Multi- to Unilamellar Transitions in Catanionic Vesicles

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Cytochrome-c Affects the Monoolein Polymorphism: Consequences for Stability and Loading Efficiency of Drug Delivery Systems

Structural properties and polymorphism of monoolein (MO) in aqueous solutions have been studied for a long time, and the final picture can be considered definite. The presence of bicontinuous phases and the ability to encapsulate hydrophilic, hydrophobic, and amphiphilic compounds, together with the capability to protect and slowly release the entrapped molecules, designated MO phases as good matrices for the sustained release of drugs. Because phase stability, loading efficiency, and bioavailability are strongly correlated, the interplay between MO phases and entrapped compounds is worthy of investigation. In this paper, low angle X-ray diffraction has been used to describe the effects of a model protein (the cytochrome-c) on the monoolein cubic phases as a function of both incubation time and protein concentration in the soaking solutions. Results show that the MO polymorphism is strongly modified by the protein, underlying the very large affinity of the cytochrome-c toward monoolein. However, the different phases have a different sensibility to cytochrome-c, as phase transitions occur when the protein amount exceeds some different critical values, probably related to the structure characteristics (2 cytochrome-c per unit cell at the Pn3m to Im3m cubic phase transition and 10–20 cytochrome-c per unit cell at the Im3m to P4$_3$32 cubic phase transition). Moreover, although equilibration times resulted to be quite long (more than 10 days), the fraction of cytochrome-c incorporated into the MO phases is very high (up to 20% v/v inside the P4$_3$32 cubic phase). Such results are intriguing: even if they may be specific to the cytochrome-c/MO case, the need of assessing the structural characteristics of lipid matrices before their use as drug delivery systems is evident

Structure-dynamics relationship in crystallizing poly(ethylene terephthalate) as revealed by time-resolved X-ray and dielectric methods

The isothermal cold crystallization of poly(ethylene terephthalate) was investigated by simultaneous small and wide angle X-ray scattering (SAXS and WAXS) and dielectric spectroscopy (DS). By this experimental approach (SWD), simultaneously collected information was obtained about the specific changes occurring in both crystalline and amorphous phases during crystallization. The main features which are directly derived from our experiments can be explained assuming the formation of a heterogeneous multiple lamellar population arrangement. The rigid amorphous phase can be associated with the intra-lamellar stack amorphous phase. The restriction of the amorphous phase mobility mainly occurs in the inter-lamellar stacks regions probably due to the formation of secondary lamellae. © 2004 Elsevier Ltd. All rights reservedMCYT (grant FPA2001-2139) Spain. IHP-Contract HPRI-CT-1999-00040 of the European Commission (EC(ERBFMGEDT 950059) and II-00-015 EC).Peer Reviewe

Cytochrome‑<i>c</i> Affects the Monoolein Polymorphism: Consequences for Stability and Loading Efficiency of Drug Delivery Systems

Structural properties and polymorphism of monoolein (MO) in aqueous solutions have been studied for a long time, and the final picture can be considered definite. The presence of bicontinuous phases and the ability to encapsulate hydrophilic, hydrophobic, and amphiphilic compounds, together with the capability to protect and slowly release the entrapped molecules, designated MO phases as good matrices for the sustained release of drugs. Because phase stability, loading efficiency, and bioavailability are strongly correlated, the interplay between MO phases and entrapped compounds is worthy of investigation. In this paper, low angle X-ray diffraction has been used to describe the effects of a model protein (the cytochrome-<i>c</i>) on the monoolein cubic phases as a function of both incubation time and protein concentration in the soaking solutions. Results show that the MO polymorphism is strongly modified by the protein, underlying the very large affinity of the cytochrome-<i>c</i> toward monoolein. However, the different phases have a different sensibility to cytochrome-<i>c</i>, as phase transitions occur when the protein amount exceeds some different critical values, probably related to the structure characteristics (2 cytochrome-<i>c</i> per unit cell at the <i>Pn</i>3<i>m</i> to <i>Im</i>3<i>m</i> cubic phase transition and 10–20 cytochrome-<i>c</i> per unit cell at the <i>Im</i>3<i>m</i> to <i>P</i>4₃32 cubic phase transition). Moreover, although equilibration times resulted to be quite long (more than 10 days), the fraction of cytochrome-<i>c</i> incorporated into the MO phases is very high (up to 20% v/v inside the <i>P</i>4₃32 cubic phase). Such results are intriguing: even if they may be specific to the cytochrome-<i>c</i>/MO case, the need of assessing the structural characteristics of lipid matrices before their use as drug delivery systems is evident