Freeze-fracture Electron Microscopy Characterization of Nano-&Microparticles Suitable for Drug&Gene Delivery

Freeze-fracture electron microscopy, Nanoparticles, Drug &Gene DeliveryThe potency of drug/gene-loaded nanoparticles is frequently depending upon their morphology adopted in a biological relevant environment. Freeze-fracture electron microscopy (ff-em) is a powerful techniques to monitor the self-assembling of lipid-, polymer-, as well as protein/peptide-based drug and gene carries on a nano-size resolution scale (resolution limit in our hands is 2 nm for periodical structures). Ff-em allows not only the characterization of nano- and micoparticles suitable for drug/gene delivery but also is the method of choice to study their fate related to drug/gene load, application milieu, and during interaction with cells [1-3]. Furthermore it allows distinguishing between bilayer and non-bilayer structures [4-7]. Using ff-em we studied the morphology of a wide variety of nano- and microparticles suitable for drug and gene delivery such as quantum dots, micelles, including spherical-, disc-, and worm-type micelles, small unilamellar liposomes, multilamellar liposomes, niosomes, lipid-stabilized gas bubbles, cochleate cylinder, depofoam particles, and drug crystals[1-3, 8-13]. Because of their small size, nanoparticles such as spherical micelles (<50nm) and small liposomes (<100nm) accumulate in pathological areas and are excellent carriers for poorly water-soluble drugs [10, 11]. Depending upon helper lipid, ionic strength, and gene component CLDC adopt polymorph structures such as spaghetti/ meatballs, map-pins, as well as honeycomb structures [12, 13]. Parallel studies of transfection activity and morphology of CLDC showed that lipid precipitates displaying honeycomb structure are associated with high transfection rates under in vitro conditions. In vivo transfection activity seems to be associated with small complexes such as map-pin structure [13]. Furthermore the fracture behavior of lipid-based macromolecular assemblies indicates their adoption of bilayer or non-bilayer structures. While bilayer vesicles such as liposomes display convex and concave fracture faces, monolayer-coated gas bubbles show concave, and nanoparticles such as micelles convex fracture faces respectively. References [1] B. Sternberg, Liposome Technology, CRC Press I (1992) 363. [2] B. Sternberg, Handbook Nonmedical Applications of Liposomes CRC Press (1996) 271. [3] B. Sternberg, Medical Applications of Liposomes, Elsevier (1998) 395. [4] A. Angelova et al. J. Drug Del. Sci. Tech. (2005) 15 (1) 108. [5] A. Angelova, et al. J. Phys. Chem. B (2005), 109 (8), 3089. [6] A. Angelova, et al. Langmuir (2005), 21, 4138. [7] B. Angelova, et al. Accepted by J. Am. Chem. Soc. 01-05, (2006) [8] P. L. Kan et al. J. Phys. Chem. B (2004) 108, 8129. [9] B. Sternberg et al., Nature 378 (1995) 21. [10] V. P. Torchilin et al. PNAS (2003) 100 (4) 1972. [11] V. P. Torchilin et al. PNAS (2003) 100 (10) 603. [12] B. Sternberg et al., FEBS-Letters 356 (1994) 361. [13] B. Sternberg et al., BBA 1375 (1998) 1375

Sulfometuron incorporation in cationic micelles adsorbed on montmorillonite

The aim of this study was to understand the interactions between alkylammonium cations present as monomers and micelles and a clay mineral, montmorillonite, to develop slow release formulations of anionic herbicides, such as sulfometuron (SFM) whose leaching in soils is an environmental and economic problem. In the proposed formulation the herbicide is incorporated in positively charged micelles of quaternary amine cations, which in turn adsorb on the negatively charged clay. The adsorption of hexadecyltrimethylammonium (HDTMA) and octadecyltrimethylammonium (ODTMA) on montmorillonite was studied above and below their critical micelle concentrations (CMC). At concentrations above the CMC, the loading exceeded the clay's cation exchange capacity (CEC) and indicated higher affinity of the cation with the longer alkyl chain. An adsorption model could adequately simulate adsorption at concentrations below the CMC, and yield fair predictions for the effect of ionic strength. The model indicated that above the CMC adsorbed micelles contributed significantly to the amount of ODTMA adsorbed. Evidence for adsorption of ODTMA micelles on montmorillonite was provided by X-ray diffraction, freeze-fracture electron microscopy, and dialysis bag measurements. SFM was not adsorbed directly on the clay mineral, and adsorbed at low levels, when the organic cation was adsorbed as monomers. In contrast, a large fraction of SFM adsorbed on the clay mineral when incorporated in micelles that adsorbed on the clay.Peer Reviewe

Formulaciones arcilla-liposomas de sulfometurón para reducir la lixiviación del herbicida

2 páginas, 1 figura, 1 tabla, 1 referencia.-- Publicado en el Capítulo IV: Contaminación y Medio Ambiente.-- Trabajo presentado a la XVII Reunión Científica de la Sociedad Española de Arcillas, celebrada en Elche (Alicante) y Castellón, del 27-29 de noviembre de 2002.La movilidad de herbicidas en suelos es de gran interés desde hace mucho tiempo, por muchas razones entre las que se incluye (1): (i) su potencial para contaminar aguas subterráneas; (ii) reducción en su eficacia cuando el herbicida lixivia por debajo de la zona raíz de las malas hierbas, que puede potencialmente dañar la cosecha tratada; (iii) su potencial para volver a la superficie del suelo con el consiguiente peligro para posteriores cultivos. Las formulaciones de liberación controlada de herbicidas (FLCs) proveen una liberación lenta del ingrediente activo a una velocidad adecuada, reduciéndose de esta forma la cantidad de producto químico necesario para un control eficiente de las malas hierbas. El presente estudio demuestra que el uso de liposomas es una nueva herramienta para el diseño de formulaciones de liberación controlada de sulfometurón (SFM), un herbicida de la familia de las sulfonilureas. El herbicida se incorpora en vesículas formadas por cationes de aminas cuaternarias, dimetildidodecilamonio (DDAB) y dimetildioctadecilamonio (DDOB), que son posteriormente adsorbidos sobre una montmorillonita estándar (SWy-2). La concentración inicial en las soluciones vesiculares del herbicida era de 0.6 mM y del catión orgánico 6 mM.Peer reviewe