Diels-Alder Click Chemistry Research Articles

Suppressing molecular motions for enhanced room-temperature phosphorescence of metal-free organic materials.

Metal-free organic phosphorescent materials are attractive alternatives to the predominantly used organometallic phosphors but are generally dimmer and are relatively rare, as, without heavy-metal atoms, spin–orbit coupling is less efficient and phosphorescence usually cannot compete with radiationless relaxation processes. Here we present a general design rule and a method to effectively reduce radiationless transitions and hence greatly enhance phosphorescence efficiency of metal-free organic materials in a variety of amorphous polymer matrices, based on the restriction of molecular motions in the proximity of embedded phosphors. Covalent cross-linking between phosphors and polymer matrices via Diels–Alder click chemistry is devised as a method. A sharp increase in phosphorescence quantum efficiency is observed in a variety of polymer matrices with this method, which is ca. two to five times higher than that of phosphor-doped polymer systems having no such covalent linkage.

Self-healing polymeric gel via RAFT polymerization and Diels–Alder click chemistry

Tailor-made copolymers of furfuryl methacrylate (FMA) and butyl methacrylate (BMA) (PFMA-co-PBMA) were successfully synthesized by reversible addition fragmentation chain-transfer (RAFT) polymerization technique. The thermoreversible network was successfully achieved by Diels–Alder (DA) and retro-DA reaction between the furfuryl groups of PFMA part and a bifunctional maleimide cross-linker, bismaleimide. This process was studied by NMR spectroscopy, FT-IR spectroscopy, differential scanning calorimetry (DSC) and nano-indentation analysis. DSC analysis was used to determine of the endothermic retro-DA reaction in copolymer-DA adduct. In this investigation self-healing property of the above cross-linked material was demonstrated by monitoring the repair of a scratch in the copolymer film upon heating and cooling. This was analyzed by scanning electron microscopy (SEM).

Diels-Alder Crosslinked Block-Copolymer Gate Dielectrics for Low Voltage Operated Top-Gate Organic Field-Effect Transistors

We report a cross-linkable diblock copolymer at a mild temperature by Diels-Alder click-chemistry for a gate dielectric layer in the top-gate, bottom contact organic field-effect transistors (OFETs). The Diels-Alder reaction between poly[(methyl methacrylate)-co-(9-anthracenyl methyl methacrylate)] (P(MMA-AMA)) and 1,1′-(methylenedi-4,1-phenylene)bismaleimide (MPB) enables the preparation of robust cross-linked films at 100 °C annealing for 10 min. Poly(9,9-dioctylfluorene-alt-bithiophene (F8T2) or poly(3-hexylthiophene) (P3HT) OFETs exhibited charge carrier mobilities of 3 ∼ 4 × 10−3 cm2 V−1 s−1 with the 250 nm thick crosslinked (P(MMA-AMA)) films at gate voltages of less than −20 V. Moreover, the ratio of MMA and AMA was controlled to observe the effects of crosslinking density on the properties of the gate dielectric layer. When the portion of a crosslinkable anthracenyl unit in (P(MMA-AMA)) is increased to 50 mol.% in the base polymer, the gate leakage current of OFETs decreases below 10−8 A at Vg = −20 V.

ChemInform Abstract: The Inverse Electron Demand Diels—Alder Click Reaction in Radiochemistry

AbstractReview: 48 refs.

An injectable hyaluronic acid/PEG hydrogel for cartilage tissue engineering formed by integrating enzymatic crosslinking and Diels–Alder “click chemistry”

Injectable HA/PEG hydrogel was crosslinked by integrating the enzymatic crosslinking and Diels–Alder click chemistry and showed excellent shape recovery and anti-fatigue properties at a high compressive stress.

The inverse electron demand Diels–Alder click reaction in radiochemistry

The inverse electron-demand Diels-Alder (IEDDA) cycloaddition between 1,2,4,5-tetrazines and strained alkene dienophiles is an emergent variety of catalyst-free 'click' chemistry that has the potential to have a transformational impact on the synthesis and development of radiopharmaceuticals. The ligation is selective, rapid, high-yielding, clean, and bioorthogonal and, since its advent in 2008, has been employed in a wide variety of chemical settings. In radiochemistry, the reaction has proven particularly useful with (18) F and has already been utilized to create a number of (18) F-labeled agents, including the PARP1-targeting small molecule (18) F-AZD2281, the αv β3 integrin-targeting peptide (18) F-RGD, and the GLP-1-targeting peptide (18) F-exendin. The inherent flexibility of the ligation has also been applied to the construction of radiometal-based probes, specifically the development of a modular strategy for the synthesis of radioimmunoconjugates that effectively eliminates variability in the construction of these agents. Further, the exceptional speed and biorthogonality of the reaction have made it especially promising in the realm of in vivo pretargeted imaging and therapy, and pretargeted imaging strategies based on the isotopes (111) In, (18) F, and (64) Cu have already proven capable of producing images with high tumor contrast and low levels of uptake in background, nontarget organs. Ultimately, the characteristics of inverse electron-demand Diels-Alder click chemistry make it almost uniquely well-suited for radiochemistry, and although the field is young, this ligation has the potential to make a tremendous impact on the synthesis, development, and study of novel radiopharmaceuticals.

An interpenetrating HA/G/CS biomimic hydrogel via Diels–Alder click chemistry for cartilage tissue engineering

In order to mimic the natural cartilage extracellular matrix, a novel biological degradable interpenetrating network hydrogel was synthesized from the gelatin (G), hyaluronic acid (HA) and chondroitin sulfate (CS) by Diels–Alder “click” chemistry. HA was modified with furylamine and G was modified with furancarboxylic acid respectively. 1H NMR spectra and elemental analysis showed that the substitution degrees of HA-furan and G-furan were 71.5% and 44.5%. Then the hydrogels were finally synthesized by cross-linking furan-modified HA and G derivatives with dimaleimide poly(ethylene glycol) (MAL-PEG-MAL). The mechanical and degradation properties of the hydrogels could be tuned simply through varying the molar ratio between furan and maleimide. Rheological, mechanical and degradation studies demonstrated that the Diels–Alder “click” chemistry is an efficient method for preparing high performance biological interpenetrating hydrogels. This biomimic hydrogel with improved mechanical properties could have great potential applications in cartilage tissue engineering.

The effects of peptide modified gellan gum and olfactory ensheathing glia cells on neural stem/progenitor cell fate

The regenerative capacity of injured adult central nervous system (CNS) tissue is very limited. Specifically, traumatic spinal cord injury (SCI) leads to permanent loss of motor and sensory functions below the site of injury, as well as other detrimental complications. A potential regenerative strategy is stem cell transplantation; however, cell survival is typically less than 1%. To improve cell survival, stem cells can be delivered in a biomaterial matrix that provides an environment conducive to survival after transplantation. One major challenge in this approach is to define the biomaterial and cell strategies in vitro. To this end, we investigated both peptide-modification of gellan gum and olfactory ensheathing glia (OEG) on neural stem/progenitor cell (NSPC) fate. To enhance cell adhesion, the gellan gum (GG) was modified using Diels–Alder click chemistry with a fibronectin-derived synthetic peptide (GRGDS). Amino acid analysis demonstrated that approximately 300 nmol of GRGDS was immobilized to each mg of GG. The GG–GRGDS had a profound effect on NSPC morphology and proliferation, distinct from that of NSPCs in GG alone, demonstrating the importance of GRGDS for cell-GG interaction. To further enhance NSPC survival and outgrowth, they were cultured with OEG. Here NSPCs interacted extensively with OEG, demonstrating significantly greater survival and proliferation relative to monocultures of NSPCs. These results suggest that this co-culture strategy of NSPCs with OEG may have therapeutic benefit for SCI repair.

Poly(ethylene glycol)‐thioxanthone prepared by Diels–Alder click chemistry as one‐component polymeric photoinitiator for aqueous free‐radical polymerization

AbstractNovel water‐borne macrophotoinitiator containing thioxanthone (TX) end group was successfully synthesized by using Diels–Alder (DA) [4 + 2] click chemistry strategy. For this purpose, thioxanthone‐anthracene (TX‐A) and maleimide end‐functionalized poly(ethylene glycol) (PEG‐MI) were reacted in toluene at reflux temperature for 48 h. The final polymer (PEG‐TX) and the intermediates were characterized in detail by spectral analysis. PEG‐TX possesses absorption characteristics similar to the parent TX. The one‐component photoinitiating nature of the photointiator was demonstrated by photopolymeization of several hydrophilic vinyl monomers, such as acrylic acid, acrylamide, 2‐hydroxyethyl acrylate, and 1‐vinyl‐2‐pyrrolidone. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2109–2114, 2010