Evidence for trimerization in aqueous solutions of methylene blue

Abstract

Trimerization in Aqueous Solutions of Methylene Blue 2477 motic coefficients4 can be used to predict the variation of «12 and «21 with ionic strength if S' = 0.190 (obtained at I > 3) is assumed to be independent of ionic strength, (c) The best values of the Earned rule coefficients in the ionic strength range from 1 to 6 are « 2 = 0.048 ± 0.003 and «21 = -0.035 ± 0.005, essentially independent of ionic strength. There is no clear reason for the discrepancy between our measurements and those of Lanier, but we believe our values of Earned rule coefficients are more likely to be correct, since they have been obtained by two independent experiments using both chloride-reversible and sulfate-reversible electrodes, and are also consistent with a thermodynamically based extrap-olation from higher ionic strengths, where our results are in agreement with those of Lanier.The behavior of the Earned rule coefficients for this system at ionic strengths below 0.5 is not yet established. This is of theoretical rather than practical interest, since in this range even large deviations from the above values will not introduce appreciable error in calculated activity coefficients.

Novel temperature-activated humidity-sensitive optical sensor

“…2, and the subsequent comparison of the measured and literature values for λmax, reported for aggregated forms of MB in aqueous solutions, suggest that the blue form of the MB/HPC film is formed from a combination of monomeric and dimeric MB with λmax values of 665 nm and 605 nm, respectively [23]. However, the unusually low λmax value (530 nm), observed (see Fig.…”

“…Δλmax = -ve, as opposed to hypsochromic, i.e. Δλmax = +ve) is much larger than, and opposite to that observed, by Matsushima et al, using the thiazine dyes MB and TH in carrageenan gels, as is indicated by the colour and wavelength changes listed in Table 1 [15,[20][21][22][23][24][25][26].…”

“…This high degree of aggregation is not readily observed in aqueous solutions of MB, even at high concentrations (>10 mM) [23,30], and thus the mechanism responsible for formation of this species for MB, and all the other thiazine dyes (except TH), must be due to RH-related, significant changes in the encapsulated dye's microenvironment [25].…”

“…For example, in the case of the MB indicator, the absorbance λmax in aqueous solution of MB is ca. 665 nm (and characteristic of the monomer form of the dye), so that the dye appears blue in colour [23]. But, this value of λmax (absorption) decreases as the dye becomes increasingly aggregated, with the dimer and trimer exhibiting λmax values of 605 nm and 578 nm respectively [23], so any solution containing these species adopts a more purple colouration.…”

Methylene Blue Interactions with Reduced-Charge Smectites

“…Methylene blue is a cationic dye, which absorbs visible light near 675 nm in dilute aqueous solutions (Lewis and Bigeleisen, 1943;Braswell, 1968). When mixed with clay dispersions it is rapidly and strongly adsorbed by the clay surfaces (Margulies et al, 1988).…”