Pressure Dependence of the Selfassociation of 9‐Methylpurine in Aqueous Solution

The selfassociation of 9‐methylpurine (9‐MP) in aqueous solution has been studied by analysis of the proton chemical shift concentration dependence at pressures up to 1500 bar. To this purpose a high pressure glass cell has been developed, fitting into the standard receiver coil of a high resolution NMR spectrometer. The influence of pressure on the UV‐spectra of 9‐MP has been measured. Pressure favours self association of 9‐MP. The thermodynamic data derived from an isodesmic association model are: K (1 bar, 20°C) = 1.4 mol −1 ; K (1500 bar, 20°C) = 1.8 mol −1 ; Δ H (van't Hoff) = ‐(9.6 ± 1)kj·mol −1 and Δ V = ‐(4.0 ± 1.0)cm 3 · mol −1 .