Vanadium Dioxide Nanowire Functional Devices

Vanadium dioxide (VO2) is an interesting material due to its first order metal to insulator phase transition (MIT) at a temperature of 340 K. VO2 behaves as an insulator at room temperature while becomes metallic after transition at elevated temperatures. The crystal structure of the material also changes along with the electrical properties. VO2 nanowire which is one-dimensional nanostructure of the material shows more significant physical properties change across the phase transition due to the higher crystallinity compared to thin film. Thus, VO2 nanowire is a preferred candidate for fundamental studies for the metal-insulator phase transition mechanism as well as its potential applications for nanoscale electronics devices. Here, we have studied two functional devices based on the temperature triggered phase transition properties of the as-grown VO2 nanowires. In the first functional device, we have investigated the junction behavior of a VO2 nanowire based crossbar device at various temperatures where the crossbar contains two intersecting VO2 single nanowires. In our second device, we have studied the gating effect of VO2 single nanowire via heat excitation (instead of electric field) and proposed a thermal transistor device based on the temperature dependent phase transition properties of VO2 single nanowire

Binding of Fatty Acid Amide Amphiphiles to Bovine Serum Albumin: Role of Amide Hydrogen Bonding

The study of protein–surfactant interactions is important because of the widespread use of surfactants in industry, medicine, and pharmaceutical fields. Sodium <i>N</i>-lauroylsarcosinate (SL-Sar) is a widely used surfactant in cosmetics, shampoos. In this paper, we studied the interactions of bovine serum albumin (BSA) with SL-Sar and sodium <i>N</i>-lauroylglycinate (SL-Gly) by use of a number of techniques, including fluorescence and circular dichroism spectroscopy and isothermal titration calorimetry. The binding strength of SL-Sar is stronger than that of structurally similar SL-Gly, which differs only by the absence of a methyl group in the amide nitrogen atom. Also, these two surfactants exhibit different binding patterns with the BSA protein. The role of the amide bond and hence the surfactant headgroup in the binding mechanism is discussed in this paper. It was observed that while SL-Sar destabilized, SL-Gly stabilized the protein structure, even at concentrations less than the critical micelle concentration (cmc) value. The thermodynamics of surfactant binding to BSA was studied by use of ITC. From the ITC results, it is concluded that three molecules of SL-Sar in contrast to only one molecule of SL-Gly bind to BSA in one set of binding sites at room temperature. However, on increasing temperature four molecules of SL-Gly bind to the BSA through H-bonding and van der Waals interactions, due to loosening of the BSA structure. In contrast, with SL-Sar the binding process is enthalpy driven, and very little structural change of BSA was observed at higher temperature

Thermoreversible as Well as Thermoirreversible Organogel Formation by l‑Cysteine-Based Amphiphiles with Poly(ethylene glycol) Tail

We report here the gelation behavior of two novel l-cysteine-based amphiphiles bearing a poly­(ethylene glycol) tail. The amphiphiles were found to form transparent organogels in both apolar and aprotic polar solvents at reasonably low concentrations. In chloroform, dichloromethane, and benzene solvents, the organogels are formed at room temperature without the requirement of heating–cooling cycle due to strong hydrogen-bonding interaction between gelator molecules. The swelling kinetics, however, becomes faster on heating. Unlike most organogels of low-molecular-mass gelators, these organogels do not exhibit a gel-to-sol transition on heating but instead become rigid when heated. Surprisingly, in polar solvents, the gelation required a heating–cooling cycle, and the sol-to-gel transition was found to be reversible. The gelation abilities of the amphiphiles were correlated with the hydrogen-bonding parameters of the solvents. Intermolecular H-bonding interaction was found to be the major driving force for the organogelation. The morphology of the organogels was investigated by the use of optical as well as electron microscopy and was found to be dependent on the nature of solvent. The mechanical strengths of the organogels were studied by rheological measurements

Solution Behavior and Interaction of Pepsin with Carnitine Based Cationic Surfactant: Fluorescence, Circular Dichroism, and Calorimetric Studies

The present work reports the pH-induced conformational changes of pepsin in solution at room temperature. The conformational change makes the protein surface active. The protein was found to be present in the partially denatured state at pH 8 as well as at pH 2. The fluorescence probe and circular dichroism (CD) spectra suggested that the most stable state of pepsin exists at pH 5. The binding affinities of pepsin in its native and denatured states for a d,l-carnitine-based cationic surfactant (3-hexadecylcarbamoyl-2-hydroxypropyl)­trimethylammonium chloride (C₁₆-CAR) were examined at very low concentrations of the surfactant. The thermodynamics of the binding processes were investigated by use of isothermal titration calorimetry. The results were compared with those of (3-hexadecylcarbamoylpropyl)­trimethylammonium chloride (C₁₆-PTAC), which is structurally similar to C₁₆-CAR, but without the secondary −OH functionality near the headgroup. None of the surfactants were observed to undergo binding with pepsin at pH 2, in which it exists in the acid-denatured state. However, both of the surfactants were found to spontaneously bind to the most stable state at pH 5, the partially denatured state at pH 8, and the alkaline denatured state at pH 11. Despite the difference in the headgroup structure, both of the surfactants bind to the same warfarin binding site. Interestingly, the driving force for binding of C₁₆-CAR was found to be different from that of C₁₆-PTC at pH ≥ 5. The steric interaction of the headgroup in C₁₆-CAR was observed to have a significant effect on the binding process

Electronic Noise Spectroscopy of Quasi-Two-Dimensional Antiferromagnetic Semiconductors

We investigated low-frequency current fluctuations, i.e., electronic noise, in FePS3 van der Waals layered antiferromagnetic semiconductor. The noise measurements have been used as noise spectroscopy for advanced materials characterization of the charge carrier dynamics affected by spin ordering and trapping states. Owing to the high resistivity of the material, we conducted measurements on vertical device configuration. The measured noise spectra reveal pronounced Lorentzian peaks of two different origins. One peak is observed only near the Néel temperature, and it is attributed to the corresponding magnetic phase transition. The second Lorentzian peak, visible in the entire measured temperature range, has characteristics of the trap-assisted generation–recombination processes similar to those in conventional semiconductors but shows a clear effect of the spin order reconfiguration near the Néel temperature. The obtained results contribute to understanding the electron and spin dynamics in this type of antiferromagnetic semiconductors and demonstrate the potential of electronic noise spectroscopy for advanced materials characterization

Vanillin Benzothiazole Derivative Reduces Cellular Reactive Oxygen Species and Detects Amyloid Fibrillar Aggregates in Alzheimer’s Disease Brain

The misfolding of amyloid beta (Aβ) peptides into Aβ fibrillary aggregates is a major hallmark of Alzheimer’s disease (AD), which responsible for the excess production of hydrogen peroxide (H2O2), a prominent reactive oxygen species (ROS) from the molecular oxygen (O2) by the reduction of the Aβ-Cu(I) complex. The excessive production of H2O2 causes oxidative stress and inflammation in the AD brain. Here, we have designed and developed a dual functionalized molecule VBD by using π-conjugation (CC) in the backbone structure. In the presence of H2O2, the VBD can turn into fluorescent probe VBD-1 by cleaving of the selective boronate ester group. The fluorescent probe VBD-1 can undergo intramolecular charge transfer transition (ICT) by a π-conjugative system, and as a result, its emission increases from the yellow (532 nm) to red (590 nm) region. The fluorescence intensity of VBD-1 increases by 3.5-fold upon binding with Aβ fibrillary aggregates with a high affinity (Kd = 143 ± 12 nM). Finally, the VBD reduces the cellular toxic H2O2 as proven by the CCA assay and DCFDA assay and the binding affinity of VBD-1 was confirmed by using in vitro histological staining in 8- and 18-month-old triple transgenic AD (3xTg-AD) mice brain slices

High-Affinity Fluorescent Probes for the Detection of Soluble and Insoluble Aβ Deposits in Alzheimer’s Disease

The overproduction and deposition of the amyloid-β (Aβ) aggregates are accountable for the genesis and development of the neurologic disorder Alzheimer’s disease (AD). Effective medications and detection agents for AD are still deficient. General challenges for the diagnosis of Aβ aggregates in the AD brain are (i) crossing the blood–brain barrier (BBB) and (ii) selectivity to Aβ species with (iii) emission maxima in the 500–750 nm region. Thioflavin-T (ThT) is the most used fluorescent probe for imaging Aβ fibril aggregates. However, because of the poor BBB crossing (log P = −0.14) and short emission wavelength (482 nm) after binding with Aβ fibrils, ThT can be limited to in vitro use only. Herein, we have developed Aβ deposit-recognizing fluorescent probes (ARs) with a D-π-A architecture and a longer emission wavelength after binding with Aβ species. Among the newly designed probes, AR-14 showed an admirable fluorescence emission (>600 nm) change after binding with soluble Aβ oligomers (2.3-fold) and insoluble Aβ fibril aggregates (4.5-fold) with high affinities Kd = 24.25 ± 4.10 nM; Ka = (4.123 ± 0.69) × 107 M–1 for fibrils; Kd = 32.58 ± 4.89 nM; and Ka = (3.069 ± 0.46) × 107 M–1 for oligomers with high quantum yield, molecular weight of <500 Da, reasonable log P = 1.77, stability in serum, and nontoxicity, and it can cross the BBB efficiently. The binding affinity of AR-14 toward Aβ species is proved by fluorescence binding studies and fluorescent staining of 18-month-old triple-transgenic (3xTg) mouse brain sections. In summary, the fluorescent probe AR-14 is efficient and has an admirable quality for the detection of soluble and insoluble Aβ deposits in vitro and in vivo