Anju Gupta

Bilayer disruption and liposome restructuring by a homologous series of small Arg-rich synthetic peptides

The effects of a series of low molecular weight water-soluble cationic linear peptide analogs (LPAs, <1000 MW) with increasing hydrophobic/hydrophilic balance on lipid bilayer phase behavior and permeability were examined using liposomes composed of zwitterionic dipalmitoylphosphatidylcholine (DPPC) and mixed zwitterionic/anionic DPPC/dipalmitoylphosphatidylglycerol (DPPG) lipid bilayers. LPAs were synthesized using a previously reported alkyl linkage strategy as Arg-C(n)-Arg-C(n)-Lys, where C(n) represents the saturated alkyl linkage separating the cationic residues (n=4, 7, or 11) (Ye et al., 2007 [1]). Differential scanning calorimetry results show that the cationic LPAs bound to and disrupted DPPC and, to a greater extent, DPPC/DPPG phase behavior. When added to preformed unilamellar liposomes, the LPAs led to significant structural changes based on cryogenic transmission electron microscopy (cryo-TEM). Coupling cryo-TEM with carboxyfluorescein leakage studies indicate that the LPAs induced permeabilization through bilayer expansion, which caused membrane thinning. The effects were inconsistent with increasing LPA hydrophobicity, which suggests that a cooperative effect between electrostatic binding and hydrophobic insertion determined the location of LPAs within the bilayer and their membrane activity. Our results for LPA-induced membrane disruption correlate with previous breast cancer cell uptake studies that showed minimal LPA-C(4) uptake, but high LPA-C(11) uptake through a non-endocytic mechanism.

Pool Boiling Enhancement through Graphene and Graphene Oxide Coatings

ABSTRACT Boiling has served as an effective means to dissipate large quantities of heat over small areas. Graphene, a two-dimensional material, has garnered significant attention of researchers due to its excellent thermal properties. In this study, copper test chips are dip coated with a solution consisting of graphene oxide and graphene and its pool boiling performance with distilled water at atmospheric pressure was investigated. The surfaces were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy which confirmed the presence of graphene and graphene oxide. The contact angles measured on the coated surfaces indicated hydrophobic wetting behavior. Four heat transfer surfaces were prepared with dip coating durations of 120 s, 300 s, 600 s, and 1200 s, respectively. A Critical Heat Flux (CHF) of 182 W/cm2 and a heat transfer coefficient (HTC) of 96 kW/m2°C was obtained with the shortest coating duration which translated to an enhancement of 42% in CHF and 47% in HTC when compared to a plain uncoated surface under similar conditions. Contact angle changes were not seen to be responsible, although roughness was seen as an influencing factor contributing to the enhancement. Further studies are needed to explain the enhancement mechanism.

Phase and sedimentation behavior of oil (octane) dispersions in the presence of model mineral aggregates

Adsorption of suspended particles to the interface of surfactant-dispersed oil droplets can alter emulsion phase and sedimentation behavior. This work examines the effects of model mineral aggregates (silica nanoparticle aggregates or SNAs) on the behavior of oil (octane)-water emulsions prepared using sodium bis(2-ethylhexyl) sulfosuccinate (DOSS). Experiments were conducted at different SNA hydrophobicities in deionized and synthetic seawater (SSW), and at 0.5mM and 2.5mM DOSS. SNAs were characterized by thermogravimetric analysis (TGA) and dynamic light scattering (DLS), and the emulsions were examined by optical and cryogenic scanning electron microscopy. In deionized water, oil-in-water emulsions were formed with DOSS and the SNAs did not adhere to the droplets or alter emulsion behavior. In SSW, water-in-oil emulsions were formed with DOSS and SNA-DOSS binding through cation bridging led to phase inversion to oil-in-water emulsions. Droplet oil-mineral aggregates (OMAs) were observed for hydrophilic SNAs, while hydrophobic SNAs yielded quickly sedimenting agglomerated OMAs.

Nanoparticles in the Environment: Occurrence, Distribution, and Risks

AbstractRapid advances in nanotechnology in recent years have raised concern about the occurrence, distribution, fate, and transport of nanoparticles in the environment. Sources of nanoparticles in the environment include their widespread use in a variety of engineering operations, biomedical applications, consumer goods, food and drug delivery system, and so forth. Because they can be released into the environment either as a waste product or as a byproduct of some engineered processes or applications, nanoparticles or nanoscale materials are increasingly detected in various environmental matrices. By their very nature, nanoparticles are active at molecular levels, and there is a concern that their occurrence in the environment and unintended exposure may pose an adverse risk to human health and ecology. Because of the nature of recent nanotechnology-based applications, our understanding of nanoparticle behavior in the environment is limited. The objective of this literature review is to provide a measur...

A Multiscale Morphological Insight into Graphene Based Coatings for Pool Boiling Applications

ABSTRACT The application of graphene for pool boiling is an attractive option to facilitate compaction and promote efficient heat removal from high power density devices. In this context, chemical characterization of the depositions achieved through commonly employed coating techniques are an important topic of discussion. A detailed structure-property relationship between the morphologies obtained on the mono and multilayered graphene coatings and their corresponding pool boiling performance quantified by the experimental critical heat fluxes is presented. Three different types of graphene (G) and graphene oxide (GO) substrates are characterized: (i) nanoscale: mono and multilayer samples developed through chemical vapor deposition, (ii) Rochester Institute of Technology (RIT)-G/GO colloid generated through an oxygen embrittlement electrochemical process, and (iii) commercially available chemical vapor deposited (CVD)-G/GO colloid. The morphological features were characterized with scanning electron microscope while X-Ray Diffractometer analysis and Raman spectroscopy were used to examine the ordering and stacking of the sheets that result in the unique structural features. Fourier transform infrared and energy dispersive X-ray spectroscopy were employed to identify the overall compositional characteristics of the coated surfaces. The wettability changes and additional nucleation sites for nanoscale coatings, and multiscale roughness features and ridge microstructures for microscale coatings were identified as enhancement mechanisms.