Micellar catalysis using a photochromic surfactant: application to the Pd-catalyzed Tsuji-Trost reaction in water

Manipulation of artificial and living small objects by light driven diffusioosmotic flow

Here we report on light-triggered generation of local flow utilizing a bio-compatible non-ionic photo-active surfactant. The mechanism is based on diffusioosmotic phenomenon, where the gradient of relative concentration with respect to different chemical species near a surface leads to an osmotic pressure gradient driving liquid flow along the surface. The application of a photo-responsive surfactant allows for easy and reversible changes in concentration gradient by positioning a light source at the desired place. Along with the so-inscribed concentration gradient one can change reversible the direction and strength of the flow even in a closed system. The phenomenology of light-driven diffusioosmotic flow (LDDO) can be used in a rather flexible way: colloids can be gathered or dispersed and bio-compatibility extends the range of colloid types also to living microorganisms such as soil bacterium Pseudomonas putida. We show that DO flow can be considered a versatile method to set hydrodynamic conditions along the sample for investigating the motility of living cells. Further advantages of employing LDDO are the flexibility of flow generation in a reversible way and with spatiotemporal control, without the need to either change the channel geometry by loading a different device, or the periphery of pumps and connectors.

Photochemical cyclopropanation in aqueous micellar media - experimental and theoretical studies

While in nature, reactions occur in water-based confined compartments, for a long time, water has been often regarded as an unsuitable medium for organic reactions. We have, however, found that photochemical cyclopropanation of styrenes with diazo compounds or their precursors can be performed in micellar systems. COSMO-RS studies revealed that the reactivity correlates with the predicted critical micelle concentration (CMC), with higher CMC values delivering higher yields.

Transfer hydrogenation of ketone; an in situ approach toward an eco-friendly reduction

The use of water as a solvent in chemical reactions has recently been brought to public attention, especially in the exploration of eco-friendly procedures. It is readily available, abundantly accessible, non-toxic, non-flammable, and at a low cost. As opposed to the previous limitation of reactant solubilities associated with aqueous media, a hydrogel such as a hydroxypropyl methylcellulose (HPMC) solution can significantly improve the reactant solubility. This investigation employed water and HPMC as the reaction solvent, and the reaction medium viscosity was impressively enhanced. Silica-supported Pd particles (Pd@SiO₂) were synthesized and effectively catalyzed the reduction of acetophenone in the presence of sodium borohydride (NaBH₄) as the hydrogen source. The conversion of acetophenone to 1-phenyl ethanol remained at a very high value of >99.34% with 100% selectivity towards 1-phenyl ethanol.

The use of water as a solvent in chemical reactions has recently been brought to public attention, especially in the exploration of eco-friendly procedures.

Green protocols for Tsuji–Trost allylation: an overview

Since its inception in 1960s, the Tsuji–Trost reaction, an allylic substitution reaction with diverse nucleophiles such as phenols, amines, thiols, and active methylene compounds, has remained as one of the most useful and widely used organic reactions for the construction of C–C and C–heteroatom bonds. Allylic compounds such as allylic acetates, alcohols, halides, and carbonates undergo this transformation which plays an important role in the total synthesis of various natural products. The competence to incorporate synthetically demanding allylic functionalities makes it a beneficial tool for the synthesis of complex molecules. Over the last two decades, major advancements for this unique and facile Tsuji–Trost allylation reaction have been made with special emphasis to develop greener and sustainable protocols. This chapter presents an update on the significant progress focusing on the newly designed catalytic systems with high efficiency, the use of eco-friendly solvents or solvent-free conditions, low or room temperature conditions and waste management, along with future outlook.

Azo-Dyes-Grafted Oligosaccharides-From Synthesis to Applications

Azobenzenes are photochromic molecules that possess a large range of applications. Their syntheses are usually simple and fast, and their purifications can be easy to perform. Oligosaccharide is also a wide family of biopolymer constituted of linear chain of saccharides. It can be extracted from biomass, as for cellulose, being the principal constituent of plant cell wall, or it can be enzymatically produced as for cyclodextrins, having properties not far from cellulose. Combining these two materials families can afford interesting applications such as controlled drug-release systems, photochromic liquid crystals, photoresponsive films or even fluorescent indicators. This review will compile the different syntheses of azo-dyes-grafted oligosaccharides, and will show their various applications.

Targeting G Protein-Coupled Receptors with Magnetic Carbon Nanotubes: The Case of the A3 Adenosine Receptor

The A₃ adenosine receptor (AR) is a G protein-coupled receptor (GPCR) overexpressed in the membrane of specific cancer cells. Thus, the development of nanosystems targeting this receptor could be a strategy to both treat and diagnose cancer. Iron-filled carbon nanotubes (CNTs) are an optimal platform for theranostic purposes, and the use of a magnetic field can be exploited for cancer magnetic cell sorting and thermal therapy. In this work, we have conjugated an A₃ AR ligand on the surface of iron-filled CNTs with the aim of targeting cells overexpressing A₃ ARs. In particular, two conjugates bearing PEG linkers of different length were designed. A docking analysis of A₃ AR showed that neither CNT nor linker interferes with ligand binding to the receptor; this was confirmed by in vitro preliminary radioligand competition assays on A₃ AR. Encouraged by this result, magnetic cell sorting was applied to a mixture of cells overexpressing or not the A₃ AR in which our compound displayed indiscriminate binding to all cells. Despite this, it is the first time that a GPCR ligand has been anchored to a magnetic nanosystem, thus it opens the door to new applications for cancer treatment.

Palladium nanoparticles as efficient catalyst for C-S bond formation reactions

The development of green, economical and sustainable chemical processes is one of the primary challenges in organic synthesis. Herein, we report an efficient and heterogeneous palladium-catalyzed sulfonylation of vinyl cyclic carbonates with sodium sulfinates via decarboxylative cross-coupling. Both aliphatic and aromatic sulfinate salts react with various vinyl cyclic carbonates to deliver the desired allylic sulfones featuring tri- and even tetrasubstituted olefin scaffolds in high yields with excellent selectivity. The process needs only 2 mol% of Pd2(dba)3 and the in situ formed palladium nano-particles are found to be the active catalyst.

Sustainable Palladium-Catalyzed Tsuji-Trost Reactions Enabled by Aqueous Micellar Catalysis

Palladium-catalyzed allylic substitution, or "Tsuji-Trost" reactions, can be run under micellar catalysis conditions featuring not only chemistry in water but also numerous combinations of reaction partners that require low levels of palladium, typically on the order of 1000 ppm (0.1 mol %). These couplings are further characterized by especially mild conditions, leading to a number of cases not previously reported in an aqueous micellar medium. Inclusion of diverse nucleophiles, such as N-H heterocycles, alcohols, dicarbonyl compounds, and sulfonamides is described. Intramolecular cyclizations further illustrate the broad utility of this process. In addition to recycling studies, a multigram scale example is reported, indicative of the prospects for scale up.

Photo-initiated rupture of azobenzene micelles to enable the spectroscopic analysis of antimicrobial peptide dynamics

Antimicrobial peptides (AMPs) show promise for the treatment of bacterial infections, but many have undesired hemolytic activities. The AMP MP1 not only has broad spectrum bactericidal activity, but has been shown to have antitumor activity. The interaction between AMPs and cellular membranes gives rise to a peptide's cell-specificity and activity. However, direct analysis of the biophysical interactions between peptides and membrane is complex, in part due to the nature of membrane environments as well as structural changes in the peptide that occurs upon binding to the membrane. In order to investigate the interplay between cell selectivity, activity, and secondary structural changes involved in antimicrobial peptide activity, we sought to implement photolizable membrane mimics to assess the types of information available from infrared spectroscopic measurements that follow from photoinitiated peptide dynamics. Azo-surfactants (APEG) form micelles containing a photolizable azobenzene core, which upon irradiation can induce membrane deformation resulting in breakdown of micelles. Spectroscopic analysis of membrane deformation may provide insights into the physical behavior associated with unfolding and dissociation of antimicrobial peptides within a membrane environment. Herein, we synthesized and characterized two new azo-surfactants, APEGTMG and APEGNEt2MeI. Furthermore, we demonstrate the viability of azosurfactants as membrane mimics by examining both the membrane binding and dissociation induced secondary structural changes of the antimicrobial peptide, MP1.

Regio- and Enantioselective Preparation of Chiral Allylic Sulfones Featuring Elusive Quaternary Stereocenters

We describe here the first general asymmetric synthesis of sterically encumbered α,α-disubstituted allylic sulfones via Pd-catalyzed allylic substitution. The design and application of a new and highly efficient phosphoramidite ligand (L10) proved to be crucial, and a wide variety of challenging allylic sulfones featuring quaternary stereocenters could be obtained in good yields and with good to excellent levels of regio- and enantioselectivities under attractive process conditions. The developed methodology employs easily accessible chemical feedstock including racemic allylic precursors and sodium sulfinates. The utility of the method is further demonstrated by the synthesis of the sesquiterpene (-)-Agelasidine A.

Photoinduced synthesis of allylic sulfones using potassium metabisulfite as the source of sulfur dioxide

Synthesis of allylic sulfones through a photoinduced three-component reaction of aryl/alkyl halides, potassium metabisulfite, and allylic bromides under ultraviolet irradiation at room temperature is developed. Diverse allylic sulfones are generated in moderate to good yields.

Unlocking Structure-Self-Assembly Relationships in Cationic Azobenzene Photosurfactants

Azobenzene photosurfactants are light-responsive amphiphiles that have garnered significant attention for diverse applications including delivery and sorting systems, phase transfer catalysis, and foam drainage. The azobenzene chromophore changes both its polarity and conformation (trans-cis isomerization) in response to UV light, while the amphiphilic structure drives self-assembly. Detailed understanding of the inherent relationship between the molecular structure, physicochemical behavior, and micellar arrangement of azobenzene photosurfactants is critical to their usefulness. Here, we investigate the key structure-function-assembly relationships in the popular cationic alkylazobenzene trimethylammonium bromide (AzoTAB) family of photosurfactants. We show that subtle changes in the surfactant structure (alkyl tail, spacer length) can lead to large variations in the critical micelle concentration, particularly in response to light, as determined by surface tensiometry and dynamic light scattering. Small-angle neutron scattering studies also reveal the formation of more diverse micellar aggregate structures (ellipsoids, cylinders, spheres) than predicted based on simple packing parameters. The results suggest that whereas the azobenzene core resides in the effective hydrophobic segment in the trans-isomer, it forms part of the effective hydrophilic segment in the cis-isomer because of the dramatic conformational and polarity changes induced by photoisomerization. The extent of this shift in the hydrophobic-hydrophilic balance is determined by the separation between the azobenzene core and the polar head group in the molecular structure. Our findings show that judicious design of the AzoTAB structure enables selective tailoring of the surfactant properties in response to light, such that they can be exploited and controlled in a reliable fashion.

Catalytic Organic Reactions in Water toward Sustainable Society

Traditional organic synthesis relies heavily on organic solvents for a multitude of tasks, including dissolving the components and facilitating chemical reactions, because many reagents and reactive species are incompatible or immiscible with water. Given that they are used in vast quantities as compared to reactants, solvents have been the focus of environmental concerns. Along with reducing the environmental impact of organic synthesis, the use of water as a reaction medium also benefits chemical processes by simplifying operations, allowing mild reaction conditions, and sometimes delivering unforeseen reactivities and selectivities. After the "watershed" in organic synthesis revealed the importance of water, the development of water-compatible catalysts has flourished, triggering a quantum leap in water-centered organic synthesis. Given that organic compounds are typically practically insoluble in water, simple extractive workup can readily separate a water-soluble homogeneous catalyst as an aqueous solution from a product that is soluble in organic solvents. In contrast, the use of heterogeneous catalysts facilitates catalyst recycling by allowing simple centrifugation and filtration methods to be used. This Review addresses advances over the past decade in catalytic reactions using water as a reaction medium.

Micellization and Single-Particle Encapsulation with Dimethylammoniopropyl Sulfobetaines

Sulfobetaines (SBs) are a class of zwitterionic surfactants with a reputation for enhancing colloidal stability at high salt concentrations. Here, we present a systematic study on the self-assembly of SB amphiphiles (sultaines or hydroxysultaines) in aqueous solutions, as a function of chain length and composition, ionic strength, and in the presence of alkanethiol-coated Au nanoparticles (GNPs). The diameters of the micelles assembled from SB and amidosulfobetaine (ASB) generally increase monotonically with chain length, although ASB micelles are smaller relative to alkyl SB micelles with similarly sized tailgroups, and oleyl sulfobetaine (OSB) micelles are slightly larger. SB amphiphiles can stabilize alkanethiol-coated GNPs in physiologically relevant buffers at concentrations well below their CMC, with size increases corresponding to single-particle encapsulation. SB-encapsulated GNPs were prepared by three different methods with SB:GNP weight ratios of 10:1, followed by dispersion in water or 1 M NaCl. The low hydrodynamic size of the SB micelles and SB-coated NPs is within the range needed for efficient renal clearance.

Photoresponsive amphiphilic azobenzene–PEG self-assembles to form supramolecular nanostructures for drug delivery applications

Self-assembled smart nanostructures have emerged as controlled and site-specific systems for drug delivery applications.

Barton decarboxylation under ultrasonic continuous flow

Barton decarboxylation was performed in ultrasonic continuous flow for bulkier syntheses and enhanced yields compared to conventional heating.

Azobenzenes and catalysis

Azobenzene is the most extensively used class of chromophore in a large variety of applications.

Carbohydrate-based surfactants as photocontrollable inhibitors of ice recrystallization

We report the synthesis and photocontrollable ice recrystallization inhibition (IRI) activity of a panel of carbohydrate-based surfactants.

One-Pot Synthesis of Allylic Sulfones, Ketosulfones, and Triflyl Allylic Alcohols from Domino Reactions of Allylic Alcohols with Sulfinic Acid under Metal-Free Conditions

A metal-free tandem procedure by using a sulfonylation reaction of aryl allylic alcohols followed by an iodobenzenediacetate (PIDA)-promoted oxidative functionalization has been established. Allylic sulfones, γ-ketosulfones, and triflyl allylic alcohols have been constructed in a single operation. The methodology incorporates the sulfonyl (both aryl and triflyl) functionality with a simple work-up procedure.

First pinacol coupling in emulsified water: key role of surfactant and impact of alternative activation technologies

For the first time, the influence of surfactants on the radical pinacol coupling reaction is investigated. The rate and selectivity of this reductive C-C coupling are compared under three different activation technologies: thermal activation, microwave irradiation, and sonication. The use of IgepalCO520, a neutral surfactant, led to the successful conversion of aromatic or α,β-unsaturated aliphatic carbonyl compounds in moderate to excellent yield (55-90 %). An insight on the potential mechanism involved in the reaction is also proposed, based on microscopic observations and particle size measurement.

Nano-Fe3O4 encapsulated-silica supported boron trifluoride as a novel heterogeneous solid acid for solvent-free synthesis of arylazo-1-naphthol derivatives

Fe₃O₄@SiO₂–BF₃ nanoparticles were prepared as a novel solid acid and effectively applied for the solvent-free synthesis of arylazo-1-naphthols at room temperature.

One-step Barton decarboxylation by micellar catalysis – application to the synthesis of maleimide derivatives

Maleimides being studied or used in various applications, for the first time, a facile entry to Barton decarboxylation in aqueous media is described to obtain in one step substituted N-phenylmaleimide synthons.