Explore The Stable Conformations Of Tripeptides Using Ala-tripeptide As An Example

Firstly, this article tries to explore a quick method to confirm the stable conformations ofala-tripeptide. At first we scan the potential energy surface of ala-tripeptide using thehf/6-31g（d,p） method, the dihedral angels φ2、ψ2were fixed when we scan dihedral angelsφ1、ψ1. From the results, we can find that when the fixed dihedral angels changed, thecontours of the figures are alike. From this we know that there is little impact between thesetwo groups of dihedral angels. On the basis of the stable conformations of ala-dipeptide, setthe initial dihedral angels of ala-tripeptide to the dihedral angels of ala-dipeptide`s stableconformation, then we can get the stable conformations of ala-tripeptide faster, the structureswere optimized using B3LYP/6-31g（d,p） method. Using this method as a base, we get thestable conformations of other tripeptides in a same way.We can get the properties of big systems of molecules using ABEEMσπ/MM faster andaccurately, we get the stable conformations of ala-tripeptide`s and other tripeptides usingABEEMσπ/MM on the basis of the method above, then we compare the results with theresults of B3LYP/6-31g（d,p） method. The average deviation of the dihedral angels ofala-dipeptide`s different stable conformations is3.79°;and the average deviation of thedihedral angels of other tripeptides`stable conformations is2.92°, it shows that we can get thestable conformations of tripeptides using ABEEMσπ/MM accurately. The total energy is animportant physical quantity of a molecule, then we caculte the total energies of differenttripeptides using ab initio （MP2/6-311++G（d,p）） method and ABEEMσπ/MM, the absolutederibation is between0.0036kcal/Mol and0.0813kcal/Mol, the relative deribation isbetween0.0064×10^-6and0.1165×10^-6, the linear correlation coefficient is1, it shows that wecan get the total energies of tripeptides using ABEEMσπ/MM accurately.