Design procedures for gas sparged contractors for both low and high viscosity liquids were developed to predict overall kLa. Bubble size close to the orifice, for moderately high gas rates, was found to increase at a rate proportional to one third power of gas rate and one tenth power of liquid viscosity. Bubble breakup phenomenon was shown to be related to liquid turbulence in the vessel rather than gas turbulence in the orifice. Procedures were developed through a simple liquid circulation model to obtain a criterion for the onset of bubble breakup. Results indicate that intense liquid mixing and high interfacial area can be achieved in low viscosity liquids by gas sparging alone. In high viscosity fluids, bubble breakup was not observed. The liquid circulation model predicts laminar flow at these experimental conditions over the complete range of gas rates observed.

The Sherwood number and drag coefficient for a single gas bubble moving in a power law fluid and a Bingham plastic fluid are obtained using perturbation methods. The perturbation parameters for power law and Bingham plastic fluids are m (= n – 1/2) and E (=  τ oR/U μ o), respectively. It is found that in the case of power law fluid, mass transfer and drag increase with increasing pseudoplasticity. These theoretical results are found to be in good agreement with the available experimental data and the data obtained in the present study. In the case of Bingham plastic fluid, mass transfer and drag are found to increase with increase in the Bingham number NB (= 2ε). Contours of plug flow regions, where local stresses are less than the yield stress, are obtained as a function of the Bingham number NB. These results qualitatively predict the zero terminal velocity observed for bubble motion in liquids with very high yield stress. They are also in good agreement with the trends of the results obtained previously for solid sphere motion in Bingham plastic fluids.

Three fatty acyl conjugates of (-)-2',3'-dideoxy-5-fluoro-3'-thiacytidine (FTC, emtricitabine) were synthesized and evaluated against HIV-1 cell-free and cell-associated virus and compared with the corresponding parent nucleoside and physical mixtures of FTC and fatty acids. Among all the compounds, the myristoylated conjugate of FTC (5, EC(50) = 0.07-3.7 μM) displayed the highest potency. Compound 5 exhibited 10-24 and 3-13-times higher anti-HIV activity than FTC alone (EC(50) = 0.7-88.6 μM) and the corresponding physical mixtures of FTC and myristic acid (14, EC(50) = 0.2-20 μM), respectively. Cellular uptake studies confirmed that compound 5 accumulated intracellularly after 1 h of incubation and underwent intracellular hydrolysis in CCRF-CEM cells. Alternative studies were conducted using the carboxyfluorescein conjugated with FTC though β-alanine (12) and 12-aminododecanoic acid (13). Acylation of FTC with a long-chain fatty acid in 13 improved its cellular uptake by 8.5-20 fold in comparison to 12 with a short-chain β-alanine. Compound 5 (IC(90) = 15.7-16.1 nM) showed 6.6- and 35.2 times higher activity than FTC (IC(90) = 103-567 nM) against multidrug resistant viruses B-NNRTI and B-K65R, indicating that FTC conjugation with myristic acid generates a more potent analogue with a better resistance profile than its parent compound.

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The present study demonstrates the relationship between conventional and quantum mechanical (QM) NMR spectroscopic analyses, shown here to assist in building a convincingly orthogonal platform for the solution and documentation of demanding structures. Kaempferol-3-O-robinoside-7-O-glucoside, a bisdesmosidic flavonol triglycoside and botanical marker for the aerial parts of Withania somnifera, served as an exemplary case. As demonstrated, QM-based 1H iterative full spin analysis (HiFSA) advances the understanding of both individual nuclear resonance spin patterns and the entire 1H NMR spectrum of a molecule and establishes structurally determinant, numerical HiFSA profiles. The combination of HiFSA with regular 1D 1H NMR spectra allows for simplified yet specific identification tests via comparison of high-quality experimental with QM-calculated spectra. HiFSA accounts for all features encountered in 1H NMR spectra: nonlinear high-order effects, complex multiplets, and their usually overlapped signals. As HiFSA replicates spectrum patterns from field-independent parameters with high accuracy, this methodology can be ported to low-field NMR instruments (40–100 MHz). With its reliance on experimental NMR evidence, the QM approach builds up confidence in structural characterization and potentially reduces identity analyses to simple 1D 1H NMR experiments. This approach may lead to efficient implementation of conclusive identification tests in pharmacopeial and regulatory analyses: from simple organics to complex natural products.