Design of novel porous melamine-formaldehyde materials for molecular recognition

Abstract

Porous materials have played a pivotal role in the hosting of guest species. They provide a good diffusion medium, display high surface area and often the pores are size specific and bear the correct functionality to enhance retention of analytes. This work shows how such materials, based on melamine-formaldehyde (MF) chemistry are designed.

The melamine motif has been known to form supramolecular aggregates in solution with other triazine-containing molecules. It was, thus, anticipated that cross-linked MF networks would carry over the same recognition properties into solid matrices. Also, recognition was thought to be enhanced significantly if different chemical functions were brought into the material.
With this in mind, the successful introduction of different chemical groups onto the melamine motif was shown. These new derivatives were then converted into resins, using formaldehyde, and further cross-linked to produce porous materials. Thorough structural characterisation was carried out at this stage and a clear level of understanding/control has been gained on how to tune the porosity within such matrices.

Analysis of functionality was carried out using various spectroscopic techniques, the most important one being infrared studies. This revealed that two characteristic peaks in all cross-linked systems (with and without incorporated derivatives) appear at 1350cm-1 and 1150 cm-1, although the nature of these is yet to be elucidated. When different functional groups were incorporated into MF networks, the infrared spectra varied slightly. Additionally, determining cross-linking density within materials using spectroscopic techniques was investigated but has not yet been fully accomplished.

Finally the extent of molecular retention of certain analytes within porous MF materials was evaluated. The pre-ground materials were successfully used as stationary phases in HPLC columns, behaving extremely well under the high pressure conditions. Out of the various analytes injected, certain amino acids displayed variation in retention and elution depending on the composition of the stationary phase.