Narrow Results

Bilirubin is an insoluble yellow pigment produced from heme catabolism and serves as a diagnostic marker of liver and blood disorders. Here, a systematic study of several interactions and arrangements between different forms of natural bilirubin and poly-5, 2${}^{\prime }$-5${}^{\prime }$, 2${}^{\prime \prime }$-terthiophene-3-carboxylic acid/Mn(II)₂ complex, PTTCA–Mn(II)₂, as a biosensor of bilirubin has been investigated extensively. The PTTCA–Mn(II)₂ biosensor detects natural bilirubin through the mediated electron transfer by the Mn${}^{2+}$. Initially, density functional theory (DFT) using B3LYP and different basis sets including 6-31G* and 6-311G** has been employed to calculate the details of electronic structure and electronic energies of natural biliverdin and $\delta$-, $\beta$- and $\gamma$-bilirubin. Next, the interaction of the PTTCA–Mn(II)₂ biosensor, being in three possible spin states, with $\delta$-, $\beta$- and $\gamma$-natural bilirubin with 1:1 and 1:2 stoichiometry using UB3LYP/6-31G* method has been investigated. Natural population analysis (NPA) calculations have been used to derive more suitable interaction sites of bilirubin with Mn${}^{2+}$ ions in PTTCA–Mn(II)₂ biosensor. Investigation of different manganese complexes with bilirubin shows that the most stable complex is high spin state (total electron spin $S=5∕2$) rather than intermediate and low spin states with 1:2 stoichiometry. Also, the temperature effect and interferences from other biological compounds such as ascorbic acid, L-glutamic acid, uric acid, creatine, glucose and dopamine have been investigated. The nature of the interaction between manganese metal cations and natural bilirubin is also discussed employing NPA, molecular orbital (MO) analysis and Bader’s Atoms in Molecule (AIM) theory.

“Non-fluorescent” chlorophyll catabolites (NCCs) were named “rusty pigments” originally, as they easily oxidized to yellow chlorophyll catabolites (YCCs) and other colored natural “phyllobilins.” In the present work, binding of Zn(II)-ions by YCC and its methyl ester YCC-Me, and structural investigations of the resulting Zn(II)-complexes are reported. Binding of Zn-ions to the weakly luminescent YCC or YCC-Me in DMSO produces orange-yellow complexes that exhibit strong green emission. The Zn-complex of YCC-Me was isolated and characterized by UV-vis-, fluorescence-, mass- and NMR-spectra. The data revealed a 2:1 complex, Zn(YCC-Me)${}_2$, in which YCC-Me serves as bidentate ligand. The Zn(II)-center in Zn(YCC-Me)${}_2$ is, thereby, deduced to be coordinated in a pseudo tetrahedral fashion. Formation of Zn(YCC-Me)${}_2$ (and of Zn(YCC)${}_2)$ is compatible with an isomerization of the lactam form of ring D to the corresponding lactim tautomer in these neutral Zn(II)-complexes.

The degradation of the green pigment chlorophyll in plants is known to yield phyllobilins as highly abundant linear tetrapyrroles. Recently, a split path of the degradation pathway has been discovered, leading to so-called dioxobilin-type (or type-II) phyllobilins. The first characterized type-II phyllobilin was colorless featuring four deconjugated pyrrole units. Similar to the type-I branch, for which yellow oxidation products of the colorless phyllobilins – the type-I phylloxanthobilins – are known, a type-II phylloxanthobilin has recently been characterized from senescent leaves of grapevine. Type-I phylloxanthobilins appear to be actively produced in the plant, are known to possess interesting chemical properties, and were shown to act as potent antioxidants that can protect cells from oxidative stress. Here we report the isolation and structural characterization of a type-II phylloxanthobilin from de-greened leaves of savoy cabbage, which turned out to be structurally closely related to bilirubin. Bilirubin is known to possess high antioxidative activity; in addition, savoy cabbage is considered to promote health benefits due to its high content in antioxidants. We therefore investigated the in vitro antioxidative potential of the newly identified type-II phylloxanthobilin using two different approaches, both of which revealed an even higher antioxidative activity for the type-II phylloxanthobilin from savoy cabbage compared to bilirubin.

The degradation of the green pigment chlorophyll in plants is known to yield phyllobilins as highly abundant linear tetrapyrroles. Recently, a split path of the degradation pathway has been discovered, leading to so-called dioxobilin-type (or type-II) phyllobilins. The first characterized type-II phyllobilin was colorless featuring four deconjugated pyrrole units. Similar to the type-I branch, for which yellow oxidation products of the colorless phyllobilins — the type-I phylloxanthobilins — are known, a type-II phylloxanthobilin has recently been characterized from senescent leaves of grapevine. Type-I phylloxanthobilins appear to be actively produced in the plant, are known to possess interesting chemical properties, and were shown to act as potent antioxidants that can protect cells from oxidative stress. Here we report the isolation and structural characterization of a type-II phylloxanthobilin from de-greened leaves of savoy cabbage, which turned out to be structurally closely related to bilirubin. Bilirubin is known to possess high antioxidative activity; in addition, savoy cabbage is considered to promote health benefits due to its high content in antioxidants. We therefore investigated the in vitro antioxidative potential of the newly identified type-II phylloxanthobilin using two different approaches, both of which revealed an even higher antioxidative activity for the type-II phylloxanthobilin from savoy cabbage compared to bilirubin.