Secondary structure elements in polylactic acid models

Abstract

Geometry optimization results are reported on putative elements of secondary structure in decameric units of polylactic acid (PLA) analogous to those seen in protein structure-helical structures (α, π, 3 10 ) as well as a β-sheet-employing molecular mechanics, semiempirical, ab initio and density functional methods. The four possible structures of the deca-PLA are generally predicted, with all methods to be within ∼15 kcal/mol of each other, with the more stable conformation varying depending on the method employed. The highest-level method employed here (M062x/6-311+G**) predicts that the α, π and 3 10 structures have very similar energies, with π slightly favored by values within the error limits of the method; this is in contrast with results obtained with less accurate semiempirical and empirical methods, which predict larger differences and other structures as favorites. Relative energies of poly-l and poly-d,l lactic acid structures indicate the former to be energetically-favored over the latter. Three types of weak interactions appear to dictate the relative stabilities of secondary structure elements in polylactic acid structures.

In Depth Study on Solution-State Structure of Poly(lactic acid) by Vibrational Circular Dichroism

“…Through XRD pattern and modeling calculation in a previous study, it has been speculated that left-handed PLLA is incorporated in the hydrophobic cavity of left-handed amylose. 38 To study, if any, the structural changes of PLLA upon complexation, we measured the IR and VCD spectra of PLLA−amylose complex in DMSO-d 6 .…”

“…Structural studies of crystalline PLA have revealed that it displays a left-handed 10 3 helix in an α-crystalline form, and left-handed 3 1 helices in β- and γ-forms. ,,− The conformation in a dilute solution state or a single-molecular state has been studied by theoretical calculation, for which the use of DFT has been extensive, ,,, but only a few experimental evidence have been provided to support such simulations. , In order to clarify the structural details of oligo( l -lactic acid)s and PLLA in a solution state, we next carried out the DFT calculations of the oligomers.…”

“…Poly(lactic acid) (PLA) (Figure 1), a biocompatible and environmentally benign thermoplastic employed as surgical suture, as implant materials, and in drug delivery systems, exists as a helix in its α-, β-, and γ-crystalline states. 5,6 Like other chiral poly(α-hydroxy acid)s (H−[OCHR−CO] n −OH), PLA is a biodegradable polyester analogue of polypeptide. The similarity of PLA and polyalanine has been suggested over 40 years and the studies on its conformation has been of interest.…”

“…Intense research efforts have been devoted to construct and analyze artificial helical molecules including polyisocyanide, polyguanidine, polyacetylene, and polysilane in an attempt to mimic biologically functional helices. − Biodegradable synthetic helices such as polyester should be more practical for future use in biochemical and pharmaceutical fields due to their controllable bioaccumulation. Poly(lactic acid) (PLA) (Figure ), a biocompatible and environmentally benign thermoplastic employed as surgical suture, as implant materials, and in drug delivery systems, exists as a helix in its α-, β-, and γ-crystalline states. , Like other chiral poly(α-hydroxy acid)s (H–[OCHR–CO] n –OH), PLA is a biodegradable polyester analogue of polypeptide. The similarity of PLA and polyalanine has been suggested over 40 years and the studies on its conformation has been of interest. , However, the application of PLA to peptidomimetics has been obstructed in part by the lack of a convenient and accurate method to study the solution-state conformation of polyester.…”

Computational investigation of spectroscopic parameters in putative secondary structure elements for polylactic acid and comparison with experiment

“…In terms of the importance of solvation, this is estimated by comparing values computed in water (as a limit of very polar medium) and vacuum (as a limit of completely non-polar medium). Further detail on geometry optimizations and on relative energies of the structures are given elsewhere [30]. …”