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.

Interaction of cisplatin and two potential antitumoral platinum(ii) complexes with a model lipid membrane: a combined NMR and MD study

Multinuclear NMR and MD calculations highlighted the different interactions of cisplatin and two potential antitumoral Pt(ii) complexes with a model membrane.

Boron nitride nanotubes for boron neutron capture therapy as contrast agents in magnetic resonance imaging at 3 T

The applicability of boron nitride nanotubes (BNNTs) containing Fe paramagnetic impurities as contrast agents in magnetic resonance imaging (MRI) was investigated. The measurement of longitudinal and transverse relaxation times of water protons in homogeneous aqueous dispersions of BNNTs wrapped with poly(L-lysine) at different concentrations allowed longitudinal (r(1)) and transverse (r(2)) relaxivities to be determined at 3T. The r(2) value was comparable to those of commercial superparamagnetic iron oxide nanoparticles, indicating that Fe-containing BNNTs have the potential to be used as T(2) contrast-enhancement agents in MRI at 3T.

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.

Structure and dynamics of high molecular weight glutenin subunits of durum wheat (Triticum durum) in water and alcohol solutions studied by electron paramagnetic resonance and circular dichroism spectroscopies

Complementary information on the structure and dynamics of high molecular weight glutenin subunits (HMW-GS) of durum wheat (Triticum durum) was obtained by means of two spectroscopic techniques. Electron paramagnetic resonance was used to investigate the dynamics of the HMW-GS hydrated with two 2-propanol/water mixtures at temperatures between 268 and 308 K by specific spin labeling of their cysteine residues. Spectra were of a composite type, resulting from two populations of spin labels differing in molecular mobility, both undergoing isotropic rotational diffusion. Diffusional coefficients and populations of the fast- and slow-moving spin labels, determined by an accurate spectral line shape analysis, are discussed as a function of temperature and water content in the solvent systems. Far-UV circular dichroism was employed to provide information on the secondary structure of the HMW-GS in three different solvents [aqueous 50% (v/v) 2-propanol, aqueous 0.1% (v/v) trifluoroacetic acid, and trifluoroethanol]. For the first one, the influence of temperature on HMW-GS structure was also investigated.

Degradation of gluten by proteases from dry and germinating wheat (Triticum durum) seeds: An in vitro approach to storage protein mobilization

Vital gluten was used as an ideal substrate to investigate the role of some proteases in storage protein degradation. Aspartic proteinase and carboxypeptidase were identified as endogenous enzymes adsorbed on gluten and their optimum pH values determined. SDS-PAGE of soluble products released by gluten digestion revealed that the activity of these proteases plays a minor role in protein mobilization, whereas cysteine proteinase, purified from wheat seeds at the fourth day of germination, is extremely effective, producing a remarkable protein degradation in short times. Synergistic effects of aspartic and cysteine proteinase were not observed. Spin labeling of the sulfhydryl groups of gluten proteins enabled a comparative EPR investigation of the consequences of proteolytic degradation on gluten elasticity. It was found that storage protein mobilization brings a loss of elasticity to the polymeric network of gluten, which is particularly marked when the hydrolysis is performed by cysteine proteinase.

Front-surface absorbance spectra of wheat flour: determination of carotenoids

Front-surface absorbance spectra of wheat flours in the 250-650 nm region can be obtained by measuring reflectance spectra with a conventional spectrofluorometer suitably set to detect light scattered from powder samples. The spectra recorded on flour samples, obtained from seeds of four bread and five durum wheats, show high-intensity absorption bands due to aromatic amino acids of wheat proteins and low-intensity bands due to chromophores bound to low-molecular-weight compounds. The intensity of these last bands is proportional to the concentration of the corresponding chromophores present in the flour; thus, it can be used to measure the content of the compounds containing the chromophore(s). In particular, a quantitative determination of the carotenoids actually present in the flours is made, obtaining information on the original content of the seeds. This determination is important, as, for example, xanthophylls are well-known antioxidants and free-radical scavengers involved in aging processes of seeds. Reflectance measurements on powder samples are far more economic in terms of time and materials consumption than methods such as extraction and HPLC analysis of extracts and, in addition, give an evaluation of the overall content of carotenoids with absorption bands in the spectral range 450-500 nm. Application of the technique to other food powders with low-intensity absorption bands in the near-UV and vis region is possible.

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.