Density function theory (DFT) at the level of B3LYP/6-31＋＋g** was employed to theoretically investigate the intramolecular proton transfer through water bridge chain from carboxyl to amino in glycine cluster. The number of water molecules plays an important role in the proton transfer through water bridge chain. When the number of water molecules in water bridge chain is less than 5, the proton transfer through water bridge chain will complete cooperatively in one step, otherwise the proton transfer will complete in two steps via an intermediate. With the increase of water molecule chain increasing the activation energy but reducing the free energy of the reaction, so, the increase of water molecule chain is not in favor of the proton transfer dynamically, but is in favor of proton transfer thermally.

Key words: hydrated glycine, proton transfer, zwitterions, water bridge chain, DFT