The combined effect of silanols and the reversed-phase ligand on the retention of positively charged analytes

The nature of the interaction of positively charged analytes with the surface of reversed-phase bonded phases has been investigated as a function of both pH and volume fraction of organic modifier. Studies of the combined effect of both the parameters have been previously reported by us, and the data presented here further demonstrate a multiplicative interaction between pH and the concentration of organic modifier in the mobile phase. Fitting of the data as functions of pH and eluent composition clearly shows that the hydrophobically assisted ion-exchange process dominates over a purely reversed-phase or a pure ion-exchange retention mechanism. The underlying theory is developed in detail, and the mechanism is elucidated using several reversed-phase packings of substantially different character.     

Role of ion pairing in anionic additive effects on the separation of cationic drugs in reversed-phase liquid chromatography

Mobile phase additives can significantly affect the separation of cationic drugs in reversed-phase liquid chromatography (RPLC). Although there are many applications for anionic additives in RPLC separations, the retention mechanism of basic drugs in the presence of inorganic and highly hydrophilic anionic species in the mobile phase is not at all well understood. Two major retention mechanisms by which anionic additives can influence the retention of cations are: (1) ion pair formation in the mobile phase with subsequent retention of the neutral ion pair; (2) pre-sorption of anionic additives on the stationary phase followed by "dynamic ion-exchange" or "electrostatic interaction" with the analytes. Because the use of ion pair chromatography in the separation of proteins, peptides, and basic drugs is rapidly increasing, understanding the retention mechanism involved is becoming more important, especially for the smaller commonly used hydrophilic anionic additives (e.g., formate HCOO, chloride Cl-, trifluoroacetate CF3COO-, perchlorate ClO4-, and hexafluorophosphate PF6-). In this work, we compared various anionic additives in light of their effects on the retention of basic drugs. As did many others we found that the addition of anionic additives (Cl-, CF3COO-, ClO4-, PF6-) profoundly influences the retention of basic drugs. In order to explain the data and differentiate the mechanisms by which the anionic additives perturb the chromatography, we used ion pair formation constants independently measured by capillary electrophoresis (CE) under the mobile phase conditions (pH, solvent composition) identical to those used in chromatography. Agreement between the predicted and experimental chromatographic data under various conditions was evaluated. Under specific circumstances (e.g., pH, stationary phase, and nature of anionic additive), we conclude that the ion pair mechanism is more important than the dynamic ion-exchange and at other conditions it remains a significant contribution.     

Evaluation of hydrogen ion concentrations in prostates from rats and dogs using fluorescent confocal microscopy

The knowledge of intracellular spatial distribution of pH in prostates in animal models reflective of human prostate may have implications for drug development upon pH dependent drug delivery and activity. Freshly dissected prostate tissues (in vitro) or the entire prostate gland (in vivo) were loaded with fluorescent dyes and viewed using confocal microscopy. Images were initially taken in tissues perfused with RPMI-1640 medium. Calibration in situ was performed with high potassium buffers of known pH containing nigericin. Acetoxymethyl ester carboxy-SNARF-1 was visible in epithelial cells (but not stroma) in rat and dog prostates. The pH of lysosomes in prostate epithelial cells was 5.2 as determined by fluorescence of Lyso Sensor Green DND-189. A method of in situ confirmation of tissue viability was developed by a secondary loading and visualization of the BCECF fluorescent dye. Besides the direct measurement of the pH in rat and dog tissues (pH ≈ 7.0), a method of pH measurement in prostate tissue (rather than in cell culture) was developed.     

Kinetic study of the reactions of the hydroxyl radical with ethane and propane

Absolute rate coefficients for the reactions of the hydroxyl radical with ethane (k₁, 297–300 K) and propane (k₂, 297–690 K) were measured using the flash photolysis–resonance fluorescence technique. The rate coefficient data were fit by the following temperature-dependent expressions, in units of cm³/molecule·s: k₁(T) = 1.43 × 10^?14T^1.05 exp (?911/T) and k₂(T) = 1.59 × 10^?15T^1.40 exp (-428/T). Semiquantitative separation of OH-propane reactivity into primary and secondary H-atom abstraction channels was obtained.     

Acylaluminum dichlorides

Evidence has been obtained for the formation of acylaluminium dichlorides by transmetalation between Cp₂Zr(Cl)(acyl) and AlCl₃. They have been shown to be reactive toward electrophiles at both the carbon and the oxygen of the acyl group.     

Elastic scattering and ω meson production near the threshold of π−p→ω+n

Measurements are reported of the differential cross section for the reaction π^?+p→ω+n from threshold to a final-state c.m. momentum $\text{P}{}^1\text{of}\text{200}\text{MeV}\text{/c}$. The previously reported fall in total cross section $\text{σ/P}{}^1$ below about 100 MeV/c is again seen. The differential cross section remains close to isotropic over the entire range. A paralle experiment on the variation in the elastic differential cross section across the threshold shows evidence of this threshold. The elastic data cover a range of incident moments from 1010 to 1180 MeV/c in steps of 5 MeV/c.     

Morphometric analysis of hair cells in the chinchilla cochlea

Ten chinchilla cochleas which ranged in length from 16.00 to 19.71 m were used for this study. The cross-sectional area and perimeter of the inner and outer hair cells and their nuclei were determined at two locations per cochlear turn and at the junction between each of the turns (11 locations from apex to base). Some interanimal variation in hair cell dimensions was noted. However, none of these size variations could be attributed to any known differences among the animals. It was concluded that the data reported here represent the natural variation in hair cell size in chinchillas. The data establish a baseline to which the dimensions of cells from abnormal cochleas can be compared, regardless of the length of the cochlea or the base-to-apex location of the cells.     

Evidence for the production of slow antiprotonic hydrogen in vacuum

We present evidence showing how antiprotonic hydrogen, the quasistable antiproton (p)-proton bound system, has been synthesized following the interaction of antiprotons with the molecular ion H2+ in a nested Penning trap environment. From a careful analysis of the spatial distributions of antiproton annihilation events, evidence is presented for antiprotonic hydrogen production with sub-eV kinetic energies in states around n=70, and with low angular momenta. The slow antiprotonic hydrogen may be studied using laser spectroscopic techniques.     

Functional polymers: scanning force microscopy insights

Scanning force microscopy (SFM) and related techniques make it possible to visualize polymer systems with a molecular resolution. Beyond imaging, they also enable the unveiling of a variety of (dynamic) physico-chemical properties of both isolated polymer chains and their supramolecular architectures, including structural, mechanical and electronic properties. This article reviews recent progress in the use of SFM on polymers, with a particular emphasis on the mechanical properties of copolymers and single polymer chains, as well as on the bottom-up fabrication of supramolecular polymeric (helical) nanostructures in particular based upon pi-conjugated macromolecules as building blocks for nanoelectronics. Through a detailed understanding of the polymer behavior, we propose solutions for the generation of organic functional (nano)systems.     

Flexible isosurfaces: Simplifying and displaying scalar topology using the contour tree

The contour tree is an abstraction of a scalar field that encodes the nesting relationships of isosurfaces. We show how to use the contour tree to represent individual contours of a scalar field, how to simplify both the contour tree and the topology of the scalar field, how to compute and store geometric properties for all possible contours in the contour tree, and how to use the simplified contour tree as an interface for exploratory visualization.