Vibrational spectroscopic studies and ab initio calculations of sulfanilamide

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Abstract

FT-Raman and FT-IR spectra of sulfanilamide were recorded and analyzed. The vibrational frequencies of the compound have been computed using the Hartree–Fock/6-21G* basis and compared with the experimental values. The assignments of the observed bands were made on the basis of available literature.

Introduction

Sulfanilamides were successfully employed as effective chemotherapeutic agents for the prevention and cure of bacterial infections in human biological systems [1]. Moreover, sulfadrugs and their complexes, have applications as diuretic, antiglaucoma or antiepileptic drugs among others [2], [3], [4]. The sulfanilamides exert their antibacterial action by the competitive inhibition of the enzyme dihydropterase synthetase towards the substrate p-aminobenzoate [5]. Furthermore, metal sulfanilamides get much attention owing to their antimicrobial activity. Extensive study of the crystal structure of three forms of sulfanilamide [6], [7], [8], [9] and the characterization of sulfanilamide and its derivative complexes has been reported [10], [11], [12], [13]. However, reports of IR and Raman studies on the structures of free sulfanilamide and its derivative complexes are too few. IR spectra of SO2 group in sulfonamide derivatives and related compounds had been reported by Rastelli et al. [14], Narang and Gupta [15] and Blasco et al. [2] had described IR characterization of Cu(II) complexes of sulfanilamide. SO2 vibrations and NH2 modes of amino and sulfonamide group of sulfanilamide had been investigated by Narang and Gupta [15]. In addition to these vibrations, in order to deduce structural differences upon coordination, υSN vibrations of sulfanilamide had been reported by Blasco et al. [2]. Ab initio quantum mechanical calculations for the assignment of IR spectrum of sulfanilamide had been reported by Topacli and Topacli [16]. In the present study the FT-IR, FT-Raman and theoretical calculations of the frequencies of the title compound are reported.

Section snippets

Experimental

Sulfanilamide was procured from Sigma–Aldrich, USA. The FT-IR and FT-Raman spectra (Fig. 1, Fig. 2) were recorded using a Bruker IFS 66V FT-IR/FT-Raman spectrometer.

Computational details

The vibrational frequencies were calculated using Gaussian03 program package [17]. The frequency values computed at the Hartree–Fock level contain known systematic errors due to the negligence of electron correlation [18]. We, therefore, have used the scaling factor value of 0.8929 for HF/6-21G*. Parameters corresponding to optimized geometry of sulfanilamide (Fig. 3) is given in Table 1.

Results and discussion

In making assignments we have been helped by the published studies on selected organic structures [19], selected benzene derivatives [20] and Silverstein and Webster [21]. The observed Raman and IR bands with their relative intensities and calculated frequencies and assignments are given in Table 2. The modes are numbered as suggested by Miller [22]. The calculated vibrational spectrum has no imaginary frequencies which helped to confirm that the structure of the title compound deduced

Acknowledgements

C. Yohannan Panicker would like to thank the University Grants Commission, India for awarding a Teacher Fellowship and Hema Tresa Varghese thanks University Grants Commission, India for a minor research grant.

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