Hydration - Introduction

    The importance of the shape-function relationship in biomolecules is well known. For proteins, nucleotides and other biomolecules to carry out their tasks, they must have the correct three-dimensional conformation. Water, with its large dipole moment and ability to act as both an excellent hydrogen bond donor and acceptor, forms strong interactions with and dissolves biomolecules which typically contain functional groups that are polar, acidic, basic, hydrogen bond donors and/or hydrogen bond acceptors. As a result, water plays an important roll in the conformation of biomolecules, yet one that is not well understood at this time.
    With the recent development of soft ionization techniques such as matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI), it has become possible to study large, fragile biomolecules in the gas phase by mass spectrometric methods. This technique allows hydration effects to be studied one water molecule at a time, providing a bridge between the gas and solution phases.
    In an attempt to better understand the interaction between biomolecules and water, we have performed temperature-dependent equilibrium experiments on an electrospray ionization mass spectrometer equipped with a drift cell to measure ΔH° and ΔS° values for reactions of gas-phase protonated and deprotonated peptides (P±zH) with water.

    Molecular mechanics (MM) and density functional theory (DFT) have also been used to determine hydration energies as well as structures for the species involved in the above reaction.
    The following aspects of peptide hydration have been summarized in reference 1:

  • The significance of ionic groups
  • Hydration of ionic groups
    • The ammonium group
    • The guanidinium group
    • The carboxylate group
  • Molecules with several ionic groups
    • Multiply charged ions
    • Salt bridges
  • Structural changes induced by hydration
    • Change of conformation
    • Zwitterion formation
  • Entropy of hydration

    More detailed information can be found in the following pages and in references 2 to 4:


  1. "Hydration of Small Peptides" T. Wyttenbach, D. Liu, M. T. Bowers Int. J. Mass Spectrom. 2005, 240, 221-232

  2. "Hydration of Protonated Primary Amines: Effects of Intermolecular and Intramolecular Hydrogen Bonds" D. Liu, T. Wyttenbach, M. T. Bowers Int. J. Mass Spectrom. 2004, 236, 81-90

  3. "Investigation of Noncovalent Interactions in Deprotonated Peptides: Structural and Energetic Competition between Aggregation and Hydration" D. Liu, T. Wyttenbach, C. J. Carpenter, M. T. Bowers J. Am. Chem. Soc. 2004, 126, 3261-3270

  4. "Sequential Hydration of Small Protonated Peptides" D. Liu, T. Wyttenbach, P. E. Barran, M. T. Bowers J. Am. Chem. Soc. 2003, 125, 8458-8464

Bowers group members who have worked on these projects include: