This thesis investigates the development of novel quaternary ammonium compounds (QACs) with the aim of addressing the growing concerns regarding bacterial resistance and environmental impacts associated with conventional QACs. The research focusses on two different QAC series: traditional derivatives based on pyridine-4-aldoxime and biodegradable "soft" variants derived from 3-substituted quinuclidine. While the structural modifications of the traditional QACs resulted in potent antiviral properties, their antibacterial efficacy was impaired, possibly due to an increased polarity of the backbone that hinders electrostatic interactions with the bacterial membrane. Consequently, the polarity of the amide bond in the "soft" QAC variants was diminished by the addition of long hydrocarbon chains in its extension, resulting in compounds with a dual mechanism of action, lower toxicity and an improved biodegradability profile. In addition, the research emphasizes the importance of fine-tuning the hydrophobic/hydrophilic ratio, as demonstrated by the example of 3-aminoquinuclidine derived QACs in which the amino functional group mimics bis-QAC by protonation under physiological conditions. These derivatives showed potent bactericidal activity against a variety of bacterial strains, including the ability to disrupt biofilm formation and induce bacterial cell death by destabilization of the membrane and generation of the reactive oxygen species. Taken together, the obtained results and the established structure-activity relationships provide valuable insights for the rational design and synthesis of next-generation QACs with improved efficacy, biosafety profile and potential therapeutic applications.