Structure and electronic properties of "DNA-gold-nanotube" systems: a quantum chemical analysis

The development of novel DNA sensors is a crucial issue in the diagnosis of pathogenic and genetic diseases. We have used density functional theory (DFT) to investigate the performance of hybrid DNA sensors consisting of a gold atom (Au) deposited on two types of single-walled carbon nanotubes: armchair SWCNT(8,0)/Au and zigzag SWCNT(5,5)/Au and compared these with bare Au. We also chose adenine:thymine (A:T) as a Watson-Crick base pair of the DNA double helix. In the recognition probe, SWCNT/Au/A, adenine is immobilized on the SWCNT/Au supporter via its active N7 anchor point. After thymine hybridization (SWCNT/Au/A:T), the overall modulations compared with the original systems. Due to the complimentary functions of gold, which acts as a powerful electron withdrawing and transmitting group and of the SWNCTs, which act as electron collecting centers, respectively, the hybrid systems, "SWNCTs/Au", were found to exhibit more stability and sensitivity than the Au center alone. The changes in the HOMO-LUMO band gaps and in the atomic partial charges upon binding of thymine were rather small, but the change of the overall dipole moment was considerably larger in SWCNT/Au/A than it was in Au/A alone. The overall results suggest that the "SWCNTs/gold" system is a potential candidate for a nanostructure-based DNA sensor.     

Crystal Structure, Thermal and Magnetic Behavior of Inorganic–Organic Hybrid [VIV 4O10 VV 2O4] (C6H14N2)·H2O Polymeric Framework

Summary The inorganic–organic hybrid [V^IV ₄O₁₀V^V ₂O₄] (C₆H₁₄N₂)·H₂O polymeric framework was prepared under mild hydrothermal conditions from a mixture of DABCO and V₂O₅ in deionized water with a 1:1:450 mole ratio, at neutral pH. The reaction was carried out at 180 °C for 3 days under autogenous pressure yielding phase pure crystals product. The crystal structure was studied using both powder and single crystal X-ray crystallography, revealing the structure to be of the ({UuDd}:T*)α′ type in the SP+T class and Z-T subclass. The presence of the organic cation was confirmed by FT-IR spectrum and chemical composition analysis. The structure was thermally stable up to over 400 °C, and showed ferromagnetic character at room temperature with the maximum molar susceptibility of 8.26 × 10⁻³ emu/mol⁻¹ at zero applied field.     

Probing chirality of a lipid tubular by confocal Raman microscopy

The chiral phospholipids 1,2-bis-(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9 PC) can self assemble into lipid nanotubules. This hollow cylindrical supramolecular structure shows promise in a number of biotechnological applications. The mechanism of lipid tubule formation was initiated by assembling of lipid bilayer sheets from amphiphilic solution. Upon cooling, small ribbons were detached from the sheets and rolled up into helical tubules. The lipid tubules obtained were 0.6-0.8 microm in diameter and approximately 50 microm in length. Raman spectra of individual polymerized lipid tubules were measured by focused laser excitation of 532 nm leading to intense and reproducible Raman spectra. The chirality of lipid tubules was investigated by atomic force microscopy (AFM) and confocal Raman microscopy. We report the Raman mapping images revealing helical tubular profiles of C=C stretching and C[triple bond]C stretching of lipid tubules. Circular dichroism property of lipid tubules has also been probed with a 532 nm laser.     

PH sensitive structural uniformity of rice husk ash‐derived MCM‐41 silica

In this study, highly uniform MCM‐41 mesoporous silica was synthesised from rice husk ash‐derived sodium silicate using cetyltrimethyl ammonium chloride (CTAC) as a template. The chemical composition of the gel mixture was based on a SiO₂:CTAC:H₂O molar ratio of 1:0.5:75. When the pH value was initially controlled at ranges of 5.0–10.5 for 5 h and then immediately adjusted to 11.25 for the next 1 h, the structural uniformity of MCM‐41 was abruptly increased by 3.3–7.5 times of the single pH value at 11.25, respectively. Moreover, thermal and hydrothermal stabilities at 900 and 250°C were clearly observed. © 2012 Canadian Society for Chemical Engineering     

UNIFORMITY OF CHANGE IN POROUS CATALYST ACTIVITY DURING A MULTI-PULSE TAP EXPERIMENT

Uniformity of change in catalyst activity during a multi-pulse TAP experiment with porous catalyst was theoretically analyzed for a TAP reactor with the ratio of the catalyst bed thickness to the reactor length of 1/30. The analysis was performed by simulation of an irreversible adsorption process. The catalyst change is described by the change in the occupied/unoccupied fractional surface coverages. The intraparticle uniformity is indicated by a small magnitude of Δθ _p,max , the maximum difference between the occupied fractional surface coverages at the outermost and the innermost of the catalyst pellet during the multi-pulse experiment. In the interparticle region, the indicating quantity is Δθ _b,max , the maximum difference between the pellet-outermost fractional surface coverages at the inlet and the outlet of the catalyst bed. It was found that Δθ _p,max generally depends only on the effectiveness factor in the first pulse experiment, η. For η ≥ 0.94, Δθ _p,max  ≤ 0.05. In addition, Δθ _b,max depends only on the gas conversion in the first pulse experiment, X. For X ≤ 0.7, Δθ _b,max  ≤ 0.05.     

DEM MODELING AND SIMULATION OF A DOWN-FLOW CIRCULATING FLUIDIZED BED

A mathematical model based on the distinct element method (DEM) was developed to investigate the hydrodynamics in a gas-solid down-flow circulating fluidized bed reactor (downer). The models consist of the equations of particle motion and fluid motion. The contact force is calculated by using the analogy of a spring, dashpot, and friction slider. Simulation results show that the radial solids holdup and particle velocity profiles are uniform in the core region. Near the wall, the solids holdup is higher with lower particle velocity. An increase in the particle size decreases the solids holdup and increases the particle velocity. The solids holdup decreases with superficial gas velocity but increases with solids circulation rate. Particle velocity increases with gas velocity and solids circulation rate. The solids holdup and particle velocity are almost uniform along the height of the downer except near the distributor. The hydrodynamic behavior from this simulation showed trends similar to those of the experimental results. The results obtained from this model fit better with the experimental results than Kimm's and Bolkan's models do.     

Independence of active substance profiles from the pulse response experimental procedure

The described computational experiment focuses on producing a controlled catalyst activity distribution. Using TAP technique, the activity profile on the solid catalytic material surface is created by adsorption of pulsed feed gas or the like process and is controlled by the total amount of pulsed gas following the coincidence property. The coincidence property is also applicable for other diffusion + irreversible adsorption processes like wet impregnation to prepare catalyst with nonuniform distribution of catalytic material. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3574–3577, 2013     

A solution strategy for the film model for non-isothermal gas–liquid reactions

A general solution strategy for the film model for gas–liquid reaction has been proposed using the boundary element method (BEM) of discretization over subintervals in gas–liquid films. Non-isothermal effects in the film are included and the associated temperature changes near the gas–liquid interface are computed. The accuracy of the solution procedure is first established using some simple isothermal and non-isothermal benchmark problems and with semi-analytical solutions. Then illustrative results are presented for a non-isothermal series reaction system to illustrate effects of various parameters such as Arrhenius number, solubility changes with temperature, effect of volatility of the liquid phase reactant, etc. The proposed solution method provides fast and accurate values for interfacial fluxes and fluxes into the bulk liquid in addition to concentration profiles. Hence the method is extremely useful for coupling local effects of the film model with global effects based on CFD coupled compartmental model for gas–liquid reactors.     

On the dynamical instability of packed-bed reactors in the presence of catalyst deactivation

Due to the thermal instability of the packed-bed reactor running an exothermic reaction, unsteady-state operation (for example a fluctuating inflow temperature) can result in a variety of thermal responses. These include the amplification of input temperature perturbations and high-temperature pre-extinction waves. Catalyst deactivation adds further dynamical features to these scenarios. We explore them numerically, using a first-order exothermic reaction and a pseudo-homogeneous (single phase) model of the PBR together with a first-order deactivation model of the catalyst. At low deactivation rate, moving hot spots are found, as well as a non-uniform activity profile of the catalyst. At high deactivation rate, however, high-temperature waves (so-called pre-extinction waves) are followed by the complete extinction of the reactor. The amplification of input temperature perturbations is generally enhanced by the presence of catalyst deactivation. Finally, a power-law model is derived numerically that predicts the resonance frequency for amplification as a function of operating parameters.     

Crystal Structures,Thermogravimetric and Magnetic Properties of Four Organodiamine Templated Vanadium Oxide Frameworks: Influences of Diaminoalkane Templates

Absract A series of four diaminoalkane templated vanadium oxide polymeric frameworks, [V₂^IVO₈V₂^VO₂](C₂H₁₀N₂), [V₂^IVO₈V₂^VO₂](C₃H₁₂N₂), [V₄^IVO₁₀V₂^VO₄](C₄H₁₄N₂) and [V₄^IVO₁₀V₂^VO₄](C₅H₁₆N₂), have been successfully prepared under hydrothermal conditions. The crystal structures are fully characterized revealing layered structures composed of common inorganic building units, namely {V^IVO₅} square pyramids and {V^VO₄} tetrahedra. The layer registries are different depending on the molecular structure of the diaminoalkanes, and can be accounted for by the organic-inorganic interface interactions. The analysis of hydrogen bonds indicates their important role in directing two- and three-dimensional structural architectures. The influences of different diaminoalkanes are also apparent in both thermogravimetric and complex magnetic behaviors, and are discussed in details.