Submolar Concentrations Research Articles

Origin of the dual-band laser emission from 7-diethylamino-4-methylcoumarin (C1) in solution: effect of hydrogen-bonding interaction by hydroxylic molecules

Ultraviolet absorption measurements on 7-diethylamino-4-methylcoumarin (Cl) and its rigid analogue C102 in which the 7-amino group is structurally prevented from twisting in n-butyl acetate (nBuOAc) solutions containing submolar concentrations of n-butyl alcohol showed weak 2:1 alcohol:dye complexation. These results contrast with those from fluorescence measurements which revealed a 1:1 alcohol:dye excited state complex for the Cl dye. These results together with N2 laser excited amplified spontaneous emission (ASE), and laser gain measurements on Cl and C102 in nBuOAc with alcohol or acetonitrile co-solvent show that dual ASE from Cl originates from a quasi-equilibrium concentration of hydrogen-bonded or acetonitrile-solvated excited state complex. The results are inconsistent with a TICT-nBuOAc exciplex for Cl in nBuOAc. The laser gain of the twin ASE peaks at 420 nm and 455 nm from Cl can be tuned by adding a small quantity of hydroxylic co-solvent to dried nBuOAc. ASE was found to be a selective probe for a H-bonded Cl complex whose fluorescence is normally obscured by that from the "free" dye. Key words: aminocoumarins, dual amplified spontaneous emission, excited state hydrogen-bonding complex, laser gain.

Uncoating-like modification of poliovirus capsid resulting from the cooperative effects of subfreezing temperature and submolar concentrations of urea.

Inactivation of poliovirus at subfreezing temperature in the presence of unusually low concentrations of urea (less than or equal to 0.5 M) was investigated. Whereas serotypes 1 and 2 are very sensitive, type 3 is resistant. Inactivation cannot be attributed to concentration of solutes since temperature must be reduced below -13 degrees C for loss of infectivity. Characteristics of the inactivated virion are similar to those of virions in the early stages of uncoating in HeLa cells, viz., loss of infectivity, sensitivity to proteases and detergents, change in isoelectric point, retention of intact genome, and in some instances, loss of VP4. The molecular basis for inactivation is considered to be dissociation of water bound to capsid proteins thereby causing irreversible denaturation of native tertiary structure. The results of this study are discussed in terms of their relevance to the early stages of uncoating in vivo.

Fluorescence and triplet yield quenching of β-apo-14′-carotenal (C 22 aldehyde) by aromatic molecules

Abstract The fluorescence and triplet yields of β-apo-14′-carotenal in cyclohexane at room temperature are quenched in the presence of submolar concentrations of aromatic molecules predominantly through a dynamic interaction. The observed Stern-Volmer constants KSVF for fluorescence quenching vary from 0.06 M−1 for mesitylene to 45 M−1 for indole, giving excited state quenching rate constants in the range of 6 × 107 − 4.5 × 1010 M−1 s−1. With methoxy-substituted benzene derivatives as quenchers, the KSVF data correlate well with the half-wave oxidation potentials of the quenchers, suggesting a modest involvement of charge transfer. Interestingly, the Stern-Volmer constants KSVT for triplet yield quenching are significantly higher than the corresponding KSVF values. This result is explained in terms of scheme(s) where the singlet excited state species that acts as precursor for triplet is assumed to be kinetically distinguishable from that responsible for fluorescence.

Storage of mercury at submolar concentrations.

Storage of mercury at submolar concentrations.