Post-transition Metal Ions Research Articles

Doping Sn4+ ionized cocatalyst in CdSe/S colloidal crystal for promoting photocatalytic CO2 reduction under visible light

The exploration of low-cost and efficient cocatalysts is vitally important for attaining reliable and affordable photocatalytic CO2 conversion. Here, it is found that post-transition metal ions (Sn4+) doped CdSe/S colloidal crystal can serve as effective photocatalyst for CO2 reduction under visible light, in which Sn4+ serves as an ionized cocatalyst. Specifically, Sn4+ doped CdSe/S colloidal crystal shows an improved and stable photocatalytic CO2 reduction performance with CO generation rate of 50.3 μmol h−1 and H2 generation rate of 7.8 μmol h−1 in the presence of triethanolamine as sacrificial agent. The improved photocatalytic activity can be ascribed to the increased light harvesting ability, enhanced CO2 adsorption capability and the improved surface charge transfer efficiency induced by Sn4+ dopant.

Combinatorial Screening of Cu-W Oxide-Based Photoanodes for Photoelectrochemical Water Splitting.

Metal oxide libraries for photoanodes for the oxygen evolution reaction (OER) were generated by printing a metal salt solution in an array layout, followed by calcination to yield 22 ternary metal oxide systems. The libraries included a ternary metal cation system based on CuWO4 with one out of eight transition or posttransition metal ions Cr, Mn, Fe, Co, Ni, Zn, Bi, and Ga in different overall atomic ratios. The photocatalyst libraries were screened by scanning photoelectrochemical microscopy for the highest anodic photocurrents. Array elements that showed promising performance were printed in another set of eight libraries with smaller increments of overall composition. Improved performance with respect to CuWO4 was found for Ga, Co, and Ni as the third element. A comparison of the most active composition of those arrays within one library showed the highest activity for Cu48Ga3W49Ox. Printing spots of identical composition (Cu48Ga3W49Ox, Cu44Ni9W47Ox, and Cu44Co9W47Ox) over a larger area facilitated further characterization by X-ray photoelectron spectroscopy ultraviolet photoelectron spectroscopy (UPS), X-ray diffraction, scanning electron microscopy, chopped light voltammetry, and scanning electrochemical microscopy for the OER. High and stable steady-state photocurrents were generated in a photoelectrochemical cell for all three electrodes even at a low constant bias voltage. The best overall photoanode composition Cu48Ga3W49Ox showed currents that were 36 times higher than the currents of the binary Cu50W50Ox system. Significant n-doping was found by UPS valence band spectra for Ga-containing materials.

Effects of rare earth, transition and post transition metal ions on structural and optical properties and photocatalytic activities of zirconia (ZrO2) nanoparticles synthesized via the facile precipitation process

Abstract This work aims to study the structural, optical and photocatalytic properties of pure and different metal ions, such as rare earth samarium, transition scandium and post transition stannic ions doped zirconia (ZrO2) nanoparticles, synthesized via the facile precipitation process. The effects of the different metal ions on the physic-chemical properties of zirconia were analysized by using different techniques. The structural properties of the synthesized samples were studied by the XRD and FTIR analyses, which confirm that both the pure and different metal ions doped zirconia nanoparticles reveal a tetragonal structure with an average crystallite size in the range of 9.46–4.05 nm and are in good agreement with the TEM results. The smooth spherical surface morphologies and presence of elements of the samples have been confirmed by the SEM and EDX analyses. The Optical properties of the different metal ions doped ZrO2 nanoparticles were evaluated using UV–vis absorption and PL emission spectroscopies. Blue shifts were observed and the band gap energies of the samples found to be in the range of 5.51–5.65 eV, which are higher than that of bulk ZrO2. The enhanced broad green emissions at 578 nm in the PL spectra correspond to the 5D0–7F1 transition, which contributes to the crystallinity and presence of defects concentration in the samples. The performances of the pure and different metal ions doped zirconia nanoparticles in the photocatalytic degradation of methyl orange (MeO) dye under UV light were evaluated, and the degradation percentage (%) found to be in the range of 58.48–98.24%; the results have been comparatively discussed. The detailed mechanism for the degradation of the MeO dye by using metal ions doped ZrO2 catalyst is discussed. The Chemical oxygen demand (COD) test has been done to confirm the total quantity of oxygen required for the oxidation of the organic MeO dye solution into mineralization.

Oil industry waste based non-magnetic and magnetic hydrochar to sequester potentially toxic post-transition metal ions from water

Solid waste conversion to value-added products is a stepping stone towards sustainable environment. Herein, sesame oil cake (SOC), an oil industry waste was utilized as a precursor to develop hydrochar (HC) samples by varying reaction temperature (150–250 °C) and time span (2–8 h), chemically treated with 10% H2O2 to optimize a sample with maximum yield and Pb(II) adsorption. Highest yield (29.2 %) and Pb(II) (24.57 mg/g at Co: 15 mg/L) adsorption was observed on SOCHC@200 °C/6 h, magnetized (mSOCHC@200 °C/6 h) for comparative study. XRD displayed highly crystalline SOCHC@200 °C/6 h and amorphous mSOCHC@200 °C/6 h, both having a characteristic cellulose peak at 14.9°. mSOCHC@200 °C/6 h displayed superparamagnetic behavior with 11.2 emu/g saturation magnetization. IR spectra confirmed the development of samples rich in oxygen containing functionalities; an additional peak for iron oxides appeared at 586 cm−1 in mSOCHC@200°C/6 h spectrum. Four major peaks at 531.9, 399.9, 348.2 and 284.7 eV, assigned to O 1s, N 1s, Ca 2p and C 1s, respectively were observed during XPS analyses. An additional peak at 710.3 eV, ascribed to Fe 2p was observed in mSOCHC@200C/6 h XPS spectrum, while a peak at 143.2 eV for Pb 4f appeared in spectra of both Pb(II) saturated samples. pH dependent (maximum at ∼6.7), exothermic Pb(II) adsorption was found. About 50–70% (at Co: 25 mg/L) adsorption on both SOCHC@200 °C/6 h and mSOCHC@200 °C/6 h was accomplished in a minute, attaining equilibrium in 180 and 240 min, respectively. Error functions and superimposed qe, exp. and qe, cal. values supported Langmuir isotherm model applicability, with respective qm values of 304.9 and 361.7 mg/g at 25 °C for SOCHC@200 °C/6 h and mSOCHC@200 °C/6 h. Kinetic data was fitted to PSO model. Highest (between 92.2 and 88.9 %) amount of Pb(II) from SOCHC@200 °C/6 h and mSOCHC@200 °C/6 h was eluted by 0.01 M HCl.

A study on formaldehyde gas sensing and optoelectronic properties of Bi-doped CdO thin films deposited by an economic solution process

Doped metal oxide semiconductors have received greater attention for the development of gas sensor, working at low temperature, as well as of optoelectronics. In this work, a post transition metal ion of bismuth (Bi) doped cadmium oxide (CdO) thin films were deposited by a cost-effective pyrolytic spray process at substrate temperature of 300 °C. The effects of Bi-doping concentrations on the microstructural, gas sensing and optoelectronic properties of CdO thin films are systematically studied. The CdO film doped with 0.75 wt% of Bi exhibits high response (86.20%) to formaldehyde at a low operating temperature of 130 °C with satisfactory stability, selectivity and anti-interference to humidity. The response mechanism to formaldehyde is discussed in details. Optical results indicate that an improved transmittance above 80% in visible and NIR region was observed for all the Bi-doped CdO thin films with an enhanced optical band gap, in comparison with undoped CdO. Photoluminescence study indicates the presence of optical defects such as neutral donors and deep centers in CdO thin films. The high figure of merit value (4.56 × 10−3 Ω-1) obtained from 0.50 wt% of Bi-doped CdO is superior to the previously reported. The improved carrier mobility (78 cm2/V⋅s) is obtained from 0.25 wt% of Bi-doped CdO thin film. The present investigation indicated that the Bi-doped CdO thin films would be an attractive candidate for formaldehyde gas sensing and optoelectronic applications.

Adsorption of cadmium by a high-capacity adsorbent composed of silicate-titanate nanotubes embedded in hydrogel chitosan beads

ABSTRACT In this study, we developed a nanoparticle-based mesoporous composite that consisted of silicate-titanate nanotubes (STNTs) supported in hydrogel chitosan beads (STNTs-Ch beads) and was studied for Cd2+ adsorption. By using Fourier-transform infrared spectroscopy, transmission and scanning electron microscopy coupled to an energy-dispersive X-ray spectrometer, we could determine that the hollow STNTs were highly dispersed in the walls of the hollow beads. The dispersion was attributed to the effect of pH when the composite was prepared and we observed a non-interaction between STNTs and chitosan. The adsorption studies of Cd2+ showed that the kinetic rate (k 2) increased 3-fold and that the diffusion rate (K d) increased 2-fold after the embedment. Moreover, the maximum capacity of adsorption of STNTs-Ch beads was 2.3 times higher than that of STNTs alone. The treatment of a synthetic Cd2+ solution and a real leachate in continuous mode showed two phases in which it was observed higher removed fractions of transition metal ions (Cd2+, Co2+, Ni2+, Zn2+ and Cu2+) and the post-transition metal ion Pb2+, in comparison to the removed fractions of alkali and alkali-earth metal ions (Ca2+, K+, Mg2+). The composite was successfully reused four times when adsorbing Cd2+, saving three times the needed amounts of TiO2, SiO2 and chitosan for the production of the material. This composite was produced in a simple way and shows the potential for wastewater treatment.

Nitric oxide generation from S-nitrosoglutathione: New activity of indium and a survey of metal ion effects

S-Nitrosothiols (RSNOs) such as S-nitrosoglutathione (GSNO) are known to produce nitric oxide (NO) through thermal, photolytic, and metal ion-promoted pathways, which has led to their increasing use as exogenous sources of therapeutic NO. Despite the burgeoning NO release applications for RSNOs, their susceptibility to metal-promoted decomposition has rarely been examined in a uniform manner through the specific measurement of NO release. In this study, the ability of various transition and post-transition metal ions to promote NO release from GSNO was surveyed by chemiluminescence-based NO detection. Substantial NO formation (>10-fold increase relative to GSNO baseline) was detected after the addition of Cu2+, Au3+, Pd2+, Pt2+, and V3+. Modest increases were observed in the cases of Co2+, Hf4+, Fe2+, Fe3+, Mn2+, Hg2+, Ni2+, Ag+, Sn2+, and Zr4+, while no effect was evident for Al3+, Cr3+, Pb2+, Sc3+, and Zn2+. It was further observed that In+ compounds initiate the apparent NO-forming decomposition of GSNO, while In0 and In3+ are inactive, indicating that In+ exerts a previously unknown effect on GSNO.

Hydrogen Activation by Silica-Supported Metal Ion Catalysts: Catalytic Properties of Metals and Performance of DFT Functionals.

Single-site heterogeneous catalysts (SSHC) have received increasing attention due to their well-defined active sites and potentially high specific activity. Detailed computational studies were carried out on a set of potential SSHC's, i.e., silica-supported metal ions, to investigate the reactivity of these catalysts with H2 as well as to evaluate the performance of density functional theory (DFT) methods in conjunction with triple-ζ quality basis sets (i.e., cc-pVTZ) on reaction energetics. The ions considered include 4d and 5d metals as well as several post-transition metal ions. A representative cluster model of silica is used to calculate reaction free energies of the metal hydride formation that results from the heterolytic cleavage of H2 on the M-O bond. The hydride formation free energy is previously shown to be strongly correlated with the catalytic activity of such catalysts for alkene hydrogenation. ONIOM calculations (CCSD(T)//MP2) are used to assess the accuracy and reliability of the MP2 results and it is found that MP2 is a suitable level of theory for gauging the performance of DFT functionals. The performance of various DFT functionals is assessed relative to MP2 results and it is found that the wB97xd and PBE0 functionals have the lowest standard deviation (STD) value while the MN12SX and PBE functionals have the lowest mean absolute deviation (MAD) values. The B3LYP functional is shown to have similar MAD and STD values as the top performing functionals. Potential active SSHC's for exergonic hydrogen activation predicted in this study include mostly late and post transition metal ions, i.e., Au3+, Pd2+, Pt4+, Pd4+, Ir4+, Hg2+, Rh3+, Pb4+, Tl3+, In3+, Ir3+, Os4+, Cd2+, Ru2+, and Ga3+. This study provides important guidance to future computational studies of such catalyst systems.

Synthesis, coordination properties and DFT studies of novel trans-disubstituted hexaaza-macrocycles containing pyridine and/or ethyldioxolane arms

Novel trans-disubstituted hexaaza-macrocyclic ligands L1 and L2 were successfully prepared by the alkylation of the trans secondary amines presented in L with pyridine and ethyldioxolane groups, respectively. The coordination properties of compounds L1 and L2 towards different transition, post-transition and lanthanoid metal ions were explored. Colorless crystals of [NaL1]I and L2´Br2, suitable for X-ray diffraction, were obtained by slow evaporation of an acetonitrile solution of compounds L1 or L2, showing an anti conformation between the methyl groups and the pendant arms in trans positions. The [ML1]n+ (M = Ni2+, Cu2+, Zn2+) systems were investigated by DFT calculations (B3LYP model).

(Invited) Materials Design of High-Energy Cation/Anion Redox in Li-Rich Cathode Materials: Li5FeO4, Li4Mn2O5, and Li2MO3

The energy density of many lithium metal oxide battery cathodes is limited by redox reactions associated with the transition metal alone. Anionic redox reactions are affording new opportunities to increase this energy density. Here, we present results from first-principles density functional theory (DFT) calculations aimed at understanding the combined cation/anion redox of Li-rich materials, and designing new materials that will enable high-capacity, reversible cycling with minimal oxygen evolution. We illustrate this approach on three Li-rich compounds: Li5FeO4, Li4Mn2O5, and Li2MnO3. Li5FeO4: Initial removal of Li is accompanied by Fe migration to form a disordered rocksalt structure. A local Li6-O coordination of oxygen, identified by DFT calculations, raises the O 2p band and enables reversible O-/O2- redox behavior, previously unknown in this material. This insight leads to the prediction and subsequent experimental demonstration of anionic and cationic redox reactions with good reversibility and without any obvious O2 gas release. Li4Mn2O5: We study the recently-reported, high-capacity, disordered rocksalt-type Li4Mn2O5 compound and also determine the ground state ordered structure of Li4Mn2O5 via a DFT-based enumeration method. DFT calculations show that the delithiation process occurs via a three-step reaction pathway involving the complex interplay of cation and anion redox reactions: i) Mn3+ ➝ Mn4+ (LixMn2O5, 4 > x > 2), ii) O2− ➝ O1− (2 > x > 1), and iii) Mn4+ ➝ Mn5+ (1 > x > 0) concomitant with Mn migration from the original octahedral site to the adjacent tetrahedral site. Finally, we predict that alloying with M = V and Cr in Li4(Mn,M)2O5 would produce new stable compounds with substantially improved electrochemical properties. Li2 MO3: We catalog the family of Li2 MO3 compounds as active cathodes or inactive stabilizing agents using high-throughput density functional theory (HT-DFT). With an exhaustive search based on design rules that include phase stability, cell potential, resistance to oxygen evolution, and metal migration, we predict a number of new Li2MIO3–Li2MIIO3 active/inactive electrode pairs, in which MI and MII are transition- or post-transition metal ions, that can be tested experimentally for high-energy-density lithium-ion batteries.

Bond-length distributions for ions bonded to oxygen: metalloids and post-transition metals

Bond-length distributions have been examined for 33 configurations of the metalloid ions and 56 configurations of the post-transition metal ions bonded to oxygen, for 5279 coordination polyhedra and 21 761 bond distances for the metalloid ions, and 1821 coordination polyhedra and 10 723 bond distances for the post-transition metal ions. For the metalloid and post-transition elements with lone-pair electrons, the more common oxidation state between n versus n+2 is n for Sn, Te, Tl, Pb and Bi and n+2 for As and Sb. There is no correlation between bond-valence sum and coordination number for cations with stereoactive lone-pair electrons when including secondary bonds, and both intermediate states of lone-pair stereoactivity and inert lone pairs may occur for any coordination number > [4]. Variations in mean bond length are ∼0.06–0.09 Å for strongly bonded oxyanions of metalloid and post-transition metal ions, and ∼0.1–0.3 Å for ions showing lone-pair stereoactivity. Bond-length distortion is confirmed to be a leading cause of variation in mean bond lengths for ions with stereoactive lone-pair electrons. For strongly bonded cations (i.e. oxyanions), the causes of mean bond-length variation are unclear; the most plausible cause of mean bond-length variation for these ions is the effect of structure type, i.e. stress resulting from the inability of a structure to adopt its characteristic a priori bond lengths.

Novel di-substituted hexaaza-macrocyclic ligands bearing hydrazine and/or indole arms: synthesis, sensor properties and catalytic activity

Novel trans-disubstituted hexaaza-macrocyclic ligands L1, L2 and L3 were successfully prepared by the alkylation of the trans secondary amines presented in L with ethyl acetate, acetohydrazide and indole groups, respectively. The coordination properties of compounds L2 and L3 towards different transition, post-transition and lanthanide metal ions were explored. Their responses towards some of these cations were also evaluated in solution by UV–vis absorption and emission spectroscopy. Crystals of [NaL1]Br·2H2O suitable for X-ray diffraction were obtained by slow evaporation of an acetonitrile solution of compound L1, showing an anti conformation between the methyl groups and the pendants arms in trans. The catalytic activity of L2 and their nitrate complexes (Co2+, Ni2+, Cu2+, Zn2+) towards the decomposition of hydrogen peroxide (catalase activity) was also studied.

Exploring the ability of cations to facilitate binding between inorganic oxyanions and humic acid

The mobility and fate of inorganic oxyanions in the environment can be greatly influenced by interactions with natural organic matter (NOM). There is increasing evidence that this interaction between two anionic species is facilitated by cationic bridges, but detailed mechanistic studies into this system are challenging due to the heterogeneous nature of NOM. This work examines the ability of cations (FeIII, CrIII, AlIII, or GaIII) to form ternary complexes with Suwannee River humic acid (SRHA) and the oxyanions of As (AsIII and AsV) and Se (SeIV and SeVI). Complexes were characterized by separating SRHA from unbound species using size exclusion chromatography coupled to ICP-MS to determine its metal content. Unlike CrIII and FeIII, the post-transition metal ions AlIII and GaIII proved ineffective at forming ternary complexes with any of the oxyanions, although minor complexation was observed with GaIII, suggesting that electrostatic interactions are not the primary driving force behind the stabilization of these ternary complexes. The results also show differences in the behavior of FeIII and CrIII that may indicate that the two cations stabilize the ternary complexes by different mechanisms.

Transition and post-transition metal ions in borate glasses: Borate ligand speciation, cluster formation, and their effect on glass transition and mechanical properties.

A series of transition and post-transition metal ion (Mn, Cu, Zn, Pb, Bi) binary borate glasses was studied with special consideration of the cations impact on the borate structure, the cations cross-linking capacity, and more generally, structure-property correlations. Infrared (IR) and Raman spectroscopies were used for the structural characterization. These complementary techniques are sensitive to the short-range order as in the differentiation of tetrahedral and trigonal borate units or regarding the number of non-bridging oxygen ions per unit. Moreover, vibrational spectroscopy is also sensitive to the intermediate-range order and to the presence of superstructural units, such as rings and chains, or the combination of rings. In order to clarify band assignments for the various borate entities, examples are given from pure vitreous B2O3 to meta-, pyro-, ortho-, and even overmodified borate glass compositions. For binary metaborate glasses, the impact of the modifier cation on the borate speciation is shown. High field strength cations such as Zn2+ enhance the disproportionation of metaborate to polyborate and pyroborate units. Pb2+ and Bi3+ induce cluster formation, resulting in PbOn- and BiOn-pseudophases. Both lead and bismuth borate glasses show also a tendency to stabilize very large superstructural units in the form of diborate polyanions. Far-IR spectra reflect on the bonding states of modifier cations in glasses. The frequency of the measured cation-site vibration band was used to obtain the average force constant for the metal-oxygen bonding, FM-O. A linear correlation between glass transition temperature (Tg) and FM-O was shown for the metaborate glass series. The mechanical properties of the glasses also correlate with the force constant FM-O, though for cations of similar force constant the fraction of tetrahedral borate units (N4) strongly affects the thermal and mechanical properties. For paramagnetic Cu- and Mn-borate glasses, N4 was determined from the IR spectra after deducing the relative absorption coefficient of boron tetrahedral versus boron trigonal units, α = α4/α3, using NMR literature data of the diamagnetic glasses.

Peculiar photoinduced properties of water-soluble, early lanthanide(III) porphyrins

Water-soluble, early lanthanide(III) mono- and bisporphyrin complexes possess very similar UV–Vis absorption as well as photophysical and photochemical properties, as a consequence of a special type of aggregation, through the peripheral substituents. In the absence of the bidentate, O-donor acetate ligand, bisporphyrin can form too, which has slightly redshifted and broadened absorption bands, compared to those of the monoporphyrin. Also the bisporphyrin displays a blueshifted and less intense fluorescence, related to the free-base porphyrin. The formation of complexes and the transformation between the mono- and bisporphyrins are very slow reactions in dark at room temperature. These reactions are accelerated by the photolysis of the system, which are considerable by-processes of the photoredox degradation. Depending on the wavelength of irradiation, two types of photoproducts can appear: during the photolysis at the Soret-band, a radical type intermediate can be observed, which disappears in dark. However, during the irradiation at the Q-bands, a new photoproduct appears, which is stable in dark and undetectable in the case of post-transition metal ions' out-of-plane porphyrin complexes.

Bis(2-pyridylmethyl)alkyl(thioalkyl)diamines as promising scaffolds for the construction of fluorescent and redox chemosensors for transition and post-transition metal ions

N,N′-Bis(2-pyridylmethyl)propylendiamine (1) and N,N′-bis(2-pyridylmethyl)-1,5-diamino-3-thiapentane (2) have been functionalised at the secondary nitrogen atoms with dansylamidoethyl (L1, L3), 2-quinolinylmethyl (L2, L4) and ferrocenylmethyl (L6, L7) pendant arms with the intention to study their potentiality as receptor units in molecular sensors. The optical response of L1–L4 to the presence of the metal ions Cu2+, Zn2+, Cd2+, Hg2+ and Pb2+ has been investigated in MeCN/H2O (4:1 v/v) solution. The electrochemical response of L6 and L7 to the presence of the same metal ions has been investigated in anhydrous MeCN/CH2Cl2 10:1 (v/v) solution. Results are compared and discussed with the aim to clarify the mutual role played by the bis(2-methylpyridyl)alkyl(thioalkyl)diamines and the signalling units attached to them in reaching the selectivity of the responses observed.

Novel emissive podands based on 8-OH-quinoline: Synthesis, fluorescence materials, DFT and complexation studies

Two novel chemosensors with podand structures (L1 and L2) derived from 1,5-bis(2-aminophenoxy)-3-oxopenthane bearing two flexible 8-hydroxyquinoline units have been synthesized and characterized.Several nitrate complexes of transition (Cu2+), post-transition (Zn2+) and lanthanide (Eu3+ and Sm3+) metal ions have been synthesized with tetrafluoroborate salts and characterized. In order to study their potential utility as fluorescent probes, the coordination ability of chemosensors (L1 and L2) towards those metal ions has been explored in solution (by UV–Vis and emission spectroscopy) and in gas phase (by MALDI mass spectrometry).Density functional theory has been employed to explore the emission properties of the three-protonation states of the chemosensor. From this study, the anomalous red shift observed in the fluorescence spectra of the dianionic sensors can be attributed to subtle structural differences between their anionic and dianionic forms. Furthermore, a plausible explanation for the low fluorescence of the neutral form is provided in the form of a non-radiative relaxation involving the imine double-bond isomerization.All new compounds have been characterized by microanalysis, melting points, IR, UV–Vis and fluorescence emission spectroscopy and MALDI-TOF-mass spectrometry.

New emissive dopamine derivatives as fluorescent chemosensors for metal ions: A CHEF effect for Al(III) interaction

Three new Schiff-base ligands 1–3 derivatives from neurotransmitter dopamine, bearing an indazole (1), methylimidazole (2) or hydroxynaphthaldehyde (3) units were successfully synthesized and characterized by elemental analysis, 1H NMR, 13C NMR, IR (infrared), ESI-TOF (electrospray ionization-time of flight-mass), UV–Vis absorption and emission spectroscopy. The interaction with the metal ions Li+, Na+, Mg2+, Ca2+, Zn2+, Cd2+, Cu2+, Ni2+, Ag+, Fe3+ and Al3+ has been explored by absorption and fluorescence emission spectroscopy. Compound 3 shows to be the most emissive one, with a quantum yield of 0.022, followed by compound 2 (ϕ=0.009) and 1 (ϕ=0.001). Compound 1 reveals quite selective for Al3+, generating an emissive complex formed by three units of 1 per metal ion. On the other hand compound 3, shows a ratiometric effect with Al3+ appearing as a new emission band centred at 530nm. With the other transition and post-transition metal ions, a quenching in the emission was observed, being 3 the most sensitive one, being quenched by 0.34ppm of Zn2+ and Cu2+, 0.48ppm of Ni2+, 0.061ppm of Fe3+ and 0.047ppm of Al3+. In most cases a stoichiometry of three ligands by one metal ion was postulated. In order to study the fluorescence properties in the solid state, the Al3+ metal complexes of 1 (4) and 3 (5) were synthesized as new emissive materials. In both cases a very strong emissive systems were obtained, with a quantum yield of 0.01 and 0.04 for 4 and 5.

Novel Small Stable Gold Nanoparticles Bearing Fluorescent Cysteine–Coumarin Probes as New Metal-Modulated Chemosensors

Emissive molecular probes based on amino acid moieties are very appealing because of their application as new building blocks in peptide synthesis. Two new bioinspired coumarin probes (L1 and L2) were synthesized and fully characterized by elemental analysis, infrared, (1)H NMR, (13)C NMR, UV-vis absorption and emission spectroscopy, matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS), lifetime measurements, and X-ray crystal diffraction. Their sensing ability toward alkaline earth, transition, and post-transition metal ions (Ca(2+), Zn(2+), Cd(2+), Cu(2+), Ni(2+), Hg(2+), Ag(+), and Al(3+)) and their acid-base behavior (H(+), OH(-)) were explored in absolute ethanol by absorption and fluorescence spectroscopy. Compound L1 shows a strong complexation constant with the soft metal ions Zn(2+), Cd(2+), and Ag(+). Compound L2 shows a high fluorescence quantum yield, and it could be used as a non-pH-dependent fluorescent biological probe. Very small gold nanoparticles (AuNPs) using compounds L1 and L2 as stabilizers were obtained by using a reductive method and were characterized by UV-vis, light scattering, and transmission electron microscopy (TEM). Dynamic light scattering and TEM studies show that the formation of small nanoparticles is around 4.27 ± 0.64 nm for L1 and around 2.69 ± 0.96 nm for L2. The new stable Cou@AuNPs behaved as supramolecular chemosensors, which have been selective for the heavy element Hg(2+), with a concomitant change of color from pink to dark red/brown and an increase of size up to 100-fold.

Novel emissive phenylurea-based macrocyclic chemosensor: Synthesis, fluorescent and complexation studies

A new emissive macrocycle ligand bearing three phenylurea groups (L1) has been synthesized and fully characterised. Several mononuclear complexes with nitrate, perchlorate and tetrafluoroborate salts of transition and post-transition metals (Cu2+, Ni2+, Co2+, Zn2+ and Cd2+) were synthesized and characterised. For comparative purposes, the coordination ability of two nonfluorescent macrocyclic ligands (L2 and L3) containing three nitrophenylurea pendant-arms towards the same metal ions were studied. The interaction with transition and post-transition metal ions, and anions was explored in solution by UV–Vis and emission spectroscopy with ligand L1. All new compounds were characterised by microanalysis, IR, UV–Vis and fluorescence emission, FAB and ESI mass spectrometry and conductivity measurements.