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Biomedical subjects

Mihail Barboiu

Publications and source records attributed to Mihail Barboiu.

11 recordsLinked to original sources
PubMed2006

Columnar self-assembled ureido crown ethers: an example of ion-channel organization in lipid bilayers.

The self-assembly of ureido crown-ether derivatives has been examined in homogeneous solution, in the solid state, and in planar bilayer membranes. The self-assembly is driven by head-to-tail hydrogen bonding between the urea functional groups. Dimers and higher oligomers are formed in CDCl3 solution as assessed by the change in the ureido NH chemical shift as a function of concentration. Single-crystal X-ray diffraction shows that an antiparallel association of the ureas produces columnar channels composed of face-to-face crown ethers. Powder X-ray diffraction studies also show the presence of a minor phase based upon a parallel urea association leading to an alternative columnar arrangement of the crown ethers. In bilayer membranes at low concentration of ureido crown ether added, membrane disruption is observed together with rare single-channel openings, but at higher concentration, a rich array of interconverting channel conductance states is observed. The channel results are interpreted as arising from discreet stacks of ureido crown ethers where the transport of cations would occur via the macrocycles, admixed with larger pores formed by association of the crown ether headgroups around a central large pore.

Journal Article↗
PubMed2005

Silver(I) coordination polymers containing heteroditopic ureidopyridine ligands: the role of ligand isomerism, hydrogen bonding, and stacking interactions.

New silver (I) coordination polymers has been successfully designed and synthesized using heteroditopic ureidopyridine ligands 1 and 2 via a combination of coordinations bonds, hydrogen bonding, and pi-pi stacking interactions. This study shows an example of the orientation of the pyridine nitrogen relative to the urea moiety (4-substituted, 1, or 3-substituted, 2), used to control the packing of resulting crystalline coordination polymers. The ureidopyridine ligands present some flexibility because of the conformational rotation around the central urea moiety. The co-complexation of the silver(I) cation by two pyridine moieties and of the PF(6)(-) counteranion by the urea moiety results in the formation of discrete [1(2)Ag](+)PF(6)(-), (3) and [2(2)Ag](+)PF(6)(-), (4) complexes presenting restricted rotation around the central urea functionality. The geometrical information contained in the structures of ligands 1 and 2 and the heteroditopic complexation of silver hexafluorophosphate are fully exploited in an independent manner resulting in the emergence of quasi-rigidly preorganized linear and angular building blocks of 3 and 4, respectively. Additional pi-pi stacking contacts involving interactions between the pi-donor benzene and the pi-acceptor pyridine systems reinforce and direct the self-assembly of the above-described combined structural motifs in the solid state. Accordingly, linear and tubular arrays of pi-pi stacked architectures are generated in the solid state by synergistic and sequential metal ion complexation, hydrogen bonding, and pi-pi stacking interactions.

Journal Article↗
PubMed2004

Dynamic chemical devices: modulation of photophysical properties by reversible, ion-triggered, and proton-fuelled nanomechanical shape-flipping molecular motions.

The terpy-derived (terpy=terpyridine) ligand 1 has an extended W shape in which the two appended photoactive pyrenyl groups are held apart. On binding of a zinc(II) ion with a terpy group, ligand 1 is converted into complex 2 whereby it adopts a U shape, thus stacking the aromatic units. This structural modification leads to a very pronounced change in photophysical properties: from a highly fluorescent free ligand to a very weakly emitting complex. The W/U structural switching can be reversibly induced by the addition of a competitive tren ligand, which binds and releases a zinc(II) ion under protonation/deprotonation cycles, thus leading to oscillations in light emission. Therefore, the present system performs periodic modulation of optical output through a nanomechanical shape-flipping motion, triggered by metal ion binding and fuelled by acid-base neutralisation energy. Overall, it represents an ion-triggered opto-mechanical supramolecular device.

Journal Article↗
PubMed2004

Metallosupramolecular zippers generated by self-organization of self-complementary molecular clefts.

The binding of Co(2+) and Pb(2+) ions to the terpyridine and pyridine subunits of the ligand 1 leads to the self-complementary molecular clefts 2-6, which result from the crossover combination of orthogonal-terpyridine and linear-pyridine metal-coordination subprograms and are stabilized by strong pi-pi stacking interactions. Four different cleft-type entities, [Co(2+) (2)(1)(2)] (3), [Pb(2+) (2)(1)(2)] (4), [Co(2+) (4)(1)(2)] (5), [Pb(2+) (4)(1)(2)] (6), are generated in both solution and the solid state, and may be interconverted as a function of metal/ligand stoichiometry. One- and two-dimensional metallosupramolecular zipper architectures result from self-assembly in the solid state driven by a combination of different pi-pi stacking subprograms. The U-shaped geometry of the ligand influences the possibility of zipping and thus, in turn, the generation of different zipper architectures. The structures of 2-5 have been confirmed by X-ray crystallography; that of 6 is based on NMR spectral data.

Journal Article↗
PubMed2004

Ion-driven ATP pump by self-organized hybrid membrane materials.

We report new hybrid organic-inorganic materials, based on macrocyclic receptors 1-3 self-organized in tubular superstructures prepared by sol-gel process. Fourier transform infrared (FTIR) and NMR spectroscopic analyses demonstrate that the self-organization by hydrogen bonding of organogel superstructures of 2 and 3 were preserved in the hybrid materials throughout the sol-gel process. The molecular arrangement of heteroditopic receptors defines a particularly attractive functional transport device for both cation (tubular macrocycles) and anion (sandwich-urea) directional-diffusion transport mechanism in the hybrid membrane material. This system has been employed successfully to design a solid dense membrane, functioning as an ion-powered adenosine triphosphate (ATP(2)(-)) pump, and illustrates how a self-organized hybrid material performs interesting and potentially useful functions.

Adenosine Triphosphate↗
PubMed2003

Self-assembly, structure, and dynamic interconversion of metallosupramolecular architectures generated by Pb(II) binding-induced unfolding of a helical ligand.

The binding of lead(II) cations to the terpyridine-type subunits of the helical ligand 1 leads to the self-assembly of different polynuclear metallosupramolecular architectures of nanometric size. Three different entities are generated and may be interconverted as a function of metal/ligand stoichiometry: a [4 x 4]Pb(16)(II) grid-type array 2, a [4 # 4]Pb(12)(II) double-cross species 4, and an intermediate complex 3. The structures of 2 and 4 have been confirmed by X-ray crystallography; that of 3 is based on NMR spectral data. The interconversion of the three species generates dynamic diversity and represents an expression of constitutional dynamic chemistry. In the course of ion binding, the helical molecules of ligand 1 unwrap to yield fully extended strands arranged in perpendicular fashion in the architectures 2-4 generated. This process amounts to molecular motions in two directions which confer to the present systems characteristics of two-dimensional nanomechanical devices, capable of performing 2D-contraction/extension motions. The triple features of self-organization, dynamic interconversion, and potential addressability displayed by the processes described trace a self-fabrication approach to nanoscience and nanotechnology.

Journal Article↗
PubMed2003

Self-organized heteroditopic macrocyclic superstructures.

[structure: see text] The synthesis of heteroditopic macrocyclic ureido receptors and of their NaX complexes is described. NMR studies and determination of the crystal structure show the formation of self-organized dimeric or polymeric superstructures by a cooperative macrocyclic cation complexation, anion-hydrogen bonding, and pi-pi stacking interactions. Membrane transport experiments show a direct relation between the synergetic ion-pair recognition and the transport properties of these molecular information transfer devices.

Journal Article↗
PubMed2003

Dynamic chemical devices: generation of reversible extension/contraction molecular motion by ion-triggered single/double helix interconversion.

The polyheterocyclic strands 1-H and 2-H adopt a helical shape enforced by the pyridine-pyrimidine helicity codon. The crystal structure of 2-H shows the formation of stacks of dimers of right- and left-handed individual helices. Treatment of 1-H and 2-H with silver triflate results in the generation of double-helical entities 1-DH and 2-DH, containing two strands and two silver ions. NMR studies and determination of the crystal structure of 2-DH indicate that the duplex is stabilized by coordination of each Ag(+) ion to two terminal bipyridine units, one from each strand, and by pronounced pi-pi stacking interactions between the internal heterocycles of the strands, yielding a very robust double helical structure. Reversible interconversion of the single and double helix may be achieved by addition of a cryptand capable of sequestering Ag(+) and releasing it by protonation. Thus, successive addition of acid and base leads to reversible interconversion between the shorter ( approximately 3.6 A) single helix and the longer ( approximately 10.3 A) double helix, resulting in the generation of pronounced extension/contraction motion. The system 1,2-H/1,2-DH represents a dynamic chemical device undergoing ionic modulation of reversible molecular mechanical motion fueled by acid/base neutralization.

Crystallography, X-Ray↗
PubMed2003

Functional supramolecular devices: [M4IIL4]8+ [2 x 2]-grid-type complexes as multilevel molecular electronic species.

The [M(4)(II)L(4)](8+) [2 x 2]-grid-type complexes 1-8 present a set of features of particular interest for potential applications. All complexes exhibit multiple reduction levels at low reduction potentials paired with rather high stability. The modulation of the reduction potentials is possible by introduction of appropriate substituents on the ligands. The Co(II)(4) complexes 1-5 present a remarkable regularity in the disposition of the reduction levels, indicating the ability of the Co(II) sites to transmit electronic interactions between reduced ligands. In general, all investigated molecular systems 1-8 show characteristics typical for multilevel supramolecular electronic devices.

Journal Article↗
PubMed2002

Dynamic chemical devices: modulation of contraction/extension molecular motion by coupled-ion binding/pH change-induced structural switching.

Dynamic chemical devices involve morphological or constitutional modifications in molecular or supramolecular systems, induced by internal or external physical or chemical triggers. Reversible changes in shape result in molecular motions and define motional dynamic devices presenting mechanical-like actions of various types. Suitably designed polyheterocyclic strands such as compounds 1-5 wrap into helical conformations. The binding of lead(II) ions to the coordination subunits contained in the strand leads to complete uncoiling and yields a polymetallic complex presenting a fully extended shape. The addition of a cryptand complexing agent that strongly binds lead(II) ions and releases them under protonation allows a reversible pH-modulation of lead(II) levels in the medium, which in turn induces coiling/uncoiling of the molecular strand. This system thus represents a motional dynamic device which performs a mechano-chemical process, realizing alternating extension/contraction motions triggered by ion binding. It achieves a linear motor-type of action of very large stroke amplitude fueled by ionic processes.

Crystallography, X-Ray↗