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Covalent organic frameworks (COFs) are an emerging class of crystalline materials that are attracting increasing attention due to their high porosity, crystallinity, and tunable properties. Consequently, the strategic design of COF-based photocatalysts for various applications, including energy and environmental remediation, has attracted considerable interest. In particular, the sustainable production of clean fuel – hydrogen (H2) – by water splitting is a promising means to meet the global energy demand and to address the atmospheric CO2 concentration caused by the excessive use of fossil fuels. In this regard, COFs offer potential advantages due to their modular nature, which facilitates their rational design from suitable organic building blocks to achieve optimal properties of visible light harvesting properties and easy charge transport. As a result, extensive research has been devoted to the design of photoresponsive COFs for efficient water splitting to generate hydrogen. Here, we provide a comprehensive review of recent developments in the strategic design of COF-based photocatalysts for solar fuel production via water splitting. The various organic linkers used in the construction of photocatalytic COFs and their structure–property correlations are discussed in detail. The role of bandgap engineering in tuning the hydrogen evolution efficiency of COFs is also discussed. Furthermore, the current challenges and future perspectives of COF-based solid catalysts for green and sustainable clean fuel production are presented. Indeed, this review demonstrates the importance of COF-based photocatalysts for the visible-light-driven hydrogen evolution reaction (HER) and can be beneficial for the future design of photocatalytic systems. [ABSTRACT FROM AUTHOR]

The aim of the work was to formulate piroxicam-loaded solid lipid microparticles (SLMs) using natural biodegradable lipids and to evaluate the in vitro and in vivo properties of the formulations. The lipid matrix composition consisted of 1 : 2 ratios of dika wax from Irvingia gabonensis and goat fat or beeswax. Varying amounts of the drug (0.5, 0.25 and 0.1%) were loaded into the SLMs. The SLMs were formulated using a melt homogenization method and analysed using animal model standard methods. In vivo anti-inflammatory studies were performed using Wistar rats and showed stable formulations with spherical particles within the range of 35 ± 0.577 to 50 ± 1.527 μm. The encapsulation efficiency (EE) ranged from 43.20% to 89.03% and was significantly affected by the amount of drug loaded (p < 0.05). The formulations also exhibited a stable pH from 24 h to 2 months, meaning that there was no degradation of the active pharmaceutical ingredient (API) and the excipients. The in vitro drug release increased with the amount of drug loaded with an approximately 86% release at 600 min for formulations containing 0.5% drug, and 24% for formulations with 0.1% drug. Absorption of the SLMs was enhanced compared with a market formulation and the SLMs had better anti-inflammatory properties, which attests to the effects of the lipids at improving the oral absorption of piroxicam. Hence, piroxicam-loaded SLMs are a possible alternative to the current market formulations. [ABSTRACT FROM AUTHOR]

Two polysaccharide-based hydrogels made of only κ-carrageenan (4%; w/v) or of a mixture of methylcellulose:κ-carrageenan (2%; w/v) were used to encapsulate cationic nioplexes. These vesicular particles were made of a synthetic aminolipid and polysorbate-80 (Tween-80), as a non-ionic surfactant agent. According to oscillatory rheological measurements, the presence of nioplexes did not compromise the mechanical integrity of the gels. In vitro niosomal release experiments demonstrated the liberation of nioplexes up to 24 h, and the curves were fitted according to Higuchi, Korsmeyer–Peppas and Weibull equation models, which indicated Fickian-diffusion controlled mechanisms. Besides nioplexes, cervical cancer cells were also entrapped within the biohydrogels. Cell release confirmed that these materials did not affect the cell viability, allowing cells to spread and proliferate after 24 h. The applicability of these biocompatible hydrogels was also extended to gene delivery. In this regard, the best silencing activities were found when cationic niosomes were complexed with antisense oligonucleotides in KC hydrogels. Nioplexes were able to release through the hydrogel and promoted silencing of luciferase expression in the presence of serum without using commercially available cationic lipids. Overall, the formation of such hybrid materials by integrating cationic nioplexes within biodegradable hydrogels provides a new perspective for the delivery of macromolecular therapeutics. [ABSTRACT FROM AUTHOR]

The remarkable effect of anions on the transition from supramolecular gels to crystalline phases has been described. An amino acid-based metallohydrogel was transformed into different metal–organic frameworks through the selective picking of anions. The metallohydrogel and the resulting metal–organic frameworks (MOFs) were thoroughly characterized. The results demonstrated controlled access over the binding of a particular anion to selectively form a particular MOF. [ABSTRACT FROM AUTHOR]

In this feature article, we discuss a series of contributions dealing with the in situ fabrication of supramolecular metallogels (i.e. using low molecular weight ligands and metal ions) that show self-healing properties of the bulk gel phase after complete physical segregation. Most of the advances in this area have taken place during the last three years and are mainly represented by organogels, whereas examples of hydrogels and organic-aqueous gels are still a minority. In situ gelation via metal-coordination of low molecular weight compounds is conceptually different from the use of premade (e.g. in solution) coordination polymers and polymeric structures as gelators and ligands, respectively. In the case of in situ gelation, the cooperative effects of all components of the mixture (i.e. ligand, metal ion, counterions and solvent molecules) in an appropriate ratio under well-defined experimental conditions play a crucial role in the gelation phenomenon and self-healing properties of the material. [ABSTRACT FROM AUTHOR]

Progress in the chemical sciences has formed the world we live in, both on a macroscopic and on a nanoscopic scale. The last decade has witnessed the development of high performance materials that store charge in many ways: from solar cells to fuel cells, and from batteries to supercapacitor devices. One could argue that inorganic hybrid materials have played a central, starring role for the assembly of various electrochemical energy conversion systems. However, energy conversion systems fabricated from biopolymers has just emerged as a new prospect. Here, we summarize the main research results on the attractive use of biohydrogels for the fabrication of either conductive electrolytes or electrodes for battery science and technology. [ABSTRACT FROM AUTHOR]

Hydrogen-bonding organocatalysis has emerged as a promising biomimetic alternative to Lewis acid catalysis. Urea, thiourea and squaramide moieties represent the most common hydrogen-bond donors used for the preparation of these catalysts. However, their significant tendency to undergo self-quenching (self-aggregation) often decreases their solubility and reactivity. Recently, scientists have found a promising way around this problem by immobilizing the hydrogen-bonding organocatalysts on metal–organic frameworks (MOFs). Along with advantageous modular synthesis and recycling properties, the tunable porosity and topology of MOFs also allows fast mass transport and/or interactions with substrates. Herein, we highlight the existing examples dealing with the fabrication and testing of hydrogen-bonding organocatalyst-containing MOFs, providing also our vision for further advances in this area. The results derived from these studies will likely serve as inspiration for the future development of superior hydrogen-bonding organocatalysts to accomplish in confined spaces chemical transformations that are either slow or unaffordable under standard homogeneous conditions. [ABSTRACT FROM AUTHOR]

Solid-state organic electrochemical supercapacitors (OESCs) have been fabricated using poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes, a biohydrogel as electrolyte system, and polyaniline fibers as redox additive. The effectivity of sodium alginate, κ-carrageenan, chitosan and gelatin hydrogels as electrolytic media has been evaluated considering different criteria. Results indicate that κ-carrageenan-based hydrogel is the most suitable to perform as electrolyte due to the appropriate combination of properties: mechanical stability, ease of preparation, lack of water leaking, and good medium for the electrochemical response of PEDOT electrodes. Cyclic voltammetry and galvanostatic charge–discharge assays indicate that OESCs based on PEDOT electrodes and κ-carrageenan hydrogel as electrolyte exhibits a good supercapacitor response in terms of specific capacitance, cycling stability, small leakage current and low self-discharging tendency. On the basis of these good properties, four OESC devices were assembled in series and used to power a red LED, confirming that, in addition to advantageous characteristics (e.g. elimination of liquid leaking and enhancement of the device compactness), the designed biohydrogel-containing OESC exhibits potential for practical applications. On the other hand, preliminary assays have been performed loading the κ-carrageenan hydrogel with polyaniline nanofibers, which act as a redox additive. OESC devices prepared using such loaded biohydrogel have been found to be very promising and, therefore, future work is oriented towards the improvement of their design. [ABSTRACT FROM AUTHOR]

The first proof of concept for the application of intragel green-to-blue photon upconversion to a chemical reaction is reported. The developed method allows the photoreduction of aryl halides at room temperature under aerobic conditions. [ABSTRACT FROM AUTHOR]

Understanding and controlling phase transformations is a timely subject of investigation because they are essential for the fabrication of high-performance materials with applications in energy, sensors, biomedical, and information-related technologies. Such transformations at the nanoscale arise from both diffusion kinetics and surface thermodynamics, whose reasoning represents a major intellectual challenge in multicomponent systems. In particular, the study of interconversion routes between stable and metastable states provides a useful foundation for the rational design of hard and soft materials. Here, we highlight some recent studies that have demonstrated the possibility of transforming rigid (hard) MOFs into flexible (soft) gel materials in quantitative (or nearly quantitative) yields, and vice versa albeit involving different mechanisms and starting materials. These works represent a new paradigm in the growing areas of crystal engineering and stimuli-responsive gels by building new bridges between advanced functional materials that have been traditionally studied in very different research fields. [ABSTRACT FROM AUTHOR]

The delicate interface between gelation and crystallization can be exemplified using a multicomponent gelator solution (MGS-I) consisting of (1R,2R)-1,2-diaminocyclohexane l-tartrate (1) in MeOH (0.128 M) and concentrated HCl (2.4 equiv. with respect to 1). Solubilization of 1 occurs due to an ionic dissociation–exchange process induced by HCl. A transient chloride-containing assembly of 1 in solution, resembling that in its crystalline state, acts as a supramolecular synthon for the growth of gel networks in the presence of different organic solvents at low temperature. These gels have very short lifetimes (ca. 1–72 h in most cases) as a consequence of the thermodynamic formation of insoluble (1R,2R)-1,2-diaminocyclohexane dihydrochloride (2). However, a more robust formulation can be obtained by replacing MeOH with DMSO, which in the presence of HCl provides similar solubilization of diaminocyclohexane (DAC) tartrate salt 1, but it delays the destabilization of solvated supramolecular aggregates. The new formulation (MGS-II) offers a series of major advantages in comparison to MGS-I, such as the formation of homogeneous, transparent and more elastic gels within seconds at room temperature and at much lower concentrations. Moreover, MGS-II has high tolerance to the nature of the dicarboxylic acid derivative, which acts as an extender and a stabilizer of the physical network. Very interestingly, MGS-II can selectively gel solvents in multiphasic systems and can be also combined with warmed solutions of other gelators for the preparation of supramolecular hybrid gel systems with superior properties. [ABSTRACT FROM AUTHOR]

Two metallohydrogels based on an amino acid-based ligand and Zn(n) salts were synthesized. These hydrogels show an uncommon, reversible, time-dependent transformation from the opaque to transparent state. These hydrogels also exhibit gradual dissolution in water (pH < 7) over time. A water-soluble stimulant, caffeine, could be in situ loaded into the hydrogels and slowly released during dissolution. [ABSTRACT FROM AUTHOR]

Gold [Au(0)] nanoparticles immobilized into a stable covalent organic framework (COF) have been synthesized via the solution infiltration method. The as-synthesized Au(0)@TpPa-1 catalyst shows high recyclability and superior reactivity for nitrophenol reduction reaction than HAuCl4.3H2O. [ABSTRACT FROM AUTHOR]

The effectiveness of neutral pH chitosan hydrogel beads (CSHB) as a green organocatalyst for a variety of C–C bond forming reactions (i.e. aldol reaction, Knoevenagel condensation, nitroaldol (Henry) reaction, Michael addition) has been comprehensively evaluated. Reaction rates, conversions and selectivities were studied as a function of a series of input variables including size, pH and reactive surface area of the beads, catalyst loading, temperature, molecular weight of the biopolymer, concentration, solvent system and molar ratio of reactants. Moreover, the catalytic biohydrogel beads were characterized by a variety of techniques including, among others, SEM, FT-IR, TGA and DSC. [ABSTRACT FROM AUTHOR]

We describe a general user-friendly platform for fine-tuning the drug release properties of low-molecular-weight hydrogels by a combination of supramolecular co-assembly of complementary molecular structures and controlled photochemical thiol–ene cross-linking. Other critical features such as thermomechanical stability and morphology of the nanostructured hydrogels are also tailored by this approach. [ABSTRACT FROM AUTHOR]

As part of a continuing scientific challenge, a substantial effort during the past few decades has been devoted towards altering the selectivity of chemical transformations by arranging the potential reactants in a number of organized and confining media. Such systems, having features significantly different from those of isotropic solutions, include, for example, micelles, microemulsions, molecular aggregates, liquid crystals, and zeolites. Among these materials, stimuli-response gels constitute another important class of nanostructured and dynamic systems with high active surface areas and remarkable diffusion properties. Within this group, polymer gels have been traditionally used to obtain catalytic and reactive soft materials. Moreover, gels made of low-molecular-weight compounds represent a major novelty in this area as potential soft-vessels to carry out chemical reactions with control on product selectivity. In addition, the possibility of integrating switchable catalytic functions in both organo- and hydrogels shall accelerate the development of robust platforms for the ‘bottom–up’ tailor-fabrication of more sophisticated functional materials. The present critical reviewreports on the most important results published during the last decade regarding the use of ‘smart’ gels that has displayed promising properties as selective soft-nanoreactors and/or heterogeneous recyclable catalysts (152 references). [ABSTRACT FROM AUTHOR]

A series of octakis(alkyloxy)-substituted Zn(ii)-phthalocyanines were efficiently incorporated into an organogel made of (1R,2R)-trans-1,2-bis(dodecanoylamino)cyclohexane by means of multiple cooperative non-covalent interactions, and SEM revealed the formation of unique brush-like nanostructures. [ABSTRACT FROM AUTHOR]

Correction for ‘Highly selective metallogel from 4-biphenylcarboxy capped diphenylalanine and FeCl3’ by Supriya Sasmal et al., CrystEngComm, 2019, DOI: URL URL="HTTP://DX.DOI.ORG/10.1039/C9CE00695H"10.1039/c9ce00695h/URL. [ABSTRACT FROM AUTHOR]

Correction for ‘Highly selective metallogel from 4-biphenylcarboxy capped diphenylalanine and FeCl3’ by Supriya Sasmal et al., CrystEngComm, 2019, DOI: URL URL="HTTP://DX.DOI.ORG/10.1039/C9CE00695H"10.1039/c9ce00695h/URL. [ABSTRACT FROM AUTHOR]

A multiresponsive metallohydrogel based on an amino acid-derived low molecular weight (LMW) ligand and a Zn(II) salt was prepared. This hydrogel showed remarkable shape-persistent, self-standing, load-bearing and self-healing properties, which is uncommon in LMW hydrogels.