Topological Analysis and Frequency Dependent Hyperpolarizability Calculations of FDDNP: a DFT Study

Abstract

Abstract. The topological and fi rst-hyperpolarizability properties of 2-(1-{6-[(2-fl uoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile (FDDNP) were studied using DFTB3LYP method. The static and dynamic electronic (hyper)polarizabilities of conformers were calculated and a simple two-state model was employed to explain the fi rst hyperpolarizability differences in two conformers. The second harmonic generation property was evaluated at the typical wavelengths of Cr:forsterite, Nd:YAG(neodymium-doped yttrium aluminium garnet) and Ti:sapphire lasers to predict the compound conformers potency for second harmonic generation imaging in biological studies.Keywords: second-harmonic generation, FDDNP, near-infrared, QTAIM. IntroductionOptical imaging techniques based on nonlinear optical phenomena have been widely incorporated in microscopy using ultra-fast pulsed lasers. There have been described many applications in cellular and tissue imaging due to the ability to spatially resolve subcellular details with high molecular contrast [1].The employed near-infrared (NIR) wavelengths reduce scattering and maximize tissue penetration. These characteristics boost nonlinear microscopy as an elective method for imaging cells with micrometer-resolution deep into the living tissues. Both labeled and label-free second harmonic generation (SHG) imaging techniques have been employed in biological studies. For example, the non-centrosymmetric structure of fi brillar collagen is the major source of the SHG signals in different tissues [2,3], and for cellular and subcellular samples. For this purpose, several SHG labels have been used [4,5].The 2-(1-{6-[(2-fl uoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile (FDDNP) is a functional fl uorescent biomarker belonging to the family of dicyanovinyl naphthalene labels, which binds to its ligand through hydrophobic interactions [6]. FDDNP also binds to amyloid plaques with high affi nity [7]. Fluorescence imaging microscopy of amyloid aggregates has a key role in diagnosing Alzheimer's disease and other neurodegenerative diseases [8,9].According to the importance of second-harmonic generation, as one of the nonlinear excitation families with deep imaging, 3D capabilities and intrinsic contrast in certain tissues, the study of nonlinear optical properties of biomaterials and their labels plays an essential role in development of medicinal optic devices. So far, only a few electronic structure studies on FDDNP and other dicyanovinyl naphthalene biomarkers, based on ab initio calculations have been performed. Petrič et al.[6] performed a combined experimental and theoretical study on FDDNP and its analogs to explain the chemical modifi cation effects on binding affi nity of biomarkers to amyloid plaques and their fl uorescence Quantum yields. Given the close relationship between the structure and nonlinear activities, and the functional importance of default molecule, it is necessary to develop a deeper vision on electron-topological properties, in order to predict its di...

2,2′-[(Disulfanediyl)bis{5-[(1E)-(2-hydroxybenzylidene)amino]-1,3-thiazole-4,2-diyl}]diphenol: synthesis, crystal structure and calculation of molecular hyperpolarizability

“…The crystal structure of the title Schiff base compound without any optimization was used in the calculations. The polarizability and the first hyperpolarizability tensor components were appraised by the density functional theory (DFT) method in the GAUSSIAN98W program (Frisch et al, 1998) by means of the finite-field (FF) method with a field step of 0.001 au (Akhtari et al, 2016) at the B3LYP/6-311G(d,p) level of theory. Furthermore, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) ( Fig.…”