Performance evaluation on a wide set of matrix-assisted laser desorption ionization matrices for the detection of oligosaccharides in a high-throughput mass spectrometric screening of carbohydrate depolymerizing enzymes

Compared to other analytical methods, matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) presents several unique advantages for the structural characterization of degradation products of carbohydrates. Our final goal is to implement this technique as a high-throughput platform, with the aim of exploring natural bio-diversity to discover new carbohydrate depolymerizing enzymes. In this approach, a variety of carbohydrates will be used as enzymes substrates and MALDI-MS will be employed to monitor the oligosaccharides produced. One drawback of MALDI, however, is that the choice of the matrix is largely dependent on the chemical properties of the analyte. In this context, our objective in the present work was to find the smallest set of MALDI matrices able to detect chemically heterogeneous oligosaccharides. This was done through the performance evaluation of more than 40 MALDI matrices preparations. Homogeneity of analyte-matrix deposits was considered as a critical feature, especially since the final objective is to fully automate the analyses. Evaluation of the matrices was done by means of a rigorous statistical approach. Amongst all tested compounds, our work proposes the use of the DHB/DMA ionic matrix as the most generic matrix, for rapid detection of a variety of polysaccharides including neutral, anionic, methylated, sulfated, and acetylated compounds. The selected matrices were then used to screen crude bacterial incubation media for the detection of enzymatic degradation products.     

Environmental effects on vibrational properties of carotenoids: experiments and calculations on peridinin

Carotenoids are employed in light-harvesting complexes of dinoflagellates with the two-fold aim to extend the spectral range of the antenna and to protect it from radiation damage. We have studied the effect of the environment on the vibrational properties of the carotenoid peridinin in different solvents by means of vibrational spectroscopies and QM/MM molecular dynamics simulations. Three prototypical solvents were considered: cyclohexane (an apolar/aprotic solvent), deuterated acetonitrile (a polar/aprotic solvent) and methanol (a polar/protic solvent). Thanks to effective normal mode analysis, we were able to assign the experimental Raman and IR bands and to clarify the effect of the solvent on band shifts. In the 1500-1650 cm(-1) region, seven vibrational modes of the polyene chain were identified and assigned to specific molecular vibrations. In the 1700-1800 cm(-1) region a strong progressive down-shift of the lactonic carbonyl frequency is observed passing from cyclohexane to methanol solutions. This has been rationalized here in terms of solvent polarity and solute-solvent hydrogen bond interactions. On the basis of our data we propose a classification of non-equivalent peridinins in the Peridinin-Chlorophyll-Proteins, light-harvesting complexes of dinoflagellates.     

Biomimetic versus enzymatic high-potential electrocatalytic reduction of hydrogen peroxide on a functionalized carbon nanotube electrode

We report the non-covalent functionalization of a multi-walled carbon nanotube (MWCNT) electrode with a biomimetic model of the horseradish peroxidase (HRP) active site. By modifying the MWCNT electrode surface with imidazole-modified polypyrrole, a new biomimetic complex of HRP was synthesized on the MWCNT sidewalls via the coordination of imidazole (Im) to the metal centre of iron protoporphyrin IX, affording (Im)(PP)Fe^III. Compared to the pi-stacking of non-coordinated (PP)Fe^III on a MWCNT electrode, the (Im)(PP)Fe^III-modified MWCNT electrode exhibits higher electrocatalytic activity with an I _max = 0.52 mA cm^–2 for the reduction of H₂O₂, accompanied by a high onset potential of 0.43 V vs. Ag/AgCl. The performances of these novel surface-confined HRP mimics were compared to those of a MWCNT electrode modified by HRP. Although the enzyme electrode displays a higher electrocatalytic activity towards H₂O₂ reduction, the (Im)(PP)Fe^III-modified MWCNT electrode exhibits a markedly higher operational stability, retaining 63% of its initial activity after one month.     

Dipolar and V-shaped structures incorporating methylenepyran and diazine fragments

Thirteen novel dipolar and V-shaped chromophores with pyranylidene electron-donating part, diazine electron-withdrawing part and various π-linkers were synthesized. The extent of intramolecular charge transfer, structure-property relationships and optical properties were further investigated by UV/Vis absorption, electrochemistry, and DFT calculations.     

Mild addition of carbon nucleophiles to pyridine and quinoline N-oxides under different activation conditions

In the course of our syntheses of functionalised pyridine and quinoline derivatives, we examined the reactivities of pyridine and quinoline N-oxides towards the nucleophilic addition of acidic carbon derivatives. Different activating reagents were used, such as PyBroP, triflic anhydride and a combination of pyrrolidine phosphoramide and triflic anhydride.