Aggregation and antimicrobial properties of gemini surfactants with mono- and di-(2-hydroxypropyl)ammonium head-groups: Effect of the spacer length and computational studies

https://doi.org/10.1016/j.molliq.2020.112579Get rights and content

Highlights

  • Gemini surfactants with (CH2)n spacer groups and different head group have been synthesized.

  • Self-assembly of gemini surfactants with different spacers is investigated.

  • These cationic gemini surfactants exhibit a high antibacterial capacity.

Abstract

Cationic gemini surfactants, alkanediyl-α,ω-bis[(2-hydroxypropyl)dodecylammonium] dibromide (abbreviated as C12-s-C12[iso-Pr(OH)] and C12-s-C12[iso-Pr(OH)]2, with s = 2, 3, 4 and 5) have been synthesized, and their aggregation properties in aqueous solution have been studied by surface tension, electrical conductivity and dynamic light scattering methods. On the basis of the results of studying aqueous solutions of the synthesized gemini surfactants by tensiometric and conductometric methods, their principal surfactivity parameters, such as the degree of counterion binding (β), critical micelle concentration (CMC), effectiveness of surface tension reduction (πCMC), surface excess concentration (Γmax), area per molecule at the interface (Amin), changes of Gibbs free energies of adsorption (ΔGad) and micellization (ΔGmic) have been calculated. For both classes of these gemini surfactants, a character of the surfactivity parameters change with an elongation of the spacer chain was defined and comparative analysis with other ammonium-type gemini surfactants having different head-groups was performed. Using dynamic light scattering method, regularities of variation of the aggregates sizes were studied depending on the number of 2-hydroxypropyl groups and the spacer chain length was investigated. Meanwhile, it was revealed that the mentioned gemini surfactants possess antimicrobial properties. The mechanism of the epoxide ring opening and salt formation reactions were calculated by using Kohn–Sham DFT with the B3LYP functional. The epoxide ring opening via primary (dodecylamine) and secondary (INT2) amines was determined as exergonic (13.4 and 4.4 kcal/mol) reactions as observed experimentally.

Introduction

Because of the elevating demand, researches on gemini surfactants are expanding. The gemini surfactants are bearing very peculiar features (e.g., high surfactivity, low Krafft point, smaller CMC compared to conventional surfactants [1,2]). These particularities boost the effectiveness of the applicability of gemini surfactants [3,4]. Due to these circumstances, synthesis of such surfactants by more rational ways and their study attract more and more interest. As known, physico-chemical properties of traditional surfactants depend on alkyl chain length and nature of head-group [5]. In the case of gemini surfactants, in addition to these factors, spacer chain length and nature are also important [6]. The most studied gemini surfactants are of alkanediyl-α,ω-bis(dialkyl-alkylammonium bromide) class [7,8]. For these surfactants, variation of properties depending on nature of alkyl chain, head-group and spacer was studied in a wider form. It was established that lengthening of hydrophobic alkyl chain, replacement of the methyl group linked to nitrogen atom by ethyl, propyl and butyl groups and elongation of spacer chain cause a change in CMC and Krafft point [9]. But this variation is not monotonic with elongation of chains and is characterized by presence of maximum or minimum. In the case of the gemini surfactants having amide group in hydrophilic part, with an increase of the spacer-chain length (alk = 12, s = 2–12), the CMC decreases [10]. When elongating the spacer chain in the gemini surfactants with imidazolium head-group ([C12–s–C12im]Br2, s = 2, 4, 6), the CMC increases [11]. In the case of 1,10-(alkane-1,5-diyl)-bis(1-dodecyl pyrrolidinium)bromide (C12–Cs–C12PB, s = 3, 4, 6, 8, 10, 12, 14, and 16) gemini surfactants, the CMC rises when the spacer chain is lengthened from C3 to C4, but then the CMC is lowered with a subsequent elongation of the alkylene chain [12]. M. Borse and coauthors have determined that, when the methyl group bonded to the nitrogen atom of the cationic gemini surfactant is substituted by ethylol group, the CMC diminishes [13,14]. They also established that, in the case of alkanediyl-α,ω-bis[methyl(2-hydroxylethyl) dodecylammonium] dibromide (abbreviated as 12-s-12 (OH), with s = 4, 6, 8 and 10 methylenes) class surfactants, increasing the spacer chain from C4 to C6 brings about a rise in the CMC. However, with a further chain elongation, the CMC value starts to decrease. Average degree of ionization of micelles (αave) becomes increased with lengthening the spacer chain. In the alkanediyl-α,ω-bis[methyl(2-hydroxylethyl) hexadecylammonium] dibromide (abbreviated as 16-s-16 (OH), with s = 2, 3 and 4 methylenes) class surfactants, elongation of the methylene-based chain causes a rise in the CMC [15]. In the gemini surfactants, where both methyl groups in the head-group are replaced by ethylol group, for example, in the gemini surfactants with dihydroxyethylamino head-groups (abbreviated as 12-s-12 (OH)2 with s = 4, 6, 8 and 10 methylenes), an increase in the spacer chain length leads to a decrease in the CMC. When the ethylol group connected to the nitrogen atom in the head-group is substituted by 2-hydroxypropyl group, the value of CMC decreases [16]. Therefore, obtainment and study of the gemini surfactants containing 2-hydroxypropyl group are of a large interest.

The submitted article is devoted to synthesis of the new gemini surfactants of the C12-s-C12[iso-Pr(OH)] and C12-s-C12[iso-Pr(OH)]2 class as well as a study of the regularities of variation of properties of these surfactants in dependence on the spacer chain size. Meanwhile, a relationship between antimicrobial properties of the obtained surfactants and the spacer nature has been investigated.

Section snippets

Materials and instruments

Propylene oxide (PO) was used as a product (99.97–99.98% purity) of “Organic Synthesis” factory (Sumgayit, Azerbaijan). Ethylenediamine (purity ≥99% Alfa Aesar®, Great Britain), 1-dodecyl amine (purity>98% Alfa Aesar GmbH & Co KG, Germany), 1-bromododecane (purity>98% Alfa Aesar, England), 1,3-dibromopropane (purity>97% Sigma-Aldrich), 1,4-dibromobutane (purity>99% Sigma-Aldrich, China) and 1,5-dibromopentane (purity>97% Sigma-Aldrich) of analytical grade were taken. 1H NMR and 13C NMR spectra

Synthesis of the gemini surfactants

To synthesize the gemini surfactants having different spacers, a two-step reaction was conducted. At the first step, dodecylamine was propoxylated by PO. Here, depending on the dodecylamine:PO mol ratio (1:1 or 1:2), mono- or di-2-hydroxypropyldodecylamine are obtained. At the second step, the obtained aminoalcohols via the quaternization reaction with dibromoalkanes are converted to salts. For synthesis of the gemini surfactants with s = 2, the synthesized two aminoalcohols were reacted with

Conclusion

Cationic gemini surfactants containing the fragments (C12-s-C12[iso-Pr(OH)], C12-s-C12[iso-Pr(OH)]2) with mono-and di-2-hydroxypropyl groups and the spacer length s = 2–5 were synthesized. The micellization capabilities of the synthesized gemini surfactants were evaluated by tensiometric and conductometric methods. It was determined that, in the case of the both classes gemini surfactants, with an elongation of the spacer chain, CMC, at first, decreases, then rises whereas β becomes lowered.

CRediT authorship contribution statement

Ziyafaddin H. Asadov:Project administration, Visualization, Writing - original draft. Gulnara A. Ahmadova: Investigation, Data curation. Ravan A. Rahimov: Writing - review & editing, Supervision, Methodology. Seyid-Zeynab F. Hashimzade: Investigation, Resources, Writing - original draft. Yusif Abdullayev: Writing - review & editing, Supervision, Software. Etibar H. Ismailov: Validation. Samira A. Suleymanova: Validation. Nahida Z. Asadova: Investigation. Fedor I. Zubkov: Validation, Formal

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The publication was prepared with the support of the “RUDN University Program 5-100” (Fedor I. Zubkov determined the degree of purity and analyzed the spectroscopic results of the obtained surfactants). The authors thank the Institute of Petrochemical Processes of National Academy of Sciences of Azerbaijan for supporting this research and the Center for Computational Research (CCR) at the University at Buffalo for providing computational resources.

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