Imidazole Research Articles

Microneedle-Array-Mediated Transdermal Delivery of GCV-Functionalized Zeolitic Imidazolate Framework-8 Nanoparticles for KSHV Treatment

Kaposi’s sarcoma-associated herpesvirus (KSHV) is a variety of the human gamma-herpesvirus that often leads to the occurrence of malignant tumors. In addition, the occurrence of Kaposi’s sarcoma is a major cause of death among AIDS patients. Ganciclovir (GCV) is the most widely used drug against KSHV infection in the clinic. GCV can restrict the in vivo synthesis of DNA polymerase in KSHV, thereby inhibiting the replication of the herpesvirus. However, GCV still suffers from poor specificity and transmembrane capabilities, leading to many toxic side effects. Therefore, developing a drug delivery system that increases GCV concentrations in target cells remains a significant clinical challenge. In this study, zeolite imidazole salt framework-8 (ZIF-8), a biocompatible porous material constructed by coordinating zinc ions and 2-methylimidazole, was used to load GCV. A nano-delivery system with a microneedle structure was also constructed using a polydimethylsiloxane (PDMS) microneedle mold to fabricate MN/GCV@ZIF-8 arrays. These arrays not only offered good skin-piercing capabilities but also significantly inhibited the cleavage and replication of the virus in vivo, exerting an anti-KSHV function. For these reasons, the arrays were able penetrate the skin’s stratum corneum at the tumor site to deliver GCV and play an anti-KSHV role.

Dynamic proton migration in dual linkage-engineered D-π-A system for photosynthesis H2O2 generation

Accelerated charge migration and proton transfer to the reaction site are critical factors for improving photocatalytic efficiency. However, realizing both simultaneously is challenging because of the sluggish water (proton source) oxidation kinetics and interdependent redox reactions. Herein, we design an imide and hydrogen bond to connect carbon nitride ports of the D-π-A system with the dual-engineered linkages. The system uses an acetylene functional group and an imidazole ring as spatially separated water oxidation and oxygen reduction reaction (ORR) catalytic centers for photogenerated charge separation, respectively. The imine bond is a bridge grafted to the oxidation site to act as a hydrogen proton trap, and the hydrogen bond formed between reduction site and carbon nitride is used as the channel for instantaneous proton delivery to the reduction center. In situ characterization confirms that the linking sites protonation optimizes the pathway of ORR to H2O2 and facilitates the *OOH intermediates generated. It is concluded that proton transport plays a critical role in optimizing photocatalytic H2O2 production. Our work provides a strategy to improve dynamic proton transfer mechanisms.

Catalytic production of fused tetracyclic high-energy-density fuel with biomass-derived cyclopentanone and benzoquinone

High-energy-density (HED) fuels (e.g. JP-10) are of great importance in safeguarding territorial air security, since they can increase the flight range and payload of military aircrafts. To reduce the reliance on limited petroleum source, the production of HED fuel with renewable biomass feedstocks is highly appealing. But currently, most of the synthetic biofuels, due to their intrinsic ring structure, are incapable of competing with JP-10 in terms of energy density and freezing point. By emulating the structural characteristic of JP-10, we herein design and prepare a special C16 fused tetracyclic biofuel using renewable cyclopentanone and benzoquinone as feedstocks. Key to success depends on selective dehydration of vicinal diol (dimer of cyclopentanone) over Amberlyst-15 in [Hmim]Cl. The Amberlyst-15/[Hmim]Cl system effectively suppresses the dominant pinacol-type rearrangement pathway and also exhibits good reusability for the dehydration. The hydrogen-bonding interaction between vicinal diol and imidazolium ring, as well as electrostatic force between carbocation intermediate and chloride anion contribute to the high diene selectivity. The compact ring framework gives rise to a density of 0.966 g/mL, combustion heat of 43.1 MJ/L, freezing point of ‒67 °C, and kinematic viscosity of 12.4 cSt, which are comparable to the properties of JP-10. It is expected that this as-prepared HED biofuel may potentially serve as a renewable alternative to petroleum fuel JP-10.

Delayed linker addition (DLA) synthesis of dual linker ZIF-8 for separation mono- and di-branched isomers of hexane

The separation of mono- and di-branched C6 alkane isomers is one of the most challenging industrial processes for the production of high-octane gasoline components. In this work, ZIF-8 with dual ligands of imidazole (IM) and 2-methylimidazole (2-MIM), named as DLA-ZIF-8-IM, was synthesized by the method of delayed linker addition, and the microstructure of DLA-ZIF-8-IM was analyzed. Adsorption thermodynamic, kinetic and separation properties of C6 alkane isomers were investigated. The results show that compared with SALE-ZIF-8-IM prepared by the solvent-assisted ligand exchange method, the synthesis method of DLA-ZIF-8-IM is simpler and the BET specific surface area and pore volume (2136 m2·g−1 and 0.72 cm3·g−1) of DLA-ZIF-8-IM are increased by 21 % and 14 %, which is more conducive to adsorption and diffusion of 3-methylpentane (3MP) on DLA-ZIF-8-IM. The equilibrium adsorption capacity of 3MP on DLA-ZIF-8-IM reaches up to 2.89 mmol·g−1, which is 1.1 times than that on SALE-ZIF-8-IM, and the ratio of diffusion time constants between 3MP and 2,3-dimethylbutane (23DMB) on DLA-ZIF-8-IM (5.13) is 2.2 times than that on SALE-ZIF-8-IM. Moreover, at 30℃, the breakthrough adsorption capacity of 3MP on DLA-ZIF-8-IM is 1.46 mmol·g−1, which is 1.6 times more than that of SALE-ZIF-8-IM (0.90 mmol·g−1), while the breakthrough adsorption capacity of 23DMB is basically the same. The separation factor between 3MP and 23DMB on DLA-ZIF-8-IM is 2.96 via the synergy of thermodynamic and kinetic mechanism and the dynamic adsorption capacity of 3MP reaches 1.46 mmol·g−1. DLA-ZIF-8-IM achieves complete separation of C6 alkane mixtures for obtaining single high-purity product. This work provides a novel synthesis strategy for developing C6 alkane (clear) adsorption separation materials by modulating microporous structures of dual-ligand MOFs.

Thermotropic liquid crystalline and fluorescence resonance energy transfer under temperature excitation of imidazolium salt/CdTe quantum dots composites

ABSTRACT The optical characteristics and surface area of quantum dots (QDs) render them a compelling platform for the development of composite materials based on fluorescence resonance energy transfer (FRET). A novel luminescent liquid crystal nanocomposite (CBphCM-CdTe) has been successfully prepared through the ionic self-assembly route using imidazolium salt (CBphCM) and CdTe QDs. DSC and POM analyses confirm that CBphCM-CdTe undergoes the smectic A and C phases, but its liquid crystal temperature range is narrower compared to that of pure CBphCM. Concurrently, CBphCM-CdTe exhibits excellent fluorescence characteristics. Increasing temperature serves as a trigger for fluorescence resonance energy transfer between CdTe QDs and CBphCM, wherein the fluorescence of CdTe QDs is quenched, while the fluorescence intensity of CBphCM increases with rising temperature. A strong correlation exists between temperature and fluorescence intensity within the liquid crystal temperature range. Such thermochromic materials are anticipated to facilitate innovative development in dynamic thermo-optical sensing, thereby enabling enhanced control over light manipulation in stimuli-responsive devices.

Mxene-decorated spinel oxides as innovative activators of peroxymonosulfate for degradation of caffeine in WWTP effluents: Insights into mechanisms

In the frame of the environmental issues related to the efficiency of wastewaters treatment, the generation of advanced oxidation processes (AOPs) by 2D materials appears one of the most promising solutions. In this study, a novel catalytic system for peroxymonosulfate activation (PMS) was designed based on MXene (Ti3C2Tx) decorated with spinel oxides Co3O4, Fe3O4 and CoFe2O4 catalysts. Their efficiency in caffeine (CAF) degradation via PMS activation was assessed. The insertion of spinel oxides inside the multilayer structure of MXene along with their uniform surface decoration was demonstrated by SEM and TEM analyses and it also avoided the aggregation of the magnetic particles, thus increasing their efficiency. Among the different catalysts, the MXene/CoFe2O4 (MXCF) stood out as the most effective, mainly due to the Fe and Co redox cycles. The complete degradation of CAF was achieved in the dark within 10 min at natural pH using 0.2 g/L of MXCF and 0.5 mM of PMS. The novelty of current study lies in the efficient activation of PMS by, for the first time, MXCF in the dark along with mechanistic elucidation of PMS activation. The important role of Co3+/Co2+ and Fe3+/Fe2+ redox cycles alongside surface bound functional groups were highlighted. Radical scavenging and EPR experiments confirmed •OH and 1O2 as the main ROS involved in the CAF degradation. The CAF degradation pathways pointed to hydroxylation and imidazole ring opening mechanisms and MXCF catalyst also exhibited high efficiency in the degradation of sulfamethoxazole and phenol via PMS activation. To further highlight the relevance of the obtained results, treatment of tertiary effluents of wastewaters treatment plant (WWTP) in Bratislava contaminated by CAF exhibited a complete pollutant degradation after 3 h by supplying 0.2 g/L of catalyst and 2 mM PMS in the dark.

DFT-based, Monte Carlo and Grand Canonical Monte Carlo simulations of nitro-organic pollutants 4-nitrophenol, 2-nitrophenol, 9-nitroanthracene and nitrogen trifluoride interacting with water in zeolite imidazole framework (ZIF-8)

We report in this study the behaviour of adsorbed Nitrogen-volatile organic compounds (NVOCs) such as 2NP (2-Nitrophenol), 4NP (4-Nitrophenol), 9NAnt (9-Nitroanthracene), NF3 (Nitrogen trifluoride) with and without water in Zinc-Imidazolate Framework (ZIF-8) using the Density Functional Theory (DFT). The work considers both single and multiple molecular capture of different species of pollutants, along with theoretical research based on force fields to determine the maximum number of molecules that can be loaded inside the material. Negative adsorption energy is obtained when each pollutant is considered separately or in mixtures. The values range from −2.6 kJ/mol to −137.1 kJ/mol depending on the size of adsorbed species. Modelling of the adsorbed pollutants on ZIF-8 towards the use of the code CASTEP show the possible interaction with the imidazole rings of the bulk crystal. The interaction energy (Eint) indicates that the capture of 2NP and 4NP is more favourable with H2O than 9NAnt and NF3. More specifically, Eint corresponding to one water molecule with one pollutant (4NP, 2NP, 9NAnt, NF3) is −0.473, −5.580, +0.588, and +8.307 kJ/mol, respectively. The Connolly surface was calculated to gain a better understanding of the volume and surface accessibility of ZIF-8, which helps to predict and support CASTEP results. Finally, an isotherm study was conducted using a Monte Carlo simulation, which proved useful in interpreting the most probable mechanism of the competing mixed capture. The results obtained were similar to those provided by Density Functional Theory (DFT).

Methanol tolerable ultrathin proton exchange membrane fabricated via in-situ ionic self-crosslinking strategy for high-performance DMFCs

Proton exchange membranes (PEMs) with high proton conductivity, mechanical stability, and methanol barrier capability is urgently needed for direct methanol fuel cell (DMFCs). In response, a series of highly sulfonated polybenzimidazoles (SPBI) were synthesized, followed by the creation of a unique in-situ ionic self-crosslinking mechanism via acid-base pair interactions between –SO3- and protonated N within the imidazolium rings of SPBI in an acidic milieu. The in-situ ionic self-crosslinking not only significantly enhances the mechanical stability of the prepared membrane, but also constructs a microstructure with a free volume radius smaller than the molecular dimensions of methanol, subsequently imparting unparalleled resistance to methanol permeation. After being reduced to an ultrathin thickness of 15 μm, the optimal SPBI-SO3H-200 % membrane obtains remarkable high specific proton conductivity of 33.48 S cm−2. Furthermore, the assembled DMFC demonstrates an exceptionally low methanol crossover current density of 188.25 mA/cm2 alongside high power density of 109.92 mW cm−2 within 2 M methanol fuel, significantly outperforming the methanol crossover current density of 386.06 mA/cm2 and power density of 87.13 mW cm−2 achieved by a single cell assembled with Nafion 115 membrane.

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

AbstractMesoionic 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‐raydiffraction 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.

DFT Study on the His-Tag Binding Affinity of Metal Ions in Modeled Hexacationic Metal Complexes.

Histidine oligomers (His-tags) are commonly used as affinity tags in recombinant protein purification to enable in vitro experimental studies, including biochemical and biophysical assays and structure determination. His-tags enable protein purification by specifically and efficiently coordinating bivalent metal ions present in the purification resins, such as Cu2+, Zn2+, and Ni2+. Although His-tags, combined with Ni2+-based resins, are widely used due to their biophysical properties and commercial availability, the structure and nature of the metal cation coordination have remained unclear. In this study, the chemical structure of metal-coordinating His-tags was modeled to elucidate the metal preferences for better binding and to determine the structural changes that occur upon metal coordination. 6His-tag is a string of 6 histidine residues usually coordinated to bivalent metal ions (M2+), such as Ni2+, Zn2+, and Cu2+, through the nitrogen atoms of the imidazole rings. The metals complete their octahedral coordination shell with the lone pair of electrons of the oxygen atoms of the resin to which they are attached to. The resin was modeled as an oxalaldehyde group with the closed formula of (OCH)4. The geometry optimizations were carried out using the DFT method at the B3LYP/6-31g (d, p) level and in implicit water using the IEFPCM solvent model. The impact of Ni2+, Zn2+, and Cu2+ metals on the resin binding ability of 6His-tags was tested by adding amino acids to the N-terminus of metal-coordinated hexahistidine chains. The activity of the metals as electron donors or acceptors to the coordination bonds that they form was estimated by calculating the NBO energies. The complexation enthalpies of metal-bearing resin with hexahistidine, naked or having an amino acid tail, were calculated. Our results showed that Ni2+ has the highest affinity for the recombinant 6His-tag.

Formation of amino acid–based imidazole salts considerably increased the determined level of fluorescent advanced glycation end products in biscuits

Glycine, serine, and γ-aminobutyric acid are effective scavengers of reactive carbonyl species and should inhibit the formation of advanced glycation end products (AGEs). However, here we found that amino acids unexpectedly increased the intensity of fluorescent AGEs in biscuits. This study aimed to elucidate these contradictory findings and highlight concerns regarding the determination of fluorescent AGEs in foods. In gliadin-methylglyoxal (MGO) glycation model, amino acids were found to induce formaldehyde formation from MGO. Thereafter, formaldehyde and MGO reacted with the amino acids to generate imidazole salts. The imidazole salts exhibited broad fluorescence range, overlapping with the fluorescence range used to determine fluorescent AGEs in foods, thus resulting in an apparent increase in fluorescent AGEs content after amino acid addition. Since amino acids are ubiquitous in food materials, the formation of imidazole salts during food processing may result in an overestimation of fluorescent AGEs in foods.

Eutectic binary phase diagram and kinetically stable homogeneous co-amorphous mixtures of two imidazole drugs

Amorphous multicomponent formulations allow improving the solubility and thus the bioavailability of active pharmaceutical ingredients (APIs) that are poorly soluble in water, provided that the molecular mobility in such formulations does not promote crystallization in the amorphous (glassy) state during their shelf life. Multicomponent formulations may involve a single API mixed with excipients, but also two mutually compatible APIs. Here, we describe kinetically stable amorphous binary mixtures of two commercial antifungal imidazole APIs, bifonazole and clotrimazole, which have similar melting points and glass transition temperatures. The equilibrium phase diagram of this binary system, as determined by differential scanning calorimetry, follows the Schroeder-van Laar-LeChatelier predictions, as typically found for compounds that are miscible as liquids but immiscible in the crystalline form, and is characterized by an experimental eutectic composition close to equimolar composition (xbifonazole = 0.45) and eutectic melting point Te = 392 K. The glass transition temperature Tg varies linearly with composition, as found in ideal liquid mixtures. Dielectric spectroscopy characterization is carried out to investigate the relaxation dynamics of each amorphous API separately, and of the amorphous mixtures (both in the supercooled liquid and glass state). A single structural α relaxation is observed in all supercooled liquid mixtures, confirming their homogeneity. Both pure amorphous APIs display conformational secondary relaxations: the one of bifonazole stems from the torsional rotation of the imidazole ring; the one of clotrimazole is significantly slower than that of bifonazole, and is related to small-angle librations of the imidazole and chlorobenzene rings. Conformational relaxation processes are observed also in binary mixtures, which display also a Johari-Goldstein relaxation as pure clotrimazole. Despite the presence of both primary and secondary relaxations, the binary mixtures are observed to remain amorphous for at least twelve months both at Tg and slightly above it.

Imidazolium-based ionic liquids as proton reservoir for stable polyaniline cathode in zinc-iodine batteries

Aqueous zinc (Zn)-iodine (I2) batteries (ZIBs) are promising large-scale energy storage systems with high safety and low cost. However, the practical application of ZIBs is hindered by the dissolution of I3- ions, which leads to the shuttle effect and the loss of active iodine. Herein, we adopt an electrolyte modification strategy using two imidazolium-based ionic liquids (1-butyl-3-methylimidazolium iodide ([BMIM]I) and 1-ethyl-3-methylimidazolium iodide ([EMIM]I)) as electrolyte additives to restrain the dissolution of I3- ions and enhance the performance of ZIBs. To be specific, the imidazole rings in [BMIM]+ and [EMIM]+ can be used as the proton sources, promoting the conversion of imine to protonated amines –NH+= in the polyaniline and subsequent adsorption of I3- ions. Therefore, the dissolution of I3- ions and shuttle effect are prevented, facilitating the reaction kinetics of cathode. As a proof of concept, the ZIB using [BMIM]I and [EMIM]I as electrolyte additives demonstrates remarkable cycling performance (72.2 % capacity retention after 1000 cycles) at a high current density of 20 mA cm−2

4-Halomethyl-Substituted Imidazolium Salts: A Versatile Platform for the Synthesis of Functionalized NHC Precursors.

N,N'-Diarylimidazolium salts containing haloalkyl functional groups that are reactive with various nucleophiles are considered to be promising reagents for the preparation of functionalized N-heterocyclic carbene (NHC) ligands, which are in demand in catalysis, materials science, and biomedical research. Recently, 4-chloromethyl-functionalized N,N'-diarylimidazolium salts became readily available via the condensation of N,N'-diaryl-2-methyl-1,4-diaza-1,3-butadienes with ethyl orthoformate and Me3SiCl, but these compounds were found to have insufficient reactivity in reactions with many nucleophiles. These chloromethyl salts were studied as precursors in the synthesis of bromo- and iodomethyl-functionalized imidazolium salts by halide anion exchange. The 4-ICH2-functionalized products were found to be unstable, whereas a series of novel 4-bromomethyl functionalized N,N'-diarylimidazolium salts were obtained in good yields. These bromomethyl-functionalized imidazolium salts were found to be significantly more reactive towards various N, O and S nucleophiles than the chloromethyl counterparts and enabled the preparation of previously inaccessible heteroatom-functionalized imidazolium salts, some of which were successfully used as NHC proligands in the preparation of Pd/NHC and Au/NHC complexes.

MOF-derived strategy for in-situ assembly of nickel phyllosilicate nanoflowers: Enhancing smoke suppression, flame retardancy and mechanical properties of epoxy resins

Epoxy resin (EP) is a highly versatile polymer extensively used in high-end applications, including aerospace components, electronics encapsulation and adhesives. To custom-design flame retardant materials for high-performance epoxy resins, a MOF-derived zeolitic imidazolate framework-8@nickel phyllosilicate (ZIF@Ni-PS) was synthesized through the in-situ assembly of nickel phyllosilicate nanoflowers. The results showed that the smoke suppression, flame retardancy, and mechanical properties of the EP composites containing 5 wt% ZIF@Ni-PS were significantly enhanced. The peak heat release rate (pHRR) and the peak smoke production rate (pSPR) were reduced by 33.2 % and 12.7 %, respectively. The presence of ZIF@Ni-PS promoted the formation of a dense, high-quality carbon layer that isolated heat and oxygen transfer, effectively reducing heat release during combustion and suppressing smoke generation. Furthermore, the imidazole ring and Zn ions on the surface of ZIF@Ni-PS facilitated the formation of coordination and hydrogen bonds with the epoxy (EP), thereby enhancing the dispersion, compatibility, and mechanical properties of the epoxy resin matrix. This study presents a straightforward preparation method for high-performance EP composites, providing a novel pathway for EP research.

Chitosan modified with an ionic liquid with two imidazolium rings for efficient removal of reactive black 5

Chitosan modified with an ionic liquid with two imidazolium rings for efficient removal of reactive black 5

Theoretical exploration of energetic molecular design strategy: functionalization of C or N and structural selection of imidazole or pyrazole.

In researching energetic materials with high energy density, it is an effective method to introduce explosophoric groups. In this study, four series of energetic compounds were designed by functionalizing with C- or N-, introducing energetic groups -CH(NO2)2, -CF(NO2)2, -C(NO2)2(NF2), -C(NO2)3, and-CH(NF2)2 into imidazole and pyrazole structures. Density functional theory was employed to optimize the structure of the target compound and subsequently to predict and evaluate its performance based on this. Meanwhile, the sensitivity of the compounds was predicted based on their electrostatic potential analysis. Following analysis of the geometric structure, detonation performance, and sensitivity of the compounds, three factors were discussed: energetic groups, functionalization methods, and skeleton structure differences. The results indicate that C-functionalization has advantages only in density, but N-functionalization is better in thermal stability, heat of formation, and sensitivity. Meanwhile, the data shows that imidazole-based compounds exhibited greater density and detonation performance in the target compounds designed within this study, while pyrazoles have a higher heat of formation and chemical stability. By analyzing the design strategy of C- or N-functionalization of novel high-energy groups on energetic imidazole or pyrazole rings and selecting a more suitable molecular construction strategy, this study provides a theoretical approach for the development of new energetic materials with excellent performance. Gaussian 09 and Multiwfn 3.8 packages are the software used for calculation, and the electrostatic potentials were depicted using the VMD program. In this study, the imidazole and pyrazole derivatives were optimized at the B3PW91/6-311G (d, p) level to acquire the relevant data for the compounds.

Charge reversible hyaluronic acid-based drug delivery system with pH-responsive dissociation for enhanced drug delivery

Improving the efficiency of drug delivery is one of the most important goals in the field of drug delivery. One strategy for drug delivery efficiency is to make the drug delivery system capable of charge reversal. In this study, we used hyaluronic acid (HA) as the skeleton to anchor dimethylmaleic anhydride-modified polylysine (PLL-DMMA) and N-(3-Aminopropyl)-imidazole (IMI) to construct a pH-sensitive (IMI/Zn2+)-HA-PLL-DMMA system via Zn coordination. The (IMI/Zn2+)-HA-PLL-DMMA system can detach DMMA moieties and expose PLL with a positive charge in the acidic tumor microenvironment (TME), which enhances cellular uptake in cancer cells through charge reversal. Once the drug-loaded (IMI/Zn2+)-HA-PLL-DMMA enters cancer cells, it specifically responds and disassembles in the acidic TME, resulting in drug release and inhibition of cancer cell viability. The (IMI/Zn2+)-HA-PLL-DMMA system is designed to regulate drug release behavior with Zn2+ and IMI groups as control units. The HA-based system shows synergistic selective drug delivery in suppressing tumor cells and has potential in cancer therapy.

Anionic N-Heterocyclic Carbenes from Mesoionic Imidazolium-4-pyrrolides: The Influence of Substituents, Solvents, and Charge on their 77Se NMR Chemical Shifts.

Mesoionic compounds are the starting material for the synthesis of unique anionic N-heterocyclic carbenes. Herein, mesoionic imidazolium pyrrolides synthesized from pyrrole-2-carbaldehyde via various N-alkyl-4-pyrroyl-imidazoles are described. These were converted into nine new 4-(pyrrol-2-yl)-substituted imidazolium salts and transformed into the mesoionic title compounds using an anion exchange resin. The DFT-calculated (B3LYP/6-311++G**) CREF values indicate a great potential for the formation of anionic N-heterocyclic carbenes by deprotonation, which were generated and reacted with selenium to obtain selenoureas. The 77Se NMR shifts investigated under systematic variation of conditions are dependent on the substitution pattern (ΔδSe = 133 ppm) and the steric demand of the substituents. Solvent dependencies of the 77Se NMR shifts were investigated applying toluene-d8, THF-d8, CDCl3, CD2Cl2, pyridine-d5, acetone-d6, DMSO-d6, CD3CN, AcOD, and MeOD. The influences of the referencing method on the 77Se shifts using external or internal Me2Se or Ph2Se2 and solvent can add up to ΔδSe = ca. 80 ppm. In addition, we observed a temperature dependence of both the selenoureas and the reference reagent Ph2Se2 as well as a 77Se shift difference of the analyte caused by interaction with internally added Ph2Se2. The negative charge of deprotonated selenoureas shifts the values by an additional -20 ppm.

The infrared spectrum of the protic ionic liquid 1-methylimidazolium nitrate: An ab initio molecular dynamics simulation study

Complex features observed in the infrared (IR) spectrum of the protic ionic liquid 1-methylimidazolium nitrate, [C1im][NO3], are assigned using ab initio molecular dynamics (AIMD) simulation. AIMD is used at the same level of theory to simulate the known X-ray crystal structure of [C1im][NO3] and a cluster of ionic pairs representing the liquid phase. The calculation of several single particle and collective time correlation functions of velocity forms the basis for the AIMD simulation assignment of the infrared spectra. The AIMD simulation demonstrates that the lift of the degeneracy of the anion asymmetric stretching mode, νas(NO3), due to symmetry breaking and coupling to external modes result in multiple band splitting in the crystal spectrum in the region of the νas(NO3) mode. Owing of the intrinsic anharmonic characteristic of the AIMD simulation, the calculation accounts for the broad band in the high-frequency range of the IR spectrum caused by the cation ν(NH) stretching mode in strong cation–anion hydrogen bond. The AIMD simulation of the liquid captures spectral changes upon melting of [C1im][NO3] due to loosening of the NH···O hydrogen bond and changes in the [NO3]- interaction with other hydrogen atoms of the imidazolium ring. The AIMD simulation assigns the intermolecular stretching mode of the hydrogen bond, ν(NH…O), as the band at 183 cm−1 in the far infrared spectrum of the [C1im][NO3] crystal.