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Biomedical subjects

Jean-Marie Lehn

Publications and source records attributed to Jean-Marie Lehn.

At least 19 recordsLinked to original sources
PubMed2007

Solid-state self-assembly of polymeric double helicates leading to linear arrays of silver(I) ions and reversible strand/double helix interconversion in solution.

Reaction of a bent py-hyz-pym-hyz-pym 1 and of a linear py-hyz-py-hyz-pym 3 (py=pyridine; pym=pyrimidine; hyz=hydrazone) ligand strands with silver(I) tetrafluoroborate in CH(3)NO(2) generates double-helical dinuclear 2 and trinuclear 4 complexes. These complexes form polymeric, highly ordered solid-state structures, with wirelike, linear continuous or discontinuous polycationic Ag(n) (+) arrays with Ag--Ag distances of 2.78 to 4.42 A. Ligand 5, an isomer of 1, is found to yield a [2x2] grid-type complex 6. Titration experiments reveal the formation of linear rack-type dinuclear species from 1 and 5. Acid-base modulated, reversible interconversion between strand 1 and double helicate 2 may be achieved by using tren as a competing complexing agent (tren=N(CH(2)CH(2)NH(2))(3)). Progressive addition of silver(I) ions to a 1:1 mixture of 1 and 5 leads to the preferential formation of the double helicate 2 over the grid complex 6, illustrating a process of self-organisation with selection of the correct ligand.

Cations↗
PubMed2006

Driven evolution of a constitutional dynamic library of molecular helices toward the selective generation of [2 x 2] gridlike arrays under the pressure of metal ion coordination.

Constitutional dynamics, self-assembly, and helical-folding control are brought together in the efficient Sc(OTf)3/microwave-catalyzed transimination of helical oligohydrazone strands, yielding highly diverse dynamic libraries of interconverting constituents through assembly, dissociation, and exchange of components. The transimination-type mechanism of the ScIII-promoted exchange, as well as its regioselectivity, occurring only at the extremities of the helical strands, allow one to perform directional terminal polymerization/depolymerization processes when starting with dissymmetric strands. A particular library is subsequently brought to express quantitatively [2 x 2] gridlike metallosupramolecular arrays in the presence of ZnII ions by component recombination generating the correct ligand from the dynamic set of interconverting strands. This behavior represents a process of driven evolution of a constitutional dynamic chemical system under the pressure (coordination interaction) of an external effector (metal ions).

Journal Article↗
PubMed2006

Investigation of guanosine-quartet assemblies by vibrational and electronic circular dichroism spectroscopy, a novel approach for studying supramolecular entities.

The self-assembly of guanosine-5'-hydrazide G-1 in D(2)O, in the presence and absence of sodium cations, has been investigated by chiroptical techniques: electronic (ECD) and the newly introduced vibrational (VCD) circular dichroism spectroscopy. Using a combination of ECD and VCD with other methods such as IR, electron microscopy, and electrospray ionization mass spectrometry (ESI-MS) it was found that G-1 produces long-range chiral aggregates consisting of G-quartets, (G-1)(4), subsequently stacked into columns, [(G-1)(4)](n), induced by binding of metal cations between the (G-1)(4) species. This process, accompanied by gelation of the sample, is highly efficient in the presence of an excess of sodium cations, leading to aggregates with strong quartet-quartet interaction. Thermally induced conformational changes and conformational stability of guanosine-5'-hydrazide assemblies were studied by chiroptical techniques and the melting temperature of the hydrogels formed was obtained. The temperature-dependent experiments indicate that the long-range supramolecular aggregates are dissociated by increasing temperature into less ordered species, monomers, or other intermediates in equilibrium, as indicated by MS experiments.

Binding Sites↗
PubMed2006

DyNAs: constitutional dynamic nucleic acid analogues.

Dynamic cationic polymers were generated in aqueous media from functionally complementary monomers bearing nucleobase groups. (1)H NMR spectroscopy was used to follow the polycondensation reaction of the nucleobase-appended dihydrazides 1 and 2 with the dialdehydes B and C. The reversibility of these polymers was established by proton NMR spectroscopy through exchange of the dihydrazide 2 with polymer 1 B. The polymers 1 B, 2 B, 1 C, and 2 C represent dynamic biopolymers of nucleic acid type, DyNAs. Electrostatic interaction of these polymers with polyanionic entities, such as polyphosphates, polynucleotides, and polyaspartic acid, was shown to take place. It induces a change in size of the dynamic polymer, as it responds by an increase in degree of polymerization to an increase of the overall anionic charge introduced, that is, to the total electrostatic interaction.

Aldehydes↗
PubMed2006

Time scales of membrane fusion revealed by direct imaging of vesicle fusion with high temporal resolution.

Membrane fusion is a vital process of life involved, for example, in cellular secretion via exocytosis, signaling between nerve cells, and virus infection. In both the life sciences and bioengineering, controlled membrane fusion has many possible applications, such as drug delivery, gene transfer, chemical microreactors, or synthesis of nanomaterials. Until now, the fusion dynamics has been elusive because direct observations have been limited to time scales that exceed several milliseconds. Here, the fusion of giant lipid vesicles is induced in a controlled manner and monitored with a temporal resolution of 50 micros. Two different fusion protocols are used that are based on synthetic fusogenic molecules and electroporation. For both protocols, the opening of the fusion necks is very fast, with an average expansion velocity of centimeters per second. This velocity indicates that the initial formation of a single fusion neck can be completed in a few hundred nanoseconds.

Animals↗
PubMed2006

Suppression of hypoxia-induced HIF-1alpha and of angiogenesis in endothelial cells by myo-inositol trispyrophosphate-treated erythrocytes.

Allosteric regulation of oxygen delivery by RBCs may have significant effects on tumor growth. Indeed, angiogenesis, the formation of new blood vessels, is induced in growing tumors by low oxygen partial pressure. Hypoxia-inducible genes are switched on, among which are the VEGF gene and its receptors. Most important, under hypoxia, hypoxia-inducible factor 1alpha has a significantly prolonged half-life and up-regulates a number of hypoxia genes. Human microvascular endothelial cells (MECs), when subjected in vitro to hypoxia, align to form vessel-like structures as in the angiogenic process. We report here that, when cultured in hypoxic conditions in the presence of human RBCs loaded with a new membrane-permeant allosteric effector of Hb, myo-inositol trispyrophosphate (ITPP), endothelial cells (ECs) do not align, i.e., do not form "vessel"-like structures, because the "loaded" RBCs are capable of releasing under hypoxia more oxygen than their "normal" counterparts. Levels of VEGF and of hypoxia-inducible factor 1alpha, elevated in the human MECs under hypoxia, were dramatically reduced or even suppressed in the presence of the ITPP-loaded RBCs. Treatment of these ECs directly with free ITPP at different concentrations had no effect on their ability to undertake angiogenesis. Incubation with ITPP enhances the capacity of Hb to release bound oxygen, leading to higher oxygen tension in the hypoxic environment, thus inhibiting hypoxia-induced angiogenesis. These observations are suggestive of a potential in vivo role of ITPP-loaded, "low-O2-affinity" RBCs in cancer therapy.

Allosteric Regulation↗
PubMed2006

Discrimination of metallosupramolecular architectures in solution by using diffusion ordered spectroscopy (DOSY) experiments: double-stranded helicates of different lengths.

The translational diffusion coefficients of various helicates have been determined by using NMR diffusion spectroscopy (Diffusion Ordered SpectroscopY, DOSY), in order to investigate the individual behaviour of the helicates according to their length (different nuclearities; 1-5 metals), to the nature of the metal involved (CuI or AgI), as well to their bulkiness due to the presence of substituents on the periphery of the assembly. Furthermore, the spectrum of a mixture of helicates belonging to the same series, but with different lengths and nuclearities, showed the signals of each component, with no observable cross-linking, confirming the self-recognition properties of the helicates.

Journal Article↗
PubMed2006

Addressing metal centres in supramolecular assemblies.

Supramolecular metal ion assemblies are deposited from their solutions onto highly orientated pyrolytic graphite (HOPG) substrates to be imaged by scanning tunnelling microscopy (STM). Since the structural and electronic information of STM measurements are strongly entangled, the spectroscopic interpretation and analysis of the images of such molecular assemblies has proven to be challenging. This tutorial review focuses on a general room temperature scanning tunnelling spectroscopy (STS) protocol, current induced tunnelling spectroscopy (CITS), applied to free-standing 1D and 2D arrangements of supramolecular metal ion assemblies rendering local tunnelling probabilities with submolecular resolution. The size of the investigated molecular assemblies was confirmed by comparison with X-ray crystallographic data, while the consistency of the spectroscopic investigations and of the determined positions of the metal ions within the assemblies was checked by DFT calculations. Due to the genuine level structure of coordinated metal centers, it was possible to map exclusively the position of the coordination bonds in supramolecular transition metal assemblies with submolecular spatial resolution using the CITS technique. CITS might thus constitute an important tool to achieve directed bottom-up construction and controlled manipulation of fully electronically functional, two-dimensional molecular designs.

Journal Article↗
PubMed2006

Selective product amplification of thymine photodimer by recognition-directed supramolecular assistance.

Two symmetric ditopic supramolecular templates (1 and 2) each presenting two hydrogen bonding recognition subunits were synthesized. Each such subunit comprises the same donor and acceptor pattern, capable of binding a substrate molecule with complementary hydrogen bonding groups to form a supramolecular complex. Substrate molecules, such as thymine or uracil derivatives, yield 2 : 1 complexes with the acceptors involving two hydrogen bonds to each subunit with ideal orientation for subsequent [2 + 2] dimerization upon photoirradiation. Selective syn photoproduct formation and concomitant suppression of the trans isomer are favored by orientation of the two guest nucleobases within the template cleft. Complementary donor and acceptor hydrogen bonding induced positioning of the two substrates and steric hindrance within the template clefts are responsible for the selective product formation.

Catalysis↗
PubMed2006

Homo- and heteroassemblies of lactim/lactam recognition patterns on highly ordered pyrolytic graphite: An STM investigation.

The 2D assembly of phthalhydrazide 1 and aminopyrimidine 2 derivatives equipped with C16 and C8 alkyl chains, respectively, on highly ordered pyrolytic graphite (HOPG) was studied by scanning tunneling microscopy. Well-defined, rather complex surface layer patterns emerge resulting from a delicate balance of (self-) complementary (strong) hydrogen bonds and van der Waals force-driven ordering of the alkyl substituents on the HOPG surface. The four different compounds and their 1:1 mixtures yield seven different 2D structures. Phthalhydrazide offers in principle three tautomeric forms, with the lactim/lactam being the most stable. Depending on the solvent, different morphologies can be obtained. In one case, the special self-assembly of achiral 1a leads to a 2D chiral packing with the left- and right-hand motifs present in different domains. We assume that pure 1a is expressed in its lactim/lactam form, whereas in a 1:1 mixture with 2a it switches to the bislactam form. These features display a process of dynamic diversity generation through tautomerism resulting in different nanostructures in response to environmental parameters.

Journal Article↗
PubMed2006

Conjecture: imines as unidirectional photodriven molecular motors-motional and constitutional dynamic devices.

Compounds containing the C==N group, such as imines and their derivatives, may undergo syn-anti isomerization by two different routes: 1) photochemically, by out-of-plane rotation around the carbon-nitrogen double bond through a "perpendicular" form, and 2) thermally, by in-plane nitrogen inversion through a "linear" transition state. When the two interconversions occur in sequence, a full, closed process is accomplished, restoring the initial state of the system along two different steps. In a chiral imine-type compound, for example, with an asymmetric center next to the C==N function, photoinduced rotation may be expected to occur in one sense in preference to the opposite one. Thus, photoisomerization followed by thermal isomerization in a chiral imine compound generates unidirectional molecular motion. Generally, imine-type compounds represent unidirectional molecular photomotors converting light energy into mechanical motion. As they are also able to undergo exchange of the carbonyl and amine partners, they present constitutional dynamics. Thus, imine-type compounds are double dynamic, motional, and constitutional devices.

Imines↗
PubMed2006

Messages in molecules: ligand/cation coding and self-recognition in a constitutionally dynamic system of heterometallic double helicates.

Double helicates are known to exhibit self-recognition characteristics determined by the coordination geometry of the metal involved as well as by the topicity of the ligands. Combining tridentate (terpyridine, T) or bidentate (bipyridine, B) subunits in a tritopic strand affords a set of ligands able to assemble by pairs to form double helicates, homo- or heterostranded, homo- or heterotopic, depending on the coordination properties of the metals involved. The four ligand strands, BBB, TTT, BBT, and TBT form constitutionally dynamic sets of double helicates with the metal ions Cu(I), Cu(II), and Zn(II); these helicates correspond to the correct coding of the BB, BT, and TT pairs for tetra-, penta-, and hexacoordinate Cu(I), Cu(II), and Zn(II) cations, respectively.

Journal Article↗
PubMed2006

Formation of RACK- and grid-type metallosupramolecular architectures and generation of molecular motion by reversible uncoiling of helical ligand strands.

The interaction of appropriate metal ions (Pb(II), Zn(II)) with helical ligand strands, obtained by hydrazone polycondensation, generates polymetallic supramolecular architectures of rack and grid types, by uncoiling of the ligand. The interconversion between the helical free ligand and the linearly extended ligand in the complexes produces reversible ion-induced, nanomechanical molecular motions of large amplitude. It has been integrated in an acid-base neutralisation fuelled process, which links the extension/contraction of the ligand strands to alternating changes in pH.

Contraindications↗
PubMed2006

Dynamic chemical devices: photoinduced electron transfer and its ion-triggered switching in nanomechanical butterfly-type bis(porphyrin)terpyridines.

A series of butterfly-type molecular constructs has been prepared in good yield by using a double Stille coupling synthetic protocol. They are composed of a terpyridine (terpy) scaffold and two wings composed of appended porphyrins that are capable of switching from an extended W geometry to a compact U geometry upon cation coordination of the terpy unit. The porphyrin moieties exist in the constructs either as free bases or they can be sequentially metallated, thus giving rise to wings of different "colours". Stationary and time-resolved emission studies of the HZn, ZnAu and Zn2Au constructs show that the electronic properties are strongly dependent on the geometry. In the extended W conformation an energy-transfer process is seen from the free base to the Zn-metallated porphyrin. In the U conformation in Zn2Au the donor luminescence resulting from the singlet excited state of the Zn wing is strongly, quenched not only due to the heavy atom effect but also due to a fast electron-transfer process to the ground state of the Au wing. Furthermore, the binding of (alpha,omega)-diamine substrates to the Zn(II)-porphyrin sites can also influence the conformation of the system. For the Zn2Zn construct, single-crystal diffraction experiments with synchrotron radiation allowed the structure to be solved by direct methods and fully refined; it shows the expected U conformation. The central Zn atom is six-coordinate, whereby the zinc atom is coordinated by the eta3-terpy ligand as well by monodentate and semi-chelating acetate anions. The structure is made rigid by hydrogen bonds involving the aqua ligands on the outer Zn centres and acetate oxygen atoms. The present system thus represents a double-trigger-modulated optomechanical switching device with selective substrate binding for either metal atoms or tailored ligands. Both energy- and electron-transfer processes can be controlled opening a means of improving the on/off ratio in future constructs.

Chemical Phenomena↗
PubMed2006

Tunable fluorene-based dynamers through constitutional dynamic chemistry.

Dynamic covalent iminofluorene-based oligomers and polymers have been generated. They undergo constitutional recomposition under the effect of two parameters, acidity and ZnII metal ions. As a result, marked changes in physical properties take place. The results illustrate the response of such a dynamic system to chemical effectors (H+ nd ZnII), thus demonstrating the adaptive behavior of the system under the pressure of external factors. They also point to the possibility of modulating optical properties (UV-visible absorption and fluorescence) by constitutional recomposition in response to a specific trigger. Such features allow the development of dynamic materials, the functional properties of which may respond to external stimuli.

Journal Article↗
PubMed2006

Protonic and temperature modulation of constituent expression by component selection in a dynamic combinatorial library of imines.

The constitutional recomposition of a dynamic library of imines displays a complex behavior under the effect of two parameters, acidity and temperature. A qualitative analysis of the quantitative data is presented. The results illustrate the response of such a dynamic system to a physical stimulus (temperature) and a chemical effector (H+), thus demonstrating its adaptive behavior under the pressure of external factors. They also point to the possibility of modulating a given functional property (optical, electronic, ionic) by constitutional recomposition induced by a specific trigger. Such features are of great interest for the development of stimuli-responsive, functional dynamic materials.

Journal Article↗