Powder Compaction: Compression Properties of Cellulose Ethers

Effective development of matrix tablets requires a comprehensive understanding of different raw material attributes and their impact on process parameters. Cellulose ethers (CE) are the most commonly used pharmaceutical excipients in the fabrication of hydrophilic matrices. The innate good compression and binding properties of CE enable matrices to be prepared using economical direct compression (DC) techniques. However, DC is sensitive to raw material attributes, thus, impacting the compaction process. This article critically reviews prior knowledge on the mechanism of powder compaction and the compression properties of cellulose ethers, giving timely insight into new developments in this field

Tailoring the nature of magnetic coupling of Fe-porphyrin molecules to ferromagnetic substrates

We demonstrate that an antiferromagnetic coupling between paramagnetic Fe-porphyrin molecules and ultrathin Co and Ni magnetic films on Cu(100) substrates can be established by an intermediate layer of atomic oxygen. The coupling energies have been determined from the temperature dependence of x-ray magnetic circular dichroism measurements. By density functional theory+U calculations the coupling mechanism is shown to be superexchange between the Fe center of the molecules and Co surface-atoms, mediated by oxygen. © 2009 The American Physical Society

Protonic defects and water incorporation in Si and Ge-based apatite ionic conductors

Apatite-type oxide-ion conductors have attracted considerable interest as potential fuel cell electrolytes. Atomistic modelling techniques have been used to investigate oxygen interstitial sites, protonic defects and water incorporation in three silicate and three germanate-based apatite-systems, namely La8Ba2(SiO4)(6)O-2, La-9.33(SiO4)(6)O-2, La-9.67(SiO4)(6)O-2.5, La8Ba2(GeO4)(6)O-2, La-9.33(GeO4)(6)O-2, and La-9.67(GeO4)(6)O-2.5. The simulation models reproduce the complex experimental structures for all of these systems. The interstitial defect simulations have examined the lowest energy configuration and confirm this site to be near the Si/GeO4 tetrahedra. The water incorporation calculations identify the O-H protonic site to be along the O-4 oxygen channel as seen in naturally occurring hydroxy-apatites. The results also show more favourable and exothermic water incorporation energies for the germanate based apatites. This is consistent with recent experimental work, which shows that Ge-apatites take up water more readily than the silicate analogues

Utilizing the interaction with surfaces to create new molecular-based spin-hybrid systems

Spin-hybrid systems consisting of magnetic molecules on surfaces are studied by means of X-ray absorption spectroscopy. The relevant magnetic interactions of paramagnetic molecules on ferromagnetic surfaces are analyzed utilizing the element specificity of the X-ray magnetic circular dichroism revealing the magnetic coupling for these systems. By the help of X-ray natural dichroism the orientation of the molecules on the surfaces and the electronic structure is probed. The structural properties are correlated to the magnetic characteristics to achieve a more complete understanding of the spin-hybrid systems. The possibility to tailor the magnetic coupling for these systems is demonstrated by modifying the interface of the molecules and the substrate by using an intermediate layer of atomic oxygen