Serotonin can be synthesised from the amino acid tryptophan in two steps. [Figure 3.1: Structure of Tryptophan] [Figure 3.2: Structure of Serotonin]

1. (a)(i)In a buffer solution at pH 5.9, a sample of tryptophan does not move during electrophoresis. Draw the structures of the ions formed by tryptophan at pH 1.0 and pH 5.9.[2]
2. (a)(ii)Tryptophan can combine with valine to form a dipeptide. Use the Data Booklet to draw the structure of this dipeptide.[2]
3. (b)Complete the following table to show the structures of the products formed and the type of reaction occurring when serotonin reacts with the four reagents in separate reactions. reagent Na excess Br₂(aq) excess CH₃COCl excess H₂/Pt catalyst structure of product type of reaction[8]
4. (c)(i)By reference to the Data Booklet, suggest how the infra-red spectrum of M would differ from that of serotonin.[1]
5. (c)(ii)The proton NMR spectrum of M dissolved in CDCl₃ shows eight peaks due to the eight different types of proton present in the molecule. The proton NMR spectrum of M dissolved in D₂O was recorded. Predict the number of peaks that would be seen in the proton NMR spectrum of M in D₂O. Explain your answer.[2]
6. (d)Polymer N is biodegradable, unlike polyethene which is not. Explain why N is biodegradable.[1]

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