1,720,999 research outputs found
Metal complexes as fluorescent probes for sensing biologically relevant gas molecules
Full text linkThe last decades have seen a marked escalation in interest in the biology of naturally occurring gases. Examples of the most significant of these gases are nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S). All of them feature a number of physiological and/or pathophysiological functions within the human body. For example, NO regulates vasodilatation in the circulatory system and long-term potentiation in the brain. CO modulates vasorelaxation, vascular smooth muscle cell growth and tissue injury. H2S relaxes vascular smooth muscle and inhibits smooth muscle cell proliferation. In addition, it acts as neuromodulator in the central nervous system. Furthermore, it is also well acknowledged that all of them are differently associated with various human diseases. However, for the advancement of our understanding of the physiological and pathological roles played by these signal transductors, there is a pressing need for methods allowing their detection in both aqueous and gaseous media. The aim of this review is to highlight the recent developments in the field of metal complexes as fluorescent probes for the detection of gasotransmitters and to provide a general overview of fluorescent sensors implemented so far for NO, CO and H2S
Chemically reversible binding of H2S to a zinc porphyrin complex: towards implementation of a reversible sensor via a “coordinative-based approach”
No full textBinding of hydrogen sulfide (H2S) to a zinc porphyrin complex and the stabilization of the related zinc hydrosulfido adduct are explored. High-resolution MALDI Fourier transform ion cyclotron resonance mass spectrometry (HR MALDI-FT-ICR) and 1H NMR experiments provide evidence that HS− coordination occurs at the zinc centre. The coordination of HS− occurs in a reversible manner and modulates fluorescence emission of a tetra(N-methylpyridyl)porphine zinc complex (TMPyPZn). The results highlight the potential of TMPyPZn and related systems for the implementation of fast and simple H2S sensors via a coordinative-based approach
Interaction of monohydrogensulfide with a family of fluorescent pyridoxal-based Zn(ii) receptors
Full text linkH2S and its conjugate base HS- have recently gained increasing attention for their reactivity with bioinorganic targets. However, so far, stable adducts of bioinorganic compounds with H2S/HS- are still scarce due to the propensity of sulfide to form insoluble metal sulfides. In this work, we studied the reactivity of HS- with a family of fluorescent zinc complexes via a variety of spectroscopic techniques. The complexes selected for this study feature a pyridoxal moiety with different substituent groups on the ligand framework. Interaction of the complexes under investigation with HS- results in the displacement of the coordinated ligand from the Zn center with the concomitant precipitation of ZnS in the case of complexes 1 and 3, whereas for complex 2 our data points to the coordination of HS- to the metal center likely assisted by hydrogen bonding with the OH of the pyridoxal moiety. In the presence of HS-, the fluorescence emission of complex 2 is enhanced, whereas the fluorescence emission of complexes 1 and 3 is quenched. The results highlight the potential of complex 2 to be implemented as a HS- fluorescent sensor via a coordinative-based approach
Binaphthyl-bridged Salen and Salan complexes of zirconium as precatalysts for α-olefin polymerization
No full textA comparative study on the polymerization of alpha-olefins catalyzed by Salen and Salan zirconium complexes
No full textA new Salan zirconium complex is synthesized and tested as a precatalyst for the polymerization of ethylene and higher a-olefins. Its catalytic behavior is compared to that of a previously reported and related Salen zirconium complex. Analysis of the produced polyolefins reveals that the two different catalytic systems
produce polymers with the same microstructure: atactic polymers from propene versus highly isotactic polymers from higher a-olefins. The identification of the end groups indicates a
prevailing primary regiochemistry of polyinsertion of the a-olefins for both Salan and Salen zirconium complexes. These observations strongly suggest the formation of very similar
active species in both systems
Heteroscorpionate-based Zn2+, Co2+ and Cu2+ Complexes: Synthesis, Characterization and Hydrogen Sulfide Sensing
No full textOlefin polymerization promoted by a stereorigid bridged diimonobis(phenolate)zirconium complex
Full text linkABSTRACT: Two diiminobis(phenolate) zirconium complexes [C6H10-{NdCH-(3,5-tBu2C6H2-2-O)-O}2]- ZrX2 [X ) CH2Ph (1), Cl (3)] have been synthesized and characterized by NMR solution spectroscopy. Complex 1 was found conformationally stable and isolated in the octahedral C2 symmetric form. When exposed to the light in hydrocarbon solution, 1 readily undergoes to 1,2 benzyl migration converting the diiminobis(phenolate) ligand in the corresponding benzylamidoiminobis(phenolate). Complex 3 is more thermally stable and found in slow equilibrium between the cis-R and cis-â forms with the former largely prevalent (9:1 molar ratio). The rate of interconversion between the two diastereoisomers was estimated in 3.6 10-1 s-1 by NMR exchange spectroscopy (EXSY). 1 and 3 are active ethylene polymerization catalysts after reaction with MAO or [CPh3][B(C6F5)4]/Al-iBu3. The polydispersity index of polyethylene produced by 1 is about 2, suggesting the presence of a single active species and that the symmetry of the precatalyst is retained during polymerization. The catalyst is stable over 3 h, and the polymerization activity linearly increases with time. Copolymers of ethylene with propylene or 1-hexene were synthesized, and the 13C NMR analysis of their microstructure suggested the highly regioregular 1,2 insertion of the 1-olefin and the inability of the ligand environment to express stereochemical control during monomer insertion
Phenoxyaldimine and Phenoxyketimine Titanium Complexes in Propene Polymerization. A Different Effect of o-Phenoxy Halide Substituents
No full textNew fluorinated bis(phenoxyaldimine)- and bis(phenoxyketimine)titanium(IV) complexes bearing
o-halide substituents on the phenolate rings were synthesized and tested as catalysts for propene polymerization.
Polymerization of propene at subambient temperature in the presence of bis(N-(3,5-dibromosalicylidene)-2,3,4,5,6-
pentafluoroaniline)titanium dichloride activated by methylaluminoxane resulted in the unexpected production of
a prevailingly isotactic polypropylene. The observed microstructure is that expected for an “enantiomorphic site”
mechanism of steric control. End group analysis, also using deuterium labeling techniques, indicated a primary
insertion in the initiation step, while a secondary insertion was observed in the termination step. The microstructures
of the homopolymer and of a copolymer of propene with trace amounts of ethylene are consistent with the presence
of (shorter) highly isotactic primary blocks and (longer) poorly isotactic secondary blocks. Similar results were
obtained with the bis(phenoxyaldimine) titanium complexes bearing chlorides or iodides on the ligand phenol
rings. The isotacticity of the produced polypropylenes decreases as the size of the halide substituents is reduced.
A new phenoxyketimine titanium complex bearing o-bromine substituents on the phenolate rings produced, under
similar polymerization conditions, truly atactic polypropylene, at variance with the isospecific phenoxyketimine
titanium complexes bearing alkyl substituents
Organometallic sulfur complexes: Reactivity of the hydrogen sulfide anion with cobaloximes
No full textThe reaction of alkylcobaloxime [Co(dmgH)2(CH2CH3)(py)] (1) (dmgH = the anion of dimethyl-glyoxime) with KSH in water solution resulted in the selective displacement of the pyridine axial ligand affording the derivative K[Co(dmgH)2(CH2CH3)(SH)] (2). An 1H-1H EXSY experiment revealed that the substitution is reversible and occurs in a slow exchange regime. Attempts to grow crystals of the HS- adduct led to isolation of a rare example of the unexpected trisulfido-bridged dinuclear complex K2[Co2(dmgH)2(CH2CH3)2(μ-S3)]. It was shown that the glyoximato ligands provided the metal centre with a coordination environment quite robust to prevent decomposition and constitute a suitable platform for developing the chemistry of organometallic complexes bearing hydrogensulfido or oligosulfido ligands
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