Helical region of the potential energy surface of α‐aminoisobutyric acid: A theoretical study

The helical region of the potential energy surface of blocked α‐aminoisobutyric acid (Aib) dipeptide has been studied by using ab initio and semiempirical quantum mechanical methods, as well as force‐field‐derived methods. Depending on the method, an α‐helix or a 310‐helix is found to be the energy minimum. The conformations obtained from computations performed at the ab initio quantum mechanical level, as well as by using the AMBER force field, are in excellent agreement with X‐ray data. Semiempirical results display some important differences with regard to experimental data. On the other hand, the CVFF force field predicts no energy minimum in the helical region of the Aib potential energy surface.