B(E2) values in 150Nd and the critical point symmetry X(5).

Lifetimes of states in 150Nd were measured using the recoil distance method following Coulomb excitation of 150Nd by a 132 MeV 32S beam. The experiment was performed at the Yale Tandem accelerator, employing the SPEEDY gamma-ray detector array and the New Yale Plunger Device. Reduced transition probabilities in 150Nd are compared to the predictions of the critical point symmetry X(5) of the phase/shape transition that occurs for the N = 90 rare earth isotones. Very good agreement was observed between the parameter-free (apart from scale) X(5) predictions and the low-spin level scheme of 150Nd, revealing this as the best case thus far for the realization of the X(5) symmetry.

Dynamics of biomolecules: assignment of local motions by fluorescence anisotropy decay.

Many biological systems have multiple fluorophores that experience multiple depolarizing motions, requiring multiple lifetimes and correlation times to define the fluorescence intensity and anisotropy decays, respectively. To simplify analyses, an assumption often made is that all fluorophores experience all depolarizing motions. However, this assumption usually is invalid, because each lifetime is not necessarily associated with each correlation time. To help establish the correct associations and recover accurate kinetic parameters, a general kinetic scheme that can examine all possible associations is presented. Using synthetic data sets, the ability of the scheme to discriminate among all nine association models possible for two lifetimes and two correlation times has been evaluated. Correct determination of the association model, and accurate recovery of the decay parameters, required the global analysis of related data sets. This general kinetic scheme was then used for global analyses of liver alcohol dehydrogenase anisotropy data sets. The results indicate that only one of the two tryptophan residues in each subunit is depolarized by process(es) independent of the enzyme's rotations. By applying the proper kinetic scheme and appropriate analysis procedures to time-resolved fluorescence anisotropy data, it is therefore possible to examine the dynamics of specific portions of a macromolecule in solution.