Mono Complexes Research Articles

Nickel Bis(dithiolene) Complexes and Tetrathiafulvalenes from Sterically Hindered Di‐ and Tetra‐substituted Dithiine‐dithiolo‐thione Precursors

Three variants of 5,6‐dihydro‐1,4‐dithiin‐2,3‐(1’,3’‐dithiole‐2’‐thione) (dddt) bearing up to four substituents on the ethylene bridge have been obtained by hetero‐Diels‐Alder reaction. The substituted dddt derivatives have the advantage of providing modulation of the steric hindrance and stereogenic centres, and represent valuable intermediates for both tetrathiafulvalene (TTF) and metal‐dithiolene complexes. Within this work, disubstituted and tetrasubstituted dddt derivatives have been used for the synthesis of Ni(II) monoanionic and neutral complexes, as well as for tetra‐ and octa‐methylated EDT‐TTF and BEDT‐TTF (EDT = ethylenedithio, BEDT = bis(ethylenedithio)) derivatives. While the influence of the bulkiness and number of the substituents is observed in the solid state packing of both types of materials (complexes and TTF), the absence of the counterion in the case of the neutral complexes translated into increased intermolecular interactions between the donors and the formation of 1D and 2D layers. The two examples of tetrasubstituted TTF radical cation salts reported in here show semiconducting behaviour due to the formation of dimers and lateral interactions through the S atoms. Our findings highlight the importance of substitution on these type of dddt precursors and their potential for electroactive molecular materials.

Lanthanide Complexes with 1,4,7-Trimethyl-1,4,7-triazacyclononane

The reaction of 1,4,7-trimethyl-1,4,7-triazacyclononane with samarium, gadolinium, and terbium chloride tetrahydrofuranates gives mononuclear complexes [LnCl3(Me3tacn)(THF)n] (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane; Ln = Sm (I), Gd (II), n = 1; Ln = Tb (III), n = 0). The treatment of complexes I or II with 1,2,4-triphenylcyclopentadienyl potassium affords mono(cyclopentadienyl) complexes [CpPh3LnCl2(Me3tacn)] (CpPh3 = = 1,2,4-triphenylcyclopentadienyl; Ln = Sm (IV), Gd (V)). Complexes IV and V are formed even when a twofold excess of CpPh3K is used. The molecular structure of complexes I–V was established by X-ray diffraction analysis (CCDC nos. 2299485 (I), 2299487 (II), 2299486 (III), 2305352 (IV), 2306051 (V)).

Dye induced luminescence properties of gold(I) complexes with near unity quantum efficiency.

To study the effect of a dye on the photoluminescence (PL) properties of metal complexes, a series of gold(I) complexes were synthesized, containing a 7-amino-4-methylcoumarin luminophore. The complexes are comprised of a coumarin moiety featuring different ancillary ligands, specifically N-heterocyclic carbenes, triphenylphosphine, and diphenyl-2-pyridylphosphine. The synthesized gold(I) complexes are luminescent both in solution and the solid state at room temperature and 77 K. Complexes of different nuclearity, i.e., mono-, di- and trinuclear compounds were synthesized. A clear trend between the nuclearity and the quantum yields can be seen. The coumarin dye not only improves the PL properties, but also enhances the luminescence of trinuclear clusters, which are otherwise known to be weak emitters in solution. The optical absorption properties were investigated in detail by quantum chemical calculations.

Phosphine-incorporated Metal-Organic Framework for Palladium Catalyzed Heck Coupling Reaction.

As an emerging material with the potential to combine the high efficiency of homogeneous catalysts and high stability and recyclability of heterogeneous catalysts, metal-organic frameworks (MOFs) have been viewed as one of the candidates to produce catalysts of the next generation. Herein, we heterogenized the highly active mono(phosphine)-Pd complex on surface of UiO-66 MOF, as a catalyst for Suzuki and Heck cross coupling reactions. The successful immobilization of these Pd-monophosphine complexes on MOF surface to form UiO-66-PPh2-Pd was characterized and confirmed via comprehensive set of analytical methods. UiO-66-PPh2-Pd showed high activity and selectivity for both Suzuki and Heck Cross Coupling Reactions. This strategy enabled facile access to mono(phosphine) complexes which are challenging to design and require multistep synthesis in homogeneous systems, paving the way for future MOF catalysts applications by similar systems.

Half-Sandwich Zirconium and Hafnium Amidoborane Complexes: Precursors of Hydride Derivatives.

Half-sandwich zirconium(IV) and hafnium(IV) complexes with amidoborane and hydride ligands have been isolated in the stoichiometric reactions of mono(pentamethylcyclopentadienyl)metal alkyl and amido derivatives with the amine-boranes NHR2BH3 (R2 = H2, Me2, HtBu). Treatment of the tris(trimethylsilylmethyl) complexes [M(η5-C5Me5)(CH2SiMe3)3] with NH3BH3 (3 equiv) gives the seven-coordinate species [M(η5-C5Me5)(NH2BH3)3] (M = Zr (1), Hf (2)) with three κ2N,H-NH2BH3 ligands. The tris(neophyl) [M(η5-C5Me5)(CH2CMe2Ph)3] or tris(dimethylamido) [M(η5-C5Me5)(NMe2)3] derivatives react with NHMe2BH3 (≥3 equiv) to afford bis(dimethylamidoborane) hydride complexes [M(η5-C5Me5)H(NMe2BH3)2] (M = Zr (3), Hf (4)) via thermally unstable [M(η5-C5Me5)(NMe2BH3)3] species. The reaction of [M(η5-C5Me5)(NMe2)3] and NH2tBuBH3 (≥4 equiv) affords analogous mixed amidoborane hydride derivatives [M(η5-C5Me5)H(NHtBuBH3)(NMe2BH3)] (M = Zr (5), Hf (6)) with κ2N,H-NHtBuBH3 and κ3N,H,H-NMe2BH3 ligands. The addition of NHR2BH3 (≥1 equiv) on the mono(dimethylamido) complexes [M(η5-C5Me5)Cl2(NMe2)] in hexane leads to the precipitation of the ionic compounds [(NHR2)2BH2][{M(η5-C5Me5)Cl2}2(μ-H)3] (R2 = Me2, M = Zr (7), Hf (8); R2 = HtBu, M = Zr (9), Hf (10)). Molecular hydride species [Cl2(η5-C5Me5)M(μ-Cl)(μ-H)2M(η5-C5Me5)Cl(NH2tBu)] (M = Zr (11), Hf (12)) could be isolated from mixtures of complexes [M(η5-C5Me5)Cl2(NMe2)] and lower ratios of NH2tBuBH3. The zirconium complex 11 decomposes in solution to give the mononuclear tert-butylamido derivative [Zr(η5-C5Me5)Cl2(NHtBu)] (13) along with other byproducts.

Assessing the activity and stereoselectivity of heterobimetallic Zr/Co complexes catalyzed terminal alkyne dimerization: A DFT study

Early/late heterobimetallic complexes are widely recognized as one of the most effective catalysts for activating coupling reactions. Herein, DFT calculations were used to investigate the specific mechanisms of terminal alkyne dimerization facilitated by two types of Zr/Co complexes: the bis (phosphinoamide) complex B and the mono (phosphinoamide) complex C. In addition, their reaction activities were compared with that of three ligand‐bridged Zr/Co complex A. The results show that the activated mechanisms of the three reactions are similar, all of them contain inner‐ and outer‐sphere mechanisms, and the inner one is the optimal process. Compared to A, the terminal alkyne dimerizations activated by B and C have the lower energy barriers and better selectivity for the E‐isomer; thus, the mono‐ and bis‐(phosphinoamide) Zr/Co complexes are expected to show better activity and selectivity than tris (phosphinoamide) complexes. The stereoselectivity of E‐, Z‐, and gem‐isomers is controlled by the reductive elimination process. The IRI analysis reveals that the selectivity for E‐ and Z‐isomers is influenced due to the notable repulsion and vdW interaction between the second alkyne and the MeNPMe2 ligand. Our work provides a theoretical basis for experimental applications and offers inspiration for the design of high selectivity heterobimetallic complexes.

Cationic Bis(Gold) Indenyl Complexes.

Reaction of (P)AuOTf [P=P(t-Bu)2o-biphenyl] with indenyl- or 3-methylindenyl lithium led to isolation of gold η1-indenyl complexes (P)Au(η1-inden-1-yl) (1 a) and (P)Au(η1-3-methylinden-1-yl) (1 b), respectively, in >65 % yield. Whereas complex 1 b is static, complex 1 a undergoes facile, degenerate 1,3-migration of gold about the indenyl ligand (ΔG≠ 153K=9.1±1.1 kcal/mol). Treatment of complexes 1 a and 1 b with (P)AuNTf2 led to formation of the corresponding cationic bis(gold) indenyl complexes trans-[(P)Au]2(η1,η1-inden-1,3-yl) (2 a) and trans-[(P)Au]2(η1,η2-3-methylinden-1-yl) (2 b), respectively, which were characterized spectroscopically and modeled computationally. Despite the absence of aurophilic stabilization in complexes 2 a and 2 b, the binding affinity of mono(gold) complex 1 a toward exogenous (P)Au+ exceed that of free indene by ~350-fold and similarly the binding affinity of 1 b toward exogenous (P)Au+ exceed that of 3-methylindene by ~50-fold. The energy barrier for protodeauration of bis(gold) indenyl complex 2 a with HOAc was ≥8 kcal/mol higher than for protodeauration of mono(gold) complex 1 a.

Cryptate binding energies towards high throughput chelator design: metadynamics ensembles with cluster-continuum solvation.

A tiered forcefield/semiempirical/meta-GGA pipeline together with a thermodynamic scheme designed with error cancellation in mind was developed to calculate binding energies of [2.2.2] cryptate complexes of mono- and divalent cations. Stable complexes of Na, K, Rb, Ca, Zn and Pb were generated, revealing consistent cation-N lengths but highly variable cation-O lengths and an amine stacking mechanism potentially augmenting the cation size selectivity. Metadynamics, used for searching the high-dimensional potential energy surface, together with a cluster-continuum model for affordable - yet accurate - solvation modeling, enabled the discovery of more stable geometries than those previously reported. Similar solvation energy curve shapes for lone vs. coordinated ions enabled rapid solvation convergence via the cancellation of errors stemming from finite cluster sizes. An R2 of 0.850 vs. experimental aqueous binding energies was obtained, validating this scheme as the backbone of a high-throughput workflow for chelator design.

Preparation of Mono and Bis‐Hydrazino‐Substituted N‐Heterocyclic Carbene Boranes

AbstractWe report the formation of NHC complexes of mono‐ and bis‐hydrazino boranes with N−N−B and N−N−B−N−N chains via the reaction of NHC‐boranes with electrophilic azo reagents. The influence of steric hindrance on the carbene and on the azo reagent has been shown to be crucial for the reactivity. The hydroboration of dissymmetric azo reagents is regioselective only when the latter is sufficiently electronically twisted. Bis‐hydrazino borane complexes with two different hydrazine arms could be obtained via sequential addition.

Platinum(II) complexes containing pyridyl-substituted thiourea dianion and monoanion ligands: Synthesis, structural chemistry, and theoretical investigations

Reactions of cis-[PtCl2(PPh3)2] with the 2-pyridyl-substituted thioureas py(CH2)nNHC(S)NHC6H4R (R = H, OMe or NO2; n = 0, 1 or 2) in methanol with Et3N base, followed by precipitation with water gave good yields of the complexes [Pt{SC(NC6H4R)(N(CH2)npy)}(PPh3)2]. The compounds were characterised 1H NMR, 31P{1H} NMR, FTIR and single crystal X-ray crystallography. The initial NMR investigation indicated the possibility of isomerism in the complexes. 31P{1H} NMR investigations revealed the presence of an initial distal isomer for the dianion complexes, which underwent solution phase isomerization into the proximal isomeric forms of the complexes and/or a mixture of the proximal and distal isomers. The opposite trend was recorded for the monoanionic complex with the formation of an initial proximal isomer and subsequent isomerisation into 1:3 mixture of the distal and proximal isomeric forms of the complex. The degree of isomerization was observed to be related to the difference in energy between the two isomeric forms of the complex and the nature and size of the R substituents in the complex. The molecular geometries of a number of the compounds showed a distorted square-planar geometry defined by a NP2S donor set. The thiourea ligand acts as (N,S)-chelating dianionic ligand so that each donor atom is opposite a phosphane-P atom; a trans-influence is evident on the Pt-P bonds. In each complex, the pyridyl-substituted nitrogen is coordinated to platinum. The cationic complex [Pt{SC(NPh)(NHCH2py)}(PPh3)2]+ was also isolated as its BF4- salt by addition of excess NaBF4 to the reaction mixture. In this complex, the thiourea monoanion coordinates in a distal manner, with the NHCH2py group remote from the platinum centre. Charge-assisted ammonium-NH…N(pyridyl) bonding leads to dimeric aggregates. These, along with the neutral molecules [Pt{SC(Np-C6H4R2)(N(CH2)npy)}(PPh3)2] are assembled into the three-dimensional crystal via weak non-covalent interactions. Characterisation by 31P{1H} NMR spectroscopy showed the presence of several isomeric species in solution.

Transformation of the Cyclo-P5 Middle Deck in [(Cp*Fe)(Cp'''Co)(µ,η5:η4-P5)] upon Functionalization - A Comprehensive Study of Reactivity.

[(Cp*Fe)(Cp'''Co)(µ,η 5 :η 4 -P5)](1) was functionalized by main group nucleophiles and subsequently electrophilically quenched or oxidized. Reacting 1 with group 14 nucleophiles revealed different organo-substituted P5R middle-decks depending on the steric and electronic effects of the used alkali metal organyls (2: R = tBu; 3: R = Me). With group 15 nucleophiles, first isolatable monosubstituted complexes with phosphanides could be obtained as P5 ligands containing exocyclic {PR2} units (4: R = Cy, H; 5: R = Ph). These monoanionic complexes 2-5 were isolated and electrophilic quenching revealed novel types of neutral functionalized polyphosphorus complexes. These complexes bear formal chains of P5R'R'' (6: R' = tBu, R' = Me) in a 1,3-disubstitution pattern or P6R'R''R''' units (7: R' = Cy, R'' = H, R''' = Me; 8: R' = Me, R'' = Ph, R''' = Me) in a 1,1,3-substitution as middle-decks stabilized by one {Cp'''Co} and one {Cp*Fe} fragment. One-electron oxidation of 2, 3 or 5 by AgBF4 gave access to paramagnetic triple-decker complexes bearing P5R middle-decks in various coordination fashions (R = tBu (10), R = PPh2 (12)). For R = Me (11) a dimerization is observed revealing a diamagnetic tetranuclear cluster containing a unique dihydrofulvalene-type P10R2 ligand.

Mixed-Valence Conductors from Ni Bis(diselenolene) Complexes with a Thiazoline Backbone.

Highly conducting, mixed-valence, multi-component nickel bis(diselenolene) salts were obtained by electrocrystallization of the monoanionic species [Ni(Me-thiazds)2]-1 (Me-thiazds: N-methyl-1,3-thiazoline-2-thione-4,5-diselenolate), with 1:2 and 1:3 stoichiometries depending of the counter ion used (Et4N+ and nBu4N+ vs Ph4P+, respectively). This behavior strongly differs from that of the corresponding monoanionic dithiolene complexes whose oxidation afforded the single component neutral species. This provides additional rare examples of mixed-valence conducting salts of nickel diselenolene complexes, only known in two examples with the dsit (1,3-dithiole-2-thione-4,5-diselenolate) and dsise (1,3-dithiole-2-selone-4,5-diselenolate) ligands. The mixed-valence salts form highly dimerized or trimerized bi- and trimetallic units, rarely seen with such nickel complexes. Transport measurements under a high pressure (up to 10 GPa) and band structure calculations confirm the semiconducting character of [Ph4P][Ni(Me-thiazds)2]3 and the quasi metallic character of [Et4N][Ni(Me-thiazds)2]2 and [NBu4]x[Ni(Me-thiazds)2]2 salts (0 < x < 1).

Ionic mononuclear [Fe] and heterodinuclear [Fe,Ru] bis(diphenylphosphino)alkane complexes: Synthesis, spectroscopy, DFT structures, cytotoxicity, and biomolecular interactions

Iron(II) and Ru(II) half-sandwich compounds encompass some promising pre-clinical anticancer agents whose efficacy may be tuned by structural modification of the coordinated ligands. Here, we combine two such bioactive metal centres in cationic bis(diphenylphosphino)alkane-bridged heterodinuclear [Fe2+, Ru2+] complexes to delineate how ligand structural variations modulate compound cytotoxicity. Specifically, Fe(II) complexes of the type [(η5–C5H5)Fe(CO)2(κ1–PPh2(CH2)nPPh2)]{PF6} (n = 1–5), compounds 1–5, and heterodinuclear [Fe2+, Ru2+] complexes, [(η5–C5H5)Fe(CO)2(μ–PPh2(CH2)nPPh2))(η6–p–cymene)RuCl2]{PF6} (n = 2–5) (compounds 7–10), were synthesized and characterised. The mononuclear complexes were moderately cytotoxic against two ovarian cancer cell lines (A2780 and cisplatin resistant A2780cis) with IC50 values ranging from 2.3 ± 0.5 μM to 9.0 ± 1.4 μM. For 7–10, the cytotoxicity increased with increasing Fe⋅⋅⋅Ru distance, consistent with their DNA affinity. UV–visible spectroscopy suggested the chloride ligands in heterodinuclear 8–10 undergo stepwise substitution by water on the timescale of the DNA interaction experiments, probably affording the species [RuCl(OH2)(η6-p-cymene)(PRPh2)]2+ and [Ru(OH)(OH2)(η6-p-cymene)(PRPh2)]2+ (where PRPh2 has R = [−(CH2)5PPh2–Fe(C5H5)(CO)2]+). One interpretation of the combined DNA-interaction and kinetic data is that the mono(aqua) complex may interact with dsDNA through nucleobase coordination. Heterodinuclear 10 reacts with glutathione (GSH) to form stable mono- and bis(thiolate) adducts, 10-SG and 10-SG2, with no evidence of metal ion reduction (k1 = 1.07 ± 0.17 × 10−1 min−1 and k2 = 6.04 ± 0.59 × 10−3 min−1 at 37 °C). This work highlights the synergistic effect of the Fe2+/Ru2+ centres on both the cytotoxicity and biomolecular interactions of the present heterodinuclear complexes.

Theoretical study of the electronic structure of the complexes of gold, silver, and copper mono- and bimetallic nanoclusters decorated on graphitic carbon nitride (g-C3N4): DFT and TD-DFT studies of photocatalytic activity

In this study, metal-decorated g-C3N4 complexes are investigated using the DFT method. It is found that metal cluster decoration results in a better light absorption region, reduced band gap, and improved HOMO and LUMO separation compared to g-C3N4.

Pd(II), Ni(II), and Cu(II) complexes of α,α'-ditolylmethanone dipyrroethene.

Dipyrromethenes containing two pyrrole rings connected by one meso-carbon are versatile monoanionic bidentate ligands and form coordination complexes with many metals/nonmetals/metalloids. Dipyrroethenes containing one additional meso-carbon compared to dipyrromethenes have more space between coordinating pyrrole nitrogens and provide a good coordination environment but have not been explored as ligands in coordination chemistry. Dipyrroethenes are dianionic bidentate ligands and by suitable modifications, the coordination environment of dipyrroethenes can be changed further. Herein, we successfully synthesized α,α'-ditolylmethanone dipyrroethene which is a bipyrrolic tetradentate ligand with an ONNO ligand core and used it for the synthesis of novel Pd(II), Ni(II), and Cu(II) metal complexes by treating it with respective metal salts in CH2Cl2/CH3OH at room temperature. The X-ray crystallographic structure of the metal complexes showed that the M(II) ion was coordinated to the ONNO atoms of the ligand in a perfect square planar geometry. The NMR studies of Pd(II) and Ni(II) complexes also supported the highly symmetric nature of the metal complexes. The absorption spectra of the metal complexes showed strong bands in the region of 300-550 nm. The electrochemical studies of metal complexes revealed that only ligand-based oxidation and reduction were observed. The DFT and TD-DFT studies were in agreement with the experimental observations. Our preliminary studies indicated that the Pd(II) complex can be used as a catalyst for the Fujiwara-Moritani olefination reaction.

α-Diimine Cisplatin Derivatives: Synthesis, Structure, Cyclic Voltammetry and Cytotoxicity

Three new Pt(II) complexes [(dpp-DAD)PtCl2] (I), [(Mes-DAD(Me)2)PtCl2] (II) and [(dpp-DAD(Me)2)PtCl2] (III) were synthesized by the direct reaction of [(CH3CN)2PtCl2] and corresponding redox-active 1,4-diaza-1,3-butadienes (DAD). The compounds were isolated in a single crystal form and their molecular structures were determined by X-ray diffraction. The purity of the complexes and their stability in solution was confirmed by NMR analysis. The Pt(II) ions in all compounds are in a square planar environment. The electrochemical reduction of complexes I-III proceeds in two successive cathodic stages. The first quasi-reversible reduction leads to the relatively stable monoanionic complexes; the second cathodic stage is irreversible. The coordination of 1,4-diaza-1,3-butadienes ligands with PtCl2 increases the reduction potential and the electron acceptor ability of the DAD ligands. The synthesized compounds were tested in relation to an adenocarcinoma of the ovary (SKOV3).

Phosphorescent cyclometalated iridium(III) complexes with mono‐, di‐, and tetranuclear as two channel probes to light up the nuclei of living cells

By altering the reaction ratio of precursor Ir2(ppy)4Cl2 and bridging ligand of 4,4‐bipyridine (bpy), a series of phosphorescent cyclometalated iridium(III) complexes of mono‐, di‐, and tetranuclear have been successfully obtained and characterized for the first time. The dissociation of bpy ligand can be accelerated by light irradiation or placing these complexes in glutathione (GSH) abundant aqueous solution, bpy releasing rate follows the order Ir1 &gt; Ir2 &gt; Ir3 &gt; Ir4, and with an addition of histidine, a significant blue shift from orange to green phosphorescence was observed. Herein, the cellular dissociation of bpy can be monitored by an orange‐to‐green phosphorescent blue shift, and nuclei of living cells can be lighted up by a set of probes with two phosphorescent channels, and subsequent cellular uptake translocation from cytoplasm to nucleus of Ir complexes could be observed by confocal imaging within 4 h. Besides, the changes of cellular phosphorescence intensity in two fluorescent channels recorded by flow cytometry could reflect different speed of bpy release in human normal and cancer cells. Besides, Ir1–4 exert significant anticancer effect in the dark with low photocytotoxicity, by effectively inducing reactive oxygen species generation, mitochondrial membrane potential depletion, and interacting with biomolecules, and they eventually induce late apoptosis of Hela cell.

Novel complexes derived from tetra-(2-pyridyl) pyrazine (TPPZ): Spectroscopic, DFT, molecular docking, and biological studies

In continuation of our previous study to synthesize a series of novel complexes isolated from polypyridyl-azine as the main ligand (tetra-(2-pyridyl) pyrazine (TPPZ)) or in the presence of co-ligand, mono and polymetallic chelates such as [Cu(TPPZ)(SCN)Cl] (1), [Ag2(TPPZ)(NO3)2]. H2O (2) and [(OsO2)3(TPPZ)].2·5H2O.C2H4Cl2(3) were synthesized and characterized. In addition, a series of VO2+ complexes, [(VO)2(TPPZ)OH(SO4)0.5][(VO)4(OH)10].H2O (4), [(VO)2(TPPZ)EtOH.SO4][(VO)2(SO4)3dipy].12.H2O (5), and [VO(acac)(HTPPZ)]2Cl.CH3CN (6) was investigated in detail. Crystal data of Cu(II) complex (1) indicates monoclinic, P21/a, a = 10.6983(3) Å, b = 19.9128(9) Å, c = 11.5958(5) Å, α = γ = 90.00° ≠ β = 108.819(3), V = 2338.2 (2) Å3 and Z = 4. The chelates were characterized by elemental analyses and spectral (FTIR, electronic, and EPR) studies. Also, cyclic voltammetry studies were investigated. The modeling study of TPPZ and their complexes were approved with the Gaussian09 program in DFT/B3LYP. Os4+ and VO2+-mono complexes show superiority as promising anticancer agent for the PC-3 cell lines. Molecular modeling is utilized to examine the molecular characteristics and binding propensity of ligands and their complexes with 3s7s and 3IG7 protein and to signify inhibitory strength.

Interaction of the Fungal Metabolite Harzianic Acid with Rare-Earth Cations (Pr3+, Eu3+, Ho3+, Tm3+).

Rare-earth elements (REEs) are in all respect a class of new contaminants that may have toxic effects on organisms and microorganisms and information on their interactions with natural ligands should be of value to predict and control their diffusion in natural environments. In the current study, we investigate interactions of tripositive cations of praseodymium, europium, holmium, and thulium with harzianic acid (H2L), a secondary metabolite produced by selected strains of fungi belonging to the Trichoderma genus. We applied the same techniques and workflow previously employed in an analogous study concerning lanthanum, neodymium, samarium, and gadolinium tripositive cations. Therefore, in the current study, HPLC-ESI-HRMS experiments, circular dichroism (CD), and UV-Vis spectrophotometric absorption data, as well as accurate pH measurements, were applied to characterize bonding interactions between harzianic acid and Pr3+, Eu3+, Ho3+, and Tm3+ cations. Problems connected to the low solubility of harzianic acid in water were overcome by employing a 0.1 M NaClO4/(CH3OH + H2O 50/50 w/w) mixed solvent. For Pr3+, Ho3+, and Tm3+, only the mono complexes PrL+, HoL+, and TmL+ were detected and their formation constant determined. Eu3+ forms almost exclusively the bis complex for which the corresponding formation constant is reported; under our experimental conditions, the mono complex EuL+ is irrelevant. Combining the results of the present and previous studies, a picture of interactions of harzianic acid with rare-earth cations extending over 8 of the 17 REEs can be composed. In order to complement chemical information with toxicological information, a battery of bioassays was applied to evaluate the effects of praseodymium, europium, holmium, and thulium tripositive cations on a suite of bioindicators including Aliivibrio fischeri (Gram-negative bacterium), Raphidocelis subcapitata (green alga), and Daphnia magna (microcrustacean), and median effective concentration (EC50) values of Pr3+, Eu3+, Ho3+, and Tm3+ for the tested species were assessed.

Solution Equilibrium Studies on Salicylidene Aminoguanidine Schiff Base Metal Complexes: Impact of the Hybridization with L-Proline on Stability, Redox Activity and Cytotoxicity.

The proton dissociation processes of two tridentate salicylidene aminoguanidine Schiff bases (SISC, Pro-SISC-Me), the solution stability and electrochemical properties of their Cu(II), Fe(II) and Fe(III) complexes were characterized using pH-potentiometry, cyclic voltammetry and UV-visible, 1H NMR and electron paramagnetic resonance spectroscopic methods. The structure of the proline derivative (Pro-SISC-Me) was determined by X-ray crystallography. The conjugation of L-proline to the simplest salicylidene aminoguanidine Schiff base (SISC) increased the water solubility due to its zwitterionic structure in a wide pH range. The formation of mono complexes with both ligands was found in the case of Cu(II) and Fe(II), while bis complexes were also formed with Fe(III). In the complexes these tridentate ligands coordinate via the phenolato O, azomethine N and the amidine N, except the complex [Fe(III)L2]+ of Pro-SISC-Me in which the (O,N) donor atoms of the proline moiety are coordinated beside the phenolato O, confirmed by single crystal X-ray crystallographic analysis. This binding mode yielded a stronger Fe(III) preference for Pro-SISC-Me over Fe(II) in comparison to SISC. This finding is also reflected in the lower redox potential value of the iron-Pro-SISC-Me complexes. The ligands alone were not cytotoxic against human colon cancer cell lines, while complexation of SISC with Cu(II) resulted in moderate activity, unlike the case of its more hydrophilic counterpart.