Successful intracellular delivery of genes requires an efficient carrier, as genes by themselves cannot diffuse across cell membranes. Because of the toxicity and immunogenicity of viral vectors, nonviral vectors are gaining tremendous interest in research. In this work, we have investigated the temperature-dependent DNA condensation efficiency of various compositions of a thermosensitive block copolymer viz., poly(N-isopropylacrylamide)-b-poly(2-(diethylamino)ethyl methacrylate) (PNIPA-b-PDMAEMA). Three different copolymer compositions of varying molecular weights were successfully synthesized via the RAFT polymerization technique. Steady-state fluorescence and circular dichroism (CD) spectroscopies, dynamic light scattering (DLS) and zeta potential measurements, agarose gel electrophoresis, and atomic force microscopy techniques were utilized to study the interaction of the copolymers with DNA at temperatures above and below the critical aggregation temperature (CAT). All these experiments revealed that, above the CAT, there was formation of highly stable and tight polymer–DNA complexes (polyplexes). The size of polyplexes was dependent on the temperature up to a certain charge ratio, as determined by the DLS results. The results obtained from temperature-dependent fluorescence spectroscopy, CD, and gel electrophoresis indicated that the DNA molecules were shielded more from aqueous exposure above the CAT because of the formation of relatively more compact complexes. The polyplexes also exhibited changes in the particle morphology below and above the CAT, with particles generated above CAT being more spherical in morphology. These results suggested at the possibility of modulating the complex formation by temperature modification. The present biophysical studies would provide new physical insight into the design of novel gene carriers.
Defect engineering, such as modification of oxygen vacancy density, has been considered as an effective approach to tailor the catalytic performance on transition-metal oxide nanostructured surfaces. The role of oxygen vacancies (O V ) on the surface of the as-prepared, zinnia-shaped morphology of CuO nanostructures and their marigold forms on calcination at 800 °C has been investigated through the study of model catalytic reactions of reduction of 4-nitrophenol and aerobic oxidation of benzyl alcohol. The O V on the surfaces of different morphologies of CuO have been identified and quantified through Rietveld analysis and HRTEM, EPR, and XPS studies. The structure− activity relationships between surface oxygen vacancies (O V ) and catalytic performance have been systematically investigated. The enhanced catalytic performance of the cubic CuO nanostructures compared to their as-prepared forms has been attributed to the formation of surface oxygen species on the reactive and dominant (110) surface that has low oxygen vacancy formation energy. The mechanistic role of surface oxygen species in the studied reactions has been quantitatively correlated with the catalytic activity of the different morphological forms of the CuO nanostructures.
It is essential to replace the conventional toluene chlorination process to produce industrially important benzaldehyde with a more ecofriendly process. In that direction, we have developed polymer-conjugated magnetic nanoparticles as "green catalysts". Poly[(N-isopropylacrylamide-b-acrylic acid)] and poly-[(N-isopropylacrylamide-r-N-vinylpyrrolidone)-b-(acrylic acid)] coated magnetic nanoparticles showed high catalytic activity in the synthesis of benzaldehyde by styrene oxidation reaction at room temperature in water using hydrogen peroxide as an oxidizer. The presence of hydrophilic polymers on nanoparticle surfaces improved the aqueous dispersibility, enabling quasi-homogeneous catalysis in water at room temperature. The conversion of styrene to benzaldehyde and styrene oxide can be regulated by varying the temperature, owing to the temperature responsiveness of the block copolymers. Parameters like catalyst concentration, temperature, and time were varied to achieve an optimal reaction condition. The catalysts can be quickly recovered using their magnetic property and reused without noticeable loss in catalytic activity. Thus, these two nanoparticle systems showed great potential for green nanocatalysts in industrial use.
An ideal DNA carrier is one that is capable of effectively condensing DNA into complexes of optimum size and shape, preventing premature decomplexation in the bloodstream and efficiently releasing the DNA into affected cells. In this context, we have developed a novel β-cyclodextrin (β-CD)-based four-arm star-shaped polymer inclusion complex (IC) with arms made of a poly(L-histidine)-based cationic polymer. The polymer was well characterized by gel permeation chromatography, NMR, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. We have also investigated its DNA complexation and release properties. Bisadamantane containing a disulfide bond was synthesized that linked two such poly(L-histidine)-containing β-CD units via guest−host interactions to prepare the presented IC. Besides using the conventional steady-state fluorescence spectroscopy, the ability of this IC to condense DNA to form polyplexes and their release behavior have been established by using the time-resolved fluorescence spectroscopy technique. Thiazole orange (TO) was used for the first time as a DNA-intercalating dye in the time-resolved fluorescence spectroscopic study. The superior DNA-condensing ability of the IC as compared to that of the precursor two-arm β-CD and linear poly(L-histidine) of a comparable molecular weight, as confirmed by dynamic light scattering, zeta potential, atomic force microscopy, and gel electrophoresis studies, could be attributed to a higher charge density. The IC−DNA polyplexes were found to be stable in a medium similar to an extracellular fluid but could efficiently release DNA in the presence of 10 mM glutathione, a concentration prevalent in the intracellular fluid of cancer cells. Hence, here, we have successfully demonstrated the synthesis of a novel biocompatible star-shaped IC with the potential to carry and release DNA in cancer cells and also established the feasibility of using the time-resolved fluorescence spectroscopic technique to study the complexation behavior of the polycation and DNA using TO as a DNAintercalating dye.
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