F. Zhang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 162–171
169
in Fig. 5. According to the B3LYP/6-311++G (d, p) method, the en-
ergy level of the highest occupied molecular orbital (EHOMO) is about
ꢁ7.1 eV and the lowest unoccupied molecular orbital (ELUMO) is
about ꢁ1.9 eV. As a result, the EHOMO ꢁ ELUMO gap in the compound
is about 5.2 eV. For the compound, the LUMO and LUMO + x (x: 0–6)
energies predicted by the DFT method were quite low (ꢁ1.9398 to
ꢁ0.0237 eV with B3LYP/6-311++G (d,p)), and are therefore excel-
lent electron acceptors, indicating that their interaction with the
base-pairs of some insects should be quite strong. Transition state
the fact that the molecular vibrational intensities increase with
temperature [44]. The correlation equations between heat capac-
ity, entropy, enthalpy and Gibbs free energy with temperatures
were filled by quadratic formulas, and the corresponding fitting
factors (R2) for these thermodynamic properties are 0.99931,
0.99987, 0.99928 and 0.9995, respectively. The corresponding
fitting equations are as follows and the correlation graphs were
shown in Figs. 7.
transition of
p–
pꢂ type is observed with regard to the molecular
orbital theory. The calculated absorption spectrum with B3LYP/6-
311++G (d, p) method in gas phase showed band with peaks at
211.8, 238.8 and 323.7 nm matching well with the corresponding
experimental absorptions at 208.9, 250.5 nm, respectively. The ex-
cited state lies at 211.8 nm are mainly formed by the Hꢁ4 ? L+1
transition. The excited state located at 238.8 nm is given by the
Hꢁ4 ? L and Hꢁ1 ? L+1 transition. The excited state located at
323.7 nm is given by the H ? L and Hꢁ1 ? L transitions.
Table 5
The calculated atomic orbital occupancies and energy with B3LYP /6-311++G (d, p)
theoretical level.
Atom Type(AO) Occ.
Energy
1.99922 ꢁ10.18003 C17 Cor(1S)
Val(2S)
Atom Type(AO) Occ.
Energy
C1
N2
O3
Cor(1S)
Val(2S)
1.99891 ꢁ10.08785
0.98113 ꢁ0.27791
0.91818
ꢁ0.18488
ꢁ0.07564
ꢁ0.11006
ꢁ0.12430
Val(2px) 0.97463 ꢁ0.14172
Val(2py) 0.89347 ꢁ0.12371
Val(2pz) 0.94183 ꢁ0.12617
Val(2px) 0.93345
Val(2py) 1.12800
Val(2pz) 1.01964
Though the simulated spectrum of the title compound in the
gas phase has given a reasonable agreement on the band maximum
positions with the experiment results, the calculation including
solvent effect was also carried out with the expectation of a better
match-up between the simulated and the experimental results. On
the basis of the optimized geometry in H2O solution, the excited
states were obtained by the application of TDDFT-B3LYP/6-
311++G (d, p) theoretical level in combination with PCM to repro-
duce a solvent effect. The simulated spectrum in solution also
shows three maximum bands centered at 235.6 nm and
298.5 nm. Contrary to the expectation, the simulated spectrum
with inclusion of the solvent effect did not give a better match-
up result to the experimental. This may be due to the interactions
between the thiamethoxam molecules and solvent molecules.
Cor(1S)
Val(2S)
1.99926 ꢁ14.22422 S18
1.21701 ꢁ0.56844
Cor(1S)
Cor(2S)
Val(3S)
Cor(2px) 1.99984
Val(3px) 1.04533
2.00000 ꢁ87.71191
1.99907
1.65226
ꢁ8.88060
ꢁ0.77770
ꢁ5.94687
ꢁ0.20912
ꢁ5.94433
ꢁ0.23095
ꢁ5.94415
ꢁ0.24929
Val(2px) 1.46993 ꢁ0.29358
Val(2py) 1.31692 ꢁ0.29384
Val(2pz) 1.48045 ꢁ0.29003
Cor(1S)
Val(2S)
1.99977 ꢁ18.98248
1.62477 ꢁ0.91584
Cor(2py) 1.99985
Val(3py) 1.34723
Cor(2pz) 1.99992
Val(3pz) 1.43564
Val(2px) 1.41113 ꢁ0.33309
Val(2py) 1.81164 ꢁ0.35143
Val(2pz) 1.70576 ꢁ0.35864 N19 Cor(1S)
1.99959 ꢁ14.42332
1.05792
H4
H5
C6
Val(1S)
Val(1S)
Cor(1S)
Val(2S)
0.80264 ꢁ0.01306
0.83748 ꢁ0.03334
1.99923 ꢁ10.17635
0.97974 ꢁ0.27398
Val(2S)
ꢁ0.51484
ꢁ0.28137
ꢁ0.27784
ꢁ0.31451
ꢁ0.00511
0.02303
Val(2px) 1.06087
Val(2py) 1.07062
Val(2pz) 1.16455
Val(2px) 0.89238 ꢁ0.13809 H20 Val(1S)
Val(2py) 0.77020 ꢁ0.10747 H21 Val(1S)
Val(2pz) 1.17086 ꢁ0.15244 H22 Val(1S)
0.80028
0.77784
0.78246
Molecular electrostatic potential
0.00854
The molecular electrostatic potential (MEP) is best suited for
identifying sites for intra- and intermolecular interactions [41,42].
In drug-receptor, it is a very useful descriptor in understanding sites
for electrophilic and nucleophilic reactions as well as hydrogen
bonding interactions [42]. To predict reactive sites for the investi-
gated pymetrozine molecule, MEP was calculated with B3LYP/6-
311++G (d, p) optimized geometry. The negative (red and yellow)
regions of MEP are related to nucleophilic recognition and the posi-
tive (blue) one to electrophilic recognition shown in Fig. 6. Negative
regions in the studied molecule are found around the O25 and O26
atoms indicating a possible site for nucleophilic attack. According to
these calculated results, the MEP map shows that the negative po-
tential sites are on electronegative atoms as well as the positive po-
tential sites are around the hydrogen atoms. These sites give
information about the region from where the compound can have
noncovalent interactions. For the MEP surface in the studied mole-
cule the negative region associated with O25 and O26 atoms and
also the weak positive region by the nearby H22 atom are indicative
of a weak intramolecular (N19AO25ꢃ ꢃ ꢃH22 2.449 Å) hydrogen
bonding [43]. Thus the compound provides higher binding opportu-
nity for the receptor molecule, such as proteins without any steric
hindrance posed by amino acid chains of receptor.
C7
C8
N9
Cor(1S)
Val(2S)
1.99910 ꢁ10.11545 N23 Cor(1S)
1.99920 ꢁ14.13598
0.98639 ꢁ0.25170
Val(2S)
1.38243
ꢁ0.55163
ꢁ0.22636
ꢁ0.23144
ꢁ0.20403
Val(2px) 0.93620 ꢁ0.11714
Val(2py) 1.23024 ꢁ0.14869
Val(2pz) 1.02663 ꢁ0.13380
Cor(1S)
Val(2S)
Val(2px) 0.83667 ꢁ0.08429
Val(2py) 0.87335 ꢁ0.08084
Val(2pz) 0.86522 ꢁ0.13587
Cor(1S)
Val(2S)
Val(2px) 1.51069
Val(2py) 1.34955
Val(2pz) 1.21196
1.99912 ꢁ10.19117 C24 Cor(1S)
1.99905 ꢁ10.20134
0.71791 ꢁ0.13576
Val(2S)
0.99555
ꢁ0.32982
ꢁ0.22113
ꢁ0.14846
ꢁ0.19331
Val(2px) 0.98710
Val(2py) 0.96256
Val(2pz) 1.02392
1.99923 ꢁ14.22058 O25 Cor(1S)
1.99979 ꢁ18.93163
1.20623 ꢁ0.55929
Val(2S)
1.75948
ꢁ0.90087
ꢁ0.25807
ꢁ0.28695
ꢁ0.27399
Val(2px) 1.44379 ꢁ0.29047
Val(2py) 1.31123 ꢁ0.28613
Val(2pz) 1.50567 ꢁ0.28739
Val(2px) 1.31723
Val(2py) 1.86903
Val(2pz) 1.48108
H10 Val(1S)
H11 Val(1S)
C12 Cor(1S)
Val(2S)
0.82312 ꢁ0.02948 O26 Cor(1S)
1.99978 ꢁ18.92652
0.79720 ꢁ0.02044
1.99895 ꢁ10.10763
0.98126 ꢁ0.26867
Val(2S)
1.75006
ꢁ0.89364
ꢁ0.27605
ꢁ0.25520
ꢁ0.26991
0.01407
Val(2px) 1.75796
Val(2py) 1.36573
Val(2pz) 1.49223
Val(2px) 1.08797 ꢁ0.12235
Val(2py) 1.05179 ꢁ0.17000 H27 Val(1S)
0.79120
Val(2pz) 1.11072 ꢁ0.17080 Cl28 Cor(1S)
2.00000 ꢁ100.22125
1.99962 ꢁ10.51574
H13 Val(1S)
H14 Val(1S)
N15 Cor(1S)
Val(2S)
0.78373 ꢁ0.01174
0.74753 0.02190
Cor(2S)
Val(3S)
1.83363
ꢁ1.02970
ꢁ7.24674
ꢁ0.31604
ꢁ7.24414
ꢁ0.32685
ꢁ7.24484
1.99923 ꢁ14.18187
Cor(2px) 1.99995
Val(3px) 1.57645
Cor(2py) 1.99996
Val(3py) 1.77586
Cor(2pz) 1.99996
1.41505 ꢁ0.55332
Val(2px) 1.47162 ꢁ0.22446
Val(2py) 1.08827 ꢁ0.18730
Val(2pz) 1.47795 ꢁ0.22685
Thermodynamic properties
The temperature dependence of the thermodynamic properties
heat capacity at constant volume (Cv), entropy (S), enthalpy (H)
and Gibbs free energy (G) for the title compound were also deter-
mined by B3LYP/6-311++G (d, p) method and are listed in Table 4.
It can be observed that these thermodynamic functions are
increasing with temperature ranging from 100 to 1000 K due to
C16 Cor(1S)
Val(2S)
1.99929 ꢁ10.09652
1.07220 ꢁ0.27667
Val(3pz) 1.72318
ꢁ0.32575
Val(2px) 1.15537 ꢁ0.13074
Val(2py) 1.07625 ꢁ0.12320
Val(2pz) 1.04231 ꢁ0.11857