Spectroscopic and Computational Study of ZnCl₂–Methanol Low-Melting-Temperature Mixtures

Alcoholic electrolyte mixtures have wide applications in industries. In this study, a series of mixtures composed of ZnCl2 and methanol (MeOH) with ZnCl2 mol % from 6.7 to 25 were prepared, and their spectral, structural, and thermodynamic properties were studied using infrared (IR) spectroscopy, differential scanning calorimetry (DSC), and density functional theory (DFT) calculations. The DFT-assisted analysis of excess spectra, supported by 2D-correlation spectroscopy, led to the identification of the major constituents of ZnCl2–MeOH mixtures, namely, MeOH monomer, MeOH dimer, and ZnCl2–3MeOH complex, produced after dissociation of MeOH trimer which represents the bulk methanol. The Hirshfeld charge analysis showed that in the competition between the O–H···Cl hydrogen bond (H-bond) and Zn ← O coordination bond to transfer charge in ZnCl2–MeOH complexes, the latter always dominates, making MeOH positively charged. The phase diagram of the binary system showed the presence of V-shaped glass transition temperatures (Tg), characteristic of low-melting mixture solvents (LoMMSs). The present study provides insights into the microscopic properties of the system and sheds light on the understanding of the general principles to prepare deep-eutectic solvents (DESs) or LoMMSs using inorganic salts and alcoholic compounds

Solvent Effect Inside the Nanocage of Zeolite Catalysts: A Combined Solid-State NMR Approach and Multiscale Simulation

Solvent effect plays an important role in manipulating the chemical reactivity, equilibrium constant, and reaction rate. Such effect is observed in heterogeneous catalysis, especially for the acidic zeolite catalyst with molecularly size pores (≤1 nm). Nevertheless, it is a great challenge to systematically investigate the intermolecular interaction and the mechanism of solvent effect on the catalytic performance inside the acidic zeolite nanocages. Here, we used the state-of-the-art solid-state NMR (SSNMR) experimental techniques combined with multiscale theoretical simulations to quantitatively investigate the solvent effect on the reactant electronic property and reaction activity. In particular, a series of ¹³C CP/MAS solid-state NMR experiments with acetone probe for H-ZSM-5 zeolite were performed via changing the coadsorption amount of nitromethane solvent. It is found that the solvent effect accounts for the enhancement of the apparent Brønsted acidic strength of zeolite catalysts, and thus promotes the catalytic reactivity. Furthermore, multiscale theoretical simulations for coabsorption configurations and electronic properties were employed to elucidate the mechanism of solvent effect on the zeolite catalysis. Therefore, so far for the first time the quantitative relationship between solvent effect and the catalytic performance inside the H-ZSM-5 zeolites has been established, and the mechanism of solvent effect in nanocage of zeolites was systematically elucidated

Supramolecular Chemistry of Cucurbiturils: Tuning Cooperativity with Multiple Noncovalent Interactions from Positive to Negative

Rational control of the cooperativity of multiple noncovalent interactions often plays an important role in the design and construction of supramolecular self-assemblies and materials, especially in precision supramolecular engineering. However, it still remains a challenge to control the cooperativity of multiple noncovalent interactions through tuning the hydrophobic effect. In this work, we demonstrate that the binding cooperativity of cucurbit[8]­uril­(CB[8])-mediated homoternary complexes is strongly influenced by the amphiphilicity of guest molecule side groups on account of an interplay between both classical (entropy-driven) and nonclassical (enthalpy-driven) hydrophobic effects. To this end, we rationally designed and prepared a series of guest molecules bearing a benzyl group as the CB[8] homoternary binding motif with various hydrophilic and hydrophobic side groups for cooperative control. By gradually tuning side groups of the guest molecules from hydrophilic to hydrophobic, we are able to control the binding from positive to negative cooperativity. An advanced molecular recognition process and self-assembling system can be developed by adjusting the positive and negative cooperativity. The ability to regulate and control the binding cooperativity will enrich the field of supramolecular chemistry, and employing cooperativity-controlled multiple noncovalent interactions in precision supramolecular engineering is highly anticipated