This study describes a novel liposomal formulation for siRNA delivery, based on the mixture of the neutral lipid monoolein (MO) and cationic lipids of the dioctadecyldimethylammonium (DODA) family. The cationic lipids dioctadecyldimethylammonium bromide (DODAB) and chloride (DODAC) were compared in order to identify which one will most efficiently induce gene silencing. MO has a fluidizing effect on DODAC and DODAB liposomes, although it was more homogeneously distributed in DODAC bilayers. All MO-based liposomal formulations were able to efficiently encapsulate siRNA. Stable lipoplexes of small size (100-160 nm) with a positive surface charge (>+45 mV) were formed. A more uniform MO incorporation in DODAC:MO may explain an increase of the fusogenic potential of these liposomes. The siRNA-lipoplexes were readily internalized by human nonsmall cell lung carcinoma (H1299) cells, in an energy dependent process. DODAB:MO nanocarriers showed a higher internalization efficiency in comparison to DODAC:MO lipoplexes, and were also more efficient in promoting gene silencing. MO had a similar gene silencing ability as the commonly used helper lipid 1,2-dioleyl-3-phosphatidylethanolamine (DOPE), but with much lower cytotoxicity. Taking in consideration all the results presented, DODAB:MO liposomes are the most promising tested formulation for systemic siRNA delivery.
Dioctadecyldimethylammonium bromide (DODAB) is a double chain cationic lipid, which assembles as bilayer structures in aqueous solution. The precise structures formed depend on, e.g., lipid concentration and temperature. We here combine differential scanning calorimetry (DSC) and X-ray scattering (SAXS and WAXS) to investigate the thermal and structural behavior of up to 120 mM DODAB in water within the temperature range 1–70°C. Below 1 mM, this system is dominated by unilamellar vesicles (ULVs). Between 1 and 65 mM, ULVs and multilamellar structures (MLSs) co-exist, while above 65 mM, the MLSs are the preferred structure. Depending on temperature, DSC and X-ray data show that the vesicles can be either in the subgel (SG), gel, or liquid crystalline (LC) state, while the MLSs (with lattice distance d = 36.7 Å) consist of interdigitated lamellae in the SG state, and ULVs in the LC state (no Bragg peak). Critical temperatures related to the thermal transitions of these bilayer structures obtained in the heating and cooling modes are reported, together with the corresponding transition enthalpies.
PAPERarrangement at the air/water interface and the preserved luminescence in LB films are consistent with theoretical predictions using a semi-empirical Sparkle/AM1 calculation method for the molecule in vacuum. These tools were used for the first time to predict the behavior of organized films.
h i g h l i g h t s• On increasing DDAB concentration, the following phase sequence appears: monomer, vesicle, lamellae.• DDAB unilamellar vesicles are formed in water only in a very narrow concentration range.• DDAB multilamellar vesicles co-exist with unilamellar vesicles in this concentration range.• Phase separation occurs in DDAB/water, with lamellae on top and vesicles on bottom.• The reverse melting temperature of DDAB/water is around 9.5 • C. g r a p h i c a l a b s t r a c t a b s t r a c t This work aims to delineate the single isotropic vesicle phase (Ves) in the binary didodecyldimethylammonium bromide (DDAB)/water system, limited by the critical vesicle concentrations, CVC 1 ≈ 0.05 mM (2.3 × 10 −3 wt%) and CVC 2 ≈ 0.7 mM (3.1 × 10 −2 wt%), as the onset of unilamellar vesicle formation and of two-phase separation into Ves + Lam (lamellar) phases, respectively. Isothermal titration calorimetry (ITC), turbidity, and crossed polaroids observations indicate that below CVC 1 the dispersion is dominated by free monomers or micelles, but rich in uni-and multilamellar vesicles between CVC 1 and CVC 2 , with CVC 2 = 0.21 mM (9.5 × 10 −3 wt%) being the onset of multilamellar vesicle formation. Above CVC 2 , the volume of the Lam phase increases, while the volume for the Ves phase decreases to vanish around CVC 3 ≈ 21 mM (0.95 wt%). Differential scanning calorimetry (DSC) data show that the gel-to-liquid crystalline transition at T m ≈ 16 • C is highly cooperative ( T 1/2 ≈ 0.3 • C), and the melting enthalpy ( H m ) increases with DDAB concentration. Because of the remarkably slow liquid crystalline-to-gel kinetics, a cooling transition around T m ≈ 9.5 • C is reported here for the first time, we ascribe to the liquid crystalline-to-gel transition (thermal hysteresis T m ≈ 6.5 • C). Vesicle and lamellar structure formation E. Feitosa et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 480 (2015) 253-259 is supported also by hydrodynamic diameter (D H ) data, being 100-140 and 800-1200 nm, respectively, at 25 • C. The zeta potential ( ) increases with DDAB concentration but does not change much with temperature, indicating no pronounced structural change when temperature varies around T m .
This paper reports the study of structural and luminescence parameters of a seven-coordination compound containing b-diketone butyl methoxy-dibenzoyl-methane (bmdm) and triphenylphosphine oxide (tppo), both acting as antennae. The complex was obtained by substitution of water molecules in the [RE(bmdm) 3 (H 2 O) 2 ] precursor, where RE = Eu 3+ or Gd 3+ . The structural data determined by X-ray monocrystal diffraction reveal that the compound crystallizes in a triclinic space group P 1 and the coordination polyhedron is near a capped trigonal prism, with a symmetry site near a C 2v point group. The ground state geometry was determined using Sparkle/AM1 implemented in mopac2009 software, and compared with that obtained by monocrystal. The triplet (T) and singlet (S) levels were determined using INDO/S-CIS implemented in the Zindo software, the results obtained are very close to the experimental measurements. The intensity parameters O 2 and O 4 were calculated from emission spectrum. The high value of the O 2 parameter (37.2 Â 10 À20 cm 2 ) shows a highly polarizable environment around the europium ion and a high degree of covalence between the ligand and metal, showing that tppo molecules contribute to an increase in the covalence between the metal and ligand. The transfer rates show a predominance in the transfer process when compared with back transfer ones, with the main channel of transfer processes: T
Dioctadecyl‐dimethyl‐ammonium bromide (DODAB) vesicles can be characterized by their differential scanning calorimetry (DSC) thermograms comprised of two endotherms at Ts ≈ 36 °C and Tm ≈ 45 °C in the heating, ascribed respectively to the subgel‐to‐gel and gel‐to‐liquid crystalline transitions, and two exotherms at T′m ≈ 40 °C and T′s ≈ 16 °C in the cooling, ascribed respectively to the liquid crystalline‐to‐gel and gel‐to‐subgel transitions. It has been reported but not proved that the Tm‐transitions, the T′m‐transitions, the Ts‐transitions, and the T′s‐transitions are reverse to each other, displaying hystheresis ΔTm ≈ 5 °C and ΔTs ≈ 20–25 °C, respectively. By investigating the effects of the initial scanning temperature (Ti) on the transition enthalpies (ΔHm, ΔHs, ΔH′m and ΔH′s), we have seen that these transitions are the reverse to each other and display different kinetics.
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