FUNCTIONAL DETERGENT PROBES OF MICELLE STRUCTURE. ABSORPTION, FLUORESCENCE AND QUENCHING MEASUREMENTS

Abstract— The absorption and fluorescence spectra of two functional ionic detergents containing an indole chromophore have been studied as micelle probes and have been compared to the corresponding spectra of 1-methylindole. The quenching of the fluorescence of the probes by NO^-₂ and Co²⁺ has also been investigated. Based on the results obtained, it is concluded that 1-methylindole is associated with the surface of HDTBr micelles, whereas it is located in the interior of SDS micelles. The chromophore of the indole detergents is considered to be located in the interior of HDTBr and SDS micelles.     

Reacting polymers with highly correlated initial conditions

We propose and theoretically study an experiment designed to measure short-time polymer reaction kinetics in melts or dilute solutions. The photolysis of groups centrally located along chain backbones, one group per chain, creates pairs of spatially highly correlated macroradicals. We calculate time-dependent rate coefficients κ(t) governing their first-order recombination kinetics, which are novel on account of the far-from-equilibrium initial conditions. In dilute solutions (good solvents) reaction kinetics are intrinsically weak, despite the highly reactive radical groups involved. This leads to a generalised mean-field kinetics in which the rate of radical density decay - ∼S(t), where S(t) ∼t ^{- (1 + g/3)} is the equilibrium return probability for 2 reactive groups, given initial contact. Here g≈ 0.27 is the correlation hole exponent for self-avoiding chain ends. For times beyond the longest coil relaxation time τ, - ∼S(t) remains true, but center of gravity coil diffusion takes over with rms displacement of reactive groups x(t) ∼t ^1/2 and S(t) ∼ 1/x ³(t). At the shortest times ( t 10^-6s), recombination is inhibited due to spin selection rules and we find ∼tS(t). In melts, kinetics are intrinsically diffusion-controlled, leading to entirely different rate laws. During the regime limited by spin selection rules, the density of radicals decays linearly, n(0) - n(t) ∼t. At longer times the standard result - ∼d ³(t)/d (for randomly distributed ends) is replaced by ∼d2x ³(t)/d ² for these correlated initial conditions. The long-time behavior, t > τ, has the same scaling form in time as for dilute solutions. Received 18 May 2000     

SOLVENT SENSITIVITY OF TYPE II PHOTOREACTIONS OF KETONES AS A DEVICE TO PROBE SOLUTE LOCATION IN MICELLES

Abstract. The solvent sensitivity of the Type II reaction is employed as a device to investigate the properties of detergent solutions. The quantum yield for Type II reaction and the ratio of cleavage to cyclization are used as specific monitors of local solvent properties of micelles. Our results indicate that the average position of phenyl alkyl ketones is either on the micelle surface or in the Stern layer. The absence of significant residence time of the excited ketone in the aqueous phase is confirmed by the lack of quenching of Type II reaction by Eu³⁺ in micellar solutions.     

USEFUL PHOTOLUMINESCENCE PROBES OF MICELLAR SYSTEMS—CYCLIC AZOALKANES AS FLUORESCENCE ACCEPTORS AND 1,5-DIMETHYLNAPHTHALENE AS A FLUORESCENCE DONOR

Abstract— Certain cyclic azoalkanes are shown to exhibit substantial fluorescence intensity and attractive absorption parameters in detergent solutions. Quenching of the fluorescence of detergent solutions of 1,5-dimethylnaphthalene by these bicyclic azoalkanes has been investigated and is found to provide a useful system to study properties of micellar systems.     

CHEMILUMINESCENCE FROM CARBENE OXIDATION

Abstract— The chemiluminescent reaction between carbenes and O₂ in Freon 113 at and above 77 K was investigated. The reaction was found to be general for phenylated carbenes and independent of precursor. Spectra obtained by optical multichannel analyzer (OMA) are consistent with the emission being from the excited ketone formed. Kinetics studies at 77 K indicate that the decay of the chemi-luminescence is significantly faster than the decay of the carbene as monitored by fluorescence and electron paramagnetic resonance.     

Two-photon excitation induced fluorescence of a trifluorophore-labeled DNA

Two-photon excitation of a trifluorophore (6-carboxyfluorescein, N,N,N',N'-tetramethyl-6-carboxyrhodamine and cyanine-5 monofunctional dye) labeled DNA, which has a scaffold of 26 nucleotides, was achieved using focused laser light of a Q-switched Nd-YAG laser (1064 nm). The observed fluorescence signature (emission ratio from the three fluorophores) of the labeled DNA after two-photon excitation is very different from the fluorescence signatures produced by one-photon excitation at different wavelength. The additional fluorescence signatures produced by two-photon excitation of the fluorescent oligonucleotides will facilitate their use as combinatorial fluorescence energy transfer tags for multiplex genetic analysis.     

Photochemistry of macrocyclic ketones within zeolites: competition between norrish type I and type II reactivity

Photolysis of macrocyclic mono- and diketones (1 and 2) included in X and Y zeolites gives Norrish type I products in addition to the products obtained via the Norrish type II process, the only observed process in isotropic media. Enhancement of the type I over the type II process is cation-dependent and especially large enhancements are obtained with Li and Na as cations. The zeolite effect is attributed to a reduction in the rate of the Norrish type II -hydrogen abstraction process.