1H NMR Chemical Shifts Research Articles

Spectroscopic (FT-IR, NMR, single crystal XRD) and DFT studies including FMO, Mulliken charges, and Hirshfeld surface analysis, molecular docking and ADME analyses of 2-amino-4′-fluorobenzophenone (FAB)

In this work, synthesis, and crystal structure of molecule 2-amino-4′-fluorobenzophenone (FAB) is confirmed by using FT-IR, FT-Raman, 1H and 13C NMR chemical shifts, compared with calculated parameters using B3LYP/ 6-311+G(d) basis sets in water were found in good agreement. The optimized geometry of the molecule (FAB) was compared to the experimental XRD values. DFT calculations of the molecular electrostatic potential (MEP), frontier molecular orbitals (FMO), Hirshfeld surface analysis, Mulliken charges recognize the chemically active sites of this molecule responsible for its chemical reactivity. In silico molecular docking analyses of molecule (FAB) have been done with vascular endothelial growth factor receptor 2 (VEGFR2) kinase inhibitors. Further, the bioavailability of molecule (FAB) was investigated by ADME and p450 analyses.

Investigation of Barrier Potential, Structure (Monomer & Dimer), Chemical Reactivity, NLO, MEP, and NPA Analysis of Pyrrole-2- Carboxaldehyde Using Quantum Chemical Calculations

In this work, the structural conformation of pyrrole-2-carboxaldehyde was evaluated using potential energy surface (PES) scan employing DFT computations using B3LYP method with 6-311++G(d,p) level of basis set. The molecule assumed cis form in conformational ground state being more stable than the trans by 15.21 kJ mol−1 due to the orientation of the N–C–C = O dihedral angle. Existence of hydrogen bonds due to intra- and inter-molecular interactions was envisaged. The geometrical parameters of optimized monomeric and dimeric forms have been computed. The computational structural parameters of monomer are in good agreement with its experimental counterparts. The HOMO-LUMO energies were employed for determination of chemical reactivity descriptors. The electronic properties such as frontier molecular orbitals and Global reactivity descriptors were predicted using TD-DFT method. The local reactivity descriptors such as Fukui functions were investigated to determine the electrophilic and nucleophilic attacks within the molecule. The calculated first order hyperpolarizability value exhibited its suitability for non-linear optical applications. Furthermore, the electrophilic and nucleophilic regions of the molecule were studied by molecular electrostatic potential and Fukui functions. 1H and 13C NMR chemical shifts were evaluated using GIAO method employing the same level of theory. NPA analysis and thermodynamic parameters were also calculated.

Undescribed diphenyl ethers betaethrins A-I from a desert plant endophytic strain of the fungus Phoma betae A.B. Frank (Didymellaceae)

Ten diphenyl ethers (DPEs), including nine undescribed analogs named betaethrins A-I, were isolated from the desert plant endophytic fungus Phoma betae A.B. Frank (Didymellaceae). Their structures were determined mainly by NMR, HR-ESI-MS spectral and X-ray diffraction experiments. Betaethrins D-I possessed different fatty acid chains connected with the B-ring, which was the first report in all DPEs. The shielding effect of the B-ring on H-6 (A-ring) in methyl barceloneate, betaethrin A and betaethrins D-F (asterric acid analogs) was first observed and analyzed, which could differentiate the 1H-NMR chemical shift values of H-4/H-6 without the assistance of 3-OH. An empirical rule was then suggested: the steric hindrance between the A- and B-rings in asterric acid analogs might prevent these two aromatic rings from rotating freely, which led to the 1H-NMR chemical shift value of H-6 being in the high field zone due to the shielding effect of the B-ring on H-6. Based on the empirical rule, the chemical shift values of the A-ring in methyl barceloneate were revised. The possible biosynthesis of these isolates was postulated. Betaethrin H showed moderate cytotoxicity against MCF-7 and HepG2 cancer cell lines. Betaethrins A-F, H and I displayed strong antioxidant activities. These results further implied that endophytic fungi from unique environments, such as desert plants, with few chemical studies are an important resource of undescribed and bioactive metabolites.

Comparison of Computational and Previous Experimental Studies on Naphthyl Pyridyl Pyrazole (NPP)

The naphthyl pyridyl pyrazole (NPP) was the subject of a theoretical inquiry. The data determined through the calculations were supported by experimental results from 1HNMR and X-Ray techniques. Geometrical parameters and optimized energies for the NPP molecule were determined via density functional theory (DFT) at the B3LYP 6-311++G (d, p) level of theory. The vibrational spectra were obtained and the fundamental vibrations were assigned. 1HNMR chemical shifts were recorded by using the gauge-invariant atomic orbital (GIAO) method. Further, electronic properties such as HOMO and LUMO energies were determined via time-dependent density functional theory (TD-DFT). The results of the calculations were found to be comparable to the experimental results obtained.

Synthesis, characterization, vibrational analysis and computational studies of a new Schiff base from pentafluoro benzaldehyde and sulfanilamide

This work presents the characterization of (E)-4-(((perfluorophenyl)methylene)amino)benzenesulfonamide (PFNI) by spectral techniques and quantum chemical calculations. The structure was investigated by FT-IR, UV–Vis and NMR techniques. The geometrical parameters and energies have been obtained from Density functional theory (DFT) B3LYP (cc-pVDZ) basis set calculation. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned on the basis of potential energy distribution (PED) of the vibrational modes, calculated with VEDA program. 1H and 13C NMR chemical shifts of the molecule were calculated using Gauge-independent atomic orbital method (GIAO). The electronic properties such as excitation energies, wavelength performed by Time dependent density functional theory (TD-DFT) results complements with the experimental findings. NBO analysis has been performed for analyzing charge delocalization throughout the molecule. The calculation results were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. To provide information about the interactions between staphylococcus aureus (4EMW) protein and the novel compound theoretically, docking studies were carried out using autodock-4.

Stable bidentate silylene adducts of alkaline‐earth amides

AbstractThe coordination chemistry of silylenes is known for a vast number of elements of all blocks of the periodic table. However, only a handful of examples of silylene complexes have been reported for heavy alkaline‐earth elements, which is mainly attributed to the “hard‐soft” mismatch between the “hard” metal center and the “soft” silicon donor. Herein, we report the synthesis and characterization of a series of alkaline‐earth silylene complexes comprising a bidentate pyridyl‐amido‐silylene ligand. The isolated Ca, Sr and Ba complexes show considerably increased stability in comparison to other known alkaline‐earth silylene complexes. The molecular structures of all three complexes are essentially similar. Interestingly, depending on the central metal, the 1H NMR chemical shifts of the ortho‐H atom show unexpected large differences. DFT computations were conducted to elucidate this trend in the NMR resonances.

Synthesis, single crystal structure, DNA binding and antioxidant properties of 5-(4-(dimethylamino)phenyl)-3-(thiophen-2-yl)-pyrazoline-1-carbothioamide

Compound 3c (5-(4-(dimethylamino)phenyl)-3-(thiophen-2-yl)-pyrazoline-1-carbothioamide) was synthesized and characterized experimentally using UV-Vis, FT-IR, ESI-MS and NMR (1H and 13C) analysis. The compound shows strong antioxidant activity with IC50 value of 0.632±0.002 μg/mL. The compound crystallizes as a monoclinic system, P21/c centro-symmetric space group, Z = 8 and size of the corresponding unit cell: a = 11.7134(10) Å, b = 17.3334(15) Å, c = 16.9831(14) Å, α = 90˚, β = 108.038(2)˚, γ = 90˚. DNA binding measurements (UV-vis., fluorescence, cyclic voltammetry and competitive assay using ethidium bromide) of compounds showed intercalative mode of interaction. The binding constant (Kb), Gibbs free energy (ΔG) of compound 3c were found to be 1.3×105 M−1 and ‒67.17 KJmol−1, respectively. The calculated Ksv values at two different temperatures (298 and 303 K) are 3.02×103 and 2.16×103 M−1 respectively. To optimize molecular structure and compute wavenumbers of normal vibrational modes, B3LYP method and 6-311 ++ G (d, p) basis set were used. Hirshfeld surface analysis provides a thorough illustration of the intermolecular interactions on crystal surface, and fingerprint plots were discovered. Experimental bond lengths and bond angles corroborated well with the computational parameters. The GIAO approach was used to estimate 1H-NMR and 13C-NMR chemical shifts, and compared to experimental spectra. Electronic properties such as UV-Vis (in gas phase, ethanol and DMSO) were analyzed using TD-DFT method and the PCM solvent model, and results were compared to experimental UV-Vis spectra.

Synthesis, spectroscopic (13C/1H-NMR, FT-IR) investigations, quantum chemical modelling (FMO, MEP, NBO analysis), and antioxidant activity of the bis-benzimidazole molecule

In the current study, we first synthesized the molecule 1,2-Bis(2-benzimidazolyl)-1,2-ethanediol, called C1. The structural properties of C1 were explored by spectroscopic investigation (FT-IR and NMR (1H and 13C)) and computational study using density functional theory (DFT) calculation at B3LYP functional and 6-311++G(d,p) basis set in the gaseous phase and DMSO solvent for the first time. The results of the theoretical calculations were compared with experimental studies and the analysis of the results of optimized parameters of molecular geometry, infrared vibrational frequencies, and 1H and 13C NMR chemical shifts for the structure of the main molecule by B3LYP/6-311++G(d,p) in the gas phase revealed mutual agreement between the experimental and computational data. Furthermore, global reactivity properties, frontier molecular orbitals (FMOs) analysis, molecular electrostatic potential (MEP), and natural bond orbital (NBO) characteristics were evaluated to specify the reactivity properties of the title compound using the same level. The antioxidant activity of the studied compound was also investigated by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, and the results revealed that it has good inhibition of 42.9% at the concentration of 1 mg/mL which can give an idea about the biological activity of the molecule C1.

Synthesis and computational studies on a coumarin derivative: 4-chloromethyl coumarin-7-yl-methacrylate

In this article, we report the synthesis, X-ray structure determination, geometric parameters, vibrational frequencies, NMR, and UV spectra of a coumarin derivative titled 4-chloromethyl coumarin-7-yl-methacrylate (CCMA). In the study, the theoretical vibrational frequencies, NMR and UV spectra, and optimized geometric parameters were computed by using density functional theory with the hybrid methods B3LYP/6-31+G(d,p) basis set. The optimized geometric parameters, vibrational frequencies, and 1H and 13C NMR chemical shifts values were contrasted with experimental values of the title molecule. The theoretical vibrational frequencies were found in concordance with the matching experimental data. The electronic properties of the molecule were studied using the molecular frontier orbital energies, ESP surfaces, the natural bond orbital (NBO), and nonlinear optical (NLO) properties. The study findings show that the molecule has nucleophilic regions around O atoms and the transition from the ground state to the first excited state with the electronic absorption peaks at 318.19 nm in gas. In this study, the remarkable electron delocalization occurred between the donor (C4-C5) anti bond and acceptor (C6-C9) anti bond with 249.60 kcal/mol stabilization energy in the title molecule. Calculated NLO parameters show that CCMA can be used as the NLO material.

Complete 1H and 13C NMR chemical shift assignments of mono-to tetrasaccharides as basis for NMR chemical shift predictions of oligo- and polysaccharides using the computer program CASPER

Carbohydrate structure can be elucidated or confirmed by using NMR spectroscopy as the prime technique. Prediction of 1H and 13C NMR chemical shifts by computational approaches makes this assignment process more efficient and the program CASPER can perform this task rapidly. It does so by relying on chemical shift data of mono-, di-, and trisaccharides. In order to improve accuracy and quality of these predictions we have assigned 1H and 13C NMR chemical shifts of 30 monosaccharides, 17 disaccharides, 10 trisaccharides and one tetrasaccharide; in total 58 compounds. Due to different rotamers, ring forms, α- and β-anomeric forms and pD conditions this resulted in 74 1H and 13C NMR chemical shift data sets, all of which were refined using total line-shape analysis for the 1H resonances in order to obtain accurate chemical shifts. Subsequent NMR chemical shift predictions for three sialic acid-containing oligosaccharides, viz., GD1a, a disialyl-LNnT hexasaccharide and a polysialic acid-lactose decasaccharide, and NMR-based structural elucidations of two O-antigen polysaccharides from E. coli O174 were performed by the CASPER program (http://www.casper.organ.su.se/casper/) resulting in very good to excellent agreement between experimental and predicted data thereby demonstrating its utility for carbohydrate compounds that have been chemically or enzymatically synthesized, structurally modified or isolated from nature.

Barrier Potential, Structure (Monomer and Dimer), Inter- and Intra-Molecular Interactions, Vibrational Analysis, Fukui Functions, MESP, NBO, UV and NMR Analysis of Pyridine-3-Carboxylic Acid Using Spectroscopic and DFT Approach

Pyridine-3-carboxylic (or nicotinic) (P3CA) acid has been recorded by using different spectroscopic tools like NMR (13C, 1H), UV–Vis, FT-IR and FT-Raman spectral analysis. The structural conformation examined by potential energy scan for the titled compound was obtained by using DFT computations through B3LYP method with 6–311++G(d,p) basis set. Using optimized monomer structure, the dimeric structures (head-to-tail and tail-to-tail) are obtained. The title compound exhibits inter-molecular as well as intra-molecular hydrogen bonding forming a supramolecular network. The geometrical parameters of both monomer and dimer are coinciding with the observed ones. Using vibrational frequencies, Infrared and Raman intensities were computed. The rms error between the experimental and scaled quantum mechanical frequencies is 9.77 cm−1 for P3CA. From the scaled quantum mechanical method, reliable vibrational assignments were made using PED. The site of chemical reactivity and selectivity of the title compound were estimated from frontier molecular orbitals and local reactivity descriptors. The reactive areas around the compound were evaluated by using MESP. The interactions of donor and acceptor are studied by NBO analysis. The 13C and 1H NMR chemical shifts of the title compound were determined using the gauge independent atomic orbital (GIAO) method in DMSO-d6 solution. By using UV–visible spectrum, the maximum absorption wavelength was obtained and compared with the TD-DFT method.

Spectroscopic analysis, DFT studies and molecular docking of 2,3‐dichloro‐benzylidine‐(2‐trifluoromethyl‐phenol)‐amine

Abstract2,3‐dichloro‐benzylidine‐(2‐trifluoromethyl‐phenol)‐amine (2DBTP) has been synthesized and characterized by various spectroscopic techniques including FT‐IR, FT‐Raman, UV‐Vis and 1H, 13C NMR spectroscopy. The equilibrium geometry and harmonic vibrational frequencies were investigated by density functional theory (DFT) at B3LYP/6‐311++G(d,p) basis set. The vibrational wavenumber assignments were made on the basis of total energy distribution (TED) calculations using Veda 4 program. The harmonic wavenumbers calculated at DFT were in line with the experimental values. The non‐linear optical properties (NLO) were calculated. Stability of the molecule arises from hyperconjugative interactions and charge delocalization was analyzed by natural bond orbital (NBO) analysis. Molecular electrostatic potential (MEP), mulliken atomic charges were also calculated. The energy gap of the molecule was found by HOMO and LUMO calculation. TD‐DFT calculations have been carried out on the optimized geometry to further understand the electronic transitions in the UV‐Vis spectrum of the compound. In addition, the 1H and 13C NMR chemical shift values of 2DBTP in the ground state were also calculated using Gauge invariant atomic orbital (GIAO) method. The molecular docking solved the binding mode of 2XCT complex with the ligand. The investigated molecule revealed the inhibition activity of the ligand against anti‐bacterial protein topoisomerase DNA gyrase enzyme (PDB ID: 2XCT).

Synthesis, spectroscopic characterization (FT-IR, NMR, UV-Vis), DFT study, antibacterial and antioxidant in vitro investigations of 4,6-bis((E)-1-((3-(1H-imidazol-1-yl)propyl)imino)ethyl)benzene-1,3-diol

A new bis-Schiff base derived from N-(3-Aminopropyl)imidazole and 4, 6-diacetylresorcinol was obtained. The bis Schiff base RS was characterized through mass spectrometry, elemental analysis, infrared, UV-Vis, 1H and 13C NMR spectroscopy. The B3LYP method was used to calculate the optimized structure of the molecule through density functional of theory (DFT) using the 6-31G (d, p) basis set. The 1H and 13C NMR chemical shifts with respect to TMS were calculated using the (GIAO) method in DMSO‑d6 and compared with the experimental data. In addition, the frontier molecular orbitals, electronic properties and the molecular electrostatic potential (MEP) of RS were investigated using DFT calculations. The compound showed significant antibacterial activity against Staphylococcus aureus. The DPPH free radical scavenging assay was used to evaluate the antioxidant activity. The effective concentration (EC50) showed that the compound has a good antioxidant activity.

Synthesis, spectral, structural and antimicrobial activities of Ethyl-4-｛[-(1-(2-(4-nitrobenzoyl)hydrazono)ethyl]｝-3,5-dimethyl-1H-pyrrole-2-carboxylate

A new ethyl-4-{[-(1-(2-(4-nitrobenzoyl)hydrazono)ethyl]}-3,5-dimethyl-1H-pyrrole-2-carboxylate (ENBHEDPC) has been synthesized, characterized (FT-IR, 1H and 13C NMR, UV-Visible, DART-Mass spectroscopy, elemental analysis) and evaluated for antituberculosis and antibacterial activity. Quantum chemical calculations have been performed by DFT level of theory using the B3LYP functional and 6–311++G(d,p) as basis set. The 1H and 13C NMR chemical shifts and electronic transitions are calculated using gage including atomic orbitals (GIAO) and time dependent density functional theory (TD-DFT) approach in DMSO as solvent. Combined theoretical and experimental wavenumber analyses confirm the existence of dimer. Hydrogen bonding and other multiple interactions have been analyzed by Bader's ‘Atoms in molecules’ AIM theory in detail. The intermolecular hydrogen bond energy of dimer is calculated as -12.28 kcal/mol. The calculated thermodynamic parameters show that reaction is exothermic and non-spontaneous at room temperature. The local reactivity descriptors analyses determine the reactive sites within molecule by nucleophilic attack. Nonlinear optical (NLO) behavior of title compound is investigated by the computed value of the first hyperpolarizability (β0). The synthesized compound show good antimicrobial and antituberculosis activity.

“Effect of water and ions on the rheological behavior of a low viscosity ammonium-based ionic liquid”

The protic ionic liquid trihexylammonium octanoate, [T6AC7COO], was used to extract copper(II), cobalt(II) and nickel(II) ions from aqueous metal nitrate solutions, in presence or absence of SCN− ions. The ionic liquid and the organic phases were characterized by 1H NMR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and rheological experiments. The analysis of 1H NMR chemical shifts of the organic phases shows an up-field shift of the proton of the +NH group of the cation of the ionic liquid, attributable to the existence of hydrogen bonding between this proton and water. The presence of water in the ionic liquid phase increases its viscosity, despite water reduces the interactions between cation and anion of the ionic liquid. This unusual enhancement in viscosity can be associated to the change in its heterogeneous structural organization, as strong interactions between the anion of the ionic liquid and molecules of water. The presence of SCN− anions in the extracted phase increases even more the viscosity of the ionic liquid. This increment can be associated to the interactions between SCN− anions with molecules of water via hydrogen bonding. The rheological measurements in steady state shear show that the ionic liquid and the organic phases exhibit a Newtonian behavior over the range examined, however, the results of the dynamic oscillatory shear experiments show that all the samples exhibit a viscoelastic characteristic, and at low frequencies can be described by the Maxwell model with a single stress relaxation.

Structural elucidation of a novel pyrrolizidine alkaloid isolated from Crotalaria retusa L.

A novel pyrrolizidine alkaloid was isolated and purified from the aerial parts of Crotalaria retusa L. Structural elucidation of the alkaloid was established by analyses of high field NMR spectra and quantum mechanical calculations. The 1H and 13C NMR chemical shifts for eight candidate structures were calculated and compared with the experimental NMR data applying the corrected mean absolute error (CMAE) and the statistical probability methodology (DP4). The interpretation of the experimental NMR spectra and CMAE and DP4 analyses established that the novel pyrrolizidine alkaloid is (3S*,4R*,5S*,8a1R*,13aR*)-3-hydroxy-3,4,5-trimethyl-4,5,8,8a1,10,12,13,13a-octahydro-2H- [1,6]dioxacycloundecino [2,3,4 gh]pyrrolizine-2,6(3H)-dione.

Vibrational Spectroscopic Investigations, Electronic Properties, Molecular Structure and Quantum Mechanical Study of an Antifolate Drug: Pyrimethamine

The computational modelling supported by experimental results can explain the molecular structure, vibrational assignments, reactive sites and several structural properties. In this context, the spectroscopic (FT-IR, FT-Raman and NMR) analysis, electronic properties (HOMO and LUMO energies) and molecular structure of pyrimethamine (Pyr) were investigated by density functional theory (DFT) method associated with three levels of theory viz., B3LYP, MN15 and wB97XD with 6-311++G(d,p) and def2TZVPP as basis sets, respectively in the Gaussian 16 programs. The 1H and 13C NMR chemical shifts were calculated with a gauge-independent atomic orbital (GIAO) approach by also applying the same levels of theory and basis sets. All experimental results were compared with theoretical data. Although the results revealed high degrees of correlation between the theoretical and experimental values for spectroscopic properties using the three methods. Furthermore, the atomic and natural charges, energy band gap and chemical reactivity were determined, while the frontier molecular orbital (FMO) and molecular electrostatic potential (MEP) surfaces were plotted to explain the reactive nature of the title molecule.

Synthesis, crystal structure, spectroscopic, quantum chemical investigation, molecular docking and ADMET prediction of 2(E)-3-(anthracen-9-yl)-1-(1-methyl-1H-pyrrol-2-yl) prop-2-en-1-one

In the present study, 2(E)-3-(anthracen-9-yl)-1-(1-methyl-1H-pyrrol-2-yl) prop-2-en-1-one (3AMP) crystal was grown by slow evaporation method. The single crystal X-ray diffraction analysis and density functional theory (DFT) calculations were carried out for 3AMP crystal. The 3AMP crystallizes in orthorhombic space group Pbca with a = 14.818 (8) Å, b = 9.796 (5) Å, c = 23.239 (11) Å. Hirshfeld surface and finger print plots were analyzed to confirm the existence of intra-, inter-molecular and other weak interactions using Crystal Explorer. The optimized molecular structure and harmonic wavenumbers were calculated by DFT method using B3LYP functional with 6-31G(d,p) basis set. The FT-IR, 1H, 13C NMR and UV–Vis spectra of 3AMP were recorded and analyzed. The optimized geometrical parameters, calculated wavenumbers by DFT method were compared with the experimental results. Natural bond orbital (NBO) analysis was carried out to evaluate the intra- and inter-molecular interactions in the crystal. The energy gap for 3AMP was calculated as 3.156 eV. Molecular electrostatic potential (MEP), Mulliken atomic charges and non-linear optical (NLO) properties for the title crystal were calculated. In addition, gauge invariant atomic orbital (GIAO) method was used to calculate the 1H and 13C NMR chemical shifts in the ground state. To obtain the electronic transitions in UV–Vis spectra of the title molecule in DMSO and ethanol solvents, TD-DFT calculations were performed on the optimized geometry. Furthermore, the compound was subjected to in silico ADMET evaluation. Molecular docking study was carried out to determine the interactions of ligand with the protein Hyaluronidase (PDB ID: 1FCQ).

Antimony(III) Dithiocarbamates: Synthesis, Spectral, Theoretical and Biological Activities

Antimony(III) dithiocarbamate complexes tris(N,N-difurfuryldithiocarbamato-S,S′)antimony(III) (1) and tris(N-furfuryl-N-(2-phenylethyl)dithiocarbamato-S,S′)antimony(III) (2) have been synthesized and characterized by CHN analysis, FT-IR, 1H NMR, 13C NMR spectra and antimicrobial studies. The characteristic thioureide ν(C-N) bands occur at 1459 and 1469 cm-1 for complexes 1 and 2, respectively. 1H NMR and 13C NMR chemical shifts have been calculated using GIAO approach and the calculated chemical shifts shows good agreement with experiential shifts. The computational calculations of the antimony(III) complexes have been carried out by DFT/B3LYP using LANL2DZ basis set. The FMOs, MEP, Mulliken charge distribution and chemical activity parameters were calculated at the same level of theory. The antimicrobial activities of the antimony(III) complexes were assayed at the concentrations 400 and 800 μg/mL against four bacterial (Vibrio cholera, Staphylococcus aureus, Klebsiella pneumoniae and Escherichia coli) and two fungal species (Candida albicans and Aspergillus niger) by Agar-well disc diffusion method.

Understanding of the interactions between azole-anion-based ionic liquids and 2-methyl-3-butyn-2-ol from the experimental perspective: the cage effect.

The interactions between azole-anion-based ionic liquids (AILs) and 2-methyl-3-butyn-2-ol (MBY) play an important role in AIL-promoted carboxylative cyclization of MBY with CO2. To better understand the interactions between AILs ([P66614][Im], [P66614][4-MeIm], and [P66614][4-BrIm]) and MBY, a detailed investigation from the experimental perspective has been carried out in this study. The results show that the derivative of viscosity (η) with the mole fraction of AIL (xAIL) of AIL + MBY mixtures appears to have the maximum value when xAIL ≈ 0.3, while 1H NMR chemical shifts of P-CH2 of [P66614]+ reach the minimum value at xAIL ≈ 0.3, indicating that [P66614]+ of AILs tend to self-aggregate. The interaction parameters (gji-gii) of the systems obtained from η by the Eyring-UNIQUAC equation are positive, and the difference between the bulk and local composition (xi-xii) is always negative, indicating that AILs can interact with MBY. Moreover, excess molar volumes and isentropic compressibility deviations are all negative deviations and become more negative as the temperature increases, reaching a minimum value at xAIL ≈ 0.30, indicating that azole-based anions can form H-bonds with MBY, and MBY molecules tend to enter the aggregates formed by AILs. Consequently, the cage effect is proposed to describe the interactions between AILs and MBY: MBY first enters the cage formed by the aggregation of [P66614]+, and then forms H-bonds with azole-based anions. Finally, the sizes of the particles of the [P66614][Im] + MBY mixture from dynamic light scattering increase first and then decrease with xAIL, with the maximum of 122 nm at xAIL ≈ 0.25, which confirms the rationality of the cage effect.