Interactions between 3H-indole derivatives, their
cations and anions, and microheterogeneous environments
like micelles and vesicles have been studied extensively in our
laboratory recently. We report herein the
interactions of
2-(p-aminophenyl)-3,3-dimethyl-5-cyano-3H-indole
(1) and
2-[p-(dimethylamino)phenyl]-3,3-dimethyl-5-cyano-3H-indole (2) with aqueous
solutions of β-cyclodextrin (β-CD), studied by absorption
and
fluorescence steady-state and time-resolved measurements. The
stoichiometries of the cyclodextrin:guest
inclusion complexes have been determined by steady-state fluorescence
measurements. The data reveal that
two types of complexes, i.e., 1:1 and 2:1 types are formed.
Thermodynamic parameters are calculated at six
different temperatures. Spectral characteristics, bandwidths, and
photophysical parameters indicate that
molecule 2 is better protected against hydrophilic
interactions. Protonation reactions carried out at
different
concentrations of β-CD show that the protonation is inhibited at the
indolic nitrogen, contrary to what was
observed in other microheterogeneous media. Time-resolved
measurements and global analysis of the results
are best described by a discrete triple exponential decay law clearly
indicating that the guest molecules
experience three different environments in aqueous solutions: bulk
water and a stepwise 1:1 and 2:1 (β-cyclodextrin:guest) inclusion complexation. The effective polarity
of the cyclodextrin cavity is equivalent
with the polarity of an 80:20 methanol−water mixture at the β-CD
rim where the indolic (tertiary) nitrogen
is likely to be located near the “alcoholic” secondary rim of the
macrocycle.
We report on the rotational diffusion and vibrational population relaxation dynamics of the probe molecules
perylene and 1-methylperylene in selected aliphatic aldehyde and ketone solvents. The reorientation data
demonstrate that, for both solvent systems, there is a change in the nature of the solvent−solute interactions
with both probe molecules as the hydrodynamic volume of the solvent molecules approaches that of the
probes. The solvent-dependent change in behavior occurs for different solvent aliphatic chain lengths in the
two systems. Vibrational population relaxation measurements for two probe molecule vibrational modes reveal
efficient intermolecular coupling in all cases. The data point to the role of the solvent aldehyde proton in
mediating solvent−solvent and solvent−solute interactions, leading to chromophore dynamics reminiscent
of those seen in the n-alcohols. Reorientation of the two probes in the ketones yields results that are more
consistent with those seen in the alkanes, suggesting the relative weakness of dipole−induced dipole interactions
relative to hydrogen-bonding interactions in the solvation of perylene and 1-methylperylene.
Electroreduction of Ni(II) and Co(II) has been carried out in aqueous mixtures of formamide, acetamide and urea. Electrode kinetics in terms of theories of irreversible waves have been studied. After calculating the rate constants by DELAHAY1 and Kou-TECKY2 treatments separately their variation with electrode potential has been used to calculate the product ‘ana’. The rate constants and ‘ana’ calculated from two different approaches show remarkable agreement. `ana’ records a gradual decrease with increasing amide content of the aqueous mixture.
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