B30H8, B39H9 2−, B42H10, B48H10, and B72H12: polycyclic aromatic snub hydroboron clusters analogous to polycyclic aromatic hydrocarbons

Calculations performed at the ab initio level using the recently reported planar concentric π-aromatic B₁₈H₆ ²⁺(1) [Chen Q et al. (2011) Phys Chem Chem Phys 13:20620] as a building block suggest the possible existence of a new class of B_3n H _m polycyclic aromatic hydroboron (PAHB) clusters—B₃₀H₈(2), B₃₉H₉ ^2?(3), B₄₂H₁₀(4/5), B₄₈H₁₀(6), and B₇₂H₁₂(7)—which appear to be the inorganic analogs of the corresponding C _n H _m polycyclic aromatic hydrocarbon (PAHC) molecules naphthalene C₁₀H₈, phenalenyl anion C₁₃H₉ ^?, phenanthrene/anthracene C₁₄H₁₀, pyrene C₁₆H₁₀, and coronene C₂₄H₁₂, respectively, in a universal atomic ratio of B:C?=?3:1. Detailed canonical molecular orbital (CMO), adaptive natural density partitioning (AdNDP), and electron localization function (ELF) analyses indicate that, as they are hydrogenated fragments of a boron snub sheet [Zope RR, Baruah T (2010) Chem Phys Lett 501:193], these PAHB clusters are aromatic in nature, and exhibit the formation of islands of both σ- and π-aromaticity. The predicted ionization potentials of PAHB neutrals and electron detachment energies of small PAHB monoanions should permit them to be characterized experimentally in the future. The results obtained in this work expand the domain of planar boron-based clusters to a region well beyond B₂₀, and experimental syntheses of these snub B_3n H _m clusters through partial hydrogenation of the corresponding bare B_3n may open up a new area of boron chemistry parallel to that of PAHCs in carbon chemistry.

N(4)-Tolyl-2-acetylpyridine thiosemicarbazones and their platinum(II,IV) and gold(III) complexes: cytotoxicity against human glioma cells and studies on the mode of action

Complexes [Au(2Ac4oT)Cl][AuCl₂] (1), [Au(H_py2Ac4mT)Cl₂]Cl·H₂O (2), [Au(H_py2Ac4pT)Cl₂]Cl (3), [Pt(H2Ac4oT)Cl]Cl (4), [Pt(2Ac4mT)Cl]·H₂O (5), [Pt(2Ac4pT)Cl] (6) and [Pt(L)Cl₂OH], L = 2Ac4mT (7), 2Ac4oT (8), 2Ac4pT (9) were prepared with N(4)-ortho- (H2Ac4oT), N(4)-meta- (H2Ac4mT) and N(4)-para- (H2Ac4pT) tolyl-2-acetylpyridine thiosemicarbazone. The cytotoxic activities of all compounds were assayed against U-87 and T-98 human malignant glioma cell lines. Upon coordination cytotoxicity improved in 2, 5 and 8. In general, the gold(III) complexes were more cytotoxic than those with platinum(II,IV). Several of these compounds proved to be more active than cisplatin and auranofin used as controls. The gold(III) complexes probably act by inhibiting the activity of thioredoxin reductase enzyme whereas the mode of action of the platinum(II,IV) complexes involves binding to DNA. Cells treated with the studied compounds presented morphological changes such as cell shrinkage and blebs formation, which indicate cell death by apoptosis induction.     

Genetic mapping of a putative Thinopyrum intermedium-derived stripe rust resistance gene on wheat chromosome 1B

Key message

Stripe rust resistance transferred from Thinopyrum intermedium into common wheat was controlled by a single dominant gene, which mapped to chromosome 1B near Yr26 and was designated YrL693.

Abstract

Stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) is a highly destructive disease of wheat (Triticum aestivum). Stripe rust resistance was transferred from Thinopyrum intermedium to common wheat, and the resulting introgression line (L693) exhibited all-stage resistance to the widely virulent and predominant Chinese pathotypes CYR32 and CYR33 and to the new virulent pathotype V26. There was no cytological evidence that L693 had alien chromosomal segments from Th. intermedium. Genetic analysis of stripe rust resistance was performed by crossing L693 with the susceptible line L661. F₁, F₂, and F_2:3 populations from reciprocal crosses showed that resistance was controlled by a single dominant gene. A total 479 F_2:3 lines and 781 pairs of genomic simple sequence repeat (SSR) primers were employed to determine the chromosomal location of the resistance gene. The gene was linked to six publicly available and three recently developed wheat genomic SSR markers. The linked markers were localized to wheat chromosome 1B using Chinese Spring nulli-tetrasomic lines, and the resistance gene was localized to chromosome 1B based on SSR and wheat genomic information. A high-density genetic map was also produced. The pedigree, molecular marker data, and resistance response indicated that the stripe rust resistance gene in L693 is a novel gene, which was temporarily designated YrL693. The SSR markers that co-segregate with this gene (Xbarc187-1B, Xbarc187-1B-1, Xgwm18-1B, and Xgwm11-1B) have potential application in marker-assisted breeding of wheat, and YrL693 will be useful for broadening the genetic basis of stripe rust resistance in wheat.     

Modeling the effect of H-bonding interactions and molecular packing on the molecular structure of [Ag(ethylnicotinate)2]NO3 complex

The gas phase molecular structure of a single isolated molecule of [Ag(Etnic)₂NO₃];1 where Etnic = Ethylnicotinate was calculated using B3LYP method. The H-bonding interaction between 1 with one (complex 2) and two (complex 3) water molecules together with the dimeric formula [Ag(Etnic)₂NO₃]₂;4 and the tetrameric formula [Ag(Etnic)₂NO₃]₄;5 were calculated using the same level of theory to model the effect of intermolecular interactions and molecular packing on the molecular structure of the titled complex. The H-bond dissociation energies of complexes 2 and 3 were calculated to be in the range of 12.220–14.253 and 30.106–31.055 kcal?mol^?1, respectively, indicating the formation of relatively strong H-bonds between 1 and water molecules. The calculations predict bidentate nitrate ligand in the case of 1 and 2, leading to distorted tetrahedral geometry around the silver ion with longer Ag–O distances in case of 2 compared to 1, while 3 has a unidentate nitrate ligand leading to a distorted trigonal planar geometry. The packing of two [Ag(Etnic)₂NO₃] complex units; 4 does not affect the molecular geometry around Ag(I) ion compared to 1. In the case of 5, the two asymmetric units of the formula [Ag(Etnic)₂NO₃] differ in the bonding mode of the nitrate group, where the geometry around the silver ion is distorted tetrahedral in one unit and trigonal planar in the other. The calculations predicted almost no change in the charge densities at the different atomic sites except at the sites involved in the C–H?O interactions as well as at the coordinated nitrogen of the pyridine ring.

Mono- and digalactosyldiacylglycerols: potent nitric oxide inhibitors from the marine microalga Nannochloropsis granulata

Chemical investigation of a marine microalga, Nannochloropsis granulata, led to the isolation of four digalactosyldiacylglycerols namely, (2S)-1-O-eicosapentaenoyl-2-O-palmitoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (1), (2S)-1-O-eicosapentaenoyl-2-O-palmitoleoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (2), (2S)-1-O-eicosapentaenoyl-2-O-myristoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (3), and (2S)-1,2-bis-O-eicosapentaenoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (4), together with their monogalactosyl analogs (5–8). Among the isolated galactolipids 2 and 3 were new natural products. Complete stereochemistry of 1, 4, 5, 7, and 8 was determined for the first time by both spectroscopic techniques and classical degradation methods. Both mono- and digalactosyldiacylglycerols isolated from N. granulata possessed strong nitric oxide (NO) inhibitory activity against lipopolysaccharide-induced NO production in RAW264.7 macrophage cells through downregulation of inducible nitric oxide synthase expression indicating the possible use as anti-inflammatory agents.     

Lipids isolated from the cultivated red alga Chondrus crispus inhibit nitric oxide production

A MeOH extract of cultivated Chondrus crispus showed dose-dependent nitric oxide (NO) inhibition of lipopolysaccharide-induced NO production in macrophage RAW264.7 cells. NO inhibition-guided fractionation of the extract led to identification of eicosapentaenoic acid (EPA, 1), arachidonic acid (AA, 2), lutein (3), and eight galactolipids as active components. Based on spectral analysis, the isolated galactolipids were identified as (2S)-1,2-bis-O-eicosapentaenoyl-3-O-β-d-galactopyranosylglycerol (4), (2S)-1-O-eicosapentaenoyl-2-O-arachidonoyl-3-O-β-d-galactopyranosylglycerol (5), (2S)-1-O-(6Z,9Z,12Z,15Z-octadecatetranoyl)-2-O-palmitoyl-3-O-β-d-galactopyranosylglycerol (6), (2S)-1-O-eicosapentaenoyl-2-O-palmitoyl-3-O-β-d-galactopyranosylglycerol (7), (2S)-1,2-bis-O-arachidonoyl-3-O-β-d-galactopyranosylglycerol (8), (2S)-1-O-arachidonoyl-2-O-palmitoyl-3-O-β-d-galactopyranosylglycerol (9), (2S)-1-O-eicosapentaenoyl-2-O-palmitoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (10), and (2S)-1-O-arachidonoyl-2-O-palmitoyl-3-O-(β-d-galactopyranosyl-6-1α-d-galactopyranosyl)-glycerol (11). All the isolated compounds showed significant NO inhibitory activity. This is the first report of the isolation and identification of individual galactolipids from C. crispus. Moreover, (2S)-1,2-bis-O-arachidonoyl ?3-O-β-d-galactopyranosylglycerol (8) is a novel compound.     

Synthesis, characterization and electrocatalysis of diiron propanediselenolate derivatives as the active site models of [FeFe]-hydrogenases

As an extension of our study on the H-cluster model compounds, a series of diiron propanediselenolate (PDS)-type models have been successfully synthesized. Reaction of diselenol HSe(CH₂)₃SeH with Fe₃(CO)₁₂ in THF (tetrahydrofuran) at reflux gave the parent model compound [μ-Se(CH₂)₃Se-μ]Fe₂(CO)₆ (1) in 48% yield. Further reaction of 1 with PPh₃ or PPh₂H in the presence of Me₃NO in MeCN at room temperature afforded the phosphine-monosubstituted model compounds [μ-Se(CH₂)₃Se-μ]Fe₂(CO)₅(L) (2, L = PPh₃; 3, L = PPh₂H) in 76% and 68% yields, respectively. Similarly, the N-heterocyclic carbene I_Mes-monosubstituted model compound [μ-Se(CH₂)₃Se-μ]Fe₂(CO)₅(I_Mes) (4) could be prepared in 46% yield by reaction of imidazolium salt I_Mes · HCl with n-BuLi followed by treatment of the resulting I_Mes ligand with 1 in THF at room temperature. Compounds 1-4 were fully characterized by elemental analysis and various spectroscopic methods. While the structures of 1-4 were further confirmed by X-ray crystallography, the comparative study of 1 and its analog [μ-S(CH₂)₃S-μ]Fe₂(CO)₆ demonstrates that 1 is a better catalyst for TsOH proton reduction to hydrogen under electrochemical conditions.     

Mapping the pathway of heteroborane isomerisation: Two parallel “1,2 → 1,7” isomerisations of a crowded molybdacarborane and the isolation of isomerisation intermediates

The reaction between [7,8-Ph₂-7,8-nido-C₂B₉H₉]²⁻ and [(η-C₇H₇)Mo(MeCN)₃]⁺ affords five products. Four have been isolated and shown to be structural isomers of (η-C₇H₇)MoPh₂C₂B₉H₉. Compound 1 has a pseudocloso structure. In solution it gives way to the non-icosahedral compound 2 which in turn rearranges into the “1,2 → 1,7” C-atom isomerised compound 5 having a 2,1,8-MoC₂B₉ structure. A further “1,2 → 1,7” C-atom isomerised species, compound 4, is also isolated but has a 1,2,4-MoC₂B₉ architecture. Compound 4 forms via an intermediate 3, which is too unstable to characterise. Structurally the sequence of compounds 1, 2 and 5 maps well onto the sequential diamond-square-diamond isomerisation mechanism of 1,2-closo-C₂B₁₀H₁₂ into 1,7-closo-C₂B₁₀H₁₂ proposed by Wales. An alternative pathway from the notional first product of the metallation, 1,2-Ph₂-3-(η-C₇H₇)-3,1,2-closo-MoC₂B₉H₉, is required to rationalise the intermediate compound 3 and, from it, compound 4.     

Methyl or ethyl makes the difference: Synthesis and solid-state structure of 9,10-dialkyl-9,10-dihydro-9,10-digallaanthracenes

The donor-free 9,10-dialkyl-9,10-dihydro-9,10-digallaanthracenes 1 (alkyl: methyl) and 2 (alkyl: ethyl) were prepared by reaction of 1,2-di(chloromercurio)benzene with the corresponding trialkylgallium and isolated as colourless air- and moisture sensitive crystalline compounds. In the solid-state structure of 1, two slightly different monomers 1A and 1B are found, which form a dimer 1A?1B held together by “medium” strong gallium arene π-interactions. Further weak π-interactions between 1A and 1A and 1B and 1B constitute a one-dimensional coordination polymer containing strands of the composition [?(1A?1B)?(1B?1A)?]_n. In contrast, compound 2 crystallizes in the form of distinct molecular units without any further intermolecular π-interactions. The molecular units possess D_2d symmetry and are built by strong π-interactions between two digallaanthracene monomers. Two symmetrical aryl group bridges between two gallium atoms are observed for the first time in the subunits of 2. By addition of a Lewis-base (THF, Pyridine) to 2, a monomeric planar digallaanthracene framework is restored, as proven by an X-ray crystal structure analysis of 2 · 2Py. The different structures of 1 and 2 are explained on the basis of steric effects.     

Cosuppression of RBCS3B in Arabidopsis leads to severe photoinhibition caused by ROS accumulation

Key message

Cosuppression of an Arabidopsis Rubisco small subunit gene RBCS3B at Arabidopsis resulted in albino or pale green phenotypes which were caused by ROS accumulation

Abstract

As the most abundant protein on Earth, Rubisco has received much attention in the past decades. Even so, its function is still not understood thoroughly. In this paper, four Arabidopsis transgenic lines (RBCS3B-7, 18, 33, and 35) with albino or pale green phenotypes were obtained by transformation with a construct driving expression of sense RBCS3B, a Rubisco small subunit gene. The phenotypes produced in these transgenic lines were found to be caused by cosuppression. Among these lines, RBCS3B-7 displayed the most severe phenotypes including reduced height, developmental arrest and plant mortality before flowering when grown under normal light on soil. Chloroplast numbers in mesophyll cells were decreased compared to WT, and stacked thylakoids of chloroplasts were broken down gradually in RBCS3B-7 throughout development. In addition, the RBCS3B-7 line was light sensitive, and PSII activity measurement revealed that RBCS3B-7 suffered severe photoinhibition, even under normal light. We found that photoinhibition was due to accumulation of ROS, which accelerated photodamage of PSII and inhibited the repair of PSII in RBCS3B-7.     

Cloning of seed dormancy genes (TaSdr) associated with tolerance to pre-harvest sprouting in common wheat and development of a functional marker

Key message

After cloning and mapping of wheat TaSdr genes, both the functional markers for TaSdr - B1 and TaVp - 1B were validated, and the distribution of allelic variations at TaSdr - B1 locus in the wheat cultivars from 19 countries was characterized.

Abstract

Seed dormancy is a major factor associated with pre-harvest sprouting (PHS) in common wheat (Triticum aestivum L.). Wheat TaSdr genes, orthologs of OsSdr4 conferring seed dormancy in rice, were cloned by a comparative genomics approach. They were located on homoeologous group 2 chromosomes, and designated as TaSdr-A1, TaSdr-B1 and TaSdr-D1, respectively. Sequence analysis of TaSdr-B1 revealed a SNP at the position -11 upstream of the initiation codon, with bases A and G in cultivars with low and high germination indices (GI), respectively. A cleaved amplified polymorphism sequence marker Sdr2B was developed based on the SNP, and subsequently functional analysis of TaSdr-B1 was conducted by association and linkage mapping. A QTL for GI co-segregating with Sdr2B explained 6.4, 7.8 and 8.7 % of the phenotypic variances in a RIL population derived from Yangxiaomai/Zhongyou 9507 grown in Shijiazhuang, Beijing and the averaged data from those environments, respectively. Two sets of Chinese wheat cultivars were used for association mapping, and results indicated that TaSdr-B1 was significantly associated with GI. Analysis of the allelic distribution at the TaSdr-B1 locus showed that the frequencies of TaSdr-B1a associated with a lower GI were high in cultivars from Japan, Australia, Argentina, and the Middle and Lower Yangtze Valley Winter Wheat Region and Southwest Winter Wheat Region in China. This study provides not only a reliable functional marker for molecular-assisted selection of PHS in wheat breeding programs, but also gives novel information for a comprehensive understanding of seed dormancy.     

β-Diketiminato 3d-metal compounds: Synthesis, characterization and catalytic behavior towards ethylene

The lithium β-diketiminate (1c, [Li{N(2,6-ⁱPr₂C₆H₃)C(Ph)CHC(^tBu)NH}]₂ represented as (LiL)₂) reacted with 3d-metal (II) chlorides to afford the corresponding compounds (2-7). All metal compounds were fully characterized by elemental, spectroscopic analyses and the single-crystal X-ray diffraction. The coordination geometries around the metals are shown to be tetrahedral within the trinuclear Co₂Li compound (2), planar in ML₂ (M = Co, 3), pseudo-tetrahedral conformation in the ML₂ with M as Mn (4), Fe (5) or Zn (6), and square planar in the dinickel compound (7). Indicated by the trimetallic Co₂Li compound 2, a six-membered ring is constructed of three metal atoms and three bridged chlorides as a twisted conformation. An inversion center is present in the centroid of the Ni₂Cl₂ four-membered ring within compound 7. The plausible mechanism of forming ML₂ was proposed through the chloro-bridged multinuclear compounds on the basis of isolated intermediates of trinuclear (2) and dinuclearic (7) compounds. Upon treatment with methylaluminoxane (MAO), the nickel compound 7 possessed good activity towards ethylene oligomerization, whereas the other metal compounds showed moderate activities towards ethylene polymerization.     

Metal–drug synergy: new ruthenium(II) complexes of ketoconazole are highly active against Leishmania major and Trypanosoma cruzi and nontoxic to human or murine normal cells

In our ongoing search for new metal-based chemotherapeutic agents against leishmaniasis and Chagas disease, six new ruthenium–ketoconazole (KTZ) complexes have been synthesized and characterized, including two octahedral coordination complexes—cis,fac-[Ru^IICl₂(DMSO)₃(KTZ)] (1) and cis-[Ru^IICl₂(bipy)(DMSO)(KTZ)] (2) (where DMSO is dimethyl sulfoxide and bipy is 2,2′-bipyridine)—and four organometallic compounds—[Ru^II(η⁶-p-cymene)Cl₂(KTZ)] (3), [Ru^II(η⁶-p-cymene)(en)(KTZ)][BF₄]₂ (4), [Ru^II(η⁶-p-cymene)(bipy)(KTZ)][BF₄]₂ (5), and [Ru^II(η⁶-p-cymene)(acac)(KTZ)][BF₄] (6) (where en is ethylenediamine and acac is acetylacetonate); the crystal structure of 3 is described. The central hypothesis of our work is that combining a bioactive compound such as KTZ and a metal in a single molecule results in a synergy that can translate into improved activity and/or selectivity against parasites. In agreement with this hypothesis, complexation of KTZ with Ru^II in compounds 3–5 produces a marked enhancement of the activity toward promastigotes and intracellular amastigotes of Leishmania major, when compared with uncomplexed KTZ, or with similar ruthenium compounds not containing KTZ. Importantly, the selective toxicity of compounds 3–5 toward the leishmania parasites, in relation to human fibroblasts and osteoblasts or murine macrophages, is also superior to the selective toxicities of the individual constituents of the drug. When tested against Trypanosoma cruzi epimastigotes, some of the organometallic complexes displayed activity and selectivity comparable to those of free KTZ. A dual-target mechanism is suggested to account for the antiparasitic properties of these complexes.     

Influence of carbohydrate source on xanthone content in root cultures of Gentiana dinarica Beck

The effects of different types and concentrations of sugars on root growth and xanthone production in root culture of Gentiana dinarica were investigated. The results showed that sucrose, glucose and fructose all supported root growth, and sucrose was superior in terms of growth index, dry mass and fresh/dry mass ratio then fructose or glucose at the same concentrations. However, considering equimolar concentration of sugars, their contribution to the root growth was similar. The HPLC analysis of roots indicated the presence of xanthone compounds, and the contents of norswertianin-1-O-primeveroside (1), norswertianin-1-O-glucoside (2), gentioside (3) and norswertianin (4) were evaluated. In all samples, norswertianin-1-O-primeveroside (1) was present in highest concentration, followed by norswertianin-1-O-glucoside (2), whereas gentioside (3) and norswertianin (4) were present in lower amounts. The production of xanthones was affected by both type and concentration of sugar. In general, roots growing in media supplemented with sucrose contained higher levels of xanthones. The amounts of xanthone primeveroses (1) and (3) increased with the increase of concentrations of all types of sugars, whereas higher sugar concentrations resulted in reduction of the contents of norswertianin-1-O-glucoside (2) and aglycone norswertianin (4). The roots were also evaluated regarding the content of total phenolics and higher accumulation of total phenolic compounds was observed in roots grown in fructose-containing medium. Antioxidant activity was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, and high correlation between total phenolic content and antiradical activity was observed (r = ?0.83).     

6-Halogenopyridin-2-olato complexes with the diruthenium(2+) core: Equilibria between head-to-head and head-to-tail structures

The dinuclear bis(6-X-pyridin-2-olato) ruthenium complexes [Ru₂(μ-XpyO)₂(CO)₄(PPh₃)₂] (X = Cl (4B) and Br (5B)), [Ru₂(μ-XpyO)₂(CO)₄(CH₃CN)₂] (X = Cl (6B), Br (7B) and F (8B)) and [Ru₂(μ-ClpyO)₂(CO)₄(PhCN)₂] (9B) were prepared from the corresponding tetranuclear coordination dimers [Ru₂(μ-XpyO)₂(CO)₄]₂ (1: X = Cl; 2: X = Br) and [Ru₂(μ-FpyO)₂(CO)₆]₂ (3) by treatment with an excess of triphenylphosphane, acetonitrile and benzonitrile, respectively. In the solid state, complexes 4B-9B all have a head-to-tail arrangement of the two pyridonate ligands, as evidenced by X-ray crystal structure analyses of 4B, 6B and 9B, in contrast to the head-to-head arrangement in the precursors 1-3. A temperature- and solvent-dependent equilibrium between the yellow head-to-tail complexes and the red head-to-head complexes 4A-7A and 9A, bearing an axial ligand only at the O,O-substituted ruthenium atom, exists in solution and was studied by NMR spectroscopy. Full ¹H and ¹³C NMR assignments were made in each case. Treatment of 1 and 2 with the N-heterocyclic carbene (NHC) 1-butyl-3-methylimidazolin-2-ylidene provided the complexes [Ru₂(μ-XpyO)₂(CO)₄(NHC)], X = Cl (11A) or Br (12A). An XRD analysis revealed the head-to-head arrangement of the pyridonate ligands and axial coordination of the carbene ligand at the O,O-substituted ruthenium atom. The conversion of 11A and 12A into the corresponding head-to-tail complexes was not possible.     

An efficient lipase-catalyzed enantioselective hydrolysis of (R,S)-azolides derived from N-protected proline, pipecolic acid, and nipecotic acid

In the Candida antarctica lipase B-catalyzed hydrolysis of (R,S)-azolides derived from (R,S)-N-protected proline in water-saturated methyl tert-butyl ether (MTBE), high enzyme activity with excellent enantioselectivity (V _S V _R ^?1 ?>?100) for (R,S)-N-Cbz-proline 1,2,4-triazolide (1) and (R,S)-N-Cbz-proline 4-bromopyrazolide (2) was exploited in comparison with their corresponding methyl ester analog (3). Changing of the substrate structure, water content, solvent, and temperature was found to have profound influences on the lipase performance. On the basis of enzyme activity and enantioselectivity and solvent boiling point, the best reaction condition of using 1 as the substrate in water-saturated MTBE at 45 °C was selected and further employed for the successful resolution of (R,S)-N-Cbz-pipecolic 1,2,4-triazolide (5) and (R,S)-N-Boc-nipecotic 1,2,4-triazolide (9). Moreover, more than 89.1 % recovery of remained (R)-1 is obtainable in five cycles of enzyme reusage, when pH 7 phosphate buffers were employed as the extract at 4 °C.     

Towards the mechanism of heteroborane isomerisation: 1,2 → 1,2 and 1,2 → 1,7 low-temperature isomerisations from metallations of [5-I-7,8-Ph2-7,8-nido-C2B9H8]

The reaction between [5-I-7,8-Ph₂-7,8-nido-C₂B₉H₈]²⁻ and NiCl₂(dppe) affords 1,2-Ph₂-4,4-dppe-12-I-4,1,2-closo-NiC₂B₉H₈ (1) and 1,8-Ph₂-2,2-dppe-10-I-2,1,8-closo-NiC₂B₉H₈ (2). Reaction between the same carborane ligand and cis-PtCl₂(PMe₂Ph)₂ yields three species, 1,8-Ph₂-2,2-(PMe₂Ph)₂-10-I-2,1,8-closo-PtC₂B₉H₈ (3), 1,8-Ph₂-2,2-(PMe₂Ph)₂-12-I-2,1,8-closo-PtC₂B₉H₈ (4), and 1,8-Ph₂-2,2-(PMe₂Ph)₂-7-I-2,1,8-closo-PtC₂B₉H₈ (5). Compounds 1-5 have been characterised spectroscopically and crystallographically. The 4,1,2-MC₂B₉ architecture of 1 constitutes a “1,2 → 1,2” cage C atom isomerisation, and the 2,1,8-MC₂B₉ architectures of 2-5 a 1,2 → 1,7 cage C atom isomerisation, relative to the presumed first product of the metallations, 1,2-Ph₂-3,3-L₂-9-I-3,1,2-closo-MC₂B₉H₈ [M = Ni, L₂ = dppe; M = Pt, L₂ = (PMe₂Ph)₂]. The location of the (iodide) labelled boron vertex in the products allows speculation as to the mechanism of these isomerisations and the possible involvement of triangle face rotation is discussed.     

Fine-tuning the luminescent properties of metal-chelating 8-hydroxyquinolines through amido substituents in 5-position

New series of 5-substituted-8-hydroxyquinolines HL_n (1-6) bearing aliphatic or aromatic amido groups were synthesised. The chelating ability of these ligands toward the zinc(II) ion was tested and the photophysical characterisation of the resulting complexes (ZnL_n)₂ · 2H₂O (7-12) is reported and compared to those of the uncomplexed ligands. The photophysical data of 1-6 revealed interesting differences between aliphatic (1-3) and aromatic (4-6) amido-substituted species which, however, are no longer evident upon metal complexation. In fact while the ligands 1-3 showed a very high quantum yield (2, λ_em=470 nm; Φ=0.22) higher than that of the unsubstituted HQ compound, the ligands 4-6 displayed low quantum yield, similar to that of the complexes 7-12, which was in turn lower than that of ZnQ₂·2H₂O. The behaviour of these compounds is discussed with particular reference to the possibility of controlling the photophysical properties of such compounds through selective modification of the amido substituents.     

Gallium(III) complexes with 2-acetylpyridine-derived thiosemicarbazones: antimicrobial and cytotoxic effects and investigation on the interactions with tubulin

Complexes [Ga(2Ac4pFPh)₂]NO₃ (1), [Ga(2Ac4pClPh)₂]NO₃ (2), [Ga(2Ac4pIPh)₂]NO₃ (3), [Ga(2Ac4pNO₂Ph)₂]NO₃·3H₂O (4) and [Ga(2Ac4pT)₂]NO₃ (5) were obtained with 2-acetylpyridine N(4)-para-fluorophenyl-(H2Ac4pFPh), 2-acetylpyridine N(4)-para-chlorophenyl-(H2Ac4pClPh), 2-acetylpyridine N(4)-para-iodophenyl-(H2Ac4pIPh), 2-acetylpyridine N(4)-para-nitrophenyl-(H2Ac4pNO₂Ph) and 2-acetylpyridine N(4)-para-tolyl-(H2Ac4pT) thiosemicarbazone. 1–5 presented antimicrobial and cytotoxic properties. Coordination to gallium(III) proved to be an effective strategy for activity improvement against Pseudomonas aeruginosa and Candida albicans. The complexes were highly cytotoxic against malignant glioblastoma and breast cancer cells at nanomolar concentrations. The compounds induced morphological changes characteristic of apoptotic death in tumor cells and showed no toxicity against erythrocytes. 2 partially inhibited tubulin assembly at high concentrations and induced cellular microtubule disorganization, but this does not appear to be the main mechanism of cytotoxic activity.