Determination of porphyrins and metalloporphyrins using liquid chromatography-diode array detection and mass spectrometry

A HPLC procedure has been optimized and successfully applied to porphyrins of environmental interest, such as etio and octaethylporphyrins and their VO and Ni compounds. The use of UV-Vis diode array allowed the detection of the analytes within the 5-15 ng/ml range. In order to achieve greater specificity and some structural information, the coupling of liquid chromatography with mass spectrometry was investigated, and the particle beam interface conditions were optimized. Electron impact (EI) spectra, comparable to those reported in the literature were obtained. The entire procedure has been applied to a real marine sediment, previously spiked with porphyrins to resemble oil-contaminated samples. The results pointed out that the method is suitable for such levels of analytes (5-10 microg/ml), allowing their identification and quantification with no need for purification steps.     

Unconventional Extraction of Total Non-Polar Carotenoids from Pumpkin Pulp and Their Nanoencapsulation

Pumpkin is considered a functional food with beneficial effects on human health due to the presence of interesting bioactives. In this research, the impact of unconventional ultrasound-assisted extraction (UAE) and microwave-assisted extraction techniques on the recovery of total non-polar carotenoids from Cucurbita moschata pulp was investigated. A binary (hexane:isopropanol, 60:40 v/v) and a ternary (hexane:acetone:ethanol, 50:25:25 v/v/v) mixture were tested. The extracts were characterized for their antioxidant properties by in vitro assays, while the carotenoid profiling was determined by high-performance liquid chromatography coupled with a diode array detector. UAE with the binary mixture (30 min, 45 °C) was the most successful extracting technique, taking into consideration all analytical data and their correlations. In parallel, solid lipid nanoparticles (SLN) were optimized for the encapsulation of the extract, using β-carotene as a reference compound. SLN, loaded with up to 1% β-carotene, had dimensions (~350 nm) compatible with increased intestinal absorption. Additionally, the ABTS ((2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) assay showed that the technological process did not change the antioxidant capacity of β-carotene. These SLN will be used to load an even higher percentage of the extract without affecting their dimensions due to its liquid nature and higher miscibility with the lipid with respect to the solid β-carotene.     

Binding modes identification through molecular dynamic simulations: A case study with carnosine enantiomers and the Teicoplanin A2‐2‐based chiral stationary phase

In the present study, an in silico methodology able to define the binding modes adopted by carnosine enantiomers in the setting of the chiral recognition process is described. The inter‐ and intramolecular forces involved in the enantioseparation process with the Teicoplanin A2‐2 chiral selector and carnosine as model compound are successfully identified. This approach fully rationalizes, at a molecular level, the (S) < (R) enantiomeric elution order obtained under reversed‐phase conditions. Consistent explanations were achieved by managing molecular dynamics results with advanced techniques of data analysis. As a result, the time‐dependent identification of all the interactions simultaneously occurring in the chiral selector‐enantiomeric analyte binding process was obtained. Accordingly, it was found that only (R)‐carnosine is able to engage a stabilizing charge–charge interaction through its ionized imidazole ring with the carboxylate counter‐part on the chiral selector. Instead, (S)‐carnosine establishes intramolecular contacts between its ionized functional groups, that limit its conformational freedom and impair the association with the chiral selector unit.     

Preparation and characterization of MgB2 superconductor

The MgB₂ superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties. The upper critical field, irreversibility line and critical current density have been determined using magnetization data. The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition. The surface analysis using X-ray photoelectron spectroscopy shows that MgB₂ is sensitive to atmospheric degradation.     

Diastereo- and enantioseparation of a N-Boc amino acid with a zwitterionic quinine-based stationary phase: Focus on the stereorecognition mechanism

A chiral chromatography method enabling the simultaneous diastereo- and enantioseparation of N^α-Boc-N⁴-(hydroorotyl)-4-aminophenylalanine [Boc-Aph(Hor)-OH, 1] was optimized with a quinine-based zwitterionic stationary phase. The polar-ionic eluent system consisting of ACN:MeOH:water—49.7:49.7:0.6 (v/v/v) with formic acid (4.0 mM) and diethylamine (2.5 mM), allowed the successful separation of the four acid stereoisomers: α_d,d-/d,l-1 = 1.08; α_d,l-/l,d-1 = 1.08; α_l,d-/l,l-1 = 1.40.