Synthetic approaches to break the chemical shift degeneracy of glycans

NMR spectroscopy is the leading technique for determining glycans’ three-dimensional structure and dynamic in solution as well as a fundamental tool to study protein-glycan interactions. To overcome the severe chemical shift degeneracy of these compounds, synthetic probes carrying NMR-active nuclei (e.g., 13 C or 19 F) or lanthanide tags have been proposed. These elegant strategies permitted to simplify the complex NMR analysis of unlabeled analogues, shining light on glycans’ conformational aspects and interaction with proteins. Here, we highlight some key achievements in the synthesis of specifically labeled glycan probes and their contribution towards the fundamental understanding of glycans

Deoxyfluorination tunes the aggregation of cellulose and chitin oligosaccharides and highlights the role of specific hydroxyl groups in the crystallization process

Cellulose and chitin are abundant structural polysaccharides exploited by nature in a large number of applications thanks to their crystallinity. Chemical modifications are commonly employed to tune polysaccharide physical and mechanical properties, but generate heterogeneous mixtures. Thus, the effect of such modifications is not well understood at the molecular level. In this work, we examined how deoxyfluorination (site and pattern) impact the solubility and aggregation of well-defined cellulose and chitin oligomers. While deoxyfluorination increased solubility in water and lowered the crystallinity of cellulose oligomers, chitin was much less affected by the modification. The OH/F substitution also highlighted the role of specific hydroxyl groups in the crystallization process. This work provides guidelines for the design of cellulose- and chitin-based materials. A similar approach can be imagined to prepare cellulose and chitin analogues capable of withstanding enzymatic degradation

Spectroscopic and Theoretical Studies of Some 3-(4 '-Substituted phenylsulfanyl)-1-methyl-2-piperidones

The analysis of the IR carbonyl bands of some 3-(4 '-substituted phenylsulfanyl)1- methyl-2-piperidones 1-6 bearing substituents: NO2 (compound 1), Br (compound 2), Cl (compound 3), H (compound 4) Me (compound 5) and OMe (compound 6) supported by B3LYP/ 6-31+ G(d, p) and PCM calculations along with NBO analysis (for compound 4) and X-ray diffraction (for 2) indicated the existence of two stable conformations, i.e., axial (ax) and equatorial (eq), the former corresponding to the most stable and the least polar one in the gas phase calculations. the sum of the energy contributions of the orbital interactions (NBO analysis) and the electrostatic interactions correlate well with the populations and the vCO frequencies of the ax and eq conformers found in the gas phase. Unusually, in solution of the non-polar solvents n-C6H14 and CCl4, the more intense higher IR carbonyl frequency can be ascribed to the ax conformer, while the less intense lower IR doublet component to the eq one. the same.CO frequency trend also holds in polar solvents, that is nu(CO(eq)) < nu(CO(ax)). However, a reversal of the ax/eq intensity ratio occurs going from non-polar to polar solvents, with the ax conformer component that progressively decreases with respect to the eq one in CHCl3 and CH2Cl2, and is no longer detectable in the most polar solvent CH3CN. the PCM method applied to compound 4 supports these findings. in fact, it predicts the progressive increase of the eq/ax population ratio as the relative permittivity of the solvent increases. Moreover, it indicates that the computed.CO frequencies of the ax and eq conformers do not change in the non-polar solvents n-C6H14 and CCl4, while the.CO frequencies of the eq conformer become progressively lower than that of the ax one going from CHCl3 to CH2Cl2 and to CH3CN, in agreement with the experimental IR values. the analysis of the geometries of the ax and eq conformers shows that the carbonyl oxygen atom of the eq conformer is free for solvation, while the O-[CO]center dot center dot center dot H[o-Ph] hydrogen bond that takes place in the ax conformer partially hinders the approach of the solvent molecules to the carbonyl oxygen atom. Therefore, the larger solvation that occurs in the carbonyl oxygen atom of the eq conformer is responsible for the observed and calculated decrease of the corresponding frequency. the X-ray single crystal analysis of 2 indicates that this compound adopts the most polar eq geometry in the solid. in fact, in order to obtain the largest energy gain, the molecules are arranged in the crystal in a helical fashion due to dipole moment coupling along with C-H center dot center dot center dot O and C-H center dot center dot center dot pi(Ph) hydrogen bonds.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)MIUR (PRIN)Univ São Paulo, Inst Chem, Conformat Anal & Elect Interact Lab, BR-05513970 São Paulo, BrazilUniversidade Federal de São Paulo, UNIFESP, Inst Environm Chem & Pharmaceut Sci, BR-09972270 Diadema, SP, BrazilUniv Fed Sao Carlos, Dept Chem, BR-13565905 Sao Carlos, SP, BrazilUniv Ferrara, Dept Chem, I-44100 Ferrara, ItalyUniversidade Federal de São Paulo, UNIFESP, Inst Environm Chem & Pharmaceut Sci, BR-09972270 Diadema, SP, BrazilCAPES: 808/2009Web of Scienc

The H2 velocity structure of inner knots in HH 212: asymmetries and rotation

High-resolution R~50 000 long-slit spectroscopy of the inner knots of the highly symmetrical protostellar outflow HH 212 was obtained in the 1-0 S(1) line of H2 at 2.12 micron with a spatial resolution of ~0.45 arcsec. At the resulting velocity resolution of ~6 km s-1, multiple slit oriented observations of the northern first knot NK1 clearly show double-peaked line profiles consistent with either a radiative bow shock or dual (forward and reverse) shocks. In contrast, the velocity distribution of the southern first knot SK1 remains single-peaked, suggesting a significantly lower jet velocity and possibly a different density variation in the jet pulses in the southern flow compared to the northern flow. Comparison with a semi-empirical analytical model of bow shock emission allows us to constrain parameters such as the bow inclination to the line of sight, the bow shock and jet velocities for each flow. Although a few features are not reproduced by this model, it confirms the presence of several dynamical and kinematical asymmetries between opposite sides of the HH 212 bipolar jet. The position-velocity diagrams of both knots exhibit complex dynamics that are broadly consistent with emission from a bow shock and/or jet shock, which does not exclude jet rotation, although a clear signature of jet rotation in HH 212 is missing. Alternative interpretations of the variation of radial velocity across these knots, such as a variation in the jet orientation, as well as for the velocity asymmetries between the flows, are also considered. The presence of a correlation between flow velocity and collimation in each flow is suggested.Comment: Accepted for publication in Astronomy and Astrophysics, 16 page

Modeling the high-energy emission in GRB 110721A and implications on the early multiwavelength and polarimetric observations

GRB 110721A was detected by the Gamma-ray Burst Monitor and the Large Area Telescope (LAT) onboard the Fermi satellite and the Gamma-ray Burst Polarimeter onboard the IKAROS solar mission. Previous analysis done of this burst showed: i) a linear polarization signal with position angle stable ($\phi_p= 160^\circ\pm11$) and high degree of $\Pi=84^{+16}_{-28}$, ii) an extreme peak energy of a record-breaking at 15$\pm$2 MeV, and iii) a subdominant prompt thermal component observed right after the onset of this burst. In this paper, the LAT data around the reported position of GRB 110721A are analysed with the most recent software and then, the LAT light curve above 100 MeV was obtained. The LAT light curve is modelled in terms of adiabatic early-afterglow external shocks when the outflow propagates into a stellar wind. Additionally, we discuss the possible origins and also study the implications of the early-afterglow external shocks on the extreme peak energy observed at 15$\pm$2 MeV, the polarization observations and the subdominant prompt thermal component.Comment: 9 pages and one figure. Accepted for publication in Ap

Applicazioni della spettroscopia di fotoelettroni XPS per la caratterizzazione chimica di materiali

Nello studio dei materiali vengono generalmente descritte ed analizzate le proprietà massive degli stessi. Tuttavia le interazioni tra materiali diversi dipendono particolarmente dallo stato chimico e fisico delle superfici di contatto e molte delle loro proprietà chimico/fisiche sono fortemente influenzate ed in molti casi controllate da effetti di superficie. La conoscenza delle stesse diventa quindi di fondamentale importanza per la comprensione di molti processi quali ossidazione, fenomeni di segregazione, corrosione, diffusione, ecc.. La caratterizzazione, in termini qualitativi e quantitativi, sia della composizione degli strati superficiali del materiale tal quale che delle variazioni strutturali e composizionali indotte in seguito ai più svariati trattamenti richiede pertanto l'uso di una tecnica sperimentale che permetta l'identificazione delle specie chimiche presenti in regioni di spessore dell'ordine dei 50-100 Å. Queste informazioni possono essere ottenute da misure di spettroscopia di fotoelettroni (XPS, X-ray Photoelectron Spectroscopy), una tecnica superficiale di caratterizzazione che permette di discriminare in base al diverso stato di ossidazione i vari elementi chimici fornendo quindi informazioni sui composti presenti e sulla loro distribuzione relativa. Inoltre, modificando in maniera opportuna le modalità sperimentali di acquisizione dei dati è possibile restringere l'analisi a strati superficiali sempre più sottili fino a spessori dell'ordine dei pochi Å (inferiori a 10 Å) ottenendo in maniera non distruttiva dei profili di distribuzione in profondità delle stesse specie chimiche. Verranno presentati i risultati che si possono ottenere nello studio di materiali di diversa complessità, quali elettrodi di diamante conduttore, materiali ceramici di interesse tecnologico a base di ZrB2 o HfB2, inibitori per la protezione di bronzi. In particolare saranno discussi gli effetti sugli stessi di trattamenti chimici ed elettrochimici e la formazione di film passivanti con particolare attenzione alle variazioni di composizione superficiale indotte dai processi applicati. Una particolare attenzione sarà data alla all’attendibilità delle procedure utilizzate per l’elaborazione dei dati sperimentali

Symbolic or utilitarian? Juggling interpretations of Neanderthal behavior: new inferences from the study of engraved stone surfaces

Different categories of finds reveal how Neanderthals have manifested at different moments behaviors not ascribable to the utilitarian sphere, but to the aesthetic or symbolic. When the majority of this evidence dates to the few millennia that preceded the spread of Anatomically Modern Humans in Europe, these are grounds to continue the debate regarding the emergence of complex behavior, seen as an autonomous phenomenon of Neanderthal man or as the result of contact with immigrant populations. Re-examination of pebbles or flaked stones, a large part of such evidence, using a rigorous technological and taphonomic approach integrated with experimental tests, has already revealed these materials to be insignificant or natural, rather than anthropic, in origin. The following work seeks to shed light on the uncertainty existing around those stones and lithic artefacts bearing surface lines and scratches; these are of doubtful anthropic origin, but have not, as yet, been definitively interpreted. Generally, these findings are occasional in Mousterian sites, and when they are recovered with an excellent degree of preservation, different methods and levels of observation can be used for investigating them. The case studies taken into account are three sites in north Italy, where the surfaces of pebbles and flakes reveal a variety of signs and modifications attributable to various utilitarian acts. Of these, preventive cleaning of flint nodules has not been excluded, even if the traces on some tools reveal intentionality and repetition of gestures applied to the construction of a curated artifact

Electrochemical behavior of ZrB2 in aqueous solutions

The corrosion behavior of a dense ZrB2 material (hot pressed with 2.5 wt % Si3N4 as a sintering aid) in aqueous acid solutions containing different aggressive anions such as chlorides, perchlorates, sulfates, oxalates, and fluorides was investigated by means of several experimental techniques. The methodology adopted consists in polarization curve recording, gravimetric corrosion rate determination, and potentiostatic tests coupled to solution analysis, scanning electron microscope observations and X-ray photoelectron spectroscopy surface chemical characterization. During the corrosion process, ZrB2 is converted into both soluble [boric acid and complexes of the different anions with Zr(IV)] and insoluble (mainly ZrO2) corrosion products. The experimental results, compared to literature data, show that the higher the stability of the Zr(IV) soluble complex formed by a particular anion, the higher the corresponding solution aggressiveness and consequently the lower the protectivity of the surface oxide film. The solution aggressiveness was found to increase in the following order: perchlorates = chlorides << sulfates = oxalates < fluorides