2D IR OF GUANIDINE IN WATER

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Recent FTIR investigations of the OH stretch mode of water in guanidine solutions revealed a large frequency shift to lower frequency of the O-H stretch mode after guanidine addition, arising questions about the structure of the solvation shell of water molecules around the guanidine ions. Guanidine is often used as a protein denaturant. It may act as a denaturant because it binds to proteins directly since it has 3 NH2 groups that mimic water molecules in their H-bonding ability. The goal of this project is to generate a microscopic description of the interaction between guanidine and water and deduce why guanidine is so effective as a denaturant in biology. It has been postulated that guanidine changes the structure of the water network. By using dual frequency 2D-IR, we are able to visualize the interaction between guanidine and the surrounding water as well as the water-water interactions. By using 2D-IR, we should be able to tell between the following: Are the water molecules surrounding guanidine isolated from the bulk water? Do the frequency fluctuations of the OH stretch modes of the solvation shell manifest coupling to the ion? Or are the water molecules surrounding guanidine similar in their physical properties to the bulk water?