Application of low-rank approximation using truncated singular value decomposition for noise reduction in hyperpolarized 13 C NMR spectroscopy.

Dissolution dynamic nuclear polarization allows in vivo studies of metabolic flux using 13 C-hyperpolarized tracers by enhancing signal intensity by up to four orders of magnitude. The T1 for in vivo applications is typically in the range of 10-50 s for the different 13 C-enriched metabolic substrates; the exponential loss of polarization due to various relaxation mechanisms leads to a strong reduction of the signal-to-noise ratio (SNR). A common solution to the problem of low SNR is the accumulation/averaging of consecutive spectra. However, some limitations related to long delays between consecutive scans occur: in particular, following biochemical kinetics and estimate apparent enzymatic constants becomes time critical when measurement scans are repeated with the typical delay of about 3 T1 . Here we propose a method to dramatically reduce the noise, and therefore also the acquisition times, by computing, via truncated singular value decomposition, a low-rank approximation to the individual complex time-domain signals. Moreover, this approach has the additional advantage that the phase correction can be applied to the spectra already denoised, thus greatly reducing phase correction errors. We have tested the method on (1) simulated data; (2) performing dissolution of hyperpolarized 1-13 C-pyruvate in standard conditions and (3) in vivo data sets, using a porcine model injected with hyperpolarized Na-1-13 C-acetate. It was shown that the presented method reduces the noise level in all the experimental data sets, allowing the retrieval of signals from highly noisy data without any prior phase correction pre-processing. The effects of the proposed approach on the quantification of metabolic kinetics parameters have to be shown by full quantification studies.

Structural characterization of magnesium silicate hydrate: towards the design of eco-sustainable cements.

Magnesium-based cement is one of the most interesting eco-sustainable alternatives to standard cementitious binders. The reasons for the interest towards this material are twofold: (i) its production process, using magnesium silicates, brine or seawater, dramatically reduces CO2 emissions with respect to Portland cement production, and (ii) it is very well suited to applications in radioactive waste encapsulation. In spite of its potential, assessment of the structural properties of its binder phase (magnesium silicate hydrate or M-S-H) is far from complete, especially because of its amorphous character. In this work, a comprehensive structural characterization of M-S-H was obtained using a multi-technique approach, including a detailed solid-state NMR investigation and, in particular, for the first time, quantitative (29)Si solid-state NMR data. M-S-H was prepared through room-temperature hydration of highly reactive MgO and silica fume and was monitored for 28 days. The results clearly evidenced the presence in M-S-H of "chrysotile-like" and "talc-like" sub-nanometric domains, which are approximately in a 1 : 1 molar ratio after long-time hydration. Both these kinds of domains have a high degree of condensation, corresponding to the presence of a small amount of silanols in the tetrahedral sheets. The decisive improvement obtained in the knowledge of M-S-H structure paves the way for tailoring the macroscopic properties of eco-sustainable cements by means of a bottom-up approach.

Dynamics of ethylene-propylene random copolymers by (1)H and (13)C solid-state NMR.

The dynamic behavior of three completely amorphous ethylene-propylene random copolymers with slightly different structural properties was investigated by means of a multifrequency global fitting approach, presented in a previous paper. To this end, the trends of NMR (1)H and (13)C spin-lattice relaxation times with temperature, obtained at different frequencies, were analyzed by means of unified motional models for the segmental main-chain motion and rotation of methyl groups about their ternary symmetry axis. To evaluate the reliability of both the models and the method used with respect to the dimensionality of the data set, as well as to identify the minimal data set to be used for getting reliable dynamic information on similar systems, the fitting results obtained from the analysis of three different experimental data sets collected on the same polymer were compared. The data collected on the three polymers using the minimal data set were analyzed and the results discussed to evaluate the degree of sensitivity of the method to differences in the dynamic behavior of structurally similar systems. The results demonstrated that the method shows good sensitivity to the use of different dynamic models depending on the number and/or type of relaxation curves included in the analysis and that variations in the dynamic features of the same motions on different systems can be revealed even in the presence of polymeric systems characterized by very similar structural properties.

Orientational order of fluorinated mesogens containing the 1,3,2-dioxaborinane ring: a multidisciplinary approach.

Orientational order properties of two fluorinated liquid crystals containing the 1,3,2-dioxaborinane ring have been investigated by means of optical, dielectric, and (13)C and (19)F NMR spectroscopies. The optical birefringence and dielectric anisotropy values determined in the mesomorphic phases were analyzed in terms of well-established theoretical models to obtain the order parameters relative to the principal axis of the polarizability tensor and molecular dipole moment, respectively. A large set of data, including (13)C and (19)F chemical shift anisotropies and (13)C-(19)F and (1)H-(19)F couplings relative to nuclei on the aromatic rings, was acquired in the NMR experiments and analyzed to determine local order parameters (principal order parameter and biaxiality) for different rigid fragments of the mesogen aromatic core using advanced DFT methods for the calculation of geometrical parameters and chemical shift tensors. A critical analysis of the dependence of the order parameters on the data set employed and on the theoretical assumptions and approximations has also been performed. The orientational order parameters obtained using the different techniques are compared and discussed in relation to the reference frame associated with the anisotropic properties monitored.

Orientational order of difluorinated liquid crystals: a comparative 13C-NMR, Optical, and dielectric study in nematic and smectic B phases.

Structural and orientational order properties of 3Cy2CyBF2 and of 5CyCy2BF2 have been investigated by means of (13)C-NMR, optical, and dielectric spectroscopy methods. In the case of NMR, order parameters have been independently obtained from the analysis of either (13)C-(19)F dipolar couplings or (13)C chemical shift anisotropies, both measured from (13)C-{(1)H} NMR static spectra. The assignment of the (13)C resonances has been carried out thanks to the comparison with solution state spectra and DFT calculations, and the relevant geometrical parameters and (13)C chemical shift tensors needed to derive orientational order parameters have been calculated by DFT methods. In the analysis of (13)C-(19)F dipolar couplings, empirical corrections for vibrations and anisotropic scalar couplings have been included. Dielectric measurements have been performed over a broad frequency range for two orientations of the nematic director with respect to the measuring field. At low frequencies (static case) a positive dielectric anisotropy has been determined, which has enabled the calculation of the order parameters according to a well-tested procedure. At high frequencies the dielectric anisotropy changes its sign, a property which can be useful in designing a dual addressing display. The nematic order parameter determined from optical, dielectric, and NMR methods have been compared: their trends with temperature are very similar, apart from some slight shifts, and were analyzed by Haller and Chirtoc models. The differences among the results obtained by the four methods have been discussed in detail, also with reference to the assumptions and approximations used in each case, and to the results recently reported for similar fluorinated nematogens. The presence of a non-negligible order biaxiality has been related to the presence of a CH2CH2 bridging group, linking one cyclohexylic unit with either the other cyclohexyl or the phenyl ring.

A multinuclear solid-state magnetic resonance study of the interactions between the inorganic and organic coatings of BaSO4 submicronic particles.

Silica-coated BaSO4 submicronic particles, modified on the surface by treatment with stearic acid, have been characterized by means of 29Si, 13C, and 1H magic-angle-spinning (MAS) high-resolution techniques, and low-resolution 1H-FID analysis. Two types of adsorbed water were identified; adsorbed either inside or on the surface of BaSO4, most of the latter being removed by the silica coating. Evidences of silica-stearic acid interactions were found involving either carboxylic acid or carboxylate functional groups, and occurring by means of hydrogen and/or covalent bonds. Stearic acid was present as monolayer only, its chain being mostly rigid, even though a small fraction was subjected to fast inter-conformational motions.

Orientational order of a liquid crystal with three chiral centers by a combined 13C NMR and DFT approach.

In this work, the liquid crystal (S)-2-methylbutyl-[4'-(4' '-heptyloxyphenyl)-benzoyl-4-oxy-(S)-2-((S)-2')-benzoyl)-propionyl)]-propionate (ZLL 7/*) was investigated by means of 13C NMR spectroscopy. This compound has a very peculiar mesomorphic behavior, showing the following phases: paraelectric SmA, ferroelectric SmC*, antiferroelectric SmC*A, re-entrant ferroelectric SmC*re, and ferroelectric hexatic Sm*HEX. The structural and orientational ordering properties of ZLL 7/* have been determined by exploiting the nuclear chemical shielding properties of 13C. To this aim, solid-state NMR techniques such as CP, SPINAL-64, and SUPER have been used in combination with DFT calculations. The agreement between experimental and in vacuo DFT shielding parameters appears to be satisfactory. The orientational order parameters obtained from the 13C shielding analysis have been discussed, taking into account different data analysis approaches and comparing them to those previously obtained from an independent 2H NMR study.

A new hydrogel for the extended and complete prednisolone release in the GI tract.

The issue of incomplete release of poorly soluble drugs from sustained-release oral formulations is addressed using prednisolone (PDS) as the model drug and a novel highly swelling hydrogel as the rate-controlling material. The hydrogel was formed by heating N-carboxymethylchitosan (CMC) to 80 degrees C for 24 h. Swelling, alkalimetry, FTIR, DSC, and solid-state NMR studies showed that the treatment produced physical crosslinking, i.e., polymer chain entanglement. A controlled-release system was prepared by coating an inert compacted support of ethylcellulose (50 mg; diameter, 6 mm) with a CMC layer containing dispersed PDS powder (10-50 microm). The system was heated to crosslink the CMC coating, then drug release to simulated GI fluids was studied in vitro. The drug release pattern and term were modulated via the layer mass (LM) (10 or 14 mg cm(-2)) and/or the drug-polymer wt ratio (D/P) (1:5 or 2:5). The rate parameter, K, and the time exponent, n, of the Peppas equation were: K=26.6+/-0.3 h(-n), n = 0.78+/-0.02 (LM, 10 mg cm(-2); D/P, 1:5); K = 24.7+/-0.7 h(-n), n = 0.56+/-0.02 (LM, 14 mg cm(-2); D/P, 1:5); K = 20.7+/-0.3 h(-n), n = 0.76+/-0.01 (LM, 10 mg cm(-2); D/P, 2:5). Hydrogel swelling was faster than drug release. This was controlled, in a first stage, by drug dissolution-diffusion in the swollen gel, and subsequently, by diffusion. The drug release rate was unaffected by the GI pH variations, and slightly affected by the environmental hydrodynamics. The system promises an extended and complete release of poorly soluble drugs in the GI tract.

Solid-state NMR characterization of diastereoisomeric chiral stationary phases and their soluble models.

Two diastereoisomeric chiral stationary phases (CSPs), devised for enantioselective HPLC, showing unexplained differences in their chromatographic performances, have been characterized, together with their soluble models, by means of 13C-cross polarization/magic angle spinning (CP/MAS), 1H-MAS and 1H-free induction decay (FID) analysis. The NMR investigation of the soluble models has not highlighted significant structural/conformational differences between the two diastereoisomers, but has constituted a useful support for the analysis of the more complex NMR data of the CSPs. The organic chiral selectors of the stationary phases show a poor internal mobility and no conformational differences between the two diastereoisomers have been observed. On the contrary, interesting differences between the two CSPs have been found involving the silanols on the silica surface and the dynamics of the linking chains between the organic selectors and the silica surface itself. An explanation of the chromatographic behaviour has been proposed in terms of different proximity of the organic moieties with respect to the inorganic surface in the two CSPs.

Correlation between 1H FID and T1rho components in heterogeneous polymer systems: an application to SBS.

Wideline 1H FID and relaxation measurements of a relatively simple motionally heterogeneous system, the triblock copolymer styrene-butadiene-styrene, have been performed in a temperature range between the polystyrene and polybutadiene glass transition temperatures. The two FID and the two spin lattice relaxation time in the rotating frame (T1rho) components found at each temperature have been correlated by means of a two-dimensional approach. It is shown that this approach allows dynamic information, not accessible simply by interpreting proton T1 and T1rho data, to be revealed. In the case examined, the correlation found could be confirmed by high-resolution 1H T1rho-selective 13C Cross Polarization experiments.

Cage: software for a critical analysis of (2)H spin-lattice relaxation in liquid crystals.

A software package of Mathematica, aimed at the analysis of (2)H NMR Zeeman (T(1Z)) and quadrupolar (T(1Q)) spin-lattice relaxation times in liquid crystals in terms of diffusional models, is presented. The models most commonly used to describe internal, overall, and collective motions in liquid-crystalline phases are considered, and dynamic parameters are obtained by means of either single point or global target approaches using simulation or fitting procedures. The use of the software as a tool for highlighting the problems encountered in this kind of analysis as well as for dealing with such problems following suitable strategies is illustrated by means of applications to experimental (2)H relaxation times of three different calamitic liquid crystals.

Preparation, characterisation and photosensitivity studies of solid dispersions of diflunisal and Eudragit RS100 and RL100.

Solid dispersions of diflunisal (DIF) with Eudragit RS100 (RS) and RL100 (RL) with different drug-to-polymer ratios were prepared by a solvent method (coevaporates) and were characterised in the solid state in comparison with the corresponding physical mixtures. The work was aimed at characterising the interactions occurring between DIF and RS or RL polymers, along with their influence on the in-vitro drug-dissolution pattern. The findings suggest that the drug did not change its crystalline form within the polymer network. Drug dispersion in the polymer matrix strongly influences its dissolution rate, which appears slower and more gradual while increasing the polymer ratios. Moreover, DIF is known to be a photosensitive compound, and its photoproduct has been found to be a toxic agent. This can be evidenced by testing red blood cell membranes for their resistance to the osmotic shock induced by UVA irradiation in the presence of DIF. The presence of some DIF/RS coevaporates was shown to reduce significantly the drug photosensitization process towards cell membranes. This suggests the possibility of combining the design of a drug delivery system with a photoprotective strategy.

Conformational dynamics of a metallomesogen studied by 2H-NMR spectroscopy

In this work we present a quantitative analysis of both quadrupolar splittings and deuterium Zeeman and quadrupolar spin-lattice relaxation times reported in the literature for two isotopomers of Azpac, an acetylacetonate derivative of the cyclopalladated 4, 4'-bis(hexyloxy) azoxybenzene. Azpac-d(4) is deuterated at the aromatic rings and Azpac-d(26) is deuterated on the alkoxy chains. The additive potential method is used to model the splittings, while the derived spectral densities are interpreted using the decoupled model in conjunction with the Nordio model. The two side chains are assumed to be noninteracting and identical in their conformations in order to limit the size of the transition rate matrix needed to describe correlated internal bond rotations in the chains. Rotational diffusion constants and internal jump rate constants are derived for this metallomesogen.

Methods for correlating T1rho and FID components in wideline 1H NMR studies of motionally heterogeneous polymer systems.

We address the problem of correlating the observed FID and T1rho components in wideline 1H relaxation measurements of motionally heterogeneous polymers, and show that different methods of data treatment can highlight different aspects of the correlations present. For a sample of polypropylene we find that the T1rho relaxation behaviour is driven by relaxation associated with the intermediate FID component, which strongly suggests a motionally inhomogeneous amorphous region in the sample.

The SPORT-NMR software: a tool for determining relaxation times in unresolved NMR spectra.

A software package which allows the correct determination of individual relaxation times for all the nonequivalent nuclei in poorly resolved NMR spectra is described. The procedure used, based on the fitting of each spectrum in the series recorded in the relaxation experiment, should improve the analysis of relaxation data in terms of quantitative dynamic information, especially in anisotropic phases. Tests on simulated data and experimental examples concerning 1H and 13C T1rho measurement in a solid copolymer and 2H T1Z and T1Q measurement in a liquid crystal are shown and discussed.

A method for analysing proton NMR relaxation data from motionally heterogenous polymer systems.

Historically, the results of studies of the motional processes present in polymers above the glass transition temperature (Tg) by proton NMR spin-lattice relaxation in either the laboratory or rotating frames (T1 or T1p) have shown poor agreement with the results from similar studies carried out using other techniques such as dielectric or mechanical relaxation. We believe that this is mainly because of the complication of the NMR results due to magnetisation transport, either by spin diffusion or by bulk diffusion of the polymer. We suggest a novel approach to the analysis of proton NMR relaxation data from a motionally heterogeneous polymer, and show that the results of such an analysis are intrinsically reasonable and of the form expected for dielectric or mechanical relaxation.

Solid state NMR study of sodium thiocyanate/poly(ethylene oxide) electrolytes.

1H-, 13C-, 23Na-solid state NMR measurements have been used to characterise the morphology and the dynamics of several NaSCN-PEO mixtures. Selective 13C-MAS experiments allowed to determine the composition of the (PEO)nNaSCN samples in terms of the different phases present, as well as the real stoichiometry of the crystalline complex. 1H- and 13C-spin-lattice relaxation times provided estimates of the dimensions of the different domains and gave information on the dynamics of the polymer chains. 23Na-MAS spectra and 2D nutation experiments allowed to individuate the presence of different environments for the sodium cations on the basis of their quadrupolar interactions.