Marjan Versluijs-Helder

Effect of the reduction treatment on the structure and reactivity of silica-supported copper particles

Abstract Silica-supported copper particles of high thermostability have been subjected to oxidation-reduction treatments after which the metal particle size, the surface structure, and the catalytic hydrogenolysis of methyl acetate were investigated. The metal particle size was assessed from the dissociative adsorption of nitrous oxide, X-ray line broadening, and transmission electron microscopy. The surface structure of the copper particles was derived from infrared spectra of adsorbed carbon monoxide. The hydrogenolysis of methyl acetate was used as a structure-sensitive test reaction to illustrate the effect of the surface structure on the activity of the catalyst. The copper particle size is not affected by reduction treatments up to 873 K, whereas the surface structure of the copper particles and thereby the oxygen uptake during dissociative adsorption of nitrous oxide and the activity of the catalyst in the hydrogenolysis of methyl acetate strongly depend upon the temperature and duration of the reduction treatment. Without a change of the copper particle size, prolonged reduction of the catalyst results in more densely packed copper surfaces that are more susceptible to penetration of oxygen during passivation with nitrous oxide and less active in the hydrogenolysis of methyl acetate. The rearrangement of the surface structure of the copper particles is reversible upon repeated oxidation-reduction cycles.

Comparative effects of DDT, allethrin, dieldrin and aldrin-transdiol on sense organs of Xenopus laevis

The effects of DDT, allethrin, dieldrin and aldrin-transdiol were studied in two different sense organs of Xenopus laevis; the lateral-line organ and the cutaneous touch receptors. DDT and allethrin produced pronounced repetitive firing in both preparations. Dieldrin and aldrin-transdiol, on the other hand, failed to induce any sign of repetitive activity. Aldrin-transdiol, however, caused a marked increase in the rate of spontaneous firing of the lateral-line organ, later followed by a blockade. The repetitive activity in the cutaneous touch receptors, whether induced by DDT or allethrin, was not distinguishable from repetitive firing of the afferent nerve fibers and showed no marked dependence on temperature. This contrasts sharply with the know negative temperature coefficient of the DDT- or allethrin-induced repetitive activity in the lateral-line organ.

Effect of polymer composition on rheological and degradation properties of temperature-responsive gelling systems composed of acyl-capped PCLA-PEG-PCLA.

In this study, the ability to modulate the rheological and degradation properties of temperature-responsive gelling systems composed of acyl-capped poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) (PCLA-PEG-PCLA) triblock copolymers was investigated. Eight polymers with varying molecular weight of PCLA, caproyl/lactoyl ratio (CL/LA) and capped with either acetyl- or propionyl-groups were synthesized by ring-opening polymerization of L-lactide and ε-caprolactone in toluene using PEG as initiator and tin(II) 2-ethylhexanoate as catalyst, and subsequently reacted in solution with an excess of acyl chloride to yield fully acyl-capped PCLA-PEG-PCLA. The microstructure of the polymers was determined by (1)H NMR, and the thermal properties and crystallinity of the polymers in dry state and in 25 wt % aqueous systems were studied by differential scanning calorimetry and X-ray diffraction. Rheological and degradation/dissolution properties of aqueous systems composed of the polymers in 25 wt % aqueous systems were studied. (1)H NMR analysis revealed that the monomer sequence in the PCLA blocks was not fully random, resulting in relatively long CL sequences, even though transesterification was demonstrated by the enrichment with lactoyl units and the presence of PEG-OH end groups. Except the most hydrophilic polymer composed of acetyl-capped PCLA1400-PEG1500-PCLA1400 having a CL/LA molar ratio of 2.5, the polymers at 25 wt % in buffer were sols below room temperature and transformed into gels between room temperature and 37 °C, which makes them suitable as temperature-responsive gelling systems for drug delivery. Over a period of weeks at 37 °C, the systems containing polymers with long CL sequences (~8 CL) and propionyl end-groups became semicrystalline as shown by X-ray diffraction analysis. Degradation of the gels by dissolution at 37 °C took 100-150 days for the amorphous gels and 250-300 days for the semicrystalline gels. In conclusion, this study shows that changes in the polymer composition allow an easy but significant modulation of rheological and degradation properties.

Excitatory and depressant effects of dieldrin and aldrin-transdiol in the spinal cord of the toad (Xenopus laevis)

An investigation was made into the action of the insecticide dieldrin and one of its metabolites, aldrin-transdio, on the isolated spinal cord of the toad, Xenopus laevis. Conventional electrophysiological techniques were used for stimulating and recording of dorsal and ventral spinal roots. An augmentation of polysynaptic reflex activity along with a marked reduction of orthodromic postsynaptic inhibition could be demonstrated in preparations isolated from dieldrin-poisoned animals. However, application of dieldrin to the isolated spinal cord failed to produce any significant effect. Application of aldrin-transdiol, on the other hand, caused a potentiation of spinal reflex activity and an increase in spontaneous activity of ventral and dorsal roots. Aldrin-transdiol also produced a marked reduction of spinal inhibitory mechanisms. The excitatory effects of aldrin-transdiol were followed by a strong depressant action on spinal excitability.

Carbon‐Supported Base Metal Nanoparticles: Cellulose at Work

Pyrolysis of base metal salt loaded microcrystalline cellulose spheres gives a facile access to carbon-supported base metal nanoparticles, which have been characterized with temperature-dependent XRD, SEM, TEM, ICP-MS and elemental analysis. The role of cellulose is multifaceted: 1) it facilitates a homogeneous impregnation of the aqueous base metal salt solutions, 2) it acts as an efficacious (carbonaceous) support material for the uniformly dispersed base metal salts, their oxides and the metal nanoparticles derived therefrom, and 3) it contributes as a reducing agent via carbothermal reduction for the conversion of the metal oxide nanoparticles into the metal nanoparticles. Finally, the base metal nanoparticles capable of forming metastable metal carbides catalytically convert the carbonaceous support into a mesoporous graphitic carbon material.

Extended Structure Design with Simple Molybdenum Oxide Building Blocks and Urea As a Directing Agent

We report here a simple one-pot directed synthesis of an oxomolybdate urea composite in which elementary molybdenum oxide building blocks are linked together with the aid of urea. This type of directed material design resulted in large rod-like crystals of an inorganic-organic hybrid extended structure of {MoO 3(NH 2-CO-NH 2)} infinity consisting of right- and left-handed helical units. In the crystal structure urea acts both as a glue that links the inorganic molybdenum units into a helix and as a supramolecular linker for the stabilization of the crystal structure as a whole. This type of molecular topology resulted in an unexpectedly high thermal stability.

The influence of cetomacrogol ointment processing on structure: A definitive screening design

Abstract Batch‐to‐batch variability is a challenge for the industrial scale production of ointments. Therefore the current investigation focussed on identifying and understanding critical process parameters (CPPs) for cetomacrogol ointment. This was evaluated using a definitive screening design (DSD) approach in which fourteen batches were produced under predefined and controlled conditions using the following variables: addition of SiO2 nanoparticles, mixing speed, cooling rate, heating temperature, container filling temperature and isothermal mixing at the filling temperature. Ointment structure was evaluated using a number of rheological parameters. One of these parameters, yield stress was found to be strongly influenced by filling temperature and mixing speed (p = 0.0065 and p = 0.0013 respectively). Both significantly affect ointment structure and they also have a significant interaction (p < 0.05). Understanding the ointment production process can help in defining a processing window to produce ointment of constant quality.

Shell decoration of hydrothermally obtained colloidal carbon spheres with base metal nanoparticles

The preparation of base metal nanoparticles supported on the shell of colloidal carbon spheres (CCS) is reported. Hydrothermal treatment of a sucrose solution gave conglomerates of ca. 30 μm of CCS (diameter 2–8 μm), which consist of a hydrophobic core with a hydrophilic shell due to the presence of oxygen containing functional groups. The CCS were loaded by wet impregnation with various metal salts (copper, nickel, cobalt, iron). Subsequent pyrolysis under inert conditions at T = 800 °C led to the carbothermal reduction of the impregnated metal salts by the support material. The base metal nanoparticles (size ca. 35–70 nm) are supported on the circumference of the CCS in line with its core–shell structure. Moreover, in the case of nickel, cobalt and iron nanoparticles, all capable of forming metastable metal carbides, the carbonised shells are converted into nanostructures of graphitic carbon, viz., catalytic graphitisation occurs. The spheres were characterised by scanning- and transmission electron microscopy, X-ray diffraction, Raman spectroscopy, elemental analysis, infrared spectroscopy and thermogravimetric analysis.

Elucidation of the variability in consistency of pharmacopoeia quality petrolatum

Abstract The Pharmacopeia monograph for petrolatum poorly defines the material’s physical properties. Indeed, differences between petrolatum grades can be substantial; yield stress varies between 65 and 280 Pa which can be compared with the consistency of respectively thin cream or thick ointment. This variation is not only due to differences in composition or refining process but also as a result of different processing; for example, thermal history influences petrolatum structure considerably. Slow cooling of petrolatum resulted in a yield stress of 26 Pa and fast cooling in 79 Pa. X-ray showed that crystallinity was 0.7% for the first cooling case and 1.5% for the second one. Crystallite size was estimated to be 20–50 nm. To investigate if this relatively small difference in crystallinity may induce the difference in consistency, 15 nm SiO2 particles were added to petrolatum. Indeed, a small increase in SiO2 concentration led to a major increase in yield stress. This was argued to be due to the small size of the particles, resulting in a large increase in absolute number of particles. The Pharmacopeia does not unambiguously define the pharmaceutical excipient petrolatum. As a consequence, the formulator has to take care of selecting the appropriate grade as well as to carefully control the processing of the material in order to achieve a consistent pharmaceutical product.