Omniphilic Polymeric Sponges by Ice Templating

Sponges that absorb a large quantity of solvent relative to their weight, independent of the solvent polarity, represent useful universal absorbents for laboratory and industrial spills. We report the preparation of macroporous polymer sponges by ice templating of polyethylenimine aqueous solutions and their cross-linking in the frozen state. The as-prepared monolith is hydrophilic and absorbs over 30-fold its weight in water. Modification of this sponge using valeroyl chloride renders it omniphilic; viz., a modified sponge absorbs over 10-fold its dry weight of either water or hexane. Modification using palmitoyl chloride that has a longer chain length results in the preparation of a hydrophobic sponge with a water contact angle around 130°, which retains its oleophilicity underwater. The solvent absorbed in these sponges can be simply squeezed out, and the sponges are stable to several hundred cycles of compression. The large pore sizes of these sponges allow rapid absorption of even high viscosity solvents such as pump oil. Finally, we demonstrate that these sponges are also able to separate apolar oils that are emulsified in water using surfactants. These high porosity sponges with controllable solvophilicity represent inexpensive, high performance universal absorbents for general solvent spills

Iron Complex Catalyzed Selective C–H Bond Oxidation with Broad Substrate Scope

The use of a peroxidase-mimicking Fe complex has been reported on the basis of the biuret-modified TAML macrocyclic ligand framework (Fe–bTAML) as a catalyst to perform selective oxidation of unactivated 3° C–H bonds and activated 2° C–H bonds with low catalyst loading (1 mol %) and high product yield (excellent mass balance) under near-neutral conditions and broad substrate scope (18 substrates which includes arenes, heteroaromatics, and polar functional groups). Aliphatic C–H oxidation of 3° and 2° sites of complex substrates was achieved with predictable selectivity using steric, electronic, and stereoelectronic rules that govern site selectivity, which included oxidation of (+)-artemisinin to (+)-10β-hydroxyartemisinin. Mechanistic studies indicate Fe^V(O) to be the active oxidant during these reactions

Investigation of C–C Bond Formation Mediated by Bombyx mori Silk Fibroin Materials

The formation of C–C bonds is a prerequisite for all life on earth. Understanding the role of proteins in mediating the formation of these bonds is important for understanding biological mechanisms in evolution, as well as for designing “green catalysts”. In this work, the ability of silk fibroin (SF) proteins to mediate selective C–C bond formation under mild conditions was comprehensively evaluated and compared between different SF-based materials and other proteins. Aqueous SF solution (ASFS), freeze-dried SF (FDSF), mesoporous SF (MPSF), and SF hydrogel (SFHG) materials were prepared and characterized by a variety of techniques including, among others, FE-SEM, ICP-OES, FT-IR, and TGA. The nitroaldol (Henry) reaction, Knoevenagel condensation, and direct aldol reaction were used as models for this study, in which the recovery and reusability of the protein was also evaluated

Large Centimeter-Sized Macroporous Ferritin Gels as Versatile Nanoreactors

Organized assemblies of bionanoparticles such as ferritin provides templates that can be exploited for nanotechnological applications. Organization of ferritin into well-defined three-dimensional assemblies is challenging and has attracted considerable attention recently. We have synthesized, for the first time, large (centimeter-sized) self-standing macroporous scaffold monoliths from ferritin bionanoparticles, using dynamic templating of surfactant H₁ domains. These scaffolds comprise three-dimensionally connected strands of ferritin, organized as a porous gel with porosity ∼55 μm. The iron oxide inside the ferritin scaffold can be easily replaced with catalytically active monodisperse zerovalent transition metal nanoparticles using a very simple protocol. Since the ferritin is cross-linked in the scaffold, it is significantly robust with enhanced thermal stability and better tolerance toward several organic solvents in comparison to the native ferritin bionanoparticle. In addition, the scaffold macropores facilitate substrate and reagent transport and hence the monoliths containing active Pd or iron oxide nanoparticles inside apo-ferritin bionanoparticles were used as a recyclable heterogeneous catalyst for the oxidation of 2,3,6-trimethyl phenol to 2,3,6-trimethyl-1,4-benzoquinone (precursor for Vitamin E synthesis) and for Suzuki–Miyaura cross-coupling reaction in both aqueous and organic solvents. The protein shell around the nanoparticles protects them from agglomeration, a phenomenon that otherwise plagues nanoparticles-based catalysis. The presence of macropores allow the ferritin scaffold to act as catalytic monolith for continuous flow reactions having rapid reaction rates, while offering a low pressure drop. Finally, the Pd@apo-ferritin scaffold was immobilized inside a steel cartridge and used for the continuous flow hydrogenation of alkenes to their corresponding alkanes for 15 cycles without any loss of activity

Controlled Synthesis of End-Functionalized Mannose-6-phosphate Glycopolypeptides for Lysosome Targeting

The ubiquitous expression of the mannose-6-phosphate receptor on the majority of human cells makes it a valid target in the quest to deliver therapeutics selectively to the lysosome. In this work end-functionalized polyvalent mannose-6-phosphate glycopolypeptides (M6P-GPs) with high molecular weights (up to 22 kDa) have been synthesized via NCA polymerization. These synthetic M6P-GPs were found to display minimal toxicity to cells in vitro and show exceptional selectivity for trafficking into lysosomes in various cell lines. Comparison of the cellular uptake behavior of M6P-GP and the corresponding mannose-GP polymer reveals that incorporation of the phosphate moiety at the 6-position of mannose completely alters its trafficking behavior and becomes exclusively lysosome specific. We also demonstrate that trafficking of M6P-GPs in mammalian cells is likely associated with the CI-MPR receptor pathway

Synthesis of Silk Fibroin–Glycopolypeptide Conjugates and Their Recognition with Lectin

Silk fibroin (SF), the natural fibrous protein created by the Bombyx mori silk worm, is being increasingly explored as a biomaterial for tissue engineering due to its excellent mechanical strength, high oxygen/water permeability, and biocompatibility. It is also well known that surface modification of SF with organic ligands such as the extracellular protein binding Arg-Gly-Asp (RGD) peptides help adhesion and proliferation of cells bettera key requirement for it to function as extracellular matrices. In this work, we have conjugated synthetic glycopolypeptides (GPs) that were synthesized by controlled ring-opening polymerization of α<i>-manno</i>-lys <i>N</i>-carboxyanhydrides (NCAs) onto SF by using Cu catalyzed click reaction to synthesize a new hybrid material (SF–GP), which we believe will have both the mechanical properties of native SF and the molecular recognition property of the carbohydrates in the GP. By controlling the amount of GP grafted onto SF, we have made three SF–GP conjugates that differ in their ability to assemble into films. SF–GP conjugates having a very high content of GP formed completely water-soluble brush-like polymer that displayed very high affinity toward the lectin concanavalin-A (Con-A). Films cast from SF–GP conjugates using lower amounts of grafted GP were more stable in water, and the stability can be modulated by varying the amount of GP grafted. The water-insoluble film SF–GP₂₅ was also found to bind to fluorescently labeled Con-A, as was seen by confocal microscopy. Such SF–GP hybrid films may be useful as mimics of extracellular matrices for tissue engineering

Synthesis and Self-assembly of Amphiphilic Homoglycopolypeptide

The synthesis of the amphiphilic homoglycopolypeptide was carried out by a combination of NCA polymerization and click chemistry to yield a well-defined polypeptide having an amphiphilic carbohydrate on its side chain. The amphiphilicity of the carbohydrate was achieved by incorporation of an alkyl chain at the C-6 position of the carbohydrate thus also rendering the homoglycopolypeptide amphiphilic. The homoglycopolypeptide formed multimicellar aggregates in water above a critical concentration of 0.9 μM due to phase separation. The multimicellar aggregates were characterized by DLS, TEM, and AFM. It is proposed that hydrophobic interactions of the aliphatic chains at the 6-position of the sugar moieties drives the assembly of these rod-like homoglycopolypeptide into large spherical aggregates. These multimicellar aggregates encapsulate both hydrophilic as well as hydrophobic dye as was confirmed by confocal microscopy. Finally, amphiphilic random polypeptides containing 10% and 20% α-d-mannose in addition to glucose containing a hydrophobic alkyl chain at its 6 position were synthesized by our methodology, and these polymers were also found to assemble into spherical nanostructures. The spherical assemblies of amphiphilic random glycopolypeptides containing 10% and 20% mannose were found to be surface bioactive and were found to interact with the lectin Con-A

Fe-TAML Encapsulated Inside Mesoporous Silica Nanoparticles as Peroxidase Mimic: Femtomolar Protein Detection

Peroxidase, such as horseradish peroxidase (HRP), conjugated to antibodies are routinely used for the detection of proteins via an ELISA type assay in which a critical step is the catalytic signal amplification by the enzyme to generate a detectable signal. Synthesis of functional mimics of peroxidase enzyme that display catalytic activity which far exceeds the native enzyme is extremely important for the precise and accurate determination of very low quantities of proteins (fM and lower) that is necessary for early clinical diagnosis. Despite great advancements, analyzing proteins of very low abundance colorimetrically, a method that is most sought after since it requires no equipment for the analysis, still faces great challenges. Most reported HRP mimics that show catalytic activity greater than native enzyme (∼10-fold) are based on metal/metal-oxide nanoparticles such as Fe₃O₄. In this paper, we describe a second generation hybrid material developed by us in which approximately 25 000 alkyne tagged biuret modified Fe-tetraamido macrocyclic ligand (Fe-TAML), a very powerful small molecule synthetic HRP mimic, was covalently attached inside a 40 nm mesoporous silica nanoparticle (MSN). Biuret-modified Fe-TAMLs represent one of the best small molecule functional mimics of the enzyme HRP with reaction rates in water close to the native enzyme and operational stability (pH, ionic strength) far exceeding the natural enzyme. The catalytic activity of this hybrid material is around 1000-fold higher than that of natural HRP and 100-fold higher than that of most metal/metal oxide nanoparticle based HRP mimics reported to date. We also show that using antibody conjugates of this hybrid material it is possible to detect and, most importantly, quantify femtomolar quantities of proteins colorimetrically in an ELISA type assay. This represents at least 10-fold higher sensitivity than other colorimetric protein assays that have been reported using metal/metal oxide nanoparticles as HRP mimic. Using a human IgG expressing cell line, we were able to demonstrate that the protein of interest human IgG could be detected from a mixture of interfering proteins in our assay

Mechanism of Alcohol Oxidation by Fe^V(O) at Room Temperature

Selective oxidation of alcohol to its corresponding carbonyl compound is an important chemical process in biological as well as industrial reactions. The heme containing enzyme CytP450 has been known to selectively oxidize alcohols to their corresponding carbonyl compounds. The mechanism of this reaction, which involves high-valent Fe^IV(O)−porphyrin^•+ intermediate with alcohol, has been well-studied extensively both with the native enzyme and with model complexes. In this paper, we report for the first time the mechanistic insight of alcohol oxidation with Fe^V(O) complex of biuret TAML (bTAML), which is isoelectronic with Fe^IV(O)−porphyrin^•+ intermediate form in CytP450. The oxidations displayed saturation kinetics, which allowed us to determine both the binding constants and first-order rate constants for the reaction. The <i>K</i> and <i>k</i> values observed for the oxidation of benzyl alcohol by Fe^V(O) at room temperature (<i>K</i> = 300 M^–1, <i>k</i> = 0.35 s^–1) is very similar to that obtained by CytP450 compound I at −50 °C (<i>K</i> = 214 M^–1, <i>k</i> = 0.48 s^–1). Thermodynamic parameters determined from van’t Hoff’s plot (Δ<i>H</i>∼ −4 kcal/mol) suggest hydrogen bonding interaction between substrate and bTAML ligand framework of the Fe^V(O) complex. Analysis of H/D KIE (<i>k</i>_H/<i>k</i>_D ∼ 19 at 303 K), Hammett correlation and linearity in Bell-Evans-Polyanski plot points to the C–H abstraction as the rate determination step. Finally, experiments using Fe^V(O¹⁸) for benzyl alcohol oxidation and use of the “radical clock” cyclobutanol as a substrate shows the absence of a rebound mechanism as is observed for CytP450. Instead, an ET/PT process is proposed after C–H abstraction leading to formation of the aldehyde, similar to what has been proposed for the heme and nonheme model compounds

Bioactive Polymersomes Self-Assembled from Amphiphilic PPO-<i>Glyco</i>Polypeptides: Synthesis, Characterization, and Dual-Dye Encapsulation

Glycopolypeptide-based polymersomes have promising applications as vehicles for targeted drug delivery because they are capable of encapsulating different pharmaceuticals of diverse polarity as well as interacting with specific cell surfaces due to their hollow structural morphology and bioactive surfaces. We have synthesized glycopolypeptide-<i>b</i>-poly­(propylene oxide) by ROP of glyco-<i>N</i>-carboxyanhydride (NCA) using the hydrophobic amine-terminated poly­(propylene oxide) (PPO) as the initiator. This block copolymer is composed of an FDA-approved PPO hydrophobic block in conjugation with hydrophilic glycopolypeptides which are expected to be biocompatible. We demonstrate the formation of glycopolypeptide-based polymersomes from the self-assembly of glycopolypeptide-<i>b</i>-poly­(propylene oxide) in which the presence of an ordered helical glycopolypeptide segment is required for their self-assembly into spherical nanoscale (∼50 nm) polymersomes. The polymersomes were characterized in detail using a variety of techniques such as TEM, AFM, cryo-SEM, and light-scattering measurements. As a model for drugs, both hydrophobic (RBOE) and hydrophilic (calcein) dyes have been incorporated within the polymersomes from solution. To substantiate the simultaneous entrapment of the two dyes, spectrally resolved fluorescence microscopy was performed on the glycopeptide polymersomes cast on a glass substrate. We show that it is possible to visualize individual nanoscale polymersomes and effectively probe the dyes’ colocalization and energy-transfer behaviors therein as well as investigate the variation in dual-dye encapsulation over a large number of single polymersomes. Finally, we show that the galactose moieties present on the surface can specifically recognize lectin RCA₁₂₀, which reveals that the polymersomes’ surface is indeed biologically active