The research, conducted entirely in silico using advanced quantum chemical methods, modeled the behavior of Mg(II), Fe(II), Fe(III), Co(II), Co(III) and Cu(II) porphyrines under static magnetic fields ranging from 0.1 to 100 Arbitrary Magnetic Field Units, where one AMFU exceeds 1000 Tesla. The team used density functional theory with the B3LYP functional and a 6-31G** basis set, drawing initial structures in Fujitsu Scigress 2.0, optimizing them in Gaussian 0.9, and then applying the Amsterdam Modelling Suite with a non-relativistic orbital momentum L-dot-B method to simulate the field’s influence before recalculating structural and electronic properties.

The results reveal a consistent pattern: static magnetic fields decreased the stability of every metalloporphyrine examined. The researchers measured this through heat of formation, where less negative values indicate reduced stability. Across all six metal centers, the heat of formation became progressively less negative as flux density increased. For Mg(II) porphyrine, considered a simplified model of chlorophyll, the value shifted from -803 kJ·mol⁻¹ at zero field to -698 kJ·mol⁻¹ at 100 AMFU when the molecule was oriented along the X-axis. The effect depended strongly on how the molecule sat within the Cartesian coordinate system, with X-axis orientation generally producing the strongest destabilization, followed by Y- and Z-axes.

Alongside the loss of stability came a rise in dipole moment, signaling growing molecular asymmetry. The macrocyclic ring, normally flat with D4h symmetry, lost its planarity under the field’s influence. The deformed skeletons adopted one of four characteristic conformations: saddle, ruffle, dome or wave. In Mg(II) porphyrine specifically, the central magnesium atom was ejected from the molecular center as Mg-N bond lengths increased, stretching from roughly 1.9 Å at zero field to over 2.4 Å at the highest flux density along the X-axis.

The electronic consequences were equally significant. Charge density at the ring nitrogen atoms changed irregularly with increasing field strength, and the Mg-N bonds, described as intermediate between ionic and atomic in character, weakened as the external magnetic field reduced the durability of the binding electron pair. The positive charge on the central magnesium atom rose with flux density, which the authors note should enhance its ability to bind Lewis bases and potentially promote photosynthesis, provided the reaction site is not obscured by steric hindrance from the deformed ring.

Iron porphyrines, representing heme and hemin, showed their own distinct responses. The Fe(II) molecule was already non-planar before any field was applied, and the static magnetic field deepened its deformation. Remarkable elongation of some C-H bonds occurred at 10 and 100 AMFU when the molecule sat in the X-Y plane. The positive charge density at the iron atom generally decreased with increasing flux density along the X-axis but increased along the Z and Y axes, a pattern the authors describe as beneficial for accepting Lewis bases such as carbon monoxide. Fe(III) porphyrine, by contrast, resisted deformation more effectively along the X and Z axes, though its iron atom also showed irregular charge shifts and its N-Fe bonds generally lengthened with rising field strength.

Cobalt porphyrines, the structural basis of vitamin B12, behaved differently again. The Co(II) atom, being bidentate, largely inhibited the bending deformation seen in other metalloporphyrines, instead producing local distortion within the macrocycle. When the field acted along the Z-axis, the molecule flattened, cycling through dome-flat-flat-dome conformations as flux density increased. Along the X or Y axis, a wave-mode deformation emerged. Notably, the positive charge density at the Co(II) atom always increased relative to the field-free state, enhancing its capacity to bind Lewis bases, with Y-axis orientation producing the most reactive configuration. The Co(III) cation, however, moved in the opposite direction: field exposure decreased its ability to coordinate Lewis bases, and its presence favored elongation of C-H bonds to a degree suggesting possible dissociation.

Cu(II) porphyrine, the model for hemocyanin in blue-blooded invertebrates, presented perhaps the most unusual behavior. Even without any applied field, both nitrogen atoms bound to copper carried positive charge density, a rarity among the molecules studied. A field of just 0.1 AMFU flipped the charge at N1 to negative when the molecule was oriented along the X or Z axis, while the Y-axis orientation required the full 100 AMFU to achieve the same conversion. The positive charge on the copper atom itself invariably increased with field strength, which should facilitate coordination of Lewis bases, though the N-Cu bond lengths varied irregularly and were least sensitive to elongation along the Z-axis.

Ranking the six metalloporphyrines by stability loss under the field, the order from most to least affected was Fe(III)⁺, Co(III)⁺, Fe(II), Co(II), Cu(II) and Mg(II). The authors conclude that static magnetic fields, even at the lowest simulated flux density of 0.1 AMFU, influence the biological role of metalloporphyrines through changes in electron density at the central metal atoms, steric hindering of the deformed ring, and polarization of bonds from pure valence character toward ionic character. Regardless of orientation along the X, Y or Z axes, the field always destabilized the molecules, and the resulting deformation facilitated additional ligation of the central metal atom, an effect the researchers suggest could potentially be harnessed in synthetic modifications of metalloporphyrines.

The findings carry a speculative connection to astrophysics. The authors note the recent discovery of the highest-energy cyclotron resonance scattering feature from the galactic ultraluminous X-ray pulsar Swift J0243.6+6124, where magnetic fields exceed 1.6 billion Tesla near the surface of the neutron star. Such extreme fields, they argue, reinforce the plausibility that high-density static magnetic fields genuinely deteriorate metalloporphyrine integrity, lending cosmic-scale weight to the computational predictions. While the simulations remain theoretical and the Arbitrary Magnetic Field Unit vastly exceeds typical terrestrial exposures, the work opens a provocative question about whether the magnetic environments surrounding living systems, from MRI scanners to planetary fields, might subtly reshape the chemistry of life’s most essential metal complexes.

Subject of Research: Numerical simulation of static magnetic field effects on biologically essential metalloporphyrines

Article Title: Potential risk resulting from the influence of static magnetic field upon living organisms. Numerically simulated effects of the static magnetic field upon metalloporphyrines

Article References: Ciesielski, W., Girek, T., Oszczęda, Z., Soroka, J. A., & Tomasik, P. (2022). Potential risk resulting from the influence of static magnetic field upon living organisms. Numerically simulated effects of the static magnetic field upon metalloporphyrines. BioRisk, 18, 115-132. https://doi.org/10.3897/biorisk.18.86616

Image Credits: AI Generated

DOI: 10.3897/biorisk.18.86616

Keywords: static magnetic field, metalloporphyrines, porphine, chlorophyll, heme, vitamin B12, hemocyanin, density functional theory, molecular deformation, charge density, BioRisk, computational chemistry