Comparative Study of the Photostability of Two Glycine Molecules in Different Medium
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.220
Comparative Study of the Photostability of Two Glycine Molecules in Different Medium Satish Kumar and Ashok Jangid Department of Physics and Computer Science, Dayalbagh Educational Institute, Dayalbagh, Agra282005, India
ABSTRACT
The photostability of two glycine molecules has been investigated using quantum mechanical methods i.e. at CASSCF/NEVPT2 level theory. It is found that the molecule in water shows vast photostability as a comparison to vacuum. The energies are calculated around HOMO and LUMO orbital. The NEVPT2 computed energies are reasonably matched with experimental results. The study shows that the molecule returns from higher electronically excited states to ground state through CI and AC crossings and these crossings provide a minimum energy path along derivative coupling and gradient differences vector.
INTRODUCTION The photo triggered phenomenon in biological molecules play a crucial role in many scientific and technological fields. It is of fundamental importance to understand photo physical properties of biological system. The study of photostability of the biological system will help to understand the molecular architecture of life in the beginning of biological evolution. The incident ultra violet (UV) light is absorbed by molecule and as a result molecule reaches to electronically higher excited states. From higher excited states, the molecule returns to ground state by the photo deactivation process without losing its functionality. The phenomenon is known as photostability of biomolecules under exposure to UV irradiation [1]. The photostability and its physical mechanism can be explained by photostablizers [2]. The mechanism of photostability in biological systems can be understood by Born-Oppenheimer ab initio theory. Therefore, the understanding of preserved fossils and existing terrestrial life serves as guide in the search for bio-signature in the universe [3]. The potential energy surfaces are the plot of the energies of the electronically excited states with reactions coordinates such as bond length, dihedral angle etc. Whenever, two electronic states are crossed each other, at
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point where energy of two states is same known as conical intersection CI [4].The fundamental concept of the conical intersection (CI) of potential energy surfaces has been explained by Neumann and Wigner [5]. The path, it follows through potential energy surfaces is known as the minimum energy path MEP [6]. The potential energy surfaces PESs of molecule are crossed at CI point and can switch efficiently from higher PES to ground state by CI and avoided crossing AC [5, 7]. In past, the photostability of the planar pyrrole-pyridine hydrogen-bonded system has been studied along hydrogen bonds in DN
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