Theoretical Investigation the Compounds of Lanthanum Coordinated with Dihydromyricetin

2019 International Conference on Applied Mathematics, Statistics, Modeling, Simulation (AMSMS 2019) ISBN: 978-1-60595-648-0

Wen-bo LAN1, Chang-ming NIE2, Xiao-feng WANG1, Li-ping HE1, 1 3,* Yu LIU and Yan-bin MENG 1College of Public Health, Xiangnan University, Chenzhou 423043, China 2School of Chemistry and Chemical Engineering, University of South China, Hengyang, 421001 China 3Medical Department, Xiangnan University, Chenzhou 423043, China *Corresponding author

Keywords: Dihydromyricetin, Lanthanum, Density functional theory, Binding energy.

Abstract. In order to study in depth the complexes formed by dihydromyricetin and lanthanum which may have a good medical effect. Theoretical study of the molecular structure of dihydromyricetin (DMY) compound containing lanthanum were carried out by using density functional theory (DFT) under the B3LYP/6-311G (d, p) level. All the results shown that the coordination compounds of lanthanum with dihydromyricetin (DMY) could form some different molecular modeling, for example, in this article it involved two complexes, one with a ratio of 1:3 (1La:3DMY), the other with a ratio of 1:4 (1La:4DMY). The main parameters of infrared frontier, atomic charge distribution, binding energy, and molecular orbital and energy from the theoretical simulation for La-3DMY and La-4DMY compounds were analyzed and compared with each other. What’s more, this work was expected to provide significant information for understanding the characteristics of La-DMY compounds at the molecular level and offer valuable comprehensive guides for future experiments.

Introduction Dihydromyricetin (DHM, Fig. 1), often called ampelopsin, as a major bioactive constituent of rattan tea, belongs to the flavonoid [1-3]. Furthermore, DHM has a significant hypoglycemic, hypolipidemic effect, and element of lanthanum has been shown a wide range of applications in the field of clinical physiotherapy. Lanthanum chloride, a non-radioactive light Rare earth compound, has specific selectivity and high affinity to tumor cells and tumor tissues that can induce apoptosis [4-6]. Therefore, we hypothesized that compound formed by DHM with lanthanum will have a better medical effect. What’s more, before researching, there are medical properties that we can calculate them at the molecular level and make some important predictions. With the rapid development of computational chemistry, the calculation accuracy at the B3LYP level by density functional theory has been demonstrated to reach the level of high-precision [7-11]. Meanwhile, computational chemistry calculations have been introduced into the molecular structure of compound and complication [12-18]. The theoretical study is low cost, green and high-efficiency, which turned out to be very satisfying. It could provide some important theoretical basis and reasonable guidance for the theoretical plan and synthesis experiment on the effective compounds. What’s more, until current study, there is no report on combining the compounds of DHM with lanthanum. In this article, we chose the appropriate oxygen atoms as the coordination atoms and carry out a theoretical study on La-3DMY and La-4DMY by using computational chemical software in DFT (density functional theory) calculations with the B3LYP/6-311G** basis set level. Some meaningful structural information and important properties of La-3DMYand La-4DMY were obtained, for example, the molecular configuration parameters, the IR spectral properties, the mulliken atomic charge, the molecular orbital and the binding energy.

Computational Software and Methods By using the Gaussian 09 software package, all the information for the compounds La-3DMY and La-4DMY have been obtained under the density functional theory (DFT)/B3LYP calculations level [19-22]. And the scalar relativistic effects were taken into account through using the Lanl2DZ basis sets on the lanthanum atom. While the other atoms for C, H, O et al. were adopted the 6-311G (d,p) basis set [23-24]. For the La-3DMY and La-4DMY, the main parameters of infrared and characterization are compared and analyzed with each other. All the information, including the geometric structures, infrared spectroscopy, frontier molecular orbital, and binding energy obtained under the optimized structure were calculated and analyzed.

Figure 1. Molecular structure of dihydromyricetin.

Rescults and Discussion

TheLa-3DMY and the La-4DMY Structures

Figure 2. Optimized structures of La-3DMY and La-4DMY. Firstly, we chose the coordination atoms by calculating the DMY. And by analyzing the atomic coordination bond angle, we found that the lanthanum atoms more likely formed coordination bond with two adjacent atoms of oxygen. And through theoretical calculation, the result was shown (in figure 1) that the oxygen (Oa) and (Ob) have more natural negative charges than any other two adjacent oxygen atoms, which means the oxygen might have better coordination ability for lanthanum. In addition, where were Oa and Ob have the smallest space location and we have tried other O atoms to coordinate with lanthanum and found that the compound formed with other O atoms have large higher energy than the corresponding compound which lanthanum coordinated with O a and O b atoms. The theoretical calculation of the molecules was performed by using the DFT calculation in the level of B3LYP/6-311G** for the La-3DMYand La-4DMY. Their optimized configurations were shown in Fig. 2, (a) and (b) represent La-3DMY and La-4DMY, respectively. From the optimized structure, it could be seen that the lanthanum occupies the central position of the compounds molecular structure. The main structural parameters from the molecular simulation were listed in Table 1 and Table 2. As shown in Table 1, the average bond length of La-O in La-3DMY is 2.550Å, and the average bond length of La-O in La-4DMY is 2.561Å. The bond lengths of La-O in La-3DMY are slightly shorter than those of the La-4DMY. It means that the bond energy of La-O in La-3DMY is

24 stronger than that of La-4DMY. The O-La-O bond angles of the La-3DMY and the La-4DMY were listed in Table 2. These results could offer valuable structural parameter guides for future experiments. Table 1. The comparison of bond length (Å) of the La-3DMY and the La-4DMY value of quantum chemistry. Bonds La-3DMY La-4DMY La-O1 2.539 2.582 La-O2 2.552 2.536 La-O3 2.548 2.571 La-O4 2.514 2.554 La-O5 2.513 2.577 La-O6 2.632 2.555 La-O7 \ 2.582 La-O8 \ 2.528

Table 2. The comparison of bond angles (°) of the La-3DMY and La-4DMY value of quantum chemistry. Bonds La-3DM La-4DM Bonds La-3DMY La-4DMY O1-La-O2 65.19 62.67 O3-La-O5 146.98 90.29 O1-La-O3 111.84Y 70.31Y O3-La-O6 97.84 144.68 O1-La-O4 91.88 106.68 O3-La-O7 \ 86.68 O1-La-O5 93.26 82.05 O3-La-O8 \ 137.65 O1-La-O6 148.31 82.40 O4-La-O5 94.59 144.84 O1-La-O7 \ 162.64 O4-La-O6 111.36 150.17 O1-La-O8 \ 150.36 O4-La-O7 \ 86.75 O2-La-O3 99.77 96.45 O4-La-O8 \ 85.65 O2-La-O4 146.22 90.41 O5-La-O6 64.66 63.38 O2-La-O5 110.41 138.89 O5-La-O7 \ 68.65 O2-La-O6 99.99 90.20 O5-La-O8 \ 103.53 O2-La-O7 \ 151.98 O6-La-O7 \ 103.28 O2-La-O8 \ 98.38 O6-La-O8 \ 74.70 O3-La-O4 64.65 62.62 O7-La-O8 \ 62.84 Infrared Spectroscopy The La-3DMY and the La-4DMY’s infrared spectra obtained by molecular simulations under the same B3LYP level were shown in Fig. 3. There was no imaginary frequency in the calculated infrared vibrations for the two complexes structures. It means that these two structures are at a stable level. The result showed that the C=O stretching vibration absorption peak of the La-3DMY appeared at 1646 cm-1, the C-O stretching vibration absorption peak from the coordination atoms appeared at 1514cm-1, and the stretching vibration absorption peak from the O-H almost appeared at 3661cm-1 and 3691cm-1. While, in the La-4DMY, the C=O stretching vibration absorption peak of the La-4DMY appeared at 1644 cm-1 and 1604cm-1, where were in 1604cm-1 may be caused by the O of the C=O (O-10) formed a hydrogen bond [25-26]. The numbers of O atoms were shown in Fig. 2 b. The coordination atoms of C-O stretching vibration absorption peak appeared at 1514cm-1, the O-H stretching vibration absorption peak almost appeared at 3661cm-1 and 3691cm-1, only the O-H (O-9) stretching vibration absorption peak appeared at 3290cm-1, which may be caused by the hydrogen bond from the O (O9). Atomic Charge Distribution Under the computational simulation, we obtained the La-3DMY and the La-4DMY’s atomic charges, and the atomic charges for the La-3DMYand the La-4DMY were listed in Table 3. The numbers for the part atoms were shown in Fig. 2. The net charges of the coordination atoms of O1, O2, O3, O4, O5 and O6 in La-3DMY were −0.470, −0.504, −0.419, −0.511, −0.418 and −0.511, respectively. While

the charges of the coordination atoms of O1, O2, O3, O4, O5 O6, O7 and O8 were -0.602, -0.603, -0.603, -0.602, -0.538, -0.532, -0.537 and -0.532, respectively. The positive electric charge values of La in the La-3DMY and the La-4DMY were +1.562 and +2.426, respectively. It’s cleared that the coordination atoms of the La-4DMY possess more negative charges than the corresponding coordination atoms of the La-3DMY. This indicated that the donor atoms in the La-3DMY and the La-4DMY could coordinate with the lanthanum ion with different binding modes. In addition, it provided an important theoretical foundation in nucleophilic replacement reaction.

Figure 3. Infrared spectra simulation of the La-3DMY and the La-4DMY (the back line and the red line represent the La-3DMY and the La-4DMY).

Table 3. The atomic charge comparison of the 3DMY-La with the 4DMY-La. Atom 3DMY-La 4DMY-La La 1.562 2.426 O(1) -0.470 -0.602 O(2) -0.504 -0.603 O(3) -0.419 -0.603 O(4) -0.511 -0.602 O(5) -0.418 -0.538 O(6) -0.511 -0.532 O(7) \ -0.537 O(8) \ -0.532 Binding Energy The binding energy is usually used to measure the strength of combination for the compound. The binding energy for the La-3DMY and La-4DMY compounds are calculated under the same level. In this paper, the binding energies for the La-3DMY and La-4DMYwere calculated by the equation (1). In the equation, the part ΔWAB(R) represents the binding energy, and the AB(R) stands for the total energy of the complex system. And the terms A(R) and B(R) stand for the energy of the two separate portions A and B, respectively.

ΔWAB(R) =AB(R)-A(R)-B(R) (1) The binding energy of the La-3DMY was -141.163KJ/mol, while the La-4DMY was -194.060KJ/mol. This means the binding energy that each dihydromyricetin coordinated with lanthanum in La-4DMY complex slightly stronger than that of the La-3DMY compound by 1.607KJ/mol. Molecular Orbital and Energy Under the same level, the molecular bonding orbitals of the La-3DMY and the La-4DMY were given by theoretical calculation. And the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) plots for the La-3DMY and the La-4DMY were presented in Fig. 4. As shown in Fig. 4, for the La-3DMY, the EHOMO was −6.1947 eV and the ELUMO was

26 −4.2910 eV. The energy gap between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) equals 1.9037 eV, that’s to say, ΔELa-3DMY=1.9037 eV, which indicated that the La-3DMY could get the excited state, and the 1.9037 eV would be absorbed by the ground state molecule. However, for the La-4DMY, EHOMO and ELUMOwere calculated to be −5.5591 eV and −4.7495 eV, respectively, and the energy gap (ΔE) is 0.8096 eV, it means the ΔELa-4DMY=0.8096 eV. Generally, HOMO and LUMO orbitals determine the way in which molecules interact with other species, and the ΔE helps in characterizing the chemical reactivity and kinetic stability of the molecule [27-30]. It's obvious to see that the La-3DMY’ stability is over the La-4DMY. For the two structures, both of the electron delocalization was increased, and the energies of the occupied orbitals were decreased. Thus, the stability was certainly enhanced in the system. These results thus showed that the two conformations may stably exist. It will provide important basis for the further study of the experiments.

Figure 4. The frontier molecular orbits and energies of the La-3DMY and the La-4DMY. The red part represents the positive phase energy in the molecular orbital and the green portions represent those of the negative phase. (a) La-3DMY (HOMO, -6.1947eV), (b) La-3DMY (LUMO, -4.2910eV), (c) La-4DMY (HOMO,-5.5591 eV), (d) La-4DMY (LUMO, -4.7495eV).

Summary The compound, La-3DMY and La-4DMY, were theoretically simulated by using DTF calculations at the B3LYP/6-311G** level, and the main geometrical structural parameters and infrared characterization data of the La-3DMY and La-4DMY were compared to each other. DMY monomers are coordinated with La with minimal space resistance, one is the La-3DMY, and the other is the La-4DMY. And the donor atoms in the La-3DMY or the La-4DMY could coordinate with the lanthanum ion with different binding modes. Even each dihydromyricetin coordinated slightly stronger with lanthanum in La-4DMY complex than in the La-3DMY compound. The molecular energy showed that the La-3DMY has higher stability than the La-4DMY. The forecast of the La-3DMY and La-4DMY would provide a theoretical basis and guidance for the experiment on the molecular level. Furthermore, the studying for compounds that the other numbers’ coordination of DMY and different coordination atoms coordinated with lanthanum is on the way. What’s more, we could further develop the study of the compounds formed by lanthanum and DMY in medical properties in the near future.

Acknowledgement This work was supported by the Opening Topic Fund Project of Hunan Province University Innovation Platform (grant number 14K089) and the Scientific Research Fund of Hunan Provincial Education Department, China [grant number 17C1473, 18B495, 18C1034].

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