Reactivity of pyrrole pigments,XIX. On the structure of Cu(II) and Zn(II) chelates of dipyrrins in solution

Summary The Cu(II) and Zn(II) chelates of 1,2,3,7,9-pentamethyldipyrrin and 1,2,3,7,9-pentamethyl-8-sulfodipyrrin are studied. When metal acetates are used for the formation of the metal complexes, dipyrrinate metal acetates could be detected as precursors of thebis-dipyrrinates.

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Reaktivität von Pyrrolpigmenten, 19. Mitt. Über die Struktur von Cu(II)- und Zn(II)-Chelaten von Dipyrrinen in Lösung

Zusammenfassung Die Cu(II)- und Zn(II)-Chelate von 1,2,3,7,9-Pentamethyldipyrrin und 1,2,3,7,9-Pentadimethyl-8-sulfodipyrrin wurden untersucht. Bei Einsatz von Metalldiacetaten für die Komplexbildung wurden Dipyrrinmetallacetate als Vorläufer derbis-Dipyrrinate nachgewiesen.

     

Towards a tunable tautomeric switch in azobenzene biomimetics: implications for the binding affinity of 2-(4'-hydroxyphenylazo)benzoic acid to streptavidin

The tautomeric equilibria of 2-(4'-hydroxyphenylazo)benzoic acid (HABA) and 2-(3',5'-dimethyl-4'-hydroxyphenylazo)benzoic acid (3',5'-dimethyl-HABA) have been studied by a combination of spectroscopic and computational methods. For neutral HABA in solvents of different polarity (toluene, chloroform, DMSO, DMF, butanol, and ethanol) the azo tautomer (AT) is largely predominant. For monoanionic HABA, the hydrazone tautomer (HT) is the only detected species in apolar solvents such as toluene and chloroform, while the AT is the only detected species in water and a mixture of both tautomers is detected in ethanol. Comparison of the results obtained for HABA and its 3',5'-dimethylated derivative shows that dimethylation of the hydroxybenzene ring shifts the tautomeric preferences towards the hydrazone species. These findings have been used to examine the differences in binding affinity to streptavidin, as the lower affinity of HABA can be explained in terms of the larger energetic cost associated with the tautomeric shift to the bioactive hydrazone species. Overall, these results suggest that a balanced choice of chemical substituents, embedding environment, and pH can be valuable for exploitation of the azo-hydrazone tautomerism of HABA biomimetics in biotechnological applications.     

Divalent ligand for intramolecular complex formation to streptavidin

Monovalent ligand and divalent ligand have been synthesized, and their thermodynamic parameters of complexation to avidin and streptavidin have been analyzed in terms of multivalent binding.     

Reconfigurable Swarms of Nematic Colloids Controlled by Photoactivated Surface Patterns

Different phoretic driving mechanisms have been proposed for the transport of solid or liquid microscopic inclusions in integrated chemical processes. It is now shown that a substrate that was chemically modified with photosensitive self‐assembled monolayers enables the direct control of the assembly and transport of large ensembles of micrometer‐sized particles and drops that were dispersed in a thin layer of anisotropic fluid. This strategy separates particle driving, which was realized by AC electrophoresis, and steering, which was achieved by elastic modulation of the nematic host fluid. Inclusions respond individually or in collective modes following arbitrary reconfigurable paths that were imprinted by irradiation with UV or blue light. Relying solely on generic material properties, the proposed procedure is versatile enough for the development of applications that involve either inanimate or living materials.     

Cover Picture

The cover picture shows the process of building functional amphiphilic protein-polymer hybrids in a modular fashion. Monolayers of biotinylated polystyrene (purple) bind the protein streptavidin (blue), resulting in the formation of giant amphiphiles. The remaining free binding sites are subsequently used to associate biotinylated biomacromolecules (yellow), such as the iron-storage protein ferritin. The use of covalent conjugates of streptavidin and horseradish peroxidase leads to the formation of reactive surfaces, which are capable of catalyzing organic reactions. Further details on these giant amphiphiles are reported by Nolte and co-workers on p. 4732 ff.     

Reactivity of pyrrole pigments,XX. On the structure of Cu(II) and Zn(II) tripyrrin-1-one chelates in solution

Summary The Cu(II) and Zn(II) chelates of 12,14-dimethyl-2,3,7,8-tetraethyl-15H-tripyrrin-1-one, 12,13-dimethyl-2,3,7,8-tetraethyl-15H-tripyrrin-1-one, and their sulfonate derivatives are studied. The chelates show the expected structure of an NH dideprotonated ligand chelating the metal ion. However, in the case of the Zn chelate of 12,14-dimethyl-2,3,7,8-tetraethyl-15H-tripyrrin-1-one the ligand is only monodeprotonated, and the lactam ring is tautomerized to a hydroximino function.

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Reaktivität von Pyrrolpigmenten, 20. Mitt. Über die Struktur von Cu(II)- und Zn(II)-Chelaten von Tripyrrin-1-onen in Lösung

Zusammenfassung Die Cu(II)- und Zn(II)-Chelate von 12,14-Dimethyl-2,3,7,8-tetraethyl-15H-tripyrrin-1-on, 12,13-Dimethyl-2,3,7,8-tetraethyl-15H-tripyrrin-1-on und ihrer Sulfonate wurden untersucht. Erwartungsgemäß findet man einen NH-dideprotonotierten Liganden im Chelat; im Zn-Complex von 12,14-Dimethyl-2,3,7,8-tetraethyl-15H-tripyrrin-1-on ist der Ligand nur einfach deprotoniert, und das Lactam ist zur Hydroximinogruppe tautomerisiert.

     

Reactivity of pyrrole pigments,XXI: Structure and reactivity of Cu(II) and Zn(II) bilindione chelates

Summary Several Mn, Cu, and Zn chelates of etiobiliverdin-IV-, mesobiliverdin-IX, and its dimethyl ester are studied. The results show that the chemical constitution of the Cu biliverdin chelate corresponds to a formal metal oxidation state of (II) coordinated to a neutral radical of the NH trideprotonated biliverdin. The reactivity of the Cu(II) bilindione chelates in nucleophilic solvents agrees with that expected for a neutral radical structure of the ligand; in CH₃OH, they undergo oxidation towards dimethoxybilipurpurins. The magnetic behaviour of Cu(II) etiobiliverdinate-IV- in the solid state shows an intramolecular weak antiferromagnetic coupling d⁹Cu-to--radical (J=–23 cm^–1) and an intermolecular weak antiferromagnetic coupling -radical-to--radical (J=–45 cm^–1). The analogy of this magnetic behaviour to that of the cation radical of metalloporphyrins is discussed.

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Reaktivität von Pyrrolpigmenten, 21. Mitt.: Struktur und Reaktivität von Cu(II)- und Zn(II)-Chelaten von Bilindionen

Zusammenfassung Einige Mn, Cu and Zn Chelate von Etiobiliverdin-IV-, Mesobiliverdin-IX und seinem Dimethylester werden untersucht. Im Komplex koordiniert ein Metallatom (mit der Formalladung II) mit einem Neutralradikal des dreifach NH-deprotonierten Bilindions. Die Reaktivität des Komplexes gegenüber nukleophilen Lösungmitteln entspricht erwartungsgemäß dem eines neutralen -Radikals; in CH₃OH wird er zu Dimethoxybilipurpurin oxidiert. Bei Cu(II)-Etiobiliverdinat-IV beobachtet man im festen Zustand neben schwacher, antiferromagnetischer Kupplung zwischen d⁹Cu und -Radikal (J=–23 cm^–1) auch eine schwache, intermolekulare, antiferromagnetische Wechselwirkung zwischen zwei -Radikalen (J=–45 cm^–1). Dieses magnetische Verhalten wird dem des -Kationradikals von Metalloporphyrinen gegenübergestellt.

     

Chiral-symmetry selection in soft monolayers under vortical flow

Herein, we report and interpret a new chiral-selection phenomenon in the orientational ordering of soft-assembled domains that arise spontaneously in Langmuir monolayers of an azobenzene derivative at the air/water interface. The orientational chirality of isolated sub-millimeter domains was unambiguously assessed by optical microscopy. The selection process, quantified by using an enantiomeric excess parameter, was controlled by stirring the aqueous subphase. We have studied the dependence of this process on stirring rate and handedness, stirring time, temperature, and on the initial state of the monolayer. The influence of the concomitant cis/trans isomerization on the reported chiral-selection process is also discussed.