Role Of Amine Groups Research Articles

Desorption hysteresis of antibiotics on biochar produced at high temperature: The role of amine groups and amidation reaction

Knowledge of antibiotic desorption from high-temperature biochar is essential for assessing their environmental risks, and for the successful application of biochar to remove antibiotics. In previous studies, irreversible pore deformation, formation of charge-assisted hydrogen bonds or amide bonds were individually proposed to explain the desorption hysteresis of antibiotics on biochars, leading to a debate on hysteresis mechanism. In this study, desorption of sulfamethoxazole (SMX), ciprofloxacin (CFX) and tetracycline (TET) on a wood chip biochar produced at 700 °C (WBC700) and its oxidized product (O-WBC700) was investigated to explore the underlying hysteresis mechanism. Significant desorption hysteresis was observed for SMX, CFX and TET on WBC700 and O-WBC700. Hysteresis index (HI) of each antibiotic was higher on O-WBC700 with more oxygen-containing groups than WBC700, and was higher at lower equilibrium concentration. HI of antibiotics on WBC700 (or O-WBC700) increased in the order of SMX < CFX < TET. The calculated adsorption enthalpy of each antibiotic on WBC700 was positive, indicating an endothermic process. These phenomena together with FTIR, XPS spectra confirmed that the desorption hysteresis mechanism of antibiotics on high-temperature biochar is the formation of amide bonds by amidation reaction, but not the pore deformation or the hydrogen bond. Moreover, antibiotic can form amide bonds with WBC700 only if the amine group with pKa > 4.0, and the HI values were positively correlated with their pKa values. Amine group of antibiotics with higher pKa value show more nucleophilicity and could form stronger amide bonds with carboxyl group of biochar. The obtained results could help to solve the debate on desorption hysteresis mechanism of antibiotics on high-temperature biochars, and provide a new insight into the role of amine groups and amidation reaction on the hysteresis.

Catalytic behavior of copper–amine complex supported on mesoporous silica SBA-15 toward mono-Aza-Michael addition: role of amine groups

This work concerns the preparation and modification of mesoporous silica SBA-15 with different amine-copper complexes in order to study their impact on the catalytic behavior via Aza Michael addition. Firstly, SBA-15 was prepared hydrothermally, then functionalized by mono-, di- and tri-amine, and in the second step, copper (II) was anchored. The catalytic activity of these solids was evaluated at room temperature under liquid-phase conditions. Effects of catalyst nature, catalyst mass, reaction time and the starting reagents nature were investigated. Cu@SBA-15 (non-aminated) was shown to be efficient in the Aza Michael addition, but after its second re-use, a progressive decrease in the product yield was obtained due to copper leaching. The catalytic behavior of all prepared catalysts showed a selective reaction via the mono-Aza-Michael addition. Amongst all the catalysts, the one containing the monoamine-copper complex led to the highest yield. This catalyst was used in four consecutive cycles without significant loss of activity, which confirms its stability.

Atomistic insight into the role of amine groups in thermoresponsive poly(2-dialkylaminoethyl methacrylate)s

The role of amine groups in the phase separation of thermoresponsive poly(2-dialkylaminoethyl methacrylate)s with dimethyl-, diethyl-, and diisopropylaminoethyl substituents has been studied by atomistic molecular dynamics simulations. The polymer chains present a more compact conformation at higher temperatures, losing contact with the water molecules. In the vicinity of the amine groups, the exclusion of water molecules increases with the increasing hydrophobicity of the amine moieties above the lower critical solution temperature. In particular, the potential of mean force results suggest that the formation of hydrogen bonding between the amine groups and water molecules involves more entropic contributions at higher temperatures in the cases of the diethylaminoethyl and diisopropylaminoethyl groups. These results provide insight for the rational design of side chains of thermoresponsive polymers for smart materials and devices.