Hydration process of cement in the presence of a cellulosic additive. A calorimetric investigation

In the cement industry, the extrusion technique is used to produce flat shapes with improved resistance to compression. Extrusion is a plastic-forming process that consists of forcing a highly viscous plastic mixture through a shaped die. The material should be fluid enough to be mixed and to pass through the die, and on the other hand, the extruded specimen should be stiff enough to be handled without changing in shape or cracking. These characteristics are industrially obtained by adding cellulosic polymers to the mixture. The aim of this work is to understand the action mechanism of these additives on the major pure phases constituting a typical Portland cement: tricalcium silicate (C(3)S), dicalcium silicate (C(2)S), tricalcium aluminate (C(3)A), and tetracalcium iron-aluminate (C(4)AF). In particular, a methylhydroxyethyl cellulose (MHEC) was selected from the best-performing polymers for further study. The effect of this additive on the hydration kinetics (rate constants, activation energies, and diffusional constants) was evaluated by means of differential scanning calorimetry (DSC) while the hydration products were studied by using thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). MHEC addition in calcium silicate pastes produces an increase in the induction time without affecting the nucleation-and-growth period. A less dense CSH gel was deduced from the diffusional constants in the presence of MHEC. Moreover, CSH laminar features and poorly structured hydrates were noted during the first hours of hydration. In the case of the aluminous phases, the additive inhibits the growth of stable cubic hydrated phases (C(3)AH(6)), with the advantage of the metastable hexagonal phases being formed in the earliest minutes of hydration.     

New hydrogels from interpenetrated physical gels of agarose and chemical gels of polyacrylamide: Effect of relative concentration and crosslinking degree on the viscoelastic and thermal properties

In this article, we report on the viscoelastic and thermal properties of agarose–polyacrylamide (PAAm) interpenetrating polymer hydrogels (IPHs) and semi‐IPHs as a function of agarose concentration and PAAm crosslinking degree. The results demonstrated that the agarose is able to gel in the presence of crosslinked and linear IPHs. In addition, the reticulation of PAAm in the presence of agarose is confirmed for the case of IPHs giving rise to systems with dimensional stability at high temperatures. The formation of a fully IPH was ascertained at low agarose concentrations. A study of the morphology and nanoscale elasticity of the different systems has been carried out with atomic force microscopy/ultrasonic force microscopy (UFM). UFM data provide further evidence of interpenetration, allowing us to visualize—if present—phase‐separated domains with nanoscale resolution for the various crosslinking degrees and PAAm and agarose concentrations used during the formation of the IPHs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Redox and electrocatalytic properties of mimochrome VI, a synthetic heme peptide adsorbed on gold

Mimochrome VI (MC-VI) is a synthetic heme peptide containing a helix-heme-helix sandwich motif designed to reproduce the catalytic activity of heme oxidases. The thermodynamics of Fe(III) to Fe(II) reduction and the kinetics of the electron-transfer process for MC-VI immobilized through hydrophobic interactions on a gold electrode coated with a nonpolar SAM of decane-1-thiol have been determined through cyclic voltammetry. Immobilization slightly affects the reduction potential of MC-VI, which under these conditions electrocatalytically turns over molecular oxygen. This work sets the premise for the exploitation of totally synthetic mimochrome-modified electrode surfaces for clinical and pharmaceutical biosensing.     

Crucigasterins A-E, antimicrobial amino alcohols from the Mediterranean colonial ascidian Pseudodistoma crucigaster

Five new unsaturated 2-amino-3-alcohols, crucigasterins A-E (2-6), were isolated together with known related compound 7 from the Mediterranean ascidian Pseudodistoma crucigaster and characterised as diacetyl derivatives (2a-6a) by spectroscopic methods. The threo-relative configuration of the amino alcohol portion was inferred by NOE analysis of the oxazolidinone derivative of crucigasterin A (2) as well as by ¹³C NMR comparison with synthetic threo and erythro model compounds. The co-occurring metabolites were assumed to have the same relative configuration as 2 by comparison of the diagnostic carbon value of C-1. The absolute stereochemistry of compound 7 that had not been previously reported was determined by applying the modified Mosher’s method on the corresponding N-acetyl derivative. The same absolute configuration was suggested for the other co-occurring crucigasterins by biogenetic considerations. Antibacterial and antifungal activities of selected crucigasterins were also evaluated.     

Adapting the semi-explicit assembly solvation model for estimating water-cyclohexane partitioning with the SAMPL5 molecules

We describe here some tests we made in the SAMPL5 communal event of ‘Semi-Explicit Assembly’ (SEA), a recent method for computing solvation free energies. We combined the prospective tests of SAMPL5 with followup retrospective calculations, to improve two technical aspects of the field variant of SEA. First, SEA uses an approximate analytical surface around the solute on which a water potential is computed. We have improved and simplified the mathematical model of that surface. Second, some of the solutes in SAMPL5 were large enough to need a way to treat solvating waters interacting with ‘buried atoms’, i.e. interior atoms of the solute. We improved SEA with a buried-atom correction. We also compare SEA to Thermodynamic Integration molecular dynamics simulations, so that we can sort out force field errors.     

Changes in the reactivity of the fluorescent reagents carbazole-9-carbonyl chloride and 9-carbazolylacetic acid in the presence of cyclodextrins

Carbazole-9-carbonyl chloride (C9CC) and 9-carbazolylacetic acid (9CAA) were selected as model fluorescent reagents. The effect of different chemically modified cyclodextrins (CDs) added to the aqueous solutions of these reagents was studied in water and in buffered aqueous solutions at pH 4.5 and 8.8. The CDs employed were 2-hydroxypropyl-β-cyclodextrin (HP-βCD), 2,3-di-O-methyl-β-cyclodextrin (DM-βCD) and 2,3,6-tri-O-methyl-β-cyclodextrin (TM-βCD). The inclusion of these reagents inside the cavities of the CDs was verified and this process can affect the derivatization reaction because CDs can modify the reactivity of the guest molecules. The basic conditions necessary for the derivatization reaction between C9CC and amines lead to the formation of carbazole anion through hydrolysis followed by decarboxylation. In the presence of CDs, the hydrolysis-decarboxylation of carbazole-9-carbonyl chloride is faster than in buffered aqueous homogeneous solutions. The behaviour observed for these reagents in aqueous solutions of CDs was compared to the one observed in basic ethanolic solutions. These changes are particularly noticeable in the case of 2,3-di-O-methyl-β-CD and 2-hydroxypropyl-β-CD. The characteristics of the fluorescent reagents are compared to carbazole and 9-methylcarbazole as model compounds. This paper was presented at XIIIth International Cyclodextrin Symposium. Torino, Italy, May 14–17, 2006.     

Adiabatic squeezing of molecular wave packets by laser pulses

Strong pulse sequences can be used to control the position and width of the molecular wave packet. In this paper we propose a new scheme to maximally compress the wave packet in a quasistatic way by freezing it at a peculiar adiabatic potential shaped by two laser pulses. The dynamic principles of the scheme and the characteristic effect of the different control parameters are presented and analyzed. We use two different molecular models, electronic potentials modeled by harmonic oscillators, with the same force constants, and the Na(2) dimer, to show the typical yield that can be obtained in compressing the initial (minimum width) molecular wave function.     

First synthesis of an α-d-Fucp3NAc containing oligosaccharide: a study on d-Fucp3NAc glycosylation

3-Acetamido-3,6-dideoxy-d-galactopyranose (d-Fucp3NAc) is an aminosugar almost exclusively found in phytopathogenic O-antigens. The glycosylation reaction involving d-Fucp3NAc donors was studied with several rhamnosyl acceptors, revealing that the best yields and highest α-stereoselectivity were obtainable by coupling a N-phenyl trifluoroacetimidate glycosyl donor in a ternary mixture (dioxane/DME/toluene 4:1:1) as solvent. For the first time a synthetic access to α-d-Fucp3NAc containing oligorhamnans, that are interesting molecules for studying the effects of O-antigen model oligosaccharides on the modulation of plant response to bacteria, was reported. An example is the pentasaccharide repeating unit of the major O-antigen component from Pseudomonas syringae pv. holci IMV 8300, which was synthesized as its methyl glycoside.