Synthesis and characterisation of the carboxylate linked osmium clusters [{Os3H(CO)10}2(CO2CH2CO2)], [{Os3H(CO)10}2(CO2C2H4CO2)], [{Os3H(CO)10}2(C4O4)] and [{Os3H(CO)10}2(C4O4){Co2(CO)6}]

Reactions between the activated cluster [Os₃(CO)₁₀(NCMe)₂] and malonic acid, succinic acid and dicarboxylic acetylene, respectively, lead to the formation of the linked cluster complexes [{Os₃H(CO)₁₀}₂(CO₂CH₂CO₂)] (1), [{Os₃H(CO)₁₀}₂(CO₂C₂H₄CO₂)] (2), and [{Os₃H(CO)₁₀}₂(C₄O₄)] (3) in good yield. Cluster 3 was subsequently treated with [Co₂(CO)₈] and this results in the addition of a “Co₂(CO)₆” group giving [{Os₃H(CO)₁₀}₂(C₂O₄){Co₂(CO)₆}] (4). The X-ray crystal structures are reported for 2–4. In each structure the two triangular triosmium units are linked by the carboxylate groups and within each complex the carboxylate groups are chelating and bridge two osmium atoms.     

Optically active transition-metal compounds. 93. X-ray determination of the structure and absolute configuration of (+) 578-C5H5Fe(CO) [P(C6H5)3] COCH3

The structure and absolute configuration of (+)₅₇₈- C₅H₅Fe(CO)[P(C₆H₅)₃]COCH₃ have been determined by single crystal X-ray diffraction methods. The substance crystallizes in the monoclinic space group P2₁ with cell constants of a = 8.084(14), b = 8.527(2), c32.706(21) Å and β = 104.32(10)°; V 2184.18 ų and D(calc: Z 4 mol/unit cell) = 1.381 g cm^-3. There are two independent molecules in the asymmetric unit, which allowed us to gauge the effect of packing on the conformation of those groups able, in principle, to be twisted by crystalline forces. Only minor changes in conformations were observed, the largest being at the terminal CH₃ of the acetyl ligand (0.065 Å). All other differences in conformation are less than 0.036 Å. The plane of the acetyl ligand is close to being aligned with the FeC(CO) bond, making the acetyl oxygen point in the direction of the phosphorus atom. It is suggested that in phosphine exchange reactions this conformation persists in solution while the acetyl oxygen, intra- molecularly, attacks the adjacent phosphorus atom to form a dihapto acetyl species as the first intermediate, in which there is retention of configuration at Fe.With the priority of the ligand sequence as C₅H₅ > P(C₆H₅)₃ > CO > COCH₃, the absolute configuration at Fe is (S). So, the formation of (−)₅₇₈- C₅H₅Fe(CO)[P(C₆H₅)₃]COCH₃ by reaction of (+)₅₇₈- C₅ H₅ Fe(CO)[P(C₆H₅)₃] COOC₁₀H₁₉ and LICH₃ requires an inversion to occur at the Fe center.     

Re(CO)(3)(H(2)O)(3)(+) binding to lysozyme: structure and reactivity

The reaction of Re(CO)(3)(H(2)O)(3)(+) with hen egg white lysozyme in aqueous solution results in a single covalent adduct. Both NMR spectroscopy and single crystal X-ray diffraction show that the rhenium tricarbonyl cation binds to His15 via replacement of one of the coordinated water molecules. The formation of this adduct does not greatly affect the structure of the protein.     

Uracilato and 5-halouracilato complexes of Cu(II), Zn(II) and Ni(II). X-ray structures of [Cu(uracilato-N(1))(2)(NH(3))(2)].2(H(2)O), [Cu(5-chlorouracilato-N(1))(2)(NH(3))(2)](H(2)O)(2), [Ni(5-chlorouracilato-N(1))(2)(en)(2)].2H(2)O and [Zn(5-chlorouracilato-N(1))(NH(3))(3)].(5-chlorouracilato-N(1)).(H(2)O)

Four new complexes of uracilato and 5-halouracilato with the divalent metal ions Cu(II), Zn(II) and Ni(II) were obtained and structurally characterized. [Cu(uracilato- N(1))(2)(NH(3))(2)].2(H(2)O) (1) and [Cu(5-chlorouracilato-N(1))(2)(NH(3))(2)](H(2)O)(2) (2) complexes present distorted square planar co-ordination geometry around the metal ion. Although an additional axial water molecule is present [Cu(II)-OH(2)=2.89 A (for 1) and 2.52 A (for 2)] in both cases, only in the complex 2 would be considered in the limit of a bond distance. The Zn(II) in [Zn(5-chlorouracilato-N(1))(NH(3))(3)].(5-chlorouracilato-N(1)).(H(2)O) presents a tetrahedral co-ordination with three ammonia molecules and the N(1) of the corresponding uracilato moiety. A non-coordinated uracilato molecule is present as a counterion and a recognition between co-ordinated and free ligands, by means a tandem of H-bonds, should be mentioned. Finally, the complex [Ni(5-chlorouracilato-N(1))(2)(en)(2)] (H(2)O)(2) (where en is ethylenediamine) presents a typical octahedral trans co-ordination with additional hydrogen bonds between 5-chlorouracilato and the NH(2) groups of ethylenediamine units.     

Synthesis, characterization and properties of chromium(III) complex [Cr(SA)(en)2]Cl.2H2O

The reaction of chromium(III) chloride, salicylic acid (SA) and ethylenediamine (en) led to the formation of chromium complex [Cr(SA)(en)(2)]Clx2H(2)O(1). The crystal structure belongs to monoclinic system with the space group P2(1), R(1)=0.0358. In this compound, Cr(III) atom is six-coordinated in octahedral coordination geometry by one phenolic hydroxyl oxygen, one carboxylate oxygen from the salicylic acid and four nitrogen atoms from two ethylenediamine molecules, respectively. The transfer manners of Cr(III) from the title compound to the low-molecular-mass chelator, ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) and the iron-binding protein apoovotransferrin (apoOTf) were followed by a combination of UV-visible (UV-Vis) and fluorescence spectra in 0.01M Hepes at pH 7.4. The results show that Cr(III) can be transferred from the complex to apoovotransferrin with the retention of the salicylate acted as a synergistic anion.     

Crystal structures of the dimeric cobalt compounds [Co(PPhMe2)(CO)3]2 and [Co2(PPhMe2)3(CO)5]

The molecular structures of the dimeric cobalt compounds [Co(PPhMe₂)(CO)₃]₂ and [Co₂(PPhMe₂)₃(CO)₅] have been characterised by X-ray crystallography. The compound [Co₂(PPhMe₂)₃(CO)₅] contains both bridging and terminal carbonyl groups in the solid state.     

Synthesis and characterization of bis[salicylideneaminato] palladium(II) complexes. Molecular structure of bis[N-(n-butyl)(3-benzyloxy)-2-salicylideneaminato]-palladium(II), pd(C18H20NO2)2]

Transition metal compounds having liquid crystalline properties can be interesting materials for practical applications. Attempting to correlate mesomorphic properties with molecular structure and crystal packing mode, we have investigated some complexes obtained from Schiff bases of long chain aliphatic amines and salicylaldehyde or 2,3-dihydroxybenzaldehyde derivatives. The X-ray structural analysis of bis[N-(n-butyl)(3-benzyloxy)-2-salicylideneaminato] palladium [II] is also reported.     

Structural chemistry of dicyclopentadienidehalides of lanthanides Part 4. Erbiumdicyclopentadienidechloride [Er(C5 H5)2Cl]2

The crystal structure of erbiumdicyclopentadienidechloride [Er(C₅H₅)₂Cl]₂ has been determined from X-ray diffraction data. The compound crystallizes in space group P2₁/c with a=11.056(3), b= 8.015(1), c=12.154(3) Å, β=110.28(2)°, V= 1010.2(7) ų, D_c=2.189 g cm⁻³ and Z=2 dimers. The structure has been refined by full-matrix least- squares techniques to a conventional R factor of 0.027 for 2042 reflections (with I > 2σ(I)). In the unit cell centrosymmetric dimers of orte type exist with bridging chlorine atoms and C₅H₅ groups bonded in η⁵-fashion to the metal (mean ErC 2.59 Å). The [Er(C₅H₅)₂Cl]₂-type is compared to the [Sc(C₅H₅)₂Cl]₂-type structure which is realized in several dicyclopentadienidebromides of the lanthanides.     

Oligonucleotide analogues containing the internucleotide linker C3'-NH-CO-CH2-N(CH3)-C5'

Oligonucleotide analogues were synthesized whose internucleoside linker contains an amide bond and a methylamino group (C3'-NH-CO-CH2-N(CH3)-C5'). Melting curves for duplexes formed by modified oligonucleotides and natural oligonucleotides complementary to them were measured, and the melting temperatures and thermodynamic parameters of duplex formation were calculated. The introduction of one modified dinucleoside linker into the oligonucleotide only slightly decreases the melting temperatures of these duplexes compared with unmodified ones. The CD spectra of modified duplexes were studied, and their spatial structures are discussed.     

Sulfhydryl-selective, covalent labeling of biomolecules with transition metallocarbonyl complexes. Synthesis of (eta5-C5H5)M(CO)3(eta1-N-maleimidato) (M = Mo, W), X-ray structure, and reactivity studies

The photochemical reaction of (eta5-C5H5)Mo(CO)3I with maleimide in the presence of diisopropylamine yielded complex (eta5-C5H5)Mo(CO)3(eta1-N-maleimidato) 4 in 52% yield. The single-crystal X-ray structure of this complex was determined and shows unusual interactions between oxygen atoms of the maleimidato ligand and carbon atoms of the cis-CO ligands. The tungsten analogue of 4, (eta5-C5H5)W(CO)3(eta1-N-maleimidato) 5, was synthesized in 37% yield by the reaction of (eta5-C5H5)W(CO)3I with the thallium(I) salt of maleimide. Complexes 4 and 5 reacted with cysteine ethyl ester and glutathione to afford products of the addition of the sulfhydryl group to the ethylenic bond of the maleimidato ligand. The reaction of 4 and 5 with glutathione proceeded faster than the reaction of the analogous complex (eta5-C5H5)Fe(CO)2(eta1-N-maleimidato) (3). However, all these complexes react with glutathione more slowly than N-ethylmaleimide. Complexes 4 and 5 were used for labeling of bovine serum albumin (BSA), enriched in thiol groups by reaction with Traut's reagent. Reaction of thiolated BSA containing 7.4 SH groups with 4 and 5 gave bioconjugates bearing 6.9 and 6.4 metallocarbonyl moieties, respectively. Under the same conditions, reaction with 3 afforded a BSA conjugate containing 7.6 metallocarbonyl moieties. Labeling was presumed to be site-specific, as the number of metallocarbonyl entities matched very well with the initial number of SH groups measured for the thiolated BSA sample. IR spectra of BSA labeled with 4 and 5 show intense nu(C[triple bond]O)) bands (2042 and 1948 cm(-1) in the latter case), enabling sensitive detection of the bioconjugates in biological samples. Complexes 4 and 5 (especially the latter) should be of interest as heavy atom phasing reagents for protein X-ray crystallography.     

Solvent cage effects: the influence of radical mass and volume on the recombination dynamics of radical cage pairs generated by photolysis of [CpCH2CH2N(CH3)C(O)(CH2)nCH3Mo(CO)3]2 (n = 3, 8, 13, 18) (Cp = eta 5-C5H4) complexes

The photochemistry of the [(CpR)Mo(CO)(3)](2) molecules, where CpR = eta(5)-C(5)H(4)(CH(2))(2)C(O)NCH(3)(CH(2))(n)CH(3) (n = 3, 8, 13, and 18), was examined using femtosecond pump-probe transient absorption spectroscopy. The goal of this study was to investigate the importance of radical size and mass on the dynamics and efficiency of geminate radical-radical recombination. The femtosecond results demonstrated the lack of any size/mass dependence of the recombination efficiency. This finding contrasts with results from a prior study that did find a size/mass dependence using a steady-state photochemical technique. To explain these conflicting results, it is proposed that the femtosecond pump-probe results are a measurement of the efficiency of primary geminate recombination whereas the steady-state method results are a measurement of the sum of primary and secondary geminate recombination efficiencies. The size/mass dependence is evident in the latter because secondary geminate recombination is a slower diffusive recombination process and therefore depends on the steric properties of the radicals. Although the existence of primary and secondary recombination channels is often taken for granted, experimental differentiation of primary and secondary caging has proven to be difficult because it is not possible for a single experimental technique to span the entire timescale for recombination of a radical cage pair and adequately resolve these recombination pathways.     

Ternary complexes metal [Co(II), Ni(II), Cu(II) and Zn(II)]--ortho-iodohippurate (I-hip)--acyclovir. X-ray characterization of isostructural [(Co, Ni or Zn)(I-hip)(2)(ACV)(H(2)O)(3)] with stacking as a recognition factor

Four ternary metal--ortho-iodohippurate (I-hip)--acyclovir (ACV) complexes, [M(I-hip)(2)(ACV)(H(2)O)(3)] where M is Co(II) (1), Ni(II) (2), Cu (3) and Zn(II) have been obtained by reaction between the corresponding binary complexes M(II)(I-hip)(2)xnH(2)O and ACV. Three ternary complexes (M=Co, Ni and Zn) and the corresponding Zn(II)--ortho-iodohippurate binary derivative have been structurally characterized by X-ray diffraction: The studies show these three ternary complexes are isostructural and present, in solid state, an interesting stacking between the nucleobase and the aryl ring of the hippurate moiety, which probably promotes the formation of ternary complexes. Moreover, the two different ligands interact between them by means of ancillary hydrogen bonds with water molecules coordinated to the metal ion. It must be mentioned that these two recognition factors, hydrogen bonds plus stacking, could explain the reason for the isostructurality of these ternary derivatives with so different three metal ions, with diverses trends in coordination numbers and geometries. In solid state, there are two enantiomeric molecules that are related by an inversion center as the crystal-building unit (as a translational motif) for the ternary complexes.     

DNA methylation in 5-aza-2''-deoxycytidine-resistant variants of C3H 10T1/2 C18 cells.

A cell line (T17) was derived from C3H 10T1/2 C18 cells after 17 treatments with increasing concentrations of 5-aza-2'-deoxycytidine. The T17 cell line was very resistant to the cytotoxic effects of 5-aza-2'-deoxycytidine, and the 50% lethal dose for 5-aza-2'-deoxycytidine was ca. 3 microM, which was 30-fold greater than that of the parental C3H 10T1/2 C18 cells. Increased drug resistance was not due to a failure of the T17 cell line to incorporate 5-aza-2'-deoxycytidine into DNA. The cells were also slightly cross-resistant to 5-azacytidine. The percentage of cytosines modified to 5-methylcytosine in T17 cells was 0.7%, a 78% decrease from the level of 3.22% in C3H 10T1/2 C18 cells. The DNA cytosine methylation levels in several clones isolated from the treated lines were on the order of 0.7%, and clones with methylation levels lower than 0.45% were not obtained even after further drug treatments. These highly decreased methylation levels appeared to be unstable, and DNA modification increased as the cells divided in the absence of further drug treatment. The results suggest that it may not be possible to derive mouse cells with vanishingly low levels of 5-methylcytosine and that considerable de novo methylation can occur in cultured lines.     

Solvent dependent photophysics of fac-[Re(CO)(3)(11,12-X(2)dppz)(py)](+)(X = H, F or Me).

The photophysical properties of [Re(CO)(3)(dppz)(py)](+) (dppz = dipyrido-[3,2-a:2',3'-c] phenazine) and its 11,12 substituted derivatives [Re(CO)(3)(dppzMe(2))(py)](+) and [Re(CO)(3)(dppzF(2))(py)](+) have been examined in organic and aqueous environments using phosphorescence and picosecond transient visible and infrared absorption spectroscopic methods. The roles of the intraligand IL(pi-pi*) and metal-to-ligand charge transfer MLCT(phz) excited states are evaluated and used to explain the major effect of difluoro-substitution, which is particularly remarkable in water, where the excited state of [Re(CO)(3)(dppzF(2))(py)](+) is strongly quenched.     

C(3)-C(4) Intermediate Species in Alternanthera (Amaranthaceae) : Leaf Anatomy, CO(2) Compensation Point, Net CO(2) Exchange and Activities of Photosynthetic Enzymes

Two naturally occurring species of the genus Alternanthera, namely A. ficoides and A. tenella, were identified as C₃-C₄ intermediates based on leaf anatomy, photosynthetic CO₂ compensation point (Γ), O₂ response of г, light intensity response of г, and the activities of key enzymes of photosynthesis. A. ficoides and A. tenella exhibited a less distinct Kranz-like leaf anatomy with substantial accumulation of starch both in mesophyll and bundle sheath cells. Photosynthetic CO₂ compensation points of these two intermediate species at 29°C were much lower than in C₃ plants and ranged from 18 to 22 microliters per liter. Although A. ficoides and A. tenella exhibited similar intermediacy in г, the apparent photorespiratory component of O₂ inhibition in A. ficoides is lower than in A. tenella. The г progressively decreases from 35 microliters per liter at lowest light intensity to 18 microliters per liter at highest light intensity in A. tenella. It was, however, constant in A. ficoides at 20 to 25 microliters per liter between light intensities measured. The rates of net photosynthesis at 21% O₂ and 29°C by A. ficoides and A. tenella were 25 to 28 milligrams CO₂ per square decimeter per hour which are intermediate between values obtained for Tridax procumbens and A. pungens, C₃ and C₄ species, respectively. The activities of key enzymes of C₄ photosynthesis, phosphoenolpyruvate carboxylase, pyruvate Pi dikinase, NAD malic enzyme, NADP malic enzyme and phosphoenolpyruvate carboxykinase in the two intermediates, A. ficoides and A. tenella are very low or insignificant. Results indicated that the relatively low apparent photorespiratory component in these two species is presumably the basis for the C₃-C₄ intermediate photosynthesis.     

95Mo NMR spectra of MoO2(C8H7N2S)2 and X-ray crystal structure of Mo2O4(C8H7N2S)2(C3H7NO)2

The facile preparation of MoO₂(C₈H₇N₂S)₂ is given and its complex behaviour in dimethylformamide, as revealed by ⁹⁵Mo NMR spectroscopy, discussed. The X-ray crystal structure of one of the products obtained from this dimethylformamide solution is briefly described. This structure indicates that the Mo(VI) has been reduced to Mo(V) and is based on the [Mo₂O₄]²⁺ core.     

Crystal packing and hydrogen bonding in platinum(II) nucleotide complexes: X-ray crystal structure of [Pt(MeSCH(2)CH(2)SMe)(5'-GMP-N7)(2)].6H(2)O

We have synthesised the complex [Pt(CH(3)SCH(2)CH(2)SCH(3))(5'-GMP-N7)(2)].6H(2)O (1), where 5'-GMP is 5'-guanosine monophosphate, and determined its X-ray crystal structure. Pt(II) adopts a square-planar geometry in which the bases are coordinated head-to-tail (HT) in the Delta configuration. The nucleotide conformation in this complex is almost identical to that in the previously reported complex [Pt(en)(5'-GMP-N7)(2)].9H(2)O (2), in which there is outer sphere macrochelation via intramolecular H-bonding between the monoanionic phosphate groups and the coordinated ethylenediamine (en) NH. It is therefore apparent that intermolecular interactions rather than intramolecular H-bonding determines the orientation of the sugar-phosphate side-chain in these Pt(II) bisnucleotide complexes in the solid state.     

Two new scorpionates vanadium haloperoxidases model complexes: synthesis and structure of VO(O2)(pzH)(HB(pz)3) and VO(O2)(pzH)(B(pz)4) (pzH = pyrazole(C3H4N2))

Using vanadate, poly(1H-pyrazol-1-yl)borate and pyrazole as starting materials, two new neutral peroxovanadium(V) complexes with poly(1H-pyrazol-1-yl)borate, VO(O(2))(pzH)(HB(pz)(3))(1) and VO(O(2))(pzH)(B(pz)(4))(2), were synthesized successfully. Both complexes were characterized by elemental analysis, IR, UV-vis and NMR spectra. And the structure of complex 1 was determined by X-ray diffraction, which is somewhat relevant for haloperoxidase enzymes. Cytotoxic effects also are discussed on 3T3 cell proliferation. In the concentration range (0.1-100mumol), both complexes have an inhibiting cellular proliferation effect. When the cells cultivated with the complexes at high dose, the toxicity effect of both complexes is more and more predominant.