Mild Aqueous Conditions Research Articles

Postsynthesis and Effective Baeyer–Villiger Oxidation Properties of Hierarchical FAU-type Stannosilicate

Sn–Y zeolite, with hierarchical pore systems and extremely low Al content, was successfully prepared via a convenient postsynthetic route which involves proper predealumination and subsequent (NH4)2SnCl6 treatment under mild aqueous condition. The Sn ions were incorporated into the framework of properly dealuminated Y zeolite through reacting with the defect sites generated in the industrial steaming treatment, the first-step acid treatment, and the second Sn incorporation process under acidic conditions. The acidic medium achieved by adding HCl in the Sn incorporation process affected not only the amount of incorporated Sn and residual Al but also the coordination state of inserted Sn ions. Compared with hydrothermally synthesized Sn-Beta, postsynthesized Sn–Y zeolite exhibited outstanding catalytic performances in the Baeyer–Villiger oxidation reactions of ketones especially when bulky tert-butyl hydroperoxide was employed as the oxidant due to an open pore structure of 3-dimensional 12-membered ring (1...

"A novel highly stable and injectable hydrogel based on a conformationally restricted ultrashort peptide".

Nanostructures including hydrogels based on peptides containing non protein amino acids are being considered as platform for drug delivery because of their inherent biocompatibility and additional proteolytic stability. Here we describe instantaneous self-assembly of a conformationally restricted dipeptide, LeuΔPhe, containing an α,β-dehydrophenylalanine residue into a highly stable and mechanically strong hydrogel, under mild physiological aqueous conditions. The gel successfully entrapped several hydrophobic and hydrophilic drug molecules and released them in a controlled manner. LeuΔPhe was highly biocompatible and easily injectable. Administration of an antineoplastic drug entrapped in the gel in tumor bearing mice significantly controlled growth of tumors. These characteristics make LeuΔPhe an attractive candidate for further development as a delivery platform for various biomedical applications.

Catalytic Fehling's Reaction: An Efficient Aerobic Oxidation of Aldehyde Catalyzed by Copper in Water

AbstractThe first example of homogeneous copper‐catalyzed aerobic oxidation of aldehydes is reported. This method utilizes atmospheric oxygen as the sole oxidant, proceeds under extremely mild aqueous conditions, and covers a wide range of various functionalized aldehydes. Chromatography is generally not necessary for product purification.

Catalytic Fehling's Reaction: An Efficient Aerobic Oxidation of Aldehyde Catalyzed by Copper in Water.

The first example of homogeneous copper-catalyzed aerobic oxidation of aldehydes is reported. This method utilizes atmospheric oxygen as the sole oxidant, proceeds under extremely mild aqueous conditions, and covers a wide range of various functionalized aldehydes. Chromatography is generally not necessary for product purification.

Ruthenium-Catalyzed Methylation of Amines with Paraformaldehyde in Water under Mild Conditions.

Methylated amines are highly important for a variety of pharmaceutical and agrochemical applications. Existing routes for their formation result in the production of large amounts of waste or require high reaction temperatures, both of which impact the ecological and economical footprint of the methodologies. Herein, we report the ruthenium-catalyzed reductive methylation of a range of aliphatic amines, using paraformaldehyde as both substrate and hydrogen source, in combination with water. This reaction proceeds under mild aqueous reaction conditions. Additionally the use of a secondary phase for catalyst retention and recycling has been investigated with promising results.

Suzuki–Miyaura Cross-Coupling in Aqueous Medium Using Recyclable Palladium/Amide-Silica Catalyst

Silica-immobilized benzamide palladium complex was prepared and characterized. The complex exhibits excellent catalytic activity and stability for Suzuki–Miyaura cross-coupling reaction under mild aqueous reaction condition. Various aryl bromides were coupled with arylboronic acids in i-PrOH/H2O, under open air at room temperature, in the presence of 0.22 mol% of the catalyst to afford corresponding cross-coupled products in high yields. Furthermore, the novel heterogeneous catalyst can be conveniently recovered by simple filtration and reused several times without significant loss in activity.

N-terminal specific conjugation of extracellular matrix proteins to 2-pyridinecarboxaldehyde functionalized polyacrylamide hydrogels.

Polyacrylamide hydrogels have been used extensively to study cell responses to the mechanical and biochemical properties of extracellular matrix substrates. A key step in fabricating these substrates is the conjugation of cell adhesion proteins to the polyacrylamide surfaces, which typically involves nonspecifically anchoring these proteins via side-chain functional groups. This can result in a loss of presentation control and altered bioactivity. Here, we describe a new functionalization strategy in which we anchor full-length extracellular matrix proteins to polyacrylamide substrates using 2-pyridinecarboxaldehyde, which can be co-polymerized into polyacrylamide gels and used to immobilize proteins by their N-termini. This one-step reaction proceeds under mild aqueous conditions and does not require additional reagents. We demonstrate that these substrates can readily conjugate to various extracellular matrix proteins, as well as promote cell adhesion and spreading. Notably, this chemistry supports the assembly and cellular remodeling of large collagen fibers, which is not observed using conventional side-chain amine-conjugation chemistry.

Oxidation of 5-hydroxymethyl furfural to 2,5-diformylfuran in aqueous media over heterogeneous manganese based catalysts

Manganese-copper layered double hydroxides prepared following a conventional procedure were investigated for the selective oxidation of 5-hydroxymethyl-2-furfural into 2,5-diformylfuran. After checking the effect of the different parameters it has been found that a composition corresponding to Mn0.70Cu0.05Al0.25, of the catalyst already calcined, led to the highest conversion (90%) and selectivity (87% in DFF). Noteworthy, this has been achieved working under mild aqueous conditions (90°C and 8bars O2). The performances of the catalysts were closely associated to the strength of the basic sites.

Thiol-ene click hydrogels for therapeutic delivery.

Hydrogels are of growing interest for the delivery of therapeutics to specific sites in the body. For use as a delivery vehicle, hydrophilic precursors are usually laden with bioactive moieties and then directly injected to the site of interest for in situ gel formation and controlled release dictated by precursor design. Hydrogels formed by thiol-ene click reactions are attractive for local controlled release of therapeutics owing to their rapid reaction rate and efficiency under mild aqueous conditions, enabling in situ formation of gels with tunable properties often responsive to environmental cues. Herein, we will review the wide range of applications for thiol-ene hydrogels, from the prolonged release of anti-inflammatory drugs in the spine to the release of protein-based therapeutics in response to cell-secreted enzymes, with a focus on their clinical relevance. We will also provide a brief overview of thiol-ene click chemistry and discuss the available alkene chemistries pertinent to macromolecule functionalization and hydrogel formation. These chemistries include functional groups susceptible to Michael type reactions relevant for injection and radically-mediated reactions for greater temporal control of formation at sites of interest using light. Additionally, mechanisms for the encapsulation and controlled release of therapeutic cargoes are reviewed, including i) tuning the mesh size of the hydrogel initially and temporally for cargo entrapment and release and ii) covalent tethering of the cargo with degradable linkers or affinity binding sequences to mediate release. Finally, myriad thiol-ene hydrogels and their specific applications also are discussed to give a sampling of the current and future utilization of this chemistry for delivery of therapeutics, such as small molecule drugs, peptides, and biologics.

The partial oxidation of propane under mild aqueous conditions with H2O2 and ZSM-5 catalysts

We report the oxidation of propane under mild aqueous conditions using H2O2 as the oxidant.

Novel chemoselective (18)F-radiolabeling of thiol-containing biomolecules under mild aqueous conditions.

We report a novel prosthetic group based on a heterocyclic methylsulfone derivative for the rapid, stable, and chemoselective (18)F-labeling of thiol-containing (bio)molecules under mild aqueous reaction conditions. Compared to established maleimide approaches, the new methodology displays some clear advantages for imaging probe development.

Iminoboronates are efficient intermediates for selective, rapid and reversible N-terminal cysteine functionalisation.

We show that formyl benzeno boronic acids (2FBBA) selectively react with N-terminal cysteines to yield a boronated thiazolidine featuring a B-N bond. The reaction exhibits a very rapid constant rate (2.38 ± 0.23 × 102 M-1 s-1) under mild aqueous conditions (pH 7.4, 23 °C) and tolerates different amino acids at the position adjacent to the N-cysteine. DFT calculations highlighted the diastereoselective nature of this ligation reaction and support the involvement of the proximal boronic acid in the activation of the imine functionality and the stabilisation of the boronated thiazolidine through a chelate effect. The 2FBBA reagent allowed the effective functionalisation of model peptides (C-ovalbumin and a laminin fragment) and the boronated thiazolidine construct was shown to be stable over time, though the reaction was reversible in the presence of benzyl hydroxylamine. The reaction proved to be highly chemoselective, and 2FBBA was used to functionalize the N-terminal cysteine of calcitonin in the presence of a potentially competing in-chain thiol group. This exquisite selectivity profile enabled the dual functionalisation of calcitonin and the interactive orthogonal modification of this peptide when 2FBBA was combined with conventional maleimide chemistry. These results highlight the potential of this methodology to construct complex and well-defined bioconjugates.

Aerosol-assisted synthesis of mesoporous aluminosilicate microspheres: the effect of the aluminum precursor

Spray-dried mesoporous aluminosilicates, with spherical morphology, high surface area and accessible porosity, have been synthesized under mild acidic aqueous conditions by using different aluminum precursors.

Low temperature selective oxidation of methane to methanol using titania supported gold palladium copper catalysts

Selective oxidation of methane using AuPdCu/TiO2 catalysts.

Peptide Bond Formation in Water Mediated by Carbon Disulfide.

Demonstrating plausible nonenzymatic polymerization mechanisms for prebiotic monomers represents a fundamental goal in prebiotic chemistry. While a great deal is now known about the potentially prebiotic synthesis of amino acids, our understanding of abiogenic polymerization processes to form polypeptides is less well developed. Here, we show that carbon disulfide (CS2), a component of volcanic emission and sulfide mineral weathering, and a widely used synthetic reagent and solvent, promotes peptide bond formation in modest yields (up to ∼20%) from α-amino acids under mild aqueous conditions. Exposure of a variety of α-amino acids to CS2 initially yields aminoacyl dithiocarbamates, which in turn generate reactive 2-thiono-5-oxazolidone intermediates, the thio analogues of N-carboxyanhydrides. Along with peptides, thiourea and thiohydantoin species are produced. Amino acid stereochemistry was preserved in the formation of peptides. Our findings reveal that CS2 could contribute to peptide bond formation, and possibly other condensation reactions, in abiogenic settings.

Silk fibroin/copolymer composite hydrogels for the controlled and sustained release of hydrophobic/hydrophilic drugs

In the present study, a composite system for the controlled and sustained release of hydrophobic/hydrophilic drugs is described. Composite hydrogels were prepared by blending silk fibroin (SF) with PLA–PEG–PLA copolymer under mild aqueous condition. Aspirin and indomethacin were incorporated into SF/Copolymer hydrogels as two model drugs with different water-solubility. The degradation of composite hydrogels during the drug release was mainly caused by the hydrolysis of copolymers. SF with stable β-sheet-rich structure was not easily degraded which maintained the mechanical integrity of composite hydrogel. The hydrophobic/hydrophilic interactions of copolymers with model drugs would significantly alter the morphological features of composite hydrogels. Various parameters such as drug load, concentration ratio, and composition of copolymer were considered in vitro drug release. Aspirin as a hydrophilic drug could be controlled release from composite hydrogel at a constant rate for 5 days. Its release was mainly driven by diffusion-based mechanism. Hydrophobic indomethacin could be encapsulated in copolymer nanoparticles distributing in the composite hydrogel. Its sustained release was mainly degradation controlled which could last up to two weeks. SF/Copolymer hydrogel has potential as a useful composite system widely applying for controlled and sustained release of various drugs.

Chemoenzymatic Synthesis of Optically Pure l- and d-Biarylalanines through Biocatalytic Asymmetric Amination and Palladium-Catalyzed Arylation

A chemoenzymatic approach was developed and optimized for the synthesis of a range of N-protected nonnatural l- and d-biarylalanine derivatives. Starting from 4-bromocinnamic acid and 4-bromophenylpyruvic acid using a phenylalanine ammonia lyase (PAL) and an evolved d-amino acid dehydrogenase (DAADH), respectively, both enantiomers of 4-bromophenylalanine were obtained and subsequently coupled with a panel of arylboronic acids to give the target compounds in high yield and optical purity under mild aqueous conditions.

ChemInform Abstract: Silver‐Catalyzed Double‐Decarboxylative Cross‐Coupling of α‐Keto Acids with Cinnamic Acids in Water: A Strategy for the Preparation of Chalcones.

AbstractThe coupling fails when either aliphatic α‐keto acids or crotonic acid are used.

Design and Synthesis of Water-Soluble Multifunctionalizable Thiol-Reactive Polymeric Supports for Cellular Targeting.

Design and synthesis of novel water-soluble polymers bearing reactive side chains are actively pursued due to their increasing demand in areas such as bioconjugation and drug delivery. This study reports the fabrication of poly(ethylene glycol) methacrylate based thiol-reactive water-soluble polymeric supports that can serve as targeted drug delivery vehicles. Thiol-reactive maleimide units were incorporated into polymers as side chains by use of a furan-protected maleimide containing monomer. Atom transfer radical polymerization (ATRP) was employed to obtain a family of well-defined copolymers with narrow molecular weight distributions. After the polymerization, the maleimide groups were activated to their reactive form, ready for conjugation with thiol-containing molecules. Efficient functionalization of the maleimide moieties was demonstrated by conjugation of a tripeptide glutathione under mild and reagent-free aqueous conditions. Additionally, hydrophobic thiol-containing dye (Bodipy-SH) and a cyclic peptide-based targeting group (cRGDfC) were sequentially appended onto the maleimide bearing polymers to demonstrate their efficient multifunctionalization. The conjugates were utilized for in vitro experiments over both cancerous and healthy breast cell lines. Obtained results demonstrate that the conjugates were nontoxic, and displayed efficient cellular uptake. The presence of the peptide based targeting group had a clear effect on increasing the uptake of the dye-conjugated polymers into cells when compared to the construct devoid of the peptide. Overall, the facile synthesis and highly efficient multifunctionalization of maleimide-containing thiol-reactive copolymers offer a novel and attractive class of polyethylene glycol-based water-soluble supports for drug delivery.

Atmospheric-Pressure Plasma Deposited Epoxy-Rich Thin Films as Platforms for Biomolecule Immobilization-Application for Anti-Biofouling and Xenobiotic-Degrading Surfaces

In this work, an atmospheric-pressure dielectric barrier discharge process is exploited for the fast deposition of adherent epoxy-rich layers acting as a versatile platform for the efficient one-step biomolecule immobilization in mild aqueous conditions. Particular attention is given to the influence of the plasma process parameters on the chemical and morphological properties of the deposited layers and on their subsequent exploitation for chemical interfacial reactions. As a proof-of-concept, two enzymes with drastically different biological properties, namely dispersin B and a laccase, are immobilized onto functionalized metallic surfaces. The pH of the enzyme solution appears as a key parameter to control the amount of immobilized enzyme on the plasma functionalized surfaces, thus leading to bioactive surfaces with improved stability and activity.