Terminal Nitrogen Atom Research Articles

Specificity of Protein Arginine Methyltransferases (PRMTs): How Does the Trypanosoma brucei PRMT7 Limit its Activity to Monomethylation of its Target Proteins?

In the family of the nine mammalian enzymes that modify proteins by adding one or two methyl groups to the terminal guanidino nitrogen atoms of acceptor proteins, PRMT7 is unique in producing solely monomethylarginine (MMA) products. The other eight PRMTs catalyze the formation of symmetrically or asymmetrically dimethylated arginine (SDMA or ADMA) residues. Since these modifications are often recognized by reader proteins specific for MMA, SDMA, or ADMA, the biological functions of PRMTs are closely linked to the type of methylation. SDMA and ADMA residues on certain proteins have been known to up‐regulate or down‐regulate transcription, suggesting a possible regulatory function for MMA markers produced by PRMT7. In order to understand the nature of monomethylation and what keeps PRMT7 from dimethylating its substrates, we have focused our attention on the residues of its active site from the protozoan Trypanosoma brucei responsible for sleeping sickness in humans. By using site‐directed mutagenesis, we have mutated several residues including those in the “double E” loop known to interact with the methyl‐accepting substrate arginine residues and then assayed its level and type of methylation via high resolution cation exchange chromatography. Here we present results suggesting that most of these enzyme modifications result in significantly reduced activity but no change in MMA specificity. However, we have found that a mutation of glutamate‐181 (a double E residue) to an aspartate residue not only significantly diminishes enzyme activity but also confers to the enzyme the ability to asymmetrically dimethylate arginines, generating ADMA products. This result pinpoints a crucial residue in maintaining the specificity of PRMT7.Support or Funding InformationEWD was a Frey Fellow of the Damon Runyon Cancer Research Foundation. This work was also supported by grants from NIH including GM026020 (S.G.C.) and a Ruth L. Kirschstein National Service Award GM007185 (to K.J. and R.A.W.).

Can Cyclen Bind Alkali Metal Azides? A DFT Study as a Precursor to Synthesis.

Can cyclen (1,4,7,10-tetraazacyclododecane) bind alkali metal azides? This question is addressed by studying the geometric and electronic structures of the alkali metal azide-cyclen [M(cyclen)N3] complexes using density functional theory (DFT). The effects of adding a second cyclen ring to form the sandwich alkali metal azide-cyclen [M(cyclen)2N3] complexes are also investigated. N3(-) is found to bind to a M(+) (cyclen) template to give both end-on and side-on structures. In the end-on structures, the terminal nitrogen atom of the azide group (N1) bonds to the metal as well as to a hydrogen atom of the cyclen ring through a hydrogen bond in an end-on configuration to the cyclen ring. In the side-on structures, the N3 unit is bonded (in a side-on configuration to the cyclen ring) to the metal through the terminal nitrogen atom of the azide group (N1), and through the other terminal nitrogen atom (N3) of the azide group by a hydrogen bond to a hydrogen atom of the cyclen ring. For all the alkali metals, the N3-side-on structure is lowest in energy. Addition of a second cyclen unit to [M(cyclen)N3] to form the sandwich compounds [M(cyclen)2N3] causes the bond strength between the metal and the N3 unit to decrease. It is hoped that this computational study will be a precursor to the synthesis and experimental study of these new macrocyclic compounds; structural parameters and infrared spectra were computed, which will assist future experimental work.

A highly active multi‐usable palladium pyridylfluorene film‐based catalyst for C–C cross‐coupling reactions

The two terminal pyridyl nitrogen atoms of 2,7‐bis(4‐pyridyl)fluorene (1) were coordinated to Pd(II) ions to give self‐assembled, multilayer films using the layer‐by‐layer (LbL) method. The films were prepared by alternately dipping the substrate, pre‐coated with a polyethyleneimine layer, in aqueous solutions of PdCl2 and ethanol solutions of 1. The resulting films were characterized using UV–visible absorption spectroscopy, atomic force microscopy (AFM), X‐ray photoelectron spectroscopy, scanning electron microscopy (SEM) and inductively coupled plasma atomic emission spectroscopy (ICP‐AES). UV–visible spectra and SEM images show almost uniform growth of the film in a near ideal LbL manner. AFM images show that nanostructured aggregates of Pd(II) complexes form on the surface. With an increase in the number of Pd(II)/1 bilayers, more particulate aggregates are distributed on the surface. When released from the substrate, the Pd(II) complex nanostructure shows high catalytic activity for Suzuki–Miyaura and Mizoroki–Heck cross‐coupling reactions. The catalyst loading is as low as 9.1 × 10−3 mol% Pd, as measured using ICP‐AES, and high turnover numbers of up to 1.08 × 104 are obtained. Copyright © 2015 John Wiley & Sons, Ltd.

Pd- and Ni-Pyridyl Complexes Deposited as Films for Suzuki–Miyaura and Mizoroki–Heck Cross Coupling Reactions

A pyridyl fluorene ligand, 2,7-bis(4-pyridyl)-9,9-diethylfluorene (1), has been synthesized by a simple route. The ability of the two linearly terminal pyridyl nitrogen atoms of 1 to coordinate with the Pd(II) or Ni(II) ions has enabled the use of 1 as a linking ligand in the preparation of (PdCl2/1) n , (Ni(NO3)2/1) n films, PdCl2/1 and Ni(NO3)2/1 complex. The resulting films and complexes were characterized by UV–vis spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectrometer. The application of films and complexes as catalysts for Suzuki–Miyaura and Mizoroki–Heck reactions was carried out. (PdCl2/1) n films show high catalytic activity in the reactions with the Pd loading of ppm. (Ni(NO3)2/1) n multilayers as the active catalytic moieties for these reactions were investigated with very low Ni(II)-loading. The (Pd or Ni/1) n multilayer films were used as high active catalysts for the C-C formation with extremely low M(II)-loading in ppm level.

Chelating Energetic Material Nickel Semicarbazide 2,4,6‐Trinitroresorcinol: Synthesis, Structure, and Thermal Behavior

AbstractThrough a one‐pot reaction of NiCO3·2Ni(OH)2·H2O, aminourea hydrochloride (SCZ·HCl) and 2,4,6‐trinitroresorcinol (TNR), a halogen‐free and lead‐free chelating energetic material (CEM) [Ni(SCZ)3]TNR was synthesized. We confirmed the structure of [Ni(SCZ)3]TNR by infrared spectroscopy, X‐ray diffraction, and elemental analysis. The complex is triclinic with P$\bar{1}$(2)/n space group. Cell parameters are: a = 1.04008(17) nm, b = 1.3719(2) nm, c = 1.4897(2) nm, V = 2.0337(6) nm3, Z = 4. The central nickel atom is six‐coordinate with three oxygen atoms of carbonyl groups and three terminal nitrogen atoms of the hydrazine groups from three SCZs to form a distorted octahedron. Differential scanning calorimetry and analysis applied to assess the thermal decomposition behavior. The DSC curve with a linear heating rate of 10 °C·min–1 shows that [Ni(SCZ)3]TNR is thermally stable with one exothermic peak temperatures of 78.8 °C and two exothermic peak temperatures of 216.8 °C and 308.1 °C. The kinetic parameters were obtained by non‐isothermal reaction kinetics. The equation can be expressed as lnk = 24.49–243.3 × 103/RT. Moreover, the values of the critical temperature of thermal explosion, ΔS≠, ΔH≠, ΔG≠, and the enthalpies of formation were obtained as 206.5 °C, –145.543 J·mol–1·K–1, 237.18 kJ·mol–1, 305.84 kJ·mol–1, and –2.65 MJ·kg–1, respectively.

Insights on the UV/Vis, Fluorescence, and Cyclic Voltammetry Properties and the Molecular Structures of ZnII Tetraphenylporphyrin Complexes with Pseudohalide Axial Azido, Cyanato‐N, Thiocyanato‐N, and Cyanido Ligands

AbstractThe syntheses, spectroscopic and photophysical properties, and molecular structures of azido‐ (1), cyanato‐N‐ (2), thiocyanato‐N‐ (3), and cyanido‐ (4) (meso‐tetraphenylporphyrinato)zinc(II) complexes are reported. These species were prepared by using cryptand‐222 to solubilize the pseudohalide salts in organic solvents. The UV/Vis spectra of these zinc metalloporphyrins are solvent‐dependent and exhibit large redshifted Soret bands compared with those of the [Zn(Porph)L] derivatives in which Porph is a meso‐porphyrinato ligand and L is a monodentate neutral axial ligand. The room‐temperature fluorescence spectra of the zinc complexes 1–4 indicate that the Q bands are not very affected by the nature of the axial ligands, and their positions are very close to those of previously reported (meso‐porphyrinato)zinc complexes. The quantum yields of the S1 → So fluorescence of 1–4 range between 2.8 and 5.5 %, and their fluorescence lifetimes are the same (1.7 ns). Cyclic voltammetry investigations on 1–4 show that the characteristic potentials for the reduction and the two first oxidations of the porphyrin ring are not very affected by the nature of the axial ligand. A third irreversible oxidation of the porphyrin ring is observed. Additional anodic irreversible waves are observed for the thiocyanato‐N (3) and cyanido (4) species. The solid‐state molecular structures of 1–4 are the first examples of zinc porphyrin complexes with anionic ligands. The average equatorial zinc–pyrrole N atom (Zn–Np) distances for 1–4 range between 2.083(1) and 2.117(2) Å and are much longer than those of the related pentacoordinate zinc porphyrin complexes with monodentate neutral ligands. As a consequence, the displacement of the Zn2+ cation from the mean 24‐atom plan of the porphyrin core is significant (ca. 0.5 Å), and the porphyrin core is very distorted. The crystal structures of 1–4 are stabilized by weak intermolecular π interactions, C–H···Cg (Cg are the centroids of some six‐membered phenyl rings and five‐membered pyrrole rings). The molecular structure of 1 is further stabilized by weak intermolecular C–H···N hydrogen bonds between one carbon atom of cryptand‐222 and the terminal nitrogen atom of the azido ligand.

Indolo[3,2-c]quinoline G-quadruplex stabilizers: a structural analysis of binding to the human telomeric G-quadruplex.

A library of 5-methylindolo[3,2-c]quinolones (IQc) with various substitution patterns of alkyldiamine side chains were evaluated for G-quadruplex (G4) binding mode and efficiency. Fluorescence resonance energy transfer melting assays showed that IQcs with a positive charge in the heteroaromatic nucleus and two weakly basic side chains are potent and selective human telomeric (HT) and gene promoter G4 stabilizers. Spectroscopic studies with HT G4 as a model showed that an IQc stabilizing complex involves the binding of two IQc molecules (2,9-bis{[3-(diethylamino)propyl]amino}-5-methyl-11H-indolo[3,2-c]quinolin-5-ium chloride, 3 d) per G4 unit, in two non-independent but equivalent binding sites. Molecular dynamics studies suggest that end-stacking of 3 d induces a conformational rearrangement in the G4 structure, driving the binding of a second 3 d ligand to a G4 groove. Modeling studies also suggest that 3 d, with two three-carbon side chains, has the appropriate geometry to participate in direct or water-mediated hydrogen bonding to the phosphate backbone and/or G4 loops, assisted by the terminal nitrogen atoms of the side chains. Additionally, antiproliferative studies showed that IQc compounds 2 d (2-{[3-(diethylamino)propyl]amino}-5-methyl-11H-indolo[3,2-c]quinolin-5-ium chloride) and 3 d are 7- to 12-fold more selective for human malignant cell lines than for nonmalignant fibroblasts.

Theoretical Studies on the Mechanism of the Azido-Tetrazole of Azido-s-triazine

The B3LYP/aug-cc-pvDZ level of theory has been applied to the study of the molecular structures, electronic structures and the azido-tetrazole isomerization of 1-azido-s-triazine, 1,3-diazido-s-triazine and 1,3,5-triazido-s-triazine. NBO analysis was applied to investigate the atomic natural charge and stabilization interaction energies among molecules. The results showed that the reaction initially proceeds through the loss of the linearity of the azido group and the approaching of the terminal nitrogen atom of the azide group to the nitrogen atom of the ring. This is followed by an attack of the lone pairs on N atoms in the ring to the azido group, leading to the formation of the N-N bonds. Many factors, including bending of the bond angle, electrostatic attraction, orbital delocalization and the stabilization interaction give rise to a large free energy barrier for the cyclization process. The results also show that the second and third cyclization is relatively easier than the first one.

Nano structure zinc (II) Schiff base complexes of a N3-tridentate ligand as new biological active agents: Spectral, thermal behaviors and crystal structure of zinc azide complex

In this work, synthesis of some new five coordinated zinc halide/pseudo-halide complexes of a N3-tridentate ligand is presented. All complexes were subjected to spectroscopic and physical methods such as FT-IR, UV–visible, 1H and 13C NMR spectra, thermal analyses and conductivity measurements for identification. Based on spectral data, the general formula of ZnLX2 (X=Cl−, Br−, I−, SCN− and N3−) was proposed for the zinc complexes. Zinc complexes have been also prepared in nano-structure sizes under ultrasonic irradiation. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for confirmation of nano-structure character for the complexes. Among the complexes, zinc azide complex structure was analyzed by X-ray crystallography. This complex crystallizes as a triplet in trigonal system with space group of P31. The coordination sphere around the zinc center is well shown as a distorted trigonal bipyramidal with three nitrogen atoms from Schiff base ligand and two terminal azide nitrogen atoms attached to zinc ion. Various intermolecular interactions such as NH⋯N, CH⋯N and CH⋯π hydrogen bonding interactions stabilize crystalline lattice so that they causes a three dimensional supramolecular structure for the complex. In vitro screening of the compounds for their antimicrobial activities showed that ZnLI2, ZnL(N3)2, ZnLCl2 and ZnL(NCS)2 were found as the most effective compound against bacteria of Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli respectively. Also ZnLI2 and ZnLCl2 complexes were found more effective against two selected fungi than others. Finally, thermal behaviors of the zinc complexes showed that they are decomposed via 2–4 thermal steps from room temperature up to 1000°C.

Eco‐friendly Trifoliate Stable Energetic Zinc Nitrate Co­ordination Compounds: Synthesis, Structures, Thermal and Explosive Properties

AbstractThree trifoliate environmental friendly coordination compounds, [Zn(SCZ)3](NO3)2 (1) (SCZ = semicarbazide), [Zn(CHZ)3](NO3)2 (2) (CHZ = carbohydrazide), and [Zn(MCZ)3](NO3)2·H2O (3) (MCZ = methyl carbazate), were synthesized by the reaction of zinc nitrate with its corresponding ligands. The products were characterized by elemental analysis and FT‐IR spectroscopy. Furthermore, compound 1 and 2 were characterized by X‐ray single crystal diffraction. The crystal structures of both 1 and 2 belong to the monoclinic P21/c space group. Remarkably, in all the three compounds, the central zinc cations are six‐coordinated with three oxygen atoms of carbonyl groups and three terminal nitrogen atoms of the hydrazine groups from three SCZ / CHZ / MCZ molecules, which can form three five‐member (Zn–O–C–N–N) rings and exhibit a distorted octahedron. Thermal stabilities of 1 to 3 were studied by differential scanning calorimetry (DSC) and showed that they are all thermostable. The non‐isothermal kinetics parameters were calculated by the Kissinger's method and Ozawa's method, respectively. The energies of combustion, enthalpies of formation, critical temperature of thermal explosion, entropies of activation (ΔS≠), enthalpies of activation (ΔH≠), and free energies of activation (ΔG≠) were measured and calculated. Sensitivity tests revealed that 1–3 are insensitive to mechanical stimuli. The studies of all these three zinc compounds showed that they have potential applications as heat‐stable insensitive energetic materials, especially the semicarbazide coordination compound 1, which has higher crystal density.

Exploring the Effects of Axial Pseudohalide Ligands on the Photophysical and Cyclic Voltammetry Properties and Molecular Structures of MgII Tetraphenyl/porphyrin Complexes

AbstractThe (meso‐tetraphenylporphyrinato)magnesium(II) complexes with azido (1), cyanato‐N (2), and thiocyanato‐N (3) ligands were prepared by using 2.2.2‐cryptand to solubilize the azide, cyanato, and thiocyanato salts in dichloromethane solvent. These species were characterized by UV/Vis and IR spectroscopy, mass spectrometry, and electrochemistry. The first reduction potential and the two first oxidation potentials of the porphyrin rings of these species are not affected by the nature of the axial ligand, and an unusual third irreversible oxidation of the porphyrin ring is observed. The anodic behavior of the magnesium azide derivative is complicated by the appearance of additional signals for ligand‐centered electron transfers that originate from the release of the azido ligand of 1. The room‐temperature fluorescence spectra of the magnesium complexes 1–3 indicate that the Soret and Q bands are not particularly affected by the nature of the axial ligands. The quantum yields of the S1→S0 fluorescence are between 0.10 and 0.19, and the fluorescence lifetimes range between 3.7 and 6.1 ns at room temperature. Complexes 1–3 crystallize in the monoclinic crystal system in the same space group, P21/n. The molecular structure of 1 is the first example of a magnesium azide complex. The average equatorial magnesium–Npyrrole bond lengths (Mg–Np) are higher than those of the related pentacoordinate magnesium porphyrin species and decreases from 1 [2.1187(16) Å] to 2 [2.1108(15) Å] to 3 [2.0962(13) Å]; the distance between the magnesium center and the 24‐atom mean plane of the porphyrin ring (Mg–PC) also decreases from 1 to 2 to 3 with values of 0.6629(7), 0.6598(7), and 0.5797(6) Å, respectively. Complex 1 shows major doming and saddle distortions, whereas 2–3 exhibit relatively high ruffling and moderate doming deformations. The molecular structure of 1 is stabilized by weak intermolecular C–H···N hydrogen bonds between one carbon atom of the phenyl ring and the terminal nitrogen atom of the azido ligand, and the lattice of 2 exhibits weak intermolecular C–H···O H bonds between one carbon atom of the phenyl ring and the terminal oxygen atom of the NCO– ligand. The crystal structure of 3 is mainly sustained by weak intermolecular C–H···Cg π interactions between a carbon atom of 2.2.2‐cryptand and the centroid of one pyrrole ring.

Synthesis and structure of new copper(II) coordination compounds with 8-quinoline aldehyde semicarbazones and thiosemicarbazones

Copper(II) salts were reacted with various quinoline aldehyde chalcogensemicarbazones to yield compounds formulated as Cu(HL)X2 · nH2O (I: HL = quinoline aldehyde thiosemicarbazone (HL1), X = ClO4, n = 2; II: HL = quinoline aldehyde 4-C2H5-thiosemicarbazone (HL1a), X = NO3, n = 0; III: HL = quinoline aldehyde semicarbazone (HL2), X = ClO4, n = 3 and IV: HL = quinoline aldehyde 4-Ph-semicarbazone (HL2a), X = NO3, n = 1). Regardless of the reagent ratio, the products were compounds having the metal: ligand ratio of 1: 1, where the organic ligand was coordinated tridentate in a molecular form. Single-crystal X-ray diffraction showed that, depending on the chalcogen atom in the organic ligand (S or O), the substituent in the 4th position (at the terminal nitrogen atom), and the specifics of the acido ligand, complexes I–IV had appreciably differing molecular structure organizations. The structures of I and III are formed by a 1D charged coordination polymer, ClO4− anions, and water molecules and may be described by the formula [Cu(HL)(H2O)(ClO4)]n(ClO4)n · nH2O. Copper(II) coordination polyhedra in I and II are (4 + 2) and (4 + 1 + 1) tetragonal bipyramids, respectively. In II and IV, the structures are monomeric and can be described as [Cu(HL1a)(NO3)2] with the metal coordination polyhedron shaped as a (4 + 1) tetragonal pyramid in II and as [Cu(HL2a)(H2O)(NO3)](NO3) with the metal coordination polyhedron shaped as a (3 + 2) trigonal bipyramid in IV. The structure of II is built of molecular complexes, each comprising, apart from ligand HL1a, two monodentate coordinated NO3− groups. The oxygen atom of one anion together with the NNS donor atom set of ligand HL1a form the base, and the oxygen atom of the other anion is in the apex of the coordination polyhedron. In IV, the structure is ionic and built of NO3− anions and [Cu(HL2a)(H2O)(NO3)]+ complex cations, where a cationic coordination polyhedron has a trigonal-bipyramidal configuration with organic ligand HL2a positioned along the long edge. The bipyramidal base is made up by the oxygen atoms of the coordinated water molecule and monodentate nitrato group and the nitrogen atom N2 of the azomethyne group.

Syntheses and characterization of palladium(II) complexes with a bidentate bis-NHC ligand having methyl and aryl substituents on terminal nitrogen atoms

An imidazolium salt, N-chloromethyl-N′-methylimidazolium bromide was prepared as an intermediate for the syntheses of unsymmetrical bidentate bis-NHC ligands bearing methyl and aryl substituents on the terminal nitrogen atoms. Three bis-NHC ligand precursors and their corresponding palladium(II) complexes were also prepared. 1H NMR spectra of the imidazolium salts of the bidentate ligands implied that the carbene on a methyl-substituted imidazolylidene ring is a stronger donor than one on an aryl-substituted ring. The crystal structures of the palladium(II) complexes showed a distorted square-planar structure. The complexes demonstrated good catalytic performance in the Heck reaction.

Antitumoral, Antihypertensive, Antimicrobial, and Antioxidant Effects of an Octanuclear Copper(II)-Telmisartan Complex with an Hydrophobic Nanometer Hole

A new Cu(II) complex with the antihypertensive drug telmisartan, [Cu8Tlm16]·24H2O (CuTlm), was synthesized and characterized by elemental analysis and electronic, FTIR, Raman and electron paramagnetic resonance spectroscopy. The crystal structure (at 120 K) was solved by X-ray diffraction methods. The octanuclear complex is a hydrate of but otherwise isostructural to the previously reported [Cu8Tlm16] complex. [Cu8Tlm16]·24H2O crystallizes in the tetragonal P4/ncc space group with a = b = 47.335(1), c = 30.894(3) Å, Z = 4 molecules per unit cell giving a macrocyclic ring with a double helical structure. The Cu(II) ions are in a distorted bipyramidal environment with a somewhat twisted square basis, cis-coordinated at their core N2O2 basis to two carboxylate oxygen and two terminal benzimidazole nitrogen atoms. Cu8Tlm16 has a toroidal-like shape with a hydrophobic nanometer hole, and their crystal packing defines nanochannels that extend along the crystal c-axis. Several biological activities of the complex and the parent ligand were examined in vitro. The antioxidant measurements indicate that the complex behaves as a superoxide dismutase mimic with improved superoxide scavenger power as compared with native sartan. The capacity of telmisartan and its copper complex to expand human mesangial cells (previously contracted by angiotensin II treatment) is similar to each other. The antihypertensive effect of the compounds is attributed to the strongest binding affinity to angiotensin II type 1 receptor and not to the antioxidant effects. The cytotoxic activity of the complex and that of its components was determined against lung cancer cell line A549 and three prostate cancer cell lines (LNCaP, PC-3, and DU 145). The complex displays some inhibitory effect on the A549 line and a high viability decrease on the LNCaP (androgen-sensitive) line. From flow cytometric analysis, an apoptotic mechanism was established for the latter cell line. Telmisartan and CuTlm show antibacterial and antifungal activities in various strains, and CuTlm displays improved activity against the Staphylococcus aureus strain as compared with unbounded copper(II).

Mechanistic studies on the diazo transfer reaction

The mechanism of the diazo transfer reaction which converts amines to azides has been studied with labeled amino acids and labeled imidazole-1-sulfonyl azides. Retention of amine nitrogen in the amine, and transfer of the two terminal nitrogen atoms of the imidazole-1-sulfonyl azide to the product, were unambiguously established.

Crystal structures of 5-Bromo-2-hydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, and 2-hydroxynaphthalene-1-carbaldehyde 4-(2-pyridyl) thiosemicarbazones

5-Bromo-2-hydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, and 2-hydroxynaphthalene-1-carbaldehyde 4-(2-pyridyl) thiosemicarbazones (I–III, respectively) were synthesized and their crystal structures were determined by X-ray diffraction. All these molecules are almost planar. The presence of bulky substituents at the terminal nitrogen atoms of these molecules does not lead to changes in the conformation of the thiosemicarbazide moiety. Depending on the nature of substituents in the phenol rings, the crystals are composed of either centrosymmetric dimers (I) or infinite chains (II and III). In the concentration range of 10−5–10−7 mol/L, thiosemicarbazones I–III selectively inhibit the growth of human myeloid leukemia HL60 cells.

A computational study of the non-covalent bindings in complexes pairing sulfur tetroxide (SO4(C2V)) with the nitrous oxide (NNO)

The computational investigations are carried out on heterodimers containing sulfur tetroxide (SO4(C2V)) with the nitrous oxide (NNO) through MP2/cc–pVDZ and MP2/aug–cc–pVTZ//MP2/cc–pVDZ levels. Eight heterodimers are located on the potential energy surface of SO4(C2V)–NNO system. Binding energies of heterodimers in the SO4(C2V)–NNO system corrected with BSSE and ZPE are in the range of 1.17–7.90 kJ/mol. The calculated results reveal that the individual interaction of NNO terminal nitrogen atom with one of oxygen atoms of OSO ring in the SO4(C2V) monomer leads to the formation of the more stable heterodimer of SO4(C2V)–NNO system. The atoms in molecules theory were applied to analyze the nature of intermolecular interactions.

Alkali metal salts of formazanate ligands: diverse coordination modes as a result of the nitrogen-rich [NNCNN] ligand backbone.

Alkali metal salts of redox-active formazanate ligands were prepared, and their structures in the solid-state and in solution are determined. The nitrogen-rich [NNCNN] backbone of formazanates results in a varied coordination chemistry, with both the internal and terminal nitrogen atoms available for bonding with the alkali metal. The potassium salt K[PhNNC(p-tol)NNPh]·2THF (1-K) is dimeric in the solid state and even in THF solution, as a result of the K atom bridging via interaction with a terminal N atom and the aromatic ring of a second unit. Conversely, for the compounds Na[MesNNC(CN)NNMes]·2THF (2-Na) and Na[PhNNC((t)Bu)NNPh] (3-Na) polymeric and hexameric structures are found in the solid state respectively. The preference for binding the alkali metal through internal N atoms (1-K and 2-Na) to give a 4-membered chelate, or via internal/external N atoms (5-membered chelate in 3-Na), contrasts with the 6-membered chelate mode observed in our recently reported formazanate zinc complexes.

ChemInform Abstract: Bicyclization of Diazomethanes: A Synthetic Strategy for Fused Pyrazoles.

On the terminal diazo nitrogen atom, two CN bonds are formed in the bicyclization reaction of the readily available acyclic substrates with diazomethanes as 1,3-dipoles. The tandem 1,3-dipolar cycloaddition/intramolecular aza-addition/oxidative aromatization reaction can tolerate a variety of functional groups and proceeds under mild metal-free conditions to give substituted analogues of withasomnine alkaloids in good to high yields in a single step.

Versatile Reactivity of Scorpionate‐Anchored YttriumDialkyl Complexes towards Unsaturated Substrates

A series of unusual chemical-bond transformations were observed in the reactions of high active yttrium-dialkyl complexes with unsaturated small molecules. The reaction of scorpionate-anchored yttrium-dibenzyl complex [Tp(Me2)Y(CH2Ph)2(thf)] (1, Tp(Me2)=tri(3,5-dimethylpyrazolyl)borate) with phenyl isothiocyanate led to C=S bond cleavage to give a cubane-type yttrium-sulfur cluster, {Tp(Me2)Y(μ3-S)}4 (2), accompanied by the elimination of PhN-C(CH2Ph)2. However, compound 1 reacted with phenyl isocyanate to afford a C(sp(3)) H activation product, [Tp(Me2)Y(thf){μ-η(1):η(3)-OC(CHPh)NPh}{μ-η(3):η(2)-OC(CHPh)NPh}YTp(Me2)] (3). Moreover, compound 1 reacted with phenylacetonitrile at room temperature to produce γ-deprotonation product [(Tp(Me2))2Y](+)[Tp(Me2)Y(N=C=CHPh)3](-) (6), in which the newly formed N=C=CHPh ligands bound to the metal through the terminal nitrogen atoms. When this reaction was carried out in toluene at 120 °C, it gave a tandem γ-deprotonation/insertion/partial-Tp(Me2)-degradation product, [(Tp(Me2)Y)2(μ-Pz)2{μ-η(1):η(3)-NC(CH2Ph)CHPh}] (7, Pz=3,5-dimethylpyrazolyl).