Abstract— This investigation explores the interaction between single walled carbon nanotubes and the linoleic acid, a polyun- saturated fatty acid, present in low density lipoprotein, which is highly susceptible to oxidation. Molecular models were built and theoretical studies were performed using the PM6 semiem- pirical method and the density functional theory. The strength of the interaction was estimated from the interaction energy cal- culation. Negative values of E int indicated that all evaluated sys- tems are stable. Although, the interaction occurs through weak forces, CH··· π , OH··· π and CH···N, collectively such interac- tions are strong enough and may be considered as chemisorp- tion. Keywords— Carbon nanotubes, linoleic acid, lipid peroxida- tion, density functional theory. I I NTRODUCTION Experimental evidence has attributed to lipid peroxida- tion an important role in the pathogenesis of atherosclerosis. The structural changes experienced by low-density lipopro- tein (LDL) after oxidation can significantly increase their atherogenic characteristics [1, 2]. About half of the content of fatty acids in LDL consists of polyunsaturated fatty acids (PUFAs), mainly linoleic acid (LA) [3, 4]. As consequence, oxygenated derivatives of LA have been found in human atherosclerotic lesions, as main peroxidation products [5, 6]. The hypothesis that antioxidants may inhibit LDL oxida- tion and reduce the incidence of coronary events has encour- aged the development of various investigations. Some stud- ies have been conducted using antioxidant vitamins (beta- carotene, vitamin C and vitamin E) and a synthetic antiox- idant (Probucol), obtaining results in favor and against of its use [7, 8]. On the other hand, statins are drugs widely used in the treatment of hypercholesterolemia [9]. However, there is some concern because a relationship between statins use and the risk of developing other pathologies has been found [10]. Therefore, it is important the search of alternative treat- ments to prevent or inhibit lipid peroxidation. On this direc- tion, the use of certain nanomaterials such as carbon nan- otubes (CNTs) could be considered. Doping and function- alization enhance biocompatibility and solubility of these nanomaterials, and can alter its cellular interaction pathways, resulting in a reduction in the cytotoxic effects [11], which has opened the possibility of its application in medicine field. In addition, antioxidant activity has also been reported in CNTs [12, 13], which could be useful for the treatment of different diseases, including the atherosclerosis. Modeling and simulation have been well established as in- strumental in the study of CNTs [14, 15, 16]. Theoretical re- search is based on the development of a molecular model that allows the description, research and prediction of properties of interest. Electronic structure methods are the fundamen- tal level of theory used for the description of the systems at nanoscale. These methods use the laws of quantum me- chanics and are characterized by different levels of approach to the solution of the Schr¨ odinger equation. Semiempirical methods, ab initio and the density functional theory (DFT) are classified as electronic structure methods [17]. As a first approach to the study of the inhibition of lipid peroxidation applying CNTs, we evaluated theoretically the interaction of the LA and perfect single walled carbon nan- otubes (SWCNTs) and doped with nitrogen (SWCNT4N), using the PM6 semiempirical method [18] and the DFT [19, 20]. We took advantage of the highly cost effective semiempirical method to perform geometry optimization of SWCNT-LA and SWCNT4N-LA. The optimized coordi- nates were used to perform single point calculations at DFT level. Interaction energies were estimated and considered as a criterion for evaluating the stability of the systems. End- functionalization of LA with SWCNT has been reported us- ing molecular dynamics [21], but electronic calculations are required for an adequate estimation of the interaction. II METHODOLOGY To study the interaction of SWCNTs with LA, we selected a (10,0) SWCNT, which has been commonly studied [22, 23]. Model of perfect SWCNT was built using 280 carbon atoms. Theoretical study of the interaction between carbon nanotubes and the linoleic acid, an atherogenic polyunsaturated fatty acid Ana M. Torres 1 , John Bustamante 1 , Andrés M. Garay-Tapia 2 and Tapas Kar 3 1 Universidad Pontificia Bolivariana/Centro de Bioingeniería, Grupo de Dinámica Cardiovascular, Medellín, Colombia 2 Centro de Investigación en Materiales Avanzados/Grupo de Termodinámica Computacional, Monterrey, México 3 Department of Chemistry and Biochemistry/Utah State University, Logan, UT 84321, USA © Springer Nature Singapore Pte Ltd. 2017 492 I. Torres et al. (eds.), VII Latin American Congress on Biomedical Engineering CLAIB 2016, Bucaramanga, Santander, Colombia, October 26th -28th, 2016, IFMBE Proceedings 60, DOI: 10.1007/978-981-10-4086-3_124