Recent advances and challenges in the recovery and purification of cellular exosomes

Exosomes are nanovesicles secreted by most cellular types that carry important biochemical compounds throughout the body with different purposes, playing a preponderant role in cellular communication. Because of their structure, physicochemical properties and stability, recent studies are focusing in their use as nanocarriers for different therapeutic compounds for the treatment of different diseases ranging from cancer to Parkinson's disease. However, current bioseparation protocols and methodologies are selected based on the final exosome application or intended use and present both advantages and disadvantages when compared among them. In this context, this review aims to present the most important technologies available for exosome isolation while discussing their advantages and disadvantages and the possibilities of being combined with other strategies. This is critical since the development of novel exosome‐based therapeutic strategies will be constrained to the effectiveness and yield of the selected downstream purification methodologies for which a thorough understanding of the available technological resources is needed.     

Hyperfine characterization of Bi1.9Te0.1SrNb1.9Hf0.1O9

The Aurivillius type oxide Bi_1.9Te_0.1SrNb_1.9Hf_0.1O₉ has been studied by Perturbed Angular Correlations spectroscopy using ¹⁸¹Ta probes. The spin precession curves were measured from room temperature up to 873 K. Two sites are occupied by probes and the temperature dependence of both indicates a continuous phase transition at about 625 K. One site is ordered while the other is disordered. This situation is analyzed in terms of simple models already applied to perovskites. The transition temperature of the solid solution Bi_2−xTe_xSrNb_2−xHf_xO₉ (with 0≤x≤0.5) shows a strong dependence on composition.     

Catalytic air oxidation of ambient temperature hydrocarbons

Catalytic air oxidation of the aliphatic hydrocarbons n-decane, hexanes, gasoline and diesel fuel was conducted at ambient temperature with novel iron catalysts. The concentration of n-decane in water was reduced from 1.42 g in 100 ml to 0.07 g in 100 ml in 5 h at room temperature forming carbon monoxide and water by means of intermediate aldehydes. Results of FT–IR and GC–MS analyses demonstrated formation of aldehydes and unsaturated alcohols. Carbon monoxide was detected on catalyst residues and in the vapor phase. The indicated catalytic reaction mechanisms are discussed.     

Determination of N-nitrosamines by HPTLC with Fluorescence Detection — Use of Non-Ionic Surfactants as Enhancing Agents

JPC – Journal of Planar Chromatography – Modern TLC - The dansyl derivatives of N-nitrosodimethylamine, N-nitrosodi-ethylamine, and N-nitrosodibuthylamine have been separated by HPTLC...     

Spectroscopic properties of tyrosyl radicals in dipeptides

Redox-active tyrosine residues play important roles in long-distance electron reactions in enzymes, including prostaglandin H synthase, galactose oxidase, ribonucleotide reductase, and photosystem II. Magnetic resonance and vibrational spectroscopy provide methods with which to study the structures of redox-active amino acids in proteins. In this report, ultraviolet photolysis was used to generate tyrosyl radicals from polycrystalline tyrosinate or dipeptides, and the structure of the radical was investigated with EPR and reaction-induced FT-IR spectroscopy at 77 K. Photolysis at 77 K is expected to generate a neutral tyrosyl radical through oxidation of the aromatic ring. EPR and FT-IR results obtained from (13)C-labeled tyrosine were consistent with that expectation. Surprisingly, labeling of the tyrosyl amino group with (15)N also resulted in isotope-shifted bands in the photolysis spectrum. The force constant of a NH deformation mode increased when the tyrosyl radical was generated. These data suggest an interaction between the pi system of the tyrosyl radical and the amino group. In spectra acquired from the dipeptides, evidence for a sequence-dependent interaction between the tyrosyl radical and the amide bond of the dipeptide was also obtained. We postulate that perturbation of the amino or the amide/imide groups may occur through a spin polarization mechanism, which is indirectly detected as a change in NH force constant. This conclusion is supported by density functional calculations, which suggest a conformationally sensitive delocalization of spin density onto the amino and carboxylate groups of the tyrosyl radical. These experiments provide a step toward a detailed spectral interpretation for protein-based tyrosyl radicals.     

Rationalisation of unusual changes in efficiency and retention with temperature shown for bases in reversed-phase high-performance liquid chromatography at intermediate pH

Despite the possibility of poorer peak shapes, analysis of pharmaceuticals and other bases using reversed-phase high-performance liquid chromatography (RP-HPLC) at intermediate pH gives useful increases in retention, selectivity and column loading capacity compared with low pH. Retention times of some bases showed anomalous increases with column temperature. Peak shapes for bases improved significantly at elevated temperature (up to 70 degrees C), with the weakest bases studied (pKa approximately 8) giving greater improvement than the strongest bases (pKa approximately 10). In contrast, quaternary ammonium compounds showed reduced retention with increasing column temperature (normal behaviour) and only modest improvements in peak shape. Considering these results, and pKa measurements of the bases made using capillary electrophoresis, it appears that increases in retention and improvement in efficiency may be influenced significantly by reduction in the pKa of bases with temperature, leading to reduction in protonation. It is less likely that efficiency improvements are due to the speeding up of the kinetics of silanol ion exchange, at least in the temperature range studied here.     

On the Nature of the 7-Norbornadienyllithiums. Preliminary Communication

Lithium reductions of 7-chloronorbornadiene and of bis(7-norbornadienyl)mercury both provide (C₇H₇)₂Li₂ ( 5a ). This product is accompanied by C₇H₇Li₂Cl ( 5c ) in the first case, and by C₇H₇Li ( 5b ) in the second. The theoretically anticipated properties of all three organolithiums are apparent in the consistent C_s symmetry of their hydrocarbon ligands, their protolytic destruction by 12-crown-4, and their significant J(C(7), Li) ( 5a , 7.6; 5b , 16.0; 5c 8.9 Hz).     

Effects of cetylpyridinium bromide micelles on the spectrofluorimetric characteristics of polycyclic aromatic hydrocarbons

The presence of a micellar medium of cetylpyridinium bromide (CPB) causes, in relation to the aqueous medium, important bathochromic shifts in the excitation spectra of a considerable number of polycyclic aromatic hydrocarbons (PAHs). Furthermore, the CPB acts as a quencher, provoking inhibitions of the fluorescence intensity emitted by PAHs. The micellar inhibition factors show that, generally, the quenching affects alternant hydrocarbons to a greater extent. Some interesting relationships between the hydrocarbon structure and both the characteristic wavelengths of fluorescence spectra and the values of Deltalambda are established.     

Determination of polycyclic aromatic hydrocarbons in seawater by high-performance liquid chromatography with fluorescence detection following micelle-mediated preconcentration

In this work, the nonionic surfactant polyoxyethylene-10-lauryl ether has been used for the extraction and preconcentration of 14 polycyclic aromatic hydrocarbons, classified as priority pollutants by the US Environmental Protection Agency, from seawater samples. The cloud-point preconcentration previous separation by HPLC and quantification using fluorimetric detection and wavelength programming allow to determine these pollutants with detection limits ranging from 1.0 to 1.5 x 10(2) ng/l with RSDs better than 10.4%. The methodology is evaluated using well-established extraction and preconcentration methods and GC-MS.     

Segmental distribution properties of a polymer chain near an interacting barrier

The exact distribution of segments for self-avoiding walks of lengths N=4–14 bonds in the presence of an interacting barrier on the diamond lattice has been obtained by the method of direct enumeration. Behavior for the infinite chain was estimated and compared with Rubin's results for the normal random walk. It is shown that the onset of a well defined transition for the self-avoiding walk coincides with the location predicted for the normal random walk. It was found that for a self-avoiding walk a plot of θ₂ (the fraction of segments in level z) versus the interaction parameter φ is shifted to the right (higher φ), for all z, as compared with a similar plot for the normal random walk. Conditional probabilities for a self-avoiding walk having its t th segment in level z (when φ=0) are reported.