Boosting Effect of Sterically Protected Glucosyl Substituents in Formic Acid Dehydrogenation by Iridium(III) 2-Pyridineamidate Catalysts.

[Cp*Ir(R-pica)Cl] (Cp*=pentamethylcyclopentadienyl anion, pica=2-picolineamidate) complexes bearing carbohydrate substituents on the amide nitrogen atom (R=methyl-ß-D-gluco-pyranosid-2-yl, 1; methyl-3,4,6-tri-O-acetyl-ß-D-glucopyranosid-2-yl, 2) were tested as catalysts for formic acid dehydrogenation in water. TOFMAX values over 12000 h-1 and 50000 h-1 were achieved at 333 K for 1 and 2, respectively, with TON values over 35000 for both catalysts. Comparison with the simpler cyclohexyl-substituted analogue (3) indicated that glucosyl-based complexes are much better performing under the same experimental conditions (TOFMAX=5144 h-1, TON=5000 at pH 2.5 for 3) owing to a lower tendency to isomerize to the less active k2-N,O isomer upon protonation. The 5-fold increase in TOFMAX observed for 2 with respect to 1 is reasonably due to an optimal steric protection by the acetyl substituent, which may prevent unproductive inner-sphere reactivity. These results showcase a powerful strategy for the inhibition of the common deactivation pathways of [Cp*Ir(R-pica)X] catalysts for FA dehydrogenation, paving the way for the development of better performing hydrogen storage systems.

Heterogeneous Brønsted Catalysis in the Solvent-Free and Multigram-Scale Synthesis of Polyalcohol Acrylates: The Case Study of Trimethylolpropane Triacrylate.

This article presents a thorough investigation into the synthesis of trimethylolpropane triacrylate (TMPTA) via the esterification reaction of trimethylolpropane (TMP) with acrylic acid using Amberlite™ 120 IR (H+), Amberlyst® 15, and Dowex™ 50WX8 resins as heterogeneous catalysts. Preliminary comparative tests explored the impact of air flow on water removal during the reaction and different acid-to-alcohol molar ratios (3:1, 6:1, or 9:1 mol:mol). The findings revealed that introducing air significantly enhances TMPTA yield and -OH group conversion, particularly at a 6:1 acid-to-alcohol molar ratio. Based on cost considerations, Amberlite™ 120 IR (H+) was selected as the preferred catalyst for further optimization. This included evaluating the effect of catalyst loading (10%, 5.0%, and 2.5% w/wtot) and assessing the impact of a pre-drying process on resin efficiency. The study concluded that optimal conditions did not necessitate drying, requiring 120 °C, a catalyst loading of 10% w/wtot, a 4 h reaction time, an acid:alcohol ratio of 6:1 mol:mol, the presence of MEHQ (0.1% mol/molAA), and air bubbling at 6 ± 1 Nl/h. Catalyst recycling was effectively implemented with a slight reduction in catalytic activity over consecutive runs. Furthermore, the study explored a scaled-up system with a mechanical stirrer, demonstrating the potential for multi-hundred grams scale-up. Considerations for optimizing the air flow stripping system are also highlighted. In summary, this study provides valuable insights into designing and optimizing the esterification process for TMPTA synthesis, laying the foundation for potential industrial applications.

Fluorine-Free Lithium-Ion Capacitor with Enhanced Sustainability and Safety Based on Bio-Based Æ´-Valerolactone and Lithium Bis(Oxalato)Borate Electrolyte.

In this work, the properties of a novel electrolyte based on the combination of bio-based Æ´-valerolactone (GVL) solvent with lithium bis(oxalato)borate (LiBOB) salt and its use for lithium-ion capacitors (LICs) are presented. It is shown that the 1 m LiBOB in GVL electrolyte displays good transport properties, high thermal stability, and the ability to prevent anodic dissolution. Its impact on the performance of both battery-type and capacitive-type electrodes is evaluated. In this regard, special attention is paid to the filming properties associated with LiBOB and GVL decomposition at the electrode surfaces. To the best of the authors' knowledge, the full-cell devices assembled in this study are the first example of a fluorine-free LIC. These devices exhibit a favorable energy-to-power ratio, delivering 80 Wh kg-1 AM at 10 000 W kg-1 AM along with excellent cycling stability, retaining 80% of the initial capacitance after 25 000 cycles. Furthermore, post-mortem analysis of the LIC electrodes is conducted to gain deeper insights into the degradation mechanisms within the device.

The Role of Inverted Ligand Field in the Electronic Structure and Reactivity of Octahedral Formal Platinum (IV) Complexes.

Platinum complexes are ubiquitous in chemistry and largely used as catalysts or as precursors in drug chemistry, thus a deep knowledge of their electronic properties may help in planning new synthetic strategies or exploring new potential applications. Herein, the electronic structure of many octahedral platinum complexes is drastically revised especially when they feature electronegative elements such as halogens and chalcogens. The investigation revealed that in most cases the five d platinum orbitals are invariably full, thus the empty antibonding orbitals, usually localized on the metal, are mainly centered on the ligands, suggesting a questionable assignment of formal oxidation state IV. The analysis supports the occurrence of the inverted ligand field theory in all cases with the only exceptions of the Pt-F and Pt-O bonding. The trends for the molecular complexes are mirrored also by the density of states plots of extended structures featuring octahedral platinum moieties in association with chalcogens atoms. Finally, the oxidative addition of a Se-Cl linkage to a square platinum complex to achieve an octahedral moiety has been revised in the framework of the inverted ligand field.

Ruthenium complexes bearing glucosyl ligands are able to inhibit the amyloid aggregation of short histidine-peptides.

Neurodegenerative diseases are often characterized by the formation of aggregates of amyloidogenic peptides and proteins, facilitating the formation of neurofibrillary plaques. In this study, we investigate a series of Ru-complexes sharing three-legged piano-stool structures based on the arene ring and glucosylated carbene ligands. The ability of these complexes to bind amyloid His-peptides was evaluated by ESI-MS, and their effects on the aggregation process were investigated through ThT and Tyr fluorescence emission. The complexes were demonstrated to bind the amyloidogenic peptides even with different mechanisms and kinetics depending on the chemical nature of the ligands around the Ru(II) ion. TEM analysis detected the disaggregation of typical fibers caused by the presence of Ru-compounds. Overall, our results show that the Ru-complexes can modulate the aggregation of His-amyloids and can be conceived as good lead compounds in the field of novel anti-aggregating agents in neurodegeneration.

Impact of Hydrophobic Chains in Five-Coordinate Glucoconjugate Pt(II) Anticancer Agents.

This study describes new platinum(II) cationic five-coordinate complexes (1-R,R') of the formula [PtR(NHC)(dmphen)(ethene)]CF3SO3 (dmphen = 2,9-dimethyl-1,10-phenanthroline), containing in their axial positions an alkyl group R (methyl or octyl) and an imidazole-based NHC-carbene ligand with a substituent R' of variable length (methyl or octyl) on one nitrogen atom. The Pt-carbene bond is stable both in DMSO and in aqueous solvents. In DMSO, a gradual substitution of dmphen and ethene is observed, with the formation of a square planar solvated species. Octanol/water partitioning studies have revealed the order of hydrophobicity of the complexes (1-Oct,Me > 1-Oct,Oct > 1-Me,Oct > 1-Me,Me). Their biological activity was investigated against two pairs of cancer and non-cancer cell lines. The tested drugs were internalized in cancer cells and able to activate the apoptotic pathway. The reactivity of 1-Me,Me with DNA and protein model systems was also studied using UV-vis absorption spectroscopy, fluorescence, and X-ray crystallography. The compound binds DNA and interacts in various ways with the model protein lysozyme. Remarkably, structural data revealed that the complex can bind lysozyme via non-covalent interactions, retaining its five-coordinate geometry.

γ-Valerolactone as Sustainable and Low-Toxic Solvent for Electrical Double Layer Capacitors.

In this work, γ-valerolactone (GVL), a green solvent based on largely available biomass (carbohydrates), highly biodegradable, and with low eco-toxicological profile, was used as electrolyte component in energy storage devices. This solvent allowed the realization of electrolytes with good transport properties and high thermal stability, which could be successfully applied in electrical double layer capacitors (EDLCs). GVL-based EDLCs could operate at 2.7-2.9 V and displayed good performance in term of capacitance, cycling stability, as well as specific energy and power. The results of this study indicate that the use of solvent obtained from largely available natural sources is a feasible strategy for the realization of sustainable and safe electrolytes for EDLCs.

Sustainable Ketalization of Glycerol with Ethyl Levulinate Catalyzed by the Iron(III)-Based Metal-Organic Framework MIL-88A.

The catalytic properties of a simple iron-containing MOF based on fumaric acid, MIL-88A, were investigated in the ketalization of ethyl levulinate with glycerol. The corresponding product is a component of current interest as a renewable building block for many uses. Under the following conditions (solventless, 120 °C, stoichiometric ratio, 1% cat.), the reaction proceeds with good yields (85%), and the catalyst can be recovered and recycled without loss of activity, despite some changes in the crystalline lattice and morphology. Moreover, the residual iron content in the product is in the order of units of ppm (≤2), which demonstrates the robustness of the MOF under the reaction conditions.

Halo complexes of gold(I) containing glycoconjugate carbene ligands: synthesis, characterization, cytotoxicity and interaction with proteins and DNA model systems.

New neutral carbene complexes of gold(I) [Au(Im-Me)X] (X = Cl, Au1; X = Br, Au2; X = I, Au3) have been synthesized and fully characterized by different techniques, including NMR and UV-vis absorption spectroscopy and single crystal X-ray diffraction. The carbene ligand Im-Me is decorated with a glucoside fragment via a triazole linker, obtainable through a click chemistry reaction. The compounds retain the Au-NHC fragment in aqueous solvents, and an equilibrium between the neutral halo- and the cationic di-carbene form [Au(Im-Me)2]+ is observed, whose extent follows the trend Au1 < Au2 < Au3. Cytotoxicity studies on two cancer and two non-tumorigenic cell lines reflect the solution behavior, as a certain difference among the complexes was disclosed, with the iodo complex Au3 being more active and selective. The compounds interact with both DNA and protein model systems. The X-ray structure of the adduct formed upon the reaction of Au1 with bovine pancreatic ribonuclease (RNase A) reveals Au binding at the side chain of His105 of both protein molecules A and B of the asymmetric unit. The binding of gold atoms at both the nitrogen atoms of the imidazole ring of His15 and at the N-terminal tail has been found in the adduct formed with hen egg white lysozyme.

Glucosyl Platinum(II) Complexes Inhibit Aggregation of the C-Terminal Region of the Aß Peptide.

Neurodegenerative diseases are often caused by uncontrolled amyloid aggregation. Hence, many drug discovery processes are oriented to evaluate new compounds that are able to modulate self-recognition mechanisms. Herein, two related glycoconjugate pentacoordinate Pt(II) complexes were analyzed in their capacity to affect the self-aggregation processes of two amyloidogenic fragments, Aß21-40 and Aß25-35, of the C-terminal region of the ß-amyloid (Aß) peptide, the major component of Alzheimer's disease (AD) neuronal plaques. The most water-soluble complex, 1Ptdep, is able to bind both fragments and to deeply influence the morphology of peptide aggregates. Thioflavin T (ThT) binding assays, electrospray ionization mass spectrometry (ESI-MS), and ultraviolet-visible (UV-vis) absorption spectroscopy indicated that 1Ptdep shows different kinetics and mechanisms of inhibition toward the two sequences and demonstrated that the peptide aggregation inhibition is associated with a direct coordinative bond of the compound metal center to the peptides. These data support the in vitro ability of pentacoordinate Pt(II) complexes to inhibit the formation of amyloid aggregates and pave the way for the application of this class of compounds as potential neurotherapeutics.

Lignin/Carbohydrate Complex Isolated from Posidonia oceanica Sea Balls (Egagropili): Characterization and Antioxidant Reinforcement of Protein-Based Films.

A lignin fraction (LF) was extracted from the sea balls of Posidonia oceanica (egagropili) and extensively dialyzed and characterized by FT-IR and NMR analyses. LF resulted water soluble and exhibited a brownish-to-black color with the highest absorbance in the range of 250-400 nm, attributed to the chromophore functional groups present in the phenylpropane-based polymer. LF high-performance size exclusion chromatography analysis showed a highly represented (98.77%) species of 34.75 kDa molecular weight with a polydispersity index of 1.10 and an intrinsic viscosity of 0.15. Quantitative analysis of carbohydrates indicated that they represented 28.3% of the dry weight of the untreated egagropili fibers and 72.5% of that of LF. In particular, eight different monosaccharides were detected (fucose, arabinose, rhamnose, galactose, glucose, xylose, glucosamine and glucuronic acid), glucuronic acid (46.6%) and rhamnose (29.6%) being the most present monosaccharides in the LF. Almost all the phenol content of LF (113.85 ± 5.87 mg gallic acid eq/g of extract) was water soluble, whereas around 22% of it consisted of flavonoids and only 10% of the flavonoids consisted of anthocyanins. Therefore, LF isolated from egagropili lignocellulosic material could be defined as a water-soluble lignin/carbohydrate complex (LCC) formed by a phenol polymeric chain covalently bound to hemicellulose fragments. LCC exhibited a remarkable antioxidant activity that remained quite stable during 6 months and could be easily incorporated into a protein-based film and released from the latter overtime. These findings suggest egagropili LCC as a suitable candidate as an antioxidant additive for the reinforcement of packaging of foods with high susceptibility to be deteriorated in aerobic conditions.

Square-Planar vs. Trigonal Bipyramidal Geometry in Pt(II) Complexes Containing Triazole-Based Glucose Ligands as Potential Anticancer Agents.

This article describes the synthesis, characterization, and biological activity of novel square-planar cationic platinum(II) complexes containing glucoconjugated triazole ligands and a comparison with the results obtained from the corresponding five-coordinate complexes bearing the same triazole ligands. Stability in solution, reactivity with DNA and small molecules of the new compounds were evaluated by NMR, fluorescence, and UV-vis absorption spectroscopy, together with their cytotoxic action against pairs of immortalized and tumorigenic cell lines. The results show that the square-planar species exhibit greater stability than the corresponding five-coordinate ones. Furthermore, although the square-planar complexes are less cytotoxic than the latter ones, they exhibit a certain selectivity. These results simultaneously demonstrate that overall stability is a fundamental prerequisite for preserving the performance of the agents and that coordinative saturation constitutes a point in favor of their biological action.

Homogeneous Catalysis and Heterogeneous Recycling: A Simple Zn(II) Catalyst for Green Fatty Acid Esterification.

This work describes the use of simple zinc(II) salts (ZnCl2, ZnCO3, Zn(OAc)2, ZnO, Zn(ClO4)2, Zn(TfO)2, and Zn(BF4)2) as effective catalysts for the esterification of fatty acids with long-chain alcohols and simple polyols through a homogeneous system that allows the gradual and selective removal of water. The results show that the catalytic activity depends on the nature of the counterion: the most effective are the salts with poorly coordinating anions (perchlorate and triflate) or containing basic Brønsted anions (oxide, acetate, and carbonate). However, only with the latter is it possible to fully recover the catalyst at the end of each run, which is easily filtered in the form of zinc carboxylate, given its insolubility in the ester produced. In this way, it is possible to recycle the catalyst numerous times, without any loss of activity. This beneficial prerogative couples the efficiency of the homogeneous catalysis with the advantage of the heterogeneous catalysis. The process is, therefore, truly sustainable, given its high efficiency, low energy consumption, ease of purification, and the absence of auxiliary substances and byproducts.

Synthesis and Biological Studies on Dinuclear Gold(I) Complexes with Di-(N-Heterocyclic Carbene) Ligands Functionalized with Carbohydrates.

The design of novel metal complexes with N-heterocyclic carbene (NHC) ligands that display biological activity is an active research field in organometallic chemistry. One of the possible approaches consists of the use of NHC ligands functionalized with a carbohydrate moiety. Two novel Au(I)-Au(I) dinuclear complexes were synthesized; they present a neutral structure with one bridging diNHC ligand, having one or both heterocyclic rings decorated with a carbohydrate functionality. With the symmetric diNHC ligand, the dicationic dinuclear complex bearing two bridging diNHC ligands was also synthesized. The study was completed by analyzing the antiproliferative properties of these complexes, which were compared to the activity displayed by similar mononuclear Au(I) complexes and by the analogous bimetallic Au(I)-Au(I) complex not functionalized with carbohydrates.

Glutamic Acid as Repeating Building Block for Bio-Based Films.

Commercial inexpensive preparations of poly-γ-glutamic acid were used to obtain films made with a polypeptide constituted by a single repeating unit. The homopolymer was characterized by 1H-NMR spectroscopy and thermogravimetry, as well as by zeta potential and Z-average measurements. Manipulatable materials were obtained by casting film-forming solutions prepared at pH values between 3.0 and 4.0 and containing extensively dialyzed samples of the commercial product. The analysis of the mechanical properties highlighted a marked extensibility and plasticity of the films obtained without plasticizer, even though the addition of low amounts of glycerol (1-4%) was able to further increase these features. The characterization of poly-γ-glutamic acid molecular species, performed by membrane ultrafiltration and size-exclusion chromatography, coupled with triple-detection analysis of the obtained fractions, suggested that biopolymer chain length is responsible not only for its capacity to form film, but also for conferring to the films different features depending on the homopolymer molecular weight.

Pt(II) versus Pt(IV) in Carbene Glycoconjugate Antitumor Agents: Minimal Structural Variations and Great Performance Changes.

Octahedral Pt(IV) complexes (2Pt-R) containing a glycoconjugate carbene ligand were prepared and fully characterized. These complexes are structural analogues to the trigonal bipyramidal Pt(II) species (1Pt-R) recently described. Thus, an unprecedented direct comparison between the biological properties of Pt compounds with different oxidation states and almost indistinguishable structural features was performed. The stability profile of the novel Pt(IV) compounds in reference solvents was determined and compared to that of the analogous Pt(II) complexes. The uptake and antiproliferative activities of 2Pt-R and 1Pt-R were evaluated on the same panel of cell lines. DNA and protein binding properties were assessed using human serum albumin, the model protein hen egg white lysozyme, and double stranded DNA model systems by a variety of experimental techniques, including UV-vis absorption spectroscopy, fluorescence, circular dichroism, and electrospray ionization mass spectrometry. Although the compounds present similar structures, their in-solution stability, cellular uptake, and DNA binding properties are diverse. These differences may represent the basis of their different cytotoxicity and biological activity.

Covalent Immobilization of ß-Glucosidase into Mesoporous Silica Nanoparticles from Anhydrous Acetone Enhances Its Catalytic Performance.

An immobilization protocol of a model enzyme into silica nanoparticles was applied. This protocol exploited the use of the bifunctional molecule triethoxysilylpropylisocyanate (TEPI) for covalent binding through a linker of suitable length. The enzyme ß-glucosidase (BG) was anchored onto wrinkled silica nanoparticles (WSNs). BG represents a bottleneck in the conversion of lignocellulosic biomass into biofuels through cellulose hydrolysis and fermentation. The key aspect of the procedure was the use of an organic solvent (anhydrous acetone) in which the enzyme was not soluble. This aimed to restrict its conformational changes and thus preserve its native structure. This approach led to a biocatalyst with improved thermal stability, characterized by high immobilization efficiency and yield. It was found that the apparent KM value was about half of that of the free enzyme. The Vmax was about the same than that of the free enzyme. The biocatalyst showed a high operational stability, losing only 30% of its activity after seven reuses.

Iron(III) Complexes for Highly Efficient and Sustainable Ketalization of Glycerol: A Combined Experimental and Theoretical Study.

The growing production of biodiesel as a promising alternative and renewable fuel led as the main problem the dramatic increase of its by-product: glycerol. Different strategies for glycerol derivatization have been reported so far, some more efficient or sustainable than others. Herein, we report a very promising and eco-friendly transformation of glycerol in nontoxic solvents and chemicals (i.e., solketal, ketals), proposing three new families of Fe(III) compounds capable of catalysing glycerol acetalization with unpublished turn over frequencies (TOFs), and adhering most of the principles of green chemistry. The comparison between the activity of complexes of formula [FeCl3(1-R)] (1-R = substituted pyridinimine), [FeCl(2-R,R')] (2-R,R' = substituted O,O'-deprotonated salens) and their corresponding simple salts reveals that the former are extremely convenient because they are able to promote solketal formation with excellent TOFs, up to 105 h-1. Satisfactory performances were shown with respect to the entire range of substrates, with results being competitive to those reported in the literature so far. Moreover, the experimental activity was supported by an accurate and complete ab initio study, which disclosed the fundamental role of iron(III) as Lewis acid in promoting the catalytic activity. The unprecedented high activity and the low loading of the catalyst, combined with the great availability and the good eco-toxicological profile of iron, foster future applications of this catalytic process for the sustainable transformation of an abundant by-product in a variety of chemicals.

A highly efficient and selective antitumor agent based on a glucoconjugated carbene platinum(ii) complex.

New five-coordinate Pt(ii) complexes containing a glycosylated carbene fragment were synthesized. A member of this class shows very high in vitro cytotoxicity and an exceptional selectivity toward malignant cells. The complex lacking the sugary portion fails in the recognition of cancer cells. The results support the use of glycosylation in the design of carbene Pt-based anticancer agents.

Reaction with Proteins of a Five-Coordinate Platinum(II) Compound.

Stable five-coordinate Pt(II) complexes have been highlighted as a promising and original platform for the development of new cytotoxic drugs. Their interaction with proteins has been scarcely studied. Here, the reactivity of the five-coordinate Pt(II) compound [Pt(I)(Me) (dmphen)(olefin)] (Me = methyl, dmphen = 2,9-dimethyl-1,10-phenanthroline, olefin = dimethylfumarate) with the model proteins hen egg white lysozyme (HEWL) and bovine pancreatic ribonuclease (RNase A) has been investigated by X-ray crystallography and electrospray ionization mass spectrometry. The X-ray structures of the adducts of RNase A and HEWL with [Pt(I)(Me)(dmphen)(olefin)] are not of very high quality, but overall data indicate that, upon reaction with RNase A, the compound coordinates the side chain of His105 upon releasing the iodide ligand, but retains the pentacoordination. On the contrary, upon reaction with HEWL, the trigonal bi-pyramidal Pt geometry is lost, the iodide and the olefin ligands are released, and the metal center coordinates the side chain of His15 probably adopting a nearly square-planar geometry. This work underlines the importance of the combined use of crystallographic and mass spectrometry techniques to characterize, in detail, the protein⁻metallodrug recognition process. Our findings also suggest that five-coordinate Pt(II) complexes can act either retaining their uncommon structure or functioning as prodrugs, i.e., releasing square-planar platinum complexes as bioactive species.