Investigation of inclusion complexation of acetaminophen with pillar [5]arene: UV–Vis, NMR and quantum chemical study

Hydroxyl-functionalized pillar[5]arene with high separation performance for gas chromatography

Here we report the first example of employing hydroxyl-functionalized pillar[5]arene (P5A-C10-OH) as stationary phase for capillary gas chromatographic (GC) separations. The statically coated P5A-C10-OH capillary column possessed moderate polarity and column efficiency of 3233 plates per m determined by n-dodecane. As a result, the P5A-C10-OH column exhibited high-resolution capability for the mixture of 17 analytes from apolar to polar nature. Importantly, it exhibited advantageous performance for high resolution of the challenging isomers of bromonitrobenzene, chloroaniline, bromoaniline, iodoaniline and dimethylaniline with good peak shapes over the P5A-C10 and commercial HP-35 columns. In addition, eight cis-/trans-isomers with diverse types were baseline separated on the P5A-C10-OH column. And the application of detecting isomeric impurities in real samples gave strong evidence of its potential and feasibility for the viable GC analysis.

Clofazimine pKa Determination by Potentiometry and Spectrophotometry: Reverse Cosolvent Dependence as an Indicator of the Presence of Dimers in Aqueous Solutions

The weakly basic antibiotic and anti-inflammatory drug, clofazimine (CFZ), was first described in 1957. It has been used therapeutically, most notably in the treatment of leprosy. However, the compound is extremely insoluble in aqueous media, and, indeed, there is poor consensus about what its intrinsic solubility is since the reported values range from 0.04 to 11 ng/mL. To understand the speciation and solubilization of CFZ as a function of pH, it is of paramount importance to know the true aqueous pK_a. However, there is also poor consensus about the value of the pK_a (reported measured values range from 6.08 to 9.11). In the present study, we report the determination of the CFZ ionization constant using two independent techniques. A state-of-the-art potentiometric analysis was performed, drawing on titration data in methanol-water solutions (46-75 wt % MeOH) of CFZ, using the bias-reducing consensus of two different procedures of extrapolating the apparent p_sK_a values to zero cosolvent to approximate the true aqueous pK_a as 9.43 ± 0.12 (25 °C, I = 0.15 M reference ionic strength). In parallel, spectrophotometric UV/vis titration data were acquired (250-600 nm at different pH) in 10 mM HEPES buffer solutions containing up to 54 wt % MeOH. The alternating least squares (ALS) method was used in the analysis of the absorbance-pH spectra. Uncharacteristically, the cosolvent UV/vis data in our study showed reverse cosolvent dependence (apparent pK_a values increased with increasing cosolvent) which could be explained by a dimerization of the free base. The analysis of UV/vis data obtained from 54 wt % MeOH-water solution containing 20 μM CFZ yielded the apparent pK_a 9.51 ± 0.17 (I ≈ 0.005 M). To assess whether self-assembly of CFZ was energetically feasible, density functional theory (DFT) calculations were used to study the putative CFZ dimers in aqueous and methanol media. The DFT-optimized geometries and infrared spectra of CFZ dimers using water and methanol as solvents were calculated and analyzed. Based on the lack of negative frequencies in calculated infrared spectra, it was confirmed that optimized geometries correspond to the true energetic minima. Visual analysis of optimized structures indicates the presence of stacking interactions between two CFZ molecules. The protonation site (the imine nitrogen atom) was determined by ¹H NMR spectroscopy.

Why trans and not cis? – Molecular Dynamics and DFT study on selective separation of dihaloethene isomers using perethylated pillar[5]arene

The separation of mixtures of isomers is a daunting task. It is found that perethylated pillar[5]arene can separate trans-dichloroethene from its cis isomer. This work deals with the host-guest interactions...

Metallo-Supramolecular Coordination Polymers Based on Amidopyridine Derivatives of Pillar[5]arene and Cu(II) and Pd(II) Cations: Synthesis and Recognition of Nitroaromatic Compounds

Decasubstituted pillar[5]arenes containing amidopyridine fragments have been synthesized for the first time. As was shown by UV-vis spectroscopy, the pillar[5]arenes with p-amidopyridine fragments form supramolecular associates with Cu(II) and Pd(II) cations in methanol in a 2:1 ratio. Using a sol-gel approach these associates are transformed into metallo-supramolecular coordination polymers (supramolecular gels) which were characterized as amorphous powders by scanning electron microscopy (SEM) and dynamic light scattering (DLS). The powders are able to selectively adsorb up to 46% of nitrophenols from water and were incorporated into an electrochemical sensor to selectively recognize them in aqueous acidic solution.

Theoretical study on host-guest interaction between pillar[4]arene and molecules or ions

In order to systematically explore the general rule of the host-guest chemistry for pillararenes, this work investigates the weak interactions between pillar[4]arene and some typical guests (anions, cations, and dumbbell-shaped molecules) by using density functional theory (DFT) calculations at the ωB97XD/6-311G(d,p) level. The strong molecular recognition ability of pillar[4]arene has been discussed based on the geometry structure, electronic structure, and thermodynamic properties of the host-guest complexes. The results show that the equivalent lower and upper rims of the pillar[4]arene can be combined with both anion and cation, and its cavity can accommodate the alkyl part of the dumbbell-shaped molecule. The main host-guest interactions between pillar[4]arene and guests are hydrogen bond, cation-π, anion-π, and hydrophobic interaction by visualization of weak interactions using the Multiwfn program. Pillar[4]arene will form a more stable host-guest complex with the guest, which possesses conjugate structure and weak steric repulsion. This work intends to provide a theoretical basis for enriching the host-guest chemistry, understanding the supramolecular morphology, and expanding the applications of the pillararenes.

Nature of bonding and cooperativity in linear DMSO clusters: A DFT, AIM and NCI analysis

This study aims to cast light on the nature of interactions and cooperativity that exists in linear dimethyl sulfoxide (DMSO) clusters using dispersion corrected density functional theory. In the linear DMSO, DMSO molecules in the middle of the clusters are bound strongly than at the terminal. The plot of the total binding energy of the clusters vs the cluster size and mean polarizabilities vs cluster size shows an excellent linearity demonstrating the presence of cooperativity effect. The computed incremental binding energy of the clusters remains nearly constant, implying that DMSO addition at the terminal site can happen to form an infinite chain. In the linear clusters, two σ-hole at the terminal DMSO molecules were found and the value on it was found to increase with the increase in cluster size. The quantum theory of atoms in molecules topography shows the existence of hydrogen and SO⋯S type in linear tetramer and larger clusters. In the dimer and trimer SO⋯OS type of interaction exists. In 2D non-covalent interactions plot, additional peaks in the regions which contribute to the stabilization of the clusters were observed and it splits in the trimer and intensifies in the larger clusters. In the trimer and larger clusters in addition to the blue patches due to hydrogen bonds, additional, light blue patches were seen between the hydrogen atom of the methyl groups and the sulphur atom of the nearby DMSO molecule. Thus, in addition to the strong H-bonds, strong electrostatic interactions between the sulphur atom and methyl hydrogens exists in the linear clusters.