Modification of water retention and rheological properties of fresh state cement-based mortars by guar gum derivatives

International audienceThe present study examines the influence of chemical composition and structure of guar gum derivatives on water retention capacity (WR) and rheological behavior of fresh state cement-based mortars. The investigation was also completed by adsorption isotherms. For this, original guar gum, three HydroxyPropyl Guars (HPG) and two hydrophobically modified HPGs were selected. The effect of the molar substitution (MSHP) and of hydrophobic substitution (DSAC) was investigated. The results highlight that chemical composition of HPGs has a remarkable effect on fresh state properties of mortars. The original guar gum does not impact on neither WR nor rheological behavior. Increasing MSHP leads to an improvement of the WR and the stability of mortars while the hydrophobic units further enhance WR and lead to a decrease in the yield stress and an increase in the resistance to the flow of admixed mortars

Effect of Guar Gum Derivatives on Fresh State Properties of Portland Cement-Based Mortars

International audienceMortars are traditionally made from a mixture of sand, a binder and water. However, modern factory-made mortars are currently, very complex materials. Indeed, to exhibit various properties from the fresh paste to the hardened material, mortar formulations are composed of many mineral and organic admixtures. Among organic admixtures, polysaccharides are widely used in mortar formulation to improve water retention capacity of the freshly-mixed materials. The water retention capacity is an essential property of mortars to enhance cement hydration and its adhesion to a substrate. Moreover, many polysaccharide admixtures, acting as viscosity-enhancing agents, prevent segregation and improve the homogeneity and workability of cement-based system. Indeed, the viscosity of the system strongly increases using polysaccharides. Nevertheless, polysaccharides, as sugars, act on cement hydration. The main drawback is the retarding effect in hydration mechanism and setting-time of the cement.The aim of this study is to focus on the effect of guar gum derivatives on fresh state properties of Portland cement-based mortars, such as water retention, rheological behavior and the hydration delay. This work focuses on the guar gum derivatives since their manufacturing process is low pollutant and they provide very good properties to cement-based mortars. The results highlight that the chemical composition of guar gum derivatives (MS, DS, additional alkyl chain) are the key levers to improve water retention of mortars and to adapt the rheological behavior of the cementitious paste to a specific application

Normalization of low-density microarray using external spike-in controls: analysis of macrophage cell lines expression profile

<p>Abstract</p> <p>Background</p> <p>The normalization of DNA microarrays allows comparison among samples by adjusting for individual hybridization intensities. The approaches most commonly used are global normalization methods that are based on the expression of all genes on the slide and on the modulation of a small proportion of genes. Alternative approaches must be developed for microarrays where the proportion of modulated genes and their distribution are unknown and they may be biased towards up- or down-modulated trends.</p> <p>Results</p> <p>The aim of the work is to study the use of spike-in controls to normalize low-density microarrays. Our test-array was designed to analyze gene modulation in response to hypoxia (a condition of low oxygen tension) in a macrophage cell line. RNA was extracted from controls and cells exposed to hypoxia, mixed with spike RNA, labeled and hybridized to our test-array. We used eight bacterial RNAs as source of spikes. The test-array contained the oligonucleotides specific for 178 mouse genes and those specific for the eight spikes. We assessed the quality of the spike signals, the reproducibility of the results and, in general, the nature of the variability. The small values of the coefficients of variation revealed high reproducibility of our platform either in replicated spots or in technical replicates. We demonstrated that the spike-in system was suitable for normalizing our platform and determining the threshold for discriminating the hypoxia modulated genes. We assessed the application of the spike-in normalization method to microarrays in which the distribution of the expression values was symmetric or asymmetric. We found that this system is accurate, reproducible and comparable to other normalization methods when the distribution of the expression values is symmetric. In contrast, we found that the use of the spike-in normalization method is superior and necessary when the distribution of the gene expression is asymmetric and biased towards up-regulated genes.</p> <p>Conclusion</p> <p>We demonstrate that spike-in controls based normalization is a reliable and reproducible method that has the major advantage to be applicable also to biased platform where the distribution of the up- and down-regulated genes is asymmetric as it may occur in diagnostic chips.</p

A novel Bim-BH3-derived Bcl-XL inhibitor: biochemical characterization, in vitro, in vivo and ex-vivo anti-leukemic activity

BH3-only members of the Bcl-2 family exert a fundamental role in apoptosis induction. This work focuses on the development of a novel peptidic molecule based on the BH3 domain of Bim. The antiapoptotic molecule Bcl-X(L), involved in cancer development/progression and tumour resistance to cytotoxic drugs, is a target for Bim. According to a rational study of the structural interactions between wt Bim-BH3 and Bcl-X(L), we replaced specific residues of Bim-BH3 with natural and non-natural aminoacids and added an internalizing sequence, thus increasing dramatically the inhibitory activity of our modified Bim-BH3 peptide, called 072RB. Confocal microscopy and flow cytometry demonstrated cellular uptake and internalization of 072RB, followed by co-localization with mitochondria. Multiparameter flow cytometry demonstrated that the 072RB dose-dependent growth inhibition of leukaemia cell lines was due to apoptotic cell death. No effect was observed when cells were treated with the internalizing vector alone or a mutated control peptide (single aminoacid substitution L94A). Ex-vivo derived leukemic cells from acute myeloid leukaemia (AML) patients underwent cell death when cultured in vitro in the presence of 072RB. Conversely, no significant cytotoxic effect was observed when 072RB was administered to cultures of peripheral blood mononuclear cells, either resting or PHA-stimulated, and bone marrow cells of normal donors. Xenografts of human AML cells in NOD/SCID mice displayed a significant delay of leukemic cell growth upon treatment with 072RB administered intravenously (15 mg/Kg three times, 48 hours after tumour cell injection). Altogether, these observations support the therapeutic potentials of this novel BH3 mimetic