A series of substituted 2-(2-hydroxyphenylimino) phenolic ( salen) derivatives (1-4) have been synthesized and their structures of obtained compound were characterized by analytical, FT-IR, UV-Vis and 13C{ 1H}-NMR experimentally. The geometry structure optimization, frequencies (IR), NMR, electronic character, frontier molecular orbital (HOMO-LUMO) and first static hyperpolarizability ( β tot) studies of reported compounds were calculated using DFT with B3LYP/6-311G(d,p) level of theory. The calculated HOMO and LUMO energies showed that charge transfer occurs within the molecule and from the MEP, the molecular stability and bond strength have been explained. In addition to that influence of energy gap (?E gap) between the HOMO-LUMO orbitals on the first static hyperpolarizability (β tot), we calculated the ?E gap for all the salen compounds. These results reveals that the smaller HOMO-LUMO ?E gap is, larger the β tot is.
Schiff bases are important class of organic compounds have long attracted attention, owing to their remarkable biological and pharmacological properties, such as antibacterial, antiviral, antineoplastic and antimalarial activities. The functional applications of the azomethine group of Schiff base derivatives enable their use in numerous fields, they have
Ø nucleophilic imine group,
Ø an imine carbon that has both electrophilic and nucleophilic character,
Ø configurations isomerism from the presence of the C=N double bond.
These structural features of the Schiff base compounds give its physical and chemical properties [
In addition, Schiff base compounds high potential applications in non-linear optical (NLO), optical communication, optical signal processing and transmission, optical data acquisition and storage, optical computing, and especially op- tical limiting effects utilized in the protection of optical sensors and human eyes from high-intensity laser beams [
All the chemicals and solvents used were purified and dried by standard methods. FT-IR spectra were recorded as KBr pellets with a PerkinElmer FT-IR spectrometer in 4000 - 400 cm−1 range. Microanalyses were carried out with a Vario El AMX-400 elemental analyzer at STIC, Cochin University of Science and Technology, Kerala, India. Electronic spectra were recorded in CH3CN as solvent with an Ocean optics spectrophotometer USB 4000. NMR spectra were also recorded on Bruker AVANCE III 500 MHz (AV 500) spectrometer; chemical shifts are expressed in ppm (δ units) relative to TMS signal as internal reference in DMSO.d6.
The Schiff base compounds (Scheme 1) were prepared by the reported literature procedure [
To an ethanolic solution of salcylaldehyde (SA), o-hydroxyacetophenone (AA), o-vanillin (VA) and 2-hydroxy-1-naphthaldehyde (NA) (2 cm3, 20 mmol), with o-aminophenol (2 cm3, 20 mmol) were added with stirring. The mixture was then refluxed for 4 - 6 hours with the controlled conditions about 140˚C - 180˚C. On cooling the solution, a solid compound which separated out was filtered, dried and recrystallized from ethanol/DMSO (75:25). The purity of the ligand was checked by TLC. Yield, 85%, m.p. 143.6˚C - 245˚C.
All the salen compunds were stable at room temperature, non-hygroscopic and insoluble in water partially soluble in methanol, ethanol and soluble in CH2Cl2, CHCl3, DMF, DMSO, CH3CN, etc.
All the computational studies have been carried out with the GAUSSIAN 03W program package [
A fully relaxed potential energy scan was carried out against the dihedral angle C2-C1-C7-N1 (Scheme 2) at B3LYP/6-311G(d,p) level, the minimum energy conformations from the energy scan, a further geometry optimization was performed at the same level of theory. Vibrational frequencies of the optimized structures were computed using the same level of theory and thermodynamic
Scheme 1. Preparation of Schiff base compounds.
Scheme 2. Potential energy scan (PES) for salen compounds.
corrections [
Calculated electronic properties such as dipole moment, first static hyper-po- larizability HOMO and LUMO energies, MEP, energy gap, electronic affinity (EA), electronegativity (χ), hardness (η), softness (S), electrophilic index (w) and ionization potential (IP) have been studied for all the four compounds under consideration. The DFT-based reactivity descriptors were obtained from the Equations (1)-(4) [
Electronegativity (χ)
Hardness (η)
Softness (S)
The experimental polarizability is obtained as an average polarizability, given
by
presented.
The elemental analysis data (
The FT-IR spectroscopy is a powerful tool for the assignments of fundamental functional group determinations of organic compounds. In the title compounds frequencies of the functional groups viz., ν>C=N-, νph-OH, νph-C-O, νph-N=C- and ν-N=CH-/ν-N=C(CH3)- are of great importance in the infrared spectra. The infrared spectra of all the four Schiff bases (
S. No. | Schiff bases | Molecular formulae | Melting Point (˚C) | Elemental Analysis-Found (Calc.) | ||
---|---|---|---|---|---|---|
C | H | N | ||||
1. | SA | C13H11O2N | 150.1 - 199.3 | 73.01 (73.23) | 5.06 (5.20) | 6.51 (6.57) |
2. | AA | C14H13O2N | 143.6 - 164.0 | 73.83 (73.99) | 5.59 (5.77) | 6.20 (6.16) |
3. | VA | C14H13O3N | 197.9 - 221.7 | 68.78 (69.12) | 5.20 (5.39) | 5.65 (5.76) |
4. | NA | C17H13O2N | 239.3 - 245.0 | 77.46) (77.55) | 5.00 (4.98) | 5.18 (5.32) |
the four compounds has been assigned to phenolic C-O stretching and a band due to ph-N=C- of aminophenol group exhibited in the region 1274 - 1296 cm−1. Further the spectra of all the Schiff bases showed a weak band in the 3020-3069 cm−1 region due to -N=CH-/-N=C(CH3)- groups of NA, SA, VA and AA [
Theoretically all the fundamental vibrations were active in IR. The results showed that the DFT (B3LYP) method applied in this work leads to vibrational wavenumbers which are in good agreements with the experimental data. It is noteworthy that the very important role of vibrational frequencies salen compounds, based on experimental data as well as theoretical calculations, the computed vibrational frequencies in
The UV-Visible spectra of the salen compounds (
S. No. | Schiff bases | FT-IR (cm−1) | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Experimental | DFT (B3LYP/6-311G (d,p)) | ||||||||||
ν>C=N- | νph-OH | νph-C-O | νph-N=C- | ν-N=CH-/ ν-N=C(CH3)- | ν>C=N- | νph-OH | νph-C-O / νPh-OCH3- | νph-N=C< | ν-N=CH-/ ν-N=C(CH3)- | ||
1. | SA | 1671 | 3363 | 1367 | 1274 | 3020 | 1663 | 3832 | 1305 | 1199 | 3178 |
2. | AA | 1656 | 3399 | 1362 | 1276 | 3054 | 1685 | 3833 | 1321 | 1253 | 3178 |
3. | VA | 1692 | 3375 | 1371 | 1281 | 3029 | 1708 | 3831 | 1325 | 1209 | 2987 |
4. | NA | 1642 | 3308 | 1373 | 1296 | 3069 | 1652 | 3838 | 1389 | 1279 | 3183 |
methine group. The second band, lmax = 450 - 480 nm range is assigned to an intramolecular charge transfer (ICT transition) involving the salen compounds. This band observed in salicylaldimine compounds of salen derivatives is facilitated by the presence of intramolecular hydrogen bonding between the -OH group and the azomethine nitrogen [
The formations of Schiff base were conveniently monitored by peak ratios in the 1H-NMR spectra. 1H-NMR spectra of all the four compounds (
13C-NMR spectral data (
At the minimum energy conformations (
The optimized geometrical parameters are shown in
S. No. | Schiff bases | NMR Spectral data (Experimental) | |
---|---|---|---|
1H | 13C | ||
1. | SA | 6.9 - 7.6 m, aromatic protons, 9.0 s -CH=N-, 13.8 s ph-OH | 120.0 - 160.6 ppm phenyl Carbons, 18.9 ppm -CH=N carbon |
2. | AA | 6.6 - 7.3 m, aromatic protons, 9.0 s ph-OH, 3.5 s -CH3 protons | 160 - 180.6 ppm phenyl Carbons, 19.0 ppm -C-CH3 |
3. | VA | 6.8 - 7.4 m, aromatic protons, 9.0 s -CH=N-, 14.1 s ph-OH, 3.8 s -OCH3 protons | 146 - 178.0 ppm phenyl Carbons, 19.5 ppm -CH=N- and -OCH3 |
4. | NA | 6.8 - 8.4 m, aromatic protons, 9.5 s -CH=N-, 15.8 s ph-OH | 160-180.6 ppm phenyl and naphtyl Carbons, 19.6 ppm -CH=N-carbon |
degree of deviation from the planarity due to the torsion between A-ring and the plane of aminophenol system B-ring (Scheme 2).
In
Bond parameters | SA | |
---|---|---|
Neutral | Diradical | |
C1-C2 | 1..408 | 1.482 |
C2-C3 | 1.396 | 1.459 |
C3-C4 | 1.390 | 1.358 |
C4-C5 | 1.396 | 1.439 |
C5-C6 | 1.387 | 1.359 |
C6-C1 | 1.403 | 1.436 |
C2-O1 | 1.367 | 1.234 |
O1-H5 | 0.963 | - |
C1-C7 | 1.467 | 1.376 |
C7-H6 | 1.094 | 1.092 |
C7-N1 | 1.278 | 1.340 |
N1-C8 | 1.400 | 1.280 |
C8-C9 | 1.413 | 1.528 |
C9-C10 | 1.393 | 1.472 |
C10-C11 | 1.394 | 1.348 |
C11-C12 | 1.391 | 1,454 |
C12-C13 | 1.393 | 1.349 |
C13-C8 | 1.401 | 1.456 |
C9-O2 | 1.363 | 1.214 |
O2-H11 | 0.963 | - |
C6-C1-C2 | 118.35 | 120.47 |
C1-C2-C3 | 120.37 | 115.51 |
C2-C3-C4 | 120.11 | 121.15 |
C3-C4-C5 | 120.26 | 122.19 |
C4-C5-C6 | 119.51 | 120.00 |
C5-C6-C1 | 121.41 | 120.51 |
C1-C2-O1 | 117.89 | 121.23 |
C3-C2-O1 | 121.75 | 123.26 |
C2-O1-H5 | 109.23 | - |
C2-C1-C7 | 120.45 | 118.16 |
C6-C1-C7 | 121.20 | 121.35 |
C1-C7-H6 | 116.26 | 118.70 |
C1-C7-N1 | 121.68 | 125.96 |
H6-C7-N1 | 122.06 | 114.94 |
C7-N1-C8 | 120.11 | 132.23 |
N1-C8-C9 | 117.52 | 117.14 |
---|---|---|
N1-C8-C13 | 123.42 | 124.00 |
C8-C9-C10 | 120.00 | 115.86 |
C9-C10-C11 | 120.72 | 121.35 |
C10-C11-C12 | 119.88 | 121.87 |
C11-C12-C13 | 119.59 | 121.60 |
C12-C13-C8 | 121.54 | 120.45 |
C13-C8-C9 | 117.52 | 118.83 |
C8-C9-O2 | 122.46 | 121.49 |
C9-O2-H11 | 108.61 | - |
C10-C9-O2 | 122.46 | 122.46 |
Bond parameters | AA | |
---|---|---|
Neutral | Diradical | |
C1-C2 | 1.408 | 1.493 |
C2-C3 | 1.398 | 1.462 |
C3-C4 | 1.388 | 1.355 |
C4-C5 | 1.394 | 1.438 |
C5-C6 | 1.387 | 1.358 |
C6-C1 | 1.403 | 1.441 |
C2-O1 | 1.368 | 1.235 |
O1-H11 | 0.963 | - |
C1-C7 | 1.497 | 1.394 |
C7-N1 | 1.280 | 1.363 |
N1-C8 | 1.402 | 1.286 |
C8-C9 | 1.411 | 1.533 |
C9-C10 | 1.394 | 1.472 |
C10-C11 | 1.393 | 1.348 |
C11-C12 | 1.392 | 1.454 |
C12-C13 | 1.391 | 1.350 |
C13-C8 | 1.400 | 1.457 |
C9-O2 | 1.370 | 1.215 |
O2-H10 | 0.962 | - |
C7-C14 | 1.511 | 1.507 |
C6-C1-C2 | 117.41 | 118.94 |
C1-C2-C3 | 120.44 | 115.85 |
C2-C3-C4 | 120.69 | 121.97 |
C3-C4-C5 | 119.75 | 121.34 |
C4-C5-C6 | 119.39 | 120.33 |
---|---|---|
C5-C6-C1 | 122.28 | 121.53 |
C1-C2-O1 | 119.18 | 123.16 |
C3-C2-O1 | 120.33 | 120.99 |
C2-O1-H5 | 108.77 | - |
C2-C1-C7 | 123.89 | 120.90 |
C6-C1-C7 | 118.69 | 120.12 |
C1-C7-C14 | 119.60 | 124.05 |
C1-C7-N1 | 116.03 | 117.52 |
C14-C7-N1 | 124.28 | 118.29 |
C7-N1-C8 | 123.73 | 128.59 |
N1-C8-C9 | 122.39 | 115.98 |
N1-C8-C13 | 119.33 | 125.75 |
C8-C9-C10 | 120.27 | 116.30 |
C9-C10-C11 | 120.73 | 121.26 |
C10-C11-C12 | 119.61 | 121.69 |
C11-C12-C13 | 119.74 | 121.88 |
C12-C13-C8 | 121.65 | 120.59 |
C8-C9-O2 | 117.53 | 121.40 |
C10-C9-O2 | 122.19 | 122.30 |
C9-O2-H10 | 108.76 | - |
Bond parameters | VA | |
---|---|---|
Neutral | Diradical | |
C1-C2 | 1.406 | 1.478 |
C2-C3 | 1.414 | 1.476 |
C3-C4 | 1.389 | 1.367 |
C4-C5 | 1.401 | 1.428 |
C5-C6 | 1.379 | 1.363 |
C6-C1 | 1.411 | 1.427 |
C2-O1 | 1.362 | 1.236 |
O1-H4 | 0.962 | - |
C1-C7 | 1.477 | 1.384 |
C7-H5 | 1.097 | 1.090 |
C7-N1 | 1.280 | 1.339 |
N1-C8 | 1.411 | 1.293 |
C8-C9 | 1.411 | 1.516 |
C9-C10 | 1.394 | 1.461 |
C10-C11 | 1.390 | 1.353 |
---|---|---|
C11-C12 | 1.395 | 1.449 |
C12-C13 | 1.389 | 1.353 |
C13-C8 | 1.401 | 1.445 |
C9-O2 | 1.364 | 1.225 |
O2-H10 | 0.963 | - |
C3-O3 | 1.358 | 1.357 |
O3-C14 | 1.421 | 1.436 |
C6-C1-C2 | 119.07 | 121.04 |
C1-C2-C3 | 120.33 | 115.54 |
C2-C3-C4 | 119.27 | 119.62 |
C3-C4-C5 | 120.47 | 122.49 |
C4-C5-C6 | 120.51 | 120.81 |
C5-C6-C1 | 120.33 | 119.67 |
C1-C2-O1 | 123.97 | 121.19 |
C3-C2-O1 | 115.70 | 123.26 |
C2-O1-H4 | 110.09 | - |
C2-C1-C7 | 118.44 | 117.32 |
C6-C1-C7 | 122.24 | 121.63 |
C1-C7-H5 | 114.35 | 118.53 |
C1-C7-N1 | 132.26 | 124.11 |
H5-C7-N1 | 113.29 | 117.09 |
C7-N1-C8 | 125.67 | 127.71 |
N1-C8-C9 | 122.89 | 120.95 |
N1-C8-C13 | 118.12 | 119.77 |
C8-C9-C10 | 119.81 | 116.19 |
C9-C10-C11 | 120.69 | 120.84 |
C10-C11-C12 | 120.01 | 122.25 |
C11-C12-C13 | 119.54 | 121.05 |
C12-C13-C8 | 121.29 | 120.37 |
C8-C9-O2 | 122.97 | 120.36 |
C10-C9-O2 | 117.21 | 123.44 |
C9-O2-H10 | 109.36 | - |
C2-C3-O3 | 115.24 | 121.63 |
C4-C3-O3 | 125.49 | 118.13 |
C3-O3-C14 | 118.15 | 119.07 |
Bond parameters | VA | |
Neutral | Diradical | |
C1-C2 | 1.406 | 1.478 |
C2-C3 | 1.414 | 1.476 |
C3-C4 | 1.389 | 1.367 |
C4-C5 | 1.401 | 1.428 |
C5-C6 | 1.379 | 1.363 |
C6-C1 | 1.411 | 1.427 |
C2-O1 | 1.362 | 1.236 |
O1-H4 | 0.962 | - |
C1-C7 | 1.477 | 1.384 |
C7-H5 | 1.097 | 1.090 |
C7-N1 | 1.280 | 1.339 |
N1-C8 | 1.411 | 1.293 |
C8-C9 | 1.411 | 1.516 |
C9-C10 | 1.394 | 1.461 |
C10-C11 | 1.390 | 1.353 |
C11-C12 | 1.395 | 1.449 |
C12-C13 | 1.389 | 1.353 |
C13-C8 | 1.401 | 1.445 |
C9-O2 | 1.364 | 1.225 |
O2-H10 | 0.963 | - |
C3-O3 | 1.358 | 1.357 |
O3-C14 | 1.421 | 1.436 |
C6-C1-C2 | 119.07 | 121.04 |
C1-C2-C3 | 120.33 | 115.54 |
C2-C3-C4 | 119.27 | 119.62 |
C3-C4-C5 | 120.47 | 122.49 |
C4-C5-C6 | 120.51 | 120.81 |
C5-C6-C1 | 120.33 | 119.67 |
C1-C2-O1 | 123.97 | 121.19 |
C3-C2-O1 | 115.70 | 123.26 |
C2-O1-H4 | 110.09 | - |
C2-C1-C7 | 118.44 | 117.32 |
C6-C1-C7 | 122.24 | 121.63 |
C1-C7-H5 | 114.35 | 118.53 |
C1-C7-N1 | 132.26 | 124.11 |
H5-C7-N1 | 113.29 | 117.09 |
C7-N1-C8 | 125.67 | 127.71 |
N1-C8-C9 | 122.89 | 120.95 |
---|---|---|
N1-C8-C13 | 118.12 | 119.77 |
C8-C9-C10 | 119.81 | 116.19 |
C9-C10-C11 | 120.69 | 120.84 |
C10-C11-C12 | 120.01 | 122.25 |
C11-C12-C13 | 119.54 | 121.05 |
C12-C13-C8 | 121.29 | 120.37 |
C8-C9-O2 | 122.97 | 120.36 |
C10-C9-O2 | 117.21 | 123.44 |
C9-O2-H10 | 109.36 | - |
C2-C3-O3 | 115.24 | 121.63 |
C4-C3-O3 | 125.49 | 118.13 |
C3-O3-C14 | 118.15 | 119.07 |
Bond parameters | NA | |
---|---|---|
Neutral | Diradical | |
C1-C2 | 1.399 | 1.386 |
C2-C3 | 1.411 | 1.403 |
C3-C4 | 1.368 | 1.370 |
C4-C5 | 1.417 | 1.420 |
C5-C6 | 1.433 | 1.432 |
C6-C1 | 1.444 | 1.431 |
C2-O1 | 1.365 | 1.356 |
O1-H7 | 0.962 | - |
C6-C14 | 1.420 | 1.410 |
C14-C15 | 1.377 | 1.376 |
C15-C16 | 1.410 | 1.411 |
C16-C17 | 1.373 | 1.374 |
C17-C5 | 1.418 | 1.417 |
C1-C7 | 1.461 | 1.456 |
C7-H8 | 1.092 | 1.088 |
C7-N1 | 1.285 | 1.280 |
N1-C8 | 1.403 | 1.446 |
O1-C8 | - | 1.455 |
C8-C9 | 1.414 | 1.570 |
C9-C10 | 1.393 | 1.466 |
C10-C11 | 1.391 | 1.347 |
C11-C12 | 1.397 | 1.460 |
C12-C13 | 1.390 | 1.336 |
---|---|---|
C13-C8 | 1.401 | 1.511 |
C9-O2 | 1.354 | 1.212 |
O2-H13 | 0.973 | - |
C6-C1-C2 | 118.12 | 119.75 |
C1-C2-C3 | 121.92 | 121.66 |
C2-C3-C4 | 120.16 | 119.26 |
C3-C4-C5 | 120.96 | 121.66 |
C4-C5-C6 | 119.47 | 119.05 |
C5-C6-C1 | 119.35 | 118.60 |
C5-C6-C14 | 117.26 | 117.92 |
C6-C14-C15 | 121.22 | 121.05 |
C14-C15-C16 | 121.17 | 120.86 |
C15-C16-C17 | 119.29 | 119.62 |
C16-C17-C5 | 120.98 | 120.99 |
C17-C5-C6 | 120.06 | 119.57 |
C1-C2-O1 | 118.57 | 121.68 |
C3-C2-O1 | 119.50 | 116.60 |
C2-O1-H7 | 109.29 | - |
C2-C1-C7 | 116.16 | 115.59 |
C6-C1-C7 | 125.73 | 124.62 |
C1-C7-H8 | 114.08 | 118.97 |
C1-C7-N1 | 125.64 | 125.25 |
H8-C7-N1 | 120.25 | 115.76 |
C7-N1-C8 | 121.27 | 118.22 |
C2-O1-C8 | - | 118.95 |
O1-C8-N1 | - | 116.49 |
O1-C8-C9 | - | 105.73 |
N1-C8-C9 | 114.43 | 107.54 |
N1-C8-C13 | 126.56 | 107.49 |
C8-C9-C10 | 120.37 | 117.39 |
C9-C10-C11 | 119.69 | 120.89 |
C10-C11-C12 | 120.61 | 122.62 |
C11-C12-C13 | 119.82 | 121.49 |
C12-C13-C8 | 120.56 | 121.90 |
C13-C8-C9 | 118.93 | 114.23 |
C8-C9-O2 | 119.75 | 119.08 |
C10-C9-O2 | 119.88 | 123.53 |
C9-O2-H13 | 105.52 | - |
S.No. | Salen | Energy (Hartree) | Dipole moment | Electron Affinity | Ionization Potential | Hardness | Electronegativity |
---|---|---|---|---|---|---|---|
1. | SA | −707.3695 | 1.7675 | 802.9496 | 798.4321 | −2.2586 | 800.6909 |
2. | AA | −746.6926 | 2.8269 | 1273.5922 | 1269.0747 | −2.2586 | 1271.3335 |
3. | VA | −821.6521 | 3.1964 | 235.31669 | 235.3167 | 0.05 x e−3 | 235.3167 |
4. | NA | −861.0521 | 4.8823 | 1038.2778 | 1033.7603 | −2.2588 | 1036.0191 |
Hardness,
Bond polarity is one of the factors that determine the physicochemical property of molecules. The calculated values of the total dipole moments, which signifies the relatively polarized nature of the systems and they are soluble in polar solvents like CH3CN, DMSO, CHCl3, etc.
The computed NMR chemical shifts for SA, AA, VA and NA at the DFT level of theory are in acceptable agreement with the experimental data. Differences between the calculated and measured values may be a result of solvent interactions.
The 13C-NMR chemical shifts of selected carbons were calculated on the optimized structures of SA, AA, VA and NA using GIAO/DFT method with B3LYP/6-311(d,p) basis set for all atoms. Calculated and measured 13C chemical shifts of selected atoms are numbered in
The HOMO-LUMO energy (
The spin density is often considered to be a more realistic parameter which provides a better representation of the reactivity [
Electronic Parameter/molecule | SA | AA | VA | NA |
---|---|---|---|---|
ET [Hartree] | −707.3695 | −746.6926 | −821.6521 | −861.0521 |
Dipole moment | 1.7675 | 2.8269 | 3.1964 | 4.8823 |
EHOMO [Hartree] | −0.2070 | −0.2040 | −0.2160 | −0.2040 |
ELUMO [Hartree] | −0.0590 | −0.0440 | −0.0750 | −0.0790 |
∆Egap [eV] | 3.5506 | 4.3538 | 3.8368 | 3.4014 |
Softness [eV] | 0.2214 | 0.2214 | − | 0.2214 |
Schiff bases | β | Hyperpolarizibility |
---|---|---|
SA | βXXX | −21.460 |
βXYY | −4.021 | |
βXZZ | 0.293 | |
βYYY | −0.858 | |
βYXX | −0.568 | |
βYZZ | −0.303 | |
βZZZ | 11.638 | |
βZXX | 25.110 | |
βZYY | 6.936 | |
βXYZ | −29.084 | |
βTOT | 4.359 | |
AA | βXXX | 42.610 |
βXYY | 10.466 | |
βXZZ | −5.471 | |
βYYY | 33.445 | |
βYXX | 44.704 | |
βYZZ | 14.410 | |
βZZZ | −4.000 | |
βZXX | −13.031 | |
βZYY | −7.754 | |
βXYZ | 23.881 | |
βTOT | 9.244 |
VA | βXXX | 101.759 |
---|---|---|
βXYY | 1.365 | |
βXZZ | 1.976 | |
βYYY | −38.170 | |
βYXX | −62.018 | |
βYZZ | −13.843 | |
βZZZ | 0.373 | |
βZXX | 5.855 | |
βZYY | 8.194 | |
βXYZ | 30.912 | |
βTOT | 13.455 | |
NA | βXXX | 28.769 |
βXYY | 51.498 | |
βXZZ | −5.941 | |
βYYY | 54.654 | |
βYXX | 24.052 | |
βYZZ | 8.908 | |
βZZZ | 7.978 | |
βZXX | −0.190 | |
βZYY | −1.286 | |
βXYZ | 13.656 | |
βTOT | 10.003 |
and B. Comparing all the radicals, we find that the radicals have almost the same spin density distribution with each other, indicating the presence of additional hydroxyl or o,o-dihydroxyl group on A and B-ring has almost no influence on the spin density distribution [
Electrostatic potential surfaces are mainly used to study the reactive species of electrophilic or nucleophilic attacks/substitution in the chemical reactions, biological process, catalysis and also molecular modeling. Electrostatic potential mapped surface displays the molecular size, shape and potential values. In this study, 3 dimensional surfaces of mapped onto the constant electron density surface is as shown in
The NLO response calculation was performed on the optimized geometry using the same level of theory. The first static hyperpolarizability is a third rank tensor that can be described by a 3 × 3 × 3 matrix. The 27 components of the 3D matrix
can be reduced to 10 components due to the Kleinman symmetry [
The complete equation for calculating the magnitude of the total first statichyperpolarizability from Gaussian 03W output is given as Equation (6):
Since these β values of the first static hyperpolarizability (β) tensors of the output file of Gaussian 03W are reported in atomic units (a.u.), the calculated values were converted into electrostatic units (1 a.u. = 8.6393 × 10−33 esu). The first static hyperpolarizability (β) values of these Schiff bases were calculated under static electronic field by the DFT (B3LYP/(6-311G(d,p)) method. From
Schiff bases (1-4) have been successfully synthesized and characterized by elemental analysis, FT-IR, UV-Vis, NMR spectroscopy and cyclic voltammetry. The evaluation of the quantum mechanical studies reveal significant activity in structure optimization, PES, vibrational study, NMR Chemical shifts, spin density, hardness, electronegativity, dipole moment, EHOMO/ELUMO, ∆Egap and Softness which provide the evidence for a very strong positive correlation between experimental and theoretical predictions. These compounds also have towards considerable antioxidant activity along with potential to prevent DNA oxidative damage by free radicals.
Comparison between the four considered molecules indicates compound VA that requires the lowest energy for both H atom and electron transfer mechanisms. This theoretical approach confirms the important role of A and B ring in exhibiting antioxidant properties. Inspection of deprotonation processes of dihydroxyl groups have shown that, π electron delocalization of phenyl ring A and B (evidenced from UV-Vis study) plays a major role in the stabilization of products and thus in the lowering of the associated energies. The variables related to the chemical potential allow classifying salen type of Schiff base compounds that has the tendency to give electrons more than to attract them, which demonstrates biological importance.
In addition to that in order to understand the relationship between the βtot values and the substitution groups of salen compounds, the frontier orbital compositions have been analyzed and the energy gaps between the HOMO and LUMO orbitals were also calculated. The compound VA with electron-donating group (-OCH3) will produce the larger βtot value (13.455 a.u) than lower βtot (10.003, 9.244, 4.359 a.u) for the compounds NA, AA, SA respectively. The energy gaps between the HOMO and LUMO orbitals show that the lower the HOMO-LUMO energy gap, larger the first static hyperpolarizability (βtot).
The findings of this work sustenance the view that some of these synthesized compounds are promising sources of potential drugs that may be efficient as preventive agent(s) in some diseases.
Nadhiya, V.D. and Kumaresan, R. (2017) Combined Experimental and Computational Investigation of 2-(2-Hydroxyphenylimino) Phenolic Deri- vatives: Synthesis, Molecular Structure and NLO Studies. International Journal of Organic Chemistry, 7, 185-217. https://doi.org/10.4236/ijoc.2017.72015