Self-Organized Meso- and Hybridic Phases of Poly(aspartic acid) and Poly(glutamic amino acid) with Cationic Surfactants (C n TAB, n = 14, 16) and a Silica Source (TEOS)

• Published in: Chemistry of materials 2007-04, Vol.19 (7), p.1853-1861
• Main Authors: Kodona, Eleftheria K, Alexopoulos, Charalambos, Panou, Eugenia, Pomonis, Philippos J
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm062878g

In this work the self-organized mesophases obtained by the ionic interaction of poly(amino acids) poly(l-aspartic acid (P-l-Asp) and poly(l-glutamic acid) (P-l-Glu) with the cationic surfactants C14TAB and C16TAB, as well as the mesoporous silicate materials obtained by addition and hydrolysis of tetraethyl orthosilicate (TEOS) on the hybridic mesophases, are described. The mesophases isolated at pH 6.5−8.5 were examined by X-ray diffraction (XRD) analysis for their structure, thermogravimetry for their thermal stability, scanning electron microscopy for their structural features, and circular dichroism (CD) for the conformation of the polypeptide−C n TAB (n = 14, 16) complexes. The mesophases P-l-Asp/C14TAB isolated at pH 7.5 and 8.5 showed in XRD a single peak at d = 3.45 nm and d = 3.54 nm, respectively, corresponding to typical hexagonal packing of the micellar aggregates. The mesophases P-l-Asp/C16TAB isolated at pH 7.5 showed an XRD peak at d = 3.90 nm, corresponding to a similar hexagonal packing of larger micellar aggregates and also two peaks at d = 3.37 nm and d = 1.69 nm indicating a layered configuration of the micellar sheets. The layered component decreases by the increase of pH from 7.5 to 8.5 or the addition of small amounts (0.5%) of EtOH. The P-l-Glu/C14TAB mesophases isolated at pH 7.5 and 8.5 showed a single XRD peak at d = 3.60 nm, while the P-l-Glu/C16TAB system showed also a single XRD peak at d = 4.10 nm. The CD spectra showed that the complexes P-l-Asp/C14TAB possess a more random configuration compared to the P-l-Glu/C14TAB, which have the tendency to form α- and 310-helices. The mesoporous silicate materials obtained from the systems P-l-Asp/C16TAB/TEOS and P-l-Glu/C16TAB/TEOS showed a single XRD peak corresponding to hexagonal pore arrangement typical in MCM-41 materials. The nitrogen adsorption−desorption isotherms of the silicate mesostructures indicate that they possess high surface areas in the range 500−800 m2 g-1 for the P-l-Asp/C n TAB/TEOS and 1000−1070 m2 g-1 for the P-l-Glu/C n TAB/TEOS and ordered or semi-ordered porosity depending on the hybridic system used for isolating the corresponding mesophases.