Novel Amphiphilic Dendronized Copolymers Formed by Enzyme-Mediated "Green" Polymerization

Enzymes in "Green" Synthetic Chemistry: Laccase and Lipase

Enzymes play an important role in numerous natural processes and are increasingly being utilized as environmentally friendly substitutes and alternatives to many common catalysts. Their essential advantages are high catalytic efficiency, substrate specificity, minimal formation of byproducts, and low energy demand. All of these benefits make enzymes highly desirable targets of academic research and industrial development. This review has the modest aim of briefly overviewing the classification, mechanism of action, basic kinetics and reaction condition effects that are common across all six enzyme classes. Special attention is devoted to immobilization strategies as the main tools to improve the resistance to environmental stress factors (temperature, pH and solvents) and prolong the catalytic lifecycle of these biocatalysts. The advantages and drawbacks of methods such as macromolecular crosslinking, solid scaffold carriers, entrapment, and surface modification (covalent and physical) are discussed and illustrated using numerous examples. Among the hundreds and possibly thousands of known and recently discovered enzymes, hydrolases and oxidoreductases are distinguished by their relative availability, stability, and wide use in synthetic applications, which include pharmaceutics, food and beverage treatments, environmental clean-up, and polymerizations. Two representatives of those groups-laccase (an oxidoreductase) and lipase (a hydrolase)-are discussed at length, including their structure, catalytic mechanism, and diverse usage. Objective representation of the current status and emerging trends are provided in the main conclusions.

Synthesis of Dendronized Polymers on the Au(111) Surface

Dendronized polymers (DPs) consist of a linear polymeric backbone with dendritic side chains. Fine-tuning of the functional groups in the side chains enriches the structural versatility of the DPs and imparts a variety of novel physical properties. Herein, the first on-surface synthesis of DPs is achieved via the postfunctionalization of polymers on Au(111), in which the surface-confinement-induced planar conformation and chiral configurations were unambiguously characterized. While the dendronized monomer was synthesized in situ on Au(111), the subsequent polymerization afforded only short, cross-linked DP chains owing to multiple side reactions. The postfunctionalization approach selectively produced brominated polyphenylene backbone moieties by the deiodination polymerization of 4-bromo-4″-iodo-5'-(4-iodophenyl)-1,1':3',1″-terphenyl on Au(111), which smoothly underwent divergent cross-coupling reactions with two different isocyanides to form two types of DPs as individual long chains.

Dendritic-Linear Copolymer and Dendron Lipid Nanoparticles for Drug and Gene Delivery

Polymers constitute a diverse class of macromolecules that have demonstrated their unique advantages to be utilized for drug or gene delivery applications. In particular, polymers with a highly ordered, hyperbranched structure─"dendrons"─offer significant benefits to the design of such nanomedicines. The incorporation of dendrons into block copolymer micelles can endow various unique properties that are not typically observed from linear polymer counterparts. Specifically, the dendritic structure induces the conical shape of unimers that form micelles, thereby improving the thermodynamic stability and achieving a low critical micelle concentration (CMC). Furthermore, through a high density of highly ordered functional groups, dendrons can enhance gene complexation, drug loading, and stimuli-responsive behavior. In addition, outward-branching dendrons can support a high density of nonfouling polymers, such as poly(ethylene glycol), for serum stability and variable densities of multifunctional groups for multivalent cellular targeting and interactions. In this paper, we review the design considerations for dendron-lipid nanoparticles and dendron micelles formed from amphiphilic block copolymers intended for gene transfection and cancer drug delivery applications. These technologies are early in preclinical development and, as with other nanomedicines, face many obstacles on the way to clinical adoption. Nevertheless, the utility of dendron micelles for drug delivery remains relatively underexplored, and we believe there are significant and dramatic advancements to be made in tumor targeting with these platforms.

Volume Overlap Variation within Hyperbranched Polymer Brushes Resolves Topology Effects against Protein Fouling

Hyperbranched polymer brushes with a three-dimensional dendritic structure are used in antifouling applications to obtain bioinert and compact dendritic structures. Though hyperbranched polyglycerol (HPG) is extensively utilized in the antifouling layer, there is still a lack of direct studies on the relationship between the interfacial properties and topology effect of hyperbranched polymer brushes. Here, we established the degree of chain volume overlap (D_v) to characterize the spatial shielding efficiency generated by HPG brushes and investigated the impact mechanism of the variable chain length on the interfacial physicochemical properties. The results revealed the D_v-relevant feature of performance that the most densely packed HPG brushes for a medium-length L_HPG3.07 enable the functional surface to display optimal antifouling performance toward protein adsorption by forming the most effective space barrier and hydrated layer in appropriate molecular weights and graft density. Moreover, we clarified the advance of hyperbranched polymer brushes exhibited in topology effects for imparting surface-enhanced resistance to biofouling relies on the generable higher steric hindrance as compared with linear analogs. This study established a D_v-relevant evaluation model for acquiring an optimized antifouling surface based on the appropriate choice of polymer structure, topology morphologies, and grafting parameters.

Enzymatic Synthesis and Antimicrobial Activity of Oligomer Analogues of Medicinal Biopolymers from Comfrey and Other Species of the Boraginaceae Family

This study reports the first enzymatic synthesis leading to several oligomer analogues of poly[3-(3,4-dihydroxyphenyl)glyceric acid]. This biopolymer, extracted from plants of the Boraginaceae family has shown a wide spectrum of pharmacological properties, including antimicrobial activity. Enzymatic ring opening polymerization of 2-methoxycarbonyl-3-(3,4-dibenzyloxyphenyl)oxirane (MDBPO) using lipase from Candida rugosa leads to formation of poly[2-methoxycarbonyl-3-(3,4-dibenzyloxyphenyl)oxirane] (PMDBPO), with a degree of polymerization up to 5. Catalytic debenzylation of PMDBPO using H₂ on Pd/C yields poly[2-methoxycarbonyl-3-(3,4-dihydroxyphenyl)oxirane] (PMDHPO) without loss in molecular mass. Antibacterial assessment of natural polyethers from different species of Boraginaceae family Symhytum asperum, S. caucasicum,S. grandiflorum, Anchusa italica, Cynoglossum officinale, and synthetic polymers, poly[2-methoxycarbonyl-3-(3,4-dimethoxyphenyl)oxirane (PMDMPO) and PMDHPO, reveals that only the synthetic analogue produced in this study (PMDHPO) exhibits a promising antimicrobial activity against pathogenic strains S.aureus ATCC 25923 and E.coli ATCC 25922 the minimum inhibitory concentration (MIC) being 100 µg/mL.

Dendronized Arm Snowflake Polymer as a Highly Branched Scaffold for Cellular Imaging and Delivery

Incorporation of branched structures is a major pathway to build macromolecules with desired three-dimensional (3D) structures, which are of high importance in the rational design of functional polymeric scaffolds. Dendrimers and hyperbranched polymers have been extensively studied for this purpose, but proper gain-of-function for these structures usually requires large enough molecular weights and a highly branched interior so that a spherical 3D core-shell architecture can be obtained, yet it is generally challenging to achieve precise control over the structure, high molecular weight, and high degree of branching (DoB) simultaneously. In this article, we present a set of snowflake-shaped star polymers with functional cores and dendronized arms, which ensure a high DoB and an overall globular conformation, thus facilitating the introduction of functional moieties onto the easily achieved scaffold without the need for high-generation dendrons. Using a polyglycerol dendron (PGD) as a proof of concept, we propose that this dendronized arm snowflake polymer (DASP) structure can serve as a better performing alternative to high-generation PGDs. DASPs with molecular weights of 750, 1220, 2120, and 3740 kDa were prepared with >85% yields in all cases, and we show that these DASPs have high encapsulating efficiency of Nile Red due to their high DoB and high biocompatibility due to their hydroxyl-rich nature after ketal removal, as well as high cell permeability that is molecular-weight-dependent. Introduced fluorophores such as fluorescein and difluoroboron 1,3-diphenylaminophenyl β-diketonate with suitable excitation wavelengths may turn the DASPs into stable, endosome-staining fluorophores with ultra-large Stokes shifts, narrowed emission bands, and suitability for long-term cellular tracing. Moreover, the scaffold can encapsulate antibiotic molecules and deliver them into phagolysosomes for efficient elimination of intracellular Staphylococcus aureus, which is insensitive toward many antibiotics but is a key target for the clinical success of methicillin-resistant Staphylococcus aureus infection treatment. Elimination of Staphylococcus aureus could be improved to >99.9% for chloramphenicol at 32 μg/mL with 450 μg/mL DASP.