Statistical characterization of residual noise in the low-rank approximation filter framework, general theory and application to hyperpolarized tracer spectroscopy

The use of low-rank approximation filters in the field of NMR is increasing due to their flexibility and effectiveness. Despite their ability to reduce the Mean Square Error between the processed signal and the true signal is well known, the statistical distribution of the residual noise is still undescribed. In this article, we show that low-rank approximation filters are equivalent to linear filters, and we calculate the mean and the covariance matrix of the processed data. We also show how to use this knowledge to build a maximum likelihood estimator, and we test the estimator's performance with a Montecarlo simulation of a 13C pyruvate metabolic tracer. While the article focuses on NMR spectroscopy experiment with hyperpolarized tracer, we also show that the results can be applied to tensorial data (e.g. using HOSVD) or 1D data (e.g. Cadzow filter).Comment: 26 pages, 7 figure

Fumasep FAA-3-PK-130: Exploiting multinuclear solid-state NMR to shed light on undisclosed structural properties

Fumasep FAA-3-PK-130 is considered the state-of-the-art among the different commercially available Anion Exchange Membranes (AEMs). It is produced by Fumatech GmbH as a cost-effective blend of polyetheretherketone (PEEK) and poly (phenylene oxide) (PPO) characterized by high hydroxyl ions conductivity, high thermal and chemical resistance, and high dimensional stability. Nevertheless, the chemical structure of the anion exchange sites and their contents were unknown so far. In this paper, we report a detailed structural characterization of Fumasep FAA-3-PK-130 to identify the material phase composition, the nature of the conducting moieties and their interactions with the adsorbed water molecules. A complete phase segregation between PPO and PEEK was found on a micrometric scale from 1H spinlattice relaxation times and micro-ATR analysis. Multinuclear (1H, 13C, 19F) Solid-State NMR spectra, combined with nuclear spin relaxation measurements, allowed us to identify the anion exchange moiety with benzyl-ethyldimethylammonium. This is present as functionalizing group of PPO monomers with a functionalization degree of about 40 %. Moreover, the mobility of water absorbed in the membrane was studied by 2H Solid-State NMR on samples hydrated with deuterated water under controlled relative humidity: at low relative moisture, two different types of environments were found for water molecules, compatible with two types of water-ion clusters, one of which contains water molecules with a restricted mobility, limited to C2 jumps, due to strong interactions with ions

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

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.

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)

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)

Titanium-Based Tetrakis-2,3-[5,6-di(Substituted)pyrazino]porphyrazine: Synthesis and Characterization

Tetrapyrazinoporphyrazine (TPysPz) ligands and metal complexes find, generally, application as electronic materials and catalysts. Considering the limited application of Titanium (Ti), we prepared and characterized a family of ligands and Ti-based complexes of tetrakis-2,3-[5,6-di-R8-pyrazino]porphyrazine (R = H, 2-Py, Ph). UV/Vis measurements in different solvents confirm molecular aggregation, which results more pronounced in the presence of 2-pyridil and phenyl substituents on the macrocycle edge. Because of low solubility, solid state NMR was applied for structure characterization. Additional IR and MALDI-TOF were carried out to complete the characterization. Cyclic voltammetry in DMSO/Bu4NBF4 0.1 m unveiled that our Ti complexes can take part in up to five redox events. The first two quasi-reversible reductions involve Ti(IV), whereas the further to or three occur at the expense of the TPysPz macrocycle. To test the applicability of our compounds as catalytic materials, we performed a preliminary cyclic voltammetry investigation in the solid-state, which showed typical peaks of hydrogen redox reactions

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