The complexation of (1→4) linked α-L-guluronate (G) and β-D-mannuronate (M) disaccharides with Mg(2+), Ca(2+), Sr(2+), Mn(2+), Co(2+), Cu(2+), and Zn(2+) cations have been studied with quantum chemical density functional theory (DFT)-based method. A large number of possible cation-diuronate complexes, with one and two GG or MM disaccharide units and with or without water molecules in the inner coordination shells have been considered. The computed bond distances, cation interaction energies, and molecular orbital composition analysis revealed that the complexation of the transition metal (TM) ions to the disaccharides occurs via the formation of strong coordination-covalent bonds. On the contrary, the alkaline earth cations form ionic bonds with the uronates. The unidentate binding is found to be the most favored one in the TM hydrated and water-free complexes. By removing water molecules, the bidentate chelating binding also occurs, although it is found to be energetically less favored by 1 to 1.5 eV than the unidentate one. A good correlation is obtained between the alginate affinity trend toward TM cations and the interaction energies of the TM cations in all studied complexes, which suggests that the alginate affinities are strongly related to the chemical interaction strength of TM cations-uronate complexes. The trend of the interaction energies of the alkaline earth cations in the ionic complexes is opposite to the alginate affinity order. The binding strength is thus not a limiting factor in the alginate gelation in the presence of alkaline earth cations at variance with the TM cations.

A DFT study allows one to understand the selectivity for ethene hydrogenation over dimerization by the well-characterized faujasite-supported [Rh(C2H4)2]+ complex.

Applying a density functional approach to slab models of planar, (111), and rough, (110), Pd surfaces, we determined the isomerization free energy barriers of 1-butene to be significantly lower than the hydrogenation barriers. Microkinetic modeling allows one to mirror the kinetic experiments on conversions of 1-butene at the corresponding single-crystal surfaces in a qualitative fashion. Despite the inherent limitations of such kinetic modeling, theoretical predictions are fully supported by experimental data using Pd model catalysts: i.e., Pd­(111) and Pd(110) surfaces. The isomerization mechanism was calculated to proceed via an initial dehydrogenation of 1-butene to 1-buten-3-yl as an intermediatein contrast to the commonly proposed 2-butyl intermediate, associated with the Horiuti–Polanyi mechanism. Our modeling results rule out the original assumption that isomerization has to start with a hydrogenation step to rationalize the dependence of isomerization on hydrogen. However, this hydrogen dependence may arise in the second step, after an initial dehydrogenation, as suggested by the experimental data under hydrogen-deficient conditions.