Abstract
Structural characterization of poly-l-lactic acid (PLLA) and poly(glycolic acid) (PGA) oligomers containing three units was carried out with an atomistic approach. Oligomer structures were first optimized through quantum chemical calculations, using density functional theory (DFT); rotational barriers concerning dihedral angles along the chain were then investigated. Diffusion coefficients of l-lactic acid and glycolic acid in pure water were estimated through molecular dynamic (MD) simulations. Monomer structures were obtained with quantum chemical computation in implicit water using DFT method; atomic charges were fitted with Restrained Electrostatic Potentials (RESP) formalism, starting from electrostatic potentials calculated with quantum chemistry. MD simulations were carried out in explicit water, in order to take into account solvent presence.
Highlights
Nowadays, overcoming diseases and providing worldwide medical care are high priorities.Materials science, in conjunction with biotechnology, can meet this challenge by developing safe drug delivery systems and organ implants [1].Int
poly(glycolic acid) (PGA) structure was first optimized in vacuo in order to obtain the global minimum energy structure, which was used for subsequent computations (Figure 2)
C1-O2-C3-C4 and O2-C3-C4-O5 angle values of this minimum energy geometry were estimated equal to −87° and −164°, respectively
Summary
Nowadays, overcoming diseases and providing worldwide medical care are high priorities. Among the several materials suitable for biomedical applications, polyester-based polymers hold great promises because of their feasible properties and biological affinity [2], those based on glycolic acid (GA) and lactic acid (both chiral isomers LLA and DLA and the raceme L,DLA) They are well tolerated by the human body, as their degradation products are incorporated in the tricarboxylic acid cycle, or the Krebs’ one. Their degradation process is mainly due to hydrolysis mechanism: water diffuses into the material and breaks long chains in small oligomers which are able to diffuse within and out the polymeric matrix [3,4] These biopolymers possess adequate mechanical properties (i.e., high Young modulus) that allow the employment of such materials in a wide range of applications. The ultimate goal of this work is to test the suitability of the chosen force field when dealing with small oligomers, for what concerns both structural changes (torsional barriers) and transport phenomena (diffusion coefficients)
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