title: Structure of DNA hydration shells studied by Raman spectroscopy.
abstract: We have used Raman scattering to study the water O-H stretching modes at approximately 3450 and approximately 3220 cm-1 in DNA films as a function of relative humidity (r.h.). The intensity of the 3220-cm-1 band vanishes as the r.h. is decreased from 98% to around 80%, which indicates that the hydrogen-bond network of water is disrupted in the primary hydration shell (which therefore cannot have an "ice-like" structure). The number of water molecules in the primary hydration shell was determined from the intensity of the approximately 3200-cm-1 band as about 30 water molecules per nucleotide pair. The approximately 3400-cm-1 O-H stretch band was used for determining the total water content, and this band persists at 0% r.h., implying that 5-6 tightly bound water molecules per nucleotide pair remain. The frequency of the approximately 3400-cm-1 O-H stretch mode is lower by 30 to 45 cm-1 in the primary hydration shell compared to free water. The water content as a function of r.h. obtained from these experiments agrees with gravimetric measurements. The disappearance of the approximately 3200-cm-1 band and the shift of the approximately 3400-cm-1 O-H stretch band provide a reliable way of measuring the hydration number of DNA.
authors.forename: N J
authors.initials: NJ
authors.lastname: Tao
authors.forename: S M
authors.initials: SM
authors.lastname: Lindsay
authors.forename: A
authors.initials: A
authors.lastname: Rupprecht
mesh_terms: D004247:DNA; D008094:Lithium; D009690:Nucleic Acid Conformation; D012964:Sodium; D013059:Spectrum Analysis, Raman / Q000379:methods
chemical_list: D004247:DNA; D008094:Lithium; D012964:Sodium