Access to β,γ-diamino acids. Application to the synthesis of 3-deoxyaminostatine

The synthesis of orthogonally protected diastereo- and enantiopure β,γ-diamino acids starting from natural α-amino acids is described, as well as its application to the synthesis of fully protected 3-deoxyaminostatine.     

Nano-organization of amylose-b-polystyrene block copolymer films doped with bipyridine

This paper discusses the self-assembly of rod-coil amylose-b-polystyrene (Mal-b-PS) block copolymer thick and thin films. The nano-organization falls in an interdomain spacing d of about 10 nm, much smaller than flexible-flexible petrol block copolymer systems. Additionally, hydrogen-bonding interactions between carbohydrate rods (amylose) and 4',4-bipyridine (bipy) molecules induces phase transitions. Indeed, adding bipy in maltooctadecaose-block-polystyrene (Mal18-b-PS) copolymers results, at room temperature, in the formation of a lamellar phase having Mal18 bipy-rich nanodomains instead of hexagonal close-packed (HCP) of cylinders made of Mal18, whereas a coexistence of Mal7bipy-rich cylindrical and spherical nanodomains are formed from maltoheptaose-b-polystyrene (Mal7-b-PS) copolymers instead of a poorly organized array of Mal7-based cylinders. On heating, the Mal7bipy-b-PS system shows more rich phase behavior as compared to the Mal7-b-PS one due to weakening of hydrogen bonding with temperature. Such a system is of great interest in developing active layers in light-emitting diodes (LEDs) or in photovoltaic cells to realize devices with an optimal structure, that is, having large interface area and domain size with similar exciton diffusion length (10 nm).     

Reorganization energy and pre-exponential factor from temperature-dependent experiments in electron transfer reactions. A typical example: the reduction of tert-nitrobutane

The electrochemical one-electron reduction of tert-nitrobutane in N,N'-dimethylformamide is a typical reaction, which has been shown to follow the quadratic model of outersphere electron transfer. The variation of the standard rate constant with temperature allows a separate determination of the reorganization energy and of the pre-exponential factor. The value found for the former is in agreement with independent estimates of the solvent and intramolecular reorganization energies. The value of the latter, significantly larger than the collision frequency, implies that the reaction starts to take place before close contact with the electrode surface.     

The therapeutic potential of metal-based antimalarial agents: implications for the mechanism of action

Despite recent encouraging advances against the disease, malaria remains a major public health problem affecting almost half a billion people and killing almost a million per annum. Due to a short arsenal of efficient antimalarial agents and the frequent appearance of resistance to the drugs in current use, which consequently reduce our means to treat patients, there is a very urgent and continuous need to develop new compounds. This perspective outlines a unique strategy for that purpose through the development of metal-based antimalarial agents. The examples presented here illustrate an attractive alternative to classical drugs.     

Modification of RAFT‐polymers via thiol‐ene reactions: A general route to functional polymers and new architectures

An investigation into the aminolysis of ω‐end groups of RAFT‐polymers and simultaneous thiol‐ene reactions with ene‐bearing compounds is described. Three different polymers, P(MMA), P(HPMA), and P(NIPAAm), with low PDIs were synthesized using dithiobenzoate and trithiocarbonate RAFT agents. P(NIPAAm) synthesized with trithiocarbonate RAFT agent and P(HPMA) synthesized with dithiobenzoate RAFT agent were both functionalized with a methacrylate‐modified mannose and a maleimide‐modified biotin via one‐pot simultaneous aminolysis and thiol‐ene reactions with product yields above 85%. The presence of ene‐compounds during aminolysis was shown to prevent the formation of disulfide interchain crosslinking. Using the same approach, P(MMA), P(HPMA), and P(NIPAAm) were converted to (meth)acrylate macromonomers with high yields (>80%). In the case of P(MMA), the simultaneous aminolysis and thiol‐ene addition prevented any intrachain side reactions, i.e., thiolactone formation. New architectures such as graft and block copolymers were successfully generated from the macromonomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3773–3794, 2009     

A Versatile 3D and 4D Printing System through Photocontrolled RAFT Polymerization

Reversible addition‐fragmentation chain‐transfer (RAFT) polymerization is a valuable tool for synthesizing macromolecules with controlled topologies and diverse chemical functionalities. However, the application of RAFT polymerization to additive‐manufacturing processes has been prevented due to the slow polymerization rates of typical systems. In this work, we developed and optimized a rapid visible (green) light mediated RAFT polymerization process and applied it to an open‐air 3D printing system. The reaction components are non‐toxic, metal free and environmentally friendly, which tailors these systems toward biomaterial fabrication. The inclusion of RAFT agent in the photosensitive resin provided control over the mechanical properties of 3D printed materials and allowed these materials to be post‐functionalized after 3D printing. Additionally, photoinduced spatiotemporal control of the network structure provided a one‐pass approach to 4D printed materials. This RAFT‐mediated 3D and 4D printing process should provide access to a range of new functional and stimuli‐responsive materials.     

Seeing the Light: Advancing Materials Chemistry through Photopolymerization

The application of photochemistry to polymer and material science has led to the development of complex yet efficient systems for polymerization, polymer post‐functionalization, and advanced materials production. Using light to activate chemical reaction pathways in these systems not only leads to exquisite control over reaction dynamics, but also allows complex synthetic protocols to be easily achieved. Compared to polymerization systems mediated by thermal, chemical, or electrochemical means, photoinduced polymerization systems can potentially offer more versatile methods for macromolecular synthesis. We highlight the utility of light as an energy source for mediating photopolymerization, and present some promising examples of systems which are advancing materials production through their exploitation of photochemistry.     

Molecular approach to catalysis of electrochemical reaction in porous films

Current attempts to bridge the fields of what is conventionally called ‘electrocatalysis’ and of molecular catalysis of electrochemical reactions are surveyed and discussed. It amounts in many cases to ‘heterogenize’ molecular catalytic systems. Information on the meso- to nanostructures of the resulting catalytic films forms the basis of the understanding of new modes of transport of the reactants (catalysts, substrates and cosubstrates, products) that may govern the mechanistic competitions and consequently selectivity. Efforts to adapt benchmarking procedures developed in homogeneous molecular catalysis (catalytic Tafel plots) should be encouraged, taking into account, as additional factors, the transport of electrons and reacting species (including gases) through the catalytic system.     

Numerical Prediction of Two-Phase Flow through a Tube Bundle Based on Reduced-Order Model and a Void Fraction Correlation

Predicting the void fraction of a two-phase flow outside of tubes is essential to evaluate the thermohydraulic behaviour in steam generators. Indeed, it determines two-phase mixture properties and affects two-phase mixture velocity, which enable evaluating the pressure drop of the system. The two-fluid model for the numerical simulation of two-phase flows requires interaction laws between phases which are not known and/or reliable for a flow within a tube bundle. Therefore, the mixture model, for which it is easier to implement suitable correlations for tube bundles, is used. Indeed, by expressing the relative velocity as a function of slip, the void fraction model of Feenstra et al. and Hibiki et al. developed for upward cross-flow through horizontal tube bundles is introduced and compared. With the method suggested in this paper, the physical phenomena that occur in tube bundles are taken into consideration. Moreover, the tube bundle is modelled using a porous media approach where the Darcy–Forchheimer term is usually defined by correlations found in the literature. However, for some tube bundle geometries, these correlations are not available. The second goal of the paper is to quickly compute, in quasi-real-time, this term by a non-intrusive parametric reduced model based on Proper Orthogonal Decomposition. This method, named Bi-CITSGM (Bi-Calibrated Interpolation on the Tangent Subspace of the Grassmann Manifold), consists in interpolating the spatial and temporal bases by ITSGM (Interpolation on the Tangent Subspace of the Grassmann Manifold) in order to define the solution for a new parameter. The two developed methods are validated based on the experimental results obtained by Dowlati et al. for a two-phase cross-flow through a horizontal tube bundle.