Voltammetric determination of 4-nitrophenol at a lithium tetracyanoethylenide (LiTCNE) modified glassy carbon electrode

The reduction of 4-nitrophenol (4-NP) has been carried out on a modified glassy carbon electrode using cyclic and differential pulse voltammetry (DPV). The sensor was prepared by modifying the electrode with lithium tetracyanoethylenide (LiTCNE) and poly-l-lysine (PLL) film. With this modified electrode 4-NP was reduced at −0.7 V versus SCE. The sensor presented better performance in 0.1 mol l⁻¹ acetate buffer at pH 4.0. The other experimental parameters, such as concentration of LiTCNE and PLL, pulse amplitude and scan rate were optimized. Under optimized operational conditions, a linear response range from 27 up to 23200 nmol l⁻¹ was obtained with a sensitivity of 3.057 nA l nmol⁻¹ cm⁻². The detection limit for 4-NP determination was 7.5 nmol l⁻¹. The proposed sensor presented good repeatability, evaluated in term of relative standard deviation (R.S.D.=4.4%) for n=10 and was applied for 4-NP determination in water samples. The average recovery for these samples was 103.0 (± 0.7)%.     

Ion chromatographic separation of alkali metal and ammonium cations on a C18 reversed-phase column

The separation of alkali metal (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) and ammonium cations on a C₁₈ reversed-phase column using three anionic surfactants [sodium 1-eicosyl sulphate, sodium dodecyl benzenesulphonate and sodium dodecyl sulphate (SDS)] is described. Two methods were examined: (a) “permanent” coating, with the use of a C₁₈ reversed-phase column previously coated with the surfactants; and (b) dynamic coating, with addition of the surfactants to the mobile phase. With method (a) the separation of the six cations was achieved with SDS. However, the retention times gradually decreased owing to dissolution of the SDS coating. Good separation was obtained with method (b), where 10 mM HNO₃ containing 0.1 mM SDS was used as the mobile phase with conductivity detection, and it was applied satisfactorily to real samples. The effect of system peaks on determination is also discussed.     

Inhibition of the formation and decay of stilbene core radical cations by the dendron during the photoinduced electron transfer

Formation and decay processes of stilbene core radical cation (ST*+) during the photoinduced electron transfer have been studied for a series of stilbene bearing benzyl ether-type dendrons (D). ST*+ and the radical cation of peripheral dendron (D*+) were generated by intermolecular hole transfer from biphenyl radical cation, which was generated from photoinduced electron transfer from biphenyl to the singlet-excited 9,10-dicyanoanthracene in a mixture of acetonitrile and 1,2-dichloroethane (3:1). An intramolecular dimer radical cation of benzyl groups at the terminal of stilbene dendrimer was indicated as a hole trapping site. Subsequent hole transfer from the trapping site to the core ST generated ST*+. The shielding effects of D depending on the dendrimer generation on the growth and decay of ST*+ were observed. It was revealed for the first time that D acts as the hole trapping site and the hole conductor on the way of the exothermic hole transfer from the terminal of D to the central core ST. We also found that D inhibits the charge recombination with 9,10-dicyanoanthracene radical anion because of the steric hindrance.     

A new fluorescent metal sensor with two binding moieties

A new fluorescent chelator Oxa, having two metal-binding sites, was designed and synthesized in six steps. Oxa exhibited two distinctive dissociation constants for Zn²⁺ ( μM and  μM), with considerable fluorescence increase in aqueous buffer at pH 7.2. Affinities of Oxa for the other biologically important ions such as Ca²⁺ ( μM and  mM) and Mg²⁺ ( μM and could not be determined) in the same conditions were also obtained.     

Generation of alpha-phosphonovinyl radicals and development of a new route to highly functionalized vinylphosphonates and vinylphosphonate-incorporated carbocyclic or heterocyclic compounds via a radical trapping sequence

The first direct generation of synthetically useful alpha-phosphonovinyl radicals was achieved by treatment of alpha-phosphonovinyl halides with a tributyltin radical. The alpha-phosphonovinyl radicals 2a-d were trapped with electron-rich olefins and an electron-deficient olefin to produce alpha-functionalized vinylphosphonates 3a-f in 16-55% yields. The alpha-phosphonovinyl radicals 7e-g containing the YCH2CH=CH2 (Y = O, CH2, S) substituent at the beta-position afforded mixtures of 5-exo and 6-endo cyclization products, 5e-g and 6e-g, in good yields. The 5-exo/6-endo product ratios increase in the following order of the beta-substituent: OCH2CH=CH2 > CH2CH2CH=CH2 > SCH2CH=CH2. The effects of the beta-substituents upon the cyclization reaction were discussed. Radical cyclization of alpha-phosphonovinyl radicals bearing functional groups such as geranyloxy, geranylthio, and (2-cyclohexen-1-yl)thio groups at the beta-position afforded 5-exo, 5-exo and 6-endo, and cis-fused-5,6-ring cyclization products incorporating an alpha,beta-unsaturated phosphonate unit within the ring, respectively, in good yields. The alpha-phosphonovinyl radical 20 underwent tandem radical cyclization-radical cyclization to produce a mixture of two isomeric bicyclo[4.3.0]nonenes including a vinylphosphonate moiety in high yield.     

PHOTOREACTIVATION OF Halobacterium halobium: ACTION SPECTRUM AND ROLE OF PIGMENTATION

Abstract— An action spectrum for photoreactivation was measured with Halobacterium halobium R₁m₁ to prove a role of carotenoid pigments in photoreactivation of the bacteria. The action spectrum obtained showed a main peak at 435 nm and a minor peak at about 325 nm. The action spectrum was similar to that of Streptomyces pigment (Eker et al. , 1981) suggesting that the chromophore of the photoreactivating enzyme in Halobacterium halobium is 8-OH-5-deazaflavin. The minor peak may be due to photochemical cleavage of a pyrimidine6–4 hetero adduct. The result indicates that carotenoid pigments do not play a positive role in enhancing photoreactivation. This was confirmed also by comparing the efficiency of photoreactivation at 465 nm among three strains of Halobacterium halobium having different carotenoid pigments; R₁m₁. R₁ and W5002–1.     

Bacillamide, a novel algicide from the marine bacterium, Bacillus sp. SY-1, against the harmful dinoflagellate, Cochlodinium polykrikoides

Bacillamide (1) was isolated as a new algicide against the harmful dinoflagellate, Cochlodinium polykrikoides, from the marine bacterium, Bacillus sp. SY-1, and its structure was elucidated by extensive two-dimensional NMR techniques including ¹H-¹⁵N HMBC analysis and mass analysis. Bacillamide showed algicidal activity against C. polykrikoides with LC₅₀ of 3.2 μg/ml.     

Supramolecular cation assemblies of hydrogen-bonded (NH4+/NH2NH3+)(crown ether) in [Ni(dmit)2]-based molecular conductors and magnets

Hydrogen-bonded supramolecular cation assemblies of (NH4+/NH2-NH3+)(crown ether), where the crown ether is [12]crown-4, [15]crown-5, or [18]crown-6, were incorporated into electrically conducting [Ni(dmit)2] salts (dmit2- = 2-thioxo-1,3-dithiole-4,5-dithiolate). (NH4+)([12]crown-4)[Ni(dmit)2]3(CH3CN)2 had a pyramidal shape, while ionic channels were observed in (NH4+)(0.88)([15]crown-5)[Ni(dmit)(2)]2 and (NH4+)(0.70)([18]crown-6)[Ni(dmit)(2)]2. Both (NH4+)(0.88)([15]crown-5) and (NH4+)(0.70)([18]crown-6) contained regularly spaced [Ni(dmit)(2)] stacks formed by N-H.O hydrogen bonding between the oxygen atoms in crown ethers and the NH4+ ion. NH4+ occurred nonstoichiometrically; there were vacant ionic sites in the ionic channels. The ionic radius of NH4+ is larger than the cavity radius of [15]crown-5 and [18]crown-6. Therefore, NH4+ ions could not pass through the cavity and were distributed randomly in the ionic channels. The static disorder caused the conduction electrons to be randomly localized to the [Ni(dmit)2] stacks. Hydrazinium (NH2-NH3+) formed the supramolecular cations in (NH2-NH3+)([12]crown-4)2[Ni(dmit)2]4 and (NH2-NH3+)2([15]crown-5)3[Ni(dmit)2]6, possessing a sandwich and club-sandwich structure, respectively. To the best of our knowledge, these represent the first hydrazinium-crown ether assemblies to be identified in the solid. In the supramolecular cations, hydrogen bonding was detected between the ammonium or the amino protons of NH2-NH3+ and the oxygen atoms of crown ethers. The sandwich-type cations coexisted with the [Ni(dmit)2] dimer stacks. Although the assemblies were typically semiconducting, ferromagnetic interaction (Weiss temperature = +1 K) was detected in the case of (NH2-NH3+)2([15]crown-5)3[Ni(dmit)2]6. The (NH2-NH3+)0.8([18]crown-6)[Ni(dmit)2]2 and (NH4+)0.76([18]crown-6)[Ni(dmit)2]2 crystals were isomorphous. The large and flexible [18]crown-6 allowed for maintaining the same ionic channel structure through replacement of the NH4+ cation by NH2-NH3+.     

Metastable ion study of organosilicon compounds. Part III—trimethoxyphenylsilane

The unimolecular decomposition of trimethoxyphenylsilane (1) was investigated by mass-analysed ion kinetic energy (MIKE) spectrometry, deuterium-labelling studies and from high resolution data. The characteristic fragmentations of metastable molecular ion of 1 were losses of C₆H₆ and C₇H₇^· with rearrangements. Almost complete H/D scrambling occurred in the molecular ion prior to these decompositions. The other important fragmentation routes corresponded to expulsions of CH₃O^· and C₆H₅^·. These fragmentations were followed by consecutive elimination of an H₂CO molecule, as commonly observed in the mass spectra of alkoxysilanes. In these fragmentation processes, H/D scrambling increased as the internal energy of the molecular ion was lowered. The fragmentations of 1 were compared with those of its carbon analogue, α,α,α-trimethoxytoluene.     

Short-time Fourier transform analysis of ab initio molecular dynamics simulation: collision reaction between NH+4 (NH3)2 and NH3

An analyzing technique of the ab initio molecular dynamics simulation is proposed with the use of short-time Fourier transform (ST-FT). The ST-FT analysis demonstrates the dynamical change of the vibrational states in the simulated system. Numerical assessments are preformed for the collision reaction of the ammonia cluster ion NH+(4) (NH3)(2) with the ammonia monomer NH3. Spectrogram obtained by the ST-FT method, which corresponds to the time evolution of vibrational power spectra, clarifies the relationship between the vibrational states and the reaction channels such as nonreactive collision, substitution, and incorporation.