Deep Ultraviolet Optical Anisotropy of ß-Gallium Oxide Thin Films.

ß-Crystalline phase gallium oxide (ß-Ga2O3) is an ultrawide bandgap material with prospective applications in electronics and deep ultraviolet (DUV) optoelectronics and optics. The monoclinic crystal structure of ß-Ga2O3 results in optical anisotropy to incident light with different polarization states. This attribute can lead to different optical applications in the DUV. In this article, we investigated the optical properties of ß-Ga2O3 thin films grown by pulsed laser deposition technique on sapphire substrates with different crystallographic orientations. Marked in-plane polarization anisotropy, determined by reflectance and Raman spectroscopy, was observed for ß-Ga2O3 films deposited on an r-cut sapphire substrate. In contrast, isotropic optical properties were observed in ß-Ga2O3 films deposited on a c-cut sapphire substrate.

Role of Sporopollenin Shell Interfacial Properties in Protein Adsorption.

Sporopollenin shells isolated from natural pollen grains have received attention in translational and applied research in diverse fields of drug delivery, vaccine delivery, and wastewater remediation. However, little is known about the sporopollenin shell's potential as an adsorbent. Herein, we have isolated sporopollenin shells from four structurally diverse pollen species, black walnut, marsh elder, mugwort, and silver birch, to study protein adsorption onto sporopollenin shells. We investigated three major interfacial properties, surface area, surface functional groups, and surface charge, to elucidate the mechanism of protein adsorption onto sporopollenin shells. We showed that sporopollenin shells have a moderate specific surface area (<12 m2/g). Phosphoric acid and potassium hydroxide treatments that were used to isolate sporopollenin shells from natural pollen grains also result in the functionalization of sporopollenin shell surfaces with ionizable groups of carboxylic acid and carboxylate salt. As a result, sporopollenin shells exhibit a negative ζ potential in the range of -75 to -82 mV at pH 10 when dispersed in water. The ζ potentials of sporopollenin shells remain negative in the pH range of 2.5-11, with the absolute value of ζ potential showing a decrease with the decrease in pH. The negative surface charge promotes the adsorption of protein onto the sporopollenin shell via electrostatic interaction. Despite having a moderate surface area, sporopollenin shells adsorb a significant amount of lysozyme (145-340 µg lysozyme per mg of sporopollenin shells). Lysozyme adsorption onto sporopollenin shells alters the surface, and the surface charge becomes positive at acidic pH. Overall, this study demonstrates the potential of sporopollenin shells to adsorb proteins, highlights the critical role of sporopollenin shell's interfacial properties in protein adsorption, and identifies the mechanism of protein adsorption on sporopollenin shells.

Pseudoboehmite as a drug delivery system for acyclovir.

Herpes simplex virus is among the most prevalent sexually transmitted infections. Acyclovir is a potent, selective inhibitor of herpes viruses and it is indicated for the treatment and management of recurrent cold sores on the lips and face, genital herpes, among other diseases. The problem of the oral bioavailability of acyclovir is limited because of the low permeability across the gastrointestinal membrane. The use of nanoparticles of pseudoboehmite as a drug delivery system in vitro assays is a promising approach to further the permeability of acyclovir release. Here we report the synthesis of high purity pseudoboehmite from aluminium nitrate and ammonium hydroxide containing nanoparticles, using the sol-gel method, as a drug delivery system to improve the systemic bioavailability of acyclovir. The presence of pseudoboehmite nanoparticles were verified by infrared spectroscopy, transmission electron microscopy, and X-ray diffraction techniques. In vivo tests were performed with Wistar rats to compare the release of acyclovir, with and without the addition of pseudoboehmite. The administration of acyclovir with the addition of pseudoboehmite increased the drug content by 4.6 times in the plasma of Wistar rats after 4 h administration. We determined that the toxicity of pseudoboehmite is low up to 10 mg/mL, in gel and the dried pseudoboehmite nanoparticles.

Tailoring Thermal Transport Properties by Inducing Surface Oxidation Reactions in Bulk Metal Composites.

Surface modification is used to dramatically alter the thermal properties of a bulk metallic material. Thermal barrier coatings (TBCs) are typically applied using spray deposition or laser-based techniques to create a ceramic coating on a metal substrate. In this study, an effective TBC is created directly on a metallic substrate by inducing surface chemical reactions. Aluminum-zirconium (Al-Zr) substrates are used to induce surface-limited reactions that produce a 75-80% decrease in bulk thermal conductivity and diffusivity, respectively. The substrates are cylindrical disks 12.6 mm diameter and 2 mm thickness. Thermal properties are measured using laser flash analysis (LFA) at incrementally elevated temperatures. Focused ion beam (FIB) slicing of the substrate coupled with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) show that the substrate oxidized only along the outer 20 µm of the bulk surface. The layer thickness is significantly less than typical TBCs that can range from 50 to 300 µm yet the 20 µm coating still achieves a dramatic reduction in thermal transport properties. Additionally, thermal analysis reveals a sequence of exothermic reactions starting at 439 °C that include both intermetallic (i.e., ZrAl3) and oxidation (i.e., Al2O3 and ZrO) reactions suggesting continuous surface bonding at the coating-metal interface. The onset of exothermic activity coincides with the transition in thermal properties measured using LFA. These results show that surface oxidation reactions could be used to dramatically alter the thermal transport properties of a metal substrate.

Designing CdS-Based Ternary Heterostructures Consisting of Co-Metal and CoOx Cocatalysts for Photocatalytic H2 Evolution under Visible Light.

Heterostructure formation is an effective method used for designing photocatalysts that solve problems caused by photoexcited charge recombination phenomena associated with the photocatalytic water redox reaction. This work reports a new Co-metal-incorporated ternary heterostructured photocatalyst, CdS/CoOx/Co-metal, which enhanced charge separation to increase photocatalytic H2 evolution 30.5-fold in comparison to pure CdS under visible light. This work demonstrates for the first time the effect of the Co metal on photocatalytic H2 evolution using the CdS/CoOx/Co-metal ternary heterostructure. In the ternary heterostructure, Co metal and CoOx act as photogenerated electron- and hole-capturing cocatalysts, respectively. Results from photoelectrochemical studies along with photocatalytic H2 evolution data proved the enhancement of charge transfer and separation in the CdS/CoOx/Co-metal heterostructure due to the addition of Co metal and CoOx. Hence, the synergistic charge separation improvement achieved by the combination of CoOx and the Co metal with CdS produced a photocatalytic H2 evolution rate of 9.54 µmol/h, which is the highest reported H2 evolution rate for a CdS-based system under l sun solar irradiance (>420 nm) to the best of our knowledge.

Investigation of the Fate of Proteins and Hydrophilicity/Hydrophobicity of Lycopodium clavatum Spores after Organic Solvent-Base-Acid Treatment.

Microcapsules extracted from lycopodium ( Lycopodium clavatum) spores have been increasingly used as an oral therapeutic carrier. A series of sequential treatments involving acetone, KOH, and H3PO4 are used to extract a protein-free hollow microcapsule. This study focuses on two critical aspects of lycopodium spores: the fate of native proteins and the wettability of the spores after a chemical treatment. Protein-free spores are desired to prevent an allergic reaction, whereas the wettability is critical for the formulation development. Although the chemically treated lycopodium spores are generally regarded as protein free, the studies that have reported this have not gone into significant depths to understand the nature of residual nitrogen observed even in spores thought to be protein free. Wettability of spores has not received any significant attention. Accordingly, in this study, we performed a comprehensive analysis of natural spores and spores after each chemical treatment step. We show that natural lycopodium spores are hydrophobic and contain low-molecular-weight proteins (∼10 kD). Acetone treatment partially solubilizes unsaturated phospholipids from the spores. Nevertheless, the acetone-treated spores retain native proteins and are still hydrophobic. KOH treatment, however, removes a significant amount of proteins and partially hydrolyzes esters to carboxylic acid salts and results in a hydrophilic spore with a good wettability. Finally, we show that the H3PO4 treatment removes residual proteins, hydrolyzes remaining esters to carboxylic acids, and dissolves carbohydrates. H3PO4 treatment temperature controls carbohydrate dissolution, which in turn affects the hydroxyl functional groups and hydrophilicity (wettability) of the treated spores. Spores treated at 60 °C as opposed to 160 °C are amphiphilic in nature due to the abundance of hydroxyl functional groups on the surface. In conclusion, this study confirms the removal of native proteins from treated spores and sheds light on the chemical changes that the spores undergo after chemical treatment and correlates these changes to their wettability.

Highly reactive energetic films by pre-stressing nano-aluminum particles.

Energetic films were synthesized using stress altered nano-aluminum particles (nAl). The nAl powder was pre-stressed to examine how modified mechanical properties of the fuel particles influenced film reactivity. Pre-stressing conditions varied by quenching rate. Slow and rapid quenching rates induced elevated dilatational strain within the nAl particles that was measured using synchrotron X-ray diffraction (XRD). An analytical model for stress and strain in a nAl core-Al2O3 shell particle that includes creep in the shell and delamination at the core-shell boundary, was developed and used for interpretation of strain measurements. Results show rapid quenching induced 81% delamination at the particle core-shell interface also observed with Transmission Electron Microscopy (TEM). Slower quenching elevated dilatational strain without delamination. All films were prepared at approximately a 75 : 25 Al : poly(vinylidene fluoride) PVDF weight ratio and were 1 mm thick. A drop weight impact test was performed to assess ignition sensitivity and combustion. Stress altered nAl exhibited greater energy release rates and more complete combustion than untreated nAl, but reaction dynamics and kinetics proceeded in two different ways depending on the nAl quenching rate during pre-stressing.

Edge-Oriented Graphene on Carbon Nanofiber for High-Frequency Supercapacitors.

High-frequency supercapacitors are being studied with the aim to replace the bulky electrolytic capacitors for current ripple filtering and other functions used in power systems. Here, 3D edge-oriented graphene (EOG) was grown encircling carbon nanofiber (CNF) framework to form a highly conductive electrode with a large surface area. Such EOG/CNF electrodes were tested in aqueous and organic electrolytes for high-frequency supercapacitor development. For the aqueous and the organic cell, the characteristic frequency at - 45° phase angle was found to be as high as 22 and 8.5 kHz, respectively. At 120 Hz, the electrode capacitance density was 0.37 and 0.16 mF cm-2 for the two cells. In particular, the 3 V high-frequency organic cell was successfully tested as filtering capacitor used in AC/DC converter, suggesting the promising potential of this technology for compact power supply design and other applications.

Effects of Moisture-Based Grain Boundary Passivation on Cell Performance and Ionic Migration in Organic-Inorganic Halide Perovskite Solar Cells.

Because of the polycrystalline nature, grain boundaries (GBs) in hybrid perovskite thin films play critical roles in determining the charge collection efficiency of perovskite solar cells (PSCs), material stability, and in particular the ion migration, considering their relatively soft ionic bonds with low formation energy. Different GB passivation methods are being studied, and introducing PbI2-rich phase at GBs in methylammonium lead iodide (MAPbI3) has been found to be useful. In this study, combining macroscale measurements with tip-based microscopic probing that includes scanning Kelvin probe microscopy for surface potential mapping and conductive atomic force microscopy for charge transport mapping, we revealed the effects of PbI2-rich phase at GBs, which was introduced in moisture-assisted synthesis of MAPbI3 thin films. It was found that PbI2 passivation of GBs could change the surface potential and charge carrier screening and significantly retard current conduction at the GB while enhancing conduction through the grain interior. Inhibition of ion migration at GBs, as well as enhanced PSC device performance, is reported.

In-vitro degradation characteristics of poly(e-caprolactone)/poly(glycolic acid) scaffolds fabricated via solid-state cryomilling.

Poly(e-caprolactone) (PCL)/poly(glycolic acid) (PGA) scaffolds were fabricated via solid-state cryomilling along with compression molding and porogen leaching techniques. Four types of scaffolds were produced using four distinct cryomilling times. These scaffolds were evaluated for their in-vitro degradation behavior hydrolytically in phosphate buffer saline (PBS). The degradation profiles were investigated over a period of 60 days. The percentage of weight loss, percentage of water absorption, morphology, compressive, thermal, and material properties were studied as a function of degradation time. Weight loss and water absorption demonstrated a high correlation, which showed an increasing behavior with increase in cryomilling time and degradation time. Morphology of the scaffolds analyzed through scanning electron microscopy (SEM) revealed micro-cracks on the surface of the cylindrical struts due to hydrolytic attack and dissolution of hydrophilic PGA. Changes in compressive modulus and crystallinity over the degradation period and material properties were analyzed using X-ray powder diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. DSC and XRD results indicated that hydrolytic attack had taken place during degradation, resulting in moments of increased and decreased percent crystallinity. This study successfully brought forth the differences in resultant properties of the PCL/PGA scaffolds as a function of degradation time.

Investigation of characteristics of urea and butyrylcholine chloride biosensors based on ion-selective field-effect transistors modified by the incorporation of heat-treated zeolite Beta crystals.

Urea and butyrylcholine chloride (BuChCl) biosensors were prepared by adsorption of urease and butyrylcholinesterase (BuChE) on heat-treated zeolite Beta crystals, which were incorporated into membranes deposited on ion-selective field-effect transistor (ISFET) surfaces. The responses, stabilities, and use for inhibition analysis of these biosensors were investigated. Different heat treatment procedures changed the amount of Brønsted acid sites without affecting the size, morphology, overall Si/Al ratio, external specific surface area, and the amount of terminal silanol groups in zeolite crystals. Upon zeolite incorporation the enzymatic responses of biosensors towards urea and BuChCl increased up to ~2 and ~5 times, respectively; and correlated with the amount of Brønsted acid sites. All biosensors demonstrated high signal reproducibility and stability for both urease and BuChE. The inhibition characteristics of urease and BuChE were also related to the Brønsted acidity. The pore volume and pore size increases measured for the heat-treated samples are very unlikely causes for the improvements observed in biosensors' performance, because urease and BuChE are approximately one order of magnitude larger than the resulting zeolite Beta pores. Overall, these results suggest that the zeolites incorporated into the biologically active membrane with enhanced Brønsted acidity can improve the performance of ISFET-based biosensors.

Molecular modeling of chiral-modified zeolite HY employed in enantioselective separation.

Insight into enantioselective separation utilizing chiral-modified zeolite HY could be useful in designing a chiral stationary phase for resolving pharmaceutical compounds. A model was employed to better understand the enantioseparation of valinol in zeolite HY that contains (+)-(1R;2R)-hydrobenzoin as a chiral modifier. This model incorporates the zeolite support and accounts for the flexible change. Results from grand canonical Monte Carlo and molecular dynamics simulations indicate that the associated diastereomeric complex consists of a single (+)-(1R;2R)-hydrobenzoin and a single valinol molecules located in the zeolite HY supercage. Supercage-based docking simulation predicted an enantioselectivity of 2.6 compared with that of 1.4 measured experimentally. Also, the supercage-based docking simulation demonstrated a single binding motif in the S complex, and two binding motifs in the R complex. The multiple binding modes in the R complex resulted in its lower stability. This is hypothesized to be the origin of the weaker binding between (-)-(R)-valinol and the chiral modifier, and explains why (+)-(R)-valinol is retained more in the chiral-modified zeolite system studied.

Enantioseparation of phenylglycinol in chiral-modified zeolite HY: a molecular simulation study.

A mechanism has been proposed for the separation of valinol enantiomers using a chiral-modified zeolite HY (i.e., zeolite HY containing (+)-(1R;2R)-hydrobenzoin) Molecular modeling of chiral-modified zeolite HY employed in enantioselective separation. Jirapongphan SS, Warzywoda J, Budil DE, Sacco A Jr. Chirality 2007; in press, which accurately predicted the experimentally measured enantioseparation. This methodology has been applied to predict the separation of an enantiomeric pair of phenylglycinol molecules (a precursor in the synthesis of HIV-1 protease inhibitors) using the modified zeolite HY as a CSP. Phenylglycinol and valinol molecules are similar in terms of the presence of polar (i.e., amine and hydroxyl) groups. These functional groups are important in the proposed chiral discrimination. Supercage-based docking simulations yielded an enantioselectivity of 1.3 with (+)-(S)-phenylglycinol molecule better retained in the zeolite. Also, the simulations predicted two binding modes that were the same as those in the valinol system. This suggests that specific structural features (i.e., number and type of polar groups), which generate the hypothesized binding modes, are required in an enantioseparation utilizing the chiral-modified zeolite HY.