Ligation of water to magnesium chelates of biological importance

Water binding to several Mg^{2+} chelates, ethylenediamine, ethylenediamine-N,N’-diacetate, porphyrin, chlorophyll a and bacteriochlorophyll a, to form five- and six-coordinate complexes is studied by means of density functional theory. The results obtained for magnesium chelates are compared with the properties of the respective aqua complexes and the influence of the permittivity of environment on the ligand binding energies is discussed. Although the most common coordination number of Mg^{2+} is six, in the tetrapyrrolic chelates it is reduced to five because the accommodation of the sixth water ligand results in no gain in energy. This is in line with the experimental observations made for coordination of chlorophylls in vivo. The binding between Mg^{2+} and water is mostly of electrostatic nature, which is supported by the finding that its energy is correlated both with the electron density of the chelator and with electrostatic potential determined at the ligand binding site

Preparation, structural characterization, and decomposition studies of two new γ-octamolybdates of 4-methylpyridine

We synthesized two new c -octamolybdates, and determined their crystal structures from single-crystal X-ray diffraction data. Orange-yellow tetrakis(4-meth- ylpyridinium) bis(4-methylpyridine)- c -octamolybdate 1 crystallizes in space group P2 1 /c with a = 11.586(2) A ̊ , b = 15.526(2) A ̊ , c = 16.247(2) A ̊ , b = 118.753(1) 8 , Z = 2. White tetrakis(4-methylpyridinium) bis(4-methyl- pyridine)- c -octamolybdate hydrate 2 crystallizes in space group C2/c with a = 27.086(4) A ̊ , b = 11.917(2) A ̊ , c = 19.332(2) A ̊ , b = 124.427(1) 8 , Z = 4. Results of crystal structure determinations are presented and dis- cussed in this paper. Thermal stability and decomposition studies of the obtained two new c -octamolybdates were performed using TG/DSC and XRPD methods. Both compounds decomposed with the formation of 4-meth- ylpyridinium b -octamolybdate. The two compounds are pseudo-polymorphs, exhibiting both striking similarities as well as significant differences in their structures and properties

Ligand binding properties of cobalamins

The main goal of the present density functional theory calculations is a comparative study of NO, O2, NO−2, and H2O binding to different forms of cob(II)alamins and cob(III)alamins.The comparison of binding energies of small ligands enables one to draw conclusions regarding the stability of the studied derivatives of cobalamins as well as to define the preferred form of cobalamin for each ligand. Ligands such as NO and O2 favor cob(II)alamins, while H2O and NO−2 cob(III)alamins. The obtained results are confronted with available experimental data. Finally, our findings allow one to divide the studied small ligands into two groups: NO and O2 for which the coordination to cobalamins significantly weakens their internal bonds, and NO−2 and H2O for which the effect is not observed

Ligand-tuning of the stability of Pd(II) conjugates with cyanocobalamin

Besides the well-known functions performed by vitamin B(12) (CblCN) in biochemical processes of the human body, an increasing interest has been raised by the possibility of its use as a transmembrane drug carrier, capable, among others, of enhancing the accumulation of inorganic cytostatics in cancer cells. The present study was aimed at determining the possibility of the formation of CblCN conjugates with Pd(II) complexes. A key aspect was their stability, which we attempted to tune by appropriate choice of ligands. Syntheses, spectroscopic analysis of postreaction systems and kinetic investigations of conjugate formation reactions, have been complemented by DFT modelling. The obtained results showed that ligand charge, geometry and electron affinity may have a significant impact on carrier binding and release leading to the activation of the Pd(II) complex. This provides a rationale to expect that with appropriate composition of the coordination sphere, it will be possible to extend the spectrum of less toxic inorganic chemotherapeutics