Biodefluorination and biotransformation of fluorotelomer alcohols by two alkane‐degrading Pseudomonas strains

Fluorotelomer alcohols [FTOHs, F(CF₂)_nCH₂CH₂OH, n = 4, 6, and 8] are emerging environmental contaminants. Biotransformation of FTOHs by mixed bacterial cultures has been reported; however, little is known about the microorganisms responsible for the biotransformation. Here we reported biotransformation of FTOHs by two well‐studied Pseudomonas strains: Pseudomonas butanovora (butane oxidizer) and Pseudomonas oleovorans (octane oxidizer). Both strains could defluorinate 4:2, 6:2, and 8:2 FTOHs, with a higher degree of defluorination for 4:2 FTOH. According to the identified metabolites, P. oleovorans transformed FTOHs via two pathways I and II. The pathway I led to the production of x:2 ketone [dominant metabolite, F(CF₂)_xC(O)CH₃; x = n ? 1, n = 6 or 8], x:2 sFTOH [F(CF₂)_xCH(OH)CH₃], and perfluorinated carboxylic acids (PFCAs, perfluorohexanoic, or perfluorooctanoic acid). The pathway II resulted in the formation of x:3 polyfluorinated acid [F(CF₂)_xCH₂CH₂COOH] and relatively minor shorter‐chain PFCAs (perfluorobutyric or perfluorohexanoic acid). Conversely, P. butanovora transformed FTOHs by using the pathway I, leading to the production of x:2 ketone, x:2 sFTOH, and PFCAs. This is the first study to show that individual bacterium can bio‐transform FTOHs via different or preferred transformation pathways to remove multiple ? CF₂? groups from FTOHs to form shorter‐chain PFCAs. Biotechnol. Bioeng. 2012; 109: 3041–3048. © 2012 Wiley Periodicals, Inc.     

Kinetics of 8-2 fluorotelomer alcohol and its metabolites, and liver glutathione status following daily oral dosing for 45 days in male and female rats

Fluorotelomer alcohols (FTOHs) are raw materials used in the manufacture of polymeric and surfactant products. Based on previous findings from single oral dosing in rats with radiolabeled 8-2 FTOH, glutathione (GSH) depletion and/or the presence of perfluorinated/polyfluorinated acids and aldehyde metabolites was hypothesized to account for the hepatocellular lesions observed in male rats from a 90-day subchronic oral dosing study. Further, the reported nephropathy in female rats from the subchronic experiment was hypothesized to have been initiated by a thiol metabolite produced by degradation of GSH conjugates. In the current investigation, the kinetics of 8-2 FTOH and its metabolites along with liver GSH status were evaluated in the rat following daily oral dosing with 8-2 FTOH for 45 days at 5 and 125 mg/kg/day. Liver GSH stores 1-2 h after dosing were unaffected, suggesting that GSH depletion is not likely a relevant mode of action in the liver. The tissue metabolite data indicate that the liver toxicity mode of action is likely associated with elevated levels of perfluoroalkyl acids found in males, since other polyfluorinated metabolites and 8-2 FTOH were present in livers from female rats at comparable or higher levels. Detection of the N-acetyl cysteine conjugate of the unsaturated parent telomer alcohol in urine from female rats and not male rats provides some evidence to support the mechanistic basis for the observed kidney effects. Further, the increasing levels of perfluorooctanoic acid (PFOA) in plasma from female rats over the 45-day dosing phase, while unexpected, may reflect an increased net absorption of 8-2 FTOH, slow elimination of intermediates in the metabolic pathway between 8-2 FTOH and PFOA, or altered kidney clearance. The results of this study have enhanced our understanding of 8-2 FTOH kinetics and metabolism and potential modes of action in the rat, which will guide the design of future studies for FTOHs and our need to define the mechanistic basis for the observed effects.     

Syntheses and structures of adducts of stoichiometry MX:dpex (2:1)(n), M = Cu, Ag, X = (pseudo-) halogen, dppx = Ph2E(CH2)xEPh2, E = P, As

Single crystal X-ray studies have defined the structures of a number of adducts of the form MX:dpex (2:1), M = univalent coinage metal (Cu, Ag), X = (pseudo-)halide, dpex = bis(diphenylpnicogeno)alkane, Ph₂E(CH₂)_xEPh₂, E = P, As, of diverse types, some novel. The adducts of AgCl,Br:dppm and AgNCO:dpem (x = 1) are tetranuclear as is the AgNO₃:dppp (x = 3) array, all derivative of the familiar ‘step’ structure while the combination CuCN:dppm yields a two-dimensional web of twenty-membered macro/metallacycles. Synthetic procedures for all adducts have been reported. All compounds have been characterized both in solution (¹H, ¹³C, ³¹P NMR, ESI MS) and in the solid state (IR).     

Hepatocyte or serum albumin protein carbonylation by oxidized fructose metabolites: Glyceraldehyde or glycolaldehyde as endogenous toxins?

Excessive sugar intake in animal models may cause tissue damage associated with oxidative and carbonyl stress cytotoxicity as well as inflammation. Fructose became a 100-fold more cytotoxic if hepatocytes were exposed to a non-toxic infusion of H₂O₂ so as to simulate H₂O₂ released by Kupffer cells or infiltrating immune cells. In order to determine the molecular mechanisms involved, protein carbonylation of fructose and its metabolites were determined using the 2,4-dinitrophenylhydrazine method. In a cell-free system, fructose was found to carbonylate bovine serum albumin (BSA) only if low concentrations of FeII/H₂O₂ were added. Protein carbonylation by the fructose metabolites glyceraldehyde or glycolaldehyde was also markedly increased by FeII/H₂O₂. The protein carbonylation may be attributed to glyoxal formation by hydroxyl radicals as the glyoxal trapping agent aminoguanidine or hydroxyl radical scavengers prevented protein carbonylation. Glyoxal was also much more effective than other carbonyls at causing protein carbonylation. When BSA was replaced by isolated rat hepatocytes, fructose metabolite glyceraldehyde in the presence of non-toxic 2 μM FeII:8-hydroxyquinoline (HQ) and a H₂O₂ generating system (glucose/glucose oxidase) markedly increased cytotoxicity, protein carbonylation and reactive oxygen species (ROS)/H₂O₂ formation. Furthermore this was prevented by hydroxyl radical scavengers or aminoguanidine, a glyoxal scavenger. CuII: 8-hydroxyquinoline increased H₂O₂ induced hepatocyte protein carbonylation less but was prevented by aminoguanidine. However, cytotoxicity and protein carbonylation induced by glyceraldehyde/CuII:HQ/H₂O₂ were not affected by hydroxyl radical scavengers. Although fatty liver induced by an excessive sugar diet in animal models has been proposed as the first hit for non-alcoholic steatohepatitis (NASH) we propose that oxidative stress induced by the oxidation of fructose or fructose metabolites catalysed by Fenton FeII/H₂O₂ could be a ‘second hit’. A perpetual cycle of oxidative stress in hepatocytes could lead to cytotoxicity and contribute to NASH development.     

Synthesis, structures, electrochemistry and properties of dioxo-molybdenum(VI) and -tungsten(VI) complexes with novel asymmetric N2OS, and partially symmetric N2S2, NOS2N-capped tripodal ligands

A new class of asymmetric N-capped (dianionic/trianionic) tripodal proligands [H_x(Lⁿ)] (x = 2, n = 1-6; x = 3, n = 7, 8) which possess pendant arms with N₂OS, N₂S₂ or NOS₂ donor groups and with different chelate ring sizes {5,5,5} or {5,6,5} has been prepared. Treatment of these ligands with [WO₂Cl₂(dme)] (dme = 1,2-dimethoxyethane) in the presence of base (triethylamine or KOH) leads to the formation of cis-dioxotungsten(VI) complexes of the types [WO₂(Lⁿ)] (n = 1-6) and K[WO₂(Lⁿ)] (n = 7, 8). Reaction of these tetradentate ligands with [MoO₂(acac)₂] (acac = acetylacetonate) gives the corresponding Mo(VI) analogues [MoO₂(Lⁿ)] (n = 1-6) and K[MoO₂(Lⁿ)] (n = 7, 8). Moreover, a new five coordinate dioxomolybdenum(VI) complex with an NS₂ tridentate ligand [MoO₂(L⁹)] has been synthesised using similar procedure. All these compounds have been spectroscopically characterised and the molecular structures of [MoO₂(Lⁿ)] (n = 2, 6) and [WO₂(L⁶)] have been established by X-ray diffraction analysis. The electrochemistry and the catalytic activity for oxidation of allylic and benzylic alcohols of these dioxo complexes have also been investigated.     

Influence of substituents on the structures of hybrid complexes constructed from tetranuclear copper(I) 1,2,4-triazolate clusters and octamolybdates

By changing the substituents on 1,2,4-triazole ring, six novel organic-inorganic hybrid complexes constructed from tetranuclear copper(I) 1,2,4-triazolate clusters and octamolybdates, [{Cu₄(L)_x}Mo₈O₂₆] (L = 3,5-diamino-1,2,4-triazole (datrz) and x = 4 for 1; L = 3-amino-1,2,4-triazole (3atrz) and x = 4 for 2; L = 3,5-dimethyl-1,2,4-triazole (dmtrz) and x = 4 for 3; L = 3,5-dimethyl-4-amino-1,2,4-triazole (dmatrz) and x = 6 for 4; L = 3,5-diethyl-4-amino-1,2,4-triazole (deatrz) and x = 4 for 5; L = 3,5-di(n-propyl)-4-amino-1,2,4-triazole (dpatrz) and x = 3 for 6), were obtained. The tetranuclear Cu(I) cluster in compound 1 acts as charge-compensating unit, which is the first polynuclear metal 1,2,4-triazole structure only with N1, N2 bridging mode. Compounds 2, 4, 5 and 6 are of polymeric 1D chains and 3 is of a 2D layer structure. In 2, three distinct Cu(I)-coordination geometries, distorted tetrahedral, T-shaped and V-shaped linear Cu(I), are observed in the same structure. The first extended hybrid structure constructed by δ-octamolybdates is founded in 4. A novel [Mo₈O₂₆]⁴⁻ anion is found in 5, which contains only three crystallographically independent Mo atoms. In compounds 5 and 6, terminal oxo groups of octamolybdate cluster act as μ₃-oxo bridges to link the copper(I) coordination complexes; such an unusual linking manner is unique in the coordination chemistry of octamolybdates with transition metal fragments. The influences of substituent on the structures of the tetranuclear units are also discussed in details.     

Three azido-, alk/phenoxido- and acetato-bridged tetranuclear nickel complexes featuring defective double-cubane

Three new tetranuclear nickel(II) complexes of general formula [Ni₄(L)₂(N₃)₂(CH₃COO)₂(CH₃O)₂]₂·xCH₃OH·yH₂O (HL = HL¹, HL² and HL³; x = 0, y = 1 for 1; x = 2, y = 0 for 2 and x = 2, y = 4 for 3) were synthesized and characterized by single crystal X-ray diffraction and magnetic measurements. Single crystal X-ray studies reveal that all three complexes exhibit similar tetranuclear face-shared defective double-cubane structure, having azido-, alk/phenoxido- and acetato-bridges. Magnetic susceptibility measurements on the complexes in the range of 300-2 K indicate ferromagnetic coupling between the metal ions. The slightly different magnetic behaviors observed are probably caused by subtle structural differences between the respective [Ni₄O₄N₂] cores induced by ligand variation.     

Chemical implantation of Group 4 cations on silica via cyclopentadienyl- and N,N-dialkylcarbamato derivatives

Chemical implantation of Group 4 cations [Ti(III), Ti(IV), Zr(IV), Hf(IV)] has been carried out under mild conditions by the reaction of polycyclopentadienyl- (MCp_n; M = Ti, n = 3, 4; M = Zr, Hf, n = 4), mixed cyclopentadienyl/N,N-dialkylcarbamato (ML_x(O₂CNEt₂)_y; M = Ti, L = Cp, C₅Me₅ (Cp*), x = 2, y = 1; M = Hf, L = Cp, x = 1, y = 3), and N,N-dialkylcarbamato (M(O₂CNR₂)_n, M = Ti, n = 3, R = ⁱPr; M = Ti, Hf, n = 4, R = Et; M = Zr, n = 4, R = ⁱPr) derivatives, with the silanol groups of amorphous silica. Cyclopentadiene/pentamethylcyclopentadiene and/or carbon dioxide and the secondary amine are released in the process. The amount of implanted cations depends on the metal and on the ligands, the pentamethylcyclopentadienyl complex being less reactive than the unsubstituted congener. The starting complexes and the final products have been characterized by EPR or by ¹³C CP-MAS NMR spectroscopy.     

Stereochemically non-rigid helical mercury(II) complexes

Reactions of the 1:2 condensate (L) of benzil dihydrazone and 2-acetylpyridine with Hg(ClO₄)₂ · xH₂O and HgI₂ yield yellow [HgL₂](ClO₄)₂ (1) and HgLI₂ (2), respectively. Homoleptic 1 is a 8-coordinate double helical complex with a Hg(II)N₈ core crystallising in the space group Pbca with cell dimensions: a = 16.2250(3), b = 20.9563(7), c = 31.9886(11) Å. Complex 2 is a 4-coordinate single helical complex having a Hg(II)N₂I₂ core crystallising in the space group P2₁/n with cell dimensions a = 9.8011(3), b = 17.6736(6), c = 16.7123(6) Å and β = 95.760(3)^o. In complex 1, the N-donor ligand L uses all of its binding sites to act as tetradentate. On the other hand, it acts as a bidentate N-donor ligand in 2 giving rise to a dangling part. From variable temperature ¹H NMR studies both the complexes are found to be stereochemically non-rigid in solution. In the case of 2, the solution process involves wrapping up of the dangling part of L around the metal.     

Syntheses, structures, and magnetic properties of 3d-4f heterometallic complexes constructed from pyrazole-bridged CuLn dinuclear units

A series of pyrazole-bridged heterometallic 3d-4f complexes, [CuDy(ipdc)₂(H₂O)₄] · (2H₂O)(H₃O⁺) (1) and [CuLn(pdc)(ipdc)(H₂O)₄] · H₃O⁺ (Ln = Ho (2), Er (3), Yb (4); H₃ipdc = 4-iodo-3,5-pyrazoledicarboxylic acid; H₃pdc = 3,5-pyrazoledicarboxylic acid), {[Cu₃Ln₄(ipdc)₆(H₂O)₁₆] · xH₂O}_n (Ln = Sm (5), x = 8.5; Ln = Eu (6), x = 7; Ln = Gd (7), Tb (8), x = 9), have been synthesized and structurally characterized. Ligand H₃ipdc was in situ obtained by iodination of ligand H₃pdc. Complexes 1-4 are pyrazole-bridged heterometallic dinuclear complexes, and 2-4 are isostructural. Complexes 5-8 are isostructural and comprised of an unusual infinite one-dimensional tape-like chain based on pyrazole-bridged heterometallic dinuclear units. The magnetic properties of compounds 1-4, 7 and 8 have been investigated through the magnetic measurement over the temperature range of 1.8-300 K.     

Bifunctional chelates with mixed aromatic and aliphatic amine donors for labeling of biomolecules with the {Tc(CO)3} and {Re(CO)3} cores

A series of tridentate ligands consisting of mixed aromatic and aliphatic amine derivatives of single amino acid chelates and phenylpiperazine have been developed, and their reactions with [NEt₄]₂[ReBr₃(CO)₃] have been investigated. The compounds [Re(CO)₃{(NC₅H₄CH₂)NCH₃(C₂H₄)NHCH₃}]Br (4), [Re(CO)₃{(NC₅H₄CH₂)NCH₃(C₂H₄)NCH₃(CH₂)_xCOOC₂H₅}]Br (x = 1, 5; x = 4, 6) [Re(CO)₃{(NC₅H₄CH₂)NH(C₂H₄)N(CH₃)₂}]Br (7), [Re(CO)₃{(NC₅H₄CH₂)N(CH ₂COOC₂H₅)(C₂H₄)N(CH₃)₂}]Br (8) and [Re(CO)₃(NC₅H₄CH₂)(C₂H₄NH₂)N(CH₂)₃-CH₃Ophenpip]Br (9) (phenpip: phenylpiperazine, -C₆H₄-(CH₂CH₂)₂N-) were prepared and characterized by elemental analysis, NMR, IR, HSMS and X-ray crystallography. All complexes exhibit fac-{Re(CO)₃N₃} coordination geometry in the cationic molecular unit. Crystal data for C₁₃H₁₇BrN₃O₃Re (4): orthorhombic, Pbca, a = 13.4510(8) Å, b = 10.5728(6) Å, c = 22.5378(13) Å, V = 3205.2(3) ų, Z = 8; C₁₇H₂₃BrN₃O₅Re (5): orthorhombic, Pcca, a = 16.5907(7) Å,b = 14.8387(6) Å, c = 16.7075(7) Å, V = 4113.1(3) ų, Z = 8; C₁₃H₂₅BrN₃O₇Re (7 · 4H₂O): monoclinic, P2₁/n, a = 14.0698(17) Å, b = 9.6760(12) Å, c = 15.6099 (19) Å, β = 114.930(2)°, V = 1927.1(4) ų, Z = 4; C₁₇H₂₃BrN₃O₅Re (8): monoclinic, P2₁/n, a = 7.5312(5) Å, b = 16.0366(10) Å, c = 16.8741(10) Å, β = 98.9990(10)°, V = 2012.9(2) ų, Z = 4.     

Synthesis, structure and cytotoxicity studies of diisopropylammonium and triethylammonium salts of triphenylphosphinegold(I) sulfanylcarboxylates

Compounds of the type [HQ][Au(PPh₃)(xspa)] and [HP][Au(PPh₃)(xspa)] {HQ = diisopropylammonium; HP = triethylammonium; H₂xspa = 3-aryl-2-sulfanylpropenoic acids [x: p = 3-phenyl-, f = 3-(2-furyl)-, t = 3-(2-thienyl)-, -o-py = 3-(2-pyridyl)-, Clp = 3-(2-chlorophenyl)-, -o-mp = 3-(2-methoxyphenyl)-, -p-mp = 3-(4-methoxyphenyl)-, -o-hp = 3-(2-hydroxyphenyl)-, -p-hp = 3-(4-hydroxyphenyl)-, diBr-o-hp = 3-(3,5-dibromo-2-hydroxyphenyl]} were synthesized and characterized by IR and NMR (¹H, ¹³C and ³¹P) spectroscopy and by FAB mass spectrometry. The structures of [HQ][Au(PPh₃)(Clpspa)] and [HQ][Au(PPh₃)(-o-mpspa)] show that the crystal contains hydrogen-bonded diisopropylammonium cations and [Au(PPh₃)(xspa)]⁻ anions. The anions in the two compounds have different structures, with the carboxylate group either coordinated or not coordinated to the gold atom, respectively. The in vitro antitumour activities against the HeLa-229, A2780 and A2780cis cell lines were determined for all complexes. The diisopropylammonium derivatives were generally found to be more active, in particular against the A2780cis cell line, and showed a high ability to circumvent the cellular resistance to cisplatin.     

Synthesis, crystal structures and characterization of three novel complexes with N-[2-(2-hydroxybenzylideneamino)ethyl]-4-methyl-benzene-sulfonamide as ligand

Reaction of the N-tosyl-ethylenediamine and salicylaldehyde forms a new sulfonamide Schiff base N-[2-(2-hydroxybenzylideneamino)ethyl]-4-methyl-benzene-sulfonamide (H₂L). Three novel complexes constructed from H₂L, namely, [M(HL)₂] · xH₂O (M = Cu, x = 0 for 1, M = Ni, x = 0 for 2 and M = Zn, x = 1 for 3) have been prepared and characterized via X-ray single-crystal diffraction, elemental analysis, X-ray powder diffraction (XRPD), FT-IR, UV-Vis, TGA and photoluminescence measurements. Complex hydrogen bonds, C-H···π and π-π stacking interactions lead 1-3 to present 1-D, 2-D and 3-D supramolecular architectures, respectively.     

Micelle formation in the presence of photosystem I

The correlation between membrane protein solubilisation and detergent aggregation in aqueous solution is studied for a series of n-alkyl-β-d-maltosides (C_xG₂ with x = 10, 11, 12 being the number of carbon atoms in the alkyl chain) using the trimeric photosystem I core complex (PSIcc) of oxygenic photosynthesis from Thermosynechococcus elongatus as model protein. While protein solubilisation is monitored via the turbidity of the solution, the aggregation behavior of the detergent is probed via the fluorescence spectrum of the polycyclic aromatic hydrocarbon pyrene. In addition, changes of the fluorescence spectrum of PSIcc in response to formation of the detergent belt surrounding its hydrophobic surface are investigated. Solubilisation of PSIcc and aggregation of detergent into micelles or belts are found to be strictly correlated. Both processes are complete at the critical solubilisation concentration (CSC) of the detergent, at which the belts are formed. The CSC depends on the concentration of the membrane protein, [prot], and is related to the critical micelle concentration (CMC) by the empirical law ln(CSC/CMC) = n¯₀ [prot], where the constant n¯₀ = (2.0 ± 0.3) μM⁻¹ is independent of the alkyl chain length x. Formation of protein-free micelles below the CSC is not observed even for x = 10, where a significant excess of detergent is present at the CSC. This finding indicates an influence of PSIcc on micelle formation that is independent of the binding of detergent to the hydrophobic protein surface. The role of the CSC in the optimisation of membrane protein crystallisation is discussed.     

Magnesium (II) poly(pyrazolyl)borate derivatives - Synthesis, spectral and structural studies

A series of magnesium complexes of general formula [Mg(Tp^x)₂] (Tp^x = Tp, Tp^∗, Tp^∗Cl, pzTp) and [Mg(Tp^x)X] (X = Cl, Tp^x = Tp^tBu or pz⁰Tp^p-Tol; X = acetate, Tp^x = Tp^tBu) were synthesised from magnesium chloride or acetate and M(Tp^x) (M = K, Na or Tl) in dichloromethane or alcoholic solution. These compounds are air-stable solids, sparingly soluble in most organic solvents; they have been characterized by elemental analysis, IR, ¹H and ¹³C NMR spectra and, in selected cases, also by conductivity and molecular weight measurements. Single crystal X-ray diffraction studies of [Mg(Tp)₂], [Mg(Tp*)₂] and [Mg(Tp*^Cl)₂] show unsolvated neutral bis(tripod ligand)magnesium(II) molecules with six-coordinate magnesium atoms (〈Mg-N〉 2.167(6), 2.19(2), 2.205(4) Å).     

The human xenobiotic-metabolizing enzyme arylamine N-acetyltransferase 1 (NAT1) is irreversibly inhibited by inorganic (Hg) and organic mercury (CH3Hg): Mechanism and kinetics

Human arylamine N-acetyltransferase 1 (NAT1) is a xenobiotic-metabolizing enzyme that biotransforms aromatic amine chemicals. We show here that biologically-relevant concentrations of inorganic (Hg²⁺) and organic (CH₃Hg⁺) mercury inhibit the biotransformation functions of NAT1. Both compounds react irreversibly with the active-site cysteine of NAT1 (half-maximal inhibitory concentration (IC₅₀) = 250 nM and k_inact = 1.4 × 10⁴ M⁻¹ s⁻¹ for Hg²⁺ and IC₅₀ = 1.4 μM and k_inact = 2 × 10² M⁻¹ s⁻¹ for CH₃Hg⁺). Exposure of lung epithelial cells led to the inhibition of cellular NAT1 (IC₅₀ = 3 and 20 μM for Hg²⁺ and CH₃Hg⁺, respectively). Our data suggest that exposure to mercury may affect the biotransformation of aromatic amines by NAT1.     

Downstream reaction of cisplatin with methionine-containing peptides: pH-dependent competition between hydrolytic cleavage and macrochelation

The pH- and time-dependent reactions of the antitumor drug cisplatin, cis-[PtCl₂(NH₃)₂], with the methionine-containing peptides Ac-Met-Gly-OH, Ac-Met-Pro-OH, Ac-Met-Pro-Gly-Gly-OH and Ac-Gly-Met-Pro-Gly-Gly-OH (Gly = glycyl, Met = d-methionyl, Pro = L-prolyl) at 313 K have been investigated by high performance liquid chromatography, mass spectrometry and nuclear magnetic resonance. As a result of the strong trans influence of the methionyl S_M atom, initial Pt-S_M binding at pH > 5 is followed by a rapid formation of tridentate machrochelates for the N-acetylated peptides. The site trans to S_M is occupied by a carboxylate O atom in the case of the κ³S_M,N_M,O_G/P macrochelates of the dipeptides and by the C-terminal glycylamide N_G2 atom for the κ³S_M,O_M,N_G2 macrochelate of Ac-Met-Pro-Gly-Gly-OH. Cisplatin simultaneously mediates the rapid hydrolytic cleavage of the Met-X (X = Gly, Pro) amide bond for both dipeptides over the whole range 2.8 ? pH ? 10.0. The released amino acids X react with the resulting κ²S_M, N_M chelate of N-acetylmethionine to afford mixed κS_M:κ²N_x,O_x complexes of the type cis-[Pt(NH₃)(Ac-Met-OH-κS)(H-X-O-κ²N_x,O_x)]⁺ as final products at pH < 5 for X = Gly and pH < 8 for X = Pro. In contrast to the dipeptides, hydrolytic cleavage of the Met-Pro amide bond in Ac-Met-Pro-Gly-Gly-OH at pH > 5 is significantly inhibited by the presence of high concentrations of the macrochelate [Pt(NH₃)(Ac-Met-Pro-Gly-Gly)-κ³S_M,O_M,N_G2]⁺. Downstream hydrolysis of the Met-Gly amide bond is competitive with upstream Ac-Gly cleavage for Ac-Gly-Met-Pro-Gly-Gly-OH at pH < 4.5.     

Two-dimensional oxides constructed from octamolybdate clusters and M/tetrapyridylpyrazine subunits (M = Co, Ni: n = 2; M = Cu: n = 1)

The hydrothermal reactions of MoO₃, tetra-2-pyridylpyrazine (tpyprz) and M(CH₃CO₂)₂ · 2H₂O (M = Co, Ni) yielded the two-dimensional oxides [M₂(tpyprz)(H₂O)₂Mo₈O₂₆] · xH₂O [M = Co, x = 1.8 (1); M = Ni, x = 0.6 (2)]. However, the reaction of (NH₄)₆Mo₇O₂₄ · 4H₂O, tpyprz and Cu(CH₃CO₂)₂ · H₂O produced [{Cu₂(tpyprz)}₂Mo₈O₂₆] · 2H₂O (3 · 2H₂O). The isomorphous structures of 1 and 2 are constructed from clusters linked through {M₂(tpyprz)(H₂O)₂}⁴⁺ subunits into two-dimensional networks. While the structure of 3 is also two-dimensional, the molybdate building block is present as the δ-isomer and the secondary-metal/ligand component consists of a one-dimensional chain. The structure of 3 is compared to that of the previously reported three-dimensional material [{Cu₂(tpyprz)}₂Mo₈O₂₆] · 7H₂O which contains clusters and structurally distinct chains.     

Synthesis and structural characterization of the adducts of silver(I) perchlorate and nitrate with triphenylphosphine and bis(pyrazolyl)methane ligands of 1:1:1 stoichiometry

Six new adducts of the form AgX:PPh₃:H₂C(pz^x)₂ (1:1:1) (H₂C(pz^x)₂ = H₂C(pz)₂ = bis(pyrazolyl)methane or H₂C(pz^Me2)₂ = bis(3,5-dimethylpyrazolyl)methane; X = ClO₄, NO₃, SO₃CF₃) have been synthesized and characterized by analytical, spectroscopic (IR, far-IR, ¹H and ³¹P NMR) and two of them also by single crystal X-ray diffraction studies for comparison with counterpart adducts with 2,2′-bipyridyl (‘bpy’) derivatives reported in a previous paper, the bpy-derived ligands forming five-membered chelate rings, while the present H₂C(pz^x)₂ should, potentially, form six-membered rings. Such is the case, the two adducts exhibiting quasi-planar N₂AgP coordination environments, perturbed by the approach of the oxyanion, unidentate in the case of the perchlorate but, in the case of the nitrate, an interesting disordered aggregate of differing unidentate modes.     

Novel triorganotin(IV) complexes of β-diketonates bearing two heterocycles in their structures

Novel triorganotin(IV) derivatives of β-diketonate Q ligands (HQ in general, in detail HQ^fur = 1-phenyl-3-methyl-4-(2-furancarbonyl)-pyrazol-5-one, HQ^thi = 1-phenyl-3-methyl-4-(2-thienylcarbonyl)-pyrazol-5-one) of general formula (Q)SnR₃·xH₂O (R = Ph, x = 0; R = Buⁿ or Me, x = 1) have been synthesized and spectroscopically and thermally characterized. Triphenyltin(IV) complexes have been isolated as anhydrous compounds while trialkyltin(IV) are always monohydrated. The structures of (Q^fur)SnPh₃ and (Q^thi)SnMe₃(OH₂) are recorded. The tin atoms are five-coordinate in both. In the first, the pyrazolonate ligand behaves as an O,O′-bidentate; there are two similar but independent molecules in the structure. In the quasi-trigonal-bipyramidal environments, Sn-O(acyl) are 2.478(3), 2.364(3), Sn-O(pyrazolonate) 2.050(2), 2.079(2), Sn-C 2.123(4)-2.162(3) Å with the longer O(acyl) and a phenyl group quasi-trans (O-Sn-C 162.5(1), 160.8(1)°). In (Q^thi)SnMe₃(OH₂), the three methyl groups are equatorial (Sn-C 2.1259(9)-2.1380(8) Å); Sn-O(Q^thi,OH₂) are 2.2143(5), 2.3350(6) Å, O-Sn-O 175.36(2)°. Trimethyltin(IV) derivatives decompose on heating with release of H₂O and SnMe₄ and formation of (Q)₂SnMe₂. Decomposition occurs also within two days after dissolution of (Q)SnMe₃(OH₂) in chloroform.