(H₂O)₁₀-（Glycine）_n（n=1-3） Complex: A Theoretical Investigation Of Configurations And Properties

Glycine, also known as amino acetic acid, plays an important role in biology andchemistry. As one of the basic material life, people are concerned about the way of thecombination of glycine and water clusters.In this paper, we will discuss about structure and property of (H2O)10-(Glycine)n(n=1-3) complexes to explore the gathered way of small organic molecular in watercluster. First, we use the Compass molecular force field and molecular dynamics ofNVT. It produces a series initial configurations of (H2O)10-(Glycine)n(n=1-3).Then,thethe1500kinds of initial configuration of (H2O)10-(Glycine)n(n=1-3) are energyminimized by density functional theory GGA/PBE. For the lower energy structures,we optimized them at UPBEPBE/6-31g(d) level and discuss their configuration andphysical properties.1.All the glycine in the configurations of the (H2O)10-Glycine are far away fromwater clusters. There are17hydrogen bonds in the most stable configuration and thesecond stale configuration, respectively. The number is larger than any of others’ andthe average length of the hydrogen bonds is shorter than that of others. Among them,all the-COOH group is attached to the water molecular. The-COOH group and watermolecular then form hydrogen bond and come into a cycle. The hydrogen atom of the-COOH group of the glycine acts as proton donor and the oxygen atom of the watermolecular acts as proton acceptor. Because of the interaction of the molecular andglycine, the length of the hydrogen bond between water molecular and glycine isshorter than that of the monomers, leading to the increase of the energy.2. All the glycine in the configurations of the (H2O)10-(Glycine)2are far awayfrom water clusters, too. The-COOH group and the-NH2group in the most stableconfiguration and the second stable configuration are attached to water molecular andthe configurations present the cage structure. There are21hydrogen bonds in the moststable configuration and22hydrogen bonds in the second most stable configuration. The number of the hydrogen bond of the two configurations is larger than that ofothers’. This states that the more hydrogen bonds, the configuration are more stale.3. All the glycine in the configurations of the (H2O)10-(Glycine)3are far awayfrom water clusters, too. And the three glycine is far away from each other. There are24hydrogen bonds in the most stable configuration and25hydrogen bonds in thesecond most stable configuration. The number of the hydrogen bond of the twoconfigurations is larger than that of others. The-COOH group and the-NH2group inthe most stable configuration and the second stale configuration are attached to watermolecular and the configurations present the cage structure. Similar to(H2O)10-Glycine and (H2O)10-(Glycine)2, the stability decreases with the hydrogenbond increasing.In our study, instead of embeding into water cluster, glycine is absorbed on thesurface of water cluster. Mainly intermolecular hydrogen bond is formed betweenH2O and the oxygen atoms of-COOH and-OH of glycine. Most of them is single andmultiple hydrogen bond. Compared with the length of hydrogen bond in water, thelength of that between the water of glycine is shorter.Because of the interaction between water and glycine, compared with monomer,the length of water and glycine get shorter. The more hydrogen bonds, the more stableconfiguration. The structure of the complexes presents stable cage structure.