NOPR Collection:

DNA and t-RNA induced circular dichroism in thiazine dyes as a technique for distinguishing between DNA and t-RNA

2019-03-22T11:52:39Z

Title: DNA and t-RNA induced circular dichroism in thiazine dyes as a technique for distinguishing between DNA and t-RNA Authors: Pal, Medini Kanta; Yadav, Ram Chandra Abstract: Metachromasia and circular dichroism (CD) induced in three thiazine dyes, viz. thionine (ThI), methylene blue (MB) and 1,9-dimethylmethyleneblue (DMMB) by DNA and t-RNA at two different concentrations of each dye and at a fixed concentration (1.00 x 10^-4M) of the respective nucleic acids are described. Both the nucleic acids act as weak chromotropes in inducing metachromasia, t-RNA being marginally stronger. While CD induced in MB by both the nucleic acids are very similar, those induced in ThI and DMMB are distinctly different characterising the two nucleic acids. Magnitude of dichroism induced in these two dyes by DNA are several fold higher than that by t-RNA, which possibly is due to the double stranded helical conformation of the former. Also, the CD spectra induced by DNA, unlike t-RNA, are sensitive to polymer/dye ratio. Interaction between the intercalated dyes is expected to be weaker, relative to that between outer bound dyes, since the intercalated dyes are separated by 10 A intercepted by two pairs of bases in between. The dichroism induced in purely intercalated dyes is monophasic, while that in outer bound dye aggregation is likely to be biphasic due to exciton splitting. Page(s): 723-728

Photoredox reactions of methylene blue on zinc oxide

2019-03-22T11:51:07Z

Title: Photoredox reactions of methylene blue on zinc oxide Authors: Sidhu, K S; Singh, Satbir; Kaur, Harinder Abstract: Photoreduction of methylene blue (MB⁺) at 366 nm (3.4 eV) in a heterogeneous medium containing ZnO (band separation = 3.2 eV) has been carried out. In oxygen-free media the product has been found to be leuco-MB which is fully converted into MB⁺ on air oxidation. An analysis of the results shows that Zno is the absorber and negligible light absorbed by MB+ cannot explain the observed conversions. Concentration of ZnO in the medium plays a more important role at higher concentrations of MB⁺. Also reaction extent decreases with increase in dye concentration but at low concentrations it is proportional to dye concentration. A unique feature of the reaction is that it is quenched by the product. Photoreduction is more efficient in solvents of high dielectric and in solvents with easily available hydrogens. Different samples of ZnO prepared from different salts behave differently in this photoreduction due to different reflectance and absorbance characteristics of these samples. A mechanism explaining the observed data and consistant with the known features of such systems have been proposed. Page(s): 729-732

Photogalvanic cells based on the photoreduction of xanthene dyes using riboflavin as a sensitizer in aqueous/micellar medium

2019-03-22T11:49:41Z

Title: Photogalvanic cells based on the photoreduction of xanthene dyes using riboflavin as a sensitizer in aqueous/micellar medium Authors: Lingamurthy, S; Bhanumathi, V; Sethuram, B; Rao, T Navaneeth Abstract: The photochemical reduction of fluorescein, eosin (Y) and rosebengal by disodium salt of EDTA using riboflavin (B₂) as a sensitizer has been studied in aqueous, neutral (triton X-100) and cationic (CTPB) micellar media. The two micelles (i.e. neutral and cationic) are found to catalyse the electron transfer from reduced riboflavin to the dye in the forward photoreaction. Oxidation of semi-reduced dye radical (DH) at the anode (Pt electrode) in a two-compartment photogalvanic (PG) cell which contains riboflavin, Na₂EDTA and dye (D) in the photoanode compartment and 1.0 M HClO₄ in the dark cathode compartment generates noticeable photocurrents. Remarkable increase in photocurrent is noticed in the micellar medium compared to that in the aqueous medium. The stability of the cell also increases in micellar medium. Page(s): 733-736

Kinetics of isothermal transformations-A novel method of treating the data

2019-03-22T11:47:39Z

Title: Kinetics of isothermal transformations-A novel method of treating the data Authors: Somasekharan, K N Abstract: A method of data analysis that linearizes In[g(ɑ)/t]versus I/T is reported. As it harnesses all mechanistic information in a single step, it provides a powerful criterion for determining the kinetic function. Since the kinetic parameters are derived in one step, computation of confidence levels and handling of compensation effect becomes easier. Page(s): 737-739