2-D Simulation of Non-isothermal Fate and Transport of a Drip-applied Fumigant in Plastic-mulched Soil Beds. I. Model Development and Performance Investigation

Pre-plant application of toxic fumigants to soil beds covered by plastic film is commonly used in agriculture to control soil-borne pathogens. Plastic mulch covers tend to physically suppress the emissive loss of gaseous fumigant to the atmosphere. When liquid fumigant metham sodium (MS) is applied in irrigation water to field soil, it is rapidly transformed to the gaseous methyl isothiocyanate (MITC). The gaseous MITC is a potential atmospheric contaminant, and any untransformed MS is a potential contaminant of underlying groundwater due to the high water solubility of MS. A finite element numerical model was developed to investigate two-dimensional MITC fate/transport under non-isothermal soil conditions. Directional solar heating on soil beds, coupled heat and water flow in the soil, and non-isothermal chemical transport were included in the model. Field soil data for MITC distribution, soil water content, meteorological data, and laboratory data were used to verify the model for soil beds covered with plastic mulch. Four possible scenarios were considered: low and high drip-irrigation rates and low and high water contents. The movement of the center of MITC mass in the soil profile was effectively simulated. The lower drip-irrigation rate of MS yielded more extensive coverage of MITC in the plastic-covered soil bed. The lower soil air contents due to higher soil water contents for the higher irrigation rate resulted in high concentrations of soil MITC. NRMSE (normalized root mean square error) calculations further verified that the model predicted fumigant fate/transport well under these non-isothermal field conditions.     

Organocatalytic stereoselective synthesis of passifloricin A

The enantioselective synthesis of passifloricin A has been achieved in high diastereomeric excess. The 1,3-polyol moiety was constructed by iterative proline-catalyzed sequential α-aminoxylation and Horner-Wadsworth-Emmons (HWE) olefination of aldehydes while the synthesis of lactone moiety was achieved by ring-closing metathesis (RCM).     

Characterization of the elusive disulfide bridge forming human Hb variant: Hb Ta-Li β83 (EF7)Gly → Cys by electrospray mass spectrometry

An electrospray mass spectrometric approach to the identification of a human hemoglobin (Hb) variant involving a Cys residue incorporation is presented. In Hb Ta-Li (beta83Gly --> Cys), Cys83 forms inter-molecular disulfide bridges. Routine analysis of the denatured Hb showed the presence of a minor beta chain variant whose mass apparently was 1 Da less than the expected mass difference of 46 Da for a Gly --> Cys substitution. Reduction of the globin chains with dithiothreitol gave an intense monomer with the expected mass difference for the Gly --> Cys substitution. After reprocessing the original raw data from the denatured Hb and taking into account the possibility of dimer formation, a component was revealed whose mass was consistent with a disulfide linked dimer of Ta-Li beta globins. The mutation was localized to peptide betaT10 by analysis of a tryptic digest. Tandem mass spectrometry and DNA sequencing confirmed the Gly --> Cys substitution occurred at residue 83 of the beta chain. Problems encountered in identifying the components in mixtures of monomers and dimers are discussed.     

Comparative study of the three different fluorophore antibody conjugation strategies

The progression in bioconjugational chemistry has significantly contributed to the evolution and success of protein biology. Mainly, antibody chemistry has been a subject of intensive study owing to the expansion of research areas warranted by using various derivatives of conjugated antibodies. Three reactive moieties (amine, sulfhydryl and carbohydrate) in the antibodies are chiefly favored for the conjugational purpose. This feature is known for decades, nevertheless, amine based conjugation is still the most preferred strategy despite the appreciation the other two methods receive in conserving the antigen binding affinity (ABA). No single report has been published, according to our knowledge, where these three conjugation strategies were applied to the same fluorophore antibody systems. In this study, we evaluated conjugation yield, time demand and cost efficiency of these conjugation procedures. Our results showed that amine based conjugations was by far the best technique due to its simplicity, rapidity, ease of operation, higher conjugate yield, cheaper cost and potential for larger fluorophore/protein labeling ratio without having much effect in ABA. Furthermore, sulfhydryl labeling clearly excelled in terms of reduced non-specific binding and mild effect in ABA but was usually complicated by an asymmetric antibody reduction due to mercaptoethylamine while carbohydrate oxidation based strategy performed the worst during our experiment.     

B and collider physics: Working group report

This report summarises the work done during WHEPP-6 (Institute of Mathematical Sciences, Chennai, India, Jan 3–15, 2000) in Working group on ‘B and collider physics’.     

A note on disturbances in a piezoelectric slab

Summary In the present note, the equations of electricity and the equations of motion have been used to investigate the disturbances in a piezoelectric slab excited by a step electric field. The application of the Laplace transform facilitates the solution of the problem.     

A high resolution field ion microscopic study of Fe40Ni40B20 metallic glass imaged at liquid hydrogen temperature

Metallic glass Fe₄₀Ni₄₀B₂₀ is imaged at liquid hydrogen temperature in field ion microscope. Pair and angular distributions are obtained from the analysis of a large number of micrographs. The pair distribution is found to exhibit features typical of metallic glasses. The angular distribution agrees well with the theoretical distribution for Lennard-Jones glass obtained by Jacobaeus et al. The closer agreement achieved has been attributed to the better experimental conditions and the improved resolution of field ion microscope.     

Rapid and selective oxidation of benzyl alcohols to aldehydes and ketones with novel vanadium polyoxometalate under solvent-free conditions

A novel vanadium polyoxometalate [(C₆H₅CH₂)(CH₃)₃N]₃[H₃V₁₀O₂₈]3H₂O works as a useful oxidant for selective and rapid oxidation of benzylic alcohols to the corresponding carbonyl compounds in the presence of PTSA under solvent-free, room temperature in excellent yield.     

Kinetics of oxidation of hydrogen peroxide by [Mn3 IV(μ-O)4(phen)4(H2O)2]4+ (phen = 1,10-phenanthroline) in weakly acidic aqueous media

In the 3.33–4.95 pH range, buffered with an excess of phenanthroline (phen), [Mn ₃ ^IV (-O)₄(phen)₄(H₂O)₂]⁴⁺ (1) quantitatively oxidises H₂O₂ to O₂; the only manganese product is [Mn ₂ ^III,IV (-O)₂(phen)₄]³⁺ (2), provided a large excess of H₂O₂ is avoided; an excess of H₂O₂ [ > 7 × (1)] reduces (1) to Mn²⁺. When (1) and H₂O₂ were mixed in the stoichiometric molar proportion (1:0.75), the measured second-order rate constant for the reduction of (1) to (2) increased with increasing [H⁺], tending to saturate at lower pH. Added phenanthroline did not affect the rate constant. The results suggest an inner-sphere mechanism, ca. 10 times higher kinetic activity for (1) than for its hydroxo derivative [Mn ₃ ^IV (-O)₄(phen)₄(OH)(H₂O)]³⁺ (1h), and a hydrolysis constant K _a = (2.9 ± 1) × 10^–4 mol dm^–3 for (1) (1h) + H⁺.