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Abstract: Our studies allowed to unravel at least partially, the “so-called” spontaneous self-assembly processes of supramolecular edifices based on metals. The formation of a tricuprous double-stranded helix in solution was found to be driven by thermodynamics via highly distorted intermediates. Dinuclear europium(III) triple-stranded helices were built in solution via alternative “braiding” and “keystone” mechanism. The overall process was also dominated by thermodynamics. Moreover, multipodal ligand with the appropriate binding sites can operate as Cu(II)/Cu(I) molecular switches. Recently, we examined ligands with neighboring binding functionalities (N,N) and (N,O) which confer to the corresponding divalent metal complexes new properties. They could operate as proton-driven multistage molecular switching devices based on region-selective metal binding. [Copyright &y& Elsevier]

Explores the pi-pi stacking-induced cooperativity in copper(I) complexes with phenanthroline ligands. Determination of the formation constants of mono- and bischelate copper(I) complexes with four phenanthroline derivatives; Influence of electron-donating methyl and anisyl substituents; Binding affinity of alpha, alpha'-diimine ligands.

Examines the demetalation dynamics of molecular dicopper(I) trefoil knots. Topological and structural effects of dicopper(I) trefoil knots on the demetalation rates; Performance of single-wavelength and multiwavelength absorption spectrophotometry; Sensitivity of the kinetic parameters to subtle structural variations.

Compares the ionophore calcimycin with its biosynthetic analogue cezomycin. Protonation; Calcium and magnesium complexation properties; Evaluation of the effect of changes in structural features on the coordination and transport of calcium and magnesium.

We report here on the coordination properties of a series of lanthanide cations (Ln=La, Nd, Eu, Tb, Er) with a tripodal homoditopic ligand L, which is bearing three diamido‐dihydroxamate arms anchored on a tertiary amine. The complexes of L with lanthanides were studied in a MeOH/H2O (80/20 by weight) solvent and a marked size‐discriminating effect depending on the intramolecular interactions was observed in the tripodal dinuclear lanthanide edifice. Positive cooperative effects favour the formation of the bimetallic LLn2 complexes compared with the monometallic analogues for the heavier lanthanide cations (Eu, Tb, Er), while the lighter ones (La, Nd) show a decrease of cooperative interactions in the corresponding bimetallic species. Moreover, increased levels of heterobimetallic complexes are detected for Ln(III) pairs containing a lighter Ln(III) ion and a heavier one. In contrast with the adjunctive ligand exchange reported for LFe2 and CDTA, the corresponding substitution reaction for LLn2 occurs according to a disjunctive mechanism. Our work thus highlights the importance of the balance between the rigidity of a tripodal structure and the flexibility of the side arms to accommodate two trivalent cations in a supramolecular ensemble. [ABSTRACT FROM AUTHOR]

The photophysical properties of a supramolecular fullerene-porphyrin ensemble resulting from the self-assembly of a pyrrolidinofullerene-imidazole derivative ( F1) with a multimetalloporphyrin array constructed around a hexasubstituted fullerene core ( F(ZnP)12) have been investigated. The fullerene hexa-adduct core of the host system does not play any active role in the cascade of photoinduced events of the supramolecular ensemble, indeed no intercomponent photoinduced processes could be observed in host F(ZnP)12. In contrast, upon axial coordination with the monosubstituted fullerene guest F1, a quantitative quenching of the fluorescence signal of the metalloporphyrins was observed for the supramolecular complex [F(ZnP)12(F1) n ] both in polar and nonpolar solvents. In toluene, the supramolecular ensemble exhibits a charge transfer emission centered around 930 nm, suggesting the occurrence of intramolecular face-to-face interactions of F1 with neighboring metalloporphyrin moieties within the self-assembled photoactive array. This mechanism is supported by the fact that a one order of magnitude increase in the binding constant was observed for the supramolecular complex [F(ZnP)12(F1) n ] when compared with a reference system lacking the pyrrolidinofullerene unit. In benzonitrile, a long-lived charge-separated state ( τ=0.3 μs) has been detected for the supramolecular adduct. [ABSTRACT FROM AUTHOR]

Abstract: We report here a thorough physico-chemical study of the coordination properties of clioquinol, an oxine-type active neurological drug in Alzheimer''s disease, toward biologically relevant divalent metal ions (Cu, Zn, Ni, Co and Mn). Using a fruitful combination of electrospray mass spectrometry, absorption spectrophotometry and potentiometry, we have characterized the mono- and bis-chelated metal ion species. The determination of the stability constants showed a classical thermodynamic behavior along the studied series with the cupric complexes being by far the most stable species. Our data are discussed within the scope of Alzheimer''s disease. [Copyright &y& Elsevier]

The plant pathogenic enterobacterium Eiwinia chiysanthemi causes important soft-rot disease on a wide range of plants including vegetables and ornamentals of economic importance. It produces a major mono(catecholate) siderophore, chrysobactin (α-N-(2,3-dihydroxybenzoyl)-D-lysyl-L-serine). To unravel the role of chrysobactin in the virulence of E. chnjsanthemi, its iron(III) coordination properties were thus investigated in aqueous solutions using electrospray ionization mass spectrometric, potentiometric, and spectrophotometric methods. Moreover, kinetic experiments allowed us to determine the uptake and release mechanisms. The formation mechanism of the 1:1 complex reveals a key role of the terminal carboxylic group of chrysobactin in the binding of either FeOH2+ or Fe2(OH)24+. The proton-driven dissociation of the ferric tris-, bis-, and mono(chrysobactin) complexes was also studied. For these three ferric complexes, a single protonation triggers the release of the bound chrysobactin molecule. Interestingly, the dissociation of the last ligand proceeded via the formation of an intermediate for which a salicylate-type mode of bonding was proposed. [ABSTRACT FROM AUTHOR]

Abstract: The N-alkylation of the 3,3′-diaminobenzidine with innocent substituents leads to unusual properties. The emission of the benzidine core can be fine-tuned by subtle modifications, and the N-substitution with benzylic groups results in photoinduced exciplexes with distinct and increased emission. This compound constitutes the first example of intramolecular exciplex containing benzidine unit. We also show that these photoinduced processes could be modulated by proton input, and that the diprotonation of the benzidine core disrupted the intramolecular communication in the excited states with a concomitant inhibition of the ligand-centred fluorescence. Furthermore, upon photo-irradiation at 254nm, semiquinone imine and quinone diimine systems are produced in CH2Cl2 of which the photolysis generates Cl radicals, which rapidly oxidize the tetraamine compounds. [Copyright &y& Elsevier]

Abstract: Cholesterol plays the role of membrane reinforcer in eukaryotes, whereas hopanoids play the same role in bacteria. Which components could have reinforced ‘primitive’ membranes? We describe here an efficient biomimetic synthesis of bi- and tri-cyclopolyprenols and demonstrate that these compounds reinforce the membranes of polyprenyl phosphate, which we speculated as ‘primitive’ membranes. [Copyright &y& Elsevier]

In the quest for fast throughput metal biosensors, it would be of interest to prepare fluorophoric ligands with surface- adhesive moieties. Biomimetic analogues to microbial siderophores possessing such ligands offer attractive model compounds and new opportunities to meet this challenge. The design, synthesis, and physicochemical characterization of biomimetic analogues of microbial siderophores from Paracoccus denitrificans and from the Vibrio genus are described. The (4S,5S)-2-(2-hydroxyphenyl)-5-methyl-4,5-dihydro-1,3-oxazole-4-carbonyl group (La), noted here as an HPO unit, was selected for its potential dual properties, serving as a selective iron(III) binder and simultaneously as a fluorophore. Three tripodal symmetric analogues cis-Lb, cis-Lc, and trans-Lc, which mainly differ in the length of the spacers between the central carbon anchor and the ligating sites, were synthesized. These ferric-carriers were built from a tetrahedral carbon as an anchor, symmetrically extended by three converging iron-binding chains, each bearing a terminal HPO. The fourth chain could contain a surface-adhesive function (Lc). A combination of absorption and emission spectrophotometry, potentiometry, electrospray mass spectrometry, and electrochemistry was used to fully characterize the corresponding ferric complexes and to determine their stability. The quenching mechanism is consistent with an intramolecular static process and is more efficient for the analogue with longer arms. Detection limits in the low nanogram per milliliter range, comparable with the best chemosensors based on natural peptide siderophores, have been determined. These results clearly demonstrate that these tris(phenol-oxazoline) ligands in a tripodal arrangement firmly bind iron(III). Due to their fluorescent properties, the coordination event can be easily monitored, while the fourth arm is available for surface-adhesive moieties. The tripodal system is therefore an ideal candidate for integration with solid-state materials for the development of chip-based devices and analytical methodologies. [ABSTRACT FROM AUTHOR]

Summary: Polyprenyl phosphates, as well as polyprenyl alcohols bearing different isopentenyl C5 units, have been synthesized. The pH range of spontaneous vesicle formation of polyprenyl phosphates with or without polyprenyl alcohols was defined by fluorescence microscopy. A variety of the acyclic or monocyclic polyprenyl phosphates studied formed stable vesicles in water over a wide range of pHs, and the addition of polyprenyl alcohols allowed the vesicle formation of polyprenyl phosphates at higher pHs. Osmotic swelling of a suspension of unilamellar vesicles using the stopped-flow/light-scattering method enabled us to evaluate the water permeability of polyprenyl phosphate vesicles with or without 10 mol% of free polyprenyl alcohol. The addition of many polyprenyl alcohols to polyprenyl phosphate vesicles decreased the water permeability, and some reduced it even more efficiently than cholesterol. [Copyright &y& Elsevier]

Abstract: Here, we report our recent progresses in the synthesis and the study of fullerene-containing supramolecular photoactive devices. Our approach is based on the self-assembly of C60 derivatives bearing an ammonium unit with functionalized crown ethers. The ammonium–crown ether interaction itself is weak and the K a values are rather low when the association results only from the binding of the cationic unit with the macrocyclic component. However, when additional recognition elements are present, the stability of the complexes can be dramatically increased. This principle is illustrated with various examples of systems resulting from the self-assembly of C60-ammonium derivatives and crown ethers bearing a porphyrin or an oligophenylenevinylene chromophore. To cite this article: J.-F. Nierengarten et al., C. R. Chimie 9 (2006) . [Copyright &y& Elsevier]

A series of ferrioxamine B analogues that target the bacterium Yersinia enterocolitica were prepared. These iron carriers are composed of three hydroxamate-containing monomeric units. Two identical monomers consist of N-hydroxy-3-aminopropionic acid coupled with β-alanine, and a third unit at the amino terminal is composed of N-hydroxy-3-aminopropionic acid and one of the following amino acids: β-alanine (1a), phenylalanine (1b), cyclohexylalanine (1c), or glycine (1d). Thermodynamic results for representatives of the analogues have shown a strong destabilization (3-4 orders of magnitude) of the ferric complexes with respect to ferrioxamine B, probably due to shorter spacers and a more strained structure around the metal center. No significant effect of the variations at the N-terminal has been observed on the stability of the ferric complexes. By contrast, using in vivo radioactive uptake experiments, we have found that these modifications have a substantial effect on the mechanism of iron(lll) uptake in the pathogenic bacteria Yersinia enterocolitica. Analogues Ia and Id were utilized by the ferrioxamine B uptake system (FoxA), while I b and 1 c either used different uptake systems or were transported to the microbial cell nonspecifically by diffusion via the cell membrane. Transport via the FoxA system was also confirmed by uptake experiments with the FoxA deficient strain of Yersinia enterocolitica. A fluorescent marker, attached to 1a in a way that did not interfere with its biological activity, provided additional means to monitor the uptake mechanism by fluorescence techniques. Of particular interest is the observation that la was utilized by the uptake system of ferrioxamine B in Yersinia enterocoiltica (FoxA) but failed to use the ferrioxamine uptake route in Pseudomonas putida. Here, we present a case in which biomimetic siderophore analogues deliberately designed for a particular bacterium can distinguish between related uptake systems of different microorganisms. [ABSTRACT FROM AUTHOR]

Equilibrium studies of BMXD complexation with copper(II) and glycylglycine were performed by potentiometric and UV–visible titration. The equilibrium constants determined by potentiometry for the ternary system are: [LCu2P3+]/[LCu24+][P-]=8.11(3), [LCu2HP4+]/[LCu2P3+][H+]=5.39(2), [LCu2H-1P2+][H+]/[LCu2P3+]=-6.33(2), [LCu2(OH)H-1P+][H+]/[LCu2H-1P2+]=-8.20(1) and [LCu2(OH)2HH-1P][H+]/[LCu2(OH)H-1P-1]=-10.33(3), which are in good agreement with the values determined by UV–visible titration. The species formed were confirmed by electrospray mass spectrometry. The association constants, determined by kinetic studies, for the association of the second molecule of glycylglycine with the LCu2P complex, for two ionic media, are 1.29 (KCl) and 1.27 (KNO3). These are in good agreement with the values determined by thermodynamic measurements 1.41 (KCl) and 1.26 (KNO3). [Copyright &y& Elsevier]

The copper(I) bis(chelate) complex Cu(L0)2 has been prepared from 2,9-diphenethyl-1, 10-phenanthroline and Cu(CH3CN)4BF4. Derivative Cu(L0)2 has been characterized by NMR, UV—vis spectroscopy, and X-ray crystallography. Interestingly, owing to the presence of the ethylene linker, the interligand π—π stacking interactions between the phenyl rings and the phenanthroline subunits in Cu(L0)2 do not induce significant distortions of the pseudotetrahedral symmetry around the Cu(I) center in the solid state or in solution. Following the synthesis of Cu(L0)2, dendrimers Cu(L1–4)2 with a Cu(I) bis(2,9-diphenethyl-1, 10-phenanthroline) core surrounded by Fréchet type dendritic branches have been prepared and the kinetics of their cyanide-assisted demetalation studied. Importantly, the surrounding dendritic wedges have no significant influence on the coordination geometry of the Cu(I) center, as deduced from their absorption spectra. Therefore, the variations of the rate constants only reflect changes resulting from the presence of the dendritic branches. The kinetics of the cyanide-mediated demetalation reaction indeed revealed that cyanide diffusion through the dendritic shell is slightly influenced by the size of the branches. Significant effects were observed in the kinetics when going from the third to the fourth generation and have been ascribed to changes in the lipophilicity around the metallic core as a result of dendritic encapsulation. [ABSTRACT FROM AUTHOR]

Azotobacter vinelandii, a nitrogen-fixing soil bacterium, secretes in iron deficiency azotobactin δ, a highly fluorescent pyoverdin-like chromopeptidic hexadentate siderophore. The chromophore, derived from 2,3-diamino-6,7 dihydroxyquinoline, is bound to a peptide chain of 10 amino acids: (L)-Asp-(g)-Ser-(L)-Hse-Gly-(D)-β-threo-HOAsp-(L)-Ser(D)-Cit-(L)-Hse-(L)-Hse lactone-(D)-Nδ-Acetyl, Nδ-HOOrn. Azotobactin δ has three different iron(III) binding sites which are one hydroxamate group at the C-terminal end of the peptidic chain (Nδ-Acetyl, Nδ-HOOrn), one α-hydroxycarboxylic function in the middle of the chain (β-threo-hydroxyaspartic acid), and one catechol group on the chromophore. The coordination properties of its iron(III) and iron(II) complexes were measured by spectrophotometry, potentiometry, and voltammetry after the determination of the acid-base functions of the uncomplexed free siderophore. Strongly negatively charged ferric species were observed at neutral p[H]’s corresponding to a predominant absolute configuration Λ of the ferric complex in solution as deduced from CD measurements. The presence of an α-hydroxycarboxylic chelating group does not decrease the stability of the iron(III) complex when compared to the main trishydroxamate siderophores or to pyoverdins. The value of the redox potential of ferric azotobactin is highly consistent with a reductive step by physiological reductants for the iron release. Formation and dissociation kinetics of the azotobactin δ ferric complex point out that both ends of this long siderophore chain get coordinated to Fe(III) before the middle. The most striking result provided by fluorescence measurements is the lasting quenching of the fluorophore in the course of the protonation of the ferric azotobactin δ complex. Despite the release of the hydroxyacid and of the catechol, the fluorescence remains indeed quenched, when iron(III) is bound only to the hydroxamic acid, suggesting a folded conformation at this stage, around the metal ion, in contrast to the unfolded species observed for other siderophores such as ferrioxamine or pyoverdin PaA. [ABSTRACT FROM AUTHOR]

The structure of the lipoplex formed from DNA and the sugar-based cationic gemini surfactant 1, which exhibits excellent transfection efficiency, has been investigated in the pH range 8.8-3.0 utilizing small-angle X-ray scattering (SAXS) and cryo-electren microscopy (cryo-TEM). Uniquely, three well-defined morphologies of the lipoplex were observed upon gradual acidification: a lamellar phase, a condensed lamellar phase, and an inverted hexagonal (H[sub II]) columnar phase. Using molecular modeling, we link the observed lipoplex morphologies and physical behavior to specific structural features in the individual surfactant, illuminating key factors in future surfactant design, viz., a spacer of six methylene groups, the presence of two nitrogens that can be protonated in the physiological pH range, two unsaturated alkyl tails, and hydrophilic sugar headgroups. Assuming that the mechanism of transfection by synthetic cationic surfactants involves endocytosis, we contend that the efficacy of gemini surfactant 1 as a gene delivery vehicle can be explained by the unprecedented observation of a pH-induced formation of the inverted hexagonal phase of the lipoplex in the endosomal pH range. This change in morphology leads to destabilization of the endosome through fusion of the lipoplex with the endosomal wall, resulting in release of DNA into the cytoplasm. [ABSTRACT FROM AUTHOR]

Examines the performance of kinetics with microperoxidases. Implication of proteolytic breakdown product to cytochrome c containing octapeptide link to iron protoporphyrin IX; Use of rapid-scan stopped-flow spectroscopy in the specimen; Effects of proton in the oxidation of microperoxidases.

Presents a speciation study of mono- and differous complexes formed with Ligand L. Examination of protonation and iron(II) coordination properties in methanol; Characterization of thermodynamic and kinetic intermediates; Proposed self-assembling mechanism of the triple-stranded diferrous helicate.

Examines the synthesis, iron coordination properties and structural characteristics of three tripodal ligands possessing hydroxamate coordination cavities by various methods. Dependence of ligand's coordination properties on their structural features; Examination of allosteric effects by spectrophotometric titrations.

Imidazole—porphyrin coordination has become an important tool in the design of self-assembled materials. A combination of spectrophotometric and stopped-flow techniques has been used to gain insight into the control of imidazole binding in the distal pocket of phenanthroline-strapped porphyrins. The binding studies of a variety of imidazole substrates in combination with both hindered and accessible receptors have permitted the determination of the thermodynamic and kinetic parameters associated with the imidazole binding. [ABSTRACT FROM AUTHOR]

C60 is a scaffold or an electron acceptor  depending on the number of addends. The role of different fullerene subunits is dramatically different in a supramolecular photosynthetic model obtained from a C60 monoadduct bearing an imidazole moiety and a C60 hexa‐adduct decorated with 12 peripheral metalloporphyrins. In their Full Paper on page 223 ff., J. ‐F. Nierengarten, N. Armaroli et al. show that only the monosubstituted C60 derivative plays an active role (electron acceptor) in the cascade of photoinduced events. [ABSTRACT FROM AUTHOR]