Cationic Ring Research Articles

Independent LUMO Reactivity in Mesoionic N‐Heterocyclic Thiones: Synthesis of a Stable Radical Anion

Mesoionic compounds, with positive and negative charges, are expected to have dual‐site highest occupied molecular orbital (HOMO, donor) and lowest unoccupied molecular orbital (LUMO, acceptor) reactivity. Herein, we report a novel class of air‐stable mesoionic N‐heterocyclic thiones (mNHTs) synthesized from abnormal N‐heterocyclic carbenes (aNHCs). DFT studies revealed a highly polarized exocyclic thione moiety and computed Fukui function analysis suggests the dual‐site HOMO/LUMO reactivity of mNHTs predicting donor property at the negatively charged ‘S’ center while acceptor property at the cationic imidazole ring. The independent LUMO reactivity of the mNHT was realized by its chemical reduction to an elusive radical anion, which was characterized by a single crystal X‐diffraction study. Further, we explore the reactivity of radical anion for the activation of SO2 gas, C‐Br bonds of aryl bromide and photocatalytic functionalization of C‐X (X = F, Br) bonds. This work unlocks the independent LUMO reactivity of a mesoionic compound.

Investigation of the double layer structure of 1-butyl-3-methylimidazolium thiocyanate at the air-water interface using sum-frequency generation vibrational spectroscopy.

The interfacial structure and adsorption behavior of 1-butyl-3-methylimidazolium thiocyanate ionic liquids (ILs) aqueous solutions were investigated using sum-frequency generation vibrational spectroscopy (SFG-VS) and surface tension measurements. Polarization-dependent measurements revealed a dramatic increase in the SFG signal for both CH and CN stretching modes with increasing ILs concentration, reaching a maximum at a mole fraction of 0.01. This concentration dependence was accompanied by a dramatic drop in surface tension. Upon further increasing the concentration, surface tension varied slightly and reached a constant value, while the SFG signal decreased significantly. Quantitative polarization analysis showed that as the bulk concentration increased, the apparent molecular orientation of the SCN- transition dipole at the interface changed from 51° to 46°, and the tilt angle of CH3 group of the butyl chain attached to the imidazole cationic ring changed from 18° to 32°. The decrease in the SFG signal can be explained by the formation of a double layer adsorption structure at the air/water interface. It was also demonstrated that the anions were adsorbed at the interface simultaneously with the cationic group, rather than by successive adsorption as proposed in a previous study. Using the Shereshefsky model, the thermodynamic Gibbs free energy of adsorption deduced from surface tension data was compared with SFG results.

Tailoring refractive index dispersion in ionic liquids: The influence of charge delocalization in cations

In this work, we study the contributions that different molecular blocks have in the wavelength-dependence of the refractive index in ionic liquids. The ionic liquids chosen for this work are combinations of the bis(trifluoromethylsulfonyl)imide anion with cations based on four different heterocycles with different extents of charge delocalization. The analysis is performed in terms of the experimental electronic polarizability, which is obtained by combining measurements of refractive index curves and densities via the Lorentz-Lorenz equation. Exploiting the additivity of electronic polarizability in ionic liquids, the contribution of the anion and the heterocycles of the cations is separated from that of the alkyl chains. Our results show important differences in these contributions, revealing a key influence of the charge delocalization in the cationic rings on the behavior of the refractive index dispersion. The understanding of how different parts of ionic liquids affect their refractive index dependence on wavelength would allow to gain precise control of this magnitude, enabling the development of customized optical materials for diverse applications in photonics and sensing technologies.

Preparation and Mechanism of Shale Inhibitor TIL-NH2 for Shale Gas Horizontal Wells.

In this study, a new polyionic polymer inhibitor, TIL-NH2, was developed to address the instability of shale gas horizontal wells caused by water-based drilling fluids. The structural characteristics and inhibition effects of TIL-NH2 on mud shale were comprehensively analyzed using infrared spectroscopy, NMR spectroscopy, contact angle measurements, particle size distribution, zeta potential, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The results demonstrated that TIL-NH2 significantly enhances the thermal stability of shale, with a decomposition temperature exceeding 300 °C, indicating excellent high-temperature resistance. At a concentration of 0.9%, TIL-NH2 increased the median particle size of shale powder from 5.2871 μm to over 320 μm, effectively inhibiting hydration expansion and dispersion. The zeta potential measurements showed a reduction in the absolute value of illite's zeta potential from -38.2 mV to 22.1 mV at 0.6% concentration, highlighting a significant decrease in surface charge density. Infrared spectroscopy and X-ray diffraction confirmed the formation of a close adsorption layer between TIL-NH2 and the illite surface through electrostatic and hydrogen bonding, which reduced the weakly bound water content to 0.0951% and maintained layer spacing of 1.032 nm and 1.354 nm in dry and wet states, respectively. Thermogravimetric analysis indicated a marked reduction in heat loss, particularly in the strongly bound water content. Scanning electron microscopy revealed that shale powder treated with TIL-NH2 exhibited an irregular bulk shape with strong inter-particle bonding and low hydration degree. These findings suggest that TIL-NH2 effectively inhibits hydration swelling and dispersion of shale through the synergistic effects of cationic imidazole rings and primary amine groups, offering excellent temperature and salt resistance. This provides a technical foundation for the low-cost and efficient extraction of shale gas in horizontal wells.

Experimental and Theoretical Study on Electron Ionization and Fragmentation of Propylene Oxide─the First Chiral Molecule Detected in the Interstellar Medium.

Propylene oxide, CH3CHOCH2, is the first chiral molecule detected in space and the third C3 oxide detected toward the Sagittarius B2 (Sgr B2 (N)) molecular cloud, the others being propanal, CH3CH2CHO, and acetone, (CH3)2CO. With homochirality being ubiquitous in the building blocks of living matter, the formation and decay paths of propylene oxide in space are of specific interest. Motivated by the significant role of photo- and secondary electrons in astrochemistry, we have studied electron ionization and fragmentation of propylene oxide. Ion appearance energies are determined and compared to threshold values for the respective processes calculated at the G4MP2 level of theory, and potential reaction pathways are computed at the DFT level of theory. Electron ionization is found to destabilize propylene oxide, leading to barrierless opening of the C1-C2 bond of the epoxy ring, hydrogen transfer, and fragmentation over the methyl vinyl ether or rupture of the C2-O bond of the epoxy ring and fragmentation of the allyl alcohol cation as an intermediate, rather than direct bond ruptures.

A New centrosymmetric supramolecular Hybrid Antimony (III)-based material :X-ray characterization, vibrational studies, theoretical (DFT and TD-DFT) studies, thermal behavior, opto-electric properties and atomic Hirshfeld surface analysis.

The new centrosymmetric hybrid material (C8H12N)4[SbCl5]2 has been successfully elaborated at room temperature by slow evaporation in the centrosymmetric monoclinic space group P21/c with the following parameters: a = 29.0349(16) Å, b = 13.1241(7) Å, c = 12.0278(7) Å, β = 95.567(2) ° Z = 4 and V = 4561.7(4) Å3. The asymmetric unit consists of two isolated [Sb2Cl10]4- dimers and four protonated cations (C8H12N)+ was optimized d by density functional theory (DFT) using the B3LYP method. The cohesion of this supramolecular material was ensured by the means of N—H…Cl hydrogen-bonding interactions yield a three-dimensional network. The infrared IR and Raman studies which were performed at room temperature charge in the 4000–400 cm -1 and 10- 3000 cm -1 frequency regions, respectively, displayed the existence of vibrational modes that correspond to the organic and inorganic groups. The assignment of wavenumbers which were based on potential energy distribution (PED), were performed using Vibrational Energy Distribution Analysis (VEDA) software. Actually, the values obtained by the B3LYP/LanL2MB are in good agreement with the experimental data.Moreover, the Hirschfeld surfaces analysis which was employed to identify the different intermolecular interactions, showed that predominate interactions were H…Cl. The Thermogravimetric analysis (TGA) reveals the decomposition of the compound remains stable above 175 °C that confirms its great thermal stability. Furthermore, the optical property of the 0D hybrid Sb(III) based halide was studied with a focus on the band gap. Theoretical investigations on the electronic structure, Simulated UV–Visible spectrum, band gap, and frontier molecular orbitals (FMOs) were undertaken using density functional theory (DFT) and time-dependent DFT (TD-DFT). Therefore, our results indicate an acceptable consistency was found between calculations and experimental results leading to consistent vibrational and optical features assignments as well as the energy gap (Eg) and the chemical reactivity descriptors which are primarily linked to the ring of the organic cation and the inorganic anion.

Ultra-stretchable and highly tough ionogels with underwater repeatable adhesion and anti-swelling capacity for real-time motion detection, signal transmission and electrochemical monitoring platforms

Hydrophobic ionogels have received growing interest as a flexible underwater sensing material. However, it remains a significant challenge to improve the tensile properties, prolonged underwater repeatable adhesion, and multifunctionality of the hydrophobic ionogel due to the restricted selection of monomers and curing strategies. Herein, a hydrophobic multifunctional fluorine-rich ionogel with ultra-stretchability and superior long-term underwater repeatable adhesion is designed by virtue of the introduction of a rigid and flexible macromolecular cross-linker and a structure of rigid cationic imidazole-benzene rings in a hydrophobic ionic liquid monomer. The macromolecular cross-linker significantly improves the mechanical properties of the ionogel because of the reduction in stress concentration. And the structure of short imidazole-benzene rings with high rigidity exposes a larger amount of adhesion groups on the surface of the ionogels compared to the flexible groups, leading to enhanced long-term underwater repeatable adhesion performance of the ionogel. The ionogels are applied to real-time monitoring of exposure to water, underwater swimming motion monitoring, underwater Morse code transmission and electrochemical monitoring platforms. And this work is expected to provide ideas for the multifunctionalization of underwater sensing technology and the integration of functional units in underwater flexible electronic skin.

Dual‐Wavelength Vat Photopolymerization 3D Printing with Hybrid Acrylate‐Epoxy Resins: Influence of Resin Composition on Microstructure and Mechanical Properties

Dual‐wavelength vat photopolymerization 3D printing represents a convenient technology for the fabrication of objects with heterogeneous and locally controlled mechanical properties. By using two λ‐orthogonal cross‐linking reactions, it is possible to produce soft and stiff photopolymers with a single resin vat by switching the light source. Herein, hybrid acrylate‐epoxy resins are selectively cured by using either visible or UV light. At 405 nm, a free radical curing of the acrylate monomers is induced while irradiation with 365 nm triggers an additional cationic ring opening reaction of the epoxy monomer yielding interpenetrating photopolymer networks. In a comprehensive approach, the influence of the resin composition and the applied wavelength on cure kinetics, film morphology, (thermo)mechanical properties, and printability are studied. Fully separated as well as homogenous network morphologies are obtained depending on the ratio between acrylate and epoxy monomers, cure rate and applied light source (405 vs 365 nm). In general, glass transition temperature, stiffness, and tensile strength of the photopolymers increase with rising epoxy content. In contrast, a higher epoxy concentration in combination with a higher amount of the cationic photoinitiator compromises on the system's orthogonality, giving rise to the important role of the resin composition in dual‐wavelength vat photopolymerization 3D printing.

Molecular dynamics investigation of ionanofluids (INFs): Towards a deeper understanding of their thermophysical, structural and dynamical properties

Ionanofluids (INFs) are a novel type of heat transfer fluids consisting of fine nanoparticles suspended in ionic liquids (ILs). They exhibit improved thermal properties, including enhanced thermal conductivity, non-volatility, and non-flammability, making them ideal candidates for various applications, especially solar concentrators. In this work, for the first time, molecular dynamics (MD) simulations are used to investigate the thermophysical, structural, and dynamical properties of a specific INF composed of the [HMIM][BF4] IL and SiC nanoparticles in the temperature range of 298.15–338.15 K and at different nanoparticle volume fractions, i.e. 1.10 %, 2.27 %, and 3.47 %. Radial distribution functions (RDFs) revealed a strong structural correlation between the fluorine atoms of anion and the HR atom of the cation ring and also with the carbon and silicon atoms of the nanoparticle. The results showed that with increasing the volume fraction of nanoparticles, ions tend to have more interactions with nanoparticles, and the interactions between the anions and cations decrease. As a result, the thermal conductivity, viscosity, and density of ions in the INF increases. Finally, we made some comparisons between the simulated thermal conductivities and viscosities of the studied INF with classical models. The results showed that, in some cases, the simulation results were even better than some models compared to the experimental values. The insights obtained from this study not only enhance our understanding of the structure and dynamic behavior of the INF, but also can contribute to the development of innovative materials and more efficient solar thermal systems.

Crystal structure and Hirshfeld surface analysis of a salt of antineoplastic kinase inhibitor vandetanib.

A salt of vandetanib, namely, 4-({4-[(4-bromo-2-fluorophenyl)amino]-6-methoxyquinazolin-7-yl}methoxy)-1-methylpiperazin-1-ium 2-(butylamino)-4-phenoxy-6-sulfamoylbenzoate acetonitrile monosolvate, C22H25BrFN4O2+·C17H19N2O5S-·C2H3N, composed of kinase inhibitor vandetanib and sulfamyl diuretic bumetanide in a 1:1 molar ratio, is reported. There is proton transfer between the piperidine ring of vandetanib and the carboxyl group of bumetanide to form the salt. In the vandetanib cation, the arene and pyrimidine rings are not coplanar, their planes subtending a dihedral angle of 60.47 (14)°. The roles of the intermolecular interactions in the crystal packing were clarified using Hirshfeld surface analysis, and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H...H (40.5%), O...H/H...C (20.7%), C...H/ H...C (18.8%) and N...C/C...N (9.0%) contacts.

Spectroscopic and electrochemical characterizations of copper complexes with thionine, azure C and azure A

Structures held together by secondary interactions such as intramolecular or intermolecular hydrogen bonding, electrostatic and π–π interaction without covalent bonds can exhibit new properties such as high orientation, optoelectronics, biocompatibility and reversibility (self‐renewal). Recently, interest has been growing surrounding novel molecules fashioned through non‐covalent interactions. These molecules have garnered attention due to their significant roles in both physical and chemical applications. However, the formation of complexes between cationic phenothiazine derivative dyes, commonly employed in electrochemical studies, and diverse metal groups presents a challenge. Therefore, the existing literature contains only a scant number of studies concerning the formation of phenothiazine complexes with metal salts. In this study, metal complexes of thionine, azure C and azure A with copper(II) chloride were prepared using two steps: dissolving and then slow evaporation of dyes‐copper(II) chloride in acetonitrile. Besides the theoretical computations, thermal, spectral, electrochemical and fluorescence techniques were performed to determine the characteristics of the monoclinic crystals of Cu–dyes complexes. Cl− ion in the dyes and copper(II) chloride conjugated to form [CuCl3]−, then this anion electrostatically bound to cationic phenothiazine ring bond to be phenothiazine+[CuCl3]−. Cu–dye complexes showed interestingly high electron transportation. In addition, prepared Cu–dye complexes have a great potential to be used in optical and spectral applications with extraordinary behaviour of their spectral and fluorescence features.

Protecting group free synthesis of nitroxide-functionalized poly(2-oxazoline)s: direct access to electroactive polynitroxides.

Herein, we report the simple and direct cationic ring opening polymerization (CROP) of a nitroxide bearing 2-oxazoline monomer to yield redox-active poly[1-oxyl-2,2,6,6-tetramethylpiperidin-4-(2-oxazoline)] (PTOx) with no requirement for protecting group chemistries. The spin and redox activity of the polymer are quantitatively retained as confirmed by cyclic voltammetry and electron paramagnetic resonance spectroscopy, while yielding a comparable oxidation potential to that of PTMA in preliminary electrochemical characterization.

Amino-modified 2-oxazoline copolymers for complexation with DNA

Novel amino-functionalized 2-oxazoline-based copolymers able to form complexes with DNA were obtained. Their efficiency of DNA condensation into polyplexes of scales appropriate for effective cellular internalization was studied.

Assessing Electrocatalyst‐Ionomer Interactions: HOR/HER Activity of Pt/C Catalyst Layers incorporating Poly(imidazolium)s

AbstractIn this work, a specifically designed C2‐protected poly(imidazolium) with a limited number of freely rotating phenyl groups was synthesized and studied as a binder for a commercial Pt/C electrocatalyst. The ionomer‐electrocatalyst interactions were extensively investigated in terms of kinetic and limiting current for the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER). A non‐monotonic evolution of the electrochemically active surface area (ECSA) was observed with the increase of the ionomer‐to‐carbon ratio. The addition of ionomer to the catalyst layer leads to an increase in stability and activity of the electrocatalyst during HOR, while substantially increasing the ionomer content leads to only a marginal decrease in ECSA. Potential phenyl adsorption and cation‐hydroxide ion‐water interactions which impart deleterious impact on electrochemical activity are minimized owing to the sterically encumbered design of the polyimidazolium which (i) limits direct molecular interaction of the imidazolium cationic ring with Pt and (ii) encumbers phenyl and imidazolium ring rotation to hinder parallel aromatic ring adsorption onto the electrocatalyst surface, hence mitigating strong adsorption/blocking interactions.

Crystalline 2π Aromatic Azadiboriridinylium: ABN Analogue of Cyclopropenylium Cation.

N-Substitution of a thermally unstable diboratriazole 1 with a trimethylsilyl group affords a remarkably stable diboratriazole derivative 2. Ring contraction of 2 with an N-heterocyclic carbene accompanied by the release of N2 as well as 1,4-hydrogen shift affords a carbene-stabilized azadiboriridine 3. Abstraction of the H-B3mem hydride in 3 with methyl trifluoromethanesulfonate leads to the isolation of a hitherto unknown azadiboriridinylium 4, the first BN analogue of cyclopropenylium cation. X-ray diffraction analysis and computational studies confirmed the delocalization of π electrons over the B2N three-membered ring, indicating the 2π aromatic feature. Compound 4 undergoes ring expansion reactions with azobenzene and pyridazine to furnish triazadiborolidinylium species 5 and 6, the latter of which possesses a cationic B2N3 ring with a pronounced 6π aromatic property. Moreover, the reaction of 4 with a diazo compound produces a cationic B2N3C pentafulvene derivative 7.

Crystalline 2π Aromatic Azadiboriridinylium: A BN Analogue of Cyclopropenylium Cation

AbstractN‐Substitution of a thermally unstable diboratriazole 1 with a trimethylsilyl group affords a remarkably stable diboratriazole derivative 2. Ring contraction of 2 with an N‐heterocyclic carbene accompanied by the release of N2 as well as 1,4‐hydrogen shift affords a carbene‐stabilized azadiboriridine 3. Abstraction of the H−B3mem hydride in 3 with methyl trifluoromethanesulfonate leads to the isolation of a hitherto unknown azadiboriridinylium 4, the first BN analogue of cyclopropenylium cation. X‐ray diffraction analysis and computational studies confirmed the delocalization of π electrons over the B2N three‐membered ring, indicating the 2π aromatic feature. Compound 4 undergoes ring expansion reactions with azobenzene and pyridazine to furnish triazadiborolidinylium species 5 and 6, the latter of which possesses a cationic B2N3 ring with a pronounced 6π aromatic property. Moreover, the reaction of 4 with a diazo compound produces a cationic B2N3C pentafulvene derivative 7.

Microstructural Analysis of Benzoxazine Cationic Ring-Opening Polymerization Pathways.

Herein, an evaluation of the initial step of benzoxazine polymerization is presented by mass spectrometry, with a focus on differentiating the phenoxy and phenolic products formed by distinct pathways of the cationic ring opening polymerization (ROP) mechanism of polybenzoxazine formation. The use of infrared multiple photon dissociation (IRMPD) and ion mobility spectrometry (IMS) techniques allows for differentiation of the two pathways and provides valuable insights into the ROP mechanism. The results suggest that type I pathway is favored in the initial stages of the reaction yielding the phenoxy product, while type II product should be observed at later stages when the phenoxy product would interconvert to the most stable type II phenolic product. Overall, the findings presented here provide important information on the initial step of the benzoxazine polymerization, allowing the development of optimal polymerization conditions and represents a way to evaluate other multifunctional polymerization processes.

Enhancement of elongation at break and UV-protective properties of poly(lactic acid) film with cationic ring opening polymerized (CROP)-lignin

In this study, the intrinsic brittleness of poly(lactic acid) (PLA) was overcome by chemical modification using ethyl acetate-extracted lignin (EL) via cationic ring-opening polymerization (CROP). The CROP was conducted to promote homopolymerization under starvation of the initiator (oxyrane). This method resulted in the formation of lignin-based polyether (LPE). LPE exhibited enhanced interfacial compatibility with nonpolar and hydrophobic PLA owing to the fewer hydrophilic hydroxyl groups and a long polyether chain. In addition, because of the UV-protecting and radical-scavenging abilities of lignin, LPE/PLA exhibited multifunctional properties, resulting in improved chemical properties compared with the neat PLA film. Notably, one of the LPE/PLA films (EL_MCF) exhibited excellent elongation at break of 297.7% and toughness of 39.92MJ/m3. Furthermore, the EL_MCF film showed superior UV-protective properties of 99.52% in UVA and 88.95% in UVB ranges, both significantly higher than those of the PLA film, without sacrificing significant transparency in 515nm. In addition, the radical scavenging activity improved after adding LPE to the PLA film. These results suggest that LPEs can be used as plasticizing additives in LPE/PLA composite films, offering improved physicochemical properties.

Design, synthesis and curing mechanism of two novel photothermal dual-curing adhesives for propellants and explosives

Photothermal dual-curing adhesive is not only required to realize the basic curing function, but also has the characteristics of rapid setting and strong curing, which possesses a vital role in the molding speed, stability and structure integrity for 3D-printed propellants and explosives. Herein, the acrylate hydroxyl terminated polybutadiene, as novel photothermal dual-curing binders, were designed and synthesized utilizing cationic ring opening polymerization and active monomer mechanism as the strategy of photothermal dual-curing reaction. The mechanical properties and thermal stability of the photothermal dual-curing elastomers were systematically investigated. The results suggested that the target MAHTPB(Acrylate hydroxy‑terminated polybutadiene)-based adhesives could be cured rapidly within 5 s under UV light irradiation and completely cured in 1.5 h under heating conditions. Specifically, the elastomer film formed by MAHTPB-based photothermal dual-curing has a tensile strength of 4.63 MPa and an elongation of 386%, which exhibits stronger mechanical properties than the elastomer film formed by single photo- or thermal-curing. As a result, the synthesized photothermally cured adhesives have performed 3D printing experiments and achieved relatively satisfactory printing effects. Our study aims to solve the problems of short photocuring time, slow curing rate and incomplete curing for traditional photocuring, which lays a solid foundation to achieve rapid prototyping and precise performance control in 3D printing of propellants and explosives.

Straightforward Access To Block And Gradient Light-Responsive Poly(2-Oxazoline)S Via Cationic Ring Opening Polymerization Of 2-Azobenzenyl-2-Oxazoline.

Light-responsive polymers are a prospective area of smart materials. The increasing number of potential applications of these materials requires the development of new polymers sensitive to external irradiation. However, most of the polymers reported so far are represented by poly(meth)acrylates. In this work, we propose the straightforward approach to the synthesis of light-responsive poly(2-oxazoline)s via cationic ring-opening polymerization of 2-azobenzenyl-2-oxazoline (2-(4-(phenyldiazenyl)phenyl)-2-oxazoline). Polymerization kinetics studies revealed significant activity of the new monomer in both homopolymerization and copolymerization with 2-ethyl-2-oxazoline. The difference in monomer reactivity allows obtaining both gradient and block copolymers via simultaneous or subsequent one-pot polymerization, respectively, leading to a set of well-defined gradient and block copoly(2-oxazoline)s with 10-40% of azobenzene units. Due to their amphiphilic nature, the materials self-assemble in water, which was proven by dynamic light scattering and transmission electron microscopy. The change in polarity caused by the isomerization of azobenzene fragments in response to UV light irradiation results in a change of nanoparticle size. The obtained results provide a new impulse for the development of light-responsive materials based on poly(2-oxazoline)s. This article is protected by copyright. All rights reserved.