Experimental detection of one case of benzene epoxidation by a peroxy radical and computational prediction of another

Reaction of the beta-styryl radical with O2 in benzene results in a low yield of benzene oxide, which is shown by isotopic labeling to arise from the solvent. Ab initio and DFT calculations elucidate the mechanism of this reaction, and identify the properties of other radicals that should be more effective promoters of the reaction. The CN radical is found to be one candidate.     

Evaluation of the secondary consolidation of columns for liquid chromatography by ultrasonic irradiation

The consolidation of packed analytical chromatography columns was carried out under ultrasonic irradiation. Columns were first packed using a conventional high pressure downward slurry method. Then, they were subjected to further bed consolidation in the presence of ultrasonic vibration. This process of further bed consolidation is referred to as secondary consolidation. Secondary consolidation was observed to occur more readily in solvents of low viscosity and at low flow-rates (low pressures). Column efficiency was not observed to be a factor affecting the process of secondary consolidation of the packed bed.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Solution-phase detection of dual microRNA biomarkers in serum

A strategy for the simultaneous detection of multiple microRNA (miRNA) targets was developed utilizing fluorophore/quencher-labeled oligonucleotide probe sets. Two miRNA targets (miR-155 and miR-103), whose misregulation has afforded them status as putative biomarkers in certain types of cancer, were detected using our assay design. In the absence of target, the complementary fluorophore-probe and quencher-probe hybridize, resulting in a fluorescence resonance energy transfer-based quenching of the fluorescence signal. In the presence of unlabeled target, however, the antisense quencher-probe can hybridize with the target, resulting in increased fluorescence intensity as the quencher-probe is sequestered beyond the Förster radius of the fluorescent-probe. The assay design was tested in multiple matrices of buffer, cellular extract, and serum; and detection limits were found to be matrix-dependent, ranging from 0.34 to 8.89 pmol (3.4–59.3 nM) for miR-155 and 2.90–11.8 pmol (19.3–79.0 nM) for miR-103. Single, double, and triple nucleotide selectivity was also tested. Additionally, miR-155 concentrations were assessed in serum samples obtained directly from breast cancer patients without the need for RNA extraction. This assay is quantitative, possesses a low detection limit, can be applied in multiple complex matrices, and can obtain single-nucleotide selectivity. This method can be employed for the multiplex detection of solution-phase DNA or RNA targets and, more specifically, for the direct detection of serum miRNA biomarkers.     

Quantum mechanics of seeing

A human being viewing a defocused television tube with sweep voltages turned off will see point scintillations at sufficiently low intensities. We show that quantum mechanics predicts these scintillations. Furthermore, by assuming a response of the human nervous system of a type not inconsistent with experiment, measurement theory is used to show that these scintillations will be distributed in proportion to the magnitude squared of the electron wave function incident upon the television tube screen. This nervous system response is to break up the wave incident upon a spot on the retina into a number of similar waves transmitted by different nerves to the brain. The number of these waves is proportional to the incident energy density. Since the theory itself predicts the proper probability distribution, it is unnecessary to introduce a postulate for it.     

Visualization of viscous fingering in high-performance liquid chromatographic columns. Influence of the header design

Using an on-column visualization technique, band profiles of solutes migrating along an HPLC column were studied. The study showed that, under conditions where viscous fingering is prevalent, the design of the inlet header has little influence on the outcome of the viscous fingers. Two types of headers were studied. The first contained a small diameter inlet frit, which localized the majority of the sample in or near the central region of the column. The second header contained a wide frit and produced a more uniform radial distribution of the sample. In both cases, the extent of viscous fingering was essentially the same.     

Physical evidence of two wall effects in liquid chromatography

Using optical on-column visualization for the study of the migration of sample bands, the radial variations of the local migration rate were studied in the region near the column wall. Photographs of small sample bands migrating along the column at various radial locations were obtained. On-column chromatograms extracted from these photographs showed evidence of two wall effects. The first of these effects was present only within the immediate vicinity of the wall. It is a direct result of the inability of the packing material to form a close packed configuration against the rigid column wall surface. The second wall effect causes a systematic variation of the migration rate of the sample band in the region of the wall, this rate increasing from the wall to the central region of the column. The corresponding images portrayed the classical "wall effect" that chromatographers have long discussed. They also show that this effect extends further into the column than anticipated. As to what are the relative contributions to the results of our observations of the wall effect and of a frit effect discussed in previous publications, this could not be ascertained.     

Visualization of solute migration in chromatographic columns quantitation of the concentration in a migrating zone

The concentration distribution across a zone of iodine migrating along a column made of glass, packed with C18-bonded silica, and eluted with carbon tetrachloride was derived from a quantitative analysis of the photographs of the zone. The photographs were scanned and turned into digital images. The intensity distributions obtained from the measurement of the grayscale intensity were converted into concentration profiles using a calibration method. This procedure is illustrated and suitable corrections are introduced to account for the transverse variation of the optical path length, as a result of using a cylindrical detector cell (the column itself), and for the refraction of light due to the differences between the refraction indices of the glass wall and the liquids involved. An error analysis is also reported. It shows that the method can reliably produce results with a precision of a few percent, allowing on-column evaluation of column performance and the derivation of the radial distributions of the column efficiency, the migration velocity of the zone, and the sample distribution at the head of the column.     

Dichlorocarbene Addition to

In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway.