Molecular structures of (555)macrotricyclic chelates appearing in 3d-element(ii) ion-hydrazinomethanethioamide-ethanedial systems according to density functional theory calculations

Thermodynamic and geometric parameters have been calculated using the hybrid density functional theory method B3LYP with the 6-31G(d) basis set and the Gaussian03 program for the macrotricyclic complexes of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) with an (NSSN)-coordinated ligand that can result from the complexation of metal hexacyanoferrates(II) with hydrazinomethanethioamide H₂N-HN-C(=S)-NH₂ and ethanedial HC(=O)-CH(=O) in gelatin-immobilized matrix implants. Bond lengths and valence and torsion angles in these complexes are reported. The Ni(II) and Cu(II) complexes are practically planar. The Mn(II), Fe(II), and Co(II) complexes are characterized by a small deviation from coplanarity, and the Zn(II) complex is noticeably noncoplanar. The additional five-membered metallacycle resulting from template ??joining?? is nearly planar in all complexes.     

Dispersion interactions in oligomerization of metal diketonates: a DFT evaluation

The structures of the oligomers of Co(II), Ni(II), Cu(II) and Zn(II) β-diketonates and their stability with respect to dissociation into the monomeric components were studied with the use of density functional theory [DFT B3LYP/6-311++G(d,p)] method taking additionally into account corrections for dispersion interactions in CAM and D3BJ approximations. The calculated geometries of the oligomers well match those experimentally determined, but stabilization energies obtained at the B3LYP-CAM and B3LYP-D3BJ approximations are significantly overestimated.     

Molecular structure and thermodynamic parameters of (5656)macrotetracyclic chelates in the 3d-element(ii) ion-hydrazinomethanethiohydrazide-2,3-butanedione ternary system according to density functional quantum-chemical calculations

The thermodynamic and geometric parameters of the macrocyclic chelates of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) with the (NNNN) coordination of the ligand donor centers formed upon complexation between the above metal ions, hydrazinomethanethiohydrazide (H₂N-HN-C(=S)-NH-NH₂), and 2,3-butanedione (H₃C-C(=O)-C(=O)-CH₃) in gelatin-immobilized matrix implants were calculated by the B3LYP 6–31G(d) density functional theory method with the use of the Gaussian 09 program package. The bond lengths, valence angles, and torsion angles were reported, and it was noted that the complexes of Fe(II), Co(II), Ni(II), and Cu(II) are almost planar, whereas the complexes of Mn(II) and Zn(II) have a quasi-pyramidal structure of the chelate unit. The additional six-membered metallocycles resulting from template cross-linking, as well as five-membered rings, are almost planar.     

A DFT study of molecular structures and tautomerizations of 2-benzoylpyridine semicarbazone and picolinaldehyde N-oxide thiosemicarbazone and their complexations with Ni(II), Cu(II), and Zn(II)

The structure optimizations of picolinaldehyde N-oxide thiosemicarbazone (Hpiotsc), 2-benzoylpyridine semicarbazone (H2BzPS), their imino tautomers and their complexes with Ni(II), Cu(II), and Zn(II) were carried out using DFT calculations. The structures of Hpiotsc and H2BzPS ligands, transition states of their tautomerizations were obtained at the B3LYP/6-31+G(d,p) level and their thermodynamic properties were derived from the frequency calculations at the same level of theory. The B3LYP/LANL2DZ-optimized structures of Hpiotsc and H2BzPS complexes with Ni(II), Cu(II), and Zn(II), and the thermodynamic properties of their complexations derived from the B3LYP/LANL2DZ-frequency calculations were obtained. The B3LYP/LANL2DZ-optimized geometrical parameters for the [Ni(Hpiotsc)₂]²⁺, [Cu(Hpiotsc).Cl₂], and [Zn(Hpiotsc).Cl₂] complexes show good agreement with their corresponding X-ray crystallographic data.     

Poly(amine ester) dendrimer with naphthyl units as a fluorescent chemosensor for Al(III), Cu(II), and Zn(II).

A poly(amine ester) dendrimer with naphthyl units (G1N6) has been synthesized as a fluorescent chemosensor for metal ions. We investigated the metal-ion recognition of G1N6 by adding each of Ag(+), Al(3+), Ba(2+), Ca(2+), Cd(2+), Co(2+), Cu(2+), Fe(3+), Mg(2+), Ni(2+), and Zn(2+) in acetonitrile solution. Large changes were observed in the fluorescence spectra of G1N6 upon the addition of Al(3+), Cu(2+), and Zn(2+).     

Synthesis, molecular and electronic structures of six-coordinate transition metal (Mn, Fe, Co, Ni, Cu, and Zn) complexes with redox-active 9-hydroxyphenoxazin-1-one ligands

A series of pseudo-octahedral metal (M = Mn, Fe, Co, Ni, Cu, Zn) complexes 4 of a new redox-active ligand, 2,4,6,8-tetra(tert-butyl)-9-hydroxyphenoxazin-1-one 3, have been synthesized, and their molecular structures determined with help of X-ray crystallography. The effective magnetic moments of complexes 4 (M = Mn, Fe, Co, and Ni) measured in the solid state and toluene solution point to the stabilization of their high-spin electronic ground states. Detailed information on the electronic structure of the complexes and their redox-isomeric forms has been obtained using density functional theory (DFT) B3LYP*/6-311++G(d,p) calculations. The energy disfavored low-spin structures of manganese, iron, and cobalt complexes have been located, and based on the computed geometries and distribution of spin densities identified as Mn(IV)[(Cat-N-SQ)](2), Fe(II)[Cat-N-BQ)](2), and Co(II)[Cat-N-BQ)](2) compounds, respectively. It has been shown that stabilization of the high-spin structures of complexes 4 (M = Mn, Fe, Co) is caused by the rigidity of the molecular framework of ligands 3 that sterically inhibits interconversions between the redox-isomeric forms of the complexes. The calculations performed on complex 4 (M = Co) predict that a suitable structural modification that might provide for stabilization of the low-spin electromeric forms and create conditions for the valence tautomeric rearrangement via stabilization of the low-spin electromer and narrowing energy gap between the low-spin ground state tautomer and the minimal energy crossing point on the intersection of the potential energy surfaces of the interconverting structures consists in the replacement of an oxygen in the oxazine ring by a bulkier sulfur atom.     

Electrochemical, spectral, and computational studies of metalloporphyrin dimers formed by cation complexation of crown ether cavities

The effect on the electrochemical oxidation and reduction potentials of 5,10,15,20-tetrakis(benzo-15-crown-5)porphyrin (TCP) and its metal derivatives (MTCP; M = Mg(II), VO(IV), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), Ag(II)) upon potassium ion induced dimerization of the porphyrins was systematically performed in benzonitrile containing 0.1 M (TBA)ClO(4) by differential pulse voltammetry technique. The HOMO--LUMO energy level diagram constructed from the electrochemical data revealed destabilization of the HOMO level and stabilization of the LUMO level upon dimer formation while such a perturbation was larger for the HOMO level than the LUMO level. The geometry and electronic structure of a representative ZnTCP and its dimer, K(4)(ZnTCP)(2), were evaluated by the ab initio B3LYP method utilizing a mixed basis set of 3-21G(*) for Zn, K, O, and N and STO-3G for C and H. The inter-porphyrin ring distance of the dimer calculated from the optimized geometry agreed with the spectroscopically determined one, and the calculated HOMO and LUMO frontier orbitals revealed delocalization on both of the porphyrins rings. The metal-metal distances calculated from the triplet ESR spectra of the K(+) induced porphyrin dimers bearing paramagnetic metal ions in the cavity followed the trend Cu--Cu < VO--VO < Ag--Ag. However, the spectral shifts resulting from the exciton coupling of the interacting porphyrin pi-systems revealed no specific trend with respect to the metal ion in the porphyrin cavity. Additionally, linear trends in the electrochemically measured HOMO--LUMO gap and the energy corresponding to the most intense visible band of both MTCP and K(4)(MTCP)(2) were observed. A reduced HOMO--LUMO gap predicted for the dimer by B3LYP/(3-21G(), STO-3G) calculations was confirmed by the results of optical absorption and electrochemical studies.     

DFT-B3LYP, NPA-, and QTAIM-based study of the physical properties of [M(II)(H2O)2(15-crown-5)] (M = Mn, Fe, Co, Ni, Cu, Zn) complexes

A density functional theory study of the structure of the title compounds with the divalent metal ions in their high-spin ground state, obtained using B3LYP/6-311++G(d,p) in vacuo and in aqueous solution simulated using a polarized continuum medium, is reported for the first time. The modeling reproduces the pseudo pentagonal bipyramidal crystallographic structures very well, including some asymmetry in the equatorial bonds lengths to the crown ether O donors. The very marked asymmetry in the Ni(2+) structure due to a Jahn-Teller distortion of a d(8) system in a D(5h) ligand field is also well reproduced. The gas phase binding energies of the complexes follow the order Mn(2+) < Fe(2+) < Co(2+) < Ni(2+) < Cu(2+) > Zn(2+), in precise agreement with the Irving-William series. Both the NPA and Bader charges show there is ligand-to-metal charge transfer; however, the values obtained from the NPA procedure, unlike those obtained from Bader's quantum theory of molecules approach, do not correlate with the electronegativity of the metal ions, the stabilization energies of the solvated complexes or the ionic radii of the metal ions, and so appear to be less reliable. The nature of the bonding between the ligands and the metal ions has been explored using the topological properties of the electron charge density. The metal-ligand bond distances were found to be exponentially correlated with the electron charge density, its Laplacian, and with its curvature in the direction of the bond path at M-O bond critical points. While the bonding with coordinated H(2)O is predominantly ionic, that to the crown ether donor atoms has some covalent character the extent of which increases across the first transition series. The delocalization indices of M-O bonds in these complexes correlate reasonably well with the electron density and its Laplacian at the bond critical points; this therefore provides a rapid and computationally very efficient way of determining these properties, from which insight into the nature of the bonding can be obtained, obviating the need for time-consuming integration over atomic basins.     

Zn(ii), Cd(ii) and Pb(ii) complexation with pyridinecarboxylate containing ligands

Herein, we report the coordination properties towards Zn(ii), Cd(ii) and Pb(ii) of two hexadentate ligands containing pyridinecarboxylate groups with ethane-1,2-diamine (bcpe) or cyclohexane-1,2-diamine (bcpc) backbones. The X-ray crystal structures of [Zn(bcpe)], [Cd(bcpe)] and [Cd(bcpc)] show hexadentate binding of the ligand to the metal ions, with the coordination polyhedron being best described as a severely distorted octahedron. The X-ray crystal structure of the Pb(ii) analogue shows the presence of tetrameric structural units [Pb(4)(bcpe)(4)] in which the four Pb(ii) ions are bridged by carboxylate oxygen atoms. While in the Zn(ii) and Cd(ii) complexes the bcpe ligand adopts a twist-wrap (tw) conformation in which the ligand wraps around the metal ion by twisting the pyridyl units relative to each other, for the Pb(ii) complex a twist-fold (tf) conformation, where a slight twisting of the pyridyl units is accompanied by an overall folding of the two pyridine units relative to each other is observed. Theoretical calculations performed at the DFT (B3LYP) level on the [Pb(bcpe)] and [Pb(bcpc)] systems indicate that the tf conformation is more stable than the tw form both in the solid state and in aqueous solution. The analysis of the natural bond orbitals (NBOs) indicate that the Pb(ii) lone-pair is polarized by a substantial 6p contribution, which results in a hemi-directed coordination geometry around the metal ion. Potentiometric studies have been carried out to determine the protonation constants of the ligands and the stability constants of the complexes with Zn(ii), Cd(ii), Pb(ii) and Ca(ii). The replacement of the ethylene backbone of bcpe by a cyclohexylene ring causes a very important increase in the stability constant of the Pb(ii) complex (ca. 2.3 logK units), while this effect is less important for Cd(ii) (ca. 1.4 logK units). However, the introduction of the cyclohexylene ring does not substantially affect the stability of the Zn(ii) and Ca(ii) complexes. The ligand bcpc shows Pb/Ca and Cd/Ca selectivities [10(8.9) and 10(9.8), respectively] superior to those of extracting agents, such as EDTA, already used in Pb(ii) and Cd(ii) removal from contaminated water and soils.     

DFT B3LYP calculation of the spatial structure of Co(II), Ni(II), and Cu(II) template complexes formed in ternary systems metal(II) ion-dithiooxamide-formaldehyde

The hybrid density functional theory B3LYP method with the 6-31G(d) basis set and the Gaussian 98 program has been used for calculating the geometric parameters of the Mn(II), Co(II), Ni(II), and Cu(II) complexes with NNSS-donor macrocyclic ligands forming in the course of template processes in the M(II)-dithiooxamide-formaldehyde systems. The bond lengths and bond angles in the complexes with the MN₂S₂ metal chelate core are reported. For all M(II) ions, the extra six-membered chelate ring that form as a result of template assembly is rotated through a rather large angle with respect to two five-membered rings and the ring itself is not planar.     

Electronic structure of the [MNH2]+ (M = Sc-Cu) complexes

B3LYP geometry optimizations for the [MNH2]+ complexes of the first-row transition metal cations (Sc+-Cu+) were performed. Without any exception the ground states of these unsaturated amide complexes were calculated to possess planar geometries. CASPT2 binding energies that were corrected for zero-point energies and including relativistic effects show a qualitative trend across the series that closely resembles the experimental observations. The electronic structures for the complexes of the early and middle transition metal cations (Sc+-Co+) differ from the electronic structures derived for the complexes of the late transition metal cations (Ni+ and Cu+). For the former complexes the relative higher position of the 3d orbitals above the singly occupied 2p(pi) HOMO of the uncoordinated NH2 induces an electron transfer from the 3d shell to 2p(pi). The stabilization of the 3d orbitals from the left to the right along the first-row transition metal series causes these orbitals to become situated below the HOMO of the NH2 ligand for Ni+ and Cu+, preventing a transfer from occurring in the [MNH2]+ complexes of these metal cations. Analysis of the low-lying states of the amide complexes revealed a rather unique characteristic of their electronic structures that was found across the entire series. Rather exceptionally for the whole of chemistry, pi-type interactions were calculated to be stronger than the corresponding sigma-type interactions. The origin of this extraordinary behavior can be ascribed to the low-lying sp2 lone pair orbital of the NH2 ligand with respect to the 3d level.     

Gas-phase theoretical prediction of the metal affinity of copper(I) ion for DNA and RNA bases

The most stable tautomeric forms of free DNA and RNA bases were considered as substrates for the interaction of Cu(+) ion. Several suitable attachment sites were selected that involved mono- and bi-coordination of the cation. B3LYP/6-311 + G(2df,2p) bond energies showed that copper ion has the major affinity for guanine and cytosine bases. The proposed values of Cu(+) ion affinity are 59.9, 60.0, 80.2, 88.0 and 69.0 kcal mol(-1) for uracil, thymine, cytosine, guanine and adenine, respectively. The preference for the mono- or bi-coordination depends on the particular tautomer for each base.     

Quantum-chemical study of intramolecular spin-forbidden rearrangements of the transition metal chelate complexes

An overview of quantum-chemical methods of studying the spin-forbidden reactions is presented. It was shown that HF and MP2 methods overestimate stabilization of the high-spin states whereas DFT methods with the use of LSDA and CGA functionals underestimate these states. Hybrid exchange-correlation density functionals B3P86 and B3LYP give the best agreement with the experimental data. The intramolecular spin-forbidden rearrangement of bis-chelate Ni(II) and Co(II) complexes was studied using the B3LYP/6-311++G (d,p) method.     

Noncovalent interactions of Zn+ with N-donor ligands (pyridine, 4,4'-dipyridyl, 2,2'-dipyridyl, and 1,10-phenanthroline): collision-induced dissociation and theoretical studies

The binding interactions in complexes of Zn(+) with nitrogen donor ligands, (N-L) = pyridine (x = 1-4), 4,4'-dipyridyl (x = 1-3), 2,2'-dipyridyl (x = 1-2), and 1,10-phenanthroline (x = 1-2), are examined in detail. The bond dissociation energies (BDEs) for loss of an intact ligand from the Zn(+)(N-L)(x) complexes are reported. Experimental BDEs are obtained from thermochemical analyses of the threshold regions of the collision-induced dissociation cross sections of Zn(+)(N-L)(x) complexes. Density functional theory calculations at the B3LYP/6-31G* level of theory are performed to determine stable structures of these species and to provide molecular parameters needed for the thermochemical analysis of experimental data. Relative stabilities of the various conformations of these N-donor ligands and their complexes to Zn(+) as well as theoretical BDEs are determined from single point energy calculations at the B3LYP/6-311+G(2d,2p) and M06/6-311+G(2d,2p) levels of theory using the B3LYP/6-31G* optimized geometries. The experimental BDEs for the Zn(+)(N-L)(x) complexes are in reasonably good agreement with values derived from density functional theory calculations. BDEs derived from M06 calculations provide better agreement with the measured values than those based on B3LYP calculations. Trends in the sequential BDEs are explained in terms of sp polarization of Zn(+) and repulsive ligand-ligand interactions. Comparisons are made to the analogous Cu(+)(N-L)(x) and Ni(+)(N-L)(x) complexes previously studied.     

1H and (113)Cd NMR Investigations of Cd(2+) and Zn(2+) Binding Sites on Serum Albumin: Competition with Ca(2+), Ni(2+), Cu(2+), and Zn(2+)

1H and (113)Cd NMR studies are used to investigate the Cd(2+) binding sites on serum albumin (67 kDa) in competition with other metal ions. A wide range of mammalian serum albumins possess two similar strong Cd(2+) binding sites (site A 113-124 ppm; site B 24-28 ppm). The two strong sites are shown not to involve the free thiol at Cys34. Ca(2+) influences the binding of Cd(2+) to isolated human albumin, and similar effects due to endogenous Ca(2+) are observed for intact human blood serum. (1)H NMR studies show that the same two His residues of human serum albumin are perturbed by Zn(2+) and Cd(2+) binding alike. Zn(2+) displaces Cd(2+) from site A which leads to Cd(2+) occupation of a third site (C, 45 ppm). The N-terminus of HSA is not the locus of the two strong Cd(2+) binding sites, in contrast to Cu(2+) and Ni(2+). After saturation of the N-terminal binding site, Cu(2+) or Ni(2+) also displaces Cd(2+) from site A to site C. The effect of pH on Cd(2+) binding is described. A common Cd(2+)/Zn(2+) binding site (site A) involving interdomain His residues is discussed.     

Calculations on the octupolar molecules with enhanced two-photon absorption cross sections based on the Zn (II) and Cu (I) as centers

The equilibrium geometries, electronic structures, as well as one- and two-photon absorption cross sections of a series of octupolar chromophores with Zn(2+) or Cu(+) as coordinate centers and 4,4'-bis(dibutylaminostyryl)-[2,2']-bis(bipyridyl) as ligands have been determined by using B3LYP/6-31G and ZINDO methods. These molecules are designed by controlled combination of two or three bipyridyl ligands with the metal centers. The results show that Zn(2+) is an effective template for the design of octupolar structures which enable it to form tetrahedral and octahedral coordinated complexes; while Cu(+) only exists in a tetrahedral coordinated complex, comparing the tetrahedral complex with Zn(2+) as the center with that of Cu(+) as the center, it is found that the complex with the Cu(+) center is a better two-photon absorption material than the former as far as the transparency/nonlinearity is concerned. Furthermore, for the same metal center of Zn(2+), both one- and two-photon absorptions of the tetrahedral complex are redshifted relative to those of the octahedral complex, is attributed to the spiroconjugation effect in the tetrahedral complex. Our theoretical findings are consistent with recent experimental observations and provide an important foundation for the design of improved transparency-nonlinearity two-photon absorption materials.     

Geometric parameters and energies of molecular structures of macrocyclic metal chelates in the ternary 3<Emphasis Type="Italic">d</Emphasis> M(II) ion-ethanedithioamide-ethanedial systems according to quantum-chemical DFT B3LYP calculations

The thermodynamic and geometric parameters of isomeric macrotricyclic Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) complexes with the (NSSN) coordination of the ligand donor centers formed in the reaction of corresponding hexacyanoferrates(II) with ethanedithioamide H₂N-C(=S)-C(=S)-NH₂ and ethanedial HC(=O)-CH(=O) in gelatin-immobilized matrix implants have been calculated by the hybrid B3LYP density functional theory method with the use of the 6–31G(d) basis set and the Gaussian 03 program package. The bond lengths and bond and torsion angles in these complexes have been reported, and it has been stated that the Mn(II), Co(II), and Cu(II) complexes are nearly planar, the Fe(II) and Ni(II) complexes are slightly nonplanar, while the Zn(II) complex exhibits a rather considerable deviation from coplanarity. The additional five-membered chelate ring resulting from template cross-linking is almost planar in all cases.     

Evaluation of the metal binding properties of the histidine-rich antimicrobial peptides histatin 3 and 5 by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) was used to investigate metal ion interactions with salivary peptides histatin 3 (H3) and histatin 5 (H5). Conformational changes of these peptides in the presence of metal ions were studied using circular dichroism spectroscopy. H3 and H5 formed high affinity complexes with Cu(2+) and Ni(2+) and, to a lesser extent, with Zn(2+). Both peptides show the potential for multiple binding sites for Cu(2+) and Ni(2+) and only a single strong binding site for Zn(2+). The binding of a third Cu(2+) ion to H3 seems to enable the binding of a fourth ion to H3. The binding of a second and third Ni(2+) ion to H5 has a similar effect in enabling the binding of a fourth ion. None of the metal ions examined stabilized a regular secondary structure for either peptide. Subtle changes in overall conformation are seen with the addition of Cu(2+) to both H3 and H5.