Stacking Interactions In Complexes Research Articles

Anthryl-functionalized cyanide-bridged Fe/Co cubes.

Two anthryl-functionalized cyanide-bridged [Fe4Co4] cube complexes, [(pzTp)Fe(CN)3Co(TpEtOAn)]4[OTf]4·8MeCN·7Et2O (1) and [NEt4]3[(pzTp)Fe(CN)3Co(TpEtOAn)]4[OTf]7·5MeCN·2Et2O (2) (pzTp- = tetrapyrazolylborate, TpEtOAn = 2,2,2-tris-(pyrazol-1-yl)ethoxy(9-methyl-anthracene)), were synthesized and characterized. The crystallographic study revealed that the [Fe4Co4] cubes are arranged into a linear supramolecular chain through significant anthryl-anthryl π-π stacking interactions in complex 1, whereas a zigzag supramolecular 1D assembly is observed in 2. The magnetic measurements showed that both compounds exhibited incomplete transitions from the paramagnetic {FeIIILS(μ-CN)CoIIHS} state to the diamagnetic {FeIILS(μ-CN)CoIIILS} state at about 200 K. The luminescence measurement of 1 in solution revealed an enhancement of the emission upon dilution or addition of perfluoronaphthalene (PFN) molecules, which could be attributed to the suppression of the aggregation-caused quenching (ACQ) effect, suggesting possible aggregation of the cube units in the solution.

Relationships between some calculated NMR data and π-π stacking binding energies in complexes involved substituted-coronenes, Benzene, and Hexafluorobenzene

The π-π stacking interactions in the Ben||substituted-coronene and HFBen||substituted-coronene complexes was studied using the computational quantum chemistry methods (where Ben and HFBen are Benzene and Hexafluorobenzene, || denotes π-π stacking interaction, substituted-coronene is coronene molecule which substituted with four X groups, and X= NH 2 , CH 3 , OH, H, F, CN, and NO). The results reveal effects of substituents and opposite nature of Ben and HFBen on the π-π stacking interactions in complexes which direct electrostatic interactions of substituents on one ring don’t manipulate π electron cloud of the other ring. Electron-withdrawing/electron-donating substituents lead to better binding energies in the Ben||substituted-coronene/HFBen||substituted-coronene complexes. Atoms in molecules (AIM) analysis and charge transfer (CT) effects, also relationships between through-space spin-spin coupling constants, J C-C and J C-F , and π-π stacking binding energies were studied in the Ben||substituted-coronene and HFBen||substituted-coronene complexes.

Directed assembly of cobalt(II) 1-H-indazole-3-carboxylic acid coordination networks by bipyridine and its derivatives: structural versatility, electrochemical properties, and antifungal activity

This paper describes the hydrothermal synthesis, full characterization, and architectural diversity of three intriguingly bioactive cobalt–organic frameworks, namely, 3D [Co(HL − )2(BPY)] n ·4nH2O (1), 2D [Co(HL − )2(BPE)] n (2), and 2D [Co(HL − )2(DPP)] n (3) coordination polymers, synthesized through a mixed ligand strategy using H 2 L (1-H-indazole-3-carboxylic acid) as a main structural block and the flexible bipyridine and its derivatives (BPY = 4,4′-bipydine, BPE = 1,2-bis(4-pyridyl)ethane, DPP = 1,3-bis(4-pyridyl)propane) as auxiliary ligand sources. Complexes 1–3 were isolated as air stable and slightly soluble crystalline solids and characterized using elemental analysis, FT-IR, electrochemical technique, thermogravimetric analysis, powder X-ray diffractometer, and single-crystal X-ray crystallography. The bipyridine derivatives played key roles in defining the structural space group and dimensionality feature of the obtained networks. The abundant H-bonding and π–π stacking interactions in complexes 1–3 gave rise to their intricate metal–organic structures of 3D (1), 2D (2), and 2D (3). In addition, the solutions of complexes 1–3 showed profound antifungal activities against the selected strain of Colletotrichum musae compared with the controlled group using benomyl as a traditional agrochemical fungicide.

Role of non-covalent interactions in three copper(II) 5-chloro-2-nitrobenzoate complexes with N-donor ligands: Syntheses, characterization and packing analyses of trans-[Cu(β-pic)2(H2O)2(5-chloro-2-nitrobenzoate)2], trans-[Cu(γ-pic)2(5-chloro-2-nitrobenzoate)2] and [trans-Cu(en)2(H2O)2](5-chloro-2-nitrobenzoate)2·2H2O

Three new copper(II) complexes trans-[Cu(β-pic)2(H2O)2(5-chloro-2-nitrobenzoate)2] 1, trans-[Cu(γ-pic)2(5-chloro-2-nitrobenzoate)2], 2 and [trans-Cu(en)2(H2O)2](5-chloro-2-nitrobenzoate)2·2H2O, 3 (where β-pic=β-picoline, γ-pic=γ-picoline and en=ethylenediamine) were prepared by the addition of β-pic, γ-pic and en, respectively, to the hydrated copper(II) 5-chloro-2-nitrobenzoate, suspended in methanol–water mixture (4:1, v/v). The newly synthesized complexes have been characterized by elemental analyses, TGA, spectroscopic techniques (FT-IR, UV–Vis and EPR), conductivity measurements, magnetic susceptibility studies and single crystal X-ray structure determination. Complex 1 crystallizes in monoclinic crystal system with P21/c space group whereas the complexes 2 and 3 crystallizes in triclinic crystal system with P1¯ space group. Single crystal X-ray structure determination revealed the presence of elongated octahedral geometry in all three complexes. Cu(II) center is covalently coordinated by two 5-chloro-2-nitrobenzoate, two β-pic moieties and two water molecules in complex 1, two bidentate 5-chloro-2-nitrobenzoate and two γ-pic moieties in complex 2. In complex 3, the copper ion is coordinated to two chelating en ligands, two water molecules; with two 5-chloro-2-nitrobenzoate as counter anions and two water molecules of crystallization. The crystal lattice in complexes 1–3 is stabilized by an intricate network of hydrogen bonding interactions (C–H…O, O–H…O in complex 1, C–H…O in complex 2 and O–H…O, N–H…O and C–H…O in 3). Besides this, π…π stacking interactions in complex 1 and C–H…π interactions in complex 2 also contribute towards stability of the crystal lattice.

Assembly of triorganotin chloride with selenite ligands to macrocyclic, zigzag, helical, and linear structures: syntheses, characterizations, and crystal structures of [R3Sn(O2SeC6H4-4-Et)] n and [R3Sn(O2SeC6H4-2-Et)] n (R = Me, C6H5) complexes

Four new triorganotin(IV) complexes, [R3Sn(O2SeC6H4-4-Et)]4 (R = Me 1), [R3Sn(O2SeC6H4-4-Et)] n (R = Ph 2), [R3Sn(O2SeC6H4-2-Et)] n (R = Me 3; Ph 4) have been synthesized by the treatment of 4-ethylbenzeneseleninic acid, 2-ethylbenzeneseleninic acid, and the corresponding triorganotin(IV) chloride with sodium ethoxide in methanol. All of the complexes were characterized by elemental analysis, FT-IR, NMR (1H, 13C, and 119Sn) spectroscopy, TGA, and X-ray crystallography. Crystal structures show that all of the complexes are generated by the bidentate oxygen atoms and the five-coordinated tin centers with trigonal bipyramid geometry. The structural analyses reveal that complex 1 has a centrosymmetric tetranuclear triorganotin selenite with 16-membered macrocycle, which is formed by trimethyltin and ligand alternate linking. A series of C–H···O and π–π stacking interactions in complex 1 play an important function in the supramolecular aggregation. Complex 3 has two 1D spring-like chiral helical chains and crystallizes in the monoclinic space group P21, which is chiral. Complex 2 and 4 are both 1D infinite neutral chain polymers and complex 2 forms a 2D supramolecular framework through intermolecular C–H···O interactions.

Optically detected triplet-state magnetic resonance studies of the DNA complexes of the bisquinoline analog of echinomycin

The polymeric DNA and model duplex oligonucleotide complexes of the bisquinoline analogue of echinomycin (2QN) have been studied by optical detection of triplet-state magnetic resonance (ODMR) spectroscopy, with the quinoline chromophores of the drug used as intrinsic probes. Plots of ODMR transition frequencies versus monitored wavelength revealed heterogeneity in the phosphorescence emission of 2QN which was ascribed to the presence of a major and minor conformation of the drug in aqueous solutions (referred to as the red and blue forms of 2QN, respectively, in this report). ODMR results, in conjunction with findings from low-temperature phosphorescence investigations, indicate that the quinoline chromophores of the major (red) form of 2QN are involved in aromatic stacking interactions in complexes with the natural DNAs from Escherichia coli, Micrococcus lysodeikticus, Clostridium perfringens, and calf thymus as evidenced by red shifts in the phosphorescence 0,0-band of the drug, reductions in the phosphorescence lifetime and zero-field splitting (zfs) D and E parameters, and polarity reversals of the ODMR slow passage signals upon complex formation between the analogue and DNA. The polarity reversals, which reflect shifts in the triplet-state sublevel populations induced by complex formation, apparently result from changes in the triplet sublevel decay constants upon binding to the natural DNAs. The 2QN complexes of the double-stranded alternating copolymers poly(dG-dC).poly(dG-dC) [abbreviated as poly[d(G-C)2]] and poly(dA-dT).poly(dA-dT) [abbreviated as poly(dA-dT).poly(dA-dT) [abbreviated as poly[d(A-T)2], the homopolymer duplexes poly(dG).poly(dC) [abbreviated as poly(dG.dC)] and poly(dA).poly(dT) [abbreviated as poly(dA.dT)], and the self-complementary oligonucleotides d(ACGT)2, d(TCGA)2, and d(ACGTACGT)2 were also investigated. The extent of reduction of the zfs D parameter (delta D) for the major form of 2QN upon complex formation with the polymeric DNAs was found to scale linearly with the standard free energy of the drug-DNA interaction (delta G degrees) calculated from previously reported binding studies for these targets [Fox, K. R., et al. (1980) Biochem. J. 191, 729-740]. This relationship between spectroscopic and thermodynamic properties of the 2QN-polynucleotide complexes is a consequence of the effects of base stacking interactions on the electronic states of the intercalator, which were postulated to arise from second-order shifts of the ground-state and the triplet-state energies of the complex on the basis of a modification of the solvent effect theory of van Egmond et al. [(1975) Chem. Phys. Lett. 34, 423-426].

Application of ODMR to the study of DNA complexes of bisintercalating antibiotics and their biosynthesized derivatives

The DNA complexes of triostin A, echinomycin, and the monoquinoline (1QN) and bisquinoline (2QN) biosynthesized derivatives of echinomycin were investigated by optical detection of triplet-state magnetic resonance (ODMR) spectroscopy, with the quinoxaline and quinoline moieties of the DNA-binding peptides used as intrinsic probes. Plots of zero-field splitting (zfs)D parameter versus monitored wavelength revealed heterogeneity in the phosphorescence emission of echinomycin, triostin A, and 2QN ascribed to the occurrence of major and minor forms of the peptides in aqueous solution. ODMR results, in conjunction with findings from phosphorescence studies, indicate that the quinoxaline and quinoline chromophores of the major forms of the peptides are involved in aromatic stacking interactions in complexes with the natural DNAs fromMicrococcus lysodeikticus, Escherichia coli, and calf thymus as evidenced by red shifts in the phosphorescence 0,0 bands of the drugs, reductions in the phosphorescence lifetimes and zfsD andE parameters, and polarity reversal of the ODMR slow passage signals upon drug complexation. The reversal in ODMR signal polarity of echinomycin and 2QN is a consequence of changes in the triplet-state sublevel decay constants upon peptide binding to the natural DNAs. The extent of reduction of theD parameter for the major form of echinomycin, 2QN, and the quinoline moiety of 1QN upon complexation with polymeric DNAs was found to correlate with the binding affinities measured for these targets [1], but no correlation was found for the quinoxaline moiety of 1QN. Preliminary studies of triostin A-DNA complexes also revealed no correlation between the reduction in zfsD-value upon complexation and binding affinity, although the largest reductions inD-value among the peptides investigated in this report were exhibited by the poly(dG-dC)·poly(dG-dC) and natural DNA complexes of triostin A.

Phosphorescence and optically detected magnetic resonance studies of echinomycin-DNA complexes

Echinomycin complexes with polymeric DNAs and model duplex oligonucleotides have been studied by low-temperature phosphorescence and optical detection of triplet-state magnetic resonance (ODMR) spectroscopy, with the quinoxaline chromophores of the drug used as intrinsic probes. Although not optically resolved, plots of ODMR transition frequencies versus monitored wavelength revealed heterogeneity in the phosphorescence emission of echinomycin, which was ascribed to the presence of two distinct quinoxaline triplet-state environments (referred to as the blue and red triplet states of echinomycin in this report). We think that a likely origin of the two triplet states of echinomycin is the occurrence of two or more distinct conformations of the drug in aqueous solutions. Spectroscopically observed perturbations of the triplet-state properties of echinomycin such as the phosphorescence emission spectrum, phosphorescence lifetime, ODMR spectrum, and zero-field splitting (zfs) energies were investigated upon drug binding to the double-stranded alternating copolymers poly(dG-dC).poly(dG-dC) [abbreviated as poly[d(G-C)2]] and poly(dA-dT).poly(dA-dT) [abbreviated as poly[d(A-T)2]], the homopolymer duplexes poly(dG).poly(dC) [abbreviated as poly(dG.dC)] and poly(dA).poly(dT) [abbreviated as poly(dA.dT)], and the natural DNAs from Escherichia coli, Micrococcus lysodeikticus, and calf thymus. Echinomycin bisintercalation complexes with the self-complementary oligonucleotides d(ACGT), d(CGTACG), and d(ACGTACGT), which are thought to model drug binding sites, were also investigated. Phosphorescence and ODMR spectroscopic results indicate that the quinoxaline chromophores of the drug are involved in aromatic stacking interactions in complexes with the natural DNAs as evidenced by red shifts in the phosphorescence 0,0 band of the drug, a small but significant reduction in the phosphorescence lifetime of the red triplet state, and reduction of the zfs D-value of both the blue and red triplet states upon drug complexation. These changes in the triplet-state properties of echinomycin are consistent with stacking interactions that increase the polarizability of the quinoxaline environment. The extent of the reduction of the D parameter for the red triplet state upon complexation with the polymeric DNAs was found to correlate with the binding affinities measured for these targets [Wakelin, L. P. G., & Waring, M. J. (1976) Biochem. J. 157, 721-740], with the single exception of the drug-poly[d(G-C)2] complex, for which an increase in the D-value was noted. In addition, upon drug binding to the natural DNAs, there is a reversal of signal polarity in the ODMR spectra of the red triplet state. Among the synthetic DNA polymers investigated, a reversal of ODMR signal polarity was found only with the echinomycin-poly[d(A-T)2] complex.(ABSTRACT TRUNCATED AT 400 WORDS)