A low molecular weight hydrogel with unusual gel aging

We describe a dipeptide hydrogel with unusual aging characteristics. Over time, a transformation from a turbid gel to a transparent gel occurs which is initiated from the air–water interface. Here, we investigate this transition and discuss the implications of this aging on the bulk properties of the gel

Relay I trapped radiation measurements

Radiation measurements of geomagnetically trapped electrons by instruments on Relay I satellite in 196

Photoresponsive gelators

Low molecular weight gels can be responsive to a range of external stimuli. The use of light as an external stimulus to modify gels is of particular interest for a number of reasons. Light is a non-invasive trigger. For example, using light it is possible to spatially target a specific area of the gel leading to patterned gel surfaces. Here, we review the different approaches that have been used to form low molecular weight gels that respond to ligh

Controlling the assembly and properties of low-molecular-weight hydrogelators

Low-molecular-weight gels are formed by the self-assembly of small molecules into fibrous networks that can immobilize a significant amount of solvent. Here, we focus on our work with a specific class of gelator, the functionalized dipeptide. We discuss the current state of the art in the area, focusing on how these materials can be controlled. We also highlight interesting and unusual observations and unanswered questions in the field

Probing the self-assembled structures and pKa of hydrogels using electrochemical methods

The surface chemistry of the aggregated structures that form the scaffold in self-assembled hydrogels - their charge, hydrophobicity and ion-binding dynamics - play an important role in determining the gel properties and the gel’s suitability for specific applications. However, there are limited methods available for the study of this surface chemistry. Here, we show that electrochemical techniques can be used to measure the surface chemical properties of the self-assembled aggregates structures and also to determine the pKa of the gelators. We also provide a method to quickly determine whether a functionalised-dipeptide will form either a gel or not. This method has scope for use in use in high-throughput screening and further complex pH-triggered self-assembled gelation systems

Dynamic Spin-Polarized Resonant Tunneling in Magnetic Tunnel Junctions

Precisely engineered tunnel junctions exhibit a long sought effect that occurs when the energy of the electron is comparable to the potential energy of the tunneling barrier. The resistance of metal-insulator-metal tunnel junctions oscillates with an applied voltage when electrons that tunnel directly into the barrier's conduction band interfere upon reflection at the classical turning points: the insulator-metal interface, and the dynamic point where the incident electron energy equals the potential barrier inside the insulator. A model of tunneling between free electron bands using the exact solution of the Schroedinger equation for a trapezoidal tunnel barrier qualitatively agrees with experiment.Comment: 4pgs, 3 fig

Drug-Phospholipid Complex-loaded Matrix Film Formulation for the Enhanced Transdermal Delivery of Quercetin

A novel quercetin-phospholipid-complex(QPLC)-loaded matrix film for improved transdermal delivery of quercetin was developed. The QPLC formulation, prepared using a solvent-evaporation method, was optimized using a central-composite design. The optimized QPLC formulation was characterized by particle size and zeta potential analysis, thermal analysis, Fourier transform infrared spectroscopy (FTIR), and proton nuclear magnetic resonance spectroscopy (1H-NMR). QPLC formulation was functionally evaluated for solubility and in vitro dissolution of quercetin. Matrix films of pure quercetin (Q-MF)or QPLC QPLC-MF) were prepared using a solvent casting method. The prepared Q-MF and QPLC-MF were characterized for weight uniformity, folding endurance, moisture content, and moisture uptake. The films were also functionally characterized for in vitro diffusion of quercetin through a dialysis membrane and ex vivo permeability of quercetin across rat skin. Finally, the anti-inflammatory activity of the films was evaluated on carrageenan-induced paw edema in Wistar albino rats. The experimental design identified the optimal formulation and process variables for the preparation of QPLC. The validation of the obtained model using these values confirmed the suitability and robustness of the model. The physical-chemical characterization of the prepared QPLC supported the formation of a stable complex. The solubility analysis of QPLC showed a 22-fold increase in quercetin aqueous solubility, compared to pure quercetin. The dissolution results exhibited a significantly higher rate and extent of quercetin dissolution from QPLC compared to that of pure quercetin. The permeability of quercetin from Q-MF and QPLC-MF across rat skin mirrored those obtained from the dissolution studies. Topical application of QPLC-MF exhibited a significant (p\u3c0.05) inhibition of carrageenan-induced paw edema in rats compared to that of Q-MF. This study provides a promising combination approach, i.e., phospholipid-based complexation and transdermal film formulation for improved transdermal delivery of quercetin and similar pharmacologically active phytoconstituents

The Advantage of Increased Resolution in the Study of Quasar Absorption Systems

We compare a new R = 120,000 spectrum of PG1634+706 (z_QSO = 1.337,m_V = 14.9) obtained with the HDS instrument on Subaru to a R = 45, 000 spectrum obtained previously with HIRES/Keck. In the strong MgII system at z = 0.9902 and the multiple cloud, weak MgII system at z = 1.0414, we find that at the higher resolution, additional components are resolved in a blended profile. We find that two single-cloud weak MgII absorbers were already resolved at R = 45,000, to have b = 2 - 4 km/s. The narrowest line that we measure in the R = 120, 000 spectrum is a component of the Galactic NaI absorption, with b = 0.90+/-0.20 km/s. We discuss expectations of similarly narrow lines in various applications, including studies of DLAs, the MgI phases of strong MgII absorbers, and high velocity clouds. By applying Voigt profile fitting to synthetic lines, we compare the consistency with which line profile parameters can be accurately recovered at R = 45,000 and R = 120,000. We estimate the improvement gained from superhigh resolution in resolving narrowly separated velocity components in absorption profiles. We also explore the influence of isotope line shifts and hyperfine splitting in measurements of line profile parameters, and the spectral resolution needed to identify these effects. Super high resolution spectra of quasars, which will be routinely possible with 20-meter class telescopes, will lead to greater sensitivity for absorption line surveys, and to determination of more accurate physical conditions for cold phases of gas in various environments.Comment: To appear in AJ. Paper with better resolution images available at http://www.astro.psu.edu/users/anand/superhigh.AJ.pd