Models SCAAS

FIGURE 4.8. A surface constrained all-atom (SCAAS) model for solvated proteins. The figure depicts the different regions of the model around Asp 3 in the protein BPTI. Region a includes the solute atoms and the unconstrained protein atoms as well as the unconstrained water molecules. Region b is the surface constraints region which is surrounded by a bulk region (see Ref. 10 for more details). 

Folding energy and catalysis, 227 Force field approach, consistent 113 Free energy, 43,47 of activation, 87-90, 92-93, 93, 138 of charging processes, 82 convergence of calculations of, 81 in proteins, SCAAS model for, 126 of reaction, 90... 

Luzhkov, V. and Warshel, A. Microscopic models for quantum mechanical calculations of chemical processes in solutions LD/AMPAC and SCAAS/AMPAC calculations of solvation energies, J.Comp.Chem 13 (1992), 199-213... 

V. Luzhkov and A. Warshel, /. Comput. Chem., 13, 199 (1992). Microscopic Models for Quantum Mechanical Calculations of Chemical Processes in Solutions LD/AMPAC and SCAAS/AMPAC Calculations of Solvation Energies. 

A. Warshel and G. King, Chem. Phys. Lett., 121, 124 (1985). Polarization Constraints in Molecular Dynamics Simulation of Aqueous Solution The Surface Constraint All Atom Solvent (SCAAS) Model. 

A drastic reduction has been introduced by King and Warshel with their SCAAS (surface constrained all atoms solvent) model. In this model the space is divided into three regions by two concentric spherical surfaces. The outer region is treated as a continuum dielectric, the inner sphere contains M and some solvent molecules (water), the intermediate layer has a thickness sufficient to contain a layer of solvent molecules. Water molecules in both internal regions are described as dipoles. The position and the orientation of such dipoles describe a solvent coordinate Q, which is coupled to a spatial coordinate R to describe a reaction in a 2D space. MD simulations are used to define the time-dependence of both coordinates (Q(r)> and / (/)). This model introduces new and important features in the area of QM/MM methods, but little attention is paid to boundary conditions. 

---