Charge Transfer Excitation of Coordination Compounds. Generation of Reactive Intermediates

Highly regenerative, fast colorimetric response for organo-toxin and oxo-anions in an aqueous medium using a discrete luminescent Cd(II) complex in a heterogeneous manner with theoretical revelation

The highly luminescent complex [CdQ₂(H₂O)₂] (1) shows ultra-selectivity and high sensitivity to the explosive organo-toxin trinitrophenol (TNP). This detection is extremely fast with a high quenching constant (5.3 × 10⁴ M^-1) and a very low limit of detection (LOD) of 137 nM/59 ppb. This motivated us to detect the lethal carcinogenic arsenical drug roxarsone (ROX), which is reported here for the first time. The quenching constant and LOD for ROX using 1 were found to be 4.9 × 10⁴ M^-1 and 86 nM (or 37 ppb), respectively. Moreover, the probe also recognizes three lethal toxic oxo-anions (MnO₄^-, Cr₂O₇^2- and CrO₄^2-) with outstanding quenching constant (2.2 × 10⁴ M^-1, 1.4 × 10⁴ M^-1 and 1.1 × 10⁴ M^-1) and very low LODs (141 nM/61 ppb, 178 nM/78 ppb and 219 nM/95 ppb). Compared to the previously reported homogeneous sensing nature of the discrete complexes, our complex showed the detection of toxic pollutants in a heterogeneous manner, which results in high recyclability and hence multi-cycle sensing capability. Interestingly, 1 shows the possibility for real-time monitoring through naked eye detection by visible colorimetric changes in solid, solution and strip paper methods, i.e., triphasic detection ability. In addition, the sensor also exhibited the cross-sensing ability for these pollutants. The experimental sensing mechanism is strongly supported by the exhaustive theoretical investigation. Based on the fluorescence signal shown by each analyte, an integrated AND-OR logic gate is constructed. Furthermore, the sensing ability of 1 remains intact towards the detection of versatile real field samples including lethal carcinogenic arsenical drug roxarsone in the real food sample.

Strontium Laminarin polysaccharide modulates osteogenesis-angiogenesis for bone regeneration

Bone regeneration and repair has become one of the major clinical challenges worldwide and it involves multiple processes including inflammation, angiogenesis and osteogenesis. In this study, we synthesized strontium Laminarin polysaccharide (LP-Sr), a novel polysaccharide-metal complex that should have therapeutic effects on modulating osteogenesis and angiogenesis. The structure and composition of the as-fabricated LP-Sr were analyzed by EDS, XRD, FITR, ¹H NMR, HPLC, etc. The results indicate that we successfully synthesized this novel polysaccharide complex. Moreover, we evaluated the biomedical potential of this complex in promoting osteogenesis and angiogenesis by cell proliferation assay, ALP staining, immunofluorescent staining of CD31 and reverse transcription polymerase chain reaction (RT-PCR). The biological experiment results show that LP-Sr can effectively promote proliferation and increase the expression of VEGF and EGFL6 in HUVECs and significantly up-regulate the expression of Col1α1 and OCN in MC3T3-E1. Besides, it is suggested that LP-Sr has positive effects on the suppression of pro-inflammatory factor IL6 in both HUVECs and MC3T3-E1. Moreover, the osteogenic and angiogenic markers, i.e. alkaline phosphatase (ALP) and CD31, exhibited high expression in LP-Sr group. Hence, we believe that LP-Sr should be a promising and novel polysaccharide complex in modulating osteogenesis-angiogenesis for bone regeneration.

A low-spin Fe(iii) complex with 100-ps ligand-to-metal charge transfer photoluminescence

Transition-metal complexes are used as photosensitizers, in light-emitting diodes, for biosensing and in photocatalysis. A key feature in these applications is excitation from the ground state to a charge-transfer state; the long charge-transfer-state lifetimes typical for complexes of ruthenium and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron and copper being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs, it remains a formidable scientific challenge to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers. Here we present the iron complex [Fe(btz)₃]³⁺ (where btz is 3,3'-dimethyl-1,1'-bis(p-tolyl)-4,4'-bis(1,2,3-triazol-5-ylidene)), and show that the superior σ-donor and π-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(iii) d⁵ complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer (²LMCT) state that is rarely seen for transition-metal complexes. The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.

Tl-Pt(CN)5 in the solid state--A multimethod study of an unusual compound containing inorganic wires

The crystal and molecular structure of a polycrystalline powder with a metal-metal bond and the composition TlPt(CN)5 has been determined by combining results from X-ray powder diffraction (XRD), extended X-ray absorption fine structure (EXAFS) and vibrational spectroscopic studies. The XRD data gave the tetragonal space group P4/nmm (No. 129), with a= 7.647(3), c=8.049(3) A, Z=2, and well-determined positions of the heavy metal atoms. The Pt-TI bond length in the compound is 2.627(2) A. The platinum atom coordinates four equivalent equatorial cyano ligands, with a fifth axial CN ligand and a thallium atom completing a distorted octahedral coordination geometry. The Tl-Pt(CN)5 entities are linked together in linear -NC-Pt-Tl-NC-Pt-Tl chains through the axial cyano ligand. These linear "wires" are the essential structural features and influence the properties of the compound. A three-dimensional network is formed by the four equatorial cyano ligands of the platinum atom that form bridges to the thallium atoms of neighbouring antiparallel chains. The platinum atom and the five nitrogen atoms from the bridging cyano groups form a distorted octahedron around the thallium atom. EXAFS data were recorded at the Pt and Tl L(III) edges for a more complete description of the local structure around the Pt and Tl atoms. The excessive multiple scattering was evaluated by means of the FEFF program. Raman and infrared absorption spectroscopy reveal strong coupling of the vibrational modes of the TlPt(CN)5 entities, in particular the metal-metal stretching mode, which is split into four Raman and two IR bands. Factor group theory shows that a structural unit larger than the crystallographic unit cell must be used to assign vibrational bands. Intra- and intermolecular force constants have also been calculated. The compound exhibits red luminescence at 700 +/- 3 nm in glycerol and has a corresponding excitation maximum at 240 nm. X-ray photoelectron spectra (XPS) show that the metal atoms have intermediate oxidation states, Pt3.2+ and Tl1.6-, between those in the parent Pt(II) and Tl(III) species and the decomposition products, Pt(IV) and Tl(I). The solid compound TlPt(CN)5 is stable to 520 degrees C. However in presence of water, a two-electron transfer between the metal atoms results in the cleavage of the metal-metal bond at 80 degrees C, forming a Pt(IV) pentacyanohydrate complex and a monovalent thallium ion.