Accurate computational prediction of the structural and vibrational properties of s-triazine derivatives in vacuo . A DFT approach Enrico Benassi a,⇑ , Michele Di Foggia b , Sergio Bonora b a S3 Center, CNR Institute of Nanoscience, Via Campi 213/a, 41125 Modena, Italy b Department Biochemistry, University of Bologna, Via Belmeloro 8/2, 40126 Bologna, Italy article info Article history: Received 10 January 2013 Received in revised form 15 February 2013 Accepted 7 March 2013 Available online 22 March 2013 Keywords: Triazines Atrazine Prometryn Simetryn DFT IR and Raman spectra abstract The well-known class of herbicides, s-triazine derivatives, are commonly used as reagents in the manu- facture of resins and pharmaceuticals, and also of solvent-refined coals. Recently, triazine derivatives have been observed to form self-assembling nanostructures on metallic surfaces. In this paper, we present a study using a DFT approach for the computational prediction of the structural and vibrational properties in vacuo of three s-triazine derivatives, viz., atrazine (N,N 0 -ethyl-isopropyl-6-chloro-1,3,5-tri- azine,2,4-diamine), prometryn (N,N 0 -diisopropyl-6-methyl-thio-1,3,5-triazine,2,4-diamine) and simetryn (N,N 0 -diethyl-6-methyl-thio-1,3,5-triazine,2,4-diamine). In particular we show that the employment of the Becke three-parameter Lee–Yang–Parr (B3-LYP) exchange-correlation functional using the aug-cc- pVQZ basis set provides an accurate prediction of the structural and vibrational properties of atrazine, prometryn, and simetryn. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Triazine is a heterocyclic six-membered ring. It is formally anal- ogous to the benzene ring but with three carbon atoms replaced by nitrogen atoms. By changing the relative position of the nitrogen atoms, three isomers of triazine can be distinguished, viz., 1,2,3-tri- azine, 1,2,4-triazine, and 1,3,5-triazine. The 1,3,5 isomer, also called s-triazine, is the best known and most used. It is a common reagent, and readily forms derivatives, which are used in the man- ufacture of resins [1,2], pharmaceuticals and herbicides [3]. More- over, recent investigations have underlined the use of triazine derivatives as self-assembling nanostructures [4,5]. Triazines were originally developed by J. R. Geigy to be used as selective herbi- cides for cereals [6]. These compounds inhibit photosynthesis in plants by blocking the electron transfer from the quinone and cyto- chrome b-559 at the reducing site of chloroplast photosystem II [7,8]. They were first introduced into the environment about 50 years ago, and more than 2 billion pounds have been applied globally. Among s-triazines, particularly atrazine (N,N 0 -ethyl-iso- propyl-6-chloro-1,3,5-triazine,2,4-diamine) and prometryn (N,N 0 - diisopropyl-6-methyl-thio-1,3,5-triazine,2,4-diamine) [9,10] and simetryn (N,N 0 -diethyl-6-methyl-thio-1,3,5-triazine,2,4-diamine) which were both synthesised later [11] are the most used triazine herbicides. These three were initially found to biodegrade poorly and to be surprisingly soluble in water (70 mg/L for atrazine and 450 mg/L for simetryn [12]) and with high mobility in soil; but to- day a more rapid biodegradation [13] and a lower water solubility [14] can be observed. In fact, it was recently shown [15–19] that s- triazine herbicides are readily metabolised by dedicated enzymes [20,21], encoded by bacteria genes. From a chemical point of view (Scheme 1), all of them have two secondary amino-groups bonded to the central ring. The two alkyl chains are identical in the cases of prometryn and simetryn, whereas atrazine presents different groups. Atrazine differs with respect to the other two species also for one chlorine atom instead of the thio-methyl group. In spite of the applicative interest of these chemicals, there is no theoretical or computational prediction of the vibrational proper- ties of s-triazines at Density Functional Theory (DFT) level in Liter- ature. The formation of complexes by triazines and their derivatives with metal ions [22,23] or water [24] has been compu- tationally investigated. Oliva et al. [25] have recently carried out a thorough study of the low-lying excited states of atrazine (1,3,5- triazine, and ametryn) from both a computational and an experi- mental point of view. In that work, the Authors determine the ground state geometry of atrazine at DFT level, by employing the B3-LYP functional and the 6-31G(d) basis set, and then other basis sets (cc-pVDZ, cc-pVTZ, and aug-cc-pVDZ) are also used for the cal- ibration of results. Nevertheless, the structural and vibrational properties are not treated in detail. The main goal of this paper is to provide a valid description of the three triazines under study at DFT level with reasonable com- putational cost, with particular emphasis on the structural and vibrational properties. This description is of interest, especially if 2210-271X/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.comptc.2013.03.010 ⇑ Corresponding author. Tel.: +39 059 2055315; fax: +39 059 2055651. E-mail address: enrico.benassi@unimore.it (E. Benassi). Computational and Theoretical Chemistry 1013 (2013) 85–91 Contents lists available at SciVerse ScienceDirect Computational and Theoretical Chemistry journal homepage: www.elsevier.com/locate/comptc