Platinum(II) Complex of Benzimidazole-Derived N-Heterocyclic Carbene: Synthesis, Characterization, and Photophysical Properties

Platinum(II) complex of benzimidazole-derived N-heterocyclic carbene with formula [PtCl2(DMSO)(bimy)] was successfully synthesized via one pot reaction between 1,3-diisopropyl benzimidazolium (bimy×HBr), Ag2O and [PtCl2(DMSO)] (DMSO = dimethyl sulfoxide). The complex was characterized by means of multinuclear (1H and 13C{1H}) magnetic resonance and single crystal X-ray diffraction (XRD). The UV-Vis absorption spectra of the compound show an absorption shoulder above 300 nm. Under excitation by 285 nm UV lamp, solution of the compound in DCM is highly emissive showing emission maxima at around 410 nm. DFT calculations were also carried out for the complex to gain insight on its electronic structure and the nature of electronic transition involved in the absorption/emission process.

Spectroscopic detection of a ubiquitous dissolved pigment degradation product in subsurface waters of the global ocean

Measurements of light absorption by chromophoric dissolved organic matter (CDOM) from subsurface waters of the tropical Atlantic and Pacific Oceans showed a distinct absorption shoulder at 410–415 nm. This indicates an underlying absorption of a pigment whose occurrence is partly correlated with the apparent oxygen utilization (AOU) but also found in the deep chlorophyll maximum. A similar absorption maximum at ~415 nm was also found in the particulate fraction of samples taken below the surface mixing layer and is usually attributed to absorption by respiratory pigments of heterotrophic unicellular organisms. In our study, fluorescence measurements of pre-concentrated dissolved organic matter (DOM) samples from 200–6000 m confirmed a previous study suggesting that the absorption at ~415 nm was related to fluorescence at 650 nm in the oxygen minimum zone. The absorption characteristics of this fluorophore was examined by fluorescence emission/excitation analysis and showed a clear excitation maximum at 415 nm that could be linked to the absorption shoulder in the CDOM spectra. The spectral characteristics of the substance found in the dissolved and particulate fraction did not match with those of chlorophyll a degradation products (as found in a sample from the sea surface) but can be explained by the occurrence of porphyrin pigments from either heterotrophs or autotrophs. Combining the observations of the fluorescence and the 415-nm absorption shoulder suggests that there are high concentrations of a pigment degradation product in subsurface DOM of all major oceans. Most pronouncedly we found this signal in the deep chlorophyll maximum and the oxygen minimum zone of tropical regions. The origin, chemical nature, turnover rate, and fate of this molecule is so far unknown.

Indications for a ubiquitous dissolved pigment degradation product in subsurface waters of the global ocean

Measurements of light absorption by chromophoric dissolved organic matter (CDOM) from sub-surface waters of the tropical Atlantic and Pacific showed a distinct absorption shoulder at 410–415 nm, indicating an underlying absorption of a pigment. A similar absorption maximum at ~410 nm was also found in the particulate fraction and is usually attributed to absorption by respiratory pigments of heterotrophic unicellular organisms. The CDOM absorption shoulder was described earlier in the Indian Ocean at 600 m depth and was related to a "deep red fluorescence" found in the same depth, i.e. in the oxygen minimum zone (Breves et al., 2003; Broenkow et al., 1983). In our study, fluorescence measurements of pre-concentrated DOM samples confirmed that the absorption at ~410 nm was related to a specific fluorescence at 650 nm. The absorption characteristic of this specific fluorophor was examined by fluorescence emission/excitation analysis and this showed a clear excitation maximum at 415 nm (in methanol) that can explain the absorption shoulder in the CDOM spectra. The spectral characteristics of the substance found in the dissolved and particulate fraction did not match with those of chlorophyll a degradation products (as found in a sample from the sea surface) but can be explained by the occurrence of respiratory pigments from heterotrophs. Combining the observations of the "deep red fluorescence" and the 410 nm-absorption shoulder suggests that there are high concentrations of a pigment degradation product (cytochrome c) in DOM of all major oceans. Most pronouncedly we found this signal in the deep chlorophyll maximum and the oxygen minimum zone of tropical regions. The origin, chemical nature, turn-over rate, and fate of this molecule is so far unknown.