Hyperchromic Effect
Definition and meaning of Hyperchromic Effect in chemistry.
The hyperchromic effect is an increase in absorbance, reflecting an increase in the molar absorptivity, of a chromophore at a given wavelength, most commonly observed when double-stranded DNA denatures into single strands. It reflects a change in absorption intensity rather than a shift in the wavelength of maximum absorption.
In more detail
In native double-stranded DNA, the stacked, parallel arrangement of aromatic base pairs partially shields them from ultraviolet light through electronic interactions between neighboring bases, a phenomenon called hypochromicity. When the strands separate (denature), base stacking is lost and the bases become more exposed to light, causing absorbance at 260 nm to rise. This hyperchromic shift is measured continuously as DNA is heated to construct a melting curve and determine the melting temperature (Tm), the point at which 50% of the DNA has denatured.
Key facts
| Field | Biochemistry |
|---|---|
| Also known as | Hyperchromicity, hyperchromic shift |
| Opposite of | Hypochromic effect |
| Common monitoring wavelength | 260 nm (nucleic acids) |
When a solution of double-stranded DNA is heated past its melting temperature, its absorbance at 260 nm increases by roughly 30 to 40%, a hyperchromic shift used in UV-vis melting experiments to confirm strand separation.
Frequently asked questions
What causes the hyperchromic effect during DNA denaturation?
Base stacking in double-stranded DNA partially quenches UV absorption through electronic interactions between adjacent aromatic bases. When the strands separate, this stacking is disrupted, exposing the bases and increasing absorbance at 260 nm.
How is the hyperchromic effect used experimentally?
It is tracked by measuring absorbance at 260 nm as a DNA sample is heated, producing a sigmoidal melting curve whose midpoint gives the melting temperature (Tm) of the duplex.