Hetero-Diels-Alder Reaction between Singlet Oxygen and Anthracene Drives Integrative Cage Self-Sorting.

A ZnII8L6 pseudocube containing anthracene-centered ligands, a ZnII4L'4 tetrahedron with a similar side length as the cube, and a trigonal prism ZnII6L3L'2 were formed in equilibrium from a common set of subcomponents. Hetero-Diels-Alder reaction with photogenerated singlet oxygen transformed the anthracene-containing "L" ligands into endoperoxide "LO" ones and ultimately drove the integrative self-sorting to form the trigonal prismatic cage ZnII6LO3L'2 exclusively. This ZnII6LO3L'2 structure lost dioxygen in a retro-Diels-Alder reaction after heating, which resulted in reversion to the initial ZnII8L6 + ZnII4L'4 ⇌ 2 × ZnII6L3L'2 equilibrating system. Whereas the ZnII8L6 pseudocube had a cavity too small for guest encapsulation, the ZnII6L3L'2 and ZnII6LO3L'2 trigonal prisms possessed peanut-shaped internal cavities with two isolated compartments divided by bulky anthracene panels. Guest binding was also observed to drive the equilibrating system toward exclusive formation of the ZnII6L3L'2 structure, even in the absence of reaction with singlet oxygen.

A High-Performance Nonlinear Optical Crystal with a Building Block Containing Expanded π-Delocalization.

Common nonlinear optical (NLO) crystals consist of traditional functional building blocks with inherent optical limitation. Herein, inspired by traditional (B3 O6 )3- inorganic building block, we theoretically identified a new type of organic functional building blocks and then successfully synthesized the first cyamelurate NLO crystal, Ba(H2 C6 N7 O3 )2 ⋅ 8 H2 O. To our surprise, the constituent (H2 C6 N7 O3 )- building block is not in structurally optimal arrangement, but Ba(H2 C6 N7 O3 )2 ⋅ 8 H2 O exhibits excellent optical properties including wide band gap of 4.10 eV, very large birefringence of 0.24@550 nm, and exceptionally strong second-harmonic generation (SHG) response of about 12×KH2 PO4 . Both the SHG response and birefringence are much larger than those of commercial NLO crystal ß-BaB2 O4 with optimally aligned (B3 O6 )3- building block. Theoretical calculations suggest that the expanded π-conjugation delocalization within (H2 C6 N7 O3 )- vs (B3 O6 )3- should be responsible to the enhanced performance. This work implies that there is still much room to develop new NLO crystals with excellent functional building blocks that may be longly neglected.

A Hydrogen Bonded Supramolecular Framework Birefringent Crystal.

Birefringent crystals could modulate the polarization of light and are widely used as polarizers, waveplates, optical isolators, etc. To date, commercial birefringent crystals have been exclusively limited to purely inorganic compounds such as α-BaB2 O4 with birefringence of about 0.12. Herein, we report a new hydrogen bonded supramolecular framework, namely, Cd(H2 C6 N7 O3 )2 ⋅8 H2 O, which exhibits exceptionally large birefringence up to about 0.60. To the best of our knowledge, the birefringence of Cd(H2 C6 N7 O3 )2 ⋅8 H2 O is significantly larger than those of all commercial birefringent crystals and is the largest among hydrogen bonded supramolecular framework crystals. First-principles calculations and structural analyses reveal that the exceptional birefringence is mainly ascribed to strong covalent interactions within (H2 C6 N7 O3 )- organic ligands and the perfect coplanarity between them. Given the rich structural diversity and tunability, hydrogen bonded supramolecular frameworks would offer unprecedented opportunities beyond the traditional purely inorganic oxides for birefringent crystals.

Host Spin-Crossover Thermodynamics Indicate Guest Fit.

Spin-crossover (SCO) metal-organic cages capable of switching between high-spin and low-spin states have the potential to be used as magnetic sensors and switches. Variation of the donor strength of heterocyclic aldehyde subcomponents in imine-based ligands can tune the ligand field for a FeII center, which results in both homoleptic and heteroleptic cages with diverse SCO behaviors. The tetrahedral SCO cage built from 1-methyl-1H-imidazole-2-carbaldehyde is capable of encapsulating various guests, which stabilize different cage spin states depending on guest size. Conversely, the SCO tetrahedron exhibits different affinities for guests in different spin states, which is inferred to result from subtle structural differences of the cavity caused by the change in metal center spin state. Examination of SCO thermodynamics across a series of host-guest complexes enabled sensitive probing of guest fit to the host cavity, providing information complementary to binding-constant determination.

Optogenetic Inhibition of Striatal GABAergic Neuronal Activity Improves Outcomes After Ischemic Brain Injury.

BACKGROUND AND PURPOSE: Striatal GABAergic neuron is known as a key regulator in adult neurogenesis. However, the specific role of striatal GABAergic neuronal activity in the promotion of neurological recovery after ischemic stroke remains unknown. Here, we used optogenetic approach to investigate these effects and mechanism. METHODS: Laser stimulation was delivered via an implanted optical fiber to inhibit or activate the striatal GABAergic neurons in Gad2-Arch-GFP or Gad2-ChR2-tdTomato mice (n=80) 1 week after 60-minute transient middle cerebral artery occlusion. Neurological severity score, brain atrophy volume, microvessel density, and cell morphological changes were examined using immunohistochemistry. Gene expression and protein levels of related growth factors were further examined using real-time polymerase chain reaction and Western blotting. RESULTS: Inhibiting striatal GABAergic neuronal activity improved functional recovery, reduced brain atrophy volume, and prohibited cell death compared with the control (P<0.05). Microvessel density and bFGF (basic fibroblast growth factor) expression in the inhibition group were also increased (P<0.05). In contrast, activation of striatal GABAergic neurons resulted in adverse effects compared with the control (P<0.05). Using cocultures of GABAergic neurons, astrocytes, and endothelial cells, we further demonstrated that the photoinhibition of GABAergic neuronal activity could upregulate bFGF expression in endothelial cells, depending on the presence of astrocytes. The conditioned medium from the aforementioned photoinhibited 3-cell coculture system protected cells from oxygen glucose deprivation injury. CONCLUSIONS: After ischemic stroke, optogenetic inhibition of GABAergic neurons upregulated bFGF expression by endothelial cells and promoted neurobehavioral recovery, possibly orchestrated by astrocytes. Optogenetically inhibiting neuronal activity provides a novel approach to promote neurological recovery.

Redox Triggers Guest Release and Uptake Across a Series of Azopyridine-Based Metal-Organic Capsules.

Precise control over guest release and recapture using external stimuli is a valuable goal, potentially enabling new modes of chemical purification. Including redox moieties within the ligand cores of molecular capsules to trigger the release and uptake of guests has proved effective, but this technique is limited to certain capsules and guests. Herein, the construction of a series of novel metal-organic capsules from ditopic, tritopic, and tetratopic ligands is demonstrated, all of which contain redox-active azo groups coordinated to FeII centers. Compared to their iminopyridine-based analogs, this new class of azopyridine-based capsules possesses larger cavities, capable of encapsulating more voluminous guests. Upon reduction of the capsules, their guests are released and may then be re-encapsulated when the capsules are regenerated by oxidation. Since the redox centers are on the ligand arms, they are modular and can be attached to a variety of ligand cores to afford varying and predictable architectures. This method thus shows promise as a generalized approach for designing redox-controlled guest release and uptake systems.

Molecular phylogeny reveals cryptic diversity in Sibynophis from China (Serpentes: Sibynophiidae).

The elucidation of species diversity and distribution is critical within the fields of evolution, genetics, and conservation. The genus Sibynophis contains rare snakes that have historically received little attention. In this study, we conducted comprehensive sampling and use both mitochondrial and nuclear genetic markers to explore Sibynophis species diversity within China. Our findings revealed that S. c. miyiensis should be considered synonymous with S. c. grahami, and S. c. grahami should be gave a specific rank as S. grahami. In addition, we discovered S. triangularis was new to China and Myanmar. Based on the specimens and molecular phylogeny results, we redefined the species distribution boundaries of each Chinese species.

Injectable hydroxypropyl chitin hydrogels embedded with carboxymethyl chitin microspheres prepared via a solvent-free process for drug delivery.

Microspheres and injectable hydrogels derived from natural biopolymers have been extensively investigated as controlled local drug delivery systems. In this study, we prepared carboxymethyl chitin microspheres (CMCH-Ms) with a diameter of 10-100 µm through physical crosslinking by increasing temperature in an aqueous two-phase system without using organic solvents, surfactants and crosslinking agents. The stable microspheres keeping spherical shape with porous microstructure in different pH environments were embeded in thermosensitive hydroxypropyl chitin (HPCH) hydrogels. The morphology, gelation rate, swelling, rheological and mechanical properties, in vitro degradation and cytotoxicity, drug loading and drug release of the CMCH-Ms/HPCH gel scaffolds were examined. In vitro degradation and cytotoxicity test indicated that CMCH-Ms/HPCH gel scaffolds were biodegradable and non-cytotoxic. Moreover, no organic solvent was used in the preparation and drug loading process of CMCH-Ms/HPCH gel scaffold. Importantly, less burst drug release and long-term sustained-release from the CMCH-Ms/HPCH composite hydrogel was observed than those from only CMCH-Ms or HPCH hydrogel. Thus, the composite CMCH-Ms/HPCH hydrogel exhibited great potential application for loading different drugs and sustained drug release in controlled local drug delivery systems.

A curved host and second guest cooperatively inhibit the dynamic motion of corannulene.

Biomolecular systems show how host-guest binding can induce changes in molecular behavior, which in turn impact the functions of the system. Here we report an artificial host-guest system where dynamic adaptation during guest binding alters both host conformation and guest dynamics. The self-assembled cage host employed here possesses concave walls and a chirotopic cavity. Complementarity between the curved surfaces of fullerenes and the inner surface of the host cavity leads the host to reconfigure stereochemically in order to bind these guests optimally. The curved molecule corannulene undergoes rapid bowl-to-bowl inversion at room temperature. Its inversion barrier is increased upon binding, however, and increased further upon formation of a ternary complex, where corannulene and a cycloalkane are both bound together. The chiral nature of the host also leads to clear differences in the NMR spectra of ternary complexes involving corannulene and one or the other enantiomer of a chiral guest, which enables the determination of enantiomeric excess by NMR.

Two isostructural Ln-MOFs showing luminescent sensing (Eu) and slow magnetic relaxation (Dy) properties.

Two isostructural lanthanide-based MOFs [Ln(HL)L]·H2O (1-Ln, Ln = Eu, Dy, H2L = 5-((pyridin-4-ylthio)methyl)isophthalic acid) were successfully obtained via the solvothermal reaction. 1-Eu exhibits high fluorescence quenching efficiency for C2O72- and Fe3+, which can be potentially used as a luminescent probe; 1-Dy behaves as a typical single-molecule magnet with an energy barrier (ΔUeff) of 54(2) K.

A dual-channel fluorescent chemosensor for discriminative detection of glutathione based on functionalized carbon quantum dots.

A convenient, fluorescent dual-channel chemosensor on the basis of bis(3-pyridylmethyl)amine-functionalized carbon quantum dots (BPMA-CQDs) nanoprobe was constructed, and it can discriminatively detect glutathione from its analogues cysteine and homocysteine based on two distinctive strategies. Two distinct fluorescence responses of BPMA-CQDs probe to Cu(II) and Ag(I) were identified and further employed to achieve selective detection of Cu(II) and Ag(I) respectively. Based on the BPMA-CQDs/Cu(II) conjugate, discriminative detection of GSH was achieved in terms of correlation between the amounts of GSH and fluorescence recovery. The addition of GSH into BPMA-CQDs/Cu(II) system induces the reduction of Cu(II) to Cu(I), which could efficiently block PET process resulting in the following fluorescence recovery. Based on the BPMA-CQDs/Ag(I) conjugate, GSH assay could also be established on the basis of fluorescence response to GSH. The introduction of GSH into the preceding system triggers the competitive coordination to Ag(I) between BPMA and GSH, and silver ions are finally taken away by GSH from the probe, where the fluorescence is restored to its original weak state. Both of the detection strategies can achieve discriminative detection of GSH from Cys and Hcy. The assays showed good stability and repeatability, and covered a broad linear range of up to 13.3µM with a lowest detection limit of 42.0nM. Moreover, both of them were utilized to monitor GSH level in live cells.