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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 99 (2012) 90–96
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Normal coordinate analysis and vibrational spectroscopy (FT-IR and FT-Raman) studies of (2S)-2-amino-3-(3,4-dihydroxyphenyl)-2-methylpropanoic acid using ab initio HF and DFT method A. Prabakaran b,c, S. Muthu a,⇑ a b c
Department of Physics, Sri Venkateswara College of Engg., Sriperumbudur 602 105, India Department of Physics, Pallavan College of Engg., Kanchipuram 631 502, India Department of Physics, Bharathiar University, Coimbatore 641 046, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
" Vibrational assignments with PED of
In this work, the complete vibrational assignments with PED were calculated using NCA calculation. NLO and NBO properties of 2ADMA were performed by DFT with 6-31G (d,p) basis set. Electronic transition within molecule and HOMO and LUMO energy of 2ADMA were studied. MEP map shows that the negative potential sites (red and yellow) are electronegative oxygen atoms, while the positive potential sites (blue) are around the hydrogen atoms. Thermodynamics properties of the title compound were calculated at the different temperatures.
2ADMA were calculated. " A thermodynamics property of the title compound was calculated at the different temperatures. " MEP, NLO, NBO and HOMO and LUMO energies of 2ADMA were studied.
a r t i c l e
i n f o
Article history: Received 18 May 2012 Received in revised form 15 August 2012 Accepted 3 September 2012 Available online 10 September 2012 Keywords: Vibrational spectra NCA UV NBO HOMO–LUMO First-order hyperpolarizability
a b s t r a c t The FT-IR and FT-Raman spectra of (2S)-2-amino-3-(3,4-dihydroxyphenyl)-2-methylpropanoic acid (2ADMA) were recorded in the region 4000–400 cm1 and 4000–100 cm1, respectively. The geometrical structure, harmonic vibrational frequency, infrared intensity, Raman activities and bonding features of this compound was carried out by ab initio HF and DFT methods with 6-31G (d,p) basis set. The complete vibrational frequency assignments were made by normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMF). The electric dipole moment (l) and the first-order hyperpolarizability (b0) values have been the computed quantum mechanically. The calculated HOMO and LUMO energies show that, the charge transfer occurs within the molecule. The charge delocalizations of these molecules have been analyzed using NBO analysis. The solvent effects have been calculated using TD-DFT in combination with the polarized continuum model (PCM), and the results are in good agreement with experimental measurements. The other molecular properties like Mulliken population analysis, electrostatic potential (ESP) and thermodynamic properties of the title compound at the different temperatures have been calculated. Finally, the calculation results were applied to simulate infrared and Raman spectra of the title compound which shows good agreement with observed spectra. Ó 2012 Elsevier B.V. All rights reserved.
⇑ Corresponding author. Tel.: +91 9443690138. E-mail address:
[email protected] (S. Muthu). 1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2012.09.014
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Introduction (2S)-2-Amino-3-(3,4-dihydroxyphenyl)-2-methylpropanoic acid (2ADMA) is the L-isomer of alpha-methyldopa. It was originally synthesized as an analog of 3,4-dihydroxyphenylalanine [1]. It also prepared from dimethoxyphenyl-acetonitrile by successive interaction with sodium ethoxide, ammonium carbonate, and potassium cyanide, followed by resolution of the racemic product [2]. It is colorless to white crystalline powder, slightly soluble in water and alcohol and insoluble in the common organic solvents [3]. When heated to decomposition it emits toxic fumes of nitrogen oxides [4]. It is an antihypertensive drug belongs with centrally acting alpha-adrenergic agonist and used for the treatment of hypertension. At present, vibrational spectroscopy is used not only for the functional group identification of organic compounds, but also to investigate the molecular conformation, reaction kinetics, etc. Correct frequency assignments for complex organic molecules can be done based on frequency agreement between the computed harmonics and the observed fundamentals. 2ADMA has been taken as the object of spectral, structural and theoretical investigations because of its interesting physicochemical and biological properties. Further, the crystal data of 2ADMA is not found from the literature. Literature survey reveals that the vibrational spectra, and the theoretical calculations of 2ADMA have not been reported earlier. The-state-of-the-art mid-infrared and FT-Raman spectral studies combined with quantum chemical computations are prevalently used nowadays as effective tools in the vibrational analysis of drug molecules [5], biological compounds [6] and natural products [7]. The reason is that fluorescence-free Raman spectra and the computed results can help unambiguous identification of vibrational modes as well as the bonding and structural features of complex organic molecular systems. In this present study, a complete vibrational analysis of the molecule was performed by combining the experimental (FT-IR and FTRaman) data and theoretical information using Pulay’s DFT based scaled quantum mechanical (SQM) method. The redistribution of electron density (ED) in various bonding, anti bonding orbital and E2 energies have been calculated by natural bond orbital (NBO) analysis to give clear evidence of stabilization originating from the hyper conjugation of various intra-molecular interactions. The UV–vis spectroscopic studies along with HOMO, LUMO analysis has been used to elucidate information regarding charge transfer within the molecule. Finally, the thermodynamic properties of the optimized structures were obtained theoretically from the harmonic vibrations. Experimental details The compound under investigation namely 2ADMA was obtained from Aldrich Chemicals, USA, and used without any further purification. The FT-IR spectrum of the compound was recorded in Bruker IFS 66V Spectrometer in the region 4000–400 cm1. The spectral resolution is ±2 cm1. The FT-Raman spectra of compound was also recorded in the same instrument with FRA 106 Raman module equipped with Nd:YAG laser source operating at 1.064 lm line width with 200 mW power. The spectra were recorded with scanning speed of 30 cm1 min1 of spectral width 2 cm1. The frequencies of all sharp bands are accurate to ±1 cm1. The UV–vis absorption spectrum of the compound was recorded in ethanol solution using Shimadzu UV-2550 spectrophotometer.
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lated by ab initio HF and DFT method with 6-31G (d,p) basis set. All the calculations were performed using the Gaussian 03W software package [8] and Gauss-view molecular visualization program package on a personal computer [9]. Scaling of the force field was performed according to the SQM procedure [10,11] using selective scaling in the normal internal coordinate representation [12]. The scale factor calculation and characterization of the normal modes using potential energy distribution (PED) were done with the MOLVIB 7.0 program written by Sundius [13]. The calculated Raman activities (Si) and have been converted to relative Raman intensities (Ii) using the following relationship derived from the basic theory of Raman scattering [14,15]
Ii ¼ 1012 ðm0 mi Þ4 ð1=mi ÞSi where Ii is the Raman intensity, Si, the Raman scattering activities, mi is the wave number of normal modes and m0 denotes the wave number of the excitation laser. For the plots of simulated IR and Raman spectra, pure Lorentzian band shapes were used with full width at half maximum (FWHM) of 10 cm1. The natural bonding orbital (NBO) calculation was performed using NBO 3.1 program [16] and was carried out in the Gaussian 03W package at the DFT/B3LYP level. The hyperconjugative interaction energy was deducted from the second order perturbation approach [17–19]. UV–vis spectra, electronic transition, vertical excitation energies, absorbance and oscillator strengths were computed with the time-dependent DFT method. The electronic properties such as HOMO and LUMO energies were determined by time-dependent DFT (TD-DFT) approach. Results and discussion Structural properties The optimized geometry structure of the title compound is shown in Fig. 1. The molecular structure of the 2ADMA belongs to a Cs point group of symmetry. The optimized structure parameter for this compound calculated by HF and B3LYP with 6-31G (d,p) basis set is listed in Table S1 (Supplementary material). The calculated geometric parameters can be used as the foundation to calculate the other parameters for the compound. To the best of our knowledge exacts experimental data of the geometrical parameter of 2ADMA are not available in literature. The molecule contains two hydroxyl groups in the benzene ring at 3 and 4 positions in place of hydrogen atoms. The calculated C–C bond length in phenyl ring varies from 1.379 to 1.392 for HF and 1.391 to 1.403 for B3LYP. The optimized bond length of the C7–C8, C7–C12 are larger and C8–C9, C10–C11, C11–C12 are shorter. With the electron donating substituent’s on benzene ring, the symmetry of the ring distorted, yielding ring angles smaller than 120° at the point of substitution and slightly larger than 120° at other position [20]. It is clearly
Computational details The optimized molecular structure, molecular electrostatic potential and vibrational spectra of the title compound were calcu-
Fig. 1. Atom numbering scheme adopted in the optimized structure of 2ADMA.
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shown that from calculated bond angle of C8–C7–C12, C8–C9–C10 and C9–C10C11 are slightly decrease, and the increase in value of the bond angles are C7–C8–C9 and C7–C12–C11. The calculated values are small difference in literature values. The small difference between the computed value is due to calculation belong with gaseous phase, and experimental value belongs to solid phase. The total energy obtained by HF and B3LYP structure optimization was found to be 740.19 a.u and 744.57 a.u, respectively. NBO analysis By using the second-order bond–antibond (donor–acceptor) NBO energetic analysis, insight into the most important delocalization schemes was obtained. The change in electron density (ED) in the (r, p) antibonding orbitals and E(2) energies have been calculated by natural bond orbital (NBO) analysis [21] using DFT method to give clear evidence of stabilization originating from various molecular interactions. The hyperconjugative interaction energy was deducted from the second-order perturbation approach [16]
Eð2Þ ¼ DEij ¼ qi ðFði; jÞ2 =ðej ei Þ where qi is the donor orbital occupancy, ei and ej are diagonal element, and F (i, j) is the off diagonal NBO Fock matrix element. The larger E(2) value the more intensive is the interaction between electron donors and acceptor, i.e. the more donation tendency from electron donors to electron acceptors and the greater the extent of conjugation of the whole system [16]. Delocalization of electron density between occupied Lewis’s type (bond or lone pair) NBO orbital and formally unoccupied (anti bond or Rydberg) non-Lewis NBO orbital corresponds to a stabilizing donor–acceptor interaction. NBO analysis has been performed on the 2ADMA molecule at the B3LYP/6-31G (d,p) level to elucidate, the intra-molecular rehybridization and delocalization of electron density within the molecule. The strong intramolecular hyperconjugation interaction of the r and p electrons of C–C to the anti C–C bond to the ring leads to stabilization of some part in the ring as evident from Table S2 (Supplementary material). The intra molecular hyperconjugative interaction of the (C7–C8) distribute to (C1–C3), (C9–O14) and (C12– H24) leading to stabilization of 1.11, 5.03 and 3.05 kJ/mol respectively. This enhanced further conjugate with anti bonding orbital of p (C9–C10), (C11–C12), leads to strong delocalization of 22.96 and 21.82 kJ/mol respectively. The same kind of interaction is calculated in the same kind of interaction energy, related to the resonance in the molecule, is electron donating from LP (1) O5 to the r (C1–C2), (C1–O4) show less stabilization of 0.54 and 8.51 kJ/mol and further LP(2)O5 conjugate with C1–O4 through antibond, i.e. p (C1–O4) leads to the strong stabilization energy of 48.15 kJ/mol.
Table 1 The calculated first order hyperpolarizability of 2ADMA with HF and B3LYP/6-31G (d,p) basis set. Parameters
HF/6-31G (d,p)
B3LYP/6-31G (d,p)
bxxx bxxy bxyy byyy bxxz bxyz byyz bxzz byzz bzzz btotal
363.9 21.6 83.41 49.7 4.0 6.27 28.8 56.4 21.23 14.9 4.375 1030 e.s.u.
381.521 6.81 43.25 52.65 18.97 6.70 16.38 48.05 29.71 16.717 3.782 1030 e.s.u.
the energy in the external electric field. When the electric field is weak and homogeneous, this expansion becomes.
E ¼ E0 la F a 1=2aab F a F b1=6 babc F a F b F c where E0 is the energy of the unperturbed molecules, Fa is the field of the origin la, aab and babc are the components of dipole moment, polarizabiltiy and the first-order hyperpolarizability respectively. The total static dipole moment l, the mean polarizability a0, the anisotropy of the polarizability Da and the mean first hyperpolarizability b0, using the x, y and z components are followed:
l ¼ ðl2x þ l2y þ l2z Þ1=2 a¼
axx þ ayy þ azz 3
Da ¼ 21=2 ½ðaxx ayy Þ2 þ ðayy azz Þ2 þ ðazz axx Þ2 þ 6a2xx 1=2 b0 ¼ ðb2x þ b2y þ b2z Þ1=2 and
bx ¼ bxxx þ bxyy þ bxzz by ¼ byyy þ bxxy þ byzz bx ¼ bzzz þ bxxz þ byyz The calculated hyperpolarizability values of 2ADMA are given in Table 1. The value of second order optical susceptibility v2 in a given depends on the molecular hyperpolarizability b, the number of chromophores and the degree of non-centro symmetry. The computed first-order hyperpolarizability, btotal of the 2ADMA molecules is 3.782 1030 e.s.u., which is 10 times that of urea.
First order hyperpolarizability
Vibrational frequencies
In discussing nonlinear optical properties, the polarization of the molecule by an external radiation field is often approximated as the creation of an induced dipole moment by an external electric field. Under the weak polarization condition, we can use a Taylor series expansion in the electric field components to demonstrate the dipolar interaction with the external radiation electric field. The first order hyperpolarizability (b0) and related properties (a, b0 and Da) of 2ADMA are calculated based on the finite-field approach. In the presence of an applied electric field, the energy to a system is a function of the electric field. The first-order hyperpolarizability is a third rank tensor that can be described by a 3 3 3 matrix. The 27 components from the 3D matrix can be reduced to 10 components due to the Kleinman symmetry [22]. The components of b are the coefficients in the Taylor series expansion of
The title compound consists of 28 atoms and has 78 normal modes of vibrations. These normal modes of 2ADMA are distributed with 58 in plane vibration and 25 out of plane vibration. A detailed vibration description can be given by normal mode analysis and compared theoretically scaled wavenumber with PED. To obtain the normal mode in molecular coordinate system and local symmetry coordinate for 2ADMA were defined by Fogarasi and Pulay [23] and were presented in Tables S3 and S4 (Supplementary material). Vibrational frequencies were calculated by using B3LYP/6-31G (d,p) and HF/6-31G (d,p) methods. Table S5 (Supplementary material) shows that scaled frequencies using SQMFF, observed frequencies in the FT-Raman and FT-IR spectra with their intensities, force constant, PEDs and proposed normal modes of the title compound. To understand, the analysis spectral features,
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Fig. 3. Comparison of experimental and computed FT-Raman spectrum of 2ADMA. Fig. 2. Comparison of experimental and computed FT-IR spectrum of 2ADMA.
comparison of stimulated and observed FT-IR and FT-Raman spectrum of 2ADMA were presented in Figs. 2 and 3, respectively. C–H vibrations The 2ADMA molecule is trisubstituted aromatic structure. It has one isolated and two adjacent C–H moieties. It causes three C–H stretching vibrations, three in-plane and three out-of-plane bending vibrations. The hetero aromatic structure shows the presence of the C–H stretching vibration in the range 3100–3000 cm1, which is the characteristic region for the ready identification of the C–H stretching vibrations [24]. In the present work, the C–H stretching vibrations are observed at 3082 and 3041 cm1 in FTRaman spectrum, whereas in the FTIR, it is assigned at 3076 cm1. The scaled vibrations calculated at 3102, 3069 and 3039 cm1 by B3LYP/6-31G (d,p) method. As showed by the PED, these three modes involve approximately 99% contribution suggesting that they are pure C–H stretching modes. The aromatic C–H in-plane bending vibration occurs within the region 1300–1000 cm1 and out-of plane bending vibrations in the region of 700–1000 cm1 [25]. The C–H in-plane bending vibration computed at 1248, 1241, 1174, 1155, 1143 and 1128 cm1 by B3LYP/6-31G (d,p) method shows excellent agreement with FT-IR bands at 1257, 1218 and 1160 cm1 and in FT-Raman band at 1170 cm1. The bands observed at 866 and 848 cm1 in FT-IR, and at 875 cm1 in FT-Raman are assigned to C–H out-of plane bending vibration for 2ADMA. This also shows good agreement with theoretically scaled harmonic wavenumber by B3LYP and HF method. The PED corresponding to this vibration is a mixed mode with C–C stretch with a contribution of 50%. Methylene vibrations For the assignments of CH2 group frequencies, basically six fundamentals can be associated with each CH2 group namely CH2 symmetric stretch; CH2 asymmetric stretch; CH2 scissoring and CH2 rocking, which belongs to in-plane vibrations and two out-of plane vibrations, viz., CH2 wagging and CH2 twisting modes, which are expected to be depolarized. In this molecule, the asymmetric and symmetric stretching vibrations were observed at 2932 cm1 and 2925 cm1 in FT-Raman and FT-IR respectively. Generally, the scissoring band in the spectra of hydrocarbons occurs nearly at 1468 cm1 while methylene twisting and wagging vibrations
are observed in the region 1350–1150 cm1 which are weaker than those resulting from methylene scissoring. A series of bands in this region, arising from the methylene group, is characteristic of the spectra of solid samples of long-chain acids [22]. According to the above-said values, in this work, the peaks at 1441 cm1 with PED of 76% and 1330 cm1 with PED of 45% are assigned to CH2 scissoring and CH2 wagging vibrations while the peak at 924 cm1 in both spectra is assigned to CH2 rocking, which is coupled with C–C stretching. All the vibrations of CH2 computed by HF and B3LYP method agree well with the experimental observations. Methyl group vibration The title compound 2ADMA possesses one CH3 group on the side substitution chain. For the assignment of CH3 group frequencies, nine fundamental can be associated with each CH3 group. The CH stretching in CH3 occurs at lower frequencies than those of aromatic ring (3100–3000 cm1). Moreover, the asymmetric stretch is usually at higher frequencies than the symmetric stretch. In the present work, the CH3 symmetric stretching frequency is assigned at 2932 cm1 in FT-Raman, whereas CH3 asymmetric frequency is assigned at 2970 cm1 in FT-IR. These assignments were also supported by literature [26] in besides to PED output. The asymmetric and symmetric bending vibrations of methyl groups normally appear in the region 1470–1440 cm1 and 1390– 1370 cm1, respectively. The bonds at1468 and 1357 cm1 in FT-IR are assigned CH3 bending mode. The rocking vibrations of the CH3 group in 2ADMA appear mixed vibrations. These modes usually appear in the region 1070–900 cm1 [27,28]. The medium band in IR spectrum at 982 cm1 and FT-Raman spectrum at 987 cm1 are assigned CH3 rocking mode. All these calculated values are in good agreement with the observed values. C–C vibration The C–C aromatic stretching vibration gives rise to characteristic bands in both the observed IR and Raman spectra, covering the spectral range from 1600–1400 cm1 [29]. Therefore, the C–C stretching vibrations of the title compound is found in 1638, 1592, 1501 and 1258 cm1 in FTIR and 1632 and 1501 cm1 in FT-Raman and these modes are confirmed by their PED values. The theoretically computed values for C–C ring in-plane bending and out-of-plane bending vibrational modes by HF and B3LYP method gives excellent agreement to experimental data.
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NH2 stretching vibrations Heteroaromatics containing an N–H group show their stretching vibrations in the region [30,28] 3500–3220 cm1. The position of the absorption in this region depends on the degree of hydrogen bonding and hence on the physical state of the sample or the polarity of the solvent. In the present work, the scaled NH2 asymmetric stretch is calculated at 3417 cm1 and NH2 symmetric stretch at 3343 cm1 with PED 100%. The various bending vibration of NH2 group of the title compound are also found to be in good agreement with the experimental data with appropriate PED.
expensive than semi-empirical methods but allow easily studies of medium-size molecules [34,35]. Test calculations have shown that the inclusion of extra polarization functions does not affect the excitation energies, besides the addition of diffuse functions lead to an increase in computation time. The maximum absorption (kmax) values obtained with B3LYP/6-31G (d,p) are 250.83, 249.41, and 217.37 nm (in ethanol) and 239.51, 237.05, and 232.85 nm (in water), shows good agreement experimental absorption values are 279 nm and 202 nm(in ethanol). These excitations correspond to p to p transition.
O–H vibration The O–H stretching is characterized by a very broad band appearing near about 3400 cm1 [22,31]. On the other hand, the hydrogen bonding in the condensed phase with the other acid molecules make vibrational spectra more complicated. Therefore, we could not observe the strong and sharp bands of the O–H vibration in the FT-IR and FT-Raman spectrum and the calculated value at 3697 cm1 was assigned to O–H stretching modes of the carboxylic groups [32]. When the OH in carboxylic acid do not form intramolecular bond, the stretching mode is to be expected at 3520 cm1 [22,33]. In this study the O–H stretching modes were calculated and assigned at 3641and 3604 cm1 for carboxylic acid groups.
Frontier molecular orbital analysis Many organic molecules that contain conjugated p electrons are characterized as hyper-polarizabilities and are analyzed by vibrational spectroscopy [36,37]. According to the TD-DFT calculated electronic absorption spectra, the maximum absorption wavelength corresponding to the electronic transition is from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). We examine the four important molecular orbitals of 2ADMA molecule, the highest and second highest occupied molecular orbitals and the lowest and second lowest unoccupied molecular orbitals which we denote HOMO, HOMO1, LUMO and LUMO-1, respectively. These MOs for water solvent is out line in Fig. S1 (Supplementary material). The lowest singlet ? singlet spin-allowed excited states of 2ADMA were taken into account for the TD-DFT calculation to investigate the properties of electronic absorption. The energy gap between HOMO and LUMO is a critical parameter in determining molecular electrical transport properties because it is a measure of electron conductivity. The lowest unoccupied molecular orbital (LUMO) energy 0.4745 eV (in ethanol) and 0.2547 eV (in water) and the highest occupied molecular orbital (HOMO) energy is 5.9925 eV (in ethanol) and 5.445 eV (in water). The energy gap of HOMO–LUMO explains the eventual charge transfer interaction within the molecule, and the frontier orbital energy gap of 2ADMA is found to be 5.518 eV (in ethanol) and 5.6997 eV (in water) obtained at TD-DFT method using 6-31G (d,p) basis set as shown in Table S7 (Supplementary material). The HOMO is located over the benzene ring and amino group, the HOMO ? LUMO transition implies an electron density transfer to O–H group from the benzene ring.
Electronic properties Absorption spectra All the molecular structure allows strong p ? p or r ? r transition in the UV–vis region with a high extinction coefficients. The lowest singlet ? singlet spin-allowed excited states were taken into account to investigate the properties of electronic absorption. The UV–vis spectrum of 2ADMA was recorded in ethanol solution as shown in Fig. 4. To support experimental observations, TD-DFT calculation electronic absorption spectra of the title compound in ethanol and water solution was performed. The experimental and computed electronic features such as the absorption wavelength (k), excitation energies (E), and oscillator strengths (f) major contributions of the transitions and assignments of electronic transitions are listed in Table S6 (Supplementary material) TD-DFT methods are computationally more
Fig. 4. UV absorption spectra of 2ADNA in ethanol solution.
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lation equation among heat capacities, entropies, enthalpy changes and temperatures were fitted by quadratic formulas and the corresponding fitting factors (R2) for these thermodynamic properties are 0.9996, 1.000 and 0.9995, respectively. The correlations between these thermodynamic properties and temperatures (T) are shown in Fig. 5. The correlation equations are as follows:
C 0p:m ¼ 22:116 þ 0:9047T 4 104 T 2 S0m ¼ 246:34 þ 1:0249T 3 104 T 2 4 2 Hm 0 ¼ 12:338 þ 0:128T þ 2 10 T
Fig. 5. Correlation graphs of thermodynamic properties at different temperature of the title compound.
Mulliken atomic charges Mulliken atomic charge calculation has an important role for the application of quantum chemical calculation of the molecular system. Atomic charge affects dipole moment, polarizability, electronic structure and other molecular properties as the system. The calculated Mulliken charge values of 2ADMA are listed in Table S8 (Supplementary material). It is clearly shown that the carbon atom attached with hydrogen atom is negative, whereas the remaining carbon atoms are positively charged in the title compound. The oxygen atoms have more negative charge whereas all the hydrogen atoms have the positive charges. The more positive charge of carbon is found for the compound for C1, C9 and C10; it is mainly due to the substitution of negative charge of an oxygen atoms. The lone pare of oxygen atoms (O13 and O14) shows the charge transferred from O to H. Illustration of atomic charge plotted for HF/6-31G (d,p) and B3LYP/6-31G (d,p) level have been shown in Fig. S2 (Supplementary material). Molecular electrostatic potential Molecular electrostatic potential have been found to be a very useful tool in investigation of correlation between molecular structures with its physiochemical property relationship, including biomolecules and drugs [38,39]. The MEPS have been plotted for 2ADMA molecule at the B3LYP/6-31G (d,p) basis set as shown in Fig. S3 (Supplementary material). The different electrostatic potential values of the surface are represented by different colors, the maximum negative region, which preferred site for electrophilic reactive as a show red and yellow region. The maximum positive region, which preferred site for nucleophilic reactivity as a show blue region and green represent by zero potentials. In the present work, the calculated result shows that the negative potentials are mainly over the electron negative oxygen atoms and positive potential are over the nucleophilic reactive hydrogen atoms. This result gives information for the region from where the compound can has intermolecular interaction. Thermodynamic properties On the basis of vibrational analyses and statistical thermodynamics, the standard thermodynamic functions, heat capacity C 0p:m entropy S0m and enthalpy ðH10 Þ were calculated using perl script [40] and are listed in Table S9 (Supplementary material). The scale factor for frequencies is still 0.96. As observed from Table S9, the values of C 0p:m ; S0m and Hm 0 all increase with the increase of temperature from 100 to 1000 K, which is attributed to the enhancement of the molecular vibration as the temperature increases. The corre-
ðR2 ¼ 0:9996Þ ðR2 ¼ 1:000Þ ðR2 ¼ 0:9995Þ
These equations could be used for the further studies on the title compound. For instance, when we investigate the interaction between the title compound and another compound, thermodynamic properties. C 0p:m , S0m and H0m could be obtained from these equations and then used to calculate the change of Gibbs-free energy of the reaction, which will help us to judge the spontaneity of the reaction Scale factors have been recommended for an accurate prediction in determining the zero-point vibration energies, heat capacities, entropies, enthalpies, Gibbs-free energies. All this thermodynamic parameters and dipole moment at room temperature (298.15 K) at different methods are also presented in Table S10 (Supplementary material). Conclusion The FT-IR and FT-Raman measurements have been made for the 2ADMA molecule. The complete vibrational assignment with PED was calculated using SQMF method. The nonlinear optical properties were calculated theoretically. The predicted first hyperpolarizability values 10 times greater than those of urea. The molecular orbital energy and kmax of the title compound were performed and compared with an experimental and theoretical method. Molecular electrostatic potential of 2ADMA shows that the negative potential site is on the electronegative oxygen atom, while the positive potential site around the hydrogen atom. Mulliken charge analysis of the title compound has been studied by HF and B3LYP method. Consistency between the calculated and experimental FT-IR and FT-Raman data shows that the B3LYP/6-31G (d,p) method can generate reliable geometry and related properties to the title compound. Finally, the thermodynamic properties to the title compound have been calculated for different temperatures, revealing the correlations among C 0p;m , S0m and Hm 0 and temperatures are obtained. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2012.09.014. References [1] J.G. Gerber, A.S. Nies, Antihypertensive agents and the drug therapy of hypertension, in: A. Goodman Gilman, T.W. Rall, A.S. Neis, P. Taylor (Eds.), The Pharmacological Basic of Therapeutics, Pergamon Press, New York, 1990, pp. 784–813. [2] A. Osol, R. Pratt (Eds.), The United States Dispensatory, 27th ed., Lippincott, Philadelphia JB, 1973. [3] J.E.F. Reynolds (Ed.), Martindale, The Extra Pharmacopeia, 29th ed., The Pharmaceutical press, London, 1989. pp. 1053. [4] N.I. Sax, R.J. Lewis, Dangerous Properties of Industrial Materials, seventh ed., Van Nostrand Reinhold, New York, 1987. pp. 1084. [5] D. Sajan, J. Binoy, B. Pradeep, K. Venkata Krishna, V.B. Kartha, I.H. Joe, V.S. Jayakumar, Spectrochim. Acta A 60 (2004) 173–180. [6] J.P. Abraham, I.H. Joe, V. George, O.F. Nielson, V.S. Jayakumar, Spectrochim. Acta A 59 (2003) 193–199.
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[7] J. Binoy, J.P. Abraham, I.H. Joe, V.S. Jayakumar, J. Aubard, O.F. Nielson, J. Raman Spectrosc. 36 (2005) 63–72. [8] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian 03, Revision C.02, Gaussian, Inc., Wallingford CT, 2004. [9] A. Frisch, A.B. Nielsen, A.J. Holder, Gaussview Users Manual, Gaussian Inc., Pittsburg, PA, 2000. [10] G. Rahght, P. Pulay, J. Phys. Chem. 99 (1995) 3093–3100. [11] P. Pulay, G. Fogarasi, G. Pongor, J.E. Boggs, A. Vargha, J. Am. Chem. Soc. 105 (1983) 7037–7047. [12] G. Fogarasi, X. Zhou, P.W. Taylor, P. Pulay, J. Am. Chem. Soc. 114 (1992) 8191– 8201. [13] T. Sundius, J. Mol. Struct. 218 (1990) 321–326. [14] G. Keresztury, S. Holly, J. Varga, G. Besenyei, A.Y. Wang, J.R. Durig, Spectrochim. Acta A 49 (1993) 2007–2026. [15] G. Keresztury, J.M. Chalmers, P.R. Griffith, Raman Spectroscopy: Theory in Handbook of Vibrational Spectroscopy, John Wiley and Sons Ltd., New York, 2002. [16] E.D. Glendening, A.E. Reed, J.E. Carpenter, F. Weinhold, NBO Version 3.1, TCI, University of Wisconsin, Madison, 1998. [17] X.-H. Li, R.-Z. Zhang, X.-Z. Zhang, Struct. Chem. 20 (2009) 1049–1054. [18] J. Chocholousova, V. Vladimin Spirko, P. Hobza, Phys. Chem. 6 (2004) 37–41. [19] A.E. Reed, L.A. Curtiss, F. Weinhold, Chem. Rev. 88 (1988) 899–926. [20] Y. Wang, S. Saebar, C.U. Pittman, J. Mol. Struct. Theochem. 281 (1993) 91–98. [21] H.W. Thomson, P. Torkington, J. Chem. Soc. 171 (1945) 640–645.
[22] D.A. Kleinman, J. Phys. Rev. 126 (1962) 1977–1979. [23] G. Fogarasi, P. Pulay, in: J.R. Durig (Ed.), Vibrational Spectra and Structure, vol. 14, Elsevier, Amsterdam, 1985, p. 125. [24] N.P.G. Roeges, A Guide to Complete Interpretation of Infrared Spectra of Organic Structures, Wiley, New York, 1994. [25] G. Varsanyi, Assignments for vibrational spectra of seven hundred benzene derivatives, 1/2, Academic Kiado, Budapset, 1973. [26] S.J. Bunce, H.G. Edwards, A.F. Johnson, I.R. Lewis, P.H. Turner, Spectrochim. Acta 49A (1993) 775. [27] N.B. Colthup, L.H. Daly, S.E. Wiberley, Introduction to Infrared and Raman Spectroscopy, Academic Press, New York, 1990. [28] F.R. Dollish, W.G. Fateley, F.F. Bentley, Characteristic Raman Frequencies of Organic Compounds, John Wiley & Sons, New York, 1997. [29] G. Varsanyi, Vibrational Spectra of Benzene Derivative, Academic Press, New York, 1969. [30] G. Socrates, Infrared Characteristic Group Frequencies, Wiley Intersciences Publication, New York, 1980. [31] D. Lin-Vien, N.B. Colthup, W.G. Fateley, J.G. Grasselli, The Handbook of Infrared and Raman Characteristic Frequencies of Organic Molecules, Academic Press, Boston, MA, 1991. [32] C.A. Tellez S, A. Claudio, E. Hollauer, T. Giannerini, M.I. Pais da Silva, M.A. Mondragon, J.R. Rodriguez, V.M. Castano, Spectrochim. Acta 60A (2004) 2171– 2180. [33] C.A. Tellez S, E. Hollauer, M.A. Mondragon, V.M. Castano, Spectrochim. Acta 57A (2001) 993–1007. [34] D. Guillaumont, S. Nakamura, Dyes Pigments 46 (2000) 85–92. [35] J. Fabian, Dyes Pigments 84 (2010) 36–53. [36] Y. Ataly, D. Avci, A. BaSoglu, Struct. Chem. 19 (2008) 239–246. [37] C. James, C. Ravikumar, T. Sundius, V. Krishnakumar, R. Kesavamoorthy, V.S. Jayakumar, I. Hubert Joe, Vib. Spectrosc. 47 (2008) 10–20. [38] J.S. Murray, K. Sen, Molecular Electrostatic Potentials Concepts and Applications, Elsevier, Amsterdam, 1996. [39] E. Scrocco, J. Tomasi, Adv. Quantum Chem. 11 (1978) 115–121. [40] K.K. Irikura, THERMO. PL, National Institute of Standards and Technology, Gaithersburg, MD, 2002.
