AFM Research in Catalysis and Medicine

Abstract

Background: In Account, we show that the AFM method allows not only monitoring the morphological changes of biological structures fixed on the surface due to H-bonds. The AFM method also makes it possible to study the self-organization of metal complexes 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 alkylarenes to hydro peroxides 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 tointermolecular 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. AFMstudies of supramolecular structures were carried out using NSG30 cantileverwith a radius of curvature of 2 nm, in the tapping mode. To form nanostructureson the surface of a hydrophobic chemically modified silicon surface as asubstrate, the sample was prepared using a spin-cotting process from solutionsof the nickel and iron complexes. The composition and the structure of thecomplex Ni2(acac)(OAc)3∙NMP∙2H2O weredetermined in earlier works [6] using various methods: mass spectrometry, UV- andIR-spectroscopy, elemental analysis, polarography. Self-assembly of supramolecular structures isdue to intermolecular interactions with a certain coordination of theseinteractions, which may be a consequence of the properties of the componentsthemselves, the participation of hydrogen bonds and other non-covalentinteractions, as well as the balance of the interaction of these componentswith the surface. UsingAFM, approaches have been developed for fixing on the surface andquantifying parameters of cells. Conclusion: This Account 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 obtained data of 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 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.

The Dual Function of PhOH Included in the Coordination Sphere of the Nickel Complexes in the Processes of Oxidation with Dioxygen

“…Using the AFM method, we have shown for the first time the possibility of the self-organization of nickel complexes{Ni(acac) 2 ∙L 2 ∙ L 3 } (L 3 = PhOH), which are not only effective catalysts of ethylbenzene oxidation but also structural and functional models of Ni-ARD (Ni-Acireductone Dioxygenase) [ 10 ], into supramolecular structures due to intermolecular H-bonds. UV spectroscopy data indicate the intra- and outer-sphere coordination of the extra-ligands L 2 and L 3 with M(acac) n (M = Ni, Fe, n = 2,3, L 2 = NMP, His, L 3 = Tyr) [ 15 , 16 ].…”

“…CO has been identified as an anti-apoptotic molecule in mammals. Recently, a human enzyme was found to regulate the activity of matrix metalloproteinase I (MMP-I), which is involved in tumor metastasis, by binding to the cytoplasmic transmembrane tail peptide MMP-I [ 16 , 17 ].…”

“… AFM three-dimensional images of structures formed on a modified silicon surface ( a ) based on complexes {Ni(acac) 2 ∙HMPA∙PhOH} with h~12–30 nm, and ( b , c ) {Ni(acac) 2 ∙NaSt∙PhOH} with h~300 nm. ( d ) Diagram of the average particle volumes based on: a-{Ni(acac) 2 ⋅His}, b-{Ni(acac) 2 ⋅His⋅Tyr}, adapted from [ 16 ]. …”