1,720,972 research outputs found
DDAB vesicles and lamellar liquid crystals. A multinuclear NMR and Optical Microscopy Study
No full textBiocompatible lipid formulations: Phase diagrams and microstructures from Optical Microscopy and multinuclear NMR Spectroscopy
No full textEffect of 1-butanol on the microstructure of lecithin/water/tripalmitin system
No full textWarm microemulsions based on lipids characterized by a melting point over 50°C have been successfully used as starting matrix in a quenching process to obtain solid lipid nanoparticles (SLN). In this work, we have investigated the effect of 1-butanol (B) on the phase behavior of the lecithin (LCT)/water (W)/tripalmitin (TP) system at 70°C. The study has been carried out at LCT/B = 1 (weight ratio). Emulsion and liquid crystalline phase regions have been observed in the ternary phase diagram, while the presence of 1-butanol in the LCT/W/B/TP system allows the formation of a wide area of liquid isotropic phase from the whole (LCT + B)/TP binary axis up to 37 wt% of water. The microstructure of this isotropic phase has been investigated by means of 1H NMR PGSE technique. The self-diffusion coefficients of the different components along oil and water dilution lines indicate a microstructural organization characterized by a highly connected water in oil domains. © 2005 Elsevier Ireland Ltd. All rights reserved
Thermal Induced Polymerization of l-Lysine forms Branched Particles with Blue Fluorescence
No full textThe polycondensation of amino acids can originate complex polymers that display fascinating structural and optical properties. Thermally induced amidation of l-lysine allows forming a branched polymer without the support of any catalyst. The polycondensation is completed at 240–250 °C; at higher temperatures, the amino acid degrades. The obtained polylysine particles have been studied by transmission electron microscopy (TEM), nuclear magnetic resonance, and infrared spectroscopy that allow for investigating the different steps of the synthesis. The resulting structure is characterized by peculiar optical properties, e.g., excitation-dependent blue fluorescence and good quantum efficiency. Hydrogen bonds and the interactions of the amino acids are considered responsible for the optical properties of both l-lysine monomer solutions at high concentrations and the branched nanopolymers
Solid lipid nanoparticle preparation by a warm microemulsion based process: Influence of microemulsion microstructure
No full textWarm microemulsions (WME) containing lipids are used as starting systems to obtain solid lipid nanoparticles (SLN) in alternative processes to those based on high pressure homogenization technique. SLN characteristics can be influenced by the microemulsion composition and the specific conditions adopted in the quenching process related to the transformation of WME into nanoparticles. To establish optimized conditions for the production of SLN starting from WME, in a first step of this work we have defined the microstructure of warm microemulsions highlighted in the lecithin (LCT)/water (W)/tripalmitin (TP)/1-butanol (B)/taurocholate sodium salt (ST) phase behavior at 70 °C. Moreover, we have further studied the LCT/W/TP/B system by evaluating the effect on the microemulsion area due to the LCT/B weight ratio, the replacement of 1-butanol with different alcohols (ROH), and the addition of taurocholate sodium salt (ST) at different LCT/ST weight ratios. The microstructure of the isotropic phase region obtained in the presence of ST has been characterized by both 1H NMR PGSE measurements and electrical conductivity. The characteristics of final nanoparticles are discussed taking into account both the microstructure of the parent WME and the conditions of the quenching process leading to SLN. The present results highlight the relevance of the microstructural characteristic of WME to assure the obtainment of SLN with average diameter in the order of 100-200 nm and narrow size distribution
Site-directed enzymatic PEGylation of the human granulocyte colony-stimulating factor
No full textPoly(ethylene glycol) (PEG) is a widely used polymer employed to increase the circulating half-life of proteins in blood and to decrease their immunogenicity and antigenicity. PEG attaches to free amines, typically at lysine residues or at the N-terminal amino acid. This lack of selectivity can present problems when a PEGylated protein therapeutic is being developed, because predictability of activity and manufacturing reproducibility are needed for regulatory approval. Enzymatic modification of proteins is one route to overcome this limitation. Bacterial transglutaminases are enzyme candidates for site-specific modification, but they also have rather broad specificity. The need arises to be able to predict a priori potential PEGylation sites on the protein of interest and, especially, to be able to design mutants where unique PEGylation sites can be introduced when needed. We investigated the feasibility of a computational approach to the problem, using human granulocyte colony-stimulating factor as a test case. The selected protein is therapeutically relevant and represents a challenging problem, as it contains 17 potential PEGylation sites. Our results show that a combination of computational methods allows the identification of the specific glutamines that are substrates for enzymatic PEGylation by a microbial transglutaminase, and that it is possible to rationally modify the protein and introduce PEG moieties at desired sites, thus allowing the selection of regions that are unlikely to interfere with the biological activity of a therapeutic protein
A new PEG-b-alanine active derivative for releasable protein conjugation
No full textA new PEGylating agent, PEG-betaAla-NHCO-OSu, has been studied for protein amino conjugation using human growth hormone (hGH) and granulocyte colony stimulating factor (G-CSF) as model therapeutic proteins. This new activated PEG possesses a convenient property for protein modification when compared to other activated carboxylate PEGs, namely, lower reactivity. When this polymer reacts with a protein, its features lead to fewer PEG-protein conjugate isomers because it preferentially binds the most nucleophilic and exposed amines. Furthermore, the conjugates obtained with PEG-betaAla-NHCO-OSu showed an interesting slow release of polymer chains upon incubation under physiological conditions. Further investigations determined that the PEG chains released are those coupled to histidine residues, and this finally yields less PEGylated species as well as free protein. This release allows a partial recovery of protein activity that is often remarkably and permanently reduced after stable PEGylation, and it occurs in water or blood without the involvement of enzymes. On the other hand, the rate of PEG release, tuned by the chemical structure of this new PEGylating agent, is not too high, and therefore, the achievement of a desired prolongation of protein half-life in vivo is still feasible. The pharmacokinetics of hGH-PEG6k-betaAla conjugate was compared to that of native hGH in rats and monkeys, and the blood residence times were increased by 10- and 7-fold, respectively. The conjugate potency was evaluated in hypophysectomized rats demonstrating a superior pharmacodynamic profile with respect to native hGH
Site-Specific Pegylation of G-CSF by Reversible Denaturation
No full textA new strategy has been developed for extending the possibility of poly(ethylene glycol) (PEG) modification to accessible thiol groups of biologically active proteins. In particular, thiol-reactive PEGs have been coupled to the cysteine 17 of granulocyte colony stimulating factor (G-CSF), which is known to be partially buried in a hydrophobic protein pocket. The PEG linking was accomplished by partial protein denaturation with 3 M guanidine.HCl in the absence of any reducing agent in order to preserve the native protein's disulfide bridges. PEG coupling occurred also, but at a lower degree, by using a 3 M solution of urea as the denaturing agent. Following the PEGylation, which was carried out in the unfolded state, the conjugated protein was refolded using dialysis or gel filtration chromatography to eliminate the denaturant. Different thiol-reactive PEGs and polymer molecular weights (5, 10, or 20 kDa) were investigated for G-CSF conjugation under denaturation. The secondary structure of the protein in the G-CSF-PEG conjugates, evaluated using circular dichroism and biological activity assay in cell culture, was maintained with respect to the native protein. Unexpectedly, conjugation enhanced the G-CSF tendency to aggregate, a problem that was overcome by a proper formulation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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