Optical Activity Principles
Optical activity refers to the interaction of a substance with plane-polarized light. Specifically, it's the compound's ability to rotate the plane of polarized light. This phenomenon occurs only when a molecule is chiral – meaning it is non-superimposable upon its mirror image.
Chirality Assessment of Options
- Solution of NaCl: Sodium chloride (NaCl) is an ionic compound composed of sodium and chloride ions. It is inherently achiral. Therefore, its solution does not exhibit optical activity.
- Solution of D-Glucose: D-Glucose is a monosaccharide. Its molecular structure contains multiple chiral centers (specifically, four in its open-chain form). Being a chiral molecule, D-Glucose solutions rotate plane-polarized light and are optically active.
- Solution of Glycine: Glycine is the simplest amino acid with the formula H2N-CH2-COOH. Its central alpha-carbon atom is bonded to two identical hydrogen atoms, making the molecule achiral. Consequently, glycine solutions are not optically active.
- Solution of L-Proline: L-Proline is an amino acid. Its alpha-carbon is attached to four different groups: a hydrogen atom, a carboxyl group, an amino group (within the ring), and the unique cyclic side chain. This makes L-Proline a chiral molecule, and its solutions exhibit optical activity.
Conclusion
Only chiral molecules rotate the plane of polarized light. From the given options, D-Glucose and L-Proline are chiral.
Therefore, the solutions that show optical activity are:
- Solution of D-Glucose
- Solution of L-Proline
Important Questions from Structure and Function of Biomolecules
- An element that is present in a nucleotide but not in a nucleoside is __________.
- Which one of the following coenzymes is utilised by alanine racemase for the conversion of L-Alanine to D-Alanine?
An octapeptide composed of these L-amino acids – Lys, Thr, Ser, Met, Arg, Trp, Tyr, Glu was subjected to analyses with the following outcomes:
P. The N-terminal sequencing analysis by Sanger's method yielded 'Ser' at the N-terminus
Q. Chymotrypsin treatment gave a pentapeptide, a ‘Tyr' containing dipeptide and a free ‘Glu'
R. Cyanogen bromide treatment gave two tetrapeptides
S. Trypsin treatment gave two tripeptides and a dipeptide
Which one of the following is the correct octapeptide sequence?
- Which of the following amino acids contain(s) two chiral carbons?
- Terpenoids are made of ________ units
