Fluid Phase Equilibria 312 (2011) 37–59 Contents lists available at SciVerse ScienceDirect Fluid Phase Equilibria j our na l ho me page: www.elsevier.com/locate/fluid Changes induced by solvent polarity in electronic absorption spectra of some nucleic acid constituents Mamdouh S. Masoud ∗ , Ahmed M. Hindawy, Amina A. Soayed, Marwa Y. Abd El-Kaway 1 Chemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt a r t i c l e i n f o Article history: Received 28 October 2010 Received in revised form 28 August 2011 Accepted 30 August 2011 Available online 17 September 2011 Keywords: Nucleic acid constituents Electronic absorption spectra Solvent effects Solvent parameters a b s t r a c t The electronic absorption spectra of some biologically active nucleic acid constituents in various solvents of different polarities and with variable physical properties have been studied at room tem- perature. These compounds are of two categories (pyrimidines: [barbital; 5,5 ′ -diethyl-barbituric acid], [SBA; 4,6-dihydroxy-2-mercapto-pyrimidin], [NBA; 5-nitro-2,4,6(1H,3H,5H)-pyrimidine trione] and [TU; 2,3-dihydro-2-thioxo-pyrimidin-4(1H)-one]) and (purines: [adenine; 6-amino purine] and [guanine; 2- amino-6-hydroxy purine]). The solvent effects on the wavenumbers of the absorption band maxima ( ’  max ) were discussed using the following solvent parameters: refractive index (n), dielectric constant (D) and empirical Kamlet–Taft solvent parameters, * (dipolarity/polarizability), ˛ (hydrogen bond donating capacity) and ˇ (hydrogen bond accepting ability) using multiple linear regression method (MLR). The solute–solvent interactions were determined on the basis of multilinear solvation energy relationships concept. The data of the studied molecules are affected by both non-specific and specific solute–solvent interactions. The solvatochromic behavior was explained. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Nucleic acid compounds either pyrimidines or purines have much attention due to the widespread range of biological appli- cations in pharmaceutical field. Thiopyrimidine derivatives exhibit antiviral and chemotherapeutic activity [1]. These are physiolog- ically important essential for the biosynthesis of proteins [2,3]. They possess a very important chemical role in industrial appli- cations where these classes of organic compounds are widely used in recent years as corrosion inhibitors for metals in acid environments [4]. In our laboratory, Masoud et al. [5–14] pub- lished a series of papers to throw light on the chemistry of the biologically active purine and pyrimidines, beside the effect of solvents on their electronic absorption spectra [15–18]. This can be influenced by non-specific interactions such as ion-dipole, dipole–dipole (Keesom interaction), induced dipole–permanent ∗ Corresponding author. E-mail addresses: drmsmasoud@yahoo.com (M.S. Masoud), chemarwa@yahoo.com (M.Y.A. El-Kaway). URL: http://www.geocities.ws/drmsmasoud (M.S. Masoud). 1 Abstracted from her Ph.D.thesis. dipole interactions (Debye interaction) or by specific interaction such as hydrogen bonding with solvents. Thus, solvents play an important role in physical and chemical processes and can deter- mine change in the position, intensity and shape of absorption bands [19,20]. Solvatochromism is a powerful tool to investi- gate the physical–chemical properties of molecules [21]. It is well known that the effects of solvents on physical–chemical phe- nomena and spectroscopic data are better analyzed in terms of a linear combination of solvent properties, including solvent dipo- larity/polarizability (*), hydrogen-bond donation ability [solvent acidity] (˛) and hydrogen-bond acceptance ability [solvent basic- ity] (ˇ). The aim of the present work is to investigate the solvent influ- ence on the UV–Vis absorption spectra of some pyrimidines and purines and to evaluate the information about intermolecular inter- actions occurring in solutions. The spectral characteristics of the studied ligands in different solvents at room temperature were analyzed by SPSS programmed. A linear correlation between exper- imental spectral values ( ’  max ) and the solvent parameters: f (n 2 ) and f (D), or the solvatochromic empirical variables (*, ˛ and ˇ) have been used to discuss the solvatochromic behavior of the ana- lyzed ligands to evaluate their contributions to the solute–solvent interactions. 0378-3812/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2011.08.028