Describe what the term racemic mixture means.
Asparagine is an amino acid with a chiral carbon atom and it shows stereoisomerism. Separate samples of asparagine are dissolved in $\text{CDCl}_3$ and examined using carbon-13 and proton ($^1\text{H}$) NMR spectroscopy. Predict the number of peaks observed in the carbon-13 and proton ($^1\text{H}$) NMR spectra of asparagine.
The isoelectric point of asparagine, asn, is at pH 5.4. Describe the meaning of the term isoelectric point.
Draw the structure of asparagine at pH 1.0.
Asparagine can polymerise to form poly(asparagine). Draw the structure of poly(asparagine), showing two repeat units. The peptide linkage should be shown displayed.
The isoelectric point of lysine, LYS, is at pH 9.8. A mixture of the dipeptide LYS-ASN and its two constituent amino acids, asparagine and lysine, is analysed by electrophoresis using a buffer at pH 5.0. The results obtained are shown in Fig. 6.3. Suggest identities for the species responsible for spots E, F and G. Explain your answers.
Thin-layer and gas-liquid chromatography can be used to analyse mixtures of substances. Each form of chromatography uses a stationary phase and a mobile phase. Complete Table 6.1 with one example of each.
An unknown amino acid is analysed by thin-layer chromatography. Two chromatographs of the unknown amino acid and four reference amino acids, P, Q, R and S, are obtained using two different solvents. Identify the unknown amino acid. Justify your answer.
A mixture containing three organic compounds is analysed by gas chromatography and mass spectrometry. The gas chromatogram is shown. The area under each peak is proportional to the mass of the corresponding compound in the mixture. The concentration of K in the mixture is $5.52 \times 10^{-2} \, \text{g dm}^{-3}$. Calculate the concentration, in $\text{mol dm}^{-3}$, of compound L in the mixture. [$M_r(\text{L}) = 116$]