Temperature modulation in PDSC for monitoring the curing under pressure

The use of pressure cell attached to a temperature modulated differential scanning calorimeter (TMDSC) is investigated to perform modulated DSC experiments at high pressures (TMPDSC). No previous reports were found on the use of TMPDSC. In this study, the proposed method is applied to the study of the pressure effect on the curing reaction of an epoxy system. Curing quasi-isothermal modulated experiments were performed at different pressures to evaluate the vitrification time. Linear heating modulated tests were also successfully performed at different pressures to separate the reversing glass transition effect from the residual exothermic cure reaction. The curing enthalpy, conversion versus temperature, and glass transition of the fully cured thermoset were also evaluated. All the studied parameters resulted to be affected by the pressure in the range from atmospheric pressure to 35 bar. It was observed that the curing enthalpy, the reaction rate and the conversion at any given time increase with any pressure increment. The usefulness of TMDSC to characterize the curing of thermosets is extended by PTMDSC to situations, i.e., aeronautics industry, where pressure curing is needed.     

New pyrazolino- and pyrrolidino[60]fullerenes with transition-metal chelating pyridine substitutents: synthesis and complexation to Ru(II)

Three pyridine-substituted fullerene adducts, bis(2,2'-bipyridine)(2'-phenyl-5'-(2-pyridinyl)-2'H-[5,6]fullereno(C(60)-I(h))[1,9]pyrazole)ruthenium-bis(hexafluorophosphate) (1), bis(2,2'-bipyridine)(2'-phenyl-5'-(4-(4'-methyl-2,2'-bipyridinyl))-2'H-[5,6]fullereno(C(60)-I(h))[1,9]pyrazole)ruthenium-bis(hexafluorophosphate) (2), and bis(2,2'-bipyridine)(1',5'-dihydro-3'-methyl-2'-(4-(4'-methyl-2,2'-bipyridinyl))-2'H-[5,6]fullereno(C(60)-I(h))[1,9]pyrrole)ruthenium-bis(hexafluorophosphate) (3), have been prepared. The common features for these complexes are the short bridges between the fullerene and the pyridine moieties. [structure: see text]     

Intercalators. 1. Nature of stacking interactions between intercalators (ethidium, daunomycin, ellipticine, and 4',6-diaminide-2-phenylindole) and DNA base pairs. Ab initio quantum chemical, density functional theory, and empirical potential study

Properties of isolated intercalators (ethidium (E), daunomycin (D), ellipticine (EL), and 4,6'-diaminide-2-phenylindole (DAPI)) and their stacking interactions with adenine...thymine (AT) and guanine...cytosine (GC) nucleic acid base pairs were investigated by means of a nonempirical correlated ab initio method. All intercalators exhibit large charge delocalization, and none of them (including the DAPI dication) exhibits a site with dominant charge. All intercalators have large polarizability and are good electron acceptors, while base pairs are good electron donors. MP2/6-31G*(0.25) stabilization energies of intercalator...base pair complexes are large (E...AT, 22.4 kcal/mol; D...GC, 17.8 kcal/mol; EL...GC, 18.2 kcal/mol; DAPI...GC, 21.1 kcal/mol) and are well reproduced by modified AMBER potential (van der Waals radii of intercalator atoms are enlarged and their energy depths are increased). Standard AMBER potential underestimates binding, especially for DAPI-containing complexes. Because the DAPI dication is the best electron acceptor (among all intercalators studied), this difference is explained by the importance of the charge-transfer term, which is not included in the AMBER potential. For the neutral EL molecule, the standard AMBER force field provides correct results. The Hartree-Fock and DFT/B3LYP methods, not covering the dispersion energy, fail completely to reveal any energy minimum at the potential energy curve of the E...AT complex, and these methods thus cannot be recommended for a study of intercalation process. On the other hand, an approximate version of the DFT method, which was extended to cover London dispersion energy, yields for all complexes very good stabilization energies that are well comparable with referenced ab initio data. Besides the vertical dependence of the interaction, an energy twist dependence of the interaction energy was also investigated by a reference correlated ab initio method and empirical potentials. It is concluded that, despite the cationic (E +1, D +1, DAPI +2) or polar (EL) character of the intercalators investigated, it is the dispersion energy which predominantly contributes to the stability of intercalator...base pair complexes. Any procedure which does not cover dispersion energy is thus not suitable for studying the process of intercalation.     

Fluorescence of a Histidine-Modified Enhanced Green Fluorescent Protein (EGFP) Effectively Quenched by Copper(II) Ions

Two histidines were introduced by site-directed mutagenesis into the structure of Enhanced Green Fluorescent Protein, replacing the serine at position 202 and the glutamine at position 204 for increasing the sensitivity of the protein towards different metal ions by creating possible metal binding sites near the chromophore group. There is no appreciable difference between the absorbance and fluorescence spectra of the two proteins (wild type and the double-histidine mutant) indicating that the mutation does not change the environment of the fluorophore. Fluorescence quenching was measured at different pH (6.5–8) and temperatures (20–45 °C) varying the concentration of metal ions. Under optimal conditions (pH?=?7.5, 20 °C) the mutant’s K_d is 16 nM, it binds copper more than 200fold stronger than the wild type EGFP.     

Quantum dot–NBD–liposome luminescent probes for monitoring phospholipase A2 activity

In this paper we describe the fabrication and characterization of new liposome encapsulated quantum dot–fluorescence resonance energy transfer (FRET)-based probes for monitoring the enzymatic activity of phospholipase A_2. To fabricate the probes, luminescent CdSe/ZnS quantum dots capped with trioctylphosphine oxide (TOPO) ligands were incorporated into the lipid bilayer of unilamellar liposomes with an average diameter of approximately 100 nm. Incorporating TOPO capped quantum dots in liposomes enabled their use in aqueous solution while maintaining their hydrophobicity and excellent photophysical properties. The phospholipid bilayer was labeled with the fluorophore NBD C₆-HPC (2-(6-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoyl-1-hexa decanoyl-sn-glycero-3-phosphocholine). The luminescent quantum dots acted as FRET donors and the NBD dye molecules acted as FRET acceptors. The probe response was based on FRET interactions between the quantum dots and the NBD dye molecules. The NBD dye molecules were cleaved and released to the solution in the presence of the enzyme phospholipase A_2. This led to an increase of the luminescence of the quantum dots and to a corresponding decrease in the fluorescence of the NBD molecules, because of a decrease in FRET efficiency between the quantum dots and the NBD dye molecules. Because the quantum dots were not attached covalently to the phospholipids, they did not hinder the enzyme activity as a result of steric effects. The probes were able to detect amounts of phospholipase A₂ as low as 0.0075 U mL^?1 and to monitor enzyme activity in real time. The probes were also used to screen phospholipase A₂ inhibitors. For example, we found that the inhibition efficiency of MJ33 (1-hexadecyl-3-(trifluoroethyl)-sn-glycero-2-phosphomethanol) was higher than that of OBAA (3-(4-octadecyl)benzoylacrylic acid).     

Primary methods for the measurement of electrolytic conductivity

This paper surveys the state of the art for primary methods for the evaluation of electrolytic conductivity in aqueous solutions as they are currently carried out in several national metrological institutes (NMIs). The theoretical and practical basic knowledge of this measurement is described. Analysis of and comments on the different approaches are offered to give emphasis to technical difficulties and possible solutions. Further development is foreseeable, ensuring a common effort for the sharing of expertise that has been undertaken at the NMIs. In particular, improvements are expected towards traceable measurements of solutions with conductivity values lower than those actually standardized, down to the level of ultrapure water.     

Novel Method for the High-Yielding Synthesis of Steroidal Hydroxamic acid Derivatives

Steroidal 17-hydroxamic acid derivatives were synthesized in high yields in palladium-catalysed carbonylation reaction of 17-iodo-androst-16-ene derivatives under mild reaction conditions.     

In Vitro Tests of FDM 3D-Printed Diclofenac Sodium-Containing Implants

One of the most promising emerging innovations in personalized medication is based on 3D printing technology. For use as authorized medications, 3D-printed products require different in vitro tests, including dissolution and biocompatibility investigations. Our objective was to manufacture implantable drug delivery systems using fused deposition modeling, and in vitro tests were performed for the assessment of these products. Polylactic acid, antibacterial polylactic acid, polyethylene terephthalate glycol, and poly(methyl methacrylate) filaments were selected, and samples with 16, 19, or 22 mm diameters and 0%, 5%, 10%, or 15% infill percentages were produced. The dissolution test was performed by a USP dissolution apparatus 1. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide dye (MTT)-based prolonged cytotoxicity test was performed on Caco-2 cells to certify the cytocompatibility properties. The implantable drug delivery systems were characterized by thermogravimetric and heatflow assay, contact angle measurement, scanning electron microscopy, microcomputed tomography, and Raman spectroscopy. Based on our results, it can be stated that the samples are considered nontoxic. The dissolution profiles are influenced by the material properties of the polymers, the diameter, and the infill percentage. Our results confirm the potential of fused deposition modeling (FDM) 3D printing for the manufacturing of different implantable drug delivery systems in personalized medicine and may be applied during surgical interventions.     

Antiproliferative Phenanthrenes from Juncus tenuis: Isolation and Diversity-Oriented Semisynthetic Modification

The occurrence of phenanthrenes is limited in nature, with such compounds identified only in some plant families. Phenanthrenes were described to have a wide range of pharmacological activities, and numerous research programs have targeted semisynthetic derivatives of the phenanthrene skeleton. The aims of this study were the phytochemical investigation of Juncus tenuis, focusing on the isolation of phenanthrenes, and the preparation of semisynthetic derivatives of the isolated compounds. From the methanolic extract of J. tenuis, three phenanthrenes (juncusol, effusol, and 2,7-dihydroxy-1,8-dimethyl-5-vinyl-9,10-dihydrophenanthrene) were isolated. Juncusol and effusol were transformed by hypervalent iodine(III) reagent, using a diversity-oriented approach. Four racemic semisynthetic compounds possessing an alkyl-substituted p-quinol ring (1–4) were produced. Isolation and purification of the compounds were carried out by different chromatographic techniques, and their structures were elucidated by means of 1D and 2D NMR, and HRMS spectroscopic methods. The isolated secondary metabolites and their semisynthetic analogues were tested on seven human tumor cell lines (A2780, A2780cis, KCR, MCF-7, HeLa, HTB-26, and T47D) and on one normal cell line (MRC-5), using the MTT assay. The effusol derivative 3, substituted with two methoxy groups, showed promising antiproliferative activity on MCF-7, T47D, and A2780 cell lines with IC₅₀ values of 5.8, 7.0, and 8.6 µM, respectively.