Theoretical study on the binding selectivity of 18-membered azacrown ethers with alkaline earth metal species

Abstract

The binding selectivity of 18-membered azacrown ethers (monoaza-N1, diaza-N2, triaza-N3, tetraaza-N4, pentaaza-N5, and hexaaza-18-crown-6 N6) with Ca 2+ , Sr 2+ , Ba 2+ have been studied by density functional theory (DFT) calculations. The complex binding selectivity was analyzed in term of interaction energies, thermodynamic properties, second order interaction energies, and charge transfer effects. The geometrical study shows that Ca 2+ and azacrown complexes acquire envelope like structure, leading to shorter bond lengths. As a result, these complex systems have the highest interaction energies. Theoretical study also showed that N6 complex with alkaline earth metal ion were shown to be more stable complex than those ligand with lower nitrogen number. The interaction energy order is N0 < N1 < N2 < N3 < N4 < N5 < N6. This trend shows that the presence of more nitrogen on the crown ether cavity increases the interaction energies by approx. 7.3 % in going from N0 to N6. It is clearly showed that the contribution of the number of nitrogen play a dominant role in the binding selectivity of these systems. Keywords: DFT method, alkaline earth, aza-crown ether, metal ion, binding selectivity ABSTRAKSelektivitas kelompok aza eter mahkota (monoaza-N1, diaza-N2, triaza-N3, tetraaza-N4, pentaaza-N5, dan hexaaza-18-mahkota-6 N6) terhadap Ca 2+ , Sr 2+ , Ba 2+ telah dikaji berdasarkan teori fungsional kerapatan. Selektivitas eter mahkota diukur berdasarkan sifat energi ikatan, sifat termodinamika, energi interaksi orde kedua dan transfer muatan. Kajian parameter geometri menunjukkan bahwa kompleks Ca 2+ dan aza eter mahkota membentuk struktur seperti amplop terlipat, sehingga memiliki panjang ikatan yang lebih pendek. Akibatnya sistem kompleks ini memiliki energi interaksi yang lebih tinggi. Kajian teoritis juga menunjukkan bahwa komplek N6 dengan logam alkali tanah paling stabil. Urutan energi iteraksi adalah N0 < N1 < N2 < N3 < N4 < N5 < N6. Urutan ini menunjukkan bahwa meningkatnya jumlah atom nitrogen pada eter mahkota, meningkatkan energi interaksi 7,3 % dari N0 ke N6. Hasil kajian menunjukkan bahwa jumlah atom nitrogen memiliki peranan dominan pada selektivitas kelompok aza eter mahkota. Kata Kunci: metode DFT, alkali tanah, aza eter mahkota, ion logam, selektivitas ikatan

Combined spectroscopic studies on post-functionalized Au25 cluster as an ATR-FTIR sensor for cations

“…It has been shown that some earth alkaline metals have binding affinities towards crown cavities, and that derived from 18C6 macrocycles in particular. [47][48][49]52 We therefore tested aqueous solutions of Ba 2+ salt. The ionic radius of barium of 135 pm, compares well with the ionic radius of K + (138 pm).…”