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.     

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.     

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.     

Flow analysis-hydride generation-Fourier transform infrared spectrometric determination of antimony in pharmaceuticals

In this work, a flow analysis system with hydride generation and Fourier transform infrared (FTIR) spectrometric detection has been developed for the determination of antimony in pharmaceuticals. The method is based on the on-line mineralization/oxidation of the organic antimonials present in the sample and pre-reduction of Sb(V) to Sb(III) with K₂S₂O₈ and KI, respectively; prior to the stibine generation. The gaseous SbH₃ is separated from the solution in a gas phase separator, and transported by means of a nitrogen carrier into a short pathway (10 cm) IR gas cell, where the corresponding FTIR spectrum is acquired by accumulating 3 scans in a continuous mode. The 1893 cm⁻¹ band was used for the quantification of the antimony. The procedure is carried out in a closed system, which reduces sample handling and makes possible the complete automation of the antimony determination. The figures of merit of the proposed method (linear range: 0-600 mg l⁻¹, limit of detection (3σ)=0.9 mg l⁻¹, limit of quantification (10σ)=3 mg Sb l⁻¹, precision (R.S.D.) less than 1% and sample frequency=28 h⁻¹), are appropriate for the designed application. Furthermore, precise and accurate results were found for the analysis of different antimonial pharmaceutical samples, indicating that the methodology developed represents a valid alternative for the determination of antimony in pharmaceuticals, which could be suitable for the routine control analysis.     

Flow analysis-vapor phase generation-Fourier transform infrared (FA-VPG-FTIR) spectrometric determination of nitrite

In this work, the coupling between flow analysis (FA)–vapor phase generation (VPG) and Fourier transform infrared spectrometry (FTIR) has been proposed as a novel and alternative strategy for the determination of nitrite. The analyte was transformed into the gaseous nitric oxide (NO) by on-line reaction with potassium iodide (KI) or ascorbic acid in acidic medium. The gaseous NO generated was transported by means of a N₂ gas carrier stream inside the IR gas cell and the corresponding FTIR spectrum was acquired in a continuous mode. The absorbance at 1876 cm⁻¹, corrected by a baseline established between 1879 and 1872 cm⁻¹ at a nominal resolution of 2 cm⁻¹, was selected as a measurement criterion. The effect of different spectroscopic and flow analysis experimental parameters, such as nominal resolution, number of scans, reducing agent and its concentration, acidic medium, reagents and sample flow rates, and the carrier gas flow rate on the analytical signal, and then in the figures of merit were initially evaluated by using a standard short path length (10 cm) IR gas cell. The optimization of the system was carried out by the univariate method. The main aims of this study were: (i) to investigate the on-line generation of gaseous nitric oxide in a continuous flow system, and (ii) the use of Fourier transform infrared spectrometry as an alternative and selective detector for the determination of nitrite. The proposed method was initially tested and applied for the determination of nitrite in samples with very high concentration of nitrite, such as frankfurters.