Showing papers by "Burkhard König published in 2007"

Synthesis, Characterisation and Ligand Properties of Novel Bi-1,2,3-triazole Ligands

Abstract: Three 1,1′-disubstituted 4,4′-bi-1H-1,2,3-triazols [R-bta; R = Bn (1), Ph (2), CH2COOH (3)] have been synthesised as bidentate, nitrogen-based ligands by a CuI-catalysed “click” reaction between 1,3-butadiyne and organic azides. Their ligand properties were investigated by preparation of the complexes [RuII(R-bta)3]Cl2 [R = Bn (4), Ph (5), CH2COOH (6)], [(Bn-bta)CuI(DPEPhos)] (7) [DPEPhos = bis{2-(diphenylphosphanyl)phenyl} ether] and [(Bn-bta)ReI(CO)3Cl] (8) following standard reaction procedures. All compounds were analysed by elemental analysis, mass spectrometry and NMR, IR, UV/Vis and luminescence spectroscopy. In addition, the molecular structures of 1–4, 7, and 8 have been determined by X-ray crystallography. In all complexes the Bn-bta acts as a bidentate ligand with structural features comparable to the analogous 2,2′-bipyridine complexes. In their electronic absorption spectra the RuII and ReI complexes exhibit a lowest energy band at around 300 nm, which is substantially higher in energy than in analogous complexes with bpy ligands. All R-bta ligands yield complexes that are not luminescent in solution or in the solid state, which makes these ligands particularly suited for use as spectator ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Photochemical cleavage of a tattoo pigment by UVB radiation or natural sunlight

Abstract: BACKGROUND: Millions of people have at least one tattoo. Complex and light absorbing molecules are implanted in the skin. When tattooed skin receives UV radiation or natural sunlight, photochemical cleavage of the pigments may occur. As a first step, we dissolved pigments in a suitable solvent and analyzed them after light irradiation. METHODS: The widespread Pigment Red 22 was dissolved in different solvents. The solutions were irradiated with either UVB radiation (up to 8 h) or with natural sunlight (110 days). After irradiation, the solutions were analyzed by means of liquid chromatography and mass spectrometry. RESULTS: A clear cleavage of the pigment was detected in all solvents and the primary decomposition products were identified. In tetrahydrofuran and dioxane, the pigment concentration decreased significantly during UVB irradiation, whereas the pigment was completely destroyed during sunlight exposure. In chloroform and dichloromethane, the pigment concentration decreased slightly during UVB irradiation, whereas the pigment was almost completely destroyed during sunlight exposure. CONCLUSION: Since chloroform and dichloromethane do not affect the cleavage process, these solvents are optimal for such in vitro experiments. We have shown the cleavage of the tattoo pigment Red 22 when exposed to UVB radiation or natural sunlight. The decomposition products are hazardous showing a potential risk of being toxic or even carcinogenic. At present, a risk assessment is not feasible since the concentration of pigments and their decomposition products in skin are unknown.

1,4,7,10-tetraazacyclododecane metal complexes as potent promoters of carboxyester hydrolysis under physiological conditions.

Abstract: New 1,4,7,10-tetrazacyclododecane ([12]aneN4 or cyclen) ligands with different heterocyclic spacers (triazine and pyridine) of various lengths (bi- and tripyridine) or an azacrown pendant and their mono- and dinuclear Zn(II), Cu(II), and Ni(II) complexes have been synthesized and characterized. The pKa values of water molecules coordinated to the complexed metal ions were determined by potentiometric pH titrations and vary from 7.7 to 11.2, depending on the metal-ion and ligand properties. The X-ray structure of [Zn2L2]μ-OH(ClO4)3·CH3CN·H2O shows each Zn(II) ion in a tetrahedral geometry, binding to three N atoms of cyclen (the average distance of Zn−N = 2.1 A) and having a μ-OH bridge at the apical site linking the two metal ions (the average distance of Zn−O- = 1.9 A). The distance between the Zn(II) ion and the fourth N atom is 2.6 A. All Zn(II) complexes promote the hydrolysis of 4-nitrophenyl acetate (NA) under physiological conditions, while those of Cu(II) and Ni(II) do not have a significant effec...

Molecular analysis of the interaction of Bordetella pertussis adenylyl cyclase with fluorescent nucleotides.

Abstract: The calmodulin (CaM)-dependent adenylyl cyclase (AC) toxin from Bordetella pertussis (CyaA) substantially contributes to the pathogenesis of whooping cough. Thus, potent and selective CyaA inhibitors may be valuable drugs for prophylaxis of this disease. We examined the interactions of fluorescent 2,3-N- methylanthraniloyl (MANT)-, anthraniloyl- and trinitrophenyl (TNP)-substituted nucleotides with CyaA. Compared with mammalian AC isoforms and Bacillus anthracis AC toxin edema factor, nucleotides inhibited catalysis by CyaA less potently. Introduction of the MANT substituent resulted in 5- to 170-fold increased potency of nucleotides. Ki values of 3MANT-2d- ATP and 2MANT-3d-ATP in the AC activity assay using Mn 2 were 220 and 340 nM, respectively. Natural nucleoside 5- triphosphates, guanine-, hypoxanthine- and pyrimidine-MANT- and TNP nucleotides and di-MANT nucleotides inhibited CyaA, too. MANT nucleotide binding to CyaA generated fluorescence resonance energy transfer (FRET) from tryptophans Trp69 and Trp242 and multiple tyrosine residues, yielding Kd values of 300 nM for 3MANT-2d-ATP and 400 nM for 2MANT-3d-ATP. Fluorescence experiments and docking approaches indicate that the MANT- and TNP groups interact with Phe306. In- creases of FRET and direct fluorescence with MANT nucleo- tides were strictly CaM-dependent, whereas TNP nucleotide fluorescence upon binding to CyaA increased in the absence of CaM and was actually reduced by CaM. In contrast to low- affinity MANT nucleotides, even low-affinity TNP nucleotides generated strong fluorescence increases upon binding to CyaA. We conclude that the catalytic site of CyaA possesses substantial conformational freedom to accommodate structur- ally diverse ligands and that certain ligands bind to CyaA even in the absence of CaM, facilitating future inhibitor design.

Tetrahydrofuran Cα-Tetrasubstituted Amino Acids: Two Consecutive β-Turns in a Crystalline Linear Tripeptide

Abstract: The synthesis of tetrahydrofuran Cα-tetrasubstituted amino acids (TAAs) and their effect on the conformation in small peptides are reported. The synthesis starts from the protein amino acid methionine, which is protected at the C and N terminus and converted into the corresponding sulfonium salt by alkylation. Simple base treatment in the presence of an aryl aldehyde leads to the formation of tetrahydrofuran tetrasubstituted Cα-amino acids in a highly diastereoselective (trans/cis ratio up to 97:3) reaction with moderate to good yields (35−78%) depending on the aldehyde used. Palladium-catalyzed coupling reactions allow a subsequent further functionalization of the TAA. The R,S,S-TAA-Ala dipeptide amide adopts a β-turn type I conformation, whereas its S,R,S isomer does not. The R,S,S-Gly-TAA-Ala tripeptide amide shows in the solid state and in solution a conformation of two consecutive β-turn type III structures, stabilized by i + 3 → i intramolecular hydrogen bonds.

Two-dimensional arrays of amphiphilic Zn2+-cyclens for guided molecular recognition at interfaces.

Abstract: The sterically guided molecular recognition of nucleobases, phosphates, adenosine, and uridine nucleotides on Langmuir monolayers and Langmuir-Blodgett monolayers of amphiphilic mono- or bis(Zn2+-cyclen)s assembled on thiolated surfaces was investigated. The stepwise selective binding of metal ions, uracil, or phosphate by dicetyl cyclen monolayers with variously tuned structures at the air/water interface was corroborated by the measurements of the corresponding LB films deposited onto quartz crystals. Two types of recognition surfaces were fabricated from Zn2+-dicetyl cyclen. The surface covered with a complex preformed in the Langmuir monolayer was capable both of imide and of phosphate binding. The similar complex formed directly in an LB film on thiolated gold was inactive with respect to imide. The surface plasmon resonance measurements evidenced the stepwise assembly of complementary nucleotides on SAM/LB templates through consecutive phosphate-Zn2+-cyclen coordination. Base pairing between nucleotides resulted in a formation of A-U bilayers comprising two complementary monolayers. Finally, we report on SAM/LB patterns designed for divalent molecular recognition of uridine phosphate by amphiphilic bis(Zn2+-cyclen).

Organische Chemie: Kurz und Bündig für die Bachelor-Prüfung

Abstract: Reaktionsmechanismen unklar oder McMurry-Kupplung vergessen? Die knappe Darstellung der Konzepte und der schnelle Zugriff auf Daten und Fakten machen dieses Repetitorium zum idealen Begleiter bei der Prufungsvorbereitung.

Synthesis of 6-Chloro-N,N,N',N'-tetrakis-pyridin-2-ylmethyl-[1,3,5]triazine-2,4-diamine

Abstract: Transition metal complexes of pyridine-containing ligands are widely used in catalysis [1], supramolecular self-assembly [2], and anion recognition [3][]

Synthesis And Characterization Of 1-(2H-tetrazol-5-YL)-1,4,7,10-tetraazacyclododecane And Its Zn(II), Ni(II), AND Cu(II) complexes

Abstract: As part of an ongoing effort to develop new metal complexes of tetraazamacrocycles with novel properties in coordination or functionalization we report here the synthesis of a new derivative of 1,4,7,10-tetraazacyclododecane (cyclen) with a tetraazole moiety directly bound to the azamacrocycle. The new ligand was obtained by reaction with cyanogen bromide giving the cyanamide, followed by a [2+3] cycloaddition with NaN3 to yield the tetraazole. The ligand and its Zn(II), Ni(II), and Cu(II) complexes were fully characterized by analytical methods. X-ray structure analysis of the Ni(II) compound shows the formation of a stable dimer by coordination of each of the two tetraazole substituents to the neighboring metal cation. Potentiometric titrations of the metal complexes indicate a possible conversion of the monomer to the dimeric structure in solution and show the pKa of the NH-atom on the tetraazole substituent to be between 4.03 and 5.3 depending on the metal ion coordinated by cyclen.

Synthesis of ({8-[4,6-Bis-(bis-pyridin-2-ylmethyl-amino)-[1,3,5]triazine-2-ylamino]-octyl}—ethoxycarbonylmethyl-amino)-acetic acid ethyl ester

Abstract: Dipicolylamine, 2,4,6-tris-chloro-triazine, iminodiacetic acid, two-prong Combination of recognition units in synthetic receptors typically increases binding constants, if cooperativityoccurs.[1] Dipicolylamine (Dpa) bis-zinc complexes are known to bind phosphate-dianions under physiologicalconditions with good affinities [2,3], whereas metal(II)-imino-diacetate (M(II)-IDA) complexes (metal(II) =copper(II), nickel(II) or zinc(II)) show affinity to N-terminal histidine.[2] Combining both units may lead to aselective binding of phosphorylated amino acid bearing N-terminal histidine. We report here a general syntheticroute to ligands bearing a Dpa and an Ida site for metal ion complexation. The use of 6-chloro-N,N,N',N'-tetrakis-pyridin-2-ylmethyl-[1,3,5]triazine-2,4-diamine (