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  • Chemistry  (232)
  • Female  (221)
  • United States  (119)
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  • 1
    Publikationsdatum: 2021-05-19
    Beschreibung: Study of survey health management and diseases in hatcheries and fish farms can help us to knowledge and application control methods such as: prevention, treatment and increase high levels of production in hatchery and farms, finally. This survey carried out from 2005 to 2008 for 4 years in sturgeon hatcheries and farms of Golestan province. Sturgeon fishes include Huso Huso, Ship sturgeon, Acipenser persicus collected and for virology, bacteriology, fungius and hematology examined. Also, physicochemical parameters measured and recorded in different stages of culture. Results of this study showed that all of samples in virology was negative and did not observe any doubetful causes. In bacteriology CFU was variation from 3/9 ×105 to 6/9×10. The most parasites that detected in this survey was Cocolanus espherolanus , Sceria binopsulus semiarmatus and Amphilina fuliacea that separates from Acipenser Percicus, especially. The results about hematology parameters some important hematological indices of ship sturgeon include: The total RBC for female and mail specimens measured as 5.3±1.5 ×105, 4.8±0.5 ×105 per mm 3 respectively. The amount of haematocrit and hemoglobin for female and mail determined: 34.3±2.8, 35±1.4 percent and 10.3±0.9, 8.9±0.8 gr/dl .The MCV: 216.3± 96.2, 736.5± 102.5, MCH: 720.2±309.5, 186±0.7 and MCHC: 30±0.8, 25.5±3.4 percent respectively.The total WBC were (female, male): 21320±1054, 20580±777 per mm 3 and neutrophil: 16.4±2.5, 17±1.4 percent and lymphocyte: 74.4±2.4, 73.5± 0.7 percent and eosinophil: 6±1.4, 6.4±0.5 percent, monocyte: 2.8±0.8, 3.5±0.7 percent. There was not any significant differences (p〉0.05) between mentioned parameters in male and female (students t-test). Also evaluation of hematological parameters in bluga ( Huso huso) include: total RBC were (male , female) 5±0.3 ×105 , 4.9±0.6 ×105 per mm 3 ,respectively and hematocrit: 33.2±6.7 , 35.4±3.4 percent and hemoglobin: 11.2±1.5 , 12.2±1gr/dl and MCV: 669.9±172.2, 723.9±982.4 and MCH: 226.2±42.5, 249.5±35.4 and MCHC: 34.1±2.4, 34.6±3.6 percent respectively. The totals WBC were (male, female): 24800±707.1, 23042±1375.4 per mm 3 and neutrophil: 18.5±0.7, 21.4±1.1 percent and lymphocyte: 73.5±1.4, 68.4±1.1 percent and eosinophil: 5±2.8, 7±1.2 percent and monocyte: 3.5±3.5, 3.2±0.8 percent. According to statistically study the count of lymphocyte had significant difference between male and female fish and this count in male was higher than female. (p≥0.05).
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Physicochemical ; Hematology ; Fish ; Sturgeon ; Huso huso ; Ship ; Acipenser percicus ; Bacteriology ; Parasitology ; Health management ; Diseases ; Survey ; Aquaculture ; Hatcheries ; Samples ; Sceria binopsulus ; Amphilina fuliacea ; Female ; Male
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 395pp.
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  • 2
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    Iranian Fisheries Science Research Institute | Tehran, Iran
    Publikationsdatum: 2021-05-19
    Beschreibung: This investigation carried out for the first time in Iran inorder to prodcution of monosex female and also sterilization in Rainbow trout. In this study, the eggs of general females were fertilized with the sperm of sex reversed male and so monosex female population was produced in second generation and sterilization carried out with oral administration of 17α methy 1 testosterone and immenrsion and oral administiration methods were used in embryonic stage and from commencing of acitve feeding of larvae, respectiverly. For sex reversal , 13 treatments were considered totally, that the most percentage of male (100%) was observedc in a treatment including of orally administration of 0.5 ppm hormone for 60 days after commencing active feeding (P〈0.001). In the other treamtnet, different percentages of sex ratio including male, female, intersex and sterility were observed. The offspring of genral eggs fertilization with the sperm of masculinized fish were 100% female, chisquare test was shown the treatment of orally administration of 30 ppm hormone for 120 days after commencing active feeding that had been considered for sterilization, was produced 90% sterile fish (P〈0.001) and was changed the sex ratio significancthy. Morphological changes of the gonads and sperm ducts in matured fish and also histological changes in the gonads of fish in the treamtints were considerable.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Morphological ; Histological ; Monosex ; Female ; Male ; Sterilization ; Rainbow trout ; Eggs ; Fertilized ; Sperm ; Population ; Sex ; Fish ; Oncorhynchus mykiss ; Rainbow trout
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 58pp.
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  • 3
    Publikationsdatum: 2021-05-19
    Beschreibung: Studies show that thyroxine can play an important role in regulating growth and other physiology activities. Since the direct role of thyroxine in growth metamorphose larval of bony fishes hasn't been proved yet, during the experiment accomplished in Shahid Ansari and Jajrood station, the hormones function in the survival of development of silver carp, grass carp and rainbow trout were studied. In this study accomplished of thyroxine baths with 0.1, 0.5 and 1 ppm (with 3 repeat). The other phase, thyroxine injected to females grass carp, silver carp, rainbow trout and barbell of Caspian Sea with different doses (1, 10 and 100 g/g B.W.). Tehn survival of development of embryo and larval and precent of fertilization were studied. Also, the percent of mortality were compared in two phases in stages of development. Result show that: 1) Trout: a)Phase of thyroxine bath: The number of hatching eggs and survival of larval in 0.5 ppm were increased to other treatment. b) Phase of hormone injection : The survival of larval in treatment of 10 g/g was 8.58% that was meaningful difference to other treatment (P〈0.05). 2) Silver carp: a)Phase of thyroxine bath: The number of hatching eggs and survival of larval in 0.5 ppm were ( 20%) increased to other treatment (P〈0.5). b) Phase of hormone injection : The survival of larval in treatment of 10 g/g was meaningful difference to other treatment (P〈0.05). 3) Grass carp : a)Phase of thyroxine bath: The number of hatching eggs and survival of larval in 0.5 ppm were 39% increased to other treatment. b) Phase of hormone injection : The survival of larval in treatment of 1 g/g was meaningful difference to other treatment (P〈0.05). 4) Barbel of Caspian Sea: Development stages wasn't determined in this fish. Number of eggs degenerated , number of eggs were the first development stages and growth of numbers increased on ovary.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Thyroxine ; Female ; Survival ; Growth ; Egg ; Larval ; Grass Carp ; Silver Carp ; Thyroxine (T4)
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 39pp.
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  • 4
    Publikationsdatum: 2021-05-19
    Beschreibung: During last 65 years the catch of mullets had increasing trends with some fluctuations in the Iranian coastal water of the Caspian Sea .In this period about 138 thousand tons of mullets have been caught. Mullet’s account for 35% of total catch annually .In recent years species composition of mullets has chanched in the Iranian coastal water of the Caspian Sea and catch composition of golden grey mullet increased from 76% in 1995 to 98% in 2006. In this survey some biological characteristics of golden grey mullet have been studied in Iranian coastal water of the Caspian Sea .Fish samples have been gathered from commercial catch of beach seine cooperatives monthly in Iranian coastal water of the Caspian Sea over 2006 and 2007. In the laboratory fishes have been measured biometrically and biological parameters have been calculated .Also catch statistics of mullets during 2006-2007 have been obtained and discussed. Results showed that the catch of mullets in beach seine cooperatives during 2006 and 2007 was 4181 and 3685 tons respectively that golden grey mullet contribute 99% and 98% of the catch composition of mullets respectively. Length range of golden grey mullet caught by beach seine cooperatives was 19-50.2 cm with mean length of 32.7 ± 6.4 (± SD) and weight range was 67-1475 gr with mean weight of 411 ± 255 gr. The age structure of this species was comprised 2-10 years old fish with mean age of 4.42 years old. In this survey totally the sex ratio of male:female of golden grey mullet was 356: 434 that was significant variation from equal sex ratio. Pick of the spawning in Guilan province was in October and in Mazandaran and Golestan provinces was in November. In October the proportion of spawning females declined from western area (Guilan province) towards eastern parts (Golestan province).The highest proportion of spawning females was in December in Golestan province. The highest GSI index value was observed in September and October and it was decreased in November and December and it was consistent during January till April. The mean absolute fecundity was 700881 ± 429987 eggs with minimum and maximum fecundity of 200112 and 2282862 eggs respectively. The Lm 50% for female golden grey mullet was calculated as 33.6 cm.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Biological ; Commercial ; Golden grey mullet ; Liza aurata ; Species ; Survey ; Samples ; Male ; Female ; Sex ratio ; Spawning ; GSI ; Fecundity ; Coastal waters
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 56pp.
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  • 5
    Publikationsdatum: 2021-05-19
    Beschreibung: Hamoun fish, Schizothorax zarudnyi, is an indigenous species of the eastern waters of Iran, which is exclusively found in this region. However recently drought occurrence in the Chahnimeh reservoirs (a semi natural water body) making them vulnerable to extinction. As an appropriate action to address this problem and according to the 3 side contract between Italian Government – UNDP - Islamic republic of Iran Government and the Italian government financial support to reduce poverty in the Province of Sistan-Baluchestan through the reinforcement and dissemination of aquaculture activities the project was developed at the Hamoun Research Unit by the Chahbahar Fisheries Research Center to record the breeding normative of 1 g weight larvae for restocking and other researching purposes. 331 broodstocks of the indigenous species Shizothorax zarudnyi weighing 800-2450 g were collected from the Chahnimeh reservoirs in early autumn, 2006. From 5/3/2007 ( the project is supported and communicated on 2010) , Ovulation was stimulated with three stimulators; pituitary extract (3-6 mg kg-1 body weight), GnRH-A (20-30 mg kg-1 body weight) and anti dopamine (10-15 mg kg-1 body weight) that was given in 2-3 doses to breeders. Of 169 injected breeders , some were injected On mid March of 2007 (12-13 ºC water tempreture) responded to the injection 25% ,while the rest were injected On April of 2008 (14-16 ºC water tempreture) responded to the injection 65%. In the present project of 167 breeders 82 were female and 87 male. Totally 30 female breeders released their eggs in different stages. 20 female breeders released their eggs completely, 3 breeders released half of their eggs and 7 released 1/3 of their eggs. The male breeders just injected in the final dose of hormontrapy and all were ready for releasing sperms however the ovulation in female breeders occurs between 353-428 h ºC and after the final dose of injection. Ripe eggs were stripped from the females and fertilization was done by the dry method. Fertilized eggs were transferred to veis incubators and troughs. Incubation period for eggs differs and larvae hatch out after about 910 days at an average water temperature of 12.5 °C. Maintained at 13-14 °C, complete absorption of yolk sac in Shizothorax zarudnyi larvae occurred after 5-8 days. Larvae were fed with a mixture of powdered milk and egg yolk in this stage followed by decapsulated Artemia cysts and nauplii of Artemia and then on formulated starter diets used for carps . Because the ponds were not ready, larvae were maintained in troughs for about ten days before they were transferred to two 1200 m2 earthen ponds where they reached a body weight of about 1 g. They were then handed over to the Iranian Fisheries department in the region. Larvae were fed with the starter feed SFCO in the earthen ponds. About 350 thousand larvae were stocked in two earthen ponds. Based on the results of present study and other studies we may conclude that artificial breeding in Schizothorax can be successfully achieved at 14-16 ºC in flow through systems using hormone therapy (combination of GnRha and anti dopamine) and larvae could be easily cultured in earthen ponds. However this species exhibits lower growth rates as compared to carps its high expenses could have an important role in economical feasible.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Economical ; Hamoun fish ; Schizothorax zarudnyi ; Breeding ; Species ; Aquaculture ; Temperature ; Female ; Eggs ; Hormontrapy ; Sperm ; Ovulation ; Larvae ; Fisheries ; Earthen ponds
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 71pp.
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  • 6
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    Iranian Fisheries Science Research Institute | Tehran, Iran
    Publikationsdatum: 2021-05-19
    Beschreibung: The biological aspects of Sepia pharaonis was studied during years 2006-07. The studied area restricted to the Bahrekan in Khouzestan province covering the depths of 2 up to 25m. The sampling methods were gillnet and bottom trawl. A total of 310 specimens collected, of which there wasn’t found any cuttlefish in the study area from July to October (5 months). The collected samples were transferred to the laboratory ashore for further biological measurements consist of: Mantle length, Body weight, sex determination. Gonado-Somatic Index, and determination of Spermatophoric Index, Spawning season, Food preference, Maturity stages and chemical analysis for food value determination. The results showed that the overall sex ratio is about M:F= 2:1 with percentage of 67.41% for males and 32.50% for females. Males are significantly bigger than females with average mantle length (ML) of 233.3 and 269.3 mm for female and male, respectively; with body weight of 1102.3 and 1450.6 g. The mantle length body weight relationship was found W=0.001 ML 2.540 (R2= 0.92) Female as: W= 0.0015 ML 4797 (R2= 0.93) male From point of feeding, the food preferences results indicated that fish is considered as main food, crabs as minor food and other marine organisms such as bivalvia and gastropods as random food. The highest vacuity Index (CV) and empty stomachs was determined for March-April and the lowest value was is December. Also, the maximum GSI was estimated for March-April months in which showing coherrances with the lowest food preference. The maximum spermatophoricfilaments were 856 and 45 for male pharaoh cuttlefish with mantle length of 300 and 185 mm, and on the other hand this values for fecundity were estimated 1589 and 53 for female specimens with 254 and 198 mm mantle length. The spawning season occurs in April- March in which accompany with migration of pharaoh cuttlefish towards shallow waters. The fishing season would be in this period in w.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Biological ; Chemical ; Sepia pharaonis ; Gillnet ; Sampling ; Specimens ; Weight ; Sex ; Gonado-somatic index ; Spawning ; Maturity ; Female ; Male ; Bivalvia ; Gastropods
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 85pp.
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  • 7
    Publikationsdatum: 2021-05-19
    Beschreibung: This study was conducted to codify the guideline and indexes of broodstock management in salmonid fish and cryopreservation, selective breeding and sex reversal in hatchery to attain responsible aquaculture development. Cryopreservation includes of sperm and egg in term of economic is important in aquaculture. In this report mentioned the type and name of material. All female and sex reversal fish are produced by steroid hormone which mentioned in this report. Selective breeding include individual selection and family selection which could be used for genetic improvement of fish.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Economic ; Broodstock ; Reproduction ; Cryopreservation ; Genetic ; Breeding ; Aquaculture ; Salmonid fish ; Sex reversal ; Hatchery ; Sperm ; Egg ; Female ; Steroid hormones
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 46pp.
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  • 8
    Publikationsdatum: 2021-05-19
    Beschreibung: Research project was conducted on some biological aspects of lobster in Oman Sea in the years1385-86. During the project some parameters such as length distribution, spawning peak, length (Carapace) at first maturity, the length at which 50% of the lobsters were found to be mature sexually, sex ratio, relative frequency index and population dynamics parameters were examined. Quantitative factors and catch composition of lobster including the amount of catch in terms of weight and number of ovigerous-female, under-sized specimens and so were compared by monthly. According to the results of present study caught specimens were male with carapace length of 22 and 110 mm respectively. The smallest ovigerous female was taken as 46mm CL when length at first maturity was estimated to be 69-70mm. the male: female ratio was 0.7: 1.3 for the whole year. A closed fishing season for the species is proposed during spring and September and October in Oman Sea. A large amount of the catches for the all sampling months came from the under-sized specimens, consist of 50 to 85% of the total catch. Therefore, presence of these small length groups have direct effects on time of closing season. Population dynamics parameters were calculated as follows: K=0.57 year, L∞= 103mm and Ǿ = 8.69. Total mortality (Z), natural mortality (M) and fishing mortality (F) coefficients were calculated as 2.73, 0.87 and 1.86, respectively. Exploitation ratio for the whole population was 0.681, indicating an overexploitation of the species. Based on the available data, the recruitment pattern for lobster was obtained for two season including spring (major) and autumn (minor). Catch per unite effort (CPUE) was calculated as 0.908 kg/Cage/day which was higher in comparison with two other areas including Ramin and Chabahar. Examination of CPUE for a 10-year period showed a decreased trend and the reduction for the year 1386 was about 30% when compared to the data from the year 1375. Moreover, the mean length during 1369-70 to 1385-86 (present study) decreased for the three areas including Pozm, Ramin and Chabahar, so that the carapas length decreased up to 10 mm in length. This sudden decrease in mean length during the 10-year period should be considered as a serious precariousness for sustainable exploitation of lobster in Oman Sea along Sistan and Baluchistan province.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Biological ; Survey ; Spiny Lobster ; Panulirus homarus ; Fishing ; Spawning ; Length ; Maturity ; Sex ratio ; Female ; Specimens ; Species ; Mortality ; Population
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 68pp.
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  • 9
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    Iranian Fisheries Science Research Institute | Tehran, Iran
    Publikationsdatum: 2021-05-19
    Beschreibung: Regarding to breeding the Litopenaeus vannamei, a total of 126 pairs of broodstocks were imported from Hawaii to Iran in 2004 and 2005 , and then transferred to the Bandargah Research Station in Bushehr. The female broodstocks were ablated, and were feeded 3 times per day with cuttlefish ,small size shrimp and Nereis worm with a ratio of 30% body weight .The water exchange were done 3 times per day. During the years 2004 and 2005 a total 1700000 naupli were produced of which 772000 specimens of pl13 and pl7 were harvested and then transferred to Helleh Site for carrying out the next culture project. The average naupli and postlarvae were 170000 and 92000 in proportion to each broodstock. Also the mean survival rate was estimated 54%.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Litopenaeus vannamei ; Broodstock ; Breeding ; Female ; Cuttlefish ; Shrimp ; Nereis worm ; Body weight ; Nauplii ; Specimens ; Survival rate ; Breeding
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 36pp.
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  • 10
    Publikationsdatum: 2021-05-19
    Beschreibung: The sex reversal technique in fish is widespread in many countries. The development of these techniques is desirable because rainbow trout males reach their gonad maturity earlier compared to the females. Rainbow trout alevins were treated with 17α-methyltestosterone incorporated in the diet (0.5. 1.5, 3, 6 and 10 mg/kg) for 60 days from the beginning of first feeding. Sex was determined at 180 and 680 dpf by sampling fish (n = 20) from each group and examining gross gonadal morphology under a dissecting microscope. Also sex reversal ratio and growth performance were determined in hormone-treated groups. These sex reversed functional males were reared for brood stock until they attained sexual maturity. At the end of experiment, normal rainbow trout eggs were fertilized with the sperms taken from sex reversed males for producing all-female populations. Examination of the results showed that 17α- methyltestosterone was effective in all treatment. The highest sex reversal ratio with 100% was observed in group treated with 0.5, 1.5 and 3 mg/kg 17α- methyltestosterone. The highest live weight ratios were observed in groups fed with 6, 0.5 17α-methyltestosterone and control group. Female progeny produced from the sex reversed males were 100 % in all males that sired offspring. All female trout stocks produced by this method have advantage in rainbow trout culture since the fish is not meant for direct human consumption and is used to generate brood stock, therefore, difference of growth parameters do not influence the success.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Sex differentiation ; Oncorhynchus mykiss ; Sex reversal ; Hormone treatment ; 17-αmethyltestosterone ; Female ; Population ; Steroids ; Gonad ; Maturity ; Rainbow trout ; Sexual
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 38pp.
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  • 11
    Publikationsdatum: 2021-05-19
    Beschreibung: This study was carried out to determine the effect of size of Barbus grypus broodstocks on reproductive ...
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Fish ; Broodstock ; Hormone ; Male ; Female
    Repository-Name: AquaDocs
    Materialart: Report , Not Known
    Format: 129pp.
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  • 12
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    Iranian Fisheries Science Research Institute | Tehran, Iran
    Publikationsdatum: 2021-05-19
    Beschreibung: 0Genetic polymorphism by means of biochemical genetic markers using polyacrylamide gel electrophoresis system in four barbus fish species has been investigated. Species scientific name were Barbus sharpeyi ; Gunther, 1847 , Barbus grypus ; Heckel, 1843, Barbus xanthopterus ; Heckel, 1843 and Barbus esocinus ; Heckel, 1843.Sampling site and location were mainly in the rivers located in Khoozestan province such as Karoon and Karkheh rivers and the Dez dam. Different organs such as blood, muscle, kidney, eye and heart were sampled and analysed for the presence of tf, es, sod and pgm alleles. High polymorphism and presence of different alleles scored, but populations were not in the H-W equilibrium. Considring results, using current and avaiable genetic markers such as microsattelits is recommended for future works.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Chemistry ; Genetics ; Genetics Markers ; Distinguish ; Barbus ; Species ; Barbus sharpeyi ; Barbus xanthopterus ; Barbus esocinus
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 62pp.
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  • 13
    Publikationsdatum: 2021-05-19
    Beschreibung: Biological characteristics of Liza klunzingeri were studied in two coastal areas, Sajaphi and Bahrekan, of eastern Khuzestan during March to February 2007. Among total 1880 measured fish specimens, 947 specimens were analyzed. The mean value of Gonado-somatic Index (GSI) for the male and female fish were calculated as 0.96± 1.39 and 3.25 ± 3.26 respectively. The GSI value was highest in November and lowest in July. The mean value of condition factor (K) was 1.25± 0.14 in male and 1.21± 0.15 for female. The highest K value were observed in June and the lowest value in February. The lenght at first maturity regardless of sexuality, was found to be 14.5 cm and the time of spawning based on reproduction pattern were determined in Nov- Dec. The length-weight relationship were calculated as Y=0.024L^2.76 (n=226R2=0.72) for males, Y=0.011L^3.00 (n=444R2= 0.78) for females and Y=0.0208L^2.82 (n=670R2 =0.82) for total fishes and also it’s found significant in level lengthweight relationship in (P〈0.05). According to biological characteristics and referring to American fisheries society (AFS) indices and Fuzzy logic expert system, Lize klunzingeri is classified as low vulnerable species.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Lize klunzinger ; Gonado-somatic Index ; GSI ; Condition factor ; Biological characteristics ; Female ; Male ; Specimens ; Fisheries
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 39pp.
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  • 14
    Publikationsdatum: 2021-05-19
    Beschreibung: Cheshmehkileh River and adjacent mountainous streams, play a strategic role as a historical axis for anthropogenic civilization, human welfare also habitat and migration pathway of commercial – biologic valuable fishes e.g. Caspian trout, Caspian kuttum, members of Cyprinidae family in south Caspian Sea drainage. Treats such as overfishing of Caspian trout and Red spotted trout stocks in mountainous headwaters, barriers construction and manipulations those are out of river carrying capacity developed by human activities, affected normal function of river as well. Sand mining big factories establishment next to the river, legal and illegal trade of river sediments, direct entry of Tonekabon landfill leakage into the river, development of Rainbow trout farms since 3 decades and huge effluents into the river containing dead fish and types of solids, escapement of cultured Rainbow trouts into the river, … are major minimum factors which needs basic information for integrating inclusively drainage management system. Cheshmehkileh River contains Headwaters of Dohezar (Daryasar & Nusha), Sehezar and Valamroud rivers during 13 monthly sampling phases between September 2009 and October 2010 based on macrozoobenthoses investigations by EPT, EPT/C EPA protocols, measurements of nominated physic-chemical and microbiologic parameters. Probability of Rainbow trouts escapement and invasion, existence, nutrition in Cheshmehkileh environment indeed investigated. Data analysis explained significant differences (P〈0.05) between groups of measured parameters in different sampling stations. Dendogram of clustered analysis based on consolidation of major biologic/ physic-chemical and microbiologic parameters, separated stations No. 1, 3, 2, 4 in one group and remained classified in different groups. Station 8 and 9 similarly separated which expressed general similarities according to Sehezar river environment which were differs in comparison with other stations. Station 11 separated according to its natural quality of water and environment. Similarities between station 10 to Sehezar river stations 8 and 9 expressed general influence of Sehezar River more than Dohezar River in Cheshmehkileh condition especially in station No. 10. High scores of EPT and EPT/C indices in upstream stations 1, 3 and 8 also low score of indices in stations 7, 13 and 6 expressed levels of environment quality between these groups of stations. Maximum average biomass of macroinvertebrates belongs to Trichoptera order in Cheshmehkileh River. Significant decrease of biomass in stations 11, 12 and 13 in comparison with other stations stated environment degradation in mentioned stations relevant to excessive sand mining as well. Pollution resistant groups of invertebrates significantly increased in downstreams against upstream stations. Also disappearing of Plecoptera order in station No. 7, 9, 10 and 13 stated low quality of environment in comparison with upstream stations. Confirmation of effects quality and quantity for point and non-point sources of imported pollutants require specific management considerations in order to present exploitations, pollutants control and emergencies for river monitoring in forthcoming years.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): River ; Pollution ; Aquaculture ; EPTC ; Assessment ; Macroinvertebrates ; Chemistry ; Microbiology
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 138pp.
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  • 15
    Publikationsdatum: 2021-05-19
    Beschreibung: The most important habitats of mudskippers are muddy areas in tidal zone of tropical mangrove forests. Mudskippers are related to Oxudercinae subfamily of Gobiid fishes. Three most distributed species of Hormozgan mudskippers were Periophthalmus waltoni, Boleophthalmus dussumieri and Scartelaos tenuis. These fishes can be considered as euryhaline and eurythermal aquatic species, because they can tolerate a wide range of salinity and temperature. A research was done since september 2008 to september 2009 in two important mangrove regions of Hormuzgan (Tyab and Khamir) to determine some ecological characteristics of inhabited mudskipper species. Results showed that nitrate levels are significantly different between tidal lines and seasons (P〈0.05). Maximum nitrite concentrations were recorded 53.2 and 92.5 µg/l in Khamir and Tyab respectively. The annual correlation matrix showed that a positive correlation between phosphate concentration and nitrite and silicate (P〈0.05). Silicate concentration was very high, because of too low density of diatoms and radiolarians. Some species of diatoms, dinoflagellates, cyanobacteria and larvae of crustacea and echinoderms were observed with different density and diversity. Sediment composition of the studied areas were categorized in three classes (clay, sand and clay - sand). Polychaetes formed dominant group of benthic fauna in Tyab and Khamir areas. High density of capitellid worms was possibly related to some environmntal stress caused by activity of fishing and cargo vessels. It was not observed significant difference between fishes length in two areas (P〈0.05); Mean lengths of P. waltoni, B. dussumieri and S. tenuis were calculated 9.85, 14.7 and 11.5 cm respectively. Spawning period of each three species in both areas were obtained from late winter to late spring based on gonadosomatic index values. Male to female sex ratio of P. waltoni, B. dussumieri and S. tenuis were calculated 1:0.45, 1:0.41and 1:0.74 respectively. Absolute fecundity of P. waltoni, B. dussumieri and S. tenuis were estimated 3558 ± 2202, 3952 ± 1030 and 6742 ± 1939 respectively. P. waltoni feeds mainly on fiddler crab, S. tenuis uses crustaceans and gastropods and B. dussumieri has a vegetarian diet.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Mudskippers ; Ecology ; Periophthalmus waltoni ; Boleophthalmus dussumieri ; Scartelaos tenuis ; Female ; Male ; Benthic fauna
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 97pp.
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  • 16
    Publikationsdatum: 2021-05-19
    Beschreibung: Aquaculture for human consuming species is being considered as the first substitution of catching aquatic species due to increase of human population and decrease of wild aquatic stocks. In this study, the hybrid sturgeon Bester (female beluga x male sterlet ) was produced for the first time in Iran. Sperm of 1.35 kg male Acipenser ruthenus was used to fertilize the eggs of 125 kg female Huso huso in Shahid Marjani Sturgeon propagation center (Agh Ghala, Golestan province). The fries of bester and control treatment of beluga were transported to International Sturgeon Research Institute (Rasht) after about one month by reaching to 490 mg and 377 mg of weight respectively. All fishes fed by artificial concentrated food (48-50% protein and 15-17% fat) after a period of feeding with Artemia and Daphnia. Sorting was carried out according to increase of fish weight for both fishes. Results showed that the imported sterlet spawners were not at the high maturation stages and especially the males had not suitable sperm quality. It showed that up to 2 months of age , these was no significant difference between bester and beluga weight but from this age up to 2 months of age the weight of beluga was greater. Meanwhile from 2 months old up to the end of the study (21 months) the weight of bester sample was significantly greater than beluga. The comparison of FCR for the whole rearing period showed no difference between bester and beluga (2.4 and 2.3 respectively). In general, the increase and decrease pattern of GR and SGR were coincided to each other, but showed monthly differences. Growth rate (GR) and specific growth rate (SGR) of bester were greater than beluga from 4th and 3rd month of rearing period respectively.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Aquaculture ; Beluga ; Sterlet ; Bester ; Growth Rate ; Aquatic ; Species ; Population ; Female ; Male ; Acipenser ruthenus ; Huso huso ; Sturgeon ; Artemia
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 55pp.
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  • 17
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    Iranian Fisheries Science Research Institute | Ahvaz, Iran
    Publikationsdatum: 2021-05-19
    Beschreibung: In order to study some biological aspects of Acanthopagrus latus Persian Gulf ....
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Fish ; Biological ; Creeck ; Female
    Repository-Name: AquaDocs
    Materialart: Report , Not Known
    Format: 95pp.
    Standort Signatur Erwartet Verfügbarkeit
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  • 18
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    Iranian Fisheries Science Research Institute | Tehran, Iran
    Publikationsdatum: 2021-05-19
    Beschreibung: Sampling of Astacus leptodactylusc were conducted in order to determination of biometrical and biological parameters suchas length , weight , sex ratio , fecundity and natural reproduction time . Two transect were selected at 49 34 and 49 36 geographical position on east Caspian Sea near to Anzali city . Metalic foulding trap with Silurus glanis as attractive diet were used to catch Astacus leptodactylusc At each line the traps were set on depth of 35,45 ,55 and 65 (5 trap at each depth) . Random sampling from each depth on tow lin for one year were conducted and the biometry performed on catched Astacus leptodactylusc where their sext uality and their ration were detemined for eacd month , season and whole year. absolute fecundity determined by cooking Astacus leptodactylusc , taking out the ovary weighing and counting them .Working fecundity assesed by separating eggs from their swiming leges while enomerate all egg . Complete randomized test of ANOVA for analysing the data were employed. The results showed average length and welght were calculated 122/07±1/74mm and 57/96±1/81gr respectively. Average absolute fecundity was 310/22 ±10/72 eggs , average working fecundity was 251/84±8/84 eggs , Average ovary weight was determined 4/31 ±619 gr and average number of eggs in one gr was 74/52±1/53 eggs .The sextual ratio in all year long was 1:1.32 . The reproduction season is about seven month from Febrary to July and the moulting of males occures two times each year. One of time is at may and the other is in September . The female molt thtina as the male start for second time.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Biometrical ; Biological ; Biology ; Astacus leptodactylus eichwaldi ; Sex ratio ; Fecundity ; Silurus glanis ; ANOVA ; Female ; Male ; Coastal water
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 78pp.
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  • 19
    Publikationsdatum: 2021-05-19
    Beschreibung: Population dynamics parameters and exploitation ratio of Jinga Shrimp, Metapenaeus affinis were studied from Sep 2011 to Dec 2011 and data collected from two landing places (Hendijan and Lifee-Bosif). During the project, more than 2200 specimens of jinga shrimp were measured. The mean value of length for the male and female were calculated as 9.8±0.86, 10.24±1.18 and mean value of weight for the male and female was as 6.730±1.64, 8.14±2.90 respectively. The length-weight relation were calculated as TW=0.024TL2.24 (n=1084,R2=0.71) for males, TW=0.011TL2.80 (n=1081,R2= 0.81) for females also we found significant different level length-weight relation in P〈0.05. The growth parameters of von Bertalanffy equation were as, L∞: 14.73 and K: 1.1 and t0: -0.02. The estimated valve of total mortality, natural mortality, fishing mortality and exploitation ratio is Z: 4.35, M: 1.68, F: 2.67, E: 0.61 respectively. By using method analyses knife-edge selection, relative yield per recruitment (Y'/R) :0.014, relative biomass per recruitment, (B'/R) :0.085., Exploitation ratio maximum sustainable yield, Emax : 0.38; biological reference points for Jinga Shrimp stock was calculated. MSY and fmsy value was 600T and 46100day respectively. Result in this study showed exploitation ratio Jinga Shrimp stock is over fishing and decreases exploitation ratio proposed.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Biological ; Jinga Shrimp ; Population ; Dynamics ; Exploitation ; Tiger tooth Croaker ; Otolithes ruber ; Metapenaeus affinis ; Population ; Male ; Female ; Mortality ; Coastal waters
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 202pp.
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  • 20
    Publikationsdatum: 2021-05-19
    Beschreibung: The present study was firstly conducted to study the rate of sexual maturity in Nereis diversicolor under suitable conditions of temperature and photoperiod. The second objective was to determine the potential of artificial breeding in these worms for mass culture. Nereis diversicolor worms were collected from the Anzali lagoon in 4000 sampling operations during the years 2004 to 2006 using Ekman grab with a surface area of 400 cm2. The water salinity, temperature and total organic matter (TOM) of sediments in the sampling region was recorded. The worms were maintained in 0.5 tons (1 x 1 m2) tanks containing clayey-muddy sediment to a height of 20 cm covered with 10 cm water (5 ‰) until they reached a weight of 200-300 mg. Sexual maturity in this species was attained at 4-6 ºC and spawning occurred at approximately 16 ºC. The first gametes were observed five weeks after the temperature increased from 6 to 16 ºC. Sexual maturity was studied at various salinities (0.5, 5, 12, and 15 ‰). Results indicate that these worms attained earlier sexual maturity at salinity of 15 ‰, compared to other salinities studied. No significant differences (P〉0.05) were observed between sexual maturity attained at 12 ‰ and 15 ‰. Stocking density (20, 50, 100, 150 worms) was studied in terms of sex and showed that number of females were higher than males and the ratio was 11:1 (female:male). No significant differences (P〉0.05) were observed between the various stocking densities and their replicates. The effect of light and photoperiod in synchronizing reproduction in male and female N. diversicolor was studied. It was evident that reproduction behavior in adult worms increased for a period of one week at the end of each month after they are exposed to a prolonged photoperiod (L:D=16:8) followed by a period of dim light (simulated using 1 W lamps). Feeding trials were carried out with Saccharomyces cerevisiae, formulated fish diets and humus. Results showed that this diet was effective in speeding up sexual maturity in worms and significant effect of treatment was observed (P〈0.05) in worms fed a diet of humus alone. Eggs and sperms were fertilized and worms developed from the young monotrochophore with jelly layer to the trochophore larvae.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Reproduction ; Sexual Maturity ; Fertilization ; Nereis Diversicolor ; Culture ; Salinity ; Temperature ; Spawning ; Female ; Male ; Larvae ; Sacchromyces cerevisiae ; Density
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 68pp.
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  • 21
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    Iranian Fisheries Science Research Institute | Tehran, Iran
    Publikationsdatum: 2021-05-19
    Beschreibung: Without Abstract.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Oncorhynchus mykiss ; Rainbow trout ; Investigation ; Female
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 64pp.
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  • 22
    Publikationsdatum: 2021-05-19
    Beschreibung: The Kutum, Rutilus frisii kutum, is one of the most important bony fishes in Iranian coastal of Caspian Sea. Its harvest range is between 9000-10000 tons in a year, nearly 60% of the income of Bony fish fishery produced by kutum fishery. The stock of this species reduced drastically in 1982 and the catch slumped to the less than 250 tons in a year. Kutum spawning grounds deterioration, illegal catch, lack of restocking program were the main cause of the decline. This Spices in nature comprised by two distinct form, autumn and spring form. It is worth to be mentioned, by the effect of Caspian Sea Bony fishes Research Center s experts in 1983, artificial spawning and releasing the fries to the sea were commenced and the catch steadily improved. But all activities concerning restocking of kutum concentrated in spring form, as at present about 260 million its fries are released into sea for restocking by Iranian Fisheries Organization, but for above reasons and lack of restocking program, the populations of autumn form gravely shrinked and neared to be extinct. Therefore, to enhance the biodiversity and boost fishers livelihood of kutum in Caspian Sea this project implemented by cooperation of Iranian Fisheries Organization (IFRO) and Caspian Environment Program (CEP) in Aquaculture Institute (Inland Waters). In this project, brooders caught from Anzali lagoon and maintained in two different condition, include of floating cages in Anzali lagoon and earthen ponds in Sefidrud Fisheries Research Station. The results showed that there weren t significant differences between two maintenance statuses in maturation period and other reproductive characteristics of brooders. The ratio of male to female was 1 to 1.4. Minimum and maximum weight measured 1450 to 3100 g (with average of 1850 g) in female and 670 to 1900 g (with average of 1165 g) in male, respectively. The first natural spawning of brooders occurred in the end of January in temperature of 8 till 10 °C in concrete ponds. Also, some of maintained brooders in earthen ponds spawned in February. The average number of absolute, function and relative fecundity determined 88565 16809, 73805 14008 and 48670 12056, respectively. For artificial spawning, male and female brooders injected by pituitary gland with dose of 2-3 and 4-5 mg/kg body weight, respectively. Approximately, 10 and 8 present of female were over-ripe and immature in March (artificial spawning time), respectively. More than 59 % of injected female brooders induced to spawning in first stage after 10-12 hours and 13 % of them in twice stage and 7-8 hours after first stage. And also, 27.6% of females didn’t positive response to injection. Dry method used for eggs fecundity and incubation period lasted 7- 10 days in 14-16 °C. In totally, eggs fertilization were more than 95% and the average of eggs fertilization percent in throughout of period measured more than 92.7 6 %. Eyed eggs appearance occurred 3 days after fecundity and its mean was 92.7 15.1%. Larvae after yolk sac absorption feed with dry milk for 4-5 days and then introduced into fertilized earthen ponds (500 m2 and equipped to aerators) in intensive condition and fed with micro pellet food for 3-4 month. In finally, more than 1.8 millions fries of 1-2 g and some more than 5 g produced and released into Anzali lagoon to its restocking for first time. It is expected that continuing of restocking process of autumn form kutum by Iranian Fisheries Organization eventuate to population increasing of this form in Caspian Sea in future.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Artificial propagation ; Culture ; Rutilus frisii kutum ; Kutum ; Bony Fish ; Fishery ; Spawning ; Biodiversity ; Aquaculture ; Brooders ; Fecundity ; Male ; Female ; Population
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 79pp.
    Standort Signatur Erwartet Verfügbarkeit
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  • 23
    Publikationsdatum: 2021-05-19
    Beschreibung: Due to the usefulness of shrimp broodstock pelleted diets, from aspects of, easier maintenance, transportation, broodstock feeding, and cheaper as compared to natural wet diets, the use of natural wet foods, include sand worm (Perinereis nuntica), cattle fish )Sepia pharaonis) and veal livier decreased and the quantity of pelleted diet increased. Survey was conducted, in tankes with a volume of 300 liters. Tanks were filled with 150 liters of water. 10 broodstock in each tank was left, with an average weight of 37±2 grams. Daily feeding rate, was twenty-five percent of their biomass. The survey was include, 9 treatments with 3 replicates in each tank as described below. Control treatment: broodstock feeding only with, sand worm (33%), cattle fish (34%) and bull livier (33%). Exprimental treatment 1: broodstock feeding with pelleted diet contain 50 percent crude protein and 8 percent crude fat (50%)+sand worm (16 %)+cattle fish (18%)+veal livier (16%). Treatment 2: broodstock feeding with pelleted diet contain 50 percent crude protein and 10 percent crude fat (50 %)+sand worm (16 %)+cattle fish (18%) and veal livier (16%). Treatment 3: broodstock feeding with pelleted diet contain 40 percent crude protein and 10 percent crude fat (50%)+sand worm (16 %)+cattle fish (18 %) and veal livier (16 %). Treatment 4: broodstock feeding with pelleted diet contain 40 percent crude protein and 8 percent crude fat (50 %)+sand worm (16 %)+cattle fish (18 %) and veal livier (16 %). Treatment 5: broodstock feeding with pelleted diet contain 50 percent crude protein and 10 percent crude fat (100 %). Treatment 6: broodstock feeding with pelleted diet contain 50 percent crude protein and 8 percent crude fat (100 %). Treatment 7: broodstock feeding with pelleted diet contain 40 percent crude protein and 10 percent crude fat (100 %). Treatment 8: broodstock feeding with pelleted diet contain 40 percent crude protein and 8 percent crude fat (100%). The results showed that, Gonadosomatic index (GSI) in treatments 3: control and 6, was significantly more than others treatments (p〈0.05). Hepatosomatic indexes, in often treatments was almost equal, and in some cases were significantly different (p〈0.05). In treatments 3 and control, absolute fequndity, was significantly more than others treatment (p〈0.05). The survival percent, in treatment 8 was significantly less than others treatments (p〈0.05). The survival percent in others treatments was not significantly difference (p〉0.05). From the aspect of mean weight of broodstock, wasn’t significant difference in treatments (p〉0.05). From the aspect of mean length of carapac, wasn’t significant difference in treatments (p〉0.05). From the aspect of mean body length, wasn’t significant difference in often treatments (p〉0.05), and in treatments 5 and 6 was significantly less than others (p〈0.05). In the determination of relasheship between kind of treatments and abundance of maturated broodsock, wasn’t significantly difference (p〉0.05). In the determination of, correlation between weight (g) and total length(cm), (r=0.71), weight and carapace length (cm) (r=0.70), the correlation was strong. Between GSI, HIS, carapace length and total length the correlation was intermediate (r=0.54). The correlation between absolutely fecundity and total length (r=0.20), absolutely fecundity and carapace length (r=0.28), absolutely fecundity and weight (r=0.35) was weak. The results showed that, the use of combination of pelleted diet and natural wet diets can increase female maturation indexes. Totally we can noted that, GSI, HIS and absolute fecundity of broodstock, that fed with pelleted diet contain 40 percent crude protein and 10 percent crude fat (50 %)+sand worm (16 %)+cattle fish (18 %) and veal livier (16 %) (treatment 3) was better than the other treatments. Positive effects of this treatnent on sexual indexes, was due to provide part of nutritional requirement of shrimp broodstock from pelleted diet.
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Natural wet diet ; Pelleted diets ; Maturation ; Male ; Female ; Western white shrimp ; Artifitial diets ; Broodstock ; Litopenaeus vannamei
    Repository-Name: AquaDocs
    Materialart: Report , Refereed
    Format: 38pp.
    Standort Signatur Erwartet Verfügbarkeit
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  • 24
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    Iranian Fisheries Science Research Institute | Ahvaz, Iran
    Publikationsdatum: 2021-05-19
    Beschreibung: Epinephelus coioides as a protogynous hermaphrodite. among caged brood stock, functional females appear ....
    Beschreibung: Iranian Fisheries Science Research Institute
    Beschreibung: Published
    Schlagwort(e): Fish ; Hermaphrodite ; Sperm ; Female
    Repository-Name: AquaDocs
    Materialart: Report , Not Known
    Format: 124pp.
    Standort Signatur Erwartet Verfügbarkeit
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  • 25
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-02-16
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 26
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-02-16
    Beschreibung: The comment and response concerning the report of oxidation of methane to methanol by water (Reports, 5 May 2017, p. 523) do not fully capture the implications of thermodynamic limitations. A nonisothermal process in which each cycle requires a large temperature swing and permits only substoichiometric methane conversion surely could not be carried out on any practical scale.
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 27
    Publikationsdatum: 2018-02-16
    Beschreibung: Labinger argues that stepwise reaction of methane with water to produce methanol and hydrogen will never be commercially feasible because of its substoichiometric basis with respect to the active site and the requirement of a large temperature swing. This comment is not touching any new ground, beyond describing the thermodynamic feasibility, thermal cycling, and the role of water as discussed previously. Most important, it does not have a solid numerical basis.
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 28
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-07-27
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 29
    Publikationsdatum: 2018-07-27
    Beschreibung: Vinyl carbocations have been the subject of extensive experimental and theoretical studies over the past five decades. Despite this long history in chemistry, the utility of vinyl cations in chemical synthesis has been limited, with most reactivity studies focusing on solvolysis reactions or intramolecular processes. Here we report synthetic and mechanistic studies of vinyl cations generated through silylium–weakly coordinating anion catalysis. We find that these reactive intermediates undergo mild intermolecular carbon-carbon bond–forming reactions, including carbon-hydrogen (C–H) insertion into unactivated sp 3 C–H bonds and reductive Friedel-Crafts reactions with arenes. Moreover, we conducted computational studies of these alkane C–H functionalization reactions and discovered that they proceed through nonclassical, ambimodal transition structures. This reaction manifold provides a framework for the catalytic functionalization of hydrocarbons using simple ketone derivatives.
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 30
    Publikationsdatum: 2018-06-22
    Beschreibung: It is commonly assumed that recognition and discrimination of chirality, both in nature and in artificial systems, depend solely on spatial effects. However, recent studies have suggested that charge redistribution in chiral molecules manifests an enantiospecific preference in electron spin orientation. We therefore reasoned that the induced spin polarization may affect enantiorecognition through exchange interactions. Here we show experimentally that the interaction of chiral molecules with a perpendicularly magnetized substrate is enantiospecific. Thus, one enantiomer adsorbs preferentially when the magnetic dipole is pointing up, whereas the other adsorbs faster for the opposite alignment of the magnetization. The interaction is not controlled by the magnetic field per se, but rather by the electron spin orientations, and opens prospects for a distinct approach to enantiomeric separations.
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 31
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-06-29
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 32
    Publikationsdatum: 2018-12-14
    Beschreibung: Theory has established the importance of geometric phase (GP) effects in the adiabatic dynamics of molecular systems with a conical intersection connecting the ground- and excited-state potential energy surfaces, but direct observation of their manifestation in chemical reactions remains a major challenge. Here, we report a high-resolution crossed molecular beams study of the H + HD -〉 H 2 + D reaction at a collision energy slightly above the conical intersection. Velocity map ion imaging revealed fast angular oscillations in product quantum state–resolved differential cross sections in the forward scattering direction for H 2 products at specific rovibrational levels. The experimental results agree with adiabatic quantum dynamical calculations only when the GP effect is included.
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 33
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-17
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 34
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-17
    Schlagwort(e): Chemistry
    Print ISSN: 0036-8075
    Digitale ISSN: 1095-9203
    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 35
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-17
    Beschreibung: The chemistry of the carbonyl group is essential to modern organic synthesis. The preparation of substituted, enantioenriched 1,3- or 1,5-dicarbonyls is well developed, as their disconnection naturally follows from the intrinsic polarity of the carbonyl group. By contrast, a general enantioselective access to quaternary stereocenters in acyclic 1,4-dicarbonyl systems remains an unresolved problem, despite the tremendous importance of 2,3-substituted 1,4-dicarbonyl motifs in natural products and drug scaffolds. Here we present a broad enantioselective and stereodivergent strategy to access acyclic, polysubstituted 1,4-dicarbonyls via acid-catalyzed [3,3]-sulfonium rearrangement starting from vinyl sulfoxides and ynamides. The stereochemistry at sulfur governs the absolute sense of chiral induction, whereas the double bond geometry dictates the relative configuration of the final products.
    Schlagwort(e): Chemistry
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  • 36
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-17
    Schlagwort(e): Chemistry
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  • 37
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-17
    Beschreibung: With the recent soaring production of natural gas, the use of methane and other light hydrocarbon feedstocks as starting materials in synthetic transformations is becoming increasingly economically attractive, although it remains chemically challenging. We report the development of photocatalytic C–H amination, alkylation, and arylation of methane, ethane, and higher alkanes under visible light irradiation at ambient temperature. High catalytic efficiency (turnover numbers up to 2900 for methane and 9700 for ethane) and selectivity were achieved using abundant, inexpensive cerium salts as photocatalysts. Ligand-to-metal charge transfer excitation generated alkoxy radicals from simple alcohols that in turn acted as hydrogen atom transfer catalysts. The mixed-phase gas/liquid reaction was adapted to continuous flow, enabling the efficient use of gaseous feedstocks in scalable photocatalytic transformations.
    Schlagwort(e): Chemistry
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  • 38
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-24
    Schlagwort(e): Chemistry
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    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 39
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-24
    Schlagwort(e): Chemistry
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  • 40
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-31
    Schlagwort(e): Chemistry
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  • 41
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-31
    Beschreibung: Intrigued by the potential of nanoscale machines, scientists have long attempted to control molecular motion. We monitored the individual 0.7-nanometer steps of a single molecular hopper as it moved in an electric field along a track in a nanopore controlled by a chemical ratchet. The hopper demonstrated characteristics desired in a moving molecule: defined start and end points, processivity, no chemical fuel requirement, directional motion, and external control. The hopper was readily functionalized to carry cargos. For example, a DNA molecule could be ratcheted along the track in either direction, a prerequisite for nanopore sequencing.
    Schlagwort(e): Chemistry
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  • 42
    Publikationsdatum: 2018-09-21
    Beschreibung: Phosphorothioate nucleotides have emerged as powerful pharmacological substitutes of their native phosphodiester analogs with important translational applications in antisense oligonucleotide (ASO) therapeutics and cyclic dinucleotide (CDN) synthesis. Stereocontrolled installation of this chiral motif has long been hampered by the systemic use of phosphorus(III) [P(III)]–based reagent systems as the sole practical means of oligonucleotide assembly. A fundamentally different approach is described herein: the invention of a P(V)-based reagent platform for programmable, traceless, diastereoselective phosphorus-sulfur incorporation. The power of this reagent system is demonstrated through the robust and stereocontrolled synthesis of various nucleotidic architectures, including ASOs and CDNs, via an efficient, inexpensive, and operationally simple protocol.
    Schlagwort(e): Chemistry
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  • 43
    Publikationsdatum: 2018-09-21
    Beschreibung: Here we report an anomalous porous molecular crystal built of C–H···N-bonded double-layered roof-floor components and wall components of a segregatively interdigitated architecture. This complicated porous structure consists of only one type of fully aromatic multijoint molecule carrying three identical dipyridylphenyl wedges. Despite its high symmetry, this molecule accomplishes difficult tasks by using two of its three wedges for roof-floor formation and using its other wedge for wall formation. Although a C–H···N bond is extremely labile, the porous crystal maintains its porosity until thermal breakdown of the C–H···N bonds at 202°C occurs, affording a nonporous polymorph. Though this nonporous crystal survives even at 325°C, it can retrieve the parent porosity under acetonitrile vapor. These findings show how one can translate simplicity into ultrahigh complexity.
    Schlagwort(e): Chemistry
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  • 44
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-09-28
    Schlagwort(e): Chemistry
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  • 45
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-09-28
    Schlagwort(e): Chemistry
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  • 46
    Publikationsdatum: 2018-09-28
    Beschreibung: Some of the simplest and most powerful carbon-carbon bond forming strategies take advantage of readily accessible ubiquitous motifs: carbonyls and olefins. Here we report a fundamentally distinct mode of reactivity between carbonyls and olefins that differs from established acid-catalyzed carbonyl-ene, Prins, and carbonyl-olefin metathesis reaction paths. A range of epsilon, zeta-unsaturated ketones undergo Brønsted acid–catalyzed intramolecular cyclization to provide tetrahydrofluorene products via the formation of two new carbon-carbon bonds. Theoretical calculations and accompanying mechanistic studies suggest that this carbocyclization reaction proceeds through the intermediacy of a transient oxetane formed by oxygen atom transfer. The complex polycyclic frameworks in this product class appear as common substructures in organic materials, bioactive natural products, and recently developed pharmaceuticals.
    Schlagwort(e): Chemistry
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  • 47
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-09-28
    Beschreibung: Alkene aminoarylation with a single, bifunctional reagent is a concise synthetic strategy. We report a catalytic protocol for the addition of arylsulfonylacetamides across electron-rich alkenes with complete anti-Markovnikov regioselectivity and excellent diastereoselectivity to provide 2,2-diarylethylamines. In this process, single-electron alkene oxidation enables carbon-nitrogen bond formation to provide a key benzylic radical poised for a Smiles-Truce 1,5-aryl shift. This reaction is redox-neutral, exhibits broad functional group compatibility, and occurs at room temperature with loss of sulfur dioxide. As this process is driven by visible light, uses readily available starting materials, and demonstrates convergent synthesis, it is well suited for use in a variety of synthetic endeavors.
    Schlagwort(e): Chemistry
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  • 48
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-10-05
    Schlagwort(e): Chemistry
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  • 49
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-10-05
    Schlagwort(e): Chemistry
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  • 50
    Publikationsdatum: 2018-10-05
    Beschreibung: Photocatalysis based on optically active, "plasmonic" metal nanoparticles has emerged as a promising approach to facilitate light-driven chemical conversions under far milder conditions than thermal catalysis. However, an understanding of the relation between thermal and electronic excitations has been lacking. We report the substantial light-induced reduction of the thermal activation barrier for ammonia decomposition on a plasmonic photocatalyst. We introduce the concept of a light-dependent activation barrier to account for the effect of light illumination on electronic and thermal excitations in a single unified picture. This framework provides insight into the specific role of hot carriers in plasmon-mediated photochemistry, which is critically important for designing energy-efficient plasmonic photocatalysts.
    Schlagwort(e): Chemistry
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  • 51
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-10-12
    Schlagwort(e): Chemistry
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  • 52
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-10-12
    Schlagwort(e): Chemistry
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  • 53
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-10-12
    Beschreibung: Single-electron reduction of a carbonyl to a ketyl enables access to a polarity-reversed platform of reactivity for this cornerstone functional group. However, the synthetic utility of the ketyl radical is hindered by the strong reductants necessary for its generation, which also limit its reactivity to net reductive mechanisms. We report a strategy for net redox-neutral generation and reaction of ketyl radicals. The in situ conversion of aldehydes to α-acetoxy iodides lowers their reduction potential by more than 1 volt, allowing for milder access to the corresponding ketyl radicals and an oxidative termination event. Upon subjecting these iodides to a dimanganese decacarbonyl precatalyst and visible light irradiation, an atom transfer radical addition (ATRA) mechanism affords a broad scope of vinyl iodide products with high Z -selectivity.
    Schlagwort(e): Chemistry
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  • 54
    Publikationsdatum: 2018-10-12
    Beschreibung: Reactions that form a product with the same reactive functionality as that of one of the starting compounds frequently end in oligomerization. As a salient example, selective aldol coupling of the smallest, though arguably most useful, enolizable aldehyde, acetaldehyde, with just one partner substrate has proven to be extremely challenging. Here, we report a highly enantioselective Mukaiyama aldol reaction with the simple triethylsilyl (TES) and tert -butyldimethylsilyl (TBS) enolates of acetaldehyde and various aliphatic and aromatic acceptor aldehydes. The reaction is catalyzed by recently developed, strongly acidic imidodiphosphorimidates (IDPi), which, like enzymes, display a confined active site but, like small-molecule catalysts, have a broad substrate scope. The process is scalable, fast, efficient (0.5 to 1.5 mole % catalyst loading), and greatly simplifies access to highly valuable silylated acetaldehyde aldols.
    Schlagwort(e): Chemistry
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  • 55
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-12-21
    Schlagwort(e): Chemistry
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  • 56
    Publikationsdatum: 2018-12-21
    Beschreibung: Single-molecule magnets (SMMs) containing only one metal center may represent the lower size limit for molecule-based magnetic information storage materials. Their current drawback is that all SMMs require liquid-helium cooling to show magnetic memory effects. We now report a chemical strategy to access the dysprosium metallocene cation [(Cp i Pr5 )Dy(Cp*)] + (Cp i Pr5 , penta-iso-propylcyclopentadienyl; Cp *, pentamethylcyclopentadienyl), which displays magnetic hysteresis above liquid-nitrogen temperatures. An effective energy barrier to reversal of the magnetization of U eff = 1541 wave number is also measured. The magnetic blocking temperature of T B = 80 kelvin for this cation overcomes an essential barrier toward the development of nanomagnet devices that function at practical temperatures.
    Schlagwort(e): Chemistry
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  • 57
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-10-19
    Schlagwort(e): Chemistry
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  • 58
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-10-19
    Beschreibung: The development of highly reactive and stereoselective catalytic systems is required not only to improve existing synthetic methods but also to invent distinct chemical reactions. Herein, a homogenized combination of nickel-based Lewis acid–surfactant-combined catalysts and single-walled carbon nanotubes is shown to exhibit substantial activity in water. In addition to the enhanced reactivity, stereoselective performance and long-term stability were demonstrated in asymmetric conjugate addition reactions of aldoximes to furnish chiral nitrones in high yields with excellent selectivities. The practical and straightforward application of the designed catalysts in water provides an expedient, environmentally benign, and highly efficient pathway to access optically active compounds.
    Schlagwort(e): Chemistry
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  • 59
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-11-02
    Schlagwort(e): Chemistry
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  • 60
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-12-14
    Schlagwort(e): Chemistry
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  • 61
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-10-26
    Schlagwort(e): Chemistry
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  • 62
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-11-02
    Beschreibung: Exploration of intermediates that enable chemoselective cycloaddition reactions and expeditious construction of fused- or bridged-ring systems is a continuous challenge for organic synthesis. As an intermediate of interest, the oxyallyl cation has been harnessed to synthesize architectures containing seven-membered rings via (4+3) cycloaddition. However, its potential to access five-membered skeletons is underdeveloped, largely due to the thermally forbidden (3+2) pathway. Here, the combination of a tailored precursor and a Pd(0) catalyst generates a Pd-oxyallyl intermediate that cyclizes with conjugated dienes to produce a diverse array of tetrahydrofuran skeletons. The cycloaddition overrides conventional (4+3) selectivity by proceeding through a stepwise pathway involving a Pd-allyl transfer and ring closure sequence. Subsequent treatment of the (3+2) adducts with a palladium catalyst converts the heterocycles to the carbocyclic cyclopentanones.
    Schlagwort(e): Chemistry
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  • 63
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-11-16
    Schlagwort(e): Chemistry
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  • 64
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-10
    Schlagwort(e): Chemistry
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  • 65
    Publikationsdatum: 2018-08-10
    Beschreibung: Understanding the practical limitations of chemical reactions is critically important for efficiently planning the synthesis of compounds in pharmaceutical, agrochemical, and specialty chemical research and development. However, literature reports of the scope of new reactions are often cursory and biased toward successful results, severely limiting the ability to predict reaction outcomes for untested substrates. We herein illustrate strategies for carrying out large-scale surveys of chemical reactivity by using a material-sparing nanomole-scale automated synthesis platform with greatly expanded synthetic scope combined with ultrahigh-throughput matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry (MALDI-TOF MS).
    Schlagwort(e): Chemistry
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  • 66
    Publikationsdatum: 2018-08-24
    Beschreibung: Researchers around the world have observed the formation of molecularly ordered structures of unknown origin on the surface of titanium dioxide (TiO 2 ) photocatalysts exposed to air and solution. Using a combination of atomic-scale microscopy and spectroscopy, we show that TiO 2 selectively adsorbs atmospheric carboxylic acids that are typically present in parts-per-billion concentrations while effectively repelling other adsorbates, such as alcohols, that are present in much higher concentrations. The high affinity of the surface for carboxylic acids is attributed to their bidentate binding. These self-assembled monolayers have the unusual property of being both hydrophobic and highly water-soluble, which may contribute to the self-cleaning properties of TiO 2 . This finding is relevant to TiO 2 photocatalysis, because the self-assembled carboxylate monolayers block the undercoordinated surface cation sites typically implicated in photocatalysis.
    Schlagwort(e): Chemistry
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  • 67
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-31
    Schlagwort(e): Chemistry
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  • 68
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-08-31
    Schlagwort(e): Chemistry
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  • 69
    Publikationsdatum: 2018-08-31
    Beschreibung: The alkaline earth metals calcium (Ca), strontium (Sr), and barium (Ba) typically engage in chemical bonding as classical main-group elements through their n s and n p valence orbitals, where n is the principal quantum number. Here we report the isolation and spectroscopic characterization of eight-coordinate carbonyl complexes M(CO) 8 (where M = Ca, Sr, or Ba) in a low-temperature neon matrix. Analysis of the electronic structure of these cubic O h -symmetric complexes reveals that the metal–carbon monoxide (CO) bonds arise mainly from [M(d )] -〉 (CO) 8 backdonation, which explains the strong observed red shift of the C-O stretching frequencies. The corresponding radical cation complexes were also prepared in gas phase and characterized by mass-selected infrared photodissociation spectroscopy, confirming adherence to the 18-electron rule more conventionally associated with transition metal chemistry.
    Schlagwort(e): Chemistry
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  • 70
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-09-07
    Schlagwort(e): Chemistry
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    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 71
    Publikationsdatum: 2018-09-07
    Beschreibung: Mystery surrounds the transition from gas-phase hydrocarbon precursors to terrestrial soot and interstellar dust, which are carbonaceous particles formed under similar conditions. Although polycyclic aromatic hydrocarbons (PAHs) are known precursors to high-temperature carbonaceous-particle formation, the molecular pathways that initiate particle formation are unknown. We present experimental and theoretical evidence for rapid molecular clustering–reaction pathways involving radicals with extended conjugation. These radicals react with other hydrocarbon species to form covalently bound complexes that promote further growth and clustering by regenerating resonance-stabilized radicals through low-barrier hydrogen-abstraction and hydrogen-ejection reactions. Such radical–chain reaction pathways may lead to covalently bound clusters of PAHs and other hydrocarbons that would otherwise be too small to condense at high temperatures, thus providing the key mechanistic steps for rapid particle formation and surface growth by hydrocarbon chemisorption.
    Schlagwort(e): Chemistry
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  • 72
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-09-14
    Schlagwort(e): Chemistry
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  • 73
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-04-27
    Schlagwort(e): Chemistry
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  • 74
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-04-27
    Schlagwort(e): Chemistry
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  • 75
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-04-27
    Beschreibung: Basic heteroarenes are a ubiquitous feature of pharmaceuticals and bioactive molecules, and Minisci-type additions of radical nucleophiles are a leading method for their elaboration. Despite many Minisci-type protocols that result in the formation of stereocenters, exerting control over the absolute stereochemistry at these centers remains an unmet challenge. We report a process for addition of prochiral radicals, generated from amino acid derivatives, to pyridines and quinolines. Our method offers excellent control of both enantioselectivity and regioselectivity. An enantiopure chiral Brønsted acid catalyst serves both to activate the substrate and induce asymmetry, while an iridium photocatalyst mediates the required electron transfer processes. We anticipate that this method will expedite access to enantioenriched small-molecule building blocks bearing versatile basic heterocycles.
    Schlagwort(e): Chemistry
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  • 76
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-05-25
    Schlagwort(e): Chemistry
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    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 77
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-05-25
    Schlagwort(e): Chemistry
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    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 78
    Publikationsdatum: 2018-10-26
    Beschreibung: Primary amines are essential constituents of biologically active molecules and versatile intermediates in the synthesis of drugs and agrochemicals. However, their preparation from easily accessible alkenes remains challenging. Here, we report a general strategy to access primary amines from alkenes through an operationally simple iron-catalyzed aminochlorination reaction. A stable hydroxylamine derivative and benign sodium chloride act as the respective nitrogen and chlorine sources. The reaction proceeds at room temperature under air; tolerates a large scope of aliphatic and conjugated alkenes, including densely functionalized substrates; and provides excellent anti-Markovnikov regioselectivity with respect to the amino group. The reactivity of the 2-chloroalkylamine products, an understudied class of amphoteric molecules, enables facile access to linear or branched aliphatic amines, aziridines, aminonitriles, azido amines, and homoallylic amines.
    Schlagwort(e): Chemistry
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  • 79
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-11-09
    Schlagwort(e): Chemistry
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    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 80
    Publikationsdatum: 2018-11-09
    Beschreibung: Despite the enormous potential for the use of stereospecific cross-coupling reactions to rationally manipulate the three-dimensional structure of organic molecules, the factors that control the transfer of stereochemistry in these reactions remain poorly understood. Here we report a mechanistic and synthetic investigation into the use of enantioenriched alkylboron nucleophiles in stereospecific Pd-catalyzed Suzuki cross-coupling reactions. By developing a suite of molecular descriptors of phosphine ligands, we could apply predictive statistical models to select or design distinct ligands that respectively promoted stereoinvertive and stereoretentive cross-coupling reactions. Stereodefined branched structures were thereby accessed through the predictable manipulation of absolute stereochemistry, and a general model for the mechanism of alkylboron transmetallation was proposed.
    Schlagwort(e): Chemistry
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  • 81
    Publikationsdatum: 2018-11-16
    Beschreibung: Heterobiaryls composed of pyridine and diazine rings are key components of pharmaceuticals and are often central to pharmacological function. We present an alternative approach to metal-catalyzed cross-coupling to make heterobiaryls using contractive phosphorus C–C couplings, also termed phosphorus ligand coupling reactions. The process starts by regioselective phosphorus substitution of the C–H bonds para to nitrogen in two successive heterocycles; ligand coupling is then triggered via acidic alcohol solutions to form the heterobiaryl bond. Mechanistic studies imply that ligand coupling is an asynchronous process involving migration of one heterocycle to the ipso position of the other around a central pentacoordinate P(V) atom. The strategy can be applied to complex drug-like molecules containing multiple reactive sites and polar functional groups, and also enables convergent coupling of drug fragments and late-stage heteroarylation of pharmaceuticals.
    Schlagwort(e): Chemistry
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  • 82
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-07-06
    Schlagwort(e): Chemistry
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  • 83
    Publikationsdatum: 2018-07-06
    Beschreibung: Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF 3 I molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF 3 fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations.
    Schlagwort(e): Chemistry
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  • 84
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-07-13
    Schlagwort(e): Chemistry
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  • 85
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-06-22
    Schlagwort(e): Chemistry
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  • 86
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-04-13
    Schlagwort(e): Chemistry
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  • 87
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-05-04
    Schlagwort(e): Chemistry
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  • 88
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-05-11
    Schlagwort(e): Chemistry
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  • 89
    Publikationsdatum: 2018-05-11
    Beschreibung: Common anionic nucleophiles such as those derived from inorganic salts have not been used for enantioselective catalysis because of their insolubility. Here, we report that merging hydrogen bonding and phase-transfer catalysis provides an effective mode of activation for nucleophiles that are insoluble in organic solvents. This catalytic manifold relies on hydrogen bonding complexation to render nucleophiles soluble and reactive, while simultaneously inducing asymmetry in the ensuing transformation. We demonstrate the concept using a chiral bis-urea catalyst to form a tridentate hydrogen bonding complex with fluoride from its cesium salt, thereby enabling highly efficient enantioselective ring opening of episulfonium ion. This fluorination method is synthetically valuable considering the scarcity of alternative protocols and points the way to wider application of the catalytic approach with diverse anionic nucleophiles.
    Schlagwort(e): Chemistry
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  • 90
    Publikationsdatum: 2018-05-18
    Beschreibung: Carbon dioxide (CO 2 ) electroreduction could provide a useful source of ethylene, but low conversion efficiency, low production rates, and low catalyst stability limit current systems. Here we report that a copper electrocatalyst at an abrupt reaction interface in an alkaline electrolyte reduces CO 2 to ethylene with 70% faradaic efficiency at a potential of –0.55 volts versus a reversible hydrogen electrode (RHE). Hydroxide ions on or near the copper surface lower the CO 2 reduction and carbon monoxide (CO)–CO coupling activation energy barriers; as a result, onset of ethylene evolution at –0.165 volts versus an RHE in 10 molar potassium hydroxide occurs almost simultaneously with CO production. Operational stability was enhanced via the introduction of a polymer-based gas diffusion layer that sandwiches the reaction interface between separate hydrophobic and conductive supports, providing constant ethylene selectivity for an initial 150 operating hours.
    Schlagwort(e): Chemistry
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  • 91
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-05-25
    Schlagwort(e): Chemistry
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    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 92
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-03-23
    Beschreibung: White phosphorus, generated in the legacy thermal process for phosphate rock upgrading, has long been the key industrial intermediate for the synthesis of phosphorus-containing chemicals, including herbicides, flame-retardants, catalyst ligands, battery electrolytes, pharmaceuticals, and detergents. In contrast, phosphate fertilizers are made on a much larger scale from phosphoric acid, obtained by treating phosphate rock with sulfuric acid. Dehydration of phosphoric acid using sodium chloride gives trimetaphosphate, and here we report that trichlorosilane, primarily used for the production of high-purity silicon, reduces trimetaphosphate to the previously unknown bis(trichlorosilyl)phosphide anion. This anion offers an entry point to value-added organophosphorus chemicals such as primary and secondary alkyl phosphines, and thus to organophosphinates, and can also be used to prepare phosphine gas and the hexafluorophosphate anion, all previously available only downstream from white phosphorus.
    Schlagwort(e): Chemistry
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  • 93
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-04-06
    Schlagwort(e): Chemistry
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  • 94
    Publikationsdatum: 2018-04-06
    Beschreibung: Cross-coupling chemistry is widely applied to carbon-carbon bond formation in the synthesis of medicines, agrochemicals, and other functional materials. Recently, single-electron–induced variants of this reaction class have proven particularly useful in the formation of C(sp 2 )–C(sp 3 ) linkages, although certain compound classes have remained a challenge. Here, we report the use of sulfones to activate the alkyl coupling partner in nickel-catalyzed radical cross-coupling with aryl zinc reagents. This method’s tolerance of fluoroalkyl substituents proved particularly advantageous for the streamlined preparation of pharmaceutically oriented fluorinated scaffolds that previously required multiple steps, toxic reagents, and nonmodular retrosynthetic blueprints. Five specific sulfone reagents facilitate the rapid assembly of a vast set of compounds, many of which contain challenging fluorination patterns.
    Schlagwort(e): Chemistry
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  • 95
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-05-04
    Beschreibung: Plasmon-induced chemical reactions of molecules adsorbed on metal nanostructures are attracting increased attention for photocatalytic reactions. However, the mechanism remains controversial because of the difficulty of direct observation of the chemical reactions in the plasmonic field, which is strongly localized near the metal surface. We used a scanning tunneling microscope (STM) to achieve real-space and real-time observation of a plasmon-induced chemical reaction at the single-molecule level. A single dimethyl disulfide molecule on silver and copper surfaces was dissociated by the optically excited plasmon at the STM junction. The STM study combined with theoretical calculations shows that this plasmon-induced chemical reaction occurred by a direct intramolecular excitation mechanism.
    Schlagwort(e): Chemistry
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  • 96
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-05-25
    Beschreibung: Identifying catalyst activation modes that exploit one-electron chemistry and overcome associated deactivation pathways will be transformative for developing first-row transition metal catalysts with performance equal or, ideally, superior to precious metals. Here we describe a zinc-activation method compatible with high-throughput reaction discovery that identified scores of cobalt-phosphine combinations for the asymmetric hydrogenation of functionalized alkenes. An optimized catalyst prepared from ( R , R )-Ph-BPE {Ph-BPE, 1,2-bis[(2 R ,5 R )-2,5-diphenylphospholano]ethane} and cobalt chloride [CoCl 2 ·6H 2 O] exhibited high activity and enantioselectivity in protic media and enabled the asymmetric synthesis of the epilepsy medication levetiracetam at 200-gram scale with 0.08 mole % catalyst loading. Stoichiometric studies established that the cobalt (II) catalyst precursor ( R , R )-Ph-BPECoCl 2 underwent ligand displacement by methanol, and zinc promoted facile one-electron reduction to cobalt (I), which more stably bound the phosphine.
    Schlagwort(e): Chemistry
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  • 97
    Publikationsdatum: 2018-06-01
    Beschreibung: Transition metal–catalyzed arene functionalization has been widely used for molecular synthesis over the past century. In this arena, copper catalysis has long been considered a privileged platform due to the propensity of high-valent copper to undergo reductive elimination with a wide variety of coupling fragments. However, the sluggish nature of oxidative addition has limited copper’s capacity to broadly facilitate haloarene coupling protocols. Here, we demonstrate that this copper oxidative addition problem can be overcome with an aryl radical–capture mechanism, wherein the aryl radical is generated through a silyl radical halogen abstraction. This strategy was applied to a general trifluoromethylation of aryl bromides through dual copper-photoredox catalysis. Mechanistic studies support the formation of an open-shell aryl species.
    Schlagwort(e): Chemistry
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  • 98
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-05-18
    Schlagwort(e): Chemistry
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  • 99
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-06-01
    Schlagwort(e): Chemistry
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    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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  • 100
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publikationsdatum: 2018-03-23
    Schlagwort(e): Chemistry
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    Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik
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