Crystal structure and spin crossover studies on bis(2,6-bis(benzimidazol-2-yl)pyridine) iron(II) perchlorate

The structure of the [Fe(bzimpy)₂](ClO₄)₂·xH₂O system (x = 0.25) was determined by single crystal X-ray structure analysis. The Fe(II) ion is hexacoordinated by six donor nitrogen atoms. The magnetic properties of the complex were investigated by powder magnetic susceptibility measurements and ESR. The freshly prepared sample does not show any traces of iron(III) impurities but these are formed as a function of time. After 1 year the sample contains 8.2% iron(III) as shown by UV spectroscopy and indicated by g_eff = 4.3 and 2.0 in its ESR spectrum. This explains the recorded ξ versus T behaviour at low temperature: with increasing temperature the ξ value decreases according to the Curie-Weiss law for a S = 5/2 system having an effective g = 4.3. Above 220 K a continuous increase in the ξ value is observed and a spin crossover applies. The spin transition is not complete at room temperature. A pronounced hysteresis is observed upon heating/cooling the sample between 220 and 414 K on the basis of magnetic data and infrared spectra.     

Tetrameric 1:1 and monomeric 1:3 complexes of silver(I) halides with tri(p-tolyl)-phosphine: A structural and biological study

Silver(I) halides react with tri(p-tolyl)phosphine (tptp, C₂₁H₂₁P) in MeOH/MeCN solutions in 1:1 or 1:3 molar ratios to give complexes of formulae {[AgCl(tptp)]₄} (1) or [AgX(tptp)₃] (X = Cl (2), Br (3), I (4)), respectively. The complexes were characterized by elemental analyses, and FT-IR far-IR, FT-Raman, TG and ¹H, ¹³C, ³¹P NMR spectroscopic techniques. Crystal structures of complexes 2-4 were determined by X-ray diffraction at room temperature (rt). The crystal structure of 1 and 4 was also determined at 100(1) and 140(2) K (lt), respectively. In complex 1 four μ3-Cl ions are bonded with four Ag(I) ions forming a cubane while the coordination sphere of silver(I) ions is completed by one P atom from a terminal tri(p-tolyl)phosphine ligand. In complexes 2-3 one terminal halogen and three P atoms from phosphine ligands form a tetrahedral arrangement around the metal ion. Complexes 1-4 were tested for in vitro cytostatic activity against sarcoma cancer cells (mesenchymal tissue) from the Wistar rat, polycyclic aromatic hydrocarbons (PAH, benzo[a]pyrene) carcinogenesis and against murine leukemia (L1210) and human T-lymphocyte (Molt4/C8 and CEM) cells. The silver(I) complexes 1-4 show strong activity.     

Bis‐ and Tetrakis(carboxylato)platinum(IV) Complexes with Mixed Axial Ligands – Synthesis,Characterization, and Cytotoxicity

A series of twelve novel diamminetetrakis(carboxylato)platinum(IV) and 18 novel bis(carboxylato)dichlorido(ethane‐1,2‐diamine)platinum(IV) complexes with mixed axial carboxylato ligands was synthesized and characterized by multinuclear ¹H‐, ¹³C‐, ¹⁵N‐, and ¹⁹⁵Pt‐NMR spectroscopy. Their cytotoxic potential was evaluated (by MTT assay) against three human cancer cell lines derived from ovarian teratocarcinoma (CH1/PA‐1), lung (A549), and colon carcinoma (SW480). In the cisplatin‐sensitive CH1/PA‐1 cancer cell line, diamminetetrakis(carboxylato)platinum(IV) complexes showed IC₅₀ values in the low micromolar range, whereas, for the most lipophilic compounds of the bis(carboxylato)dichlorido(ethane‐1,2‐diamine)platinum(IV) series, IC₅₀ values in the nanomolar range were found.     

Synthesis, molecular structure, substitution and C-C coupling reactions of ruthenium complexes containing (η-C9H7)Ru(PPh3) as a molecular unit

The 2-methallyl complex [(η⁵-C₉H₇)Ru(η³-2-MeC₃H₄)(PPh₃)] (3), prepared from [(η⁵-C₉H₇)Ru(PPh₃)₂Cl] (2) and 2-MeC₃H₄MgCl, reacts with HX (X = Cl, CF₃CO₂) in the presence of ethene to give the chiral-at-metal compounds [(η⁵-C₉H₇)Ru(C₂H₄)(PPh₃)X] (4, 5) in nearly quantitative yields. Treatment of 2 with AgPF₆ and ethene affords [(η⁵-C₉H₇)Ru(C₂H₄)(PPh₃)₂]PF₆ (6), which reacts with acetone to give the substitution product [(η⁵-C₉H₇)Ru(OCMe₂)(PPh₃)₂]PF₆ (7). The molecular structure of 7 has been determined crystallographically. Whereas treatment of 4 with CH(CO₂Et)N₂ yields the olefin complex [(η⁵-C₉H₇)Ru{η²-(Z)-C₂H₂(CO₂Et)₂}(PPh₃)Cl] (8), the reactions of 4 and 5 with Ph₂CN₂, PhCHN₂ and (Me₃Si)CHN₂ lead to the formation of the carbeneruthenium(II) derivatives [(η⁵-C₉H₇)Ru(CRR′)(PPh₃)Cl] (9-11) and [(η⁵-C₉H₇)Ru(CRR′)(PPh₃)(κ¹-O₂CCF₃)] (12-14), respectively. Treatment of 9 (R = R′ = Ph), 10 (R = H, R′ = Ph) and 11 (R = H, R′ = SiMe₃) with MeLi produces the hydrido(olefin) complexes [(η⁵-C₉H₇)RuH(η²-CH₂CPh₂)(PPh₃)] (15), [(η⁵-C₉H₇)RuH(η²-CH₂CHPh)(PPh₃)] (18a,b) and [(η⁵-C₉H₇)RuH(η²-CH₂CHSiMe₃)(PPh₃)] (19) via C-C coupling and β-hydride shift. The analogous reactions of 11 with PhLi gives the η³-benzyl compound [(η⁵-C₉H₇)Ru{η³-(Me₃Si)CHC₆H₅}(PPh₃)] (20). The η³-allyl complex [(η⁵-C₉H₇)Ru(η³-1-PhC₃H₄)(PPh₃)] (17) was prepared from 10 and CH₂CHMgBr by nucleophilic attack.     

Electrolyte effects on the intervalence transition within discrete binuclear cyano-bridged complexes. An estimation of activation free energy from static, optical and electrochemical data

A study of the metal-to-metal charge-transfer (MMCT) transition within the binuclear cyano-bridged complexes cis-[L¹³Co^III(μ-NC)Fe^II(CN)₅]⁻ (L¹³ = 12-methyl-1,4,7,10-tetraazacyclotridecan-12-amine), trans-[L¹⁴Co^III(μ-NC)Fe^II(CN)₅]⁻ (L¹⁴ = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) and trans-[L¹⁵Co^III(μ-NC)Fe^II(CN)₅]⁻ (L¹⁵ = 10-methyl-1,4,8,12-tetraazacyclopentadecan-10-amine) has been carried out in electrolyte solutions at varying concentrations. Using these data, as well as the reaction free energies obtained from electrochemical measurements, the reorganisation and activation free energies for the forward and reverse thermal electron-transfer processes have been estimated. The changes of these parameters with the electrolyte concentration, as well as those of the energy of the maximum MMCT band and the reaction free energy, are mainly due to ion-pairing effects.     

Experimental evidence that flavonoid metal complexes may act as mimics of superoxide dismutase

Radical scavenging activities of flavonoids rutin, taxifolin, (-)-epicatechin, luteolin, and their complexes with transition metal (Fe2+, Fe3+, and Cu2+) towards superoxide were determined using illumination of riboflavin as source and NBT as detector of O*2-. The scavenger potencies of flavonoid metal complexes were significantly higher than those of the parent flavonoids. To elucidate the mechanism of this phenomenon, the rates of superoxide-dependent oxidation of flavonoids and their metal complexes in photochemical system with riboflavin were examined. It was found for the first time that flavonoids bound to metal ions were much less subjected to oxidation compared with those of free compounds. The findings directly demonstrate superoxide scavenging activity of metal ions in complexes with flavonoids and support earlier suggestions that flavonoid metal complexes may exhibit superoxide dismuting activity.     

Enzyme co-localization in pea leaf chloroplasts: glyceraldehyde-3-P dehydrogenase,triose-P isomerase,aldolase and sedoheptulose bisphosphatase

Nearest neighbor analysis of immunocytolocalization experiments indicates that the enzymes glyceraldehyde-3-P dehydrogenase, triose-P isomerase and aldolase are located close to one another in the pea leaf chloroplast stroma, and that aldolase is located close to sedoheptulose bisphosphatase. Direct transfer of the triose phosphates between glyceraldehyde-3-P dehydrogenase and triose-P isomerase, and from glyceraldehyde-3-P dehydrogenase and triose-P isomerase to aldolase, is then a possibility, as is direct transfer of sedoheptulose bisphosphate from aldolase to sedoheptulose bisphosphatase. Spatial organization of these enzymes may be important for efficient CO₂ fixation in photosynthetic organisms. In contrast, there is no indication that fructose bisphosphatase is co-localized with aldolase, and direct transfer of fructose bisphosphate from aldolase to fructose bisphosphatase seems unlikely.     

Permeability of Plant Young Root Endodermis to Cu Ions and Cu-Citrate Complexes in Corn and Soybean

The non-selective apoplastic passage of Cu and Cu-citrate complexes into the root stele of monocotyledonous corn and dicotyledonous soybean was investigated using an inorganic-salt-precipitation technique. Either Cu ions or Cu-citrate complexes were drawn into root through the apoplast from the root growth medium, and K₄[Fe(CN)₆] was subsequently perfused through xylem vessels or the entire root cross section. Based on microscopic identification of the reddish-brown precipitates of copper ferrocyanide in the cell walls of the xylem of corn and soybean roots, Cu²⁺ passed through the endodermal barrier into the xylem of both species. When the solution containing 200 μM CuSO₄ and 400 μM sodium citrate (containing 199.98 μM Cu-citrate, 0.02 μM Cu²⁺) was drawn via differential pressure gradients into the root xylem while being perfused with K₄[Fe(CN)₆] through the entire root cross-section, reddish-brown precipitates were observed in the walls of the stele of soybean, but not corn root. However, when a CuSO₄ solution containing 0.02 or 0.2 μM free Cu²⁺ was used, no reddish-brown precipitates were detected in the stele of either of the two plants. Results indicated that endodermis was permeable to Cu-citrate complexes in primary roots of soybean, but not corn. The permeability of the endodermal barrier to the Cu-citrate complex may vary between dicotyledonous and monocotyledonous plants, which has considerable implications for chelant-enhanced phytoextraction.     

Synthesis,Characterization, and Biological Activities of Pendant Arm‐Pyridyltetrazole Copper(II) Complexes: DNA Binding/Cleavage Activity and Cytotoxic Studies

2‐(1H‐Tetrazol‐5‐yl)pyridine ( L ) has been reacted separately with Me₂NCH₂CH₂Cl?HCl and ClCH₂CH₂OH to yield two regioisomers in each case, N,N‐dimethyl‐2‐[5‐(pyridin‐2‐yl)‐1H‐tetrazol‐1‐yl]ethanamine ( L1 )/N,N‐dimethyl‐2‐[5‐(pyridin‐2‐yl)‐2H‐tetrazol‐2‐yl]ethanamine ( L2 ) and 2‐[5‐(pyridin‐2‐yl)‐1H‐tetrazol‐1‐yl]ethanol ( L3 )/2‐[5‐(pyridin‐2‐yl)‐2H‐tetrazol‐2‐yl]ethanol ( L4 ), respectively. These ligands, L1 – L4 , have been coordinated with CuCl₂?H₂O in 1 : 1 composition to furnish the corresponding complexes 1 – 4 . EPR Spectra of Cu complexes 1 and 3 were characteristic of square planar geometry, with nuclear hyperfine spin 3/2. Single X‐ray crystallographic studies of 3 revealed that the Cu center has a square planar structure. DNA binding studies were carried out by UV/VIS absorption; viscosity and thermal denaturation studies revealed that each of these complexes are avid binders of calf thymus DNA. Investigation of nucleolytic cleavage activities of the complexes was carried out on double‐stranded pBR322 circular plasmid DNA by using a gel electrophoresis experiment under various conditions, where cleavage of DNA takes place by oxidative free‐radical mechanism (OH ^? ). In vitro anticancer activities of the complexes against MCF‐7 (human breast adenocarcinoma) cells revealed that the complexes inhibit the growth of cancer cells. The IC₅₀ values of the complexes showed that Cu complexes exhibit comparable cytotoxic activities compared to the standard drug cisplatin.