Synthesis of 2′‐Deoxy‐1′‐homo‐N‐nucleosides with Anti‐Influenza Activity by Catalytic Methyltrioxorhenium (MTO)/H2O2 Oxyfunctionalization

This paper describes a new route for the synthesis of 1′‐homo‐N‐nucleoside derivatives by means of either methyltrioxorhenium (MTO) or supported MTO catalysts, with H₂O₂ as the primary oxidant. Under these selective conditions, the oxyfunctionalization of the heterocyclic ring and the N heteroatom oxidation were operative processes, regardless of the type of substrate used, that is, purine or pyrimidine derivatives. In addition, the oxidation of 1′‐homo‐N‐thionucleosides, showed the occurrence of site‐specific oxidative nucleophilic substitutions of the heterocyclic ring. The MTO/H₂O₂ system showed, in general, high reactivity under both homogeneous and heterogeneous conditions, affording the final products with high conversion values of substrates and from medium to high yields. Many of the novel 1′‐homo‐N‐nucleoside analogues were active against the influenza A virus, without any cytotoxic effects, retaining their activity in both protected and unprotected forms.     

Thermal stability of new biologic active copper(II) complexes with 5,6-dimethylbenzimidazole

Three new coordinative compounds that contain mixed ligands (5,6-dimethylbenzimidazole and acrylato anion) were synthesized and characterized. The features of complexes have been assigned from microanalytical, IR, UV–Vis and EPR spectra as well as thermal analysis. IR data are in accordance with unidentate nature of 5,6-dimethylbenzimidazole while the acrilato ion acts as uni- or bidentate ligand. The electronic spectra display the characteristic pattern of square pyramidal or octahedral stereochemistry, which were confirmed by the EPR spectra. Antibacterial and antifungal activities of the complexes have been determined in vitro, against various Gram-negative and Gram-positive bacteria and fungi. The tested complexes exhibited different spectra of antimicrobial activity and inhibited the microbial ability to colonize the inert surfaces, acting as potential anti-adherence and biofilm-controlling agents. Thermal decomposition evidenced several well-defined steps as dehydration (complex 2), 5,6-dimethylbenzimidazole molecule release (all complexes) and the acrylate decomposition in carbonate (complex 3). The final residue is in all cases copper (II) oxide.     

Thermal, spectral, electrochemical and biologic characterization of new Pd(II) complexes with ligands bearing biguanide moieties

New complexes [Pd(HDMBG)₂]Cl₂·H₂O, [PdL¹]Cl₂·0.5H₂O and [PdL²]Cl₂·1.5H₂O (HDMBG: dimethylbiguanide, L¹ and L²: ligands resulted from HDMBG, ammonia/hydrazine and formaldehyde template condensation) were synthesized and characterized. The features of complexes have been assigned from microanalytical, IR, UV–Vis and cyclic voltammetry data. The thermal transformations are complex processes according to TG and DTA curves including water and hydrochloric acid elimination, thermolysis processes leading to paracyanide formation as well as PdO decomposition, final product being palladium. Complexes were screened for their antimicrobial properties against some pathogenic Gram-positive and Gram-negative bacterial as well as fungal Candida albicans strains. The complexes exhibit specific antibacterial and/or antifungal activity, depending on their structure and the tested microbial strains. All complexes inhibit the microbial biofilm development on the inert substratum. It was also observed that PdCl₂ complexation minimized their cytotoxic effect on the eukaryotic cells.     

Thermal study of new biologic active complexes with mixed ligands

Five new coordinative compounds that contain mixed ligands (4,4′-bipyridine and methacrylate anion) were synthesized and characterized (elemental analysis, IR and UV–Vis spectroscopy, and thermal studies). The complexes are of the type [M(4,4′-bipy)(C₄H₅O₂)₂]·nH₂O ((1) M:Mn, n = 0; (2) Co, n = 0.5; (3) M:Ni, n = 1.5; (4) M:Cu, n = 0.5; (5) M:Zn, n = 0.5; 4,4′-bipy: 4,4′-bipyridine; C₄H₅O₂: methacrylate anion). All the tested complexes exhibited very low MIC values against Escherichia coli strains and one compound against Staphylococcus aureus. Besides the specific antimicrobial spectrum, these compounds also inhibited the microbial ability to colonize the inert surfaces, acting as potential anti-adherence and biofilm-controlling agents. The thermal behavior provided confirmation of the complexes' compositions as well as the number and the nature of water molecules and the intervals of thermal stability.     

Chemistry of HCNH+: mechanisms, structures, and relevance to Titan’s atmosphere

The chemistry of HCNH⁺ in Titan’s atmosphere is not completely understood despite previous experimental and theoretical studies. In response to recent suggestions in the literature, we have searched for specific products of the reactions of HCNH⁺ with H₂, CH₄, C₂H₂, and C₂H₄ using the flowing afterglow-selected ion flow tube technique. We have probed for an association mechanism for reaction with H₂, and associative-H₂ loss for the reactions involving CH₄, C₂H₂, and C₂H₄. In all cases, these reaction mechanisms were found to be inefficient pathways for the depletion of HCNH⁺. Our ab initio computational studies characterize the structures and energies for these mechanisms and indicate that the proposed pathways are endothermic or possess reaction barriers. We compare our studies to previous experimental and computational work, and we suggest other ion-neutral reactions with HCNH⁺ that have not been included in previous models of Titan’s ionosphere.     

Characterization of an assortment of commercially available multiwalled carbon nanotubes

The objective of this study was to characterize an assortment of as received, commercially available, non-functionalized multiwalled carbon nanotubes (MWCNT) samples (n?=?24) using thermogravimetric analysis, energy dispersive X-ray fluorescence spectrometry, high-resolution transmission electron microscopy and scanning electron microscopy. Each sample was assigned to one of six types based on nominal length and diameter. Some of the samples from the product assortment exhibited significant differences in purity and morphology from their nominal values. Variability in the physicochemical properties of MWCNTs may be a significant factor in why many toxicological investigations have findings that are difficult to reproduce. Therefore, it is strongly recommended that investigators studying these materials present characterization information in addition to providing their source.

Mechanisms of Ceftazidime and Ciprofloxacin Transport through Porins in Multidrug-Resistance Developed by Extended-Spectrum Beta-Lactamase <Emphasis Type="Italic">E.coli</Emphasis> Strains

Resistance towards antibiotics stands out today as a major issue in the clinical act of treatment of bacterial-generated infections. This process was characterized in proteoliposomes reconstituted from an E.coli strain isolated from invasive infections (blood culture) occurred in patients with a cardio-vascular device admitted for surgery. Fluorescence spectroscopy and patch-clamp technique have been used. Two types of antibiotics have been targeted: ceftazidime and ciprofloxacin. Antibiotics addition in proteoliposomes suspension undergoes a quenching in tryptophan residues from outer membrane porins structure, probably due to the formation of a transient non-fluorescent porin-antibiotic complex. Patch-clamp recordings revealed strong ion current blockages for both antibiotics, reflecting antibiotic–channel interactions but with varying strength of interaction. The present study puts forward the mechanism of multidrug-resistance in extended-spectrum beta-lactamase E.coli strains, as being caused by alterations of the antibiotics transport across the porins of the outer bacterial membrane.     

Sensing amyloid-β aggregation using luminescent dipyridophenazine ruthenium(II) complexes

The aggregation of amyloid-β (Aβ) peptides has been associated with the onset of Alzheimer's disease. Here, we report the use of a luminescent dipyridophenazine ruthenium(II) complex to monitor Aβ fibrillization. This complex is not photoluminescent in aqueous solution nor in the presence of monomeric Aβ, but it presents a strong photoluminescence in the presence of Aβ fibril aggregates. One of the advantages of this metal complex is its large Stokes shift (180 nm). Furthermore, the long-lived photoluminescence lifetime of this ruthenium complex allows its use for the detection of fibrillar proteins in the presence of short-lived fluorescent backgrounds, using time-gating technology. We will present evidence of the advantages of dipyridophenazine ruthenium(II) complexes for monitoring protein fibrillization in highly fluorescent media.     

Diverse morphologies of zinc oxide nanoparticles and their electrocatalytic performance in hydrogen production

Hydrogen is considered an attractive alternative to fossil fuels,but only a small amount of it is produced from renewable energy,making it not such a clean energy carrier after all.Producing hydrogen through water electrolysis is promising,but using a cost-effective and high-performing catalyst that has longterm stability is still a challenge.This study exploits,for the first time,the potential of zinc oxide nanoparticles with diverse morphologies as catalysts for the electrocatalytic production of hydrogen from water.The morphology of the nanoparticles(wires,cuboids,spheres)was easily regulated by changing the concentration of sodium hydroxide,used as the shape controlling agent,during the synthesis.The spherical morphology exhibited the highest electrocatalytic activity at the lowest potential voltage.These spherical nanoparticles had the highest number of oxygen vacancies and lowest particle size compared to the other two morphologies,features directly linked to high catalytic activity.However,the nanowires were much more stable with repeated scans.Density-functional theory showed that the presence of oxygen vacancies in all three morphologies led to diminished band gaps,which is of catalytic interest.     

A Redox-Active Tetrazine-Based Pincer Ligand for the Reduction of N-Oxyanions Using a Redox-Inert Metal

The reaction chemistry of the bis-tetrazinyl pyridine ligand (btzp) towards nitrogen oxyanions coordinated to zinc is studied in order to explore the reduction of the NO_x⁻ substrates with a redox-active ligand in the absence of redox activity at the metal. Following syntheses and characterization of (btzp)ZnX₂ for X=Cl, NO₃ and NO₂, featuring O−Zn linkage of both nitrogen oxyanions, it is shown that a silylating agent selectively delivers silyl substituents to tetrazine nitrogens, without reductive deoxygenation of NO_x⁻¹. A new synthesis of the highly hydrogenated H₄btzp, containing two dihydrotetrazine reductants is described as is the synthesis and characterization of (H₄btzp)ZnX₂ for X=Cl and NO₃, both of which show considerable hydrogen bonding potential of the dihydrotetrazine ring NH groups. The (H₄btzp)ZnCl₂ complex does not bind zinc in the pincer pocket, but instead H₄btzp becomes a bridge between neighboring atoms through tetrazine nitrogen atoms, forming a polymeric chain. The reaction of AgNO₂ with (H₄btzp)ZnCl₂ is shown to proceed with fast nitrite deoxygenation, yielding water and free NO. Half of the H₄btzp reducing equivalents form Ag⁰ and thus the chloride ligand remains coordinated to the zinc metal center to yield (btzp)ZnCl₂. To compare with AgNO₂, experiments of (H₄btzp)ZnCl₂ with NaNO₂ result in salt metathesis between chloride and nitrite, highlighting the importance of a redox-active cation in the reduction of nitrite to NO.