Single molecular insight into steric effect on C-terminal amino acids with various hydrogen bonding sites

Amino acids are basic units to construct a protein with the assistance of various interactions.During this building process,steric hindrance derived from amino acid side groups or side chains is a factor that could not be ignored.In this contribution,adsorption behaviors of C-terminal amino acid derivatives with amino acid residues fused in 3,4,9,10-perylenetetracarboxylic dianhydride were investigated by scanning tunneling microscopy(STM)and density functional theory(DFT)calculations at various liquid/solid interfaces.STM results at 1-phenyloctane/HOPG interface show that N,N'-3,4,9,10-perylenedicarboximide(GP)and N,N'-methyl-3,4,9,10-perylenedicarboximide(AP)formed linear and herringbone structures,respectively.The driving force could be attributed to different H-bonding sites induced by steric hindrance at side groups.N,N'-Benzyl-3,4,9,10-perylenedicarboximide(PP)generates both linear and herringbone structures because steric hindrance changes the H-bonding sites between PP molecules,whereas N,N'-isopropyl-3,4,9,10-perylenedicarboximide(LP)failed to be imaged because of strong steric hindrance coming from larger side group.To further investigate the impact of steric hindrance,we utilized octanoic acid(OA)as solvent to capture the adsorption details of LP and PP.We found that OA molecules drag PP and LP molecules in a different direction to generate linear structure,impeding the molecular rotation.The structure–solvent relationship shows that the steric hindrance is brought by the large side group,which makes it easier to recognize OA molecules at the interface.These results demonstrate that steric effect plays a significant role in altering interaction sites of the compounds during the adsorption process at the liquid/solid interface.

Formation Sites and Microscopic Conformation Study on the Konjac Glucomannan Molecular Helices

In this work, the formation sites, helical parameters and hydrogen bond positions of Konjac glucomannan molecular helices were investigated using molecular dynamic simulation method. To our interest, the KGM chain is mainly composed by local left and right helix struetttres. The formation sites of KGM chain might locate at the chain-segments containing acetyl groups, and the left helix is the favorable conformation of KGM. Temperature-dependent molecule conformation study indicates that the right helix is dominant when the temperature is lower than 343 K, above which, however, the left helix is dominating （right helix disappears）. In addition, intramolecular hydrogen bonds in the left helix can be found at the -OH groups on C（2）, C（4） and C（6） of mannose residues; comparably, the intramolecular hydrogen bonds in the right helix can be mainly observed at the -OH groups on C（4） and C（6） of the mannose residues and C（3） of the glucose residues. In conclusion, molecular dynamic simulation is an efficient method for the microscopic conformation study of glucomannan molecular helices.

A New Peer-to-Peer Topology for Video Streaming Based on Complex Network Theory

A new wave of networks labeled Peer-to-Peer(P2P) networks attracts more researchers and rapidly becomes one of the most popular applications.In order to matching P2 P logical overlay network with physical topology,the position-based topology has been proposed.The proposed topology not only focuses on non-functional characteristics such as scalability,reliability,fault-tolerance,selforganization,decentralization and fairness,but also functional characteristics are addressed as well.The experimental results show that the hybrid complex topology achieves better characteristics than other complex networks' models like small-world and scale-free models;since most of the real-life networks are both scale-free and small-world networks,it may perform well in mimicking the reality.Meanwhile,it reveals that the authors improve average distance,diameter and clustering coefficient versus Chord and CAN topologies.Finally,the authors show that the proposed topology is the most robust model,against failures and attacks for nodes and edges,versus small-world and scale-free networks.