Sol-Gel Dipping Devices for H2S Visualization.

In this contribution we report the synthesis and full characterization, via a combination of different spectroscopies (e.g., 1H NMR, UV-vis, fluorescence, MALDI), of a new family of fluorescent zinc complexes with extended π-conjugated systems, with the final aim of setting up higher performance H2S sensing devices. Immobilization of the systems into a polymeric matrix for use in a solid-state portable device was also explored. The results provided proof-of-principle that the title complexes could be successfully implemented in a fast, simple and cost-effective H2S sensing device.

Paper-Strip-Based Sensors for H2S Detection: A Proof-of-Principle Study.

In this work, the authors explored the interaction of a suite of fluorescent zinc complexes with H2S. The authors provide evidence that HS- binds the zinc center of all the complexes under investigation, allowing them to possibly function as sensors by a 'coordinative-based' approach. Naked-eye color changes occur when treating the systems with HS-, so the fluorescence responses are modulated by the presence of HS-, which has been related to a change in the energy level and coupling of excited states through a computational study. The results show the potential of the systems to function as HS-/H2S colorimetric and fluorescent sensors. Paper-strip-based sensing experiments foresee the potential of using this family of complexes as chemosensors of HS- in more complex biological fluids.

Fluorescent salen-type Zn(II) Complexes As Probes for Detecting Hydrogen Sulfide and Its Anion: Bioimaging Applications.

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.

Therapeutic potential of a pyridoxal-based vanadium(IV) complex showing selective cytotoxicity for cancer versus healthy cells.

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 <24% in other cancer cell lines and in human normal epidermal keratinocytes, lung cells and peripheral blood mononuclear cells. The mechanism of Pyr2 enV(IV) effect relied on apoptosis induction; this was triggered by ROS increase, followed by mitochondrial membrane depolarization. Indeed, the addition of N-acetyl cysteine to cell cultures abated Pyr2 enV(IV)-induced apoptosis. These results disclose the pro-apoptotic activity of Pyr2 enV(IV) and its mechanism, relying on intracellular ROS increase.

Bi-enzyme sensor for phenolic compounds with fluorescent read-out.

In this paper, the use of tyrosinase (Ty) from Streptomyces antibioticus, labeled with a fluorescent tag, in combination with soluble quinoprotein (PQQ-containing) glucose dehydrogenase (s-GDH) to measure trace amounts of phenols is explored. Proof of concept is provided by a series of experiments, which show a clear quantitative dependence of the response on the phenol concentration. One of the advantages of the detection system is that apart from a standard fluorimeter no further instrumentation is required.

Iron and manganese pyridoxal-based complexes as fluorescent probes for nitrite and nitrate anions in aqueous solution.

Water-soluble iron and manganese pyridoxal-based complexes pyr2enFeCl (1) and pyr2enMnCl (2) (pyr2en = N,N'-ethylenebis(pyridoxylideneiminato) have been synthesized and characterized. Proof-of-principle results that the title complexes can be efficiently used as fluorescent probes for nitrite and nitrate detection are provided. The fluorescent complex pyr2enFeCl (1) selectively recognizes nitrate anions by fluorescent enhancement in an aqueous solution displaying high binding affinities. ESI-MS experiments clearly show the binding of these anions via the substitution of the chloride anion at the metal center. The pyridoxal-based manganese complexes of NO2(-) and NO3(-) have been isolated, and their structures have been established by single-crystal XRD. Density functional theory (DFT) calculations show that the substitution of the chloride anion at the metal center by the nitrite or nitrate anion is favored by the gain in the energies of hydration.

Cooperative effects of Schiff base binuclear zinc complexes on the synthesis of aliphatic and semi-aromatic polyesters.

In this paper, we use mono- and bimetallic complexes based on Earth-abundant, cheap and benign zinc for the synthesis of sustainable aliphatic and semi-aromatic polyesters. Tridentate and hexadentate aldimine-thioetherphenolate ligands were used to obtain the desired zinc complexes by the reaction of proligands with opportune equivalents of zinc bis[bis(trimethylsilyl)amide]. The obtained bimetallic complexes 1 and 2 and the monometallic complex 3 were used as catalysts in the Ring-Opening Polymerization (ROP) of landmark cyclic esters, such as ε-caprolactone and lactide, and in the Ring-Opening COPolymerization (ROCOP) of cyclohexene oxide and phthalic anhydride under different reaction conditions. All catalysts were active in these two classes of reactions, showing good control of the polymerization processes. Interestingly, the bimetallic complexes have higher activity compared to their monometallic counterparts, highlighting the cooperation between the two zinc centers.

Salen, salan and salalen zinc(II) complexes in the interaction with HS-: time-resolved fluorescence applications.

In the current work we investigate the route of interaction of a newly synthesized family of zinc complexes with HS- by a plethora of different spectroscopic techniques. A computational analysis on the time dependent density functional theory (TD-DFT) level explored the overall fluorescence properties of the title complexes and their different fluorescence responses to HS-. Time-resolved fluorescence experiments were also performed and highlight the great potential of the current systems to be implemented as HS- fluorescent sensors.

A FRET enzyme-based probe for monitoring hydrogen sulfide.

Fluorescently labeled cobalt peptide deformylase (Co-PDF) can be efficiently used as a fluorescence-resonance-energy-transfer-based sensing device for hydrogen sulfide (H(2)S). The proof of concept of our sensor system is substantiated by spectroscopic, structural, and theoretical results. Monohydrogen sulfide coordination to Co-PDF and Ni-PDF was verified by X-ray crystallography. Density functional theory calculations were performed to gain insight into the characteristics of the coordination adduct between H(2)S and the cobalt cofactor in Co-PDF.

Heteroscorpionate-based Co2+, Zn2+, and Cu2+ complexes: coordination behavior, aerobic oxidation, and hydrogen sulfide detection.

The coordination behavior and reactivity of the phenol-substituted bis(pyrazolyl)methane ligands, (3,5-(t)Bu(2)-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L1-H) and 2-phenol-bis(3,5-Me(2)-pyrazol-1-yl)methane (L2-H) have been investigated in the metal complexes (L1-H)CoCl(2) (1), (L1-H)ZnCl(2) (2), (L3)CuCl(2) (3), (L2)(2)Co(2)Cl(2) (4) (L2-H)ZnCl(2) (5), and (L2-H)CuCl(2)·H(2)O (6). The mononuclear tetrahedral cobalt complex 1 was isolated and fully characterized by X-ray single crystal diffraction and (1)H NMR spectroscopy and relaxometry. The neutral L1-H is κ(2)-coordinated to the metal center whereas the not coordinated hydroxy-phenyl group is involved in extended intermolecular hydrogen bonds. Aerobic oxidation of L1-H was observed in the reaction of this ligand with CuCl(2) to yield the para-quinone derivative L3 (L3 = 2-(t)Bu-6-(bis(3,5-Me(2)-pyrazol-1-yl)methyl)cyclohexa-2,5-diene-1,4-dione). Upon oxidation L3 resulted κ(2)-coordinated to the tetrahedral Cu(II) metal center, affording 3. The reaction of L2-H with CoCl(2)·6H(2)O produced the elimination of 1 equiv of hydrochloric acid and the formation of the binuclear complex 4 in which one cobalt is in an octahedral environment featuring two κ(3)-coordinated deprotonated ligands whereas the second cobalt center is detected in tetrahedral coordination geometry, bound to the octahedral cobalt via two phenoxo bridging moieties. Interestingly L2-H, (3-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L4-H), or (5-(t)Bu-2-phenol)bis(3,5-Me(2)-pyrazol-1-yl)methane (L5-H) were not oxidized in the reaction with CuCl(2). The reaction of the ligand L2-H with ZnCl(2) and CuCl(2)·2H(2)O yielded the κ(2)-coordinated tetrahedral complex 5 and the square planar complex 6, respectively. The application of the cobalt complex 1 as molecular dosimeter for H(2)S was explored and compared to that of the zinc analogue 2. Density functional theory (DFT) calculations and NMR experiments to assess the possible mechanisms of H(2)S detection by both 1 and 2 are also described.

The contribution of metalloporphyrin complexes in molecular sensing and in sustainable polymerization processes: a new and unique perspective.

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.

Imidazo-pyridine-based zinc(II) complexes as fluorescent hydrogen sulfide probes.

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.

Salen-type aluminum and zinc complexes as two-faced Janus compounds: contribution to molecular sensing and polymerization catalysis.

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.

A protein-based oxygen biosensor for high-throughput monitoring of cell growth and cell viability.

Fluorescently labeled hemocyanin has been previously proposed as an oxygen sensor. In this study, we explored the efficacy of this biosensor for monitoring the biological oxygen consumption of bacteria and its use in testing bacterial cell growth and viability of Escherichia coli, Pseudomonas aeruginosa, Paracoccus denitrificans, and Staphylococcus simulans. Using a microwell plate, the time courses for the complete deoxygenation of samples with different initial concentrations of cells were obtained and the doubling times were extracted. The applicability of our fluorescence-based cell growth assay as an antibacterial drug screening method was also explored. The results provide a proof-of-principle for a simple, quantitative, and sensitive method for high-throughput monitoring of prokaryotic cell growth and antibiotic susceptibility screening.

New zinc complexes bearing kappa2-heteroscorpionate ligands: influence of second-sphere bonding interactions on reactivity and properties.

New zinc complexes (LOMe)ZnCl(2) (1) and (LOH)ZnCl(2)(2) of the heteroscorpionate ligands 1-[(3,5-di-tert-butyl-2-methoxyphenyl)(3,5-dimethyl-pyrazol-1-yl)methyl)]-3,5-dimethyl-pyrazole (LOMe) and 2,4-di-tert-butyl-6-[bis(3,5-dimethyl-pyrazol-1-yl)methyl]phenol (LOH) have been synthesized. The X-ray molecular structure of 2 was reported and compared with the one of the iron(II) complex (LOH)FeI(2) (3). The complexes 2-3 adopt a tetrahedral structure in the solid state in which the LOH ligand is kappa(2)-coordinated to the metal via the imino nitrogens of the two pyrazolyl rings. The hydroxyl phenyl group is not coordinated to the metal but found to be involved in an intermolecular hydrogen bond. The solution structures of 1 and 2 are consistent with this tetrahedral C(S) symmetric geometry. Dilution and (1)H-(1)H Nuclear Overhauser Effect Spectroscopy (NOESY) experiments revealed that the free ligands LOMe and LOH are involved in intra- and intermolecular hydrogen bonding interactions. Coordination of LOMe and LOH to ZnCl(2) was investigated by NMR titration methods. Association constants (K(a)) of (8.6 +/- 0.4) x 10(2) M(-1) and (7.8 +/- 0.3) x 10(2) M(-1) were obtained in methanol/water solutions (95:5) for LOMe and LOH, respectively. Coordination of bis(3,5-dimethyl-pyrazol-1-yl)methane (bpm) ligand to ZnCl(2) is weaker, as evidenced by the lower value of the association constant (5.3 +/- 0.3) x 10(2) M(-1). When bpm was added to solutions of 1 or 2, an equilibrium shifted toward the (bmp)ZnCl(2) species was observed. The thermodynamic parameters for this reaction were determined by VT NMR analysis. The optical properties of the ligands (LOMe, LOH) and of the corresponding zinc complexes 1 and 2 were also investigated by means of UV-vis and fluorescence spectroscopy to assess the potential use of these ligands as fluorescent sensors for Zn(2+) detection.

Interaction of monohydrogensulfide with a family of fluorescent pyridoxal-based Zn(ii) receptors.

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.

Chemically reversible binding of H2S to a zinc porphyrin complex: towards implementation of a reversible sensor via a "coordinative-based approach".

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.

Selective detection of ATP and ADP in aqueous solution by using a fluorescent zinc receptor.

We report on the successful use of a new zinc complex for the selective fluorescent detection of ADP and ATP in water. This is achieved by the complementary coordination of the phosphate groups to the metal centre and hydrogen bonding of the adenosine with the coordinated ligand.

Fluorescence-based biosensors.

The field of optical sensors has been a growing research area over the last three decades. A wide range of books and review articles has been published by experts in the field who have highlighted the advantages of optical sensing over other transduction methods. Fluorescence is by far the method most often applied and comes in a variety of schemes. Nowadays, one of the most common approaches in the field of optical biosensors is to combine the high sensitivity of fluorescence detection in combination with the high selectivity provided by ligand-binding proteins. In this chapter we deal with reviewing our recent results on the implementation of fluorescence-based sensors for monitoring environmentally hazardous gas molecules (e.g. nitric oxide, hydrogen sulfide). Reflectivity-based sensors, fluorescence correlation spectroscopy-based (FCS) systems, and sensors relying on the enhanced fluorescence emission on silver island films (SIFs) coupled to the total internal reflection fluorescence mode (TIRF) for the detection of gliadin and other prolamines considered toxic for celiac patients are also discussed herein.

D-serine-dehydratase from Saccaromyces cerevisiae: a pyridoxal 5'- phosphate-dependent enzyme for advanced biotech applications.

The Saccaromices cerevisiae D-serine dehydratase is a pyridoxal 5'-phosphate dependent enzyme that requires zinc for its function. It catalyses the conversion of D-serine into pyruvate and ammonia with the K(m) and k(cat) values of 0.39 mM and 13.1 s(-1) respectively. In this work, a new methodology for monitoring D-serine is presented. Our results show that this enzyme could be successfully used as a biological probe for detection of D-serine via fluorescence spectroscopy.