Advances in Molecular Relaxation and Interaction Processes最新文献

A new method (justified by permittivity measurement) is proposed to study dielectric relaxation by means of the interface air-dielectric response.

The characterization established here for a single relaxation (the distribution of relaxation times is represented by a Dirac function) can be used when a generalization is wanted for more complex cases (symmetric or asymmetric distribution function of relaxation times).

Application of this method to a series of mono-substituted benzenes is shown in this paper.

A Raman investigation of pentaziridinocyclodiphosphathiazene -DNA interactions in vitro suggests that the alkylating sites on DNA for this powerful antitumour agent are essentially the oxygen atoms of the ribose backbone with a second order dialkylating effect on the N(7) and $\text{N}$H₂ positions of Adenine. These contrasts with the case of hexaziridinocyclotriphosphazene which interacts with the DNA by the same two routes but through a balanced mode.

A suitable extension of the Mori theory to deal with non-hermitian hamiltonians leads to a rigorous justification of models of “reduced” kind for radiationless decay phenomena. By using the model of an excited state sequentially coupled to two dissipative quasicontinua it is shown that the generalized theory leads to a reduced model consisting of only two “virtual” states. The standard Mori approach, on the contrary, would result in a chain of more than two states (probably an infinite number of states). It is shown, furthermore, that the biexponential decay behaviour can rigorously be justified in two different ways. The first model only consisists ofcouplings of intramolecular type. The second model also involves an external thermal bath. The generalized Mori theory, when applied to the second model leads to a non phenomenological justification for the kinetic scheme. It is shown, furthermore, that excitations by strong radiation fields result in a different decay behaviour according to whether the former or the latter scheme is applied.

The association equilibrium of three 10-N-alkyl derivatives of acridine orange in aqueous solution has been studied spectrophotometrically. The ΔF_D, ΔH_D, and ΔS_D of dimerization have been computed through the experimental light absorption spectra.

The results are in favour of the assumption that hydrophobic interactions play a relevant role on the dye stacking in aqueous solution.

Carbon-13 spin-lattice relaxation times and nuclear Overhauser enhancement factors are reported for neat toluene and octafluorotoluene at 301 K. A thorough analysis of the experimental data shows the overall reorientation of these molecules to be that of an axially symmetric ellipsoid, with diffusion coefficients D_⊥ = 6.45 and

A stopped flow study of the kinetics of association of nickel malonate in water-urea has been made. A commercial stopped flow-T-jump instrument was modified for this purpose. Up until 3M urea the rate constants for association depend only upon the solvent dielectric constants. Above 3M, urea enters the first coordinative sphere of nickel (II) and alters the rate. The effect of water activity changes is found to be negligible compared to the changes produced by the variation in dielectric constant.

The dynamics of a fluctuation model, broadly based on an earlier model of Bueche, is considered for the motion of a molecule in a glass-forming material. The molecule is assumed to occupy a number of local states in four equivalent manifolds and relaxes by motion between the local states and between manifolds. The dipole-moment correlation function, and hence the dielectric relaxation behaviour, is calculated for a range of relaxation parameters. Two general processes are found being (i) a family of ‘fast’ relaxation modes due to motion between the local states and (ii) a single ‘slow’ relaxation mode due to motion out of one manifold into adjacent manifolds. This pattern is qualitatively in accord with observations of and α processes in glass-forming systems but the observed α-processes are generally rather broader than a ‘slow’ single relaxation-time process which results from the present model.