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Review
. 2021 Jun 24;22(13):6793.
doi: 10.3390/ijms22136793.

Quaternary Ammonium Compounds (QACs) and Ionic Liquids (ILs) as Biocides: From Simple Antiseptics to Tunable Antimicrobials

Anatoly N Vereshchagin  1 , Nikita A Frolov  1 , Ksenia S Egorova  1 , Marina M Seitkalieva  1 , Valentine P Ananikov  1
Affiliations
Review

Quaternary Ammonium Compounds (QACs) and Ionic Liquids (ILs) as Biocides: From Simple Antiseptics to Tunable Antimicrobials

Anatoly N Vereshchagin et al. Int J Mol Sci. .

Abstract

Quaternary ammonium compounds (QACs) belong to a well-known class of cationic biocides with a broad spectrum of antimicrobial activity. They are used as essential components in surfactants, personal hygiene products, cosmetics, softeners, dyes, biological dyes, antiseptics, and disinfectants. Simple but varied in their structure, QACs are divided into several subclasses: Mono-, bis-, multi-, and poly-derivatives. Since the beginning of the 20th century, a significant amount of work has been dedicated to the advancement of this class of biocides. Thus, more than 700 articles on QACs were published only in 2020, according to the modern literature. The structural variability and diverse biological activity of ionic liquids (ILs) make them highly prospective for developing new types of biocides. QACs and ILs bear a common key element in the molecular structure-quaternary positively charged nitrogen atoms within a cyclic or acyclic structural framework. The state-of-the-art research level and paramount demand in modern society recall the rapid development of a new generation of tunable antimicrobials. This review focuses on the main QACs exhibiting antimicrobial and antifungal properties, commercial products based on QACs, and the latest discoveries in QACs and ILs connected with biocide development.

Keywords: antibacterial; antimicrobial; biocide; ionic liquid; quaternary ammonium compound.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
General structures and types of QACs.
Figure 2
Figure 2
Biocide market in USA.
Figure 3
Figure 3
Biocide applications (HVAC—heating, ventilation, and air conditioning).
Figure 4
Figure 4
Commercial alkyl QACs.
Figure 5
Figure 5
Commercial QACs based on pyridine.
Figure 6
Figure 6
Commercial QACs–biguanide derivatives.
Figure 7
Figure 7
Number of publications involving QACs from 1935 to 2020 (SciFinder, January 2021).
Figure 8
Figure 8
“Soft” mono-QACs.
Figure 9
Figure 9
CSA-based mono-QACs.
Figure 10
Figure 10
Mono-QACs containing hydrazide bridges.
Figure 11
Figure 11
Mono-QACs containing N-chloramines.
Figure 12
Figure 12
Mono-QACs containing hydroxyl groups.
Figure 13
Figure 13
Isatin-based mono-QACs.
Figure 14
Figure 14
Mono-QACs containing aryl substituents.
Figure 15
Figure 15
Picolinic mono-QACs.
Figure 16
Figure 16
Pyridoxin-based mono-QACs.
Figure 17
Figure 17
Mono-QACs from Wuest’s and Minbiole’s works.
Figure 18
Figure 18
Cations and anions commonly used in ILs with known antimicrobial activity.
Figure 19
Figure 19
Cations and anions used in antimicrobial API-ILs.
Figure 20
Figure 20
Alkyl bis-QACs.
Figure 21
Figure 21
Alkyl bis-QACs containing aromatic spacers.
Figure 22
Figure 22
Bis-QACs containing saturated heterocycles.
Figure 23
Figure 23
Mixed bis-QACs.
Figure 24
Figure 24
Bis-QACs containing saturated heterocycles.
Figure 25
Figure 25
Bis-QACs containing unsaturated heterocycles.
Figure 26
Figure 26
Pyridine-based bis-QACs without spacers and with alkyl spacers.
Figure 27
Figure 27
Pyridine-based bis-QACs containing aromatic spacers.
Figure 28
Figure 28
Pyridine-based bis-QACs containing mixed spacers.
Figure 29
Figure 29
Pyridine-based bis-QACs containing pentaerythritol.
Figure 30
Figure 30
Examples of dicationic ILs with tested antimicrobial activity. The numbers of substances correspond to those in Table 5.
Figure 31
Figure 31
Alkyl multi-QACs.
Figure 32
Figure 32
Multi-QACs with aromatic fragments.
Figure 33
Figure 33
Spectrum of biologically active homogeneous poly-QACs.
Figure 34
Figure 34
Copolymer poly-QACs.
Figure 35
Figure 35
Examples of poly-ILs with tested antimicrobial activity. The numbers of substances correspond to those in Table 8.
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