Nitrogen fixation by nitrogenases: a quantum chemical study

Article Abstract:

The mechanism of ammonia formation by nitrogenase was investigated using the hybrid density functional method B3LYP with large basis sets. The chosen model clusters contain a net neutral ionic charge with the iron atoms in the low Fe(II) oxidation state having ferromagnetically coupled spins. A significant finding was that placing a hydrogen atom on a bridging sulfur causes substantial change in the affinity of the cluster for N2. Without the hydrogen atom N2 forms only a weak end-on bond to one of the iron atoms. In contrast, N2 becomes strongly activated in a bridging coordination in the presence of the hydrogen atom.

Molecular structure, Hydrogen bonding, Hydrogen bonds, Atoms, Nitrogenase, Nitrogen, Nitrogen fixation

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Acidic property of MFI-type gallosilicate determined by temperature-programmed desorption of ammonia

Article Abstract:

A study was conducted to characterize the acidic features of gallosilicate samples supporting different composites using temperature-programmed desorption. Powder x-ray diffraction was obtained using a Rigaku Miniflex Plus diffractometer to describe the crystal structure. Results indicated that the number of acid sites on H-gallosilicate with MFI structure correlated with the number of the gallium atoms isomorphoous-substituted into the framework.

Silicates, Gallium

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Crystal potential formula for the calculation of crystal lattice sums

Article Abstract:

A novel formula for determining the potential energy of the central unit cell of a finite crystal is presented. The formula called the crystal potential formula was derived based on a two-center Cartesian multipole expansion. A numerical implementation of the crystal potential formula revealed that it is very efficient for computing the crystal energies as a function of the molecules contained in the unit cell.

Crystal lattices

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