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RISS 인기검색어
- 검색키워드
- 저자 : Abu-Dief, Ahmed M. (검색결과 2 건)
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Abu-Gharib, Ezz A.,EL-Khatib, Rafat M.,Nassr, Lobna A.E.,Abu-Dief, Ahmed M. Korean Chemical Society 2011 대한화학회지 Vol.55 No.3
7-hydroxy-2H-chromen-2-one(HC)와 7-hydroxy-2H-chromen-2-one-4-acetic acid(HCA)의 염기성 가수분해반응을 aqueous-methanol과 aqueous-acetone 혼합물에서 283 K에서 313 K의 온도 범위에서 속도론적으로 연구하였다. 반응의 활성화 파라미터를 구하고 토의하였다. 게다가, 물, 물-에탄올, 물-아세톤 혼합물 내에서 화합물들에 대한 활성화 에너지 장벽의 변화를 속도론적 데이터로부터 추정하였다. 활성화 장벽의 변화는 HC and HCA의 가수분해 반응과 거의 같았다. HC와 HCA의 염기성 가수분해는 $k_{obs}=k_2[OH^-]$와 같은 속도법칙을 따른다. 메탄올 또는 아세톤의 비가 증가함에 따라 HC 와 HCA의 속도 상수들이 감소하는 것은 $OH^-$ 이온이 불안정해지기 때문이다. 활성화 엔트로피가 큰 음의 값을 갖는 다는 것은 반응이 중간 착물의 형성을 경유하며 진행된다는 것을 의미하며, 또한 중간 착물이 경직성과 안정도를 갖는다는 것을 의미한다. 그러므로, 중간 착물의 고리 열림이 속도 조절 단계가 될 것이다. Base hydrolysis of 7-hydroxy-2H-chromen-2-one (HC) and 7-hydroxy-2H-chromen-2-one-4-acetic acid (HCA) in aqueous-methanol and aqueous-acetone mixtures were studied kinetically at temperature range from 283 to 313 K. The activation parameters of the reactions were evaluated and discussed. Moreover, the change in the activation energy barrier of the investigated compounds from water to water-methanol and water-acetone mixtures was estimated from the kinetic data. It is observed that the change in activation barriers is more or less the same for the hydrolysis of HC and HCA. Base hydrolysis of HC and HCA follows a rate law with $k_{obs}=k_2[OH^-]$. The decrease in the rate constants of HC and HCA as the proportion of methanol or acetone increases is due to the destabilization of $OH^-$ ion. The high negative values of entropy of activation support the proposal mechanism, i.e. the investigated reaction takes place via the formation of an intermediate complex. Moreover, these values refer to the rigidity and stability of the intermediate complex. Thus, the ring opening of the intermediate complex would be the rate controlling step.
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Electric, Thermoelectric and Magnetic Properties of Nickel(II) Imine Nanocomplexes
A. Elshafaie,Laila H. Abdel-Rahman,Ahmed M. Abu-Dief,Samar Kamel Hamdan,A. M. Ahmed,E. M. M. Ibrahim 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2018 NANO Vol.13 No.7
Production of novel organic semiconductor nanomaterials is essential for enabling the development of personal, portable and flexible electronic modules. This work presents Ni(II)-Schiff base complexes with enhanced Seebeck coefficient and weak ferromagnetic ordering for thermoelectric and magnetic devices. Four Ni(II)-Schiff base complexes (namely [Ni(C12H10N3O4Br)] · 2H2O, [Ni(C16H11N3O4] · 2H2O, [Ni(C21H14N5O8Br)] and [Ni(C25H17N5O8)] · 1/2H2O) have been synthesized in nanosized dimensions. The electrical and thermoelectric properties have been studied, and comprehensive discussions have been presented to understand the electrical conduction mechanisms. The electrical conductivity measurements reveal that the conduction is due to the charge carriers hoping between the atomic sites of the same energy levels in the molecule as well as the transfer of the charge carriers between the neighboring complex molecules due to overlapping of their orbitals. The thermoelectric measurement confirms that the nanocomplexes (NCs) are non-degenerate P-type semiconductors with enhanced Seebeck coefficient values compared with those reported for other organic materials. The NCs exhibit antiferromagnetic to paramagnetic transitions with the increase of temperature and weak ferromagnetic ordering at 300 K.
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