Stefan Vanicek

Enhanced kinetic stability of pure and Y-doped tetragonal ZrO2.

The kinetic stability of pure and yttrium-doped tetragonal zirconia (ZrO2) polymorphs prepared via a pathway involving decomposition of pure zirconium and zirconium + yttrium isopropoxide is reported. Following this preparation routine, high surface area, pure, and structurally stable polymorphic modifications of pure and Y-doped tetragonal zirconia are obtained in a fast and reproducible way. Combined analytical high-resolution in situ transmission electron microscopy, high-temperature X-ray diffraction, and chemical and thermogravimetric analyses reveals that the thermal stability of the pure tetragonal ZrO2 structure is very much dominated by kinetic effects. Tetragonal ZrO2 crystallizes at 400 °C from an amorphous ZrO2 precursor state and persists in the further substantial transformation into the thermodynamically more stable monoclinic modification at higher temperatures at fast heating rates. Lower heating rates favor the formation of an increasing amount of monoclinic phase in the product mixture, especially in the temperature region near 600 °C and during/after recooling. If the heat treatment is restricted to 400 °C even under moist conditions, the tetragonal phase is permanently stable, regardless of the heating or cooling rate and, as such, can be used as pure catalyst support. In contrast, the corresponding Y-doped tetragonal ZrO2 phase retains its structure independent of the heating or cooling rate or reaction environment. Pure tetragonal ZrO2 can now be obtained in a structurally stable form, allowing its structural, chemical, or catalytic characterization without in-parallel triggering of unwanted phase transformations, at least if the annealing or reaction temperature is restricted to T ≤ 400 °C.

Next generation of buccadhesive excipient: Preactivated carboxymethyl cellulose.

AIM Assessment of preactivated carboxymethyl cellulose as potential excipient for buccal drug delivery. METHODS Firstly, carboxymethyl cellulose (CMC) and cysteine (SH) were covalently coupled via amide bond formation to obtain thiolated carboxymethyl cellulose (CMC-SH). Further, preactivated carboxymethyl cellulose (CMC-S-S-MNA) was obtained by preactivation with 2-mercaptonicotinic acid (MNA). Sulforhodamine 101 (SRH101) was used as a model drug for permeation study through buccal mucosa. CMC-S-S-MNA was evaluated with respect to mucoadhesive and permeation enhancing effect and cytotoxicity. RESULTS Thiolated carboxymethyl cellulose exhibited a total amount of 112.46 ± 0.46 thiol groups. CMC-S-S-MNA exhibited around 50% of preactivated thiol groups. The preactivated polymer showed no toxic effect. Furthermore, compared to unmodified CMC, CMC-S-S-MNA revealed 3.0-fold improved mucoadhesive properties according to the rotating cylinder method and 8.8-fold enhancement in mucoadhesiveness by tensile assay, respectively. CONCLUSION Preactivated carboxymethyl cellulose fulfills the requirements as potential excipient of being mucoadhesive and permeation enhancing for the buccal drug delivery.

Highly Electrophilic, Catalytically Active and Redox-Responsive Cobaltoceniumyl and Ferrocenyl Triazolylidene Coinage Metal Complexes

Abstract A convenient access to a triad of triazoles with ferrocenyl and cobaltoceniumyl substituents is reported. N‐Alkylation, deprotonation and metalation with CuI/AgI/AuI synthons affords the heteroleptic triazolylidene complexes. Due to the combination of neutral, electron‐donating ferrocenyl substituents and cationic, strongly electron‐withdrawing cobaltocenium substituents, the mesoionic carbene (MIC) ligands of these complexes are electronically interesting “push–pull”, “pull–push” and “pull–pull” metalloligands with further switchable redox states based on their fully reversible FeII/FeIII, (ferrocene/ferrocenium) and CoIII/CoII, (cobaltocenium/cobaltocene) redox couples. These are the first examples of metal complexes of (di)cationic NHC ligands based on cobaltoceniumyl substituents. DFT calculated Tolman electronic parameter (TEP) of the new MIC ligands, show these metalloligands to be extremely electron‐poor NHCs with properties unmatched in other carbene chemistry. Utilization of these multimetallic electronically tunable compounds in catalytic oxazoline synthesis and in antitumor studies are presented. Remarkably, 1 mol % of the AuI complex with the dicationic MIC ligand displays full catalytic conversion, without the need for any other additives, in less than 2 hours at ambient temperatures. These results thus firmly establish these new classes of cobaltoceniumyl based (di)cationic MIC ligands as prominent players in several branches of chemistry.

Physico-chemical properties of unusual Ga2O3 polymorphs

A comparative structural and spectroscopic study, combined with reactivity tests in (inverse) water–gas shift and methanol steam reforming reaction, has been performed on various Ga2O3 polymorphs with special focus on δ-Ga2O3 and ε-Ga2O3 with the aim of highlighting the eventual intrinsic physico-chemical properties of the latter two. Using this comparative approach, the question whether δ-Ga2O3 in fact is a nanocrystalline modification of ε-Ga2O3, a mixture of ε-Ga2O3 and β-Ga2O3, or a single polymorphic form could be answered: especially Raman spectroscopy measurements, alongside reactivity tests, indicate that δ-Ga2O3 exhibits lots of properties of ε-Ga2O3. In fact, particularly in Raman measurements it appears as a mixture of ε-Ga2O3 and β-Ga2O3.Graphical abstract

Cobaltocenylidene: A Mesoionic Metalloceno Carbene, Stabilized in a Gold(III) Complex

Abstract Oxidative addition of cobaltoceniumdiazonium bis(hexafluoridophosphate) with (pseudo)halide aurates gave gold(III) complexes containing zwitterionic cobaltoceniumide as a ligand. Its selenium derivative, cobaltoceniumselenolate, was obtained by an electrophilic aromatic substitution reaction of iodocobaltocenium iodide with Na2Se. Spectroscopic and structural data in combination with DFT calculations showed that this cobaltocenylidene species is a mesoionic carbene quite different from common N‐heterocyclic carbenes. Its ligand properties (TEP, singlet‐triplet gap, nucleophilicity, π‐acidity, Brønsted basicity) are in part comparable to those of cyclic (amino)(alkyl/aryl)carbenes. Electrochemistry data showed that the mesoionic cobaltoceniumides are more electron‐rich than their parent ferrocenes. The reversible reduction of the tricyanido gold complex appears 50 mV negative of the cobaltocenium/cobaltocene couple, whereas that of the selenide derivative is shifted cathodically by 550 mV.

Molecular Structure of 1,2-Dibenzoyl-1′,2′,3′,4′,5′-pentamethylruthenocene Dioxime Hydrochloride

The dioxime of 1,2-dibenzoylpentamethylruthenocene is synthesized from its parent diketone and hydroxylamine under standard basic conditions. The slightly air-sensitive product is crystallized in the form of its monohydrochloride. The solid-state structure is the first example of a dioxime monohydrochloride showing a typical metallocene core with peripheral intramolecular N–H–N and O–H–Cl hydrogen bonding.