Development of Catalytic PolyHIPEs using MOFs for the hydrolysis of dipeptides

Metal Organic Frameworks (MOFs) are materials that have shown impressive catalytic activity in a variety of reactions. Poly high internal phase emulsions (PolyHIPEs) are highly porous templated networks that have shown the ability to store active catalysts within their pores. This work looks at the use of MOFs and polyHIPE-MOFs in the hydrolysis of diglycine in water and water/THF. MOF-808 is known to be one of the most effective MOFs in catalysis and has been used in a number of reactions. Therefore, it was decided that MOF-808 was the main focus in the hydrolysis studies, and would be subsequently embedded in the polyHIPE. The hydrolysis studies proved that MOF-808 was an extremely effective catalyst under a number of different conditions. The superabsorbent swelling ability of the polyHIPE made up of styrene and divinylbenzene was important in the hydrolysis studies, as the polymer was only effective when a 50:50 mixture of d-THF and D2O was used. This was evident from the swelling studies of the polyHIPE, which showed a major difference from 100 % water to a 50:50 mix with THF. This was due to the water being absorbed onto the surface of the polymer, but it was unable to absorb inside the polymer where the active catalyst was stored. The other MOFs used in this study showed varying levels of success in the hydrolysis of diglycine, although compared to MOF-808 the percentage conversion to glycine was extremely low. The MOFs used were mainly zirconium based although a titanium and bimetallic (Zr-Ti) MOF were used to compare the effect of metal centres. The zirconium, titanium and bimetallic equivalent MOFs varied in there catalytic activity, the titanium MOF showed the least conversion, there was a slight increase in conversion for the zirconium MOF and a significant increase for the bimetallic MOF. This was due to the large surface areas and porosity from the titanium metal centre and the stability provided by the zirconium metal centre.