Catalytic Light-Driven Strategy for Transforming Oximes to Carbonyls

Oxime and carbonyl functional groups serve as powerful chemical hubs for constructing complex synthetic targets and valuable molecular scaffolds. In furthering this value, we report a photopromoted catalytic deoximation protocol for converting oximes and their derivatives to carbonyl functional groups. This strategic approach benefits from the use of renewable light energy input and ambient air conditions, in addition to demonstrating good substrate scope, functional group tolerance, and product yields. In offering, insights into these reactivity mechanistic studies are communicated, and the value of this protocol is further shown through one-pot operations.

Bromine indirubin FLIM/PLIM sensors to measure oxygen in normoxic and hypoxic PDT conditions

BACKGROUND

The induction of phototoxicity during photodynamic therapy (PDT) is dependent on oxygen availability. For this reason, the development of sensors to measure oxygen and oxygen consumption is extremely important.

APPROACH

In this project we have used Fluorescence Lifetime imaging (FLIM) and Phosphorescence Lifetime Imaging/ delayed Fluorescence Lifetime Imaging (PLIM/dFLIM) to investigate the ability of bromine indirubin derivatives as oxygen sensors.

RESULTS

The oxygen sensitivity of bromine indirubins was detected through PLIM/dFLIM. Moreover, we have observed, by measuring nicotinamide adenine dinucleotide (NADH) FLIM, that bromine indirubin has a significant impact on cellular metabolism by shifting the SCC-4 Cells metabolism from oxidative phosphorylation (OXPHOS) to glycolysis.

CONCLUSIONS

In conclusion, this study successfully achieves its goals and provides important insights into the use of indirubin as a potential oxygen consumption sensor with the capability to identify and differentiate between normoxic and hypoxic regions within the cells.

Oxime - Urethane Structure-based Dynamically Crosslinked Polyurethane with Robust Reprocessing Property

Crosslinked polyurethane with excellent mechanical property, solvent resistance and transparency has become one of the most widely used materials. However, the presence of chemical crosslinks makes it difficult to be reprocessed once moulded, which largely restricts its recycling and reusing, resulting in the serious waste problems. Therefore, it is of great significance to prepare a new type of crosslinked polyurethane with reprocessing function. In this work, a novel reprocessable polyurethane (DOPUs) based on reversible dibutanone oxime-carbamate bonds was facilely prepared. The gel fraction of DOPUs is all higher than 95%, endowing it with excellent solvent resistance. Meanwhile, the visible light transmittance of DOPUs can reach up to 97.48%. After four thermal recycles, the tensile strength and elongation at break of recycled DOPUs can still remain at 3.21 MPa and 219.09%, respectively. Importantly, the synthesized DOPUs exhibit excellent elastic shape memory and permanent shape reconstruction properties under thermal stimulation. The dibutanone oxime-carbamate bonds can also be degraded under UV irradiation, making this material easily degradable. Hence, this material has potential applications in coatings, elastomers and some other fields. This article is protected by copyright. All rights reserved.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Polymeric Nitric Oxide Delivery Nanoplatforms for Treating Cancer, Cardiovascular Diseases, and Infection

The shortened Abstract is as follows: Therapeutic gas nitric oxide (NO) has demonstrated the unique advances in biomedical applications due to its prominent role in regulating physiological/pathophysiological activities in terms of vasodilation, angiogenesis, chemosensitizing effect, and bactericidal effect. However, it is challenging to deliver NO, due to its short half-life (<5 s) and short diffusion distances (20-160 µm). To address these, various polymeric NO delivery nanoplatforms (PNODNPs) have been developed for cancer therapy, antimicrobial and cardiovascular therapeutics, because of the important advantages of polymeric delivery nanoplatforms in terms of controlled release of therapeutics and the extremely versatile nature. This reviews highlights the recent significant advances made in PNODNPs for NO storing and targeting delivery. The ideal and unique criteria that are required for PNODNPs for treating cancer, cardiovascular diseases and infection, respectively, are summarized. Hopefully, effective storage and targeted delivery of NO in a controlled manner using PNODNPs could pave the way for NO-sensitized synergistic therapy in clinical practice for treating the leading death-causing diseases.

Indoline Catalyzed Acylhydrazone/Oxime Condensation under Neutral Aqueous Conditions

Acylhydrazones formation has been widely applied in materials science and biolabeling. However, their sluggish condensation rate under neutral conditions limits its application. Herein, indolines with electron-donating groups are reported as a new catalyst scaffold, which can catalyze acylhydrazone, hydrazone, and oxime formation via an iminium ion intermediate. This new type of catalyst showed up to 15-fold rate enhancement over the traditional aniline-catalyzed reaction at neutral conditions. The identified indoline catalyst was successfully applied in hydrogel formation.

Targeting organophosphorus compounds poisoning by novel quinuclidine-3 oximes: development of butyrylcholinesterase-based bioscavengers

A library of 14 mono-oxime quinuclidinium-based compounds with alkyl or benzyl substituent were synthesized and characterized in vitro as potential antidotes for organophosphorus compounds (OP) poisoning treatment. We evaluated their potency for reversible inhibition and reactivation of OP inhibited human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) and evaluated interactions by molecular docking studies. The reactivation was notable for both AChE and BChE inhibited by VX, cyclosarin, sarin and paraoxon, if quinuclidinium compounds contained the benzyl group attached to the quinuclidinium moiety. Out of all 14, oxime Q8 [4-bromobenzyl-3-(hydroxyimino)quinuclidinium bromide] was singled out as having the highest determined overall reactivation rate of approximately 20,000 M^-1 min^-1 for cyclosarin-inhibited BChE. Furthermore, this oxime in combination with BChE exhibited a capability to act as a bioscavenger of cyclosarin, degrading within 2 h up to 100-fold excess of cyclosarin concentration over the enzyme. Molecular modeling revealed that the position of the cyclohexyl moiety conjugated with the active site serine of BChE directs the favorable positioning of the quinuclidinium ring and the bromophenyl moiety of Q8, which makes phosphonylated-serine easily accessible for the nucleophilic displacement by the oxime group of Q8. This result presents a novel scaffold for the development of new BChE-based bioscavengers. Furthermore, a cytotoxic effect was not observed for Q8, which also makes it promising for further in vivo reactivation studies.

Toward Stimuli-Responsive Dynamic Thermosets through Continuous Development and Improvements in Covalent Adaptable Networks (CANs)

Covalent adaptable networks (CANs), unlike typical thermosets or other covalently crosslinked networks, possess a unique, often dormant ability to activate one or more forms of stimuli-responsive, dynamic covalent chemistries as a means to transition their behavior from that of a viscoelastic solid to a material with fluid-like plastic flow. Upon application of a stimulus, such as light or other irradiation, temperature, or even a distinct chemical signal, the CAN responds by transforming to a state of temporal plasticity through activation of either reversible addition or reversible bond exchange, either of which allows the material to essentially re-equilibrate to an altered set of conditions that are distinct from those in which the original covalently crosslinked network is formed, often simultaneously enabling a new and distinct shape, function, and characteristics. As such, CANs span the divide between thermosets and thermoplastics, thus offering unprecedented possibilities for innovation in polymer and materials science. Without attempting to comprehensively review the literature, recent developments in CANs are discussed here with an emphasis on the most effective dynamic chemistries that render these materials to be stimuli responsive, enabling features that make CANs more broadly applicable.

Covalent Attachment of P15 Peptide to Ti Alloy Surface Modified with Polymer to Enhance Osseointegration of Implants

Titanium (Ti) and its alloys are used in orthopedic and dental implants due to their excellent physical properties and biocompatibility. Although Ti exhibits superior osteoconductive properties compared to those of polymer-based implants, improved bone-on growth properties are required for enhanced surgical outcomes and improved recovery surgical interventions. Herein, we demonstrate a novel surface modification strategy to enhance the osteoconductivity of Ti surfaces through the grafting-from procedure of a reactive copolymer via surface-initiated atom transfer radical polymerization (SI-ATRP). Then, postpolymerization conjugation of the P15 peptide, an osteoblast binding motif, was successfully carried out. Subsequent in vitro studies revealed that the surface modification promoted osteoblast attachment on the Ti discs at 6 and 24 h. Moreover, mineral matrix deposition by osteoblasts was greater for the surface-modified Ti than for plain Ti and P15 randomly absorbed onto the Ti surface. These results suggest that the strategy for postpolymerization incorporation of P15 onto a Ti surface with a polymer interface may provide improved osseointegration outcomes, leading to enhanced quality of life for patients.

Gas chromatography-Fourier transform infrared spectroscopy reveals dynamic molecular interconversion of oximes

This study reports gas chromatography (GC) combined with Fourier transform infrared (FTIR) spectroscopy to investigate the elution profiles of individual oxime isomers undergoing characteristic interconversion (dynamic chromatography) in GC. The use of a light-pipe FTIR interface enables on-line acquisition of FTIR spectra, which in turn render unambiguous identification of the individual molecules. Here, acetaldehyde oxime and propionaldehyde oxime were chosen for comparison of elution behaviour under varying temperature and carrier flow velocities. The choice of selective responses (wavenumber selectivity), which were relatively stronger for each isomer, enabled display and retracing of the individual isomer over the chromatographic time scale and thus provided characteristic single isomer profiles. Chemometric data analysis using the multivariate curve resolution technique further confirmed this isomer elution profile. Simulation of the spectrum for each isomer allowed comparison with instrument-generated FTIR spectra to confirm the elution order of E and Z isomers. The effect of changing chromatographic parameters (temperature, flow) on interconversion rates and/or extents were studied and the corresponding change in FTIR spectrum intensity was noted. The GC-FID data acquired concurrently with GC-FTIR analyses ratified isomerisation chromatographic profiles.

A versatile method for the selective core-crosslinking of hyaluronic acid nanogels via ketone-hydrazide chemistry: from chemical characterization to in vivo biodistribution

Nanogels show long in vivo blood circulation time and high tumor accumulation.

Maximizing the symbiosis of static and dynamic bonds in self-healing boronic ester networks

Networks that contain boronic ester crosslinks undergo dynamic bond exchange that enables self-healing behavior and reprocessing.

Dynamic Covalent Hydrogels for Triggered Cell Capture and Release

A dual-responsive, cell capture and release surface was prepared through the incorporation of phenylboronic acid (PBA) groups into an oxime-based polyethylene glycol (PEG) hydrogel. Owing to its PEG-like properties, the unfunctionalized hydrogel was nonfouling. The use of highly efficient oxime chemistry allows the incorporation of commercially available 3,5-diformylphenyl boronic acid into the hydrogel matrix. Thus, the surface properties of the hydrogel were modified to enable reversible cell capture and release. Boronic ester formation between PBA groups and cell surface carbohydrates enabled efficient cell capture at pH 6.8. An increase to pH 7.8 resulted in cell detachment. This capture-and-release procedure was performed on MCF-7 human breast cancer cells, NIH-3T3 fibroblast cells, and primary human umbilical vein endothelial cells (HUVECs) and could be cycled with negligible loss in activity. The facile preparation of PBA-functionalized surfaces presented here has applications in biomedical fields such as cell diagnostics and cell culture.

Near-IR-induced dissociation of thermally-sensitive star polymers

Responsive systems sensitive to near-infrared (NIR) light are promising for triggered release due to efficient deep tissue penetration of NIR irradiation relative to higher energy sources (e.g., UV), allowing for spatiotemporal control over triggering events with minimal potential for tissue damage. Herein, we report star polymers containing thermally-labile azo linkages that dissociate during conventional heating or during localized heating via the photothermal effect upon NIR irradiation. Controlled release during conventional heating was investigated for the star polymers loaded with a model dye, with negligible release being observed at 25 °C and >80% release at 90 °C. Star polymers co-loaded with NIR-responsive indocyanine green showed rapid dye release upon NIR irradiation (λ ≥ 715 nm) due to the photothermally-induced degradation of azo linkages within the cores of the star polymers. This approach provides access to a new class of delivery and release systems that can be triggered by noninvasive external stimulation.

Radical Departure: Thermally-Triggered Degradation of Azo-Containing Poly(β-thioester)s

The design and synthesis of a new class of thermally-labile poly(β-thioester)s is reported. Aliphatic azo linkages were incorporated into the main chain of the polymers to allow for degradation to lower molecular weights upon heating. These polymers displayed a temperature-dependent degradation profile with a significant increase in decomposition rate as the temperature was raised from 60 to 95 °C. This approach was further extended to prepare amphiphilic triblock copolymers containing poly(β-thioester)s and poly(ethylene glycol) (PEG). The resulting block copolymers were capable of self-assembly into micelles in water. Moreover, the assembled nanoparticles underwent dissociation as a result of exposure to heat.

Star Polymers

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

Co-delivery of nitric oxide and antibiotic using polymeric nanoparticles

The rise of hospital-acquired infections, also known as nosocomial infections, is a growing concern in intensive healthcare, causing the death of hundreds of thousands of patients and costing billions of dollars worldwide every year. In addition, a decrease in the effectiveness of antibiotics caused by the emergence of drug resistance in pathogens living in biofilm communities poses a significant threat to our health system. The development of new therapeutic agents is urgently needed to overcome this challenge. We have developed new dual action polymeric nanoparticles capable of storing nitric oxide, which can provoke dispersal of biofilms into an antibiotic susceptible planktonic form, together with the aminoglycoside gentamicin, capable of killing the bacteria. The novelty of this work lies in the attachment of NO-releasing moiety to an existing clinically used drug, gentamicin. The nanoparticles were found to release both agents simultaneously and demonstrated synergistic effects, reducing the viability of Pseudomonas aeruginosa biofilm and planktonic cultures by more than 90% and 95%, respectively, while treatments with antibiotic or nitric oxide alone resulted in less than 20% decrease in biofilm viability.

Extremely rapid and versatile synthesis of high molecular weight step growth polymers via oxime click chemistry

Extremely rapid step growth polymerization was achieved using an oxime click chemistry approach.

The emergence of oxime click chemistry and its utility in polymer science

The synthesis of new, highly functional and dynamic polymeric materials has risen dramatically since the introduction of click chemistry in 2001.

Doubly-dynamic-covalent polymers composed of oxime and oxanorbornene links

Two sets of reversible covalent linkages distributed in series along a polymer backbone were used to prepare a new class of doubly dynamic-covalent polymers capable of reversibly dissociatingviatwo distinct pathways.

Synthesis of Miktoarm Branched Conjugated Copolymers by ROMPing In and Out

Architecture represents an underutilized yet promising control element in polymer design due to the challenging synthesis of compositionally varied branched copolymers. We report the one-pot synthesis of miktoarm branched polymers by ring-opening metathesis polymerization. In this work, we graft to and from telechelic poly(3-hexylthiophene), which is end-capped by oxime click chemistry, using various norbornene monomers. The self-assembly of the resulting miktoarm H-shaped conjugated polymers is studied in solution and in the solid state. A dual stimuli-responsive miktoarm polymer is prepared which displays pH-switchable lower critical solution temperature and fluorescence.

Postpolymerization Modification of Poly(dihydropyrimidin-2(1H)-thione)s via the Thiourea-Haloalkane Reaction to Prepare Functional Polymers

A highly reactive thiourea-contained polycondensate, poly(dihydropyrimidin-2(1H)-thione) (poly(DHPMT)) has been facilely synthesized via the Biginelli polycondensation using thiourea and a difunctional compound containing benzaldehyde and β-keto ester groups as monomers. The thiourea moiety in the polymer structure has similar reactivity as the thiourea, thus the poly(DHPMT) is an excellent polymer precusor for preparing new functional polymers through the postpolymerization modification (PPM) strategy. After simple reaction with functional haloalkanes, the parent poly(DHPMT) could be almost completely converted (>99%) to daughter polymers containing alkene or alkyne side groups. Then, the daughter polymers have been further transferred to granddaughter polymers through another PPM via thiol-ene or Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions. Besides, when 3-phenylpropargyl chloride was used as the reactant, a bright yellow fluorescent polymer could be simply achieved due to the in situ formed conjugated heterocycle in the polymer structure, further demonstrating the diversity of the functional polymers through PPM. Considering the easily available monomers, simple polycondensation, and the excellent reactivity of the thiourea moiety in the polymer structure, this thiourea-contained Biginilli polycondensate might be a versatile platform for new functional polymer preparation.

Self-healing hydrogels containing reversible oxime crosslinks

Self-healing oxime-functional hydrogels have been developed that undergo a reversible gel-to-sol transition via oxime exchange under acidic conditions. Keto-functional copolymers were prepared by conventional radical polymerization of N,N-dimethylacrylamide (DMA) and diacetone acrylamide (DAA). The resulting water soluble copolymers (P(DMA-stat-DAA)) were chemically crosslinked with difunctional alkoxyamines to obtain hydrogels via oxime formation. Gel-to-sol transitions were induced by the addition of excess monofunctional alkoxyamines to promote competitive oxime exchange under acidic conditions at 25 °C. The hydrogel could autonomously heal after it was damaged due to the dynamic nature of the oxime crosslinks. In addition to their chemo-responsive behavior, the P(DMA-stat-DAA) copolymers exhibit cloud points which vary with the DAA content in the copolymers. This thermo-responsive behavior of the P(DMA-stat-DAA) was utilized to form physical hydrogels above their cloud point. Therefore, these materials can either form dynamic-covalent or physically-crosslinked gels, both of which demonstrate reversible gelation behavior.