title: A zeta potential value determines the aggregate's size of penta-substituted [60]fullerene derivatives in aqueous suspension whereas positive charge is required for toxicity against bacterial cells.
abstract: BACKGROUND
  The cause-effect relationships between physicochemical properties of amphiphilic [60]fullerene derivatives and their toxicity against bacterial cells have not yet been clarified. In this study, we report how the differences in the chemical structure of organic addends in 10 originally synthesized penta-substituted [60]fullerene derivatives modulate their zeta potential and aggregate's size in salt-free and salt-added aqueous suspensions as well as how these physicochemical characteristics affect the bioenergetics of freshwater Escherichia coli and marine Photobacterium phosphoreum bacteria. Dynamic light scattering, laser Doppler micro-electrophoresis, agarose gel electrophoresis, atomic force microscopy, and bioluminescence inhibition assay were used to characterize the fullerene aggregation behavior in aqueous solution and their interaction with the bacterial cell surface, following zeta potential changes and toxic effects.
  
  
  RESULTS
  Dynamic light scattering results indicated the formation of self-assembled [60]fullerene aggregates in aqueous suspensions. The measurement of the zeta potential of the particles revealed that they have different surface charges. The relationship between these physicochemical characteristics was presented as an exponential regression that correctly described the dependence of the aggregate's size of penta-substituted [60]fullerene derivatives in salt-free aqueous suspension from zeta potential value. The prevalence of DLVO-related effects was shown in salt-added aqueous suspension that decreased zeta potential values and affected the aggregation of [60]fullerene derivatives expressed differently for individual compounds. A bioluminescence inhibition assay demonstrated that the toxic effect of [60]fullerene derivatives against E. coli cells was strictly determined by their positive zeta potential charge value being weakened against P. phosphoreum cells in an aquatic system of high salinity. Atomic force microscopy data suggested that the activity of positively charged [60]fullerene derivatives against bacterial cells required their direct interaction. The following zeta potential inversion on the bacterial cells surface was observed as an early stage of toxicity mechanism that violates the membrane-associated energetic functions.
  
  
  CONCLUSIONS
  The novel data about interrelations between physicochemical parameters and toxic properties of amphiphilic [60]fullerene derivatives make possible predicting their behavior in aquatic environment and their activity against bacterial cells.
authors.affiliation: Department of Microbiology, Orenburg State University, Orenburg, Russia. dgderyabin@yandex.ru.
authors.forename: Dmitry G
authors.initials: DG
authors.lastname: Deryabin
authors.affiliation: Department of Microbiology, Orenburg State University, Orenburg, Russia. lv.efremova@yandex.ru.|All-Russia Research Institute of Beef Cattle Breeding, RAS, Orenburg, Russia. lv.efremova@yandex.ru.
authors.forename: Ludmila V
authors.initials: LV
authors.lastname: Efremova
authors.affiliation: Department of Microbiology, Orenburg State University, Orenburg, Russia. avasilchenko@gmail.com.|Institute of Cellular and Intracellular Symbiosis, RAS, Orenburg, Russia. avasilchenko@gmail.com.
authors.forename: Alexey S
authors.initials: AS
authors.lastname: Vasilchenko
authors.affiliation: Institute for Ecology and Genetics of Microorganisms, RAS, Perm, Russia. radimira@list.ru.
authors.forename: Evgeniya V
authors.initials: EV
authors.lastname: Saidakova
authors.affiliation: Department of Microbiology, Orenburg State University, Orenburg, Russia. sizova.l78@yandex.ru.|All-Russia Research Institute of Beef Cattle Breeding, RAS, Orenburg, Russia. sizova.l78@yandex.ru.
authors.forename: Elena A
authors.initials: EA
authors.lastname: Sizova
authors.affiliation: Institute for Problems of Chemical Physics of RAS, Chernogolovka, Russia. troshin2003@inbox.ru.
authors.forename: Pavel A
authors.initials: PA
authors.lastname: Troshin
authors.affiliation: Institute for Problems of Chemical Physics of RAS, Chernogolovka, Russia. zhilenkow91@inbox.ru.
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Zhilenkov
authors.affiliation: Institute for Problems of Chemical Physics of RAS, Chernogolovka, Russia. eka57671232@yandex.ru.
authors.forename: Ekaterina A
authors.initials: EA
authors.lastname: Khakina
authors.forename: Ekaterina E
authors.initials: EE
authors.lastname: Khakina
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology*; D004926:Escherichia coli / Q000187:drug effects*; D004927:Escherichia coli Infections / Q000188:drug therapy; D037741:Fullerenes / Q000737:chemistry* / Q000494:pharmacology*; D006801:Humans; D010776:Photobacterium / Q000187:drug effects*; D055672:Static Electricity; D014867:Water / Q000737:chemistry
chemical_list: D000900:Anti-Bacterial Agents; D037741:Fullerenes; D014867:Water; C069837:fullerene C60