Preventing corona effects: multi-phosphonic acid poly(ethylene glycol) copolymers for stable stealth iron oxide nanoparticles

When disperse in biological fluids, engineered nanoparticles are selectively coated with proteins, resulting in the formation of a protein corona. It is suggested that the protein corona is critical in regulating the conditions of entry into the cytoplasm of living cells. Recent reports describe this phenomenon as ubiquitous and independent of the nature of the particle. For nanomedicine applications however, there is a need to design advanced and cost-effective coatings that are resistant to protein adsorption and that increase the biodistribution in vivo. In this study, phosphonic acid poly(ethylene glycol) copolymers were synthesized and used to coat iron oxide particles. The copolymer composition was optimized to provide simple and scalable protocols as well as long-term stability in culture media. It is shown that polymers with multiple phosphonic acid functionalities and PEG chains outperform other types of coating, including ligands, polyelectrolytes and carboxylic acid functionalized PEG. PEGylated particles exhibit moreover exceptional low cellular uptake, of the order of 100 femtograms of iron per cell. The present approach demonstrates that the surface chemistry of engineered particles is a key parameter in the interactions with cells. It also opens up new avenues for the efficient functionalization of inorganic surfaces.Comment: 21 page, 7 figures,Biomacromolecules 201

Self-assembly Of Complex Salts Of Cationic Surfactants And Anionic-neutral Block Copolymers. Dispersions With Liquid-crystalline Internal Structure

We report the synthesis of complex salts made from the cationic surfactant dodecyltrimethylammonium and diblock copolymers poly(acrylic acid)-block-poly(acrylamide) of different molecular weights. In water, the complex salts self-assemble into stable hierarchical aggregates with a dense core and a diffuse shell. In contrast to earlier reports, the surfactant/polymer aggregates exhibit a liquid crystalline structure of Pm3n cubic symmetry. The crystal structure is analogous to that obtained with homopolymer. Size and aggregation numbers were estimated from a combination of light and small-angle X-ray scattering experiments. It is found that the size of the aggregates decreases with increasing diblock asymmetry. 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Tuning methyl 4,6-O-benzylidene alpha-D-glucopyranosides' gelation ability by minor group modifications

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Ten methyl 4,6-O-benzylidene alpha-D-glucopyranosides were synthesized for the purpose of studying systematically the effect of small group changes at position 4 of the aromatic ring on the ability to gelate organic solvents. The gelation properties are discussed on the basis of small angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) measurements, and scanning electron microscopy (SEM) observations. Sol-gel transition temperatures were determined simultaneously by DSC and temperature-dependent FTIR measurements. The current study emphasizes that carbohydrates furnish not only valuable information about structural requirements for organogelator design, but also for molecular assembly systems in general. (C) 2012 Elsevier Ltd. All rights reserved.3536978Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Evidence of a two-step process and pathway dependency in the thermodynamics of poly(diallyldimethylammonium chloride)/poly(sodium acrylate) complexation

Recent studies have pointed out the importance of polyelectrolyte assembly in the elaboration of innovative nanomaterials. Beyond their structures, many important questions on the thermodynamics of association remain unanswered. Here, we investigate the complexation between poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium acrylate) (PANa) chains using a combination of three techniques: isothermal titration calorimetry (ITC), static and dynamic light scattering and electrophoresis. Upon addition of PDADMAC to PANa or vice-versa, the results obtained by the different techniques agree wellwith each other, and reveal a two-step process. The primary process is the formation of highly charged polyelectrolyte complexes of size 100 nm. The secondary process is the transition towards a coacervate phase made of rich and poor polymer droplets. The binding isotherms measured are accounted for using a phenomenological model that provides the thermodynamic parameters for each reaction. Small positive enthalpies and large positive entropies consistent with a counterion release scenario are found throughout this study. Furthermore, this work stresses the importance of the underestimated formulation pathway or mixing order in polyelectrolyte complexation

Photoacoustic study of the influence of the cooling temperature on the CO2_2 emission rate by Carica papaya L. in modified atmosphere

The monitoring of trace gas emitted by papaya fruits and assessments of its mass loss can contribute to improve the conditions for their storage and transport. The C0$_2$ emission rate by the papaya fruits, monitored by a commercial infrared-based gas analyzer, was influenced by the temperature and storage time. The fruits stored at temperature of 13 °C accumulated more CO$_2$ inside the PEBD bags than those fruits stored at 6 °C. The loss of mass of the fruits progressively increased with storage time for both temperatures until the saturation of the moisture inside the PEBD bag, been more pronounced at 13 ºC

Polyelectrolyte assisted charge titration spectrometry: Applications to latex and oxide nanoparticles

The electrostatic charge density of particles is of paramount importance for the control of the dispersion stability. Conventional methods use potentiometric, conductometric or turbidity titration but require large amount of samples. Here we report a simple and cost-effective method called polyelectrolyte assisted charge titration spectrometry or PACTS. The technique takes advantage of the propensity of oppositely charged polymers and particles to assemble upon mixing, leading to aggregation or phase separation. The mixed dispersions exhibit a maximum in light scattering as a function of the volumetric ratio X, and the peak position XMax is linked to the particle charge density according to σ∼D0XMax where D0 is the particle diameter. The PACTS is successfully applied to organic latex, aluminum and silicon oxide particles of positive or negative charge using poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate). The protocol is also optimized with respect to important parameters such as pH and concentration, and to the polyelectrolyte molecular weight. The advantAssemblage Macromoléculaire Hors-équilibre Compréhension, Contrôle & nouvelles structure

Determinação da escala de coloração da casca e do rendimento em suco do maracujá-amarelo em diferentes épocas de colheita Determination of the peel color scale and juice yield of yellow passion fruits in different harvest seasons

Este trabalho teve como objetivo determinar uma escala de coloração da casca para identificar o estádio de maturação do maracujá-amarelo e avaliar o rendimento em suco, em diferentes épocas de colheita. Os experimentos foram constituídos de 2 épocas de colheita, contemplando a estação de menor temperatura e menor precipitação de chuvas (EP1-Maio/Setembro), a estação de maior temperatura e precipitação de chuvas (EP2-Outubro/Dezembro) e 7 estádios de maturação, com 10 repetições. Os resultados foram avaliados pelo teste de Tukey, a 5% de significância. O parâmetro b de Hunter foi utilizado como o indexador da mudança da coloração amarela. Verificou-se que a mudança de coloração ocorreu no sentido da base para o pedúnculo do fruto. Os frutos da época EP2 apresentaram a maior espessura de casca e o menor rendimento em suco, nos estádios iniciais de amadurecimento. Nos frutos com mais de 65,9% da casca amarelada, a época de colheita não influenciou na espessura da casca e no rendimento em suco, apresentando níveis máximos de suco. Frutos da época EP1 apresentaram o máximo rendimento a partir do estádio com 21,3% de cor amarela.<br>This work had the aim to determinate the peel color scale intended to identify the ripening stage of the yellow passion fruit and evaluate its juice yield in different harvest seasons. The experiments were constituted of 2 harvest seasons and they were accomplished during the period of low temperatures and less precipitation (EP1 - May/September) and high temperatures and more precipitation (EP2 - October/December), and seven ripening stages using ten replications. The results were compared by applying the Tukey test at the level of 5% of probability. Hunter b parameter was used as the yellowing index. It was verified that the yellow color progressed from the base to the fruit peduncle. Fruits from the EP2 season presented the lowest juice yield and the highest peel thickness in the early ripening stages. In fruits with at least 65% of yellow color peel, the harvest season did not influence in the peel thickness and in the juice yield, showing the highest level of juice. Fruits from the EP1 season showed the higher juice yield after 21,3% yellow color

Soluble Aggregates in Aqueous Solutions of Polyion-Surfactant Ion Complex Salts and a Nonionic Surfactant.

Water-soluble aggregates based on two polyion-surfactant ion "complex salts", consisting of hexadecyltrimethylammonium (C16TA(+)) and polyacrylate (PA(-)) with either 25 or 6000 repeating units, with added nonionic surfactant octaethylene glycol monododecyl ether (C12E8) have been investigated. A previous phase study has shown that added C12E5 or C12E8 can solubilize complex salts in aqueous systems, and that increasing the poly(ethylene oxide) chain length of the nonionic surfactant and/or decreasing the polyion length favors dissolution. In this work we report on dynamic light scattering, NMR diffusometry, small-angle X-ray scattering, and isothermal titration calorimetry measurements performed to characterize the solubilized composite aggregates in dilute aqueous solution in terms of size and stoichiometry. It was found that mixed aggregates of polyacrylate, C16TA(+) ions, and C12E8, with almost constant stoichiometry, coexist with free micelles of C12E8 at all investigated mixing ratios. The length of the polyion only weakly affects the stoichiometry of the mixed aggregates while strongly affecting their size and water solubility