| 28601. |
- Kann, Nina, 1964
(författare)
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Applications of the Nicholas Reaction in the Synthesis of Natural Products
- 2012
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Ingår i: Current Organic Chemistry. - : Bentham Science Publishers Ltd.. - 1385-2728. ; 16:3, s. 322-334
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Forskningsöversikt (refereegranskat)abstract
- The Nicholas reaction involves the treatment of a cobalt carbonyl-stabilized propargylic cation with a variety of nucleophiles to form a new carbon-carbon or carbon-heteroatom bond. Several features of this reaction make it especially well suited for applications in natural product synthesis, in particular when cyclic and polycyclic target molecules are involved. This review summarizes the results in this area from the last ten years, including approaches towards terpenes, alkaloids and marine natural products.
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| 28602. |
- Kann, Nina, 1964, et al.
(författare)
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Conformational properties of 1,4- and 1,5-substituted 1,2,3-triazole amino acids-building units for peptidic foldamers
- 2015
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Ingår i: Organic and Biomolecular Chemistry. - : Royal Society of Chemistry (RSC). - 1477-0539 .- 1477-0520. ; 13:9, s. 2776-2785
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Tidskriftsartikel (refereegranskat)abstract
- Peptidic foldamers have recently emerged as a novel class of artificial oligomers with properties and structural diversity similar to that of natural peptides, but possessing additional interesting features granting them great potential for applications in fields from nanotechnology to pharmaceuticals. Among these, foldamers containing 1,4- and 1,5-substitued triazole amino acids are easily prepared via the Cu- and Ru-catalyzed click reactions and may offer increased side chain variation, but their structural capabilities have not yet been widely explored. We here describe a systematic analysis of the conformational space of the two most important basic units, the 1,4-substitued (4Tzl) and the 1,5-substitued (5Tzl) 1,2,3-triazole amino acids, using quantum chemical calculations and NMR spectroscopy. Possible conformations of the two triazoles were scanned and their potential minima were located using several theoretical approaches (B3LYP/6-311++G(2d,2p), ωB97X-D/6-311++G(2d,2p), M06-2X/6-311++G(2d,2p) and MP2/6-311++G(2d,2p)) in different solvents. BOC-protected versions of 4Tzl and 5Tzl were also prepared via one step transformations and analyzed by 2D NOESY NMR. Theoretical results show 9 conformers for 5Tzl derivatives with relative energies lying close to each other, which may lead to a great structural diversity. NMR analysis also indicates that conformers preferring turn, helix and zig-zag secondary structures may coexist in solution. In contrast, 4Tzl has a much lower number of conformers, only 4, and these lack strong intraresidual interactions. This is again supported by NMR suggesting the presence of both extended and bent conformers. The structural information provided on these building units could be employed in future design of triazole foldamers.
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| 28603. |
- Kann, Nina, 1964
(författare)
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Recent Applications of Polymer Supported Organometallic Catalysts in Organic Synthesis
- 2010
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Ingår i: Molecules. - : MDPI AG. - 1420-3049 .- 1420-3049. ; 15:9, s. 6306-6331
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments concerning the application of polymer supported organometallic reagents in solid phase synthesis are reviewed, with a special focus on methodology for carbon-carbon formation. Examples of reactions that are covered include the classical Suzuki, Sonogashira and Heck coupings, but also aryl amination, epoxide opening, rearrangements, metathesis and cyclopropanation. Applications in the field of asymmetric synthesis are also discussed.
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| 28604. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
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A continuum-based multiphase DNS method for studying the Brownian dynamics of soot particles in a rarefied gas
- 2019
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 210
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Tidskriftsartikel (refereegranskat)abstract
- In the mitigation of particulate matter (PM) using filters, the interplay between particle motion, geometry and flow conditions determines the overall performance. In such flows, molecular effects on the particle motion manifest as impeded momentum transfer and a meandering Brownian motion. Other particles and walls induce hydrodynamic interactions, which may further influence PM nucleation, growth and aggregation. Here, we formulate a multiphase direct numerical simulation framework to investigate these complex flows by including the molecular interactions in a consistent manner. The basis for this framework is a coupling between the Langevin description of particle motion with a mirroring immersed boundary method. We show that the method is able to capture the diffusion dynamics of a Brownian particle, including its transition from a particle-inertia dominated, correlated ballistic regime to a non-correlated diffusive one, and that the method also can be used to reproduce the meandering motion of realistic soot particles.
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| 28605. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
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A hydrodynamic basis for off-axis Brownian diffusion under intermediate confinements in micro-channels
- 2021
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Ingår i: International Journal of Multiphase Flow. - : Elsevier BV. - 0301-9322. ; 143
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Tidskriftsartikel (refereegranskat)abstract
- The mobility of a Brownian particle diffusing in a micro-channel is heterogeneous and spatially dependent on the surrounding hydrodynamic resistance fields. The positional asymmetry of such a diffusing particle leads to anisotropies in the observed diffusive behavior. In this paper, we probe such directionally varying diffusive behavior of a spherical nanoparticle diffusing at a location off-set from the centerline of a square micro-channel in a quiescent fluid. This investigation is carried out over varying degrees of intermediate hydrodynamic confinements. A coupled Langevin-immersed boundary method is used for these assessments. We observe that the co-axial diffusivity may be slightly enhanced during off-axis hindered diffusion when compared with a corresponding centerline diffusive behavior. We attribute this increased particle diffusivity to a reduced co-axial fluid resistance through a hydrodynamic basis derived using steady-state CFD solutions to the corresponding Stokes problem. For co-axial motion, the particle creates a recirculating flow pattern around itself when moving along the centerline, whereas it drags along the fluid in between itself and the wall when in close proximity to the latter. These contrasting flow behaviors are responsible for the unexpected enhancement of the co-axial diffusivity for some off-axis positions under intermediate hydrodynamic confinements.
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| 28606. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
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Assessment of hindered diffusion in arbitrary geometries using a multiphase DNS framework
- 2021
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 230
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Tidskriftsartikel (refereegranskat)abstract
- The hydrodynamics around a Brownian particle has a noticeable impact on its hindered diffusion in arbitrary geometries (such as channels/pores) due to reduced mobility close to walls. These effects are difficult to describe at sub-pore scales, wherein a complete analytical solution of the underlying hydrodynamics is challenging to obtain. Here, we propose a coupled Langevin-multiphase direct numerical simulation (DNS) framework, that fully resolves the hydrodynamics in such systems and consequently provides an on-the-fly capability to probe local instantaneous particle diffusivities. We validate and establish the capabilities of this framework in square micro-channels (under varying degrees of hydrodynamic confinement) and in an arbitrary pore. Our results show that directional variations in mean-squared displacements, velocity auto-correlation functions and diffusivities of the Brownian particle, due to inherent asymmetries in the geometry are adequately captured. Further, a local anisotropy in the hydrodynamic resistances along the co-axial direction of the channel is also noted.
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| 28607. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
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Assessment of pore diffusion in a micro-channel using an immersed boundary method
- 2017
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Ingår i: Conference Proceedings of the 14th Conference on Multiphase Flows in Industrial plants (MFIP17).
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Konferensbidrag (refereegranskat)abstract
- In this paper, we formulate a computational framework for the assessment of pore diffusivity in a simple micro-channel. Diffusion under such conditions is of interest to both biological and physico-chemical applications that deal with the transport of particles in a rarefied fluid (whereparticle and molecular length scales are comparable), such as particulate matter removal in exhaust gas, diffusion of lipids through bio-membranes etc. The mobility of these particles may be influenced by neighboring particles and walls, as well as history effects in the surrounding flow. When a particle is not small in relation to the pore, these effects can no longer be accounted for via a point-particle method.Here, we treat the stochastic transport of particles in a bounded micro-channel within a continuum framework using a multiphase direct numerical simulation technique, the immersed boundary method. We show how this continuum method can be used to resolve the meandering path followed by a small particle subjected to Brownian motion, and present detailed investigations of the influence of the particle on the surrounding fluid flow field. Finally, we also discuss the advantages, challenges and implications of resolving a molecular phenomenon with a continuum technique.
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| 28608. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
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CFD-DEM studies of grain segregation patterns on a conceptual destoner
- 2015
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Ingår i: The 16th International Conference on Fluid Flow Technologies (CMFF15), Budapest, Hungary.
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Konferensbidrag (refereegranskat)abstract
- Removal of contaminants from ‘food grade’ quality grains is of great importance in food and grain processing operations. A thorough understanding of the inherent granular segregation profiles on this processing equipment is a pivotal step in the design and development of more efficient processes. One such grain cleaning operation is the ‘density-based separation’ using a destoner. This process removes stones and other heavy material from lighter food grains using a vibrating deck and fluidizing air. In this paper we formulate a CFD-DEM framework (set up and implemented in the OpenFOAM® environment) to study granular segregation patterns on a destoner. The scheme is first validated by comparing simulations with experimental data using a gas-solid fluidized-bed test case. A good agreement between the experiments and the simulations is noted. This proposed framework is then used to characterize the combined effects of deck inclination and fluidization velocities on the separation profiles generated from a virtual destoner. We have found these profiles to be highly sensitive to changes in fluidization conditions, with the gradual development of segregation zones at velocities close to the minimum fluidization velocity of the heavier component. A deck inclination of 5 degrees and a fluidization velocity of 2.0 m/s is considered optimal while steeper slopes (inclinations of 15 degrees) and lower air velocities (0 and 1.5 m/s) are deemed unsuitable for segregation.
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| 28609. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
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Design and performance optimization of gravity tables using a combined CFD-DEM framework
- 2017
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 318, s. 423-440
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we formulate a computational framework for the characterization and performance optimization of gravity tables. Segregation of a multi-dispersed population of grains is assessed using a comprehensive numerical framework integrating Computational Fluid Dynamics (CFD) simulations with a Discrete Element Method (DEM) setup in the open-source software OpenFOAM. We have carried out combined qualitative and quantitative assessments of process conditions, such as deck shape, deck inclination (longitudinal and transverse), vibration speed and fluidizing air velocities at the surface. We assess the performance of our framework by employing a quantitative metric rhostat, which represents the efficiency of separation in terms of density differences between the two separated product fractions. Additionally, qualitative flow behaviour is evaluated by examining relevant velocity and material distribution trends. We show that these separation profiles are highly sensitive to changes in the design and process conditions, with the presence of discernible optimal operating points. For the chosen gravity table, we have identified a longitudinal tilt of 6 degrees, an eccentric speed between 300 and 350 RPM, deck air velocities of up to 1.5 m/s and a transverse tilt of 0.75 degrees as a set of optimal operating conditions.
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| 28610. |
- Kannan, Ananda Subramani, 1989, et al.
(författare)
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Segregation phenomena in gravity separators: A combined numerical and experimental study
- 2016
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Ingår i: Powder Technology. - : Elsevier BV. - 1873-328X .- 0032-5910. ; 301, s. 679-693
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we formulate a computational framework for characterizing and optimizing the performance of adestoner, an example of a density-based separation technique. The numerical framework combines ComputationalFluid Dynamics (CFD) simulations with a Discrete Element Method (DEM), implemented in an opensourcecomputation package (OpenFOAM). This framework is validated first by comparing the simulationswith experiments for a standardized test case and further with our experimental study of a pilot-scale destoner.We evaluate the combined effects of process conditions, such as separator deck inclination, vibration speed andfluidization velocities on destoner performance. Our simulations showhowthe heavy product fraction in the discardsstreamincreases over timewith a corresponding accumulation of the ‘valuable’ light product at the base ofthe deck, indicating segregation between the stones (heavy product) and the grains (light product).We also findthat these separation profiles are highly sensitive to changes in deck surface air velocities, with the gradual developmentof segregation zones at velocities close to the minimum fluidization velocity of the heavier component.Optimal separation is seen at a deck inclination of 4° and a fluidization velocity of between 1.75 and2 m/s. Our simulation results also agree well with the experimental findings indicating the usability of the proposedframework for the design and optimization of gravity separators.
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