PROTON CHEMICAL SHIFT IN UREAS-ELECTROLYTE-WATER SYSTEMS

The proton magnetic resonance of water in aqueous electrolytes solutions has been determined in the absence and presence of 6M ureas at 34°C. The electrolytes used in this paper are MgCl2 and NaClO4. The former is a typical structure maker and the latter a typical structure breaker. The ureas used are urea, tetramethylurea and 1, 3-dimethylurea. The first two are structure breakers and the last is a structure maker at 6M concentration. All proton shifts, Δδ, were reported in cps relative to pure water or to 6M ureas aqueous solutions. The positive shift for MgCl2 became higher (a downfieled shift) in the presence of urea and tetramethylurea and less positive (an upfield shift) in the presence of 1, 3-dimethylurea. The negative shift for NaClO4 became more negative in the presence of 1, 3-dimethylurea and less negative in the presence of urea and tetramethylurea. These results suggest that urea and tetramethylurea, structure breakers, increase the structuremaking propensity of MgCl2 and decrease the structure-breaking propensity of NaClO4 and that 1, 3-dimethylurea acts vice versa. The effects of ureas on proton shifts for the electrolytes are explained in terms of water structure changes caused by ureas.