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We studied the reactivity of HS− with a family of zinc complexes. The different fluorescence trends observed for 1 and 3 in the presence of HS− has been related with the possible existence of non-radiative decay paths, by means of a DFT-analysis.

Copolymerization of ethylene with polar vinyl monomers to yield functionalized and possibly easier recyclable polyolefins is challenging and it is currently being pursued mainly using expensive Pd-based catalysts. Herein, the copolymerization of ethylene and methyl acrylate (MA) is achieved by the dibenzocycloheptyl-substituted aryliminopyridyl Ni(II) complexes, affording copolymers with selectively in-chain incorporated MA units as well as both in-chain and end-of-chain inserted MA units depending on the catalyst structure and the reaction conditions

Metal catalyzed polymerizations are among the most important chemical reactions, accounting for the production of about 400 million tons per year of polymeric materials, 50% of which are polyolefins. The CIRCC research units at the University of Salerno, founded by the late Professor Adolfo Zambelli, a coworker of Giulio Natta and a pioneer in the studies of stereospecific polymerization catalysts, has a consolidated expertise in this field. Although often considered a “mature” area of research, olefin polymerization catalysis continues to drive great interest of both industrial and academic scientists. On the other hand, strong political and economic pressure toward the development of “green” and possibly biodegradable alternatives to olefin-based polymers stimulated our group to direct increasing research efforts in the area of sustainable polymers. In this perspective, we focus on the most recent work from the CIRCC research units involved in homogeneous catalysis for polymerization of a variety of monomers, with the aim to address how the concepts and the expertise developed for olefin polymerization can be applied to the development of different metal-catalyzed polymerizations and copolymerizations. Of course, although the results are discussed in the frame of the most important literature contributions, a comprehensive review of such a wide and diversified topic is out of the scope of the paper. References to reviews covering the different types of metal catalyzed polymerizations are provided in each chapter.

The last two decades have witnessed the development of homogeneous catalysts for ethylene homo- and co-polymerization reactions based on late transition metals. When Pd(II) is the metal of choice, the best ligand-metal combination deals with either bidentate nitrogen-donor molecules or phosphinobenzene sulfonate derivatives. In this contribution we have investigated the coordination chemistry to Pd(II) of a bidentate phosphorus ligand, namely 4,5-bis(diphenylphosphino)acenaphthene (1). Starting from the neutral complex, [Pd(1)(CH3)Cl], we obtained the cationic derivatives [Pd(1)(CH3)(L)][SbF6], with L being either CH3CN or 3,5-lutidine. Using in situ NMR spectroscopy we investigated the reaction of [Pd(1)(CH3)(NCCH3)][SbF6] with ethylene, at room temperature, and ambient ethylene pressure. We discovered that [Pd(1)(CH3)(NCCH3)][SbF6] acts as a catalyst for butenes and hexenes synthesis with the relevant Pd-ethyl intermediate as the catalyst resting state. At the same time the color of the solution turned from pale yellow to light red due to the formation of the dinuclear species [Pd(μ-η2−C6H5)PPh)−PPh2]2[SbF6]2. Both the neutral Pd(II) complex, activated in situ by NaSbF6, and the monocationic acetonitrile derivative were tested in the ethylene homopolymerization reaction at high pressure, leading to low molecular weight, branched, polyethylene.

In this work, we investigate the mode of interaction of a family of fluorescent zinc complexes with HS- and H2S. Different experiments, performed by diverse spectroscopic techniques, provide evidence that HS- binds the zinc center of all the complexes under investigation. Treatment with neutral H2S exhibits a markedly different reactivity which indicates selectivity for HS- over H2S of the systems under investigation. Striking color changes, visible to the naked eye, occur when treating the systems with HS- or by an H2S flow. Accordingly, also the fluorescence is modulated by the presence of HS-, with the possible formation of multiple adducts. The results highlight the potential of the devised systems to be implemented as HS-/H2S colorimetric and fluorescent sensors. Bioimaging experiments indicate the potential of using this class of compounds as probes for the detection of H2S in living cells.

The synthesis of functionalized polyolefins through coordination – insertion polymerization is a highly challenging reaction. The ideal catalyst, in addition to show a high productivity, has to be able to control the copolymer microstructure and, in particular, the way of the polar vinyl monomer incorporation. In this contribution we have modified the typical Brookhart’s catalyst by introducing in the fourth coordination site of palladium an hemilabile, potentially bidentate ligand, such as a thiophenimine (N-S). The obtained cationic Pd(II) complexes, [Pd(Me)(N-N)(N-S)][PF6], generated active catalysts for the ethylene/methyl acrylate (MA) copolymerization leading to the desired copolymer with a different incorporation of the polar monomer depending on both the reaction medium and the N-S ligand. Surprisingly enough, the produced copolymers have the inserted acrylate both at the end of the branches (T(MA)) and in the main chain (M(MA)) in a ratio M(MA) : T(MA) that goes from 9 : 91 to 45 : 55 moving from dichloromethane to trifluoroethanol (TFE) as a solvent for the catalysis and varying the N-S ligand. The catalytic behavior of the new complexes was compared to that of the parent compound [Pd(Me)(N-N)(MeCN)][PF6], highlighting that when the copolymerization is carried out in trifluoroethanol this complex is also able to produce the E/MA copolymer with MA inserted both in main chain and at the end of the branches. Accurate NMR studies on the reactivity of the precatalyst [Pd(Me)(N-N)(MeCN)][PF6] with the two comonomers allowed us to discover that in the fluorinated solvent the catalyst resting state is an open chain intermediate having both the organic fragment, originated from the migratory insertion of MA into the Pd-Me bond, and the acetonitrile coordinated to palladium and not the six-membered palladacycle typically observed for the Pd--diimine catalysts. This discovery is also supported by both DFT calculations and in situ NMR studies carried out on [Pd(Me)(N-N)(N-S)][PF6] complexes that point out that N-S remains in the palladium coordination sphere during catalysis. The open chain intermediate is responsible for the growth of the copolymer chain with the polar monomer inserted into the main chain.

A series of dimethyl aluminum complexes of the type [E,O]AlMe2 stabilized by phenoxy-imine, phenoxy-thioether and phenoxy-amine ligands have been tested as catalysts for the ring-opening copolymerization of epoxides and anhydrides. All complexes revealed to be active in the copolymerization of cyclohexene oxide with succinic anhydride showing activities higher than pentacoordinate salen aluminum complexes. Interestingly, these complexes revealed to be active in the copolymerization of limonene oxide with phthalic anhydride. A moderate influence of the ligand structure on the efficiency and selectivity of the catalyst was also observed. Some mechanistic insights have been gained through NMR studies allowing the identification of a zwitterionic species formed in the initiating step of the polymerization reaction.

Three-coordinated Zn(II) complexes bearing sterically encumbered bidentate monoanionic [N,N−] pyridylamido ligands efficiently catalyze the ring opening polymerization of lactide (LA) and e-caprolactone (CL). Owing to the polymerization controlled nature and high rate, precise stereodiblock poly(LLA-b-DLA) with different block lengths can be easily produced by one-pot sequential monomer addition at room temperature in short reaction times. NMR, SEC and DSC analyses confirm the production of highly isotactic diblock copolymers which crystallize in the high melting stereocomplex phase. Stereo-triblock and tetrablock copolymers of L-LA, D-LA and rac-LA have been synthesized similarly. Finally, a diblock poly(CL-b-LA) has been easily obtained by sequential addition of e-caprolactone and lactide under mild conditions.

Nickel-based ethylene polymerization catalysts have unique features, being able to produce macromolecules with a variable content of branches, resulting in polymers ranging from semicrystalline plastics to elastomers to hyperbranched amorphous waxes and oils. In addition to Brookhart's α-diimine catalysts, iminopyridine Ni(II) complexes are among the most investigated systems. We report that Ni(II) complexes bearing aryliminopyridine ligands with bulky substituents both at the imino moiety and in the 6-position of pyridine afford either hyperbranched low molecular weight polyethylene oils or prevailingly linear crystalline polyethylenes or both depending on the ligand structure and the reaction conditions. The formation of multiple active species in situ is suggested by analysis of the post-polymerization catalyst residues, showing the partial reduction of the imino function. Some related arylaminopyridine Ni(II) complexes were also synthesized and tested, showing a peculiar behavior, i.e. the number of branches of the produced polyethylenes increases while ethylene pressure increases.

In this work we explore the interaction of HS− with a family of fluorescent zinc complexes. In particular we selected a family of complexes with N,O-bidentate ligands aiming at assessing whether the zinc-chelating ligand plays a role in influencing the reactivity of HS− with the complexes under investigation. Different experiments, performed by diverse spectroscopic techniques, provide evidence that HS− binds the zinc center of all the complexes included in this study. The results highlight the potential of the devised systems to be used as HS−/H2S fluorescent sensors via a coordinative-based approach. To shed light on the species formed in solution when HS−/H2S interacts with the title complexes and aiming to rationalize the photophysical properties of the sensing constructs, we performed a computational analysis based on the time dependent density functional theory (TD-DFT). Preliminary bio-imaging experiments were also performed and the results indicate the potential of this class of compounds as probes for the detection of H2S in living cells.

This review highlights the recent developments in the field of metalloporphyrins as optical probes for biologically relevant molecules, such as nitric oxide (NO) and hydrogen sulfide (H2S), and as catalysts for the preparation of sustainable polymers such as polyesters, by the ring-opening polymerization (ROP) of cyclic esters and the ring-opening co-polymerization (ROCOP) of epoxides and anhydrides, and polycarbonates by the chemical fixation of carbon dioxide (CO2). The great potential of porphyrins is mainly due to the possibility of making various synthetic modifications to the porphyrin ring, such as modifying the coordinated metal, peripheral substituents, or even the molecular skeleton. Due to the strict structure–property relationships, one can use porphyrinoids in several different applications such as, for instance, activation of molecular oxygen or catalysis of photosynthetic processes. These possibilities broaden the application of porphyrins in several different fields of research, further mimicking what nature does. In this context, here, we want to provide evidence for the great flexibility of metalloporphyrins by presenting an overview of results obtained by us and others in the research fields we are currently involved in. More specifically, we report a survey of our most significant achievements regarding their use as optical probes in the context of the results reported in the literature from other research groups, and of the use of porphyrin metal(III) complexes as catalysts for sustainable polymerization processes. As for the optical probe section, in addition to the metalloporphyrins synthesized ad hoc in the laboratory, the present work also covers the natural proteins containing a porphyrin core.

The aim of the present review is to highlight the most recent achievements in different fields of application of salen-based zinc and aluminum complexes. More specifically this article focuses on the use of aluminum and zinc salen-type complexes as optical probes for biologically relevant molecules, as catalysts for the ring opening polymerization (ROP) of cyclic esters and co-polymerization of epoxides and anhydrides (ROCOP) and in the chemical fixation of carbon dioxide (CO2). The intention is to provide an overview of the most recent results from our group within the framework of the state-of-art-results in the literature.

In this work, we investigate the mode of interaction of a family of fluorescent zinc complexes with HS– and H2S. Different experiments, performed by diverse spectroscopic techniques, provide evidence that HS– binds the zinc center of all the complexes under investigation. Treatment with neutral H2S exhibits a markedly different reactivity which indicates selectivity for HS– over H2S of the systems under investigation. Striking color changes, visible to the naked eye, occur when treating the systems with HS– or by an H2S flow. Accordingly, also the fluorescence is modulated by the presence of HS–, with the possible formation of multiple adducts. The results highlight the potential of the devised systems to be implemented as HS–/H2S colorimetric and fluorescent sensors. Bioimaging experiments indicate the potential of using this class of compounds as probes for the detection of H2S in living cells., In this work, we studied the reactivity of HS− with a family of fluorescent zinc complexes via a variety of spectroscopic techniques. Interaction with HS− results in its coordination to the Zn center for all the complexes under investigation. Treatment with neutral H2S exhibits a markedly different reactivity which indicates selectivity for HS− over H2S. Striking color changes, visible to the naked eye, occurred when treating the systems with HS− or by an H2S flow.

The introduction of polar functional groups into the polyolefin skeleton is a challenging goal of high interest, and coordination-insertion polymerization represents the most powerful and environmentally friend approach to achieve it. Till now the most considerable catalysts are based on Pd(II) complexes and only a few examples on Ni(II) derivatives have been reported. We have now investigated a series of Ni(II) complexes with four pyridylimino ligands, both aldimines and ketimines, differing for the substituent present in position 6 on the pyridine ring (either a methyl group or a 2,6-dimethyl-substituted phenyl ring). These complexes generated active catalysts for the copolymerization of ethylene with methyl acrylate, yielding low molecular weight, hyperbranched copolymers with the polar monomer content ranging between 0.2 and 35 mol % and inserted in a variety of modes, some of which were never observed before. The way of incorporation of the polar monomer goes from “in-chain only” to “everywhere but in-chain”, and it is dictated by both the activation mode and the solvent used to dissolve the nickel precatalyst.

The solution structure of AlMe2 F and its reactivity with a prototypical ansa-metallocene have been investigated by advanced NMR techniques, in an attempt to indirectly shed some light on the structure and working principles of methylalumoxane (MAO) mixtures in olefin polymerization. In solution, AlMe2 F gives rise to a complex equilibrium of oligomeric species, including a heterocubane [(Me2 Al)4 F4 ] tetramer, resembling the behavior of MAO. This complex mixture reacts with (ETH)ZrMe2 (ETH=rac-[ethylenebis(4,5,6,7-tetrahydro-1-indenyl)]) to afford [(ETH)ZrMeδ+ (μ-F)(AlMe2 F)n AlMe3δ- ] inner-sphere ion pairs through successive insertions/deinsertions of AlMe2 F units into the Zr⋅⋅⋅(μ-F) bond.

A pentadentate cage-like cyclam-based fluorescent ligand has been designed, synthesized and characterized by monodimensional and bidimensional NMR analysis. To further characterize the title ligand ESI-MS, Uv-vis and fluorescence experiments have been also performed. Its suitability as a chemosensor for the detection of Cu2+ ions has been successfully explored via a variety of spectroscopic techniques (i.e. ESI-MS, Uv-vis and fluorescence). The Job's plot experiment together with the ESI-MS experiments indicate a 1:1 stoichiometry for the binding of Cu2+ to the cyclam-based ligand. Fluorescence experiments corroborate this hypothesis. The system resulted selective in the recognition of copper and stable for a week, as assessed via fluorescence spectroscopy. The Cu(II) complex has been isolated and tested as a fluorescent probe for the detection of H2S. NMR and ESI-MS investigation provided evidence that H2S recognition occurs via a copper displacement mechanism, as reported in the literature for different copper complexes. The system functions with a selective response to HS- harnessing a concentration-dependent 'turn-on' of the initial fluorescence intensity.

The activation of a prototypical nickel(II) Brookhart catalyst by either methylalumoxane (MAO) or diethylaluminum chloride (AlEt2Cl) under a variety of conditions showed that a proper choice of the mode of activation is a powerful tool to modulate the polymer microstructure. In particular, use of AlEt2Cl instead of MAO resulted in the production of more branched polyethylenes with a higher content of long chain branches and even some “branches on branches”. Characterization of these materials by NMR, thermal, X-ray diffraction, and mechanical analyses provided insight into the relationships between the microstructure and the crystallization behavior and the elasticity of the polymers. For these branched polyethylenes, a transition from plastomeric toward elastomeric behavior occurs for branch concentrations much lower than for ethylene–propylene copolymers and like those observed for ethylene copolymers with bulkier comonomers. For elastomeric materials, reduction of branch concentration implies two relev...

Binding 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.

Three-coordinated Zn(ii) complexes bearing sterically encumbered bidentate monoanionic [

WOS:000458689800019; International audience; Hydrogen sulfide (H2S) is an important biological messenger, which recently joined nitric oxide (NO) and carbon monoxide (CO) as an endogenously produced gasotransmitter. This discovery resulted in a renewed interest towards H2S and, in particular, in its reactivity with biological and bioinorganic targets. However, in the scientific literature studies exploring the reactivity of H2S/HS- with non-heme proteins are rare. In this work, we studied the interaction of HS- with the natural metalloprotein Cu-azurin and its cobalt variant via UV-Vis, fluorescence, and EPR spectroscopy, as well as X-ray diffraction. Interaction of HS- significantly enhances the fluorescence emission of fluorescently labelled copper azurin in buffered solutions and at physiological pH. In contrast, fluorescently labelled cobalt azurin undergoes a fluorescence quenching in the presence of HS- in line with the changes observed in the absorption spectrum of the construct. The results highlight the potential of azurin for implementation in a fast and simple HS- sensor.

The development of efficient homogeneous catalysts for the synthesis of functionalized polyolefins is a challenging topic. Palladium(II) complexes with ?-diimine ligands having a phenanthrene skeleton and 2,6-disubstituted aryl rings (Ar-BIP) were synthesized, characterized, and tested as precatalysts in the copolymerization of ethylene with methyl acrylate. The direct comparison with analogous complexes having the corresponding ?-diimines with an acenaphthene skeleton (Ar-BIAN) was performed. X-ray characterization in the solid state and NMR analysis in solution of both neutral [Pd(Ar-BIP)(CH3)Cl] and monocationic [Pd(Ar-BIP)(CH3)(NCCH3)][PF6] complexes indicate that the Ar-BIP ligands have a higher Lewis basicity and are more strongly coordinated to the metal center in comparison to the Ar-BIAN counterparts. Therefore, the Pd(Ar-BIP) cationic complexes can be regarded as electron-rich metal cations. In addition, they create a higher steric congestion around palladium in comparison to Ar-BIAN, regardless of the substituents on the aryl rings. The monocationic species generate active catalysts for the ethylene/methyl acrylate copolymerization leading to copolymers with Mn values up to 37000 and a content of polar monomer of 5.3 mol %. A detailed study of the catalytic behavior points out that Pd(Ar-BIP) catalysts show a good affinity for the polar monomer, have a good thermal stability, and favor the cleavage of the catalyst resting state, leading to copolymers with Mw values higher than those of the macromolecules produced with the corresponding Pd(Ar-BIAN) under the same reaction conditions. NMR characterization of the produced copolymers points out that the polar monomer is inserted both at the end of the branches and into the main chain, with an enchainment more selective than that achieved when the copolymerization is carried out in dichloromethane. In situ NMR investigations allowed us to detect relevant intermediates of the catalytic cycle and shed light on the nature of possible deactivated species.

H2S 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.

In the last few decades there has been a continuous effort toward the synthesis of polymers from renewable resources. In this context we have presently developed novel and fully bio-based functionalized polymacrolactones bearing pendant eugenol moieties. These polymeric materials were obtained by exploiting the ring-opening copolymerization of two macrolactones, ω-6-hexadecenlactone (6HDL) and ω-pentadecalactone (PDL), both derived from renewable resources, in the presence of a pyridylamidozinc(II) complex, to produce random poly(6HDL-co-PDL) copolymers. Eugenol, a natural occurring essential oil with anti-microbial properties, was modified in its mercapto derivative, the 4-(3-mercaptopropyl)-2-methoxyphenol (TE). Subsequently, the thiol-ene addition reaction of the TE to the C C double bond of the 6HDL monomeric units of the poly(6HDL-co-PDL) copolymers produced the functionalized polymacrolactones with pendant eugenol moieties. This synthetic approach allowed to modulate the amount of eugenol pendant groups on the polymeric chains. The melting temperatures and the thermal degradation behavior of the TE-functionalized copolymers were dependent on the copolymers composition. The antimicrobial activity of TE-functionalized copolymers was tested for the bacterium E. coli on films. The toxicity of the samples was dependent on the amount of TE groups in the films. Our approach demonstrated the feasibility to covalently attach eugenol moieties to a polymacrolactone main chain and to impart antimicrobial properties to the macromolecular chains.

In the present work, we explored the reactivity of HS− with a family of fluorescent metal complexes via a variety of spectroscopic techniques. The complexes under investigation are obtained by complexation of zinc or nickel with pyridoxal-based ligands. More specifically complexes 1 and 2 are zinc complexes namely L1Zn(II) and L2Zn(II) where L1 stands for N,N′-phenylenebis(pyridoxyliminato) and L2 is N,N′-binaphthylenebis(pyridoxyliminato), whereas complex 3 is a nickel complex (L3Ni(II)) where L3 is N,N′-ethylenebis(pyridoxyliminato). A combination of NMR, ESI-MS, UV–vis and fluorescence experiments provide evidence that HS− binds the metal center in the case of complexes 1 and 3 whereas for complex 2, ZnS precipitation and hydrolysis of the organic ligand occur. Fluorescence experiments indicate that in the presence of HS− complex 1 undergoes a consistent fluorescence enhancement whereas for complex 3 the parent fluorescence exhibits a visible quenching. The results highlight the potential of complex 1 to be implemented as a HS− fluorescent sensor via a coordinative-based approach.

Five new Zn(II) complexes bearing pyridylamido ligands with different substituents at the pyridine and at the amido moieties were synthesized and evaluated as catalysts for the alternating copolymerization of carbon dioxide and cyclohexene oxide. Polymers with carbonate linkages ranging between 86 and 99% and a slightly isotactic-enriched structure were selectively obtained under a variety of reaction conditions, including 1 atm of CO2 pressure, without any cocatalyst. Some experimental and theoretical evidence suggested that different initiating species are involved in the catalytic cycle, including dimeric [(Lx)Zn(μ-OR)]2 and [(Lx)Zn(μ-O2COR)] complexes similar to those involved in the classical β-diiminate Zn(II) catalysts.

A “turn on” fluorescence-based probe for sensing H2S in water via a coordinative-based approach has been successfully devised. The probe can selectively detect H2S in aqueous solutions over other anions, biothiols, and common oxidants such as H2O2. 1H NMR spectroscopy and ESI-MS experiments provide evidence that the turn-on response in the presence of H2S is due to binding of the target anion to the copper center.

The controlled and pseudo-living ring-opening polymerization of a large ring size lactone, ω-6-hexadecenlactone (6HDL), was achieved for the first time by a dimethyl(salicylaldiminato) aluminum initiator. The obtained poly(ω-6-hexadecenlactone) was functionalized by thiol–ene coupling reaction. By epoxidation of the double bond a poly(6,7-epoxy-ω-hexadecalactone) was formed. The subsequent opening of the epoxide by NaCNBH3 produced a poly(6,7-epoxy-ω-hexadecalactone) with occasional inter and intra ether-type crosslinks. Modifications occurred without any change in the degree of polymerization. The obtained polymeric samples were characterized by NMR, GPC and DSC and X-ray diffraction analysis. The “polyethylene-like” orthorhombic crystal lattice of poly(ω-6-hexadecenlactone) is deformed in the poly(6,7-epoxy-ω-hexadecalactone) and is replaced by a hexagonal packing when the poly(ester) chains are hydroxylated. Furthermore, copolymerization of 6HDL with smaller e-caprolactone produced random copolymers, with average sequence block lengths of 2, while the sequential addition of 6HDL and e-caprolactone or rac-lactide allowed the preparation of block-copolymers. The block and random copolymers were also semicrystalline.

The reaction of MgBu2 and ZnEt2 or Zn{N[Si(CH3)3]2}2 with a tridentate monoanionic pyrrolylpyridiylimino [N-,N,N] proligand gave homoleptic species, as exclusive products, in high yields. The complexes were characterized in solution by 1D and 2D NMR analysis and by single crystal X-ray crystallography. The new homoleptic complexes were tested as initiators in the polymerization of e-caprolactone and lactide in the presence of an exogenous alcohol. For both complexes, the polymerizations proceed via an "activated monomer" mechanism that, in the case of the magnesium complex, was correlated with the coordinative flexibility of the ligands, resulting in extremely high productivities under mild conditions.

The solution structure of AlMe

H 2 S is an important biological messenger but its reactivity and physiological concentrations are largely controversial. On the other hand, reactivity of H 2 S with biologically relevant metal scaffolds for the selective tracking of H 2 S in biological fluids is underexplored. In this work we investigated interaction of monohydrogensulfide with a series of zinc porphyrins by 1 H NMR, UV–vis and ESI mass experiments. The results provide evidence that HS − binds the metal center for all the investigated complexes.

Two dinuclear aluminum alkyl complexes bearing salen ligand with alkyl backbone of different length between the nitrogen atoms (1,3-propylene (1) and 1,5-pentylene (2)) and the related hemi-salen aluminum complex (3) were tested as catalysts in the ring-opening copolymerization of cyclohexene oxide (CHO) and limonene oxide (LO) with succinic anhydride (SA) and phthalic anhydride (PA). The effects of different reaction conditions (cocatalyst and reaction solvent) on the productivity and selectivity of the reactions were evaluated. The comparison of the catalytic behavior of the dinuclear complexes bearing the aluminum reactive centers at different distances as well as of their mononuclear counterpart suggested that the copolymerization follows a monometallic pathway differently from what observed in the homopolymerization of CHO.

Vanadium compounds can exert anticancer effects, partly due to inhibition of tyrosine phosphatases. Here, we report the effect of N,N'-ethylenebis (pyridoxylideneiminato) vanadium (IV) complex (Pyr2 enV(IV)), that induced 93% and 57% of cell mortality in A375 (human melanoma) and A549 (human lung carcinoma) cells, respectively; the mortality was

The monomethylaluminum complexes 1 and 2, bearing pyrrolylpyridylamido as dianionic [−NNN–] tridentate ligands with general formula [NNN]AlMe, were synthesized and tested as initiators in the ring-opening polymerization (ROP) of e-caprolactone, l-lactide, and d,l-lactide. In the presence of 1 equiv of alcohol, compounds 1 and 2 were highly active initiators in the ROP of e-CL (TOF up to 4000 molCL molAl–1 h–1), and they showed moderate activity in the ROP of lactides (TOF up to 1.7 molLA molAl–1 h–1). The polymerization processes proceeded with a living mechanism; moreover, the obtained PLAs resulted isotactic-enriched with Pm values up to 76%. More interestingly, this class of catalysts promoted the random copolymerization of e-caprolactone and lactides. In particular, compound 1 allowed excellently controlled random copolymerization of e-caprolactone and d,l-lactide as indicated by both the values of the reactivity ratios of the two monomers (rLA = 1.17; rCL = 1.36) and the average lengths of the caproy...

We have successfully synthesized poly(lactide), poly(glycolide), and poly(lactide- co -glycolide) copolymers in bulk by ring-opening homo- and copolymerization of glycolide and l -lactide, using sodium hydride as the environmentally friendly and nontoxic initiator. Random copolymers were obtained, and the microstructure was characterized by nuclear magnetic resonance ( 1 H and 13 C NMR) and matrix-assisted laser desorption ionization mass spectrometry (MALDI MS). The mechanism of reaction was elucidated by analysis of the polymer end groups. Homopolymer and copolymers films and their blends were obtained, and structure and physical properties analyzed. Thermal degradation analysis showed superior characteristics of copolymers with respect to the blends. Transport properties of water vapor were also evaluated and correlated to the copolymer composition.

The 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.

While our society is becoming more and more aware of the importance of sustainable development, green chemistry and renewability, poly(glycolide) (PGA), poly(lactide) (PLA) and their copolymers have already proven to be a valid, renewable alternative to the petrobased plastics in a wide range of applications. The most efficient way to obtain these polymers is via ring-opening polymerization (ROP) of their cyclic esters, and the most common initiator is tin octoate. Although it is FDA approved, its cytotoxicity raises several issues, along with the need of a more benign initiator. We have already reported the polymerization of ?-caprolactone promoted by sodium hydride (NaH). We now report on the use of NaH as initiator in the ROP of L-lactide, glycolide and in their copolymerization for the synthesis of poly[glycolide-co-(L-lactide)]s (PLGAs). NaH is not only a commercially available, cheap and easy-to-handle compound, but also a non-toxic initiator. Polymerization runs have been performed in bulk, without solvents, and random copolymers were obtained in the case of PLGAs. Their microstructure was characterized by nuclear magnetic resonance (1H and 13C NMR) and matrix assisted laser desorption time of flight mass spectrometry (MALDI MS). Thermal properties were studied via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Transport properties to water vapour were also evaluated and correlated to the copolymer composition.

Group 4 metals complexes bearing anilidomethylpyridine ligands have been synthesized and characterized by nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and single-crystal X-ray...

A series of monoanionic, bidentate 2-anilidomethylpyridine ligands were synthesized and used to prepare bis(chelate) Zr(IV) and Hf(IV) bis(dimethylamido) complexes . All complexes were characterized by NMR spectroscopy and elemental analysis. The solution structures of the complexes were more or less fluxional, depending on the substituent on the ligands. The complexes were tested as catalysts for the polymerization of ethylene and propene, in combination with different activators. Use of Al i Bu 2 H – methylaluminoxane as the co-catalyst resulted in the generation of catalysts producing high molecular weight polyethylenes with good activities, but yielding only stereoirregular and poorly regioregular polypropylenes.

In this work we present an innovative optical sensing methodology based on the use of biomolecules as molecular gating nano-systems. Here, as an example, we report on the detection of analytes related to climate change. In particular, we focused our attention on the detection of nitric oxide (NO) and oxygen (O2). Our methodology builds on the possibility of modulating the excitation intensity of a fluorescent probe used as a transducer and a sensor molecule whose absorption is strongly affected by the binding of an analyte of interest used as a filter. The two simple conditions that have to be fulfilled for the method to work are: (a) the absorption spectrum of the sensor placed inside the cuvette, and acting as the recognition element for the analyte of interest, should strongly change upon the binding of the analyte and (b) the fluorescence dye transducer should exhibit an excitation band which overlaps with one or more absorption bands of the sensor. The absorption band of the sensor affected by the binding of the specific analyte should overlap with the excitation band of the transducer. The high sensitivity of fluorescence detection combined with the use of proteins as highly selective sensors makes this method a powerful basis for the development of a new generation of analytical assays. Proof-of-principle results showing that cytochrome c peroxidase (CcP) for NO detection and myoglobin (Mb) for O2 detection can be successfully used by exploiting our new methodology are reported. The proposed technology can be easily expanded to the determination of different target analytes.

Phosphido-diphosphine Group 3 metal complexes 1–4 [(o-C6H4PR2)2P-M(CH2SiMe3)2; R = Ph, 1: M = Y, 2: M = Sc; R = iPr, 3: M = Y, 4: M = Sc] are very efficient catalysts for the ring-opening polymerization (ROP) of cyclic esters such as e-caprolactone (e-CL), L-lactide, and δ-valerolactone under mild polymerization conditions. In the ROP of e-CL, complexes 1–4 promote quantitative conversion of high amount of monomer (up to 3000 equiv) with very high turnover frequencies (TOF) (∼4 × 104 molCL/molI h) showing a catalytic activity among the highest reported in the literature. The immortal and living ROP of e-CL and L-lactide is feasible by combining complexes 1–4 with 5 equiv of 2-propanol. Polymers with controlled molecular parameters (Mn, end groups) and low polydispersities (Mw/Mn = 1.05–1.09) are formed as a result of fast alkoxide/alcohol exchange. In the ROP of δ-valerolactone, complexes 1–4 showed the same activity observed for lactide (L- and D,L-lactide) producing high molecular weight polymers with narrow distribution of molar masses. Complexes 1–4 also promote the ROP of rac-β butyrolactone affording atactic low molecular weight poly(hydroxybutyrate) bearing unsaturated end groups probably generated by elimination reactions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011