🧲 Spectroscopy: Biomolecular NMR
Nuclear Magnetic Resonance (NMR) spectroscopy exploits the magnetic properties of atomic nuclei with non-zero spin ($I = 1/2$: $^1H, ^{13}C, ^{15}N$) to determine macromolecular structures and conformational dynamics directly in solution.
1. 2D & 3D Heteronuclear NMR Experiments
- ¹H-¹⁵N HSQC (Heteronuclear Single Quantum Coherence): Provides a definitive “protein fingerprint” where every amino acid residue (except proline) yields a single cross-peak representing its backbone amide $N-H$ group. Dispersed peaks indicate folded tertiary structure; collapsed central peaks indicate unfolded disorder.
- NOESY (Nuclear Overhauser Effect Spectroscopy): Generates cross-peaks via dipole-dipole cross-relaxation through space (not through chemical bonds). Intensity is inversely proportional to the sixth power of distance ($I propto r^{-6}$), providing precise spatial distance restraints (< 5 Å) to fold the 3D structure.