Hyperchromic shift refers to an increase in the absorption of light, leading to a higher absorbance, often observed in certain chemical or biological substances upon undergoing a structural change. This shift is typically associated with changes in the electronic or molecular environment of a chromophore a part of a molecule responsible for its color.
Hyperchromic shift is commonly observed in the context of nucleic acids, particularly DNA and RNA. In the UV-VIS spectrum, nucleic acids exhibit characteristic absorption peaks associated with their nucleobases (adenine, thymine, cytosine, guanine, and uracil). When there is a change in the structure or conformation of the nucleic acid, such as denaturation or melting of DNA strands, it can lead to a hyperchromic shift.
Key points about hyperchromic shift in nucleic acids:
Denaturation of DNA: DNA consists of two complementary strands held together by hydrogen bonds between complementary nucleotide bases. When DNA undergoes denaturation, the hydrogen bonds break, and the two strands separate. This structural change often results in an increase in the absorption of UV light.
Base stacking: Hyperchromic shift is associated with changes in the stacking interactions between adjacent nucleobases in the denatured state. The disruption of base stacking can lead to an increase in the absorbance of UV light.
Measurement: Hyperchromic shift is quantified by measuring the increase in absorbance at a specific wavelength (commonly around 260 nm for nucleic acids) before and after the structural change
Biological significance: Hyperchromic shift is relevant in studies related to DNA melting, DNA-protein interactions, and processes such as polymerase chain reaction (PCR) where the denaturation and renaturation of DNA are involved.
Hyperchromic shift is not limited to nucleic acids; similar phenomena can be observed in other chromophoric molecules undergoing conformational changes. The increase in absorbance is attributed to changes in the electronic environment or the exposure of additional chromophores to incident light.