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.
Summary: Reaction of active esters of O‐protected D‐and L‐tartaric acid with L‐lysine 2,5‐diketopiperazine afforded optically active low molecular weight compounds with Tg ≈ 130 °C. 13C NMR results indicated that the condensation product consisted of cyclic oligomers made from 1 to 6 repeating units. Mass spectrometric analysis by MALDI‐TOF ascertained such interpretation and suggested a revision of previous work reporting on polymerization of 2,5‐diketopiperazines.MALDI‐TOF profile of cKT‐LL.magnified imageMALDI‐TOF profile of cKT‐LL.
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