Reconciling low- and high-salt solution behavior of sulfobetaine polyzwitterions

We investigate the water-solubility upon salt additions, of homogeneous families of sulfobetaine-based polyzwitterions. These polymers bear both positive ammonium, and negative sulfonate charges on each monomer and as a result present an upper critical solution temperature (UCST) in the 0-100 degrees C temperature range. Two chemistries are investigated, with either a carboxylate-carrying function (SPE) or an amido-carrying one (SPP). In agreement with the literature published on pSPEs, we find that an addition of simple salts improves the water-solubility of pSPEs, as well as that of pSPPs, yet only once a threshold concentration of added salt has been reached in the solution. We verify using scaling arguments that the onset of solubility promotion, corresponds exactly to the complete screening of the attraction between positive and negative charges inside a polyzwitterionic coil. On the contrary, for salt concentrations smaller than the threshold concentration, we observe that an addition of salt can be adverse to the solubility of polyzwitterions, depending on the degree of polymerization, the type of salt, and the type of zwitterionic motive. Thanks to zeta-potential measurements and systematic variations of these three parameters, we demonstrate, in agreement with theoretical prediction, that this molecular weight-dependent enhanced solubility at small salt concentrations is due to charge asymmetry resulting from partial hydrolysis, combined with specific interactions between salts and zwitterion constituents, evidencing the complexity of the solution behavior of these macromolecules. We thereby reconcile the different behaviors in the domains of low- and high-salinity.     

Ab initio ONIOM-molecular dynamics (MD) study on the deamination reaction by cytidine deaminase

We applied the ONIOM-molecular dynamics (MD) method to the hydrolytic deamination of cytidine by cytidine deaminase, which is an essential step of the activation process of the anticancer drug inside the human body. The direct MD simulations were performed for the realistic model of cytidine deaminase by calculating the energy and its gradient by the ab initio ONIOM method on the fly. The ONIOM-MD calculations including the thermal motion show that the neighboring amino acid residue is an important factor of the environmental effects and significantly affects not only the geometry and energy of the substrate trapped in the pocket of the active site but also the elementary step of the catalytic reaction. We successfully simulate the second half of the catalytic cycle, which has been considered to involve the rate-determining step, and reveal that the rate-determining step is the release of the NH3 molecule.     

Methods to Analyse the Texture of Alginate Aerogel Microspheres

Nitrogen adsorption at 77 K has been applied to the study of the texture of alginate aerogel microspheres obtained by CO₂ supercritical drying of alcogels. The limited volume shrinkage suggests that the aerogels preserve the texture of the hydrogels. Alginate aerogels presents a N₂ adsorption at small pressure higher than reference non-porous silica, to be attributed to the polarity of the surface or to a small microporous volume. The aggregated nanobead strings of the guluronic-rich gels accounts for a significant mesoporosity. The N₂ adsorption results correspond to electron microscopy observations for features smaller than 50 nm.     

Acidity of Alginate Aerogels Studied by FTIR Spectroscopy of Probe Molecules

Supercritical drying of alginate gels is an efficient way to prepare aerogels with high surface area (>300 m² · g⁻¹). FTIR spectroscopy allows to monitor the adsorption of NH₃ from the gas phase onto the acid sites of the alginate. Free carboxylic groups are effective Brønsted sites, whereas the divalent cations used in the ionotropic gelation present the properties of Lewis sites. The ratio between Brønsted and Lewis sites provides infomation on the role of pH in alginate gelation and suggests that non-buffered gelation by transition-metal cations is a mixed ionotropic-acid process.     

Continuous Flow Synthesis of Propofol

Herein, we report a continuous flow process for the synthesis of 2,6-diisopropylphenol—also known as Propofol—a short-acting intravenous anesthesia, widely used in intensive care medicine to provide sedation and hypnosis. The synthesis is based on a two-step procedure: a double Friedel–Crafts alkylation followed by a decarboxylation step, both under continuous flow.     

Finite element modelling of cold drawing for high-precision tubes

Cold tube drawing is a metal forming process that allows manufacturers to produce high-precision tubes. The dimensions of the tube are reduced by pulling it through a conical converging die with or without inner tool. In this study, finite element modelling has been used to give a better understanding of the process.This paper presents a model that predicts the final dimensions of the tube with very high accuracy. It is validated thanks to experimental tests. Moreover, five studies are performed with this model, such as investigating the influence of the die angle on the drawing force or the influence of relative thickness on tube deformation.     

Shadowgraphy investigation of laser-induced forward transfer: Front side and back side ablation of the triazene polymer sacrificial layer

Thin films of a photodecomposible triazene polymer are used as sacrificial layer for the micro-deposition of sensitive materials by laser-induced forward transfer. To understand the ablation process of this sacrificial layer, the ultraviolet laser ablation of triazene films was investigated by time-resolved shadowgraphy. Irradiation from the film side shows a complete decomposition into gaseous fragments, while ablation through the substrate causes ejection of a solid flyer of polymer. The occurence of the flyer depends on the film thickness as well as on the applied fluence, and a compact flyer is obtaind when these two parameters are optimized.     

Laser ablation of energetic polymer solutions: effect of viscosity and fluence on the splashing behavior

Laser plasma thrusters are a new kind of propulsion system for small satellites, and work with the thrust created by the laser ablation of a target. Liquid polymer solutions are very promising fuels for such systems, provided that no splashing of the target occurs, because ejection of droplets strongly decreases the performances of the system. We have investigated the nanosecond infrared laser ablation of glycidyl azide polymer solutions containing carbon nanoparticles as absorber. Shadowgraphy imaging revealed two cases, namely splashing regime and solid-like behavior. The transition between both regimes depends on the viscosity of the solution and on the laser fluence, and is explained by the recoil force acting on the target. Appropriate conditions to avoid splashing were identified, showing that this liquid polymer solution is a suitable fuel for laser plasma thrusters.     

Facile Synthesis of Diastereoisomerically and Optically Pure 2‐Substituted Hexahydro‐1H‐pyrrolizin‐3‐ones

We report a short synthetic route that provides optically active 2‐substituted hexahydro‐1H‐pyrrolizin‐3‐ones in four steps from commercially available Boc (tert‐but(oxy)carbonyl))‐protected proline. Diastereoisomers (−)‐ 11 and (−)‐ 12 were assembled from the proline‐derived aldehyde (−)‐ 8 and ylide 9 via a Wittig reaction and subsequent catalytic hydrogenation (Scheme 3). Cleavage of the Boc protecting group under acidic conditions, followed by intramolecular cyclization, afforded the desired hexahydro‐1H‐pyrrolizinones (−)‐ 1 and (+)‐ 13 . Applying the same protocol to ylide 19 afforded hexahydro‐1H‐pyrrolizinones (−)‐ 25 and (−)‐ 26 (Scheme 5). The absolute configuration of the target compounds was determined by a combination of NMR studies (Figs. 1 and 2) and X‐ray crystallographic analysis (Fig. 3).     

Reactions associated with ionization in water: a direct ab initio dynamics study of ionization in (H2O)17

Quasiclassical ab initio simulations of the ionization dynamics in a (H(2)O)(17) cluster, the first water cluster that includes a fourfold coordinated (internally solvated) water molecule, have been carried out to obtain a detailed picture of the elementary processes and energy redistribution induced by ionization in a model of aqueous water. General features observable from the simulations are the following: (i) well within 100 fs following the ionization, one or more proton transfers are seen to take place from the "ionized molecule" to neighboring molecules and beyond, forming a hydronium ion and a hydroxyl radical; (ii) two water molecules close to the ionized water molecule play an important role in the reaction, in what we term a "reactive trimer." The reaction time is gated by the encounter of the ionized water molecule with these two neighboring molecules, and this occurs anytime between 10 and 50 fs after the ionization. The distances of approach between the ionized molecule and the neighboring molecules indeed display best the time characteristics of the transfer of a proton, and thus of the formation of a hydronium ion and a OH radical. These findings are consistent with those for smaller cyclic clusters, albeit the dynamics of the proton transfer displays more varieties in the larger cluster than in the small cyclic clusters. We used a partitioning scheme for the kinetic energy in the (H(2)O)(17) system that distinguishes between the reactive trimer and the surrounding "medium." The analysis of the simulations indicates that the kinetic energy of the surrounding medium increases markedly right after the event of ionization, a manifestation of the local heating of the medium. The increase in kinetic energy is consistent with a reorganization of the surrounding medium, electrostatically forced in a very short time by the water cation and in a longer time by the formation of the hydronium ion.