Periodic binary Si:Ti, Si:Al mixed macroporous oxides with ultra-high heteroatom loading: a facile sol-gel approach

Highly ordered macroporous mixed metal oxides were prepared with very high mixed metal ratios using an optimized silicon alkoxide prehydrolysis process. The homogenous solutions completely filled the interstitial voids in polymethylmethacrylate (PMMA) artificial opal templates. Subsequent template removal resulted in highly ordered aluminosilicate and titanosilicate inverse opal pore networks. The optimized process allowed the fabrication of periodic binary metal oxide frameworks with 2:1 Si:Al loadings and 1:1 Si:Ti loadings. The mixed metal oxides did not show any phase segregation during high temperature template removal as evidenced by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and Fourier transform infrared spectroscopy (FT-IR). The as formed macroporous metal oxides demonstrate excellent substrate adherence and mechanical stability and showed refractive index modulation in direct relation to the silicon/heterometal ratio in the precursor sol

Formation of Inverse Topology Lyotropic Phases in Dioleoylphosphatidylcholine/Oleic Acid and Dioleoylphosphatidylethanolamine/Oleic Acid Binary Mixtures

The addition of saturated fatty acids (FA) to phosphatidylcholine lipids (PC) that have saturated acyl chains has been shown to promote the formation of lyotropic liquid-crystalline phases with negative mean curvature. PC/FA mixtures may exhibit inverse bicontinuous cubic phases (<i>Im</i>3<i>m</i>, <i>Pn</i>3<i>m</i>) or inverse topology hexagonal phases (H_II), depending on the length of the acyl chains/fatty acid. Here we report a detailed study of the phase behavior of binary mixtures of dioleoylphosphatidylcholine (DOPC)/oleic acid (OA) and dioleoylphosphatidylethanolamine (DOPE)/oleic acid at limiting hydration, constructed using small-angle X-ray diffraction (SAXD) data. The phase diagrams of both systems show a succession of phases with increasing negative mean curvature with increasing OA content. At high OA concentrations, we have observed the occurrence of an inverse micellar <i>Fd</i>3<i>m</i> phase in both systems. Hitherto, this phase had not been reported for phosphatidylethanolamine/fatty acid mixtures, and as such it highlights an additional route through which fatty acids may increase the propensity of bilayer lipid membranes to curve. We also propose a method that uses the temperature dependence of the lattice parameters of the H_II phases to estimate the spontaneous radii of curvature (<i>R</i>₀) of the binary mixtures and of the component lipids. Using this method, we calculated the <i>R</i>₀ values of the complexes comprising one phospholipid molecule and two fatty acid molecules, which have been postulated to drive the formation of inverse phases in PL/FA mixtures. These are −1.8 nm (±0.4 nm) for DOPC­(OA)₂ and −1.1 nm (±0.1 nm) for DOPE­(OA)₂. <i>R</i>₀ values estimated in this way allow the quantification of the contribution that different lipid species make to membrane curvature elastic properties and hence of their effect on the function of membrane-bound proteins

Linear <i>ds</i>DNA Partitions Spontaneously into the Inverse Hexagonal Lyotropic Liquid Crystalline Phases of Phospholipids

Recently, we reported that DNA associated with inverse hexagonal (H_II) lyotropic liquid crystal phases of the lipid 1,2-dioleoyl-<i>sn</i>-glycero-3-phosphoethanolamine (DOPE) was actively transcribed by T7 RNA polymerase. Our findings suggested that key components of the transcription process, probably the T7 RNA polymerase and the DNA, remained associated with the monolithic H_II phase throughout transcription. Here, we investigate the partitioning of DNA between an H_II lyotropic liquid crystal phase and an isotropic supernatant phase in order to develop insights into the localization of DNA in liquid crystalline environments. Our results show that linear double stranded DNA (<i>ds</i>DNA) molecules partition spontaneously into monolithic preformed H_II liquid crystal phases of DOPE. We propose that this process is driven by the increase in entropy due to the release of counterions from the DNA when it inserts into the aqueous pores of the H_II phase