DIDFERENT TYPES OF SYSTEMS/METHODS: STERICALLY POLYMERIC FLOCCULATED PLOYMER GRA
ID: 636087 • Letter: D
Question
DIDFERENT TYPES OF SYSTEMS/METHODS: STERICALLY POLYMERIC FLOCCULATED PLOYMER GRAFTED You have prepared 10 ?m diameter polystyrene microparticles densely coated with casein (milk protein), whose isoelectric point, pI 4.6. The coated particles are dissolved in pure water at pH 7 to form a stabilized suspension. Particle Casein (a) (6) Describe the mechanism by which the microparticle solution is stabilized. (b) (8) Now your boss wants you to quickly recover the particles from solution by somehow causing them to aggregate and precipitate, after which they can be filtered. Without changing the solvent, describe two different methods you could use to destabilize the system.Explanation / Answer
a) - Isoelectric point of a protein is the point where net charge on a protein is zero.
- When pH of the medium is more than pI, the protein gets predominantly negatively charged. This is because, in higher pH the medium becomes basic. This deprototizes the acid groud forming COO-. This makes the protein negatively charged. When the pH is less that pI the protein gets positively charged. This is because the medium becomes acidic. Protonation of the amino group takes place forming NH2. But in neutral solutions (with pH = 7) the molecule has no net charge.
- Casein is a phosphoprotein, with phosphate groups & carboxylic acid and amino groups. It is almost fully insoluble in water. As casein is not charged in water ( water being a neutral solution) and is also almost completely insoluble, the suspension of wate/r and casein is stable.
b) Two methods:
1. Flocculation -
Flocculation a phenomena in surface chemistry where suspended particles in a particular solvent are made to clump together and aggregate. Casein water system can be destabilized using this method. Casein being a neutral molecule in water will not show any electrostatic repultions. The particles can be brought together leading to aggregation. Casein being of higher molecular weight than water will sediment at the bottom of the solven. This can be filtered and casein particles can be obtained.
b. Heating:
When you heat the suspention of Casein in water, the casein particles aggregate together and come out of solution. This way they can be filtered and obtained.
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