Semi-Rigid (Aminomethyl) Piperidine-Based Pentadentate Ligands for Mn(II) Complexation

Two pentadentate ligands built on the 2-aminomethylpiperidine structure and bearing two tertiary amino and three oxygen donors (three carboxylates in the case of AMPTA and two carboxylates and one phenolate for AMPDA-HB) were developed for Mn(II) complexation. Equilibrium studies on the ligands and the Mn(II) complexes were carried out using pH potentiometry, 1H-NMR spectroscopy and UV-vis spectrophotometry. The Mn complexes that were formed by the two ligands were more stable than the Mn complexes of other pentadentate ligands but with a lower pMn than Mn(EDTA) and Mn(CDTA) (pMn for Mn(AMPTA) = 7.89 and for Mn(AMPDA-HB) = 7.07). 1H and 17O-NMR relaxometric studies showed that the two Mn-complexes were q = 1 with a relaxivity value of 3.3 mM−1 s−1 for Mn(AMPTA) and 3.4 mM−1 s−1 for Mn(AMPDA-HB) at 20 MHz and 298 K. Finally, the geometries of the two complexes were optimized at the DFT level, finding an octahedral coordination environment around the Mn2+ ion, and MD simulations were performed to monitor the distance between the Mn2+ ion and the oxygen of the coordinated water molecule to estimate its residence time, which was in good agreement with that determined using the 17O NMR data.

Synthesis, Structures, and Water Adsorption of Two Coordination Polymers Constructed by M(II) (M = Ni (1) and Zn (2)) with 1,3-Bis(4-Pyridyl)Propane (bpp) and 1,2,4,5-Benzenetetracarboxylate (BT4−) Ligands

Two coordination polymers (CPs), with chemical formulas {[Ni2(bpp)2(BT)(H2O)6] 1.5(EtOH) 1.5H2O}n (1) and [Zn(bpp)(BT)0.5]·5H2O (2) (bpp = 1,3-bis(4-pyridyl)propane, and BT4− = tetraanion of 1,2,4,5-Benzenetetracarboxylic acid), have been synthesized and structurally characterized by single-crystal X-ray diffraction methods. In compound 1, the coordination environments of two crystallographically independent Ni(II) ions are both distorted octahedral bonded to two nitrogen donors from two bpp ligands and four oxygen donors from one BT4- ligand and three water molecules. Both bpp and BT4− act as bridging ligands with bis-monodentate and 1,4-bis-monodentate coordination modes, respectively, connecting the Ni(II) ions to form a 2D layered metal-organic framework (MOF). Adjacent 2D layers are then arranged orderly in an ABAB manner to complete their 3D supramolecular architecture. In 2, the coordination environment of Zn(II) ion is distorted tetrahedral bonded to two nitrogen donors from two bpp ligands and two oxygen donors from two BT4− ligands. Both bpp and BT4- act as bridging ligands with bis-monodentate and 1,2,4,5-tetrakis-monodentate coordination modes, respectively, connecting the Zn(II) ions to form a 3D MOF. The reversible water de-/adsorption behavior of 1 between dehydrated and rehydrated forms has been verified by cyclic Thermogravimetric (TG) analyses through de-/rehydration processes. Compound 1 also exhibits significant water vapor hysteresis isotherms.

MTH1 inhibitor amplifies the lethality of reactive oxygen species to tumor in photodynamic therapy

Although photodynamic therapy (PDT) has been clinically applied tumor hypoxia still greatly restricts the performance of this oxygen-dependent oncological treatment. The delivery of oxygen donors to tumor may produce excessive reactive oxygen species (ROS) and damage the peripheral tissues. Herein, we developed a strategy to solve the hypoxia issue by enhancing the lethality of ROS. Before PDT, the ROS-defensing system of the cancer cells was obstructed by an inhibitor to MTH1, which is a key for the remediation of ROS-caused DNA damage. As a result, both nuclei and mitochondrial DNA damages were increased, remarkably promoting cellular apoptosis. The therapeutic results demonstrated that the performance of PDT can be improved by the MTH1 inhibitor, leading to efficient cancer cell killing effect in the hypoxic tumor. This strategy makes better use of the limited oxygen, holding the promise to achieve satisfactory therapeutic effect by PDT without generating redundant cytotoxic ROS.

Synthesis and spectroscopic characterization of ternary copper(ii) complexes containing nitrogen and oxygen donors as functional mimics of catechol oxidase and phenoxazinone synthase

Two ternary copper(ii) complexes 1 [(Cu2Me4en)4(EDTA)] and 2 [(CuMe4en)2(MIDA)] containing the mixed ligand system of 1,1′,4,4′-tetramethylethylenediamine (Me4en) (L) and N-methyliminodiacetic (MIDAH2) (L′) or ethylenediaminetetraacetic acid (EDTAH4) (L′) were synthesized.

Synthesis, spectral characterization and antimicrobial activity of some M(II) complexes with Ciprofloxacin

Ciprofloxacin, CFL is a drug that belongs to the second generation of fluoroquinolone antibiotics with a wide range of effects on Gram-positive and Gram-negative bacteria. The aim of this work was to investigate the interaction of CFL as ligand with divalent biological cations (Mn2+, Ni2+ and Co2+) in approximate physiological conditions. Synthesized complexes were characterized using FTIR and stereo-microscopy. Antimicrobial screening was performed on bacterial strains of Escherichia coli, Salmonella Enteritidis, Enterococcus faecalis and Staphylococcus aureus. The results of FTIR spectroscopy showed that the M(II) complexes with CFL were formed through the oxygen donors of the carboxyl and carbonyl group of the ligand. Stereo-microscopic characterization revealed the difference in color and size of crystals of the ligand and metal complexes. Antimicrobial screening has shown that CFL and complexes have almost similar antimicrobial activity against investigated bacterial strains.

Reversible and Vapochromic Chemisorption of Ammonia by a Copper(II) Coordination Polymer

The single crystal X-ray structure determination of {[Cu(tpt)(o-phthalate)]·31/3(C2H2Cl4)}n (tpt=2,4,6-tri-4-pyridyl-1,3,5-triazine, C2H2Cl4=1,1,2,2-tetrachloroethane=TCE) shows a 3D network in which CuII centres are linked by 3-connecting tpt ligands with the topology of a 12,3 net. CuII centres are further linked by o-phthalate dianions. The copper coordination geometry is square pyramidal, with o-phthalate oxygen donors trans to each other in the basal plane and the remaining positions taken by the pyridines of three linking tpt units. The solvent accessible void space is ~65%. The pale blue-green crystalline desolvate, obtained by heating to 200°C or washing the TCE solvate with acetone is formulated as [Cu(tpt)(o-phthalate)]n. Powder X-ray diffraction and electron paramagnetic resonance spectroscopy show that the crystal structure and the CuII geometry changes upon desolvation. The crystalline desolvated phase sorbs two equivalents of ammonia per copper ion. The adduct, mauve [Cu(tpt)(o-phthalate)(NH3)2]n, shows reasonable crystallinity and is stable up to ~150°C under ambient conditions before the reversible desorption (minimum 10 cycles) of the guest ammonia. The colour change and high desorption temperature, along with changes in g values, is suggestive of chemisorption in two steps with Cu–ammine bonding in the loaded phase.

Crystal structures of sodium-, lithium-, and ammonium 4,5-dihydroxybenzene-1,3-disulfonate (tiron) hydrates

The solid-state structures of the Na+, Li+, and NH4 + salts of the 4,5-dihydroxybenzene-1,3-disulfonate (tiron) dianion are reported, namely disodium 4,5-dihydroxybenzene-1,3-disulfonate, 2Na+·C6H4O8S2 2−, μ-4,5-dihydroxybenzene-1,3-disulfonato-bis[aqualithium(I)] hemihydrate, [Li2(C6H4O8S2)(H2O)2]·0.5H2O, and diammonium 4,5-dihydroxybenzene-1,3-disulfonate monohydrate, 2NH4 +·C6H4O8S2 2−·H2O. Intermolecular interactions vary with the size of the cation, and the asymmetric unit cell, and the macromolecular features are also affected. The sodium in Na2(tiron) is coordinated in a distorted octahedral environment through the sulfonate oxygen and hydroxyl oxygen donors on tiron, as well as an interstitial water molecule. Lithium, with its smaller ionic radius, is coordinated in a distorted tetrahedral environment by sulfonic and phenolic O atoms, as well as water in Li2(tiron). The surrounding tiron anions coordinating to sodium or lithium in Na2(tiron) and Li2(tiron), respectively, result in a three-dimensional network held together by the coordinate bonds to the alkali metal cations. The formation of such a three-dimensional network for tiron salts is relatively rare and has not been observed with monovalent cations. Finally, (NH4)2(tiron) exhibits extensive hydrogen-bonding arrays between NH4 + and the surrounding tiron anions and interstitial water molecules. This series of structures may be valuable for understanding charge transfer in a putative solid-state fuel cell utilizing tiron.

A new nitrogen rich open chain diazine ligand system: synthesis coordination chemistry and magneto-structural studies

A new series of open chain diazine ligands that have a central bipyridne unit with two side-arms offering a range of ketone/alkoxide oxygen donors, diazine and pyridine terminal groups show a strong preference for binding three metals.