Here are a few questions about water that I have either read, or which recurringly occured to me through reading about the stuff that life's made from. Some of them are easy to answer, some are difficult. Some are general questions, others are subsets of these general questions. Most of them are connected. Many are of the "simple-yet-extremely-tricky-to-answer" kind. I know the answer to some of the questions, don't know those to others, and am not sure about yet other ones.
1. What is the strength of an average hydrogen bond in bulk water?
2. What is the strength of an average hydrogen bond in "biological water" (solvating proteins for example) and the strength of a hydrogen bond in the first hydration shell?
3. What is the lifetime of an average hydrogen bond in bulk water? In biological water?
4. Is hydrogen bond exchange between water a discrete phenomenon or a concerted one?
5. How many hydrogen bonds on an average does a water molecule form in bulk? In confinement? In biological water?
6. Is there a long-range "hydrophobic bond"?
7. Can one always predict de novo whether displacement of a water molecule from a hydrophobic pocket of a protein by a ligand will lead to greater binding affinity? How?
8. How does enthalpy-entropy compensation work in case of water?
9. What is the difference between hydration dynamics of bulk water and biological water?
10. What is the exact difference between hydrogen bonding structure and dynamics in ice and liquid water?
11. How does the molecular structure and hydrogen bond network of liquid water change according to the temperature? What is the difference between these properties for bulk water at room temperature and at 4 degrees celsius (at maximum density)? For biological water? Corollary of this question: what changes does the molecule structure of water undergo at low temperatures in biological systems and around biomolecules?
12. How do we explain the Hofmeister effect- the differential ability of various ions to precipitate proteins?
13. How does the hydrophobic effect depend on size of solute? On conformation?
14. Can we develop a comprehensive first principles water model?
More to come as I think about this. Some of these questions have been addressed before at the Water in Biology blog.
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