Modeling of submicrometer aerosol penetration through sintered granular membrane filters

We present a deep-bed aerosol filtration model that can be used to estimate the efficiency of sintered granular membrane filters in the region of the most penetrating particle size. In this region the capture of submicrometer aerosols, much smaller than the filter pore size, takes place mainly via Brownian diffusion and direct interception acting in synergy. By modeling the disordered sintered grain packing of such filters as a simple cubic lattice, and mapping the corresponding 3D connected pore volume onto a discrete cylindrical pore network, the efficiency of a granular filter can be estimated, using new analytical results for the efficiency of cylindrical pores. This model for aerosol penetration in sintered granular filters includes flow slip and the kinetics of particle capture by the pore surface. With a unique choice for two parameters, namely the structural tortuosity and effective kinetic coefficient of particle adsorption, this semiempirical model can account for the experimental efficiency of a new class of "high-efficiency particulate air" ceramic membrane filters as a function of particle size over a wide range of filter thickness and texture (pore size and porosity) and operating conditions (face velocity).     

PHOTOMODIFICATION OF HUMAN ERYTHROCYTES: EXTERNAL HEAVY ATOM EFFECT, SELECTIVE PERMEABILITY AND PROPERTIES OF THE ANION PERMEATION PATHWAY

Abstract— Anion permeability was studied in normal and photomodified erythrocytes and the role of anion species in photomodification and singlet oxygen generation was evaluated. Relative permeability to halides and nitrate was assessed using lysis rates in valinomycin-treated cells to make anion permeation rate-limiting. In non-photomodified cells the normal high temperature dependence (E:, = 67 kJ/mol; 16 kcalhol), selectivity sequence (NO, > I > Br > F > Cl) and sensitivity to block by the stilbene derivative HzDIDS were confirmed. In cells photomodified by illumination in the presence of phloxine B the anion permeability was severely perturbed. The temperature dependence was strongly reduced, the permeability to ions other than fluoride increased, leading to a reversal of the F/CI selectivity, and the capacity to be blocked by HIDIDS was lost. Pretreatment with NEM and posttreatment with DTE did not affect rates of photohemolysis. The amount of photomodification varied with species of anion present in the reaction medium, being greatest for F and smallest for I. Rates of singlet oxygen generation in aqueous solution measured by the RNO bleaching method followed the same anion sequence, suggesting a strong external heavy atom effect.     

Enthalpies of Dilution of Aqueous Solutions of NaOH, KOH, and CsOH at 300, 325, and 350°C

Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of KOH and CsOH at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and for aqueous solutions of NaOH, KOH, and CsOH at 350°C and 17.6 MPa. Previously collected dilution enthalpies for aqueous solutions of NaOH at 300°C and 9.3 MPa and at 325°C and 12.4 MPa were included when fitting the Pitzer parameters. The concentration range of the hydroxide solutions was 0.5–0.02 molal. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for alkali metal ion association with hydroxide ion were estimated from the heat data. For all systems, the enthalpy changes and entropy changes were positive and had accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.     

Proton affinity of β-oxalylaminoalanine (BOAA): Incorporation of direct entropy correction into the single-reference kinetic method

A new version of the single-reference-extended kinetic method is presented in which direct entropy correction is incorporated. Results of calibration experiments with the monodentate base pyridine and the bidentate base ethylenediamine are presented for which the method provides proton affinities in excellent agreement with published values and reasonable predictions for the protonation entropies. The method is then used to determine the proton affinity and protonation entropy of the non-protein amino acid beta-oxalylaminoalanine (BOAA). The PA of BOAA is found to be 933.1 +/- 7.8 kJ/mol and a prediction for the protonation entropy of -39 J mol(-1) K(-1) is also obtained, indicating a significant degree of intramolecular hydrogen bonding in the protonated form. These results are supported by hybrid density functional theory calculations at the B3LYP/6-311++G**//B3LYP/6-31+G* level. They indicate that the preferred site of protonation is the alpha-nitrogen atom (PA = 935.0 kJ/mol) and that protonated BOAA has a strong hydrogen bond between the hydrogen on the alpha-amino group and one of the carbonyl oxygen atoms on the side chain.     

Comparison of total folate concentrations in foods determined by microbiological assay at several experienced U.S. commercial laboratories

Analysis of total folate concentration measured by microbiological assay in a variety of foods submitted in a routine manner to experienced laboratories that regularly perform folate analysis on fee-for-service basis was evaluated. Homogenates of fresh strawberries, frozen spinach, orange juice, frozen meat and vegetable pizza, dry macaroni, and dried pinto beans were prepared and stored under conditions previously determined to maintain stability of folate content. An aliquot of each composite and of 3 certified reference materials were sent on each of 4 occasions to 4 laboratories. Results for macaroni and pizza, the only folic acid-fortified foods, had considerably lower between-laboratory variation (CV(B)) with CV(B) of 9-11% versus >45% for other foods. Mean total folate ranged from 14 to 279 microg/100 g for a mixed vegetable reference material, from 5 to 70 microg/100 g for strawberries, and from 28 to 81 microg/100 g for wholemeal flour. Only 1 laboratory reported using a tri-enzyme extraction, and all laboratories used folic acid fortified foods as internal control materials. Users of commercial total folate analysis should understand the uncertainty in values determined by microbiological assay, particularly for foods containing primarily naturally occurring folate, which may not be apparent when replicate samples are not submitted for analysis.     

Synthesis and Structure of Environmentally Relevant Perfluorinated Sulfonamides

Alkylated perfluorooctanesulfonamides are compounds of environmental concern. To make these compounds available for environmental and toxicological studies, a series of N-alkylated perfluorooctanesulfonamides and structurally related compounds were synthesized by reaction of the corresponding perfluoroalkanesulfonyl fluoride with a suitable primary or secondary amine. Perfluoroalkanesulfonamidoethanols were obtained from the N-alkyl perfluoroalkanesulfonamides either by direct alkylation with bromoethanol or alkylation with acetic acid 2-bromo-ethyl ester followed by hydrolysis of the acetate. N-Alkyl perfluorooctanesulfonamidoacetates were synthesized in an analogous way by alkylation of N-alkyl perfluoroalkanesulfonamides with a bromo acetic acid ester, followed by basic ester hydrolysis. Alternatively, N-alkyl perfluoroalkanesulfonamides can be alkylated with an appropriate alcohol using the Mitsunobu reaction. Perfluorooctanesulfonamide was synthesized from the perfluorooctanesulfonyl fluoride via the azide by reduction with Zn/HCl. All perfluorooctanesulfonamides contained linear as well as branched C₈F₁₇ isomers, typically in a 10:1 to 30:1 ratio. The crystal structures of N-ethyl and N,N-diethyl perfluorooctanesulfonamide show that the S-N bond has considerable double bond character. This double bond character results in a significant rotational barrier around the S-N bond (ΔG^≠ = 62-71 kJ mol⁻¹) and a preferred solid state and solution conformation in which the N-alkyl groups are oriented opposite to the perfluorooctyl group to minimize steric crowding around the S-N bond.     

Tetramethylcyclopentadienylselenium derivatives

Bis(1,2,3,4-tetramethylcyclopentadienyl)selane (1) has been prepared by the reaction of tetramethylcyclopentadienyllithium (Cp(t)Li) with selenium bis(diethyldithiocarbamate). Treatment of Cp(t)Li with elemental selenium, followed by air oxidation, led to loss of the allylic hydrogen atom, and formation of the novel tricyclic compound 1,4,5,6,7,10,11,12-octamethyltricyclo[7.3.0.0]-2,8-diselenadodeca-3,5,9,11-tetraene (2). The sulfur analogue of 2 has been obtained by a similar procedure. The X-ray crystal structures of compounds 1 and 2 have been determined, and the molecular geometry observed for has been probed using DFT calculations.     

The partial hydrogenation of small unsaturated molecules by osmium cluster compounds. The reaction of diispropylcarbodiimide with H2Os3(CO)10

The products (μ-H)[μ-η²-(CH₃)₂CHNHCNCH(CH₃)₂]Os₃(CO)₁₀, I, and (μ-H)- [μ-η²-(CH₃)₂CHNHCO]Os₃(CO)₉[CNCH(CH₃)₂], II have been obtained from the reaction of H₂Os₃(CO)₁₀ with diisopropylcarbodiimine. Both products have been investigated by infrared and ¹H NMR spectroscopies, and by single crystal X-ray diffraction analyses. For I: Space group, P2₁/c, a12.840(4), b  15.724(4), c 12.638(4) Å, β 106.91(2)°, V  2441(2) ų, Z4, ? calc  2.66 g/cc. For 2869 reflections, R  0.051 and R_w  0.052. I contains an N-hydrido, N-isopropylamidinyl ligand bridging one edge of a triangular cluster of three osmium atoms. It was apparently formed by the incorporation of one carbodiimide molecule into the coordination sphere of the cluster followed by the transfer of one hydride ligand to one of the nitrogen atoms. For II: Space group P2 ₁/n;a  13.936(7), b  12.146(2), c  15.509(6) Å, β  105.20(4)°, V  2533(3) Å, Z  4, ?calc  2.57 g/cc. For 3065 reflections, R  0.052 and R_w  0.057. II contains an N-hydrido, N-isopropylformamido ligand bridging one edge of a triangular cluster of three osmium atoms and an isopropylisocyanide ligand. The molecule appears to have been formed by the cleavage of an NCH(CH₃)₂ moeity from one carbodiimide molecule and the transfer of it together with one hydride ligand to the carbon atom of a carbonyl group. The resultant formamido ligand bridges an edge of the cluster. The remaining fragment of the carbodiimide molecule bonds to one of the metal atoms of the cluster as a terminal isocyanide ligand. When heated, I loses one mole of carbon monoxide and forms the new cluster complex (μ-H)[μ₃-η²-(CH₃)₂CHNHCNCH-(CH₃)₂]Os₃(CO)₉ III. On the basis of electron counting schemes, III is believed to contain a triply-bridging amidinyl ligand serving as a five electron donor. Most importantly, no II was formed from I indicating that it is not a precursor -to II. A mechanism for the formation of I and II is presented and discussed.