NMR Reveals How Ultraviolet Light Damages a DNA Fragment's Bases

This 1974 paper by Rahn and Schleich, published in Nucleic Acids Research, is a chemistry study of how ultraviolet light alters the structure of a DNA-derived molecule — not a biological or skincare study.

The researchers worked with apurinic acid, a single-stranded polydeoxyribonucleotide (a chain of DNA building blocks missing certain bases) produced by chemically removing purine bases from DNA. Using proton magnetic resonance, a technique that reads molecular structure by tracking how hydrogen atoms respond in a magnetic field, they measured signals from the thymine and cytosine bases in water at 25°C. They found two distinct thymine methyl signals, separated by 0.045 parts per million, which they linked to whether a thymine base sat next to another pyrimidine base or not.

When the sample was exposed to ultraviolet light, one signal weakened and two new signals appeared, matching known UV-damage products called cyclobutane dimers, formed between cytosine-thymine and thymine-thymine pairs. These new signals vanished after photoreversal, a process that undoes this type of damage. The authors conclude apurinic acid is a workable model for studying such chemical changes, but the study is confined to test-tube chemistry — it says nothing about living cells, tissue, or biological effects.