Frontiers in Computational Chemistry presents contemporary research on molecular modeling techniques used in drug discovery and the drug development process: computer aided molecular design, drug discovery and development, lead generation, lead optimization, database management, computer and molecular graphics, and the development of new computational methods or efficient algorithms for the simulation of chemical phenomena including analyses of biological activity. The fourth volume of this series features four chapters covering natural lead compounds, computer aided drug discovery methods in Parkinson's Disease therapeutics, studies of aminoacyl tRNA synthetase inhibition in bacteria, computational modeling of halogen bonds in biological systems and molecular classification of caffeine and its metabolites.