Microscopic Characterization of GRP1 PH Domain Interaction with Anionic Membranes

The pleckstrin homology (PH) domain of general receptor for phosphoionositides 1 (GRP1-PHD) binds specifically to phosphatidylinositol (3,4,5)-triphosphate (PIP₃), and acts as a second messenger. Using an extensive array of molecular dynamics (MD) simulations employing highly mobile membrane mimetic (HMMM) model as well as complementary full membrane simulations, we capture differentiable binding and dynamics of GRP1-PHD in the presence of membranes containing PC, PS, and PIP₃ lipids in varying compositions. While GRP1-PHD forms only transient interactions with pure PC membranes, incorporation of anionic lipids resulted in stable membrane-bound configurations. We report the first observation of two distinct PIP₃ binding modes on GRP1-PHD, involving PIP₃ interactions at a “canonical” and at an “alternate” site, suggesting the possibility of simultaneous binding of multiple anionic lipids. The full membrane simulations confirmed the stability of the membrane bound pose of GRP1-PHD as captured from our HMMM membrane binding simulations. By performing additional steered membrane unbinding simulations and calculating nonequilibrium work associated with the process, as well as metadynamics simulations, on the protein bound to full membranes, allowing for more quantitative examination of the binding strength of the GRP1-PHD to the membrane, we demonstrate that along with the bound PIP₃, surrounding anionic PS lipids increase the energetic cost of unbinding of GRP1-PHD from the canonical mode, causing them to dissociate more slowly than the alternate mode. Our results demonstrate that concurrent binding of multiple anionic lipids by GRP1-PHD contributes to its membrane affinity, which in turn control its signaling activity. © 2019 Wiley Periodicals, Inc.     

MEMS-Based Nanomechanics: Influence of MEMS Design on Test Temperature

Microelectromechanical system (MEMS) devices based on electro-thermal actuation have been used over the past few years to perform tensile tests on nanomaterials. However, previous MEMS designs only allowed small (e.g., <100 nm) total displacement range without a significant increase in temperature near the nanospecimens (<20°C), thereby limiting the design of the load sensor or the range of nanomaterials to test. Here we characterize the thermo-mechanical behavior of three MEMS devices, using optical displacement measurements, micro-Raman temperature measurements, and finite element modeling. We observe the increase in temperature near the nanospecimen gap per displacement of thermal actuator to linearly decrease with the distance between nanospecimen gap and thermal actuator. We also present a MEMS device that can provide up to 1.6 μm of total displacement with less than 10°C increase in temperature near the nanospecimens, more than one order of magnitude improvement with respect to previously published MEMS material testing setups. This MEMS device can be used for accurate, temperature-controlled tensile testing of nanocrystalline metallic nanobeams.     

Study on groundwater quality in parts of Rajasthan with special reference to uranium contamination

Journal of Radioanalytical and Nuclear Chemistry - Herein, a practical and simple reduction method was used to prepared the nanoscale composites of hydroxyapatite (HAP) coated with zero valent iron...     

Energy transfer from acraflavine to rhodamine B in methanol and glycerol:water solution

Excitation energy transfer from acraflavine to rhodamine B in methanol at 300 K is found to be through the mechanism of exciton migration even though the acceptor concentration is about 10 times the donor concentration. The transfer is more efficient at 230 K. In glycerol: water solvent at 300 K the energy migration has been found to persist even upto the acceptor concentration about 50 times the donor concentration. Our results agree with those of Bojarski [2] in as much as the energy migration has been observed even though the acceptor concentration is greater than the donor concentration, but differ in the sense that the migration does not cease at the acceptor concentration 3 times the donor as observed by Bojarski. These effects have been attributed to facilitation of the exciton migration as in glassy media reported by us previously [14,15]. By a quantitative analysis of acceptor emission, we have concluded that the quantum efficiency of transfer is unity. Part of the acraflavine band has been found to transfer radiatively also.     

Cathodo-luminescence spectra of alkali halides

Cathodo-luminescence spectra of fourteen alkali halides and of some mixed crystals of NaCl and KCl have been studied. The spectra show broad structureless bands. In some ten halides it is possible to find a strong band whose peak position shifts towards longer wavelengths as the inter-atomic distance increases. For pottasium halides the relationship λ_max=1380d, where “d” is the inter-atomic distance, holds approximately but is not generally true. A mechanism of cathodo-luminescence in alkali halides has been postulated, and an interpretation of the above band and of some NaCl bands has been made on that basis.     

Structural,Electronic and NLO Properties of 6-aminoquinoline: A DFT/TD-DFT Study

Journal of Fluorescence - A computational study based on the DFT/TD-DFT approach was performed to explore various properties of 6-aminoquinoline (6AQ). The geometrical parameters, molecular...     

An x-ray biplanar photodiode and the x-ray emission from magnetically confined laser produced plasma

Development of a single and multichannel biplanar vacuum photodiode for x-ray detection is reported, which has been used to study the x-ray emission from laser produced plasma expanding across an externally applied magnetic field. Two to three times enhancement in x-ray emission has been observed which was found correlated with decrease in size of the x-ray emitting plasma plume (expansion velocity of plasma). Experimental observations were found in close agreement with the analytical model based on an increase in plasma density as a result of plasma confinement in magnetic field. Temporal evolution of x-ray emission indicates that recombination radiation seems to be playing an important role in x-ray enhancement.     

Volume effect of laser produced plasma on X-ray emissions

An investigation of x-ray emission from Cu plasma produced by 1.054 μm Nd:glass laser pulses of 5 ns duration, at 2 × 10¹² − 2 × 10¹³ W cm⁻² is reported. The x-ray emission has been studied as a function of target position with respect to the laser beam focus position. It has been observed that x-ray emissions from ns duration plasma show a volume effect similar to subnanosecond plasmas. Due to this effect the x-ray yield increases when target is moved away relative to the best focal plane of the laser beam. This result supports the theoretical model of Tallents and has also been testified independently using suitably modified theoretical model for our experimental conditions. While above result is in good agreement with similar experimental results obtained for sub-nanosecond laser produced plasmas, it differs from result claiming filamentation rather than pure geometrical effect leading to x-ray enhancement for ns plasmas.