Search

Patellamides are highly bioactive compounds found along with other cyanobactins in the symbiosis between didemnid ascidians and the enigmatic cyanobacterium Prochloron. The biosynthetic pathway of patellamide synthesis is well understood, the relevant operons have been identified in the Prochloron genome and genes involved in patellamide synthesis are among the most highly transcribed cyanobacterial genes in hospite. However, a more detailed study of the in vivo dynamics of patellamides and their function in the ascidian-Prochloron symbiosis is complicated by the fact that Prochloron remains uncultivated despite numerous attempts since its discovery in 1975. A major challenge is to account for the highly dynamic microenvironmental conditions experienced by Prochloron in hospite, where light-dark cycles drive rapid shifts between hyperoxia and anoxia as well as pH variations from pH ~6 to ~10. Recently, work on patellamide analogues has pointed out a range of different catalytic functions of patellamide that could prove essential for the ascidian-Prochloron symbiosis and could be modulated by the strong microenvironmental dynamics. Here, we review fundamental properties of patellamides and their occurrence and dynamics in vitro and in vivo. We discuss possible functions of patellamides in the ascidian-Prochloron symbiosis and identify important knowledge gaps and needs for further experimental studies.

Five copper(II) complexes 1-5 with aromatic nitrogen-containing heterocycles, pyrimidine (pm, 1), pyrazine (pz, 2), quinazoline (qz, 3 and 4) and phthalazine (phtz, 5) have been synthesized and structurally characterized by spectroscopic and single-crystal X-ray diffraction techniques. The crystallographic results show that, dependent on the ligand structure, complexes 1-5 are of different nuclearity. The antimicrobial efficiency of complexes 1-5 has been evaluated against three clinically relevant microorganisms and none of the complexes showed significant growth inhibiting activity, with values of minimum inhibitory concentrations (MIC) in the mM range. Since in many bacteria, pathogenicity and virulence are regulated by intercellular communication processes, quorum sensing (QS), the effect of the copper(II) complexes on bacterial QS has also been examined. The results indicate that the investigated complexes inhibit violacein production in Chromobacterium violaceum CV026, suggesting an anti-QS activity. In order to differentiate, which of the QS pathways was affected by the copper(II) complexes, three biosensor strains were used: the PAO1 Delta rhlIpKD-rhlA and the PA14-R3 Delta lasIPrsaI lux strain to directly measure the levels of C4-HSL (N-butanoyl-homoserine lactone) and 3OC12-HSL (N-3-oxo-dodecanoyl- homoserine lactone), respectively, and PAO1 Delta pqsA mini-CTX luxPpqsA for the detection of AHQs (2-alkyl-4-quinolones). Complexes 1-5 were shown to be efficient inhibitors of biofilm formation of the human opportunistic pathogen Pseudomonas aeruginosa PAO1, with the qz-containing complex 3 being the most active. Finally, the most anti-QS-active complexes 1 and 3 showed synergistic activity against a multi-drug resistant clinical isolate of P. aeruginosa, when supplied in combination with the known antibiotics piperacillin and ceftazidime.

Five silver(I) complexes with aromatic nitrogen-containing heterocycles, phthalazine (phtz) and quinazoline (qz), were synthesized, characterized and analyzed by single-crystal X-ray diffraction analysis. Although different AgX salts reacted with phtz, only dinuclear silver(I) complexes of the general formula {[Ag(X-O)(phtz-N)](2)(mu-phtz-N,N')(2)} were formed, X = NO3- (1), CF3SO3- (2) and ClO4- (3). However, reactions of qz with an equimolar amount of AgCF3SO3 and AgBF4 resulted in the formation of polynuclear complexes, {[Ag(CF3SO3-O)(qz-N)](2)}(n) (4) and {[Ag(qz-N)][BF4]}(n) (5). Complexes 1-5 were evaluated by in vitro antimicrobial studies against a panel of microbial strains that lead to many skin and soft tissue, respiratory, wound and nosocomial infections. The obtained results indicate that all tested silver(I) complexes have good antibacterial activity with MIC (minimum inhibitory concentration) values in the range from 2.9 to 48.0 mu M against the investigated strains. Among the investigated strains, these complexes were particularly efficient against pathogenic Pseudomonas aeruginosa (MIC = 2.9-29 mu M) and had a marked ability to disrupt clinically relevant biofilms of strains with high inherent resistance to antibiotics. On the other hand, their activity against the fungus Candida albicans was moderate. In order to determine the therapeutic potential of silver(I) complexes 1-5, their antiproliferative effect on the human lung fibroblastic cell line MRC5, has been also evaluated. The binding of complexes 1-5 to the genomic DNA of P. aeruginosa was demonstrated by gel electrophoresis techniques and well supported by molecular docking into the DNA minor groove. All investigated complexes showed an improved cytotoxicity profile in comparison to the clinically used AgNO3. (C) 2015 Elsevier Inc. All rights reserved.

Five silver(I) complexes with aromatic nitrogen-containing heterocycles, phthalazine (phtz) and quinazoline (qz), were synthesized, characterized and analyzed by single-crystal X-ray diffraction analysis. Although different AgX salts reacted with phtz, only dinuclear silver(I) complexes of the general formula {[Ag(X-O)(phtz-N)](2)(mu-phtz-N,N')(2)} were formed, X = NO3- (1), CF3SO3- (2) and ClO4- (3). However, reactions of qz with an equimolar amount of AgCF3SO3 and AgBF4 resulted in the formation of polynuclear complexes, {[Ag(CF3SO3-O)(qz-N)](2)}(n) (4) and {[Ag(qz-N)][BF4]}(n) (5). Complexes 1-5 were evaluated by in vitro antimicrobial studies against a panel of microbial strains that lead to many skin and soft tissue, respiratory, wound and nosocomial infections. The obtained results indicate that all tested silver(I) complexes have good antibacterial activity with MIC (minimum inhibitory concentration) values in the range from 2.9 to 48.0 mu M against the investigated strains. Among the investigated strains, these complexes were particularly efficient against pathogenic Pseudomonas aeruginosa (MIC = 2.9-29 mu M) and had a marked ability to disrupt clinically relevant biofilms of strains with high inherent resistance to antibiotics. On the other hand, their activity against the fungus Candida albicans was moderate. In order to determine the therapeutic potential of silver(I) complexes 1-5, their antiproliferative effect on the human lung fibroblastic cell line MRC5, has been also evaluated. The binding of complexes 1-5 to the genomic DNA of P. aeruginosa was demonstrated by gel electrophoresis techniques and well supported by molecular docking into the DNA minor groove. All investigated complexes showed an improved cytotoxicity profile in comparison to the clinically used AgNO3.

Five copper(II) complexes 1-5 with aromatic nitrogen-containing heterocycles, pyrimidine (pm, 1), pyrazine (pz, 2), quinazoline (qz, 3 and 4) and phthalazine (phtz, 5) have been synthesized and structurally characterized by spectroscopic and single-crystal X-ray diffraction techniques. The crystallographic results show that, dependent on the ligand structure, complexes 1-5 are of different nuclearity. The antimicrobial efficiency of complexes 1-5 has been evaluated against three clinically relevant microorganisms and none of the complexes showed significant growth inhibiting activity, with values of minimum inhibitory concentrations (MIC) in the mM range. Since in many bacteria, pathogenicity and virulence are regulated by intercellular communication processes, quorum sensing (QS), the effect of the copper(II) complexes on bacterial QS has also been examined. The results indicate that the investigated complexes inhibit violacein production in Chromobacterium violaceum CV026, suggesting an anti-QS activity. In order to differentiate, which of the QS pathways was affected by the copper(II) complexes, three biosensor strains were used: the PAO1 Delta rhlIpKD-rhlA and the PA14-R3 Delta lasIPrsaI lux strain to directly measure the levels of C4-HSL (N-butanoyl-homoserine lactone) and 3OC12-HSL (N-3-oxo-dodecanoyl- homoserine lactone), respectively, and PAO1 Delta pqsA mini-CTX luxPpqsA for the detection of AHQs (2-alkyl-4-quinolones). Complexes 1-5 were shown to be efficient inhibitors of biofilm formation of the human opportunistic pathogen Pseudomonas aeruginosa PAO1, with the qz-containing complex 3 being the most active. Finally, the most anti-QS-active complexes 1 and 3 showed synergistic activity against a multi-drug resistant clinical isolate of P. aeruginosa, when supplied in combination with the known antibiotics piperacillin and ceftazidime.

Die Entwicklung von makrocyclischen Chelatoren, die mit Kupferionen thermodynamisch stabile und kinetisch inerte Komplexe bilden, ist in den letzten Jahren zunehmend in den Fokus der Forschung gerückt. Das ergibt sich insbesondere aus der Möglichkeit, Radiokupfernuklide aufgrund günstiger kernphysikalischer Eigenschaften sowohl für diagnostische (64Cu) als auch therapeutische (67Cu) Anwendungen einzusetzen. Hervorzuheben ist der Azamakrocyclus Cyclam (1,4,8,11-Tetraazacyclodecan), da dieser mit Kupfer(II)-Ionen Komplexe hoher thermodynamischer Stabilität bildet. Zudem weist der Chelator weitere Funktionalisierungsmöglichkeiten auf, um in Hinblick auf eine nuklearmedizinische Anwendung pharmakologisch relevante Moleküle wie beispielsweise Peptide oder Proteine (Antikörper oder Antikörperfragmente) kovalent zu binden und damit eine spezifische Anreicherung im Tumorgewebe zu ermöglichen. Allerdings erfordert das Maßschneidern der Eigenschaften von neuen bifunktionellen Chelatoren Kenntnisse über den Einfluss der Substituten auf die Stabilität der gebildeten Kupfer(II)-Komplexe. Die thermodynamische Stabilität lässt keine Aussagen über das Verhalten in vivo zu. Die Ursache für die kinetische Labilität in Säugetieren ist noch nicht vollständig verstanden, wird aber u. a. auf kupferbindende Enzyme bzw. Proteine zurückgeführt. Die Bioverteilung der Radiokupferkomplexe wird aber auch von weiteren Parameter, wie Hydrophilie, Ladung und Polarisierbarkeit beeinflusst. Mit dieser Arbeit wurde ein wesentlicher Beitrag zur Entwicklung von 64Cu Chelaten auf Basis von Cyclam-Propionsäure-Liganden geleistet. Diese Stoffklasse ist bisher synthetisch wenig erschlossen und Radiokupfer-markierte Komplexe zudem bisher gar nicht beschrieben. Daher ist es von besonderem Interesse die kinetische Stabilität Radiokupfer-markierter Cyclam-Propionsäure-Derivate zu untersuchen und mit einer Reihe bekannter Radiokupfer-markierter Cyclam-Essigsäure-Komplexe zu vergleichen. Es wurden vier N-funktio

With computational resources becoming more efficient and more powerful and at the same time cheaper, computational methods have become more and more popular for studies on biochemical and biomimetic systems. Although large efforts from the scientific community have gone into exploring the possibilities of computational methods on large biochemical systems, such studies are not without pitfalls and often cannot be routinely done but require expert execution. In this review we summarize and highlight advances in computational methodology and its application to enzymatic and biomimetic model systems. In particular, we emphasize on topical and state-of-the-art methodologies that are able to either reproduce experimental findings, e.g., spectroscopic parameters and rate constants, accurately or give predictions on short-lived intermediates and fast reaction processes in nature. Moreover, we give examples of processes where certain computational methods dramatically fail.

A series of dinuclear cobalt(II) complexes has been prepared and characterized to generate functional and spectroscopic models for cobalt(II) substituted phosphoesterase enzymes such as the potential bioremediator GpdQ. Reaction of ligands based on 2,2'-(((2-hydroxy-5-methyl-1,3-phenylene) bis(methylene))bis((pyridin-2-ylmethyl)azanediyl)))diethanol (L1) and 2,6-bis(((2-methoxyethyl)(pyridin-2-ylmethyl)amino)methyl)-4-methylphenol (L2) with cobalt(II) salts afforded [Co2(CO2EtH 2L1)(CH3COO)2](PF6), [Co 2(CO2EtL2)(CH3COO)2](PF 6), [Co2(CH3L2)(CH3COO) 2](PF6), [Co2(BrL2)(CH3COO) 2](PF6), and [Co2(NO2L2)(CH 3COO)2](PF6). Complexes of the L2 ligands contain a coordinated methyl-ether, whereas the L1 ligand contains a coordinated alcohol. The complexes were characterized using mass spectrometry, microanalysis, X-ray crystallography, UV-vis-NIR diffuse reflectance spectroscopy, IR absorption spectroscopy, solid state magnetic susceptibility measurements, and variable-temperature variable-field magnetic circular dichroism (VTVH MCD) spectroscopy. Susceptibility studies show that [Co 2(CO2EtH2L1)(CH3COO) 2](PF6), [Co2(CO2EtL2)(CH 3COO)2](PF6), and [Co2(CH 3L2)(CH3COO)2](PF6) are weakly antiferromagnetically coupled, whereas [Co2(BrL2)(CH 3COO)2](PF6) and [Co2(NO 2L2)(CH3COO)2](PF6) are weakly ferromagnetically coupled. The susceptibility results are confirmed by the VTVH MCD studies. Density functional theory calculations revealed that magnetic exchange coupling occurs mainly through the phenolic oxygen bridge. Implications of geometry and ligand design on the magnetic exchange coupling will be discussed. Functional studies of the complexes with the substrate bis(2,4-dinitrophenyl) phosphate showed them to be active towards hydrolysis of phosphoester substrates.

Die Entwicklung von Komplexbildnern für Kupferradionuklide im Hinblick auf eine nuklearmedizinische Anwendung ist ein intensiv bearbeitetes und in rascher Entwicklung begriffenes Forschungsgebiet. Dabei spielen verschiedene Faktoren – wie die günstigen kernphysikalischen Eigenschaften der verfügbaren Kupferradionuklide (Halbwertszeit, Umwandlungsart und -energien), die synthetische Zugänglichkeit und Modifizierbarkeit der Liganden sowie Markierungsausbeute und In-vivo-Stabilität der radioaktiven Kupferkomplexe – eine entscheidende Rolle. Liganden auf der Basis des 3,7-Diazabicyclo[3.3.1]nonans (Bispidine) besitzen für derartige radiopharmazeutische Anwendungen ein hohes Potential. Sie bilden mit Cu2+ sehr stabile Koordinationsverbindungen, wobei die Komplexstabilität im Bereich makrocyclischer Chelatoren liegt (logK ~ 20). Ferner weisen Bispidin-Derivate eine schnelle Komplexbildungskinetik mit Cu2+ auf. Damit sind radioaktiv markierte Bispidin-Liganden prinzipiell für einen Einsatz in der Nuklearmedizin (64Cu: Diagnostik, 67Cu: Therapie) geeignet und zwar insbesondere dann, wenn das Ligand-Grundgerüst mit zielsuchenden Biomolekülen, wie spezifischen Peptiden, Antikörpern oder Nukleinsäurebausteinen, funktionalisiert werden kann. Im Rahmen der vorliegenden Arbeit wurden neuartige sechszähnige Bispidin-Derivate mit Pyridyl-, Imidazolyl- und/oder Benzimidazolyl-Donoreinheiten mit Hilfe einer doppelten Mannich-Kondensation synthetisiert sowie koordinationschemisch und spektroskopisch charakterisiert. • Die Darstellung dieser Liganden erfolgte durch eine systematische Variation der Donoreinheiten an den C2/C4-Kohlenstoffatomen sowie den tertiären Aminostickstoffatomen N3/N7. Hierbei wurde insbesondere untersucht, wie sich der Einbau der unterschiedlichen Donorgruppen an den verschiedenen Positionen des Grundgerüsts auf das Löslichkeits- und Komplexbildungsverhalten auswirkt. Auf der Basis NMR-spektroskopischer Untersuchungen konnte gezeigt werden, dass die Einführung vo

A new cyclic octapeptide, cyclo(Ile-Ser-(Gly)Thz-Ile-Thr-(Gly)Thz) (PatN), related to patellamide A, has been synthesized and reacted with copper(II) and base to form mono- and dinuclear complexes. The coordination environments around copper(II) have been characterized by EPR spectroscopy. The solution structure of the thermodynamically most stable product, a purple dicopper(II) compound, has been examined by simulating weakly dipole−dipole coupled EPR spectra based upon structural parameters obtained from force field (MM and MD) calculations. The MM−EPR method produces a saddle-shaped structure for [Cu2(PatN)(OH2)6] that is similar to the known solution structure of patellamide A and the known solid-state structure of [Cu2(AscidH2)CO3(OH2)2]. Compared with the latter, [Cu2(PatN)] has no carbonate bridge and a significantly flatter topology. The MM−EPR approach to solution-structure determination for paramagnetic metallopeptides may find wide applications to other metallopeptides and metalloproteins.

Magnetic anisotropy in cyanide-bridged single-molecule magnets (SMMs) with FeIII−CN−MII (M = Cu, Ni) exchange-coupled pairs was analyzed using a density functional theory (DFT)-based ligand field model. A pronounced magnetic anisotropy due to exchange was found for linear FeIII−CN−MII units with fourfold symmetry. This results from spin–orbit coupling of the [FeIII(CN)₆]³⁻ unit and was found to be enhanced by a tetragonal field, leading to a ²Eg ground state for FeIII. In contrast, a trigonal field (e.g., due to τ2g Jahn–Teller angular distortions) led to a reduction of the magnetic anisotropy. A large enhancement of the anisotropy was found for the FeIII−CN−NiII exchange pair if anisotropic exchange combined with a negative zero-field splitting energy of the S = 1 ground state of NiII in tetragonally compressed octahedra, while cancellation of the two anisotropic contributions was predicted for tetragonal elongations. A recently developed DFT approach to Jahn–Teller activity in low-spin hexacyanometalates was used to address the influence of dynamic Jahn–Teller coupling on the magnetic anisotropy. Spin Hamiltonian parameters derived for linear Fe−M subunits were combined using a vector-coupling scheme to yield the spin Hamiltonian for the entire spin cluster. The magnetic properties of published oligonuclear transition-metal complexes with ferromagnetic ground states are discussed qualitatively, and predictive concepts for a systematic search of cyanide-based SMM materials are presented.

The topology of the ground-state potential energy surface of M(CN)₆ with orbitally degenerate ²T2g (M = TiIII (t2g¹), FeIII and MnII (both low-spin t2g⁵)) and ³T1g ground states (M = VIII (t2g²), MnIII and CrII (both low-spin t2g⁴)) has been studied with linear and quadratic Jahn-Teller coupling models in the five-dimensional space of the εg and θ2g octahedral vibrations (Tg⊗(εg+θ2g) Jahn-Teller coupling problem (Tg = ²T2g, ³T1g)). A procedure is proposed to give access to all vibronic coupling parameters from geometry optimization with density functional theory (DFT) and the energies of a restricted number of Slater determinants, derived from electron replacements within the t2g 1,5 or t2g2,4 ground-state electronic configurations. The results show that coupling to the θ2g bending mode is dominant and leads to a stabilization of D₃d structures (absolute minima on the ground-state potential energy surface) for all complexes considered, except for [Ti(CN)₆]³⁻, where the minimum is of D₄ h symmetry. The Jahn-Teller stabilization energies for the D₃d minima are found to increase in the order of increasing CN-M π back-donation (TiIII< VIII< MnIII< FeIII< MnII< CrII). With the angular overlap model and bonding parameters derived from angular distortions, which correspond to the stable D₃d minima, the effect of configuration interaction and spin-orbit coupling on the ground-state potential energy surface is explored. This approach is used to correlate Jahn-Teller distortion parameters with struct

Exchange coupling across the cyanide bridge in a series of novel cyanometalate complexes with CuII-NC-MIII (M = Cr and low-spin Mn,Fe) fragments has been studied using the broken-symmetry DFT approach and an empirical model, which allows us to relate the exchange coupling constant with σ-, π-, and π*-type spin densities of the CN⁻ bridging ligand. Ferromagnetic exchange is found to be dominated by π-delocalization via the CN⁻π pathway, whereas spin polarization with participation of σ orbitals (in examples, where the dz ² orbital of MIII is empty) and π* orbitals of CN⁻ yields negative spin occupations in these orbitals, and reduces the CuII- MIII exchange coupling constant. When the dz ² orbital of MIII is singly occupied, an additional positive spin density appears in the σ(CN) orbital and leads to an increase of the ferromagnetic Cu- NC-M exchange constant. For low-spin [MIII(CN)₆]³⁻ complexes, the dz² orbital occupancy results in high-spin metastable excited states, and this offers interesting aspects for applications in the area of molecular photomagnetism. The DFT values of the exchange coupling parameters resulting from different occupations of the t2g orbitals of low-spin (t2g⁵) FeIII are used to discuss the effect of spin-orbit coupling on the isotropic and anisotropic exchange coupling in linear Cu-NC-Fe pairs.