An insight into the interaction of L-proline with the transition metal cations Fe(2+), Co(2+), Ni(2+): a gas phase theoretical study

Development of a vortex-assisted switchable-hydrophilicity solvent-based liquid phase microextraction for fast and reliable extraction of Zn (II), Fe (II), Pb (II), and Cd (II) from various baby food products

This manuscript describes the development of a novel liquid phase microextraction (LPME) method for the extraction and determination of Zn (II), Fe (II), Pb (II), and Cd (II) in various infant/baby food and supplements products. The method is based on vortex-assisted extraction combined with a switchable-hydrophilicity solvent (SHS) sample preparation. The SHS, which undergoes reversible phase changes triggered by pH change, enables selective extraction and easy phase separation. A flame atomic absorption spectroscopy was used in the final determination step. Optimization studies revealed, that the optimal pH of the sample solution (after digestion) during analytes extraction is 5.5. A l-proline is added to the sample (375 mM) to ensure the complexation of the target metal cations. After the complexation step, 750 µL of SHS - a N, N-Dimethylcyclohexylamine along with 0.9 mL of 2 M of acetic acid solution is added (hydrophilicity switch-on stage) and mixed manually to obtain a homogeneous solution. In the last stage, 0.45 mL of 10 M NaOH solution (hydrophilicity switch-off stage) is added to the sample solution and a vortex for 100 s is applied to ensure the effective extraction and separation of the complex containing the analytes. At this stage, a cloudy solution is immediately obtained. Finally, the effective phase separation is obtained at the centrifugation step (4000 rpm for 2 mins). The method limit of detection was as 0.03, 0.009, 0.6, and 0.2 ng/L for Zn (II), Fe (II), Cd (II), and Pb (II) respectively with RSD% below 2.0 %. The analysis of certified reference materials and real samples proved the full applicability of the method for routine analysis, contributing to the field of heavy metal analysis and ensuring the safety of baby products. According to the AGREE methodology, this method can be named as green analytical chemistry method with a score of 0.77.

Pickering interfacial catalysts for asymmetric organocatalysis

A catalytically active Pickering emulsion was established for asymmetric aldol reaction. Both high reactivity and high selectivity were achieved on the emulsion interface via tailoring the hydrophobicity of the proline-functionalized nanoparticles.

Interaction of l-proline with group IIB (Zn2+, Cd2+, Hg2+) metal cations in the gas and aqueous phases: a quantum computational study

The gas and aqueous phase complexation geometries, electronic interactions, and metal ion affinities of Zn2+, Cd2+, and Hg2+ metal cations with the two most stable conformations of l-proline complexes were studied. The complexes were optimized by density functional theory (B3LYP) using the 6-311++G(d,p) orbital basis set and relativistic pseudopotentials for the metal cations. The interactions of the metal cations at different nucleophilic sites of l-proline were considered as were three modes of interactions including salt bridged, charge solvated 1, and charge solvated 2, which are indicative of binding in a bidentate manner through the carboxylate group, carbonyl and hydroxyl oxygen, and carbonyl oxygen and the nitrogen atom of l-proline. All of the coordination patterns were characterized by both charge transfer and ionic interactions between l-proline and the metal cation. The metal ion affinity (MIA) and interaction energy were also computed for all of the complexes at both the gas and aqueous phases. Results showed that the order of MIA at the gas and aqueous phases are different. MIA order at the gas phase was in the order of Zn2+ > Hg2+ > Cd2+ whereas at the aqueous phase, the order of Zn2+ > Cd2+ > Hg2+ was obtained for MIA. The infrared stretching vibrational modes of the N–H and O–H groups of free l-proline were compared with l-proline–M2+ in both CS1 and CS2 coordination patterns at the gas phase and results showed a considerable shift to lower frequency during complexation process.