Collective behavior of stabilized reaction-diffusion waves

Stabilized wave segments in the photosensitive Belousov-Zhabotinsky reaction are directionally controlled with intensity gradients in the applied illumination. The constant-velocity waves behave like self-propelled particles, and multiple waves interact via an applied interaction potential. Alignment arises from the intrinsic properties of the interacting waves, leading to processional and rotational behavior.     

Nonlinear prediction,filtering, and control of chemical systems from time series

Prediction, filtering and control of nonlinear systems is formulated in terms of corresponding nonlinear surfaces in the phase space of delayed system readings and control parameters. The construction of these surfaces from time series and their use is demonstrated with a simple chemical model in the chaotic regime. (c) 1997 American Institute of Physics.     

Quantitative lid dynamics of MDM2 reveals differential ligand binding modes of the p53-binding cleft

The oncoprotein MDM2 regulates the activity and stability of the tumor suppressor p53 through protein-protein interaction involving their N-terminal domains. The N-terminal lid of MDM2 has been implicated in p53 regulation; however, due to its flexible nature, limited data are available concerning its role in ligand binding. The quantitative dynamics study using NMR reported here shows, for the first time, that the lid in apo-MDM2 slowly interconverts between a "closed" state that is associated with the p53-binding cleft and an "open" state that is highly flexible. Our results reveal that apo-MDM2 predominantly populates the closed state, whereas the p53-bound MDM2 exclusively populates the open state. Unlike p53 binding, the small molecule MDM2 antagonist nutlin-3 binds to the cleft essentially without perturbing the closed lid state. The lid dynamics thereby represents a signature for the experimental and virtual screening of therapeutic antagonists that target the p53-MDM2 interaction.     

Protein Conformational Flexibility from Structure‐Free Analysis of NMR Dipolar Couplings: Quantitative and Absolute Determination of Backbone Motion in Ubiquitin

A robust procedure for the determination of protein‐backbone motions on time scales of pico‐ to milliseconds directly from residual dipolar couplings has been developed that requires no additional scaling relative to external references. The results for ubiquitin (blue in graph: experimental N? HN order parameters) correspond closely to the amplitude, nature, and distribution of motion found in a 400 ns molecular‐dynamics trajectory of ubiquitin (red).

     

Synthesis of the enantiomers of the dual function 2‐nitroimidazole radiation sensitizer RB 6145

Short, efficient pathways are described for the synthesis of racemic 2‐nitroimidazole radiation sensitizer RB‐6145 ( 2a ) and each of its corresponding (R)‐ and (S)‐enantiomers ( 2b and 2c , respectively). The synthesis of each enantiomer commences with the appropriate chiral epichlorohydrin and utilizes a novel application of 3‐trimethylsilyl‐2‐oxazolidinone ( 3b ) as a mild, safe surrogate for highly toxic aziridine. The synthesis of the (R)‐enantiomer ( 2b ) has been successfully scaled up to provide multi‐kilo quantities of material for early stage preclinical evaluation.     

Spatiotemporal dynamics of networks of excitable nodes

A network of excitable nodes based on the photosensitive Belousov-Zhabotinsky reaction is studied in experiments and simulations. The addressable medium allows both local and nonlocal links between the nodes. The initial spread of excitation across the network as well as the asymptotic oscillatory behavior are described. Synchronization of the spatiotemporal dynamics occurs by entrainment to high-frequency network pacemakers formed by excitation loops. Analysis of the asymptotic behavior reveals that the dynamics of the network is governed by a subnetwork selected during the initial transient period.     

Time-resolved IR detection and study of an iminooxirane intermediate

[reaction: see text] Iminooxirane 4 has been generated by the reaction of phenylchlorocarbene (2) with phenyl isocyanate (3) and studied by nanosecond time-resolved infrared spectroscopy. Iminooxirane 4 (1830 cm(-1)) isomerizes to alpha-lactam 5 (1880 cm(-1)) at an observed rate of 3 x 10(4) s(-1). Peak assignments were confirmed by a combination of B3LYP calculations and isotopic labeling. An acyclic transition state was found computationally for the isomerization reaction.     

Identification of a vibrational frequency corresponding to H-atom translocation in hypericin

Using time-resolved infrared spectroscopy, ab initio quantum mechanical calculations and synthetic organic chemistry a region in the infrared spectrum of triplet hypericin has been found between 1400 and 1500 cm-1 corresponding to the translocation of the hydrogen atom between the enol and the keto oxygens, O...H...O. This result is discussed in the context of the photophysics of hypericin and of eventual measurements to observe directly the excited-state H-atom transfer.