Diffusion of condensable vapors in single adsorbent particles measured via concentration-swing frequency response

A concentration-swing frequency response method is extended to examine mass transfer mechanisms and the concentration dependence of mass transfer rates for adsorption of condensable vapors in single adsorbent particles. The adsorption kinetics of water and hexane in BPL activated carbon and the adsorption of water in silica gel are determined at several different concentrations. The mechanism that best describes the adsorption of water in BPL activated carbon is nanopore diffusion. The diffusivity of water in BPL activated carbon has a clear minimum at approximately P/Po = 0.5, and the concentration dependence of the diffusion data are not described well by the Darken relationship. Both nanopore diffusion and the Glueckauf linear driving force models can be used to describe the diffusion of hexane in BPL activated carbon for the pressure range studied, and the dependence of the diffusivity on concentration can be described approximately using the Darken relationship. However, the diffusion of water in silica gel cannot be described by the nanopore diffusion model and is best characterized by the Glueckauf linear driving force model. The results illustrate the ability of concentration-swing frequency response to accurately determine adsorption rate mechanisms and quantify the complex adsorption kinetics of condensable vapors using small quantities of adsorbent.     

A Database of Alkaline-Earth-Coordinated Peptide Cross Sections: Insight into General Aspects of Structure

A database of 1470 collision cross sections (666 doubly- and 804 triply-charged) of alkaline-earth-coordinated tryptic peptide ions [where the cation (M²⁺) correspond to Mg²⁺, Ca²⁺, or Ba²⁺] is presented. The utility of such an extensive set of measurements is illustrated by extraction of general properties of M²⁺-coordinated peptide structures. Specifically, we derive sets of intrinsic size parameters (ISPs) for individual amino acid residues for M²⁺-coordinated peptides. Comparison of these parameters with existing ISPs for protonated peptides suggests that M²⁺ binding occurs primarily through interactions with specific polar aliphatic residues (Asp, Ser, and Thr) and the peptide backbone. A comparison of binding interactions for these alkaline-earth metals with interactions reported previously for alkali metals is provided. Finally, we describe a new analysis in which ISPs are used as probes for assessing peptide structure based on amino acid composition.      

Nonsymmetric Markov processes and hypothesis (H)

Let (X(t),P ^x) and (X(t))},PP}^x) be two Hunt processes in duality with respect to an excessive measure and having resolvents that commute. The main result of this article is that if there is an with 0<<1 so that (U ¹ U ¹ f,f)–U ¹ f² for everyf in ²(), thenX(t) satisfies Hunt's hypothesis (H): every set that is semipolar forX(t) is polar forX(t).     

NMR spectral assignments of three aspidofractinine alkaloids, kopsine, fruticosine and fruticosamine

1D and 2D NMR techniques were used to assign fully the spectra of three aspidofractinine alkaloids, kopsine (1), fruticosamine (2) and fruticosine (3), isolated from a cultivated specimen of the plant Kopsia fruticosa (Apocynaceae). The assignment of the NMR data for 1, 2 and 3 will help in the future assignments of related alkaloids.     

Optimization and characterization of a sulfate based electrodeposition method for alpha-spectroscopy of actinide elements using chemometric analysis

Alpha-spectrometric measurements using Si detectors is the standard method for the determination of alpha emitting actinide elements. This method requires the preparation of sources for analysis which do not degrade the energy spectrum of the emitted alpha particles via sample self-absorption. A variety of methods for the electrodeposition of actinides have been reported in the literature, many of which require long deposition times and lack reproducibility. A sulfate based method has been evaluated for the preparation of these sources using chemometric analysis to optimize the method and evaluate several variables and their interactions with the goal to achieve high yield source preparation in 1 hour or less. Typical resolution for this method is 30 keV or less with recoveries approaching unity.     

Oxidation reactions of azines.

Condensation of 2-([2.2]paracyclophan-4-yl)propene with formaldehyde and amines gave 4-paracyclophanyl substituted -piperidols which were readily dehydrated to the corresponding tetrahydropyridines. N-Methyl substituted 4-paracyclophanyltetrahydropyridine has been oxidized to the corresponding piperidin-2-one.For communication 2, see [1]. This article is also communication 4 in the series Synthesis, structure and biological activity of [2.2]paracyclophanes (for communication 3, see [2]).Russian University of National Friendship, Moscow 117198. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 653–658, May, 1997,     

Evaluation of thermal analysis equipment for the determination of vapor pressure and heat of vaporization

A rapid, relatively simple method for determining vapor pressure and heat of vaporization on small amounts of organic compounds is described. A DuPont 900 differential thermal analyzer (DTA), a Perkin—Elmer Model DSC-1B differential scanning calorimeter (DSC), and a Thomas—Hoover (TH) melting point apparatus were evaluated in this work. Vapor pressure data for a wide variety of organic liquids were obtained by measuring the boiling points of the liquids at pressures ranging from 20 to 735 torr. A computer was used to rapidly plot the experimental data. The average deviations of boiling points from the literature values were 2.3°C for the DTA 1.2°C for the DSC, and 1.5°C for the TH. The vapor pressure data were used to solve the Haggenmacher equation for heat of vaporization (ΔH_v). The deviations of the experimental values for ΔH_v. from the literature values were 5.5%, 8.3%. and 3.3% for the DTA, DSC, and TH methods, respectively.     

Preferred conformations of enol ethers in solution: Detection of an equilibrium by kinetic nuclear overhauser effects

n.O.e. difference spectra reveal that the preferred solution conformation of methyl enol ethers has the methyl group $\text{syn}$-periplanar to the double bond; n.O.e kinetics in a methoxy—heptatriene demonstrate the presence of both possible periplanar conformations, the energy difference being $\text{ca}$ 1 kcal/mole.     

Synthesis of β=iodo-t-butyl and methyl ethers from the reaction of alkenes with t-butyl and methyl hypoiodites

$\text{t}$-Butyl or methyl hypoiodite, generated from potassium t-butoxide or sodium methoxide and iodine monochloride, react with olefins via a bridged iodonium ion intermediate giving the $\text{trans}$-vicinal iodo -$\text{t}$-butyl or -methyl ethers.