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.     

NANOCAVITY EFFECTS ON N2O DECOMPOSITION ON DIFFERENT TYPES OF FE-ZEOLITES (Fe-FER,Fe-BEA,Fe-ZSM-5 AND Fe-FAU): A COMBINED THEORETICAL AND EXPERIMENTAL STUDY

Nitrous oxide decomposition on iron-exchanged zeolites (Fe-FER, Fe-ZSM-5, Fe-BEA, and Fe-FAU) has been studied both theoretically, by using the ONIOM (B3LYP/6-31G(d,p):UFF) method, and experimentally, by temperature programmed reaction, to determine the effect of different zeolitic nanostructured pore networks on the catalytic activity. The ONIOM quantum mechanical calculations show that the nitrous oxide molecule adsorbs with slightly stronger interactions energies on Fe-FER and Fe-ZSM-5 than on the larger pore Fe-BEA and Fe-FAU zeolites. In the transition state leading to the decomposition of nitrous oxide, the smallest pore ferrierite zeolite exerts the strongest van der Waals interactions on the reacting species and, thus, results in the lowest activation energy. Therefore, the predicted intrinsic activity trend is Fe-FER > Fe-BEA ～ Fe-ZSM-5 ～ Fe-FAU. On the other hand, the temperature programmed reaction on zeolites containing trace amounts of iron impurities shows an observed activity trend of Fe-FER > Fe-BEA > Fe-ZSM-5 > > Fe-FAU. The experimentally observed activity trend can be explained by the intrinsic activity of each zeolite except for Fe-FAU. Nitrous oxide decomposition in Fe-FAU could be limited by the mass transfer process and not governed by the intrinsic activity. It is known that cations are preferentially located on the six-membered ring in the sodalite cage of the faujasite, to which the reactants have a very limited access.     

Comprehensive molecular,probiotic, and quorum-sensing characterization of anti-listerial lactic acid bacteria,and application as bioprotective in a food (milk) model

Listeria monocytogenes is a major foodborne pathogen that adversely affects the food industry. In this study, 6 anti-listerial lactic acid bacteria (LAB) isolates were screened. These anti-listerial LAB isolates were identified via 16S rRNA gene sequencing and analyzed via repetitive extragenic palindromic-PCR. Probiotic assessment of these isolates, comprising an evaluation of the antibiotic susceptibility, tolerance to lysozyme, simulated gastric and intestinal juices, and gut conditions (low pH, bile salts, and 0.4% phenol), was carried out. Most of the isolates were resistant to streptomycin, vancomycin, gentamycin, kanamycin, and ciprofloxacin. All of the isolates were negative for virulence genes, including agg, ccf, cylA, cylB, cylLL, cylLS, cylM, esp, and gelE, and hemolytic activity. Furthermore, autoinducer-2 (a quorum-sensing molecule) was detected and quantified via HPLC with fluorescence detection after derivatization with 2,3-diaminonaphthalene. Metabolites profiles of the Lactobacillus sakei D.7 and Lactobacillus plantarum I.60 were observed and presented various organic acids linked with antibacterial activity. Moreover, freeze-dried cell-free supernatants from Lb. sakei (55 mg/mL) and Lb. plantarum (40 mg/mL) showed different minimum effective concentration (MEC) against L. monocytogenes in the food model (whole milk). In summary, these anti-listerial LAB isolates do not pose a risk to consumer health, are eco-friendly, and may be promising candidates for future use as bioprotective cultures and new probiotics to control contamination by L. monocytogenes in the food and dairy industries.     

The versatile synthesis method for hierarchical micro‐ and mesoporous zeolite: An embedded nanocarbon cluster approach

In this work, we are reporting for the first time the synthesis of hierarchical micro‐ and mesoporous zeolite using silica–carbon (SiO₂/C) composites prepared by pyrolysis of carbonaceous gases in the presence of silica gel. The pyrolysis effectively yielded carbon deposited onto the raw silica material. The obtained SiO₂/C composites were utilised as a bifunctional material, mesoporous template and silica source, for the zeolite synthesis. Tetrapropylammonium hydroxide (TPAOH) was used as a microporous template. The combination of the obtained composites and the TPAOH for the hydrothermal synthesis resulted in the formation of hierarchical micro‐ and mesoporous ZSM‐5. The results from the SEM, TEM, and N₂ adsorption/desorption isotherms, and ²⁷Al MAS NMR characterisations of the synthesised samples obtained after the removal of the templates confirmed the successful formation of the micro‐ and mesoporous zeolites. The mesoporosity of the zeolites could be controlled by adjusting the carbon content in the SiO₂/C composites while the carbon content could be controlled by varying the deposition time and the concentration of the carbonaceous gases used. This controllable and efficient synthesis method is considered to be a promising method for creating hierarchical micro‐ and mesoporous zeolites. © 2011 Canadian Society for Chemical Engineering     

Density functional theory study on catalytic cracking of n‐hexane on heteropoly acid: A comparison with acidic zeolite

We have performed a direct comparison of n‐hexane cracking catalysed by a zeolite (H‐ZSM‐5) and a heteropoly acid (phosphotungstic acid, HPW). This comparison was examined by employing density functional theory, including dispersion energy, M06‐L, for the purpose of understanding these two catalysts for this industrially important reaction. The predicted adsorption energies of hexane are ?21.4 and ?6.8 kcal/mol for H‐ZSM‐5 and HPW, respectively. The protolytic cracking mechanism is proposed to proceed via the first step of the C–C activation and is found to be the rate‐determining step with activation energies of 42.8 and 41.4 kcal/mol for H‐ZSM‐5 and HPW, respectively. We also discuss the advantages and disadvantages of both catalysts for hydrocarbon cracking and give a perspective of utilising cutting‐edge molecular design for a tailor‐made hybrid catalyst. © 2011 Canadian Society for Chemical Engineering