Evgeny Polushkin

Phase behavior of cationic amphiphiles and their mixtures with helper lipid influences lipoplex shape, DNA translocation, and transfection efficiency.

Cationic lipids are widely used for gene transfection, but their mechanism of action is still poorly understood. To improve this knowledge, a structure-function study was carried out with two pyridinium-based lipid analogs with identical headgroups but differing in alkyl chain (un)saturation, i.e., SAINT-2 (diC18:1) and SAINT-5 (diC18:0). Although both amphiphiles display transfection activity per se, DOPE strongly promotes SAINT-2-mediated transfection, but not that of SAINT-5, despite the fact that DOPE effectively facilitates plasmid dissociation from either lipoplex. This difference appears to correlate with membrane stiffness, dictated by the cationic lipid packing in the donor liposomes, which governs the kinetics of lipid recruitment by the plasmid upon lipoplex assembly. Because of its interaction with the relatively rigid SAINT-5 membranes, the plasmid becomes inappropriately condensed, which results in formation of structurally deformed lipoplexes. This structural deformation does not affect its cellular uptake but, rather, hampers plasmid translocation across endosomal and/or nuclear membranes. This is inferred from the observation that both lipoplexes effectively translocate much smaller oligonucleotides into cells. In fact, SAINT-5/DOPE-mediated transfection is greatly improved when, before lipoplex assembly, the plasmid is stabilized by condensation with polylysine. The results emphasize a role of the structural shape of the plasmid in gaining cytosolic/nuclear access. Moreover, it has been proposed that such a translocation is promoted when the lipoplex adopts the hexagonal phase, and data are presented that demonstrate that the lamellar SAINT-5/DOPE lipoplex adopts such a phase after its interaction with acidic phospholipid-containing membranes.

Tridirectional protonic conductivity in soft materials

ATR IR spectra were measured on a Fourier transform infrared (FTIR) Perkin-Elmer System 2000 spectrometer equipped with a SpectraTech horizontal ATR cell (60 incident angle, Ge ATR crystal). Titanium dioxide mesoporous films were deposited on ITO glass by the reverse-micellar route and the photosensitizer RuL2(NCS)2 was attached as in [3]. The ureasil precursors were synthesized as in [18]. Synthesis of class II nanocomposite gels using ureasil precursors, their enrichment with the iodine/ iodide couple, and their deposition in a DSPEC was carried out as follows: absolute ethanol (2 mL) was mixed with the ureasil precursor (PP-4000, 2 g). KI (0.5 M) and I2 (0.05 M) were added to the above mixture with stirring at ambient conditions. The mixture was continuously stirred for about 3 h. Then acetic acid (0.35 mL) was added and stirring continued for another 4 h at ambient conditions. At the end of this period, a viscous brown fluid was obtained. A few drops of this solution were applied to the electrode-bearing TiO2 film with attached dye and we placed the second (platinized) electrode on top, simply by pressing the two electrodes together. Connections were made with silver paste and a copper ribbon as seen schematically in Figure 4.

Nanoporous Network Channels from Self‐Assembled Triblock Copolymer Supramolecules

Supramolecular complexes of a poly(tert-butoxystyrene)-block-polystyrene-block-poly(4-vinylpyridine) triblock copolymers and less than stoichiometric amounts of pentadecylphenol (PDP) are shown to self-assemble into a core-shell gyroid morphology with the core channels formed by the hydrogen-bonded P4VP(PDP)complexes. After structure formation, PDP was removed using a simple washing procedure, resulting in well-ordered nanoporous films that were used as templates for nickel plating.

Annealing-Induced Changes in Double-Brush Langmuir-Blodgett Films of alpha-Helical Diblock Copolypeptides

The effect of annealing on the structure and the helix orientation in Langmuir-Blodgett (LB) monolayers of diblock copolymers (PLGA-b-PMLGSLGs) of poly(alpha-L-glutamic acid) (PLGA) and poly(gamma-methyl-L-glutamate-ran-gamma-stearyl-L-glutamate) with 30 mol % of stearyl substituents (PMLGSLG) with unidirectional helix orientation deposited on hydrophilic silicon substrates was characterized by means of small-angle X-ray reflectivity, transmission Fourier transform infrared spectroscopy, and atomic force microscopy. Upon annealing at 100 degrees C for 24 h, the alpha-helices became less tilted toward the substrate surface normal. Surface area shrinkage accompanied the change in tilt, indicated by an increase in both film thickness and electron density, resulting in more compact and uniform films. The enhancement of the helix orientation by thermal annealing was greater for the PMLGSLG block and for the diblock copolymers with the shorter block lengths. For these diblock copolymers, annealing resulted in postorientation of the PMLGSLG block helices almost perpendicular to the substrate surface. This effect originates from a considerable increase in intermolecular packing of the PLGA block caused by hydrogen bonds between the carboxylic groups upon annealing, as well as the high mobility of the PMLGSLG block helices for rearrangement favored by the melted side chain mantle at elevated temperatures.

Fenton detemplation of ordered (meso)porous materials

This article describes a new methodology (Fenton detemplation), which consists of removing the template by chemical oxidation and develop the materials porosity. The oxidizing agents are OH* radicals, which are generated from H 2 O 2 in the presence of catalytic amounts of Fe cations. This is known as Fentons chemistry, classically applied in wastewater treatment. It is innovative to implement this protocol in heterogeneous catalysis, and it displays many possibilities for the preparation of zeolites & mesoporous supports. The radicals are produced at low temperature <353 K, which is a key aspect for preserving the virgin structure of the material. The paper discusses two cases: beta zeolite and all-silica SBA-15, showing improved properties due to the better preservation of the structure, as a consequence of the mild conditions applied in detemplation and overcoming the problems associated to calcination.