Adrian M. V. Brânzanic

Research

Electronic structure & reactivity

I use electronic-structure theory — density functional theory, and methods beyond it — in close collaboration with experimentalists, to explain how metals, clusters and functional molecules bind and transform. The unifying question is how the immediate environment of a metal or a cluster controls its oxidation state, spin, reactivity and the routing of electrons. Several linked themes run through the work.

Cobalamin (vitamin B12) reactivity

The cobalt corrin at the heart of vitamin B12 is a remarkably versatile redox and coordination platform. In a long-running collaboration I have helped show that its Co(III) centre forms a whole family of axial adducts once thought out of reach — with hydrogen peroxide[10], organic peroxides[17], hypochlorite[16], chlorite[25] and oxidised-cysteine derivatives[18] — each pinned down by matching experiment to DFT and TD-DFT. One of them, a cobalt–chlorite complex, turns out to be a stable analogue of the first intermediate in the catalytic cycle of the heme enzyme chlorite dismutase[33].

Peroxide & hydroperoxo adducts Hypochlorite & chlorite oxidation Oxidised-cysteine corrinoids Analogue of chlorite dismutase
UV–vis spectra and reaction kinetics of the aquacobalamin–hydrogen peroxide adduct.
Spectra & kinetics of the aquacobalamin–H2O2 adduct · Inorg. Chem. (2021) [10]
Reaction scheme of cyano- and aquacobalamin oxidised by hypochlorite.
Oxidation of cobalamins by hypochlorite · JBIC (2023) [16]
DFT-optimised structures of the chlorite adduct of aquacobalamin.
DFT structures of the chlorite adduct of aquacobalamin · JBIC (2025) [25]

Heme, siroheme & the logic of the macrocycle

The same iron behaves very differently inside heme, siroheme or a corrin, and much of my work asks how the macrocycle sets the chemistry. Using electron-transport (Green’s-function) methods I explained why sulfite reductase employs siroheme rather than ordinary heme[6]: the modified ring suppresses stray charge-transfer routes and channels electrons cleanly to the catalytic iron[8]. Earlier work set out the ferrous–sulfite (FeSO2) intermediates of the enzyme’s own reaction[5]. I also study high-valent ferryl intermediates[26] — contributing the computational analysis to a 2026 Nature Communications study showing that ferryl species in a heme peroxidase owe their unexpectedly long Fe–O bonds to accessible ferric-oxyl excited states[31]. A related study rationalises why biology pairs cobalt with the corrin of B12 but nickel with the corphin of coenzyme F430, tracing it to the conjugation of the ring[32].

Siroheme–[Fe4S4] coupling Ferryl / high-valent iron Ferric-oxyl excited states Corrin vs corphin — Co vs Ni
Heme peroxidase protein fold and active-site structures behind the ferryl intermediate.
Ferric-oxyl excited states behind long Fe–O bonds in a heme peroxidase · Nat. Commun. (2026) [31]
Electron-transport model with the siroheme active site as an island between two gold electrodes.
Electron-transport model: the siroheme active site as an “island” between two electrodes · Chem. Commun. [6]
Structures comparing the cobalt corrin with the nickel corphin of coenzyme F430.
Why cobalt pairs with corrin but nickel with the corphin of F430 · Chem. Eur. J. (2026) [32]

Cluster & main-group bonding

With Alexandru Lupan and R. Bruce King I study how the number of skeletal electrons dictates the shape of electron-deficient cages. A series of studies mapped how hydrogen-rich dimetallaboranes obey the Wade–Mingos electron-counting rules — reproducing and rationalising the experimentally known structures[1, 2, 3, 4] — and how cationic gold “superatom” clusters display spherical aromaticity and surface σ-holes[7], connecting the language of borane chemistry to bare-metal clusters.

Hydrogen-rich dimetallaboranes Wade–Mingos electron counting Gold superatom clusters Spherical aromaticity & σ-holes
Low-energy isomers of the nine-atom gold cluster with relative energies.
Low-energy isomers of the Au9 superatom cluster · Phys. Chem. Chem. Phys. (2019) [7]
Isosurfaces of the spherical-aromatic electron density in cationic gold clusters.
Spherical-aromatic density & σ-holes in cationic gold clusters · PCCP (2019) [7]
Optimised seven-vertex hydrogen-rich dimetallaborane cage structures for Ru and Os.
Seven-vertex hydrogen-rich dimetallaborane cages · J. Organomet. Chem. [2]

Binding & activating small molecules

Whether a metal can grip an inert molecule like dinitrogen and make it react depends sensitively on its coordination environment. I study how the ligand field around iron[19] — and around manganese and cobalt — tunes the binding and activation of N2, finding that low oxidation states and carbanion ligands are decisive[23]. The work bears directly on the nitrogenase mechanism and on the question of whether an “iron-free” nitrogenase is feasible.

N2 binding & activation Coordination-environment effects Relevance to nitrogenase Fe / Mn / Co
Octahedral metal model with four water ligands, an axial R ligand and an end-on N2.
Octahedral M(H2O)4R–N2 model probing N2 binding at Mn and Co · J. Coord. Chem. (2024) [23]

Photofunctional molecules & applied computation

I provide the excited-state and electronic-structure analysis for functional molecules and materials developed with experimental groups in Cluj-Napoca. This includes phenothiazine and phenothiazinium dyes for fluorescence imaging[21], photodynamic therapy (as singlet-oxygen photosensitisers)[15, 27] and the colorimetric sensing of nitroaromatic explosives[34], together with computational support for green corrosion inhibitors[22, 29, 30] and for luminescent zinc[24] and europium[28] materials.

Phenothiazine dyes (TD-DFT) Singlet-oxygen photosensitisers Nitroaromatic sensing Corrosion inhibitors & luminescent materials
Computed structures of phenothiazinium photosensitiser molecules.
Phenothiazinium photosensitisers against melanoma · Bioorg. Chem. (2025) [27]
UV–vis titration curves for colorimetric sensing of nitroaromatic explosives.
Colorimetric dual sensing of nitroaromatic explosives · Dyes and Pigments (2026) [34]
Emission spectra and luminescent single crystals of europium Schiff-base complexes.
Luminescent Eu(III) Schiff-base complexes · J. Mol. Struct. (2025) [28]

Spectroscopy, redox & structure

Computed electronic structure is most powerful when anchored to experiment. I use it to interpret and predict spectra — including a fresh look at one of chemistry’s most familiar demonstrations, the intense blue of the iodine–starch complex[14] — and to unpick reaction mechanisms, such as the selenium and sulfur redox chemistry that generates reactive radicals in biology[9, 11]. The same toolkit of classical and QM/MM molecular dynamics follows larger assemblies in motion, from the non-heme-iron protein hemerythrin[13] to polylactic acid at a bioceramic surface[12].

Electronic spectra (TD-DFT) Iodine–starch complex Selenium / sulfur redox Molecular dynamics
Iodide chains threaded inside the helical amylose cavity of the iodine–starch complex.
Iodide chains threading the amylose helix — the blue of the iodine–starch complex · Molecules (2022) [14]
Bell-shaped pH profile of the observed rate constant for the glutathione–selenite reaction.
pH profile of the first step of the glutathione–selenite reaction · Inorg. Chim. Acta [9]
Molecular-dynamics trace of the inter-monomer distance in hemerythrin.
Molecular dynamics of hemerythrin and its derivatives · Studia UBB Chemia [13]

Foundations of quantum chemistry

Alongside the calculations I keep a distinct interest in the foundations of the theory itself — a project I call Quale Mechanics, a reading of the qualitative content of quantum mechanics[20], and an account of the covalent bond as a stabilised “Fermi heap”. The aim is the same as in the computational work: to say precisely what is happening beneath a familiar chemical picture, and to map uncertainty openly rather than hide it.

Quale Mechanics Foundations of the chemical bond Honest uncertainty
Diagram mapping Plato's divided line onto the passage from wavefunction to observable.
Quale Mechanics: Plato’s divided line read onto the quantum world [20]
Methods. Density functional theory and time-dependent DFT; QM/MM and QM/MM molecular dynamics for enzyme active sites; classical molecular dynamics; and non-equilibrium Green’s-function transport for electron channelling — chosen by calibration against difficult cases rather than defaults, and validated against experimental spectroscopy, crystallography and electrochemistry.

See the underlying papers

Each theme is backed by peer-reviewed work with collaborators in Cluj-Napoca and beyond — thirty-four articles from 2014 to 2026.

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