Solvent Specified Conformation in Poly(α-l-glutamic acid) Thin Films

• Published in: Biomacromolecules Vol. 5; no. 4; pp. 1214 - 1218
• Main Authors: Wu, Xiaodong, Yang, Suizhou, Njus, Jeffrey M, Nagarajan, Ramaswamy, Cholli, Ashok L, Samuelson, Lynne A, Kumar, Jayant
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-07-2004
• Subjects: Aminoacid polymers; Applied sciences; Circular Dichroism - methods; Exact sciences and technology; Magnetic Resonance Spectroscopy - methods; Molecular Conformation; Physicochemistry of polymers; Polyglutamic Acid - chemistry; Solvents - chemistry; Spectroscopy, Fourier Transform Infrared - methods; Surface Properties; Synthetic biopolymers; Solvent effect; Solid state; Glutamic acid polymer; Fabrication structure relation; Experimental study; Aminoacid polymer; Conformation; Thin film; Hydrogen bond
• ISSN: 1525-7797; 1526-4602
• DOI: 10.1021/bm034540a

The ability to control conformational properties of polypeptides in their films is of considerable interest for many possible applications of these materials. By rational choice of the solvent system for film fabrication, control over the conformation of the main chain, the intermolecular hydrogen bonding in the side chain is easily achieved in poly(α-l-glutamic acid) (PLGA) thin films. The spectral data from circular dichromism (CD), FT-IR, and solid state 13C NMR spectroscopies suggest that the β-sheet conformation is dominant in PLGA films cast from trifluoroacetic acid (TFA) solution, whereas the right-handed α-helix is dominant in those cast from pyridine or DMF solution. In comparison with films cast from TFA solutions, the films fabricated from pyridine or DMF solutions exhibit strong intermolecular hydrogen bondings between −COOH groups and have a more ordered arrangement of side chains. Moreover, the extent of α-helix conformation of the PLGA backbone in films cast from pyridine or DMF solution is several times higher than that observed in the PLGA powder precipitated from aqueous solution at pH 4. All spectroscopic studies indicate clearly that the solvents (used for casting these films) play a crucial role in directing the organization of PLGA in these thin films.