Showing papers by "Mihail Barboiu published in 2007"

Functional G‐Quartet Macroscopic Membrane Films

Abstract: G-quartets, formed by the hydrogen-bonding self-assembly of four guanosine (G) residues and stabilized by alkali-metal cations, play an important role in biology, in particular in nucleic acid telomers of potential interest to cancer therapy. The G-quartet architecture represents a nice example of a dynamic supramolecular system that has been used as a building block for gelators, columnar polymeric aggregates, self-organized surfaces, and prototypes of chemical dynamic devices. 5] . In the last few decades, G-quartets and the similar folic acid quartet have also been proposed as powerful scaffolds for building synthetic ion channels. Although stable in organic solvents, they do not seem to have defined transport functions in hydrophobic membranes. Barrel-stave, lipophilic, calix[4]arene, and 8-aromatic–guanosine conjugates have been used to stabilize the formation of G-quartets. Recently, a new strategy based on reversible metathesis was successfully used by Davis et al. to generate a rich array of interconverting ionchannel conductance states of a unimolecular G-quartet in a phospholipid membrane. Despite such impressive progress, considerable challenges still lie ahead and the more significant one is to improve the stability of G-quartet dynamic aggregates in polymeric devices, such as films or membranes, to extend (address) the transport studies to the macroscopic level. Several earlier studies reported the preparation of discrete supramolecular assemblies of nucleobases embedded in synthetic polymers and hybrid materials. However, the “dynamic communication” between the supramolecular self-assembly of nucleobases and the polymerization processes, which kinetically and stereochemically might communicate, is not so trivial. For all these reasons, in this study building blocks of guanosine (1; Scheme 1), 2-formylphenylboronic acid (2), and bis(3-aminopropyl)polytetrahydrofuran (PTHF, 3 ; numberaverage molecular weight Mn ca. 1100 gmol ) are used as molecular precursors to conceive G-quartet polymeric membrane materials at the macroscopic scale. Our efforts involve the successive synthesis of the ditopic bisiminoboronic 4 and bisiminoboronate-guanosine 5macromonomers, and then the self-assembly of 5 into G-quartet-type supramolecular superstructures (Scheme 1). The main strategy consists of generating (amplifying) dynamic supramolecular G-quartets by K ion templating, from a dynamic pool of oligomeric ribbon-type or cyclic supramolecular architectures. Then, the G-quadruplex architectures are fixed in self-supporting polymeric membrane films. A standard sample without potassium chloride, which resulted in the formation of an H-bond ribbon-type superstructure of the guanine moieties, was prepared as reference under the same conditions as described above (Figure 1). Scheme 1. Synthesis of bisiminoboronic 4 and bisiminoboronate-guanosine 5 macromonomers, and the self-assembly of 5 into G-quartettype superstructures.

Temperature induced single-crystal-to-single-crystal transformations and structure directed effects on magnetic properties.

Abstract: The binding of CoII, NiII, and CuII cations to the lithium 3-pyridinesulfonate ligand in an aqueous solution leads to single crystals of coordination polymers 1−3. The solid-state architectures of 1−3 which resulted from the combination of ligand-water heterocomplexation processes are linear coordination polymers packed into parallel alternatively stratified layers. These layers are interconnected through intermolecular hydrogen-bonding interactions occurring between the coordinated water molecules and the noncoordinating oxygen atoms of the sulfonate groups. Consequently, this leads to the formation of the cross-linked 3D (1, 2) or layered 2D (3) networks exhibiting 12-point or four-point hydrogen bond contacts between each unit with eight or four adjacent neighbors, respectively. The reversible structural rearrangement of these frameworks proceeds from the “relaxed” room-temperature phase to the “contracted” low-temperature phase in response to an external thermal stimulus. The reversibility of the cont...

Self-Optimizing Charge-Transfer Energy Phenomena in Metallosupramolecular Complexes by Dynamic Constitutional Self-Sorting

Abstract: In this paper we report an extended series of 2,6-(iminoarene)pyridine-type ZnII complexes [(Lii)2Zn]II, which were surveyed for their ability to self-exchange both their ligands and their aromatic arms and to form different homoduplex and heteroduplex complexes in solution The self-sorting of heteroduplex complexes is likely to be the result of geometric constraints Whereas the imine-exchange process occurs quantitatively in 1:1 mixtures of [(Lii)2Zn]II complexes, the octahedral coordination process around the metal ion defines spatial-frustrated exchanges that involve the selective formation of heterocomplexes of two, by two different substituents; the bulkiest ones (pyrene in principle) specifically interact with the pseudoterpyridine core, sterically hindering the least bulky ones, which are intermolecularly stacked with similar ligands of neighboring molecules Such a self-sorting process defined by the specific self-constitution of the ligands exchanging their aromatic substituents is self-optimiz

Dynamic supramolecular hybrid and mesoporous membranes

Abstract: La selectivite du transport par membrane peut etre induite par l'utilisation de transporteurs ou des canaux transmembranaires. Du point de vue mecanistique nous utilisons des transporteurs qui peuvent s'auto-assembler dans des agregats presentant des caracteristiques intermediaires entre les molecules monomeres de type transporteur et les superstructures polymeres de type canaux ioniques. Nous avons etudie les proprietes de transport par membranes hybrides solides denses ou par des materiaux membranaires mesoporeux englobant ces systemes hybrides supramoleculaires generes par auto-assemblage dynamique par liaisons hydrogene des uree-ethers-couronnes, acides amines aromatiques et nucleosides. Cet article de revue presente une synthese des differentes methodes qui peuvent etre utilises pour la preparation des membranes hybrides supramoleculaires. Les principes de fonctionnement des membranes a reconnaissance moleculaire ou auto-organisees sont presentes pour mieux comprendre la conception controlee des chemins de transport ionique preferentiels. Finalement, ces systemes ont ete utilises avec succes pour elaborer des membranes a sites dynamiques complexantes immobilisees dans un nanoespace hybride mesoporeux.

Sodium trifluoromethanesulfonate acetonitrile solvate

Abstract: In the structure of the title salt, Na+·CF3SO3−·C2H3N, two symmetry-related acetonitrile molecules take part in the octa­hedral coordination of the Na+ cation, which is located on an inversion center. The trifluoromethanesulfonate anions and acetonitrile molecules lie on mirror planes. The Na+ ions are arranged in layers, sandwiched by trifluoro­methane­sulfonate double layers with the lipophilic CF3 groups pointing outwards and towards those of neighbouring double layers.

Bis(μ‐trifluoromethanesulfonato‐κ2O:O′)bis[aqua(1,4,7,10,13,16‐hexaoxacyclooctadecane‐κ6O)barium(II)] bis(trifluoromethanesulfonate)

Abstract: The crystal structure of the title compound, [Ba2(CF3O3S)2(C12H24O6)2(H2O)2](CF3O3S)2, comprises a ten-coordinated Ba2+ cation that is coordinated by 18-crown-6, trifluoro­methane­sulfonate counter-ions and a water mol­ecule, and an uncoordinated counter-ion. The dinuclear cation lies on a center of inversion. Each coordinated triflate group chelates a Ba atom while being monodentate to the adjacent Ba atom. The uncoordinated counter-ion is hydrogen bonded to the cation. Hydrogen bonds form infinite tubular arrays.