Ambrettolide via Olefin Metathesis Under True High Concentration Conditions

The effect of temperature on ethylene evolution from ethephon-treated sour cherry (Prunus cerasus L. cv. Montmorency) leaves was determined subsequent to foliar application. The upper surface of uniform fully expanded leaves was treated in the field with 125 μg of ethephon, (2-chloroethyl)phosphonic acid. After 24 hours, leaves were detached and ethylene was measured during incubation at temperatures between 10 and 34°C. Ethephon degradation in buffered solutions was also monitored between 10 and 50° and over a range in pH from 3.0 to 7.0. The effect of temperature on rate of endogenous ethylene evolution was examined for sweet cherry shoots and sour cherry leaves, and was calculated for several other tissues and species from values found in the literature. The rate of ethylene evolution from both ethephon-treated leaves and buffered solutions was markedly temperature dependent, with an apparent energy of activation (Ea) of 30 to 32 kcal mole-1. There was no pH-temperature interaction affecting the Ea for buffered solutions. A generalized Ea for endogenous ethylene evolution was about 13 kcal mole-1.

To study the postharvest physiology of white peaches, “Okubo” and “Hakuho” peaches were held at 10°C, 15°C, 20°C, 25°Cand 30°C, respectively. Respiration, ethylene evolution, firmness, readiness of peeling, sugars, edible quality and other components of ripening were determined during ripening.1. A more rapid increase and a higher peak in ethylene evolution, an earlier peak in respiration and a more rapid attaining of readiness of peeling were observed in “Okubo” peaches ripened at 20°C than in those ripened at 25°C, whereas softening proceeded at 20°Cas rapidly as at 25°C. A few days after the respiratory climacteric peak, “Okubo” peaches ripened at 20°Cand 25°C showed a peak in ethylene evolution, followed by a rapid decline. At the respiratory climacteric peak, “Okubo” peaches were fully ripe at 20°Cand over-ripe at 25°C.2. Higher rates of ethylene evolution on the first day after harvest and a more rapid rate of softening were observed in “Hakuho” peaches than in “Okubo” peaches. An earlier peak in respiration and a more rapid rate of softening were observed in “Hakuho” peaches ripened at 25°C than in those ripened at 20°C, whereas ethylene evolution increased at 25°C as rapidly as at 20°C.3. Gradual increases in respiration and ethylene evolution and delayed softening and attaining of readiness of peeling were observed in peaches ripened at 10°C and 15°C. “Okubo” peaches ripened at 10°C and 15°C attained about the same rates of ethylene evolution and the same degrees of softening and peeling as those ripened at 25°C, while poor flavor developed at 10°C. The rates of ethylene evolution at 15°C remained relatively constant for a long period after the respiratory climacteric peak, as compared with those at 25°C. Full ripening required about three times at 10°C and two times at 15°C as much time as at 25°C.4. Ethylene evolution was suppressed and tended to decrease during ripening at 30°C. Although the respiratory climacteric failed to develope at 30°C, softening proceeded in “Hakuho” peaches as rapidly as at 25°C and it proceeded in “Okubo” peaches at a slightly slower rate than at 25°C for a few days after harvest and subsequently at approximately the same rate.5. The reducing sugar content increased gradually at 30°C during ripening. The increase in soluble pectin content seemed to be significantly related to the degree of softening.6. These data suggest the following. The ripening temperature influenced flesh color, rates of ethylene evolution and softening, and certain other ripening phenomena. Ethylene stimulated an occurrence of a respiration climacteric and other ripening reactions such as softening and readiness of peeling. Respiration, ethylene evolution, softening, readiness of peeling and other ripening reactions proceeded relating to each other during ripening, but these interrelations were influenced by factors such as variety and ripening temperature.

abstractWe examined the relationship between ethylene evolution and carbohydrate content in leaf blades excised from rice (Oryza sativa L. cv. Nipponbare) seedlings at the four-leaf stage. The rate of ethylene evolution from the excised leaf blades sampled at various times exhibited diurnal fluctuation ; it was the lowest at 5 : 00, increased to the maximum at 13 : 00, then decreased. The sucrose content in leaf blades showed the same fluctuation as the rate of ethylene evolution. Application of sucrose stimulated the evolution of ethylene and increased the contents of glucose, fructose and sucrose in the leaf blades. After the application of glucose or fructose, both the rate of ethylene evolution and sugar content increased, but glucose and fructose increased much less than sucrose. In these experiments, sucrose content was closely correlated with the rate of ethylene evolution in rice leaf blades. From these data we concluded that sucrose content regulated the rate of ethylene evolution from leaf blades in young rice seedlings.

Ethylene evolution from detached fruiting apple spurs was measured after application of various bloom and post-bloom thinning agents. Ethylene evolution from fresh detached spurs of `Splendor' apple trees increased one day after application of a bloom thinning spray of ethephon or NAA, and remained higher than rates of ethylene evolution by detached spurs from unsprayed control trees for 6 (NAA) or 10 (ethephon) days. Both ethylene evolution and fruit abscission during the initial drop period were higher on trees treated with ethephon compared to NAA, however final fruit set was similar for these two treatments. Ethylene evolution was significantly higher following NAA application onto `Fuji' trees compared with NAAm, but final fruit set was reduced by a similar amount (≈20%) for both of these materials. Application of BA to `Pacific Rose™' apple trees when the average diameter of spur fruit was either 4 mm (6 days after full bloom) or 7 mm (12 days after full bloom) resulted in a significant increase in the rate of ethylene evolution and also reduced final fruit set. When application of BA was delayed until the average diameter of spur fruit was 14 mm (24 days after full bloom) neither the rate of ethylene evolution or final fruit set was affected. Although an increase in the rate of ethylene evolution was a prerequisite for thinning in the present experiments, the magnitude of this increase was not related to the final thinning efficacy. Chemical names used: benzyladenine (BA); 2-chloroethyl phosphonic acid (ethephon); naphthaleneacetic acid (NAA); naphthalene acetamide (NAAm).

Ethylene evolution and abscission of young cotton (Gossypium hirsutum L.) bolls were shown, in earlier papers, to increase when plants were subjected to conditions that decreased photosynthesis and sugar content of bolls (dim light, long warm nights). Moisture stress also increased ethylene evolution by young bolls, but it did not decrease their concentrations of fructose, glucose, or sucrose. When detached bolls were incubated for 16 or 24 hours at high or low humidity, their rate of ethylene evolution increased markedly at low humidity and slightly at high humidity. These results suggest that water deficit stimulates ethylene evolution by young bolls directly through partial desiccation, but do not exclude the possibility of a stimulus from moisture-stressed plants. Although attached and detached bolls both lost only a small percentage of their water content, detached bolls lost more for a given rate of ethylene evolution than bolls on moisture-stressed plants. The increased rate of ethylene evolution by young cotton bolls on plants subjected to a water deficit is probably adequate, in many cases, to cause their abscission.

SummaryExperiments were conducted to determine the relationships between the occurrence of storage disorders in ‘Royal Delicious’ apple (Malus ×domestica Borkh.) and fruit Ca2+ ion contents, rates of ethylene evolution and respiration, and lipoxygenase (LOX) activity. Apples were stored at 0º ± 1ºC and 90 – 95% relative humidity and sampled each month, up to 6 months, for storage disorders, fruit Ca2+ ion contents, rates of ethylene evolution and respiration, and LOX activity. Storage disorders such as bitter pit, cork spot, and brown core appeared after 3 months and increased in frequency at subsequent samplings. Regardless of the presence or absence of storage disorders, fruit showed a decline in Ca2+ ion concentration during storage. Ca2+ ion concentrations (means of 3, 4, 5, and 6 month samples) were significantly higher in disorder-free fruit [0.419 mg g–1 dry weight (DW)] than in fruit showing bitter pit (0.329 mg g–1 DW) or cork spot (0.340 mg g–1 DW), but were not significantly higher than in fruit with brown core (0.393 mg g–1 DW). Conversely, LOX activity was significantly lower in disorder-free fruit [0.168 µmoles linolenic acid oxidised min–1 g–1 fresh weight (FW)] compared to symptomatic fruit. LOX activity increased with the duration of storage in all fruit samples. The rates of ethylene evolution (58.5 µl C2H4 kg–1 FW fruit h–1) and respiration (16.0 ml CO2 kg–1 FW fruit h–1) were significantly lower in disorder-free fruit than in symptomatic fruit. The rates of ethylene evolution and respiration increased between 3 – 5 months in storage. After 5 months in storage, they remained stable or declined in all fruit. The correlations (R2) between Ca2+ ion content vs. the presence of physiological disorders such as bitter pit (–0.77), cork spot (–0.75), and brown core (–0.64), and between Ca2+ ion contents vs. LOX activity were strongly negative (–0.94). In contrast; the correlation between LOX activity vs. physiological disorders was strongly positive. Our study concluded that an inverse relationship existed between fruit Ca2+ ion content and the occurrence of bitter pit, cork spot, and/or brown core, and between fruit Ca2+ ion content and LOX activity. Moreover, the relationship between LOX activity and the presence of storage disorders was strongly positive.

Tomato plants (Lycopersicon esculentum Mill. ‘Heinz 1350’, yellow-green-5, and neglecta-1) were grown in sand culture with 15 mm or and with K+ varying from 0 to 8 mm. Other nutrients were provided at the concentrations of Hoagland's solution. The medium supplying was buffered with CaCO3 (pH 6.9) or was unbuffered (pH 3.4). Silver ions (0.01 μm) were incorporated in the nutrient solution in one experiment. Ammonium nutrition relative to nutrition elevated rates of ethylene evolution from all genotypes, but yg-5 and neg-1 showed resistance to toxicity and exhibited relatively low ethylene evolution. Ethylene evolution declined as K+ supply increased. Accelerated rates of ethylene evolution did not occur at tissue K+ concentrations >10 g·kg−1 of the dry weights of shoots with nutrition, but higher K+ levels were required with nutrition. Putrescine concentrations in leaves of ‘Heinz 1350’ supplied with were 2 to 5 times greater than in leaves of plants supplied with . Potassium deficiency increased putrescine accumulation regardless of N form. Spermidine concentrations in leaves of plants supplied with were lower than in those supplied with , whereas spermine concentrations were unaffected by treatments. ‘Heinz 1350’ grown in -based nutrient solutions with 0.01 μΜ Ag+ had low rates of ethylene evolution and developed few symptoms of toxicity. Quantities of ethylene and putrescine produced by tomato genotypes susceptible to the nutritional stresses were linked directly to the degree of stress imposed, and symptoms of toxicity were related to increased ethylene synthesis.

The relationships of fruit age, abscisic acid (ABA) concentration, ethylene evolution, and abscission rates were studied in an effort to determine why cotton (Gossypium hirsutum L., cv. Deltapine 16) fruits rarely abscise more than 15 days after anthesis. Because abscission of cotton fruits is increased by conditions that limit photosynthesis, greenhouse-grown plants with fruits of various ages were placed in dim light for 3 days to induce high rates of fruit abscission. Abscission rates, ABA concentrations, and ethylene evolution rates were determined for fruits of various ages. Almost all of the young fruits abscised, but abscission rate declined with age until almost no abscission was observed in fruits that were 15 or more days past anthesis.Dim light increased the ABA concentrations of fruits that were 6 to 11 days old but did not increase ABA concentrations in fruits that were younger or older. The concentration of ABA declined with fruit age from peak values at 4 and 6 days after anthesis. Dim light also increased ethylene evolution from fruits up to 10 days old but had little effect on ethylene production or abscission of fruits more than 11 days old. Ethylene evolution declined with fruit age from peak values at 4 and 6 days after anthesis. Fruits of various ages (from plants not exposed to dim light) were sliced to induce high rates of wound ethylene production. The results indicated that the capacity for ethylene production declined with fruit age, parallel with a decline in abscission rate. Decreases in ABA concentration and ethylene evolution with fruit age indicate that change in the capacity to synthesize these hormones, especially in response to stress, is one cause of the decline in abscission rates as cotton fruits become older.

SummaryIsogenic diploid and tetraploid tomato plants, cv Moneymaker, were grown in nutrient solution in a greenhouse. Fruits were detached at known physiological stages and analysed for various ripening parameters. The rate of ethylene evolution by tetraploid tomatoes reached its peak four days after its detectable onset, in contrast to six days for the diploid tomato. The rates of evolution at the peak were similar for both types of tomato. At the same physiological age, in respect of the onset of ethylene evolution, the pH, titratable acidity, electrical conductivity and sugar content of the juice of ripe tetraploid tomato fruits were no different from those of diploid fruits. The pigment content was lower and the activity of pectolytic enzymes (polygalacturonase and polymethylgalacturonase) was higher in tetraploid fruits. Their taste was inferior to that of the diploids. The relevance to the ripening process of the ethylene level and of the time interval between the onset of the upsurge in ethylene ev...

Ethylene evolution from leaves, stems, inflorescences and fruits of the olive plant (Olea europaea L.) cv. Manzanillo was studied at various stages of their development. Mature non‐growing organs, particularly leaves, have a constant, low, and uniform rate of ethylene evolution. Ethylene evolution from detached mature olive leaves was constant during the first 12 h after excision. Leaves on shoots maintained in vitro kept a constant rate of ethylene evolution for at least the first 5–6 days. Leaf injury significantly increased ethylene evolution. Ethylene evolution from injured and non‐injured control leaves could be markedly inhibited aminoethoxyvinylglycine (AVG) applied to the leaves or fed to the shoot. The use of excised olive shoots and leaves as an in vitro model system for studies of induced metabolic processes such as abscission and developing water stress was suggested.

In the present study, effect of chitosan coating on storage quality of plum fruit (Prunus salicina Lindley. cv. Santa Rosa) was investigated under supermarket conditions during 2013 at ICAR-IARI. After coating the plum fruits with 2% chitosan and water, they were stored at 20±1°C and 90±2% RH for 15 days. Fruit firmness, colour characteristics (hue and chroma), respiration and ethylene evolution rate, physiological loss in weight, antioxidant activity and total phenols were measured along with the activities for pectin methylesterase and malondialdehyde content. Chitosan application resulted in better firmness of fruits, retarded ethylene evolution and respiration rates and least colour changes as compared with the control. Reduction of total phenolics and antioxidant activity were also significantly inhibited by chitosan. Furthermore, fruits coated with chitosan also exhibited a significantly lower pectin methylesterase activity throughout the storage period. Moreover, the production of malondialdehyde was significantly reduced in the coated samples. The results clearly demonstrate that dip treatment of fruits in 2% chitosan could be an effective means to enhance the shelf-life and maintain postharvest quality of Santa Rosa plums during storage.

Previous results have shown that a nutritional stress increases the rate of young boll abscission from cotton (Gossypium hirsutum L.) plants. Tests were conducted to determine whether a nutritional stress affects the rate of ethylene evolution by 4‐day‐old bolls. Fruiting cotton plants were subjected to conditions that should decrease photosynthesis (dim light, short days), increase respiration (long warm nights), or change the demand for products of photosynthesis (partial boll removal, changing boll load during a growing season).As little as one day of dim light caused a measurable increase in ethylene. Partial boll removal slightly decreased the effects of subsequent exposure to dim light. Bolls from plants exposed to three consecutive long warm nights produced more ethylene than bolls from control plants. Rate of ethylene evolution by bolls of field‐grown plants increased almost eightfold from June 25, when the boll load was light, to July 30, when the boll load was heavy.Sugar analyses indicated significant negative correlations between sugar content of bolls and their rate of ethylene evolution.The results indicate that a nutritional stress increased rates of ethylene evolution by young cotton bolls. This additional ethylene is probably a causal factor in the increased rates of boll abscission that occur when cotton plants are subjected to conditions that promote a nutrltional stress.

Five compounds were evaluated for consistent promotion of sour cherry (Prunus cerasus L. cv. Montmorency) fruit abscission under field conditions: (2-chloroethyl)phosphonic acid (ethephon); 2-chloroethyl-tris-(2-methoxyethoxy)-silane (CGA 13586); 2-chloroethyl-methylbis-(phenylmethoxy)-silane (CGA 15281); 1,1,5,5-tetra-methyl-3-dimethylaminodithiobiuret (ER 3952), and beta-hydroxyethylhydrazine (BOH). The compounds were applied to mature trees at equimolar concentrations, and rates of ethylene evolution, effects of temperature on rates of ethylene evolution, and fruit removal forces were measured. Ethephon generated ethylene at adequate rates and was a good promoter of fruit abscission, but its activity was markedly affected by temperature. CGA 15281 promoted fruit abscission with minimal effect of temperature on ethylene evolution. ER 3952 was also a good fruit loosener, although it did not release ethylene directly. CGA 13586 and BOH were not effective in promoting fruit abscission and were poor ethylene generators.

To meet cost targets for GW-scale deployment of proton exchange membrane water electrolyzers (PEMWEs), iridium (Ir) loading needs to be reduced by about factor of ten to below 0.1 mg/cm2. However, catalyst layer integrity for low IrOx catalyst loadings can suffer from poor in-plane electric conductivity and overall poor particle-to-particle connectivity. To study low catalyst loadings a rigorous methodology is needed, where catalyst layer inhomogeneities can be identified before extensive activity and durability studies. Here, we present a framework for testing low loading IrOx catalysts within membrane electrode assembly (MEA), where loading study was conducted using two Ishifuku catalysts having different structures: amorphous and crystalline. By varying catalyst loading, electrochemical descriptors were obtained such as mass specific activity, exchange current density, specific surface charge and others. The change in voltage in kinetic region between various catalyst loadings corresponded to Tafel slope, indicating that the catalyst surface area reduction was the major reason for the activity loss at lower loadings. In-plane electric conductivity losses were minimum (<0.05 V) for the entire current density range (up to 8 A/cm2), which indicates good quality of catalyst layer coatings but also the use of fine microporous layer (MPL) on porous transport layer (PTL) helped reduce the electric contact resistances. We performed voltage breakdown analysis for polarization curves, as well as pseudo-capacitance breakdown for cyclic voltammetry using equivalent circuit models. The amorphous catalyst showed higher activity across all the loadings and current densities, lower Tafel slope, higher surface charge and about 5 times higher mass activity and exchange current density (Figure 1) compared to crystalline catalyst. The physical characterization of the two catalysts through x-ray photoemission spectroscopy (XPS), Raman spectroscopy, BET analysis, x-ray diffraction, electron imaging reveals the morphological and surface characteristics for each catalyst. Amorphous Ishifuku catalyst is confirmed to have amorphous structure with high population of µ1 oxygen species on the surface that are believed to be responsible for high oxygen evolution reaction (OER) rates. Overall, here we show that loading study is a necessary first step for catalyst layer characterization with low catalyst loadings. Figure 1. Intrinsic activity of amorphous IrOx and crystalline IrO2 through catalyst loading study on MEAs. (a) BETsurface area as a function of anode loading, slope indicates the specific surface area. b, j 0,s acquisition normalized by BET surface area through linear correlation with varying anode loading. c, Intrinsic current densities at various anode loading normalized by BET area from HFR-free polarization curves. Figure 1

Although cyclopropanation with donor/acceptor carbenes can be conducted under low catalyst loadings (<0.001 mol %), such low loading has not been generally effective for other classes of carbenes such as acceptor carbenes. In this current study, we demonstrate that ethyl diazoacetate can be effectively used in the cyclopropanation of N-Boc-2,5-dihydropyrrole with dirhodium(II) catalyst loadings of 0.005 mol %. By appropriate choice of catalyst and hydrolysis conditions, either the exo- or endo-3-azabicyclo[3.1.0]hexanes can be formed cleanly with high levels of diastereoselectivity with no chromatographic purification.