Polydimethylsiloxane as a packing material in a programmed temperature vaporizer to introduce large-volume samples in capillary gas chromatography

The viability of using polydimethylsiloxane (PDMS) as a retaining material inside a programmed temperature vaporizer injector for the introduction of large-volume samples in gas chromatography is assessed. To that end, materials made up of Volaspher A-2 and coated with different percentages of PDMS (5%, 15%, and 50%) are considered. In addition, adsorbent (Tenax TA) and absorbent (PDMS) materials are comparatively studied in terms of their retention capacity. A relative standard deviation lower than 5.0% is obtained from the injection of PDMS, whereas values up to 49% are provided by Tenax TA. Significantly higher amounts of different volatile compounds are retained by PDMS in comparison with Tenax TA. In conclusion, the use of PDMS as a packing material seems to be viable for large-volume sampling and particularly recommendable for minor compounds occurring in complex matrices.     

Determination of molecular parameters of hydroxyethyl and hydroxypropyl celluloses by chromatography with dual detection

Hydroxyethylcellulose (HEC) and hydroxypropylcellulose (HPC) were studied by means of size exclusion chromatography with dual detection, i.e. employing simultaneously a refractive index (concentration sensitive) and a multiangle light scattering (molecular weight sensitive) detectors. The eluent was water and water solutions containing different concentrations of ionic salts. Molecular weight distributions and averages, coefficients of the scaling law of molecular dimensions and unperturbed dimensions were thus obtained from a single polydisperse sample of each polymer. Measurements were performed at 25 degrees C and the anomalous chromatographic behaviour, due to a combination of ion and size exclusion mechanisms, found when using pure water as eluent is transformed into a size exclusion mechanism by the addition of ionic salts. However, the two polymers behave on a different way in presence of salts. Thus, HEC, which is of low degree of substitution (DS), is close to theta conditions in the aqueous salt solutions (i.e. the q exponent of the scaling law has a value close to 0.5), whereas in the case of HPC the addition of salt improves the quality of the solvent up to a value of q around 0.6. Unperturbed dimensions are also calculated for both celluloses.     

Absorbents as packing materials in on-line coupling of reversed phase liquid chromatography and gas chromatography via a programmed temperature vaporizer

Dynamic binding capacity (DBC) measurements of cation-exchange resins were performed with two human monoclonal antibodies. DBC showed a pH dependent maximum, which was shifted to lower pH values with increasing buffer concentrations and increasing salting-out effect of the buffer anion according to the Hofmeister series. As this downshift correlates well with zeta potential values, a measurement of the latter allows the determination of the pH value for maximum DBC under a given set of conditions. Thus, the use of zeta potential values can accelerate the purification process development and helps to understand the protein adsorption mechanism.     

Repositioning of Ligands That Target the Spike Glycoprotein as Potential Drugs for SARS-CoV-2 in an In Silico Study

The worldwide health emergency of the SARS-CoV-2 pandemic and the absence of a specific treatment for this new coronavirus have led to the use of computational strategies (drug repositioning) to search for treatments. The aim of this work is to identify FDA (Food and Drug Administration)-approved drugs with the potential for binding to the spike structural glycoprotein at the hinge site, receptor binding motif (RBM), and fusion peptide (FP) using molecular docking simulations. Drugs that bind to amino acids are crucial for conformational changes, receptor recognition, and fusion of the viral membrane with the cell membrane. The results revealed some drugs that bind to hinge site amino acids (varenicline, or steroids such as betamethasone while other drugs bind to crucial amino acids in the RBM (naldemedine, atovaquone, cefotetan) or FP (azilsartan, maraviroc, and difluprednate); saquinavir binds both the RBM and the FP. Therefore, these drugs could inhibit spike glycoprotein and prevent viral entry as possible anti-COVID-19 drugs. Several drugs are in clinical studies; by focusing on other pharmacological agents (candesartan, atovaquone, losartan, maviroc and ritonavir) in this work we propose an additional target: the spike glycoprotein. These results can impact the proposed use of treatments that inhibit the first steps of the virus replication cycle.     

Tuning the Topological Landscape of DNA–Cyclodextrin Nanocomplexes by Molecular Design

Original molecular vectors that ensure broad flexibility to tune the shape and surface properties of plasmid DNA (pDNA) condensates are reported herein. The prototypic design involves a cyclodextrin (CD) platform bearing a polycationic cluster at the primary face and a doubly linked aromatic module bridging two consecutive monosaccharide units at the secondary face that behaves as a topology-encoding element. Subtle differences at the molecular level then translate into disparate morphologies at the nanoscale, including rods, worms, toroids, globules, ellipsoids, and spheroids. In vitro evaluation of the transfection capabilities revealed marked selectivity differences as a function of nanocomplex morphology. Remarkably high transfection efficiencies were associated with ellipsoidal or spherical shapes with a lamellar internal arrangement of pDNA chains and CD bilayers. Computational studies support that the stability of such supramolecular edifices is directly related to the tendency of the molecular vector to form noncovalent dimers upon DNA templating. Because the stability of the dimers depends on the protonation state of the polycationic clusters, the coaggregates display pH responsiveness, which facilitates endosomal escape and timely DNA release, a key step in successful transfection. The results provide a versatile strategy for the construction of fully synthetic and perfectly monodisperse nonviral gene delivery systems uniquely suited for optimization schemes.     

Hybrid materials: Magnetite-Polyethylenimine-Montmorillonite, as magnetic adsorbents for Cr(VI) water treatment

Hybrid materials formed by the combination of a sodium rich Montmorillonite (MMT), with magnetite nanoparticles (40nm, Fe(3)O(4) NPs) coated with Polyethylenimine polymer (PEI 800g/mol or PEI 25000g/mol) were prepared. The intercalation of the magnetite nanoparticles coated with PEI among MMT platelets was achieved by cationic exchange. The resulting materials presented a high degree of exfoliation of the MMT sheets and a good dispersion of Fe(3)O(4) NPs on both the surface and among the layers of MMT. The presence of amine groups in the PEI structure not only aids the exfoliation of the MMT layers, but also gives to the hybrid material the necessary functionality to interact with heavy metals. These hybrid materials were used as magnetic sorbent for the removal of hexavalent chromium from water. The effect that pH, Cr(VI) concentration, and adsorbent material composition have on the Cr(VI) removal efficiency was studied. A complete characterization of the materials was performed. The hybrid materials showed a slight dependence of the removal efficiency with the pH in a wide range (1-9). A maximum amount of adsorption capacity of 8.8mg/g was determined by the Langmuir isotherm. Results show that these hybrid materials can be considered as potential magnetic adsorbent for the Cr(VI) removal from water in a wide range of pH.