The leaching mechanism of hydraulic mortars as part of autogenic self-healing process

Summarization: Historic mortars have exhibited long term durability which has been largely attributed to their self-healing properties. The aim of this work is the study of the autogenic self-healing mechanism as observed in historic mortars as well as the simulation of the phenomenon in laboratory prepared lime-pozzolan and natural hydraulic lime mortars. One of the most significant parameters in autogenous self-healing phenomenon is the source of the calcium ions, which controls the formation of new healing phases inside cracks. In this study, an electrochemically accelerated leaching procedure was designed to examine the influence of mineralogy and curing time on the dissolution of Ca-bearing phases of lime-pozzolan and NHL mortars, which are characterized by high portlandite content. It was found that, apart from portlandite, Ca+2 are also leached from C2S and C–S–H phases and it was shown that this phenomenon takes place in two separate time-frames: an early period (t  28 d) where decalcification of C–S–H and dissolution of secondary portlandite are dominant. The phenomenon was further studied on mortar specimens where healing of micro cracks was observed by precipitation of secondary calcite inside cracks and voids, highlighting the role of leached Ca+2 on the autogenic self-healing mechanism. It is proved that, contrary to what is believed about the autogenic healing, besides portlandite, the contribution of hydraulic phases is also significant. Overall, this study confirms the significant role of the Ca-leaching process in the autogenic self-healing mechanism and highlights the different sources of calcium ions, as well as the different time frames of the events. Finally, the findings elucidate the high self-healing potential of traditional mortars which contribute to their prolonged service life.Presented on: Journal of Cultural Heritag

“Switching on” the single-molecule magnet properties within a series of dinuclear cobalt( iii )–dysprosium( iii ) 2-pyridyloximate complexes

The use of 2-pyridinealdoxime (paoH), methyl 2-pyridyl ketone oxime (mepaoH), phenyl 2-pyridyl ketone oxime (phpaoH) and pyridine-2-amidoxime (NH2paoH) for the synthesis of dinuclear CoIII/DyIII complexes is described in the absence or presence of an external base. Complexes [CoDy(pao)3(NO3)3] (1), [CoDy(mepao)3(NO3)3] (2), [CoDy(phpao)3(NO3)3] (3) and [CoDy(NH2pao)3(NO3)3]·3MeOH (4·3MeOH) have been isolated and their structures have been determined by single-crystal X-ray crystallography. The complexes crystallize in non-centrosymmetric (2, 3) or centrosymmetric (1, 4·3MeOH) trigonal space groups and form a family of triply-oximate bridged dinuclear Co(III)–Dy(III) complexes. The crystals of 1, 3 and 4·3MeOH contain mixtures of Δ and Λ enantiomers, whereas complex 2 is enantiomerically pure (Λ). A 3-fold crystallographic axis (C3) passes through two metal ions in all complexes. The low-spin CoIII and DyIII ions are bridged by three oximate groups belonging to the η1:η1:η1:μ 2-pyridyloximate ligands. The CoIII centre is octahedrally coordinated by the six nitrogen atoms of the deprotonated organic ligands in a facial arrangement. The DyIII centre is bound to an O9 set of donor atoms, its coordination sphere being completed by three bidentate chelating nitrato groups. The coordination polyhedron around DyIII in 1 is best described as the Johnson tricapped trigonal prism, while the coordination geometries of the DyIII centres in 2, 3 and 4·3MeOH are best described as consisting of spherical tricapped trigonal prismatic coordination polyhedra. The spectroscopic data of the complexes are also reported and discussed in the infra-red region in terms of the coordination modes of the ligands involved. The magnetic properties of these complexes were studied between 300 and 1.8 K revealing mainly the depopulation of the DyIIImj sublevels of the ground 6H15/2 state. The intrinsic magnetic anisotropy of the DyIII centers is clearly observed by the non-superimposed magnetization (M) versus H/T data, but single-molecule magnet (SMM) properties were detected only for the mepao−-containing complex 2. The origin of these properties in 2 is critically discussed and supported by computational studies

Immobilization of lipid substrates: application on phospholipase A2 determination

The purpose of the study was to assess a fluorimetric assay for the determination of total phospholipase A2 (PLA2) activity in biological samples introducing the innovation of immobilized substrates on crosslinked polymeric membranes. The immobilized C12-NBD-PtdCho, a fluorescent analogue of phosphatidylcholine, exhibited excellent stability for 3 months at 4 °C and was not desorbed in the aqueous reaction mixture during analysis. The limit of detection was 0.5 pmol FA (0.2 pg) and the linear part of the response curve extended from 1 up to 190 nmol FA/h/mL sample. The intra- and inter-day relative standard deviations (%RSD), were ≤6 and ≤9 %, respectively. Statistical comparison with other fluorescent methods showed excellent correlation and agreement. Semiempirical calculations showed a fair amount of electrostatic interaction between the NBD-labeled substrate and the crosslinked polyvinyl alcohol with the styryl pyridinium residues (PVA-SbQ) material, from the plane of which, the sn-2 acyl chain of the phospholipid stands out and is accessible by PLA2. Atomic Force Microscopy revealed morphological alterations of the immobilized substrate after the reaction with PLA2. Mass spectrometry showed that only C12-NBD-FA, the PLA2 hydrolysis product, was detected in the reaction mixture, indicating that PLA2 recognizes PVA-SbQ/C12-NBD-PtdCho as a surface to perform catalysis.</p