scientific reason behind using mango leaves

Mango or Aam tree is one of the sacred tree symbols of Hinduism. Five leaves of this tree in a pot which are besmeared with sindoor or vermilion is a common site in any Hindu religious ceremony. Throughout India this tree is planted and worshipped by devouts. With the passage of time this tree acquired many names. In Sanskrit mango tree is called Amra and in Hindi and Bengali this is called Aam. In Gujarat this tree is called Amlo and Tamilians call it Mamaran. Telugu-speaking people describe it as Arnramu. In Kerala this is called Mram or Mavu.
Since the days of the Puranas the aam tree is personified with various Gods, Goddesses and spirits. According to the research scholars, in Aam Vriksha, Lakshmi, Govardhan, Gandharva and fertility God reside.
1. Tying a mango leave "Thoranam" in the main entrance: Leaves of mango are used for the control of evil spirits. Mango leaves in bunches are said to absorb the negative energy from anyone entering your home. It is just to eliminate the drushti - i.e. the negative effects, at a place where the celebrations are held - be it at home or any public place. So it is placed in the entrance. Mango leaves have antibacterial activity against gram positive bacteria. 

2. Using mango leaves on the Kalasam and putting a cocanut in the middle of them: Purna Kumbha mainly contains ‘water’ – the veritable life principle. Thus it is a direct worship of Varuna – the God of rain. He is the harbinger of rain which ensures fertility on earth and which nourishes animals and human beings. Apart from water, Purna Kumbha is filled with twigs or leaves of five trees – Ashwatha (peepul), Vata (Banyan), Amra (Mango), Panasa (Jackfruit) and Bakula (Elengi). The mouth of the pot is covered with a husked coconut, which is decorated from the sides with mango leaves.  
Except for water, what goes in the pot varies from region to region. Mango leaves and the coconut is a constant factor in most areas. 
Mango leaves are placed to represent Kama or fertility God. All the items used in the Purna Kumbha signify life in its bloom and plenty. It also indicates that human beings are part of nature and when nature thrives human beings too flourish. 

3. Using mango leaves for pouring ghee into the Homa Kundam: For placing ghee, Purasu leaves are required. If it is not available Palasha (Jackfruit) leaves can be used. If that is also not available Mango leaves can be used. 4) Mangifera indica (Mango) A large evergreen tree, with a heavy, dome-shaped crown. The mango is the most popular fruit in India. The unripe, fully developed mangoes of pickling varieties contain citric, malic, oxalic, succinic and two unidentified acids. The ripe fruits constitute a rich source of vitamin A; some varieties contain fairly good amounts of vitamin C also. ß-Carotene and xanthophyll are the principal pigments in ripe mango. The leaves contain the glucoside mangiferine.

  The bark of the mango tree contains tannin (16-20%). Mangiferine has been isolated from the bark. The bark is astringent; it is used in diphtheria and rheumatism; it is believed to possess a tonic action on the mucous membrane. It is astringent, anthelmintic, useful in hemoptysis, hemorrhage, nasal catarrh, diarrhea, ulcers, diphtheria, rheumatism and for lumbrici.