1,721,238 research outputs found
Solid State NMR Spectroscopy: A multiscale "lens" for understanding complex materials
No full textComplexity is an intrinsic feature typical of the most attractive innovative materials in many different research and application fields, as chemistry, optoelectronics, energy, recycling, medicine. Complexity arises from the coexistence of different chemical components, interfaces and phases, as well as from structural disorder and/ or heterogeneity. Complexity often hinders a detailed characterization of advanced materials, which, on the other hand, is crucial for understanding the functional performances and orienting the design and optimization of innovative materials. Solid State NMR spectroscopy (SSNMR) is an extremely powerful technique, which can effectively bridge this gap. Indeed, it can be applied to substantially every kind of soft and hard material and, by exploiting many nuclear probes and properties, it allows structural and dynamic properties to be characterized on very wide spatial (0.1-100 nm) and frequency (Hz-GHz) scales [1]. In this contribution I will show case studies of advanced materials characterized in the ICCOM-CNR/UNIPI joint lab [2], which, with the acquisition within the year of a last generation SSNMR spectrometer, will be the largest Italian laboratory for the study of materials by SSNMR. Hopefully this contribution will further increase the opportunity for the DSCTM community of taking advantage of this technique.
References:
[1] a. M. Geppi, S. Borsacchi, G. Mollica, C. A. Veracini, Appl. Spectr. Rev. 2009, 44, 1; b. M. Geppi, S. Borsacchi, G. Mollica, Encyclopedia of Magnetic Resonance, Wiley 2008.
[2] (a) F. Martini, M. Tonelli, M. Geppi, F. Ridi, S. Borsacchi, L. Calucci, Cem. Concr. Res. 2017, 102, 60; (b) F. Martini, S. Borsacchi, G. Barcaro, M. Caporali, M. Vanni, M. Serrano-Ruiz, M. Geppi, M. Peruzzini, L. Calucci J. Phys. Chem. Lett. 2019, 10, 5122; (c) E. Carignani, S. Borsacchi, P. Blasi, A. Schoubben, M. Geppi Mol. Pharmaceutics 2019, 16, 2569-2578
Qualità delle acque superficiali
No full textPer quanto riguarda la valutazione delle acque sotto-superficiali, la mancanza di precisi e sistematici riferimenti conoscitivi rende difficile tentare un qualsiasi tipo di analisi delle condizioni idriche del comprensorio se non su porzioni e/o per aspetti particolari della problematica. Del resto, non era possibile pensare di costituire ex-novo una banca dati, spazialmente e temporalmente adeguata, sulla base delle risorse messe a disposizione dal Progetto.
Ciò nondimeno, una valutazione esauriente dell’argomento sembra quanto mai necessaria alla luce dell’importanza che il fattore idrico riveste sugli equilibri fisici, chimici, biologici e gestionali dell’azienda, il cui sistema delle acque si presenta complesso e articolato, anche alla luce delle specifiche condizioni geo-morfologiche presenti nell’ambiente considerato.
Un’ulteriore difficoltà è rappresentata poi dal fatto che il materiale prodotto nel corso degli anni attraverso l’esecuzione di una serie di studi, a vario titolo condotti sulla tenuta di San Rossore, risulta spesso frammentato, poco disponibile e del tutto estraneo a qualunque tentativo di integrazione e riordino, che invece potrebbe consentirne una piena ed efficace utilizzazione.
In questa sede si procede all'integrazione e all'interpretazione delle informazioni disponibili con l'intenzione di stimolare lo sviluppo di nuove ricerche e attività di monitoraggio piuttosto che per proporre una valutazione completa ed esauriente sullo stato del comparto acqua all’interno del comprensorio
Dynamics by Solid-State NMR: Detailed Study of Ibuprofen Na Salt and Comparison with Ibuprofen
No full textThe various internal rotations and interconfor-
mational jumps of the Na-salt form of ibuprofen in the solid
state were characterized in detail by means of the simultaneous
analysis of a variety of low- and high-resolution NMR experi-
ments aimed at measuring several 13C and 1H spectral and
relaxation properties at different temperatures and frequencies.
The results were first qualitatively analyzed to identify the
motions of the different molecular fragments and to assign
them to specific frequency regimes (slow, 106 Hz). Subsequently, a simultaneous fit of the experimental data sets most sensitive to each frequency range was performed by using suitable motional models, thus obtaining, for each motion, correlation times and activation energies. The motions so characterized were: the rotations of the three methyl groups and of the isobutyl group, occurring in the fast regime, and the π-flip of the phenyl ring, belonging to the intermediate motional regime. The results obtained for the Na-salt form were compared with those of the acidic form of ibuprofen, previously obtained from a similar solid-state NMR approach: despite the very similar chemical structure of the two compounds, their dynamic properties in the solid state are noticeably different
Detailed Characterization of the Dynamics of Ibuprofen in the Solid State by a Multi-Technique NMR Approach
No full textThe internal rotations and interconformational jumps of ibu- profen in the solid state are fully characterized by the simulta- neous analysis of a variety of low- and high-resolution NMR ex- periments for the measurement of several 13C and 1H spectral and relaxation properties, performed at different temperatures and, in some cases, frequencies. The results are first qualitative- ly analyzed to identify the motions of the different molecular fragments and to assign them to specific frequency ranges (slow, 106 Hz). In a second step, a simultaneous fit of the experimental data sets most sensitive to each frequency range is performed by means of suitable motional models to obtain, for each motion, values of correlation times and activation energies. The rotations of the three methyl groups around their ternary symmetry axes, which occur in the fast regime, are characterized by slightly different activation energies. Thanks to the simultaneous analy- sis of 1H and 13C data, the p-flip of the dimeric structure made by the acidic groups is also identified and seen to occur in the fast regime. On the contrary, the p-flip of the phenyl ring is found to occur in the slow motional regime, while the rota- tions of the isobutyl and propionic groups are frozen. The ap- proach used appears to be of general applicability for studying the dynamics of small organic molecules
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Proton conducting membranes in fully anhydrous conditions at elevated temperature: Effect of Nitrilotris(methylenephosphonic acid) incorporation into Nafion- and poly(styrenesulfonic acid)
No full textNitrilotris(methylenephosphonic acid) (NTMPA) was incorporated in various proportions into Nafion and poly(styrenesulfonic acid) (PSSA) to make membranes with proton conductivity under fully anhydrous conditions. NTMPA is anchored to the polymer matrix by ionic bond between the basic nitrogen and the acidic sulfonic group of the polymer. The NTMPA molecule also possesses six phosphonic terminals with relevant hydrogen-bonding activity, enabling proton transport by a hopping mechanism even in the absence of water. Morphological and structural characteristics of these composite membranes were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Thermal stability was assessed by TGA. Proton-conduction up to 190°C was investigated by electrochemical impedance spectroscopy. Moreover, 31P solid-state nuclear magnetic resonance (NMR) spectroscopy was applied to investigate condensation of the phosphonic groups at elevated temperature. The Nafion/NTMPA composites were homogeneous at the molecular level and exhibited excellent thermal stability. These membranes were flexible, robust and translucent. For the PSSA/NTMPA composite a heterogeneous structure was observed with bulk, micrometer-size NTMPA particles dispersed in the polymer matrix. The membranes appeared opaque and fragile, but exhibited fairly good thermal resistance. For both classes of membranes, moderate condensation of the P-OH terminals leading to dimeric phosphonic and mixed sulfonic/phosphonic anhydrides was observed after prolonged thermal treatment at elevated temperature (>170°C) and zero humidity. However, this process is completely reversed by humidification. Both Nafion/NTMPA and PSSA/NTMPA composite membranes displayed good proton conductivity (>10-2Scm-1) under fully anhydrous conditions at elevated temperature. Importantly, the present work demonstrates a general and versatile concept to design water-free proton-conducting membranes rationally and straightforwardly. That is anchoring a compound with proton-solvent characteristics to a suitable matrix. These ideas are applicable utilizing vast classes of polymer matrices and proton conducting fillers
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