Chapter 14, Problem 14.51P

Interpretation Introduction

Interpretation:

Which portion of doxorubicin intercalates into DNA and why it has little difficulty doing so, is to be explained.

Concept introduction:

The nitrogenous bases form hydrogen bonds between opposing DNA strands to form the double helix of DNA found in the nucleotides. The four nitrogenous bases found in DNA are guanine (G), adenine (A), cytosine (C), and thymine (T)., Guanine is always paired with cytosine, and Adenine is always paired with thymine. These are recognized as base pairs.

Each of these ring systems is aromatic, consists of atoms that have planar geometries, and are ${\text{sp}}^{\text{2}}$ hybridized. The aromaticity of nitrogenous bases is advantageous. First, it allows each base pair to be planar and to maximize the overlap of the p orbitals that make up the π system of MOs. The hydrogen bonding essentially locks complementary bases in the same plane. DNA base pairs are “stacked” on the inside of DNA. The second advantage of aromaticity of base pairs is it provides stability to the DNA double helix. Because nitrogenous bases are stacked on top of one another, p AOs from the aromatic system of one nitrogenous base overlaps with p AOs from another nitrogenous base attached to an adjacent sugar. This is a stabilizing interaction called $\text{π}$ stacking.