molecules Article Polymer–Colloid Complexes Based on Cationic Imidazolium Amphiphile, Polyacrylic Acid and DNA Decamer Darya A. Kuznetsova 1 , Dinar R. Gabdrakhmanov 1, Denis M. Kuznetsov 1, Svetlana S. Lukashenko 1, Valery M. Zakharov 2, Anastasiia S. Sapunova 1, Syumbelya K. Amerhanova 1, Anna P. Lyubina 1, Alexandra D. Voloshina 1 , Diana V. Salakhieva 3 and Lucia Ya. Zakharova 1,* 1 FRC Kazan Scientific Center, Russian Academy of Sciences, Arbuzov Institute of Organic and Physical Chemistry, Arbuzov str. 8, 420088 Kazan, Russia; [email protected] (D.A.K.); [email protected] (D.R.G.); [email protected] (D.M.K.); [email protected] (S.S.L.); [email protected] (A.S.S.); [email protected] (S.K.A.); [email protected] (A.P.L.); [email protected] (A.D.V.) 2 Kazan National Research Technological University, Karl Marx str., 68, 420015 Kazan, Russia; [email protected] 3 Institute of Fundamental Medicine and Biology, Kazan (Volga Region) Federal University, Kremlyovskaya St. 18, 420008 Kazan, Russia; [email protected] * Correspondence: [email protected]; Tel.: +7-(843)-273-22-93 Abstract: The solution behavior and physicochemical characteristics of polymer–colloid complexes based on cationic imidazolium amphiphile with a dodecyl tail (IA-12) and polyacrylic acid (PAA) or Citation: Kuznetsova, D.A.; Gabdrakhmanov, D.R.; Kuznetsov, DNA decamer (oligonucleotide) were evaluated using tensiometry, conductometry, dynamic and D.M.; Lukashenko, S.S.; Zakharov, electrophoretic light scattering and fluorescent spectroscopy and microscopy. It has been established V.M.; Sapunova, A.S.; Amerhanova, that PAA addition to the surfactant system resulted in a ca. 200-fold decrease in the aggregation S.K.; Lyubina, A.P.; Voloshina, A.D.; threshold of IA-12, with the hydrodynamic diameter of complexes ranging within 100–150 nm. Salakhieva, D.V.; et al. Electrostatic forces are assumed to be the main driving force in the formation of IA-12/PAA complexes. Polymer–Colloid Complexes Based Factors influencing the efficacy of the complexation of IA-12 with oligonucleotide were determined. on Cationic Imidazolium Amphiphile, The nonconventional mode of binding with the involvement of hydrophobic interactions and the Polyacrylic Acid and DNA Decamer. intercalation mechanism is probably responsible for the IA-12/oligonucleotide complexation, and Molecules 2021, 26, 2363. https:// a minor contribution of electrostatic forces occurred. The latter was supported by zeta potential doi.org/10.3390/molecules26082363 measurements and the gel electrophoresis technique, which demonstrated the low degree of charge neutralization of the complexes. Importantly, cellular uptake of the IA-12/oligonucleotide complex Academic Editors: Ramón G. Rubio and Tamar Greaves was confirmed by fluorescence microscopy and flow cytometry data on the example of M-HeLa cells. While single IA-12 samples exhibit roughly similar cytotoxicity, IA-12–oligonucleotide complexes Received: 2 February 2021 show a selective effect toward M-HeLa cells (IC50 1.1 µM) compared to Chang liver cells (IC50 Accepted: 15 April 2021 23.1 µM). Published: 19 April 2021 Keywords: imidazolium; amphiphile; polyacrylic acid; oligonucleotide; complexation Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. 1. Introduction Interactions between oppositely charged surfactants and synthetic polyelectrolytes are currently the focus of modern research [1–6]. This is mainly due to the possibility of the control of the properties of these systems by the variation of the chemical struc- Copyright: © 2021 by the authors. ture, ratio and concentration of components, molecular weight of the polymer, pH of the Licensee MDPI, Basel, Switzerland. medium, temperature and ionic strength [7–9]. In addition, the fabrication of complexes This article is an open access article can be mediated by different mechanisms, including the hydrophobic effect, van der Waals distributed under the terms and interactions and hydrogen bonding, with the contribution of dominating electrostatic in- conditions of the Creative Commons teractions [10–13]. For these reasons, mixtures of polyelectrolytes and oppositely charged Attribution (CC BY) license (https:// surfactants are characterized by the complicated behavior of solutions [14–16]. The addi- creativecommons.org/licenses/by/ tion of a high-molecular-weight component can change the aggregation thresholds of the 4.0/). Molecules 2021, 26, 2363. https://doi.org/10.3390/molecules26082363 https://www.mdpi.com/journal/molecules Molecules 2021, 26, x 2 of 17 surfactants are characterized by the complicated behavior of solutions [14–16]. The addi- tion of a high-molecular-weight component can change the aggregation thresholds of the system [17–20]. Moreover, the investigation of polymer–colloid systems allows simulating the interaction of cationic amphiphiles with natural polymers such as DNA, proteins and so on [7,21–23]. This is of importance in gene therapy [24,25] because the application of naked DNA molecules is complicated due to their huge size, the electrostatic repulsion between nucleotides and negatively charged cell membranes and the immune response Molecules 2021, 26, 2363 2 of 17 observed [26]. Therefore, efficient transfection can be achieved using optimized carriers of polynucleotides, which allow compacting large DNA molecules and recharging them. systemThis allows [17–20]. Moreover,genetic material the investigation to be ofrecognized polymer–colloid by the systems cell allows[27,28], simulating pass through the cell themembrane interaction by of cationicthe endocytosis amphiphiles mechanism with natural polymers[29] and such receive as DNA, protection proteins and from biodegrada- sotion. on [ 7From,21–23 this]. This point is of of importance view, cationic in gene surfactants therapy [24,25 are] because among the the application most prospective of carriers naked[30–34 DNA], including molecules isthose complicated bearing due an to theirimidazolium huge size, the moiety electrostatic [35– repulsion38]. Imidazolium am- between nucleotides and negatively charged cell membranes and the immune response phiphiles and DNA were documented to form sustainable nontoxic complexes that pro- observed [26]. Therefore, efficient transfection can be achieved using optimized carriers of polynucleotides,tect from enzymatic which allow degradation compacting large and DNA provide molecules a andcharge recharging density them. sufficient This for DNA allowstransport genetic through material the to be cell recognized membrane by the [35]. cell [27 Nonviral,28], pass throughvectors the based cell membrane on the mixture of lipids byand the imidazolium endocytosis mechanism amphiphiles [29] and were receive reported protection and from were biodegradation. less effective From than this commercially pointavailable of view, lipofectamine cationic surfactants 2000 are; however among the, they most prospectivehad lower carriers toxicity [30 [36].–34], includ- ing those bearing an imidazolium moiety [35–38]. Imidazolium amphiphiles and DNA were documentedA brief literature to form sustainableoverview nontoxicmakes it complexes obvious thatthat protect the fabrication from enzymatic of complexes based degradationon amphiphiles and provide and polyelectrolytes a charge density sufficient of various for DNA types transport is urgent. through Nevertheless, the cell despite the membranelong-term [35 study]. Nonviral of these vectors systems, based onthere the mixtureis little of understanding lipids and imidazolium of the factors am- influencing phiphilestheir functional were reported activity. and were Much less effectiveattention than is commercially paid to the available interaction lipofectamine of cationic surfactants 2000; however, they had lower toxicity [36]. with anionic synthetic polyelectrolytes because they could simulate complexation be- A brief literature overview makes it obvious that the fabrication of complexes based ontween amphiphiles DNA and and polyelectrolytesamphiphilic compounds. of various types Unlike is urgent. strong Nevertheless, polyelectrolytes, despite the weak polyelec- long-termtrolytes studydemonstrate of these systems, complicated there is and little tunable understanding solution of the behavior, factors influencing which is controlled by theirthe charge functional density activity. of Much a polymer attention chain, is paid which to the, interactionin turn, is of determined cationic surfactants by the nature of mac- withromolecules, anionic synthetic concentration polyelectrolytes of charged because theyadditives, could simulate solution complexation pH, etc. For between cationic surfactant– DNA and amphiphilic compounds. Unlike strong polyelectrolytes, weak polyelectrolytes demonstratepolyacrylic complicated acid (PAA) and binary tunable solutionsystems behavior,, the critical which isionization controlled bydegree the charge αc should be taken densityinto account. of a polymer The chain, theoretical which, invalue turn, of is determinedαc = 0.35 can by thebe naturecalculated of macromolecules, based on Manning’s coun- concentrationterion condensation of charged additives,theory [39]. solution Typically, pH, etc. For electrostatic cationic surfactant–polyacrylic interactions prevail above αc, acidwhile (PAA) the binary hydrophobic systems, the effect critical in ionizationcombination degree withαc should hydrogen be taken binding into account. contributes to com- The theoretical value