Synthesis and evaluation of ion-imprinted composite membranes of Cr(vi) based on β-diketone functional monomers

Using Cr(vi) as the imprinted ions and 2-allyl-1,3-diphenyl-1,3-propanedione (ADPD) (a compound synthesized by independent design) as the functional monomer, a series of chromium ion-imprinted composite membranes (Cr(vi)-IICMs) and corresponding non-imprinted composite membranes (NICMs) were synthesized and tested. The results showed that the Cr(vi)-IICM₁₀ membrane prepared under optimal experimental conditions exhibited a high adsorption capacity towards Cr(vi) (Q = 30.35 mg g⁻¹) and a high imprinting factor (α = 2.70). The structural characteristics of Cr(vi)-IICM₁₀ and NICM₁₀ were investigated using FE-SEM, ATR-FTIR, and BET techniques combined with UV-Vis photometry and inductively coupled plasma emission spectrometry (ICP-OES) to evaluate the adsorption performance and permeation selectivity, while the effect on adsorption permeance of varying the experimental conditions including the solvent type, pH, and temperature was also investigated. The results showed that Cr(vi)-IICM₁₀ is a mesoporous material with excellent permeation selectivity, reusability, and favorable pH response, and that its adsorption behavior is in accordance with the Langmuir model and pseudo-first-order kinetics. Thus, Cr(vi)-IICM₁₀ shows great potential towards utilization as a “smart membrane” to control the separation and removal of Cr(vi) in wastewater, and also proved a reasonable design of the new functional monomer ADPD.

Using Cr(vi) as the imprinted ions and 2-allyl-1,3-diphenyl-1,3-propanedione (a compound of independent design) as the functional monomer, a series of chromium ion-imprinted composite membranes and corresponding non-imprinted composite membranes were synthesized and tested.

The keto-enol tautomerization of ethyl acetoacetate in choline ionic liquids: the role of cation and anion in switching the tautomeric equilibrium

In this work, density functional theory (DFT) calculations were carried out to study the role of the explicit treatment of four different choline-based ionic liquids (CS, CP, NS, and NP) by utilizing two different cations and anions in the tautomeric equilibrium of ethyl acetoacetate (EAA). The involvement of the acidic N-H proton from the cationic part of NS and NP ionic liquid offers the possibility to have two more additional transition states for the tautomeric equilibrium of EAA. The computed results demonstrated that a high activation free energy barrier (ΔG = 49.4 kcal mol^-1) is associated with the direct enol to keto (E → K) interconversion via a 4-membered ring transition state. Upon explicit involvement of the cationic part of ionic liquids in the tautomeric equilibrium via a 6-membered ring transition state (CAT), ΔG is substantially reduced to 21.88 kcal mol^-1. Further, ΔG is drastically reduced to 10.57 kcal mol^-1 upon the involvement of the anionic part of the ionic liquid explicitly via an 8-membered ring transition state (AAT). The W-shaped TS in the CAT pathway causes steric hindrance and increases the energy penalty, while the sickle-shaped TS in AAT facilitates easy proton transfer without the influence of the steric factor. In addition, the RDG scatter graphs predict large negative values of ρ*, which indicate that the hydrogen bonding network in AAT is stronger, enhancing the delocalization of the electron density. The QTAIM analysis substantiated the role of intermolecular hydrogen bonding interactions between the ionic liquid and EAA and within the anion-cation pair in stabilizing the keto group of EAA. Besides, the involvement of the acidic N-H proton in the transition state is the key factor in influencing the energetics of the keto-enol tautomerization reaction. The present study illustrates molecular-level insights into the role of individual ions of ionic liquids and also provides adequate ideas for designing novel ionic liquid-based catalysts for industrially relevant chemical reactions.

DFT Study To Explore the Importance of Ring Size and Effect of Solvents on the Keto-Enol Tautomerization Process of α- and β-Cyclodiones

We have explored the effect of ring size on keto-enol tautomerization of α- and β-cyclodiones using the M062X-SMDaq/6-31+G(d,p)//M062X/6-31+G(d,p) level of theory. The calculated results show that the activation free energy barrier for the keto-enol tautomerization process of α-cyclopropanedione (1) is 54.9 kcal/mol, which is lower compared to that of the other cyclic diketo systems studied here. The four-membered α- and β-cyclobutanedione (2 and 6) do not favor keto-enol tautomerization unlike other studied cyclic systems because of the ring strain developed in the transition-state geometries and their corresponding products. Water-assisted keto-enol tautomerization with one molecule reveals that the free energy activation barriers reduce almost half compared to those for the uncatalyzed systems. The two-water-assisted process is favorable as the activation free energy barriers lowered by ∼10 kcal/mol compared to those of the one-water-assisted process. The ion-pair formation seems to govern the lowering of activation barriers of α- and β-cyclodiones with two water molecules during the keto-enol tautomerization process, which however also overcomes the favorable aromatization in the three-membered ring system. The free energy activation barriers calculated with the M062X-SMDaq/6-31+G(d,p) level predicted that the keto-enol tautomerization process for the α-cyclodiones follows the following trend: 2 > 3 > 4 > 5 > 1. Water-assisted tautomerization of α-cyclodiones also predicted 1-W and 1-2W as the most favored processes; however, 5-W and 5-2W were found to be disfavored in this case. The β-cyclodione systems also showed similar trends as obtained with α-diketone systems. The influence of bulk solvent on the keto-enol tautomerization process favors the formation of the enol form in a more polar solvent medium even under mixed solvent conditions in acetonitrile and hexane at M062X-SMDacetonitrile/6-31+G(d,p) and M062X-SMDhexane/6-31+G(d,p) levels of theory.

Metal-free regioselective formation of C-N and C-O bonds with the utilization of diaryliodonium salts in water: facile synthesis of N-arylquinolones and aryloxyquinolines

Regioselective construction of crucial C-N and C-O bonds leading to N-arylquinolones and aryloxyquinolines has been accomplished by employing easily accessible diaryliodonium salts and quinolones in water under metal- and ligand-free conditions. This operationally simple strategy is significant due to mild reaction conditions, high product yields, recyclability of released iodoarenes and scalability to the gram level. The practical utility of the developed protocol was proved by the arylation of medicinally important heterocycles like acridin-9(10H)-one, 3-methylquinoxalin-2(1H)-one and 1H-benzo[d]imidazol-2(3H)-one.

DFT studies on quantum mechanical tunneling in tautomerization of three-membered rings

Amino–imino and keto–enol tautomerization processes in three-membered ring systems have been explored to examine the role of quantum mechanical tunneling along with aromaticity. The DFT calculations shed light on the role of aromaticity in tautomerization processes and as perceived this property may not contribute entirely to facilitate the formation of tautomeric forms.

Mimicking multivalent protein–carbohydrate interactions for monitoring the glucosamine level in biological fluids and pharmaceutical tablets

Easily synthesizable ESIPT probe for dual mode sensing of glucosamine in pure water.

Insight into the Mechanism of the Pechmann Condensation Reaction Using NMR

The mechanism of the Pechmann condensation is still controversial despite the technological and biochemical importance of coumarins. Here, we present NMR evidence for a mechanism featuring the sequence of initial electrophilic aromatic substitution followed by transesterification and a final dehydration. This mechanism has been convincingly defined and supported by the temporal evolution of two key intermediates which could be purified and identified.