Computational requirements, MOPAC

In short, each reaction family could be described with a maximiun of three parameters (A, Eo, a). Procurement of a rate constant from these parameters required only an estimate of the enthalpy change of reaction for each elementary step. In principle, this enthalpy change of reaction amoimted to the simple calculation of the difference between the heats of formation of the products and reactants. However, since many model species, particularly the ionic intermediates and olefins, were without experimental values, a computational chemistry package, MOPAC, ° was used to estimate the heat of formations on the fly . Ihe organization of the rate constants into quantitative structure-reactivity correlations (QSRC) reduced the number of model parameters greatly Ifom O(IO ) to 0(10). 

The computational effort or time required for the generation of an SCF using MOPAC rises as the third power of the size of the system. For MOZYME, the time is expected to be simply proportional to the size of the system. In Table 2 is presented the time required for single SCF calculations on a series of polypeptides, calculated on a SUN SPARC-2, a workstation running at about 6 megaflops. The largest system reported corresponds to the entire protein Rhizomucor meihei lipase. 

---