Photoinitiated Reaction Research Articles

Photo-controlled cascade DNA hybridization for amplified electrochemical biosensor with tunable sensing performance

BackgroundPrecise control of the biorecognition process in DNA biosensors, especially for those with signal amplification, remains a challenge. It is of great significance to introduce external stimuli into the DNA system for a controllable trigger of nucleic acid cascade amplification and further for excellent biosensors. ResultsIn this study, a photo-initiated hybridization chain reaction (HCR) was designed for controllable and sensitive electrochemical biosensor via the incorporation of azobenzene moiety into the assembly unit. Under the coexistence of UV light and target DNA, a number of HCR products with biotin tags were generated and fixed on the electrode surface. Subsequently, the bound streptavidin-labeled horseradish peroxidase (SA-HRP) effectively catalyzed H2O2-mediated oxidation of tetramethylbenzidine (TMB), producing significant electrochemical current signals. A tunable sensing performance with different dynamic response ranges and sensitivity was achieved by adjusting the number of the inserted azobenzene moieties and the control of UV light. A limit of detection as low as 2.5 fM (S/N = 3) could be obtained in the case of one azobenzene and under UV exposure. Moreover, the photo-controlled DNA biosensor exhibited good discrimination ability even against single-base mismatch and was able to be applied in serum samples. SignificanceThe proposed electrochemical DNA biosensor based on dual-triggered HCR amplification may represent a promising path to achieve sensitive and accurate bioanalysis. Also, the tunable dynamic range of the developed biosensor will provide the possibility of clinical applications.

A modern approach to intermittent illumination for the characterization of chain-propagation in photoredox catalysis

Photoredox catalysis has become an invaluable tool for the construction of organic molecules, allowing for unparalleled control over radical intermediates enabled by the mild conditions achieved through visible-light activation of a photocatalyst. These reactions can be classified under two distinct mechanistic paradigms: closed photocatalytic cycles, and photoinitiated chain reactions. While optimization strategies for each of these classes of reaction differ significantly, organic chemists still lack a straightforward means for probing chain-propagation. In this work, we report a simple and accessible approach to performing intermittent illumination studies for characterizing chain reactions in photoredox catalysis. Using modern LED technologies to precisely control the rate of sample illumination, we were able to validate the presence or absence of product-forming chain reactions in four previously reported photoredox protocols. Furthermore, this technique also allows for the determination of chain-propagating lifetimes through a simple graphical analysis. Given the operational simplicity and ease of accessibility, we believe this intermittent illumination technique will be of great value to practitioners of the field moving forward.

Group 7 carbonyl complexes of a PNN-heteroscorpionate ligand.

A series of rhenium and manganese carbonyl complexes of a heteroscorpionate ligand with an atypical N2P-donor set has been prepared to better understand their electronic and CO releasing properties. Thus, the ligand, pz2TTP, with an a,a-bis(pyrazol-1-yl)tolyl group decorated with an ortho-situated di(p-tolyl)phosphanyl reacts with carbonyl group 17 reagents to give [fac-(κ2NP-pz2TTP)Re(CO)3Br], 1, and [fac-(κ3N2P-pz2TTP)M(CO)3](OTf = O3SCF3), 2-M (M = Re, Mn), if care is taken during the preparation of the manganeses derivative. When heated in CH3CN, 2-Mn slowly transforms to [fac,cis-(κ3N2P-pz2TTP)Mn(CO)2(NCCH3)](OTf), 3-Mn. In contrast, the corresponding 3-Re can only be prepared from 2-Re using Me3NO; pure 3-Mn can also be prepared by this method. Experimental and density functional calculations at the M06L/Def2-TZVP/PCM(CH3CN) level show that the replacement of a carbonyl with an acetonitrile solvent decreases the oxidation potential by around 0.8 V per carbonyl released, making decarbonylated species potent reductants. At the same time, the electronic spectrum broadens and undergoes a red-shift, making dicarbonyl complexes more susceptible to photo-initiated decarbonylation reactions than tricarbonyls. When 2-Mn or 3-Mn are irradiated in with 390 nm LED light in aerated solutions, [trans-Mn(pz2TTP = O)2](OTf)2, 4, along with insoluble manganese oxides are rapidly formed.

Periodic Trends in Intra-ionic Excited State Quenching by Halide.

The preassociation of reactants in a photoinitiated redox reaction through the use of noncovalent interactions can have a significant impact on excited state reactivity. As these noncovalent interactions render some stabilization to the associated species, they impact the kinetics and thermodynamics of photoinitiated electron transfer. Reported herein is a novel iridium(III) photocatalyst, equipped with an anion-sensitive, amide-substituted bipyridine ligand, and its reactivity with the halides (X = I-, Br-, Cl-) in acetonitrile and dichloromethane. A noteworthy periodic trend was observed, where the size and electron affinity dramatically altered the observed photoredox behavior. The binding affinity for the halides increased with decreasing ionic radius (Keq ∼103 to >106) in a polar medium but association was stoichiometric for each halide in a nonpolar medium. Evidence for the static quenching of iodide and bromide is presented while dynamic quenching was observed with all halides. These results highlight how the photophysics of halide adducts and the thermodynamics of intra-ionic photo-oxidation are impacted as a consequence of preassociation of a quencher through hydrogen bonding.

Synthesis of 1,3-Dicarbonyl Azepines via Photoinitiated Reactions of Aryl Azides with Carbon-Based Nucleophiles.

A photoinduced one-pot method for the synthesis of azepines by the reaction of aryl azides with 1,3-dicarbonyl compounds under weakly basic conditions is described. This method offers a simple route for the synthesis of 1,3-dicarbonyl-substituted azepines in good to excellent yields and high regioselectivity and was tested on 1,3-dicarbonyl compounds with different acidity levels. The resulting azepines have electrophilic and nucleophilic centers of varying degrees of activity, which facilitate reactions leading to further structural transformations.

Plasmonic heterostructures enabled photo-responsive Li-ion supercapacitors

Photo-responsive devices have the ability to harness light energy and use it to achieve specific outcomes or functions with greater sensitivity and selectivity, as well as faster response times. In this study, we have developed heterojunction supports using 1D imidazole frameworks. An electron beam is used to segregate the highly conductive plasmonic silver nanoparticles at the phase boundary of the AgVO3 interface. A photoresponsive Li-ion supercapacitor has been fabricated. We show intermolecular electron transfer in photoexcited silver imidazolate complexes through interactions with neighboring molecules or redox-active species surrounding the heterostructure. Electrochemical investigations reveal that the interfacial confinement of Ag helps to passivate surface defects and achieve better photo-initiated charge transfer reactions. This study provides a new perspective on dynamically controlling complex heterostructures using plasmonic effects for their application in energy storage using a photo-responsive supercapacitor.

Chitosan-based electroconductive inks without chemical reaction for cost-effective and versatile 3D printing for electromagnetic interference (EMI) shielding and strain-sensing applications

The burgeoning interest in biopolymer 3D printing arises from its capacity to meticulously engineer tailored, intricate structures, driven by the intrinsic benefits of biopolymers—renewability, chemical functionality, and biosafety. Nevertheless, the accessibility of economical and versatile 3D-printable biopolymer-based inks remains highly constrained. This study introduces an electroconductive ink for direct-ink-writing (DIW) 3D printing, distinguished by its straightforward preparation and commendable printability and material properties. The ink relies on chitosan as a binder, carbon fibers (CF) a low-cost electroactive filler, and silk fibroin (SF) a structural stabilizer. Freeform 3D printing manifests designated patterns of electroconductive strips embedded in an elastomer, actualizing effective strain sensors. The ink's high printability is demonstrated by printing complex geometries with porous, hollow, and overhanging structures without chemical or photoinitiated reactions or support baths. The composite is lightweight (density 0.29 ± 0.01 g/cm3), electroconductive (2.64 ± 0.06 S/cm), and inexpensive (20 USD/kg), with tensile strength of 20.77 ± 0.60 MPa and Young's modulus of 3.92 ± 0.06 GPa. 3D-printed structures exhibited outstanding electromagnetic interference (EMI) shielding effectiveness of 30–31 dB, with shielding of >99.9 % incident electromagnetic waves, showcasing significant electronic application potential. Thus, this study presents a novel, easily prepared, and highly effective biopolymer-based ink poised to advance the landscape of 3D printing technologies.

Water-in-oil emulsion templated polyurethanes with uniform porosity

Porous PU foams have been receiving great attention because of their low density, lightweight, and high surface area. However, preparing PU foams with controlled porosity, pore size, and pore morphology is often difficult with commonly used methods like gas blowing. Here, highly controllable porous PU with small, uniform pore morphology and tunable material properties have been synthesized using water-in-oil polymerized high internal phase emulsion (PolyHIPE) templating and photoinitiated thiol-ene reactions between vinyl-functionalized polyurethane prepolymers and thiol-functionalized crosslinkers. The PolyHIPEs exhibited highly interconnected open-cell structures with pore sizes ranging from 5 to 10 μm. The storage moduli and elastic moduli of PU polyHIPEs derived from flexible HDI-PUs were low compared to stiff IPDI-PU based polyHIPEs. Furthermore, the storage moduli of relatively soft HDI-PU polyHIPEs were affected by the stoichiometric ratio of thiol crosslinker and vinyl-PU whereas no considerable effect on the stiffer IPDI-PU based polyHIPEs. In summary, this work presents an approach to synthesize porous polyurethane polyHIPEs with potential applications in aerospace, automotive, and biomedical industries.

Synthesis of Silicon and Germanium Oxide Nanostructures via Photonic Curing; a Facile Approach to Scale Up Fabrication.

Silicon and Germanium oxide (SiOx and GeOx) nanostructures are promising materials for energy storage applications due to their potentially high energy density, large lithiation capacity (~10X carbon), low toxicity, low cost, and high thermal stability. This work reports a unique approach to achieving controlled synthesis of SiOx and GeOx nanostructures via photonic curing. Unlike conventional methods like rapid thermal annealing, quenching during pulsed photonic curing occurs rapidly (sub-millisecond), allowing the trapping of metastable states to form unique phases and nanostructures. We explored the possible underlying mechanism of photonic curing by incorporating laws of photophysics, photochemistry, and simulated temperature profile of thin film. The results show that photonic curing of spray coated 0.1 M molarity Si and Ge Acetyl Acetate precursor solution, at total fluence 80 J cm-2 can yield GeOx and SiOx nanostructures. The as-synthesized nanostructures are ester functionalized due to photoinitiated chemical reactions in thin film during photonic curing. Results also showed that nanoparticle size changes from ~48 nm to ~11 nm if overall fluence is increased by increasing the number of pulses. These results are an important contribution towards large-scale synthesis of the Ge and Si oxide nanostructured materials which is necessary for next-generation energy storage devices.

Photo-initiated thiol-ene reaction of multi-functional thiol and olefinic organosilicon compounds leading to porous polymers: Solution polymerization and photolithography

Photo-initiated thiol-ene reaction between multi-functional thiol compounds and unsaturated organosilicon compounds in ethanol/dimethyl sulfoxide mixed solvent successfully yielded porous polymers. The morphology of the porous polymer was formed by connected particles, whose diameters ranged from 1 to 6 μm. An increase in the number of thiol group of multi-functional thiol compounds decreased the particle size and increased the Young's modulus of the porous polymers. Porous polymers absorbed various organic solvents and showed high water repellency. Photolithography based on the thiol-ene reaction led to the patterning by the porous polymers.

Rational design and facile preparation of hybrid superhydrophobic epoxy coatings modified by fluorinated silsesquioxane-based giant molecules via photo-initiated thiol-ene click reaction with potential applications

First, several fluorinated silsesquioxane-based giant molecules (G-SQs) were easily prepared by the photo-initiated thiol-ene click reaction of octa(mercaptopropyl)silsesquioxane (SH8-SQ) with monovinyl(heptatrifluoropropyl)silsesquioxane (CF3-SQ) and perfluorohexyl ethylene with varying stoichiometric ratios. Then, G-SQs were used as low surface energy substances to modify epoxy acrylate resin (EA), which allowed adhesion to different substrates to prepare hydrophobic coatings via photo-initiated thiol-ene click reaction. The hybrid coating can impart stable superhydrophobic properties to cotton fabrics, which possess self-cleaning and oil–water separation function. The cotton fabrics coated by G-SQs-EA can perform oil–water separation very well, whose oil–water separation fluxes and efficiencies are 34,000 L m−2 h−1 and 99 %, respectively. The hybrid hydrophobic coating also provides effective corrosion protection for copper and the corrosion protection effect is further improved by increasing coating thickness. The corrosion current density, corrosion rate and impedance (0.01 Hz) reached 1.17*10−2 μA·cm−2, 0.14 μm yr−1 and 1026 kΩ cm−2, respectively. These excellent results indicate that EA coating modified by G-SQs has potential applications in many fields.

Metal-Phenolic Network Directed Coating of Single Probiotic Cell Followed by Photoinitiated Thiol-Ene Click Fortification to Enhance Oral Therapy.

Probiotics-based oral therapy has become a promising way to prevent and treat various diseases, while the application of probiotics is primarily restricted by loss of viability due to adverse conditions in the gastrointestinal (GI) tract during oral delivery. Layer-by-layer (LbL) single-cell encapsulation approaches are widely employed to improve the bioavailability of probiotics. However, they are generally time- and labor-intensive owing to multistep operation. Herein, a simple yet efficient LbL technique is developed to coat a model probiotic named Escherichia coli Nissle 1917 (EcN) through polyphenol-Ca2+ network directed allyl-modified gelatin (GelAGE) adsorption followed by cross-linking of GelAGE via photoinitiated thiol-ene click reaction to protect EcN from harsh microenvironments of GI tract. LbL single-cell encapsulation can be performed within 1h through simple operation. It is revealed that coated EcN exhibits significantly improved viability against acidic gastric fluid and bile salts, and enhanced colonization in the intestinal tract without loss of proliferation capabilities. Furthermore, oral therapy of coated EcN remarkably relieves the pathological symptoms associated with colitis in mice including down-regulating inflammation, repairing epithelial barriers, scavenging reactive oxygen species (ROS), and restoring the homeostasis of gut microbiota. This simplified LbL coating strategy has great potential for various probiotics-mediated biomedical and nutraceutical applications.

Synthesis of high concentration polycarboxylate superplasticizers via a photoinitiated one-pot method

Polycarboxylate superplasticizers (PCEs) are primarily liquid products (40 wt%) with narrow application range, which incur high transportation and storage costs. However, the high reaction viscosity makes it challenging to produce high concentration PCEs. In our study, high concentration PCEs are successfully synthesized by a photoinitiated one-pot method at room temperature. The results show that the reaction viscosity of photoinitiation is slightly higher than that of traditional initiation systems, but the photoinitiated reaction remains stable and controllable, with no occurrence of violent polymerization. The impact of varying reaction concentrations on the polymerization rate, molecular structure, and properties of PCEs has been studied under the photoinitiated one-pot method. The results indicate that an increase in reaction concentration leads to a rise in polymerization rate, molecular weight, and molecular gyration radius of the polymers. The conversion rate of the macromonomer exceeds 80%, while the polydispersion index (PDI) for molecular weight is below 2 with a narrow distribution. Furthermore, the monomer polymerization ratio of the product remains close to the feeding ratio at different reaction concentrations. Finally, it is observed that PCEs with a high concentration of 80 wt% exhibit favorable dispersion, rheology and adsorption properties. This study presents a new method for synthesizing high concentration PCEs using photoinitiation.

Asymmetric Block Extension of Star-Shaped [PEG-SH]4 - toward Poly(dehydroalanine)-Functionalized PEG Hydrogels for Catch and Release of Charged Guest Molecules.

With the incorporation of polyampholytic segments into soft matter, hydrogels can serve as a reservoir for a variety of charged molecules which can be caught and released upon changes in pH value. Asymmetric block extension of one arm for star-shaped poly(ethylene glycol) [PEG26 -SH]4 using short segments of polyampholytic poly(dehydroalanine) (PDha) is herein demonstrated while maintaining the functional thiol end groups for network formation. For subsequent hydrogel synthesis with up to 10wt.% PDha a straightforward and biocompatible photoinitiated thiol-ene click reaction is exploited. The investigation of the swelling properties of the hydrogel revealed responsive behavior toward ionic strength and variations in pH value. Moreover, the reversible adsorption of the model dyes methylene blue (MB) and acid orange 7 (AO7) is investigated by UV-vis measurements and the procedure can be successfully transferred to the adsorption of the adhesion peptide RGDS resulting in an uptake of 1.5 wt% RGDS with regard to the dry weight of the hydrogel.

Highly Conductive, Anti-Freezing Hemicellulose-Based Hydrogels Prepared via Deep Eutectic Solvents and Their Applications.

Hydrogels containing renewable resources, such as hemicellulose, have received a lot of attention owing to their softness and electrical conductivity which could be applied in soft devices and wearable equipment. However, traditional hemicellulose-based hydrogels generally exhibit poor electrical conductivity and suffer from freezing at lower temperatures owing to the presence of a lot of water. In this study, we dissolved hemicellulose by employing deep eutectic solvents (DESs), which were prepared by mixing choline chloride and imidazole. In addition, hemicellulose-based DES hydrogels were fabricated via photo-initiated reactions of acrylamide and hemicellulose with N, N'-Methylenebisacrylamide as a crosslinking agent. The produced hydrogels demonstrated high electrical conductivity and anti-freezing properties. The conductivity of the hydrogels was 2.13 S/m at room temperature and 1.97 S/m at -29 °C. The hydrogel's freezing point was measured by differential scanning calorimetry (DSC) to be -47.78 °C. Furthermore, the hemicellulose-based DES hydrogels can function as a dependable and sensitive strain sensor for monitoring a variety of human activities.

Strong Binding of C-Glycosylic1,2-Thiodisaccharides to Galectin-3─Enthalpy-Driven Affinity Enhancement by Water-Mediated Hydrogen Bonds.

Galectin-3 is involved in multiple pathways of many diseases, including cancer, fibrosis, and diabetes, and it is a validated pharmaceutical target for the development of novel therapeutic agents to address unmet medical needs. Novel 1,2-thiodisaccharides with a C-glycosylic functionality were synthesized by the photoinitiated thiol-ene click reaction of O-peracylated 1-C-substituted glycals and 1-thio-glycopyranoses. Subsequent global deprotection yielded test compounds, which were studied for their binding to human galectin-3 by fluorescence polarization and isothermal titration calorimetry to show low micromolar Kd values. The best inhibitor displayed a Kd value of 8.0 μM. An analysis of the thermodynamic binding parameters revealed that the binding Gibbs free energy (ΔG) of the new inhibitors was dominated by enthalpy (ΔH). The binding mode of the four most efficient 1,2-thiodisaccharides was also studied by X-ray crystallography that uncovered the unique role of water-mediated hydrogen bonds in conferring enthalpy-driven affinity enhancement for the new inhibitors. This 1,2-thiodisaccharide-type scaffold represents a new lead for galectin-3 inhibitor discovery and offers several possibilities for further development.

Photochemistry sample sticks for inelastic neutron scattering.

Every material experiences atomic and molecular motions that are generally termed vibrations in gases and liquids or phonons in solid state materials. Optical spectroscopy techniques, such as Raman, infrared absorption spectroscopy, or inelastic neutron scattering (INS), can be used to measure the vibrational/phonon spectrum of ground state materials properties. A variety of optical pump probe spectroscopies enable the measurement of excited states or elucidate photochemical reaction pathways and kinetics. So far, it has not been possible to study photoactive materials or processes in situ using INS due to the mismatch between neutron and photon penetration depths, differences between the flux density of photons and neutrons, cryogenic temperatures for INS measurements, vacuum conditions, and a lack of optical access to the sample space. These experimental hurdles have resulted in very limited photochemistry studies using INS. Here we report on the design of two different photochemistry sample sticks that overcome these experimental hurdles to enable in situ photochemical studies using INS, specifically at the VISION instrument at Oak Ridge National Laboratory. We demonstrate the use of these new measurement capabilities through (1) the in situ photodimerization of anthracene and (2) the in situ photopolymerization of a 405nm photoresin using 405nm excitation as simple test cases. These new measurement apparatus broaden the science enabled by INS to include photoactive materials, optically excited states, and photoinitiated reactions.

One-pot ternary sequential reactions for photopatterned gradient multimaterials

One-pot ternary sequential reactions for photopatterned gradient multimaterials

Post-coordination photoinitiated macromolecular thiol-ene coupling reaction for construction of metallo-supramolecular complexes of ABCL2-type miktoarm star copolymers and self-assembly of the complexes in water

In this paper, we focus on investigating synthesis of metallo-supramolecular architectures of ABCL2-type miktoarm star copolymers PCL(-b-PDPA)-b-[(Tpyp)2-b-PMPC] (A, PCL; B, PDPA; C, PMPC; L, Tpyp) with ruthenium(II) (Ru(II)) ions and exploring self-assembly behavior of the complexes in water. Direct coordination of PCL(-b-PDPA)-b-[(Tpyp)2-b-PMPC] to Ru(II) ions and post-coordination photoinitiated macromolecular thiol-ene coupling reaction strategies were explored to construct Ru(II) coordination complexes, respectively. The result indicates that the post-coordination coupling reaction was more suitable strategy for constructing this kind of coordination complexes, which may avoid a larger steric hindrance generated from the coexistence of the three arms of PCL(-b-PDPA)-b-[(Tpyp)2-b-PMPC] leading to the disadvantageous influence on the formation of the bis(terpyridine)-Ru(II) complex. It should be mentioned that, however, although a photoinitiated macromolecular thiol-ene radical coupling reaction is facile, so far to achieve complete reaction of the target groups (i.e., alkene groups) has remained a challenge. Therefore, herein a post-coordination thiol-ene coupling reaction was explored carefully and an appropriate condition for the complete reaction of the alkene groups was given. Interestingly, the Ru(II) coordination complexes could self-assemble to form 2D platelets. This should be attributed to the unique metallo-supramolecular architecture. It is expected that the exploration can provide strategies for construction of complicated and exquisite metallo-supramolecular architectures and novel self-assemblies.

Facile UV-Induced Surface Covalent Modification to Fabricate Durable Superhydrophobic Fabric for Efficient Oil-Water Separation.

In this work, a durable superhydrophobic fabric was fabricated by using a facile UV-induced surface covalent modification strategy. 2-isocyanatoethylmethacrylate (IEM) containing isocyanate groups can react with the pre-treated hydroxylated fabric, producing IEM molecules covalently grafted onto the fabric's surface, and the double bonds of IEM and dodecafluoroheptyl methacrylate (DFMA) underwent a photo-initiated coupling reaction under UV light radiation, resulting in the DFMA molecules further grafting onto the fabric's surface. The Fourier transform infrared, X-ray photoelectron spectroscopy and scanning electron microscopy results revealed that both IEM and DFMA were covalently grafted onto the fabric's surface. The formed rough structure and grafted low-surface-energy substance contributed to the excellent superhydrophobicity (water contact angle of ~162°) of the resultant modified fabric. Notably, such a superhydrophobic fabric can be used for efficient oil-water separation, for example a high separation efficiency of over 98%. More importantly, the modified fabric exhibited excellent durable superhydrophobicity in harsh conditions such as immersion in organic solvents for 72 h, an acidic or alkali solution (pH = 1-12) for 48 h, undergoing laundry washing for 3 h, exposure to extreme temperatures (from -196° to 120°), as well as damage such as 100 cycles of tape-peeling and a 100-cycle abrasion test; the water contact angle only slightly decreased from ~162° to 155°. This was attributed to the IEM and DFMA molecules grated onto the fabric through stable covalent interactions, which could be accomplished using the facile strategy, where the alcoholysis of isocyanate and the grafting of DFMA via click coupling chemistry were integrated into one-step. Therefore, this work provides a facile one-step surface modification strategy for preparing durable superhydrophobic fabric, which is promising for efficient oil-water separation.