Mass Spectrometry Reveals Complexing Properties of Modified PNP-Lariat Ether Containing Benzyl Derivative of (S)-Prolinamine.

Natalia Gutowska,Marek Kowalczuk,Piotr Seliger,Jarosław Romański,Magdalena Zięba,Grazyna Adamus

doi:10.3390/molecules25010136

Abstract

In the investigation presented here the synthesis of new lariat ether derivative obtained from the modification of tetrapyrrolidinyl-PNP-crown ether macrocycle is described. The polyheterotopic molecular coreceptor consisted of the replacement of chlorine atoms with an optically active (S)-(1-benzylpyrrolidin-2-yl) methanamine. The structure was confirmed by using elemental analysis, mass spectrometry, and NMR spectroscopy. This work covers results concerning the complexing properties of the new ligand towards Ag+, Cu2+, Co2+, Ni2+, and Zn2+ ions. The formation of non-covalent complexes of 1:1 stoichiometry with the Cu2+, Co2+, Ni2+, and Zn2+ ions have been confirmed by mass spectrometry. Due to the previous work and application possibilities, a large emphasis was put on the investigation of the complexation ability of lariat ether with silver (I) cation to determine stability constants by direct potentiometric method. In this case, the formation of four different forms of complexes AgL, Ag2L, Ag3L, and Ag4L has been proved. The observed unusual binding through the nitrogen atoms from the exocyclic substituents may provide the structural unit to build a new coordination polymers.

Highlights

In order to obtain a compound with specific practical applications, supramolecular chemistry is centered at modification of the properties of macrocycles through structural modification
Potentiometric and NMR studies were presented for the investigated ligand complexes with silver ions in acetonitrile and methanol
Ligand with silver ions forms four types of complexes with different stoichiometry-AgL, Ag2 L, Ag3 L, and Ag4 L, with the most stable 1:1 form observed in both solvents

Summary

Introduction

In order to obtain a compound with specific practical applications, supramolecular chemistry is centered at modification of the properties of macrocycles through structural modification. Typical modifications include changing the ring size of the macrocyclic ligand, the types of donor atoms and the kinds of substituents [1,2,3]. Lariat ethers are still attractive research objects due to the possible creation of interesting structures of complexes the both with cations as well as anions. The side arms provide the possibility of incorporating atoms or groups with a lone pair of electrons enabling additional cooperation with the heteroatoms of the macrocycle ring, providing three-dimensional coordination of the guest cation [4,5,6]. Intensive development of the lariat ethers concept has led to Molecules 2020, 25, 136; doi:10.3390/molecules25010136 www.mdpi.com/journal/molecules

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Conclusion