Olefin Cross-Metathesis as a Source of Polysaccharide Derivatives: Cellulose ω-Carboxyalkanoates

Smart fluorescent polysaccharides: Recent developments and applications

Polysaccharides are ubiquitous, generally benign in nature, and compatible with many tissues in biomedical situations, making them appealing candidates for new materials such as therapeutic agents and sensors. Fluorescent labeling can create the ability to sensitively monitor distribution and transport of polysaccharide-based materials, which can for example further illuminate drug-delivery mechanisms and therefore improve design of delivery systems. Herein, we review fluorophore selection and ways of appending polysaccharides, utility of the product fluorescent polysaccharides as new smart materials, and their stimulus-responsive nature, with focus on their biomedical applications as environment-sensitive biosensors, imaging, and as molecular rulers. Further, we discuss the advantages and disadvantages of these methods, and future prospects for creation and use of these self-reporting materials.

Co-assembly of stearoylated cellulose nanocrystals and GO (or CNTs) for the construction of superhydrophobic hierarchical structure with enhanced photothermal conversion

The development of photothermal materials with high photothermal-conversion efficiencies is important in a range of applications, such as power generation, sterilization, desalination, and energy-production. To date, a few reports have been published related to improving the photothermal conversion performances of photothermal materials based on self-assembled nanolamellae. Herein, hybrid films of co-assembled stearoylated cellulose nanocrystals (SCNCs) and polymer-grafted graphene oxide (pGO)/polymer-grafted carbon nanotubes (pCNTs) were prepared. The chemical compositions, microstructures, and morphologies of these products were characterized, and it was found that the self-assembled SCNC structures exhibited numerous surface nanolamellae due to crystallization of the long alkyl chains. The hybrid films (i.e., SCNC/pGO and SCNC/pCNTs films) consisted of ordered nanoflake structures, confirming the co-assembly behavior of the SCNCs with pGO or pCNTs. The melting temperature (~65 °C) and latent heat of melting (87.87 J/g) of SCNC_1.07 indicate its potential to induce the formation of nanolamellar pGO or pCNTs. Under light irradiation (50-200 mW/cm²), the pCNTs exhibited a higher light absorption capacity than pGO, and as a result, the SCNC/pCNTs film exhibited the best photothermal performance and electrical conversion, ultimately demonstrating its potential for use as a solar thermal device in practical applications.

Synthesis and Fabrication of a Betulin-Containing Polyolefin Electrospun Fibrous Mat for Antibacterial Applications

Biocompounds play a significant role in the area of renewable polymers in terms of sustainability, as they can be employed or converted into monomers for polymerization in a manner similar to many petroleum-derived monomers. In this work, betulin, a plant-derived triterpene with antibacterial and antiviral properties, was converted to two kinds of α,ω-diene derivatives with different methylene spacer lengths between the olefin and the ester group via an esterification reaction. Polyolefins were subsequently made by acyclic diene metathesis (ADMET) polymerization of betulin-based α,ω-diene. The polymer consists of rigid betulin and flexible unsaturated aliphatic segments, which was confirmed by NMR spectroscopy and gel permeation chromatography (GPC). The influence of different parameters including temperature, catalysts, and catalyst loading on ADMET polymerization was investigated. These polyolefins with high molar mass (up to 20.0 kg/mol) were obtained in an elevated yield (≥95%). Thermal analysis of these (co)polymers showed excellent thermal stability (up to 360 °C) and tunable glass transition temperatures depending on the nature of betulin and alkene segments. To evaluate the antimicrobial potential of betulin-containing polymers, the fabrication of polyolefin fibrous mats (ca. 400 nm diameter) via the electrospinning technique was successfully achieved. Their morphology and hydrophobicity were studied by scanning electron microscopy (SEM) and water contact angle analyses. The fibrous mats possessed broad-spectrum antibacterial property, providing a feasible strategy to design betulin-based polymeric fibers for many applications in the biomedical field.

A Versatile Method for Preparing Polysaccharide Conjugates via Thiol-Michael Addition

Polysaccharide conjugates are important renewable materials. If properly designed, they may for example be able to carry drugs, be proactive (e.g., with amino acid substituents) and can carry a charge. These aspects can be particularly useful for biomedical applications. Herein, we report a simple approach to preparing polysaccharide conjugates. Thiol-Michael additions can be mild, modular, and efficient, making them useful tools for post-modification and the tailoring of polysaccharide architecture. In this study, hydroxypropyl cellulose (HPC) and dextran (Dex) were modified by methacrylation. The resulting polysaccharide, bearing α,β-unsaturated esters with tunable DS (methacrylate), was reacted with various thiols, including 2-thioethylamine, cysteine, and thiol functional quaternary ammonium salt through thiol-Michael addition, affording functionalized conjugates. This click-like synthetic approach provided several advantages including a fast reaction rate, high conversion, and the use of water as a solvent. Among these polysaccharide conjugates, the ones bearing quaternary ammonium salts exhibited competitive antimicrobial performance, as supported by a minimum inhibitory concentration (MIC) study and tracked by SEM characterization. Overall, this methodology provides a versatile route to polysaccharide conjugates with diverse functionalities, enabling applications such as antimicrobial activity, gene or drug delivery, and biomimicry.

Cellulose-Based Superhydrophobic Surface Decorated with Functional Groups Showing Distinct Wetting Abilities to Manipulate Water Harvesting

Inspired by the distinct functions of desert beetles with efficient droplet nucleation and lotus leaves with excellent droplet removal, an integrated method is presented for the design of a superhydrophobic surface decorated with hydrophilic groups that can efficiently nucleate and remove water droplets. We constructed a cellulose-based superhydrophobic surface containing numerous olefin terminal groups by solvent exchange and spray coating. This surface is different from most of the reported biomimicking water harvesting surfaces that rely on complicated lithography and micropatterning techniques requiring special instruments. The obtained superhydrophobic surface was further modified using various thiol compounds via a thiol-ene reaction to manipulate the water harvesting property. The modified surfaces containing hydrophobic groups (e.g., 1-octadecanethiol and 1H,1H,2H,2H-perfluorodecanethiol) or a strong hydrophilic group (e.g., 3-mercaptopropionic acid and 6-mercapto-1-hexanol) exhibited insufficient fog collecting abilities due to poor water droplet nucleation or strong water adhesion. By contrast, the modified surface decorated with moderately hydrophilic amino groups combines the advantages of biological surfaces with distinct wetting features (such as fog-harvesting beetles and water-repellent lotus leaves), resulting in accelerated water nucleation and less compromise of the water removal efficiency. Molecular dynamic simulations revealed that the efficient droplet nucleation is attributed to the hydrophilic amino groups whereas the rapid droplet removal is due to the maintained superhydrophobicity of the amino group-modified surface. This strategy of decorating a superhydrophobic surface with moderately hydrophilic functional groups provides insight into the manipulation of droplet nucleation and removal for water collection efficiency.

Conjugation of bile esters to cellulose by olefin cross-metathesis: A strategy for accessing complex polysaccharide structures

Bile salts tend to form micelles in aqueous media and can thereby contribute to drug solubilization; they also exhibit crystallization inhibition properties that can stabilize supersaturated drug solutions. Herein, we explore conjugation of bile salts with polysaccharides to create new, amphiphilic polysaccharide derivatives with intriguing properties, portending broad utility in various applications. We introduce efficient conjugation of cholesterol (as a model steroid), lithocholic acid, and deoxycholic acid by mild, modular olefin cross-metathesis reactions. These small molecules were first modified with an acrylate group from the A-ring hydroxyl, then reacted with cellulose derivatives bearing olefin-terminated metathesis "handles". Successful conjugation of bile acids has demonstrated chemoselective cross-metathesis with complex, polyfunctional structures, and large multi-ring systems. It also enabled an efficient, general pathway for polysaccharide-bile salt conjugates, which promise synergy for applications such as amorphous solid dispersion (ASD).

Olefin Cross-Metathesis in Polymer and Polysaccharide Chemistry: A Review

Olefin cross-metathesis, a ruthenium-catalyzed carbon-carbon double bond transformation that features high selectivity, reactivity, and tolerance of various functional groups, has been extensively applied in organic synthesis and polymer chemistry. Herein, we review strategies for performing selective cross-metathesis and its applications in polymer and polysaccharide chemistry, including constructing complex polymer architectures, attaching pendant groups to polymer backbones and surfaces, and modifying polysaccharide derivatives.

Tandem modification of amphiphilic cellulose ethers for amorphous solid dispersion via olefin cross-metathesis and thiol-Michael addition

Tandem olefin cross-metathesis (CM) and thiol-Michael addition for modification of cellulose derivatives”.

Mechanistic Design of Chemically Diverse Polymers with Applications in Oral Drug Delivery

Polymers play a key role in stabilizing amorphous drug formulations, a recent strategy employed to improve solubility and bioavailability of drugs delivered orally. However, the molecular mechanism of stabilization is unclear, therefore, the rational design of new crystallization-inhibiting excipients remains a substantial challenge. This article presents a combined experimental and computational approach to elucidate the molecular features that improve the effectiveness of cellulose polymers as solution crystallization inhibitors, a crucial first step toward their rational design. Polymers with chemically diverse substituents including carboxylic acids, esters, ethers, alcohols, amides, amines, and sulfides were synthesized. Measurements of nucleation induction times of the model drug, telaprevir, show that the only effective polymers contained carboxylate groups in combination with an optimal hydrocarbon chain length. Computational results indicate that polymer conformation as well as solvation free energy are important determinants of effectiveness at inhibiting crystallization and show that simulations are a promising predictive tool in the screening of polymers. This study suggests that polymers need to have an adequate hydrophilicity to promote solvation in an aqueous environment, and sufficient hydrophobic regions to drive interactions with the drug. Particularly, the right balance between key substituent groups and lengths of hydrocarbon side chains is needed to create effective materials.

Stimuli-responsive nanoparticles from ionic cellulose derivatives

Stimuli-responsive nanoparticles (NPs) based on sustainable polymeric feedstock still need more exploration in comparison with NPs based on synthetic polymers. In this report, stimuli-responsive NPs from novel ionic cellulose derivatives were prepared via a facile nanoprecipitation. Cellulose 10-undecenoyl ester (CUE) with a degree of substitution (DS) of 3 was synthesized by esterification of cellulose with 10-undecenoyl chloride. Then, CUE was modified by photo-induced thiol-ene reactions, in order to obtain organo-soluble ionic cellulose derivatives with DSs of ∼3, namely cellulose 11-((3-carboxyl)ethylthio)undecanoate (CUE-MPA), cellulose 11-((2-aminoethyl)thio)undecanoate (CUE-CA), cellulose 11-(2-(2-(diethylamino)ethyl)thio)undecanoate (CUE-DEAET) and cellulose 11-(2-(2-(dimethylamino)ethyl)thio)undecanoate (CUE-DMAET). CUE-MPA could be transformed into NPs with average diameters in the range of 80-330 nm, but these NPs did not show particular stimuli-responsive properties. Moreover, the dropping technique resulted in smaller NPs than a dialysis technique. Stable NPs with average diameters in the range of 90-180 nm showing pH-responsive and switchable sizes were obtained from CUE-DEAET and CUE-DMAET possessing tertiary amines using nanoprecipitation. Thus, altering the terminal functional groups will be a new approach to prepare stimuli-responsive cellulose-derived polymeric NPs.

Amphiphilic hydroxyalkyl cellulose derivatives for amorphous solid dispersion prepared by olefin cross-metathesis

Olefin CM followed by transfer hydrogenation is an efficient method for synthesizing amphiphilic hydroxypropyl cellulose derivatives.

Multifunctional cellulose esters by olefin cross-metathesis and thiol-Michael addition

Post-cross-metathesis thiol-Michael addition affords functionally diverse cellulose esters.

Synthesis of amide-functionalized cellulose esters by olefin cross-metathesis

Cellulose esters with amide functionalities were synthesized by cross-metathesis (CM) reaction of terminally olefinic esters with different acrylamides, catalyzed by Hoveyda-Grubbs 2nd generation catalyst. Chelation by amides of the catalyst ruthenium center caused low conversions using conventional solvents. The effects of both solvent and structure of acrylamide on reaction conversion were investigated. While the inherent tendency of acrylamides to chelate Ru is governed by the acrylamide N-substituents, employing acetic acid as a solvent significantly improved the conversion of certain acrylamides, from 50% to up to 99%. Homogeneous hydrogenation using p-toluenesulfonyl hydrazide successfully eliminated the α,β-unsaturation of the CM products to give stable amide-functionalized cellulose esters. The amide-functionalized product showed higher Tg than its starting terminally olefinic counterpart, which may have resulted from strong hydrogen bonding interactions of the amide functional groups.

Acrylate metathesis via the second-generation Grubbs catalyst: unexpected pathways enabled by a PCy3-generated enolate

The diverse applications of acrylate metathesis range from synthesis of high-value α,β-unsaturated esters to depolymerization of unsaturated polymers. Examined here are unexpected side reactions promoted by the important Grubbs catalyst GII. Evidence is presented for attack of PCy3 on the acrylate olefin to generate a reactive carbanion, which participates in multiple pathways, including further Michael addition, proton abstraction, and catalyst deactivation. Related chemistry may be anticipated whenever labile metal-phosphine complexes are used to catalyze reactions of substrates bearing an electron-deficient olefin.

Imparting functional variety to cellulose ethers via olefin cross-metathesis

Olefin cross-metathesis (CM) was applied to impart functional variety to a series of cellulose ether derivatives.