Dipicolinate Dianion Research Articles

Mito-Specific Ratiometric Terbium(III)-Complex-Based Luminescent Probe for Accurate Detection of Endogenous Peroxynitrite by Time-Resolved Luminescence Assay.

The level of peroxynitrite (ONOO-) is closely related to the pathogenesis of a series of diseases. Hence, the accurate sensing of ONOO- is very important for a better understanding of its biological functions. Here, a time-resolved ratiometric nanoprobe (TD-DC) composed of an energy donor unit (Tb(DPA)3, where DPA signifies a dipicolinate dianion ligand) and an energy receptor unit (DC) was designed. The response of TD-DC toward ONOO- in vitro was assessed by luminescence intensity and lifetime. The results demonstrated that TD-DC could precisely (39 nM) detect ONOO- with high selectivity and efficiency (29 s). TD-DC was further successfully employed in sensing endogenous ONOO- in A-375 cells. Moreover, it could specifically localize in the mitochondrion, where endogenous ONOO- is mainly generated. The above results revealed that TD-DC is efficient and useful for real-time detection of ONOO- at subcellular levels.

Structural resemblance and variation in transition metal complexes derived from dipicolinic acid and guanylhydrazine

New aminoguanidinium transition metal dipicolinates of the formula (AgunH)[MIII(dip)2]·xH2O, M = Cr, x = 1.5; Fe, x = 2, (AgunH)2[MII(dip)2]·nH2O, where M = Mn, n = 2; Co or Ni, n = 0 and Zn, n = 1, and [Cu(Agun)2][Cu3(dip)4(Agun)2]·4H2O have been prepared by the reaction of respective metal nitrates with aqueous mixture of dipicolinic acid (H2dip) and aminoguanidine bicarbonate (AgunH·HCO3) in appropriate mole ratios. These compounds have been characterized by various physico-chemical techniques. Among them Ni, Cu, Cr and Fe complexes have been structurally characterized. The asymmetric units of the Ni and Cr structures contain two independent molecules, whereas Fe has four. Unlike these, the copper compound has a unique structure with a tri-nuclear centrosymmetric anionic complex and cationic bis(aminoguanidine)copper(II). In all of these compounds, the dipicolinate dianion is acting as a tridentate (O,N,O) donor ligand, except copper in-which one of the dipicolinates is tetradentate (O,N,O,O). Cytotoxicity and DPPH scavenging activity studies reveal that the copper complex exhibits superior activity to that of cobalt and nickel.

The hydration number n of calcium dipicolinate trihydrate, CaDP· nH 2O, and its effect on the IR spectra of sporulated Bacillus bacteria

Previous results have shown a unique “quartet” of peaks in the infrared spectra of the sporulated phase of Bacillus bacteria, the four peaks being observed reproducibly for many different species of Bacillus endospores. We consistently observe bands at 766, 725, 701, and 659 cm −1 with the same relative amplitudes, as well as other spore peaks at 1441, 1277, and 1015 cm −1. We have suggested that the peaks arise from calcium dipicolinate, not the conjugate acid. In this paper we conduct a theoretical and experimental study to show that the IR peaks not only arise from the calcium dipicolinate, a known spore component, but specifically the trihydrate salt, CaDP·3H 2O. This is shown by calculating the absolute IR frequencies and intensities of the lone dipicolinate dianion, the calcium salt, as well as the mono-, di- and tri-hydrate salts of calcium dipicolinate. The quartet peaks arise from the crystalline trihydrate salt as verified both experimentally and using quantum chemistry methods. When the calculated intensities are not normalized, only the trihydrate spectrum shows low frequency modes (below 1000 cm −1, including the quartet) having intensities comparable to those of the pyridine ring. The vibrational modes in this region are associated with many internal coordinate motions including contributions from the Ca 2+ counterion and the three waters including Ca–O–H bends, H 2O–Ca–O torsions and O–C–O bends.

Aqua(dipicolinato-κ3O,N,O′)(1,10-phenanthroline-κ2N,N′)zinc(II) monohydrate

The title compound, [Zn(C7H3NO4)(C12H8N2)(H2O)]·H2O, is isostructural with the manganese(II) analogue. The Zn atom is coordinated by a tridentate dipicolinate dianion, a bidentate 1,10-phenanthroline mol­ecule and a water mol­ecule, resulting in a substanti­ally distorted ZnO3N3 octa­hedral grouping. The crystal packing is consolidated by O—H⋯O hydrogen bonds and probable π–π stacking.

X-ray crystal structure of [VO(DPA)(H2O)2]·2H2O (DPA=Dipicolinate dianion)

The X-ray crystal structure of the trans-diaqua complex [VO(DPA)(H2O2)]·2H2O (1) (DPA=dipicolinate dianion) has been determined. Comparison with the known structure of [VO(DPA)(o-phen)]·3H2O (2), obtained from (1) by displacement of the two coordinated aqua molecules, shows that the coordination sphere around vanadium is reorganised during this reaction.

Intermolecular chiral recognition probed by enantiodifferential excited-state quenching kinetics.

Time-resolved chiroptical luminescence (TR-CL) measurements are used to study the kinetics of chirality-dependent excited-state quenching processes in aqueous solution. Experiments are carried out on samples that contain a racemic mixture of chiral luminophore molecules (L) in solution with a small, optically active concentration of chiral quencher molecules (Q). The luminophores are excited with a pulse of unpolarized light to create an initially racemic excited-state population of lambda L* and delta L* enantiomers, and TR-CL measurements are then used to monitor the differential decay kinetics of the lambda L* and delta L* subpopulations. Observed differences between the lambda L* and delta L* decay kinetics reflect differential rate processes and efficiencies for lambda L*-Q versus delta L*-Q quenching actions, and they are diagnostic of chiral discriminatory interactions between the luminophore and quencher molecules. In this study, the luminophores are either Eu(dpa)3(3-) or Tb(dpa)3(3-) coordination complexes (where dpa denotes a dipicolinate dianion ligand), and the quenchers are diastereomeric structures of Cr(H2O)4(ATP), Rh(H2O)4(ATP) and Rh(H2O)3(ATP) (where ATP identical to adenosine triphosphate). The Ln(dpa)3(3-) (Ln identical to En3+ or Tb3+) complexes have three-bladed propeller-like structures of D3 symmetry, and in aqueous solution they exist as a racemic mixture of left-handed (lambda) and right-handed (delta) configurational isomers (enantiomers). The results show that the chiral quencher molecules can distinguish between the lambda and delta enantiomeric structures of the luminophores in their excited-state quenching actions. The degree and sense of enantiomeric preference in these quenching actions are governed by the electronic and stereochemical properties of the quencher molecules. Twenty-one different luminophore-quencher systems are examined in this study, and they exhibit interestingly diverse enantiodifferential quenching kinetics. The results reflect the extraordinary sensitivity of chiral recognition and discrimination processes to relatively small, and sometimes subtle, changes in molecular electronic and stereochemical structure.

Polarized Optical Spectra, Transition Line Strengths, and the Electronic Energy-Level Structure of Eu(dpa)33- Complexes in Single Crystals of Hexagonal Na3[Yb0.95Eu0.05(dpa)3]·NaClO4·10H2O

Polarized optical absorption and emission measurements are used to locate and assign 52 crystal-field energy levels split out of the 4f6 electronic configuration of Eu3+ in single crystals of Na3[Yb0.95Eu0.05(dpa)3]·NaClO4·10H2O (where dpa ≡ dipicolinate dianion ≡ 2,6-pyridinedicarboxylate). In these crystals, each Eu3+ is coordinated to three dipicolinate (dpa) ligands, and the tris-terdentate Eu(dpa)33- chelate structures have trigonal-dihedral (D3) symmetry. The combined optical absorption and emission measurements provide access to the energy-level structures of 27 different 4f6[SL]J multiplet manifolds of Eu3+, and 21 of these multiplet manifolds are represented among the 52 crystal-field levels that are characterized with respect to both location (energy) and symmetry properties. The energy-level data obtained from experiment are analyzed in terms of a model Hamiltonian that includes consideration of both isotropic and nonisotropic 4f-electron/crystal-field interactions. A parametrized form of this Hamiltonian is used to perform parametric fits of calculated-to-experimental energy-level data, and the results obtained from these data fits show a root mean square (rms) deviation of 9.8 cm-1 between calculated and observed energies. The Hamiltonian parameters evaluated from the energy-level analyses provide information about both the anisotropies and the overall strength of the 4f-electron/crystal-field interactions that contribute to the energy-level structure of Eu(dpa)33- complexes. In addition to energy-level data, the absorption measurements performed in this study permit the quantitative determination of relative optical line strengths for 22 different Stark-level-to-Stark-level transitions observed in the low-temperature axial absorption spectra of Eu(dpa)33- in Na3[Yb0.95Eu0.05(dpa)3]·NaClO4·10H2O.

Polarized Optical Absorption and Emission Spectra and the Electronic Energy-Level Structure of Tb(dpa)33- Complexes in Na3[Yb0.95Tb0.05(dpa)3]·NaClO4·10H2O

Polarized optical absorption and emission measurements are used to locate and assign 60 crystal-field energy levels split out of the 4f8 electronic configuration of Tb3+ in single crystals of Na3[Yb0.95Tb0.05(dpa)3]·NaClO4·10H2O (where dpa ≡ dipicolinate dianion ≡ 2,6-pyridinedicarboxylate). In these crystals, each Tb3+ ion is coordinated to three dipicolinate (dpa) ligands, and the tris-terdentate Tb(dpa)33- chelate structures have trigonal-dihedral (D3) symmetry. The combined optical absorption and emission measurements provide access to the energy-level structures of the 17 lowest-energy 4f8[SL]J multiplet manifolds of Tb3+, and all of these multiplet manifolds are represented among the 60 crystal-field levels that are characterized with respect to both location (energy) and symmetry properties. The energy-level data obtained from experiment are analyzed in terms of a model Hamiltonian that includes consideration of both isotropic and nonisotropic 4f-electron/crystal-field interactions. A parametrized ...

The determination of chiroptical dissymmetry factors and electric- vs. magnetic-dipole transition amplitude ratios from circularly polarized excitation and emission measurements on racemic Eu(dpa) 33− in aqueous solution

A combination of circularly polarized excitation and emission measurements is used to determine the chiroptical properties of Eu(dpa) 3− 3 complexes in aqueous solution (dpadipicolinate dianionpyridine-2,6-dicarboxylate). Intrinsic chiroptical dissymmetry factors are measured for four absorptive and three emissive transitions, and the results are used to calculate ratios of electric- versus magnetic-dipole transition amplitudes.

Chirality-dependent excited-state quenching of Eu(dpa) 33− and Tb(dpa) 3+3 luminophores by diastereomeric structures of Δ-[Co( trans-1,2-cyclohexanediamine) 3] 3+ in aqueous solution

Four diastereomers of Δ-[Co( trans-1,2-cyclohexanediamine) 3] 3+ are examined as enantioselective excited-state quenchers of chiral Eu(dpa) 3 3− and Tb(dpa) 3 3− luminophores (dpadipicolinate dianion) in solution. In their quenching actions, all four diastereomers can distinguish between and interact differentially with the Λ and Δ enantiomers of the luminophores, but their enantiomeric preferences show interesting variations that may be correlated with chelate-ring conformational structure.

Chiral recognition between dissymmetric Ln(dpa)33- and cobalt(III)-nucleotide complexes in aqueous solution. Enantioselective luminescence quenching as a probe of intermolecular chiral discrimination

Time-resolved chiroptical luminescence spectroscopy is used to investigate enantioselective excited-state quenching processes in solution samples that contain a racemic mixture of chiral luminophores and a small concentration of dissymmetric quencher molecules. The luminophores are Ln(dpa) 3 3- complexes (Ln≡Eu 3+ or Tb 3+ , dpa≡a dipicolinate dianion) that have tris(terdentate) chelate structures of D 3 symmetry with either left-handed (Λ) or right-handed (4) configurational chirality about the trigonal axis. The quenchers are 6-coordinate Co(III) complexes with the general stoichiometric formula Co(NH 3 ) 4 (ndp) or Co(NH 3 ) 4 (ntp), were ndp denotes a diphosphate nuceotide ligand and ntp denotes a triphosphate nucleotide ligand.

Germination of Spores of Bacillus stearothermophilus Induced by Analogues of Dipicolinate Di-Anion

The structural specificity required for induction of germination of spores of Bacillus stearothermophilus by analogues of dipicolinate in buffer at pH 5.5 is similar to that found previously with spores of Bacillus megaterium and calcium chelate salts at pH 8. 4H-pyran-2,6-dicarboxylate, but no other analogue tested, is as effective as dipicolinate di-anion.