Metal-organic chemistry

The electron density versus NICSzz (the out-ofplane
component of nucleus-independent chemical shifts
(NICS)) scan for assessing magnetic aromaticity among similar
molecules with different ring sizes is improved by scanning the
Laplacian of electron density versus NICSzz to include molecules
containing different types of atoms. It is demonstrated
that the new approach not only reproduces the results of the
previous method but also surpasses that in the case of species
with different atom types. The relative positions of curves in the
plots of the Laplacian of electron density versus NICSzz correlate well with the ring current intensities of these molecules both near
and far from the ring planes of the considered molecules. Accordingly, relative magnetic aromaticity of a number of planar
hydrocarbons and a group of double aromatic metallic/semimetallic species are studied and discussed.

The distributions of dissolved iron and organic iron-binding ligands were examined in water column profiles and deckboard incubation experiments in the southern California Current System (sCCS) along a transition from coastal to semi-oligotrophic waters. Analysis of the iron-binding ligand pool by competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) using multiple analytical windows (MAWs) revealed three classes of iron-binding ligands present throughout the water column (L 1 −L 3), whose distributions closely matched those of dissolved iron and nitrate. Despite significant biogeochemical gradients, ligand profiles were similar between stations, with surface minima in strong ligands (L 1 and L 2), and relatively constant concentrations of weaker ligands (L 3) down to 500 m. A phytoplankton grow-out incubation, initiated from an iron-limited water mass, showed dynamic temporal cycling of iron-binding ligands. A biological iron model was able to capture the patterns of the strong ligands in the grow-out incubation relatively well with only the microbial community as a biological source. An experiment focused on remineralization of particulate organic matter showed production of both strong and weak iron-binding ligands by the heterotrophic community, supporting a mechanism for in-situ production of both strong and weak iron-binding ligands in the subsurface water column. Photochemical experiments showed a variable influence of sunlight on the degradation of natural iron-binding ligands, providing some evidence to explain differences in surface ligand concentrations between stations. Patterns in ligand distributions between profiles and in the incubation experiments were primarily related to macronutrient concentrations, suggesting microbial remineralization processes might dominate on longer timescales over short-term changes associated with photochemistry or phytoplankton growth.