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Gels
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Advances in Xerogels: From Design to Applications
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Advances in Xerogels: From Design to Applications

A special issue of Gels (ISSN 2310-2861). This special issue belongs to the section "Gel Processing and Engineering".

Deadline for manuscript submissions: closed (28 February 2023) | Viewed by 25850

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Dr. Francesco Caridi

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Guest Editor
Department of Mathematics and Informatics, Physic and Earth Sciences (MIFT), University of Messina, 98166 Messina, Italy
Interests: environmental radioactivity; gamma spectrometry; liquid scintillation; alpha spectrometry; gas radon detection; emanometry; ionizing radiations
Special Issues, Collections and Topics in MDPI journals
Dr. Giuseppe Paladini

E-Mail Website
Guest Editor
Department of Mathematical and Computer Sciences, Physical Sciences and Earth Sciences, University of Messina, 98166 Messina, Italy
Interests: biopolymers; xerogels; nanocellulose; drug delivery systems; FTIR-ATR spectroscopy; Raman spectroscopy; neutron spectroscopy; material characterization
Special Issues, Collections and Topics in MDPI journals
Dr. Andrea Fiorati

E-Mail Website
Guest Editor
Department of Chemistry, Materials, and Chemical Engineering, “G. Natta”, Politecnico di Milano, 20133 Milan, Italy
Interests: nanocellulose; biomaterials; materials characterization; chemical-physical approaches; nanostructured and composite materials; hydrogels; mass transfer phenomena; food packaging
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The design of novel xerogels for several applications has become a hot topic in the field of material science and engineering. Since their structures and morphologies can be conveniently controlled during the synthesis process, the development of xerogels has gained increased interest within the scientific community.

Based on these considerations, this Special Issue of Gels aims at collecting high-quality papers on the latest breakthroughs and advances in the field of the xerogels science from design to application. In particular, we encourage submissions focused on both well-established and/or non-conventional methods for the synthesis and characterization of xerogels. The aim is to obtain insights into fundamental and applied aspects related to any kind of organic/inorganic xerogel-like materials. Cutting-edge studies, both theoretical and experimental, focused on the structural, chemical, rheological and dynamical properties of xerogels and xerogel-based derivatives are warmly welcomed.

As Guest Editors, we would like to kindly invite you to contribute a research paper or a review on any topic related to this thread.

Prof. Dr. Francesco Caridi
Dr. Giuseppe Paladini
Dr. Andrea Fiorati
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Gels is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Xerogels synthesis
  • Xerogels fundamentals
  • Xerogels properties
  • Xerogels applications
  • Physical-chemical features of xerogels
  • Xerogels structural-property correlations
  • Xerogels dynamical-property correlations.

Published Papers (12 papers)

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Editorial

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3 pages, 193 KiB  
Editorial
Editorial on the Special Issue: “Advances in Xerogels: From Design to Applications”
by Andrea Fiorati, Francesco Caridi and Giuseppe Paladini
Gels 2023, 9(6), 446; https://doi.org/10.3390/gels9060446 - 27 May 2023
Cited by 1 | Viewed by 859
Abstract
Xerogels are solid materials derived from gels which consist of interconnected particles or polymers dispersed in a liquid [...] Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)

Research

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18 pages, 3327 KiB  
Article
A Non-Hydrolytic Sol–Gel Route to Organic-Inorganic Hybrid Polymers: Linearly Expanded Silica and Silsesquioxanes
by Katrin Krupinski, Jörg Wagler, Erica Brendler and Edwin Kroke
Gels 2023, 9(4), 291; https://doi.org/10.3390/gels9040291 - 02 Apr 2023
Cited by 2 | Viewed by 1451
Abstract
Condensation reactions of chlorosilanes (SiCl4 and CH3SiCl3) and bis(trimethylsilyl)ethers of rigid, quasi-linear diols (CH3)3SiO–AR–OSi(CH3)3 (AR = 4,4′-biphenylene (1) and 2,6-naphthylene (2)), with release of [...] Read more.
Condensation reactions of chlorosilanes (SiCl4 and CH3SiCl3) and bis(trimethylsilyl)ethers of rigid, quasi-linear diols (CH3)3SiO–AR–OSi(CH3)3 (AR = 4,4′-biphenylene (1) and 2,6-naphthylene (2)), with release of (CH3)3SiCl as a volatile byproduct, afforded novel hybrid materials that feature Si–O–C bridges. The precursors 1 and 2 were characterized using FTIR and multinuclear (1H, 13C, 29Si) NMR spectroscopy as well as single-crystal X-ray diffraction analysis in case of 2. Pyridine-catalyzed and non-catalyzed transformations were performed in THF at room temperature and at 60 °C. In most cases, soluble oligomers were obtained. The progress of these transsilylations was monitored in solution with 29Si NMR spectroscopy. Pyridine-catalyzed reactions with CH3SiCl3 proceeded until complete substitution of all chlorine atoms; however, no gelation or precipitation was found. In case of pyridine-catalyzed reactions of 1 and 2 with SiCl4, a Sol–Gel transition was observed. Ageing and syneresis yielded xerogels 1A and 2A, which exhibited large linear shrinkage of 57–59% and consequently low BET surface area of 10 m2⋅g−1. The xerogels were analyzed using powder-XRD, solid state 29Si NMR and FTIR spectroscopy, SEM/EDX, elemental analysis, and thermal gravimetric analysis. The SiCl4-derived amorphous xerogels consist of hydrolytically sensitive three-dimensional networks of SiO4-units linked by the arylene groups. The non-hydrolytic approach to hybrid materials may be applied to other silylated precursors, if the reactivity of the corresponding chlorine compound is sufficient. Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)
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19 pages, 3494 KiB  
Article
Green Chemistry for the Transformation of Chlorinated Wastes: Catalytic Hydrodechlorination on Pd-Ni and Pd-Fe Bimetallic Catalysts Supported on SiO2
by Julien G. Mahy, Thierry Delbeuck, Kim Yên Tran, Benoît Heinrichs and Stéphanie D. Lambert
Gels 2023, 9(4), 275; https://doi.org/10.3390/gels9040275 - 25 Mar 2023
Cited by 3 | Viewed by 1225
Abstract
Monometallic catalysts based on Fe, Ni and Pd, as well as bimetallic catalysts based on Fe-Pd and based on Ni-Pd supported on silica, were synthesized using a sol–gel cogelation process. These catalysts were tested in chlorobenzene hydrodechlorination at low conversion to consider a [...] Read more.
Monometallic catalysts based on Fe, Ni and Pd, as well as bimetallic catalysts based on Fe-Pd and based on Ni-Pd supported on silica, were synthesized using a sol–gel cogelation process. These catalysts were tested in chlorobenzene hydrodechlorination at low conversion to consider a differential reactor. In all samples, the cogelation method allowed very small metallic nanoparticles of 2–3 nm to be dispersed inside the silica matrix. Nevertheless, the presence of some large particles of pure Pd was noted. The catalysts had specific surface areas between 100 and 400 m2/g. In view of the catalytic results obtained, the Pd-Ni catalysts are less active than the monometallic Pd catalyst (<6% of conversion) except for catalysts with a low proportion of Ni (9% of conversion) and for reaction temperatures above 240 °C. In this series of catalysts, increasing the Ni content increases the activity but leads to an amplification of the catalyst deactivation phenomenon compared to Pd alone. On the other hand, Pd-Fe catalysts are more active with a double conversion value compared to a Pd monometallic catalyst (13% vs. 6%). The difference in the results obtained for each of the catalysts in the Pd-Fe series could be explained by the greater presence of the Fe-Pd alloy in the catalyst. Fe would have a cooperative effect when associated with Pd. Although Fe is inactive alone for chlorobenzene hydrodechlorination, when Fe is coupled to another metal from the group VIIIb, such as Pd, it allows the phenomenon of Pd poisoning by HCl to be reduced. Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)
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14 pages, 691 KiB  
Article
Sol-Gel Films Doped with Enzymes and Banana Crude Extract as Sensing Materials for Spectrophotometric Determination
by Maria A. Morosanova and Elena I. Morosanova
Gels 2023, 9(3), 240; https://doi.org/10.3390/gels9030240 - 18 Mar 2023
Cited by 4 | Viewed by 969
Abstract
Chromogenic enzymatic reactions are very convenient for the determination of various biochemically active compounds. Sol-gel films are a promising platform for biosensor development. The creation of sol-gel films with immobilized enzymes deserves attention as an effective way to create optical biosensors. In the [...] Read more.
Chromogenic enzymatic reactions are very convenient for the determination of various biochemically active compounds. Sol-gel films are a promising platform for biosensor development. The creation of sol-gel films with immobilized enzymes deserves attention as an effective way to create optical biosensors. In the present work, the conditions are selected to obtain sol-gel films doped with horseradish peroxidase (HRP), mushroom tyrosinase (MT) and crude banana extract (BE), inside the polystyrene spectrophotometric cuvettes. Two procedures are proposed: the use of tetraethoxysilane-phenyltriethoxysilane (TEOS-PhTEOS) mixture as precursor, as well as the use of silicon polyethylene glycol (SPG).In both types of films, the enzymatic activity of HRP, MT, and BE is preserved. Based on the kinetics study of enzymatic reactions catalyzed by sol-gel films doped with HRP, MT, and BE, we found that encapsulation in the TEOS-PhTEOS films affects the enzymatic activity to a lesser extent compared to encapsulation in SPG films. Immobilization affects BE significantly less than MT and HRP. The Michaelis constant for BE encapsulated in TEOS-PhTEOS films almost does not differ from the Michaelis constant for a non-immobilized BE. The proposed sol-gel films allow determining hydrogen peroxide in the range of 0.2–3.5 mM (HRP containing film in the presence of TMB), and caffeic acid in the ranges of 0.5–10.0 mM and 2.0–10.0 mM (MT- and BE-containing films, respectively). BE-containing films have been used to determine the total polyphenol content of coffee in caffeic acid equivalents; the results of the analysis are in good agreement with the results obtained using an independent method of determination. These films are highly stable and can be stored without the loss of activity for 2 months at +4 °C and 2 weeks at +25 °C. Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)
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19 pages, 6710 KiB  
Article
Stimuli-Responsive Properties of Supramolecular Gels Based on Pyridyl-N-oxide Amides
by Sreejith Sudhakaran Jayabhavan, Baldur Kristinsson, Dipankar Ghosh, Charlène Breton and Krishna K. Damodaran
Gels 2023, 9(2), 89; https://doi.org/10.3390/gels9020089 - 20 Jan 2023
Cited by 3 | Viewed by 2012
Abstract
The nature of functional groups and their relative position and orientation play an important role in tuning the gelation properties of stimuli-responsive supramolecular gels. In this work, we synthesized and characterized mono-/bis-pyridyl-N-oxide compounds of N-(4-pyridyl)nicotinamide (L1–L [...] Read more.
The nature of functional groups and their relative position and orientation play an important role in tuning the gelation properties of stimuli-responsive supramolecular gels. In this work, we synthesized and characterized mono-/bis-pyridyl-N-oxide compounds of N-(4-pyridyl)nicotinamide (L1–L3). The gelation properties of these N-oxide compounds were compared with the reported isomeric counterpart mono-/bis-pyridyl-N-oxide compounds of N-(4-pyridyl)isonicotinamide. Hydrogels obtained with L1 and L3 were thermally and mechanically more stable than the corresponding isomeric counterparts. The surface morphology of the xerogels of di-N-oxides (L3 and diNO) obtained from the water was studied using scanning electron microscopy (SEM), which revealed that the relative position of N-oxide moieties did not have a prominent effect on the gel morphology. The solid-state structural analysis was performed using single-crystal X-ray diffraction to understand the key mechanism in gel formation. The versatile nature of N-oxide moieties makes these gels highly responsive toward an external stimulus, and the stimuli-responsive behavior of the gels in water and aqueous mixtures was studied in the presence of various salts. We studied the effect of various salts on the gelation behavior of the hydrogels, and the results indicated that the salts could induce gelation in L1 and L3 below the minimum gelator concentration of the gelators. The mechanical properties were evaluated by rheological experiments, indicating that the modified compounds displayed enhanced gel strength in most cases. Interestingly, cadmium chloride formed supergelator at a very low concentration (0.7 wt% of L3), and robust hydrogels were obtained at higher concentrations of L3. These results show that the relative position of N-oxide moieties is crucial for the effective interaction of the gelator with salts/ions resulting in LMWGs with tunable properties. Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)
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12 pages, 3797 KiB  
Article
Optimising Soy and Pea Protein Gelation to Obtain Hydrogels Intended as Precursors of Food-Grade Dried Porous Materials
by Lorenzo De Berardinis, Stella Plazzotta and Lara Manzocco
Gels 2023, 9(1), 62; https://doi.org/10.3390/gels9010062 - 12 Jan 2023
Cited by 4 | Viewed by 3077
Abstract
Dried porous materials based on plant proteins are attracting large attention thanks to their potential use as sustainable food ingredients. Nevertheless, plant proteins present lower gelling properties than animal ones. Plant protein gelling could be improved by optimising gelation conditions by acting on [...] Read more.
Dried porous materials based on plant proteins are attracting large attention thanks to their potential use as sustainable food ingredients. Nevertheless, plant proteins present lower gelling properties than animal ones. Plant protein gelling could be improved by optimising gelation conditions by acting on protein concentration, pH, and ionic strength. This work aimed to systematically study the effect of these factors on the gelation behaviour of soy and pea protein isolates. Protein suspensions having different concentrations (10, 15, and 20% w/w), pH (3.0, 4.5, 7.0), and ionic strength (IS, 0.0, 0.6, 1.5 M) were heat-treated (95 °C for 15 min) and characterised for rheological properties and physical stability. Strong hydrogels having an elastic modulus (G′) higher than 103 Pa and able to retain more than 90% water were only obtained from suspensions containing at least 15% soy protein, far from the isoelectric point and at an IS above 0.6 M. By contrast, pea protein gelation was achieved only at a high concentration (20%), and always resulted in weak gels, which showed increasing G′ with the increase in pH and IS. Results were rationalised into a map identifying the gelation conditions to modulate the rheological properties of soy and pea protein hydrogels, for their subsequent conversion into xerogels, cryogels, and aerogels. Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)
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15 pages, 2989 KiB  
Article
Pd-Loaded Cellulose NanoSponge as a Heterogeneous Catalyst for Suzuki–Miyaura Coupling Reactions
by Laura Riva, Gloria Nicastro, Mingchong Liu, Chiara Battocchio, Carlo Punta and Alessandro Sacchetti
Gels 2022, 8(12), 789; https://doi.org/10.3390/gels8120789 - 02 Dec 2022
Cited by 3 | Viewed by 1539
Abstract
The (eco)design and synthesis of durable heterogeneous catalysts starting from renewable sources derived from biomass waste represents an important step for reducing environmental impacts of organic transformations. Herein, we report the efficient loading of Pd(II) ions on an eco-safe cellulose-based organic support (CNS), [...] Read more.
The (eco)design and synthesis of durable heterogeneous catalysts starting from renewable sources derived from biomass waste represents an important step for reducing environmental impacts of organic transformations. Herein, we report the efficient loading of Pd(II) ions on an eco-safe cellulose-based organic support (CNS), obtained by thermal cross-linking between TEMPO-oxidized cellulose nanofibers and branched polyethyleneimine in the presence of citric acid. A 22.7% w/w Pd-loading on CNS was determined by the ICP-OES technique, while the metal distribution on the xerogel was evidenced by SEM–EDS analysis. XPS analysis confirmed the direct chelation of Pd(II) ions by means of the high number of amino groups present in the network, so that further functionalization of the support with specific ligands was not necessary. The new composite turned to be an efficient heterogeneous pre-catalyst for promoting Suzuki–Miyaura coupling reactions between aryl halides and phenyl boronic acid in water, obtaining yields higher than 90% in 30 min, by operating in a microwave reactor at 100 °C and with just 2% w/w of CNS-Pd catalyst with respect to aryl halides (4.5‰ for Pd). At the end of first reaction cycle, Pd(II) ions on the support resulted in being reduced to Pd(0) while maintaining the same catalytic efficiency. In fact, no leaching was observed at the end of reactions, and five cycles of recycling and reusing of CNS-Pd catalyst provided excellent results in terms of yields and selectivity in the desired products. Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)
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16 pages, 3453 KiB  
Article
Fabrication of Poly(vinyl alcohol)/Chitosan Composite Films Strengthened with Titanium Dioxide and Polyphosphonate Additives for Packaging Applications
by Tăchiță Vlad-Bubulac, Corneliu Hamciuc, Cristina Mihaela Rîmbu, Magdalena Aflori, Maria Butnaru, Alin Alexandru Enache and Diana Serbezeanu
Gels 2022, 8(8), 474; https://doi.org/10.3390/gels8080474 - 28 Jul 2022
Cited by 7 | Viewed by 1920
Abstract
Eco-innovation through the development of intelligent materials for food packaging is evolving, and it still has huge potential to improve food product safety, quality, and control. The design of such materials by the combination of biodegradable semi-synthetic polymers with natural ones and with [...] Read more.
Eco-innovation through the development of intelligent materials for food packaging is evolving, and it still has huge potential to improve food product safety, quality, and control. The design of such materials by the combination of biodegradable semi-synthetic polymers with natural ones and with some additives, which may improve certain functionalities in the targeted material, is continuing to attract attention of researchers. To fabricate composite films via casting from solution, followed by drying in atmospheric conditions, certain mass ratios of poly(vinyl alcohol) and chitosan were used as polymeric matrix, whereas TiO2 nanoparticles and a polyphosphonate were used as reinforcing additives. The structural confirmation, surface properties, swelling behavior, and morphology of the xerogel composite films have been studied. The results confirmed the presence of all ingredients in the prepared fabrics, the contact angle of the formulation containing poly(vinyl alcohol), chitosan, and titanium dioxide in its composition exhibited the smallest value (87.67°), whereas the profilometry and scanning electron microscopy enlightened the good dispersion of the ingredients and the quality of all the composite films. Antimicrobial assay established successful antimicrobial potential of the poly(vinyl alcoohol)/chitosan-reinforced composites films against Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, Pseudomonas aeruginosa, and Candida albicans. Cytotoxicity tests have revealed that the studied films are non-toxic, presented good compatibility, and they are attractive candidates for packaging applications. Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)
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12 pages, 4169 KiB  
Article
Metallic Strontium as a Precursor of the Al2O3/SrCO3 Xerogels Obtained by the One-Pot Sol–Gel Method
by Eliza Romanczuk-Ruszuk, Bogna Sztorch, Zbigniew Oksiuta and Robert E. Przekop
Gels 2022, 8(8), 473; https://doi.org/10.3390/gels8080473 - 27 Jul 2022
Cited by 1 | Viewed by 1467
Abstract
Two series of binary xerogel systems of Sr/Al with molar ratios of 0.1, 0.25, 0.5, and 1.0 were synthesized by the sol–gel technique with metallic strontium component as a precursor. The influence of the metallic precursor on the properties of the final xerogel [...] Read more.
Two series of binary xerogel systems of Sr/Al with molar ratios of 0.1, 0.25, 0.5, and 1.0 were synthesized by the sol–gel technique with metallic strontium component as a precursor. The influence of the metallic precursor on the properties of the final xerogel was determined. The properties of the gels were determined on the basis of X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), low temperature nitrogen adsorption, transmission, and scanning electron microscopy with Energy Dispersive X-ray Spectroscopy (TEM, SEM, and SEM/EDS). The Al2O3/SrCO3 xerogels were tested as supports for platinum catalysts. Hydrogen chemisorption was used to determine the platinum dispersion of the Pt/Al2O3-SrCO3 systems. The original method of synthesis allows to obtain highly dispersed and stable strontium carbonate phases that allow for obtaining a high (42–50%) dispersion of platinum nanoparticles. Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)
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17 pages, 2356 KiB  
Article
Ordered Mesoporous Silica Prepared in Different Solvent Conditions: Application for Cu(II) and Pb(II) Adsorption
by Ana-Maria Putz, Oleksandr I. Ivankov, Alexander I. Kuklin, Vasyl Ryukhtin, Cătălin Ianăşi, Mihaela Ciopec, Adina Negrea, László Trif, Zsolt Endre Horváth and László Almásy
Gels 2022, 8(7), 443; https://doi.org/10.3390/gels8070443 - 15 Jul 2022
Cited by 16 | Viewed by 1607
Abstract
In this work, the synthesis of ordered mesoporous silica of MCM-41 type was investigated aimed at improving its morphology by varying the synthesis conditions in a one-pot process, employing different temperatures and solvent conditions. 2-methoxyethanol was used as co-solvent to ethanol. The co-solvent [...] Read more.
In this work, the synthesis of ordered mesoporous silica of MCM-41 type was investigated aimed at improving its morphology by varying the synthesis conditions in a one-pot process, employing different temperatures and solvent conditions. 2-methoxyethanol was used as co-solvent to ethanol. The co-solvent ratio and the synthesis temperature were varied. The pore morphology of the materials was characterized by nitrogen porosimetry and small angle neutron scattering (SANS), and the particle morphology by transmission electron microscopy (TEM) and ultra-small angle neutron scattering (USANS). The thermal behavior was investigated by simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC) measurements. The SANS and N2 sorption results demonstrated that a well-ordered mesoporous structure was obtained at all conditions in the synthesis at room temperature. Addition of methoxyethanol led to an increase of the pore wall thickness. Simultaneously, an increase of methoxyethanol content led to lowering of the mean particle size from 300 to 230 nm, according to the ultra-small angle scattering data. The ordered porosity and high specific surfaces make these materials suitable for applications such as adsorbents in environmental remediation. Batch adsorption measurements of metal ion removal from aqueous solutions of Cu(II) and Pb(II) showed that the materials exhibit dominantly monolayer surface adsorption characteristics. The adsorption capacities were 9.7 mg/g for Cu(II) and 18.8 mg/g for Pb(II) at pH 5, making these materials competitive in performance to various composite materials. Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)
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18 pages, 4227 KiB  
Article
4-Dialkylamino-2,5-dihydroimidazol-1-oxyls with Functional Groups at the Position 2 and at the Exocyclic Nitrogen: The pH-Sensitive Spin Labels
by Dmitrii G. Trofimov, Yuri I. Glazachev, Artem A. Gorodetsky, Denis A. Komarov, Tatyana V. Rybalova and Igor A. Kirilyuk
Gels 2022, 8(1), 11; https://doi.org/10.3390/gels8010011 - 23 Dec 2021
Cited by 3 | Viewed by 2281
Abstract
Local acidity and electrostatic interactions are associated both with catalytic properties and the adsorption activity of various materials, and with the vital functions of biomolecules. The observation of acid–base equilibria in stable free radicals using EPR spectroscopy represents a convenient method for monitoring [...] Read more.
Local acidity and electrostatic interactions are associated both with catalytic properties and the adsorption activity of various materials, and with the vital functions of biomolecules. The observation of acid–base equilibria in stable free radicals using EPR spectroscopy represents a convenient method for monitoring pH changes and the investigation of surface electrostatics, the advantages of which are especially evident in opaque and turbid samples and in porous materials such as xerogels. Imidazoline nitroxides are the most commonly used pH-sensitive spin probes and labels due to the high sensitivity of the parameters of the EPR spectra to pH changes, their small size, and their well-developed chemistry. In this work, several new derivatives of 4-(N,N-dialkylamino)-2,5-dihydrioimidazol-1-oxyl, with functional groups suitable for specific binding, were synthesized. The dependence of the parameters of their EPR spectra on pH was studied. Several showed a pKa close to 7.4, following the pH changes in a normal physiological range, and some demonstrated a monotonous change of the hyperfine coupling constant by 0.14 mT upon pH variation by four units. Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)
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Review

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15 pages, 3952 KiB  
Review
Insights into the Role of Biopolymer-Based Xerogels in Biomedical Applications
by H. P. S. Abdul Khalil, Esam Bashir Yahya, Husnul Azan Tajarudin, Venugopal Balakrishnan and Halimatuddahliana Nasution
Gels 2022, 8(6), 334; https://doi.org/10.3390/gels8060334 - 29 May 2022
Cited by 15 | Viewed by 5621
Abstract
Xerogels are advanced, functional, porous materials consisting of ambient, dried, cross-linked polymeric networks. They possess characteristics such as high porosity, great surface area, and an affordable preparation route; they can be prepared from several organic and inorganic precursors for numerous applications. Owing to [...] Read more.
Xerogels are advanced, functional, porous materials consisting of ambient, dried, cross-linked polymeric networks. They possess characteristics such as high porosity, great surface area, and an affordable preparation route; they can be prepared from several organic and inorganic precursors for numerous applications. Owing to their desired properties, these materials were found to be suitable for several medical and biomedical applications; the high drug-loading capacity of xerogels and their ability to maintain sustained drug release make them highly desirable for drug delivery applications. As biopolymers and chemical-free materials, they have been also utilized in tissue engineering and regenerative medicine due to their high biocompatibility, non-immunogenicity, and non-cytotoxicity. Biopolymers have the ability to interact, cross-link, and/or trap several active agents, such as antibiotic or natural antimicrobial substances, which is useful in wound dressing and healing applications, and they can also be used to trap antibodies, enzymes, and cells for biosensing and monitoring applications. This review presents, for the first time, an introduction to biopolymeric xerogels, their fabrication approach, and their properties. We present the biological properties that make these materials suitable for many biomedical applications and discuss the most recent works regarding their applications, including drug delivery, wound healing and dressing, tissue scaffolding, and biosensing. Full article
(This article belongs to the Special Issue Advances in Xerogels: From Design to Applications)
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