Structures and Reaction Mechanism of Novel Metal-Carbene Complexes Derived from Hypervalent Diazadiselenathiapentalenes

Abstract

Novel metal-carbene complexes (4) with a metallapentalene framework have been obtained from hypervalent diazadiselenathiapentalenes (3) by treating with Pt(PPh₃)₄, Pd(PPh₃)₄ and RhCl(PPh₃)₃. X-Ray investigations revealed that the central hypervalent sulfur atom in 3 was substituted by a metal atom to form M-Se bonds in the resultant metallapentalene framework.     

Syntheses,Structures, and Reactivities of Sulfur-Containing Cycloalkenes

Sulfur-containing cycloalkenes possessing disulfide units 1, 2, and 3 were obtained by oxidation of cis-disodium ethene-1,2-dithiolate, and their crystal structures were determined by the X-ray crystallographic analyses. Compound 1 was found to give the ring expansion product 3 in acetonitrile even at room temperature and also form reactive thioaldehyde under irradiation.     

Influences of aging on thermal decomposition mechanism of high performance oxidizer ammonium dinitramide

Ammonium dinitramide (ADN) is one of the several promising new solid propellant oxidizers. ADN is of interest because its oxygen balance and energy content are high, and it also halogen-free. One of the most important characteristics of a propellant oxidizer, however, is stability and ADN is known to degrade to ammonium nitrate (AN) during storage, which will affect its performance. This study focused on the effects of aging on the thermal decomposition mechanism of ADN. The thermal behaviors of ADN and ADN/AN mixtures were studied, as were the gases evolved during their decomposition, using differential scanning calorimetry (DSC), thermogravimetry–differential thermal analysis-infrared spectrometry (TG–DTA-IR), and thermogravimetry–differential thermal analysis-mass spectrometry (TG–DTA-MS). The results of these analyses demonstrated that the decomposition of ADN occurs via a series of distinct stages in the condensed phase. The gases evolved from ADN decomposition were N₂O, NO₂, N₂, and H₂O. In contrast, ADN mixed with AN (to simulate aging) did not exhibit the same initial reaction. We conclude that aging inhibits early stage, low temperature decomposition reactions of ADN. Two possible reasons were proposed, these being either a decrease in the acidity of the material due to the presence of AN, or inhibition of the acidic dissociation of dinitramic acid by NO ₃ ^? .     

Fully automated reagent peak‐free liquid chromatography fluorescence analysis of highly polar carboxylic acids using a column‐switching system and fluorous scavenging derivatization

In this study, we combined a column‐switching system with a fluorous scavenging derivatization method to develop a fully automated reagent peak‐free LC fluorescence detection protocol for the analysis of highly polar carboxylic acids. In this method, highly polar carboxylic acids were derivatized with fluorescent 1‐pyrenemethylamine in the presence of 1‐ethyl‐3‐(3‐dimethylaminopropyl)carbodiimide and 1‐hydroxy‐1H‐benzotriazole. Residual excess of the unreacted reagent was tagged with 2‐(perfluorooctyl)ethyl isocyanate and then removed selectively using a fluorous column‐switching system placed in front of an analytical reversed‐phase column. The signal of the fluorous‐tagged unreacted reagent was completely absent in the resulting chromatograms; therefore, it did not interfere with the quantification of each acid especially those eluted before 20 min. The detection limits (S/N = 3) for the examined acids were in the range from 4.0 to 22 fmol per injection. We have applied this method to comparative analysis of highly polar carboxylic acids in urine samples obtained from diabetes mellitus type‐II model mice and their control.     

Electrothermal atomic absorption spectrometric determination of cadmium in environmental samples with niobium wire preconcentration method

A preconcentration method by adsorption of cadmium on a niobium wire was developed for the environmental waters, followed by electrothermal atomic absorption spectrometry with a tungsten tube atomizer. After the preconcentration, the niobium wire was directly inserted into the tungsten tube atomizer. In the preconcentration (adsorption) process of cadmium, the optimal immersing time was 60?s. The effects of large amounts of concomitants on the preconcentration of cadmium were evaluated. When 10³–10⁴ fold excess of matrix elements existed in aqueous solution at pH 4 and 9, the cadmium response was profoundly affected by the matrix elements. However, the cadmium absorption signal was not significantly influenced at pH 7. Therefore, pH 7 was selected for the application into the real environmental samples. Under the optimal conditions, the detection limit (3S/N) for cadmium by the niobium wire preconcentration method was 7.0?pg?mL^?1 and the relative standard deviation was 6.8%. The method with preconcentration on a niobium wire was applied to the determination of cadmium in water and proved to be sensitive, simple and convenient. Because this preconcentration method can be utilized in the in situ treatment of trace cadmium in environmental water samples, it was unnecessary to carry the water samples to the analytical work place. The technique was shown to be useful for the determination of cadmium in environmental water samples at 0.1–1?µg?L^?1 levels.     

Synthesis,Crystal Packing,and Ambipolar Carrier Transport Property of Twisted Dibenzo[g,p]chrysenes

A versatile method for the synthesis of dibenzo[g,p]chrysene (DBC) derivatives based on regio‐ and stereoselective stannyllithiation to diarylacetylenes is described. This method affords a variety of DBCs possessing both electron‐donating and electron‐withdrawing functional groups. These twisted molecules take brickwork packing structures in single crystals. Thus, ambipolar carrier transport properties with mobility values of up to 10^?3 cm² V^?1 s^?1 in the amorphous state were achieved. Functional groups on DBC frameworks are considered to increase carrier mobility through the enhancement of intermolecular interactions in the brickwork packing structures.     

Phosphonated Near‐Infrared Fluorophores for Biomedical Imaging of Bone

The conventional method for creating targeted contrast agents is to conjugate separate targeting and fluorophore domains. A new strategy is based on the incorporation of targeting moieties into the non‐delocalized structure of pentamethine and heptamethine indocyanines. Using the known affinity of phosphonates for bone minerals in a model system, two families of bifunctional molecules that target bone without requiring a traditional bisphosphonate are synthesized. With peak fluorescence emissions at approximately 700 or 800 nm, these molecules can be used for fluorescence‐assisted resection and exploration (FLARE) dual‐channel imaging. Longitudinal FLARE studies in mice demonstrate that phosphonated near‐infrared fluorophores remain stable in bone for over five weeks, and histological analysis confirms their incorporation into the bone matrix. Taken together, a new strategy for creating ultra‐compact, targeted near‐infrared fluorophores for various bioimaging applications is described.     

Hot Branching Dynamics in a Light‐Harvesting Iron Carbene Complex Revealed by Ultrafast X‐ray Emission Spectroscopy

Iron N‐heterocyclic carbene (NHC) complexes have received a great deal of attention recently because of their growing potential as light sensitizers or photocatalysts. We present a sub‐ps X‐ray spectroscopy study of an Fe^IINHC complex that identifies and quantifies the states involved in the deactivation cascade after light absorption. Excited molecules relax back to the ground state along two pathways: After population of a hot ³MLCT state, from the initially excited ¹MLCT state, 30 % of the molecules undergo ultrafast (150 fs) relaxation to the ³MC state, in competition with vibrational relaxation and cooling to the relaxed ³MLCT state. The relaxed ³MLCT state then decays much more slowly (7.6 ps) to the ³MC state. The ³MC state is rapidly (2.2 ps) deactivated to the ground state. The ⁵MC state is not involved in the deactivation pathway. The ultrafast partial deactivation of the ³MLCT state constitutes a loss channel from the point of view of photochemical efficiency and highlights the necessity to screen transition‐metal complexes for similar ultrafast decays to optimize photochemical performance.     

Fusion of Different Crosslinked Polymers Based on Dynamic Disulfide Exchange

Crosslinked polymers (CLPs) exhibit exceptional mechanical properties as well as good chemical and solvent resistance. However, their reprocessing, recycling, and modification remain difficult. One promising approach to overcome this limitation is to introduce dynamic covalent bonds that enable chain‐exchange reactions and network‐structure rearrangements in identical polymer networks (A–A fusion), resulting in self‐healing and reprocessing properties. Reported here is the fusion of two distinct polymer networks (A–B fusion) by the dynamic behavior of bis(2,2,6,6‐tetramethylpiperidin‐1‐yl)disulfide (BiTEMPS) at the interface between different CLPs. The appearance, swelling behavior, and mechanical properties of the fused samples indicate exchange reactions of the BiTEMPS units and the formation of topological bonds at the interface, commensurate with the generation of a CLP that exhibits tunable properties.