Redox-regulated ethylene binding to a rhenium-thiolate complex.

This thesis reports the reactivity of the rhenium-thiolate complex, tris(2-diphenylphosphinobenzenethiolato)rhenium(III), [Re(DPPBT) 3 ] ( 1 ) and its oxidized derivatives with ethylene. The reactivity has been studied by electrochemical, spectroelectrochemical, and chemical methods. Based on the cyclic voltammetric data, ( 1 ) shows two reversible one electron oxidations and a single reduction. The three redox events are observed at potentials of 420, -340 and -1620 mV versus a ferrocene reference. The events span formal oxidation states from Re(II) to Re(V) although significant ligand participation in the redox events makes these formal assignments misleading with respect to the electronic structure of the complexes. Bulk oxidation of ( 1 ) (E applied = +23 mV) in the presence of ethylene yields {[(ethane-1,2-diylbis(thio-2,1-phenylene)diphenyl-phosphino)(2-diphenylphosphinobenzenethiolato)]rhenium(III)} ( 6 ) from the addition of the alkene across cis sulfur sites. Electronic spectra recorded during the oxidation reveal two stages. The first stage is assigned as the one electron oxidation of ( 1 ) to tris(2-diphenylphosphinobenzenethiolato)rhenium(IV) ( 3 ), which is indicated by the intensity increases at 390 and 581 nm. During the second stage, a reaction occurs between ( 3 ) and ethylene that yields {[(ethane-1,2-diylbis(thio-2,1-phenylene)diphenyl-phosphino)(2-diphenylphosphinobenzenethiolato)]rhenium(II)} ( 5 ), which is oxidized to ( 6 ) as shown by the intensity loss at 390 and 581 nm and simultaneous intensity gain at 484 nm. The formal Re(III)/Re(II) reduction potential of ( 6 ) is shifted approximately +1520 mV consistent with the formation of two thioether donors. Complex ( 6 ) is stable in solution, but reduction at an applied potential of -977 mV initiates C-S bond cleavage and release of ethylene. The spectroscopic results reveal the pathway to be the reverse of the C-S bond formation. Oxidation of ( 1 ) using AgPF 6 followed by an ethylene purge yields (6)[PF 6 ] . The +ESI-MS of (6)[PF 6 ] shows a parent ion peak at m/z = 547.0710 (z = 2). The complex (6)[PF 6 ] crystallizes as a long thin orange plate in the monoclinic space group C2/c with unit cell dimensions of a = 29.009(18) Å; b = 22.577(18) Å; c = 43.99(3) Å; and ß = 96.182(17)°. The kinetic and equilibrium parameters associated with C-S bond formation/cleavage were extracted from cyclic voltammograms at multiple scan rates using the DigiSim software package. The rate constants for C-S formation between ( 3 ) and ethylene, k f , and for C-S bond cleavage for ( 5 ), k r , were extracted from simulation of the CV data at 7 scan rates ranging from 100 to 1000 mV/s for 3 independent trials. Average values for k f and k r are (1.2 ± 0.2) × 10 -1 M -1 s -1 and (3.0 ± 0.4) × 10 -2 s -1 , respectively. From these, K 2 was calculated as 4.0 ± 0.8 in agreement with predictions from the UV-visible study. K 1 and K 3 are equilibrium constants for ethylene binding/release between ( 1 ) and {[(ethane-1,2-diylbis(thio-2,1-phenylene)diphenyl-phosphino)(2-diphenyl-phosphinobenzenethiolato)]rhenium(I)} ( 8 ), and tris(2-diphenylphosphinobenzenethiolato)rhenium(V) ( 4 ) and ( 6 ), respectively. From the redox potentials and the equilibrium constant K 2 , values for K 1 and K 3 were determined. K 1 has a calculated value of (1.9 ± 0.4) × 10 -11 consistent with observation of an unstable C-S bond. In contrast, the calculated value of K 3 , (2.5 ± 0.9) × 10 9 , is large and is consistent with the observed stability of ( 6 ). The large differences in equilibrium constants as a function of oxidation state provide a means to easily gate ethylene addition/release

Carbon-sulfur bond formation/cleavage reactions of metal-stabilized thiyl radicals by electrochemical and chemical methods.

The oxidation of metallothiolates is complicated by non-innocence or potential redox activity of sulfur to yield thiyl (RS•) radicals. In some instances, the one-electron oxidation of metal thiolates yields a product with the unpaired electron nearly equally delocalized between metal and sulfur such that, a specific site of oxidation cannot be defined. We refer to these complexes as metal-stabilized thiyl radicals. This dissertation explores reversible carbon-sulfur bond formation between metal-stabilized thiyl radicals and unsaturated hydrocarbons. Oxidation of the metal thiolate precursors [Ru(DPPBT)3]- Ru-l, and Re(DPPBT)3, Re-l, (DPPBT = diphenylphosphino-benzenethiolato), generates reactive species add with alkenes, alkynes, and dienes to yield metal-dithioether products. The electrochemical experiment reveals the addition of alkenes to [Ru-l]+ as an irreversible process. The oxidized intermediate [Re-l]+ binds alkenes reversibly with equilibrium binding constants that vary with complex charge. This dissertation employs the complex, [Ru-l]- to investigate metal-stabilized thiyl radical reactivity with alkenes, alkynes, and dienes. The successful works allow us to establish the scope and limits of these reactions. The rate constants of substrates are obtained through digital simulation of cyclic voltammograms at multiple scan rates. The electronic effects provide a measure of the relative reactivity of the substituted styrenes toward the metal-coordinated thiyl radicals, which yields a Hammett correlation (p = -0.7(1)) consistent with an electrophilic character for our thiyl radical complexes. Experimentally determined rate constants range from 4.6(5) x 107 M-1 S-l for electron-rich alkenes to 2.7(2) x 104 M-1 S-l for electron-poor alkenes. For cyclic alkenes, the rate of addition correlates with ring strain; knorbornene \u3e kcyclopentene \u3e kcyclohexene. The rate constant of alkyne addition are found to be approximately 100 times lower than alkenes as well-known. The dienes are obtained the addition rate in range between alkenes and alkynes. Crystalline samples of the ethylene addition products [Ru-l•C2H4]+ and [Re-l•C2H4]+ are obtained from preparative scale reactions using chemical oxidants. Chemical oxidation of [Ru-l]¨ in the presence of m-methylstyrene, pmethyl styrene, cyclohexene, and l-octyne yields the dithioether complexes [Ru-l• m-methylstyrenet]+, [Ru-l•p-methylstyrene]+, [Ru-l•cyclohexenet]+, and [Ru-l•octynet]+. All chemically synthesized complexes were fully characterized including 31P NMR and mass spectrometry

Current status of shrimp farming and diseases in Cambodia

The farming of penaeid shrimps in Cambodia began in 1989 and has significantly expanded since 1991. Shrimp cultivation has been carried out in the four coastal provinces, i.e. Kampot, Kep, Preah Sihanouk Ville, and Koh Kong. Black tiger shrimp (Penaeus monodon) and whiteleg shrimp (P. vannamei) are the main species being cultured extensively and intensively in brackishwater ponds in Kampot, Kep, and Preah Sihanouk Ville, and Koh Kong, respectively. Extensive shrimp ponds were constructed close to the mangrove areas with some containing mangroves within the pond and stocking density ranging from 5,000 to 20,000 postlarvae/ha. However, the productivity remains low at >100 kg/ ha/ year. On the contrary, intensive culture has a stocking density ranging from 300,000 to 500,000 postlarvae/ha. While high cost of investment for farm establishment, pond construction and farm operation are required, productions of newly established farms have reached 7 to 8 metric tons (MT) /ha per crop. The occurrence of white spot disease, monodon baculovirus disease, and yellow head disease was first reported in 1999 among cultured P. monodon in Koh Kong province causing a number of farmers to stop the intensive cultivation of black tiger shrimp. To date, only a small proportion of shrimp farmers have ventured into extensive shrimp farming with approximately 10 ha of shrimp areas currently in operation. To mitigate the negative impacts of shrimp diseases and promote the expansion of the shrimp industry in Cambodia, development of a national reporting system for aquatic animal diseases; capacity building for detection, monitoring and disease surveillance; creation of National Guidelines On Good Shrimp Aquaculture Practices; establishment of subresearch centers and concomitant funding support for marine aquaculture development and extension services; establishment of local shrimp hatcheries and provision of hands-on trainings for farmers; and strengthening collaborations among provincial officers, researchers and farmers network should be accordingly instituted

Stability of Soil Block on Low Interface Friction Plane With and Without Side Supports

Slope instability is a challenging problem in geotechnical engineering. The main focus of this paper is to investigate the stability of a soil block, with and without side supports, resting on a low interface friction plane by employing a three-dimensional finite element analysis (3D FEA). In the numerical model, the soil block is modeled as a volume element with Mohr-Coulomb material in a drained condition. Interface elements are used at the bottom plane in order to capture the shear sliding on the interface plane. Side interface elements with fully rough surfaces are also used in the slip analysis with side supports. A failure analysis is performed by means of the gravity loading method. The results of 3D FEA are compared with those of the existing physical models for both cases. Extensive parametric studies of a slip analysis with side supports are carried out in order to develop an empirical equation for the stability number as a function of four normalized parameters. Finally, the paper presents an application of the proposed equation to the prediction of the failure width and the required width for the excavation of an actual mine

20-059 Cucumis melo

Scientific name: Cucumis meloPlant name: melonJP No.: JP274046Collection date: 2021/1/11Country (Province): Cambodia (Stung Treng)Latitude: 13 33 48.5Longitude: 106 02 32.5Altitude (m): 55Collectors: Sreynech Ouch, Dolla Ros, Sophany Sakhan, Vathany Thun, Makara Ouk, Katsunori Tanaka, Yoichi Kawaz

JP274072, B-15, Amaranthus blitum

Scientific name: Amaranthus blitumPlant name: amaranthJP No.: JP274072Collection date: 2020/11/25Country (Province): Cambodia (Kampong Thom)Latitude: 12 36 48.5Longitude: 105 05 15.3Altitude (m): 14Collectors: Sreynech Ouch, Katsunori Tanaka, Dolla Ros, Sophany Sakhan, Vathany Thun, Makara Ouk, Yoichi Kawazu, Kenji Kat

JP274125, B-68, Cucurbita moschata

Scientific name: Cucurbita moschataPlant name: pumpkinJP No.: JP274125Collection date: 2020/11/30Country (Province): Cambodia (Siem Reap)Latitude: 13 29 23.5Longitude: 103 56 29.2Altitude (m): 46Collectors: Sreynech Ouch, Katsunori Tanaka, Dolla Ros, Sophany Sakhan, Vathany Thun, Makara Ouk, Yoichi Kawazu, Kenji Kat

JP274094, B-37, Cucurbita moschata

Scientific name: Cucurbita moschataPlant name: pumpkinJP No.: JP274094Collection date: 2020/11/26Country (Province): Cambodia (Preah Vihear)Latitude: 13 26 02.9Longitude: 105 08 02.6Altitude (m): 63Collectors: Sreynech Ouch, Katsunori Tanaka, Dolla Ros, Sophany Sakhan, Vathany Thun, Makara Ouk, Yoichi Kawazu, Kenji Kat

Current status of sustainable aquaculture in Cambodia

In Cambodia, the extension of technologies in fish aquaculture is a vital activity that contributes to improving the daily livelihood of the rural poor farmer communities. Technology extension was introduced since 1994 through a project of the Asian Institute of Technology (AIT) and other local non-government organizations (NGOs) or international organizations (IOs) in some fish production deficient provinces. Prior to the introduction of such activities, wild fish were still abundant. From then to date, aquaculture extension is being done under the Freshwater Aquaculture Improvement and Extension Project Phase II of Japan International Cooperation Agency (FAIEXII-JICA), and Department for International Development/Danish International Development Agency (DFID/DANIDA) Projects. Recently, aquaculture extension is one of the national policies under the National Rectangular Strategy Policies of the Government. There are several different freshwater aquaculture systems including floating cage/pen culture, earthen pond culture and rice-fish culture, and other fish culture in smallwater bodies or aquaculture-based fisheries in Cambodia as practiced in over 20 provinces and cities, with less development focused on coastal aquaculture. Freshwater aquaculture production continued to grow over the past two decades and increased from 1,610 tons in 1984 to 20,760 tons in 2004, representing 11.9 times increase or growth of 16.3% per year This further increased to 74,000 tons in 2012, representing 11.9 times increase or a growth rate of 15% per year. However, aquaculture development in Cambodia is in its infancy stage compared to other countries in the region. It has encountered some problems and constraints during its development, which include inadequate and unreliable supply of good quality seed; lack of capital, fund or credit for aquaculture investment; inadequate knowledge of aquaculture technology; inadequate manpower for aquaculture extension service; and climate change, which have adversely impacted aquaculture development in Cambodia. In order to achieve the goal of supplying the nation s future fishery requirements through aquaculture, the Cambodia Fisheries Administration (FiA) published the Strategic Planning Framework (SPF) for Fisheries (2010-2019). Within this framework, the scenarios for future fish demand-supply for 2019 suggest that aquaculture production will increase by 15% per year to 185,000 tons by the end of 2019

20-062 Cucurbita moschata

Scientific name: Cucurbita moschataPlant name: pumpkinJP No.: JP274049Collection date: 2021/1/11Country (Province): Cambodia (Stung Treng)Latitude: 13 33 48.5Longitude: 106 02 32.5Altitude (m): 55Collectors: Sreynech Ouch, Dolla Ros, Sophany Sakhan, Vathany Thun, Makara Ouk, Katsunori Tanaka, Yoichi Kawaz