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Solvation dynamics of the fluorescence probe, coumarin 102, in anionic surfactant, sodium alkyl sulfate (CnH2n+1SO4Na; n = 8, 10, 12, and 14), and cationic surfactant, alkyltrimethylammonium bromide (CnH2n+1N(CH3)3Br; n = 10, 12, 14, and 16), micelle solutions have been investigated by a picosecond streak camera system. The solvation dynamics in the time range of 10^-10−10^-8 s is characterized by a biexponential function. The faster solvation time constants are about 110−160 ps for both anionic and cationic micelle solutions, and the slower solvation time constants for sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions are about 1.2−2.6 ns and 450−740 ps, respectively. Both the faster and the slower solvation times become slower with longer alkyl chain surfactant micelles. The alkyl-chain-length dependence of the solvation dynamics in both sodium alkyl sulfate and alkyltrimethylammonium bromide micelles can be attributed to the variation of the micellar surface density of the polar headgroup by the change of the alkyl chain length. The slower solvation time constants of sodium alkyl sulfate micelle solutions are about 3.5 times slower than those of alkyltrimethylammonium bromide micelle solutions for the same alkyl-chain-length surfactants. The interaction energies of the geometry optimized mimic clusters (H2O−C2H5SO4^- and H2O−C2H5N(CH3)3⁺) have been estimated by the density functional theory calculations to understand the interaction strengths between water and alkyl sulfate and alkyltrimethylammonium headgroups. The difference of the slower solvation time constants between sodium alkyl sulfate and alkyltrimethylammonium bromide micelle solutions arises likely from their different specific interactions.

The solvation dynamics of formamide and N,N-dimethylformamide in Aerosol OT reverse micelles has been investigated in this work. The solvation dynamics of formamide and N,N-dimethylformamide in the reverse micelles is more than 100 times slower than that of the pure solvents. The solvation dynamics of formamide in the reverse micelle solution depends strongly on the molar ratio between formamide and Aerosol OT (w = [polar solvent]/[Aerosol OT]), but that of N,N-dimethylformamide in the reverse micelle solution shows a tiny w dependence. We have estimated the interaction energies of the geometry-optimized clusters of a simple model of the Aerosol OT polar headgroup (CH3SO3^-) and formamide or N,N-dimethylformamide by ab initio calculations (the second-order Møller−Plesset perturbation theory) to find their interactions. The interaction energies of the mimic clusters estimated by the ab initio calculations and the features of the slow solvation dynamics and w dependence in formamide and N,N-dimethylformamide reverse micelles are discussed.

Steady-state and time-resolved fluorescence spectroscopies were used to investigate the local environments of coumarin 102 (C102) probe molecules when encapsulated within an amphiphilic starlike macromolecule (ASM). ASMs are promising surfactant-type nanoscale transporters of hydrophobic drug molecules. They consist of a hydrophobic core, in which small, hydrophobic molecules such as C102 can be encapsulated, and a hydrophilic shell that makes the whole assembly water-soluble. Steady-state fluorescence spectroscopy revealed that C102 molecules sense a very polar environment when encapsulated in ASMs. Both time-correlated single-photon counting and fluorescence upconversion techniques indicated that the solvent reorganization and diffusive reorientation of the C102 solvatochromic fluorescent probe are significantly slowed compared to the rates in aqueous solutions. These results provide insight into the dynamics of drugs encapsulated within ASMs.

Ultrafast photoinduced electron transfer between excited oxazine-1 (OX1) dye and electron donating solvents aniline (AN) and N,N-dimethylaniline (DMA) has been studied with the femtosecond fluorescence up-conversion technique. Ultrafast and highly nonexponential fluorescence decay of OX1 is observed in AN and DMA. The fastest component observed is about 60 fs in DMA and assigned to fluorescence quenching due to an electron transfer reaction. Fluorescence decays are observed to be strongly dependent on the wavelength of observation in DMA and moderately dependent in AN. The wavelength dependence is assigned to fluorescence from different configurations of OX1 and solvent molecules. The energy parameters for electron transfer are estimated and discussed.

The deuterium isotope effects on the volume phase transition of a typical temperature-sensitive polymer gel (poly(N-isopropylacrylamide) (PNIPAM) gel) and the phase separation of the linear polymer (PNIPAM) have been investigated. For the comparison between the bulk change and the microenvironment change, the deuterium isotope effects of PNIPAM gel and linear PNIPAM solution have also been investigated by using a fluorescence probe. Both the transition temperature of the polymer gel and the phase separation temperature of the linear polymer in heavy water are about 0.7 °C higher than those in water. However, the deuterium isotope effects on the difference of the transition temperatures in the heating process and the cooling process in the microenvironments of PNIPAM gel and linear PNIPAM solution are not observed.

We have investigated the solvation dynamics of methanol and acetonitrile in reverse micelles for the first time. The solvation dynamics of both methanol and acetonitrile in reverse micelles show nonexponential features and unusual slow solvation components (from a few hundreds of picosecond to several nanoseconds). Interestingly, the solvation dynamics of methanol in reverse micelles becomes faster with a larger ratio of polar solvent to surfactant (w = [polar solvent]/[Aerosol OT]) of micelles. However, the w dependence of the solvation dynamics of acetonitrile in reverse micelles is not observed. The different w dependence of solvation dynamics in methanol and acetonitrile within reverse micelles should be arising from the presence of the intermolecular hydrogen-bonding network.

Intermolecular electron transfer (ET), which occurs faster than solvation dynamics, has been investigated using the fluorescence up-conversion technique. The ultrafast ET processes have been observed from the electron-donating solvents to the excited coumarin dyes. In this work we have mainly focused our attention on the roles of the substitution of electron-donating solvent molecules in the ET dynamics. We have used aniline, N-monoalkylanilines, and N,N-dialkylanilines as electron-donating solvents and five 7-amino coumarins as acceptor molecules. For these systems the free energy gaps have been estimated from the cyclic voltammetry measurement and the steady-state absorption and fluorescence measurements. The experimental results indicate that the ET rate depends largely on the substituent groups of the solvent molecules. In N,N-dialkylanilines the ET rate gets smaller as the size of the alkyl substituent group becomes larger. For N-monoalkylanilines, however, the ET dynamics are not changed by the different alkyl substituent groups. In many donor−acceptor combinations we recognized that the ET rate is much faster than the solvation time. We simulated the results by the two-dimensional ET model with solvent and nuclear coordinates and found that the N-alkyl substituent effect on the ET rate appears to be mainly due to the changes in the electronic matrix element. We have also investigated the deuterium isotope effect on the ET dynamics using N-deuterated-N-monoalkylanilines as donor solvents. For the fastest ET the isotope effect is hardly observable, whereas the effect is quite large (~20%) for slower ET. The deuterium isotope effect seems to mainly come from the change of stabilization energies in intermolecular hydrogen-bonding interaction by deuteration. The extent of deuterium isotope effect on ET is similar for all N-monoalkylanilines used. This result indicates that the size of the alkyl groups does not affect much the hydrogen-bonding interaction.

A recently established method for determining the surface temperature of adjuvant-inflamed rat's paw was used to examine the anti-inflammatory potencies of various nonsteroidal and steroidal anti-inflammatory drugs, which are currently in clinical use. The results were compared with those obtained by the carrageenin paw edema method and with the inhibitory potencies on prostaglandin E2 generation. The clinically effective single doses of the drugs were better correlated with the effective doses on local hyperthermia than with those on carrageenin paw edema, or with the inhibitory activities of the drugs on prostaglandin E2 generation from cultured rat synovial cells. Although care should be taken to avoid false-positive anti-inflammatory effects arising from vasoconstrictor activity or toxicity, determination of lowering effects on local hyperthermia in this inflammatory model may be useful for the evaluation of anti-inflammatory compounds.

The femtosecond dynamics of liquid aniline, its N-methylated derivatives, two deuterium isotopes, and some mixtures are studied by means of the optically heterodyne detected optical Kerr effect. All data can be effectively described by three contributions: an oscillatory response associated with librational motion which is most significant at early times, a dual exponential relaxation occurring on the picosecond time scale, and a response at intermediate times which is fit to a model describing collisional dynamics, but is of uncertain origin in these complex liquids. The frequency of the librational response of aniline itself is anomalous and is interpreted in terms of a dimer like structure in the liquid. The librational response for the methylated derivatives is typical of that found in other aromatic liquids. The slowest relaxation times are not well described by simple diffusional rotational reorientation models. It is proposed that some structural relaxation may make a nonhydrodynamic contribution to the slow relaxation. For both fast and slow relaxation components the effect of deuteration is slight. The electronic hyperpolarizability is also determined from the data and increases with increasing degree of methylation. The measured pure liquid dynamics are used to calculate the solvation time correlation function, which is compared with earlier measurements of the solvation dynamics on anilines. The calculation of the solvation dynamics from the pure liquid dynamics (as measured by OHD-OKE) is not particularly successful for this class of weakly polar liquids.