Determination of Debye Temperatures and Lamb-Mössbauer Factors for LnFeO3 Orthoferrite Perovskites (Ln = La, Nd, Sm, Eu, Gd)

Lanthanide orthoferrites have wide-ranging industrial uses including solar, catalytic and electronic applications. Here a series of lanthanide orthoferrite perovskites, LnFeO3 (Ln = La; Nd; Sm; Eu; Gd), prepared through a standard stoichiometric wet ball milling route using oxide precursors, has been studied. Characterisation through X-ray diffraction and X-ray fluorescence confirmed the synthesis of phase-pure or near-pure LnFeO3 compounds. 57Fe Mössbauer spectroscopy was performed over a temperature range of 10 K to 293 K to observe hyperfine structure and to enable calculation of the recoil-free fraction and Debye temperature (θD) of each orthoferrite. Debye temperatures (Ln = La 474 K; Nd 459 K; Sm 457 K; Eu 452 K; Gd 473 K) and recoil-free fractions (Ln = La 0.827; Nd 0.817; Sm 0.816; Eu 0.812; Gd 0.826) were approximated through minimising the difference in the temperature dependent experimental Centre Shift (CS) and theoretical Isomer Shift (IS), by allowing the Debye temperature and Isomer Shift values to vary. This method of minimising the difference between theoretical and actual values yields Debye temperatures consistent with results from other studies determined through thermal analysis methods. This displays the ability of variable-temperature Mössbauer spectroscopy to approximate Debye temperatures and recoil-free fractions, whilst observing temperature induced transitions over the temperature range observed. X-ray diffraction and Rietveld refinement show an inverse relationship between FeO6 octahedral volume and approximated Debye temperatures. Raman spectroscopy show an increase in the band positions attributed to soft modes of Ag symmetry, Ag(3) and Ag(5) from La to GdFeO3 corresponding to octahedral rotations and tilts in the [010] and [101] planes respectively

Importance of the difference in surface pressures of the cell membrane in doxorubicin resistant cells that do not express Pgp and ABCG2

P-glycoprotein (Pgp) represents the archetypal mechanism of drug resistance. But Pgp alone cannot expel drugs. A small but growing body of works has demonstrated that the membrane biophysical properties are central to Pgp-mediated drug resistance. For example, a change in the membrane surface pressure is expected to support drug–Pgp interaction. An interesting aspect from these models is that under specific conditions, the membrane is predicted to take over Pgp concerning the mechanism of drug resistance especially when the surface pressure is high enough, at which point drugs remain physically blocked at the membrane level. However it remains to be determined experimentally whether the membrane itself could, on its own, affect drug entry into cells that have been selected by a low concentration of drug and that do not express transporters. We demonstrate here that in the case of the drug doxorubicin, alteration of the surface pressure of membrane leaflets drive drug resistance

Predicting In Vivo Efficacy of Potential Restenosis Therapies by Cell Culture Studies: Species-Dependent Susceptibility of Vascular Smooth Muscle Cells

Although drug-eluting stents (DES) are successfully utilized for restenosis therapy, the development of local and systemic therapeutic means including nanoparticles (NP) continues. Lack of correlation between in vitro and in vivo studies is one of the major drawbacks in developing new drug delivery systems. The present study was designed to examine the applicability of the arterial explant outgrowth model, and of smooth muscle cells (SMC) cultures for prescreening of possible drugs. Elucidation of different species sensitivity (rat, rabbit, porcine and human) to diverse drugs (tyrphostins, heparin and bisphsophonates) and a delivery system (nanoparticles) could provide a valuable screening tool for further in vivo studies. The anticipated sensitivity ranking from the explant outgrowth model and SMC mitotic rates (porcine>rat>>rabbit>human) do not correlate with the observed relative sensitivity of those animals to antiproliferative therapy in restenosis models (rat≥rabbit>porcine>human). Similarly, the inhibitory profile of the various antirestenotic drugs in SMC cultures (rabbit>porcine>rat>>human) do not correlate with animal studies, the rabbit- and porcine-derived SMC being highly sensitive. The validity of in vitro culture studies for the screening of controlled release delivery systems such as nanoparticles is limited. It is suggested that prescreening studies of possible drug candidates for restenosis therapy should include both SMC cell cultures of rat and human, appropriately designed with a suitable serum

Nanobiomagnetics

The application of nanomagnetic materials to biological systems has produced significant advances in research, diagnosis, and treatment of numerous pathologies. This chapter summarizes the major applications of magnetic materials: magnetic targeting, drug and gene delivery, magnetic separation, the use of magnetic beads in manipulating single molecules, as contrast agents in magnetic resonance imaging, and for hyperthermia. Biocompatibility requirements for magnetic materials used in these applications are reviewed. “Nanobiomagnetism” is the intersection of nanomagnetism and medicine that focuses on biological systems and/or processes. Magnetism is an inherent facet of life, from iron in blood to the ability of magnetotactic bacteria, birds, honeybees and other creatures to navigate by the Earth’s magnetic field. Iron plays a critical part in many aspects of human neurophysiology. Naturally occurring iron in the body usually is stored within ferritin, which are 12-nm hollow spherical shells that each can hold up to 2,500 iron atoms in the form of mineralized ferrihydrite. Anomalous amounts of iron—possibly in nanoscale form—are associated with many neurodegenerative disorders such as Alzheimer’s, Parkinson’s, and Huntington’s diseases. The ability of magnets to act on objects at a distance makes them valuable medical tools. A 1624 report described the extraction of an iron splinter from an eye using a magnet. Safety pins, bullets and grenade splinters were removed using magnets. Grazing cows are fed magnets to prevent sharp metallic objects they eat from damaging the intestines. The invention of stronger, smaller permanent magnets made possible more delicate applications, such as temporarily fixing prosthesis in dentistry, guiding catheters through the body, and navigating within the brain. Nanoscale materials have a special relevance to biomedical applications due to their size compatibility with cells (10–100 μm), viruses (20–450 nm), proteins (5–50 nm) and genes (2 nm wide by 10–100 nm long). Nanoparticles are small enough to move inside the body without disrupting normal functions, and can access spaces inaccessible by other means. Cells react to the topography of their environment on size scales as small as 5 nm - up to 1000 times smaller than their own size. Changes in response to topography literally can induce growth or death. Nanostructured materials allow study of these critical processes on a single-cell level. Notice: The term Nanobiomagnetics ® ™ has been registered as a federal trademark by Nanobiomagnetics, Inc., of Oklahoma City, OK

Magnetic studies of iron oxide nanoparticles coated with oleic acid and Pluronic® block copolymer

We have prepared and studied iron-oxide nanoparticles coated with oleic acid (OA) and Pluronic® polymer. The mean diameter of the iron-oxide nanoparticles was 9.3(±)0.8 nm. Saturation magnetization values measured at 10 K varied from 66.1(±0.7) emu/g to 98.7(±0.5) emu/g. At 300 K the loops showed negligible coercive field. The peaks in zero-field-cooled susceptibility decreased from 280 to 168 K with increasing OA concentration up to 10.6 wt %, and remained nearly constant for higher concentrations. This suggests that incomplete coverage of the OA allows small, interacting agglomerates to form