Density functional theory using the zero-order regular approximate two-component relativistic Hamiltonian has been applied to calculate the 195Pt chemical shifts for the complexes [PtCl6]2-, [PtCl4]2-, and [Pt2(NH3)2Cl2((CH3)3CCONH)2(CH2COCH3)]Cl. It is demonstrated that, in contrast to recent findings by other authors, platinum chemical shift calculations require not only a basis set beyond polarized triple-zeta quality for the metal atom but also, in principle, the consideration of explicit solvent molecules in addition to a continuum model for the first two complexes. We find that the inclusion of direct solvent-solute interactions at the quantum mechanical level is important for obtaining reasonable results despite that fact that these solvent effects are rather nonspecific. The importance of solvent effects has also implications on how experimental data should be interpreted. Further, in contrast to several previous studies of heavy-metal NMR parameters, functionals beyond the local density approximation were required both in the geometry optimization and the NMR calculations to obtain reasonable agreement between the computed and experimental NMR data. This comes with the disadvantage, however, of increased Pt-ligand bond distances leading to less good agreement with experiment for structural data. A detailed analysis of the results for the two chloroplatinate complexes is presented. The same computational procedure has then been applied to the dinuclear Pt(III) complex. Chemical shifts have been calculated with respect to both [PtCl6]2- and [PtCl4]2- chosen as the NMR reference, yielding good agreement with experiment. The determination of preferred solvent locations around the complexes studied turned out to be important for reproducing experimental data.
The isotropic one-bond and two-bond 199Hg-199Hg nuclear magnetic spin-spin coupling constants (J-couplings) of [Hg-Hg-Hg]2+ were calculated using density functional theory, the zeroth-order regular approximation (ZORA) to treat relativistic effects, and Born-Oppenheimer molecular dynamics (BOMD) including SO2 molecules explicitly for the description of solvent effects. The final BOMD average of 150 kHz for 1J (199Hg-199Hg) agrees well with the experimental spin-spin coupling of 140 kHz measured in liquid SO2, while computations not considering explicit solvation at the quantum-mechanical level yielded one-bond coupling constants between 230 and 260 kHz. The two-bond coupling is similarly strongly affected by solvent effects. An analysis of the BOMD data shows that the effect is mainly due to close contacts between the terminal Hg atoms of [Hg-Hg-Hg]2+ and the solvent's oxygen atoms. The results highlight the importance of solvent effects for the NMR parameter of heavy metals and demonstrate the usefulness of treating such solvent effects with the help of molecular dynamics-based averaging.
Novel water-soluble polymeric photosensitizers based on the natural polymer dextran were synthesized and studied. The modified dextran contained photoactive anthracene (An) chromophores. They were soluble in water with the solubility decreasing with an increase in the number of An moieties bound to the polymeric chain. In aqueous solutions, the macromolecules adopted a compact conformation which resulted in the formation of hydrophobic microdomains. The properties of these domains were characterized with molecular probes such as perylene and pyrazolo-quinoline derivative. The polymer absorbed in the UV/vis region and photosensitized reactions mediated by energy and/or electron transfer from electronically excited An to the molecules of organic compounds solubilized in polymeric microdomains or resided in water.
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