The "click" trick: Many reactions are classified as click reactions even though some are limited to certain applications. Thus, there is danger that the term "click" will become meaningless over time and simply a synonym for "successful". To prevent this, the original click criteria are evaluated in this Essay specifically for the synthetic polymer field and a set of criteria are specified that distinguishes click from other efficient reactions. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

"Clicking" polymers or just efficient linking: What is the difference?

Nanotechnology has attracted much attention because it possesses many advantages to engineer new organized nanomaterials and endow them with improved performance. In recent decades, mesoporous silica nanoparticles (MSNs) have been proven to be excellent solid supports owing to their superior properties. Molecular and supramolecular switches have also received a lot of interest in the past decade on account of their unique features. Materials derived from the combination of MSNs as solid supports and molecular/supramolecular switches as movable entities have emerged in the literature and are playing prominent roles in materials science nowadays. Thus, in this review, we chose to gather significant and typical examples of intelligent materials, which comprise MSNs surface-immobilized with molecular and supramolecular switches, and overview their wide applications in many fields such as controlled release of cargo molecules for disease therapy and cell imaging. Utilizing the switching ability of molecular and supramolecular switches, smart hybrid nanomaterials are endowed with intelligently controllable properties in response to a variety of external stimuli such as pH variation, enzyme, light irradiation, temperature, redox, magnetic field, competition, and ultrasound. In order to rationalize the presentation concisely, we will introduce molecular switches and supramolecular switches cooperated with MSNs based on their different features and the actuations they are responsive for.

Molecular and supramolecular switches on mesoporous silica nanoparticles.

Mesoporous solid bases are extremely desirable in green catalytic processes, due to their advantages of accelerated mass transport, negligible corrosion, and easy separation. Great progress has been made in mesoporous solid bases in the last decade. In addition to their wide applications in the catalytic synthesis of organics and fine chemicals, mesoporous solid bases have also been used in the field of energy and environmental catalysis. Development of mesoporous solid bases is therefore of significant importance from both academic and practical points of view. In this review, we provide an overview of the recent advances in mesoporous solid bases, which is basically grouped by the support type and each category is illustrated with typical examples. Cooperative catalysts derived from the incorporation of additional functionalities (i.e. acid and metal) into mesoporous solid bases are also included. The fundamental principles of how to design and fabricate basic materials with mesostructure are highlighted. The mechanism of the formation of basic sites in different mesoporous systems is discussed as well.

Design and fabrication of mesoporous heterogeneous basic catalysts

Silica-nanosphere-based organic–inorganic hybrid nanomaterials: synthesis, functionalization and applications in catalysis

The discovery of bioactive glasses (BGs) in the late 1960s by Larry Hench et al. was driven by the need for implant materials with an ability to bond to living tissues, which were intended to replace inert metal and plastic implants that were not well tolerated by the body. Among a number of tested compositions, the one that later became designated by the well-known trademark of 45S5 Bioglass® excelled in its ability to bond to bone and soft tissues. Bonding to living tissues was mediated through the formation of an interfacial bone-like hydroxyapatite layer when the bioglass was put in contact with biological fluids in vivo. This feature represented a remarkable milestone, and has inspired many other investigations aiming at further exploring the in vitro and in vivo performances of this and other related BG compositions. This paradigmatic example of a target-oriented research is certainly one of the most valuable contributions that one can learn from Larry Hench. Such a goal-oriented approach needs to be continuously stimulated, aiming at finding out better performing materials to overcome the limitations of the existing ones, including the 45S5 Bioglass®. Its well-known that its main limitations include: (i) the high pH environment that is created by its high sodium content could turn it cytotoxic; (ii) and the poor sintering ability makes the fabrication of porous three-dimensional (3D) scaffolds difficult. All of these relevant features strongly depend on a number of interrelated factors that need to be well compromised. The selected chemical composition strongly determines the glass structure, the biocompatibility, the degradation rate, and the ease of processing (scaffolds fabrication and sintering). This manuscript presents a first general appraisal of the scientific output in the interrelated areas of bioactive glasses and glass-ceramics, scaffolds, implant coatings, and tissue engineering. Then, it gives an overview of the critical issues that need to be considered when developing bioactive glasses for healthcare applications. The aim is to provide knowledge-based tools towards guiding young researchers in the design of new bioactive glass compositions, taking into account the desired functional properties.

Bioactive Glasses and Glass-Ceramics for Healthcare Applications in Bone Regeneration and Tissue Engineering.

Bifunctional mesoporous silica nanoparticles as cooperative catalysts for the Tsuji–Trost reaction – tuning the reactivity of silica nanoparticles

The synthesis of bifunctional mesoporous silica nanoparticles is described. Two chemically orthogonal functionalities are incorporated into mesoporous silica by co-condensation of tetraethoxysilane with two orthogonally functionalized triethoxyalkylsilanes. Post-functionalization is achieved by orthogonal surface chemistry. A thiol-ene reaction, Cu-catalyzed 1,3-dipolar alkyne/azide cycloaddition, and a radical nitroxide exchange reaction are used as orthogonal processes to install two functionalities at the surface that differ in reactivity. Preparation of mesoporous silica nanoparticles bearing acidic and basic sites by this approach is discussed. Particles are analyzed by solid state NMR spectroscopy, elemental analysis, infrared-spectroscopy, and scanning electron microscopy. As a first application, these particles are successfully used as cooperative catalysts in the Henry reaction.

Preparation of Bifunctional Mesoporous Silica Nanoparticles by Orthogonal Click Reactions and Their Application in Cooperative Catalysis

A novel synthetic route toward poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl) (PTMA) is described. The polymerization of alkoxyamine-based monomers by atom transfer radical polymerization (ATRP) was investigated, as the polyalkoxyamine serves as the precursor for PTMA. The polydispersity indices (PDIs) and the kinetic data of the polymerization indicate a controlled reaction. The oxidative C–O bond cleavages of the polyalkoxyamine lead to PTMA. This transformation occurs with excellent yields, and it is possible to transfer the narrow PDIs of the prepolymer to PTMA. The material is characterized in detail using cyclic voltammetry in solution and magnetic susceptibility measurements as well as multinuclear solid state NMR and EPR spectroscopies. The conversion of the precursor polymer to the polynitroxide can be conveniently monitored by 1H and 19F magic-angle spinning (MAS) as well as 13C{1H} cross-polarization (CP)-MAS NMR. In addition, the intermolecular interaction of the nitroxide side c...

Polynitroxides from alkoxyamine monomers: structural and kinetic investigations by solid state NMR

Mixed-alkali effects in the system [xNa2O(1 – x)Li2O]0.46[yAl2O3(1 – y)P2O5]0.54 (0 ≤ x ≤ 1; y = 0, 0.08, 0.16) have been examined using dc-conductivity measurements, thermal analysis, Raman spectroscopy, and various complementary solid-state NMR approaches. In contrast to the results of an earlier study reporting results on mixed-alkali aluminophosphate glasses with very similar chemical compositions (Faivre, A.; Viviani, D.; Phalippou, J. Solid State Ionics2005, 176, 325), ionic conductivities and Tg values exhibit composition dependences typical of “normal” mixed-alkali effect behavior. The 31P MAS NMR spectra have been quantitatively analyzed in terms of Q(n)m units, where “n” denotes the number of P–O–P linkages and “m” is the number of Al atoms connected to P. The data suggest that the number of P–O–Al linkages is maximized, and that no Al–O–Al linkages occur. 23Na triple-quantum MAS NMR studies indicate a monotonic trend in isotropic chemical shifts, consistent with intimate Na/Li mixing. In agreem...

Mixed-Alkali Effects in Aluminophosphate Glasses: A Re-examination of the System [xNa2O(1 – x)Li2O]0.46[yAl2O3(1 – y)P2O5]0.54

The structure of mixed-network former glasses in the system (M2O)0.33[(Ge2O4)x(P2O5)1–x]0.67.(M = Na, K) has been studied by 31P and 23Na high-resolution and dipolar solid state nuclear magnetic resonance (NMR) techniques, O-1s X-ray photoelectron spectroscopy, and Raman spectroscopy. Using an iterative fitting procedure, a quantitative structural model has been developed that is consistent with all of the experimental data and which provides a detailed description of network connectivities, network modification processes, and spatial cation distributions. Formation of heteroatomic P–O–Ge linkages is generally preferred over homoatomic P–O–P and Ge–O–Ge linkages, as shown by a detailed comparison with a random linkage model. An exception occurs in glasses with low germanium contents (x = 0.2) where a pronounced nonlinear dependence of the glass transition temperature on x can be related to a cross-linking of the sodium ultraphosphate network by fully polymerized germanium species, possibly including also ...

Frederik Behrends

Papers

Bifunctional mesoporous silica nanoparticles as cooperative catalysts for the Tsuji–Trost reaction – tuning the reactivity of silica nanoparticles

Preparation of Bifunctional Mesoporous Silica Nanoparticles by Orthogonal Click Reactions and Their Application in Cooperative Catalysis

Polynitroxides from alkoxyamine monomers: structural and kinetic investigations by solid state NMR

Mixed-Alkali Effects in Aluminophosphate Glasses: A Re-examination of the System [xNa2O(1 – x)Li2O]0.46[yAl2O3(1 – y)P2O5]0.54

Mixed Network Former Effects in Oxide Glasses: Spectroscopic Studies in the System (M2O)1/3[(Ge2O4)x(P2O5)1–x]2/3