Using semi-empirical quantum mechanics and monte carlosimulation for construction of potential energy surfaces of conformations of new thiosemicarbazone reagent and complexes with metal ions

Journal of Science and Technology, Vol. 39A, 2019

© 2019 Industrial University of Ho Chi Minh City

USING SEMI-EMPIRICAL QUANTUM MECHANICS AND MONTE CARLO

SIMULATION FOR CONSTRUCTION OF POTENTIAL ENERGY

SURFACES OF CONFORMATIONS OF NEW THIOSEMICARBAZONE

REAGENT AND COMPLEXES WITH METAL IONS

NGUYEN MINH QUANG2,3, TRAN NGUYEN MINH AN3

, PHAM NU NGOC HAN1

,

NGUYEN THI AI NHUNG2

, PHAM VAN TAT1*

1

Faculty of Science and Engineering, Hoa Sen University, Ho Chi Minh City 2

Faculty of Chemistry, Hue University of Sciences, Hue University 3

Faculty of Chemical Engineering, Industrial University of Ho Chi Minh City

[email protected]; [email protected], [email protected],

[email protected]; [email protected]

Abstract: In this study, the conformational analysis of the MeL2 complexes of new thiosemicarbazone

reagents with metal cations Cd2+, Ni2+, Cu2+, Hg2+, Pb2+, Mn2+ and Zn2+ is to find the conformations with

the most suitable energy of the whole molecular system. The search method incorporates MM+ and PM3

calculations with Monte Carlo techniques using the Metropolis algorithm in terms of T = 298K to 473K.

The initial selection conformation was done randomly after 15 repeatable conformations and 30

conformations rejected. The conformations are chosen to change by changing the torsional-dihedral angle

at the position of the metal cation associated with the donor atoms N and S of thiosemicarbazone

reagents. The search method is performed by the random changes of the dihedral angles to create new

structures and then minimizes the energy for each of these angles using MM+ and PM3 calculation

methods. The lowest energy suitability is accumulated while high or duplicate energy structures are

discarded. The bond lengths of metal ion and donor atoms of metal-thiosemicarbazone complex are

evaluated by the interatomic potential energy surfaces.

Keywords: thiosemicarbazone reagents; Monte Carlo simulation; PM3 and MM calculation; potential

energy surface (PES).

1. INTRODUCTION

The generation of new starting conformations for the energy minimization uses random

variation of dihedral angles. Rotation is used for acyclic bond dihedral angles. For dihedral

angles in a ring, dihedral angles are rotated by the "torsional flexing" motion of Kolossváry and

Guida [[1]] which effectively leads to new ring conformations while avoiding large atomic

displacements that can decrease the efficiency of optimization.

Nowadays, thiosemicarbazone reagent is still one of the organic reagents that have many

applications in medicine and in analytical chemistry [[1],[2]]. Some thiosemicarbazone reagents

are known to treat [[3]] anticancer bioactivity, but it can form stability complexes with metal

ions. This property of thiosemicarbazone reagent can be used in analyzing environmental and

food samples. For these reasons, the search for a stability conformation for thiosemicarbazone

complexes has so far not been conducted carefully. The conformational search of cyclic

molecules plays a central role in studying molecular structure and dynamics.

In this work, we report a new method for the conformational search combining the molecular

mechanics methods with Monte Carlo search technique. Then energy minima of the metal￾thiosemicarbazone complexes were performed by the semi-empirical method PM3 SCF and

MM+ molecular mechanics to calculate the energy. The conformations are considered the