Development and Validation of a Novel Stability Indicating UPLC <Emphasis Type="SmallCaps">M</Emphasis>ethod for Analysis of Related Compounds and Assay of Bexarotene,an Anti-Cancer Agent

A novel liquid chromatographic method for the analysis of four potential impurities in the anti-cancer agent Bexarotene has been developed and validated using efficient chromatographic separation, achieved on a C₁₈ column (50 mm × 2.1 mm, 1.7-μm particles) with a simple isocratic mobile phase at a flow rate of 0.5 mL min^?1. The mobile phase consisted of a 70:30:0.1 (v/v/v) mixture of acetonitrile, water and trifluoroacetic acid, and quantification was achieved by use of ultraviolet detection at 260 nm. Resolution between Bexarotene and its four potential impurities was greater than 2.0. Regression analysis showed the r value (correlation coefficient) was >0.999 for Bexarotene and its four impurities. The method was capable of detecting all four impurities of Bexarotene at levels below 0.10 μg in a Bexarotene test concentration of 0.5 mg mL^?1 using an injection volume of 5 μL. The recovery for Bexarotene in assay method at a 100% level was observed to be 99.1 ± 0.32% with % RSD value of 0.5% for drug substance and 98.9 ± 0.46% for Bexarotene capsules with % RSD value of 0.4%. Recovery of imp-1, imp-2, imp-3, and imp-4 from bulk drug samples ranged from 96.3 to 102.0%. Recovery of imp-1, imp-2, imp-3, and imp-4 from Bexarotene Capsule samples ranged from 97.2 to 101.4%. A solution of Bexarotene in ethanol was stable for 48 h. The drug was also subjected to stress conditions as prescribed by ICH Guidelines. Degradation was found to occur under acidic and basic hydrolysis stress conditions; however, the drug was stable to oxidative, photolytic, and thermal stress. Assay of the stressed samples was calculated relative to a qualified reference standard and the mass balance was found to be close to 99.8%. The method was validated for linearity, accuracy, precision, and robustness.     

In vivo Confocal Raman Spectroscopic Analysis of the Effects of Infrared Radiation in the Human Skin Dermis

Human skin is the outer covering of the body, and its composition changes with overexposure to environmental pollution and solar radiation. Infrared (IR) radiation is capable of penetrating more deeply into the skin producing free radicals causing irreversible damage. Confocal Raman spectroscopy was considered as a potential tool for the in vivo analysis of the different metabolic conditions with respect to different depths of the skin. In this regard, this work verifies the influence of infrared radiation on the skin dermis after having been exposed to 432 J cm^?2 which corresponds to the dose received in a day in the summer time in a tropical region. This study was performed with 17 female volunteers who were divided into two groups. The marked skin area was exposed twice to IR radiation for a duration of 30 min each with an interval of 30 min. The spectral signatures were collected in the fingerprint region before (T0) and after 60 min (T60) of IR irradiation. The analysis shows that, on average, no significant variations occurred in group I and decreased collagen was observed in group II. However, when considering the effect seen in each individual, collagen degradation was detected in 60% of volunteers.     

Quality by Design enabled enhanced bioanalytical extraction and UFLC determination of vilazodone from rat serum

An ultrafast liquid chromatographic bioanalytical method was developed and validated for the determination of vilazodone in Wistar rat serum. Principles of quality by design were implemented for enhancing the bioanalytical liquid–liquid extraction of vilazodone from rat serum. A Box–Behnken design was utilized in the studies by selecting extraction time, centrifugation speed, and vortex time as the critical method variables for evaluating their effect on the analytical attribute, i.e., %recovery of vilazodone. Chromatographic separation was achieved within a run time of 10?min using a C-18 column and mobile phase comprising of methanol:phosphate buffer of pH 7 (85:15 v/v) flowing at 1.5?mL/min. Photodiode array detection was performed at 242?nm. Results of validation studies were satisfactory. The method was linear over a concentration of 100–2,000?ng/mL with acceptable accuracy and precision. Limits of detection and quantitation for the developed method were 50 and 100?ng/mL, respectively. This QbD-based approach was found suitable for routine bioanalysis of vilazodone in the biological matrix.     

Supramolecular Gating of Ion Transport in Nanochannels

Several covalent strategies towards surface charge‐reversal in nanochannels have been reported with the purpose of manipulating ion transport. However, covalent routes lack dynamism, modularity and post‐synthetic flexibility, and hence restrict their applicability in different environments. Here, we introduce a facile non‐covalent approach towards charge‐reversal in nanochannels (<10 nm) using strong charge‐transfer interactions between dicationic viologen (acceptor) and trianionic pyranine (donor). The polarity of ion transport was switched from anion selective to ambipolar to cation selective by controlling the extent of viologen bound to the pyranine. We could also regulate the ion transport with respect to pH by selecting a donor with pH‐responsive functional groups. The modularity of this approach further allows facile integration of various functional groups capable of responding to stimuli such as light and temperature to modulate the transport of ions as well as molecules.     

Optical microwell array for large scale studies of single mitochondria metabolic responses

Microsystems based on microwell arrays have been widely used for studies on single living cells. In this work, we focused on the subcellular level in order to monitor biological responses directly on individual organelles. Consequently, we developed microwell arrays for the entrapment and fluorescence microscopy of single isolated organelles, mitochondria herein. Highly dense arrays of 3-μm mean diameter wells were obtained by wet chemical etching of optical fiber bundles. Favorable conditions for the stable entrapment of individual mitochondria within a majority of microwells were found. Owing to NADH auto-fluorescence, the metabolic status of each mitochondrion was analyzed at resting state (Stage 1), then following the addition of a respiratory substrate (Stage 2), ethanol herein, and of a respiratory inhibitor (Stage 3), antimycin A. Mean levels of mitochondrial NADH were increased by 29 % and 35 % under Stages 2 and 3, respectively. We showed that mitochondrial ability to generate higher levels of NADH (i.e., its metabolic performance) is not correlated either to the initial energetic state or to the respective size of each mitochondrion. This study demonstrates that microwell arrays allow metabolic studies on populations of isolated mitochondria with a single organelle resolution.

Flexible and Rigid Amine‐Functionalized Microporous Frameworks Based on Different Secondary Building Units: Supramolecular Isomerism,Selective CO2 Capture,and Catalysis

We report the synthesis, structural characterization, and porous properties of two isomeric supramolecular complexes of ([Cd(NH₂?bdc)(bphz)_0.5]?DMF?H₂O}_n (NH₂?bdc=2‐aminobenzenedicarboxylic acid, bphz=1,2‐bis(4‐pyridylmethylene)hydrazine) composed of a mixed‐ligand system. The first isomer, with a paddle‐wheel‐type Cd₂(COO)₄ secondary building unit (SBU), is flexible in nature, whereas the other isomer has a rigid framework based on a μ‐oxo‐bridged Cd₂(μ‐OCO)₂ SBU. Both frameworks are two‐fold interpenetrated and the pore surface is decorated with pendant ?NH₂ and ?N?N? functional groups. Both the frameworks are nonporous to N₂, revealed by the type II adsorption profiles. However, at 195 K, the first isomer shows an unusual double‐step hysteretic CO₂ adsorption profile, whereas the second isomer shows a typical type I CO₂ profile. Moreover, at 195 K, both frameworks show excellent selectivity for CO₂ among other gases (N₂, O₂, H₂, and Ar), which has been correlated to the specific interaction of CO₂ with the ?NH₂ and ?N?N? functionalized pore surface. DFT calculations for the oxo‐bridged isomer unveiled that the ?NH₂ group is the primary binding site for CO₂. The high heat of CO₂ adsorption (ΔH_ads=37.7 kJ mol^?1) in the oxo‐bridged isomer is realized by NH₂???CO₂/aromatic π???CO₂ and cooperative CO₂???CO₂ interactions. Further, postsynthetic modification of the ?NH₂ group into ?NHCOCH₃ in the second isomer leads to a reduced CO₂ uptake with lower binding energy, which establishes the critical role of the ?NH₂ group for CO₂ capture. The presence of basic ?NH₂ sites in the oxo‐bridged isomer was further exploited for efficient catalytic activity in a Knoevenagel condensation reaction.     

Substrate inhibition: Oxidation of D-sorbitol and D-mannitol by potassium periodate in alkaline medium

In the oxidation of D-sorbitol and D-mannitol by potassium periodate in alkaline media, substrate inhibition was observed with both substrates, i.e., a decrease in the rate of the reaction was observed with an increase in the concentration of substrate. The substrate inhibition was attributed to the formation of stable complex between the substrate and periodate. The reactions were found to be first order in case of periodate and a positive fractional order with hydroxide ions. Arrhenius parameters were calculated for the oxidation of sorbitol and mannitol by potassium periodate in alkali media.     

Structural Stability and Unfolding Properties of Cutinases from Thermobifida fusca

A comparative analysis of the structural and functional aspects along with equilibrium unfolding of two homologous cutinases, Cut1 and Cut2, from Thermobifida fusca was carried out. The CD and fluorescence profile at different pH in the range of 6 to 9 showed no structural variations for both cutinases, indicating their stability to a wide range of pH. Tryptophan quenching studies suggested that all the four Trp residues in the protein are in inaccessible hydrophobic pockets. Further, near-UV CD analysis of tertiary structure revealed a dissimilar distribution of aromatic amino acid on the surface of these two enzymes. Denaturation profiles obtained in aqueous solutions of the guanidine hydrochloride revealed different tolerance levels for unfolding of the two cutinases, with Cut2 showing higher resistivity to unfolding in comparison to Cut1. Both cutinases retained all the structural parameters even in the presence of 8 M urea, indicating the protein to be highly resistant to urea-induced unfolding. Structural study by homology modeling revealed a high resemblance of secondary structure between the two cutinases; however, their tertiary structure, hydrophobicity, and surface electrostatic properties were very different, which contributed to the difference in the structural stability of these two cutinases.     

Enhanced photocatalytic activity of ultra-high aspect ratio ZnO nanowires due to Cu induced defects

We report the synthesis of ZnO nanowires in ambient air at 650°C by a single-step vapor transport method using two different sources Zn (ZnO nanowires-I) and Zn:Cu (ZnO nanowires-II). The Zn:Cu mixed source co-vaporize Zn with a small amount of Cu at temperatures where elemental Cu source does not vaporize. This method provides us a facile route for Cu doping into ZnO. The aspect ratio of the grown ZnO nanowires-II was found to be higher by more than five times compared ZnO nanowires-I. Photocatalytic activity was measured by using a solar simulator and its ultraviolet-filtered light. The ZnO nanowires-II shows higher catalytic activity due to increased aspect ratio and higher content of surface defects because of incorporation of Cu impurities.     

Electrostatic hand pressure knapsack spray system with enhanced performance for small scale farms

Electrostatic force fields have been employed and enhanced in the design of an electrostatic knapsack spray system for increasing the deposition efficiency and reducing the drift of pesticides. The designed induction charge based electrostatic sprayer offers optimum electrode position and electrical conductivity of liquid. The experiments were conducted in ambient conditions for liquid feed rate 340 ml/min at hand pressure of 30 psi. The charge-to-mass ratio was found to be 0.419 mC/kg at 3.25 kV by a spray liquid of conductivity 10.25 mS/cm. There has been 2–3 fold increase of chemical deposition with better uniformity on the target (potted plant).