Theoretical investigation of sulforaphane molecule S ¸ akir Erkoc ¸ a, * , Figen Erkoc ¸ b a Department of Physics, Middle East Technical University, 06531 Ankara, Turkey b Department of Biology Education, Gazi University, 06500 Ankara, Turkey Received 22 February 2004; accepted 16 August 2004 Available online 19 December 2004 Abstract The structural and electronic properties of the broccoli sulforaphane molecule have been investigated theoretically by performing semi- empirical molecular orbital (PM3) and density functional theory calculations. The geometry of the molecule has been optimized by PM3 method and the electronic properties and the vibrational spectra of the molecule have been calculated by density functional theory in its ground state. q 2005 Elsevier B.V. All rights reserved. Keywords: Sulforaphane; Antioxidant; Semi-empirical PM3 method; Density functional theory 1. Introduction Interest in use of medicinal botanicals for disease prevention and therapy have increased in recent years in many countries around the world. Both nutritive chemicals and non-nutritive constituents of plants such as phytochem- icals, are considered important for their cancer preventive potential [1–7]. Sulforaphane (SFN) is in the isothiocyanate secondary plant metabolite group of chemicals, mainly occurring in the Cruciferae. SFN is the aglycone breakdown product of the secondary metabolite glucosinolate glucoraphanin via action of myrosinase (thioglucoside glucohydrolase) an enzyme present in cruciferous vegetables, where sulfor- aphane is found. Myrosinase action produces sulforaphane nitrile in lesser amounts than SFN, however, it has been shown to be less potent than SFN as an inducer of phase II detoxification enzymes. Isothiocyanates are extracted by maceration of the cruciferous vegetables such as broccoli, cauliflower, cabbage, brussels sprouts and kohlrabi. Young broccoli sprouts and cauliflower sprouts are especially rich in glucoraphanin. Sprouts contain 10–100 times the phase II inducer activity of mature broccoli plants [8]. Glucosinolates are also present in stalks, florets and leaves of broccoli [9–11]. Jeffrey et al. [12] pointed out that an understanding of glucosinolate hydrolysis appears key to determining post- harvest, processing and food preparation methods for optimizing dietary SFN. Along this line, Nestle [8], in a review on broccoli sprouts in cancer prevention, provided the ‘American Cancer Society Guidelines for Diet and Cancer Prevention’ as a table and cited ‘Choose most of the foods you eat from plant sources’. On the basis of nutritional, epidemiological research and experimental results, the review concludes that researchers recently have estimated that plant-based diets prevent 20–50% of all cases of cancer [1,8]. In a recent review, Owuor et al. [13] have characterized signal transduction events that are turned-on by two classes of potential cancer chemopreventive compounds: phenolic compounds/antioxidants and isothiocyanates. Low concen- trations of these compounds activated the mitogen-activated protein kinase (MAPK) pathways, leading to the induction of phase II detoxifying enzymes for cellular protection signalling. Isothiocyanates were found to be early apoptosis (orderly or programmed cell death) activators via activation of cell death proteins such as caspases, indicating their potential beneficial effects if this occurs in preneoplastic or tumor cells. If apoptosis activation by isothiocyanates occurs in normal cells, the result is cytotoxicity. 0166-1280/$ - see front matter q 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.theochem.2004.08.057 Journal of Molecular Structure: THEOCHEM 714 (2005) 81–85 www.elsevier.com/locate/theochem * Corresponding author. Tel.: C90 312 210 32 85; fax: C90 312 210 12 81. E-mail address: erkoc@erkoc.physics.metu.edu.tr (S ¸. Erkoc ¸).