Low-magnesium, <Emphasis Type="Italic">trans</Emphasis>-cleavage activity by type III,tertiary stabilized hammerhead ribozymes with stem 1 discontinuities

Background  

Low concentrations of free magnesium in the intracellular environment can present critical limitations for hammerhead ribozymes, especially for those that are designed for intermolecular (trans) cleavage of a host or pathogen RNA. Tertiary stabilizing motifs (TSM's) from natural and artificial ribozymes with a "type I" topology have been exploited to stabilize trans-cleaving hammerheads. Ribozymes with "type II" or "type III" topologies might seem incompatible with conversion to trans-cleavage designs, because opening the loop at the end of stem 1 or stem 2 to accommodate substrate binding is expected to disrupt the TSM and eliminate tertiary stabilization.     

Chemistry of chromium bis-acetylide complexes

Abstract  

Stable paramagnetic Cr(II) and Cr(III) bis(alkynyl) complexes of the type [trans(RC≡C)₂Cr(dmpe)₂] ⁿ⁺ (R = Ph, SiMe₃, SiEt₃, C≡C–SiMe₃ n = 0, 1) were prepared and characterised by NMR, cyclic voltammetry, EPR, magnetic measurements, and X-ray single-crystal diffraction studies.     

Synthesis, characterization, and crystal structure of two zinc(II) halide complexes with the symmetrical bidentate Schiff-base ligand (3,4-MeO-ba)2en

Abstract  

In this study two zinc(II) halide complexes with the Schiff-base ligand (3,4-MeO-ba)₂en [N,N′-bis(3,4-dimethoxybenzylidene)ethane-1,2-diamine] have been synthesized and characterized by elemental analyses (CHN), single-crystal X-ray diffraction, Fourier-transform infrared (FT-IR), and ¹H nuclear magnetic resonance (NMR) spectroscopy. The metal-to-ligand ratio was found to be 1:1 within the formula ZnX₂((3,4-MeO-ba)₂en) (X = Br, I). Crystal structure analysis reveals that the coordination geometry around the zinc(II) ions in the two isotypic complexes is distorted tetrahedral. The Schiff-base ligand (3,4-MeO-ba)₂en acts as a chelating ligand and coordinates via two N atoms to the metal center and adopts an (E,E) conformation. The coordination spheres of the metal atoms are completed by the two halide atoms, which are also involved in weak non-classical hydrogen-bonding interactions of the type C–H···X–Zn.     

Expression and localization of estrogenic type 12 17β-hydroxysteroid dehydrogenase in the cynomolgus monkey

Background  

We have recently discovered that human type 12 17β-HSD (h17β-HSD12), a homolog of type 3 17β-HSD, is a new estrogen-specific 17β-hydroxysteroid dehydrogenase involved in the production of estradiol (E2). To further characterize this estradiol-producing enzyme, we have isolated the corresponding cDNA in the cynomolgus monkey (Macaca fascicularis), characterized its enzymatic activities and performed cellular localization using in situ hybridization.     

Synthesis,characterization, and biological activity of some transition metal complexes with Schiff base ligands derived from 4-amino-5-phenyl-4<Emphasis Type="Italic">H</Emphasis>-1,2,4-triazole-3-thiol and salicaldehyde

Abstract  

The coordination behaviour of a Schiff base with SNO donation sites, derived from condensation of 4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol and salicaldehyde, towards some bi- and trivalent metal ions, namely Cr(III), Mn(II), Fe(III), Co(II) (Cl, ClO₄), Ni(II) (Cl, ClO₄), Cu(II), and Zn(II), is reported. The metal complexes were characterized on the basis of elemental analysis, IR, ¹H NMR, solid reflectance, magnetic moment, molar conductance, and thermal analyses (TG, DTG, and DTA). The ionization constant of the Schiff base under investigation and the stability constants of its metal chelates were calculated pH-metrically at 25 °C and ionic strength μ = 0.1 M in 50% (v/v) ethanol–water mixture. The chelates were found to have octahedral (Mn(II)), trigonal bipyramidal (Co(II), Ni(II), Zn(II)), and tetrahedral (Cr(III), Fe(III), and Cu(II)) structures. The ligand and its binary chelates were subjected to thermal analyses and the different thermodynamic activation parameters were calculated from their corresponding DTG curves to throw more light on the nature of changes accompanying the thermal decomposition process of these compounds. The free Schiff base ligand and its metal complexes were tested in vitro against Aspergillus flavus, Candida albicans, C. tropicalis, and A. niger fungi and Bacillus subtilis and Escherichia coli bacteria in order to assess their antimicrobial potential. The results indicate that the ligand and its metal complexes possess antimicrobial properties.     

Spectral, magnetic, thermal, antimicrobial, and eukaryotic DNA studies on acetone [N-(3-hydroxy-2-naphthoyl)]hydrazone complexes

Abstract  

Acetone [N-(3-hydroxy-2-naphthoyl)] hydrazone (H₂AHNH) has been prepared and its structure confirmed by elemental analysis and ¹H NMR spectroscopy. It has been used to produce diverse complexes with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and U(VI)O₂ ions. The complexes obtained have been investigated by thermal analysis, spectral studies (¹H NMR, IR, UV–visible, ESR), and magnetic measurements. IR spectra suggest that H₂AHNH acts as a bidentate ligand. The electronic spectra of the complexes and their magnetic moments provide information about geometries. The ESR spectra give evidence for the proposed structure and the bonding for some Cu(II) complexes. Thermal decomposition of the Ni(II) and Cu(II) complexes afforded metal oxides as final products. Kinetic data were obtained for each stage of thermal degradation of some of the complexes using the Coats–Redfern method. The formation of complexes in solution was studied pH-metrically and the order of their stability constants (log K) was found to be U(VI)O₂ > Cu(II) > Zn(II) > Ni(II) > Cd(II) > Co(II). Antimicrobial and eukaryotic DNA studies were carried out.     

Studies on the synthesis, characterization, binding with DNA and activities of two cis-planaramineplatinum(II) complexes of the form: cis-PtL(NH3)Cl2 where L = 3-hydroxypyridine and 2,3-diaminopyridine

Background  

Cis-planaramineplatinum(II) complexes like their trans isomers are often found to be active against cancer cell lines. The present study deals with the synthesis, characterization and determination of activity of new cis-planaramineplatinum(II) complexes.     

The effect of NDGA-modified etchant on the enzymatic degradation resistance and mechanical properties of collagen matrix

Bio-modified etchant can significantly improve the biostability of demineralized dentin collagen matrix, which validates the concept of etch-andcrosslink in dentin bonding.     

A new aspect of Heck catalyst formation

Abstract  

The mechanism of the formation of the active Pd(0) complex from trans-dichlorobis(diethanolamine-N)palladium(II) complex in the presence of strong base was investigated by using density functional theory (M06 method). Our investigation shows that in the basic environment trans-dichlorobis(diethanolamine-N)palladium(II) complex undergoes abstraction of the alcoholic proton, and coordination of alkoxide oxygen to palladium. The intermediate complex, in which hydrogen is coordinated to Pd, undergoes reductive elimination of HCl, yielding the catalytically active low ligated Pd(0) complex.     

The possible production of natural flavours by amino acid degradation

Abstract  

This work describes the degradation of phenylalanine and tryptophane catalysed by their complexes with Fe(II), Co(II), and Cu(II). The influences of the central atom and of the reaction conditions on the degradation of the amino acids were observed. The necessary condition of the degradation is the possibility of a redox reaction on the central atom between M(II) and M(III). Moreover, the coordination sphere of the central cation of the transition metal must not be sterically shielded. The necessary conditions are fulfilled only in the Fe(II) complexes. The degradation is strictly anaerobic because due to the influence of oxygen, an irreversible oxidation of Fe(II) to Fe(III) proceeds. This reaction results in 5-hydroxy-1H-indol instead of the mixture of the degradation products, such as benzaldehyde, phenylacetaldehyde, and phenylacetic acid. The influence of the temperature on the catabolism is very important because the reaction accelerates with temperature increase. The phenylalanine anion acts as a reducing agent, and Fe(II) is spontaneously reduced to Fe(0).     

Density functional study of substituted (–SH, –S, –OH, –Cl) hydrated ions of Hg<Superscript>2+</Superscript>

Abstract  

The electronic structure of Hg(II) ions, [Hg(L) _n (H₂O) _m ] ^q (L = HO⁻, Cl⁻, HS⁻, S²⁻) has been studied. Geometries were fully optimized. The B3LYP and PBE functionals give structures in good agreement with available experimental data. Calculated stretching frequencies generally correlate well with bond lengths. The role of the water molecule(s) in the solvated Hg(II) complexes has been investigated. The solvent can act as nucleophile, as hydrogen bond acceptor or as a spectator. The trans-effect results in lengthening of the Hg–L bond length. It can be understood as a competition between ligands in trans positions for the ability to donate their electron density to the 6s AO of Hg(II). The effect of the presence of water molecules on the Hg–L bond length depends on whether or not the water molecules form a direct coordination bond with Hg(II); it will not guarantee an increase in the stability of the complexes. The interaction energy, which represents the interaction between Hg(II) and ligand L and excludes all other interactions, is nucleophilicity-dependent. The interaction energy and the strength of the ligand nucleophilicity follow the order: S²⁻ > HS⁻ > HO⁻ > Cl⁻ > H₂O. The charge transfer, ΔN, is an indication for the type and strength of the interaction between ligand and Hg(II). Increasing the positive and negative value of ΔN will decrease and increase the Hg(II) total NBO charge, respectively, while decreasing the electrophilicity of Hg(II) will decrease its charge and the charge transfer, ΔN.     

The role of the Zn(II) binding domain in the mechanism of E. coli DNA topoisomerase I

Background  

Escherichia coli DNA topoisomerase I binds three Zn(II) with three tetracysteine motifs which, together with the 14 kDa C-terminal region, form a 30 kDa DNA binding domain (ZD domain). The 67 kDa N-terminal domain (Top67) has the active site tyrosine for DNA cleavage but cannot relax negatively supercoiled DNA. We analyzed the role of the ZD domain in the enzyme mechanism.     

DFT study on the preactivation reaction of a palladium catalyst precursor in phosphine-free Heck reactions

Abstract  

The mechanism of the preactivation process of trans-dichlorobis(diethanolamine-N)palladium(II) complex is investigated using density functional theory. The role of diethanolamine (a solvent for the reaction in the absence of a strong base) and acetonitrile (solvent for the reaction in the presence of a strong base) is analyzed by using a discrete model. The Onsager model is applied to assess the effect of the bulk medium. Both models show that diethanolamine activates the complex and thus is a better suited solvent for the Heck reactions of the investigated complex.     

Dissolving the insoluble: CdF<Subscript>2</Subscript> and moist ammonia form cadmium(II) difluoride monohydrate—synthesis and crystal structure of [Cd(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>]F<Subscript>2</Subscript>·H<Subscript>2</Subscript>O

Abstract  

Hexaamminecadmium(II) fluoride monohydrate (1:1) [Cd(NH₃)₆]F₂·H₂O was synthesized from CdF₂ and liquid ammonia in open reaction vessels, so that moisture from the air was in contact with the solvent. The compound crystallizes in the chiral space group P3₁21- (No. 152) in the form of needle-shaped, colorless crystals with a = 6.8974(1) ?, c = 17.7156(5) ?, V = 729.89(3) ?³, and Z = 3.     

Room-temperature spin-transition iron compounds

Abstract  

Since the discovery of the spin transition phenomenon in tris(N,N-dialkyldithiocarbamato) iron(III) complexes [1], numerous investigations have been devoted to this field of molecular magnetism. The spin transition phenomenon is probably the most spectacular example of bistability in molecular chemistry. However, it is a challenge to obtain spin transition materials when working under ambient conditions (e.g. room temperature and pressure), which would be highly advantageous for potential applications. So far, only some Fe(II) and Fe(III) molecular systems have shown temperature-induced spin transitions around and even above room temperature. Within this review we discuss the characteristics of this class of bistable compounds in detail and we try to draw more general conclusions regarding the integration, implementation and application of spin transition compounds as switching elements in hybrid molecular devices.     

Analysis of DNA relaxation and cleavage activities of recombinant Mycobacterium tuberculosis DNA topoisomerase I from a new expression and purification protocol

Background  

Mycobacterium tuberculosis DNA topoisomerase I is an attractive target for discovery of novel TB drugs that act by enhancing the accumulation of the topoisomerase-DNA cleavage product. It shares a common transesterification domain with other type IA DNA topoisomerases. There is, however, no homology between the C-terminal DNA binding domains of Escherichia coli and M. tuberculosis DNA topoisomerase I proteins.     

Ruthenium complexes of 4,4′-bi-1,2,3-thiadiazole and azoimine ligands: syntheses,crystallography, and electrochemical studies

Abstract  

Five ruthenium complexes of the general type trans-[Ru^II(btd)(Azo)Cl₂] ({Azo = PhN=NC(COMe) = NC₆HY, where Y = H (a), Me (b), OMe (c), Cl (d) or Br (e)} and btd = 4,4′-bi-1,2,3-thiadiazole) have been prepared by the reaction of RuCl₃ with the ligands in the presence of LiCl. These complexes have been characterized by spectroscopic (IR, UV–Vis, and NMR) and electrochemical techniques. In addition, the complex trans-[Ru^II(btd)(L5)Cl₂] (complex 5) has been characterized by X-ray diffraction analysis. The electrochemical parameter for the π-excessive ligand (btd) is reported. The absorption spectrum of complex 5 in acetonitrile has been modeled by time-dependent density functional theory.     

Synthesis, structure elucidation, DNA interaction, biological evaluation, and molecular docking of an isatin-derived tyramine bidentate Schiff base and its metal complexes

Abstract  

Three new transition metal complexes [CuL₂Cl₂], [NiL₂Cl₂], and [ZnL₂Cl₂], where L = Schiff base derived from isatin (1H-indole-2,3-dione) and tyramine (4-(2-aminoethyl)phenol), have been synthesized and characterized spectroscopically. The binding properties of these complexes with calf thymus DNA have been investigated by use of electronic absorption spectroscopy, viscosity measurement, cyclic voltammetry, and molecular docking analysis. Moreover, these complexes have been found to promote the cleavage of pUC19 DNA from the supercoiled form I to the open circular form II in the presence of hydrogen peroxide. The newly synthesized compounds were screened for antibacterial activity and subjected to molecular docking studies for inhibition of the enzyme Staphylococcus aureus sortase-A, which is a novel target for antibacterials.     

Immobilized metalloporphyrins on 3-aminopropyl-functionalized silica support as heterogeneous catalysts for selective oxidation of primary and secondary alcohols

Abstract  

Iron(III), manganese(III), and cobalt(II) complexes of meso-tetrakis(p-chlorophenyl)porphyrin (Fe(TClPP)X, Mn(TClPP)X, and Co(TClPP)X, X = Cl or OAc) were immobilized onto 3-aminopropyl-functionalized silica (SF-3-APTS). SF-3-APTS acts as both axial base and support for immobilization of these metalloporphyrins. The obtained heterogeneous catalysts were characterized by Fourier transform infrared (FT-IR), UV–Vis, and inductively coupled plasma (ICP) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and thermogravimetric analysis (TGA) techniques. Their catalytic activity as biomimetic catalysts was investigated for the selective oxidation of primary and secondary benzylic alcohols to the corresponding carbonyl compounds with t-butylhydroperoxide as oxidant. SF-3-APTS–Fe(TClPP)Cl demonstrated higher catalytic activity than SF-3-APTS–Mn(TClPP)Cl and SF-3-APTS–Co(TClPP)OAc. The presence of electron-withdrawing substituents on benzylic alcohols enhances the rate of catalytic oxidation. SF-3-APTS–Fe(TClPP)Cl could be reused at least four times without significant loss of its catalytic activity.     

Synthesis and antiproliferative activity of multisubstituted N-fused heterocycles against the Hep-G2 cancer cell line

Abstract  

Pyrrolo[1,2-a]imidazole and pyrrolo[2,1-b]thiazole derivatives were synthesized in a one-pot procedure by [3 + 2] cycloaddition reactions of the corresponding imidazolium ylides and thiazolium ylides with an alkene followed by oxidative aromatization of the primary cycloadducts under the action of the mild oxidant tetrakispyridinecobalt(II) dichromate. Antiproliferative activity of 14 new bicyclic N-fused heterocycles against the human hepatocellular liver carcinoma (Hep-G2) cell line were examined by the MTT method. Some of the compounds showed favorable antiproliferative activity, especially compound 3i displayed potent antiproliferative activities with an IC₅₀ value of 0.36 μg/cm³.