Lipophilic nucleic acids — A flexible construction kit for organization and functionalization of surfaces

Lipophilic nucleic acids have become a versatile tool for structuring and functionalization of lipid bilayers and biological membranes as well as cargo vehicles to transport and deliver bioactive compounds, like interference RNA, into cells by taking advantage of reversible hybridization with complementary strands. This contribution reviews the different types of conjugates of lipophilic nucleic acids, and their physicochemical and self-assembly properties. Strategies for choosing a nucleic acid, lipophilic modification, and linker are discussed. Interaction with lipid membranes and its stability, dynamic structure and assembly of lipophilic nucleic acids upon embedding into biological membranes are specific points of the review. A large diversity of conjugates including lipophilic peptide nucleic acid and siRNA provides tailored solutions for specific applications in bio- and nanotechnology as well as in cell biology and medicine, as illustrated through some selected examples.     

Nanostructures for magnetically triggered release of drugs and biomolecules

Specific targeting and controlled release are crucial factors in the administration of drugs and therapeutic biomolecules. It has been shown that drug delivery systems can significantly benefit of the introduction of superparamagnetic nanoparticles in terms of both targeting and controlled release. Magnetic gradients can be used to target therapeutics to specific regions, while alternating magnetic fields produce frequency-dependent effects at the nanoparticle level. This review reports on the latest developments of multifunctional systems based on magnetic nanoparticles where the release of drugs and/or biomolecules is triggered by the application of an external magnetic field. The potentials of these systems are presented through examples in the fields of surface functionalized magnetic nanoparticles, magnetic polymer nanocomposites and magnetoliposomes. Recent results suggest the importance of integrating multiple functions within a single nanostructured device in order to successfully transport, localize and release drugs and biomolecules.     

Regioselective Generation of Single‐Site Iridium Atoms and Their Evolution into Stabilized Subnanometric Iridium Clusters in MWW Zeolite

Preparation of supported metal catalysts with uniform particle size and coordination environment is a challenging and important topic in materials chemistry and catalysis. In this work, we report the regioselective generation of single‐site Ir atoms and their evolution into stabilized subnanometric Ir clusters in MWW zeolite, which are located at the 10MR window connecting the two neighboring 12MR supercages. The size of the subnanometric Ir clusters can be controlled by the post‐synthesis treatments and maintain below 1 nm even after being reduced at 650 °C, which cannot be readily achieved with samples prepared by conventional impregnation methods. The high structure sensitivity, size‐dependence, of catalytic performance in the alkane hydrogenolysis reaction of Ir clusters in the subnanometric regime is evidenced.     

Dynamic Complex‐to‐Complex Transformations of Heterobimetallic Systems Influence the Cage Structure or Spin State of Iron(II) Ions

Two new heterobimetallic cages, a trigonal‐bipyramidal and a cubic one, were assembled from the same mononuclear metalloligand by adopting the molecular library approach, using iron(II) and palladium(II) building blocks. The ligand system was designed to readily assemble through subcomponent self‐assembly. It allowed the introduction of steric strain at the iron(II) centres, which stabilizes its paramagnetic high‐spin state. This steric strain was utilized to drive dynamic complex‐to‐complex transformations with both the metalloligand and heterobimetallic cages. Addition of sterically less crowded subcomponents as a chemical stimulus transformed all complexes to their previously reported low‐spin analogues. The metalloligand and bipyramid incorporated the new building block more readily than the cubic cage, probably because the geometric structure of the sterically crowded metalloligand favours the cube formation. Furthermore it was possible to provoke structural transformations upon addition of more favourable chelating ligands, converting the cubic structures into bipyramidal ones.     

Synthesis,Modification, and Biological Evaluation of a Library of Novel Water-Soluble Thiopyridone-Based Organometallic Complexes and Their Unexpected (Biological) Behavior

A series of 16 dinuclear thiopyridone-based organometallics with excellent water solubility, increased stability and remarkable cytotoxicity were synthesized and characterized. The complexes of this work formed dimeric species featuring a double positive charge in polar protic solvents, accounting for their outstanding solubility in aqueous solution. Most of them displayed higher antiproliferative activity than their parental thiomaltol complex, with unexpected cytotoxicity trends depending on the employed metal center, ligand modification, and cell line. Insights into their behavior in biological systems were gathered by means of amino-acid interaction studies, cytotoxicity tests in 3D spheroid models, laser ablation, cellular accumulation measurements, as well as cell cycle experiments.     

The role of weak hydrogen bonds in chiral recognition

Chiral recognition has been studied in neutral or ionic weakly bound complexes isolated in the gas phase by combining laser spectroscopy and quantum chemical calculations. Neutral complexes of the two enantiomers of lactic ester derivatives with chiral chromophores have been formed in a supersonic expansion. Their structure has been elucidated by means of IR-UV double resonance spectroscopy in the 3 μm region. In both systems described here, the main interaction ensuring the cohesion of the complex is a strong hydrogen bond between the chromophore and methyl-lactate. However, an additional hydrogen bond of much weaker strength plays a discriminative role between the two enantiomers. For example, the 1:1 heterochiral complex between R-(+)-2-naphthyl-ethanol and S-(+) methyl-lactate is observed, in contrast with the 1:1 homochiral complex which lacks this additional hydrogen bond. On the other hand, the same kind of insertion structures is formed for the complex between S-(±)-cis-1-amino-indan-2-ol and the two enantiomers of methyl-lactate, but an additional addition complex is formed for R-methyl-lactate only. This selectivity rests on the formation of a weak CHπ interaction which is not possible for the other enantiomer. The protonated dimers of Cinchona alkaloids, namely quinine, quinidine, cinchonine and cinchonidine, have been isolated in an ion trap and studied by IRMPD spectroscopy in the region of the ν(OH) and ν(NH) stretch modes. The protonation site is located on the alkaloid nitrogen which acts as a strong hydrogen bond donor in all the dimers studied. While the nature of the intermolecular hydrogen bond is similar in the homochiral and heterochiral complexes, the heterochiral complex displays an additional weak CHO hydrogen bond located on its neutral part, which results in slightly different spectroscopic fingerprints in the ν(OH) stretch region. This first spectroscopic evidence of chiral recognition in protonated dimers opens the way to the study of the complexes of Cinchona alkaloids involved in enantioselective catalysis. These examples show how secondary hydrogen bonds controlled by stereochemical factors govern molecular recognition processes.     

Encapsulation versus aggregation of metal-organic cages controlled by guest size variation

The strength and mode of binding (inside vs outside) of bisanionic guest molecules to a cationic, self-assembled metal-organic cage depend on their size and the stoichiometry of the addition. Herein we show that the composition of the solid/liquid phase of a heterogeneous system can be kinetically controlled by the order of the addition of two different guest compounds.     

Global Existence of Large BV Solutions in a Model of Granular Flow

In this paper we analyze a set of equations proposed by Hadeler and Kuttler [20 Hadeler , K. P. , Kuttler , C. ( 1999 ). Dynamical models for granular matter . Granular Matter 2 : 9 – 18 . [Google Scholar]], describing the flow of granular matter in terms of the heights of a standing layer and of a moving layer. By a suitable change of variables, the system can be written as a 2 × 2 hyperbolic system of balance laws, which we study in the one-dimensional case. The system is linearly degenerate along two straight lines in the phase plane, and therefore is weakly linearly degenerate at the point of the intersection. The source term is quadratic, consisting of product of two quantities, which are transported with strictly different speeds. Assuming that the initial height of the moving layer is sufficiently small, we prove the global existence of entropy-weak solutions to the Cauchy problem, for a class of initial data with bounded but possibly large total variation.     

Conditions for equivalence between Mallows distance and convergence to stable laws

Convergence in Mallows distance is of particular interest when heavy-tailed distributions are considered. For 1≦α<2, it constitutes an alternative technique to derive central limit type theorems for non-Gaussian α-stable laws. In this note, we further explore the connection between Mallows distance and convergence in distribution. Conditions for their equivalence are presented.     

Infrared-Assisted Synthesis of Prebiotic Glycine

A novel approach has been developed to synthesize complex organic molecules (COMs) relevant to prebiotic chemistry, using infrared (IR) radiation to trigger the reaction. An original laboratory reactor working at low gas density and using IR irradiation was developed. In this way, glycine, the simplest brick of life, has been synthesized by assisting ion–molecule reaction with IR laser light. The ion-molecule complex constituted by acetic acid and hydroxylamine was formed in a mass spectrometer reactor and then irradiated with IR photons. As photoproducts, we obtained both glycine structures and some of its isomers. Anharmonic vibrational frequency calculations and fragmentation dynamics simulations allow for a better interpretation of the experimental data. This novel approach can be now extended to study other new synthetic pathways responsible for the formation of further COMs also with potential prebiotic relevance.