The structural transition of a single polymer chain with chain length of 100,200 and 300 beads was investigated by parallel tempering MD simulation.Our simulation results can capture the structural change from random coil to orientationally ordered structure with decreasing temperature.The clear transition was observed on the curves of radius of gyration and global orientational order parameter P as the function of temperature,which demonstrated structural formation of a single polymer chain.The linear relationships between three components of square radius of gyration R_（gx）~2,R_（gx）~2,R_（gz）~2 and global orientational order P can be obtained under the structurally transformational process.The slope of the linear relationship between x（or y-axis） component R_（gx）~2（or R_（gy）~2） and P is negative,while that of RL as the function of P is positive.The absolute value of slope is proportional to the chain length.Once the single polymer chain takes the random coil or ordered configuration,the linear relationship is invalid.The conformational change was also analyzed on microscopic scale.The polymer chain can be treated as the construction of rigid stems connecting by flexible loops.The deviation from exponentially decreased behavior of stem length distribution becomes prominent,indicating a stiffening of the chain arises leading to more and more segments ending up in the trans state with decreasing temperature.The stem length N_（tr） is about 21 bonds indicating the polymer chain is ordered with the specific fold length.So,the simulation results,which show the prototype of a liquid-crystalline polymer chain,are helpful to understand the crystallization process of crystalline polymers.
We study the translocation of a protein-like chain through a finite cylindrical channel using the pruned-enriched Rosenbluth method （PERM） and the modified orientation-dependent monomer-monomer interaction （ODI） model. Attractive channels （εcp = -2.0, -1.0, -0.5）, repulsive chanaels （εcp： 0.5, 1.0, 2.0）, and a neutral channel （εcp =- 0） are discussed. The results of the chain dimension and the energy show that Z0 ： 1.0 is an important case to distinguish the types of the channels. For the strong attractive channel, more contacts form during the process of translocation. It is also found that an external force is needed to drive the chain outside of the channel with the strong attraction. While for the neutral, the repulsive, and the weak attractive channels, the translocation is spontaneous.
The effect of channel-protein interaction on the translocation of a protein-like chain through a finite channel under certain electric field was studied by using dynamical Monte Carlo simulations. The interior behavior of chain conformation under different interactions was investigated, such as the number of monomers outside of channel nout, monomers inside of channel nm, mean-square radius of gyration 〈 S2 〉 and the average energy 〈U〉. It shows that with strong attractive interaction, the translocation is more difficult than moderate interaction. At the same time, the dependence of translocation time with different interactions shows that moderate repulsive interaction （εcp = 0.5） accelerates the translocation. Although the waiting time for successful translocation of εep = 1.0 is the longest, the average translocation time is not very large. It is far smaller than that of εep = -1.0. The probability distributions of translocation time p（t＇） and the probability distributions of three duration times p（t1＇）, p（t2＇） and p（t3＇） were all discussed. Log-normal distributions are found. All these findings will strengthen the understanding of protein translocation.
Elastic behaviors of protein-like chains are investigated by Pruned-Enriched-Rosenbluth method and modified orientation-dependent monomer-monomer interactions model. The protein-like chain is pulled away from the attractive surface slowly with elastic force acting on it. Strong adsorption interaction and no adsorption interaction are both considered. We calculate the characteristic ratio and shape factor of protein-like chains in the process of elongation. The conformation change of the protein-like chain is well depicted. The shape of chain changes from “rod” to “sphere” at the beginning of elongation. Then, the shape changes from “sphere” to “rod”. In the end, the shape becomes a “sphere” as the chain leaves away from the surface. In the meantime, we discuss average Helmoholtz free energy per bond, average energy per bond, average adsorbed energy per bond, average α-helical energy per bond, average β-sheet energy per bond and average contact energy per bond. On the other hand, elastic force is also studied. It is found that elastic force has a long plateau during the tensile elongation when there exists adsorption interaction. This result is consistent with SMFS experiment of general polymers. Energy contribution to elastic force and contact energy contribution to elastic force are both discussed. These investigations can provide some insights into the elastic behaviors of adsorbed protein chains.
