Related Experiment Video
Updated: Mar 20, 2026
Synthesis of Cationized Magnetoferritin for Ultra-fast Magnetization of Cells
Published on: December 13, 2016
Deconvoluting electrostatic, noncovalent, and magnetic effects of iron-sulfur cofactors inside synthetic cage
Rupal Baliyan1, Alejandro Javier Castillo1, Brett N Schneider1
1Department of Chemistry, University of Minnesota, Twin Cities MN-55455, USA.
Abstract:
The electronic states of iron‑sulfur (Fe-S) clusters in metalloenzymes are critically influenced by second and outer-sphere interactions-electrostatics, hydrogen bonding, and hydrophobic contacts-that modulate cofactor redox potentials and reactivity in processes ranging from cellular respiration to nitrogen fixation. To systematically probe these effects in a well-defined synthetic environment, we previously developed host-guest complexes of [Fe4S4(SR)4]2- clusters ([1R]2-, R = Ph, -CH2CH2OH) encapsulated within naphthalenediimide (NDI)-functionalized metal-organic cages [M4L6]8+ (M = Fe, Ni, Zn; L = organic linker), demonstrating that encapsulation substantially alters cluster electronic structure. Herein, we quantitatively dissect the individual contributions from second and outer-sphere electrostatics, π-π stacking, hydrogen bonding, and magnetic coupling. By investigating the host-guest series in two charge states, 1R⊂[Ni4L6]6+ and the reduced 1R⊂[Ni4L6]0 framework featuring [NDI]•- radical panels, we isolate the specific influence of the host's electronic environment on the guest cofactors. As controls, we examine the free clusters and unencapsulated ion pairs [Ni4L6][1tBu]6+ and [Ni4L6][1tBu], for which encapsulation is precluded by weak interfacial interactions and the smaller size of [1tBu]2-. In-depth Fe 2p X-ray photoelectron, infrared, and UV-visible spectroscopic analysis establishes substantial changes in binding energy and Fe-S bond covalency, with contributions from electrostatic stabilization (+0.6 eV binding energy shift) and second-sphere π-stacking/hydrogen bonding (+0.3 - 0.5 eV). Meanwhile, analysis of reduced congeners [Ni4L6]2+, 1R⊂[Ni4L6], and [Ni4L6][1tBu] enables dissection of subtle magnetic effects arising from cofactor association with the [NDI]•- cage. These findings establish supramolecular cages as a platform for deconvoluting second and outer-sphere effects on iron‑sulfur cofactor electronic structure and redox activity--.
More Related Videos
06:53Author Spotlight: Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks
Published on: June 9, 2023
10:45Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition
Published on: February 5, 2022
Related Concept Videos
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:42Valence Bond Theory
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...
03:45Formation of Complex Ions
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
02:51Metal-Ligand Bonds
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...