Monomeric and dimeric structures, electronic properties and vibrational spectra of azelaic acid by HF and B3LYP methods Amarendra Kumar, Vijay Narayan, Onkar Prasad, Leena Sinha ⇑ Physics Department, University of Lucknow, Lucknow 226 007, India highlights " Structural, electronic and vibrational properties of monomer and hydrogen bonded dimer of Azelaic acid (AZA) investigated. " Effect of intermolecular OAHO hydrogen bonding, on the bond distances and calculated frequencies have been discussed. " The dipole moment (6.00 Debye) and hyperpolarizabilty (1.1  10 30 e.s.u.) of AZA are found to be quite high. " The frontier orbitals, MESP and contour maps drawn may lead to better understanding of the properties of the compound. article info Article history: Received 4 January 2012 Received in revised form 12 April 2012 Accepted 30 April 2012 Available online 10 May 2012 Keywords: Frontier orbitals First static hyperpolarizability Normal mode analysis Intermolecular hydrogen bond abstract Quantum chemical calculations of energies, dipole moment, polarizability, hyperpolarizability and vibra- tional wavenumbers of Azelaic acid (AZA) were carried out by using ab initio HF and B3LYP methods with 6-311++G(d,p) basis set. Hydrogen-bonded dimer of AZA, optimized by counterpoise correction, has also been studied by HF and B3LYP at the 6-311++G(d,p) level and the effects of molecular association through OAHO hydrogen bonding have been discussed. A complete vibrational analysis of AZA has been per- formed and assignments are made on the basis of potential energy distribution. The comparisons and assignments of the vibrational frequencies indicate that the experimental spectra also correspond accept- ably with those of theoretically simulated spectra except the hydrogen-bonded coupled infrared vibrations. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Azelaic acid an organic saturated dicarboxylic acid possesses diverse biological activities including the antibacterial, anti- inflammatory, free radical scavenging, anti-proliferative [1,2]. It is commonly used for the treatment of different skin conditions, including acne and rosacea [3,4]. The advent of novel drug delivery strategies, like the use of micro-emulsions, has become a focus of immense academic and pharmaceutical interest and can play a pivotal role in improving the topical delivery of anti-acne agents. Micro-emulsions of Azelaic acid (AZA), a bioactive molecule used in many skin disorders, prepared using the monosodium salt (AZA-Na) have been evaluated as delivery vehicles [5,6]. The results suggested that micro-emulsions containing AZA could be used to optimize drug targeting in acne treatment. Stamatiadis et al. [7] reported that Azelaic acid (AZA) in combination with zinc ion and vitamin B6 acts as a strong type I 5-alpha reductase (5-AR) inhibitor. The enzyme, 5-AR (both Types I and II) convert testosterone to dihydrotestosterone which contributes towards the prostate enlargement and to damage hair follicles. Jung et al. [8] have identified AZA as a molecule that accumulated at elevated levels in some parts of plants help enhance the resistance of plants to infections. Recently Kadhum et al. [9] have reported successful production of Azelaic acid by ozonolysis of oleic acid and the pro- duction of azelaic acid was confirmed by use of FT-IR and 1 H NMR spectroscopic data. A very preliminary quantum chemical study is also performed and HOMO–LUMO energies have been calculated. In this paper, we present the results from HF and B3LYP calcu- lations of the molecular structure, electronic properties and vibra- tional spectra of monomer and hydrogen bonded dimer of AZA. The Fourier-transform infrared (FT-IR) and FT-Raman spectra of the ti- tle compound have been measured. To make an explicit assign- ment of the experimental spectra, precise normal coordinate analysis has been performed. Scrupulous attention has been fo- cused on the effect of intermolecular OAHO hydrogen bonding, modeled with the B3LYP method, on the bond distances, calculated frequencies and the infrared and Raman intensities. The molecular properties of AZA such as equilibrium energy, frontier orbital en- ergy gap, 2D molecular electrostatic potential (MESP) contour 0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2012.04.089 ⇑ Corresponding author. E-mail address: sinhaleena27@gmail.com (L. Sinha). Journal of Molecular Structure 1022 (2012) 81–88 Contents lists available at SciVerse ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc