Selective prototropism of lumichrome in the liposome/graphene oxide interface: A detailed spectroscopic study

Abstract

The interactions of the biologically active fluorophores like flavins and biomolecules with nano carriers are very much important to produce targeted drug delivery systems. Also studying the interaction of graphene oxide (GO) with liposomes is essential for surface science and which have various applications. Herein, we have reported the interaction of a biologically active flavin molecule lumichrome (LU) with GO, in the absence and presence of zwitterionic 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposome by employing different spectroscopic techniques. These study also shows the prototropic tautomerization of LU, when it interacted with GO in the absence and presence of DMPC liposome. We have found that GO interacted with LU differently in the absence and presence of DMPC liposome. In the absence of DMPC liposome, LU molecules were directly adsorbed on the GO surface involving both edges and basal planes of GO via hydrogen bonding, π-π stacking between aromatic ring of LU and GO, and as a result we observe higher fluorescence quenching of LU. However, in the presence of DMPC liposome, LU molecules were partitioned inside the vesicle and in the presence of GO whole vesicle (in which LU molecules were partitioned) was placed on the edges of GO and here π-π stacking between aromatic ring of LU and GO is not possible, and as a result we observe moderate fluorescence quenching of LU. This study also indicates that zwitterionic DMPC liposome retained its structure when it interacts with GO. We have also found that in LU + GO complex, due to the direct adsorption of LU in GO surface, the prototropic tautomerization of LU is not possible, only the alloxazine form of LU exist. However, in LU + DMPC + GO complex when LU is incorporate inside the vesicle both alloxazine and isoalloxazine form of LU co-exist, indicates the prototropic tautomerization of LU in LU + DMPC + GO complex.