N-H bond insertion with methylamine or aniline to afford diamino germanes 7 and 8, respectively. The reaction of 1 with urea selectively afforded the corresponding N-H-insertion product (8).

Crystal structures of tri-chlorido-(4-methyl-piperidine)gold(III) and two polymorphs of tri-bromido(4-methyl-piperidine)-gold(III).

Tri-chlorido-(4-methyl-piperidine)-gold(III), [AuCl3(C6H13N)], 1, crystallizes in Pbca with Z = 8. Tri-bromido-(4-methyl-piperidine)-gold(III), [AuBr3(C6H13N)], 2, crystallizes as two polymorphs, 2a in Pnma with Z = 4 (imposed mirror symmetry) and 2b, which is isotypic to 1. The Au-N bonds trans to Cl are somewhat shorter than those trans to Br, and the Au-Cl bonds trans to N are longer than those cis to N, whereas the Au-Br bonds trans to N are slightly shorter than the cis bonds. The methyl and AuX 3 groups (X = halogen) occupy equatorial positions at the six-membered ring. The packing of all three structures involves chains of mol-ecules with offset stacking of the AuX 3 moieties associated with short Au⋯X contacts; for 1 and 2b these are reinforced by N-H⋯X hydrogen bonds, whereas for 2a there are no classical hydrogen bonds and the chains are inter-connected by Br⋯Br contacts.

Effects of Cu species in Cu-SSZ-13 zeolites on the performance of NOx reduction reactions

In diesel vehicle exhaust after-treatment systems, high silica Cu-SSZ-13 has received increasing attention as a commercialized catalyst owing to its high efficiency in selective catalytic reduction reactions with NH3 (NH3-SCR). However, research on the regulation of Cu2+ species within metal active centers in the pore structure of chabazite (CHA)-type zeolite to improve catalytic performance lacks sufficient depth. Herein, SSZ-13 zeolite with various Al distributions was prepared by adjusting the proportion of N,N,N-Trimethyl-1-adamantanaminiumhydroxide (TMAdaOH) and Na in the initial gel. Moreover, three representative Cu-SSZ-13 catalysts with different Cu2+ species were synthesized via an ion exchange method. 23Na MAS NMR and NO adsorption infrared spectroscopy results revealed that with increasing Na content and decreasing TMAdaOH concentration in the initial gel, the number of paired Al in the CHA framework gradually increased. Consequently, this increased the number of Cu2+-2Z sites near six-membered ring (MR) and reduced the amount of [Cu(OH)]+-Z sites near eight-MR. The fresh Cu-SSZ-13 catalyst, with a moderate amount of Cu2+-2Z and [Cu(OH)]+-Z, exhibited optimal catalytic performance across the entire temperature window. After hydrothermal aging, Cu-SSZ-13 with a higher concentration of Cu2+-2Z species featured optimal performance among all Cu-SSZ-13 catalysts above 400 °C. These findings indicated the significance of balancing the amount of both Cu2+-2Z and [Cu(OH)]+-Z in the Cu-SSZ-13 zeolite. Additionally, the results elucidated the reaction intermediates involved in the NH3-SCR process catalyzed by Cu-SSZ-13 with various Cu species.

Design of Pentanary Mixed-Chalcogenides Ag2In2SiS6-xSex (x = 1, 2) Based on the Bucket Effect: Local Structural Difference and High-Performance Nonlinear-Optical Properties Realized by Partial Congener Substitution.

Noncentrosymmetric chalcogenides are promising candidates for infrared nonlinear-optical (NLO) crystals, and exploring high-performance ones is a hot topic and challengeable. Herein, the combination of AgQ4, InQ4, and SiQ4 (Q = S, Se) units with different S/Se ratios resulted in the discovery of the tetrahedral chalcogenides Ag2In2SiS4Se2 (1) and Ag2In2SiS5Se (2). They both crystallize in the monoclinic Cc space group with different local structures. Co-occupied S/Se sites only exist in 2, and the arrangement of [In2SiQ3] six-membered rings builds different helical chains and 3D [(In2SiQ6)2-]n polyanionic frameworks in 1 and 2. They show balanced NLO performances, including phase-matchable moderate NLO responses (0.7 and 0.5 × AGS) and enhanced laser-induced damage thresholds (4.5 and 5.1 × AGS). Theoretical calculations reveal that their NLO responses are predominantly contributed by the AgQ4 and InQ4 units.

Co-combustion behavior and catalytic mechanism of high CaO/SiO2 biomass mixed with anthracite for blast furnace injection: Experiment, modeling and DFT investigation

The physical and chemical properties of apricot tree (AT), corncob (CC), and anthracite (CC) were systematically analyzed. Their combustion behaviors and blends were examined using a non-isothermal thermogravimetric method, which revealed the catalytic mechanism of biomass mineral composition in the combustion process. The presence of high CaO content resulted in better combustibility, particularly with an addition ratio of more than 50 % AT, which enhanced anthracite combustion. Kinetic analysis indicated that the random pore model had a better fit than the volume reaction model. At 75 % addition of AT and CC, the lowest apparent activation energies were observed, with values of 100.5 kJ/mol and 110.23 kJ/mol, respectively. Density functional theory calculations demonstrated that the presence of CaO caused reconfiguration in the coal's molecular structure, making it easier for aliphatic chains attached to six-membered rings to detach. The co-combustion process and catalytic combustion mechanism of biomass and coal were discussed, highlighting CaO's ability to remove oxygen-containing functional groups and aliphatic chains, while facilitating O2 diffusion within the molecular structure. Conversely, SiO2 tended to generate silicates, leading to the deactivation of CaO's catalytic effect.

Development of a facile one-pot synthesized fluorescent green polyesters as cooling water antiscalants for industrial application

Currently, antiscalants used in cooling water are expected to be environmental-friendly, good scale inhibitive, fluorescence tracing, and industrial-friendly. Aliphatic biodegradable photoluminescent polymers (BPLPs) synthesized from citric acid, aliphatic diols, and various amino acids are fluorescent polymers containing heteroatom six-membered conjugated ring chromophores. Their cross-linked BPLPs have potential for use as implant or device materials, and vivo bioimaging probes. However, so far, no one has found that BPLPs can be used as efficient antiscalants for cooling water. In this work, we demonstrate a facile one-pot microwave-assisted synthesis of BPLPs from cost-effective materials. The products were characterized by Fourier transforms infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, gel permeation chromatography, and fluorescence spectroscopy. Thus prepared BPLPs can be directly used as a novel type green fluorescent antiscalant without further purification. They have an excellent calcium phosphate inhibition efficiency that can reach 98.6 % with a dosage of 25 mg·L−1 in the static scale inhibition test at 80 °C.

On-Surface Synthesis of Organolanthanide Sandwich Complexes.

The synthesis of lanthanide-based organometallic sandwich compounds is very appealing regarding their potential for single-molecule magnetism. Here, it is exploited by on-surface synthesis to design unprecedented lanthanide-directed organometallic sandwich complexes on Au(111). The reported compounds consist of Dy or Er atoms sandwiched between partially deprotonated hexahydroxybenzene molecules, thus introducing a distinct family of homoleptic organometallic sandwiches based on six-membered ring ligands. Their structural, electronic, and magnetic properties are investigated by scanning tunneling microscopy and spectroscopy, X-ray absorption spectroscopy, X-ray linear and circular magnetic dichroism, and X-ray photoelectron spectroscopy, complemented by density functional theory-based calculations. Both lanthanide complexes self-assemble in close-packed islands featuring a hexagonal lattice. It is unveiled that, despite exhibiting analogous self-assembly, the erbium-based species is magnetically isotropic, whereas the dysprosium-based compound features an in-plane magnetization.

Dual-Strategy Tailoring Molecular Structures of Dopant-Free Hole Transport Materials for Efficient and Stable Perovskite Solar Cells.

Dopant-free hole transport materials (HTMs) are ideal materials for highly efficient and stable n-i-p perovskite solar cells (PSCs), but most current design strategies for tailoring the molecular structures of HTMs are limited to single strategy. Herein, four HTMs based on dithienothiophenepyrrole (DTTP) core are devised through dual-strategy methods combining conjugate engineering and side chain engineering. DTTP-ThSO with ester alkyl chain that can form six-membered ring by the S⋅⋅⋅O noncovalent conformation lock with thiophene in the backbone shows good planarity, high-quality film, matching energy level and high hole mobility, as well as strong defect passivation ability. Consequently, a remarkable power conversion efficiency (PCE) of 23.3 % with a nice long-term stability is achieved by dopant-free DTTP-ThSO-based PSCs, representing one of the highest values for un-doped organic HTMs based PSCs. Especially, the fill factor (FF) of 82.3 % is the highest value for dopant-free small molecular HTMs-based n-i-p PSCs to date. Moreover, DTTP-ThSO-based devices have achieved an excellent PCE of 20.9 % in large-area (1.01 cm2) devices. This work clearly elucidates the structure-performance relationships of HTMs and offers a practical dual-strategy approach to designing dopant-free HTMs for high-performance PSCs.