Effect of guanidine hydrochloride on the structure of water-dimethylformamide (DMF) solvent mixtures

Some binary liquid mixtures display microheterogeneity (MH), where molecular clustering of each component is observed on the microscale, but on the macroscale the components are fully miscible. This is suggested to be the reason behind certain mixture characteristics, such as non-ideal thermodynamic quantities and water activity. Binary solvent mixtures are also commonly used in crystallisation, as they can provide different crystallisation outcomes than the pure solvents. Our overarching project aims to investigate how the structure of binary solvent mixtures influences the outcome of solute recrystallisation. The groups prior work using MH water-acetonitrile mixtures has shown that solute-solute and solute-solvent interactions change with the occurrence of solvent clustering. In a previous experiment on NIMROD, we have investigated the structure of water-DMF mixtures at 15, 35, and 50 mole% DMF, where we saw a self-association of the individual species. We propose to investigate these solvent mixtures with guanidine hydrochloride dissolved at 10 mole% to gauge how the presence of a solute alters the structure of the solvent. 7 isotopic substitutions will be used to differentiate between water, DMF, and guanidine hydrochloride hydrogen atoms, totalling to 21 samples. Assuming 4 hours per sample and 2 hours per standard and empty, we request 5 days of beamtime on NIMROD.