Controlling protein crystallization kinetics in membrane crystallizers: effects on morphology and structure

Today, a lot of materials for applications in e.g. heterogeneous catalysis, synthetic chemistry, environmental protection, drugs, and microelectronics devices, are produced in crystalline formulation. This is a special case in life sciences, where proteins, and more specifically enzyme crystals, are the bases for advancements in bio-chemistry and biotechnology: large, single crystals, with elevated internal regularity, are needed for structure determination at atomic level [1], while smaller, highly mono-dispersed in size, and uniformly-shaped crystals are required in the large scale production of crystalline materials, as e.g. for application in chemical and bio-pharmaceutical fields [2]. It appears thus obvious that to perform enzyme crystallization process by controlling the final properties of the produced crystals, would be of fundamental advancement in the overall field of life sciences. Membrane crystallization, lying in the general field of the membrane contactors technology [3], has been proposed in the last few years as a new technique for growing protein crystals with enhanced crystallization kinetics even starting at lower levels of supersaturation. Polymeric membranes are used as physical support for solvent extraction in vapour phase from the macromolecular solution to the stripping side, and as active surface promoter of heterogeneous crystallization [4,5]. In the present work, membrane crystallization of some enzymes of particular biological and industrial applications, such as trypsin from bovine and porcine pancreas, b-glucosidase from almonds, yeast lipase, and some molecules used in microelectronics, like triglycine sulphate, has been carried out both in static and dynamic membrane crystallizers. The fundamental aspects of the crystal growth kinetics related to the governing parameter of the overall process have been investigated by kinetic, morphological and structural analysis [3].