Flexibility and Hydration of Amphiphilic Hyperbranched Arabinogalactan-Protein from Plant Exudate: A Volumetric Perspective

Impact of Hydrophobic and Electrostatic Forces on the Adsorption of Acacia Gum on Oxide Surfaces Revealed by QCM-D

The adsorption of Acacia gum from two plant exudates, A. senegal and A. seyal, at the solid-liquid interface on oxide surfaces was studied using a quartz crystal microbalance with dissipation monitoring (QCM-D). The impact of the hydrophobic and electrostatic forces on the adsorption capacity was investigated by different surface, hydrophobicity, and charge properties, and by varying the ionic strength or the pH. The results highlight that hydrophobic forces have higher impacts than electrostatic forces on the Acacia gum adsorption on the oxide surface. The Acacia gum adsorption capacity is higher on hydrophobic surfaces compared to hydrophilic ones and presents a higher stability with negatively charged surfaces. The structural configuration and charge of Acacia gum in the first part of the adsorption process are important parameters. Acacia gum displays an extraordinary ability to adapt to surface properties through rearrangements, conformational changes, and/or dehydration processes in order to reach the steadiest state on the solid surface. Rheological analysis from QCM-D data shows that the A. senegal layers present a viscous behavior on the hydrophilic surface and a viscoelastic behavior on more hydrophobic ones. On the contrary, A. seyal layers show elastic behavior on all surfaces according to the Voigt model or a viscous behavior on the hydrophobic surface when considering the power-law model.

Woodfordia fruticosa extract nanoemulsion: Influence of processing treatment on droplet size and its assessment for in vitro antimicrobial and anti-inflammatory activity

Recently, plant-derived bioactive compounds have been utilized in the preparation of several functional food products; however, stability and water solubility are major constraints to these compounds. Therefore, to overcome this problem, the synthesis of nanoemulsion (oil in water) with varying concentrations of Woodfordia fruticosa flower extract (1%−10% w/v) was carried out and characterization of nanoemulsion was done. The average droplet size of nanoemulsion samples ranges from 149.25 to 244.33 nm. The control and WFNE3 nanoemulsion showed significantly (p < 0.05) higher thermal stability when correlated with average droplet size. An insignificant difference (p > 0.05) was observed in the average droplet size and zeta potential WFNE3 (−30.3mV) with the increased temperature rate. At varied pH ranges, WFNE3 showed significantly higher (p < 0.05) stability in comparison with the control nanoemulsion sample. In terms of ionic strength, WFNE3 nanoemulsion sample showed significantly (p < 0.05) higher stability, and with an increasing concentration of salt, the colloidal system of the WFNE3 sample showed significantly (p < 0.05) higher droplet size (318.91 nm). Therefore, the antimicrobial potential of WFNE3 nanoemulsion in comparison with extract of W. fruticosa flower extract was studied against Gram-positive Staphylococcus aureus, Gram-negative bacteria Pseudomonas aeruginosa, and fungal strain Candida albicans, respectively. WFNE3 nanoemulsion sample in comparison to flower extract showed a significantly higher (p < 0.05) zone of inhibition against gram-negative bacteria as compared to the control nanoemulsion sample upon storage for 7 days. WFNE3 nanoemulsion sample showed significant (p < 0.05) higher inhibition of protein denaturation (57.89%−87.65%) and (55.36%−83.58%) in comparison to control nanoemulsion sample (54.67%−80.28%) and flower extract (51.56%−79.36%), respectively. Due to these biological activities, the WFNE3 nanoemulsion sample could be scaled up to the industrial level for the formulation of varied types of functional foods.

Interaction of the new inhibitor paxlovid (PF-07321332) and ivermectin with the monomer of the main protease SARS-CoV-2: A volumetric study based on molecular dynamics, elastic networks, classical thermodynamics and SPT

The COVID-19 pandemic has accelerated the study of drugs, most notably ivermectin and more recently Paxlovid (PF-07321332) which is in phase III clinical trials with experimental data showing covalent binding to the viral protease M^pro. Theoretical developments of catalytic site-directed docking support thermodynamically feasible non-covalent binding to M^pro. Here we show that Paxlovid binds non-covalently at regions other than the catalytic sites with energies stronger than reported and at the same binding site as the ivermectin B1a homologue, all through theoretical methodologies, including blind docking. We volumetrically characterize the non-covalent interaction of the ivermectin homologues (avermectins B1a and B1b) and Paxlovid with the mM^pro monomer, through molecular dynamics and scaled particle theory (SPT). Using the fluctuation-dissipation theorem (FDT), we estimated the electric dipole moment fluctuations at the surface of each of complex involved in this study, with similar trends to that observed in the interaction volume. Using fluctuations of the intrinsic volume and the number of flexible fragments of proteins using anisotropic and Gaussian elastic networks (ANM+GNM) suggests the complexes with ivermectin are more dynamic and flexible than the unbound monomer. In contrast, the binding of Paxlovid to mM^pro shows that the mM^pro-PF complex is the least structurally dynamic of all the species measured in this investigation. The results support a differential molecular mechanism of the ivermectin and PF homologues in the mM^pro monomer. Finally, the results showed that Paxlovid despite beingbound in different sites through covalent or non-covalent forms behaves similarly in terms of its structural flexibility and volumetric behaviour.

Adsorption Behavior of Arabinogalactan-Proteins (AGPs) from Acacia senegal Gum at a Solid-Liquid Interface

Adsorption of five different hyperbranched arabinogalactan-protein (AGP) fractions from Acacia senegal gum was thoroughly studied at the solid-liquid interface using a quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR), and atomic force microscopy (AFM). The impact of the protein/sugar ratio, molecular weight, and aggregation state on the adsorption capacity was investigated by studying AGP fractions with different structural and biochemical features. Adsorption on a solid surface would be primarily driven by the protein moiety of the AGPs through hydrophobic forces and electrostatic interactions. Increasing ionic strength allows the decrease in electrostatic repulsions and, therefore, the formation of high-coverage films with aggregates on the surface. However, the maximum adsorption capacity was not reached by fractions with a higher protein content but by a fraction that contains an average protein quantity and presents a high content of high-molecular-weight AGPs. The results of this thorough study highlighted that the AGP surface adsorption process would depend not only on the protein moiety and high-molecular-weight AGP content but also on other parameters such as the structural accessibility of proteins, the molecular weight distribution, and the AGP flexibility, allowing structural rearrangements on the surface and spreading to form a viscoelastic film.

Acacia gums new fractions and sparkling base wines: How their biochemical and structural properties impact foamability?

Foam is the first attribute observed when sparkling wine is served. Bentonite is essentially used to flocculate particles in sparkling base wines but can impair their foamability. Gums from Acacia senegal and Acacia seyal improved the foamability of different bentonite-treated base wines. Our main goal was to see how the supplementation with new fractions separated from Acacia gums by Ion Exchange Chromatography affected foamability of sparkling base wines, deepening the relation between foam behavior and characteristics of wine and gums. High molar mass fractions increased the maximal foam height and the foam height during the stability period in, respectively, 11 out and 8 out of 16 cases (69% and 50%, respectively). The properties of the supplementing gums fractions obtained by IEC and, although to a minor extent, the wine characteristics, affected positively and/or negatively the foam behavior. Wine foamability also depended on the relationship between wine and gums fractions properties.

Emulsifying properties of Acacia senegal gum: Impact of high molar mass protein-rich AGPs

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Reconstitution of gums from arabinogalactan proteins (AGP) of Acacia gum.

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Experimental design to optimize their emulsions properties.

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Relevant adsorption of high molar protein-rich AGPs at the interface.

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Combined effect of high molar protein-rich AGPS and total concentration.

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Role of apparent viscosity of bulk to long-term stability.

The impact of high molar mass protein-rich arabinogalactan-proteins (AGPs) on emulsifying properties of Acacia senegal gums were studied using reconstituted gums obtained with two distinct fractions: one containing these specific high molar mass AGPs and the other protein-poor low molar mass AGPs. To produce and stabilize limonene emulsions, the experimental design emphasized not only the role of high molar mass protein-rich AGPs, but also the importance of high total concentration. At low protein contents, reconstituted gums required a slightly higher content in high molar mass protein-rich AGPs than original A. senegal gum, that confirmed the role of low molar mass protein-rich AGPs in the adsorption at interfaces. The comparison of the creaming index between original and reconstituted gums as well as the monitoring of instability phenomena by turbiscan up to 30 days clearly demonstrated the prevalent impact of the bulk apparent viscosity in the long-term stability of emulsions.

Adsorption of Hyperbranched Arabinogalactan-Proteins from Plant Exudate at the Solid–Liquid Interface

Adsorption of hyperbranched arabinogalactan-proteins (AGPs) from two plant exudates, A. senegal and A. seyal, was thoroughly studied at the solid–liquid interface using quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR), and atomic force microscopy (AFM). Isotherms of the adsorption reveal that 3.3 fold more AGPs from A. seyal (500 ppm) are needed to cover the gold surface compared to A. senegal (150 ppm). The pH and salt concentration of the environment greatly affected the adsorption behavior of both gums, with the surface density ranging from 0.92 to 3.83 mg m−2 using SPR (i.e., “dry” mass) and from 1.16 to 19.07 mg m−2 using QCM-D (wet mass). Surprisingly, the mass adsorbed was the highest in conditions of strong electrostatic repulsions between the gold substrate and AGPs, i.e., pH 7.0, highlighting the contribution of other interactions involved in the adsorption process. Structural changes of AGPs induced by pH would result in swelling of the polysaccharide blocks and conformational changes of the polypeptide backbone, therefore increasing the protein accessibility and hydrophobic interactions and/or hydrogen bonds with the gold substrate.