ОПТИКА И СПЕКТРОСКОПИЯ, 2014, том 117, № 1, с. 86-99



УДК 539.19


© 2014 г. H. Gokce*, S. Bah^eli**

* Vocational High School of Health Services, Giresun University, 28200 Giresun, TURKEY ** Physics Department, Faculty of Arts and Sciences, Suleyman Demirel University, 32260Isparta, TURKEY

E-mail: semihabahceli@sdu.edu.tr Received May 14, 2013

Molecular geometry, experimental vibrational wavenumbers, electronic properties, and quantum chemical calculations of minaprine (Ci7H22N4O • 2HCl), (with synonym, dihydrochloride salt of N-(4-methyl-6-phe-nyl-3-pyridazinyl)-4-morpholineethamine) which is widely used as a psychotropic drug at medicinal treatment, in the ground state by using density functional theory (DFT/B3LYP) method with 6-31++G(d, p) basis set have been presented for the first time. The comparison of the observed fundamental vibrational frequencies were in a very good agreement with the experimental data. Furthermore, UV-vis TD-DFT calculations, the highest occupied molecular orbitals (HOMO-1, HOMO), lowest unoccupied molecular orbitals (LUMO, LUMO+1), molecular electrostatic potential (MEP) surface, atomic charges and thermodynamic properties of minaprine molecule have been theoretically calculated and simulated at the mentioned level.

DOI: 10.7868/S0030403414040114


Over the last three decades the minaprine which is a heterocyclic compound containing four nitrogen atoms as one ofpyrizadine derivatives has been known as psychotropic drug with antidepressant, anticataleptic and antiaggressive properties in the medicine [1—8]. Methabolic pathways of minaprine has been studied in human and five animal species [9]. The effects of mi-naprine on impairement of working memory produced by scopolamine, ethylcholine aziridinium ion or cerebral ischemia were investigated in rats [10]. Likewise, the effect of minaprine, in addition to its original antidepressive properties, exhibits cholini-metric activities and is used as acetylcholinesterase inhibitors [11, 12]. Similarly, protective effects of minaprine were examined on the cerebrum of rodents [13].

On the other hand, the comparisons between min-aprine which is chemically unrelated to other known psychotropic drugs and impramine have been done for one hundred patients in the framework of dosage amounts taken per day [14, 15]. However, the crystal-lographic structure of minaprine analogs and an ami-nopyrazidine derivative have been performed by using XRD technique [16-18].

Since the experimental studies on the molecules are rather tedious and expensive, there is another alternative way which is to employ the computational approaches in order to understand their dynamical behaviours. Therefore, the quantum chemical calculation methods provide support for experimental structural and spectroscopic studies. Recently, the quantum chemical calculation methods combined with vibrational, electronic and NMR spectroscopies have

been used as an effective technique to predict spectro-scopic, electronic and magnetic properties of molecular systems.

Up to our best knowledge, there is no study on the vibrational and electronic properties of minaprine in the literature. In this framework, the purpose of this work is to report the observed FT-IR, micro-Raman and UV-vis spectra of minaprine and to present the results of geometrical structure, vibrational frequencies and quantum chemical calculations by using DFT/B3LYP calculations with 6-31++G(d, p) basis set in ground state for the first time.


Minaprine dihydrochloride, [C17H22N4O • 2HCl], was obtained from commercial source (Sigma-Ald-rich) and used without any further purification. FT-IR and micro-Raman experimental measurements of sample were recorded in solid phase.

IR measurement for minaprine at room temperature was performed on a Perkin Elmer Spectrum FT-IR spectrometer in the region 400-4000 cm-1 with a resolution of 4 cm-1 in the transmission mode. The sample was compressed into self-supporting pellet and introduced into an IR cell equipped with KBr window.

The micro-Raman spectrum of minaprine was taken with a Jasco NRS-3100 micro-Raman (^-Raman) Spectrometer (1800 lines/mm grating and high sensitivity cooled CCD) at room temperature in the region 100-3500 cm-1. The spectrometer was calibrated with the silicon phonon mode at 520 cm-1 and microscope

objective 100x was used. The sample was excited by using 632.8 nm He—Ne laser. In order to obtain the micro-Raman spectrum of sample, the exposure time was taken as 30 s and 10 scans were accumulated.

On the other hand the UV-vis spectrum of the title compounds was recorded by using a PG Instrument T80+ ultraviolet spectrophotometer at room temperature. The UV-vis spectrum of title compound solved in water was verified with spectral bandwidth 2 nm and quartz cell 1 cm.


In this study, all calculations were carried out with the Gauss-View molecular visualization program and Gaussian 03 program package on personal computer [19, 20].

The molecular structure and vibrational computations of minaprine molecule was calculated by using Becke-3-Lee Yang-Parr (B3LYP) density functional theory method with 6-31++G(d, p) basis set in ground state [21, 22]. The positive values of all calculated vibrational wavenumbers show that the optimized molecular structure is stable. However, the wav-enumber values computed at these levels contain the well known systematic errors [23]. Therefore, in order to prevent the well known systematic errors the computed vibrational wavenumbers were scaled as 0.977 for frequencies less than 1700 cm-1 and 0.955 for frequencies higher than 1700 cm-1 for B3LYP/6-31++G(d, p) level [24]. The assingments of fundamental vibrational modes of the title molecule were performed on the basis of total energy distribution (TED) analysis by using VEDA 4 program [25].

UV-vis spectrum calculation of title molecule was performed using DFT/B3LYP method. In addition, HOMO and LUMO energy values and HOMO-LUMO energy gaps were calculated using B3LYP method with 6-31++G(d, p) basis set. Furthermore, the orbital shapes (HOMO and LUMO) and molecu-

lar electrostatic potential (MEP) surface of the mentioned molecule in 3-dimensions (3D) were plotted by using B3LYP/6-31++G(d, p) level in Gauss-View molecular visualization program [19, 20].

The Raman activities (S) calculated by using Gaussian 03 program have been converted to relative Raman intensities (I) using the following relationship:

L = f(uo - U)4Si

u,[1 - exp(-hcu,/kT)]

where u0 (cm-1) is the exciting frequency, u, is the vibrational wavenumber of the ith normal mode, h, c, and k are well known universal constants and /is the suitably chosen common scaling factor for all the peak intensities [26, 27].


Molecular Structure Analysis

Since the crystallographic structure of pure min-aprine dihydrochloride was not found in the literature we use a minaprine analog which is [C17H22N4O2+ •

2 ~ • C2O4 • C2H2O4] with PI space group and triclinic

symmetry [16]. The optimized molecular structure at B3LYP/6-31++G(d, p) level of minaprine molecule is given in Fig. 1. Furthermore, in Table 1 we present the experimental and calculated bond lenghts and bond angles as well as the calculated dihedral angles using DFT/B3LYP method with 6-31++G(d, p) basis set for the title molecule. As can be seen in Table 1, the observed and calculated using B3LYP/6-31++G(d, p) level values of bond lengths and bond angles are in a very good agreement with literature [16-18]. Furthermore, the calculated C2-C3-C13-N15 dihedral angle which is a value of 23.033° shows that the benzene and pyriza-dine aromatic rings are not in-plane. Likewise, the calculated C14-C16-N19-C21 dihedral angle which is a value of 171.423° indicates that the pyrizadine aro-

Table 1. The experimental and calculated optimized geometric parameters of minaprine molecule

Bond lengths, A X-ray [16] B3LYP Bond angles, degrees X-ray [16] B3LYP Dihedral angles, degrees B3LYP

C1- C2 1.402 1.394 C2-C1-C6 119.6 120.435 C1- C2-C3-C4 -0.493

C1- C6 1.361 1.399 C2-C1-H7 - 119.554 C1- C2-C3-C13 179.751

C1- H7 - 1.086 C6-C1-H7 - 120.010 C2- C3-C4-H9 -178.035

C2- C3 1.385 1.407 C1-C2-C3 119.7 120.673 C2- C3-C13-C12 -156.061

C2- H8 - 1.084 C1-C2-H8 - 120.668 C2- C3-C13-N15 23.033

C3- C4 1.401 1.406 C3-C2-H8 - 118.659 C3- C4-C5-C6 -0.131

C3- C13 1.490 1.486 C2-C3-C4 119.6 118.402 C3- C4-C5-H10 -179.604

C4- C5 1.384 1.396 C2-C3-C13 120.3 120.061 C12 -C13-N15- N17 -0.225

C4- H9 - 1.086 C4-C3-C13 120.1 121.537 C12 -C14-C16- N17 -0.785

C5- C6 1.364 1.397 C3-C4-C5 119.2 120.860 C12 -C14-C16- N19 177.887

C5- H10 - 1.086 C3-C4-H9 - 120.204 C12 -C14-C41- H44 -1.422

C6- H11 - 1.086 C5-C4-H9 - 118.920 C13 -N15-N17- C16 -1.309

C12 -C13 1.441 1.414 C4-C5-C6 120.6 120.212 C14 -C16-N19- H20 20.867

C12 -C14 1.341 1.377 C4-C5-H10 - 119.625 C14 -C16-N19- C21 171.423

C12 -H18 - 1.086 C6-C5-H10 - 120.161 N15 -N17-C16- N19 -176.872

C13 -N15 1.319 1.337 C1-C6-C5 121.2 119.415 C16 -N19-C21- C22 164.801

C14 -C16 1.428 1.426 C1-C6-H11 - 120.322 C16 -N19-C21- H24 43.304

C14 -C41 - 1.505 C5-C6-H11 - 120.262 N17 -C16-N19- H20 -160.393

N15 -N17 1.345 1.330 C13-C12-C14 118.5 119.908 N17 -C16-N19- C21 -9.836

C16 -N17 1.351 1.342 C13-C12-H18 - 120.484 N19 -C21-C22- H26 56.089

C16 -N19 1.317 1.379 C14-C12-H18 - 119.600 N19 -C21-C22- N39 174.643

N19 -H20 - 1.010 C3-C13-C12 122.2 122.626 H20 -N19-C21- C22 -44.657

N19 -C21 1.470 1.460 C3-C13-N15 115.8 116.733 H20 -N19-C21- H23 76.897

C21 -C22 1.525 1.532 C12-C13-N15 121.9 120.636 C21 -C22-N39- C27 72.424

C21 -H23 - 1.099 C12-C14-C16 122.0 115.619 C21 -C22-N39- C28 -162.904

C21 -H24 - 1.091 C12-C14-C41 - 122.744 C22 -N39-C27- C29 -177.851

C22 -H25 - 1.108 C16-C14-C41 121.637 C22 -N39-C28- C32 17

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