Multimode Luminescence Tailoring and Improvement of Cs2 NaHoCl6 Cryolite Crystals via Sb3+ /Yb3+ Alloying for Versatile Photoelectric Applications.

Lead-free halide double perovskites are currently gaining significant attention owing to their exceptional environmental friendliness, structural adjustability as well as self-trapped exciton emission. However, stable and efficient double perovskite with multimode luminescence and tunable spectra are still urgently needed for multifunctional photoelectric application. Herein, holmium based cryolite materials (Cs2 NaHoCl6 ) with anti-thermal quenching and multimode photoluminescence were successfully synthesized. By the further alloying of Sb3+ (s-p transitions) and Yb3+ (f-f transitions) ions, its luminescence properties can be well modulated, originating from tailoring band gap structure and enriching electron transition channels. Upon Sb3+ substitution in Cs2 NaHoCl6 , additional absorption peaking at 334 nm results in the tremendous increase of photoluminescence quantum yield (PLQY). Meanwhile, not only the typical NIR emission around 980 nm of Ho3+ is enhanced, but also the red and NIR emissions show a diverse range of anti-thermal quenching photoluminescence behaviors. Furthermore, through designing Yb3+ doping, the up-conversion photoluminescence can be triggered by changing excitation laser power density (yellow-to-orange) and Yb3+ doping concentration (red-to-green). Through a combined experimental-theoretical approach, the related luminescence mechanism is revealed. In general, by alloying Sb3+ /Yb3+ in Cs2 NaHoCl6 , abundant energy level ladders are constructed and more luminescence modes are derived, demonstrating great potential in multifunctional photoelectric applications.

Silencing of SPARC represses heterotopic ossification via inhibition of the MAPK signaling pathway.

Heterotopic ossification (HO), the pathologic formation of extraskeletal bone, can be disabling and lethal. However, the underlying molecular mechanisms were largely unknown. The present study aimed to clarify the involvement of secreted protein acidic and rich in cysteine (SPARC) and the underlying mechanism in rat model of HO. The mechanistic investigation on roles of SPARC in HO was examined through gain- and loss-of-function approaches of SPARC, with alkaline-phosphatase (ALP) activity, mineralized nodules, and osteocalcin (OCN) content measured. To further confirm the regulatory role of SPARC, levels of mitogen-activated protein kinase (MAPK) signaling pathways-related proteins (extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), p38, nuclear factor κ-B (NF-κB), and IkB kinase ß (IKKß)) were determined. Bone marrow mesenchymal stem cells were treated with pathway inhibitor to investigate the relationship among SPARC, MAPK signaling pathway, and HO. The results suggested that SPARC expression was up-regulated in Achilles tendon tissues of HO rats. Silencing of SPARC could decrease phosphorylation of ERK, JNK, p38, NF-κB, and IKKß. Additionally, silencing of SPARC or inhibition of MAPK signaling pathway could reduce the ALP activity, the number of mineralized nodules, and OCN content, thus impeding HO. To sum up, our study identifies the inhibitory role of SPARC gene silencing in HO via the MAPK signaling pathway, suggesting SPARC presents a potential target for HO therapy.

Enhanced Histochemical Detection of Iron in Paraffin Sections of Mouse Central Nervous System Tissue: Application in the APP/PS1 Mouse Model of Alzheimer's Disease.

Histochemical methods of detecting iron in the rodent brain result mainly in the labeling of oligodendrocytes, but as all cells utilize iron, this observation suggests that much of the iron in the central nervous system goes undetected. Paraffin embedding of tissue is a standard procedure that is used to prepare sections for microscopic analysis. In the present study, we questioned whether we could modify the iron histochemical procedure to enable a greater detection of iron in paraffin sections. Indeed, various modifications led to the widespread labeling of iron in mouse brain tissue (for instance, labeling of neurons and neuropil). Sites of focal concentrations, such as cytoplasmic punctate or nucleolar staining, were also observed. The modified procedures were applied to paraffin sections of a mouse model (APP/PS1) of Alzheimer's disease. Iron was revealed in the plaque core and rim. The plaque rim had a fibrillary or granular appearance, and it frequently contained iron-labeled cells. Further analysis indicated that the iron was tightly associated with the core of the plaque, but less so with the rim. In conclusion, modifications to the histochemical staining revealed new insights into the deposition of iron in the central nervous system. In theory, the approach should be transferrable to organs besides the brain and to other species, and the underlying principles should be incorporable into a variety of staining methods.

Bonded exciplex formation: electronic and stereoelectronic effects.

As recently proposed, the singlet-excited states of several cyanoaromatics react with pyridine via bonded-exciplex formation, a novel concept in photochemical charge transfer reactions. Presented here are electronic and steric effects on the quenching rate constants, which provide valuable support for the model. Additionally, excited-state quenching in poly(vinylpyridine) is strongly inhibited both relative to that in neat pyridine and also to conventional exciplex formation in polymers, consistent with a restrictive orientational requirement for the formation of bonded exciplexes. Examples of competing reactions to form both conventional and bonded exciplexes are presented, which illustrate the delicate balance between these two processes when their reaction energetics are similar. Experimental and computational evidence is provided for the formation of a bonded exciplex in the reaction of the singlet excited state of 2,6,9,10-tetracyanoanthracene (TCA) with an oxygen-substituted donor, dioxane, thus expanding the scope of bonded exciplexes.

Bonded exciplexes. A new concept in photochemical reactions.

Charge-transfer quenching of the singlet excited states of cyanoaromatic electron acceptors by pyridine is characterized by a driving force dependence that resembles those of conventional electron-transfer reactions, except that a plot of the log of the quenching rate constants versus the free energy of electron transfer is displaced toward the endothermic region by 0.5-0.8 eV. Specifically, the reactions with pyridine display rapid quenching when conventional electron transfer is highly endothermic. As an example, the rate constant for quenching of the excited dicyanoanthracene is 3.5 x 10(9) M(-1)s(-1), even though formation of a conventional radical ion pair, A*-D*+, is endothermic by approximately 0.6 eV. No long-lived radical ions or exciplex intermediates can be detected on the picosecond to microsecond time scale. Instead, the reactions are proposed to proceed via formation of a previously undescribed, short-lived charge-transfer intermediate we call a "bonded exciplex", A- -D+. The bonded exciplex can be formally thought of as resulting from bond formation between the unpaired electrons of the radical ions A*- and D*+. The covalent bonding interaction significantly lowers the energy of the charge-transfer state. As a result of this interaction, the energy decreases with decreasing separation distance, and near van der Waals contact, the A- -D+ bonded state mixes with the repulsive excited state of the acceptor, allowing efficient reaction to form A- -D+ even when formation of a radical ion pair A*-D*+ is thermodynamically forbidden. Evidence for the bonded exciplex intermediate comes from studies of steric and Coulombic effects on the quenching rate constants and from extensive DFT computations that clearly show a curve crossing between the ground state and the low-energy bonded exciplex state.

Associative return electron transfer. A bond-coupled electron transfer in the photoreactions of cyclopropylamines.

The dynamics of the geminate radical-ion pairs formed by electron transfer to the excited states of cyanoanthracenes from 2-phenylcyclopropylamines are dominated by exothermic bond cleavage of the amine radical cations. Quantitative studies of product formation as a function of the energetics of the photochemical and corresponding thermal reactions provide support for a novel mechanism in which return electron transfer in the geminate pair occurs in concert with bond formation from the ring-opened radical cations. This bond-coupled electron transfer process is referred to as an associative return electron transfer reaction. The important features of the associative electron transfer process that explain the experimental observations are described in terms of potential energy surfaces and competition between adiabatic and non-adiabatic deactivation paths.

Iron chelator research: past, present, and future.

The occurrence of in vivo iron toxicity in the human body can be categorized into iron overload and non-iron overload conditions. Iron overload conditions are common in beta-thalassemia and hereditary hemochromatosis patients, and anthracycline mediated cardiotoxicity is an example of a non-iron overload condition in cancer patients, in which the toxicity is iron-dependent. While hundreds of iron chelators have been evaluated in animal studies, only a few have been studied in humans. Examples of iron chelator drugs are desferrioxamine (DFO), deferiprone (L1), and dexrazoxane (ICRF 187). The compound ICL670 has completed phase II clinical trials and a phase III trial is planned in 2003. Triapine is currently in phase II clinical trial as an anticancer agent. CP502, GT56-252, NaHBED, and MPB0201 are examples of new chelators in preclinical/clinical development. In the past decade, many new viable utilities for iron chelators have been reported. This includes the use of iron chelators as antiviral, photoprotective, antiproliferative, and antifibrotic agents. This review will focus on the status of drug development for the treatment of iron overload in patients with beta-thalassemia and the potential use of iron chelators in the prevention and treatment of other diseases.