Comparison of Py*+/dU*- charge transfer state dynamics in 5-(1-pyrenyl)-2'-deoxyuridine nucleoside conjugates with amido-, ethylenyl-, and ethynyl linkers

Femtosecond, picosecond, and nanosecond transient absorbance (TA) and picosecond emission kinetics results are presented for three 5-(1-pyrenyl)-2'-deoxyuridine nucleosides each with a different two-atom linker joining pyrenyl C-1 to uracil C-5. The linkers are respectively -NHCO-, -(CH(2))(2)-, and -C[triple bond]C- for PAdU, PEdU, and PYdU. For all three nucleoside conjugates, most conformers undergo intramolecular charge transfer (CT) from their pyrenyl (1)(pi,pi) excited states to form Py(*+)/dU(*-) CT products in ultrashort times: 相似文献   

Synthesis of imidazoles as novel emivirine and S‐DABO analogues

5‐Alkyl‐4‐benzyl‐1,3‐dihydroimidazol‐2‐ones ( 3a‐d ) and 5‐alkyl‐4‐benzyl‐1,3‐dihydroimidazole‐2‐thiones (7a‐d) were prepared via Dakin West reaction on DL‐phenylalanine with the appropriate aliphatic acid anhydrides followed by hydrolysis and reaction with potassium cyanate or potassium thiocyanate. Compounds 3a‐d were alkylated with ethoxymethyl chloride to give the alkylated imidazoles 5a‐d which were considered analogues of Emivirine with deletion of carbonyl group at the 4‐position. Alkylation of 7a‐d afforded the corresponding S‐alkylated derivatives 8a‐p which in a similar way were considered analogues of S‐DABO. However all the imidazole derivatives were devoid of activity against HIV.     

Adsorption of phenanthrene on organoclays from distilled and saline water

Isotherms of phenanthrene adsorption on different organoclay complexes were obtained using the HPLC technique to understand the adsorption behavior and to characterize the effect of sodium chloride (NaCl) on the adsorption. The adsorbed amounts of phenanthrene on montmorillonite exchanged by organic cations such as tetraheptylammonium, benzyltrimethylammonium, hexadecyltrimethylammonium, or tetraphenylphosphonium were several times higher than those obtained using montmorillonite clay without surface modification. At the same equilibrium concentration, the adsorbed amount of phenanthrene is higher on clay modified with benzyltrimethylammonium than on clay modified with hexadecyltrimethylammonium or other cations. Adsorption of phenanthrene on clay modified with benzyltrimethylammonium increased dramatically as the concentration of NaCl increased up to 150 g/l in the aqueous solution. The shape of the curves obtained can be classified as S-type. The adsorption data obtained from salinity experiments support a mathematical model that links the Langmuir constant with the salinity constant. This model may be useful to predict the equilibrium concentration of a contaminant in saline solution. FTIR studies showed strong interactions between the aromatic rings of phenanthrene and the preadsorbed benzyltrimethylammonium on clay surfaces.     

Dosimetric investigations on radiation-induced Ag nanoparticles in a gel dosimeter

Journal of Radioanalytical and Nuclear Chemistry - Radiation-induced Ag° nanoparticles (NPs) in silver nitrate gel dosimeter incorporating various components was investigated in the dose range...     

Comparative study between two fabricated potentiometric sensors to enhance selectivity towards ferrous ions

Electroanalytical methods are highly selective for measuring electrical quantities including the charge, potential and current with their relation to chemical parameters. They are widely applied in various fields such as biochemical analysis, industrial quality control and environmental monitoring. They have many advantages over other techniques in that they are not time consuming and are specific for certain oxidation states of certain elements which give these techniques high selectivity and sensitivity features. This paper is based on two parts: the first part describes the fabrication of screen‐printed electrodes (SPEs) modified with methyl red as electroactive material, while second part describes the preparation and characterization of Fe(II)–methyl red complex using various spectroscopic tools, the complex being used for the construction of carbon paste electrodes (CPEs). The two proposed electrodes were successfully applied for the determination of Fe(II) in water and pharmaceutical (pharovit) samples. The electrodes under investigation show potentiometric response for Fe(II) in the concentration range 8.0 × 10^?7–1.0 × 10^?2 and 5.0 × 10^?7–1.0 × 10^?2 M at 25°C for SPE and CPE, respectively, and the electrode response is independent of pH in the range 1.5–7.0. These sensors show Nernstian slopes of 29.1 ± 0.2 and 29.7 ± 0.16 mV decade^?1 with detection limit values of 8.0 × 10^?7 and 5.0 × 10^?7 M for SPE and CPE, respectively. These electrodes show fast response time of 6 and 4 s and exhibit a lifetime of 100 and 30 days for SPE and CPE, respectively. The mechanism of chemical reaction between modifier and Fe(II) on the SPE surface was studied using infrared spectra, scanning electron microscopy and energy‐dispersive X‐ray analysis. The proposed potentiometric method was validated according to the IUPAC recommendations. The results obtained using the proposed sensors were comparable with those obtained with inductively coupled plasma analysis.     

Influence of hybrid nano-structures on thermal performance of shear rate dependent viscosity fluid over a heated rotating cone with Hall and ion slip currents

Journal of Thermal Analysis and Calorimetry - The fluid of shear rate dependent viscosity has totally different rheology and exhibits dynamics which play a key role in heat transfer rate and...     

Role of compositional changes on thermal,magnetic,and mechanical properties of Fe-P-C-based amorphous alloys

This work aimed to tune the comprehensive properties of Fe-P-C-based amorphous system through investigating the role of microalloying process on the crystallization behavior,glass forming ability(GFA),soft magnetic features,and mechanical properties.Considering minor addition of elements into the system,it was found that the simultaneous microalloying of Ni and Co leads to the highest GFA,which was due to the optimization of compositional heterogeneity and creation of near-eutectic composition.Moreover,the FeCoNiCuPC amorphous alloy exhibited the best anelastic/viscoplastic behavior under the nanoindentation test,which was owing to the intensified structural fluctuations in the system.However,the improved plasticity by the extra Cu addition comes at the expense of magnetic properties,so that the saturation magnetization of this alloying system is significantly decreased compared to the FeCoPC amorphous alloy with the highest soft magnetic properties.In total,the results indicated that a combination of added elemental constitutes,i.e.,Fe69Co5Ni5Cu1P13C7 composition,provides an optimized state for the comprehensive properties in the alloying system.     

Experimental and theoretical approaches to the study of the reactivity and mechanism of the substitution of phenyl 1-(2,4-dinitronaphthyl) ether with anilines derivatives

Reactions of aniline derivatives in dimethyl sulfoxide with phenyl 1-(2,4-dinitronaphthyl) ether yield aryl 1-(2,4-dinitronaphthyl) amine, which results in substitution of the phenoxy groups at the naphthyl ipso carbon atom. Rate constants were measured spectrophotometrically, and reaction proton transfer was rate limiting. The values of the rate coefficients indicate a rate-limiting proton transfer mechanism with significant substituent effects. The calculated activation parameters were of regular variation with substituents in 4- and 3-position in the aniline nucleophile, and the reaction proceeded through a common mechanism. Hammett's reaction constant showed that the reaction rate constants depend on the electron density of the nitrogen atom of aniline derivative, whereas the coefficient value obtained from the Brönsted relation indicated that the reaction was significantly associative and quite zwitterion like. Computational studies of the substitution were carried out based on density functional theory, and theoretical to the experimental agreement was achieved.