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Ionic complexes of microbial poly(γ-glutamic acid) and alkanoylcholines are fully bio-based comb-like systems able to self-organize in an ordered amphiphilic structure made of hydrophobic and hydrophilic alternating layers. Incubation of complex films under physiological conditions for one month promoted dissociation of the complex and hydrolysis of the choline ester without almost degradation of polyglutamic acid. Complex decomposition rates were depending on alkanoyl chain length and on complex stoichiometry as well. Nanoparticles with 50-100 nm diameter were successfully prepared from the stearoylcholine complex with a surfactant to polymer ratio of 0.75 and loaded with theophylline, carbamazepine or doxorubicin drugs. The releasing of the drugs from nanoparticles took place upon incubation at very different rates depending on the drug. Theophylline and carbamazepine were discharged in hours whereas doxorubicin was very slowly delivered along months. The observed differences were related to the different interaction mechanism operating between the drug and the complex., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Comb-like ionic complexes, nATMA . PG(DL)GA, were prepared from microbial poly(gamma-glutamic acid), with a nearly racemic configuration, and alkyltrimethylammoniun bromides, with linear alkyl chains containing an even number of carbon atoms, n, ranging from 12 to 22. The complexes had a nearly stoichiometric composition, displayed thermal stability up to temperatures above 200 degrees C and were insoluble in water but soluble in organic solvents. In the solid state, they were arranged in a regularly layered structure with the alkyl side chain crystallized for n > or = 18. Heating above melting entailed a contraction in the interlayer distance which varied from 1 to 10% depending on the value of n. Comparison with data reported on similar complexes obtained from nearly enantiomerically pure poly(gamma-glutamic acid) revealed an overall behavior very similar for the two series but with specific significant differences concerning side chain crystallinity and dimensional response to temperature.

The ability of microbally produced poly(gamma,d-glutamic acid) to form stable polyelectrolyte-opposite charged surfactant complexes was investigated. A sonicated sample of polyacid with a molecular weight about 10(5) Da and a content of d enantiomer higher than 90% was used in this study. Nearly stoichiometric complexes of poly(gamma,d-glutamate) anions and alkyltrimethylammonium cations bearing linear alkyl chains with even numbers of carbon atoms from 12 up to 22 were "synthesized" by precipitation from equimolar mixtures of aqueous solutions of the two components. All complexes were found to adopt stratified supramolecular structures made of alternating layers of poly(gamma,d-glutamate) and surfactant with a periodicity increasing from 3.2 up to 4.3 nm according to the length of the alkyl side chain. No definite evidence indicative of the conformation adopted by the main chain in these complexes could be afforded. In all cases, the alkyl chains are in an extended conformation and oriented normal or nearly normal to the layer planes. Polymethylene chains with more than 16 carbon atoms were partially crystallized in the complexes in a separated paraffinic phase, whereas no crystallinity was detected for shorter lengths. The crystallized paraffinic phases were found to melt reversibly at temperatures between 40 and 70 degrees C. This process was found to happen with a concomitant expansion-contraction that amounts between 2 and 8% of the long period of the structure but without significant alteration of the layered arrangement.

The stereochemical microstructure and crystalline structure of nearly racemic poly(alpha-ethyl gamma,DL-glutamate) obtained by esterification of biosynthetic poly(gamma-glutamic acid) were examined by NMR, DSC, and powder X-ray diffraction. The two enantiomerically pure poly(alpha-ethyl gamma-glutamate)s, as well as the racemic stereocopolymers with random and alternating microstructure, were prepared by chemical synthesis and studied in parallel to help in the interpretation of the data. The (13)C NMR analysis revealed that biosynthetic poly(alpha-ethyl gamma,DL-glutamate) consists of a block stereocopolymer accompanied by minor amounts of a mixture of the two optically pure homopolymers. The polymer is crystalline, with a degree of crystallinity and crystal structure essentially similar to those displayed by the optically pure polymers but clearly different from the alternating copolymer. Conversely, the racemic stereocopolymer with a random microstructure prepared by chemical synthesis is amorphous. The crystal structure of the racemic mixture of the D- and L-homopolymers seems to be very close to that of the biosynthetic stereocopolymer, although some indications suggesting the existence of a stereocomplex were found.

A series of ionic complexes with a comb-like architecture and a nearly stoichiometric composition were prepared from bacterial poly(γ, dl -glutamic acid) (PGGA) and alkyltrimethyl phosphonium bromides ( n ATMP·Br) bearing long linear alkyl chains with even numbers of carbon atoms ( n ) ranging from 12 to 22. The n ATMP·PGGA complexes were non-water soluble but readily soluble in organic solvents, and they displayed a high thermal stability. Combined DSC and XRD studies revealed that these complexes adopted an amphiphilic layered structure with the polypeptide chain and the alkyl chain separated in two differentiated phases with a nanoperiodicity that increased steadily with the length of the alkyl chain. The paraffinic phase was found to be partially crystallized in an extent that decreased with n , so that complexes with n = 12 and 14 did not show any sign of crystallinity whereas those with n from 16 to 22 showed crystalline melting in the ∼30–70 °C range. The structural transitions taking place by temperature effects were characterized by simultaneous SAXS/WAXS using synchrotron radiation at real time. In all cases, a shortening of the layer periodicity occurred upon heating with recovering of the initial structure after cooling. n ATMP·PGGA with n ≤ 16 showed strong antimicrobial activity against both E. coli and S. aureus, a property that could be related to the weak dissociation of the complexes happening upon incubation in water. The structure and properties of these complexes where comparatively discussed taking as reference their analog complexes made from PGGA and alkyltrimethylammonium bromides already studied by us. [ABSTRACT FROM AUTHOR]

Abstract: The thermal decomposition of poly(γ-glutamic acid), poly(α-methyl γ-glutamate) and ionic complexes of the polyacid with alkyltrimethyl ammonium salts was studied by TGA, GPC, and FTIR and NMR spectroscopies. It was found that both poly(γ-glutamic acid) and poly(α-methyl γ-glutamate) depolymerised above 200°C by unzipping mechanism with generation of pyroglutamic acid and methyl pyroglutamate, respectively. On the other hand, the ionic complexes degraded through a two-stage process, the first stage being cyclodepolymerisation of the poly(γ-glutamate) main chain along with decomposition of the ionic complex promoted by the adsorbed water. Decomposition of the previously generated alkyltrimethyl ammonium compound followed by unspecific cracking of the resulting nitrogenated compounds accounted for the second degradation step, at higher temperatures. Mechanisms explaining the decomposition of the three studied systems were proposed according to collected data. [Copyright &y& Elsevier]

Abstract: Stoichiometric ionic complexes of bacterial poly(γ-glutamic acid) with the cationic N-octadecyl and N-docosyl-N,N,N-trimethylammonium surfactants were mixed with alkylammonium modified bentonite (Cloisite 30B) to generate hybrid compounds covering a wide range of clay/polymer compositions. The structure of these compounds was examined by XRD and cryoTEM, which indicated extensive penetration of the biopolymer into the nanoclay galleries with widening or even destruction of the layered arrangement of the complex and the clay. Simultaneous SAXS/WAXS analysis in real time showed that hybrids with moderate inorganic contents displayed melting/crystallization upon heating/cooling within the 40–70°C interval with concomitant expansion/contraction of the intersheet spacing. 13C CP-MAS NMR revealed that an anti-to-gauche conformational interconversion of the alkyl chains was involved in the melting/crystallization process. The results provided by energy-based dynamical simulations proved the feasibility of the polyacid and the nanoclay to be homogenized in the hybrid due to the compatibilizing effect of the surfactant. [Copyright &y& Elsevier]