Amino acid overproduction by analog resistant mutants of the nitrogen fixing cyanobacteriumAnabaena sp 287

Two amino acid analog resistant mutants of the cyanobacteriumAnabaena sp 287 were isolated after MNNG mutagenesis.Anabaena ST 16, a mutant resistant to the alanine analog D-α-aminobutyric acid andAnabaena ST 25, another mutant resistant to the histidine analog l,2,4-triazole-3-alanine, released alanine and histidine, respectively, into the medium upon immobilization in alginic acid during diazotrophic growth in fluidized bed reactors. The rates of amino acid production by the mutants were 4.3 μmol mg chl^-1 h^-1 of D-alanine byAnabaena ST 16 and 16.6 μnol mg chl^-1 h^-1 of L-histidine byAnabaena ST 25. Nitrogen fixation by the mutants was not affected by the extracellular amino acid concentration. While the radioactive carbon flow was followed, the parent strain retained 93% of fixed¹⁴C and released only 7% into the medium. On the other hand,Anabaena ST 16 released 13% andAnabaena ST 25 released 29% into the medium. These mutants are beneficial in the production of radioactive amino acids using diazotrophic photobiotechnology.     

Microwave-assisted solid-phase Dötz benzannulation reaction: a facile synthesis of 2,3-disubstituted-1,4-naphthoquinones

A microwave-assisted solid-supported Dötz benzannulation of chromium carbene complexes with various alkynes has been developed. The oxidative cleavage of the resulting resin-bound 1,4-naphthols affords 2,3-disubstituted-1,4-naphthoquinone derivatives in good to moderate yields with high purities.     

Highly chemoselective coupling of allenylstannanes with organic iodides promoted by Pd(PPh3)4/LiCl: an efficient method for the synthesis of substituted allenes

An efficient method for the preparation of various monosubstituted arylallenes, disubstituted allenes and alkenylallenes via palladium-catalyzed coupling of allenylstannanes with aryl iodides or alkenyl iodides is described. The coupling reaction was carried out in the presence of Pd(PPh₃)₄ and LiCl using DMF as solvent. The possible role of LiCl in this coupling process is discussed based on the ¹¹⁹Sn NMR studies.     

Highly chemoselective palladium-catalyzed Sonogashira coupling of 5-iodouridine-5′-triphosphates with propargylamine: a new efficient method for the synthesis of 5-aminopropargyl-uridine-5′-triphosphates

An efficient palladium-catalyzed Sonogashira coupling of 5-iodouridine-5′-triphosphates with propargylamine is described. The catalytic reaction is highly chemoselective that affords exclusively 5-aminopropargyl-uridine-5′-triphosphates in good yields with high purities (>99.8%).     

Immobilization of Ru(III) complex on silica: a heterogenized catalyst for selective oxidation of alcohols in water at room temperature

We have developed a heterogenized catalyst (‘SiO₂’–NH₂–Ru^III) by the immobilization of [Ru(acac)₂(CH₃CN)₂]PF₆ on SiO₂. The catalyst was characterized by SEM, solid state NMR, EPR, FT-IR, ICP, and BET surface area analyses. ‘SiO₂’–NH₂–Ru^III catalyzed the selective oxidation of alcohols with periodic acid in water at room temperature. This protocol was applicable to the controlled oxidation of structurally diverse primary and secondary alcohols. The catalyst could be quantitatively recovered and reused up to six cycles without significant loss of catalytic activity.     

Highly regio- and chemoselective palladium-catalyzed three-component assembly of arylethylidene malononitriles,allylic chlorides,and allenylstannanes: a novel route to 1,7-enyne derivatives

[reaction: see text] An efficient method for the synthesis of 1,7-enyne derivatives via a palladium-catalyzed three-component assembly of arylethylidene malononitriles, allylic chlorides, and allenylstannanes is described.     

Sulfonated polyaniline network grafted multi-wall carbon nanotubes for enzyme immobilization, direct electrochemistry and biosensing of glucose

A new nanomaterial was prepared by grafting a layer of sulfonated polyaniline network (SPAN-NW) on to the surface of multi-walled carbon nanotube (MWNT) and effectively utilized for immobilization of an enzyme and for the fabrication of a biosensor. SPAN-NW was formed on the surface of MWNT by polymerizing a mixture of diphenyl amine 4-sulfonic acid (DPASA), 4-vinyl aniline (VA) and 2-acrylamido-2-methyl-1-propane sulfonic acid (APASA) in the presence of amine functionalized MWNT (MWNT-NH₂). The MWNT-g-SPAN-NW was immobilized with glucose oxidase (GOx) to fabricate the SPAN-NW/GOx biosensor. MWNT-g-SPAN-NW/GOx electrode showed direct electron transfer (DET) for GOx with a fast heterogeneous electron transfer rate constant (k_s) of 4.11 s^− 1. The amperometric current response of MWNT-g-SPAN-NW/GOx biosensor shows linearity up to 9 mM of glucose, with a correlation coefficient of 0.99 and a detection limit of 0.11 μM (S/N = 3). At a low applied potential of − 0.1 V, MWNT-g-SPAN-NW/GOx electrode possesses high sensitivity (4.34 μA mM^− 1) and reproducibility towards glucose.     

Hierarchically‐ordered electroactive silica‐polyaniline nanohybrid: A novel material with versatile properties

Poly(trimethoxy silylpropylaniline), a nanoporous (pore diameter of 2.4 nm), electroactive (stable reversible redox characteristics), electrochromic (yellow at ?0.10 V, blue green at +0.50 V, and dark green at +0.70 V), and pH‐sensitive, silica–polyaniline (PANI) hybrid material (designated as KGM‐1) has been synthesized in powder form by a simple one‐pot chemical synthesis as well as a “thin nanolayered film” by cyclic voltammetry. High‐resolution transmission image of KGM‐1 informs that the particles are spherical, with diameters in the range of 0.5–1.5 μm. X‐ray diffraction pattern of pristine KGM‐1 confirms the combined presence of ordered silica network and PANI chains. The surface area of calcined KGM‐1 is 40 m²/g (～15 times higher than KGM‐1), and the average pore size is 2.4 nm. The N₂ adsorption features also inform that PANI is present as a uniform layer within the pores of silica and because of that the silica pores are not completely blocked. The reversible redox transitions in PANI units and nanoporosity of KGM‐1 are effectively used for the electro‐driven loading/release of DNA or adenosine 5′‐triphosphate. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Vibrational markers of structural distortion in adenine nucleobases upon DNA damage

Oxidation is one of the common causes of chemical damage of DNA. Among the oxidized nucleobases in DNA, 8-oxoadenine (8-oxoA) and 4,6-diamino-5-formamidoadenine (FaPyA) are two of the most commonly found lesions. Relatively little information has been published so far on these lesions compared to the more mutagenic modified purines like 8-oxoguanine. In this study, we investigate the structure and vibrational spectra of these two lesions using Density Functional Theory relative to the parent compound adenine. In addition, we have incorporated a solvent environment through the Polarizable Continuum Model (PCM), as well as explicit solvent model calculations to test for the best prediction of the vibrational wavenumbers of adenine. We find that, while the explicit solvent model predicts the structure of the lesions better with respect to published X-ray diffraction structures, they do not reproduce the vibrational wavenumbers as accurately. In comparison, PCM predicts the wavenumbers better with less of the typical overestimation seen in the absence of solvent effects. Intriguingly, uniform linear scaling of the 'gas phase' calculations provides the best agreement with published experimental spectra. Finally, we demonstrate that 8-oxoA and FaPyA have unique spectral features compared to adenine by characterizing the differences in their normal modes. We propose the use of their distinct spectra as site-specific Raman probes of systems such as base-specific local probing of a DNA strand and DNA-enzyme active site interactions where the substrate can be used as an in situ probe.