Heterogeneous Photocatalytic Click Chemistry

Oxygen Coordination Promotes Single-Atom Cu(II)-Catalyzed Azide-Alkyne Click Chemistry without Reducing Agents

Unique active sites make single-atom (SA) catalysts promising to overcome obstacles in homogeneous catalysis but challenging due to their fixed coordination environment. Click chemistry is restricted by the low activity of more available Cu(II) catalysts without reducing agents. Herein, we develop efficient, O-coordinated SA Cu(II) directly catalyzed click chemistry. As revealed by theoretical calculations of the superior coordination structure to promote the click reaction, an organic molecule-assisted strategy is applied to prepare the corresponding SA Cu catalysts with respective O and N coordination. Although they both belong to Cu(II) centers, the O-coordinated one exhibits a 5-fold higher activity than the other and even much better activity than traditional homogeneous and heterogeneous Cu(II) catalysts. Control experiments further proved that the O-coordinated SA Cu(II) catalyst tends to be reduced by alkyne into Cu acetylide rather than the N-coordinated catalyst and thus facilitates click chemistry.

Single-Molecule Catalysis in the Palladium Cross-Coupling Reaction Cycle

Single-molecule (SM) methods are applied to study various types of catalytic processes in chemical and biochemical reactions. In this study, the Suzuki-Miyaura cross-coupling reaction forming a fluorescent product is investigated within the SM approximation. Stochastic analysis of emission intermittency in selected nanoscopic spots allows us to determine the single-molecule turnover frequency (SM-TOF) of the Pd catalyst in a specific probe reaction. We generate and analyze simulated intermittency time traces of a single catalyst surrounded by reactant molecules to assess the reliability of the method applied to real intermittency time trace data from hundreds of nanoscopic fluorescence spots. The results demonstrate that the proposed method can be used to evaluate the average SM-TOF of Pd in a cross-coupling reaction.

Clickable Polymerization-Induced Emission Luminogens Toward Color-Tunable Modification of Non-Traditional Intrinsic Luminescent Polymers

Non-traditional intrinsic luminescent (NTIL) polymer is an emerging field, and its color-tunable modification is highly desirable but still rarely investigated. Here, a click chemistry approach for the color-tunable modifications of NTIL polymers by introducing clickable polymerization-induced emission luminogen (PIEgen), is demonstrated. Through Cu-catalyzed azide-alkyne cycloaddition click chemistry, a series of PIEgens is successful prepared, which is further polymerized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Interestingly, after clickable modification, these monomers are nonemissive in both solution and aggregation states; while, the corresponding polymers exhibit intriguing aggregation-induced emission (AIE) characteristics, confirming their PIEgen characteristics. By varying alkynyl substitutions, color-tunable NTIL polymers are achieved with emission wavelength varying from 448 to 498 nm, revealing a series of PIEgens and verifying the importance of modification of NTIL polymers. Further luminescence energy transfer application is carried out as well. This work therefore designs a series of clickable PIEgens and opens a new avenue for the modification of NTIL polymers via click chemistry, which may cause inspirations to the research fields including luminescent polymer, NTIL, click chemistry, AIE and modification.

Photocatalytic Semi-Hydrogenation of Alkynes: A Game of Kinetics, Selectivity and Critical Timing

The semi-hydrogenation reaction of alkynes is important in the fine chemicals and pharmaceutical industries, and it is thus important to find catalytic processes that will drive the reaction efficiently and at a low cost. The real challenge is to drive the alkyne-to-alkene reaction while avoiding over-hydrogenation to the saturated alkane moiety. The problem is more difficult when dealing with aromatic substitution at the alkyne center. Simple photocatalysts based on Palladium tend to proceed to the alkane, and stopping at the alkene with good selectivity requires very precise timing with basically no timing tolerance. We report here that the goal of high conversion with high selectivity could be achieved with TiO2-supported copper (Cu@TiO2), although with slower kinetics than for Pd@TiO2. A novel bimetallic catalyst, namely, CuPd@TiO2 (0.8% Cu and 0.05% Pd), with methanol as the hydrogen source could improve the kinetics by 50% with respect to Cu@TiO2, while achieving selectivities over 95% and with exceptional timing tolerance. Further, the low Palladium content minimizes its use, as Palladium is regarded as an element at risk of depletion.

Continuous-imprinted-layer nanofiber membrane with MXene-based precise-designed nanocages for high-accuracy recognition and separation of shikimic acid

Ti₃C₂T_x (MXene) has attracted extensive attention from scholars at home and abroad due to its rich surface termination functional groups and two-dimensional multilayer structure. In this work, MXene was introduced to the membrane by vacuum-assisted filtration processes, and the formed interlayer channel facilitated the construction of recognition sites and molecular transmission. In this paper, PDA@MXene@PDA@SiO₂-PVDF dual-imprinted mixed matrix membrane (PMS-DIMs) were developed by the cooperative dual-imprinting strategy, which was used for the adsorption of shikimic acid (SA). Firstly, SiO₂-PVDF nanofiber basement membrane were prepared by electrospinning method and the first Polydopamine (PDA)-based imprinted layer was constructed on the membrane. PDA not only realized the imprinting process, PDA modification was used to give MXene nanosheets better antioxidant properties and to confer the SiO₂-PVDF nanofiber membrane the interface stability. After that, the second-imprinted sites were constructed on the stacked MXene nanosheets surface as well as between the layers. The SA dual-imprinted sites significantly increased the efficiency of the selective adsorption efficiency, when the template molecule passed through the membrane, the cooperative dual-imprinting strategy enabled multiplex recognition and adsorption of template molecules. As a consequence, which greatly improving the rebinding ability(262.17 g m^-2), and mselectivity factors (β_Catechol/SA, β_P-HB/SA, β_P-NP/SA were 2.34, 4.50 and 5.68). High stability proved the potentials of the PMS-DIMs for practical application. Precise SA-recognition sites were constructed on the PMS-DIMs, PMS-DIMs not only exhibit excellent selective rebinding properties but also have high permeability.

Visible-light induced three-component reaction for α-aminobutyronitrile synthesis by C-C bond formation using quantum dots as photocatalysts

We describe a three-component reaction of malononitrile, benzaldehyde and N,N-dimethylaniline using aluminium doped CdSeS/CdZnSeS(Al)/ZnS quantum dots (QDs) as visible light catalysts to synthesize α-aminobutyrilitriles at room temperature and under mild conditions. The reactions exhibit high functional group tolerance, and the well dispersed quantum dot catalysts are highly efficient with a turnover number (TON) greater than 1.1 × 10³ and can be recycled at least three times without significant loss of catalytic activity.

NIR-II Light Leveraged Dual Drug Synthesis for Orthotopic Combination Therapy

Pd-catalyzed bioorthogonal bond cleavage reactions are widely used and frequently reported. It is circumscribed by low reaction efficiency, which may encumber the therapeutic outcome when applied to physiological environments. Herein, an NIR-II light promoted integrated catalyst (CuS@PDA/Pd) (PDA - polydopamine) is designed to accelerate the reaction efficiency and achieve a dual bioorthogonal reaction for combination therapy. As NIR-II light can penetrate deeply into tissue, the Pd-mediated cleavage reaction can be promoted both in vitro and in vivo by the photothermal properties of CuS, beneficial to orthotopic 4T1 tumor treatment. In addition, CuS also catalyzes the synthesis of active resveratrol analogs by the CuAAC reaction. These simultaneously produced anticancer agents result in enhanced antitumor cytotoxicity in comparison to the single treatments. This is a fascinating study to devise an integrated catalyst boosted by NIR-II light for dual bioorthogonal catalysis, which may provide the impetus for efficient bioorthogonal combination therapy in vivo.

A Motor-Based Carbonaceous Nanocalabash Catalyst for Deep-Layered Bioorthogonal Chemistry

Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction has been widely regarded as a promising avenue in bioorthogonal chemistry. The emerging heterogeneous copper catalysts have been developed with a series of exciting applications such as in situ activation of prodrugs because of their excellent stability and biocompatibility. However, due largely to the complex biophysical barriers in living organisms, most synthetic bioorthogonal drugs cannot penetrate deep pathological tissues. Especially in biofilm-associated infections, the biofilms severely block the penetration of traditional antimicrobial agents and increase the antibiotic resistance, which makes it extremely difficult to eliminate the biofilms. Inspired by self-propelled biological motors, such as enzymes, herein, we develop a NIR light-controllable carbonaceous nanocalabash (CNC) motor catalyst with good biocompatibility for active targeted synthesis of drugs inside the biofilms as a robust general-purpose bioorthogonal platform. Under the NIR laser, the CNC motor catalysts display a rapid autonomous motion and generate active molecules in the deep biofilm layers, removing the biofilms and eradicating the shielded bacteria. Our work will shed light on developing a robust bioorthogonal platform for active targeted synthesis of drugs in deep-layered living systems.

Pyrazine Based Type-I Sensitizing Assemblies for Photoreduction of Cu(II) in 'One-Pot Three-Component' CuAAC Reaction Under Aerial Conditions

Photosensitizing assemblies of pyrazine derivative PDA have been developed which exhibit a high photostability, 'lighted' excited state, balanced redox potential, high transportation potential and activate oxygen via type-I pathway only. These PDA assemblies in combination with Cu(II) ions catalyze the CuAAC reaction via in situ reduction of Cu(II) ions without any reducing or stabilizing agent. The present protocol has wide substrate scope with recyclability of the catalytic system up to six catalytic cycles and is applicable to gram-scale synthesis.

Mechanistic Insight into the Light-Triggered CuAAC Reaction: Does Any of the Photocatalyst Go?

The attainment of transition-metal catalysis and photoredox catalysis has represented a great challenge over the last years. Herein, we have been able to merge both catalytic processes into what we have called "the light-triggered CuAAC reaction". Particularly, the CuAAC reaction reveals opposite outcomes depending on the nature of the photocatalyst (eosin Y disodium salt and riboflavin tetraacetate) and additives (DABCO, Et₃N, and NaN₃) employed. To get a better insight into the operating processes, steady-state, time-resolved emission, and laser flash photolysis experiments have been performed to determine reactivity and kinetic data. These results, in agreement with thermodynamic estimations based on reported data, support the proposed mechanisms. While for eosin Y (EY), Cu(II) was reduced by its triplet excited state; for riboflavin tetraacetate (RFTA), mainly triplet excited RFTA state photoreductions by electron donors as additives are mandatory, affording RFTA^•- (from DABCO and NaN₃) or RFTAH^• (from Et₃N). Subsequently, these species are responsible for the reduction of Cu(II). For both photocatalysts, photogenerated Cu(I) finally renders 1,2,3-triazole as the final product. The determined kinetic rate constants allowed postulating plausible mechanisms in both cases, bringing to light the importance of kinetic studies to achieve a strong understanding of photoredox processes.

Self-Catalyzed Sensitization of CuO Nanowires via a Solvent-free Click Reaction

Recent advances in organic surface sensitization of metal oxide nanomaterials focused on two-step approaches with the first step providing a convenient functionalized chemical "hook", such as an alkyne functionality connected to a carboxylic group in prop-2-ynoic acid. The second step then took advantage of copper-catalyzed click chemistry to deliver the desired structure (such as benzyl or perylene) attached to an azide to react with the surface-bound alkyne. The use of this approach on CuO not only resulted in a successful morphology preserving chemical modification but also has demonstrated that surface Cu(I) can be obtained during the process and promote a surface-catalyzed click reaction without additional copper catalyst. Here, it is demonstrated that this surface-catalyzed chemistry can be performed on a surface of the CuO nanomaterial without a solvent, as a "dry click" reaction, as confirmed with spectroscopic and microscopic investigations with X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, solid-state nuclear magnetic resonance, and scanning electron microscopy. Computational studies provided instructive information on the interaction between the surface prop-2-yonate and azide functional group to better understand the mechanism of this surface-catalyzed click reaction.

Single-Molecule Observations Provide Mechanistic Insights into Bimolecular Knoevenagel Amino Catalysis

While single-molecule (SM) methods have provided new insights to various catalytic processes, bimolecular reactions have been particularly challenging to study. Here, the fluorogenic Knoevenagel condensation of an aromatic aldehyde with methyl cyanoacetate promoted by surface-immobilized piperazine is quantitatively characterized using super-resolution fluorescence imaging and stochastic analysis using hidden Markov modeling (HMM). Notably, the SM results suggest that the reaction follows the iminium intermediate pathway before the formation of a fluorescent product with intramolecular charge-transfer character. Moreover, the overall process is limited by the turnover rate of the catalyst, which is involved in multiple steps along the reaction coordinate.

Flow chemistry as a tool to access novel chemical space for drug discovery

This perspective scrutinizes flow chemistry as a useful tool for medicinal chemists to expand the current chemical capabilities in drug discovery. This technology has demonstrated his value not only for the traditional reactions used in Pharma for the last 20 years, but also for bringing back to the lab underused chemistries to access novel chemical space. The combination with other technologies, such as photochemistry and electrochemistry, is opening new avenues for reactivity that will smoothen the access to complex molecules. The introduction of all these technologies in automated platforms will improve the productivity of medicinal chemistry labs reducing the cycle times to get novel and differentiated bioactive molecules, accelerating discovery cycle times.

Near-Infrared Light Dual-Promoted Heterogeneous Copper Nanocatalyst for Highly Efficient Bioorthogonal Chemistry in Vivo

Owing to better stability and biosafety, heterogeneous Cu nanoparticles (CuNPs) have been put forward as a promising candidate to complete the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. However, the inherent poor activity of Cu(0) deterred its wide bioapplication. Herein, we employed near-infrared (NIR) light to dual-promote the CuAAC reaction of a biocompatible heterogeneous copper nanocatalyst through photodynamic and photothermal effects in vitro and in vivo. Specifically, the photodynamic activity could promote the conversion of Cu(0) to Cu(I) to accelerate the catalytic process of CuAAC. The high photothermal conversion efficiency (η = 50.6%) could increase the local temperature, further promoting the whole reaction. Then, a drastically increased reaction rate in a living system ranging from cells to nematodes was achieved in our system. Meanwhile, the better antitumor efficacy has determined with in vivo tumor therapy experiments.

Three thiacalix[4]arene-based Cu(i) coordination polymers: catalytic activities for azide-alkyne cycloaddition reactions and luminescence properties

Three new coordination polymers, [Cu₂(CN)(L)(OCH₃)]·CH₃OH·3H₂O (1), [Cu₃(Br)₃(L)] (2) and [Cu(I)(L)]·1.5H₂O (3), have been solvothermally prepared by reacting L (5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra[(3-pyridylmethyl)oxy]-2,8,14,20-tetrathiacalix[4]arene) with Cu(i) halide. 1 and 2 exhibit layers. 3 displays a chain, a supramolecular layer constructed by hydrogen bonds. The performance of 1-3 was examined as heterogeneous catalysts for azide-alkyne cycloaddition reactions. Most strikingly, 1 and 2 show predominant efficiency with high regioselectivity and excellent recyclability. Remarkably, solids 1-3 all have luminescence characteristics under irradiation with a UV lamp.

Facile Solvothermal Synthesis of Hollow BiOBr Submicrospheres with Enhanced Visible-Light-Responsive Photocatalytic Performance

In this work, hierarchical hollow BiOBr submicrospheres (HBSMs) were successfully prepared via a facile yet efficient solvothermal strategy. Remarkable effects of solvents upon the crystallinities, morphologies, and microstructures of the BiOBr products were systematically investigated, which revealed that the glycerol/isopropanol volumetric ratio played a significant role in the formation of hollow architecture. Accordingly, the underlying formation mechanism of the hollow submicrospheres was tentatively put forward here. Furthermore, the photocatalytic activities of the resulting HBSMs were evaluated in detail with photocatalytic degradation of the organic methyl orange under visible light irradiation. Encouragingly, the as-obtained HBSMs with striking recyclability demonstrated excellent visible-light-responsive photocatalytic performance, which benefits from their large surface area, effective visible light absorption, and unique hollow feature, highlighting their promising commercial application in waste water treatment.

Enhancing Ru(II)-Catalysis with Visible-Light-Mediated Dye-Sensitized TiO2 Photocatalysis for Oxidative C-H Olefination of Arene Carboxylic Acids at Room Temperature

Erythrosine B sensitized TiO₂ photocatalysis has been combined with Ru(II)-catalysis to accomplish an oxidative olefination/annulation of benzoic acids with activated olefins under mild conditions that tolerates useful functionalities, such as halides, free hydroxy, acetamido, etc. The morphology of the photocatalyst is unaffected during the reaction and it can be reused. Mechanistic studies favor the involvement of a photo-induced single electron transfer process.

Highly Stable Copper(I)-Thiacalix[4]arene-Based Frameworks for Highly Efficient Catalysis of Click Reactions in Water

Environmentally friendly metal-organic frameworks (MOFs) have gained considerable attention for their potential use as heterogeneous catalysts. Herein, two Cu^I -based MOFs, namely, [Cu₄ Cl₄ L]⋅CH₃ OH⋅1.5 H₂ O (1-Cl) and [Cu₄ Br₄ L]⋅DMF⋅0.5 H₂ O (1-Br), were assembled with new functionalized thiacalix[4]arenes (L) and halogen anions X^- (X=Cl and Br) under solvothermal conditions. Remarkably, catalysts 1-Cl and 1-Br exhibit great stability in aqueous solutions over a wide pH range. Significantly, MOFs 1-Cl and 1-Br, as recycled heterogeneous catalysts, are capable of highly efficient catalysis for click reactions in water. The MOF structures, especially the exposed active Cu^I sites and 1D channels, play a key role in the improved catalytic activities. In particular, their catalytic activities in water are greatly superior to those in organic solvents or even in mixed solvents. This work proposes an attractive route for the design and self-assembly of environmentally friendly MOFs with high catalytic activity and reusability in water.

Self-triggered click reaction in an Alzheimer's disease model: in situ bifunctional drug synthesis catalyzed by neurotoxic copper accumulated in amyloid-β plaques

Cu is one of the essential elements for life. Its dyshomeostasis has been demonstrated to be closely related to neurodegenerative disorders, such as Alzheimer's disease (AD), which is characterized by amyloid-β (Aβ) aggregation and Cu accumulation. It is a great challenge as to how to take advantage of neurotoxic Cu to fight disease and make it helpful. Herein, we report that the accumulated Cu in Aβ plaques can effectively catalyze an azide-alkyne bioorthogonal cycloaddition reaction for fluorophore activation and drug synthesis in living cells, a transgenic AD model of Caenorhabditis elegans CL2006, and brain slices of triple transgenic AD mice. More importantly, the in situ synthesized bifunctional drug 6 can disassemble Aβ-Cu aggregates by extracting Cu and photo-oxygenating Aβ synergistically, suppressing Aβ-mediated paralysis and diminishing the locomotion defects of the AD model CL2006 strain. Our results demonstrate that taking the accumulated Cu ions in the Aβ plaque for an in situ click reaction can achieve both a self-triggered and self-regulated drug synthesis for AD therapy. To the best of our knowledge, a click reaction catalyzed by local Cu in a physiological environment has not been reported. This work may open up a new avenue for in situ multifunctional drug synthesis by using endogenous neurotoxic metal ions for the treatment of neurodegenerative diseases.

A green road map for heterogeneous photocatalysis

In the new millennium the well-established paradigms of organic photochemistry have come alive as the basis for a wide range of synthetic methodologies that take advantage of the enhanced redox properties of excited states. While many strategies have been developed using rare, expensive and non-reusable catalysts, the road forward should include catalysts based on more abundant elements and reusable materials. This green road leads to the exploration of heterogeneous systems that can be eventually adapted for flow photocatalysis, and also adopted for the solution of environmental problems such as water treatment and fuel generation using solar radiation. If heterogeneous photocatalysis can play a role in supplying solutions to drug synthesis, energy and potable water supplies, then photochemistry will have an unprecedented societal impact.

Allylic azides: synthesis, reactivity, and the Winstein rearrangement

Organic azides are useful synthetic intermediates, which demonstrate broad reactivity. Unlike most organic azides, allylic azides can spontaneously rearrange to form a mixture of isomers. This rearrangement has been named the Winstein rearrangement. Using allylic azides can result in low yields and azide racemization in some synthetic contexts due to the Winstein rearrangement. Effort has been made to understand the mechanism of the Winstein rearrangement and to take advantage of this process. Several guiding principles can be used to identify which azides will produce a mixture of isomers and which will resist rearrangement. Selective reaction conditions can be used to differentiate the azide isomers in a dynamic manner. This review covers all aspects of allylic azides including their synthesis, their reactivity, the mechanism of the Winstein rearrangement, and reactions that can selectively elaborate an azide isomer. This review covers the literature from Winstein's initial report to early 2019.

A Biocompatible Heterogeneous MOF-Cu Catalyst for In Vivo Drug Synthesis in Targeted Subcellular Organelles

As a typical bioorthogonal reaction, the copper-catalyzed azide-alkyne cycloaddition (CuAAC) has been used for drug design and synthesis. However, for localized drug synthesis, it is important to be able to determine where the CuAAC reaction occurs in living cells. In this study, we constructed a heterogeneous copper catalyst on a metal-organic framework that could preferentially accumulate in the mitochondria of living cells. Our system enabled the localized synthesis of drugs through a site-specific CuAAC reaction in mitochondria with good biocompatibility. Importantly, the subcellular catalytic process for localized drug synthesis avoided the problems of the delivery and distribution of toxic molecules. In vivo tumor therapy experiments indicated that the localized synthesis of resveratrol-derived drugs led to greater antitumor efficacy and minimized side effects usually associated with drug delivery and distribution.

Highly Electrophilic Titania Hole as a Versatile and Efficient Photochemical Free Radical Source

Photogenerated holes in nanometric semiconductors, such as TiO₂, constitute remarkable powerful electrophilic centers, capable of capturing an electron from numerous donors such as ethers, or nonactivated substrates like toluene or acetonitrile, and constitute an exceptionally clean and efficient source of free radicals. In contrast with typical free radical precursors, semiconductors generate single radicals (rather than pairs), where the precursors can be readily removed by filtration or centrifugation after use, thus making it a convenient tool in organic chemistry. The process can be described as an example of dystonic proton coupled electron transfer.

Surface plasmon resonances enhanced click chemistry through synergistic photothermal and hot electron effects

Surface plasmon resonance excitation on Au enhances a visible light-assisted click reaction through synergistic photothermal and hot electron effects.

Application of metal oxide semiconductors in light-driven organic transformations

Herein, we provide an up-to-date overview of metal oxide semiconductors (MOS) as versatile and inexpensive photocatalysts to enable light-driven organic transformations.

Glass wool: a novel support for heterogeneous catalysis

Heterogeneous catalysis presents significant advantages over homogeneous catalysis such as ease of separation and reuse of the catalyst. Here we show that a very inexpensive, manageable and widely available material - glass wool - can act as a catalyst support for a number of different reactions. Different metal and metal oxide nanoparticles, based on Pd, Co, Cu, Au and Ru, were deposited on glass wool and used as heterogeneous catalysts for a variety of thermal and photochemical organic reactions including reductive de-halogenation of aryl halides, reduction of nitrobenzene, Csp3-Csp3 couplings, N-C heterocycloadditions (click chemistry) and Csp-Csp2 couplings (Sonogashira couplings). The use of glass wool as a catalyst support for important organic reactions, particularly C-C couplings, opens the opportunity to develop economical heterogeneous catalysts with excellent potential for flow photo-chemistry application.

Hybrid Noble-Metals/Metal-Oxide Bifunctional Nano-Heterostructure Displaying Outperforming Gas-Sensing and Photochromic Performances

As nanomaterials are dominating 21st century's scene, multiple functionality in a single (nano)structure is becoming very appealing. Inspired by the Land of the Rising Sun, we designed a bifunctional (gas-sensor/photochromic) nanomaterial, made with TiO₂ whose surface was simultaneously decorated with copper and silver (the Cu/Ag molar ratio being 3:1). This nanomaterial outperformed previous state-of-the-art TiO₂-based sensors for the detection of acetone, as well as the Cu-TiO₂-based photochromic material. It indeed possessed splendid sensitivity toward acetone (detection limit of 100 ppb, 5 times lower than previous state-of-the-art TiO₂-based acetone sensors), as well as reduced response/recovery times at very low working temperature, 150 °C, for acetone sensing. Still, the same material showed itself to be able to (reversibly) change in color when stimulated by both UV-A and, most remarkably, visible light. Indeed, the visible-light photochromic performance was almost 3 times faster compared to the standard Cu-TiO₂ photochromic material-that is, 4.0 min versus 10.8 min, respectively. It was eventually proposed that the photochromic behavior was triggered by different mechanisms, depending on the light source used.

Low-Pressure Flow Chemistry of CuAAC Click Reaction Catalyzed by Nanoporous AuCu Membrane

Click chemistry has been widely used in bioconjugation, polymer synthesis, and the development of new anticancer drugs. Here, we report a nanoporous membrane made of AuCu alloy nanowires, which can effectively catalyze copper(I)-catalyzed 1,3-dipolar cycloaddition between azide and terminal alkyne (CuAAC) in flow condition with pressure less than one bar. Comparison studies of the nanowires before and after the reaction using X-ray photoelectron spectroscopy reveal Cu(0) and Cu(I) are main species that promote the reaction. This simple strategy can be used to synthesize a variety of compounds with triazole linkage and extended to gram level chemical production.

Indirect photopatterning of functionalized organic monolayers via copper-catalyzed "click chemistry"

Solution-based lithographic surface modification of an organic monolayer on a solid substrate is attained based on selective area photo-reduction of copper (II) to copper (I) to catalyze the azide-alkyne dipolar cycloaddition "click" reaction. X-ray photoelectron spectroscopy is used to confirm patterning, and spectroscopic results are analyzed and supplemented with computational models to confirm the surface chemistry. It is determined that this surface modification approach requires irradiation of the solid substrate with all necessary components present in solution. This method requires only minutes of irradiation to result in spatial and temporal control of the covalent surface functionalization of a monolayer and offers the potential for wavelength tunability that may be desirable in many applications utilizing organic monolayers.

Lignin Nanosphere-Supported Cuprous Oxide as an Efficient Catalyst for Huisgen [3+2] Cycloadditions under Relatively Mild Conditions

In this work, low-cost lignin nanospheres were fabricated and further applied as an efficient and sustainable support for preparing cuprous oxide (Cu₂O) "green" catalyst by using electrospraying technology. The unalloyed lignin, a special three-dimensional molecular structure, was successfully processed into uniform nanospheres under an electrospraying condition. The synthesized lignin-supported Cu₂O catalyst had a well-defined nanosphere structure, and Cu₂O nanoparticles with sizes less than 30 nm were supported by exposed layers of lignin nanospheres. There were C⁻O⁻Cu bonds formed between the lignin nanospheres and the metallic nanoparticles. The lignin nanospheres and the lignin nanosphere-supported catalyst werfe characterized by utilizing XRD, SEM, TEM, XPS, EDS, and TGA. The immobilization of Cu₂O nanoparticles on the lignin nanospheres was beneficial for dispersion of the Cu₂O nanoparticles and preventing their aggregation, which could cause catalyst deactivation, which favored the Huisgen [3+2] cycloaddition reaction. The triazole synthesis results indicated that the lignin nanosphere-supported Cu₂O catalyst had a high catalytic performance with 99% yield under solvent-free conditions. Furthermore, the as-synthesized catalyst could be recycled for four times without significantly losing its catalytic activity.

Designed heterogeneous palladium catalysts for reversible light-controlled bioorthogonal catalysis in living cells

As a powerful tool for chemical biology, bioorthogonal chemistry broadens the ways to explore the mystery of life. In this field, transition metal catalysts (TMCs) have received much attention because TMCs can rapidly catalyze chemical transformations that cannot be accomplished by bio-enzymes. However, fine controlling chemical reactions in living systems like bio-enzymes is still a great challenge. Herein, we construct a versatile light-controlled bioorthogonal catalyst by modifying macroporous silica-Pd0 with supramolecular complex of azobenzene (Azo) and β-cyclodextrin (CD). Its catalytic activity can be regulated by light-induced structural changes, mimicking allosteric regulation mechanism of bio-enzymes. The light-gated heterogeneous TMCs are important for in situ controlling bioorthogonal reactions and have been successfully used to synthesize a fluorescent probe for cell imaging and mitochondria-specific targeting agent by Suzuki-Miyaura cross-coupling reaction. Endowing the bioorthogonal catalyst with new functions is highly valuable for realizing more complex researches in biochemistry.

Dye-Assisted Transformation of Cu2O Nanocrystals to Amorphous Cu x O Nanoflakes for Enhanced Photocatalytic Performance

Amorphous Cu _x O nanoflakes with a thickness of 10-50 nm were synthesized through dye-assisted transformation of rhombic dodecahedral Cu₂O nanocrystals using a facile solution process. The morphology evolution observed by electron microscopy is highly dependent on the reaction between the surface and the dye. The crystal grain shrinks during the process until the formation of a purely amorphous nanoflake. The amorphous Cu _x O nanoflake consists of a combination of Cu(I) and Cu(II) with a ratio close to 1:1. It shows enhanced photocatalytic reactivity toward the degradation of methyl orange compared to that of rhombic dodecahedral Cu₂O nanocrystals with all active (110):Cu facets. The chemical composition and architecture remain the same after repeating degradation tests. The high surface-to-volume ratio contributes to its superior photocatalytic performance, whereas its low surface energy, confirmed by density functional theory simulations, explains its improved stability. The nanoflakes also show the ability of degrading nitrobenzene effectively, thus demonstrating great promise as a highly stable and active photocatalyst for environmental applications.

Cu2O/TiO2 nanoparticles as visible light photocatalysts concerning C(sp2)–P bond formation

A novel and efficient method has been developed for the construction of an aromatic-phosphorus (Ar-P) bond under visible light irradiation using Cu₂O/TiO₂ nanoparticles as inexpensive and available photocatalysts.

Enhanced sunlight-driven photocatalytic property of Mg-doped ZnO nanocomposites with three-dimensional graphene oxide/MoS2 nanosheet composites

Graphene oxide (GO) has been the focus of attention as it can enhance the photocatalytic activity of semiconductors due to its large specific surface area and remarkable optical and electronic properties. However, the enhancing effect is not ideal because of its easy self-agglomeration and low electronic conductivity. To improve the enhancing effect of GO for ZnO, three-dimensional GO/MoS₂ composite carriers (3D GOM) were prepared by electrostatic interactions and then, Mg-doped ZnO nanoparticles (MZ) were supported on the surface of 3D GOM by utilizing the layer-by-layer assembly method. Compared with GO/Mg-ZnO composite (GOMZ), the resultant three-dimensional GO/MoS₂/Mg-ZnO composite (GOMMZ) exhibited excellent photocatalytic performance due to the effective synergistic effect between GO and MoS₂ sheet, and its degradation rate was nearly 100% within 120 min of exposure to visible light; this degradation rate was nearly 8 times higher than that of the GOMZ composite. Moreover, the introduction of the MoS₂ sheet intensified the photocurrent density of the GOMZ composite and endowed it with optical memory ability.

Graphene oxide (GO) has been the focus of attention as it can enhance the photocatalytic activity of semiconductors due to its large specific surface area and remarkable optical and electronic properties.