Direct UV‐Induced Functionalization of Surface Hydroxy Groups by Thiol–Ol Chemistry

A novel UV‐initiated surface modification method for the direct functionalization of surface hydroxy groups with thiol‐containing molecules (termed “thiol–ol” modification) is described. This method is based on the oxidative conjugation of thiols to hydroxy groups. We demonstrate that different thiol‐containing molecules, such as fluorophores, thiol‐terminated poly(ethylene glycol) (PEG‐SH), and a cysteine‐containing peptide, can be attached onto the surface of porous poly(2‐hydroxyethyl methacrylate‐co‐ethylene dimethacrylate). Direct functionalization of other hydroxy‐group‐bearing surfaces, fabrication of micropatterns, and double patterning have been also demonstrated using the thiol–ol method.     

UV‐Induced Tetrazole‐Thiol Reaction for Polymer Conjugation and Surface Functionalization

A UV‐induced 1,3‐dipolar nucleophilic addition of tetrazoles to thiols is described. Under UV irradiation the reaction proceeds rapidly at room temperature, with high yields, without a catalyst, and in both polar protic and aprotic solvents, including water. This UV‐induced tetrazole‐thiol reaction was successfully applied for the synthesis of small molecules, protein modification, and rapid and facile polymer–polymer conjugation. The reaction has also been demonstrated for the formation of micropatterns by site‐selective surface functionalization. Superhydrophobic–hydrophilic micropatterns were successfully created by sequential modifications of a tetrazole‐modified porous polymer surface with hydrophobic and hydrophilic thiols. A biotin‐functionalized surface could be fabricated in aqueous solutions under long‐wavelength UV irradiation.     

UV‐Light‐Induced Hydrogen Transfer in Guanosine–Guanosine Aggregates

Aggregates of a lipophilic guanine (G) derivative have been studied in n‐hexane by femtosecond‐to‐microsecond UV‐visible broadband transient absorption, stationary infrared and UV‐visible spectroscopy and by quantum chemical calculations. We report the first time‐resolved spectroscopic detection of hydrogen transfer in GG aggregates, which leads to (G?H) ^. radicals by means of G⁺G^? charge transfer followed by proton transfer. These radicals show a characteristic electronic spectrum in the range 300–550 nm. The calculated superimposed spectrum of the species that result from NH???N proton transfer agrees best with the experimental spectrum.     

Photopatterning of Crosslinkable Hole‐Conducting Materials for Application in Organic Light‐Emitting Devices

Summary: Modern multilayer organic light‐emitting devices (OLED) are fabricated easily and at low cost by spin‐coating with subsequent crosslinking of the layers. For this purpose, a low‐molecular‐weight hole‐transport material based on triphenyl amines bearing crosslinkable oxetane groups was synthesized. Crosslinking of the spin‐coated layer was initiated with UV irradiation using an iodonium‐salt photoinitiator and was observed using realtime FT‐IR spectroscopy. Standard photolithography techniques can be used for structuring the material on the micrometre scale.

An AFM image of the photopatterned bis‐oxetane‐functionalized low‐molecular‐weight hole‐transport material based on triphenyl amines synthesized here.     

UV‐photoexcitation and ultrafast dynamics of HCFC‐132b (CF2ClCH2Cl)

The UV‐induced photochemistry of HCFC‐132b (CF₂ClCH₂Cl) was investigated by computing excited‐state properties with time‐dependent density functional theory (TDDFT), multiconfigurational second‐order perturbation theory (CASPT2), and coupled cluster with singles, doubles, and perturbative triples (CCSD(T)). Excited states calculated with TDDFT show good agreement with CASPT2 and CCSD(T) results, correctly predicting the main excited‐states properties. Simulations of ultrafast nonadiabatic dynamics in the gas phase were performed, taking into account 25 electronic states at TDDFT level starting in two different spectral windows (8.5 ± 0.25 and 10.0 ± 0.25 eV). Experimental data measured at 123.6 nm (10 eV) is in very good agreement with our simulations. The excited‐state lifetimes are 106 and 191 fs for the 8.5 and 10.0 eV spectral windows, respectively. Internal conversion to the ground state occurred through several different reaction pathways with different products, where 2Cl, C‐Cl bond breakage, and HCl are the main photochemical pathways in the low‐excitation region, representing 95% of all processes. On the other hand, HCl, HF, and C‐Cl bond breakage are the main reaction pathways in the higher excitation region, with 77% of the total yield. © 2015 Wiley Periodicals, Inc.     

Flavoenzyme‐Catalyzed Formation of Disulfide Bonds in Natural Products

Nature provides a rich source of compounds with diverse chemical structures and biological activities, among them, sulfur‐containing metabolites from bacteria and fungi. Some of these compounds bear a disulfide moiety that is indispensable for their bioactivity. Specialized oxidoreductases such as GliT, HlmI, and DepH catalyze the formation of this disulfide bridge in the virulence factor gliotoxin, the antibiotic holomycin, and the anticancer drug romidepsin, respectively. We have examined all three enzymes by X‐ray crystallography and activity assays. Despite their differently sized substrate binding clefts and hence, their diverse substrate preferences, a unifying reaction mechanism is proposed based on the obtained crystal structures and further supported by mutagenesis experiments.     

Polymer‐Fullerene Network Formation via Light‐Induced Crosslinking

A facile and efficient methodology for the formation of polymer‐fullerene networks via a light‐induced reaction is reported. The photochemical crosslinking is based on a nitrile imine‐mediated tetrazole‐ene cycloaddition reaction, which proceeds catalyst‐free under UV‐light irradiation (λ_max = 320 nm) at ambient temperature. A tetrazole‐functionalized polymer (M_n = 6500 g mol⁻¹, Ð = 1.3) and fullerene C₆₀ are employed for the formation of the hybrid networks. The tetrazole‐functionalized polymer as well as the fullerene‐containing networks are carefully characterized by NMR spectrometry, size exclusion chromatography, infrared spectroscopy, and elemental analysis. Furthermore, thermal analysis of the fullerene networks and their precursors is carried out. The current contribution thus induces an efficient platform technology for fullerene‐based network formation.

     

Constructing Ordered Three‐Dimensional TiO2 Channels for Enhanced Visible‐Light Photocatalytic Performance in CO2 Conversion Induced by Au Nanoparticles

As a typical photocatalyst for CO₂ reduction, practical applications of TiO₂ still suffer from low photocatalytic efficiency and limited visible‐light absorption. Herein, a novel Au‐nanoparticle (NP)‐decorated ordered mesoporous TiO₂ (OMT) composite (OMT‐Au) was successfully fabricated, in which Au NPs were uniformly dispersed on the OMT. Due to the surface plasmon resonance (SPR) effect derived from the excited Au NPs, the TiO₂ shows high photocatalytic performance for CO₂ reduction under visible light. The ordered mesoporous TiO₂ exhibits superior material and structure, with a high surface area that offers more catalytically active sites. More importantly, the three‐dimensional transport channels ensure the smooth flow of gas molecules, highly efficient CO₂ adsorption, and the fast and steady transmission of hot electrons excited from the Au NPs, which lead to a further improvement in the photocatalytic performance. These results highlight the possibility of improving the photocatalysis for CO₂ reduction under visible light by constructing OMT‐based Au‐SPR‐induced photocatalysts.     

Surface engineering of nanoparticles for highly efficient UV‐shielding composites

Overexposure to ultraviolet (UV) with high energy can not only hurt human skin but also accelerate the degradation of organic matter. Hence, the preparation of polymer‐based UV‐shielding nanocomposites has attracted substantial attention due to the low cost, easy processing and wide applications. Notably, the highly efficient UV‐shielding polymer nanocomposites are still hindered by the agglomeration of inorganic anti‐UV nanoparticles (Nps) in polymer matrix and the narrow absorption range of UV‐shielding agents. To overcome the aforementioned bottlenecks, surface engineering of anti‐UV Nps including organic modification and inorganic hybridization has been extensively employed to enhance the UV‐shielding efficiency of composites. Herein, to deliver the readers a comprehensive understanding of the surface engineering of anti‐UV Nps, we systematically summarize the recent advances in surface organic modification and inorganic hybridization related to anti‐UV Nps. The UV‐shielding mechanism and the factors affecting UV‐shielding efficiency of polymer nanocomposites are also discussed. Finally, perspectives on remaining challenges and future development of highly efficient UV‐shielding composites are outlined.     

Azodicarboxylate-Mediated Peptide Cyclisation: Application to Disulfide Bond Formation in Solution and Solid Phase

Cyclic peptides are important molecules, playing key roles in protein architecture, as chemical probes, and increasingly as crucial structural elements of clinically-useful therapeutics. Herein we report methodology using azodicarboxylates as efficient reagents for the facile synthesis of cyclic peptides through a disulfide bridge. The utility of this approach in both solution and solid-phase, and compatibility with common amino acid side chain functionalities is demonstrated, resulting in cyclic peptides in good yield and purity. This approach has significant potential application for synthesis of molecules of biological or therapeutic significance.     

UV‐photodimerization in uracil‐substituted dendrimers for high density data storage

Two series of uracil‐functionalized dendritic macromolecules based on poly (amidoamine) PAMAM and 2,2‐bis(hydroxymethylpropionic acid) bis‐MPA backbones were prepared and their photoinduced (2π+2π) cycloaddition reactions upon exposure to UV light at 257 nm examined. Dendrimers up to 4th generation were synthesized and investigated as potential materials for high capacity optical data storage with their dimerization efficiency compared to uracil as a reference compound. This allows the impact of increasing the generation number of the dendrimers, both the number of chromophores, as well as the different steric environments, on the performance of each series of dendrimers to be investigated. The (uracil)₁₂‐[G‐2]‐bis‐MPA and (uracil)₈‐[G‐1]‐PAMAM were observed to have high dimerization efficiency in solution with different behavior being observed for the PAMAM and bis‐MPA dendrimers. The dendrimers with the best dimerization efficiency in solution were then examined in the solid state as thin films cast on quartz plates, and their film qualities along with their photodimerization performance studied. High quality films with a transmission response of up to 70% in 55 s. when irradiated at 257 nm with an intensity of 70 mW/cm² could be obtained suggesting future use as recording media for optical data storage. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4401–4412, 2007     

Room Temperature CP Bond Formation Enabled by Merging Nickel Catalysis and Visible‐Light‐Induced Photoredox Catalysis

A novel and efficient C?P bond formation reaction of diarylphosphine oxides with aryl iodides was achieved by combining nickel catalysis and visible‐light‐induced photoredox catalysis. This dual‐catalytic reaction showed a broad substrate scope, excellent functional group tolerance, and afforded the corresponding products in good to excellent yields. Compared with the previously reported use of photoredox/nickel dual catalysis in the construction of C?C bonds, the methodology described herein was observed to be the first to allow for C‐heteroatom bond formation.     

Multiblock Copolymer‐Based Dual Dynamic Disulfide and Supramolecular Crosslinked Self‐Healing Networks

A new multiblock copolymer self‐healing strategy is reported that centers on the synthesis of block copolymers designed with different self‐healing motifs incorporated into individual blocks. As a proof of concept, a novel pentablock copolymer (ABCBA) consisting of a poly(ethylene glycol) middle block and self‐healable symmetric blocks of a polymethacrylate with pendant disulfide linkages and carboxylic acids is synthesized by a combination of consecutive controlled radical polymerization with hydrolytic cleavage. Disulfide exchange reactions of pendant disulfide linkages and metal–ligand interactions of pendant carboxylic acids with ferric ions allow for the formation of dual crosslinked networks with dynamic disulfide and supramolecular crosslinkages. The resultant networks possessing self‐healing viscoelasticity enable self‐healing on macroscale damages through supramolecular metal–ligand interactions and disulfide exchange reactions at room or moderate temperatures. These preliminary results suggest that the strategy can offer the versatility in the development of multifunctional self‐healable materials in dual or multiple self‐healable mechanisms.

     

Transient Substrate‐Induced Catalyst Formation in a Dynamic Molecular Network

In biology enzyme concentrations are continuously regulated, yet for synthetic catalytic systems such regulatory mechanisms are underdeveloped. We now report how a substrate of a chemical reaction induces the formation of its own catalyst from a dynamic molecular network. After complete conversion of the substrate, the network disassembles the catalyst. These results open up new opportunities for controlling catalysis in synthetic chemical systems.     

UV‐cured polyester‐acrylate nanocomposite films with silane‐grafted silica nanoparticles

UV‐curing technique was employed in this study to prepare polyester‐acrylate nanocomposite films with silane‐grafted silica nanoparticles. Methacryloxypropyl trimethoxysilane was grafted to the surfaces of silica nanoparticles to improve dispersion of silica nanoparticles as well as interfacial adhesion between the resin matrix and silica nanoparticles. The silane‐grafting was confirmed by nuclear magnetic resonance and infrared spectroscopy. The effects of the silane‐grafting on the mechanical and optical properties as well as UV‐curing behavior of the nanocomposite films were investigated. The tensile strength, transmittance, UV‐curing rate, and final chemical conversion of the nanocomposite films were increased by use of the grafted silica nanoparticles as compared to the use of neat silica nanoparticles. Copyright © 2011 John Wiley & Sons, Ltd.     

Oxygen Reduction on Anthraquinone Diazonium Compound Derivatised Multi‐walled Carbon Nanotube and Graphene Based Electrodes

In this work, graphene and multi‐walled carbon nanotubes were derivatised with anthraquinone (AQ) groups using spontaneous or electrochemical grafting of Fast Red AL salt. Glassy carbon (GC) electrodes were coated with AQ‐modified carbon nanomaterials to study the oxygen reduction reaction (ORR). These nanomaterials were characterised by X‐ray photoelectron spectroscopy and multilayer formation of AQ on the electrografted electrodes was observed. All the modified electrodes showed enhanced electrocatalytic activity towards the ORR in alkaline media. High AQ loading on the electrodes was found and the number of electrons transferred per O₂ molecule was between 2 and 4. In addition, the stability testing of AQ‐derivatised carbon nanomaterial‐coated GC electrodes was performed.     

2‐Nitroveratryl as a Photocleavable Thiol‐Protecting Group for Directed Disulfide Bond Formation in the Chemical Synthesis of Insulin

Chemical synthesis of peptides can allow the option of sequential formation of multiple cysteines through exploitation of judiciously chosen regioselective thiol‐protecting groups. We report the use of 2‐nitroveratryl (oNv) as a new orthogonal group that can be cleaved by photolysis under ambient conditions. In combination with complementary S‐pyridinesulfenyl activation, disulfide bonds are formed rapidly in situ. The preparation of Fmoc‐Cys(oNv)‐OH is described together with its use for the solid‐phase synthesis of complex cystine‐rich peptides, such as insulin.     

Photocontrolled On‐Surface Pseudorotaxane Formation with Well‐Ordered Macrocycle Multilayers

The photoinduced pseudorotaxane formation between a photoresponsive axle and a tetralactam macrocycle was investigated in solution and on glass surfaces with immobilized multilayers of macrocycles. In the course of this reaction, a novel photoswitchable binding station with azobenzene as the photoswitchable unit and diketopiperazine as the binding station was synthesized and studied by NMR and UV/Vis spectroscopy. Glass surfaces have been functionalized with pyridine‐terminated SAMs and subsequently with multilayers of macrocycles through layer‐by‐layer self assembly. A preferred orientation of the macrocycles could be confirmed by NEXAFS spectroscopy. The photocontrolled deposition of the axle into the surface‐bound macrocycle‐multilayers was monitored by UV/Vis spectroscopy and led to an increase of the molecular order, as indicated by more substantial linear dichroism effects in angle‐resolved NEXAFS spectra.     

Surface modification of UV‐cured epoxy resins by click chemistry

A novel method for surface modification of UV‐cured epoxy network was described. Photoinitiated cationic copolymerization of a bisepoxide, namely 3,4‐epoxy cyclohexylmethyl 3,4‐epoxycyclohexanecarboxylate (EEC) with epibromohydrine (EBH) by using a cationic photoinitiator, [4‐(2‐methylpropyl)phenyl]4‐methylphenyl‐iodonium hexafluorophosphate, in propylene carbonate solution was studied. The real‐time Fourier transform infrared spectroscopic, gel content determination and thermal characterization studies revealed that both EEC and EBH monomers take part in the polymerization and epoxy network possessing bromomethyl functional groups was obtained. The bromine functions of the cured product formed on the glass surface were converted to azide functionalities with sodium azide. Independently prepared alkyne functional poly(ethylene glycol) (PEG) was subsequently anchored to azide‐modified epoxy surface by a “click” reaction. Surface modification of the network through incorporation of hydrophilic PEG chain was evidenced by contact angle measurements. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2862–2868, 2010