Enzyme mediated calcium carbonate crystallization in the presence of natural polysaccharide

Abstract

Calcium carbonate (CaCO3) is the most abundant type of biomineral, which is readily available in nature mainly in the structural components of the living organisms. Synthesize of the biominerals in the living organisms is mainly associated with organic macromolecules. These organic materials play an important role in nucleation, growth and the morphology controls of the biominerals. On the other hand Enzymes play vital roles during formation of these biominerals. Concept is called enzyme mediated biomineralization. During the formation of the CaCO3 urease enzyme play a vital role. Urease enzyme has ability to hydrolysis of the urea and produce carbonate ions which tend to precipitate CaCO3 in the presence of calcium ions. In this research, concept of enzyme mediated biomineralization was implemented and produced biominerals artificially in the presence of chitosan which is the one of the most abundant natural polysaccharide available in nature. Experiments were done by using commercially available urease enzyme and chitosan solution was prepared by dispersing solid chitosan in 1% acetic acid solution, followed by adjusted to pH by using NaOH solution. Experiments were conducted at different urease concentrations in the presence (0.03%) or absence of the chitosan. Same experiments were conducted under the different chitosan concentrations (0 - 0.15%) with a urease concentration of 0.3 U/ml. Morphologies of precipitated CaCO3 crystals were analyzed by using Scanning Electron Microscope. Amount of CaCO3 precipitate increased with urease concentration in the presence or absence of the chitosan. The amount of precipitate in the presence of chitosan was higher than that in the absence. According to the SEM images, spherical shape crystals of CaCO3 are dominant without chitosan and rhombohedral crystals are dominant with chitosan, which would act as a binder to form rhombohedral crystal agglomeration. We also found that chitosan concentration has a significant influence on the amount of precipitate.