Hierarchical Composite with Self-Adaptive Anisotropic Deformation for Thermal Protection System.

Rigid thermal protection materials such as ultra-high-temperature ceramics are desirable for applications in aerospace vehicles, but few materials can currently satisfy the emerging high-temperature sealing requirements for dynamic gaps created by the mismatch of the thermal expansion of different protection layers. Here, we design and fabricate a flexible biomimetic anisotropic deformation composite by multilayer cocuring onto fiber fabrics. It displays superior anisotropic deformation, whose longitudinal expansion ratio is 48 times greater than the transverse expansion ratio at specific temperatures. Furthermore, the ordered carbon structure created by transition-metal-catalyzed graphitization and the C/Si synergistic effect resulting from the combination of biomimetic fiber fabrics and SR enable the in situ formation of a high-temperature-resistant SiC crystalline phase within the char layer, ultimately resulting in exceptional thermal protection properties. By constructing hollow structures in situ, the back temperature of the composite, which is only 4.33 mm thick, is stabilized at 140 °C under the condition of continuous butane flame ablation (1300 °C) for 420 s. Multilayer structure and flexible features can facilitate large-scale preparation and arbitrary cutting and bending, adapted to different thermal protection areas.

Fabrication of Highly Thermally Resistant and Self-Healing Polysiloxane Elastomers by Constructing Covalent and Reversible Networks.

The fabrication of self-healing elastomers with high thermal stability for use in extreme thermal conditions such as aerospace remains a major challenge. A strategy for preparing self-healing elastomers with stable covalent bonds and dynamic metal-ligand coordination interactions as crosslinking sites in polydimethylsiloxane (PDMS) is proposed. The added Fe (III) not only serves as the dynamic crosslinking point at room temperature which is crucial for self-healing performance, but also plays a role as free radical scavenging agent at high temperatures. The results show that the PDMS elastomers possessed an initial thermal degradation temperature over 380 °C and a room temperature self-healing efficiency as high as 65.7%. Moreover, the char residue at 800 °C of PDMS elastomer reaches 7.19% in nitrogen atmosphere, and up to 14.02% in air atmosphere by doping a small amount (i.e., 0.3 wt%) of Fe (III), which is remarkable for the self-healing elastomers that contain weak and dynamic bonds with relatively poor thermal stability. This study provides an insight into designing self-healing PDMS-based materials that can be targeted for use as high-temperature thermal protection coatings.

Flexible Thermal Protection Polymeric Materials with Self-Sensing and Self-Adaptation Deformation Abilities.

Based on the strategy of killing two birds with one stone, we introduce thermally expandable microspheres into a silicone rubber matrix to fabricate temperature-responsive controllable deformation materials, which exhibit intelligent deformation properties as well as enhanced thermal protection performance, for dynamic thermal protection in the next-generation morphing aircrafts. The formation of hollow structures endows the material with intelligent thermal management ability and makes the thermal conductivity controllable, meeting the requirements of rapid deformation and excellent thermal insulation. The dimensions of the material adaptively expand with increasing temperature, and a constant 50N force can be provided to ensure reliable sealing. Moreover, benefiting from the synergistic effect of the hollow structure and zinc borate in the ceramization process of the silicone rubber, the 10 mm thick material can reduce the temperature from 2000 to 63 °C, and the mass ablation rate is only 4.8 mg/s. To broaden the application of our material, a sensor with a sandwich structure composed of different functional layers is designed. It is pleasantly surprising to observe that the sensor can provide real-time remote warning of fire and overheating sites with a response time as short as 1 s. This synergistic strategy opens a new possibility to fabricate intelligent thermal protection materials.

Discovery of a potent and highly specific ß2 proteasome inhibitor from a library of copper complexes.

We reported the synthesis, characterization and biological activity of several copper(II) Schiff base complexes, which exhibit high proteasome inhibitory activities with particular selectivity of ß2 subunit. Structure-activity relationships information obtained from complex Na2[Cu(a4s1)] demonstrated that distinct bonding modes in ß2 and ß5 subunits determines its selectivity and potent inhibition for ß2 subunit.

Rational Design of Fluorescent Phthalazinone Derivatives for One- and Two-Photon Imaging.

Phthalazinone derivatives were designed as optical probes for one- and two-photon fluorescence microscopy imaging. The design strategy involves stepwise extension and modification of pyridazinone by 1) expansion of pyridazinone to phthalazinone, a larger conjugated system, as the electron acceptor, 2) coupling of electron-donating aromatic groups such as N,N-diethylaminophenyl, thienyl, naphthyl, and quinolyl to the phthalazinone, and 3) anchoring of an alkyl chain to the phthalazinone with various terminal substituents such as triphenylphosphonio, morpholino, triethylammonio, N-methylimidazolio, pyrrolidino, and piperidino. Theoretical calculations were utilized to verify the initial design. The desired fluorescent probes were synthesized by two different routes in considerable yields. Twenty-two phthalazinone derivatives were synthesized and their photophysical properties were measured. Selected compounds were applied in cell imaging, and valuable information was obtained. Furthermore, the designed compounds showed excellent performance in two-photon microscopic imaging of mouse brain slices.

Unravelling the correlation between metal induced aggregation and cellular uptake/subcellular localization of Znsalen: an overlooked rule for design of luminescent metal probes.

Unravelling the unique effects of metal coordination on biological behaviours is of importance to design metal based therapeutic and diagnostic agents. In this work, we chose luminescent Znsalen (ZnL1 ) as a case study to demonstrate that metal induced aggregation arising from the intermolecular Zn···O interaction influences its cellular uptake and subcellular localization. Comparative studies with the free bases (L1 and L2 ) show that ZnL1 undergoes cellular uptake through caveolae-mediated endocytosis and internalizes in endosomal/lysosomal compartments, in contrast to the localization of L1 and L2 in the mitochondria. Further studies of photophysical properties, TEM imaging and DLS analysis suggest that ZnL1 tends to form large sized fibrous structures in aqueous media. To investigate the relationship between ZnL1 aggregation and the biological behaviour, we used pyridine to tune the "aggregation-to-deaggregation" transition and found that, in the presence of pyridine, ZnL1 could localize in the mitochondria and internalize into cells through the passive diffusion pathway. Such distinctive biological behaviours resulting from the different Znsalen species clearly point out the importance of metal induced aggregation or metal speciation analysis in designing metal complexes as biological probes.

Effect of distal histidines on hydrogen peroxide activation by manganese reconstituted myoglobin.

Myoglobins provide an opportunity to investigate the effect of the secondary coordination sphere on the functionality and reactivity of non-native metal porphyrins inside well-defined protein scaffolds. In this work, we reconstituted myoglobin by the replacement of natural heme with manganese(iii) protoporphyrin IX and firstly investigated the effect of distal histidine on the reaction of Mn(III) porphyrin with H2O2 and one-electron oxidation of ABTS. We have prepared L29H, F43H, H64F, L29H/H64F, F43H/H64F, L29H/F43H and L29H/F43H/H64F mutants and reconstituted apo-myoglobins with manganese(iii) protoporphyrin IX. Distal histidine at the 64 position plays an essential role in binding H2O2 through hydrogen bond formation, which facilitates the coordination of H2O2 to the Mn center. The second histidine at the 43 position is important in the cleavage of the O-O bond and to form the highly valent Mn(iv)-oxo intermediate. His29 has less efficiency to activate H2O2, because it is too far from the Mn center. The cooperative effect of dual distal histidines at positions 64 and 43 on the activation of H2O2 was observed and the F43H Mn(III)Mb mutant exhibited 5-fold and 10-fold reaction rate increases in the activation of H2O2 and one-electron oxidation of ABTS versus wild-type Mn(III)Mb. This is different from the distal histidine effect on the H2O2 activation by heme in Mb. This work will provide new insights to understand the fundamental chemistry of manganese in oxidation, and further construct biomimetic Mn models for peroxidase, inside or outside of protein scaffolds.

µ-Hydroxyl trinuclear copper(II) clusters: reactivity and unusual formation in the three-component synthesis of 1,2,3-triazoles in aqueous media.

µ-Hydroxyl trinuclear copper(II) compounds, with core structures closely resembling the central moieties in multicopper oxidases, have been extensively investigated and the importance of the prototypes in the oxidation of C-H bonds has been confirmed. In the course of study for the Cu(II) salens catalyzing the three-component (sodium azide, epoxide and non-activated terminal alkyne) 1,3-Huisgen cycloaddition, we observed the unusual formation of a µ-OH bridging trinuclear copper cluster supported by three (R,R)-N-(5-sulfonatosalicylidene)-1,2-diaminocyclohexane ligands (Cu-6) during the catalytic process. More interestingly, through comparative studies for the activity of the mononuclear copper(II) complexes (Cu-1 and Cu-5), we found that the µ-OH trinuclear copper(II) complex (Cu-6) was the active catalyst precursor. Through analysing the reaction intermediates we found that Cu(II) was partially reduced to Cu(I) and an adduct formed during catalytic process, which involves the alkyne coordinating to the Cu centers. This is the first example where a µ-OH trinuclear copper(II) complex has been isolated in copper catalyzed reactions other than catalytic oxidations, which provides a valuable clue to investigate that µ-OH copper clusters could be the intermediates in copper catalysed reactions in aqueous media.

π-π interaction assisted hydrodefluorination of perfluoroarenes by gold hydride: a case of synergistic effect on C-F bond activation.

"Synergistic effect" is prevalent in natural metalloenzymes in activating small molecules, and the success has inspired the development of artificial catalysts capable of unprecedented organic transformations. In this work, we found that the attractive π-π interaction between organic additives (as electron-donors) and the perfluorinated arenes (as electron acceptors) is effective in gold hydride catalyzed activation of C-F bonds, specifically hydrodefluorination (HDF) of perfluoroarenes catalyzed by the Sadighi's gold hydrides [(NHC)AuH] (NHC = N-heterocyclic carbene). Although a weak interaction between [(NHC)AuH] and perfluoroarenes was observed from (1)H NMR and UV-vis spectroscopies, low reactivity of [(NHC)AuH] toward HDF was found. In contrast, in the presence of p-N,N-dimethylaminopyridine (DMAP), the HDF of perfluoroarenes with silanes can be efficiently catalyzed by [(NHC)AuH], resulting in mainly the para-hydrodefluorinated products with up to 90% yield and 9 turnovers. The yield of the reaction increases with the more electron-withdrawing groups and degree of fluorination on the arenes, and the HDF reaction also tolerates different function groups (such as formyl, alkynyl, ketone, ester, and carboxylate groups), without reduction or hydrogenation of these function groups. To reveal the role of DMAP in the reactions, the possible π-π interaction between DMAP and perfluoroarenes was suggested by UV-vis spectral titrations, (1)H NMR spectroscopic studies, and DFT calculations. Moreover, (1)H and (19)F-NMR studies show that this π-π interaction promotes hydrogen transfer from [(NHC)AuH] to pyridyl N atom, resulting in C-F bond cleavage. The interpretation of π-π interaction assisted C-F activation is supported by the reduced activation barriers in the presence of DMAP (31.6 kcal/mol) than that in the absence of DMAP (40.8 kcal/mol) for this reaction. An analysis of the charge distribution and transition state geometries indicate that this HDF process is controlled by the π-π interaction between DMAP and perfluoroarenes, accompanied with the changes of partial atomic charges.

Molecular assembly directed by metal-aromatic interactions: control of the aggregation and photophysical properties of Zn-salen complexes by aromatic mercuration.

There is widespread interest in non-covalent bonding and weak interactions, such as electrostatic interactions, hydrogen bonding, solvophobic/hydrophobic interactions, metal-metal interactions, and π-π stacking, to tune the molecular assembly of planar π-conjugated organic and inorganic molecules. Inspired by the roles of metal-aromatic interaction in biological systems, such as in ion channels and metalloproteins, herein, we report the first example of the use of Hg(2+) -aromatic interactions to selectively control the assembly and disassembly of zinc-salen complexes in aqueous media; moreover, this process exhibited significant "turn on" fluorescent properties. UV/Vis and fluorescence spectroscopic analysis of the titration of Hg(2+) ions versus complex ZnL(1) revealed that the higher binding affinity of Hg(2+) ions (compared to 13 other metal ions) was ascribed to specific interactions between the Hg(2+) ions and the phenyl rings of ZnL(1); this result was also confirmed by (1)H NMR spectroscopy and HRMS (ESI). Further evidence for this type of interaction was obtained from the reaction of small-molecule analogue L(1) with Hg(2+) ions, which demonstrates the proximity of the N-alkyl group to the aromatic protons during Hg(2+)-ion binding, which led to the consequential H/D exchange reaction with D(2) O. DFT modeling of such interactions between the Hg(2+) ions and the phenyl rings afforded calculated distances between the C and Hg atoms (2.29 Å) that were indicative of C-Hg bond-formation, under the direction of the N atom of the morpholine ring. The unusual coordination of Hg(2+) ions to the phenyl ring of the metallosalen complexes not only strengthened the binding ability but also increased the steric effect to promote the disassembly of ZnL(1) in aqueous media.