Molecular reorientation dynamics and microscopic friction in liquids

Molecular rotation reorientation times are investigated using time resolved fluorescence depolarization studies of three solutes of similar size and shape (nile red, neutral nile blue and cationic nile blue) dissolved in alcohol and alkane solvents as well as an extensive compilation of previous results for neautral and charged solutes dissolved in non-polar, polar and associated solvents. A universal correlation is foung between reorientation time, solvent viscosity, and solute volume for solutes dissolved in alkanes, while strongly interacting solutes experience relatively enhanced friction, and non-polar solutes dissolved in alcohols experience reduced friction. The results are compared and contrasted with slip and stick hydrodynamic predictions, and used to develop empirical correlations, which can be used to predict molecular reorientation times with an uncetainty on the order of a factor of two in virtually any solute-solvent system.     

First measurement of the Λ→nγ branching ratio

In an experiment performed at the CERN-SPS charged hyperon beam, we have observed the radiative decay Λ→nγ, using well identified Λ from the decays of Ο^? of 116 GeV/c momentum. Neutrons and photons from the Λ decays were observed in liquid argon and lead glass detectors. From a sample of 31 candidates, containing an estimated background of 7.3 events, the decay branching ratio was measured to be Γ(Λ→nγ)/Γ(Λ→all)=(1.02±0.33)×10^?3.     

Inclusive Pomeron-Pomeron interactions at the CERN ISR

Data are presented for the first time on inclusive Pomeron-Pomeron interactions which produce a central systemX (composed mainly of multimeson states) in proton-proton collisions at \(\sqrt s \) at the CERN ISR. The systemX has a Feynman-x distribution which is sharply peaked atx _f=0, is inconsistent with any significant contributions from Reggeon exchange processes, and has an invariant mass dependence in good agreement with the predicted formM _x ^?2 . Kaon production is about 15% of pion production, nearly independent ofM _x, while proton-antiproton production averages about 5% of pion production and increases withM _x. The structure of the central systemX develops into a jetlike shape, asM _x increases, as would be expected from a model of Pomeron fragmentation. The shape of thex _f(π) distribution in the center of mass of theX system (although not proving existence) is consistent with asoft partonic substructure of the Pomeron.     

Direct molecular detection of nucleic acids by fluorescence signal amplification

An integrated PCR-free DNA sensor, which combines a sequence-specific receptor, an optical polymeric transducer, and an intrinsic fluorescence amplification mechanism, is reported. This sensor is based on the different conformations adopted by a cationic polythiophene when electrostatically bound to ss-DNA or ds-DNA, and on the efficient and fast energy transfer between the resulting fluorescent polythiophene/ds-DNA complex and neighboring fluorophores attached to ss-DNA probes. This molecular system allows the detection of only five molecules in 3 mL of an aqueous solution, or 3 zM, in 5 min. Moreover, this work demonstrates, for the first time, the direct detection of single nucleotide polymorphisms (SNPs) from clinical samples in only a few minutes, without the need for nucleic acid amplification.     

Global thermodynamics of hydrophobic cavitation, dewetting, and hydration

Pure water experimental and simulation results are combined to predict the thermodynamics of cavity formation, spanning atomic to macroscopic length scales, over the entire ambient liquid temperature range. The resulting cavity equation of state is used to quantify dewetting excess contributions to cavity formation thermodynamics and construct a thermodynamic perturbation theory of hydrophobic hydration. Predictions are compared with large cavity simulations and experimental rare-gas hydration thermodynamics data (for He, Ne, Ar, Kr, Xe, and Rn). Key findings include the strong temperature dependence of the critical length scale for hydrophobic dewetting and the evaluation of fundamental solute-solvent interaction contributions to rare-gas hydration chemical potentials.     

Adaptive silver films for detection of antibody-antigen binding

Antibody-antigen binding events at a monolayer protein concentration have been demonstrated on nanostructured adaptive silver films (ASFs) using surface-enhanced Raman scattering (SERS) and luminescence-based assays. It is shown that proteins stabilize and restructure the ASF to increase the SERS signal while preserving antigen-binding activity. Evidence for antibody-antigen binding on the ASF substrates is the distinct SERS spectral changes of the surface-bound antibody or antigen without special tags. The activity of the surface-bound proteins and their practical application are validated by independent immunochemical assays. Results are presented to demonstrate that these surfaces can be extended to protein arrays with detection applications distinct from current SERS, fluorescence, or luminescence methods.     

Typology of secondary cyanobacterial metabolites from minimum spanning tree analysis

Recently, two main events have spurred a rapid increase in cyanobacteria chemical, toxicological, and ecological research. The first deals with the interest in isolating compounds from these organisms as source of active products with potential therapeutic applications. The second pertains the crucial problem of harmful cyanobacterial blooms in the aquatic environments.

In this context, 594 secondary metabolites belonging to more than 30 genera of cyanobacteria were retrieved from literature. In order to perform their typology, they were first associated with 87 different molecular archetypes and two orphan classes. These 89 groups of molecular structures were then confronted to minimum spanning tree analysis. Attempts were made to graphically derive chemotaxonomical relationships. The interest of QSAR models for estimating the potential pharmacological interest of the cyanobacterial secondary metabolites was also discussed.     

SOKOBAN and other motion planning problems

We consider a natural family of motion planning problems with movable obstacles and obtain hardness results for them. Some members of the family are shown to be PSPACE-complete thus improving and extending (and also simplifying) a previous NP-hardness result of Wilfong. The family considered includes a motion planning problem which forms the basis of a popular computer game called SOKOBAN. The decision problem corresponding to SOKOBAN is shown to be NP-hard. The motion planning problems considered are related to the “warehouseman's problem” considered by Hopcroft, Schwartz and Sharir, and to geometric versions of the motion planning problem on graphs considered by Papadimitriou, Raghavan, Sudan and Tamaki.