Molecular organization of nalidixate conjugated calixarenes in bacterial model membranes probed by molecular dynamics simulation and Langmuir monolayer studies

Two p-tert-butylcalix[4]arene derivatives bearing one or two nalidixic acid groups connected to the lower rim of p-tert-butylcalix[4]arene through the propylenic spacer were studied upon interaction with model bacterial membranes. Indeed, these derivatives were developed recently as new macrocyclic antibiotic carriers for antibacterial therapy. To obtain molecular level information about the interaction between the calixarene conjugates and a membrane lipid, atomistic molecular dynamics simulation, as well as surface pressure, surface potential, polarization modulation infrared reflection–absorption spectroscopy, and Brewster angle microscopy studies of 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE)–calixarene derivative films were performed. The results obtained indicate that the interaction between the calixarene derivatives and DMPE occurs via the phosphate and carbonyl groups present in the lipid. Although both calixarene derivatives increase the chain tilt and conformational disordering of the DMPE molecules, these effects are more important in the case of the monosubstituted derivative. Importantly, the two derivatives have an opposite impact on hydration of the phosphoglyceride polar head