Validation of LC/MS electrospray ionisation method for the estimation of ursodiol in human plasma and its application in bioequivalence study

A novel High Performance Liquid Chromatography-electrospray mass spectrometric method has been developed for the estimation of Ursodiol (Ursodeoxycholic acid)--a bile acid, in human plasma using Ornidazole as internal standard. The methodology involved solid phase extraction of the analyte from human plasma matrix. The chromatographic separation was achieved within seven minutes by an isocratic mobile phase containing 1.0 mM ammonium acetate and Acetonitrile (65:35, v/v), flowing through XTerra MS C18, 100 x 2.1, 3.5 microm analytical column, at a flow rate of 0.2 ml/min. Ion signals were measured in negative mode for Ursodiol and internal standard at m/z 391.3 and 278.1, respectively. A detailed validation of the method was performed as per USFDA guidelines and the standard curves were found to be linear in the range 50.0 ng/ml to 3000.0 ng/ml with the mean correlation coefficient more than 0.99. The absolute recovery was more than 54.90% for Ursodiol and 76.51% for internal standard. Ursodiol was stable for sixty-nine days at -70 degrees C and for eight hours at ambient temperature. After extraction from plasma, the reconstituted samples of Ursodiol were stable in autosampler at 10 degrees C for forty-eight hours. Upon subjecting to three freeze thaw cycles, there was no change in the recovery of the analyte. The integrity of the plasma samples remained unaffected even upon four-fold dilution with drug free human plasma. The method was simple, specific, sensitive, precise, accurate and suitable for bioequivalence and pharmacokinetic studies. It was successfully applied to the pilot bioequivalence study of Ursodiol in male human subjects.     

Selecting oxygen source for partial oxidation of methane to methanol using microwave plasmas

The methanol selectivity in partial oxidation of methane in microwave plasma reactors is improved by using H₂O in the presence or absence of O₂. The use of H₂O₂ as an oxygen source has a similar effect, although it is less effective than H₂O. The addition of H₂ to the system has little effect on selectivity. Two pathways are suggested for the formation of methanol. One involves a CH₃O^* or CH₃O₂ ^* intermediate, while the other involves a direct combination of CH₃ ^* and OH^* radicals. The first pathway is favored in the presence of O₂ while the latter is favored in the presence of H₂O or H₂O₂. The best results are obtained for the CH4-O₂-H₂O system when methanol is formed through both pathways.     

Mechanical Properties and Failure Behavior of Physically Assembled Triblock Copolymer Gels with Varying Midblock Length

Mechanical properties including the failure behavior of physically assembled gels or physical gels are governed by their network structure. To investigate such behavior, we consider a physical gel system consisting of poly(styrene)‐poly(isoprene)‐poly(styrene)[PS‐PI‐PS] in mineral oil. In these gels, the endblock (PS) molecular weights are not significantly different, whereas, the midblock (PI) molecular weight has been varied such that we can access gels with and without midblock entanglement. Small angle X‐ray scattering data reveals that the gels are composed of collapsed PS aggregates connected by PI chains. The gelation temperature has been found to be a function of the endblock concentration. Tensile tests display stretch‐rate dependent modulus at high strain for the gels with midblock entanglement. Creep failure behavior has also been found to be influenced by the entanglement. Fracture experiments with predefined cracks show that the energy release rate scales linearly with the crack‐tip velocity for all gels considered here. In addition, increase of midblock chain length resulted in higher viscous dissipation leading to a higher energy release rate. The results provide an insight into how midblock entanglement can possibly affect the mechanical properties of physically assembled triblock copolymer gels in a midblock selective solvent. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1014–1026     

Organo-modified mesoporous silica for sorption of carbon dioxide

Abstract  

Organo-modified mesoporous silica SBA-15 has been studied for sorption of carbon dioxide (CO₂). The SBA-15 sample was functionalized with a branched chain polymer, polyethylenimine (PEI), of different molecular weights (1,300 and 2,000 g mol⁻¹). Surface modification was carried out by impregnation of silica by PEI or by grafting with (3-chloropropyl)triethoxysilane, followed by substitution of chlorine atoms by PEI ligands. The prepared modified mesoporous materials were characterized by nitrogen adsorption/desorption at 77 K, high-resolution transmission electron microscopy, small-angle X-ray scattering, and thermal methods. Sorption of CO₂ was studied by gravimetric method at 303 K. The total amount of sorbed CO₂ varied between 0.19–0.67 mmol/g for respective samples. Regeneration of the materials after adsorption was achieved by thermal treatment at 343 K.     

Helicenoid-based bis-1,2,3-triazole tweezer: Synthesis and selective iodide sensing

Abstract

Novel helicenoid based 1,2,3-triazole tweezer 4 was synthesized using a multistep synthetic protocol with high yields from 2,7-Dihydroxynaphtlene 3 as a precursor. This helicenoid-based bis-1,2,3-triazole tweezer 4 selectively causes non-covalent interaction with iodide anion. The UV-vis absorption exhibited enhancement while fluorescence spectra exhibited significant quenching. ¹H NMR titration showed shift of 1,2,3-triazole C-H signal with an increase in iodide concentration. Association constant of 3.818?×?10⁴ M^?1 was recorded for the host interaction with iodide ions. This value of association constant for iodide sensing using 1,2,3-triazole is the best reported so far for hosts with 1,2,3-triazole moiety and suggests that the helicenoid geometry is responsible for this remarkable behavior.     

Multiphoton ionization and Coulomb explosion of C2H5Br clusters: a mass spectrometric and charge density study

Using time‐of‐flight mass spectrometry (TOFMS), laser‐induced photochemistry of ethyl bromide clusters has been investigated at three different wavelengths (viz. 266, 355 and 532 nm) utilizing nanosecond laser pulses of ~5 × 10⁹ W/cm². An interesting finding of the present work is the observation of multiply charged atomic ions of carbon and bromine at 355 and 532 nm, arising from the Coulomb explosion of (C₂H₅Br)_n clusters. At 266 nm, however, the (C₂H₅Br)_n clusters were found to exhibit the usual multiphoton dissociation/ionization behaviour. The TOFMS studies are complemented by measuring the total charge density of the ionized volume at 266, 355 and 532 nm, using the parallel plate method, and the charge densities were found to be ~2 × 10⁹, 6 × 10⁹ and 2 × 10¹¹ charges/cm³, respectively. The significantly higher charge density and the presence of energetic, multiply charged atomic ions at 532 nm are explained by the higher ponderomotive energy of the 532 nm photon, coupled with the Coulomb stability of the residual multiply charged ethyl bromide clusters generated upon laser irradiation, due to their larger effective cluster size at 532 nm than at 355 and 266 nm. Copyright © 2011 John Wiley & Sons, Ltd.     

Design and Development of Axially Chiral Bis(naphthofuran) Luminogens as Fluorescent Probes for Cell Imaging

Designing chiral AIEgens without aggregation-induced emission (AIE)-active molecules externally tagged to the chiral scaffold remains a long-standing challenge for the scientific community. The inherent aggregation-caused quenching phenomenon associated with the axially chiral (R)-[1,1′-binaphthalene]-2,2′-diol ((R)-BINOL) scaffold, together with its marginal Stokes shift, limits its application as a chiral AIE-active material. Here, in our effort to design chiral luminogens, we have developed a design strategy in which 2-substituted furans, when appropriately fused with the BINOL scaffold, will generate solid-state emissive materials with high thermal and photostability as well as colour-tunable properties. The excellent biocompatibility, together with the high fluorescence quantum yield and large Stokes shift, of one of the luminogens stimulated us to investigate its cell-imaging potential. The luminogen was observed to be well internalised and uniformly dispersed within the cytoplasm of MDA-MB-231 cancer cells, showing high fluorescence intensity.     

New metal free organic dyes incorporating heterocyclic Benzofuran core as conjugated spacer: Synthesis,Opto-electrochemical,DFT and DSSC studies

Synthesis of a series of new organic photosensitizers, designated as BZ1 - BZ4 , was achieved by incorporating benzofuran core as π-spacer, triphenylamine (TPA) and 4-methoxy triphenylamine (4-MeO-TPA) as donors and cyanoacrylic acid (CAA) and rhodanine-3-acetic acid (RAA) as acceptor/anchoring groups. Structurally, dyes BZ1 and BZ2 carry TPA and 4-MeO-TPA as donors, respectively, whereas CAA constitutes as a common acceptor. On the other hand, BZ3 and BZ4 incorporate TPA and 4-MeO-TPA as donors, respectively, and RAA serves as a common acceptor. Key steps to access BZ1 - BZ4 involved Wittig olefination, reduction of cyano groups to aldehyde, and finally Knoevenagel condensation. In UV–visible spectra, dyes BZ1 - BZ4 exhibited intramolecular charge transfer (ICT) maxima in the range of 503 nm to 534 nm and their extinction coefficients varied from 22,600 to 40,400 M⁻¹ cm⁻¹. Using cyclic voltammetry and UV–visible data, we calculated the optical band gaps, (E₀₋₀) of BZ1-BZ4 to be 2.09, 2.00, 2.01, and 1.93 eV, respectively. DFT studies revealed that HOMOs of dyes were localized essentially on the donors triphenylamine groups, whereas the LUMOs are largely confined over electron acceptors CAA and RAA as well as partly diffused into the benzofuran spacer. DSSCs, configured using BZ1 - BZ4 as photosensitizers, showed fill factors (ff) in the range of 0.57 to 0.76, comparable to standard N3 dye (0.67). In addition, BZ1 and BZ2 dyes with CAA as an acceptor also exhibited decent open circuit voltage (V_oc) in the range of 0.61 to 0.63 relative to the 0.66 observed for N3 dye. Dyes BZ1-BZ2 carrying CAA as an acceptor exhibited an efficiency (η) of 2.03% and 1.49%, respectively, against the benchmark N3 dye, showing η of 5.02%. Due to poor V_oc and short circuit current density (I_sc), dyes BZ3-BZ4 carrying RAA as acceptor/anchoring group performed significantly poor, showing η of 0.08%, and 0.32%, respectively.