Effect of irradiation on kinetic behavior of Salmonella Typhimurium and Staphylococcus aureus in lettuce and damage of bacterial cell envelope

This study evaluated effect of gamma irradiation on survival of Salmonella Typhimurium and Staphylococcus aureus on lettuce and damage of cell envelope. S. Typhimurium and S. aureus were inoculated on red leaf lettuce, and they were irradiated at 0, 0.5, 1, 1.5, 2, 2.5, and 3 kGy, and the samples were then stored at 7 and 25 °C for 7 days. Survival of S. Typhimurium and S. aureus were enumerated on xylose lysine deoxycholate agar and Baird–Parker agar, respectively. D₁₀ value (dose required to reduce 1 log CFU/leaf) was calculated, and kinetic parameters (maximum specific growth rate; μ_max and lag phase duration; LPD) were calculated by the modified Gompertz model. In addition, cell envelope damage of the pathogens was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). D₁₀ values were 0.35 and 0.33 kGy for S. Typhimurium and S. aureus, respectively. During storage at 7 °C, S. Typhimurium and S. aureus had significant (P<0.05) growth only on non-irradiated samples up to about 2.5 and 4 log CFU/leaf at 0.42 and 1.28 log CFU/leaf/day of μ_max, respectively. At 25 °C, cell counts of S. Typhimurium and S. aureus on the samples irradiated at 0 and 0.5 kGy increased (P<0.05) up to 3–6 log CFU/leaf. The μ_max of both pathogens were higher in 0 kGy (1.08–2.27 log CFU/leaf/day) and 0.5 kGy (0.58–0.92 log CFU/leaf/day), and LPDs ranged from 1.53 to 3.14 day. SEM and TEM observations showed that cells irradiated at 1.5 and 3 kGy showed disrupted cell membrane. These results indicate that gamma irradiation could be a useful decontamination technology to improve food safety of lettuce by destroying cells of S. Typhimurium and S. aureus.     

Using a nanopore for single molecule detection and single cell transfection

We assert that it is possible to trap and identify proteins, and even (conceivably) manipulate proteins secreted from a single cell (i.e. the secretome) through transfection via electroporation by exploiting the exquisite control over the electrostatic potential available in a nanopore. These capabilities may be leveraged for single cell analysis and transfection with single molecule resolution, ultimately enabling a careful scrutiny of tissue heterogeneity.     

Anion-controlled circular dichroism spectral changes in Hg2+ complexes with a chiral bidentate ligand

Anion-controlled circular dichroism (CD) spectral changes in Hg(2+) complexes with a chiral bidentate ligand are reported. Although the Hg(CF(3)SO(3))(2) and Hg(CF(3)CO(2))(2) complexes with (R)-(-)-1-(naphthalen-1-yl)-N,N-bis(pyridin-4-ylmethyl)ethanamine, (R)-(-)-1, show significant CD spectral changes, no CD spectral changes were observed in the HgCl(2), HgBr(2), Hg(CN)(2), or Hg(CH(3)CO(2))(2) complexes. X-ray analysis indicates that both the (R)-(-)-1-Hg(CF(3)SO(3))(2) and (R)-(-)-1-HgCl(2) complexes form a coordination polymer and a discrete 2:3 [=(R)-(-)-1/HgCl(2)] complex with a figure-eight structure. X-ray crystallography revealed that (i) the Hg-Hg distances bridged by anions vary depending on the anions used and (ii) a coordination polymer cannot be formed when the Hg-Hg distances are too short. Therefore, the formation of a coordination polymer is required to give the observed significant CD spectral changes.     

pH-dependent electron-transport properties of carbon nanotubes

Carbon nanotube electrochemical transistors integrated with microfluidic channels are utilized to examine the effects of aqueous electrolyte solutions on the electron-transport properties of single isolated carbon nanotubes. In particular, pH and concentration of supporting inert electrolytes are examined. A systematic threshold voltage shift with pH is observed while the transconductance and subthreshold swing remain independent of pH and concentration. Decreasing pH leads to a negative shift of the threshold voltage, indicating that protonation does not lead to hole doping. Changing the type of contact metal does not alter the observed pH response. The pH-dependent charging of SiO2 substrate is ruled out as the origin based on measurements with suspended nanotube transistors. Increasing the ionic strength leads to reduced pH response. Contributions from possible surface chargeable chemical groups are considered.     

CHARMM general force field: A force field for drug‐like molecules compatible with the CHARMM all‐atom additive biological force fields

The widely used CHARMM additive all‐atom force field includes parameters for proteins, nucleic acids, lipids, and carbohydrates. In the present article, an extension of the CHARMM force field to drug‐like molecules is presented. The resulting CHARMM General Force Field (CGenFF) covers a wide range of chemical groups present in biomolecules and drug‐like molecules, including a large number of heterocyclic scaffolds. The parametrization philosophy behind the force field focuses on quality at the expense of transferability, with the implementation concentrating on an extensible force field. Statistics related to the quality of the parametrization with a focus on experimental validation are presented. Additionally, the parametrization procedure, described fully in the present article in the context of the model systems, pyrrolidine, and 3‐phenoxymethylpyrrolidine will allow users to readily extend the force field to chemical groups that are not explicitly covered in the force field as well as add functional groups to and link together molecules already available in the force field. CGenFF thus makes it possible to perform “all‐CHARMM” simulations on drug‐target interactions thereby extending the utility of CHARMM force fields to medicinally relevant systems. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Non-crossing quantile regression via doubly penalized kernel machine

Quantile regression provides a more complete statistical analysis of the stochastic relationships among random variables. Sometimes quantile regression functions estimated at different orders can cross each other. We propose a new non-crossing quantile regression method using doubly penalized kernel machine (DPKM) which uses heteroscedastic location-scale model as basic model and estimates both location and scale functions simultaneously by kernel machines. The DPKM provides the satisfying solution to estimating non-crossing quantile regression functions when multiple quantiles for high-dimensional data are needed. We also present the model selection method that employs cross validation techniques for choosing the parameters which affect the performance of the DPKM. One real example and two synthetic examples are provided to show the usefulness of the DPKM.     

Blue upconversion luminescence of CaMoO4:Li+/Yb3+/Tm3+ phosphors prepared by complex citrate method

Li⁺/Tm³⁺/Yb³⁺ co-doped CaMoO₄ upconversion (UC) phosphor was prepared by complex citrate-gel method and UC luminescence properties were investigated. Li⁺/Tm³⁺/Yb³⁺ co-doped CaMoO₄ has intense blue emission induced by ¹G₄??³H₆ transition at 476?nm that is improved 10 times more than that of Li⁺ undoped sample and weak red emission at 647 nm generated by ³F₂??³H₆ transition under excitation at 980?nm. The optimum doping concentration of Li⁺ ions was investigated and UC mechanism of Li⁺/Tm³⁺/Yb³⁺ co-doped CaMoO₄ was discussed in detail.     

SnO2 quantum dots decorated BiOI nanoflowers as a high-performance electrode material for supercapacitor application

Journal of Solid State Electrochemistry - The rational design of low-cost electrode materials with superior redox activity and high electrochemical conductivity has attracted extensive interest for...     

Structural Characteristics of Er Doped LiNbO3 Thin Films Grown by the Liquid Phase Epitaxy Method

Erbium (Er³⁺) doped LiNbO₃ single crystal thin films have been grown LiNbO₃ (001) substrate by the liquid phase epitaxy method. The crystallinity was determined by high‐resolution X‐ray diffraction. The lattice mismatch between Er³⁺ doped LiNbO₃ films and LiNbO₃ (001) substrate was investigated by X‐ray rocking curve analysis. Also we studied the structural characteristics of Er³⁺ doped LiNbO₃ films and surface morphology dependent on the film thickness.     

Suppression of secondary PL emission by indirect photoexcitation

A blend of a newly synthesized polyfluorene(PDHBF) and polyvinylcarbazole(PVK) exhibits a photoluminescence(PL) emission spectrum of PDHBF without an increase in the PL intensity on photoexcitation at 340 nm, the UV-visible absorption maximum of PVK, despite of a substantial spectrum overlap. However, the indirect photoexcitation of the blend suppresses the secondary emission of the PL with the maximum at 520 nm. The chromophores generating the secondary emission are formed when the chromophores are photoexcited above the critical energy level of an excited state. The chromophores formed by the energy transfer have energy lower than the critical energy and fail to form the excimers. A low temperature PL study of the blend in a cryogenic chamber proves that the energy transfer in the system takes place mainly between the excimers of PVK generated by the partially eclipsed dimeric states of two carbazole units and the fluorophores of PDHBF.