Showing papers in "Zeitschrift für Naturforschung B in 2013"

Ionic Liquids for the Synthesis and Stabilization of Metal Nanoparticles

Abstract: The synthesis and stabilization of metal nanoparticles (M-NPs) from metals, metal salts, metal complexes and metal carbonyls in ionic liquids (ILs) is reviewed. The electrostatic and steric properties of ionic liquids allow for the stabilization of M-NPs without the need of additional stabilizers, surfactants or capping ligands. The synthesis of M-NPs in ILs can be carried out by chemical or electroreduction, thermolysis and photochemical methods including decomposition by microwave or sono-/ultrasound irradiation. Gas-phase syntheses can use sputtering, plasma/glow-discharge electrolysis and physical vapor deposition or electron beam and γ-irradiation. Metal carbonyl precursors Mx(CO)y contain the metal atoms already in the zero-valent oxidation state needed for M-NPs so that no extra reducing agent is necessary. Microwave-induced thermal decomposition of precursors in ILs is a rapid and energy-saving access to M-NPs because of the significant absorption efficiency of ILs for microwave energy due to their ionic charge, high polarity and high dielectric constant. M-NP/IL dispersions can be applied in catalytic reactions, e. g., in C–C coupling or hydrogenation catalysis.

Surface-active Ionic Liquids for Micellar Extraction of Piperine from Black Pepper

Abstract: We present the application of ionic liquid-aqueous micellar solutions as isolation media for the pharmaceutically active ingredient piperine from black pepper. Several surface-active ionic liquids including a biodegradable betaine derivative were used for the extraction of piperine, and a strong correlation between extraction yield and the critical micelle concentration of the respective ionic liquid was found. A scaled strategy for the isolation of piperine was developed that allowed recovery and recycling of the aqueous ionic liquid micellar solution for five runs without any loss in extraction efficiency.

[HMIM][Br9]: a Room-temperature Ionic Liquid Based on a Polybromide Anion

Abstract: [hmim][Br9] is prepared by addition of Br2 to [hmim]Br in a molar ratio of 5:1 (-40 °C, 72 h).

The Differential Capacitance of Ionic Liquid / Metal Electrode Interfaces – A Critical Comparison of Experimental Results with Theoretical Predictions

Abstract: Results of potential-dependent differential capacitance measurements on the interface between six different ionic liquids and the (111) surface of single-crystalline gold are presented. The measurements were done by means of broadband impedance spectroscopy in a frequency range from 10 mHz to 1 MHz. We discuss the influence of the IL cation, the IL anion and the cations’ alkyl chain length on the interfacial capacitance. Our results suggest that (i) there is no simple relationship between the cation size and the value of the differential capacitance, (ii) the general shape of the potentialdependent differential capacitance curve is more strongly influenced by the IL anion, and (iii) experimental differential capacitance curves do not exhibit a simple “camel-” or “bell-shaped” curvature as predicted by mean-field theories. Furthermore, the broadband measurements show that two capacitive processes can be distinguished, which take place on millisecond and second time scales, respectively. While a millisecond time scale is expected for double-layer charging governed by the bulk conductivity of the IL, the existence of a slow process points to additional barriers for charge transport at the interface. The capacitance contribution of the slow process is most pronounced for ILs based on the N-butyl-N-methyl-pyrrolidinium ([Pyr1,4]) cation. A comparison of capacitance data with insitu STM data from previous studies suggests that the slow process is connected to herringbone-type structures at the interface. While the herringbone superstructure of the Au(111) surface is well known in aqueous electrochemistry, a herringbone-type structure of adsorbed ions was described in a recent MD simulation paper by Federov and coworkers (K. Kirchner, T. Kirchner, V. Ivaništĕv, M. V. Fedorov, Electrochim. Acta 2013, in press: doi: 10.1016/j.electacta.2013.05.049). Graphical Abstract The Differential Capacitance of Ionic Liquid / Metal Electrode Interfaces – A Critical Comparison of Experimental Results with Theoretical Predictions

BIOnic Liquids: Imidazolium-based Ionic Liquids with Antimicrobial Activity

Abstract: We have synthesized twelve new ionic liquids composed of an imidazolium-based cation in combination with an anion that shows antiobiotic or analgesic activity. These “BIOnic Liquids” have been tested towards their antibiotic activity in a standardized microbiological assay. A surprizingly large number of compounds shows high activity towards a set of bacteria which cannot be explained as simple cumulative effects. The general concept opens up completely new possibilities for the future development of pharmaceutically active compounds. Graphical Abstract BIOnic Liquids: Imidazolium-based Ionic Liquids with Antimicrobial Activity

Solvent-free Synthesis of 1,2-Disubstituted Derivatives of 1,2- Dihydroisoquinoline, 1,2-Dihydroquinoline and 1,2-Dihydropyridine

Abstract: A one-pot and efficient approach to the synthesis of dialkyl 2-[1-[(alkoxycarbonyl)anilino]-2(1H)- (isoquinolin-2-yl) (or -quinolin-1-yl or -pyridin-1-yl)]-2-butenedioates is described. This method involves a three-component reaction between isoquinoline, quinoline or pyridine, dialkyl acetylenedicarboxylates and N-phenylcarbamates under solvent-free conditions, without using any catalyst and at room temperature. The mild reaction conditions and good yields of the products exhibit the synthetic advantage of this method. Graphical Abstract Solvent-free Synthesis of 1,2-Disubstituted Derivatives of 1,2- Dihydroisoquinoline, 1,2-Dihydroquinoline and 1,2-Dihydropyridine

Synthesis, Crystal Structure, DNA-binding Properties and Antioxidant Activities of a Lutetium(III) Complex with the Bis(N-salicylidene)-3- oxapentane-1,5-diamine Ligand

Abstract: A Schiff base ligand bis(N-salicylidene)-3-oxapentane-1,5-diamine (H2L) and its lutetium(III) complex, with composition Lu2(L)2(NO3)2, were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structure of the Lu(III) complex has been determined by single-crystal X-ray diffraction. It reveals a centrosymmetric binuclear neutral entity where Lu(III) metal centers are bridged by two phenoxo oxygen atoms. The DNA-binding properties of the Lu(III) complex were investigated by spectrophotometric methods and viscosity measurements, and the results suggest that the Lu(III) complex binds to DNA via a groove binding mode. Additionally, the antioxidant activity of the Lu(III) complex was determined by the superoxide and hydroxyl radical scavenging methods in vitro, which indicate that it is a scavenger for OH· and O-· 2 radicals. Graphical Abstract Synthesis, Crystal Structure, DNA-binding Properties and Antioxidant Activities of a Lutetium(III) Complex with the Bis(N-salicylidene)-3- oxapentane-1,5-diamine Ligand

Thermally Stable 3,6-Disubstituted 1,2,4,5-Tetrazines

Abstract: Several 3,6-disubstituted 1,2,4,5-tetrazines were synthesized by nucleophilic substitution using 3,6-bis-(3,5-dimethyl-pyrazol-1-yl)-1,2,4,5-tetrazine and 3,6-dichloro-1,2,4,5-tetrazine as electrophiles. All new compounds were characterized by 1H NMR, 13C NMR and vibrational spectroscopy, mass spectrometry and elemental analysis (C,H,N). For analysis of the thermostability, differential scanning calorimetry (DSC) was used. Especially, the symmetrically bis-3,5-diamino-1,2,4- triazolyl-substituted derivative shows a very high thermal stability up to 370 °C. Therefore its energetic properties were determined and compared with thoses of hexanitrostilbene (HNS). The crystal structures of 3,6-bishydrazino-1,2,4,5-tetrazine, 3,6-dichloro-1,2,4,5-tetrazine and 3-amino-6-(3,5- diamino-1,2,4-triazol-1-yl)-1,2,4,5-tetrazine dihydrate have been determined by low-temperature X-ray diffraction Graphical Abstract Thermally Stable 3,6-Disubstituted 1,2,4,5-Tetrazines

TiO2 Nanoparticles as an Efficient Catalyst for the One-pot Preparation of Tetrahydrobenzo[c]acridines in Aqueous Media

Abstract: The advantages of this novel multicomponent reaction protocol are operational simplicity, easy work up, reusability of the catalyst and an environmentally friendly procedure.

Synthesis and anti-HIV activity of new fused chromene derivatives derived from 2-amino-4-(1-naphthyl)-5-oxo-4H,5H-pyrano[3,2-c]chromene-3-carbonitrile

Abstract: New chromene derivatives (III), (IV), and (X) inhibit HIV-1 and HIV-2 replication in cell cultures, with compound (III) being the most active one.

Complexation to Cadmium(II) of a Tetradentate Ligand Resulting from the Condensation of 2-Pyridinecarbaldehyde with N-(2- Aminoethyl)propane-1,3-diamine

Abstract: The reaction of 2-pyridinecarbaldehyde with N-(2-aminoethyl)propane-1,3-diamine in a 2 : 1 molar ratio under microwave irradiation gave 2-(2-(pyridin-2-yl)-tetrahydropyrimidin-1(2H)-yl)-N(pyridin-2-ylmethylene)ethanamine (L) as a mixture with the isomer 3-(2-(pyridin-2-yl)imidazolidin1-yl)-N-(pyridin-2-ylmethylene)propan-1-amine (L∗). The molecules were characterized by elemental analyses and spectroscopic methods. Percentages of L and L∗ were evaluated through integration of selected 1H NMR signals. The cadmium iodide complex of L, [Cd(L)I2]·H2O (1), was prepared and identified by elemental analysis, FT-IR, Raman, and 1H NMR spectroscopy, and single-crystal X-ray diffraction. In the crystal structure of 1 the cadmium atom with four coordinated nitrogen atoms and two iodide ions has a distorted octahedral geometry. A water molecule is also incorporated in the crystal network. Several hydrogen bonds including N–H···O, C–H···O, C–H···I, and O–H···I interactions are present in the crystal structure of 1.

Coordination of N-Heterocyclic Carbene to H2SiX2 (X = Cl, OTf) and H3SiOTf (OTf = OSO2CF3): Synthesis of Donor-stabilized Parent Silylium Salts with Four- and Five-coordinate Silicon Atoms

Abstract: The reactivity of the N-heterocyclic carbene (NHC) 1,3-bis(2,6-diisopropylphenyl)imidazol-2- ylidene towards dichlorosilane H2SiCl2, bis(trifluoromethanesulfonato)silane H2Si(OTf)2 (OTf = OSO2CF3), and silyl trifluoromethanesulfonate H3SiOTf has been investigated. It turned out that the coordination of the NHC ligand can occur stepwise to form the three neutral compounds (NHC)SiH2Cl2 (1), (NHC)2SiH2Cl2 (2), (NHC)SiH2(OTf)2 (3), as well as the two ion pairs [(NHC)SiH3]+(OTf-) (4) and [(NHC)2SiH3]+(OTf-) (5); the latter represent the first NHC adducts of the parent silylium cation (H3Si+). The multinuclear NMR and IR spectroscopic data of the products reflect the characteristics of four-, five-, and six-coordinate silane complexes. All new compounds were structurally characterized by single-crystal X-ray diffraction analyses Graphical Abstract Coordination of N-Heterocyclic Carbene to H2SiX2 (X = Cl, OTf) and H3SiOTf (OTf = OSO2CF3): Synthesis of Donor-stabilized Parent Silylium Salts with Four- and Five-coordinate Silicon Atoms

The Stannides RE2Ni2Sn (RE = Pr, Ho, Er, Tm) – Structural Transition from the W2B2Co to the Mo2B2Fe Type as a Function of the Rare Earth Size

Abstract: The stannides RE2Ni2Sn (RE=Pr, Ho, Er, Tm) were synthesized by arc-melting of the elements and characterized by powder X-ray diffraction. Pr2Ni2Sn crystallizes with the orthorhombic W2B2Co-type structure, Immm, a=443.8(1), b=572.1(1), c=855.1(2) pm, wR2=0.0693, 293 F2 values, 13 variables. A structural transition to the tetragonal Mo2B2Fe type occurs for the heavier rare earth elements. The structures of Ho2Ni2Sn (a=729.26(9), c=366.66(7) pm, wR2=0.0504, 250 F2 values, 12 variables), Er2Ni2Sn (a=727.2(2), c=364.3(1) pm, wR2=0.0397, 262 F2 values, 12 variables), and Tm2Ni2Sn (a=725.2(1), c=362.8(1) pm, wR2=0.0545, 258 F2 values, 12 variables) were refined from single-crystal diffractometer data. The switch in structure type is driven by the size of the rare earth element. The [Ni2Sn] substructures are composed of Ni2Sn2 squares and Ni4Sn2 hexagons in Pr2Ni2Sn, and of Ni3Sn2 pentagons in Er2Ni2Sn. The Ni4Sn2 hexagons and Ni3Sn2 pentagons exhibit Ni2 pairs with Ni-Ni distances of 247 pm in Pr2Ni2Sn, and of 250 pm in Er2Ni2Sn. Graphical Abstract The Stannides RE2Ni2Sn (RE = Pr, Ho, Er, Tm) – Structural Transition from the W2B2Co to the Mo2B2Fe Type as a Function of the Rare Earth Size

Novel Insensitive Energetic Nitrogen-rich Polymers Based on Tetrazoles

Abstract: Nitrogen-rich polymers were synthesized by radical polymerization using the reaction of 5- aminotetrazole with methacryloyl chloride and acryloyl chloride, respectively. The nitrogen content of poly(methacrylamidotetrazole) and poly(acrylamidotetrazole), as well as the energetic character of these compounds was increased by nitration of the amido moiety. The products remained however insensitive and had a very good thermal stability. All substances were characterized by using vibrational spectroscopy (IR), mass spectrometry, elemental analysis, as well as multinuclear NMR spectroscopy. Additionally, the impact and friction sensitivities were determined by BAM standards, and also the sensitivity against electrostatic discharge was studied. The energetic properties were investigated by bomb-calorimetric measurements and calculations with the EXPLO5 software, and the thermal stability was investigated by differential scanning calorimetry. All compounds are thermally highly stable materials. The high stability of the polymers towards impact and friction and the good energetic character makes these polymers promising candidates for applications as environmentally friendly nitrogen-rich polymers

Review. Regioselective Functionalization of Pyridines using a Directed Metalation or a Halogen/Metal Exchange

Abstract: This review describes the various ways of functionalizing the pyridine scaffold using either directed metalation or halogen/metal exchange. Deprotonation can be accomplished with different lithium amides or alkyllithium reagents at low temperature. Milder conditions and higher functional group tolerance can be achieved by using ate-bases with different metals (Cd, Mg, Zn) or TMP (2,2,6,6- tetramethylpiperidyl) metal reagents (metal=Mg, Zn, Zr). With alkyllithium reagents it is also possible, by carefully adjusting the reaction conditions, to perform bromine/lithium exchange reactions. Organomagnesium reagents, like iPrMgX (X=Br, Cl LiCl), may be used for exchanging more sensitive iodinated or brominated pyridines Graphical Abstract Review. Regioselective Functionalization of Pyridines using a Directed Metalation or a Halogen/Metal Exchange

Hydroalumination versus Deprotonation of Alkynes with Sterically Demanding Substituents

Abstract: Treatment of sterically highly shielded terminal alkynes, H-C≡C-aryl, with dialkylaluminium and dialkylgallium hydrides, R2E-H, afforded by hydrogen release dimeric dialkylelement alkynides with a four-membered E2C2 heterocycle independent of the bulk of the aryl groups. A rare example of a monomeric alkynylaluminium compound was only obtained with very bulky CH(SiMe3)2 groups attached to the metal atoms and by salt elimination reaction. The steric shielding by the bulky aryl groups did not prevent condensation reactions. Hydroalumination of 1-(trimethylsilyl)-2-(2,6- dimethylphenyl)ethyne using Me2Al-H resulted in a divinyl compound by elimination of trimethylaluminium Graphical Abstract Hydroalumination versus Deprotonation of Alkynes with Sterically Demanding Substituents

Zahramycins A-B, Two New Steroids from the Coral Sarcophyton trocheliophorum

Abstract: The two new steroids zahramycins A (I) and B (II) are isolated from the coral Sarcophyton trocheliophorum.

Synthesis and Crystal Structures of New 1,3-Disubstituted Imidazoline-2-thiones

Abstract: Two methods (MeOH/K2CO3, pyridine/Et3N) were assessed for the introduction of sulfur into the 2-position of 1,3-disubstituted quaternary imidazolium salts 1-9 (Cl, I, BF4, PF6, CH3OSO3 were used as anions) to yield nine 1,3-disubstituted imidazoline-2-thiones 10-18 (1, 10: R1 = CH3, R2 = CH3; 2, 11: R1 = OCH2Ph, R2 = CH3; 3, 12: R1 = OCH3, R2 = CH3; 4, 13: R1 = OCH3, R2 = OCH3; 5, 14: R1 = NH2, R2 = CH2Ph; 6, 15: R1 = NCHPh, R2 = CH3; 7, 16: R1 = NH2, R2 = CH3; 8, 17: R1 = NCHPh, R2 = NCHPh; 9, 18: R1 = NH2, R2 = OCH3). Compounds 11-18 represent N-alkyloxy and N-amino imidazoline-2-thiones, whereas 10 served as reference compound. The first method was advantageous for the conversion 1 → 10 due to faster reaction, whereas in the reaction 2 → 11 considerable amounts of by-products were formed. Pure thiones 11, 14, 16, 17, and 18 were obtained only by the second method. Both methods worked for the synthesis of the methoxy derivatives 12 and 13 from 3 and 4, and the benzylideneamino derivative 15 from 6. 1-Amino-3- methylimidazoline-2-thione (16) was also prepared by hydrolysis of the benzylideneamino derivative 15. Crystal structures of seven 1,3-disubstituted imidazoline-2-thiones were determined by singlecrystal X-ray diffraction. Intermolecular C-H···S contacts were identified and, additionally, N-H···S interactions in aminothiones 14 and 16. The 1H NMR shifts of 10 and 13 were satisfactorily correlated with the Kamlet-Abboud-Taft π* and b parameters in ten solvents. From the lack of correlation with the a parameter and from the C=S bond length (average 1.68 Å ) a significant contribution of a mesoionic imidazolium-2-thiolate resonance structure seems unlikely. Graphical Abstract Synthesis and Crystal Structures of New 1,3-Disubstituted Imidazoline-2-thiones

Oxidation Reactions Catalyzed by Polyoxomolybdate Salts

Abstract: Ionic compounds containing the polyoxomolybdate anion [Mo6O19](2-) and [(n-C4H9)(4)P](+) (tetra-butylphosphonium), [(n-C4H9)(3)P(n-C14H29)](+) (tributyl (tetradecyl)phosphonium), [Dbmim](+) (1-butyl-3-methylimidazolium) and [Dbmim] (1,2-dimethyl-3-butylimidazolium) cations were prepared and characterized, including the determination of three of the solid state structures by single-crystal X-ray diffraction. These compounds were applied as catalysts for the epoxidation of olefins with urea hydrogen peroxide (UHP) as oxidant in the ionic liquid [Bmim]PF6. Additionally, the oxidation of sulfides to sulfoxides with hydrogen peroxide (H2O2) in several solvents was investigated. The polyoxomolybdate catalysts showed a good performance for epoxydation of olefins as well as for oxidation of sulfides. Furthermore, the catalysts can be recycled several times in oxidation reactions. We present this methodology for the oxidation reaction in a simple, economically, technically, and environmentally benign manner.

A Novel Route to Isoquinoline[2,1-g][1,6]naphthyridine, Pyrazolo[5,1-a] isoquinoline and Pyridazino[4´,5´:3,4]pyrazolo[5,1-a]isoquinoline Derivatives With Evaluation of Antitumor Activities

Abstract: Routes towards the synthesis of the title compounds are described from isoquinoline derivatives.

Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

Abstract: The vicinity of a hydrogen bond donor (O-H) and a hydrogen bond acceptor (C=O or C=N-R) in salicylaldehydes and ortho-Schiff bases results in significant structural variations compared to the monosubstituted derivatives that are reflected in the electronic structure and thus in the spectroscopic properties. This interplay between intramolecular hydrogen bonding and multicenter pi-electron delocalization is the origin of the concept of resonance-assisted hydrogen bonding (RAHB). Herein, the complexity is extended from one hydrogen bond donor-acceptor pair in salicylaldehyde and ortho-Schiff bases to three hydrogen bond donor-acceptor pairs in 2,4,6-tricarbonyl- and 2,4,6-triimine-substituted phloroglucinols (1,3,5-trihydroxybenzene), respectively. To evaluate the changes in the molecular and electronic structures, we have performed a comprehensive computational, spectroscopic, and structural study starting from monosubstituted benzene derivatives as references over ortho-disubstituted derivates to the sixfold-substituted derivatives. Whereas in salicylaldehydes, ortho-Schiff bases, and 2,4,6-tricarbonyl-phloroglucinols the phenolic O-protonated tautomers represent the energy minima, the N-protonated tautomers represent the energy minima in 2,4,6-triiminephloroglucinols. The analysis provides a keto-enamine resonance structure with six exocyclic double bonds to be dominant for these species reminiscent of [6]radialenes, which were termed heteroradialenes. These heteroradialenes are non-aromatic alicycles. However, the predominance of this resonance structure does not represent a sudden change going from the 2,4,6-tricarbonyl- to the 2,4,6-triimine-phloroglucinols, but a gradual increase of analogous resonance structure contributions is observed even in salicylaldehyde and ortho-Schiff bases demonstrating some hetero-ortho-quinodimethane character. These changes are, besides in the molecular structures, well reflected in the IR spectra, which can therefore be used as a simple tool to probe the electronic structures in these systems. Interruption of the delocalized pi system supporting the intramolecular hydrogen bond, L e. going from 2,4,6-triimine- to 2,4,6-triamine-substituted phloroglucinols, reestablishes an O-protonated aromatic phloroglucinol system.

Cerium Valence Change in the Solid Solutions Ce(Rh1-xRux)Sn

Abstract: The solid solutions Ce(Rh1-xRux)Sn were investigated by means of susceptibility measurements, specific heat, electrical resistivity, X-ray absorption spectroscopy (XAS), and 119Sn Mössbauer spectroscopy. Magnetic measurements as well as XAS data show a cerium valence change in dependence on the ruthenium content. Higher ruthenium content causes an increase from 3.22 to 3.45 at 300 K. Furthermore χ and χ-1 data indicate valence fluctuation for cerium as a function of temperature. For example, Ce(Rh0:8Ru0:2)Sn exhibits valence fluctuations between 3.42 and 3.32 in the temperature range of 10 to 300 K. This could be proven by using the interconfiguration fluctuation (ICF) model introduced by Sales and Wohlleben. Cerium valence change does not influence the tin atoms as proven by 119Sn Mössbauer spectroscopy, but it influences the electrical properties. Ce(Rh0:9Ru0:1)Sn behaves like a typical valence fluctuating compound, and higher ruthenium content causes an increase of the metallic behavior Graphical Abstract Cerium Valence Change in the Solid Solutions Ce(Rh1-xRux)Sn

A Polyketide Metabolite from an Endophytic Fusarium equiseti in a Medicinal Plant

Abstract: A new polyketide, fusaequisin A (1), was isolated from rice cultures of Fusarium equiseti SF-3-17, an endophytic fungus previously discovered during screening of medicinal plants in Cameroon. The structure of 1 was determined using spectroscopic methods. Fusaequisin A (1) exhibited moderate antimicrobial activity against Staphylococcus aureus NBRC 13276 and Pseudomonas aeruginosa ATCC 15442 at a concentration of 200 μg per disk.

Isolation and Characterization of Limonoids from Kigelia africana

Abstract: Two new limonoids, 1-O-deacetyl-2a-methoxykhayanolide (1) and kigelianolide (2), together with deacetylkhayanolide E (3), 1-O-deacetyl-2α-hydroxykhayanolide E (4) and khayanolide B (5) were isolated from the ethyl acetate-soluble fraction of the methanolic extract of Kigelia africana. The structures of these limonoids (1-5) were elucidated by the combination of 1D (1H and 13C NMR) and 2D (HMQC, HMBC and COSY) NMR spectroscopy and mass spectrometry (EIMS, HREIMS), and in comparison with literature data of related compounds. The structure of compound 1 was further confirmed by X-ray crystallography, and the absolute stereochemistry of compounds 1 and 2 was determined by electronic circular dichroism (ECD) spectroscopy. Limonoids 1-5 showed weak inhibitory activities against the enzymes acetylcholinesterase (AChE), butyrycholinesterase (BChE) and lipoxygenase (LOX) in a concentration-dependent manner with IC50 values in the ranges 137.5 - 225.2 μM for AChE, 185.4 - 241.5 μM for BChE and 281.2 - 189.6 μM for LOX Graphical Abstract Isolation and Characterization of Limonoids from Kigelia africana

Depsidones from an Endophytic Fungus Chaetomium sp. Associated with Zanthoxylum leprieurii

Abstract: spp.have afforded more than 250 bioactive metabolites,among them the cytotoxic alkaloid chaetominine [6],antimalarial depsidones [7], azaphilones [8], and thecytotoxic chaetoconvosins [9], which have drawn theattention of both synthetic chemists and pharmacolo-gists.In the course of our screening program for newantimicrobial and cytotoxic metabolites from en-dophytic fungi inhabiting Cameroonian medicinalplants [10,11], an endophytic fungus

The Effect of Centrifugal Force on the Assembly and Crystallization of Binary Colloidal Systems : Towards Structural Gradients

Abstract: In this study, the effect of centrifugal force on the assembly and crystallization of binary colloidal mixtures is demonstrated. Monolithic pieces have been prepared which are characterized by a structural gradient along the direction of the centrifugal force. For a given number ratio of monodisperse 154 and 300 nm latex spheres, the absolute latex concentration was varied and with it the sedimentation velocity of the individual particle species. For three different concentrations it has been demonstrated that the structure of the binary colloidal assembly obtained after centrifugation is affected significantly. For the largest initial latex absolute concentrations, the structural variation along the packed latex column in the ultracentrifuge tube is minimal, while a decrease in the absolute concentrations leads to crystalline packing in defined regions of the column. The observation of the thermodynamically favored structure resembling NaCl, but also of the aluminum boride AlB2 analog as well as unordered, glass-like packing depending on the mutual latex concentration under unchanged particle number and size ratio, shows that by centrifugation kinetically favored states can be realized. This result implies that centrifugation of binary latex mixtures is a promising route for investigating the self-organization of binary colloidal systems since the sedimentation velocities of the two particle species are different, and thus the local concentrations and mixing ratios vary continuously also enabling rare packing motifs. Graphical Abstract The Effect of Centrifugal Force on the Assembly and Crystallization of Binary Colloidal Systems: Towards Structural Gradients

Nucleophilic Reactivities of Schiff Bases

Abstract: The nucleophile-specific parameters N and sN, as defined by the linear free energy relationship log k = sN(N+E) (J. Am. Chem. Soc. 2001, 123, 9500 - 9512), were determined for five imines 1a-e by studying the kinetics of their reactions with benzhydrylium ions in dichloromethane solution at 20 °C. These parameters allowed us to include representative Schiff bases into our comprehensive nucleophilicity scale and compare their reactivities with those of other N-nucleophiles Graphical Abstract Nucleophilic Reactivities of Schiff Bases

Epoxidation of Olefins Catalyzed by Polyoxomolybdates Formed in-situ in Ionic Liquids

Abstract: Polyoxomolybdates were generated in situ by treating a carboxylic acid-functionalized ionic liquid with an aqueous solution of sodium molybdate. This reaction mixture was applied in the catalytic epoxidation of olefins using hydrogen peroxide as oxidant. The influence of acid and catalyst concentration as well as of the reaction temperature was investigated. The system showed a good performance for the epoxidation reaction and can be reused several times without a significant loss of activity. We present an easy, cheap and environmentally friendly catalytic system for the epoxidation of cis-cyclooctene. Graphical Abstract Epoxidation of Olefins Catalyzed by Polyoxomolybdates Formed in-situ in Ionic Liquids

Preparation of CaCO3 and CaO Replicas Retaining the Hierarchical Structure of SpruceWood

Abstract: The principal structural characteristics of softwood (spruce) were replicated in CaCO3 and CaO on various levels of hierarchy from the macroscopic to the submicron scale. Positive replicas were obtained by infiltrating pretreated softwood templates with a Ca(OCOOCH3)2 precursor solution which hydrolyzed into CaCO3 nanoparticles. They reproduce the hierarchical porous structure of the wood template. Calcination at temperatures from 350 to 900 °C yields calcite as the main polymorph. Mechanical stability of the replica is optimized when the specimen is calcined at 900 °C Graphical Abstract Preparation of CaCO3 and CaO Replicas Retaining the Hierarchical Structure of SpruceWood

Synthesis of 1,4-Disubstituted 1,2,3-Triazoles from Aromatic a-Bromoketones, Sodium Azide and Terminal Acetylenes via Cu/Cu(OTf)2-catalyzed Click Reaction under Microwave Irradiation

Abstract: Reaction of aromatic a-bromoketones, sodium azide and aromatic or aliphatic terminal acetylenes in the presence of Cu/Cu(OTf)2 following the classical method (aqueous acetonitrile at room temperature) and under microwave irradiation (H2O at 85 °C) leads to 1,4-disubstituted 1,2,3-triazoles as the final products after simple filtration. Graphical Abstract Synthesis of 1,4-Disubstituted 1,2,3-Triazoles from Aromatic a-Bromoketones, Sodium Azide and Terminal Acetylenes via Cu/Cu(OTf)2-catalyzed Click Reaction under Microwave Irradiation