Polyhalides as scaffolds for supramolecular, ion-conducting crown ether stacks

"Crown ethers, such as dibenzo-18-crown-6 (DB18C6) are in principle perfect building blocks to be stacked on top of each other for one-dimensional (1D) channel formation. However, in the more than 1000 publications on crown ethers in the solid state, only one case was of channel formation described, but not as main focus of research.[1] We now present a way to systematically induce the stacking of DB18C6 with the help of polyhalides, which play the roles of scaffolds via halogen bonding.[2] These compounds can be considered as ""supramolecular straws"". Using for example potassium as couter ion for triiodide for example, we obtained a solid which contains three differently filled, parallel channels in the solid state, which are arranged between the polyhalide anions. Exchanging potassium with sodium by immersion of a single crystal into NaOH solution leads to a single-crystal-to-single-crystal transformation into a compound with two channel types. This transition from a system crystallizing initially in the P2-space group to yield a compound in Pccn is only possible under these very special conditions. We will further present how the ion transport through these channels can be quantified and which process is involved in ion exchange. The role of the polyhalide anions, which cannot be replaced by other linear anions, will be emphasized as well. "

New metal Aryloxide complexes as ceramic precursors and Initiators for ROP

In addition to the development of new energy-producing processes, finding new energy-saving procedures offers a promising solution to meet our energy needs in the long run. Indeed, cheap organometallic precursors for oxide materials and catalysis are key technologies for energy saving. A wide variety of metal alkoxides/aryloxides[1] has been used not only as precursors for oxide materials, but also as initiators and catalysts for ring-opening polymerization (ROP). Ceramic oxide materials are widely used for many applications, exceptionally in lithium-ion batteries (LIB) material for the last for these recent decades. Also, due to the use of cyclic esters in the tailoring synthesis of biodegradable and bioresorbable materials, interest in the development of well-defined initiators and catalysts has increased. For both cited reasons, iron-based aryloxide complexes offer many advantages, such as the large abundance of iron, their low toxicity and even their biocompatibility[1]. Aryloxide/alkoxide complexes have been also proposed like good route precursors due to their high solubility, low decomposition temperatures, cross linking ability, ease of modification and commercial availability[2].

Antimicrobial complexes of Schiff base ligands and copper family metal ions

Schiff base complexes were extensively studied because of their catalytic properties in various fields and partly for their biological activity[1]. The utilisation of copper (II)[2] and silver (I)[3] can introduce antimicrobial properties to these structures or enhance them; thus provides new fields of applications, like in medicine. Compared to classical Schiff bases, the synthesis of dual N,N-donor Schiff bases is facile too, and the resulting product contains several coordination sides for diverse metals. Applying these unique advantages, we developed several antibacterial Schiff base metal complexes. Our ligand system is based on functionalized pyridine end-capped imine linker units which differ in the nature of the linker chain, such as ethylene glycols or alkyl chains. Substitution on the pyridine rings offer the possibility to attach oligomers or polymer chains which can work e.g. as handles. By applying, for example, mechanical force, like ultra-sonication, the metal ions can be released (Figure 1) by an external trigger and used for catalysis or in medicine, where its antimicrobial properties are required. Figure 1: Schematic illustration of controlled silver release from a ligand-polymer system by applied force (arrows).

Cr(II) complex: water reductant and starting compound for new Cr(III) compounds

The use of alkali aryloxide reagents in organo-metallic synthesis often depends on their solubility, a property derived from their structure. The regain of interest of alkali aryloxides also originates from the discovery of high-temperature superconducting compounds, which has generated a great interest in the formation of oxide materials and other ceramics. Thus, many alkoxides of yttrium and copper are common precursors for oxide materials. Moreover, the synthesis of heterobimetallic alkoxides has provided a facile route for obtaining soluble, volatile, and generally monomeric species. These heterobimetallic complexes can thus serve as valuable precursors for making metal oxides but it is not the only possible application for this type of compounds. These complexes can be used as starting compounds for syntheses of more complex structures. In this work, the salt elimination and ligand exchange reaction of chromium(II) chloride with lithium phenoxide yields a mixed metal lithium-chromium(II) phenoxide. Using this latter as intermediately formed starting material and combining the substitution reaction with an oxidation process, we have gained access to new polynuclear chromium(III) aryloxide complexes. While a 1D coordination polymer based on chromium(III) is obtained in a first reaction by serendipity, the controlled addition of water to the Cr(II) complex leads to three new discrete chromium(III) cluster compounds. The use of deuterated species allowed to confirm the oxidation based on the addition of water by detection of H2, HD and D2. During these investigations, we have also identified a THF-adduct of chromium(II) chloride, used in the literature as precursor in numerous syntheses, but with a hitherto unknown structure. Figure 1: Oxidation of a Cr(II) complex by water and formation of a new Cr(III) complex.

Polymorphism, what it is and how to identify it

Polymorphism is a very important phenomenon not only in basic research, but certainly in pharmaceutical industry and materials science. Polymorphs possess different properties, for instance the solubility or the mechanical resistance can differ dramatically from one polymorph to the other - properties which can be crucial for their application. Hence, it is important to be able to control the formation of polymorphs and to understand their formation. We here gave some insights into the basic knowledge of polymorph formation and their identification and characterization in order to give an overview on the current state of the art. In order to give interested peoples a tool in hand to test their compounds for polymorphism, we established a series of flow sheets to follow, depending on the class of compounds, hoping that they are useful for many scientists who are not so well acquainted with polymorphism. The presented schemes resume thus the identification steps for polymorphs. It should also help to use the term polymorph correctly in order to reduce the number of publications in which this term is not used in a correct way.

Nanoencapsulation of Silver-Based Antimicrobial Drugs

Implant-associated infections still remain an issue in medicine and can cause various medical complications. In order to ensure proper host-cell integration and biocompatibility to an implant, it is essential to prevent bacterial adhesion during the critical period of 6 hours after surgery. Moreover, as the implants are increasingly used in medicine, bacteria are becoming more resistant to antibiotics, in such a way that new developments in preventing and curing infections are more than ever needed. Silver compounds and nanoparticles are gaining more interest from the scientific society as a replacement to antibiotics. However, silver compounds may be too soluble and even toxic for the host. Encapsulation might be very advantageous in order to increase the stability and biocompatibility of silver drugs. In addition, it allows a more controllable release of antimicrobial agents. In this study, ceria nanocapsules with integrated silver nanoparticles (Ag/CeO2 NCs) were synthesized according to the method depicted in the figure below. The capsules were then characterized using XRD, TEM, SEM, and FT-IR. Silver nanoparticles (Ag NPs) are visible on the surface as well as in the cavity of Ag/CeO2 NCs, suggesting that they were integrated within the ceria shell. This system can release silver during a period exceeding 3 months, which demonstrates a good release control of the antimicrobial agent. The Ag/CeO2 NCs have a low cytotoxicity towards human alveolar epithelial cells, but allow only a poor cell attachment. In order to improve the cell attachment on the nanocapsules, as well as to reduce the silver being released, a TiO2 coating around the Ag/CeO2 NCs was added to this system. This resulted in the so-called Ag/CeO2/TiO2 NCs. These novel nanocontainers were also characterized in order to evaluate the cytotoxicity and antimicrobial activity.