Interpreting the conductive atomic force microscopy measured inhomogeneous nanoscale surface electrical properties of Al‐doped ZnO films

In this work, conductive atomic force microscopy is used to study the inhomogeneous surface electrical conductivity of Al‐doped ZnO thin films at a nanoscale dimension. To this end, Al‐doped ZnO films were deposited onto the soda lime glass substrates at substrate temperature (T_s) varying from 303 to 673 K in radio frequency magnetron sputtering. The obtained local surface electrical conductivity values are found to be influenced by their bulk electrical resistivity, surface topography and tip geometry. Further, the average (local) surface conductivity from the film surface is found to increase with increasing T_s from 303 to 623 K, beyond which they decrease until 673 K. Copyright © 2016 John Wiley & Sons, Ltd.     

Study of Densities, Viscosities and Ultrasonic Speeds of Binary Mixtures Containing 1,2-Dimethoxyethane and an Alkan-l-ol at 298.15 K

The viscosity deviation (Δη), the excess molar volume (V ^E) and the ultrasonic speed (u) have been investigated from viscosity (η) and density (ρ ) measurements of binary liquid mixtures of 1,2-dimethyoxyethane with methanol, ethanol, propan-1-ol, butan-1-ol, pentan-1-ol, hexan-1-ol or octan-1-ol over the entire range of composition at 298.15 K. The excess volumes are negative over the entire range of composition for all of the mixtures with the exception of hexan-1-ol and octan-1-ol. The excess isentropic compressibilities (K _S ^E) and viscosity deviations are negative for all of the mixtures. The magnitudes of the negative values of V ^E decrease with the number of carbon atoms of the alkan-1-ol. The trend of increasing K _S ^E values with the chain length of the alkanol is similar to that observed in the case of V ^E. Graphs of V ^E, Δ η, K _S ^E, Δ u, L _f ^E and Z ^E against composition are presented as a basis for a qualitative discussion of the results.     

A review on electrospun nanofibers for multiple biomedical applications

Electrospinning is a well-known technique since 1544 to fabricate nanofibers using different materials like polymers, metals oxides, proteins, and many more. In recent years, electrospinning has become the most popular technique for manufacturing nanofibers due to its ease of use and economic viability. Nanofibers have remarkable properties like high surface-to-volume ratio, variable pore size distribution (10–100 nm), high porosity, low density, and are suitable for surface functionalization. Therefore, electrospun nanofibers have been utilized for numerous applications in the pharmaceutical and biomedical field like tissue engineering, scaffolds, grafts, drug delivery, and so on. In this review article, we will be focusing on the versatility, current scenario, and future endeavors of electrospun nanofibers for various biomedical applications. This review discusses the properties of nanofibers, the background of the electrospinning technique, and its emergence in chronological order. It also covers the various types of electrospinning methods and their mechanism, further elaborating the factors affecting the properties of nanofibers, and applications in tissue engineering, drug delivery, nanofibers as biosensor, skin cancer treatment, and magnetic nanofibers.     

The stability of poly(m-carborane-siloxane) elastomers exposed to heat and gamma radiation

Poly(m-carboranyl-siloxane) elastomers containing a mixture of di-methyl- and methylphenyl-silyl units were synthesised using the ferric chloride catalysed condensation reaction between di-chloro-diorganosilane and bis(di-methylmethoxysilyl)-m-carborane. These elastomeric materials were originally developed to have greater stability to extreme thermal environments and retain tailorable physical and chemical properties relative to comparable non-carborane containing elastomers. Prepared samples were aged either by heating in air at elevated temperatures or by gamma irradiation from a ⁶⁰Co source. Multinuclear (¹H, ¹³C and ¹¹B) solid and solution state nuclear magnetic resonance (NMR) was used to assess degradation. This included measurements of segmental chain dynamics using a solid-echo pulse sequence reflecting changes in crosslink density and assessing changes to the carborane fragment by ¹¹B and ¹H Magic Angle Spinning (MAS) methods. Thermogravimetric measurements were also performed to assess thermal stability. Gamma radiation (to a dose of 1 MGy) was found to induce only a small degree of elastomer hardening as evidenced by a reduction in segmental chain dynamics. The carborane cage however, remained intact at these dose levels. Thermal degradation was observed to lead to oxidative crosslinking, the degree of which is dependent on temperature. At temperatures below 350 °C, only small changes in segmental dynamics were observed commensurate with only minor weight loss at this temperature. At temperatures above 350 °C, the degradation of the elastomer increased dramatically with decreased segmental dynamics and presumed partial oxidation of the carborane cage. The integrity of the m-carborane cage and the segmental dynamics were found to be significantly reduced at temperatures above 580 °C, in line with the known cage rearrangement temperature for icosahedral carboranes.     

Stability of self-assembled monolayers on titanium and gold

Methyl- and hydroxyl-terminated phosphonic acid self-assembled monolayers (SAMs) were coated on Ti from aqueous solution. Dodecyl phosphate and dodecyltrichlorosilane SAMs were also coated on Ti using solution-phase deposition. The stability of SAMs on Ti was investigated in Tris-buffered saline (TBS) at 37 degrees C using X-ray photoelectron spectroscopy, contact angle goniometry, and atomic force microscopy. For comparison purposes, a hydroxyl-terminated thiol SAM was coated on Au, and its stability was also investigated under similar conditions. In TBS, a significant proportion of phosphonic acid or phosphate molecules were desorbed from the Ti surface within 1 day, while the trichlorosilane SAM on Ti or thiol SAM on Au was stable for up to 7 days under similar conditions. The stability of hydroxyl-terminated phosphonic acid SAM coated Ti and thiol SAM coated Au was investigated in ambient air and ultraviolet (UV) light. In ambient air, the phosphonic acid SAM on Ti was stable for up to 14 days, while the thiol SAM on Au was not stable for 1 day. Under UV-radiation exposure, the alkyl chains of the phosphonic acid SAM were decomposed, leaving only the phosphonate groups on the Ti surface after 12 h. Under similar conditions, decomposition of alkyl chains of the thiol SAM was observed on the Au surface accompanied by oxidation of thiolates.     

Dispersing nanotubes with surfactants: a microscopic statistical mechanical analysis

A first theoretical study of surfactant-stabilized carbon nanotube dispersions is presented. Density functional theory is used to compute potential of mean force between nanotubes in an aqueous solution of cationic surfactant n-decyltrimethylammonium chloride. In agreement with experimental results, it is found that stable dispersions can be prepared for surfactant bulk concentrations below the critical micelle concentration. Computed density profiles of head and tail segments indicate that surfactants adsorb on nanotube surfaces in a random fashion rather than form cylindrical micelles, which is also in agreement with recent small-angle neutron scattering measurements.     

Quantitative evaluation of benzene, toluene, and xylene in the larvae of Drosophila melanogaster by solid-phase microextraction/gas chromatography/mass spectrometry for potential use in toxicological studies

A simple, rapid, and solvent-free method for quantitative determination of benzene, toluene, and Xylene in exposed Drosophila larvae was developed using headspace solid-phase microextraction (HS-SPME) coupled to GC/MS. Larvae fed on standard Drosophila food mixed with benzene, toluene, and Xylene for 48 h were homogenized in Milli-Q water. Extraction of benzene, toluene, and Xylene was performed at 65 degrees C for 30 min on the SPME fiber (silica-fused). Subsequently, the fiber was desorbed in the GC injection port, followed by GC/MS analysis in the selected-ion monitoring mode. An external calibration curve was used for the quantification of benzene, toluene, and Xylene in the exposed organism. Recoveries were in the range of 78-82% (intraday) and 76-81% (interday) in larvae, and 91-96% (intraday) and 87-92% (interday) in the diet. LOD with an S/N of 3:1 and LOQ with an S/N of 10:1 were in the range of 0.01-0.023 and 0.034-0.077 microg/L, respectively. Percent RSD values for benzene, toluene, and Xylene were in the range of 0.50-0.81 (intraday) and 0.89-1.23 (interday) for retention time, and 2.16--3.85 (intraday) and 2.99-4.95 (interday) for peak concentration, showing good repeatability. This method was sensitive enough to quantitate benzene, toluene, and Xylene in small exposed organisms like Drosophila larvae. The SPME/GC/MS method developed may have wider applications in various in vivo toxicological studies.     

Development and validation of a high-performance liquid chromatographic method for determination of eprosartan in bulk drug and tablets

A simple, precise, and accurate isocratic RP-HPLC method was developed and validated for determination of eprosartan in bulk drug and tablets. Isocratic RP-HPLC separation was achieved on a Phenomenex C18 column (250 x 4.6 mm id, 5 microm particle size) using the mobile phase 0.5% formic acid-methanol-acetonitrile (80 + 25 + 20, v/v/v, pH 2.80) at a flow rate of 1.0 mL/min. The retention time of eprosartan was 7.64 +/- 0.05 min. The detection was performed at 232 nm. The method was validated for linearity, precision, accuracy, robustness, solution stability, and specificity. The method was linear in the concentration range of 10-400 microg/mL with a correlation coefficient of 0.9999. The repeatability for six samples was 0.253% RSD; the intraday and interday precision were 0.21-0.57 and 0.33-0.71% RSD, respectively. The accuracy (recovery) was found to be in the range of 99.86-100.92%. The drug was subjected to the stress conditions hydrolysis, oxidation, photolysis, and heat. Degradation products produced as a result of the stress conditions did not interfere with detection of eprosartan; therefore, the proposed method can be considered stability-indicating.     

Preparation and physicochemical characterization of carbamazepine (CBMZ): para-sulfonated calix[n]arene inclusion complexes

The formation of inclusion complexes with para-sulfonated calix[n]arene (PSC[n]A) was studied for carbamazepine (CBMZ), a poorly water soluble anticonvulsant drug. The effect of PSC[4]A and PSC[6]A on aqueous solubility of carbamazepine was studied extensively. The complete complexation of the drug was achieved after 48 h of shaking with PSC[n]A in water and evaporation of water to get solid complex. The interaction between PSC[n]A and CBMZ in solid state inclusion complexes was accomplished by aqueous phase solubility studies, HPLC, DSC, PXRD, FTIR, UV–Vis, and FT-Raman spectroscopy. The solubility of CBMZ increases as a function of PSC[n]A concentration. The results of the two phase solubility experiments are in good conformity to signify the formation of 1:1 (PSC[6]A:CBMZ) and 2:1 PSC[4]A:CBMZ complexes. The order of dissolution rate of CBMZ is inclusion complex > physical mixture > drug alone. The purpose of this study was to enhance solubility resulting in high dissolution rate and bioavailability of this essentially water insoluble drug.     

Validated ultra-performance liquid chromatography tandem mass spectrometry method for the determination of pramipexole in human plasma

A sensitive and high throughput ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS-MS) method has been developed for the determination of pramipexole, a dopamine agonist, in human plasma. Sample preparation involved liquid-liquid extraction of pramipexole and ranitidine as the internal standard (IS) in ethyl acetate from 100 μL human plasma. The chromatographic separation is achieved on a Waters Acquity UPLC BEH C18 (100 mm × 2.1 mm, 1.7 μm) analytical column using an isocratic mobile phase, consisting of 10 mM ammonium formate (pH 7.50)-acetonitrile (15:85, v/v), at a flow-rate of 0.5 mL/min. The precursor → product ion transition for pramipexole (m/z 212.1 → 153.0) and IS (m/z 315.0 → 176.1) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) and positive ion mode. The method was validated over a wide dynamic concentration range of 20-4020 pg/mL. Matrix effect is assessed by post-column infusion experiment and the process efficiency were 91.9% and 85.7% for pramipexole and IS, respectively. The method is rugged and rapid with a total run time of 1.5 min and is applied to a bioequivalence study of 0.25 mg PPX tablet formulation in 30 healthy Indian male subjects under fasting condition.