D-, L-arginine derived polyamidoamino acids and sodium deoxycholate: the importance of self-assembly in chiral recognition

Chiral synthetic polymers have widespread applications, from stereoselective synthesis to chiral recognition. Chiral centers, either in the main chain or as side pendants, allow polymers to selfassemble into ordered conformations [1], due to their structure-directing power. Recently, a new class of chiral polymers emerged, named polyamidoamino acids (PAACs). ARGO7 isomers, the first synthesized polymers, were obtained in water by stepwise polyaddition of L-,D- or D,L-arginine to N,N’-methylenebisacrylamide [2]. These polymers maintained the chirality of the parent aminoacids and proved capable to self-organize into pH dependent conformations [3]. L-ARGO7 resulted highly citobiocompatible [2] and preferentially localize in the perinuclear region of Balb/3T3 cells. It remains to be ascertained whether any chiral interactions may arise with other biological components, as well. To assess chiral recognition, sodium deoxycholate (NaDC), one of the components of bile salts, was chosen as a chiral model surface. Through a stepwise mechanism, NaDC is able to form chiral micelles, whose self-assembly behaviour is affected by pH, concentration and ionic strength. Pulsed-gradient spin echo NMR (PGSE-NMR), circular dichroism (CD), dynamic light scattering (DLS) and zeta potential (ZP) emphasised the complex equilibria behind chiral recognition. In particular, NaDC showed three main pH dependent behaviour: homogeneous solution, gel phase, flocculation and aggregation. All of them are characterised by different CD patterns. ARGO7 isomers proved able to chirally and/or electrostatically interact with all the different NaDC conformations. Evidence of chiral recognition was detected in NaDC gel phase by means of CD spectroscopy. Both D- and L-ARGO7 led to changes in shape and magnitude of CD patterns, whereas D,L-ARGO7 did not modify the CD spectra of NaDC. Incoming SANS studies will probably highlight the mechanisms and dynamics of these polyelectrolyte-micelle systems. References 1. L. Zhou, J. Yue, Y. Fan, Y. Wang, Langmuir 2018, 34, 12924. 2. P. Ferruti, N. Mauro, L. Falciola, V. Pifferi, C. Bartoli, M. Gazzarri, F. Chiellini, E. Ranucci, Macromol. Biosci. 2014, 14, 390. 3. A. Manfredi, N. Mauro, A. Terenzi, J. Alongi, F. Lazzari, F. Ganazzoli, G. Raffaini, E. Ranucci, P. Ferruti, ACS Macro Lett. 2017, 6, 987.