Differences between eccentric and rotary tablet machines in the evaluation of powder densification behaviour

Differences in the dynamics of powder densification between eccentric and rotary machine were pointed out by compressing at different compression pressures microcrystal line cellulose, lactose monohydrate and dicalcium phosphate dihydrate and recovering the corresponding stress/strain data in both machines equipped to monitor punches displacement and compression forces. Heckel plots were then obtained from these stress/strain data. Curves obtained in the rotary machine possess a narrower zone of linearity for the calculation of P-Y and D-A. The effect of the different compression mechanism of the rotary machine on the shape of the Heckel plot is more noticeable in a non-deforming material such as dicalcium phosphate. The effect of the longer dwell time of the rotary machine on the porosity reduction occurring after the maximum pressure has been reached, is more noticeable in a ductile material such as microcrystalline cellulose. Heckel parameters obtained in the rotary press are in some cases different from those recovered in the eccentric machine because of the longer dwell time, machine deflection and punch tilting occurring in the rotary machine, although theoretically they could better describe the material densification in a high speed production rotary machine

Inferring the Demographic History of African Farmers and Pygmy Hunter–Gatherers Using a Multilocus Resequencing Data Set

The transition from hunting and gathering to farming involved a major cultural innovation that has spread rapidly over most of the globe in the last ten millennia. In sub-Saharan Africa, hunter–gatherers have begun to shift toward an agriculture-based lifestyle over the last 5,000 years. Only a few populations still base their mode of subsistence on hunting and gathering. The Pygmies are considered to be the largest group of mobile hunter–gatherers of Africa. They dwell in equatorial rainforests and are characterized by their short mean stature. However, little is known about the chronology of the demographic events—size changes, population splits, and gene flow—ultimately giving rise to contemporary Pygmy (Western and Eastern) groups and neighboring agricultural populations. We studied the branching history of Pygmy hunter–gatherers and agricultural populations from Africa and estimated separation times and gene flow between these populations. We resequenced 24 independent noncoding regions across the genome, corresponding to a total of ∼33 kb per individual, in 236 samples from seven Pygmy and five agricultural populations dispersed over the African continent. We used simulation-based inference to identify the historical model best fitting our data. The model identified included the early divergence of the ancestors of Pygmy hunter–gatherers and farming populations ∼60,000 years ago, followed by a split of the Pygmies' ancestors into the Western and Eastern Pygmy groups ∼20,000 years ago. Our findings increase knowledge of the history of the peopling of the African continent in a region lacking archaeological data. An appreciation of the demographic and adaptive history of African populations with different modes of subsistence should improve our understanding of the influence of human lifestyles on genome diversity

The role of several L-HPCs in preventing the tablet capping during direct compression of metronidazole

Several low-hydroxypropyl cellulose (L-HPC) derivatives (LH-11, 21, 22, 31 and 32) differing in granulometric particle size or in hydroxypropyl content were considered in the present study. The L-HPC grades were characterized as pure powders, in order to determine both compression and densification behaviour, in presence or in absence of magnesium stearate as lubricant, and then, were physically mixed in different proportions with metronidazole, which was also previously characterized as pure powder. The tabletability and compressibility of these binary mixtures were then evaluated, in presence or in absence magnesium stearate as lubricant at two different compression speeds (20 and 70 mm/s). It was observed that both binary mixture compression behaviour and capping tendency were influenced by compression speed and by the presence of lubricant. Differences in anti-capping efficiency between the L-HPCs may be related to their hydroxypropyl content. This parameter influences the interaction between the metronidazole and the polymer particles, and consequently the ability of the binary system to undergo densification under compression

PCBs contaminatie van de noordzee : concentraties en fluxes

Les biphényles polychlorés ou PCBs ont eu de très nombreuses applications industrielles en raison de leur stabilité et de leurs excellentes propriétés diélectriques. Vu leurs impacts sur l'écosystème, leur utilisation a été fortement restreinte en 1986. cette étude avait pour but de déterminer quelques années après leur quasi interdiction leur transfert d'un compartiment à l'autre de l'écosystème, et, in fine, les flux de PCBs vers la mer du nord

Ketoprofen-poly(vinylpyrrolidone) physical interaction

Amorphous solid solutions were obtained in different proportions by dissolving ketoprofen (Ket) and poly(vinylpyrrolidone) (PVP) K30 in methanol and by evaporating them under reduced pressure. Their physical properties were studied by powder X-ray diffraction and by differential scanning calorimetry and compared to that of same physical mixtures (PM). The interaction of Keto andpoly(vinylpyrrolid one) K30 in the solidstate was then investigatedby 13C NMR CPMAS analysis. The results indicated that in the Ket–(PVP) co-precipitates, the ket molecules, interacting with their carboxylic group through hydrogen bonding with the poly(vinylpyrrolidone) moieties, are molecularly and irregularly dispersed within the amorphous solvendum that acts as mechanical substratum for amorphous stabilization. In their simple PM, no evidence exists of the Ket-polymer interaction during the considered time interval

Influence of crystal habit on the compression and densification mechanism of ibuprofen

Ibuprofen was recrystallized from several solvents by two different methods: addition of a non-solvent to a drug solution and cooling of a drug solution. Four samples, characterized by different crystal habit, were selected: sample A, sample E andsample T, recrystallizedrespectively from acetone, ethanol andTHF by addition of water as non-solvent andsample M recrystallized from methanol by temperature decrease. By SEM analysis, sample were characterized with the respect of their crystal habit, mean particle diameter and elongation ratio. Sample A appears stick-shaped, sample E acicular with lamellar characteristics, samples T and M polyhedral. DSC and X-ray diffraction studies permit to exclude a polymorphic modification of ibuprofen during crystallization. For all samples micromeritics properties, densification behaviour and compression ability was analysed. Sample M shows a higher densification tendency, evidenciated by its higher apparent and tapped particle density. The ability to densificate is also pointed out by D0’ value of Heckel’s plot, which indicate the rearrangement of original particles at the initial stage of compression. This fact is relatedto the crystal habit of sample M, which is characterizedby strongly smoothed coins. The increase in powder bed porosity permits a particle–particle interaction of greater extent during the subsequent stage of compression, which allows higher tabletability andcompressibility

Improved Compression Properties of Propyphenazone Spherical Crystals

Spherical propyphenazone crystals were produced by an agglomeration technique using a three solvents system. After selecting the best propyphenazone solvent (ethyl alcohol), non-solvent (demineralized water) and bridging liquid (isopropyl acetate), several of their ratios were tested by a Sheffe´ ternary diagram. Micromeritic properties of agglomerates such as flowability, were improved and their compression behavior was investigated and compared to that of raw crystals. By compression and densification studies, along with tablet SEM analysis, we have been able to explain the compression mechanism of propyphenazone spherical crystals and have shown that their better tablet:ability can be due to the small size of individual particles in the agglomerate

The spray drying of acetazolamide as a method to modify crystal properties and to improve compression behaviour

Acetazolamide shows a very poor compression ability and tablets must usually be produced through a wet granulation process. However, the possibility to obtain pure acetazolamide for direct compression could be interesting for industrial application. With the scope to obtain a material for direct compression, three different crystallisation methods were chosen, with respect to acetazolamide solvent solubility. (a) Acetazolamide was dissolved in an ammonia solution and then spray dried. It was possible to characterise the spherical particles as a mixture of two polymorphic forms, I and II by Powder X-ray diffraction study. (b) Pure form I was obtained by slowly cooling to room temperature a boiling water solution. (c) Pure form II, the marketed form, was obtained by neutralisation of an ammonia solution. Their compression behaviour was investigated firstly by a rotary press. Whilst pure polymorphic forms I and II could not be compressed, the spray dried particles showed very good compression properties. In fact, tablets were obtained only by spray dried particles, which show very good properties under compression and the absence of capping tendency. On the other hand, it was impossible to obtain tablets from polymorphic forms I and II, whatever compression pressures were used. In order to explain their densification mechanism, a single-punch tablet machine, equipped for the measurement of the upper punch displacement in the die, was used. From calculated Heckel’s parameters, it was demonstrated that the spray dried material shows a greater particle rearrangement in the initial stage of compression due to its spherical habit and minor wrinkledness of particle surface. The crystalline structure due to the presence of polymorphic forms I and II concur to lowering the intrinsic elasticity of the material. This fact avoids the risk of the rupturing the interpaticulate bonds, which are formed during the compression, concurring to the consolidation of the tablet