Influence of ice formation on the dynamic and thermodynamic properties of aqueous solutions

Water dynamics in solutions with biological or non-biological solutes has been intensely studied when both components (solvent and solute) are amorphous. Here, we apply broadband dielectric spectroscopy combined with calorimetric measurements to analyze the dynamics of the aqueous solutions tri-propylene glycol (3PG) and ε-poly (lysine) (ε-PLL), after their water becomes semi-crystalline. Various crystallization levels were explored by conducting experiments with different annealing times at temperatures above the glass transition temperature (Tg). We find that the amount of ice depends on both the time and temperature of the annealing, and that this, in turn, affects Tg and dynamics of the amorphous part of the samples. However, it should be noted that the observed differences are relatively small for the degrees of crystallinity we have studied (up to about 26 wt% of the water). This also implies that the dynamic crossover of the water relaxation from a high temperature non-Arrhenius behavior to a low temperature Arrhenius dependence is unaffected by the partial crystallization and still occurs as a single crossover at the calorimetric Tg. Thus, we cannot detect two different crossovers, as commonly observed for other types of two-component systems, such as two glass formers

A review of pectin-based material for applications in water treatment

This article belongs to the Section Green Materials.Climate change and water are inseparably connected. Extreme weather events cause water to become more scarce, polluted, and erratic than ever. Therefore, we urgently need to develop solutions to reduce water contamination. This review intends to demonstrate that pectin-based materials are an excellent route to detect and mitigate pollutants from water, with several benefits. Pectin is a biodegradable polymer, extractable from vegetables, and contains several hydroxyl and carboxyl groups that can easily interact with the contaminant ions. In addition, pectin-based materials can be prepared in different forms (films, hydrogels, or beads) and cross-linked with several agents to change their molecular structure. Consequently, the pectin-based adsorbents can be tuned to remove diverse pollutants. Here, we will summarize the existing water remediation technologies highlighting adsorption as the ideal method. Then, the focus will be on the chemical structure of pectin and, from a historical perspective, on its structure after applying different cross-linking methods. Finally, we will review the application of pectin as an adsorbent of water pollutants considering the pectin of low degree methoxylation.The present work was supported by CSIC (I-COOP2020 COOPB20502), the Ministerio de Ciencia, Innovación y Universidades code PID2019-104650 GB-C21 (MCIN/ AEI /10.13039/501100011033), IT1566-22 (Basque Government), UBA (UBACYT 2018-2020 N°20020170100381BA), ANPCyT (PICT 2017-2362), MINCyT (“Programa Ciencia y Tecnología Contra el Hambre” IF-2021-4378615-APN-SSCI#MCT).Peer reviewe

Dynamics of aqueous peptide solutions in folded and disordered states examined by dynamic light scattering and dielectric spectroscopy

[EN] Characterizing the segmental dynamics of proteins, and intrinsically disordered proteins in particular, is a challenge in biophysics. In this study, by combining data from broadband dielectric spectroscopy (BDS) and both depolarized (DDLS) and polarized (PDLS) dynamic light scattering, we were able to determine the dynamics of a small peptide [ε-poly(lysine)] in water solutions in two different conformations (pure β-sheet at pH = 10 and a more disordered conformation at pH = 7). We found that the segmental (α-) relaxation, as probed by DDLS, is faster in the disordered state than in the folded conformation. The water dynamics, as detected by BDS, is also faster in the disordered state. In addition, the combination of BDS and DDLS results allows us to confirm the molecular origin of water-related processes observed by BDS. Finally, we discuss the origin of two slow processes (A and B processes) detected by DDLS and PDLS in both conformations and usually observed in other types of water solutions. For fully homogeneous ε-PLL solutions at pH = 10, the A-DLS process is assigned to the diffusion of individual β-sheets. The combination of both techniques opens a route for understanding the dynamics of peptides and other biological solutions.Financial support through the Grant No. PID2019-104650GBC21 (Spanish Government ‘‘Ministerio de Ciencia, Innovacion y Universidades’’), LINKB20012 (CSIC), Project No. IT-1175-19 (Basque Government) are gratefully acknowledged

Appendix A. Supplementary data for Dual crosslinking of low-methoxyl pectin by calcium and europium for the simultaneous removal of pharmaceuticals and divalent heavy metals

- Viscosity measurement and molecular weight determination: Figure S-1. Huggins and Kramer plot for our pectin. - Criteria to fit kinetic adsorption experiments: Table S1. Table with model used to fit kinetic adsorption experiments and parameters qmax, K1, K2, adjusted R2 (Adj. R2), Akaike information criterion (AIC) and Bayesian information criterion (BIC) for the kinetic experiments for the cross-link of pectin by Ca2+, Eu3+ and P-Ca2+ by Eu3+. PFO: Pseudo First Order kinetic model. PSO: Pseudo Second Order kinetic model. Figure S-2. Adsorption kinetic experiments for the cross-link of LM pectin (P-NC) by Ca2+ (a),Eu3+ (b), and P-Ca2+ by Eu3+ (c). Each graph shows the fitting by the pseudo first order (PFO) and pseudo second order (PSO) kinetic models. Figure S-3. Scanning electronic microscopy images of pectin-based films with (a) neat pectin, and cross-linked with (b) Ca, (c) Eu and (d) Ca+Eu. On these images, EDX was performed. Table S2. Element content of neat pectin, Pe-Ca, Pe-Eu and Pecin-Ca – Eu obtained by EDX.Peer reviewe

Dual crosslinking of low-methoxyl pectin by calcium and europium for the simultaneous removal of pharmaceuticals and divalent heavy metals

The contamination of water resources by heavy metals and pharmaceuticals is a significant threat to human health and the environment. Pectin is a promising material for removing heavy metals from water. However, its removal efficacy for other types of pollutants is limited. In this study, we developed a novel approach to enhance the remediation capacity of pectin (with a low degree of methylation) by crosslinking it with different agents: calcium, europium, and their combination. We performed scanning electron microscopy, infrared spectroscopy, and X-ray diffraction experiments to understand the molecular structure of pectin after gelation with the three agents. Our results showed that calcium, europium, and their combination all induce the gelation of pectin. However, the reticulated pectin structures exhibited significant structural differences depending on the type of crosslinking agent used, which affected the adsorption capacity. Specifically, calcium cations partially formed a crystalline “egg-box” structure, whereas europium cations produced a more homogeneous network without crystalline regions. The dual-crosslinking system comprising calcium and europium cations resulted in an intermediate network with both crystalline and amorphous regions. Our findings suggest that dual-cross-linked pectin is a highly effective adsorbent for the simultaneous removal of both heavy metals and pharmaceutical products. This novel approach of crosslinking pectin with multiple agents has the potential to significantly enhance its remediation capacity, offering a promising solution for the simultaneous removal of multiple pollutants from water.This work was supported by the Ministerio de Ciencia, Innovación y Universidades code PID2019-104650GB-C21 (MCIN/AEI/10.13039/501100011033), CSIC (I-COOP2020 COOPB20502), and IT1566-22 (Basque Government).Peer reviewe

The nature of the low-temperature crossover of water in hard confinement

The dynamics of water confined in mesoporous MIP (2–3 nm pores in size) with silica gel (secondary silica; further, the abbreviation SG will be used) and MAP (10–35 nm pores in size) without SG borosilicate glasses have been studied by broadband dielectric spectroscopy (BDS), nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC). MIP samples contain secondary silica inside the pores and provide a confinement size of about 2–3 nm, whereas MAP samples are free of secondary silica and provide a confinement size of about 10–35 nm. It is shown by BDS and NMR techniques that water exhibits a dynamic crossover of around 180 K when it is confined in MIP samples. By contrast, water confined in larger pores (MAP) does not exhibit any changes in its relaxation behavior. It is also shown that the crossover temperature depends on the hydration level (the higher the hydration level, the lower the crossover temperature). Below the crossover temperature, we find that water reorientation is isotropic (NMR) and that the temperature-dependent dielectric relaxation strength (BDS) follows the tendency expected for a solid-like material. In contrast, water reorientation is related to long-range diffusion above the crossover temperature, and the dielectric relaxation strength follows the tendency expected for a liquid-like material. Furthermore, the calorimetric results are compatible with crossing a glass transition near 180 K. Finally, the results are discussed within the Gibbs–Thomson model. In this framework, the crossover could be related to ice crystals melting.The work was partially carried out under the Israel – Russian Agreement on International Research Cooperation (since 2019, joint research project “The dynamic crossover phenomenon in the hydrated nanoporous glasses”). The fragment of this work related to the synthesis of glasses and characterization of their porous structure was supported by the Ministry of Science and Higher Education of the Russian Federation as part of the IChS RAS state assignment no. 1021050501068-5-1.4.3. The study was performed with the support from the Israel Ministry of Aliyah and Integration. J.H.M. and S.C. also acknowledge the financial support through the grant nos. PID2019-104650GB-C21 (MICINN-Spain and FEDER-UE) and IT1566-22 (Basque Government).Peer reviewe

Climate Change Decreases Nitrogen Pools and Mineralization Rates in Northern Hardwood Forests

Nitrogen (N) supply often limits the productivity of temperate forests and is regulated by a complex mix of biological and climatic drivers. In excess, N is linked to a variety of soil, water, and air pollution issues. Here, we use results from an elevation gradient study and historical data from the long-term Hubbard Brook Ecosystem Study (New Hampshire, USA) to examine relationships between changes in climate, especially during winter, and N supply to northern hardwood forest ecosystems. Low elevation plots with less snow, more soil freezing, and more freeze/thaw cycles supported lower rates of N mineralization than high elevation plots, despite having higher soil temperatures and no consistent differences in soil moisture during the growing season. These results are consistent with historical analyses showing decreases in rates of soil N mineralization and inorganic N concentrations since 1973 that are correlated with long-term increases in mean annual temperature, decreases in annual snow accumulation, and a increases in the number of winter thawing degree days. This evidence suggests that changing climate may be driving decreases in the availability of a key nutrient in northern hardwood forests, which could decrease ecosystem production but have positive effects on environmental consequences of excess N