New ferrocene-integrated multifunctional guanidine surfactants: synthesis, spectroscopic elucidation, DNA interaction studies, and DFT calculations

Three new ferrocene-substituted aliphatic guanidines were successfully synthesized and well characterized by means of several analytical methods such as FT-IR, H-1 and C-13-NMR, Raman, atomic absorption spectroscopy (MS), and elemental analysis. The amphiphilic nature of ferrocene-based guanidines has been evaluated by determining their critical micelle concentration (CMC) through tensiometry, and UV-visible spectroscopy. The results obtained through both the techniques are in good agreement with each other. It was observed that the alkyl chain length played a major part in determining the CMC in pure ethanol as well as in an ethanol/water mixture. The quantum mechanical parameters such as the energy of frontier molecular orbitals (E-HOMO and E-LUMO) and the Mulliken charge distribution on the optimized structures was determined using a DFT/B3LYP method combined with the 6-31G(d,p) basis set in the gas phase. The shift in the peak potential, current and absorption maxima of the studied ferrocenyl guanidines in the presence of DNA revealed that cyclic voltammetry coupled with UV-visible spectroscopy provided a way to elaborate the DNA interaction mechanism, a pre-requisite for the design of new anticancer agents and understanding of the molecular basis of their action. The synthesized ferrocenyl derivatives exhibited good scavenging activity against the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH). These complexes were also scanned for their in vitro cytotoxicity against the human carcinoma cell line (MCF-7) and a normal cell line (MCF-10A) by means of an MTT assay, thereby rendering G-18 as the most potent chemotherapeutic drug.