Crosslinking Vinyl-Addition Polynorbornenes via Difunctional Diazirines to Generate Low Dielectric-Constant and Low Dielectric-Loss Thermosets.

Thermosets having low dielectric constant (Dk < 3) and low dielectric dissipation factor (Df < 0.003), high glass transition temperature (Tg > 150 °C), and good adhesion to copper are desirable for the low loss layers of the copper clad laminates (CCL) in next generation printed circuit boards. Three different difunctional diazirines are evaluated for both thermal and photochemical crosslinking of a high Tg vinyl-addition polynorbornene resin: poly(5-hexyl-1-norbornene) (poly(HNB)). The substrate polymer, crosslinked by the carbenes generated from the activated diazirines, forms thermosets with Dk < 2.3 and Df < 0.001 at 10 GHz depending on the identity of the diazirine and the loading. The Dk and Df values for one composition are stable for 1600 h at 125 °C in air and for 1400 h at 85 °C and 85% relative humidity, suggesting good long-term reliability of this thermoset. Adhesion of poly(HNB) to copper can be enhanced by priming the copper surface with a diazirine prior to high temperature lamination; peel strength values of greater than 7.5 N cm-1 are achieved. Negative-tone photopatterning of poly(HNB) with diazirines upon exposure to 365 nm light is demonstrated.

Safety Evaluation of a Prototypical Diazirine-Based Covalent Crosslinker and Molecular Adhesive.

bis-Diazirine reagents are increasingly being used as polymer crosslinkers, adhesives, and photopatterning agents in the materials sciences literature, but little effort has been made thus far to document their chemical safety profile. Here, we describe the results of a detailed toxicity assessment of a representative bis-diazirine. Safety was evaluated by a series of in vitro assays, which found the product to be non-mutagenic in bacterial tester strains TA98 and TA100, non-corrosive and non-irritating to skin, and requiring no classification for eye irritation or serious damage. While in vitro tests do not capture the integrated whole animal system, and thus cannot completely rule out the possibility of adverse responses, the results of this study suggest a desirable safety profile for bis-diazirine reagents and provide a solid foundation upon which to add in vivo assessment of safety risk and dose-response studies.

Multiple Stabilization Effects of Benzylhydrazine on Scalable Perovskite Precursor Inks for Improved Perovskite Solar Cell Production.

Perovskite precursor inks suffer various forms of degradation, such as iodide anion oxidation and organic cation breakdown, hindering reliable perovskite solar cell manufacturing. Here we report that benzylhydrazine hydrochloride (BHC) not only retards the buildup of iodine as previously reported but also prevents the breakdown of organic cations. Through investigating BHC and iodine chemical reactions, we elucidate protonation and dehydration mechanisms, converting BHC to harmless volatile compounds, thus preserving perovskite film crystallization and solar cell performance. This inhibition effect lasts nearly a month with minimal BHC, contrasting control inks without BHC where organic cations fully react in less than a week. This enhanced understanding, from additive stabilization to end products, promises improved perovskite solar cell production reliability.

A Cleavable Crosslinking Strategy for Commodity Polymer Functionalization and Generation of Reprocessable Thermosets.

Covalently crosslinked polymeric materials, known as thermosets, possess enhanced mechanical strength and thermal stability relative to the corresponding uncrosslinked thermoplastics. However, the presence of covalent inter-chain crosslinks that makes thermosets so attractive is precisely what makes them so difficult to reprocess and recycle. Here, we demonstrate the introduction of chemically cleavable groups into a bis-diazirine crosslinker. Application of this cleavable crosslinker reagent to commercial low-functionality polyolefins (or to a small-molecule model) results in the rapid, efficient introduction of molecular crosslinks that can be uncoupled by specific chemical inputs. These proof-of-concept findings provide one potential strategy for circularization of the thermoplastic/thermoset plastics economy, and may allow crosslinked polyolefins to be manufactured, used, reprocessed, and re-used without losing value. As an added benefit, the method allows the ready introduction of functionality into non-functionalized commodity polymers.

Improvements in Drug-Delivery Properties by Co-Encapsulating Curcumin in SN-38-Loaded Anticancer Polymeric Nanoparticles.

SN-38 is an immensely potent anticancer agent although its use necessitates encapsulation to overcome issues of poor solubility and stability. Since SN-38 is a notoriously challenging drug to encapsulate, new avenues to increase encapsulation efficiency in polymer nanoparticles (PNPs) are needed. In this paper, we show that nanoprecipitation with curcumin (CUR) increases SN-38 encapsulation efficiencies in coloaded SN-38/CUR-PNPs based on poly(ε-caprolactone)-block-poly(ethylene glycol) (PCL-b-PEG) by up to a factor of 10. In addition, we find a dramatic decrease in PNP polydispersities, from 0.34 to 0.07, as the initial CUR-to-polymer ratio increases from 0 to 10, with only a modest increase in PNP size (from 40 to 55 nm). Compared to coloaded PNP formation using nanoprecipitation in the bulk or in a gas-liquid, a two-phase microfluidic reactor shows similar trends with respect to CUR content, although improvements in SN-38 encapsulation efficiencies both with and without CUR are found using the microfluidic method. Additional precipitation studies without copolymer suggest that CUR increases the dispersion of SN-38 in the solvent medium of micelle formation, which may contribute to the observed encapsulation enhancement. Cytotoxicity studies of unencapsulated SN-38/CUR mixtures show that addition of CUR does not significantly affect SN-38 potency against either U87 (glioblastoma) or A204 (rhabdomyosarcoma) cell lines. However, we find significant differences in the potencies of SN-38/CUR-PNP formulations depending on initial CUR amounts, with an optimized formulation showing subnanomolar cytotoxicity against A204 cells, significantly more potent than either free SN-38 or PNPs containing only SN-38.

Discovery of salicyl benzoate UDP-glycosyltransferase, a central enzyme in poplar salicinoid phenolic glycoside biosynthesis.

The salicinoids are anti-herbivore phenolic glycosides unique to the Salicaceae (Populus and Salix). They consist of a salicyl alcohol glucoside core, which is usually further acylated with benzoic, cinnamic or phenolic acids. While salicinoid structures are well known, their biosynthesis remains enigmatic. Recently, two enzymes from poplar, salicyl alcohol benzoyl transferase and benzyl alcohol benzoyl transferase, were shown to catalyze the production of salicyl benzoate, a predicted potential intermediate in salicinoid biosynthesis. Here, we used transcriptomics and co-expression analysis with these two genes to identify two UDP-glucose-dependent glycosyltransferases (UGT71L1 and UGT78M1) as candidate enzymes in this pathway. Both recombinant enzymes accepted only salicyl benzoate, salicylaldehyde and 2-hydroxycinnamic acid as glucose acceptors. Knocking out the UGT71L1 gene by CRISPR/Cas9 in poplar hairy root cultures led to the complete loss of salicortin, tremulacin and tremuloidin, and a partial reduction of salicin content. This demonstrated that UGT71L1 is required for synthesis of the major salicinoids, and suggested that an additional route can lead to salicin. CRISPR/Cas9 knockouts for UGT78M1 were not successful, and its in vivo role thus remains to be determined. Although it has a similar substrate preference and predicted structure as UGT71L1, it appears not to contribute to the synthesis of salicortin, tremulacin and tremuloidin, at least in roots. The demonstration of UGT71L1 as an enzyme of salicinoid biosynthesis will open up new avenues for the elucidation of this pathway.

A Chan-Evans-Lam approach to trisubstituted vinyl ethers.

Trisubstituted vinyl ethers were accessed via Chan-Evans-Lam coupling of vinyl trifluoroborates and primary aliphatic alcohols. This approach complements prior methods that required the use of neat liquid alcohol coupling partners. A palladium-catalyzed redox-relay Heck reaction was used to convert several vinyl ethers into aldehyde-functionalized 1,3-dihydroisobenzofurans.

Efficient purification of the diarylheptanoid oregonin from red alder (Alnus rubra) leaves and bark combining aqueous extraction, spray drying and flash-chromatography.

INTRODUCTION: The diarylheptanoid xyloside oregonin ((5S)-1,7-bis(3,4-dihydroxyphenyl)-5-(ß-d-xylopyranosyloxy)-heptan-3-one) has significant medicinal potential and is found at high concentration in leaves and bark of red alder (Alnus rubra). OBJECTIVES: To establish inexpensive and easily scaled methods for the extraction and purification of oregonin from timber by-products. METHODS: We developed a method combining aqueous extraction with spray drying of red alder extract into a powder, thus reducing the need for organic solvents used in traditional Soxhlet extraction or in solvent partitioning. Flash chromatography was utilised to purify oregonin from crude spray-dried alder extract. RESULTS: Crude spray-dried alder extract was comprised of an average of 9% of the diarylheptanoid compound oregonin. Less than 10% thermal degradation of oregonin was observed using extraction temperatures between 25°C and 50°C, followed by spray drying. The structure of purified oregonin was validated using high-performance liquid chromatography (HPLC), mass spectrometry (MS), ultraviolet spectroscopy (UV), and nuclear magnetic resonance (NMR). CONCLUSION: The developed method was robust, repeatable, and yielded purified oregonin of greater than > 95% purity (average of 95.8%). Our analysis represents the most complete NMR characterisation of oregonin reported to date.

Microfluidic Manufacturing of SN-38-Loaded Polymer Nanoparticles with Shear Processing Control of Drug Delivery Properties.

Two-phase gas-liquid microfluidic reactors provide shear processing control of SN-38-loaded polymer nanoparticles (SN-38-PNPs). We prepare SN-38-PNPs from the block copolymer poly(methyl caprolactone- co-caprolactone)- block-poly(ethylene oxides) (P(MCL- co-CL)- b-PEO) using bulk and microfluidic methods and at different drug-to-polymer loading ratios and on-chip flow rates. We show that, as the microfluidic flow rate ( Q) increases, encapsulation efficiency and drug loading increase and release half times increase. Slower SN-38 release is obtained at the highest Q value ( Q = 400 µL/min) than is achieved using a conventional bulk preparation method. For all SN-38-PNP formulations, we find a dominant population (by number) of nanosized particles (<50 nm) along with a small number of larger aggregates (>100 nm). As Q increases, the size of aggregates decreases through a minimum and then increases, attributed to a flow-variable competition of shear-induced particle breakup and shear-induced particle coalescence. IC25 and IC50 values of the various SN-38-PNPs against MCF-7 cells show strong flow rate dependencies that mirror trends in particle size. SN-38-PNPs manufactured on-chip at intermediate flow rates show both minimum particle sizes and maximum potencies with a significantly lower IC25 value than the bulk-prepared sample. Compared to conventional bulk methods, microfluidic shear processing in two-phase reactors provides controlled manufacturing routes for optimizing and improving the properties of SN-38 nanomedicines.

Microfluidic Processing Approach to Controlling Drug Delivery Properties of Curcumin-Loaded Block Copolymer Nanoparticles.

We apply gas-liquid microfluidic reactors containing flow-variable, high-shear "hot spots" to produce curcumin-loaded polymer nanoparticles (CUR-PNPs) comprised of poly(caprolactone)- block-poly(ethylene oxide) (PCL- b-PEO) block copolymers at various flow rates and CUR loading ratios. CUR-PNPs prepared using the conventional nanoprecipitation method (bulk method) showed decreased encapsulation efficiency and increased drug precipitation as the loading ratio increased. However, CUR-PNPs prepared by microfluidic manufacturing showed both increased encapsulation efficiency and increased drug loading as either the flow rate or the loading ratio increased. This enabled microfluidic CUR loading percentages of up to 30% to be achieved in this study, which to our knowledge is a record for block copolymer PNPs. As well, it is shown that increased flow rate of microfluidic manufacturing leads to decreased mean CUR-PNP sizes (down to ∼50 nm) and narrower size distributions, along with significantly different CUR release kinetics compared to CUR-PNPs prepared at slower flow rates. In vitro antiproliferation experiments against MDA-MB-231 cells give an average IC50 value of 24 µM for CUR-PNPs compared to 13 µM for free CUR at the same incubation time of 72 h. Compared to conventional bulk and single-phase microfluidic strategies, this unique two-phase reactor represents an exciting manufacturing platform for optimizing polymeric CUR nanomedicines though flow-directed shear processing.

Controlling Structure and Function of Polymeric Drug Delivery Nanoparticles Using Microfluidics.

We demonstrate control of multiscale structure and drug delivery function for paclitaxel (PAX)-loaded polycaprolactone-block-poly(ethylene oxide) (PCL-b-PEO) polymeric nanoparticles (PNPs) via synthesis and flow-directed shear processing in a two-phase gas-liquid microfluidic reactor. This strategy takes a page from the engineering of commodity plastics, where processing rather than polymer chemistry provides an experimental handle on properties and function. PNPs formed from copolymers with three different PCL block lengths show sizes, morphologies, and loading efficiencies that depend on both the PCL block length and the microfluidic flow rate. By varying flow rate and comparing with a conventional bulk method of PNP preparation, we show that flow-variable shear processing provides control of PNP sizes and morphologies and enables slower PAX release times (up to 2 weeks) compared to bulk-prepared PNPs. Antiproliferative effects against cultured MCF-7 breast cancer cells were greatest for PNPs formed at an intermediate flow rate, corresponding to small and low-polydispersity spheres formed uniquely at this flow condition. Formation and flow-directed nanoscale shear processing in gas-liquid microfluidic reactors provides a manufacturing platform for drug delivery PNPs that could enable more effective and selective nanomedicines through multiscale structural control.

Salicylates are interference compounds in TR-FRET assays.

Given the importance of high-throughput screening in drug discovery, the identification of compounds that interfere with assay readouts is crucial. The pursuit of false positives wastes time and money, while distracting development teams from more promising leads. In the context of TR-FRET assays, most interfering compounds are dyes or aggregators. In the course of our studies on the PD1-PDL2 interaction, we discovered that salicylic acids, an extremely common compound subclass in screening libraries, interfere with TR-FRET assays. While the precise mechanism of interference was not established, our data suggest that interaction of the salicylate with the cryptand-ligated europium FRET donor is responsible for the change in assay signal.

Revisiting the mechanistic origins of Thiele's ester dimerization: probing the reliability of predictive models for cycloadditions.

The Diels-Alder dimerization of cyclopentadiene carboxylic acid (or ester) affords only three products out of a total of 36 possible regioisomers. In this Communication, we compare two competing conceptual models for their ability to rationalize the selective formation of these three compounds. We find that calculated ΔHf values and orbital energy levels are sufficient to describe gross reactivity for the system, but that orbital coefficient arguments (and frontier molecular orbital theory in general) do not reliably predict the regioisomeric outcome for the reaction. By contrast, Deslongchamps' radical stabilization logic (a consequence of the bent bond model of reactivity) correctly predicts all three Diels-Alder products. We anticipate that these data will stimulate broader consideration of radical stabilization effects as a predictive tool for cycloaddition chemistry.

Expansion of Thiele's Acid Chemistry in Pursuit of a Suite of Conformationally Constrained Scaffolds.

The Diels-Alder dimer of cyclopentadiene carboxylate, Thiele's acid has conformational properties that make it attractive as a molecular scaffold for applications in supramolecular and biological chemistry. However, a lack of known reaction methodology for derivatives of Thiele's acid (or the corresponding esters) has hampered its utilization in these fields. We describe an improved preparation of Thiele's esters and survey the chemistry of these versatile intermediates. As part of this effort, we also describe the synthesis of a suite of Thiele's acid (or ester) analogues spanning a broad range of cleft angles.

Diastereoselective tandem reactions of substituted 3-sulfolenes with bis-vinyl ketones leading to highly functionalized bicyclic and tricyclic frameworks.

The base-promoted reaction of 3-sulfolene with bis-vinyl ketones was shown in earlier work to proceed through a γ-1,2 addition/anionic oxy-Cope cascade; a subsequent treatment with base induced a second γ-1,2 addition to provide a [3.3.0] bicyclic framework that our group then exploited in the design of rigidified enzyme inhibitors for influenza neuraminidase. Out of a desire to expand the range of structural archetypes accessible through these couplings (and hopefully access additional conformationally-constrained inhibitor platforms) we have revisited this methodology, this time using substituted starting reagents. We show that judicious choice of the newly added substituent can control the exclusive formation of one of four new structural types, each formed as a single diastereomer. These include bicyclo[3.2.1] sulfones and spiro[5.4] sulfones, as well as an expanded collection of our original bicyclo[3.3.0] sulfone scaffolds, this time incorporating adjacent quaternary centres or additional rings.

Investigation of quantitative structure-reactivity relationships in the aliphatic Claisen rearrangement of bis-vinyl ethers reveals a dipolar, dissociative mechanism.

Kinetic investigations of substituent effects in the thermal rearrangement of bis-vinyl ether substrates are reported. Findings indicate that the influence of the various substituent patterns on the rate of rearrangement in these compounds differs from that documented in the literature for the analogous [3,3]-sigmatropic rearrangement of allyl vinyl ethers. In addition, the thermochemical data collected suggests the existence of a dissociative transition state with significant dipolar character. These findings provide a unique contribution to the already extensive body of literature dedicated to mechanistic investigation of the Claisen rearrangement of aliphatic allyl vinyl ethers.

Functionalization of Polydimethylsiloxane with Diazirine-Based Linkers for Covalent Protein Immobilization.

Biomolecule attachment to solid supports is critical for biomedical devices, such as biosensors and implants. Polydimethylsiloxane (PDMS) is commonly used for these applications due to its advantageous properties. To enhance the biomolecule immobilization on PDMS, a novel technique is demonstrated using newly synthesized diazirine molecules for the surface modification of PDMS. This nondestructive process involves a reaction between diazirine molecules and PDMS through C-H insertion with thermal or ultraviolet activation. The success of the PDMS modification is confirmed by various surface characterization techniques. Bovine serum albumin (BSA) and immunoglobulin G (IgG) are strongly attached to the modified PDMS surfaces, and the amount of protein is quantified using iodine-125 radiolabeling. The results demonstrate that PDMS is rapidly functionalized, and the stability of the immobilized proteins is significantly improved with multiple types of diazirine molecules and activation methods. Confocal microscopy provides three-dimensional images of the distribution of immobilized IgG on the surfaces and the penetration of diazirine-based linkers through the PDMS substrate during the coating process. Overall, this study presents a promising new approach for functionalizing PDMS surfaces to enhance biomolecule immobilization, and its potential applications can extend to multimaterial modifications for various diagnostic and medical applications such as microfluidic devices and immunoassays with relevant bioactive proteins.

Diazirine-Functionalized Polyurethane Crosslinkers for Isocyanate-Free Curing of Polyol-Based Coatings.

Polyurethane coatings have strong material properties due to the hydrogen bonding inherent to the urethane groups. However, installing this urethane moiety usually requires curing through difficult-to-handle isocyanates. In this work, we show the development of a polyurethane-based crosslinker that can be used to formulate a one-component polyurethane coating with material properties similar to those of isocyanate-based polyurethane coatings. To achieve this, we used diazirine functionalities that generate carbenes upon heating, which react with alcohol functionalities in a polyol to generate a crosslinked network with a high storage modulus.