Structural study of tungstate fluorophosphate glasses by Raman and X-ray absorption spectroscopy

Transparent glasses were synthesized in the NaPO₃-BaF₂-WO₃ ternary system and several structural characterizations were performed by X-ray absorption spectroscopy (XANES) at the tungsten L_I and L_III absorption edges and by Raman spectroscopy. Special attention was paid to the coordination state of tungsten atoms in the vitreous network.XANES investigations showed that tungsten atoms are only six-fold coordinated (octahedra WO₆) and that these glasses are free of tungstate tetrahedra (WO₄).In addition, Raman spectroscopy allowed to identify a break in the linear phosphate chains as the amount of WO₃ increases and the formation of P-O-W bonds in the vitreous network indicating the modifier behavior of WO₆ octahedra in the glass network. Based on XANES data, we suggested a new attribution of several Raman absorption bands which allowed to identify the presence of W-O⁻ and WO terminal bonds and a progressive apparition of W-O-W bridging bonds for the most WO₃ concentrated samples (?30% molar) due to the formation of WO₆ clusters.     

1,2,3,4-tetrahydro-8-hydroxymanzamines, alkaloids from two different haplosclerid sponges

The isolation and characterization of two new sponge alkaloids, 1,2,3,4-tetrahydro-2-N-methyl-8-hydroxymanzamine A (2) and 1,2,3,4-tetrahydro-8-hydroxymanzamine A (3), is described. These compounds were obtained from Papua New Guinea sponges of the genera Petrosia and Cribochalina, which are in different families of the order Haplosclerida. These new manzamines are close in structure to 8-hydroxymanzamine (4) recently reported from Pachypellina, a Haplosclerid sponge belonging to a different family than that of the two preceding sponges. The cytotoxicity of 2 is described and the biogenetic relationship of 2 or 3 to manzamine A (1) and to nine other related polycyclic diamine and one monoamine type alkaloids is described.     

A biotechnological process involving filamentous fungi to produce natural crystalline vanillin from maize bran

A new process involving the filamentous fungi Aspergillus niger and Pycnoporus cinnabarinus has been designed for the release of ferulic acid by enzymic degradation of a cheap and natural agricultural byproduct (autoclaved maize bran) and its biotransformation into vanillic acid and/or vanillin with a limited number of steps. On the one hand, the potentialities of A. niger I-1472 to produce high levels of polysaccharide-degrading enzymes including feruloyl esterases and to transform ferulic acid into vanillic acid were successfully combined for the release of free ferulic acid from autoclaved maize bran. Then vanillic acid was recovered and efficiently transformed into vanillin by P. cinnabarinus MUCL 39533, since 767 mg/L of biotechnologic vanillin could be produced in the presence of cellobiose and XAD-2 resin. On the other hand, 3-d-old high-density cultures of P. cinnabarinus MUCL39533 could be fed with the autoclaved fraction of maize bran as a ferulic acid source and a. niger I-1472 culture filtrate as an extracellular enzyme source. Under these conditions, P. cinnabarinus MUCL39533 was shown to directly biotransform free ferulic acid released from the autoclaved maize bran by A. niger I-1472 enzymes into 584 mg/L of vanillin. These processes, involving physical, enzymic, and fungal treatments, permitted us to produce crystallin vanillin from autoclaved maize bran without any purification step.     

Ceramic microreactors for heterogeneously catalysed gas-phase reactions

The high surface to volume ratio of microchannel components offers many advantages in micro chemical engineering. It is obvious, however, that the reactor material and corrosion phenomena play an important role when applying these components. For chemical reactions at very high temperatures or/and with corrosive reactants involved, microchannel components made of metals or polymers are not suited. Hence, a modular microreactor system made of alumina was developed and fabricated using a rapid prototyping process chain. With exchangeable inserts the system can be adapted to the requirements of various reactions. Two heterogeneously catalysed gas-phase reactions (oxidative coupling of methane, isoprene selective oxidation to citraconic anhydride) were investigated to check the suitability of the system at temperatures of up to 1000 degrees C. Apart from the high thermal and chemical resistance, the lack of any blind activity was found to be another advantage of ceramic components.     

Evaluation of retention and release processes of two antibiotics from the biocompatible core-shell microparticles

By dropwise addition of a chitosan solution into different non-solvent, such as: 1 N and 2 N NaOH as well as 1 N NaOH: C₂H₅OH mixture (2:1, v/v) at temperature of 25 °C and 50 °C under stirring, the spherical pure chitosan microparticles were performed. As solvents for chitosan was used 0.1 N acetic acid or 0.1 N HCl. The immersion of the pure chitosan microparticles in hyaluronan solution led to complex microparticles, namely chitosan microparticles covered by a hyaluronan layer. For all the microparticles performed the behaviours in the retention process of two antibiotics: chloramphenicol succinate sodium salt and cefotaxime sodium salt were analyzed. Also, the study shows the release behaviour of cefotaxime sodium salt by the microparticles loaded with this drug. Among the microparticles performed a type of complex microparticles can be considered a suitable drug delivery system for cefotaxime. These microparticles were performed by dropwise addition of chitosan solution in 0.1 N acetic acid into the 1 N NaOH: C₂H₅OH (2:1, v/v) non-solvent at 20 °C for 3 h, followed by their washing up to alkalinity loss and the immersion in hyaluronan solution of 10 g/L concentration for 24 h.     

Neutral and Anionic Square Planar Palladium(0) Complexes Stabilized by a Silicon Z-Type Ligand

Anionic [Pd(0)−X]⁻ ate complex were proposed as key intermediates in Pd-catalyzed cross-coupling for decades, but their isolation remained elusive. Herein, a chelating Lewis acidic bis(amidophenolato)silane is introduced as a strong Z-type ligand which enables the characterization of the first anionic [Pd(0)−X]⁻ ate complex. Intriguingly, these compounds and the neutral L−Pd(0) analogs exhibit a square planar coordination that is highly unusual for a d¹⁰ metal. Theoretical methods scrutinize the interaction between the Lewis acidic Si(IV) center and the late transition metal, while reactivity studies shed light on the potential role of anionic additives in oxidative addition reactions.     

Biodegradable High-Density Polyethylene-like Material

We report a novel polyester material generated from readily available biobased 1,18-octadecanedicarboxylic acid and ethylene glycol possesses a polyethylene-like solid-state structure and also tensile properties similar to high density polyethylene (HDPE). Despite its crystallinity, high melting point (T_m=96 °C) and hydrophobic nature, polyester-2,18 is subject to rapid and complete hydrolytic degradation in in vitro assays with isolated naturally occurring enzymes. Under industrial composting conditions (ISO standard 14855-1) the material is biodegraded with mineralization above 95 % within two months. Reference studies with polyester-18,18 (T_m=99 °C) reveal a strong impact of the nature of the diol repeating unit on degradation rates, possibly related to the density of ester groups in the amorphous phase. Depolymerization by methanolysis indicates suitability for closed-loop recycling.     

Observing the Entry Events of a Titanium-Based Photoredox Catalytic Cycle in Real Time

Titanium-based catalysis in single electron transfer (SET) steps has evolved into a versatile approach for the synthesis of fine chemicals and first attempts have recently been made to enhance its sustainability by merging it with photo-redox (PR) catalysis. Here, we explore the photochemical principles of all-Ti-based SET-PR-catalysis, i.e. in the absence of a precious metal PR-co-catalyst. By combining time-resolved emission with ultraviolet-pump/mid-infrared-probe (UV/MIR) spectroscopy on femtosecond-to-microsecond time scales we quantify the dynamics of the critical events of entry into the catalytic cycle; namely, the singlet-triplet interconversion of the do-it-all titanocene(IV) PR-catalyst and its one-electron reduction by a sacrificial amine electron donor. The results highlight the importance of the PR-catalyst's singlet-triplet gap as a design guide for future improvements.     

Non-Random Island Nucleation in the Electrochemical Roughening on Pt(111)

Many chemical surface systems develop ordered nano-islands during repeated reaction and restoration. Platinum is used in electrochemical energy applications, like fuel cells and electrolysers, although it is scarce, expensive, and degrades. During oxidation-reduction cycles, simulating device operation, nucleation and growth of nano-islands occurs that eventually enhances the dissolution. Preventing nucleation would be the most effective solution. However, little is known about the atomic details of the nucleation; a process almost impossible to observe. Here, we analyze the nuclei-distance distribution mapping out the underlying atomic mechanism: a rarely observed, non-random nucleation takes place. Special, preferential nucleation sites that a priori do not exist, develop initially via a precursor and eventually form a semi-ordered Pt-oxide structure. This precursor mechanism seems to be general, possibly explaining also the nano-island formation on other surfaces/reactions.