Well-defined Molecular Weight Research Articles

A supramolecular formulation of icariin@sulfonatoazocalixarene for hypoxia-targeted osteoarthritis therapy

Osteoarthritis (OA) is the most prevalent joint disease and icariin is a promising drug for its treatment. However, the clinical use of icariin is hindered by poor water solubility, low bioavailability, and non-specific release and biological distribution. Herein, sulfonated azocalix[4]arene (SAC4A) with enhanced water solubility, recognition capacity, and designed responsiveness was used to improve the efficiency of icariin for OA therapy. SAC4A, a macrocycle with well-defined molecular weight and structure, could encapsulate and enhance water solubility of various drugs. In addition, SAC4A enables hypoxia-responsive release of loaded drug. Compared with icariin treatment, supramolecular complex icariin@SAC4A significantly relieved OA symptoms of rats, including more regular bone morphology and structure, and lower degree of cartilage damage. Moreover, the supramolecular formulation demonstrated various advantages, including easy preparation, hypoxia-triggered release, and small size that conducive to drug penetration.

Toward the Rational Design of Organic Catalysts for Organocatalysed Atom Transfer Radical Polymerisation.

Thanks to their diversity, organic photocatalysts (PCs) have been widely used in manufacturing polymeric products with well-defined molecular weights, block sequences, and architectures. Still, however, more universal property-performance relationships are needed to enable the rational design of such PCs. That is, a set of unique descriptors ought to be identified to represent key properties of the PCs relevant for polymerisation. Previously, the redox potentials of excited PCs (PC*) were used as a good descriptor for characterising very structurally similar PCs. However, it fails to elucidate PCs with diverse chromophore cores and ligands, among which those used for polymerisation are a good representative. As showcased by model systems of organocatalysed atom transfer radical polymerisation (O-ATRP), new universal descriptors accounting for additional factors, such as the binding and density overlap between the PC* and initiator, are proposed and proved to be successful in elucidating the experimental performances of PCs in polymerisation. While O-ATRP is exemplified here, the approach adopted is general for studying other photocatalytic systems.

TEMPO-Modified Polymethacrylates as Mediators in Electrosynthesis: Influence of the Molecular Weight on Redox Properties and Electrocatalytic Activity.

Homogeneous catalysts ("mediators") are frequently employed in organic electrosynthesis to control selectivity. Despite their advantages, they can have a negative influence on the overall energy and mass balance if used only once or recycled inefficiently. Polymediators are soluble redox-active polymers applicable as electrocatalysts, enabling recovery by dialysis or membrane filtration. Using anodic alcohol oxidation as an example, we have demonstrated that TEMPO-modified polymethacrylates (TPMA) can act as efficient and recyclable catalysts. In the present work, the influence of the molecular size on the redox properties and the catalytic activity was carefully elaborated using a series of TPMAs with well-defined molecular weight distributions. Cyclic voltammetry studies show that the polymer chain length has a pronounced impact on the key-properties. Together with preparative-scale electrolysis experiments, an optimum size range was identified for polymediator-guided sustainable reaction control.

Mechanically Driven Atom Transfer Radical Polymerization by Piezoelectricity.

Targeting sustainable and eco-friendly polymer synthesis, we demonstrate here a synergistically catalyzed atom transfer radical polymerization (ATRP) induced and controlled by interplay between ball milling (BM) and piezoelectric nanoparticles (piezoNPs). BM-induced electron transfer can be achieved through piezoNPs deformation under impact force, serving as an external stimulus to mediate polymerization. The ppm level of copper loading is sufficient in fabrication of a polymer with well-defined molecular weight and low polydispersity. High-molecular-weight polymers ranging from 33 to 74 kDa were prepared successfully through DMSO-assisted grinding. Besides, its good performance on availability of water as liquid-assisted grinding additive, the recyclability of piezoNPs, and the formation of cross-linker-free composite resin make our ATRP approach a green and practical option alongside the existent heat-, electro-, and photo-induced methods.

Mechanically induced atom transfer radical polymerization with high efficiency via piezoelectric heterostructures

A facile ultrasonication induced atom transfer radical polymerization (ATRP) mediated via piezoelectric heterostructure was developed. ZnO/BaTiO 3 heterostructure was prepared by in-situ deposition of zinc precursor on BaTiO 3 particles followed by high temperature annealing. Under ultrasonic activation, as-synthesized piezoelectric ZnO/BaTiO 3 heterostructure with an elevated macroscopic polarization could facilitate piezoelectric induced electron-hole pairs with more efficient separation and transfer, leading to the enhanced piezocatalytic in controlled living polymerization. High efficiency of ultrasonication mediated ATRP of methyl methacrylate (MMA) by ZnO/BaTiO 3 heterostructure about 63.1% conversion was achieved under 4 h ultrasonic agitation, providing PMMA homopolymer with well-defined molecular weight, narrow molecular dispersity and high end-group fidelity. Furthermore, implications of CuBr 2 /TPMA concentrations, piezoelectric materials, ZnO/BaTiO 3 heterostructure loading and distinct monomer were systematically investigated. Process of ultrasonication-mediated ATRP could be readily controlled by ultrasound switch on/off. The versatility of ultrasonication-mediated ATRP system was further verified by the preparation of star-like polymer. The ability of transfer piezoelectric-induced electrons from ZnO/BaTiO 3 heterostructure to CuBr 2 /TPMA and nature of ZnO/BaTiO 3 heterostructure were investigated to reveal the mechanism of ultrasonication mediated ATRP. A facile and robust atom transfer radical polymerization catalyzed by piezocatalyst with high efficiency was developed in this study. • Piezoelectric catalyst enabled mechanically induced atom transfer radical polymerization with high efficiency.

Efficient n-Type Small-Molecule Mixed Ion-Electron Conductors and Application in Hydrogen Peroxide Sensors.

Small-molecule semiconductors used as the channel of organic electrochemical transistors (OECTs) have been rarely reported despite their inherent advantages of well-defined molecular weight, convenient scale-up synthesis, and good performance reproducibility. Herein, three small molecules based on perylene diimides are readily prepared for n-type OECTs. The final molecules show preferred energy levels, tunable backbone conformation, and high film crystallinity, rendering them good n-type dopability, favorable volumetric capacities, and substantial electron mobilities. Consequently, the OECTs afford a record-low threshold voltage of 0.05 V and a normalized peak transconductance of 4.52 × 10-2 S cm-1, as well as impressive long-term cycling stability. Significantly, the OECTs utilized for hydrogen peroxide sensing are further demonstrated with a detection limit of 0.75 μM. This work opens the possibility of developing nonfullerene small molecules as superior n-type OECT materials and provides important insights for designing high-performance small-molecule mixed ion-electron conductors for OECTs and (bio)sensors.

An Updated Review of Bioactive Peptides from Mushrooms in a Well-Defined Molecular Weight Range.

Here, we report the current status of the bioactive peptides isolated and characterized from mushrooms during the last 20 years, considering ‘peptide’ a succession from to 2 to 100 amino acid residues. According to this accepted biochemical definition, we adopt ~10 kDa as the upper limit of molecular weight for a peptide. In light of this, a careful revision of data reported in the literature was carried out. The search revealed that in the works describing the characterization of bioactive peptides from mushrooms, not all the peptides have been correctly classified according to their molecular weight, considering that some fungal proteins (>10 kDa MW) have been improperly classified as ‘peptides’. Moreover, the biological action of each of these peptides, the principles of their isolation as well as the source/mushroom species were summarized. Finally, this review highlighted that these peptides possess antihypertensive, antifungal, antibiotic and antimicrobial, anticancer, antiviral, antioxidant and ACE inhibitory properties.

Quasiliving carbocationic polymerization of isobutylene using FeCl3 as an efficient and water-tolerant Lewis acid: synthesis of well-defined telechelic polyisobutylenes

A cost-efficient approach for the preparation of well-defined low molecular weight difunctional polyisobutulenes possessing an exo-olefin or hydroxyl group was developed in this study.

Review of photoresponsive and glycoside dendrimers in biomaterials and sensors applications.

Dendrimers are branched molecules with well-defined lengths, shapes, molecular weights, and monodispersity in comparison to linear polymers. The dual effect of the chromophore luminescence and the morphology of the synthesized dendrimers has drawn a lot of interest towards the design of dendrimers with different chromophores. Furthermore, the stimulus-responsive systems can sequester drug molecules under a preset set of parameters and release them in a different environment in response to either an exogenous or endogenous stimulus. The addition of photoresponsive moieties to different dendrimer components, such as the core or branches, magnifies the importance of the dendrimer in several related sectors of nanotechnology, such as sensors, photoswitches, electronic gadgets, and drug delivery systems. This review article focused on photoresponsive/glycoside dendrimer structures and their biomaterial applications.

Electronic and Magnetic Properties of a Three-Arm Nonconjugated Open-Shell Macromolecule.

Nonconjugated radical polymers (i.e., macromolecules with aliphatic backbones that have stable open-shell sites along their pendant groups) have arisen as an intriguing complement to π-conjugated polymers in organic electronic devices and may prove to have superior properties in magneto-responsive applications. To date, however, the design of nonconjugated radical polymers has primarily focused on linear homopolymer, copolymer, and block polymer motifs even though conjugated dendritic macromolecules (i.e., polyradicals) have shown significant promise in terms of their response under applied magnetic fields. Here, we address this gap in creating a nonconjugated, three-arm radical macromolecule with nitroxide open-shell sites using a straightforward, single-step reaction, and we evaluated the electronic and magnetic properties of this material using a combined computational and experimental approach. The synthetic approach employed resulted in a high-purity macromolecule with a well-defined molecular weight and narrow molecular weight distribution. Moreover, epoxide-based units were implemented in the three-arm radical macromolecule design, and this resulted in a nonlinear radical macromolecule with a low (i.e., below room temperature) glass transition temperature and one that was an amorphous material in the solid state. These properties allowed thin films of the three-arm radical macromolecule to have electrical conductivity values on par with many linear radical polymers previously reported, and our computational efforts suggest the potential of higher generation open-shell dendrimers to achieve advanced electronic and magnetic properties. Importantly, the three-arm radical macromolecule also demonstrated antiferromagnetic exchange coupling between spins at temperatures < 10 K. In this way, this effort puts forward key structure-property relationships in nonlinear radical macromolecules and presents a clear path for the creation of next-generation macromolecules of this type.

Helical Polycarbenes Bearing D-Prolinol Ester Pendants: An Efficient Catalyst for Asymmetric Michael Addition Reaction

A novel diazoacetate monomer (1) carrying tert-butyloxycarboryl (Boc) protected D-prolinol ester was designed and synthesized successfully. Molecular weight-controlled polymerization of 1 using the complex of π-allylPdCl coordinated Wei-phos (LR) ligand gives a series of helical polycarbenes (poly-1ms) with well-defined molecular weights (Mns) and low polydispersity (Mw/Mns). Removing the protecting Boc groups on the D-prolinol ester pendants leads to the formation of helical poly-1m-As, which showed high optical activity. Furthermore, the poly-1m-As showed high catalytic ability on asymmetric Michael addition reaction (up to 76% ee and 94/6 dr). Both the enantioselectivity and diastereoselectivity of the Michael addition reaction were increased comparing to D-prolinol as catalyst. Moreover, the helical polycarbene catalyst can be easily recovered and reused at least four times without significant loss of its enantioselectivity and diastereoselectivity.

Molecular Weight-Dependent Physical and Photovoltaic Properties of Poly(3-alkylthiophene)s with Butyl, Hexyl, and Octyl Side-Chains.

A series of poly-3-alkylthiophenes (P3ATs) with butyl (P3BT), hexyl (P3HT), and octyl (P3OT) side-chains and well-defined molecular weights (MWs) were synthesized using Grignard metathesis polymerization. The MWs of P3HTs and P3OTs obtained via gel permeation chromatography agreed well with the calculated MWs ranging from approximately 10 to 70 kDa. Differential scanning calorimetry results showed that the crystalline melting temperature increased with increasing MWs and decreasing alkyl side-chain length, whereas the crystallinity of the P3ATs increased with the growth of MWs. An MW-dependent red shift was observed in the UV–Vis and photoluminiscence spectra of the P3ATs in solution, which might be a strong evidence for the extended effective conjugation occurring in polymers with longer chain lengths. The photoluminescence quantum yields of pristine films in all polymers were lower than those of the diluted solutions, whereas they were higher than those of the phenyl-C61-butyric acid methyl ester-blended films. The UV–Vis spectra of the films showed fine structures with pronounced red shifts, and the interchain interaction-induced features were weakly dependent on the MW but significantly dependent on the alkyl side-chain length. The photovoltaic device performances of the P3BT and P3HT samples significantly improved upon blending with a fullerene derivative and subsequent annealing, whereas those of P3OTs mostly degraded, particularly after annealing. The optimal power conversion efficiencies of P3BT, P3HT, and P3OT were 2.4%, 3.6%, and 1.5%, respectively, after annealing with MWs of ~11, ~39, and ~38 kDa, respectively.

Rethinking Transition Metal Catalyzed N-Carboxyanhydride Polymerization: Polymerization of Pro and AcOPro N-Carboxyanhydrides.

Polyproline (PP) based polypeptides have broad applications as protein mimics, ordered materials, hydrogels, and surface coatings. However, a lack of rapid and efficient preparatory methods has challenged synthesis of well-defined high molecular weight materials. Here, we report facile and high-yielding methods for preparation and polymerization of Pro and trans-4-acetoxy-Pro N-carboxyanhdrides (NCAs). For decades, transition metal initiators of NCA polymerization were assumed to be nonstarters with Pro due to the lack of an amide NH proton. We carefully considered the known steps in the initiation mechanism and applied a Ni initiator that intercepts an intermediate and does not require an NH group. This initiator efficiently catalyzes controlled, living polymerization of Pro NCAs, revealing that routes alternate to the previously proposed mechanism must be at play. We also found Co species can catalyze Pro NCA polymerization, and we improved the synthetic methods to prepare the NCA monomers. Our methods are high-yielding and rapid and give tunable, end-functional PP-based homo, statistical, and block polypeptides. We characterized the conformation of PP and trans-4-hydroxy-PP by CD and confirmed the time scale for quantitative conversion from PPI to PPII helices. Overall, our data shed light on the general propagation mechanism of transition metal catalyzed NCA polymerization and have opened the door for efficient preparation of a desirable class of biomaterials.

Withdrawal: Quantitative Synthesis of Temperature-responsive Polymersomes by Multiblock Polymerization.

The current challenge for polymersomes is to prepare amphiphilic block polymers with not only well-defined molecular weight, but also precisely high-order multiblock structure in terms of the distribution of monomeric units along the chain. Here, we describe a synthesis of temperature-responsive polymersomes with precisely defined membrane structures using high-precision amphiphilic multiblock polymer via aqueous single electron transfer living radical polymerization (SET-LRP) in which poly(ethylene glycol) (PEG) macromolecules are used as initiators. We develop a one-pot, rapid and multistep sequential polymerization process with yields >99% within 30 min for each block, giving access to a wide range of high-precision multiblock polymers with very narrow molecular weight distributions (Ð ≤ 1.14). Synthesized multiblock polymers are used to form nano-sized polymersomes which are highly promising as smart carriers for high loading and triggered release of biopharmaceutics such as pharmaceutical proteins and peptides. This synthesis approach is environmentally friendly, fully translation and thus represents a significant advance in the design and synthesis of a new generation of polymer nanomaterials with precisely defined structures, which is highly attractive for applications in nanotechnology.

Fluxional bis(phenoxy-imine) Zr and Ti catalysts for polymerization

Bis(phenoxy-imine) complexes of zirconium or titanium, a type of Fenokishi-Imin catalysts, allow the production of polyethylenes with well-defined bimodal molecular weight distributions. Interestingly, by substitution of phenyl rings in the bis(phenoxy-imine) ligands by perfluorinated phenyl rings, the polymerization reaches a desired unimodal behavior. These catalysts have three isomers of similar energy that can be easily interconverted. It is likely that the bimodal behavior is due to the coexistence of more than one isomer in the reaction vessel. Here, we perform static and dynamic DFT calculations to understand the isomerization of the catalytic active species. We analyze the relative Gibbs energies of the different isomers and the barriers for the isomerization processes. Further characterization of the isomers is obtained through stereo maps, aromaticity measures, and NCI plots. Our results show that by changing the phenyl group by a perfluorinated phenyl ring, one of the isomers is particularly stabilized, thus explaining the unimodal behavior of the polyethylene production process.

Trisulfide-Bearing PEG Brush Polymers Donate Hydrogen Sulfide and Ameliorate Cellular Oxidative Stress.

A potential approach to combat cellular dysfunction is to manipulate cell communication and signaling pathways to restore physiological functions while protecting unaffected cells. For instance, delivering the signaling molecule H2S to certain cells has been shown to restore cell viability and re-normalize cell behavior. We have previously demonstrated the ability to incorporate a trisulfide-based H2S-donating moiety into linear polymers with good in vitro releasing profiles and demonstrated their potential for ameliorating oxidative stress. Herein, we report two novel series of brush polymers decorated with higher numbers of H2S-releasing segments. These materials contain two trisulfide-based monomers co-polymerized with oligo(ethylene glycol methyl ether methacrylate) via reversible addition-fragmentation chain-transfer polymerization. The macromolecules were characterized to have a range of trisulfide densities with similar, well-defined molecular weight distribution, good H2S-releasing profiles, and high cellular tolerance. Using an amperometric technique, the H2S liberated and total sulfide release were found to depend on concentrations and chemical nature of triggering molecules (glutathione and cysteine) and, importantly, the position of reactive groups within the brush structure. Notably, when introduced to cells at well-tolerated doses, two macromolecular donors which have the same proportion as of the H2S-donating monomer (30%) but differ in releasing moiety location show similar cellular H2S-releasing kinetics. These donors can restore reactive oxygen species levels to baseline values, when polymer pretreated cells are exposed to exogenous oxidants (H2O2). Our work opens up a new aspect in preparing H2S macromolecule donors and their application to arresting cellular oxidative cascades.

Synthesis of Amphiphilic and Double Hydrophilic Star-like Block Copolymers and the Dual pH-Responsiveness of Unimolecular Micelle

A series of amphiphilic star-like triblock copolymers with well-defined molecular architectures, molecular weight, and narrow polydispersity were successfully synthesized by sequential atom transfe...

Coceth sulfate characterization by electrospray ionization tandem mass spectrometry

The anionic surfactants, among which are alkyl ether sulfates (AESs), are the most used class of surfactants in cleansing applications. The negatively charged head group of AESs is a sulfate moiety linked with a variable number of ethylene oxide units, i.e. a polyethylene glycol chain. The hydrophobic part of an AES is constituted by a linear alkyl chain of carbon atoms, generally obtained from natural fatty acids. Coconut oil fatty acids, including the sodium salts of coceth sulfate (CES) with chemical formula Cx Hy (OCH2 CH2 )n OSO3 Na, are widely used as feedstock for AESs synthesis. CES is added to many cleaning products and detergents defined as non-aggressive. Currently, no detailed structural information concerning the alkyl chain length x and, more importantly, the degree of ethoxylation n has been reported. A commercial standard solution of CES was characterized by tandem mass spectrometry, employing direct injection into the electrospray ionization (ESI) source of a a linear quadrupole ion trap mass spectrometer. Two series of oligomeric species, characterized by a C12 and C14 alkyl chains, i.e. [C12 H25 (OCH2 CH2 )nOSO3 ]- and [C14 H29 (OCH2 CH2 )n OSO3 ]- with n ranging from 0 to 7, were successfully identified. The interpretation of these data was very useful for CES identification in three commercial dishwasher cleaning products. Direct injection MS/MS analysis of CES revealed a well-defined molecular weight distribution and allowed the alkyl chain composition and the number of ethylene oxide units to be to identified.

Dual Role of Doxorubicin for Photopolymerization and Therapy.

In this study, we report dual roles for doxorubicin (DOX), which can serve as an antitumor drug as well as a cocatalyst for a photoliving radical polymerization. DOX enhances the polymerization rates of a broad range of monomers, including acrylamide, acrylate, and methacrylates, allowing for high monomer conversion and well-defined molecular weights under irradiation with a blue light-emitting diode light (λmax = 485 nm, 2.2 mW/cm2). Utilizing this property, the photopolymerization of N,N-diethylacrylamide was performed in the presence of a poly(oligo(ethylene glycol) methyl ether acrylate) macroreversible addition-fragmentation chain transfer (macroRAFT) agent to prepare polymeric nanoparticles via aqueous polymerization-induced self-assembly (PISA). By varying the monomer:macroRAFT ratio, spherical polymeric nanoparticles of various diameters could be produced. Most notably, DOX was successfully encapsulated into the hydrophobic core of nanoparticles during the PISA process. The DOX-loaded nanoparticles were effectively uptaken into tumor cells and significantly inhibited the proliferation of tumor cells, demonstrating that the DOX bioactivity was not affected by the polymerization reaction.

Exploring precision polymers to fine-tune magnetic resonance imaging properties of iron oxide nanoparticles

The use of bio-polymers as stabilising agents for iron oxide-based negative magnetic resonance imaging (MRI) contrast agents has become popular in recent years, however the wide polydispersity of biologically-derived and commercially available polymers limits the ability to produce truly tuneable and reproducible behaviour, a major challenge in this area. In this work, stable colloids of iron oxide nanoparticles were prepared utilising precision-engineered bio-polymer mimics, poly(2-acrylamido-2-methylpropane sodium sulfonate) (P(AMPS)) polymers, with controlled narrow polydispersity molecular weights, as templating stabilisers. In addition to producing magnetic colloids with excellent MRI contrast capabilities (r2 values reaching 434.2 mM−1 s−1 at 25 °C and 23 MHz, several times higher than similar commercial analogues), variable field relaxometry provided unexpected important insights into the dynamic environment of the hydrated materials, and hence their exceptional MRI behaviour. Thanks to the polymer’s templating backbone and flexible conformation in aqueous suspension, nanocomposites appear to behave as “multi-core” clustered species, enhancing interparticle interactions whilst retaining water diffusion, boosting relaxation properties at low frequency. This clustering behaviour, evidenced by small-angle X-ray scattering, and strong relaxometric response, was fine-tuned using the well-defined molecular weight polymer species with precise iron to polymer ratios. By also showing negligible haemolytic activity, these nanocomposites exhibit considerable potential for MRI diagnostics.