Fate of photosensitizing furanocoumarins in tolerant and sensitive insects

The fate of [¹⁴C]xanthotoxin (8-methoxypsoralen) was studied in larvae of insect species that are tolerant (Papilio polyxenes Stoll) or sensitive (Spodoptera frugiperda J.E. Smith) to the phototoxic effects of photosensitizing psoralens. Both insects metabolize xanthotoxin by oxidative cleavage of the furan ring, but the detoxification occurs at a much more rapid rate inP. polyxenes in which >95% of an oral 5 g/g xanthotoxin dose is metabolized within 1.5 hr after treatment. The detoxification of psoralens byP. polyxenes appears to occur primarily in the midgut tissue prior to absorption, with the result that the intact phototoxin does not reach appreciable levels in body tissues. Studies with an angular furanocoumarin indicated that isopsoralens are metabolized byP. polyxenes at a somewhat slower rate than observed for psoralens; however, a reduced rate of metabolic detoxification of isopsoralens probably does not explain the fact that psoralen tolerance inP. polyxenes does not extend to the isopsoralen series.     

Decreased sensitivity of mixed-function oxidases frompapilio polyxenes to inhibitors in host plants

Caterpillars ofPapilio polyxenes, the black swallowtail, feed on umbellifers that contain both toxic furanocoumarins and methylenedioxyphenyl compounds such as myristicin and safrole. These phytosynergists enhance the toxicity of furanocoumarins by inhibiting mixed-function oxidases (MFOs), the detoxification enzymes responsible for metabolizing furanocoumarins. In model substrate assays, MFOs fromP. polyxenes are twice as active as MFOs fromHeliothis zea, a generalist herbivore not adapted to feeding on either furanocoumarins or furanocoumarin/phytosynergist combinations.P. polyxenes MFOs are 10 and 46 times less sensitive to inhibition by myristicin and safrole, respectively, thanH. zea MFOs and eight times less sensitive to inhibition by safrole than MFOs fromPapilio troilus, a closely related species that does not encounter furanocoumarin/phytosynergist combinations in its diet. Higher MFO activity and decreased sensitivity to MFO inhibitors are important adaptations that allow black swallowtail caterpillars to feed on many umbelliferous plants.     

Characterization of furanocoumarin metabolites in parsnip webworm,Depressaria pastinacella

Although metabolites of furanocoumarins have been characterized in a wide range of organisms, to date they have been identified in only a single insect species, Papilio polyxenes. Depressaria pastinacella, the parsnip webworm, like P. polyxenes a specialist on Apiaceae, routinely consumes plant tissues higher in furanocoumarin content than does P. polyxenes and is capable of faster cytochrome P-450-mediated detoxification of these compounds. In this study, we characterized metabolites of xanthotoxin, a linear furanocoumarin, and sphondin, an angular furanocoumarin, in midguts and frass of parsnip webworms. Two metabolites were isolated and identified from webworms fed artificial diet containing xanthotoxin. LC-ESI-MS analysis resulted in the determination of a MW of 266 for the compound in the frass and one of the compounds in the midgut; ¹H NMR confirmed its structure as 6-(7-hydroxy-8-methoxycoumaryl)-hydroxyacetic acid (HCHA). The second compound from the midgut had a MW of 252 and was identified by ¹H NMR and ¹³C NMR analysis as 6-(7-hydroxy-8-methoxycoumaryl)-hydroxyethanol) (HMCH). Whereas HCHA has been found in frass of Papilio polyxenes fed xanthotoxin, HMCH has not been reported previously in insects. Although the first step of metabolism of xanthotoxin in webworms as well as P. polyxenes is likely the formation of an epoxide on the furan ring, angular furanocoumarin metabolism in webworms appears to differ. The principal metabolite of sphondin was identified as demethylated sphondin (6-hydroxy-2H-furo[2,3-h]-1-benzopyran-2-one) by LC-ESI-MS and confirmed by ¹H NMR and ¹³C NMR analyses. That webworms produce metabolites of xanthotoxin in common not only with other Lepidoptera (e.g., HCHA) but with other vertebrates (e.g., HMCH) suggests a remarkable conservatism in the metabolic capabilities of cytochrome P-450s and raises the possibility that insects may share other detoxification reactions with vertebrates with respect to toxins in foodplants.     

Evaluation of Synergism in the Feeding Deterrence of Some Furanocoumarins on Spodoptera littoralis

The phagodepression activity of five furanocoumarins (FC), bergapten, xanthotoxin, psoralen, imperatorin, and angelicin, has been studied against larvae of Egyptian cotton leafworm Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) using a leaf-disk choice bioassay. The dose range used was 0–10 g/cm² for linear furocoumarins and 0–30 g/cm² for angelicin, the angular furanocoumarin. Dose–feeding deterrency activity correlations were governed by various sigmoidal functions, except in the case of imperatorin and bergapten, which had dose–response curves showing irregular traces with two maxima. All five FCs induced various degrees of phagodepression in S. littoralis; at 3 g/cm², the relative feeding deterrence was bergapten = xanthotoxin > psoralen = imperatorin = angelicin. Structure–activity correlations indicated that a methoxy group on C-5 or C-8 enhanced the activity. Comparison of experimental feeding deterrence of binary mixtures of imperatorin with xanthotoxin, bergapten, or psoralen at various relative concentrations with the calculated additive activity of each combination indicated that a proportion of 40% or more of imperatorin may exert a greater antifeedant effect on S. littoralis than the sum of individual compounds. The effect of angelicin also was examined in combination with psoralen, both of which are present in Psoralea plants. Their mixtures yielded a clear synergistic effect in the 20–80% angelicin range (coactivity coefficient = 124–133). By contrast, the effect of angelicin on xanthotoxin was only additive. In the dose–response curves of imperatorin/bergapten combinations, synergism was found at >60% imperatorin relative concentration and 1 g/cm², whereas lower proportions led to antagonism. The threshold between the two opposing effects was found to depend on the total FC concentration employed. Some natural systems contain FCs in the range of synergistic proportions recorded here and, thus, may have been produced by the host to increase its defensive effect at a lower metabolic cost.     

Impact of atmospheric pollution on linear furanocoumarin content in celery

In a series of laboratory studies, a single 4-hr acidic fog at pH levels associated with commercial celery (Apium graveolens L.) production near major population centers in California was found to stimulate development of psoralen, bergapten, xanthotoxin, and isopimpinellin within 24 hr and for at least 120 hr after exposure. At 120 hr posttreatment, the concentrations of phototoxin furanocoumarins (psoralen + bergapten + xanthotoxin) increased 540% in the leaves (to 135 g/g fresh weight) and 440% in the petioles (to 55.56 g/g fresh weight) of celery exposed to a pH 2.0 fog as compared to plants exposed to control fogs (pH 6.3–6.5). Concentrations of these compounds in test plants were 7.5 times higher than the amount known to produce contact dermatitis. The nonphototoxic isopimpinellin increased more than threefold in the leaves (to 39.23 g/g fresh weight, 120 hr) and petioles (to 25.88/gmg/g fresh weight) as compared to control plants. In contrast, a single ozone fumigation at 0.20 ppm for 2 hr generally reduced concentrations of phototoxin furanocoumarin in leaves of celery within 24 hr (ozone-treated plants = 37.9, controls = 69.5 g/g fresh weight), but levels of these chemicals in leaves of ozone-fumigated plants increased rapidly and concentrations were not significantly different at 120 hr. Isopimpinellin concentrations in foliage followed a similar trend (at 24 hr, control = 25.11, ozone treated = 10.96/gmg/g fresh weight, no difference at 120 h). In petioles, none of the linear furanocoumarin levels differed significantly at 120 hr posttreatment.     

Communal Foraging Behavior and Recruitment Communication in Gloveria sp.

The caterpillars of Gloveria sp. mark trails with a pheromone they deposit by dragging the ventral surface of the tip of the abdomen along branch pathways as they move between their communal nest and distance feeding sites. The threshold sensitivity of the caterpillar for an extract prepared from the secretory site was approximately 0.5 × 10^–3 caterpillar equivalents/cm of trail. Bioassays show that Gloveria follows neither authentic trails of Malacosoma americanum nor artificial trails prepared from 5-cholestane-3-one, a chemical previously reported to elicit trail following from other social caterpillars. Although our observations show that fed caterpillars mark heavily as they return to their nest, we found no evidence that individual caterpillars are able to recruit hungry nestmates to new food finds. In this species, recruitment to food occurs only after many caterpillars have reinforced a trail to a newly discovered food source. In contrast, hungry caterpillars of the confamilial species M. americanum, tested under identical conditions, responded strongly to the postprandial trails of individual caterpillars and rapidly abandoned depleted sites in favor of new food finds. We postulate that the difference in the efficiency with which these two species recruit nestmates to food evolved in response to differences in the spatial distribution of their food supplies.     

Furanocoumarin content and phototoxicity of rough lemon (Citrus jambhiri) foliage exposed to enhanced ultraviolet-B (UVB) irradiation

Rooted cuttings ofC. jambhiri were grown under enhanced levels of UVB radiation for 95 days. Bacterial phototoxicity and furanocoumarin content were determined in extracts made from various tissues from the aboveground biomass. Young, newly expanded leaves contained significantly higher concentrations of furanocoumarins than older leaves and stems. Additionally, the proportional concentration of psoralen was higher in young leaves than in old leaves. While treatment with UVB did not result in a change in the overall level of furanocoumarins, it did cause an increase in the ratio of psoralen to bergapten. Bacterial phototoxicity paralleled the distribution of furanocoumarin content among tissue types; analysis of covariance suggested that the phototoxic properties of the extracts could be accounted for on the basis of furanocoumarin content alone.     

Toxicity of linear furanocoumarins toSpodoptera exigua: Evidence for antagonistic interactions

The linear furanocoumarins psoralen, bergapten, and xanthotoxin were tested for toxicity to the beet armywormSpodoptera exigua (Hübner) under short ultraviolet (UVB) radiation. Increased dietary concentrations of each furanocoumarin significantly decreased insect larval weight, extended generation time, and induced higher mortality. Xanthotoxin was the most toxic, followed by psoralen and bergapten. Combining psoralen with bergapten, xanthotoxin, or both resulted in significantly antagonistic effects on insect mortality. The combination of bergapten and xanthotoxin, however, produced additive effects. The implications of these observations forS. exigua resistance in the wild plant accession ofApium prostratum and the enigma the findings represent for plant-insect relationships are discussed.     

Cytochrome P450-Mediated Metabolism of Xanthotoxin by Papilio multicaudatus

Within the genus Papilio, the P. glaucus group contains the most polyphagous Papilio species within the Papilionidae. The majority of Papilio species are associated with hostplants in the families Rutaceae and Apiaceae, and characterizing most are secondary metabolites called furanocoumarins. Recent phylogenetic studies suggest that furanocoumarin metabolism is an ancestral trait, with the glaucus group derived from ancestors associated with furanocoumarin-containing Rutaceae. In this study, we examined this relationship by conducting a gravimetric analysis of growth that used various concentrations of the furanocoumarin xanthotoxin. Papilio multicaudatus, the putative ancestor of the glaucus group, includes at least one furanocoumarin-containing rutaceous species among its hostplants; this species can consume leaf tissue containing up to 0.3% xanthotoxin with no detectable effect on relative growth rate, relative consumption rate, or efficiency of conversion of ingested food. As is the case for other Papilio species, xanthotoxin metabolism is mediated by cytochrome P450 monooxygenases (P450s). Ingestion of xanthotoxin by ultimate instar P. multicaudatus increases activity up to 30-fold in a dose-dependent fashion. Midguts of induced larvae can also effectively metabolize six other furanocoumarins, including both linear (bergapten, isopimpinellin, imperatorin) and angular (angelicin, sphondin) forms. A metabolite of xanthotoxin in the frass from xanthotoxin-treated larvae, identified as 6-(7-hydroxy-8-methoxycoumaryl)-acetic acid by MS–MS and NMR analyses, is identical to one from the frass of P. polyxenes. The occurrence of this metabolite in two swallowtails and the presence of a second metabolite of xanthotoxin, 6-(7-hydroxy-8-methoxycoumaryl)-hydroxyethanol in the frass of both P. polyxenes and Depressaria pastinacella are consistent with the suggestion that lepidopterans share as the first step of xanthotoxin metabolism the P450-mediated epoxidation of the furan ring 2′–3′ double bond.     

Attraction of 3-Methyl-1-Butanol and Ammonia Identified from Enterobacter agglomerans to Anastrepha suspensa

Tests demonstrated that volatile chemicals emitted from Enterobacter agglomerans, a bacterium that has been isolated from adults as well as fruit infested with larvae of the Caribbean fruit fly, Anastrepha suspensa (Loew) and other pest fruit flies, are attractive to female A. suspensa in laboratory bioassays. 3-Methyl-1-butanol and ammonia were identified as the two primary volatile chemicals released from active cultures of E. agglomerans. No 3-methyl-1-butanol and little ammonia (16.0 g/hr) are released from sterile tryptic soy agar plates. E. agglomerans-inoculated tryptic soy agar plates, however, released an average of 1.5 ± 0.53 g/hr 3-methyl-1-butanol and 332.9 ± 239.16 g/hr ammonia after 24 hr of growth. 3-Methyl-1-butanol lures were formulated in a membrane-based system to provide a constant release rate of synthetic chemical. Release rates ranged from 0.046 ± 0.007 to 12.16 ± 2.76 g/hr. In laboratory tests, equal numbers of females were captured in response to ammonium carbonate lures that released ammonia at the rate of 100 g/hr and to 3-methyl-1-butanol lures that released 12.16 ± 2.756 g/hr of synthetic material. The combination of the two lures was more attractive than ammonia alone. Availability of lures formulated for a range of 3-methyl-1-butanol release rates will facilitate field tests of this putative microbial attractant and may lead to a better understanding of the role of bacteria in the ecology of pest fruit flies.     

Quantification of contact oviposition stimulants for black swallowtail butterfly,Papilio polyxenes,on the leaf surfaces of wild carrot,Daucus carota

Ovipositing black swallowtail butterflies,Papilio polyxenes, make their final host-selection decisions on the basis of compounds present on the leaf surface. Little information is available, however, on the chemistry of leaf surfaces. The purpose of this study was to develop a technique to extract and quantify the concentrations of compounds from the leaf surfaces ofDaucus carota, one of the main host species forP. polyxenes, with particular reference to compounds already identified as contact oviposition stimulants, namelytrans-chlorogenic acid (CA) and luteolin-7-O-(6-O-malonyl)--d-glucopyranoside (L7MG), as well as its degradation product luteolin-7-glucoside (L7G). Plant surfaces were extracted by dipping leaves sequentially in pairs of solvents: (1) CHCl₃-MeOH, (2) near-boiling H₂O, (3) CHCl₃-near-boiling H₂O, and (4) CH₂Cl₂-CH₂Cl₂. The resulting extracts were fractionated and analyzed using high-performance liquid chromatography. The leaf-surface concentrations of each compound were calculated using regressions relating leaf surface area to leaf weight that were obtained from measurements of field-collected carrot plants. All four methods removed the three compounds from carrot leaf surfaces, but the solvent systems differed in effectiveness. The chloroform-near-boiling water solvent system performed better than the other solvent combinations, but not significantly so. This system also extracted the highest number of polar, UV-absorbing compounds. Methylene chloride was significantly less efficient than the other methods. An additional test confirmed that the chloroform-near-boiling water method removed compounds from the surface alone and probably not from the apoplast or symplast. Surface concentrations of CA (up to 600 ng/cm² leaf surface) were substantially greater than those of the two flavonoid compounds. No clear seasonal trend in concentrations was evident from the limited number of sampling dates.     

Acetone Transformation over PtCu/H[Al]ZSM5 Catalysts. Effect of Copper Content

A series of bifunctional bimetallic PtCu/H[Al]ZSM5-type catalysts was prepared and acetone transformation was carried out over them at 160°C, 1 atm, acetone/hydrogen molar ratio=3, and WHSV (weight of reactant injected per weight of catalyst per hour) ranging between 9.4 and 38 h^–1. According to the results, as copper atomic fraction (X(Cu)) increases in the bimetallic catalyst, propane formation rate decreases and methyl isobutyl ketone (MIBK) formation rate increases until X(Cu) equals 0.40. These results suggest that active metallic centers for the olefin double bond hydrogenation in the - unsaturated ketone, which leads to the MIBK formation, do not appear to be those hydrogenating the acetone carbonyl double bond to form propane. When X(Cu)>0.40, MIBK formation rate considerably decreases, meaning that practically all platinum metallic centers have been passivated for those copper atomic fractions over the PtCu/H[Al]ZSM5-type catalyst. Therefore, catalysts begin to act only by means of the acid function, and as a result a logical increase in the mesityl oxide (MO) concentration occurs, a substance that is formed by means of an acid catalysis.     

Adsorbate-assisted NO decomposition in NO reduction by C3H6 over Pt/Al2O3 catalysts under lean-burn conditions

The rates and product selectivities of the C₃H₆-NO-O₂ and NO-H₂ reactions over a Pt/Al₂O₃ catalyst, and of the straight, NO decomposition reaction over the reduced catalyst have been compared at 240C. The rate of NO decomposition over the reduced catalyst is seven times greater than the rate of NO decomposition in the C₃H₆-NO-O₂ reaction. This is consistent with a mechanism in which NO decomposition occurs on Pt sites reduced by the hydrocarbon, provided only that at steady state in the lean NO _x reaction about 14% of the Pt sites are in the reduced form. However, the (extrapolated) rate of the NO-H₂ reaction at 240C is about 10⁴ times faster than the rate of the NO decomposition reaction thus raising the possibility that NO decomposition in the former reaction is assisted by H_ads. It is suggested that adsorbate-assisted NO decomposition in the C₃H₆-NO-O₂ reaction could be very important. This would mean that the proportion of reduced Pt sites required in the steady state would be extremely small. The NO decomposition and the NO-H₂ reactions produce no N₂O, unlike the C₃H₆-NO-O₂ reaction, suggesting that adsorbed NO is completely dissociated in the first two cases, but only partially dissociated in the latter case. It is possible that some of the associatively adsorbed NO present during the C₃H₆-NO-O₂ reaction may be adsorbed on oxidised Pt sites.     

Dehydrocyclization of 1-hexene to benzene on Cu3Pt(111)

The disproportionation ofn-butane (and of isobutane) was catalyzed by sulfated zirconium oxide containing 1.5 wt% Fe, 0.5 wt% Mn, and 4.0 wt% sulfate at 2.0 atm and temperatures in the range of 30–60C. The reaction accompanies isomerization, which under some conditions is as much as one or two orders of magnitude faster than disproportionation. The conversion to each of the products increased with time on stream in a flow reactor, and then declined. The time on stream for maximum conversion was the same for each product. The results suggest that the disproportionation and isomerization reactions proceed through a common C₈ intermediate. Rates of the disproportionation reaction were determined at the time on stream corresponding to the maximum conversion at each temperature; for example, the rate of conversion ofn-butane into isopentane at 60C with ann-butane partial pressure of 0.58 atm was about 1×10^–7 mol/(g of catalyst s).     

3Z,6Z,9Z-Trienes and unsaturated epoxides as sex attractants for geometrid moths

Sex attractants for three species of geometrid moths were discovered during field screening of 3Z,6Z,9Z-trienes, and the racemic monoepoxydienes derived therefrom. MaleProbole amicaria moths were attracted to lure blends containing 6Z,9Z-cis-3,4-epoxy-nonadecadiene (6Z,9Z-cis-3,4-epoxy-19H) with 3Z,9Z-cis-6,7-epoxy-19H. 3Z,6Z,9Z-19H was positively identified and 6Z,9Z-cis-3,4-epoxy-19H was tentatively identified in extracts of female pheromone glands by coupled gas chromatography-electroantennogram detection (GC-EAD) and gas chromatography-mass spectrometry (GC-MS).Sicya macularia male moths were attracted by blends of 3Z,6Z,9Z-19H and 6Z,9Z-cis-3,4-epoxy-19H. The attractive response was strongly antagonized by small amounts of 3Z,9Z-cis-6,7-epoxy-19H, or by larger amounts of 3Z,6Z-cis-9,10-epoxy-19H.Lomographa semiclarata male moths were attracted by a variety of lures containing 3Z,6Z,9Z-17H as a major component. 3Z,6Z,9Z-17H was tentatively identified in a female pheromone gland extract by GC-EAD.Issued as NRCC No. 30258.     

Sex pheromone components of the blueberry leaftier mothCroesia curvalana kearfott (Lepidoptera: Tortricidae)

The GC-MS and GC-EAD analyses of sex-gland components and sex-gland-released volatiles have identified (E)- and (Z)-11-tetradecenal (9010) and (E)- and (Z)-11-tetradecenyl acetate (8515) as components of the sex pheromone chemical communication system ofCroesia curvalana (Kearfott). The aldehyde-to-acetate ratio of 91 was found in the gland-released components. This blend at a 0.1–1 g/day release rate from PVC lures was shown to be as effective as virgin females in the trapping of maleC. curvalana.     

What defense doesSchouwia purpurea (Cruciferae) have against the desert locust?

A field study of the food eaten by solitary desert locusts was carried out in a winter breeding area in Mauritania. The food eaten, determined by the plant epidermis found in fecal pellets, was compared to the plant's availability in the habitat.Schouwia purpurea, well represented in the diets, was dominant at the study site. Adults had a preference forTribulus terrester. Growth and feeding on these two plants were compared. The high water content ofS. purpurea leaves limited the dry matter eaten and slowed down growth. Glucosinolates were separated and quantified by gas chromatography. There are 132mol/g dry matter in green leaves. In multiple choice tests, with paper disks, glucosinolate extracts were phagostimulant at a low concentration (21mol/g dry matter) and repulsive at a higher one (214mol/ g dry matter). Biting behavior onS. purpurea was recorded and analyzed on video. The importance ofSchouwia purpurea in desert locust habitats and its defenses is discussed.     

Synergism between myristicin and xanthotoxin,a naturally cooccurring plant toxicant

Myristicin, a methylenedioxyphenyl (MDP)-containing phenylpropene constituent of the leaves of many plants in the family Umbelliferae, is a highly effective Synergist of the cooccurring furanocoumarin xanthotoxin. As little as 0.10 % in an artificial diet can increase the toxicity of xanthotoxin toHeliothis zea (Lepidotera: Noctuidae) fivefold. In addition to increasing the proportion of caterpillars dying at a given xanthotoxin concentration, myristicin also increases the rate at which they die and increases the time to molt of surviving larvae. That there was no increase in the deterrency of xanthotoxin in the presence of myristicin suggests that the mechanism of synergism is not behaviorial but rather is biochemical, via MDP competitive inhibition of microsomal mixed function oxidases.     

Lygus hesperus feeding and salivary gland extracts induce volatile emissions in plants

Induction of plant volatiles by leaf-chewing caterpillars is well documented. However, there is much less information about volatile induction by insects with different feeding habits. We studied the induction of plant volatiles by a piercing–sucking insect, the western tarnished plant bug Lygus hesperus Knight. Adults of both genders and nymphs of Lygus induced the local emission of a blend of volatiles from both cotton and maize. Feeding by Lygus also induced the systemic emission of volatiles that was similar but less complex than the blend emitted at the site of feeding. Infestation by mated, mature adult females (>4 days old), but not by nymphs or mature males, caused detectable emission of -pinene, myrcene, and (E)--caryophyllene, compounds that are stored in the glands of cotton tissue. This indicated that damage to glands in the petiole and leaf by the female ovipositor, rather than feeding, contributed significantly to the emission of these volatiles. Girdling the plant stem to disrupt phloem transport markedly decreased the movement of ¹⁴C-labeled photosynthetic products to the apex of the plant, and this treatment also markedly reduced the amount of systemically induced volatiles caused by Lygus feeding. Lygus salivary gland extracts were capable of inducing emission of the same volatile blend as measured for plants infested by feeding insects or treated with volicitin, an elicitor isolated from caterpillar regurgitant. The results indicate that L. hesperus is capable of inducing the emission of plant volatiles and that induction is caused by an elicitor that is contained in the insect salivary gland.     

Syntheses and Properties of Aromatic Polyimides Based on 1,1-Bis[4-(4-aminophenoxy)phenyl]-1-phenyl-2,2,2-trifluoroethane and 1,1-Bis[4-(4-aminophenoxy)phenyl]-1-phenylethane

A series of fluorinated polyimides were prepared from 1,1-bis[4-(4-aminophenoxy)phenyl]-1-phenyl-2,2,2-trifluoroethane with various aromatic tetracarboxylic dianhydrides via a conventional two-step procedure. These polyimides were amorphous in nature and afforded flexible and tough films. Some polyimides derived from less stiff dianhydrides were soluble in polar organic solvents. The glass-transition temperatures (T _g) of these polyimides ranged from 252 to 324C, and softening temperatures (T _s) stayed in the 254322C range. Decomposition temperatures (T _d) at 10% weight loss all occurred above 569C in both air and nitrogen atmospheres. For a comparative study, another series of analogous polyimides based on 1,1-bis[4-(4-aminophenoxy)phenyl]-1-phenylethane were also pepared and characterized.