Structure and magnetic properties of LnIII[Ru2(CO3)4] · 8H2O

Ln^III[Ru₂(CO₃)₄] · 8H₂O (Ln = Gd, Nd, Ho, Yb) is formed from the reaction of Ln^III and [Ru₂(CO₃)₄]^3? in water. These Ln^III materials have a 3D network structure composed of linked chains and μ_n-CO₃ linkages to both Ru and Ln^III sites, and are best described as Ln^III(OH₂)₄[Ru₂(CO₃)₄]_1/2[Ru₂(CO₃)₄(OH₂)₂]_1/2 · 3H₂O. Complete characterization of the Gd^III species is presented, as the other Ln^III are isostructural and exhibit large spin–orbit coupling leading to complex magnetic behavior. Magnetic ordering is not observed above 2 K.     

New coordination polymers based on a novel polynitrile ligand: Synthesis,structure and magnetic properties of the series [M(tcnoetOH)2(4,4′-bpy)(H2O)2] (tcnoetOH− = [(NC)2CC(OCH2CH2OH)C(CN)2]−; M = Fe,Co and Ni)

A novel polynitrile anionic ligand, tcnoetOH^?(=[(NC)₂CC(OCH₂CH₂OH)C(CN)₂]^?), has been synthesized by a one-pot reaction from a cyclic acetal and malononitrile. This ligand has been successfully used to prepare, with 4,4′-bpy as co-ligand, a novel series of coordination polymers formulated as [M(tcnoetOH)₂(4,4′-bpy)(H₂O)₂] with M(II) = Fe (1), Co (2) and Ni (3). These isostructural compounds present a linear chain structure consisting of octahedrally coordinated metal ions bridged by trans 4,4′-bpy ligands. The coordination sphere of the metal ions is completed with two terminal tcnoetOH^? ligand and two water molecules. The magnetic properties indicate that the three compounds are paramagnetic, as expected from the long 4,4′-bpy bridge connecting the metal atoms. Their magnetic properties have been fitted with a model of isolated ions including a zero field splitting for the Fe(II) and Ni(II) derivatives.     

A CASSCF/CASPT2 investigation on electron detachments from ScSi n − (n = 4–6) clusters

Journal of Molecular Modeling - The mechanism for the competitive adsorption of CH4 and CO2 on coal vitrinite (DV-8, maximum vitrinite reflectance R o,max = 0.58%) was revealed...     

Trinuclear palladium complexes containing terminal nitrosyl ligands: Behavior in solid state and in solution. X-ray structures of Pd3(NO)2(μ-OCOCX3)4(η2-ArH)2 (X = F,Cl; ArH = toluene or benzene)

Two trinuclear Pd(II) nitrosyl carboxylate complexes Pd₃(NO)₂(μ-OCOCX₃)₄(η²-ArH)₂ (X = F, ArH = toluene, 3a; X = Cl, ArH = benzene, 3b) have been prepared and structurally characterized. These display a linear Pd₃ array capped by terminal bent NO ligands and η²-coordinated molecules of aromatic molecules. Solution IR and NMR measurements indicate that the solid state structure of 3a is partially maintained in solution, while 3b loses benzene when dissolved in dichloromethane.     

Chemical access to the mononuclear Mn(III) [(mL)Mn(OMe)]+ complex (mLH = N,N′-bis-(2-pyridylmethyl)-N-(2-hydroxybenzyl)-N′-methyl-ethane-1,2-diamine) and electrochemical oxidation to the Mn(IV) [(mL)Mn(OMe)]2+ species

Chemical oxidation in acetonitrile of the previously reported phenolato-bridged binuclear Mn(II) complex [(mL)MnMn(mL)]²⁺ (1), where mLH is pentadentate N,N′-bis-(2-pyridylmethyl)-N-(2-hydroxybenzyl)-N′-methyl-ethane-1,2-diamine ligand [C. Hureau, et al., Chem. Eur. J. 2004, 10, 1998–2010] using iodosylbenzene PhIO (dissolved in methanol) is described. The addition of one to four equivalents of PhIO per Mn ion leads to the transient formation of the mono-μ-oxo binuclear Mn₂(III,III) complex [(mL)Mn(μ-O)Mn(mL)]²⁺ (2), previously studied. After addition of five equivalents of PhIO per Mn ion, the mononuclear Mn(III) species [(mL)Mn(OMe)]⁺ (3) is quantitatively generated. The UV–Vis spectrum of 3 displays a broad band at 456 nm (ε = 1000 L mol⁻¹ cm⁻¹) attributed to phenolato to Mn(III) charge transfer transition. Complex 3 exhibits a reversible oxidation wave at E^1/2 = 0.68 V versus SCE, and the mononuclear Mn(IV) complex [(mL)Mn(OMe)]²⁺ (3^ox) can thus be generated by exhaustive electrolysis at 1.0 V versus SCE. The 9.4 GHz EPR spectrum of complex 3^ox shows a strong transition near g = 4 consistent with a rhombically distorted S = 3/2 system with a zero-field splitting dominating the Zeeman effect. UV–Vis spectrum displays a large phenolato to Mn(IV) charge transfer transition at 670 nm (ε = 2450 L mol⁻¹ cm⁻¹).     

Selective synthesis of cerebrosides: (2S, 3R, 4E)-1-O-β-d-galactopyranosyl-N-(2′R and 2′S)-2′-hydroxytetracosanoyl-sphingenine

The cerebrosides were first isolated by Thudicum in 1874 and the structures were established by Carteret al. in 1950 (for review, see [2]). In 1961 Shapiro and Flowers [3] reported the first total synthesis of a cerebroside1 (Fig. 1) which was identified with the natural sample, only through comparison of their i.r. data. In order to confirm the absolute configuration at C-2 of natural cerebroside1, we describe here an unambiguous synthesis of two stereoisomeric cerebrosides1 and2, and found that the¹H-NMR spectra of the synthetic1 (Fig. 2) was completely identical with that of the natural cerebroside reported recently by Dabrowskiet al. [4].In planning the synthetic route, the target structures1 and2 were disconnected at the dotted lines to give three key synthetic intermediates3, 4 and5 or6 (Fig. 1).Abbreviations Bu butyl - Ph phenyl - t-BuPh₂SiCl t-butyldiphenylsilyl chloride - MTPA -methoxy--trifluoromethylphenylacetic acid - THF tetrahydrofuran Part 36 in the series Synthetic Studies on Cell-surface Glycans, for part 35, see [1]     

Mechanism of Action of the Fungicide Thiabendazole, 2-(4′-Thiazolyl) Benzimidazole

Thiabendazole, 2-(4'-thiazolyl) benzimidazole (TBZ) inhibited the growth of Penicillium atrovenetum at 8 to 10 mug/ml. Oxygen consumption with exogenous glucose was inhibited at 20 mug/ml, but endogenous respiration required more than 100 mug/ml. TBZ inhibited completely the following systems of isolated heart or fungus mitochondria: reduced nicotinamide adenine dinucleotide oxidase, succinic oxidase, reduced nicotinamide adenine dinucleotide-cytochrome c reductase, and succinic-cytochrome c reductase at concentrations of 10, 167, 10, and 0.5 mug/ml, respectively. Cytochrome c oxidase was not inhibited. Antimycin A and sodium azide caused the usual inhibition patterns for both fungus and heart terminal electron transport systems. In the presence of antimycin, the fungicide inhibited completely succinate-dichloro-phenolindophenol reductase and succinate-2, 2-di-p-nitrophenyl-(3, 3-dimethoxy-4, 4-biphenylene-5, 5-diphenylditetrazolium)-reductase at 2 and 4 mug of TBZ per ml, respectively. Coenzyme Q reductase required 15 mug/ml. TBZ reduced the uptake by P. atrovenetum of glucose and amino acids and decreased the synthesis of various cell components. At 120 mug/ml, the incorporation of labeled carbon from amino acids-U-(14)C was decreased: lipid, 73%; nucleic acids, 80%; protein, 80%; and a residual fraction, 89%. TBZ did not inhibit peptide synthesis in a cell-free protein-synthesizing system from Rhizoctonia solani. Probably the primary site of inhibition is the terminal electron transport system and other effects are secondary.     

Confidently identifying the correct K value using the ΔK method: When does K = 2?

Populations delineated based on genetic data are commonly used for wildlife conservation and management. Many studies use the program structure combined with the ΔK method to identify the most probable number of populations (K). We recently found K = 2 was identified more often when studies used ΔK compared to studies that did not. We suggested two reasons for this: hierarchical population structure leads to underestimation, or the ΔK method does not evaluate K = 1 causing an overestimation. The present contribution aims to develop a better understanding of the limits of the method using one, two and three population simulations across migration scenarios. From these simulations we identified the “best K” using model likelihood and ΔK. Our findings show that mean probability plots and ΔK are unable to resolve the correct number of populations once migration rate exceeds 0.005. We also found a strong bias towards selecting K = 2 using the ΔK method. We used these data to identify the range of values where the ΔK statistic identifies a value of K that is not well supported. Finally, using the simulations and a review of empirical data, we found that the magnitude of ΔK corresponds to the level of divergence between populations. Based on our findings, we suggest researchers should use the ΔK method cautiously; they need to report all relevant data, including the magnitude of ΔK, and an estimate of connectivity for the research community to assess whether meaningful genetic structure exists within the context of management and conservation.     

Influence of ligands on the fac⇌Δhνmer isomerization in [RuCl3(NO)(P–P)] complexes, [P–P = R2P(CH2)nPR2 (n = 1–3) and R2P(CH2)POR2, PR2–CHCH–PR2, R = Ph and (C6H11)2P-(CH2)2-P(C6H11)2]

[RuCl₃(NO)(P–P)], [P–P = R₂P(CH₂)_nPR₂ (n = 1–3) and R₂P(CH₂)POR₂, PR₂–CHCH–PR₂, R = Ph and (C₆H₁₁)₂P-(CH₂)₂-P(C₆H₁₁)₂] were obtained and characterized by ³¹P {¹H} NMR, IR spectroscopies and cyclic voltammetry. The structures of fac-[RuCl₃(NO)(P–P)], P–P = dppm (1), dppe (2), c-dppen (3) and dppp (4), mer-[RuCl₃(NO)(dcpe)] (6a) and mer-[RuCl₃(NO)(dppmO)] (7) have been determined by X-ray diffraction. Photochemical isomerization of fac- to mer-[RuCl₃(NO)(P–P)] was observed under white light in a CH₂Cl₂ solution and in solid state. The isomerization processes were followed by IR and ³¹P {¹H} spectra. The mer-[RuCl₃(¹⁵NO)(dppb)] isomer was used for the definition of the phosphorus atoms in the structure of the complex in solution. The electrochemical study shows that the oxidation/reduction processes observed in these complexes are dependent on both the isomer (fac or mer) and the solvent. In CH₂Cl₂, the NO⁺ reduction potentials are less negative for the mer-isomers than for the fac ones, while in CH₃CN solvent these potentials are, in general, very close for both isomers.     

N-Phenyl-N′-(2-chloroethyl)urea analogues of combretastatin A-4: Is the N-phenyl-N′-(2-chloroethyl)urea pharmacophore mimicking the trimethoxy phenyl moiety?

A series of novel N-phenyl-N'-(2-chloroethyl)urea derivatives potentially mimicking the structure of combretastatin A-4 were synthesized and tested for their cell growth inhibition and their binding to the colchicine-binding site of beta-tubulin. Compounds 2a, 3a, and 3b were found to inhibit cell growth at the micromolar level on four human tumor cell lines. Flow cytometric analysis indicates that the new compounds act as antimitotics and arrest the cell cycle in G(2)/M phase. Covalent binding of 2a, 3a, and 3b to the colchicine-binding site of beta-tubulin was confirmed also using SDS-PAGE and competition assays.     

Microsolvation and hydration enthalpies of CaC2O4(H2O) n (n = 0-16) and C2O4 2-(H2O) n (n = 0-14): an ab initio study

We studied hydrated calcium oxalate and its ions at the restricted Hartree–Fock RHF/6-31G* level of theory. Performing a configurational search seems to improve the fit of the HF/6-31G* level to experimental data. The first solvation shell of calcium oxalate contains 13 water molecules, while the first solvation shell of oxalate ion is formed by 14 water molecules. The first solvation shell of Ca(II) is formed by six water molecules, while the second shell contains five. At 298.15 K, we estimate the asymptotic limits (infinite dilution) of the total standard enthalpies of hydration for Ca(II), oxalate ion and calcium oxalate as ?480.78, –302.78 and –312.73 kcal mol^?1, resp. The dissociation of hydrated calcium oxalate is an endothermic process with an asymptotic limit of +470.84 kcal mol^?1.

4-(2′-Carboxyphenyl)-4-oxobutyrate: An obligatory intermediate in lawsone biosynthesis

4-(2′-Carboxyphenyl)-4-oxobutyric acid (6) has been detected in cuttings of Impatiens balsamina. It is labelled under conditions where activity from U-¹⁴C-glutamate is incorporated effectively into lawsone (1). 3-(2′-Carboxyphenyl)-3-oxopropionic acid (7) has also been encountered in the cuttings.     

Linear homobimetallic 4-thioacetyl-substituted NCN pincer palladium(II) and platinum(II) complexes with N-bidentate connecting units (NCN = [C6H2(CH2NMe2)2-2,6-R-4]−)

The synthesis and characterization of homobimetallic palladium and platinum complexes of type [(Me(O)CS-4-NCN–M ← N^∩N → M–NCN-4-SC(O)Me](OTf)₂ (Me(O)CS-4-NCN = [C₆H₂(CH₂NMe₂)₂-2,6-SC(O)Me-4]^?; N^∩N = 4,4′-bipyridine (bipy); M = Pd, 12; M = Pt, 13) is reported. The required bifunctional thio-acetyl NCN pincer starting compound NC(Br)N-4-SC(O)Me (2) has been synthesized by the consecutive reactions of NC(Br)N–I (I-1-C₆H₂(CH₂NMe₂)₂-3,5-Br-4) (1) with ^tBuLi, S₈ and Me(O)CCl, respectively. Chemoselective metallation at the C_aryl–Br bond was achieved by the reaction of 2 with the palladium(0) source [Pd₂(dba)₃] (3) (dba = dibenzylidene acetone). Treatment of thus formed [Pd(NCN-4-SC(O)Me)(Br)] (4) with [AgOTf] (8) (OTf = triflate, OSO₂CF₃) gave [Pd(NCN-4-SC(O)Me)(H₂O)][OTf] (9) which was further reacted with 0.5 equiv. of 4,4′-bipyridine (11a) to afford rigid-rod structured 12. When [Pt(tol)₂(SEt₂)]₂ (5) (tol = 4-tolyl) was used instead of 3, then 13 was produced via the in situ formation of [PtBr(NCN-4-SC(O)Me)] (7) and [Pt(NCN-4-SC(O)Me)(H₂O)][OTf] (10). Another possibility to synthesize 7 relied upon the subsequent reaction of 1 with 0.5 equiv. of 5 to give [PtBr(NCN-4-I)] (6) which further reacted with ^tBuLi, 1/8 S₈ and Me(O)CCl to afford 7. The cyclic voltammograms of 2, 7, and 13 are discussed.Complex 7 was structurally characterized by single crystal X-ray crystallography. Organometallic 7 crystallizes with three independent molecules in the asymmetric unit and displays a monomeric structure as commonly encountered in d⁸-metal pincer chemistry.     

Highly Diastereoselective Synthesis of (2′S)-[2′-2H]-2′-Deoxyribonucleosides from the Corresponding Ribonucleosides

Abstract

The four (2′S)-[2′-²H]-2′-deoxynucleosides (>90 atom % ²H), were synthesized from the corresponding ribonucleosides involving six steps of reactions, i.e., oxidation of their 2′-hydroxyl group, stereoselective reductive deuteration of the resulting 2′-ketonucleoside intermediates with NaB²H₄ in EtOH-H₂O or EtOH, triflation, bromination with LiBr, highly stereoselective Bu₃SnH-Et₃B reduction of the resulting bromide, and, finally, unmasking.     

Synthesis of (±)-Methyl 5-(1′,2′-Epoxy-2′,6′-dimethylcyclohexyl)-3-methyl-(2Z,4E)-2,4-pentadienoate

The effect of tripropyltin chloride (TPT) on transport systems in E. coli was investigated. The inhibition on uptakes of ¹⁴C-l-leucine, l-proline, adenine and methyl-(α-d-gluco)pyrano-side (α-methylglucoside) by TPT was examined. The active uptake of l-leucine which utilized ATP molecule as an energy source was 100% inhibited at the concentration of 10 µg/ml TPT. On the other hand, the uptake of l-proline which was generated by an “energied” membrane state of the cells was inhibited only 40% at the same concentration of TPT. α-Methylglucoside uptake was scarcely inhibited. Adenine uptake was intensely inhibited at 20 µg/ml TPT. The effect of the delayed addition of TPT on transport systems was also examined. l-Leucine incorporated into cells was completely released from cells by TPT. Leucine binding protein (LBP) was prepared from E. coli cells and the effect of TPT on LBP activity was examined. TPT scarcely inhibited LBP activity.     

Synthesis of the 2′-,3′-Didehydro-2′-,3′-dideoxy and 2′-,3′-Dideoxy Derivatives of 6-Azauridine and a New Route to 2′-,3′-Didehydro-2′-,3′-dideoxy-5-chlorouridine

Abstract

The 5′-O-(4,4′-dimethoxytrityl) and 5′-O-(tert-butyldimethylsilyl) derivatives of 2′-,3′-O-thiocarbonyl-6-azauridine and 2′,3′-O-thiocarbonyl-5-chlorouridine were synthesized from the parent nucleosides by reaction with 4, 4′-dimethoxytrityl chloride and tert-butyldimethylsilyl chloride, respectively, followed by treatment with 1,1′-thiocarbonyldiimidazole. Introduction of a 2′-,3′-double bond into the sugar ring by reaction of the 5′-protected 2′-,3′-O-thionocarbonates with 1, 3-dimethyl-2-phenyl-1, 3, 2-diazaphospholidiine was unsuccessful, but could be accomplished satisfactorily with trimethyl phosphite. Reactions were generally more successful with the 5′-silylated than with the 5′-tritylated nucleosides. Formation of 2′-,3′-O-thiocarbonyl derivatives proceeded in higher yield with 5′-protected 6-azauridines than with the corresponding 5-chlorouridines because of the propensity of the latter to form 2,2′-anhydro derivatives. In the reaction of 5′-O-(tert-butyldimethylsilyl)-2′-,3′-O-thiocarbonyl-6-azauridine with trimethyl phosphite, introduction of the double bond was accompanied by N³-methylation. However this side reaction was not a problem with 5′-O-(tert-butyldimethylsilyl)-2′-, 3′-O-thioarbonyl-5-chlorouridine. Treatment of 5′-O-(tert-butyldimethylsilyl)-2′-, 3′-didehydro-2′-,3′-dideoxy-6-azauridine with tetrabutylammonium fluoride followed by hydrogenation afforded 2′-,3′-dideoxy-6-azauridine. Deprotection of 5′-O-(tert-butyldimethylsilyl)-2′-, 3′-didehydro-2′-,3′-dideoxy-5-chlorouridine yielded 2′-,3′-didehydro-2′-,3′-dide-oxy-5-chlorouridine.     

Synthesis,cytotoxicity and DNA-binding properties of Pd(II), Cu(II) and Zn(II) complexes with 4′-(4-(2-(piperidin-1-yl)ethoxy)phenyl)-2,2′:6′,2″-terpyridine

Pd(II), Cu(II) and Zn(II) complexes (1–3) based on 4′-(4-(2-(piperidin-1-yl)ethoxy)phenyl)-2,2′:6′,2″-terpyridine were synthesized and characterized by UV, IR, NMR, EPR, HRMS, elemental analyses, and molar conductivity measurements. The cytotoxicity of these complexes against HL-60, BGC-823, KB, Bel-7402, A549, Hela, K562 and MCF-7 cell lines in vitro was measured by MTT method. The DNA binding property of the complexes was evaluated by UV, fluorescence, CD spectroscopies and thermal denaturation. The cytotoxicity of complexes 1 and 3 against all the tested cell lines is better than that of cisplatin. Complexes 1 and 2 exhibit 7- and 4-folds higher cytotoxicity than cisplatin against Bel-7402 cell line. Complex 3 displays the highest cytotoxicity against all the cell lines tested, and shows 7-, 14-, 8-, 11- and 8-folds higher cytotoxicity than cisplatin against Bel-7402, A549, Hela, K562 and MCF-7 cell lines. The complexes bind to DNA via intercalation mode and complex 3 stabilizes the G-quadruplex. The results reveal that all the complexes display high cytotoxicity against all the tested cancer cell lines, and complex 3 is selective for G-quadruplex over duplex DNA.