Synthesis of Lignosulfonate-Based Dispersants for Application in Concrete Formulations

Lignosulfonates (LS) are products from the sulfite pulping process that could be applied as renewable environmentally-friendly polymeric surfactants. Being widely used as plasticizers and water-reducing admixtures in concrete formulations LS compete in the market with petroleum-based superplasticizers, such as naphthalene sulfonate formaldehyde polycondensate (NSF) and copolymer polycarboxylate ethers (PCE). In this work, different chemical modification strategies were used to improve LS performance as dispersants for concrete formulations. One strategy consisted in increasing the molecular weight of LS through different approaches, such as laccase and polyoxometalate-mediated polymerization, glyoxalation, and reversible addition-fragmentation chain transfer (RAFT) polymerization. The other strategy consisted of preparing LS-based non-ionic polymeric dispersants using two different epoxidized oligomer derivatives of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). Modified LS were used to prepare cement pastes, which were examined for their fluidity. Results revealed that the most promising products are PPG-modified LS due to the introduction of PPG chains by reaction with phenolic moieties in LS. The enhanced dispersant efficiency of the ensuing products is probably related not only to electrostatic repulsion caused by the sulfonic ionizable groups in LS but also to steric hindrance phenomena due to the grafted bulky PPG chains.

Polysaccharide-Based Materials Created by Physical Processes: From Preparation to Biomedical Applications

Polysaccharide-based materials created by physical processes have received considerable attention for biomedical applications. These structures are often made by associating charged polyelectrolytes in aqueous solutions, avoiding toxic chemistries (crosslinking agents). We review the principal polysaccharides (glycosaminoglycans, marine polysaccharides, and derivatives) containing ionizable groups in their structures and cellulose (neutral polysaccharide). Physical materials with high stability in aqueous media can be developed depending on the selected strategy. We review strategies, including coacervation, ionotropic gelation, electrospinning, layer-by-layer coating, gelation of polymer blends, solvent evaporation, and freezing–thawing methods, that create polysaccharide-based assemblies via in situ (one-step) methods for biomedical applications. We focus on materials used for growth factor (GFs) delivery, scaffolds, antimicrobial coatings, and wound dressings.

Emulsion Formation and Stabilizing Properties of Olive Oil Cake Crude Extracts

The surface-active and emulsifying properties of crude aqueous ethanolic extracts from untreated olive oil cake (OOC) were investigated. OOC extracts contained important concentrations of surface-active components including proteins, saponins and polyphenols (1.2–2.8%, 7.8–9.5% and 0.7–4.5% (w/w), respectively) and reduced the interfacial tension by up to 46% (14.0 ± 0.2 mN m−1) at the oil–water interface. The emulsifying ability of OOC extracts was not correlated, however, with their interfacial activity or surface-active composition. Eighty percent aqueous ethanol extract produced the most stable oil-in-water (O/W) emulsions by high-pressure homogenization. The emulsions had average volume mean droplet diameters of approximately 0.4 µm and negative ζ-potentials of about -45 mV, and were stable for up to 1 month of storage at 5, 25 and 50 °C. They were sensitive, however, to acidic pH conditions (<5) and NaCl addition (≥25 mM), indicating that the main stabilization mechanism is electrostatic due to the presence of surface-active compounds with ionizable groups, such as saponins.

A Study with Peptide Dendrimers Reveals an Extreme pH Dependence of Antibiotic Activity Above pH 7.4

The presence of ionizable groups in antimicrobial peptides (AMPs) often induces a pH-dependent activity. Herein we report that removing eight low p<i>K</i>_a amino termini in antimicrobial peptide dendrimer (AMPD) <b>G3KL</b> provides dendrimer <b>XC1</b> with a broader pH-activity range. Furthermore, raising the pH to 8.0 reveals strong activities against <i>Klebsiella pneumoniae</i> and methicillin resistant <i>Staphylococcus aureus</i> (MRSA) against which these AMPDs are inactive at pH 7.4. We observe a similar effect with polymyxin B on MRSA. Binding experiments with a fluorescent AMPD and the effect of high salt concentration suggest that the activity increase reflects stronger electrostatic binding to the bacteria at high pH. pH-profiling of other polycationic antimicrobials (polymers, peptidomimetics, foldamers, dendrimers) might similarly enhance their activity range, with possible use for topical treatments.

A Study with Peptide Dendrimers Reveals an Extreme pH Dependence of Antibiotic Activity Above pH 7.4

The presence of ionizable groups in antimicrobial peptides (AMPs) often induces a pH-dependent activity. Herein we report that removing eight low p<i>K</i>_a amino termini in antimicrobial peptide dendrimer (AMPD) <b>G3KL</b> provides dendrimer <b>XC1</b> with a broader pH-activity range. Furthermore, raising the pH to 8.0 reveals strong activities against <i>Klebsiella pneumoniae</i> and methicillin resistant <i>Staphylococcus aureus</i> (MRSA) against which these AMPDs are inactive at pH 7.4. We observe a similar effect with polymyxin B on MRSA. Binding experiments with a fluorescent AMPD and the effect of high salt concentration suggest that the activity increase reflects stronger electrostatic binding to the bacteria at high pH. pH-profiling of other polycationic antimicrobials (polymers, peptidomimetics, foldamers, dendrimers) might similarly enhance their activity range, with possible use for topical treatments.

A Web Tool for Calculating Substituent Descriptors Compatible with Hammett Sigma Constants

<p>Electron donating or accepting power of organic substituents is an important parameter affecting many properties of parent molecules, most notably their reactivity and pKa of ionizable groups. These substituent properties are usually described by Hammett sigma constants obtained by measuring ionization of substituted benzoic acids. Although values of these constants have been measured for the most common functional groups, data for many important substituents are not available. Some time ago we reported a method to calculate substituent descriptors compatible with Hammett sigma constants using quantum chemically derived parameters. The present publication revisits the older study by applying more sophisticated methodology and a larger training data set, as well as introduces a free web tool allowing to calculate substituent descriptors compatible with Hammett sigma constants available at <a href="https://bitly.com/getsigmas">https://bitly.com/getsigmas</a>.</p><div><br></div>

A Web Tool for Calculating Substituent Descriptors Compatible with Hammett Sigma Constants

<p>Electron donating or accepting power of organic substituents is an important parameter affecting many properties of parent molecules, most notably their reactivity and pKa of ionizable groups. These substituent properties are usually described by Hammett sigma constants obtained by measuring ionization of substituted benzoic acids. Although values of these constants have been measured for the most common functional groups, data for many important substituents are not available. Some time ago we reported a method to calculate substituent descriptors compatible with Hammett sigma constants using quantum chemically derived parameters. The present publication revisits the older study by applying more sophisticated methodology and a larger training data set, as well as introduces a free web tool allowing to calculate substituent descriptors compatible with Hammett sigma constants available at <a href="https://bitly.com/getsigmas">https://bitly.com/getsigmas</a>.</p><div><br></div>

Protein-sol pKa: prediction of electrostatic frustration, with application to coronaviruses

Motivation Evolution couples differences in ambient pH to biological function through protonatable groups, in particular, those that switch from buried to exposed and alter protonation state in doing so. We present a tool focusing on structure-based discovery and display of these groups. Results Since prediction of buried group pKas is computationally intensive, solvent accessibility of ionizable groups is displayed, from which the user can iteratively select pKa calculation centers. Results are color-coded, with emphasis on buried groups. Utility is demonstrated with benchmarking against known pH sensing sites in influenza virus hemagglutinin and in variants of murine hepatitis virus, a coronavirus. A pair of histidine residues, which are conserved in coronavirus spike proteins, are predicted to be electrostatically frustrated at acidic pH in both pre- and post-fusion conformations. We suggest that an intermediate expanded conformation at endosomal pH could relax the frustration, allowing histidine protonation and facilitating conformational conversion of coronavirus spike protein. Availability and implementation This tool is available at http://www.protein-sol.manchester.ac.uk/pka/.