Synthesis of Metal-Coordinating Arenediynes And Study Of Their Reactivity in Bergman Cyclization

The Bergman cycloaromatization (BC) in which a cis-alkene-1,2-diyne (enediyne) cyclizes to form a p-benzyne diradical, typically is a very endothermic reaction, requiring a substantial amount of energy (i.e. high temperature) for it to proceed. This reaction received very little attention until a decade after its discovery, when the natural enediynes were isolated and shown to be the most active antitumor agents every discovered. Having BC at the heart of their mode of action, these natural enediynes have been very challenging to mimic from synthetic standpoints. Of particular interest is to be able to design and synthesize an enediyne that is stable at room temperature, while also being capable of being triggered to undergo BC under ambient conditions. Although a relatively new concept, metal-induced BC reactions have generally been known to decrease the demanding energy barrier. The work presented here describes several synthetic strategies towards arenediyne crown eithers and the synthesis of several arenediyne hydrazone/Schiff base ligands with extended n-systems. These synthesized enediynes are useful ligands, capable of metal-cordination and hence potentially decreasing the BC energy barrier. BC reactions of enediyne intermediates are also reported.

Synthesis of Metal-Coordinating Arenediynes And Study Of Their Reactivity in Bergman Cyclization

The Bergman cycloaromatization (BC) in which a cis-alkene-1,2-diyne (enediyne) cyclizes to form a p-benzyne diradical, typically is a very endothermic reaction, requiring a substantial amount of energy (i.e. high temperature) for it to proceed. This reaction received very little attention until a decade after its discovery, when the natural enediynes were isolated and shown to be the most active antitumor agents every discovered. Having BC at the heart of their mode of action, these natural enediynes have been very challenging to mimic from synthetic standpoints. Of particular interest is to be able to design and synthesize an enediyne that is stable at room temperature, while also being capable of being triggered to undergo BC under ambient conditions. Although a relatively new concept, metal-induced BC reactions have generally been known to decrease the demanding energy barrier. The work presented here describes several synthetic strategies towards arenediyne crown eithers and the synthesis of several arenediyne hydrazone/Schiff base ligands with extended n-systems. These synthesized enediynes are useful ligands, capable of metal-cordination and hence potentially decreasing the BC energy barrier. BC reactions of enediyne intermediates are also reported.

Thermal Diffusion Characteristics in Permafrost during the Exploitation of Gas Hydrate

Methane hydrate is the vast potential resources of natural gas in the permafrost and marine areas. Due to the occurrence of phase transition, the gas hydrate is dissociated into gas and water and absorbs lots of heat. The incomprehensive knowledge of endothermic reaction in permafrost sediments still restricted the production efficiency of hydrate commercial development. This endothermic reaction leads to a complex thermal diffusion in permafrost, which directly influences the phase transition in turn. In this research, the heat during the exploitation is transferred in two forms (specific heat and latent heat). Besides, the melting point is not constant but depends on the pore size of the reservoir rock. According to these features, a thermal diffusion model with phase transition is established. To calculate the governing equation, the pore size distribution is obtained by using the nuclear magnetic resonance (NMR) method. The heating tests are conducted and simulated to calibrate the coefficient (i.e., transverse surface relaxivity) of NMR. Then, the temperature field evolution of the hydrate reservoir during the exploitation is simulated by using the calibrated values. The results show that the temperature curves have a typical plateau related to the pore size distribution, which is effective to obtain the surface relaxivity. The heat transfer is remarkably limited by the endothermic effect of the phase transition. The hydrate recovery efficiency may depend largely on the heating capacity of the engineering operation and the rate of gas production. Compared to the conventional petroleum industry, it is significant to control the maximum temperature and temperature distribution in engineering operations during hydrate development. This research on the temperature behavior during onshore permafrost hydrate production could provide the theoretical support to control heat behavior of offshore hydrate production.

Innovative Way to Decrease the Water Consumption of Direct Evaporative Air-Cooler

In the present study the existing direct evaporative coolers (DEC) is modified in such a way that DEC consume less amount of water and provide better cooling effect. In desert area, water consumption by air cooler is a serious problem. Therefore, the present study addressed this issue and primary objective of the study is to minimize the consumption of water. For this purpose, the property of the endothermic reaction is utilized. There are few salts that produce endothermic reaction if it is diluted in water. Those salt crystals absorb heat from the surrounding environment (water) and ultimately the temperature of the overall solution gets reduced. This cold solution is then passed through honeycomb cooling pad, as a result more amount of air can be cooled using the same volume of water as compared to the traditional air-cooler. Ammonium Chloride (NH4Cl), Ammonium Nitrite (NH4NO3 ) salts satisfy the basic criteria for the endothermic reaction but NH4Cl will be more useful to use in the air-coolers, as Ammonium Nitrite is costlier and also hazardous. A salt water separator arrangement also attached with modified air-cooler which will help to regenerate Ammonium Chloride crystal from solution with the help of solar energy. In this study, firstly discussed about proposed design of an air-cooler system, which is able to nicely handle chemical solution. Then compared the study with experimental outcome which have been carried out with and without using salt. From the result it has been observed that modified design of air cooler has great potential to improve the traditional air cooler in terms of cooling effect and water consumption

AN EXPERIMENTAL EVALUATION OF RASA PANCHAKA (ATTRIBUTES) OF FOLK MEDICINAL PLANT Andrographis Macrobotrys Nees

Background and Objective: Folk medicinal plants are densely found in India which needs to be thorough-ly studied and documented. Andrographis Macrobotrys (Nees) is an erect, stout herb of Acanthaceae fami-ly is used in the treatment of snake bite, diarrhea, muscle pain, fever, jaundice, liver disorders and skin dis-ease by the tribes of Kerala. According to the principles of Ayurveda, basis for use of drug is by analysing its Rasapanchaka (attributes) namely rasa (taste), guna (qualities), vipaka (taste after digestion), virya (po-tency), and prabhava (special action). Hence assessment of Rasapanchaka is necessary for thorough knowledge of the drug. Aim of the present study is to evaluate the Rasa, Guna, Virya, Vipaka and prabha-va of Andrographis Macrobotrys Nees. Methods: Rasa of whole plant was assessed by direct perception by administering test drug to 25 volun-teers. Virya was assessed by exothermic and endothermic reaction of the drug with water in different con-centrations. Vipaka, guna and prabhava were determined through animal experimental study by adminis-tering drug to 12 Wistar Albino rats. Result and Conclusion: The assessment of study on rasapanchaka reveals that test drug possess Tiktha (bitter) rasa, Kashaya (astringent) anurasa, laghu (light), ruksha (dry), ushna (hot) guna, katu (pungent) vipaka, sheetha (cold) virya, pachana (digestive), lekhana (scraping) karma (action).

Crystal Structure and Thermal Behavior of SbC2O4OH and SbC2O4OD

The order of OH groups in the crystal structure of SbC2O4OH, a potential precursor in the synthesis of ternary oxides, was debated. Neutron diffraction on the deuteride SbC2O4OD revealed disordered OD groups with half occupation for deuterium atoms on either side of a mirror plane (SbC2O4OD at T = 298(1) K: Pnma, a = 582.07(3) pm, b = 1128.73(5) pm, c = 631.26(4) pm). O–H stretching frequencies are shifted by a factor of 1.35 from 3390 cm−1 in the hydride to 2513 cm−1 in the deuteride as seen in infrared spectra. SbC2O4OH suffers radiation damage in a synchrotron beam, which leaves a dark amorphous residue. Thermal decomposition at 564 K yields antimony oxide, carbon dioxide, carbon oxide, and water in an endothermic reaction. When using SbC2O4OH as a precursor in reactions, however, ternary oxides are only formed at much higher temperatures.