Theoretical study of the effect of radiation on thymine

The possible effects of radiation exposure to DNA are studied by investigations for the thymine residue. Detailed analysis of the various addition and other products is undertaken theoretically, using the semiempirical AM1 procedure. The results agree with the experimental finding that the loss of hydrogen on radiation exposure occurs from the C₅-methyl group and hydroxyl radical addition occurs at C₆, yielding the ‘5-yl’ radical. This radical is nonplanar, the axial conformer being slightly preferred over the equatorial one. In contrast, the other possible radical, the ‘6-yl’ radical, is almost planar. These results are important in understanding the conformational changes in DNA as a consequence of radiation exposure.     

Simultaneous densitometric determination of shikonin,acetylshikonin, and β‐acetoxyisovaleryl‐shikonin in ultrasonic‐assisted extracts of four Arnebia species using reversed‐phase thin layer chromatography

A simple, precise, and rapid high‐performance thin‐layer chromatographic (HPTLC) method for the simultaneous quantification of pharmacologically important naphthoquinone shikonin ( 1 ) together with its derivatives acetylshikonin ( 2 ), and β‐acetoxyisovalerylshikonin ( 3 ) in four species of genus Arnebia (A. euchroma, A. guttata, A. benthamii, and A. hispidissima) from the Indian subcontinent has been developed. In addition, the effect of solvents with varying polarity (hexane, chloroform, ethyl acetate, and methanol) for the extraction of these compounds was studied. HPTLC was performed on precoated RP‐18 F_254S TLC plates. For achieving good separation, mobile phase consisting of ACN/methanol/5% formic acid in water (40:02:08 v/v/v) was used. The densitometric determination of shikonin derivatives was carried out at 520 nm in reflection/absorption mode. The method was validated in terms of linearity, accuracy, precision, robustness, and specificity. The calibration curves were linear in the range of 100–600 ng for shikonin and acetylshikonin, and 100–1800 ng for β‐acetoxyisovalerylshikonin. Lower LOD obtained for compounds 1 – 3 were 18, 15, and 12 ng, respectively, while the LOQ obtained were 60, 45, and 40 ng, respectively.     

Electrochemical deposition of Bi2Te3-based thin films

The electrochemical reduction processes on stainless-steel substrates from an aqueous electrolyte composed of nitric acid, Bi³⁺, HTeO₂⁺, SbO⁺ and H₂SeO₃ systems were investigated using cyclic voltammetry. The thin films with a stoichiometry of Bi₂Te₃, Bi_0.5Sb_1.5Te₃ and Bi₂Te_2.7Se_0.3 have been prepared by electrochemical deposition at selected potentials. The structure, composition, and morphology of the films were studied by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM) and electron microprobe analysis (EMPA). The results showed that the films were single phase with the rhombohedral Bi₂Te₃ structure. The morphology and growth orientation of the films were dependent on the deposition potentials.     

ESPT of 2-(2'-pyridyl)benzimidazole at the Micelle-Water interface: selective enhancement and slow dynamics with sodium dodecyl sulfate

The effect of micellar environment on the excited state proton transfer (ESPT) of 2-(2'-pyridyl)benzimidazole (2PBI) has been investigated by steady state and time resolved fluorescence spectroscopy. The ESPT, which occurs to a rather small extent at pH 7, is found to be enhanced remarkably at the interface of sodium dodecyl sulfate (SDS) micelles and water. Such an enhancement is not observed for the cationic cetyl trimethyl ammonium bromide (CTAB) or neutral Triton X-100 micelles. This selective enhancement is explained in the light of a modification of pK(a) and a more acidic local pH in the micelle-water interface. A rise time of about 890 ps is observed in the region of tautomer emission. The origin of this rise time is explored, considering three factors, namely, diffusion controlled protonation of the normal form of 2PBI, slow and possibly incomplete solvation of the transition state, leading to a slowing down of the proton transfer process and a similar slow dynamics of the tautomeric excited state.     

Second‐sphere coordination in anion binding: cis‐diazido­bis(ethyl­ene­diamine‐κ2N,N′)cobalt(III) picrate

In the title compound, [Co(N₃)₂(C₂H₈N₂)₂](C₆H₂N₃O₇), the cations share NH₂⋯NH₂ edges with picrate anions via second‐sphere N—H⋯O hydrogen bonds.     

Silica‐Supported P2O5 as an Efficient Heterogeneous Catalyst for the One Pot Synthesis of 3‐Amino‐imidazo[2,1‐b](1,3)benzothiazole under Green Conditions

The new approach involving the solid supported catalyst for the formation of C–N bond followed by cyclization has been reported. In this work we have reported a facile, efficient, and environment‐friendly protocol for the synthesis of some new 3‐amino‐imidazo[2,1‐b](1,3)benzothiazole derivatives by one‐pot condensation of 2‐aminobenzothiazole, indole‐3‐carbaldehyde, and aryl isocyanide in the presence of silica‐supported P₂O₅ as a heterogeneous solid acid catalyst. The reaction was performed using conventional method under green conditions. The present approach offers the advantages of simple methodology, inexpensive acid catalyst, short reaction time, easy work up with excellent yield, simple purification and use of green solvent. All the newly synthesized compounds were characterized in details using physical and chemical techniques such as melting point, ¹H NMR, ¹³C NMR, and FTIR spectroscopy.     

Efficient Elemental Iodine Catalyzed One-Pot Synthesis of 2,4,5-Triarylimidazoles

Summary. Elemental iodine is used as an efficient catalyst for the synthesis of 2,4,5-triarylimidazoles in excellent yields via condensation of benzoin, ammonium acetate, and aromatic aldehydes. This is a simple, one-pot, high yielding technique using cheap, non-toxic iodine in catalytic amounts.     

Response Surface Methodology-Based Optimisation of Agarose Gel Electrophoresis for Screening and Electropherotyping of Rotavirus

Management of rotavirus diarrhoea cases and prevention of nosocomial infection require rapid diagnostic method at the patient care level. Diagnostic tests currently available are not routinely used due to economic or sensitivity/specificity constraints. Agarose-based sieving media and running conditions were modulated by using central composite design and response surface methodology for screening and electropherotyping of rotaviruses. The electrophoretic resolution of rotavirus genome was calculated from input parameters characterising the gel matrix structure and running conditions. Resolution of rotavirus genome was calculated by densitometric analysis of the gel. The parameters at critical values were able to resolve 11 segmented rotavirus genome. Better resolution and electropherotypic variation in 11 segmented double-stranded RNA genome of rotavirus was detected at 1.96% (w/v) agarose concentration, 0.073 mol l⁻¹ ionic strength of Tris base–boric acid–ethylenediamine tetraacetic acid buffer (1.4×) and 4.31 h of electrophoresis at 4.6 V cm⁻¹ electric field strength. Modified agarose gel electrophoresis can replace other methods as a simplified alternative for routine detection of rotavirus where it is not in practice.     

Electronic structure,Compton profiles and optical properties of TaC and TaN

Isotropic Compton profiles of TaC and TaN have been measured for the first time, at an intermediate resolution, using 662 keV γ-radiation. Energy bands, density of states and Fermi surface topology of TaC and TaN have been computed using linear combination of atomic orbitals with density functional theory and full potential linearised augmented plane wave method. Both band structure calculations predict the metallic character of TaC and TaN. The electron momentum densities calculated using various approaches of density functional theory are compared with the present measurements. On the basis of Mulliken’s population, it is also seen that TaC has more covalent bonding than TaN. The optical properties computed using full potential linearised augmented plane wave method are explained in terms of intraband transitions.