Sheath-assisted focusing of microparticles on lab-on-a-chip platforms

Lab-on-a-chip (LOC) technologies can take advantage of sheath flows for particle/cell focusing before sensing or sorting. The integration of focusing with other microscale manipulation techniques (e.g., sorting) creates a trade-off between the throughput of the device and its performance. Therefore, exploring the effective parameters for cells/particles focusing enables us to improve the desired output of LOC devices. A common configuration for sheath-assisted focusing is Y junctions, which are parametrically studied in this paper. First, a computational model was developed and validated by comparing it with our experimental results. Using COMSOL Multiphysics modeling, the effects of multiple parameters were studied. These parameters include the sheath flow ratio (sheath flow over total flow), width ratio (width of the sheath inlet over the total width), junction angles, and particle size on the focusing width and the distribution of the particles within the focusing region. Then, the numerical data were used to develop two generalized linear models to predict the focusing width of the particles and the standard deviation of the position of the particles. The results showed that the focusing width is greatly impacted by the sheath flow rate ratio. Further, the standard deviation of the position of the particles, which represents the concentration of the particles, is mostly dependent on the flow rate ratio, width ratio, and particle size. Our results provide a better understanding of how the device geometrical and operational factors affect the position of the particles in the development of high-performance on-chip sensing and sorting of both cells and particles.     

Geochemical characterization of miocene core sediments from Shahbazpur gas-wells (Bangladesh) in terms of elemental abundances by instrumental neutron activation analysis

Journal of Radioanalytical and Nuclear Chemistry - Geochemical characterization of Shahbazpur structure (Bengal Foredeep) in terms of elemental abundances obtained from INAA are presented by...     

σ-Holes in Iodonium Ylides: Halogen-Bond Activation of Carboxylic Acids,Phenols and Thiophenols May Enable Their X−H Insertion Reactions

The first systematic evaluation of the electrostatic potential energy maps of iodonium ylides was conducted. We determined that they possess two σ-holes of differing electron deficiencies, with the more electropositive σ-hole located opposite the dative I−C bond to the β-dicarbonyl motif, and the lesser electropositive σ-hole located opposite the iodoarene C−I bond. We also conducted the first systematic evaluation of carboxylic acids, phenols and thiophenols in the O/S-alkylation reaction of iodonium ylides. While carboxylic acids and thiophenols were found to be generally viable, only phenols possessing electron-withdrawing substituents were effective. This high-yielding and highly chemoselective reaction is believed to involve halogen-bond activation of heteroatoms, and nicely complements existing diazo-based methods for alkylation of acidic functional groups.     

Selenium Biofortification: Roles,Mechanisms, Responses and Prospects

The trace element selenium (Se) is a crucial element for many living organisms, including soil microorganisms, plants and animals, including humans. Generally, in Nature Se is taken up in the living cells of microorganisms, plants, animals and humans in several inorganic forms such as selenate, selenite, elemental Se and selenide. These forms are converted to organic forms by biological process, mostly as the two selenoamino acids selenocysteine (SeCys) and selenomethionine (SeMet). The biological systems of plants, animals and humans can fix these amino acids into Se-containing proteins by a modest replacement of methionine with SeMet. While the form SeCys is usually present in the active site of enzymes, which is essential for catalytic activity. Within human cells, organic forms of Se are significant for the accurate functioning of the immune and reproductive systems, the thyroid and the brain, and to enzyme activity within cells. Humans ingest Se through plant and animal foods rich in the element. The concentration of Se in foodstuffs depends on the presence of available forms of Se in soils and its uptake and accumulation by plants and herbivorous animals. Therefore, improving the availability of Se to plants is, therefore, a potential pathway to overcoming human Se deficiencies. Among these prospective pathways, the Se-biofortification of plants has already been established as a pioneering approach for producing Se-enriched agricultural products. To achieve this desirable aim of Se-biofortification, molecular breeding and genetic engineering in combination with novel agronomic and edaphic management approaches should be combined. This current review summarizes the roles, responses, prospects and mechanisms of Se in human nutrition. It also elaborates how biofortification is a plausible approach to resolving Se-deficiency in humans and other animals.     

Cyanoacetic acid hydrazide: An efficient access for the synthesis of multi-functional azine and azole derivatives

Herein, the synthesis of nitrogen-containing heterocyclic scaffolds from heterocyclization of cyanoacetic acid hydrazide derivatives is described. Thiosemicarbazide derivative 1a undergoes base-mediated cyclization producing pyrazole derivative of type 2 . The triazolopyridine 5 was obtained by double cyclization of 1a and benzylidene malononitrile. Compound 1b condensed with ethyl chloroformate to furnish pyrazolooxazine 8 . Compound 1b was added to benzoyl isothiocyanate under thermal condition to form oxadiazine derivative 10 while, keeping the above reactant under room temperature to form acyclic derivative 11 . Using CS₂ as a cyclizing agent for compound 1b yielded pyrazole derivative 13 . Treatment of 1b with I₂ resulted in oxidative cyclization producing pyridazine derivative 14 . Compound 1c cyclized with benzoyl isothiocyanate forming triazolothiazine derivative 18 . While using cinnamoyl isothiocyanate, the acyclic product 22 was obtained. Compound 1c was condensed with formaldehyde leading to oxadiazole derivative 25 .     

Syntheses and 13C NMR spectra of fluorinated adamantane derivatives

The syntheses of a variety of fluorine-containing adamantane derivatives are described. The ¹³C NMR spectra of those compounds with different configurations are interpreted in terms of through-bond and through-space substituent interactions.     

Face-selectivity in [4+2]-cycloadditions to novel polycyclic benzoquinones. Remarkable stereodirecting effects of a remote cyclopropane ring and an olefinic bond

π-Face selectivity in Diels-Alder reactions between specially crafted bicyclo[2.2.2]octane-fused benzoquinones, where the dienophilic moiety is imbedded in an isosteric environment, can be modulated by a remote olefinic bond and a cyclopropane ring. Quantum mechanical calculations while reproducing the observed diastereoselectivities at the TS level indicate the involvement of ground state orbital effects.     

A tabu search approach for the single machine mean tardiness problem

In this paper, a tabu search approach is proposed for solving the single machine mean tardiness scheduling problem. Simulation experiment results obtained from the tabu search approach and three other heuristics are compared. Although computation time is increased, the results indicate that the proposed approach provides a much better solution than the other three approaches.     

On the mechanism of the reduction of 1-phenyl-3-(4-pyridinylmethylene)-2-oxindole with sodium borohydride in methanol

Sodium borohydride reduction of 1-phenyl-3-(4-pyridinylmethylene)-2-oxindole 1 in methanol gives a high yield of the oxindole 2 , a precursor to linopirdine. The reduction is accelerated by methanol and the major by-products during this reduction are the diastereomeric Michael adducts between 1 and 2 and the overreduced products, 9 and 11 . Surprisingly, indole 9 is not derived from further reduction of 2 but is formed concurrently, whereas the ring opened product 11 is the unexpected reduction product derived from 2 .