Results and Discussions

Calix (4) pyrroles are macromolecules structurally related to porphyrins, they exhibit exceptional chemical and physical properties that have suggested a vast number of potential applications in host-guest chemistry. In recent years, calix (4) pyrroles have attracted a lot of attention because of their properties as binders of anions, transition metals, and neutral substrates and their new applications as anion sensors in both the optical and electrochemical realms. Calix (4) pyrroles have also been found to be biologically active species. Many researchers have synthesized functionalized and deep cavity, N-confused, extended cavity and higher order/expanded calix (4) pyrroles. They exhibit ever-increasing affinities and selectivities in chemical reactions. Generally, meso –calix (4) pyrroles have been prepared by the acid-catalyzed (homogeneous catalysis) condensation of pyrrole and suitably substituted ketone. Calix (4) pyrroles are characterized by infrared (IR), nuclear magnetic resonance (NMR) spectroscopy, X-Ray and mass spectrometry. Mass spectrometry is known to be a sensitive technique and is used not only to confirm the molecular weight, but also to assign the structure. There are only a few reports on the use of EI for molecular weight determination of extended calix pyrroles and large furan-based calixpyrroles. Recently, Prabhakar et al. reported detailed mass spectral studies to characterize meso-alkyl and mesocycloalkyl calix (4) pyrroles under EI conditions. The calix (4) pyrroles have been characterized by soft ionization techniques such as chemical ionization, fast atom bombardment, electrospray ionization and matrix-assisted laser desorption/ionization to determine the molecular weight of the compound. However, to the best of our knowledge there are no reports of detailed mass spectral studies with the use of soft ionization techniques to characterize calix (4) pyrroles towards structure elucidation. This prompted us to study the ESI mass spectral behavior of meso-calix (4) pyrroles and differentiation of some of the calix (4) pyrrole isomers.