Reproductive toxicity assessment of cellulose nanofibers, citric acid, and branched polyethylenimine in sea urchins: eco-design of nanostructured cellulose sponge framework (Part B)

In the framework of a safe-by-design approach, we previously assessed the eco-safety of nanostructured cellulose sponge (CNS) leachate on sea urchin reproduction. It impaired gamete quality, gamete fertilization competence, and embryo development possibly due to the leaching of chemical additives deriving from their chemical synthesis. To extend this observation and identify the component(s) that contribute to CNS ecotoxicity, in the present study, we individually screened the cytotoxic effects on sea urchin Arbacia lixula and Paracentrotus lividus gametes and embryos of the three main constituents of CNS, namely cellulose nanofibers, citric acid, and branched polyethylenimine. The study aimed to minimize any potential safety risk of these components and to obtain an eco-safe CNS. Among the three CNS constituents, branched polyethylenimine resulted in the most toxic agent. Indeed, it affected the physiology and fertilization competence of male and female gametes as well as embryo development in both sea urchin species. These results are consistent with those previously reported for CNS leachate. Moreover, the characterisation of CNS leachate confirmed the presence of detectable branched polyethylenimine in the conditioned seawater even though in a very limited amount. Altogether, these data indicate that the presence of branched polyethylenimine is a cause-effect associated with a significant risk in CNS formulations due to its leaching upon contact with seawater. Nevertheless, the suggested safety protocol consisting of consecutive leaching treatments and conditioning of CNS in seawater can successfully ameliorate the CNS ecotoxicity while maintaining the efficacy of its sorbent properties supporting potential environmental applications.

Silver Nanoparticles Supported onto TEMPO-Oxidized Cellulose Nanofibers for Promoting Cd2+ Cation Adsorption

Nanocellulose constitutes a sustainable and biobased solution both as an efficient sorbent material for water treatment and as support for other inorganic nanomaterials with sorbent properties. Herein, we report the synthesis of a nanocomposite by deposition of in situ-generated silver nanoparticles (AgNPs) onto TEMPO-oxidized cellulose nanofibers (TOCNFs). Following an in-depth analytical investigation, we unveil for the first time the key role of AgNPs in enhancing the adsorption efficiency of TOCNF toward Cd2+ ions, chosen as model heavy metal contaminants. The obtained nanocomposite shows a value of Cd2+ sorption capacity at equilibrium from 150 mg L-1 ion aqueous solutions of ∼116 mg g-1 against the value of 78 mg g-1 measured for TOCNF alone. A combination of field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS) analyses suggests that Cd2+ ions are mainly adsorbed in the neighborhood of AgNPs. However, XPS characterization allows us to conclude that the role of AgNPs relies on increasing the exposure of carboxylic groups with respect to the original TOCNF, suggesting that these groups are still responsible for absorption. In fact, X-ray absorption spectroscopy (XAS) analysis of the Cd-K edge excludes a direct interaction between Ag0 and Cd2+, supporting the XPS results and confirming the coordination of the latter with carboxyl groups.

Nanostructured cellulose sponge engineered for marine environmental remediation: Eco-safety assessment of its leachate on sea urchin reproduction (Part A)

Nanostructured cellulose sponges (CNS) have been developed as eco-friendly and sustainable engineered materials for marine environmental remediation. Despite their functionality, sensitivity, efficiency and specificity have been proved, CNS application is still limited since their environmental safety (eco-safety) has not been completely assessed. In this study, CNS were allowed to leach in natural seawater simulating the remediation process condition and the eco-safety of CNS leachate on sea urchin reproduction has been assessed by carrying out a multi-response integrated approach, combining standardized ecotoxicity tests, innovative bioassays and gamete quality assessment. Overall, the ecotoxicity data indicate that CNS leachate affects gamete quality, gamete fertilisation competence, and embryo development probably associated with the release of chemical additives used during the synthesis process. However, in the framework of the eco-design approach, consecutive leaching treatments and conditioning of CNS in seawater open the route for a new safety protocol successfully solving the ecotoxicity while maintaining CNS sorbent properties. A safe environmental application of the resulting conditioned CNS for seawater pollution remediation is envisaged.

Environmental safety of nanotechnologies: The eco-design of manufactured nanomaterials for environmental remediation

Nanosafety is paramount considering the risks associated with manufactured nanomaterials (MNMs) whose implications could outweigh their advantages for environmental applications. Although nanotechnology-based solutions to implement pollution control, remediation and prevention are incremental with clear benefits for public health and Earth' natural ecosystems, nanoremediation is having a setback due to the risks associated with the safety of MNMs for humans and the environment. MNMs are diverse, work differently and bionano-interactions occurring upon environmental exposure will guide their fate and hazardous outcomes. Here we propose a new ecologically-based design strategy (eco-design) having its roots in green nanoscience and LCA that will ground on an Ecological Risk Assessment approach, which introduces the evaluation of MNMs' ecotoxicity along with their performances and efficacies at the design stage. As such, the proposed eco-design strategy will allow recognition and design-out since the very beginning of material synthesis, those hazardous peculiar features that can be hazardous to living beings and the natural environment. A more ecologically sound eco-design strategy in which nanosafety is conceptually included in MNMs design will sustain safer nanotechnologies including those for the environment as remediation by leveraging any risks for humans and natural ecosystems.

Eco-Friendly Engineered Nanomaterials Coupled with Filtering Fine-Mesh Net as a Promising Tool to Remediate Contaminated Freshwater Sludges: An Ecotoxicity Investigation

The use of eco-friendly engineered nanomaterials represents a recent solution for an effective and safe treatment of contaminated dredging sludge. In this study, an eco-designed engineered material based on cross-linked nanocellulose (CNS) was applied for the first time to decontaminate a real matrix from heavy metals (namely Zn, Ni, Cu, and Fe) and other undesired elements (mainly Ba and As) in a lab-scale study, with the aim to design a safe solution for the remediation of contaminated matrices. Contaminated freshwater sludge was treated with CNS coupled with a filtering fine-mesh net, and the obtained waters were tested for acute and sublethal toxicity. In order to check the safety of the proposed treatment system, toxicity tests were conducted by exposing the bacterium Aliivibrio fischeri and the crustacean Heterocypris incongruens, while subtoxicity biomarkers such as lysosomal membrane stability, genetic, and chromosomal damage assessment were performed on the freshwater bivalve Dreissena polymorpha. Dredging sludge was found to be genotoxic, and such genotoxicity was mitigated by the combined use of CNS and a filtering fine-mesh net. Chemical analyses confirmed the results by highlighting the abetment of target contaminants, indicating the present model as a promising tool in freshwater sludge nanoremediation.

Can TEMPO-Oxidized Cellulose Nanofibers Be Used as Additives in Bio-Based Building Materials? A Preliminary Study on Earth Plasters

Interest towards cellulose nanofibers obtained from virgin and waste sources has seen a significant growth, mainly thanks to the increasing sensitivity towards the concept of circular economy and the high levels of paper recycling achieved in recent years. Inspired by the guidelines of the green building industry, this study proposes the production and characterization of TEMPO-oxidized and homogenized cellulose nanofibers (TOHO CNF) from different sources and their use as additives for earth plasters on two different raw earth samples, characterized by geotechnical laboratory tests and mineralogical analysis: a high-plasticity clay (T2) and a medium-compressibility silt (ABS). Original sources, including those derived from waste (recycled cardboard and paper mill sludge), were characterized by determining chemical content (cellulose versus ashes and lignin) and fiber morphology. TOHO CNF derived from the different sources were compared in terms of nanofibers medium diameter, crystallinity degree, thermal decomposition and oxidation degree, that is the content of carboxylic groups per gram of sample. Then, a preliminary analysis of the influence of CNF on earth plasters is examined. Adhesion and capillary absorption tests highlighted the effect of such nanofibers on blends in function of two factors, namely the cellulose original source and the oxidation degree of the fibers. In particular, for both earth samples, T2 and ABS, a significant increase in adhesion strength was observed in the presence of some TOHO CNF additives. As far as capillary sorption tests, while an undesired increase in water adsorption was detected for T2 compared to the control, in the case of ABS, a significant reduction in water content was measured by adding TOHO CNF derived from recycled sources. These results pave the way for further in-depth investigation on the role of TOHO CNF as additives for earth plasters.

Pd-Loaded Cellulose NanoSponge as a Heterogeneous Catalyst for Suzuki-Miyaura Coupling Reactions

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.

The Era of Nanomaterials: A Safe Solution or a Risk for Marine Environmental Pollution?

In recent years, the application of engineered nanomaterials (ENMs) in environmental remediation gained increasing attention. Due to their large surface area and high reactivity, ENMs offer the potential for the efficient removal of pollutants from environmental matrices with better performances compared to conventional techniques. However, their fate and safety upon environmental application, which can be associated with their release into the environment, are largely unknown. It is essential to develop systems that can predict ENM interactions with biological systems, their overall environmental and human health impact. Until now, Life-Cycle Assessment (LCA) tools have been employed to investigate ENMs potential environmental impact, from raw material production, design and to their final disposal. However, LCA studies focused on the environmental impact of the production phase lacking information on their environmental impact deriving from in situ employment. A recently developed eco-design framework aimed to fill this knowledge gap by using ecotoxicological tools that allow the assessment of potential hazards posed by ENMs to natural ecosystems and wildlife. In the present review, we illustrate the development of the eco-design framework and review the application of ecotoxicology as a valuable strategy to develop ecosafe ENMs for environmental remediation. Furthermore, we critically describe the currently available ENMs for marine environment remediation and discuss their pros and cons in safe environmental applications together with the need to balance benefits and risks promoting an environmentally safe nanoremediation (ecosafe) for the future.

Effect of UV Irradiation and TiO2-Photocatalysis on Airborne Bacteria and Viruses: An Overview

Current COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has put a spotlight on the spread of infectious diseases brought on by pathogenic airborne bacteria and viruses. In parallel with a relentless search for therapeutics and vaccines, considerable effort is being expended to develop ever more powerful technologies to restricting the spread of airborne microorganisms in indoor spaces through the minimization of health- and environment-related risks. In this context, UV-based and photocatalytic oxidation (PCO)-based technologies (i.e., the combined action of ultraviolet (UV) light and photocatalytic materials such as titanium dioxide (TiO2)) represent the most widely utilized approaches at present because they are cost-effective and ecofriendly. The virucidal and bactericidal effect relies on the synergy between the inherent ability of UV light to directly inactivate viral particles and bacteria through nucleic acid and protein damages, and the production of oxidative radicals generated through the irradiation of the TiO2 surface. In this literature survey, we draw attention to the most effective UV radiations and TiO2-based PCO technologies available and their underlying mechanisms of action on both bacteria and viral particles. Since the fine tuning of different parameters, namely the UV wavelength, the photocatalyst composition, and the UV dose (viz, the product of UV light intensity and the irradiation time), is required for the inactivation of microorganisms, we wrap up this review coming up with the most effective combination of them. Now more than ever, UV- and TiO2-based disinfection technologies may represent a valuable tool to mitigate the spread of airborne pathogens.

Synthesis and Application of Cellulose-Polyethyleneimine Composites and Nanocomposites: A Concise Review

Cellulose/polyethyleneimine composites have increasingly attracted the attention of scientific community, devoted to the design and development of new synthetic strategies and materials for different application fields. In this review, after introducing the main characteristics of the two polymeric components, we provide in the second section a critical overview on the main protocols for the synthesis of these composites, considering both the several cellulose sources and forms, and the different cross-linkers and cross-linking procedures developed for this purpose, outlining advantages and limits for the reported approaches. The last section analyses the principal results obtained in different application fields. A wide discussion is dedicated to the principal use of cellulose/polyethyleneimine composites as sorbents for water remediation from heavy metal ions and organic contaminants. Subsequently, we introduce the literature describing the use of these composites, functionalized appropriately, where necessary, as drug delivery systems, sensors, and heterogeneous catalysts for organic reactions. Finally, after a brief description of other random applications, we furnish a personal analysis of actual limits and potentialities for these systems.

Nanostructured Cellulose-Based Sorbent Materials for Water Decontamination from Organic Dyes

Nanostructured materials have been recently proposed in the field of environmental remediation. The use of nanomaterials as building blocks for the design of nano-porous micro-dimensional systems is particularly promising since it can overcome the (eco-)toxicological risks associated with the use of nano-sized technologies. Following this approach, we report here the application of a nanostructured cellulose-based material as sorbent for effective removal of organic dyes from water. It consists of a micro- and nano-porous sponge-like system derived by thermal cross-linking among (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose nanofibers (TOCNF), branched polyethylenimine 25 kDa (bPEI), and citric acid (CA). The sorbent efficiency was tested for four different organic dyes commonly used for fabric printing (Naphthol Blue Black, Orange II Sodium Salt, Brilliant Blue R, Cibacron Brilliant Yellow), by conducting both thermodynamic and kinetic studies. The material performance was compared with that of an activated carbon, commonly used for this application, in order to highlight the potentialities and limits of this biomass-based new material. The possibility of regeneration and reuse of the sorbent was also investigated.

Silver Nanoparticles for Water Pollution Monitoring and Treatments: Ecosafety Challenge and Cellulose-Based Hybrids Solution

Silver nanoparticles (AgNPs) are widely used as engineered nanomaterials (ENMs) in many advanced nanotechnologies, due to their versatile, easy and cheap preparations combined with peculiar chemical-physical properties. Their increased production and integration in environmental applications including water treatment raise concerns for their impact on humans and the environment. An eco-design strategy that makes it possible to combine the best material performances with no risk for the natural ecosystems and living beings has been recently proposed. This review envisages potential hybrid solutions of AgNPs for water pollution monitoring and remediation to satisfy their successful, environmentally safe (ecosafe) application. Being extremely efficient in pollutants sensing and degradation, their ecosafe application can be achieved in combination with polymeric-based materials, especially with cellulose, by following an eco-design approach. In fact, (AgNPs)-cellulose hybrids have the double advantage of being easily produced using recycled material, with low costs and possible reuse, and of being ecosafe, if properly designed. An updated view of the use and prospects of these advanced hybrids AgNP-based materials is provided, which will surely speed their environmental application with consequent significant economic and environmental impact.

Effect-Based Approach to Assess Nanostructured Cellulose Sponge Removal Efficacy of Zinc Ions from Seawater to Prevent Ecological Risks

To encourage the applicability of nano-adsorbent materials for heavy metal ion removal from seawater and limit any potential side effects for marine organisms, an ecotoxicological evaluation based on a biological effect-based approach is presented. ZnCl2 (10 mg L-1) contaminated artificial seawater (ASW) was treated with newly developed eco-friendly cellulose-based nanosponges (CNS) (1.25 g L-1 for 2 h), and the cellular and tissue responses of marine mussel Mytilus galloprovincialis were measured before and after CNS treatment. A control group (ASW only) and a negative control group (CNS in ASW) were also tested. Methods: A significant recovery of Zn-induced damages in circulating immune and gill cells and mantle edges was observed in mussels exposed after CNS treatment. Genetic and chromosomal damages reversed to control levels in mussels' gill cells (DNA integrity level, nuclear abnormalities and apoptotic cells) and hemocytes (micronuclei), in which a recovery of lysosomal membrane stability (LMS) was also observed. Damage to syphons, loss of cilia by mantle edge epithelial cells and an increase in mucous cells in ZnCl2-exposed mussels were absent in specimens after CNS treatment, in which the mantle histology resembled that of the controls. No effects were observed in mussels exposed to CNS alone. As further proof of CNS' ability to remove Zn(II) from ASW, a significant reduction of >90% of Zn levels in ASW after CNS treatment was observed (from 6.006 to 0.510 mg L-1). Ecotoxicological evaluation confirmed the ability of CNS to remove Zn from ASW by showing a full recovery of Zn-induced toxicological responses to the levels of mussels exposed to ASW only (controls). An effect-based approach was thus proven to be useful in order to further support the environmentally safe (ecosafety) application of CNS for heavy metal removal from seawater.

TEMPO-Nanocellulose/Ca2+ Hydrogels: Ibuprofen Drug Diffusion and In Vitro Cytocompatibility

Stable hydrogels with tunable rheological properties were prepared by adding Ca2+ ions to aqueous dispersions of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-oxidized and ultra-sonicated cellulose nanofibers (TOUS-CNFs). The gelation occurred by interaction among polyvalent cations and the carboxylic units introduced on TOUS-CNFs during the oxidation process. Both dynamic viscosity values and pseudoplastic rheological behaviour increased by increasing the Ca2+ concentration, confirming the cross-linking action of the bivalent cation. The hydrogels were proved to be suitable controlled release systems by measuring the diffusion coefficient of a drug model (ibuprofen, IB) by high-resolution magic angle spinning (HR-MAS) nuclear magnetic resonance (NMR) spectroscopy. IB was used both as free molecule and as a 1:1 pre-formed complex with β-cyclodextrin (IB/β-CD), showing in this latter case a lower diffusion coefficient. Finally, the cytocompatibility of the TOUS-CNFs/Ca2+ hydrogels was demonstrated in vitro by indirect and direct tests conducted on a L929 murine fibroblast cell line, achieving a percentage number of viable cells after 7 days higher than 70%.

Naked-Eye Heterogeneous Sensing of Fluoride Ions by Co-Polymeric Nanosponge Systems Comprising Aromatic-Imide-Functionalized Nanocellulose and Branched Polyethyleneimine

Heterogeneous colorimetric sensors for fluoride ions were obtained by cross-linking TEMPO-oxidized cellulose nanofibers (TOCNF) with chemically modified branched polyethyleneimine 25 kDa (bPEI). Functionalization of bPEI primary amino groups with aromatic anhydrides led to the formation of the corresponding mono- and bis-imides on the grafted polymers (f-bPEI). A microwave-assisted procedure allowed the optimization of the synthetic protocol by reducing reaction time from 17 h to 30 minutes. Hydrogels obtained by mixing different ratios of TOCNF, bPEI and f-bPEI were lyophilized and thermally treated at about 100 °C to promote the formation of amide bonds between the amino groups of poly-cationic polymers and the carboxylic groups of cellulose nanofibers. This approach generated a series of cellulose nanosponges S1-S3 which were characterized by FT-IR and by solid state ¹³ C CPMAS NMR. These sponge materials can act as colorimetric sensors for the selective naked-eye recognition of fluoride ions over chloride, phosphate and acetate ions at concentrations of up to 0.05 M in DMSO. Moreover, when the sponges were functionalized with perylene tetracarboxylic diimide, successful naked-eye detection was achieved with only 0.02 % w/w of chromophore units per gram of material.

Environmentally Sustainable and Ecosafe Polysaccharide-Based Materials for Water Nano-Treatment: An Eco-Design Study

Nanoremediation, which is the use of nanoparticles and nanomaterials for environmental remediation, is widely explored and proposed for preservation of ecosystems that suffer from the increase in human population, pollution, and urbanization. We herein report a critical analysis of nanotechnologies for water remediation by assessing their sustainability in terms of efficient removal of pollutants, appropriate methods for monitoring their effectiveness, and protocols for the evaluation of any potential environmental risks. Our purpose is to furnish fruitful guidelines for sustainable water management, able to promote nanoremediation also at European level. In this context, we describe new nanostructured polysaccharide-based materials obtained from renewable resources as alternative efficient and ecosafe solutions for water nano-treatment. We also provide eco-design indications to improve the sustainability of the production of these materials, based on life-cycle assessment methodology.

Ecofriendly nanotechnologies and nanomaterials for environmental applications: Key issue and consensus recommendations for sustainable and ecosafe nanoremediation

The use of engineered nanomaterials (ENMs) for environmental remediation, known as nanoremediation, represents a challenging and innovative solution, ensuring a quick and efficient removal of pollutants from contaminated sites. Although the growing interest in nanotechnological solutions for pollution remediation, with significant economic investment worldwide, environmental and human risk assessment associated with the use of ENMs is still a matter of debate and nanoremediation is seen yet as an emerging technology. Innovative nanotechnologies applied to water and soil remediation suffer for a proper environmental impact scenario which is limiting the development of specific regulatory measures and the exploitation at European level. The present paper summarizes the findings from the workshop: "Ecofriendly Nanotechnology: state of the art, future perspectives and ecotoxicological evaluation of nanoremediation applied to contaminated sediments and soils" convened during the Biannual ECOtoxicology Meeting 2016 (BECOME) held in Livorno (Italy). Several topics have been discussed and, starting from current state of the art of nanoremediation, which represents a breakthrough in pollution control, the following recommendations have been proposed: (i) ecosafety has to be a priority feature of ENMs intended for nanoremediation; ii) predictive safety assessment of ENMs for environmental remediation is mandatory; (iii) greener, sustainable and innovative nano-structured materials should be further supported; (iii) those ENMs that meet the highest standards of environmental safety will support industrial competitiveness, innovation and sustainability. The workshop aims to favour environmental safety and industrial competitiveness by providing tools and modus operandi for the valorization of public and private investments.

Microwave-assisted synthesis of TEMPO-labeled hydrogels traceable with MRI

Polymer functionalization strategies have recently attracted considerable attention for several applications in biomaterials science. In particular, technological advancements in medical imaging have focused on the design of polymeric matrices to improve non-invasive approaches and diagnostic accuracy. In this scenario, the use of microwave irradiation of aqueous solutions containing appropriate combinations of polymers is gaining increasing interest in the synthesis of sterile hydrogels without using monomers, eliminating the need to remove unreacted species. In this study, we developed a method for the in situ fabrication of TEMPO-labeled hydrogels based on a one-pot microwave reaction that can then be tracked by magnetic resonance imaging (MRI) without using toxic compounds that could be hostile for the target tissue. Click chemistry was used to link TEMPO to the polymeric scaffold. In an in vivo model, the system was able to preserve its TEMPO paramagnetic activity up to 1 month after hydrogel injection, showing a clear detectable signal on T₁-weighted MRI with a longitudinal relaxivity value of 0.29 mM s^-1, comparable to a value of 0.31 mM s^-1 characteristic of TEMPO application. The uncleavable conjugation between the contrast agent and the polymeric scaffold is a leading point to record these results: the use of TEMPO only physically entrapped in the polymeric scaffold did not show MRI traceability even after few hours. Moreover, the use of TEMPO-labeled hydrogels can also help to reduce the number of animals sacrificed being a longitudinal non-invasive technique.

Mechanical and Drug Release Properties of Sponges from Cross-linked Cellulose Nanofibers

All-organic porous sponges were obtained throughout the direct and solvent-free (oven 105 °C, time>6 h) crosslinking of TEMPO-oxidized cellulose nanofibers (TOCNF) with 25 kDa branched polyethyleneimine (bPEI) in the presence of different amounts of citric acid (CA) as co-crosslinker. The chemical and mechanical stability of these materials was provided by the formation of amide bonds between the carboxylic moieties of TOCNF and CA with the primary amines of bPEI. The mechanical properties were investigated under static and dynamic loads with both dry and wet samples. The materials had the interesting capability to recover their shape with reduced losses in mechanical resistance, while their Young's modulus progressively increased with the content of CA. In work toward developing possible applications of bPEI-TOCNF sponges in drug delivery, amoxicillin (AM) and ibuprofen (IB) were considered as model drugs. All materials showed very good performance in adsorbing both AM and IB (ca. 200 mg g^-1 ) from methanol solution. In particular, an increased adsorption of IB was observed in parallel to the increase of citrate moieties in the samples. Moreover, samples crosslinked in presence of CA showed slower kinetic release in aqueous environments than materials obtained without CA.

TEMPO-mediated oxidation of polysaccharides: An ongoing story

The oxidation of natural polysaccharides by TEMPO has become by now an "old chemical reaction" which led to numerous studies mainly conducted on cellulose. This regioselective oxidation of primary alcohol groups of neutral polysaccharides has generated a new class of polyuronides not identified before in nature, even if the discovery of enzymes promoting an analogous oxidation has been more recently reported. Around the same time, the scientific community discovered the surprising biological and techno-functional properties of these anionic macromolecules with a high potential of application in numerous industrial fields. The objective of this review is to establish the state of the art of TEMPO chemistry applied to polysaccharide oxidation, its history, the resulting products, their applications and the associated modifying enzymes.

Dynamics and interactions of ibuprofen in cyclodextrin nanosponges by solid-state NMR spectroscopy

Two different formulations of cyclodextrin nanosponges (CDNS), obtained by polycondensation of β-cyclodextrin with ethylenediaminetetraacetic acid dianhydride (EDTAn), were treated with aqueous solutions of ibuprofen sodium salt (IbuNa) affording hydrogels that, after lyophilisation, gave two solid CDNS-drug formulations. ¹H fast MAS NMR and ¹³C CP-MAS NMR spectra showed that IbuNa was converted in situ into its acidic and dimeric form (IbuH) after freeze-drying. ¹³C CP-MAS NMR spectra also indicated that the structure of the nanosponge did not undergo changes upon drug loading compared to the unloaded system. However, the ¹³C NMR spectra collected under variable contact time cross-polarization (VCT-CP) conditions showed that the polymeric scaffold CDNS changed significantly its dynamic regime on passing from the empty CDNS to the drug-loaded CDNS, thus showing that the drug encapsulation can be seen as the formation of a real supramolecular aggregate rather than a conglomerate of two solid components. Finally, the structural features obtained from the different solid-state NMR approaches reported matched the information from powder X-ray diffraction profiles.

SANS investigation of water adsorption in tunable cyclodextrin-based polymeric hydrogels

A quantitative law for the hydration-dependence of pore size in cyclodextrin-based hydrogels is provided by SANS experiments.

Correlation between collective and molecular dynamics in pH-responsive cyclodextrin-based hydrogels

The joint use of UV Raman and Brillouin scattering experiments is employed to explore phase evolutions in pH-responsive polysaccharide hydrogels.

Guest-matrix interactions affect the solvation of cyclodextrin-based polymeric hydrogels: a UV Raman scattering study

The focus of the present work is to shed light on possible modifications of the molecular properties of polysaccharide hydrogels induced by the establishment of specific non-covalent interactions during the loading of a guest compound inside the gel phase. With this aim, a case study of the encapsulation of caffeine (Caf) inside cyclodextrin-based hydrogels, namely, cyclodextrin nanosponges (NS), is systematically investigated here by using UV Raman scattering experiments. The UV Raman spectra of the hydrogels, analysed as a function of temperature, concentration of the guest molecule loaded in the gel phase and pH, prove particularly informative both on the structural rearrangements of the hydrophobic/hydrophilic groups of the polymeric network and on the breaking/formation of specific guest-matrix interactions. Analysis of the temperature dependence of dynamical parameters, i.e., the dephasing time associated with specific vibrational modes of the polymer backbone, enables the proposal of a molecular picture in which the loading of Caf in NS hydrogels tends to favour access of the water solvent to the more hydrophobic portions of the polymer matrix, which is in turn reflected in a marked increase in the solvation of the whole system. The achievements of this work appear of interest with respect to the design of new possible strategies for controlling the diffusion/release of bioactive molecules inside hydrogel networks, besides corroborating the potential of UV Raman scattering experiments to give new molecular insights into complex phenomena affecting hydrogel phases.

Transport Properties of Ibuprofen Encapsulated in Cyclodextrin Nanosponge Hydrogels: A Proton HR-MAS NMR Spectroscopy Study

The chemical cross-linking of β-cyclodextrin (β-CD) with ethylenediaminetetraacetic dianhydride (EDTA) led to branched polymers referred to as cyclodextrin nanosponges (CDNSEDTA). Two different preparations are described with 1:4 and 1:8 CD-EDTA molar ratios. The corresponding cross-linked polymers were contacted with 0.27 M aqueous solution of ibuprofen sodium salt (IP) leading to homogeneous, colorless, drug loaded hydrogels. The systems were characterized by high resolution magic angle spinning (HR-MAS) NMR spectroscopy. Pulsed field gradient spin echo (PGSE) NMR spectroscopy was used to determine the mean square displacement (MSD) of IP inside the polymeric gel at different observation times td. The data were further processed in order to study the time dependence of MSD: MSD = f(td). The proposed methodology is useful to characterize the different diffusion regimes that, in principle, the solute may experience inside the hydrogel, namely normal or anomalous diffusion. The full protocols including the polymer preparation and purification, the obtainment of drug-loaded hydrogels, the NMR sample preparation, the measurement of MSD by HR-MAS NMR spectroscopy and the final data processing to achieve the time dependence of MSD are here reported and discussed. The presented experiments represent a paradigmatic case and the data are discussed in terms of innovative approach to the characterization of the transport properties of an encapsulated guest within a polymeric host of potential application for drug delivery.

Surface-Functionalization of Nanostructured Cellulose Aerogels by Solid State Eumelanin Coating

Bioinspired aerogel functionalization by surface modification and coating is in high demand for biomedical and technological applications. In this paper, we report an expedient three-step entry to all-natural surface-functionalized nanostructured aerogels based on (a) TEMPO/NaClO promoted synthesis of cellulose nanofibers (TOCNF); (b) freeze-drying for aerogel preparation; and (c) surface coating with a eumelanin thin film by ammonia-induced solid state polymerization (AISSP) of 5,6-dihydroxyindole (DHI) or 5,6-dihydroxyindole-2-carboxylic acid (DHICA) previously deposited from an organic solution. Scanning electron microscopy showed uniform deposition of the dark eumelanin coating on the template surface without affecting porosity, whereas solid state (13)C NMR and electron paramagnetic resonance (EPR) spectroscopy confirmed the eumelanin-type character of the coatings. DHI melanin coating was found to confer to TOCNF templates a potent antioxidant activity, as tested by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays as well as strong dye adsorption capacity, as tested on methylene blue. The unprecedented combination of nanostructured cellulose and eumelanin thin films disclosed herein implements an original all-natural multifunctional aerogel biomaterial realized via an innovative coating methodology.

Vibrational signatures of the water behaviour upon confinement in nanoporous hydrogels

Vibrational spectroscopy is used to investigate how the hydrogen-bond dynamics of water is influenced by nano-confinement and hydrophobic/hydrophilic solvation effects.

N-Hydroxyphthalimide catalysts as bioactive pro-oxidants

N-Hydroxyphthalimide organocatalysts bearing lipophilic moieties exhibit a cytotoxic action by promoting oxidative stress in cells.

Functionalization of Cyclodextrins with N-Hydroxyphthalimide Moiety: A New Class of Supramolecular Pro-Oxidant Organocatalysts

N-hydroxyphthalimide (NHPI) is an organocatalyst for free-radical processes able to promote the aerobic oxidation of a wide range of organic substrates. In particular, NHPI can catalyze the hydroperoxidation of polyunsaturated fatty acids (PUFA). This property could be of interest for biological applications. This work reports the synthesis of two β-cyclodextrin derivatives (CD5 and CD6) having a different degree of methylation and bearing a NHPI moiety. These compounds, having different solubility in water, have been successfully tested for the hydroperoxidation of methyl linoleate, chosen as the PUFA model molecule.

Toward an understanding of the thermosensitive behaviour of pH-responsive hydrogels based on cyclodextrins

The molecular mechanism responsible for the thermosensitive behaviour exhibited by pH-responsive cyclodextrin-based hydrogels is explored here with the twofold aim of clarifying some basic aspects of H-bond interactions in hydrogel phases and contributing to a future engineering of cyclodextrin hydrogels for targeted delivery and release of bioactive agents. The degree of H-bond association of water molecules entrapped in the gel network and the extent of intermolecular interactions involving the hydrophobic/hydrophilic moieties of the polymer matrix are probed by UV Raman and IR experiments, in order to address the question of how these different and complementary aspects combine to determine the pH-dependent thermal activation exhibited by these hydrogels. Complementary vibrational spectroscopies are conveniently employed in this study with the aim of safely disentangling the spectral response arising from the two main components of the hydrogel systems, i.e. the polymer matrix and water solvent. The experimental evidence suggests that the dominant effects in the mechanism of solvation of cyclodextrin-based hydrogels are due to the changes occurring, upon increasing of temperature, in the hydrophobicity character of specific chemical moieties of the polymer, as triggered by pH variations. The achievements of this work corroborate the potentiality of the UV Raman scattering technique, in combination with more conventional IR experiments, to provide a "molecular view" of complex macroscopic phenomena exhibited in hydrogel phases.

TEMPO-Oxidized Cellulose Cross-Linked with Branched Polyethyleneimine: Nanostructured Adsorbent Sponges for Water Remediation

Adsorbent sponges for water remediation were prepared using TEMPO-oxidized cellulose nanofibers (TOCNFs) as three-dimensional scaffolds, and branched polyethyleneimine (bPEI, 25 KDa) as the cross-linking agent. TOCNFs were suspended in aqueous solution in the presence of variable amounts of bPEI. The mixtures were first freeze-dried and then thermally treated (from 60 to 102 °C over 10 h) promoting the formation of amide bonds between the carboxylic groups of TOCNF and the primary amines of bPEI. The resulting materials, which were characterized by FTIR and ¹³ C CP-MAS NMR spectroscopy, scanning electron microscopy, and elemental analysis, showed higher chemical and mechanical stability in water than non-reticulated cellulose composites. The high adsorption capability of the new sponges was verified for different organic pollutants (p-nitrophenol, 2,4,5-trichlorophenol, and amoxicillin), and heavy metal ion pollutants (Cu, Co, Ni, Cd), indicating their potential for water decontamination.

Multicomponent versus domino reactions: One-pot free-radical synthesis of β-amino-ethers and β-amino-alcohols

Following an optimized multicomponent procedure, an aryl amine, a ketone, and a cyclic ether or an alcohol molecule are assembled in a one-pot synthesis by nucleophilic radical addition of ketyl radicals to ketimines generated in situ. The reaction occurs under mild conditions by mediation of the TiCl4/Zn/t-BuOOH system, leading to the formation of quaternary β-amino-ethers and -alcohols. The new reaction conditions guarantee good selectivity by preventing the formation of secondary products. The secondary products are possibly derived from a competitive domino reaction, which involves further oxidation of the ketyl radicals.

Water and polymer dynamics in a model polysaccharide hydrogel: the role of hydrophobic/hydrophilic balance

The role of hydrophobicity/hydrophilicity balance in the gelation phenomena in water-swollen polymers is explored in a model polysaccharide hydrogel.

Dip in colorimetric fluoride sensing by a chemically engineered polymeric cellulose/bPEI conjugate in the solid state

A novel heterogeneous, selective dip-in sensor for fluoride has been developed by cross-linking oxidized cellulose with branched PEI functionalized with pNO₂-phenyl urea units.

Combining Raman and infrared spectroscopy as a powerful tool for the structural elucidation of cyclodextrin-based polymeric hydrogels

UV Raman spectroscopy and infrared spectroscopy have been efficiently implemented for the structural and dynamic elucidation of cyclodextrin-based polymeric hydrogels.

Effective magnetic moment in cyclodextrin–polynitroxides: potential supramolecular vectors for magnetic resonance imaging

Hepta-TEMPO β-CD has a molecular effective magnetic moment of 4.2 μ_B that is responsible of a NMR relaxivity up to 1.60 mm⁻¹ s⁻¹, not far from the values reported for Gd-based contrast agents, thus resulting a promising candidates as non-toxic MRI contrast agents.

Anomalous diffusion of Ibuprofen in cyclodextrin nanosponge hydrogels: an HRMAS NMR study

Ibuprofen sodium salt (IP) was encapsulated in cyclodextrin nanosponges (CDNS) obtained by cross-linking of β-cyclodextrin with ethylenediaminetetraacetic acid dianhydride (EDTAn) in two different preparations: CDNSEDTA 1:4 and 1:8, where the 1:n notation indicates the CD to EDTAn molar ratio. The entrapment of IP was achieved by swelling the two polymers with a 0.27 M solution of IP in D2O, leading to colourless, homogeneous hydrogels loaded with IP. The molecular environment and the transport properties of IP in the hydrogels were studied by high resolution magic angle spinning (HRMAS) NMR spectroscopy. The mean square displacement (MSD) of IP in the gels was obtained by a pulsed field gradient spin echo (PGSE) NMR pulse sequence at different observation times t d. The MSD is proportional to the observation time elevated to a scaling factor α. The α values define the normal Gaussian random motion (α = 1), or the anomalous diffusion (α < 1, subdiffusion, α > 1 superdiffusion). The experimental data here reported point out that IP undergoes subdiffusive regime in CDNSEDTA 1:4, while a slightly superdiffusive behaviour is observed in CDNSEDTA 1:8. The transition between the two dynamic regimes is triggered by the polymer structure. CDNSEDTA 1:4 is characterized by a nanoporous structure able to induce confinement effects on IP, thus causing subdiffusive random motion. CDNSEDTA 1:8 is characterized not only by nanopores, but also by dangling EDTA groups ending with ionized COO(-) groups. The negative potential provided by such groups to the polymer backbone is responsible for the acceleration effects on the IP anion thus leading to the superdiffusive behaviour observed. These results point out that HRMAS NMR spectroscopy is a powerful direct method for the assessment of the transport properties of a drug encapsulated in polymeric scaffolds. The diffusion properties of IP in CDNS can be modulated by suitable polymer synthesis; this finding opens the possibility to design suitable systems for drug delivery with predictable and desired drug release properties.

Synthesis and characterization of a hyper-branched water-soluble β-cyclodextrin polymer

A new hyper-branched water-soluble polymer was synthesized by reacting β-cyclodextrin with pyromellitic dianhydride beyond the critical conditions that allow the phenomenon of gelation to occur. The molar ratio between the monomers is a crucial parameter that rules the gelation process. Nevertheless, the concentration of monomers in the solvent phase plays a key role as well. Hyper-branched β-cyclodextrin-based polymers were obtained performing the syntheses with excess of solvent and cross-linking agent, and the conditions for critical dilution were determined experimentally. A hyper-branched polymer with very high water solubility was obtained and fully characterized both as for its chemical structure and for its capability to encapsulate substances. Fluorescein was used as probe molecule to test the complexation properties of the new material.

Aerobic oxidation of alkylaromatics using a lipophilic N-hydroxyphthalimide: overcoming the industrial limit of catalyst solubility

4,4'-(4,4'-Isopropylidenediphenoxy)bis(N-hydroxyphthalimide), which is a new lipophilic analogue of N-hydroxyphthalimide, can act as an effective catalyst in the aerobic oxidation of alkylaromatics under reduced amounts of polar cosolvent. The catalyst was selected on the basis of an in-depth study of the influence that substituents on the aromatic ring of N-hydroxyphthalimide exert on determining the NO-H bond dissociation energy (BDE). BDE values for a range of model molecules are calculated by DFT and measured by EPR spectroscopy. The new catalyst can be successfully employed in the aerobic oxidation of cumene, ethylbenzene, and cyclohexylbenzene, affording, in all cases, good conversions and high selectivity for the corresponding hydroperoxide. The effect of solvent, catalyst, and temperature has also been investigated.

Direct evidence of gel-sol transition in cyclodextrin-based hydrogels as revealed by FTIR-ATR spectroscopy

The phase transition from gel to liquid suspension in cyclodextrin (CD)-based hydrogels is in depth monitored by using Fourier transform infrared spectroscopy in attenuated total reflectance geometry. Cyclodextrin nanosponges (CDNS) synthesized by polymerization of CD with the cross-linking agent ethylenediaminetetraacetic dianhydride at different cross-linking agent/CD molar ratios have been left to evolve from gel phase into liquid suspension upon gradual increase of the hydration level. Measurements of the changes occurring in the vibrational dynamics of the system during this transition provide direct evidence of the gel-sol progress of the CNDS hydrogel, by accounting for the connectivity pattern of water molecules concurring to the gelation process. The experimental results clearly indicate that the increase of the hydration level is accompanied by the corresponding increase of the population of H2O molecules engaged in high-connectivity hydrogen-bond networks. The water tetrahedral arrangement is thus dominant above a characteristic cross-over hydration level, experimentally determined for all the investigated samples. The observation of this characteristic cross-over point for the CDNS hydrogel and its correlation with other parameters of the system (e.g. the absorption ability of CDNS and elasticity of the polymer matrix) is, once again, modulated by the cross-linking agent/CD molar ratio. The latter seems indeed to play a key role in defining the nano- and microscopic properties of nanosponge hydrogels.