Two new N-heterocyclic carbene silver(I) complexes with the π–π stacking interactions

The precursors bis[N-(alkyl)benzimidazoliumylmethyl]durene halide (1a: alkyl = C₂H₅, halide = Br^?; 1b: alkyl = n-C₄H₉, halide = Cl^?; durene = 1,2,4,5-tetramethylbenzene) and their two new NHC silver(I) complexes [Durene(CH₂BimyEtAgBr)₂] (2a) and [Durene(CH₂BimyⁿBuAgCl)₂] (2b) (Bimy = benzimidazol-2-ylidene) have been prepared and characterized. In the crystal structures of 2a and 2b the aromatic π–π stacking interactions are observed.     

Reversible switching of coordination modes of nickel(ΙΙ) complexes using a hemilabile 4,7-diazadecanediamide ligand

The reaction of NiCl₂·6H₂O with a hemilabile diaminodiamide ligand 4,7-diazadecanediamide gave a pale blue compound [Ni(C₈H₁₈N₄O₂)(H₂O)₂]·2Cl (1). In basic solution, 1 was transformed to a yellow species [Ni(C₈H₁₆N₄O₂)]·3H₂O (2) by the Ni-O to Ni-N bond rearrangement at two amide sites of the complex. Structures of 1 and 2 were characterized by single-crystal X-ray diffraction analysis. Structural data for 1 indicated that the nickel atom adopts a six-coordinated N₂O₄ environment and gives an octahedral geometry. The structure of 2 showed that the nickel atom adopts a four-coordinated N₄ environment, giving a square-planar geometry. Compounds 1 and 2 are structurally switchable in response to pH in an aqueous solution. The results presented could be useful in the design of new Ni(II)-based switching materials.     

Synthesis and exploratory coordination chemistry of the new ditertiary carbinamine ligand 2,6-bis(α-aminoisopropyl)pyridine

The new pyridine-based N∩N∩N tridentate ligand 2,6-C₅H₃N(CMe₂NH₂)₂ (1) was synthesized by the treatment of 2,6-pyridinedicarbonitrile with an excess of the organocerium reagent in situ generated from CeCl₃ and methyllithium in THF. The reaction of 1 with [RuCl₂(PPh₃)₃] in THF at ambient conditions afforded (OC-6-23)-[RuCl{2,6-C₅H₃N(CMe₂NH₂)₂}(PPh₃)₂]Cl (2). The corresponding dimethyl sulfoxide complex [RuCl{2,6-C₅H₃N(CMe₂NH₂)₂}{S(O)Me₂}₂]Cl (3) was isolated as a mixture of the (OC-6-23) and (OC-6-32) stereoisomers 3a and 3b from the reaction between 1 and (OC-6-22)-[RuCl₂{S(O)Me₂}₃(OSMe₂)] in toluene at 80 °C. A prolonged interaction in toluene at reflux temperature gave isomerically pure 3a. The metal trichloride hydrates MCl₃ · xH₂O (M = Ru, Rh, Ir; x ≅ 2-4) produced mer-[RuCl₃{2,6-C₅H₃N(CMe₂NH₂)₂}] (M = Ru: 4; Rh: 5; Ir: 6), when combined with 1 in refluxing ethanol. The crystal structures of the following compounds were determined: ligand 1 and complexes 2-5 as addition compounds 2 · CH₂Cl₂, 3a · C₇H₈, 4 · EtOH and .     

Co (II), Ni(II) and Cu(II) complexes with a new pendant armed macrocyclic ligand showing several π,π-interactions

A new ligand, L, bearing four cyanoethyl pendant groups has been synthesized by reaction of the precursor ligand L¹ with acrylonitrile. The X-ray crystal structure of ligand L reveals the presence of a nanotubular structure in the solid state connected by intermolecular π,π-stacking interactions between adjacent pyridine rings. The coordination capability towards transition metal ions [Co(II), Ni(II) and Cu(II)] has been investigated starting from the hydrated nitrate and perchlorate salts of the metals. The new ligand L and the metal complexes obtained were characterized by elemental analysis, FAB MS, conductivity measurements, magnetic studies, IR and UV-vis spectroscopy. Furthermore, the crystal structure of ligand L and of the complexes [CoL][Co(NO₃)₄] · CH₃CN (1), [NiL](NO₃)₂ (3), [NiL](ClO₄)₂ · CH₃CN · 3H₂O (4), [CuL][Cu(NO₃)₃(H₂O)₂](NO₃) · H₂O (5) and [CuL](ClO₄)₂ · 2CH₃CN (6) were determined. The nitrate ions in the complexes are located near the pyridine rings and π,π-stacking interactions between pyridine rings, nitrate ions and nitrile groups have been found.     

Metal ion size and coordination mode in complexes of a β-diketiminate ligand with pendant quinoline arms

A suite of late first row transition metal complexes has been synthesized using a monoanionic nitrogen donor β-diketiminate ligand with quinolyl pendant arms, BDI^QQH (1). BDI^QQNiOTf (2), BDI^QQCuCl (4), BDI^QQZnCl (5) were prepared from the reaction of 1 with Ni(OTf)₂, CuCl₂·2H₂O and ZnCl₂, respectively. BDI^QQNiCl (3) was synthesized from an anion exchange of 2 with ⁿBu₄NCl. Reaction of 1 and CoI₂ afforded the unexpected [(BDI^QQ)₂Co]⁺I⁻ (6). Through density functional theory (DFT) calculations, ligand geometries in BDI^QQ complexes were investigated and it was found that smaller ionic radius and higher charge destabilize 1:1 metal-ligand complexes relative to alternative 1:2 complexes like 6 owing to significant conformational strain in 1:1 complexes involving metals with small ionic radii. Synthesis and characterization of these complexes, including crystal structures of 4 and 5, are reported, in addition to the results of DFT calculations.     

Influence of coordination modes of 4,4′-bipyridine and secondary bonds on the structural assembles: Syntheses,crystal structures and properties of two lead(II) 3-sulfobenzoate coordination polymers

Two novel structures, {[Pb(3-sb)(4,4′-bipy)_0.5](H₂O)}_n (1) together with the previously reported complex {[Pb(3-sb)(H₂O)₂](4,4′-bipy)}_n (2), where 3-sb is 3-sulfobenzoate dianion and 4,4′-bipy is 4,4′-bipyridine, were synthesized and characterized by IR, elemental analyses, TGA, powder X-ray, fluorescent and single-crystal X-ray analyses. The highly ordered 2-D structure of 2 exists as π–π stacking and hydrogen-bonding interactions, while complex 1 is a 3-D network with 2-D interpenetration layers without π–π and hydrogen-bonding interactions and with abundant secondary bonding interactions. Therefore, complex 1 has thermally more stable structure than that of complex 2, and water molecules can be removed and re-combined in complex 1.     

Synthetic, electrochemical and structural aspects of a series of ferrocene-containing dicarbonyl β-diketonato rhodium(I) complexes

Treatment of [Rh(β-diketonato)(cod)] with CO resulted in better yields of [Rh(FcCOCHCOR)(CO)₂] than by treating [Rh(Cl)(CO)₂]₂ with FcCOCH₂COR, R = CF₃ (Hfctfa), CH₃ (Hfca), Ph (Hbfcm, Ph = phenyl) and Fc (Hdfcm, Fc = ferrocenyl). The single crystal structure of the fctfa rhodium(I) complex [C₁₆H₁₀F₃FeO₄Rh], monoclinic, C 2/c(15), a = 13.266(3) Å, b = 19.553(3) Å, c = 13.278(3) Å, β = 100.92(2)°, Z = 8 showed both rotational and translational displacement disorders for the CF₃ group. An electrochemical study revealed that the formal reduction potential, E⁰′, for the electrochemically reversible one electron oxidation of the ferrocenyl group varied between 0.304 (for the fctfa complex) and 0.172 V (for the dfcm complex) versus Fc/Fc⁺ in a manner that could be directly traced to the group electronegativities, χ_R, of the R groups on the β-diketonato ligands, as well as to the values of the free β-diketones. Anodic peak potentials, E_pa,Rh, for the dominant cyclic voltammetry peak associated with rhodium(I) oxidation were between 0.718 (bfcm complex) and 1.022 V (dfcm complex) versus Fc/Fc⁺. Coulometric experiments implicated a second, much less pronounced anodic wave for the apparent two-electron Rh^I oxidation that overlaps with the ferrocenyl anodic wave and that the redox processes associated with these two Rh^I oxidation waves are in slow equilibrium with each other.     

The coordination of copper(II) with β-casomorphin and its fragments

The synthesis of β-casomorphin-5 (Tyr-Pro-Phe-Pro-Gly, H₂L) and a number of its peptide fragments is described. Complexes formed between these peptides and Cu(II) have been investigated spectrophotometrically, using CD and EPR spectroscopy, and potentiometrically. Results show that, with tyrosine as the N-terminal residue, the major complex formed at physiological pH is the dimeric species, [Cu₂L₂], bonded through the phenolic O^? of the Tyr residue of one ligand and the N-terminal amine nitrogen of the second ligand molecule. There is no evidence for coordination through the peptide nitrogens unless the terminal Tyr group is removed.     

QTL fine mapping with Bayes C(π): a simulation study

Background

Accurate QTL mapping is a prerequisite in the search for causative mutations. Bayesian genomic selection models that analyse many markers simultaneously should provide more accurate QTL detection results than single-marker models. Our objectives were to (a) evaluate by simulation the influence of heritability, number of QTL and number of records on the accuracy of QTL mapping with Bayes Cπ and Bayes C; (b) estimate the QTL status (homozygous vs. heterozygous) of the individuals analysed. This study focussed on the ten largest detected QTL, assuming they are candidates for further characterization.

Methods

Our simulations were based on a true dairy cattle population genotyped for 38 277 phased markers. Some of these markers were considered biallelic QTL and used to generate corresponding phenotypes. Different numbers of records (4387 and 1500), heritability values (0.1, 0.4 and 0.7) and numbers of QTL (10, 100 and 1000) were studied. QTL detection was based on the posterior inclusion probability for individual markers, or on the sum of the posterior inclusion probabilities for consecutive markers, estimated using Bayes C or Bayes Cπ. The QTL status of the individuals was derived from the contrast between the sums of the SNP allelic effects of their chromosomal segments.

Results

The proportion of markers with null effect (π) frequently did not reach convergence, leading to poor results for Bayes Cπ in QTL detection. Fixing π led to better results. Detection of the largest QTL was most accurate for medium to high heritability, for low to moderate numbers of QTL, and with a large number of records. The QTL status was accurately inferred when the distribution of the contrast between chromosomal segment effects was bimodal.

Conclusions

QTL detection is feasible with Bayes C. For QTL detection, it is recommended to use a large dataset and to focus on highly heritable traits and on the largest QTL. QTL statuses were inferred based on the distribution of the contrast between chromosomal segment effects.     

Synthesis, structure and magnetic properties of two μ-oxo and thiocyanato-bridged manganese(II)-mercury(II) coordination polymers

Mixed-metal thiocyanate complexes [MnHg(SCN)₄(NOP)] (1) and [MnHg(SCN)₄(DMSO)] (2) (NOP = 3-methyl-4-nitropyridine-N-oxide, DMSO = dimethylsulfoxide) have been synthesized and structurally characterized by single crystal X-ray analysis. Complex 1 and 2 both contain a [Mn₂(μ₂-O)₂] lozenge, which is bridged to Hg(II) ions by end-to-end thiocyanate groups to form a 2-D and 3-D polymeric network, respectively. Magnetic studies indicate that both complexes are anti-ferromagnets, with 1 showing anti-ferrimagnetic ordering below 8.0 K.     

Organogold(I) complexes of a C2-symmetric diacetylide ligand derived from 1,1′-bi-2-naphthol

Alkynylgold(I) complexes incorporating a chiral binaphthyl group have been prepared. Bis(alkyne) reagents [rac-1,1′-C₂₀H₁₂-2,2′-(OCH₂CCH)₂] (1) and [rac-1,1′-C₂₀H₁₂-2,2′-(OC(O)CH₂CCH)₂] (2), react with [AuCl(SMe₂)] and base to give insoluble oligomeric alkynylgold(I) complexes [rac-1,1′-C₂₀H₁₂-2,2′-(OCH₂CCAu)₂]_n (3) and [rac-1,1′-C₂₀H₁₂-2,2′-(OC(O)CH₂CCAu)₂]_n (4), which react with phosphine or diphosphine ligands to give soluble complexes [rac-1,1′-C₂₀H₁₂-2,2′-(OCH₂CCAuPR₃)₂] (5), R = Ph or Cy, [rac-1,1′-C₂₀H₁₂-2,2′-(OCH₂CCAu)₂(Ph₂P(CH₂)_nPPh₂)] (6), or [rac-1,1′-C₂₀H₁₂-2,2′-(OC(O)CH₂CCAu)₂(Ph₂P(CH₂)_nPPh₂)] (7), with n = 3–5. Several of the complexes 6 and 7 are shown to exist as mixtures of isomeric forms in solution.     

Anamylopsoraceae — a new family of lichenized ascomycetes with stipitate apothecia (Lecanorales: Agyriineae)

The anatomy, chemistry and developmental morphology ofAnamylopsora pulcherrima is investigated. Some characters, including the ascus structure, suggest a close affinity with theAgyriaceae. However, the chemistry and the pycnidial structure differ as well as the ascoma ontogeny.Anamylopsora has a gymnocarpous ascoma development and the ascogonia are produced in stipes.Trapelia coarctata, as a typical member of theAgyriaceae, shows a hemiangiocarpous ascoma ontogeny. The anatomical, chemical and ontogenetical characters of several families are compared withAnamylopsora and it is shown that the genus is best placed in a monotypic familyAnamylopsoraceae Lumbsch & Lunke, fam. nova, which is placed in theAgyriineae (Lecanorales).This paper is dedicated to Prof. DrAino Henssen (Marburg) on the occasion of the 70th birthday.     

Characterization of α-nitromethyl ketone as a new zinc-binding group based on structural analysis of its complex with carboxypeptidase A

Zinc-binding groups (ZBGs) are exhaustively applied in the development of the new inhibitors against a wide variety of physiologically and pathologically important zinc proteases. Here the α-nitro ketone was presented as a new ZBG, which is a transition-state analog featured by the unique bifurcated hydrogen bonds at the active site of carboxypeptidase A based on the structural analysis. Introduction of a nitro group at the α-position of the ketone could provide more non-covalent interactions without loss of the abilities to form a tetrahedral transition-state analog.     

Comparison of two different folic acid doses with methotrexate – a randomized controlled trial (FOLVARI Study)

IntroductionThere is reasonable evidence that folic acid 5–10 mg per week leads to reduction in methotrexate (MTX) toxicity in rheumatoid arthritis (RA). However, this is based on studies conducted with lower MTX dosage than used currently. It is unclear whether higher doses of folic acid may be better in reducing toxicity.MethodsThis was a double-blind randomized controlled trial of 24 weeks duration. To be eligible, patients should have rheumatoid arthritis (1987 American College of Rheumatology criteria), be 18–75 years of age, not be on MTX and have active disease as defined by ‘Modified Disease Activity Score using three variables’ (DAS28(3)) > 3.2. MTX was started at 10 mg/week and escalated to 25 mg/week by 12 weeks. Folic acid was given at a dose of 10 mg (FA10) or 30 mg per week (FA30). Co-primary endpoints were incidence of toxicity (undesirable symptoms and laboratory abnormalities) and change in disease activity by 24 weeks. Intention-to-treat and per-protocol analyses were performed.ResultsAmong 100 patients enrolled, 51 and 49 were randomized to FA10 and FA30 respectively. By 24 weeks, there were 6 patient withdrawals in either group and mean(±SD) dose of MTX was 22.8 ± 4.4 and 21.4 ± 4.6 mg per week (p = 0.1). Frequency of patients with undesirable symptoms was non-significantly lower by 7.4 % (95 % confidence interval −27.4 to 12.7 %) in FA10 compared to FA30. There was also no difference in frequency of transaminitis (>Upper limit of normal (ULN)) (42.6, 45.7 %, p = 0.7) or transminitis as per primary endpoint (>2xULN) (10.6, 8.7 %, p = 1.0) or cytopenias (4.3, 4.3 %, p = 0.9). There was no difference in the primary end-point of occurrence of any adverse effect (symptom or laboratory) in FA10 and FA30 (46.8, 54.3 %, p = 0.5). At 24 weeks, DAS28(3) declined in both groups by a similar extent (−1.1 ± 1.0, −1.3 ± 1.0, p = 0.2) and ‘European League Against Rheumatism’ good or moderate response occurred in 56.9 and 67.4 % (p = 0.3).ConclusionsEven with the high doses of MTX used in current practice, there was no additional benefit (or harm) of a higher dose of folic acid (30 mg/week) over a usual dose (10 mg/week).

Trial Registration

Clinicaltrials.gov {"type":"clinical-trial","attrs":{"text":"NCT01583959","term_id":"NCT01583959"}}NCT01583959 Registered 15 March 2012     

Types of species of Apionidae (Coleoptera) described by Carl Peter Thunberg (1743–1828) with description of?a new genus

The type specimens of species of Apionidae described by Carl Peter Thunberg are reviewed and lecto- and paralectotypes are designated for Apion craccae Thunberg, 1813, Apion limbatum Thunberg, 1813, Apion punctigerum Thunberg, 1815 and Apion astragali Thunberg, 1815. A new genus Thunbergapion (type species Apion limbatum Thunberg, 1813) is described, figured and placed in the tribe Aplemonini Kissinger, 1968. The new combination Thunbergapion limbatum (Thunberg, 1813) is proposed. A key to the known South African genera of the tribe is given. The following new synonymies are established: Oxystoma craccae (Linnaeus, 1767) = Apion craccae Thunberg, 1813 syn. n., Ischnopterapion (Ischnopterapion) loti (Kirby, 1808) = Apion punctigerum Thunberg, 1815, syn. n., and Pseudoprotapion astragali (Paykull, 1800) = Apion astragali Thunberg, 1815, syn. n.     

Co+–H interaction inspired alternate coordination geometries of biologically important cob(I)alamin: possible structural and mechanistic consequences for methyltransferases

A detailed computational analysis employing density functional theory (DFT), atoms in molecules, and quantum mechanics/molecular mechanics (QM/MM) tools has been performed to investigate the primary coordination environment of cob(I)alamin (Co(+)Cbx), which is a ubiquitous B(12) intermediate in methyltransferases and ATP:corrinoid adenosyltransferases. The DFT calculations suggest that the simplified (Co(+)Cbl) as well as the complete (Co(+)Cbi) complexes can adapt to the square pyramidal or octahedral coordination geometry owing to the unconventional H-bonding between the Co(+) ion and its axial ligands. These Co(+)-H bonds contain appreciable amounts of electrostatic, charge transfer, long-range correlation, and dispersion components. The computed reduction potentials of the Co(2+)/Co(+) couple imply that the Co(+)-H(H(2)O) interaction causes a greater anodic shift [5-98?mV vs. the normal hydrogen electrode (NHE) in chloroform solvent] than the analogous Co(+)-H(imidazole) interaction (1?mV vs. NHE) in the reduction potential of the Co(2+)/Co(+) couple. This may explain why a β-axial H(2)O ligand has specifically been found in the active sites of certain methyltransferases. The QM/MM analysis of methionine synthase bound Co(+)Cbx (Protein Data Bank ID 1BMT, resolution 3.0??) indicates that the enzyme-bound Co(+)Cbx can also form a Co(+)-H bond, but can only exist in square pyramidal form because of the steric constraints imposed by the cellular environment. The present calculations thus support a recently proposed alternate mechanism for the enzyme-bound Co(2+)/Co(+) reduction that involves the conversion of square pyramidal Co(2+)Cbx into square pyramidal Co(+)Cbx (Kumar and Kozlowski in Angew. Chem. Int. Ed. 50:8702-8705, 2011).     

Deletion of a Gly-Pro-Pro repeat in the proα2(I) chain of procollagen I in a family with dominant osteogenesis imperfecta type IV

We have investigated one member of a family with dominant osteogenesis imperfecta type IV through three generations. In protein-chemical studies of cultured fibroblasts derived from the proband, collagen I was overmodified, with normal processing of procollagen 1, normal thermal stability, and a cyanogen bromide peptide map that suggested a C-terminal location of the structural abnormality in the collagen triple helix. Sequencing of the gene encoding the 2(I) chain of collagen I (COL1A2) indicated a nine base-pair deletion of nucleotides 3418–3426. When a polymerase chain reaction product containing the nucleotides in question was electrophoresed in a 12% polyacrylamide gel, two bands with a difference in size of nine base pairs could be shown. Sequencing of the lower molecular weight band confirmed the deletion of the nine base pairs involving codons 1003–1006 of COL1A2. The deletion introduced aSfiI restriction site that was used for confirmation of the deletion in genomic DNA from the proband. The deletion resulted in the removal of three amino acids (Gly-Pro-Pro), but this did not disrupt the Gly-X-Y sequence of the collagen triple helix, as is often the case in the more common glycine substitutions. We discuss the ways in which this deletion could result in osteogenesis imperfecta.