Molecular recognition controls the organization of mixed self-organized bis-urea-based mineralization templates for CaCO(3)

To investigate the role and importance of nondirectional electrostatic interactions in mineralization, we explored the use of Langmuir monolayers in which the charge density can be tuned using supramolecular interactions. It is demonstrated that, in mixed Langmuir monolayers of bis-ureido surfactants containing oligo(ethylene oxide) and ammonium head groups associated with matching or nonmatching spacers between the two urea groups, the organization is controlled by molecular recognition. These different organizations of the molecules lead to different nucleation behavior in the mineralization of calcium carbonate. The formation of modified calcite and vaterite crystals was induced selectively by different phases of mixed monolayers, and they were characterized by SEM, TEM, and SAED. To understand the influence of the mixed Langmuir monolayers on the crystallization process, we studied the mixtures by means of (pi-A) isotherms and Brewster angle microscopy observations. Infrared reflection-absorption spectroscopy experiments were also performed on Langmuir-Schaefer films. From these results, we conclude that the local organization of the two systems discussed here gives rise to differences in both charge density and flexibility that together determine not only polymorph selection and the nucleation face but also the morphology of the resulting crystals.     

Template adaptability is key in the oriented crystallization of CaCO3

In CaCO3, biomineralization nucleation and growth of the crystals are related to the presence of carboxylate-rich proteins within a macromolecular matrix, often with organized beta-sheet domains. To understand the interplay between the organic template and the mineral crystal it is important to explicitly address the issue of structural adaptation of the template during mineralization. To this end we have developed a series of self-organizing surfactants (1-4) consisting of a dodecyl chain connected via a bisureido-heptylene unit to an amino acid head group. In Langmuir monolayers the spacing of these molecules in one direction is predetermined by the hydrogen-bonding distances between the bis-urea units. In the other direction, the intermolecular distance is determined by steric interactions introduced by the side groups (-R) of the amino acid moiety. Thus, by the choice of the amino acid we can systematically alter the density of the surfactant molecules in a monolayer and their ability to respond to the presence of calcium ions. The monolayer films are characterized by surface pressure-surface area (pi-A) isotherms, Brewster angle microscopy, in-situ synchrotron X-ray scattering at fixed surface area, and also infrared reflection absorption spectroscopy (IRRAS) of films transferred to solid substrates. The developing crystals are studied with scanning and transmission electron microscopy (SEM, TEM), selected area electron diffraction (SAED), and crystal modeling. The results demonstrate that although all compounds are active in the nucleation of calcium carbonate, habit modification is only observed when the size of the side group allows the molecules to rearrange and adapt their organization in response to the mineral phase.     

Zirconium nitrides deposited by dual ion beam sputtering: physical properties and growth modelling

Zirconium nitrides reveal interesting optical and electrical properties which highly depend on the nitrogen stoichiometry. Indeed, the material exhibits a transition from the stable metallic ZrN (optical index for bulk at 633 nm: N=0.5−i3.2) to the metastable semi-transparent insulating Zr₃N₄ (N=3.2−i0.4). This work deals with the elaboration of homogeneous ZrN-like and Zr₃N₄-like coatings. These have been prepared using reactive Dual Ion Beam Sputtering (DIBS) using a Zr target and N₂ or N₂+Ar reactive gas. The influence of different elaboration parameters (ion energy, gas composition of the reactive beam and substrate temperature) on the nitrides composition and on their optical and electrical properties was particularly studied. A model was proposed to explain the influence of energy and temperature on the nitrogen composition. The nitrogen stoichiometry was shown to be controlled by a competitive mechanism between implantation of excess nitrogen amount in the subsurface and their elimination by exodiffusion. The first phenomenon is mainly controlled by the ion energy whereas the second one is enhanced by a high temperature and a high irradiation defects density. Therefore, the Zr₃N₄-like nitrides were obtained with low temperature and high energy (200 eV) conditions whereas high temperature and low energy led to ZrN-like materials.     

Dynamics of excited hydroxyl radicals in hydrogen-based mixtures behind reflected shock waves

The chemiluminescence originating from OH¹, the excited hydroxyl radical, is one of the most extensively used diagnostics to characterize auto-ignition delay time of gaseous mixtures behind reflected shock waves. We have carried out new experiments and modeling of this diagnostic as well as analyzed previous results for hydrogen-based mixtures, including H₂–O₂, H₂O₂–H₂O, H₂–N₂O and H₂–O₂–N₂O. The experiments were analyzed with a detailed chemical reaction model which included mechanisms for OH¹ creation, quenching and emission. Simulations of the reaction behind reflected shock waves were used to predict OH¹ emission profiles and compare this with measured results as well as profiles of temperature and the ground state concentrations of OH. Analysis of OH¹ rates of progress demonstrates that a quasi-steady state approximation is applicable and an algebraic model for OH¹ concentrations can be derived that relates emission to the product of concentrations of O and H for H₂–O₂ and H₂O₂ mixtures and an additional contribution by the product of H and N₂O when N₂O is an oxidizer.     

Immobilized antibody on a hybrid organic–inorganic monolith: Capillary immunoextraction coupled on-line to nanoLC-UV for the analysis of microcystin-LR

A complete characterization of a highly selective miniaturized immunosorbent (mIS) coupled on-line to nanoLC-UV is presented. A hybrid organic–inorganic monolith was synthesized in a 100 μm i.d. capillary via a sol–gel process using tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) as precursors. After an activation step, monoclonal antibodies specific for microcystin-LR (MC-LR), the model molecule, were grafted on this porous media. The resulting mIS was coupled on-line to nanoLC-UV. Specific retention of MC-LR on the mIS was demonstrated with extraction recovery above 70% in pure water. Synthesis and grafting were repeated leading to reproducible extraction yields. The capacity of one of the prepared sorbents was determined as being 375 pg. This miniaturized device was then applied to the selective extraction of MC-LR from blue-green algae extracts and revealed to be effective in isolating MC-LR from these complex samples thus improving the reliability of its analysis at the trace level.     

Protonation of lipids impacts the supramolecular and biological properties of their self-assembly

We assessed in this work how a chemical structure difference could influence a supramolecular organization and then its biological properties. In our case study, we considered two amphiphilic lipidic gene vectors. The chemical difference was situated on their hydrophilic part which was either a pure neutral thiourea head or a mixture of three thiourea function derivatives, thiourea, iminothiol, and charged iminothiol. This small difference was obtained thanks to the last chemical deprotection conditions of the polar head hydroxyl groups. Light, neutron, and X-ray scattering techniques have been used to investigate the spatial structure of the liposomes and lipoplexes formed by the lipids. The chemical structure difference impacts the supramolecular assemblies of the lipids and with DNA as shown by fluorescence correlation spectroscopy (FCS), X-ray, and neutron scattering. Hence the structures formed were found to be highly different in terms of liposomes to DNA ratio and size and polydispersity of the aggregates. Finally, the transfection and internalization results proved that the differences in the structure of the lipid aggregates fully affect the biological properties of the lipopolythiourea compounds. The lipid containing three functions is a better gene transfection agent than the lipid which only contains one thiourea moiety. As a conclusion, we showed that the conditions of the last chemical step can influence the lipidic supramolecular structure which in turn strongly impacts their biological properties.     

2D assembly of non-interacting magnetic iron oxide nanoparticles via"click" chemistry

Azide-terminated magnetic iron oxide nanoparticles have been assembled in 2D on alkyne-terminated self-assembled monolayers (SAMs) by the copper(i) catalyzed alkyne-azide cycloaddition (CuAAC) "click" reaction; the kinetics of the reaction is an important parameter to control the interparticle distance and thus the dipolar interactions.     

Identification of the nitroaromatic explosives in post-blast samples by online solid phase extraction using molecularly imprinted silica sorbent coupled with reversed-phase chromatography

In a previous work, a molecularly imprinted silica (MIS) sorbent was synthesized for the selective extraction of nitroaromatic explosives from real samples. This MIS packed in a cartridge was used for an off-line solid phase extraction procedure mainly based on hydrophobic and π–π interactions. In this work, the MIS was packed in a precolumn to be connected online with a reversed-phase LC system and a diode array detector. For this, the chromatographic conditions were first studied to obtain the separation of 1,3-dinitrobenzene, 1,3,5-trinitrobenzene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, 2,4,6-trinitrotoluene, and tetryl. An optimized procedure dedicated to the selective treatment of aqueous samples was then developed with the MIS for the simultaneous extraction of the nitroaromatic compounds commonly used as explosives. Finally, the four nitrotoluenes were selectively extracted and determined simultaneously with extraction recoveries higher than 90 % using the online device composed of the MIS coupled with a diphenyl chromatographic column. The potential of this sorbent was highlighted by its use for the cleanup of simulated post-blast samples.