Anisotropy and NMR spectroscopy

Abstract: In this paper, different aspects concerning anisotropy in Nuclear Magnetic Resonance (NMR) spectroscopy have been reviewed. In particular, the relevant theory has been presented, showing how anisotropy stems from the dependence of internal nuclear spin interactions on the molecular orientation with respect to the external magnetic field direction. The consequences of anisotropy in the use of NMR spectroscopy have been critically discussed: on one side, the availability of very detailed structural and dynamic information, and on the other side, the loss of spectral resolution. The experiments used to measure the anisotropic properties in solid and soft materials, where, in contrast to liquids, such properties are not averaged out by the molecular tumbling, have been described. Such experiments can be based either on static low-resolution techniques or on one- and two-dimensional pulse sequences exploiting Magic Angle Spinning (MAS). Examples of applications of NMR spectroscopy have been shown, which exploit anisotropy to obtain important physico-chemical information on several categories of systems, including pharmaceuticals, inorganic materials, polymers, liquid crystals, and self-assembling amphiphiles in water. Solid-state NMR spectroscopy can be considered, nowadays, one of the most powerful characterization techniques for all kinds of solid, either amorphous or crystalline, and semi-solid systems for the obtainment of both structural and dynamic properties on a molecular and supra-molecular scale. Graphic abstract: [Figure not available: see fulltext.

Effect of phosphate additives on the hydration process of magnesium silicate cements: Thermal and spectroscopic characterization

The role of phosphate additives on the hydration process of magnesium silicate cement pastes was investigated through a multi-technique approach. A MgO/SiO2 mixture was hydrated for 28 days either in the absence or in the presence of sodium hexametaphosphate, trimetaphosphate or orthophosphate. Information on the kinetics of the hydration reaction was acquired by monitoring the free water index by means of differential scanning calorimetry, while the hydration products were thoroughly investigated by X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and 29Si solid-state nuclear magnetic resonance spectroscopy. The overall results provide new insight into the effect of phosphates on the hydration reaction and on the structure of magnesium silicate hydrate cements. All additives showed a plasticizing effect and promoted the formation of the binding phase magnesium silicate hydrate (M–S–H), without significantly altering its structure. Sodium orthophosphate was found to be by far the best-performing additive, even better than sodium hexametaphosphate, which is commonly used in these cementitious formulations. For the first time, 31P solid-state NMR investigation allowed orthophosphate ion to be identified as the effective species

The thermo-oxidative behavior of cotton coated with an intumescent flame retardant glycine-derived polyamidoamine: A multi-technique study

Linear polyamidoamines (PAAs) derived from the polyaddition of natural α-amino acids and N,N′-methylene bis(acrylamide) are intumescent flame retardants for cotton. Among them, the glycine-derived M-GLY extinguished the flame in horizontal flame spread tests at 4% by weight add-on. This paper reports on an extensive study aimed at understanding the molecular-level transformations of M-GLY-treated cotton upon heating in air at 300◦C, 350◦C and 420◦C. Thermogravimetric analysis (TGA) identified different thermal-oxidative decomposition stages and, coupled to Fourier transform infrared spectroscopy, allowed the volatile species released upon heating to be determined, revealing differences in the decomposition pattern of treated and untreated cotton. XPS analysis of the char residues of M-GLY-treated cotton revealed the formation of aromatic nanographitic char at lower temperature with respect to untreated cotton. Raman spectroscopy of the char residues provided indications on the degree of graphitization of treated and untreated cotton at the three reference temperatures. Solid state13C nuclear magnetic resonance spectroscopy (NMR) provided information on the char structure as a function of the treatment temperature, clearly indicating that M-GLY favors the carbonization of cotton with the formation of more highly condensed aromatic structures

MONITORING THE EFFECT OF FILLER IN ELASTOMERIC MATERIALS BY TIME DOMAIN NMR SPECTROSCOPY

In the last decades, many eorts have been dedicated to the improvement of the mechanical properties of elastomeric composite materials, as they are particularly attractive for several industrial applications. As a matter of fact, these properties are mainly related to the motional constraints of the polymer network, which are due to physical entanglements and chemical cross-linking between polymer chains, and may be in uenced by the presence of dierent additives and reinforcement llers (carbon black, nanosilica, clays) [1,2]. Usually, the mechanical properties of the materials are monitored by rheological measurements, which provide only macroscopic observables; however, also a description of the topology and dynamics of the polymer network at the molecular scale is needed in order to have a more complete comprehension of the factors that in uence these properties, with the nal aim to guide the design of optimized materials. In this context, low eld 1H time domain NMR (TD-NMR) can give an important contribution [3]. In this work, we studied dierent elastomeric materials with application in the tyre industry, by TD-NMR spectroscopy, with the aim of investigating the eect of ller particles on polymer structure and dynamics. 1H Multiple Quantum (MQ) experiments [4] were used to evaluate the residual 1H-1H dipolar couplings, which arise from the fast anisotropic motion of the polymer chains and are thus directly related to the amount of topological constraints within the polymer network. Moreover, 1H relaxation times (T1, T2) [5,6] were measured to probe a wide range of motional frequencies of the polymer chains. In particular, 1H spin-lattice relaxation times (T1) were evaluated by means of Fast Field Cycling [6] experiments at dierent temperatures, covering Larmor frequencies from 10 kHz to 35 MHz. References: [1] R. Scotti, M. D'Arienzo, B. Di Credico, L. Giannini and F. Morazzoni, in Hybrid Org. Interfaces, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 151-198, (2017). [2] G. Kraus Angew. Makromol. Chemie 60, 215-248, (1977). [3] S. Borsacchi, U. Sudhakaran, L. Calucci, F. Martini, E. Carignani, M. Messori and M. Geppi Polymers (Basel) 10, 822, (2018). [4] K. Saalw?achter Prog. Nucl. Mag. Res. Sp. 51, 1-35, (2007). [5] A. Maus, C. Hertlein and K. Saalw?achter Macromol. Chem. Phys. 207, 1150-1158k, (2006). [6] R. Kimmich, Field-cycling NMR Relaxometry: Instrumentation, Model Theories and Applications, Royal Society of Chemistry, Cambridge, (2018)

STRUCTURE AND DYNAMICS OF ELASTOMERIC MATERIALS BY MEANS OF 1H TIME-DOMAIN NMR: EFFECT OF CROSS-LINKING

Elastomeric materials are nowadays of central importance in many elds of application, where they need to full specic mechanical requirements. The mechanical properties of an elastomeric material take their origin on the features and topology of the polymer network. In fact xed chemical cross-links and physical entanglements among polymer chains impose notable restrictions on chain mobility and are at the basis of rubber elasticity [1]. An additional reinforcement eect can be achieved by incorporation in the rubber matrix of dierent nanoparticles, such as carbon black, carbon nanotubes, nanosilica, and clays [2, 3]. So far extensive research eorts have been addressed to the comprehension of the relationships between the \molecular" and mechanical properties of elastomeric materials, but a full understanding is still lacking. In this frame, NMR spectroscopy can play an important role giving access to many structural and dynamics information on wide spatial and time scales. In this work we applied a combination of dierent time-domain NMR (TD-NMR) techniques to the study of elastomeric materials based on isoprene, butadiene and styrene-butadiene rubbers, with application in the tyre industry. In particular the in uence of chemical cross-links on the polymer chain dynamics in a wide spectrum of motion frequencies was investigated, by studying samples obtained using dierent vulcanization conditions. 1H Multiple Quantum (MQ) experiments [4] were used for the measurement of the residual 1H-1H dipolar interaction: the latter is dependent on the anisotopic character of the fast reorietations of chain segments and, therefore, it is related to the amount and distribution of the topological constraints within the polymer network. Further and complementary information on dierent regimes of polymer dynamics were also obtained by means of measurements of 1H spin-spin relaxation times (T2) and variable temperature 1H T1 Fast Field Cycling (FFC) [5] experiments. References: [1] S. Schl?ogl, M. L. Trutschel, W. Chasse, G. Riess, K. Saalw?achter Macromolecules 47, 2759-2773, (2014). [2] R. Scotti, M. D'Arienzo, B. Di Credico, L. Giannini, F. Morazzoni, Silica-Polymer Interface and Mechanical Reinforcement in Rubber Nanocomposites. In Hybrid Organic-Inorganic Interfaces; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, pp. 151-198, (2017). [3] G. Kraus, Reinforcement of Elastomers; Interscience Publishers: New York, (1965). [4] K. Saalw?achter Prog. Nucl. Mag. Res. Sp. 51, 1-35, (2007). [5] R. Kimmich, Field-cycling NMR Relaxometry: Instrumentation, Model Theories and Applications; The Royal Society of Chemistry, (2019)

Un gioco globale per conoscere la chimica

È ora possibile cimentarsi in italiano nella PT Challenge 2.0, un divertente gioco ideato da IUPAC, facilmente accessibile, veloce, globale e inclusivo, per conoscere aspetti fondamentali, curiosità, storia e applicazioni nella nostra vita quotidiana dell’universo degli elementi chimici, straordinariamente raccolti nel geniale strumento della Tavola Periodica. Conosciamo, divertendoci, la chimica, strumento di sviluppo sostenibile

Modification of Amorphous Mesoporous Zirconia Nanoparticles with Bisphosphonic Acids: A Straightforward Approach for Tailoring the Surface Properties of the Nanoparticles

The use of readily prepared bisphosphonic acids obtained in few steps through a thio-Michael addition of commercially available thiols on tetraethyl vinylidenebisphosphonate enables the straightforward surface modification of amorphous mesoporous zirconia nanoparticles. Simple stirring of the zirconia nanoparticles in a buffered aqueous solution of the proper bisphosphonic acid leads to the surface functionalization of the nanoparticles with different kinds of functional groups, charge and hydrophobic properties. Formation of both chemisorbed and physisorbed layers of the bisphosphonic acid take place, observing after extensive washing a grafting density of 1.1 molecules/nm2 with negligible release in neutral or acidic pH conditions, demonstrating stronger loading compared to monophosphonate derivatives. The modified nanoparticles were characterized by IR, XPS, ζ-potential analysis to investigate the loading of the bisphosphonic acid, FE-SEM to investigate the size and morphologies of the nanoparticles and 31P and 1H MAS NMR to investigate the coordination motif of the phosphonate units on the surface. All these analytical techniques demonstrated the strong affinity of the bisphosphonic moiety for the Zr(IV) metal centers. The functionalization with bisphosphonic acids represents a straightforward covalent approach for tailoring the superficial properties of zirconia nanoparticles, much straightforward compared the classic use of trisalkoxysilane or trichlorosilane reagents typically employed for the functionalization of silica and metal oxide nanoparticles. Extension of the use of bisphosphonates to other metal oxide nanoparticles is advisable

Qualità delle acque superficiali

Per 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

Detailed Characterization of the Dynamics of Ibuprofen in the Solid State by a Multi-Technique NMR Approach

The 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