Background:
In this study, we show that the AFM method not only allows monitoring the
morphological changes in biological structures fixed on the surface due to H-bonds, but also makes it
possible to study the self-organization of metal complexes by simulating the active center of enzymes
due to intermolecular H-bonds into stable nanostructures; the sizes of which are much smaller than the
studied biological objects. The possible role of intermolecular hydrogen bonds in the formation of stable
supramolecular metal complexes, which are effective catalysts for the oxidation of alkyl arenes to
hydroperoxides by molecular oxygen and mimic the selective active sites of enzymes, was first studied
by AFM.
Methods and Results:
The formation of supramolecular structures due to intermolecular hydrogen
bonds and, possibly, other non-covalent interactions, based on homogenous catalysts and models of
active centers enzymes, heteroligand nickel and iron complexes, was proven by AFM-technique. AFM
studies of supramolecular structures were carried out using NSG30 cantilever with a radius of curvature
of 2 nm, in the tapping mode. To form nanostructures on the surface of a hydrophobic, chemically
modified silicon surface as a substrate, the sample was prepared using a spin-coating process from solutions
of the nickel and iron complexes. The composition and the structure of the complex
Ni2(acac)(OAc)3·NMP·2H2O were determined in earlier works using various methods: mass spectrometry,
UV- and IR-spectroscopy, elemental analysis, and polarography. Self-assembly of supramolecular
structures is due to intermolecular interactions with a certain coordination of these interactions, which
may be a consequence of the properties of the components themselves, the participation of hydrogen
bonds and other non-covalent interactions, as well as the balance of the interaction of these components
with the surface. Using AFM, approaches have been developed for fixing on the surface and quantifying
parameters of cells.
Conclusion:
This study summarizes the authors' achievements in using the atomic force microscopy
(AFM) method to study the role of intermolecular hydrogen bonds (and other non-covalent interactions)
and supramolecular structures in the mechanisms of catalysis. The data obtained from AFM
based on nickel and iron complexes, which are effective catalysts and models of active sites of enzymes,
indicate a high probability of the formation of supramolecular structures in real conditions of
catalytic oxidation, and can bring us closer to understanding enzymes activity. With a sensitive AFM
method, it is possible to observe the self-organization of model systems into stable nanostructures due
to H-bonds and possibly other non-covalent interactions, which can be considered as a step towards
modeling the active sites of enzymes. Methodical approaches of atomic force microscopy for the study
of morphological changes of cells have been developed.
Tuning protein mechanics through an ionic cluster graft from an extremophilic protein
