Calcein release from DPPC liposomes by phospholipase A2 activity: Effect of cholesterol and amphipathic copolymers.

In this study, we evaluated the impact of incorporating diblock and triblock amphiphilic copolymers, as well as cholesterol into DPPC liposomes on the release of a model molecule, calcein, mediated by exogenous phospholipase A2 activity. Our findings show that calcein release slows down in the presence of copolymers at low concentration, while at high concentration, the calcein release profile resembles that of the DPPC control. Additionally, calcein release mediated by exogenous PLA2 decreases as the amount of solubilized cholesterol increases, with a maximum between 18 mol% and 20 mol%. At concentrations higher than 24 mol%, no calcein release was observed. Studies conducted on HEK-293 and HeLa cells revealed that DPPC liposomes reduced viability by only 5% and 12%, respectively, after 3 hours of incubation, while DPPC liposome in presence of 33 mol% of Cholesterol reduced viability by approximately 11% and 23%, respectively, during the same incubation period. For formulations containing copolymers at low and high concentrations, cell viability decreased by approximately 20% and 40%, respectively, after 3 hours of incubation. Based on these preliminary results, we can conclude that the presence of amphiphilic copolymers at low concentration can be used in the design of new DPPC liposomes, and together with cholesterol, they can modulate liposome stabilization. The new formulations showed low cytotoxicity in HEK-293 cells, and it was observed that calcein release depended entirely on PLA2 activity and the presence of calcium ions.

Dual electro-/pH-responsive nanoparticle/hydrogel system for controlled delivery of anticancer peptide.

An electro-chemo-responsive carrier has been engineered for the controlled release of a highly hydrophilic anticancer peptide, CR(NMe)EKA (Cys-Arg- N-methyl-Glu-Lys-Ala). Remotely controlled on demand release of CR(NMe)EKA, loaded in electro-responsive poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles, has been achieved by applying electrical stimuli consisting of constant positive (+0.50 V) or negative voltages (-0.50 V) at pre-defined time intervals. In addition, after loading CR(NMe)EKA/PEDOT nanoparticles into an injectable pH responsive hydrogel formed by phenylboronic acid grafted to chitosan (PBA-CS), the efficiency of the controlled peptide release has increased approximately by a factor of 2.6. The hydration ratio of such hydrogel is significantly lower in acidic environments than in neutral and basic media, which has been attributed to the dissociation of the boronate bonds between polymer chains. Hence, the electro-controlled peptide release from PBA-CS/CR(NMe)EKA/PEDOT hydrogels, in the acidic environment of tumors, combines the effects of the oxidation and reduction of PEDOT chains on the interactions with the peptide and the carrier, with the peptide concentration gradient at the interface between the collapsed hydrogel and the release medium. Furthermore, the peptide released by electro-stimulation preserved its bioactivity assessed by promoting human prostate cancer cells death. Overall, this work is a promising attempt to develop a carrier platform for small hydrophilic anticancer peptides, which delivery rationale is synergistically regulated by the electrical and pH responsiveness of the carrier.

Revealing Dynamic Behavior in High Dielectric Poly(thiourethane)-Based Vitrimer-like Materials.

Here, we have explored covalent adaptable networks (CANs) comprising poly(thiourethane)-based systems (PTUs). The PTUs were synthesized through the combination of thiol and isocyanate monomers in stoichiometric proportions, in the presence of dibutyltin dilaurate (DBTDL) as catalyst. Dynamic mechanical analysis (DMA) provided detailed insight into the vitrimeric behavior. Through these investigations, we evaluated the viscoelastic, thermomechanical, and vitrimeric properties. Additionally, broadband dielectric spectroscopy (BDS) revealed the various relaxation processes inherent in such vitrimer-like materials. We methodically examined the evolution of each relaxation in every prepared sample to comprehend the operational mechanisms in these vitrimer-like systems. Our findings underscore that depending on the PTU formulation, the glass transition temperature (Tg) and the topology freezing transition temperature (Tv) can be effectively distinguished and studied. Considering the high dipole moment of the dynamic bonds present in these systems, there is potential for utilizing them as dielectric materials working under the concept of dipolar glass polymers. Furthermore, the reversibility exhibited by their inner chemical structures positions them as promising candidates for active layers in capacitor devices, particularly for energy-related applications, with the ability to be recyclable while maintaining almost invariant both their mechanical and dielectric properties, thus promoting the extension of the lifespan of electronic devices.

Unlocking the potential of Opuntia species mucilage in chemistry.

Herein, we describe a detailed protocol to extract the mucilage from different species of the genus Opuntia spp. (i.e., Opuntia Ficus (OFi), Opuntia Dillenii (ODi) and Opuntia Robusta (ORo)). The extracted mucilage was characterized by NMR, FTIR-ATR, HPLC, and TGA. OFi was found to have the highest phenolic content, 7.84 ± 1.93 mg catechol/g mucilage. The mucilage from the three species were characterized by having a high content of monosaccharides, being mannose and glucose the most abundant components (ca. 48-73 % and 23-35 %, respectively). In the context of biomass revalorization, the mucilage was proven to serve as a reducing and stabilizing agent in the synthesis of gold nanoparticles (AuNP/mucilage). The synthesis was optimized with a mucilage concentration of 2 mg/mL using 12.5 µL of KAuCl4 and was carried out at 80 °C for 90 min. This protocol afforded spherical nanoparticles with an average size of 9.7 ± 4.0 nm that were stable for at least 14 days, as demonstrated by TEM. Synthesized AuNP/mucilage was evaluated as a plasmonic catalyst for the reduction of 4-nitrophenol as model reaction, showing a considerable enhancement in its kapp of 97 % under white light and a decrease of 24.8 % in its activation energy.

Trimethylsilanol Cleaves Stable Azaylides As Revealed by Unfolding of Robust "Staudinger" Single-Chain Nanoparticles.

Herein, we disclose a unique and selective reagent for the cleavage of stable azaylides prepared by the nonhydrolysis Staudinger reaction, enabling the on-demand unfolding of robust single-chain nanoparticles (SCNPs). SCNPs with promising use in catalysis, nanomedicine, and sensing are obtained through intrachain folding of discrete synthetic polymer chains. The unfolding of SCNPs involving reversible interactions triggered by a variety of external stimuli (e.g., pH, temperature, light, and redox potential) or substances (e.g., competitive reagents, solvents, and anions) is well known. Conversely, methods for the unfolding (i.e., intrachain disassembly) of SCNPs with stronger covalent interactions are scarce. We show that trimethylsilanol (Me3SiOH) triggers the efficient unfolding of robust "Staudinger" SCNPs with stable azaylide (-N=P-) moieties as intrachain cross-linking units showing exceptional stability toward water, air, and CS2, a standard reagent for azaylides. As a consequence, Me3SiOH arises as a rare, exceptional, and valuable reagent for the cleavage of stable azaylides prepared by the nonhydrolysis Staudinger reaction.

Highly efficient and reusable CuAu nanoparticles supported on crosslinked chitosan hydrogels as a plasmonic catalyst for nitroarene reduction.

The synthesis of CuAu-based monometallic (MNPs) and bimetallic nanoparticles (BNPs) supported on chitosan-based hydrogels for their application as catalysts is presented. The hydrogels consisted of chitosan chains cross-linked with tripolyphosphate (TPP) in the form of beads with an approximate average diameter of 1.81 mm. The MNPs and BNPs were obtained by the adsorption of metallic ions and their subsequent reduction with hydrazine, achieving a metallic loading of 0.297 mmol per gram of dry sample, with average nanoparticle sizes that were found between 2.6 and 4.4 nm. Both processes, metal adsorption and the stabilization of the nanoparticles, are mainly attributed to the participation of chitosan hydroxyl, amine and amide functional groups. The materials revealed important absorption bands in the visible region of the light spectra, specifically between 520 and 590 nm, mainly attributed to LSPR given the nature of the MNPs and BNPs inside the hydrogels. Subsequently, the hydrogels were evaluated as catalysts against the reduction of 4-nitrophenol (4NP) into 4-aminophenol (4AP), followed by UV-visible spectroscopy. The kinetic advance of the reaction revealed important improvements in the catalytic activity of the materials by synergistic effect of BNPs and plasmonic enhancement under visible light irradiation, given the combination of metals and the light harvesting properties of the nanocomposites. Finally, the catalytic performance of hydrogels containing BNPs CuAu 3:1 showed an important selectivity, recyclability and reusability performance, due to the relevant interaction of the BNPs with the chitosan matrix, highlighting the potential of this nanocomposite as an effective catalyst, with a potential environmental application.

Effects of the Solvent Vapor Exposure on the Optical Properties and Photocatalytic Behavior of Cellulose Acetate/Perylene Free-Standing Films.

The search to deliver added value to industrialized biobased materials, such as cellulose derivatives, is a relevant aspect in the scientific, technological and innovation fields at present. To address these aspects, films of cellulose acetate (CA) and a perylene derivative (Pr) were fabricated using a solution-casting method with two different compositions. Consequently, these samples were exposed to dimethylformamide (DMF) solvent vapors so that its influence on the optical, wettability, and topographical properties of the films could be examined. The results demonstrated that solvent vapor could induce the apparent total or partial preferential orientation/migration of Pr toward the polymer-air interface. In addition, photocatalytic activities of the non-exposed and DMF vapor-exposed films against the degradation of methylene blue (MB) in an aqueous medium using light-emitting diode visible light irradiation were comparatively investigated. Apparently, the observed improvement in the performance of these materials in the MB photodegradation process is closely linked to the treatment with solvent vapor. Results from this study have allowed us to propose the fabrication and use of the improved photoactivity "all-organic" materials for potential applications in dye photodegradation in aqueous media.

Lignin-Based Catalysts for C-C Bond-Forming Reactions.

Carbon-carbon (C-C) bond formation is the key reaction in organic synthesis to construct the carbon framework of organic molecules. The continuous shift of science and technology toward eco-friendly and sustainable resources and processes has stimulated the development of catalytic processes for C-C bond formation based on the use of renewable resources. In this context, and among other biopolymer-based materials, lignin has attracted scientific attention in the field of catalysis during the last decade, either through its acid form or as a support for metal ions and metal nanoparticles that drive the catalytic activity. Its heterogeneous nature, as well as its facile preparation and low cost, provide competitive advantages over other homogeneous catalysts. In this review, we have summarized a variety of C-C formation reactions, such as condensations, Michael additions of indoles, and Pd-mediated cross-coupling reactions that were successfully carried out in the presence of lignin-based catalysts. These examples also involve the successful recovery and reuse of the catalyst after the reaction.

Dual-mode colorimetric/fluorescent chemosensor for Cu2+/Zn2+ and fingerprint imaging based on rhodamine ethylenediamine bis(triazolyl silsesquioxane).

A novel dual functional and visual rhodamine ethylenediamine bis(triazolyl silsesquioxane) (RBS) chemosensor was successfully synthesized using "click" chemistry. The results have unambiguously demonstrated that RBS can act in fluorescent and colorimetric sensing of Cu2+ and Zn2+ by their respective coordination with triazole structures and, more importantly, it has also been found that triazole-amide of RBS could turn on chelation-enhanced fluorescence (CHEF) of Cu2+. Remarkably, the addition of Cu2+ triggered an enhanced fluorescent emission by 63.3-fold (ϕF = 0.41), while Zn2+ enhanced it 48.3-fold (ϕF = 0.29) relative to the original RBS (ϕF = 0.006) in acetonitrile (MeCN) solvent. The fluorescent limit of detection for Cu2+ and Zn2+ is similar and fall within 3.0 nM, while under colorimetric sensing the responses were 2.14 × 10-8 and 4.0 × 10-8 mol L-1, respectively. Moreover, the effective sensing profile of RBS and extended applications of RBS-Cu2+ and RBS-Zn2+ for fingerprinting detection and imaging were observed with adequate sensitivity, stability and legibility under the dual visual responses.

Chitosan-Enclosed Menadione Sodium Bisulfite as an Environmentally Friendly Alternative to Enhance Biostimulant Properties against Drought.

Biostimulants are an interesting strategy to increase crop tolerance to water deficits, and there is an extensive bibliography on them. However, most of them need to be treated continuously to increase protection throughout the growth cycle. In this context, we chose menadione sodium bisulfite, whose protective effect against water deficit has been previously demonstrated but only for a short period of time. Nanoencapsulation seems to be an interesting way to improve the properties of biostimulants. Our results show that menadione sodium bisulfite (MSB) encapsulated in chitosan/tripolyphosphate nanoparticles can increase the system's tolerance against an imposed water deficit and delay the need for retreatment by at least 1 week, accelerating plant recovery after rehydration. This highlights the positive properties of nanoencapsulation and shows how a simple encapsulation process can significantly improve the biostimulant protective properties, opening up new possibilities to be explored under field conditions to cope with water-deficit stress.

Self-Healing Polymeric Soft Actuators.

Natural evolution has provided multicellular organisms with sophisticated functionalities and repair mechanisms for surviving and preserve their functions after an injury and/or infection. In this context, biological systems have inspired material scientists over decades to design and fabricate both self-healing polymeric materials and soft actuators with remarkable performance. The latter are capable of modifying their shape in response to environmental changes, such as temperature, pH, light, electrical/magnetic field, chemical additives, etc. In this review, we focus on the fusion of both types of materials, affording new systems with the potential to revolutionize almost every aspect of our modern life, from healthcare to environmental remediation and energy. The integration of stimuli-triggered self-healing properties into polymeric soft actuators endow environmental friendliness, cost-saving, enhanced safety, and lifespan of functional materials. We discuss the details of the most remarkable examples of self-healing soft actuators that display a macroscopic movement under specific stimuli. The discussion includes key experimental data, potential limitations, and mechanistic insights. Finally, we include a general table providing at first glance information about the nature of the external stimuli, conditions for self-healing and actuation, key information about the driving forces behind both phenomena, and the most important features of the achieved movement.

Bimetallic NiPt nanoparticles-enhanced catalyst supported on alginate-based biohydrogels for sustainable hydrogen production.

Alginate hydrogel beads were loaded with bimetallic NiPt nanoparticles by in situ reduction of the respective polymer matrix containing precursor metallic ions using a NaBH4 aqueous solution. The alginate hydrogel beads loaded with NiPt nanoparticles were characterized by TEM, AAS, FT-IR, TGA, XPS, and oscillatory rheometry. The prepared hybrid hydrogels were proven to be effective as catalytic materials for the hydrolysis of ammonia borane (AB) for quantitative hydrogen generation using catalytic loadings of 0.1 mol%. In addition, the reaction mechanism of the hydrolytic reaction using NiPt loaded alginate hydrogel beads was determined by Langmuir-Hinshelwood model. The experimental results showed that the reaction mechanism consisted of an initial fast adsorption of reactants at the surface of the nanoparticles, followed by a rate-limiting surface reaction. The NiPt nanoalloys exhibited an enhanced behavior for hydrogen generation with a maximum TOF of 84.1 min-1, almost 71 % higher compared to monometallic platinum atoms, and likely related to a synergistic interaction between both metals. Finally, the hydrogel matrix enabled the material to be easily recovered from the reaction medium and reused in further catalytic cycles without desorption of active nanoparticles from the material.

Accessible Low-Cost Laser Pointers for the Reduction of Aryl Halides via Triplet-Triplet Annihilation Upconversion in Aerated Gels.

The search for economic alternatives in the use of expensive scientific equipment represents a way of providing many laboratories access to scientific developments that, otherwise, might be hampered by economic constraints. This inspired the purpose of this work, which was to demonstrate for the first time that we can carry out the photoreduction of aryl halides via green-to-blue upconversion in an aerated gel medium, using a simple economic set-up based on easily accessible and low-cost laser pointers. The optimized set-up consists of three laser pointers connected to a switching-mode power supply. One laser should be aligned to Z-axis and separated 5 cm from the sample, while the light incidence of the other two lasers should be adjusted to 45° and separated ca. 3 cm from the sample. The results of this study were found to be reproducible in random experiments and demonstrated that the photoreduction of several aryl halides can be carry out within 24 h of irradiation with comparable yields and mass balances, to those obtained with other very expensive pulsed laser sources. An economic estimation of the expenses concludes that we can easily reduce by >98% the total cost of this type of research by using the described set-up. Our work offers many groups with limited resources a feasible alternative to work in this area without the necessity of extremely expensive devices.

Ag@Au bimetallic nanoparticles: an easy and highly reproducible synthetic approach for photocatalysis.

An Ag@Au bimetallic nanoparticle (BNP) formulation was developed in this work. The proposed formulation was developed using photochemical and chemical methods and non-toxic reagents, showing high reproducibility and homogeneity. The synthesized BNPs have an average size of 7 nm, a core-shell-like structure (silver core and gold shell), high colloidal and long-term stability, and superior catalytic activity under darkness and white light irradiation conditions when evaluating the reduction of 4-nitrophenol to 4-aminophenolate, with respect to the monometallic Ag and Au counterparts. Furthermore, BNP concentrations as low as 2 nM were required to reach 100% conversions in less than 30 minutes. Therefore, considering future applications, the high surface-to-volume ratio of the prepared BNPs coupled with their well-defined optical properties makes them a great candidate for developing heterogeneous catalyzer materials to be applicable under sunlight as an environmentally friendly catalytic system.

CuAu bimetallic plasmonic-enhanced catalysts supported on alginate biohydrogels.

We describe the synthesis, characterization and catalytic properties of a series of hybrid materials composed of inorganic plasmonic mono- and bimetallic nanoparticles supported on organic bio-based hydrogel beads. The bimetallic materials showed a localized surface plasmon resonance in the visible region, with a maximum light absorption correlated to the metal composition of the alloyed systems. Thermogravimetric analysis revealed a total water content near to 90 % w/w, which was in good agreement with the free-volume calculated from µCT scan reconstruction of lyophilized samples. Catalytic essays for the reduction of 4-nitrophenol demonstrated that alginate beads loaded with bimetallic nanoparticles exhibit a 5.4-fold higher apparent kinetic constant (kapp) than its monometallic counterparts. Additionally, taking advantage of the plasmonic properties given by the nanoparticles is that the materials were tested as photocatalysts. The activity of the catalysts was enhanced by near 2.2 times higher in comparison with its performance in dark conditions.

New Hybrid Nanocomposites with Catalytic Properties Obtained by In Situ Preparation of Gold Nanoparticles on Poly (Ionic Liquid)/Poly (4-Vinylpyridine) Nanofibers.

In this work, we report the obtaining of new hybrid nanocomposites with catalytic activity formed by nanofibers of polymer blends and gold nanoparticles. The nanofibers were obtained by electrospinning blends of a poly (ionic liquid) (PIL) and its precursor polymer, poly (4-vinyl pyridine) (P4VPy). The characteristics of the nanofibers obtained proved to be dependent on the proportion of polymer in the blends. The nanofibers obtained were used to synthesize, in situ, gold nanoparticles on their surface by two-step procedure. Firstly, the adsorption of precursor ions on the nanofibers and then their reduction with sodium borohydride to generate gold nanoparticles. The results indicated a significant improvement in the performance of PIL-containing nanofibers over pure P4VPy NFs during ion adsorption, reaching a 20% increase in the amount of adsorbed ions and a 6-fold increase in the respective adsorption constant. The catalytic performance of the obtained hybrid systems in the reduction reaction of 4-nitrophenol to 4-aminophenol was studied. Higher catalytic conversions were obtained using the hybrid nanofibers containing PIL and gold nanoparticles achieving a maximum conversion rate of 98%. Remarkably, the highest value of kinetic constant was obtained for the nanofibers with the highest PIL content.

Porous chitosan-based nanocomposites containing gold nanoparticles. Increasing the catalytic performance through film porosity.

The preparation of porous and non-porous chitosan thin-films containing gold nanoparticles was carried out, aiming to evaluate the effect of porosity on their catalytic response using the p-nitrophenol reduction as model reaction. To achieve this, both types of samples were decorated with gold nanoparticles having similar characteristics in terms of amount, size and shape, which were synthesized following a two-step adsorption-reduction process. The results demonstrated that the presence of porosity generates a considerable enhancement of the catalytic property. This behavior is reflected in higher kinetic constant and conversion values, along with a better recyclability after consecutive cycles. The inclusion of porosity in nanocomposites afforded kobs values 7.5 times higher than the non-porous material, as well as conversion values as high as 80 % in <20 min. On the other hand, as an additional experiment, a porous sample prepared with half the amount of gold also exhibited a better performance than the non-porous catalyst, revealing that the porosity allowed to decrease the amount of catalytic metal used and still exhibiting kobs values 5.9 times higher than the non-porous specimen. These studies demonstrate that there is an important synergistic support-nanostructure relationship, which strongly influences the performance of the nanomaterial.

Biomass-derived isosorbide-based thermoresponsive hydrogel for drug delivery.

Herein, we describe the design and synthesis of a new variety of bio-based hydrogel films using a Cu(I)-catalyzed photo-click reaction. These films exhibited thermal-triggered swelling-deswelling and were constructed by crosslinking a triazide derivative of glycerol ethoxylate and dialkyne structures derived from isosorbide, a well-known plant-based platform molecule. The success of the click reaction was corroborated through infrared spectroscopy (FTIR) and the smooth surface of the obtained films was confirmed by scanning electron microscopy (SEM). The thermal characterization was carried out in terms of thermogravimetry (TGA) and differential scanning calorimetry (DSC), from which the decomposition onset and glass transition temperatures were determined, respectively. Additionally, mechanical properties of the samples were estimated by stress-strain experiments. Then, their swelling and deswelling properties were systematically examined in PBS buffer, revealing a thermoresponsive behavior that was successfully tested in the release of the anticancer drug doxorubicin. We also confirmed the non-cytotoxicity of these materials, which is a fundamental aspect for their potential use as drug carriers or tissue engineering matrices.

Efficient One-Pot Preparation of Thermoresponsive Polyurethanes with Lower Critical Solution Temperatures.

This work reports a simple and scalable strategy to prepare a series of thermoresponsive polyurethanes synthesized via copolymerization of dicyclohexyl diisocyanate with glycerol ethoxylate in a single one-pot system. These polyurethanes exhibit lower critical solution temperatures (LCST) at 57 °C. The LCST of synthesized polyurethane was determined from Dynamic Scanning Calorimetry and UV-vis measurements. Both the LCST and Tg of synthesized polyurethane was tuned by varying the ratio between hard segment (dicyclohexyl diisocyanate) and soft segment (glycerol ethoxylate). Thus, Tg values could be tuned from -54.6 °C to -19.9 °C for samples with different flexibility. The swelling and deswelling studies were done at room temperature and above the LCST respectively. The results showed that the swelling ratio increases with the increase of soft segment (glycerol ethoxylate) in synthesized polyurethanes. Furthermore, the mechanical properties of the membrane were studied by universal tensile testing measurements. Specifically, stress at break values varied from 0.35±0.07 MPa to 0.91±0.15 MPa for the tested membranes, whereas elongation at break data ranged from 101.9±20.9 % to 192.4±24.4 %, and Young's modulus varied from 0.35±0.03 MPa to 1.85±0.19 MPa. Tensile strength of the films increased with the increase of the hard segment and elongation at break decreased.

Chromophoric Dendrimer-Based Materials: An Overview of Holistic-Integrated Molecular Systems for Fluorescence Resonance Energy Transfer (FRET) Phenomenon.

Dendrimers (from the Greek dendros → tree; meros → part) are macromolecules with well-defined three-dimensional and tree-like structures. Remarkably, this hyperbranched architecture is one of the most ubiquitous, prolific, and recognizable natural patterns observed in nature. The rational design and the synthesis of highly functionalized architectures have been motivated by the need to mimic synthetic and natural-light-induced energy processes. Dendrimers offer an attractive material scaffold to generate innovative, technological, and functional materials because they provide a high amount of peripherally functional groups and void nanoreservoirs. Therefore, dendrimers emerge as excellent candidates since they can play a highly relevant role as unimolecular reactors at the nanoscale, acting as versatile and sophisticated entities. In particular, they can play a key role in the properties of light-energy harvesting and non-radiative energy transfer, allowing them to function as a whole unit. Remarkably, it is possible to promote the occurrence of the FRET phenomenon to concentrate the absorbed energy in photoactive centers. Finally, we think an in-depth understanding of this mechanism allows for diverse and prolific technological applications, such as imaging, biomedical therapy, and the conversion and storage of light energy, among others.