707 resultados para Conceitos de química
Resumo:
We address the concept of steric effect in the pursuit of establishing quantitative correlations between reactivity of molecules and their molecular shape. To this end, a set of series of SN2 reactions were modeled to compute the energy barrier height and the molecular volume, atomic charges and dipole moment of molecules. We introduced the Kappa index to characterize the shape of molecules. Quantitative correlations between the change in the energy barrier with properties of molecules and Kappa index were presented and discussed.
Resumo:
Turmeric, obtained from the dried rhizomes of Curcuma longa (Zingiberaceae), is a golden colored material, commonly used around the world for seasoning and coloring food dishes. Since antiquity, turmeric has been widely used in the treatment of several diseases in traditional Chinese and Indian medicine (Ayurveda), where it is also known by other names such as Kanchani (goddess gold) or also Gauri (having a bright and luminous face), a designation stemming from the gilded appearance of the plant material. Curcumin, the main chemical component of turmeric, is responsible both for its properties as dyes as well as its biological activities. This diarylheptanoid was first isolated almost two centuries ago and had its chemical structure determined in 1910 as being diferuloylmethane. Subsequently, more detailed and relevant data were obtained furthering the understanding of structural features of curcumin. The classical methodology for the synthesis of curcumin and other curcuminoids was described in 1960 by Pabon. Subsequently, different variations on this methodology have been developed, culminating with the synthesis of different curcuminoids. Several studies have been published in recent years on the biological activities exhibited by curcumin including its antioxidant, antitumor, anti-inflammatory, antiviral, antibacterial, antifungal, antimalarial and leishmanicidal activities.
