Estudo teórico das propriedades geométricas da curcumina em metanol usando dinâmica molecular de Car-parrinello

Abstract

Curcumin is a yellow polyphenol extracted from the rhizome of turmeric. It is used as a spice, food colorant and therapeutic agent. It has antioxidant, anti-inflammatory, antibacterial, antidiabetic, anticarcinogenic activity, among others. The curcumin molecular formula is C21H20O6, its molecular weight is 368,37 g/mol and its melting point is approximately 183 °C. Curcumin has two tautomeric isomers plans, which are the keto and enol forms. The enol form is more stable in solution and in solid state. It is also the predominant form in solution. We propose to study the geometric properties of Curcumin enol in solution with methanol making use of Car-Parrinello Molecular Dynamics. The Car-Parrinello method performs ab initio simulations using classical mechanics to describe the ionic motion, obtained from the solutions of the equations of Newton, and the Born-Oppenheimer approximation to separate the nuclear and electronic coordinates. The electronic motion is treated by quantum wave function obtained from the solution of the Schroedinger equation. A parameter of the fictitious mass that allows the wave function to adapt to changing nuclear positions so that the exchange of energy between electronic and ionic systems are considered to be avoided. Connecting the classical treatment for the ions and electrons to quantum is done by solving the Lagrange motion equations by Car-Parrinello extended Lagrangian. Curcumin was arranged in a rectangular box containing 29 molecules of methanol. We made the comparison with the theoretical results in CPMD for the molecule in vacuum. We analyze distances and angles with larger variations. We noticed that the presence of methanol shifts the mean values of lengths and bond angles of their values in vacuum. For interaction which showed larger variations, we analyzed the radial distribution function of pairs and residence time. Solvate formation observed in some places layer of Curcumin. The adiabatic separation remained constant throughout the simulation, ensuring that there were no exchange of energy between the ionic and electronic system. The results were compared with calculations for the isolated molecule and the difference suggests modifications to the geometry of the molecule.