Effects of Surface Relaxation on Enantiospecific Adsorption on Naturally Chiral Pt Surfaces

Many high Miller index metals surfaces are naturally chiral, offering opportunities for performing enantiospecific chemistry. Previous theoretical treatments of adsorption on these surfaces have used surfaces truncated from bulk crystals. This paper examines the effect of surface relaxation on enantiospecific adsorption on chiral Pt surfaces by using relaxed surface structures determined using density functional theory.     

Response to walnut olfactory and visual cues by the parasitic wasp Diachasmimorpha juglandis

Diachasmimorpha juglandis is a specialist parasitoid attacking fly larvae in the genus Rhagoletis that feed exclusively on walnut fruit husks. In a free-foraging assay comparing response to uninfested, infested, and mechanically damaged fruits, we first determined that D. juglandis use host feeding damage on the fruit as a cue for host presence. In another free-foraging assay that used artificial walnut models and wind tunnel experiments, D. juglandis distinguished infested from uninfested fruits by using either olfactory or visual cues separately. However, the response rate of wasps in the wind tunnel was raised considerably when visual cues were also available. We analyzed the volatile compounds emitted by cohorts of uninfested, mechanically damaged, and infested fruits 1, 3, 5, 8, and 10 days after oviposition by flies into the infested fruits. Total volatile emissions did not differ significantly among treatments, but quantitative changes in volatiles distinguished infested fruits from uninfested and damaged fruits. The fact that parasitoids did not distinguish between infested and damaged fruits in assays where damage was visible indicates that they rely on visual cues when those are available.     

Fiber-Matrix Interfacial Adhesion Improvement in Carbon Fiber-Bisphenol-A Polycarbonate Composites by Polymer Grafting

Fiber-matrix interfacial adhesion in thermoplastic composites is generally poor due to the lack of formation of strong covalent and/or ionic bonds between the generally inert thermoplastic resins and the surface of the reinforcing fiber. Adhesion can be improved by forming covalent linkages between the fiber and the matrix by grafting a polymer of appropriate compatibility, molecular weight, and sufficient density onto the surface of the fiber. We have grafted low molecular weight polycarbonate and polymethyl methacrylates onto the surface of carbon fibers and measured an improvement in the level of adhesion ranging from 25% to100% over the ungrafted composites. It was also observed that the level of improvement in adhesion appears to be independent of the molecular weight of the grafted polymer. Examination of the fracture surface of these composites reveals that the failure is cohesive in the matrix for the polymer grafted fiber composites, while it is adhesive for the ungrafted composites.     

NONDESTRUCTIVE EXAMINATION OF EPOXY ADHESIVE-BONDED STRUCTURES EXPOSED TO A HUMID ENVIRONMENT: A COMPARISONOF LOW- AND HIGH-FREQUENCY DIELECTRIC MEASUREMENTS

Broadband dielectric measurements (10 -2 to 3 GHz) are reported on the effects of exposure of thick film adhesive-bonded structures to moisture. Measurement of the dielectric properties over a broad frequency range allows identification of water both in voids and as a molecular dispersion in the matrix. Changes in the low frequency region of the dielectric spectrum can be attributed to a combination of processes associated with plasticisation of the adhesive, interfacial polarisation effects, and hydration of the surface oxide layer. The data obtained are complemented by mechanical testing and failure analysis of the bond structure measured as a function of the time of exposure. This study indicates that for thick film adhesives the ageing characteristics are apparently independent of the surface treatment. In one of the joints studied an additional feature is identified which appears to correlate with the premature aging of the joint structure.     

XYLANASE EFFECTS ON PULP DELIGNIFICATION

Xylanase effects on softwood pulp delignification were investigated experimentally and using mathematical models. The effect of xylanase molecular size on pulp delignification was investigated. As xylanase molecular weight decreased from 67 kDaltons to 20 kDaltons, lignin removal from pulp increased from 30 wt% to 48 wt%, respectively. The rate of xylanase-aided pulp delignification was studied using a batch system. The rate-data was fitted to a mathematical model of the batch system that enabled estimation of process parameters including xylanase and lignin effective diffusivities, lignin mass transport coefficient, and effective particle diameter for mass transport. Parameter values thus obtained were used to simulate the semi-batch delignification process, which predicted 84.6% of lignin available to UGA xylanase (MW=39,000 Daltons) would be removed in 2.5 h.     

Editorial

Editorial Introduction

Editorial     

Dufour Gland Contents of Ants of the Cataglyphis bicolor Group

The species of desert-dwelling ants of the Cataglyphis bicolor (Hymenoptera: Formicidae) group are difficult to distinguish by morphological features. Analysis of the secretion from the Dufour glands of workers of a number of colonies was undertaken to see if it provided a clear test of species. Linked 6c-ms showed in all samples straight and branched-chain alkanes, linear alkenes, ketones, aldehydes, acetates, and a group of C₂₂ to C₂₈ esters not previously identified in this genus. Contents of the Dufour glands of C. savignyi from Tunisia and Egypt were similar, and comprised straight and branched-chain alkanes, alkenes and small amounts of esters. C. bicolor from Tunisia contained compounds similar to C. savignyi but was distinguished from the latter by larger amounts of the esters. The major compound in the glands of C. viaticus was tridecane, in contrast to the pentadecane of other species. It also contained a branched alkane, 3-methyltridecane as a major component. Branched-chain esters and a wide variety of acetates were also found in this species. C. diehlii had a limited range of compounds, with branched alkanes almost completely absent and high proportions of pentadecene and dodecyl acetate. C. bombycinus, a sympatric species, but recognized as not belonging to the bicolor group by its different mandibular gland substances, was notable in having butanoate esters in its Dufour glands. Despite these differences among species, both the great variability of individuals from a single colony and the among between conspecific colonies make species diagnosis from a few individuals difficult, in contrast with postpharyngeal glands, which, as recently reported, give a clearer indication of species.     

Phylloquinone (vitamin K1) and dihydrophylloquinone content of fats and oils

Assessment of vitamin K (VK) dietary intakes has been limited by the incompleteness of VK food composition data for the U.S. food supply, particularly for VK-rich oils. The phylloquinone (VK-1) and 2′,3′-dihydrophylloquinone (dK) concentrations of margarines and spreads (n=43), butter (n=4), shortening (n=4), vegetable oils (n=6), and salad dressings (n=24) were determined by RP-HPLC with fluorescence detection. Each sample represented a composite of units or packages obtained from 12 or 24 outlets, which were geographically representative of the U.S. food supply. Butter, which is derived from animal fat sources, had less VK-1 compared to vegetable oil sources. The VK-1 and dK of the margarines and spreads increased with fat content and the degree of hydrogenation, respectively. In some margarines or spreads and in all shortenings, the dK concentrations were higher than the corresponding VK-1 concentrations. As the fat content of salad dressings increased, the VK-1 concentrations also increased. Fat-free foods had <1 μg/100 g of either form of the vitamin. No dK was detected in the salad dressings or oils tested. Some margarines, spreads, and salad dressings may be significant sources of vitamin K in the U.S. food supply.     

Enhanced biosurfactant production by <Emphasis Type="Italic">Corynebacterium alkanolyticum</Emphasis> ATCC 21511 using self-cycling fermentation

Enhanced biosurfactant production by Corynebacterium alkanolyticum ATCC 21511 was accomplished in a self-cycling fermenter (SCF) on a hexadecane substrate. The phospholipid biosurfactant produced during each cycle could be monitored rapidly using fluorescence spectroscopy. By optimizing the cycling pattern of the SCF, significantly better yields of biosurfactant were obtained than previously reported for this microorganism. It was also possible to virtually eliminate the hydrocarbon residue in the product. Harvest concentrations of 1.9 g L⁻¹ were obtained by using a two-stage fermentation. The first step was the growth of C. alkanolyticum in an SCF to yield a harvest of synchronous cells. These cells were transferred to a second vessel for the production stage. The concentration of biosurfactant could be further increased to 2.7 g L⁻¹ by the addition of more hexadecane at the beginning of the second stage.     

Effects of large mammalian herbivores and ant symbionts on condensed tannins of Acacia drepanolobium in Kenya

Condensed tannins have been considered to be important inducible defenses against mammalian herbivory. We tested for differences in condensed tannin defenses in Acacia drepanolobium in Kenya over two years among different large mammalian herbivore treatments [total exclusion, antelope only, and megaherbivore (elephants and giraffes) + antelope] and with four different ant symbiont species on the trees. We predicted that (1) condensed tannin concentrations would be lowest in the mammal treatment with the lowest level of herbivory (total exclusion), (2) trees occupied by mutualist ants that protect the trees most aggressively would have lower levels of tannins, and (3) if chemical defense production is costly, there would be a trade-off between tannin concentrations, growth, and mechanical defenses. Mean tannin concentrations increased from total exclusion treatments to wildlife-only treatments to megaherbivore + antelope treatments. In 1997, condensed tannin concentrations were significantly lower in trees occupied by the ant Crematogaster nigriceps, the only ant species that actively removed axillary buds. Contrary to our prediction, trees occupied by ant species that protect the trees more aggressively against mammalian herbivores did not have lower overall levels of condensed tannins. There was no consistent evidence of a trade-off between tannin concentrations and growth rate, but there was a positive correlation between mean thorn length and mean tannin concentrations across species of ant inhabitants and across herbivore treatments in 1997. Contrary to our expectation, trees had higher tannin concentrations in the upper parts of the canopy where there is little herbivory by mammals.