A new avibactam Gemini quaternary ammonium salt: synthesis, self-assembly, vibrational spectra, crystal structures and DFT calculations

Abstract

Avibactam ([AV]), a non-β-lactam β-lactamase inhibitor, contains a sulfonic acid group, which making separation and purification extremely difficult. The ability of the gemini quaternary ammonium salt N,N,N,N’,N’,N’-hexabutylbutanediammonium dibromide [444][Br]2 to precipitate [AV] from aqueous solutions resulted in the successful synthesis of a new avibactam gemini quaternary ammonium salt [444][AV]2. To understand the self-assembly, the transmission electron microscope (TEM) and spectra of [444] cations and [AV] anions in aqueous solution were investigated. By using a slow evaporation technique, the [444][AV]2 complex single crystal was produced from a water solvent. The title crystal structure conformation was done by single crystal X-ray diffraction (SCXRD) technique, and its belongs to the P-1 space group with the triclinic system. The thermal stability of [444][AV]2 has been investigated by TG/DSC studies, and its experimental vibrational bands (FT-IR and Raman) have been studied and assigned. The stability test indicated that [444][AV]2 exhibits outstanding physical stability under long-term and accelerated conditions. According to DFT calculations, electrostatic potential and Mulliken charges showed that [444] cations were readily adsorbed on the negatively charged [AV] anions surface sites through electrostatic attraction, and the existence of inter-molecular interactions was assessed by Hirshfeld surface of [444][AV]2 single crystal.