A quantum insight into the study of enzyme-ligand interactions

A QUANTUM INSIGHT INTO THE STUDY OF ENZYME-LIGAND INTERACTIONS 

Two distinct general approaches are possible in the area of modelling enzymatic systems using quantum mechanical (QM) methods. The first consists in studying the system, or part of it, isolated in the gas phase. The second focuses on the study of the system including solvation. 

The inclusion of the solvent surrounding would be desirable in all cases to obtain reliable results for reactions in enzymes active sites. However, the most reliable methods are computationally expensive and the direct application of e.g. ab initio QM methods to model condensed-phase systems is presently impractical. Accurate ab initio methods [295] are only viable in the study of small to medium-sized molecules whereas density functional theory [296] and semiempirical methods [297] although computationally more versatile are still very much limited considering the fact that we are dealing with thousands of atoms. However, in any approach to studying a particular subject, the quality of the model used should be paramount in the mind of the researcher and therefore any method that could succeed in providing a computationally feasible shape of reality is worth investigating. 

Like with any other method, the desired quality of the results has to be balanced with the cost of the calculation and, accordingly, a choice must be made. Generally the more cpu time you can afford to spend, the more reliable will be the results. As computer power grows, QM methods will grow more powerful as a means to study enzyme-ligand interactions. 

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