Methods and systems for calculating free energy differences using a modified bond stretch potential

Abstract

A method and system for calculating the free energy difference between a target state and a reference state. The method includes determining one or more intermediate states using a coupling parameter, performing molecular simulations to obtain ensembles of micro-states for each of the system states, and calculating the free energy difference by an analysis of the ensembles of micro-states of the system states. The method can be particularly suited for calculating physical or non-physical transformation of molecular systems such as ring-opening, ring-closing, and other transformations involving bond breaking and/or formation. A soft bond potential dependent on a bond stretching component of the coupling parameter and different from the conventional harmonic potential is used in the molecular simulations of the system states for the bond being broken or formed during the transformation.

Description

BACKGROUND[0001]Free energy is a fundamental molecular property that plays an essential role in characterizing chemical and biological systems. An understanding of the free energy behavior of many chemical and biochemical processes, such as protein-ligand binding, can be of critical importance in endeavors such as rational drug design (which involves the design of small molecules that bind to a biomolecular target).[0002]Computer modeling and simulations are often used in free energy studies. In most instances, evaluation of accurate absolute free energies from simulations is extremely difficult, if at all possible. Hence, the free energy difference between two well-delineated thermodynamic states, or relative free energy, are often used as a study system to provide insight to particular systems, such as a relative binding affinity of a ligand predicated on the measured affinity of a different but similar ligand (e.g., a congeneric ligand).[0003]In the relative free energy calculati...

AI Technical Summary

Benefits of technology

[0034]if Aa and Ab are valence-bonded to each other in the reference state and not valence-bonded in the target state, and the nonbonded interactions between Ai and Aj are excluded in the reference state but not excluded in the target state, varying each of λelecAex and λvdwAex according to a schedule for each of the intermediate states along the transformation from the reference state to the target state such that when λvdwAex is smaller than 1 for an intermediate state, λelecAex is 0 for that intermediate state; and

[0035]if Aa and Ab are not valence-bonded to each other in the reference state and valence-bonded in the target state, and the nonbonded interactions between Ai and Aj are not excluded in the reference state but excluded in the target state, varying each of λelecBex and λvdwBex according to a schedule for each of the intermediate states along the transformation from the reference state to the target state such that when λvdwAex is smaller than 1 for an intermediate state, λelecAex is 0 for that intermediate state.

Problems solved by technology

In most instances, evaluation of accurate absolute free energies from simulations is extremely difficult, if at all possible.

It is noted that such transformations may not always represent realistic physical transformations, but may involve nonphysical or “alchemical” transformations.

Under conventional methods, calculating the free energy to open a ring of a molecule into a linear structure or close a linear structure of a molecule to form a ring can be difficult.

Although one possible approach might be to annihilate a whole ring and grow a corresponding linear structure from scratch, it is computationally very inefficient and sometimes impossible when the ring is very large or the ring is fused with other rings.

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