Title: Anti-corrosion studies of a tryptamine Schiff base ligand

INTRODUCTION

Schiff bases are characterized by the -C=N- (imine functional group). They have found various applications in medicines as anti-inflammatory, antimicrobial and anti-tumor agents. Their other uses include catalysis, herbicidal, antiseptic, dyes and polymers [1]. Recent researches have reported their application as corrosion inhibitors because their electron rich imine centers adsorbed and form corrosion inhibiting surface films [2, 3].

Tryptamine is an alkaloid with an indole ring and a primary amine (Figure 1). It is an important precursor to  serotonin (a neurotransmitter). Both indole and tryptamine have been reported to have been isolated from plants and animals [4, 5].

Tryptamine Schiff base Several Schiff bases have been studied for the prevention of corrosion, however the tryptamine Schiff base 2-((2-(1H-indol-3-yl)ethyl) methylene) -λ⁴-azanyl)-λ³-methyl)-6-methoxyphenol (HL²) with chemical formula C₁₈H₁₈N₂O₂ has not been investigated for its anti-corrosion characteristics. Hence this study was done using  Density Functional Theory (DFT) to determine the behavior of a previously synthesized and characterised tryptamine Schiff base HL² [6], as an anti-corrosion compound.

 

METHODOLOGY

To study the mechanism of inhibition of HL², the computational simulation of its molecular properties was carried out using Density Functional Theory (DFT) calculations, using the Becke-3-Lee-Yang-Parr exchange (B3LYP), together with the standard double-zeta plus polarization 6-311G (d, p) basis set [B3LYP/6-31G(d)] implemented in the GAUSSIAN 03 software. Chemical parameters obtained include:

ü  Energy gap (ΔE),

ü  absolute electro negativity (χ),

ü  global hardness (η)

ü  softness (σ )

ü  number of transferred electrons (N)

ü  back donation (ΔEd-b)

ü   

RESULTS AND DISCUSSION

The results obtained from the DFT calculations of the molecules of the HL² are presented in Table1. Frontier molecular orbital maps are also presented in Figures 3 and 4.

 

CONCLUSION

The energy of highest occupied molecular orbital (E_HOMO), energy of lowest unoccupied molecular orbital (E_LUMO), energy gap (ΔE), and electronegativity (χ) values obtained for HL² using the Density Functional Theory at B3LYP/6-311G are all in agreement with values reported for effective transfer of electrons between an inhibiting system and metal surface [7,8]. Hence, HL² has a good potential to act as a corrosion inhibitor.