Apparent Activation Energies Associated with Protein Dynamics on Hydrophobic and Hydrophilic Surfaces

AbstractWith the use of single-molecule total internal reflection fluorescence microscopy (TIRFM), the dynamics of bovine serum albumin (BSA) and human fibrinogen (Fg) at low concentrations were observed at the solid-aqueous interface as a function of temperature on hydrophobic trimethylsilane (TMS) and hydrophilic fused silica (FS) surfaces. Multiple dynamic modes and populations were observed and characterized by their surface residence times and squared-displacement distributions (surface diffusion). Characteristic desorption and diffusion rates for each population/mode were generally found to increase with temperature, and apparent activation energies were determined from Arrhenius analyses. The apparent activation energies of desorption and diffusion were typically higher on FS than on TMS surfaces, suggesting that protein desorption and mobility were hindered on hydrophilic surfaces due to favorable protein-surface and solvent-surface interactions. The diffusion of BSA on TMS appeared to be activationless for several populations, whereas diffusion on FS always exhibited an apparent activation energy. All activation energies were small in absolute terms (generally only a few kBT), suggesting that most adsorbed protein molecules are weakly bound and move and desorb readily under ambient conditions

Synthesis of Colloidal Mn2+:ZnO Quantum Dots and High-TC Ferromagnetic Nanocrystalline Thin Films

We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots and the preparation of room-temperature ferromagnetic nanocrystalline thin films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation reaction in DMSO under atmospheric conditions. Synthesis was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. Zn(OAc)2 was found to strongly inhibit oxidation of Mn2+ by O2, allowing the synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from the surfaces of as-prepared nanocrystals using dodecylamine to yield high-quality internally doped Mn2+:ZnO colloids of nearly spherical shape and uniform diameter (6.1 +/- 0.7 nm). Simulations of the highly resolved X- and Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic susceptibilities, confirmed that the manganese is substitutionally incorporated into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing from bulk Mn2+:ZnO only in the magnitude of D-strain. Robust ferromagnetism was observed in spin-coated thin films of the nanocrystals, with 300 K saturation moments as large as 1.35 Bohr magneton/Mn2+ and TC > 350 K. A distinct ferromagnetic resonance signal was observed in the EPR spectra of the ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its dependence on synthetic variables are discussed in the context of these and previous theoretical and experimental results.Comment: To be published in the Journal of the American Chemical Society Web on July 14, 2004 (http://dx.doi.org/10.1021/ja048427j

Unravelling the origins of anomalous diffusion: From molecules to migrating storks

Anomalous diffusion or, more generally, anomalous transport, with nonlinear dependence of the mean-squared displacement on the measurement time, is ubiquitous in nature. It has been observed in processes ranging from microscopic movement of molecules to macroscopic, large-scale paths of migrating birds. Using data from multiple empirical systems, spanning 12 orders of magnitude in length and 8 orders of magnitude in time, we employ a method to detect the individual underlying origins of anomalous diffusion and transport in the data. This method decomposes anomalous transport into three primary effects: long-range correlations (&ldquo;Joseph effect&rdquo;), fat-tailed probability density of increments (&ldquo;Noah effect&rdquo;), and nonstationarity (&ldquo;Moses effect&rdquo;). We show that such a decomposition of real-life data allows us to infer nontrivial behavioral predictions and to resolve open questions in the fields of single-particle tracking in living cells and movement ecology. &nbsp;</p

Re-entrant Appearance of Phases in a Relaxed Langmuir Monolayer of Tetracosanoic Acid as Determined by X-Ray Scattering

The structure of the fully relaxed phases of a Langmuir monolayer of tetracosanoic acid is determined by x‐ray diffraction and reflection along an isotherm at ∼20.5 °C. Isotherms taken by allowing the surface pressure to stabilize between incremental compressions are seen to be qualitatively different from the constant‐rate nonrelaxed isotherms typically seen in the literature. At low densities the monolayer consists of an inhomogeneous film of islands of a crystalline (or hexatic) phase with molecular tilt ordering that is analogous to that of the smectic I liquid crystal. Small amounts of impurities (∼0.5% of the monolayer) account for the change in surface pressure with area in this region. Upon compression to the point that the free space between islands becomes negligible the film appears homogeneous. On further compression the time required for full relaxation becomes long (i.e., ∼ hours), the tilt angle of the molecular axis decreases and the x‐ray unit cell is compressed. Including this homogeneous I phase the phase sequence observed by diffraction upon compression is I‐U‐I‐U, where U refers to an untilted orthorhombic phase. The outer two phases of this sequence are pure phases which form homogeneous monolayers, but the inner two are inhomogeneous phases each coexisting with an amorphous phase that does not have an observable diffraction signal. At the boundaries demarcating the I and U phases, a phase whose tilt ordering is analogous to that of a smectic F phase is seen to coexist. The preceding phase sequence is sensitive to the degree of relaxation permitted the monolayer after an incremental compression. In particular, if the monolayer is not allowed to relax completely after each compression, the untilted U phase may never appear. The U↔I transition is shown to be reversible for a relaxed monolayer.Engineering and Applied Science

Detection of evolving injury to the brachial plexus during transaxillary robotic thyroidectomy.

OBJECTIVES/HYPOTHESIS: Continuous intraoperative neuromonitoring (IONM) of transcranial electric motor evoked potentials (tceMEPs) and somatosensory evoked potentials (SSEPs) has gained universal acceptance as an efficacious method for detecting emerging positional brachial plexopathy or peripheral nerve compression during spinal and shoulder surgery. This has implications for transaxillary thyroid surgery. STUDY DESIGN: Case report with literature review. METHODS: The patient underwent robotic transaxillary thyroid surgery with continuous tceMEP and SSEP monitoring of brachial plexus function. We present detailed IONM data depicting the emergence of positional brachial plexopathy. RESULTS: Significant amplitude loss of both IONM modalities were identified during an evolving positional plexopathy, which resolved upon upper extremity repositioning and conversion to an open procedure. No permanent nerve injury or deficit was noted following surgery. CONCLUSIONS: Given the potential for brachial plexus injury during robotic transaxillary thyroid surgery secondary to arm positioning, we recommend that continuous tceMEP and SSEP monitoring be considered during such procedures

Controlling Catalyst Phase Selectivity in Complex Mixtures with Amphiphilic Janus Particles

Amphiphilic Janus particles with a catalyst selectively loaded on either the hydrophobic or hydrophilic region are promising candidates for efficient and phase-selective interfacial catalysis. Here, we report the synthesis and characterization of Janus silica particles with a hydrophilic silica domain and a silane-modified hydrophobic domain produced via a wax masking technique. Palladium nanoparticles were regioselectively deposited on the hydrophobic side, and the phase selectivity of the catalytic Janus particles was established through the kinetic studies of benzyl alcohol hydrodeoxygenation (HDO). These studies indicated that the hydrophobic moiety provided nearly 100&times; the catalytic activity as the hydrophilic side for benzyl alcohol HDO. The reactivity was linked to the anisotropic catalyst design through microscopy of the particles. The catalysts were also used to achieve phase-specific compartmentalized hydrogenation and selective in situ catalytic degradation of a model oily pollutant in a complex oil/water mixture.</p

A Dysregulated Endocannabinoid-Eicosanoid Network Supports Pathogenesis in a Mouse Model of Alzheimer's Disease

SummaryAlthough inflammation in the brain is meant as a defense mechanism against neurotoxic stimuli, increasing evidence suggests that uncontrolled, chronic, and persistent inflammation contributes to neurodegeneration. Most neurodegenerative diseases have now been associated with chronic inflammation, including Alzheimer's disease (AD). Whether anti-inflammatory approaches can be used to treat AD, however, is a major unanswered question. We recently demonstrated that monoacylglycerol lipase (MAGL) hydrolyzes endocannabinoids to generate the primary arachidonic acid pool for neuroinflammatory prostaglandins. In this study, we show that genetic inactivation of MAGL attenuates neuroinflammation and lowers amyloid β levels and plaques in an AD mouse model. We also find that pharmacological blockade of MAGL recapitulates the cytokine-lowering effects through reduced prostaglandin production, rather than enhanced endocannabinoid signaling. Our findings thus reveal a role of MAGL in modulating neuroinflammation and amyloidosis in AD etiology and put forth MAGL inhibitors as a potential next-generation strategy for combating AD

Understanding and Estimating Effective Population Size for Practical Application in Marine Species Management

Effective population size (Ne) determines the strength of genetic drift in a population and has long been recognized as an important parameter for evaluating conservation status and threats to genetic health of populations. Specifically, an estimate of Ne is crucial to management because it integrates genetic effects with the life history of the species, allowing for predictions of a population’s current and future viability. Nevertheless, compared with ecological and demographic parameters, Ne has had limited influence on species management, beyond its application in very small populations. Recent developments have substantially improved Ne estimation; however, some obstacles remain for the practical application of Ne estimates. For example, the need to define the spatial and temporal scale of measurement makes the concept complex and sometimes difficult to interpret. We reviewed approaches to estimation of Ne over both long-term and contemporary time frames, clarifying their interpretations with respect to local populations and the global metapopulation. We describe multiple experimental factors affecting robustness of contemporary Ne estimates and suggest that different sampling designs can be combined to compare largely independent measures of Ne for improved confidence in the result. Large populations with moderate gene flow pose the greatest challenges to robust estimation of contemporary Ne and require careful consideration of sampling and analysis to minimize estimator bias. We emphasize the practical utility of estimating Ne by highlighting its relevance to the adaptive potential of a population and describing applications in management of marine populations, where the focus is not always on critically endangered populations. Two cases discussed include the mechanisms generating Ne estimates many orders of magnitude lower than census N in harvested marine fishes and the predicted reduction in Ne from hatchery-based population supplementation