Metabolic flux analysis of clostridium thermosuccinogenes

Clostridium thermosuccinogenes are anaerobic thermophilic bacteria that ferment various carbohydrates to succinate and acetate as major products and formate, lactate, and ethanol as minor products. Metabolic carbon flux analysis was used to evaluate the effect of pH and redox potential on the batch fermentation of C. thermosuccinogenes. In a first study, the effects of four pH values (6.50, 6.75, 7.00, and 7.25) on intracellular carbon flux at a constant redox potential of -275 mV were compared. The flux of carbon toward succinate and formate increased whereas the flux to lactate decreased significantly with a pH increase from 6.50 to 7.25. Both specific growth rate and specific rate of glucose consumption were unaffected by changes in pH. The fraction of carbon flux at the phosphoenolpyruvate (PEP) node flowing to oxaloacetate increased with an increase in pH. At the pyruvate node, the fraction of flux to formate increased with increasing pH. At the acetyl CoA node, the fraction of flux to acetate increased significantly with an increase in pH. A second study elucidated the effect of four controlled culture redox potentials (-225, -250, -275, and -310 mV) on metabolic carbon flux at a constant pH of 7.25. Lower values of culture redox potential were correlated with increased succinate, acetate, and formate fluxes and decreased ethanol and hydrogen fluxes in C. thermosuccinogenes. Lactate formation was not significantly influenced by redox potential. At the PEP node, the fraction of carbon to oxaloacetate increased with a decrease in redox potential. At the pyruvate node, the fraction of carbon to formate increased, while at the acetyl CoA node, the fraction of carbon flux to acetate increased with reduced redox potential. The presence of hydrogen in the headspace or the addition of nicotinic acid to the growth media resulted in increased hydrogen and ethanol fluxes and decreased succinate, acetate, formate, and lactate fluxes.     

Stereoselective synthesis of polyketide precursors containing an anti-1,3-diol system via a Prins cyclisation and reductive cleavage sequence

A new approach for the stereoselective synthesis of polyketide precursors containing anti-1,3-diol units flanked by a variety of alkyl branches and functional groups through a Prins cyclisation and reductive cleavage sequence is described.     

Numerical simulation of vortex induced vibrations and its control by suction and blowing

The vortex formation and shedding behind bluff structures is influenced by fluid flow parameters such as, Reynolds number, surface roughness, turbulence level, etc. and structural parameters such as, mass ratio, frequency ratio, damping ratio, etc. When a structure is flexibly mounted, the Kármán vortex street formed behind the structure gives rise to vortex induced oscillations. The control of these flow induced vibrations is of paramount practical importance for a wide range of designs. An analysis of flow patterns behind these structures would enable better understanding of wake properties and their control. In the present study, flow past a smooth circular cylinder is numerically simulated by coupling the mass, momentum conservation equations along with a dynamical evolution equation for the structure. An active flow control strategy based on zero net mass injection is designed and implemented to assess its efficacy. A three actuator system in the form of suction and blowing slots are positioned on the cylinder surface. A single blowing slot is located on the leeward side of the cylinder, while two suction slots are positioned at an angle α = 100°. This system is found to effectively annihilate the vortex induced oscillations, when the quantum of actuations is about three times the free stream velocity. The dynamic adaptability of the proposed control strategy and its ability to suppress vortex induced oscillations is verified. The exact quantum of actuation involved in wake control is achieved by integrating a control equation to decide the actuator response in the form of a closed loop feed back system. Simulations are extended to high Reynolds number flows by employing eddy viscosity based turbulence models. The three actuator system is found to effectively suppress vortex induced oscillations.     

Solvent‐mediated pseudo‐quadruple hydrogen‐bond motifs in three lamotrigine–carboxylic acid complexes

Lamotrigine, an antiepileptic drug, has been complexed with three aromatic carboxylic acids. All three compounds crystallize with the inclusion of N,N‐dimethylformamide (DMF) solvent, viz. lamotriginium [3,5‐diamino‐6‐(2,3‐dichlorophenyl)‐1,2,4‐triazin‐2‐ium] 4‐iodobenzoate N,N‐dimethylformamide monosolvate, C₉H₈Cl₂N₅⁺·C₇H₄IO₂⁻·C₃H₇NO, (I), lamotriginium 4‐methylbenzoate N,N‐dimethylformamide monosolvate, C₉H₇Cl₂N₅⁺·C₈H₈O₂⁻·C₃H₇NO, (II), and lamotriginium 3,5‐dinitro‐2‐hydroxybenzoate N,N‐dimethylformamide monosolvate, C₉H₈Cl₂N₅⁺·C₇H₃N₂O₇⁻·C₃H₇NO, (III). In all three structures, proton transfer takes place from the acid to the lamotrigine molecule. However, in (I) and (II), the acidic H atom is disordered over two sites and there is only partial transfer of the H atom from O to N. In (III), the corresponding H atom is ordered and complete proton transfer has occurred. Lamotrigine–lamotrigine, lamotrigine–acid and lamotrigine–solvent interactions are observed in all three structures and they thereby exhibit isostructurality. The DMF solvent extends the lamotrigine–lamotrigine dimers into a pseudo‐quadruple hydrogen‐bonding motif.     

Effect of electron-withdrawing groups on photovoltaic performance of thiophene-vinyl-thiophene derivative and benzochalcogenadiazole based copolymers: A computational study

We report a density functional theory study of the effect of electron-withdrawing groups such as –F, –CN, –NO₂ on the geometrical, optoelectronic, intramolecular charge transfer (ICT), and photovoltaic properties of (E)-1,2-bis(5-alkyl-[2,3′-bithiophene]-2′-yl)ethene (TVT-T) based donor-acceptor (D-A) copolymers with different acceptor units, that is, benzo[c][1,2,5]thiadiazole, benzo[c][1,2,5]oxadiazole, and benzo[c][1,2,5]selenadiazole. The computed optical absorption spectra of the designed compounds lie in the visible and near-infrared regions. Of all the studied copolymers, -CN substituted and Se-based compound displays the lowest HOMO-LUMO (E _{H - L}) gap and optical band gap (E _opt). The exciton binding energy (E _b) is found to be smaller for O-incorporated compounds and -CN substituted copolymer as well, inferring more ICT. The electron-hole coherence concentrated over the D-A units is nearly the same for -CN and -NO₂ substituted compounds, but larger in -F derivatives, indicating weak electron-hole coupling in the formers. Comparatively larger dipole moment (6.421 Debye-9.829 Debye) and charge transfer length (D _CT) (1.976 Å-3.122 Å) for -CN derivatives lead to enhanced ICT properties. The designed donors yield good hole mobilities (0.127-6.61 cm² V⁻¹ s⁻¹) and the predicted power conversion efficiencies are calculated to be as high as ~6%-7% for –CN and –NO₂ substituted compounds.     

New Synthesis of Analogues of the Antihypertensive Active Pharmaceutical Ingredient Irbesartan

A simple and new synthetic approach to various analogues of Irbesartan is described.     

Birefringence and stress growth in uniaxial extension of polymer solutions

Simultaneous measurements of extensional stresses and birefringence are rare, especially for polymer solutions. This paper reports such measurements using the filament stretch rheometer and a phase modulated birefringence system. Both the extensional viscosity and the birefringence increase monotonically with strain and reach a plateau. Estimates of this saturation value for birefringence, using Peterlin’s formula for birefringence of a fully extended polymer chain are in agreement with the experimental results. However, estimates of the saturation value of the extensional viscosity using Batchelor’s formula for suspensions of elongated fibres are much higher than observed. Reasons for the inability of the flow field to fully unravel the polymer chain are examined using published Brownian dynamics simulations. It is tentatively concluded that the polymer chain forms a folded structure. Such folded chains can exhibit saturation in birefringence even though the stress is less than that expected for a fully extended molecule.Simultaneous measurements of stress and birefringence during relaxation indicate that the birefringence decays much more slowly than the stress. The stress-birefringence data show a pronounced hysteresis as predicted by bead-rod models. The failure of the stress optic coefficient in strong flows is noted.Experiments were also performed wherein the strain was increased linearly with time, then held constant for a short period before being increased again. The response of the stress and birefringence in such experiments is dramatically different and can be traced to the different configurations obtained during stretching and relaxation. The results cast doubt on the appropriateness of pre-averaging the non-linear terms in constitutive equations.