ML Complexes Research Articles

Thermodynamic radii of lanthanide ions derived from metal–ligand complexes stability constants

Here, we describe two sets of thermodynamic ionic radii (r1 and r2) of lanthanide ions derived from the analysis of large set of the stability constants logβ1 and logβ2 of the ML and ML2 complexes of lanthanide ions M (from Ce3+ to Lu3+) with organic ligands (L) in water. It has been demonstrated that the stability constants of two metals Mi and Mj with a given ligand L are related by simple equations logβ1j = r1i/r1j.logβ1i and logβ2j = r2i/r2j.logβ2i which formally correspond to purely electrostatic interactions between spherical cations with organic molecule. Predictive performance of these equations was assessed in fivefold cross-validation procedure. The standard deviation (s) of predictions varies from 0.3 to 1.0 for logβ1 and from 0.4 to 1.2 for logβ2 as a function of the difference of Shannon ionic radii (Δrij) of Mi and Mj: s1 = 0.27 + 4.25Δrij for logβ1 and s2 = 0.39 + 5.16Δrij for logβ2. The new radii r1 and r2 steadily decrease across the Ln series, i.e., they follow the same trend as Shannon effective radii of lanthanide ions. The calculations were performed using experimental data on 2854 logβ1 values for 445 organic ligands and 947 logβ2 values for 156 organic ligands in the complexes with 13 metals.

Search for conformation of thiosemicarbazone reagents and their complexes with metals by using Monte Carlo and docking simulation

In this study, the conformation of ML2 complexes of new thiosemicarbazone reagents with metal cations Cd2+, Ni2+, Cu2+, Hg2+, Pb2+, Mn2+, and Zn2+ is investigated. The methods include MM+ and PM3 calculations with the Monte Carlo techniques using the Metropolis algorithm in the temperature range of 298–473 K. The initial selection conformation was carried out randomly after 15 repeated conformations, and 30 conformations were rejected. The conformations were chosen to change by changing the torsional-dihedral angles at the position of the metal cation associated with the donor atoms N and S of the thiosemicarbazone reagents. This was performed by randomly changing the dihedral angles to create new structures, and then the energy values of these angles were minimized with the PM3 and MM+ calculation. The lowest suitable energies were accumulated, while high- or duplicate-energy structures were discarded. The docking method was also employed to screen the most suitable metal-thiosemicarbazone complexes that bind to the active site on the SARS-CoV-2 protein. The docking method enabled us to choose the molecular conformation of the most significant Cd2+-thiosemicarbazone complex.

Performance improvement of space diversity technique using space time block coding for time varying channels in wireless environment

Performance improvement of space diversity technique using space time block coding for time varying channels in wireless environment

Studies of a Tripodal Biomimetic Siderophore Analog: An Efficient Encapsulation for Fe(III) Ion

A new tris-(2-aminoethyl)amine (TREN) capped tripodal Schiff base ligand has been developed by mimicking structural features of a natural siderophore, Bacillibactin, by substituting the catechol units with salicylaldehyde and employing amino acid as a spacer. Synthesis of the ligand N-[2-[bis[2-[[2-[(2-hydroxyphenyl)methylamino]acetyl] amino]ethyl]amino]ethyl]-2-[(2-hydroxyphenyl)methylamino]acetamide(TRENglySAL) includes condensation of salicylaldehyde and amino acid (glycine) followed by an in-situ reduction of the produced Schiff base, followed by further condensation with TREN. The complexation behavior of the ligand with Fe(III) has been investigated by potentiometric and UV-Vis spectrophotometric method at temperature 25±1oC and 0.1 M ionic strength. Seven protonation constants were obtained of the ligand: three each for secondary amine and phenolic protons and one for tertiary nitrogen of capping TREN moiety. The formation constants (log β11n) of different complex species MLH3, MLH2, MLH, ML and MLH-1 are found to be 35.15, 32.09, 27.91, 25.32 and 17.32 respectively. These results indicate that the ligand is an excellent iron-binding chelator. Significant electronic spectral variations during complex formation at higher pH also provide a scope for the ligand to act as an optical pH sensor towards Fe (III) metal ion in biological systems. Structures of the ligand and metal complexes are proposed through experimental findings along with the theoretical semi-empirical PM3 calculation. The theoretical spectroscopic results are found to be comparable with the experimental finding.

Experimental and DFT studies on complexation of uranyl with N-(2-Hydroxyethyl)iminodiacetic acid in aqueous medium

The nuclear decontaminating agents such as ethylenediamminetetraacetic acid (EDTA), picolinic acid, nitrilotriacetic acid (NTA) and citric acid are co-disposed with the nuclear waste at the storage sites. The thermal, catalytic and radiolytic degradation of this organic waste results in the formation of N-(2-Hydroxyethyl)iminodiacetic acid (HEIDA-H2) as one of the major degradation product. The knowledge on chemical speciation and aqueous thermodynamics of radionuclides in presence of organic chelates is a key input to the codes for framing safe and strategic disposal of radioactive waste. Present work aimed at the determination of thermodynamic parameters (log K, ΔG, ΔH and ΔS), speciation diagram, spectroscopic properties and structural analysis for UO22+-HEIDA complexes in aqueous solution. UO22+ forms ML and ML2 type of species with HEIDA as determined by potentiometry and further corroborated by absorption and luminescence spectroscopy. The Electrospray ionization mass spectrometry (ESI-MS) studies also identified the ML and ML2 complexes. In addition, the difference in the complexation behavior of UO22+ with HEIDA and IDA; which differ by hydroxyethyl substitution on imino nitrogen is explained on the basis of thermodynamic parameters. The 1:1 UO22+-HEIDA complex is exothermic formation while the 1:1 UO22+-IDA complexes are endothermic formations. The differences in enthalpy and entropy of formations are interpreted to reveal the role of hydroxyethyl group on UO22+- HEIDA complexation. NMR studies are carried to elucidate the structures of 1:1 and 1:2 UO22+-HEIDA complexes. The comparison of log K values with structurally similar ligands and NMR spectroscopic studies suggested the tridentate nature for HEIDA. The hydroxyethyl group was found to be uncoordinated with UO22+. The theoretical studies showed the indirect participation of hydroxyethyl group on complexation by charge polarization and by steric influence on coordinating groups.

Composition, stability and fluorescence properties of metal complexes of an aza-flavonol analog 1-methyl-2-phenyl-3-hydroxy-4(1H)-quinolone in aqueous solution

Aza-flavonols are compounds containing the 3-hydroxy-4(1H)-quinolone moiety, a unique scaffold with applications expanding from fluorescent probes and bioimaging to potential metal-related pharmaceutical drugs. Compositions and stability constants of metal complexes of an aza-flavonol 1-methyl-2-phenyl-3-hydroxy-4(1H)-quinolone (LH) in aqueous micellar medium of hexadecyltrimethylammonium bromide were established by fluorescence and spectrophotometric titrations of LH in the presence of metal ions of different type at variable pH. Strong binding with quenching of ligand fluorescence was observed for Cu2+, Fe2+/3+ and Pb2+ cations. The complexation with Zn2+ induced strong fluorescence enhancement in ZnL+ complex and smaller enhancement in ZnL2 complex. Al3+, Ga3+ and Me2Sn2+ cations induced strong fluorescence enhancement in 1:1 ML complexes, but quenching in ML2 complexes. Together with the relevant literature data these results indicate that the quenching effect in 1:2 complexes along with strong fluorescence enhancement in respective 1:1 complexes is a general phenomenon for 3-hydroxypyranone and 3-hydroxypyridinone ligands. The quantum mechanical Natural Transition Orbital analysis of ground and excited states of LH, AlL2+ and AlL2+ species reveals that the fluorescence of AlL2+ complex is quenched by an internal electron transfer process, which is absent in the 1:1 AlL2+ complex. The results emphasize strong dependence of the coordination induced fluorescence changes on the complex composition.

Stereochemistry of Hexacoordinated Zn(II), Cu(II), Ni(II), and Co(II) Complexes with Iminodiacetamide Ligands.

Metal complexes of iminodiacetamide (imda) ligands and metal ions Zn(II), Cu(II), Ni(II), and Co(II) were prepared using eight imda ligands (L1-L8) substituted with groups of different steric and electronic properties on the central amine N atom (H atom, methyl, isopropyl, and benzyl) and the para position of the phenyl rings (nitro and dimethylamino). The effect of these substituents on the stoichiometry (ML and ML2), geometry, and stereochemistry (mer, trans-fac, cis-fac) of the complexes was studied in the solid state, in solution, and by density functional theory calculations. Single-crystal and powder X-ray diffraction, thermogravimetry, and IR spectroscopy showed that in the solid state imda ligands preferentially form trans-fac ML2 complexes, with the exception of the cis-fac complex 7Zn. NMR spectroscopy of diamagnetic Zn(II) and paramagnetic Co(II) complexes revealed the formation of both ML and ML2 complexes in solution, which was also confirmed by UV-vis titrations. Variable-temperature NMR was used to study the effect of the substituent on the central amine N atom on the Zn-N bond strength and nitrogen inversion. The relative stabilities of the isomers were rationalized by computations and the optimized structures used for geometry analysis.

Dissonance Between Human and Machine Understanding

Complex machine learning models are deployed in several critical domains including healthcare and autonomous vehicles nowadays, albeit as functional blackboxes. Consequently, there has been a recent surge in interpreting decisions of such complex models in order to explain their actions to humans. Models which correspond to human interpretation of a task are more desirable in certain contexts and can help attribute liability, build trust, expose biases and in turn build better models. It is therefore crucial to understand how and which models conform to human understanding of tasks. In this paper we present a large-scale crowdsourcing study that reveals and quantifies the dissonance between human and machine understanding, through the lens of an image classification task. In particular, we seek to answer the following questions: Which (well performing) complex ML models are closer to humans in their use of features to make accurate predictions? How does task difficulty affect the feature selection capability of machines in comparison to humans? Are humans consistently better at selecting features that make image recognition more accurate? Our findings have important implications on human-machine collaboration, considering that a long term goal in the field of artificial intelligence is to make machines capable of learning and reasoning like humans.

Synthesis, spectroscopic characterization and DNA binding studies of Cu(II) complex of Schiff base containing benzothiazole moiety

A Schiff base ligand L has been synthesized by the condensation of thiophene-2-carbaldehyde and 2-amino-6-methylbenzothiazole. It has been characterized by elemental analysis, Infrared (IR), 1H NMR and mass spectrometry. Copper (II) complex, ML2 has been synthesized by the reacting ligand L and Copper (II) acetate in 2:1 molar ratio. The Cu(II) complex was characterized by elemental analysis, molar conductance, electronic spectrum, IR and electronic paramagnetic resonance spectrum. TGA has been done to check the thermal stablity of Cu(II) complex. Spectroscopic studies revealed that ligand L binds with the Cu(II) ion as bidentate fashion. On the basis of spectral studies, a distored octahedral geometry has been assigned for Cu(II) complexof ligand L. The DNA binding studies of Cu(II) complex ML2 have been investigated by UV-vis absorption and fluorescence spectroscopy. The binding mode of ML2 with CT-DNA could be assigned as intercalation of the metal complex between DNA base pairs.

Theoretical study of metal ion impact on geometric and electronic properties of terbutaline compounds

Geometric configuration, UV–Vis absorption spectra, and reactivity of the eight common metal ions (M) with the precursor (L) of terbutaline were calculated by density functional theory (B3LYP) at the level of 6−311+G(d,p) (M = Mg, Ca, Mn, Fe, Ni, Co, Cu, Zn). The binding energy of the complex and the analysis of the natural bond orbital show that the L can bind to the M(II) ion to form a stable complex ML. The results of time-dependent density functional analysis (TD DFT) show that the UV–Vis absorption spectra of the other seven ML molecules have a larger red shift than L, except that ZnL is almost invariant. The density functional activity index (DFRT) and the energy decomposition analysis (EDA) shows that the electrostatic effect is the main contribution of the complex ML, and the stereo-effect or exchange-related energy also has certain contribution.

Aminomethylene-Phosphonate Analogue as a Cu(II) Chelator: Characterization and Application as an Inhibitor of Oxidation Induced by the Cu(II)-Prion Peptide Complex.

Recently, we reported on a series of aminomethylene-phosphonate (AMP) analogues, bearing one or two heterocyclic groups on the aminomethylene moiety, as promising Zn(II) chelators. Given the strong Zn(II) binding properties of these compounds, they may find useful applications in metal chelation therapy. With a goal of inhibiting the devastating oxidative damage caused by prion protein in prion diseases, we explored the most promising ligand, {bis[(1H-imidazol-4-yl)methyl]amino}methylphosphonic acid, AMP-(Im)2, 4, as an inhibitor of the oxidative reactivity associated with the Cu(II) complex of prion peptide fragment 84-114. Specifically, we first characterized the Cu(II) complex with AMP-(Im)2 by ultraviolet-visible spectroscopy and electrochemical measurements that indicated the high chemical and electrochemical stability of the complex. Potentiometric pH titration provided evidence of the formation of a stable 1:1 [Cu(II)-AMP-(Im)2]+ complex (ML), with successive binding of a second AMP-(Im)2 molecule yielding ML2 complex [Cu(II)-(AMP-(Im)2)2]+ (log K' = 15.55), and log β' = 19.84 for ML2 complex. The CuN3O1 ML complex was demonstrated by X-ray crystallography, indicating the thermodynamically stable square pyramidal complex. Chelation of Cu(II) by 4 significantly reduced the oxidation potential of the former. CuCl2 and the 1:2 Cu:AMP-(Im)2 complex showed one-electron redox of Cu(II)/Cu(I) at 0.13 and -0.35 V, respectively. Indeed, 4 was found to be a potent antioxidant that at a 1:1:1 AMP-(Im)2:Cu(II)-PrP84-114 molar ratio almost totally inhibited the oxidation reaction of 4-methylcatechol. Circular dichroism data suggest that this antioxidant activity is due to formation of a ternary, redox inactive Cu(II)-Prp84-114-[AMP-(Im)2] complex. Future studies in prion disease animal models are warranted to assess the potential of 4 to inhibit the devastating oxidative damage caused by PrP.

Cu(ii) and Zn(ii) complexes with a poly-functional ligand derived from o-vanillin and thiophene. Crystal structure, physicochemical properties, theoretical studies and cytotoxicity assays against human breast cancer cells

New ML2 complexes were extensively characterized showing stability in solution and promising anti-tumoral results, particularly for CuL2.

Mononuclear Schiff Base Complexes Derived from 5-Azophenylsalicylaldehyde with Co(II), Ni(II) Ions: Synthesis, Characterization, Electrochemical Study and Antibacterial Properties

In the present research, 1,2-di[N-2-phenylthio-5-azophenylsalicylidene]ethane (H2L1, 1,3-di[N-2-phenylthio-5-azophenylsali-cylidene]propane(H2L2) and 1,4-di[N-2-phenylthio-5-azophenylsalicylidene]butane (H2L3) were synthesized. ML1,ML2 and ML3 complexes were prepared through the reaction of H2L1,H2L2 and H2L3 with Ni(II) and Co(II) acetate salts. The prepared ligands and their complexes were characterized with FT-IR, 1H-NMR, elemental analysis, conductivity and magnetic measurements, ESI-mass, UV-Vis spectroscopy and cyclic voltammetry. The complexes had monomeric structure according to the mass spectral data. All of the complexes had a six-coordinated octahedral geometry. The electrochemical behavior of the ligands, Ni(II) and Co(II) complexes was investigated by CV in DMF under argon atmosphere. The results show that the coordination of Ni(II) causes the ligands to be deactivated. The voltammogram of Co(II) complexes shows that the reduction of CoL1 is harder than CoL3 and CoL2 is inactive. Their antibacterial activity was investigated and the complexes exhibited better antibacterial activity than the free ligands against selective bacteria. Keywords: Schiff base complexes, 5-azophenylsalicylaldehyde, electrochemical study, antibacterial properties.

Ligand exchange method for determination of mole ratios of relatively weak metal complexes: a comparative study

Ligand exchange method is introduced as an alternative to Job’s and mole ratio methods for studying the stoichiometry of relatively weak metal complexes in solutions. The method involves adding varying amounts of a ligand (L) to an excess constant amount of a colored complex (MX) with appropriate stability and molar absorptivity. The absorbance of each solution is measured at the λmax of the initial complex, MX, and plotted against the concentration of the studied ligand, L. If the newly formed complex ML does not absorb at the λmax of the initial complex, then attenuation of the absorbance of the initial complex on adding varying quantities of the investigational ligand gives an inverse calibration line that intersects with the calibration curve of initial complex at a given point. If a line parallel to the ordinate is drawn from this point to the x-axis, the ratio of the two parts of the x-axis to the left and to the right (α/β) gives the metal to ligand molar ratio in the complex formed, ML. The new method has been applied to the study of the composition of iron (III) complexes with three bisphosphonate drugs: alendronate, etidronate, and ibandronate. The mole ratio was found to be 1:1 with the three investigated bisphosphonates and results were further confirmed by Job’s and mole ratio methods. The ligand exchange method is simpler, quicker, easier to perform and more accurate than Job’s and mole ratio methods for studying weak and relatively weak complexes.

Topoisomerase I-DNA Covalent Complexes in Myeloid Malignancies: A Potential Biomarker for Topoisomerase I Inhibitor Sensitivity

Introduction: Topoisomerase I is a nuclear enzyme that relaxes torsional strain in DNA by nicking one DNA strand, allowing rotation, then resealing the DNA backbone. This is an important enzyme in replication and transcription, and therefore has been targeted by anti-cancer agents such as camptothecins. These agents intercalate into DNA at the topoisomerase I active site and inhibit the religation step catalyzed by the enzyme, causing increased topoisomerase I-DNA complexes that impede advancing replication forks or transcription complexes, leading to DNA damage and cell death. Platinating agents also stabilize topoisomerase I-DNA covalent complexes. The topotecan/carboplatin combination has recently shown promise in combination with the PARP inhibitor veliparib in aggressive and transformed myeloproliferative neoplasms (MPNs) and chronic myelomonocytic leukemia (K Pratz et al., Clin Cancer Res. 23:899, 2017). Given that both classes of agents have a narrow therapeutic window, it is important to try to predict the sensitivity/resistance of these agents in malignancies such as acute myeloid leukemia (AML) and transformed MPNs. Some of mechanisms of drug resistance that have been described are decreased numbers of drug-stabilized topoisomerase I-DNA complexes due to drug efflux, diminished topoisomerase I expression or topoisomerase I mutation. Thus, being able to detect and quantify these DNA-protein complexes may provide insight into drug sensitivity.Methods: Using a unique monoclonal antibody that detects topoisomerase I-DNA covalent complexes (A. Patel et al., Nucleic Acids Res. 44:2816, 2016), immunofluorescence techniques were used to quantify these topoisomerase I-DNA complexes in AML cell lines (SET2, HEL, K562, U937, ML2, MV-4-11, THP1, HL60, ML1, and Molm13) and clinical AML samples. To verify the fidelity of the anti-topoisomerase I-DNA covalent complex antibody (TopIcc), siRNA knockdown methods were utilized with confirmatory immunofluorescence and Western blotting. Slot blots were additionally used to assess the presence of these complexes in AML cell lines. Western blots were performed to assess topoisomerase I levels in AML cell lines. Topotecan drug sensitivity analysis was performed by using an MTS assay.Results: With treatment of the topoisomerase I inhibitor, topotecan, there was an increase in the percentage of leukemia cells positive for the topoisomerase I-DNA covalent complexes. The degree of increase in complexes varied across cell lines and patient samples. To ensure we were detecting TopIcc by immunofluorescence, we performed a topoisomerase-I siRNA knockdown to confirm the specificity of the antibody for TopIcc's. Slot blots on multiple AML cell lines confirmed the presence of topoisomerase-DNA covalent complexes. The Western blot of all the AML cell lines, ordered from low to high TopIcc revealed increasing amounts of topoisomerase I. The MTS assay revealed lower topotecan IC50 values in three of the cell lines with higher complex formation, including Molm13, ML1 and ML2 (IC50 6-8 nM compared to 13-46 nM in the other cell lines).Conclusions: Based on recent clinical results, there has been renewed interested in topoisomerase I inhibitors, especially for aggressive and transformed MPNs. Topoisomerase I-DNA complex repair/downregulation has been a hallmark of drug resistance to topoisomerase I inhibitors. Therefore, detecting and quantifying these complexes in treated samples has been hypothesized to provide insight into the drug sensitivity, which is particularly important in camptothecins and platinating agents given their narrow therapeutic windows. Immunodetection techniques using an anti-TopIcc antibody may help predict sensitivity of AML to topoisomerase I inhibitors and will be used as a correlative biomarker study in an upcoming phase II randomized study of topotecan/carboplatin with or without veliparib or placebo in advanced myeloproliferative disorders and chronic myelomonocytic leukemia (ClinicalTrials.gov NCT03289910). DisclosuresPratz:AbbVie: Consultancy, Research Funding; Agios: Research Funding; Astellas: Consultancy, Research Funding; Boston Scientific: Consultancy; Millenium/Takeda: Research Funding. Kaufmann:Mayo Clinic: Patents & Royalties: Co-inventor on a patent held by Mayo Clinic for the use of the anti-TOP1cc antibody as a diagnostic reagent.

Probing Redox Noninnocence of Copper and Zinc Bis‐pyridylpyrrolides

A series of complexes of divalent copper and zinc carrying two systematically substituted 2,2′‐pyridylpyrrolide ligands, designated Ln to indicate the number of pyrrole CF3 substituents (n = 0, 1, 2), have been studied for their geometric and electronic structures. These reveal the pyridylpyrrolide to be a highly anisotropic nitrogen donor ligand which distorts ML2 complexes away from both planar and tetrahedral structures. Characterization includes CV and mass spectrometry, which show access to cations beyond conventional maximum metal oxidation states. EPR studies at multiple microwave frequencies of the series Cu(Ln)2 gave insight into the substituent effect on frontier orbital composition of these complexes. While Cu(L2)2 exhibited EPR spectra that were roughly comparable to those for typical, tetragonally distorted CuII complexes with the SOMO having dx²–y² character, the other two complexes exhibited more unusual EPR spectra indicative of their distinct geometry, reminiscent of equatorially‐vacant trigonal bipyramidal hybridization and fully consistent with the X‐ray crystal structure determinations of all three Cu(Ln)2. DFT calculations map both geometric and delocalization changes upon redox change, and show the relevance of oxidation at the pyrrolide donors rather than at the metal.

Synthesis, characterization, nucleic acid interaction and photoluminescence properties of (E)-(2-(2-hydroxybenzylidene)hydrazinyl)(pyridin-4-yl)methaniminium Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes

Five new metal complexes ML2 [Where, M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) and L is (E)-(2-(2-hydroxybenzylidene)hydrazinyl)(pyridin-4-yl)methaniminium)] have been synthesized and characterized by elemental analysis, molar conductivity, magnetic moment and spectroscopy (UV–Vis, FT-IR and ESR) studies. The spectral data showed that ligand is tridentating coordination through azomethine nitrogen, methaniminium nitrogen and phenolic oxygen. DNA binding studies of transition metal complexes 1–5 were examined by electronic absorption spectroscopic techniques. All the metal complexes 1–5 have shown hypochromism. Photoluminescence activity of ligand L and its metal complexes 1–5 were carried out. The ligand L showed weak emission in π→π* and n→π* excitation. The complexes 1, 2 and 4 didn't exhibited noticeable emission in three different excitation, complex 3 showed enhanced emission in π→π* and n→π* excitation and complex 5 showed enhanced emission in LMCT.

Spectral, thermal and biological characterization of complexes with a Schiff base bearing triazole moiety as potential antimicrobial species

A novel series of complexes ML(ClO4)·nH2O (M: Co, Ni, Cu, Zn; HL: 2-[(E)-(1H-1,2,4-triazol-3-ylimino)methyl]phenol) have been synthesized and characterized as mononuclear species. The features of complexes have been assigned from microanalytical, FAB-MS, IR, UV–Vis-NIR, EPR and magnetic data. The IR spectra indicate the chelate behaviour of Schiff base and the perchlorate presence either as free ion or as ligand. Electronic and magnetic data are consistent with hexa-coordination of Co(II) and Ni(II) and penta-coordination for Cu(II) ions in complexes. The simultaneous TG-DSC/MS measurements evidenced processes as water (hydration or coordination) elimination, perchlorate decomposition as well as Schiff base both fragmentation and oxidative degradation. The in vitro screening of the antimicrobial behaviour on Gram-positive and Gram-negative bacteria, as well as on fungal strains, indicates a good activity for Cu(II) and Zn(II) complexes against both planktonic or adherent cells. Moreover, Cu(II) complex also exhibited a promising antiproliferative activity on HT 29 cell line.

Study of the coordination of ortho-tyrosine and trans-4-hydroxyproline with aluminum(III) and iron(III)

The coordination of amino acids ortho-tyrosine (o-Tyr, 1) and trans-4-hydroxyproline (HPro, 2) with the biologically important trivalent metal ions Al(III) and Fe(III) in aqueous solution was investigated by 1H and 13C high resolution NMR, Laser Desorption Mass Spectrometry (LD-MS), and MS/MS experiments. Potentiometric measurements were also carried out in 0.16 M NaCl, 37 °C, by varying the pH between 2.0 and 3.5. NMR spectra recorded on aqueous solutions of amino acids 1 or 2 in the presence of the appropriate trivalent metal chloride suggested that binding of Al(III) and Fe(III) involved the COOH and NH2 functional groups of ligands, while their phenolic and alcoholic groups which did not participate in the metal coordination. Potentiometry indicated the prevalent formation of complexes having the general stoichiometry ML and ML2. Laser desorption mass spectrometry (LD-MS) and MS/MS investigation proved the isotopic compositions of ML and ML2 complexes, demonstrating their structures.

New Tridentate Schiff Base, Product of Condensation of 4-Methyl-7-hydroxy-8-formylcoumarin and N-Aminomercaptotriazole: Synthesis, Structure, and Complex Formation

A new Schiff base was prepared by the reaction of 4-methyl-7-hydroxy-8-formylcoumarin with N-aminomercaptotriazole. In solution and in solid phase the compound was shown to exist in the thione form. The compound reacts with Cu(II), Ni(II), Zn(II) and Cd(II) ions depending on the metal salt to give complexes of composition ML2 or MHLX, where HL is monodeprotonated form of the ligand. Cu(II) and Ni(II) complexes were studied by spectral and magnetochemical methods. The Zn(II) and Cd(II) complexes exhibit fluorescence.