A facile Garratt–Braverman cyclization route to intercalative DNA-binding bis-quinones

Bispropargyl ethers (both symmetrical and non-symmetrical) equipped with 1,4-dimethoxyaryl groups were synthesized. Under strongly basic conditions (KOBu^t/toluene/reflux), these ethers underwent Garratt–Braverman type cyclization to the tetramethoxy bi-aryl systems in high yields presumably via the bisallenes. The products could be successfully converted to the bis-quinones via CAN-mediated demethylation cum oxidation. This two-step protocol offers a simple route to bis-quinones, connected by C1–C2′ bonds, in good yields. Fluorescence based EB-displacement assay, CD spectroscopy and viscosity measurements confirmed the DNA-binding ability of the synthesized quinones via intercalation.     

An interesting competition between 6π-electro- and Garratt–Braverman cyclization in bis-diene-allene sulfones: synergy between experiment and theory

The reactivity of a series of bispropargyl sulfones with an ortho alkenyl moiety was studied. Under basic condition, these molecules isomerized to the bis-diene-allene system capable of undergoing 6π-electro-(EC) as well as Garratt–Braverman (GB) cyclization. The reaction generally favours the GB process but the balance can be tilted towards the 6π-EC pathway by suitable perturbation of structure and temperature. The findings are useful as the systems undergoing GB pathway can show DNA-damage activities.     

Reactivity of Bispropargyl Sulfones under Basic Conditions: Interplay Between Garratt–Braverman and Schmittel/Myers–Saito Cyclization Pathway

The preference for Garratt–Braverman (GB) over Myers–Saito (MS) and Schmittel (SCM) cyclizations has recently been demonstrated in sulfones capable of undergoing all three of the processes. As the GB cyclization is a self-quenching process, there is a need to change the selectivity to the non-self-quenching MS or SCM pathway so as to enhance the DNA-cleaving efficiency that operates through the radical-mediated process. Herein we report a conformational constraint-based strategy developed by using computations (M06-2X/6-31+G*) to switch the selectivity from GB to MS/SCM pathway which also results in greater DNA-cleavage activity. The preference for GB could be brought back by easing the constraint with the help of spacers.     

Gas chromatographic separation of hydrogen isotopes on columns packed with alumina,modified alumina and sol–gel alumina

The stationary phase of alumina adsorbents, prepared by different chemical processes, was used to study the separation behaviour of hydrogen isotopes. Three types of alumina, obtained by conventional hydroxide route alumina coated with silicon oxide and alumina prepared by internal gelation process (IGP), were used as packing material to study the separation of HT and T₂ in a mixture at various temperatures. The conventional alumina and silicon oxide coated alumina resolved HT and T₂ at 77 K temperature with different retention times. The retention times on SiO₂ coated columns were found to be higher than those of other adsorbents. However, the column filled with IGP alumina was found to be ideal for the separation of HT and T₂ at 240 K. The peaks were well resolved in less than 5 min on this column.     

Ni–Mo2C supported on alumina as a substitute for Ni–Mo reduced catalysts supported on alumina material for dry reforming of methane

In this study, alumina-supported NiMo catalysts were carburized to obtain alumina-supported nickel–molybdenum carbides as potential catalysts for dry reforming of methane. The typical carbide was compared with a low carburized material (in 5% H₂/CH₄) and a reduced NiMo catalyst. It was shown that the passivated alumina-supported NiMo catalysts by carbon lead to higher reactivity, selectivity, and stability for dry methane reforming reaction.     

Sodium acetate/MWI: a green protocol for the synthesis of tetrahydrobenzo[α]xanthen-11-ones with biological screening

Research on Chemical Intermediates - An efficient, straightforward and rapid method has been developed for the synthesis of tetrahydrobenzo[α] xanthen-11-one using sodium acetate. The reaction...     

β-Galactosidase fluorescence probe with improved cellular accumulation based on a spirocyclized rhodol scaffold

We identified a rhodol bearing a hydroxymethyl group (HMDER) as a suitable scaffold for designing fluorescence probes for various hydrolases. HMDER shows strong fluorescence at physiological pH, but phenolic O-alkylation of HMDER results in a strong preference for the spirocyclic form, which has weak fluorescence. As a proof of concept, we utilized this finding to develop a new fluorescence probe for β-galactosidase. This probe has favorable characteristics for imaging in biological samples: it has good cellular permeability, and its hydrolysis product is well-retained intracellularly. It could rapidly and clearly visualize β-galactosidase activity in cultured cells and in Drosophila melanogaster tissue, which has rarely been achieved with previously reported fluorescence probes.     

Microwave-assisted ammonium formate-mediated synthesis of Hanstzch dihydropyridines under solvent-free conditions – a green protocol

Abstract

Microwave-assisted ammonium formate-mediated eco-friendly synthesis of structurally varied Hantzsch dihydropyridines under solvent-free conditions has been successfully accomplished with good yield, minimization of toxic reagents and organic solvents in the process. The elimination of the inorganic support decreased the disposal problem and the extremely small reaction time minimized energy dissipation.     

Electronic tuning of thiazolyl-capped π-conjugated compounds via a coordination/cyclization protocol with B(C6F5)3

Electronic tuning of thiazolyl-capped π-conjugated systems via a coordination/cyclization protocol with B(C(6)F(5))(3) effectively enhances an electron-accepting character giving rise to lower reduction potentials and increases thermal stability.     

The effect of silica–alumina catalysts on degradation of polyolefins by a continuous flow reactor

Catalytic degradation of polyolefins was performed in a continuous flow reactor that allows the study of the degradation processes at steady state, characterized by constant values of reaction parameters and properties of the products. The continuous flow reactor was operated at atmospheric pressure and at feed rate of 0–1.5 kg h^?1 polyolefins over two silica–alumina catalysts having different SiO₂/Al₂O₃ mole ratio. Polyethylene (PE), polypropylene (PP) and polystyrene (PS) were degraded at 420, 380 and 360 °C respectively. The cracking effect of silica–alumina was proved by the increased amount of gaseous products and by the decreased molecular weight of liquid products. The differences in surface area and in concentration and acidic strength of active centers of the two catalysts affected the distribution of degradation products. Molar rate of degradation was increased in the presence of catalysts, however the mass rate of degradation was decreased leading to higher values of the calculated activation energies. These interesting results might open new perspectives in understanding the macroscopic mechanism for catalytic degradation of polyolefins.     

Retention and selectivity of basic drugs on solid-phase extraction sorbents: Application to direct determination of β-blockers in urine

Seven solid phase sorbent materials with reversed-phase, mixed-mode interactions (ion-exchange and reversed-phase), and molecularly imprinted polymers (MIP), namely Oasis HLB, Oasis MAX, Oasis MCX, Bond Elute Plexa, Bond Elute Plexa PAX, Bond Elute Plexa PCX, and SupelMIP sorbents, were investigated. The present study was focused on the retention and elution of pharmaceutically active substances based on several analyte-sorbent interaction properties. Basic drugs, such as β-blockers (i.e., atenolol, pindolol, acebutolol, metoprolol, labetalol, and propranolol) were selected as the model compounds for this study. These compounds are frequently encountered in anti-doping tests. The extraction efficiencies of the individual sorbents were compared based on the recovery of known amounts of the targeted analytes in a metered elution volume (500 μL) in three separate elution fractions. The elution efficiency of the total amount of the target analytes on various sorbents was not appreciably influenced by the volume of eluent required for complete elution. Based on the small matrix effects and clear baseline, SupelMIP was the most suitable sorbent for urine analysis. The relative analyte recoveries of the SPE-HPLC procedure proved satisfactory for the range from 94 % to 105 %, with an RSD ranging from 2 % to 4 %. The regression equations for all of the targeted compounds exhibited excellent linearity (r ² ?>?0.9991) over the range of 10 to 1000 ng mL^–1. The limits of detection and quantification for the selected β-blocker compounds in urine were in the ranges of 0.6 to 2.0 ng mL^–1 and 2.0 to 6.7 ng mL^–1, respectively.     

Radical cyclization–fragmentation of ω-haloalkyl cyclobutanones: a modular approach to medium-sized carbocycles

A facile radical cyclization–fragmentation sequence of ω-haloalkyl-tethered spirocyclobutanones, which are readily available by the Kulinkovich cyclopropanation of cycloalkene carboxylates and subsequent electrophilic addition to haloalkyl acetals, provides a convenient method for appending seven- and eight-membered rings onto cycloalkene carboxylates. An enantioselective preparation of a medium-sized carbocycle is possible by the use of a non-racemic, C₂-symmetric acetal.     

Disorder or complexity? Understanding a nanoscale template structure on alumina

One strategy in creating functional nanostructures is templating where active nanoparticles are arranged on a regular nanoscale array of anchor sites on an inert substrate. An extraordinarily well ordered substrate with a 4.2 nm template periodicity is an alumina (aluminum oxide) film grown on a Ni3Al(111) metallic alloy support. Templating on the alumina film is facilitated by a dot and a network superstructure that can readily be prepared but has not yet been understood at the atomic scale. By imaging the alumina surface with dynamic scanning force microscopy (SFM) operated in the noncontact mode (NC-AFM), we reveal that the main structural element of the oxide film is a lattice of hexagons with a 0.29 nm side length that is pinned to the 0.51 nm periodicity of the substrate. The surface unit cell is defined by distinguished sites forming the dot structure. Pinning the oxide film to the substrate furthermore results in a honeycomb-like topographic modulation referred to as the network structure. These findings demonstrate how long range order is generated by the superposition of complex structures that locally exhibit apparent atomic disorder.     

Complexes of TETROL with selected heterocyclics: unconventional host–guest hydrogen bonding and the correlation with host selectivity

Here we investigate and compare the more salient characteristics of host–guest complexes of (+)-(2R,3R)-1,1-4,4-tetraphenylbutane-1,2,3,4-tetraol (TETROL) with four heterocyclic guests, morpholine, piperidine, pyridine and dioxane. These guests each formed inclusion compounds with TETROL, and host:guest ratios were either 1:2 or 1:1. Single crystal diffraction experiments revealed unprecedented host behaviour in the presence of both piperidine and dioxane with respect to the mode of host–guest hydrogen bonding employed. Furthermore, by utilizing ¹H-NMR spectroscopy or gas chromatography (as applicable) as methods for analysing complexes obtained from competition experiments, we were able to identify the host selectivity order, and were gratified to discover that this order correlated precisely with host–guest hydrogen bond distance.     

Tandem addition–cyclization of o-ethynylphenyl isothiocyanates with N nucleophiles; difference of cyclization mode between primary and secondary amines

Silver triflate promotes the 6-exo-dig mode cyclization of the N-(2-ethynylphenyl)thioureas, which were easily obtained from the o-ethynylphenyl isothiocyanates and the primary amines, to provide the 2-imino-4-methylidene-1H-benzo[d][1,3]thiazines as the sole product in excellent yields. The secondary amines reacted with the o-ethynylphenyl isothiocyanates to give both the 6-exo and 5-endo-dig mode cyclization products under the same conditions.     

A novel pyrene-based “off–on” fluorescent probe with high selectivity and sensitivity for Hg2+

In this article, a novel “off–on” fluorescent probe 2-(pyren-1-ylmethylene)-1H-indene-1,3(2H)-dione ( PID ) for Hg²⁺ was designed and synthesized. The selectivity, concentration titration, pH titration, time dependence, limit of detection, and recognition mechanism of PID for Hg²⁺ in CH₃CH₂OH/H₂O solution were also investigated. The results indicated that PID exhibited high selectivity, sensitivity, and fast response to Hg²⁺, and the limit of detection was as low as 20.7 nmol/L. In addition, PID could work in a wide pH range, and the determination of Hg²⁺ in water samples showed that it could be used as a potential detection tool in practical application.     

Platinum–polytyramine composite material with improved performances for methanol oxidation

Polytyramine (PTy) is shown to be a possible alternative to other conducting polymers as a support material for fuel cell electrocatalysts such as platinum. In this work, a Pt–PTy composite was prepared via potentiodynamic deposition of polytyramine on graphite substrate, followed by the electrochemical deposition of Pt nanoparticles. The material obtained by this straightforward method exhibited, for platinum loadings as low as ca. 0.12 mg cm⁻², a specific electrochemically active surface area of the electrocatalyst of ca. 54 m² g⁻¹, together with a good electrocatalytic activity for methanol oxidation in acidic media, thus ensuring better efficiency of Pt utilization. The system Pt–PTy appears to be worthy of development for methanol fuel cell applications also because the results suggested that, when deposited as small particles in a PTy matrix, platinum is less sensitive to fouling during CH₃OH oxidation.     

An efficient green protocol for the synthesis of chalcones by a Claisen–Schmidt reaction using bismuth(III)chloride as a catalyst under solvent-free condition

Abstract

An environmentally benign protocol for the synthesis of chalcones by the Claisen–Schmidt condensation of aldehydes with ketones using eco-friendly non-toxic bismuth(III)chloride catalyst under solvent-free condition is reported. In this protocol, the reaction time is very short, yields are high, and there are no other pollutants formed.     

Separation of CO_2–N_2 using zeolite NaKA with high selectivity

The adsorption method based on solid adsorbents is one of feasible ways to capture and store CO_2. Using the ion exchange method, different zeolites Na KA varying in K+content were produced. The adsorption isotherms and kinetic uptakes were measured. The experimental results show that the optimal NaKA could adsorb significant quantities of CO_2 and little N_2. On the zeolite Na KA with 14.7 at.% K+, the adsorption capacity for pure CO_2 is over 3.10 mmol g~(-1) and the CO_2–N_2 selectivity is about 149 at ambient pressure and temperature. The kinetic CO_2–N_2 selectivity could also achieved 200 within 3 min according to the uptake data. To demonstrate the separation effectiveness, breakthrough curves of pure components and binary mixtures were investigated experimentally and theoretically in a fixed bed. It is found that the breakthrough points of CO_2 and N_2 are almost at the same time under the atmospheric pressure at 348 K with the raw gas composition CO_2/N_2(20:80, v/v). If the pressure has been increased higher than 0.1 MPa, CO_2 would break through the bed much slower than N_2. Therefore, the pressure may become the limiting factor for the separation performance of zeolites NaKA.