Hydration Water Drives the Self-assembly of Guanosine Monophosphate.

Guanosine monophosphate (GMP) is a nucleotide that can self-assemble in aqueous solution under certain conditions. An understanding of the process at the molecular level is an essential step to comprehend the involvement of DNA substructures in transcription and replication, as well as their relationship to genetic diseases, such as cancer. We present the temperature-dependent terahertz (1.5-12 THz, 50-400 cm-1 ) absorptivity spectra of aqueous Na2 GMP solution (GMP) in comparison with the aqueous solutions of other RNA nucleotides. Distinct absorption features were observed in the spectrum of GMP, which we attribute to the intramolecular modes of the self-assemblies (i.e., G-complexes) that, at 1 M, start to form at 313 K and below. Changes in broad band features of the terahertz spectrum were also observed, which we associate with the release of hydration water in the temperature-dependent formation of G-quadruplex (G4). Using a state-of-the-art THz calorimetry approach correlating spectroscopic to thermodynamic changes, we propose a molecular mechanism of hydrophilic hydration driving GMP self-assembly as a function of temperature. The free energy contribution of hydrophilic hydration is shown as a decisive factor in G4 formation. Our findings spotlight the role of hydration in the formation of macromolecular structure, and suggest the potential of hydration-tuning for regulating DNA transcription and replication.