Preparation of multi-allylic dendronized polymers via atom-transfer radical polymerization

International audienceAtom-transfer radical polymerization (ATRP) was investigated to polymerize a styrene monomer carrying carbosilane dendrons with 6 terminal allyl branches. Polymers with a monomodal molar mass distribution and low polydispersity have been produced, while by comparison the free-radical polymerization technique led to chain transfer early in the polymerization. Steric effect brought by the dendrons result in a slow polymerization rate, leading to an apparent saturation of the degree of polymerization. By pushing up the polymerization conditions (eg. increase of temperature or concentration), interchain couplings started to take place, most likely from reactions at the allyl branches. These results are very similar to the ones previously reported for the anionic polymerization of this same multi-allylic dendronized monomer. § present addresses: P.O. Schwartz, Alsachim SAS

Cationic siRNAs Provide Carrier-Free Gene Silencing in Animal Cells

siRNA-mediated gene silencing requires intracellular delivery of the nucleic acid. We have developed a carrierless molecular approach that follows the same cell entry route as cationic supramolecular complexes, yet should avoid the extracellular barriers encountered by nanoparticles. Cationic oligospermine−oligonucleotide conjugates (ZNAs, for Zip Nucleic Acids) were synthesized stepwise on an oligonucleotide synthesizer using a DMT-spermine phosphoramidite derivative. They were shown to enter cells and have access to the cytoplasm, provided their formal charge ratio N/P was >1.5. Cationic siRNAs that fulfilled this condition were shown to achieve selective inhibition of luciferase gene expression in the submicromolar concentration range in constitutively luciferase-expressing cells

"Smart" molecular engineering of metallomesogens based on Pt(II) terpyridine coordination complexes

A series of ionic tetracoordinated Pt(II) complexes based on terpyridine ligand were synthesized and characterized. Their chemical structures were engineered by using counterions of different coordination strengths and dimensions, namely non-coordinating BF4, weakly coordinating bulky gallate units, and small and strongly coordinating chlorine (Cl). The complexes containing lipophilic gallate units exhibit low temperature liquid crystalline properties. The mesomorphic properties were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction studies (SWAXS). Photophysical properties were determined in solution and condensed states

Zip nucleic acids are potent hydrolysis probes for quantitative PCR

Zip nucleic acids (ZNAs) are oligonucleotides conjugated with cationic spermine units that increase affinity for their target. ZNAs were recently shown to enable specific and sensitive reactions when used as primers for polymerase chain reaction (PCR) and reverse-transcription. Here, we report their use as quantitative PCR hydrolysis probes. Ultraviolet duplex melting data demonstrate that attachment of cationic residues to the 3′ end of an oligonucleotide does not alter its ability to discriminate nucleotides nor the destabilization pattern relative to mismatch location in the oligonucleotide sequence. The stability increase provided by the cationic charges allows the use of short dual-labeled probes that significantly improve single-nucleotide polymorphism genotyping. Longer ZNA probes were shown to display reduced background fluorescence, therefore, generating greater sensitivity and signal level as compared to standard probes. ZNA probes thus provide broad flexibility in assay design and also represent an effective alternative to minor groove binder- and locked nucleic-acid-containing probes

Zip Nucleic Acids: new high affinity oligonucleotides as potent primers for PCR and reverse transcription

Most nucleic acid-based technologies rely upon sequence recognition between an oligonucleotide and its nucleic acid target. With the aim of improving hybridization by decreasing electrostatic repulsions between the negatively charged strands, novel modified oligonucleotides named Zip nucleic acids (ZNAs) were recently developed. ZNAs are oligonucleotide–oligocation conjugates whose global charge is modulated by the number of cationic spermine moieties grafted on the oligonucleotide. It was demonstrated that the melting temperature of a hybridized ZNA is easily predictable and increases linearly with the length of the oligocation. Furthermore, ZNAs retain the ability to discriminate between a perfect match and a single base-pair-mismatched complementary sequence. Using quantitative PCR, we show here that ZNAs are specific and efficient primers displaying an outstanding affinity toward their genomic target. ZNAs are particularly efficient at low magnesium concentration, low primer concentrations and high annealing temperatures, allowing to improve the amplification in AT-rich sequences and potentially multiplex PCR applications. In reverse transcription experiments, ZNA gene-specific primers improve the yield of cDNA synthesis, thus increasing the accuracy of detection, especially for genes expressed at low levels. Our data suggest that ZNAs exhibit faster binding kinetics than standard and locked nucleic acid-containing primers, which could explain why their target recognition is better for rare targets

Emissive Zn(II) metallomesogen based on tridentate terpyridine ligand

A low temperature liquid crystal based on luminescent terpyridine Zn(II) complex is presented. The induction of the mesomorphic properties was achieved using a lipophilic gallate unit as ancillary ligands. The mesomorphic properties were investigated by polarised optical microscopy (POM), differential scanning calorimetry (DSC), thermogravimetric analysis (TA) and X-ray scattering (SWAXS) of bulk materials, while the optical properties of the complex were investigated in solution and in condensed liquid crystalline states

Tolerance of intravitreal dexamethasone implants in patients with ocular hypertension or open-angle glaucoma

Evaluate the pressure tolerance of dexamethasone implants in open-angle glaucoma (OAG+) patients and ocular hypertension (OHT+) patients compared with nonglaucomatous and nonhypertensive patients

Role of lattice defects on the magnetism of gold nanoparticles irradiated with neutrons

International audienceThe origin of the unexpected magnetic properties of nanoparticles made of gold, silver, or other diamagnetic metals remains obscure despite a large body of experimental and theoretical studies. Whereas many studies have endeavoured at finding correlations between magnetism and nanoparticle size or ligand coating, none so far has attempted at investigating the role of core crystallinity. We have irradiated gold nanoparticles with energetic neutrons or protons with the aim of nucleating lattice defects in the crystalline cores. Comparison of the magnetic behaviours before and after irradiation demonstrates clearly that the presence of defects in the crystalline lattice of the nanoparticles cores contributes efficiently to their magnetism

Playing with Pt II and Zn II Coordination to Obtain Luminescent Metallomesogens

International audienceBlue-green luminescent terpyridine-containing Pt II and Zn II complexes are reported. Equipped with lipophilic gallate units, which act as monodentate ancillary coordinating ligands and/or as anions, they display low-temperature mesomorphic properties (lamello-columnar and hexagonal mesophases for Pt II and Zn II complexes, respectively). The mesomorphic properties were investigated by polarised optical microscopy, differential scanning calorimetry, thermogravimetric analysis and X-ray scattering of bulk materials and oriented thin films. The model of self-assembly into the lamello-columnar phase of the Pt II complex has been described in detail. The optical properties of the complexes were investigated in the liquid and condensed liquid crystalline states, highlighting the delicate balance between the role of the metal in determining the type of excited state responsible for the emission, and the role of the ancillary ligand in driving intermolecular interactions for proper mesophase formation

Very intense polarized emission in self-assembled room temperature metallomesogens based on Zn(ii) coordination complexes: an experimental and computational study

International audienceThree room-temperature metallomesogens based on Zn(II) cations pentacoordinated by different chelating N^N^N terpyridines and two monodentate gallate co-ligands were designed and synthesized. Depending on the terpyridine ligand's tip functionality, the complexes self-assemble into either a 3D hexagonal mesophase or into a columnar hexagonal mesophase. A systematic study between the structure (molecular architecture, arrangement of the molecules and columns, and chains in both types of mesophases) and photophysical properties (emission maxima and yields, lifetimes of the excited states in the mesophase), correlated with investigations of single molecules in solution, was conducted. Remarkably, one complex exhibited a record quantum yield of 95.0% in solution, while in the mesophase, despite quenching due to the radiative deactivation from the ILCT state, still retained a considerable emission yield of ϕ = 20.2%. The polarized emission of an oriented film, determined for the first time in columnar metallomesogens, shows a dichroic emission ratio (I||/I⊥) of 1.30. DFT and TDDFT computational studies confirmed the origin of the observed fluorescence anisotropy from the transition dipole moment oriented along the C2 symmetry axis of the molecule combined with a high level of order in the 3D mesophase