TD-DFT calculations, electronic structure, natural bond orbital analysis, nonlinear optical properties electronic absorption spectra and antimicrobial activity application of new bis-spiropipridinon/pyrazole derivatives European Journal of Chemistry 9 (4) (2018) 287-302 European Journal of Chemistry View Journal Online View Article Online TD-DFT calculations, electronic structure, natural bond orbital analysis, nonlinear optical properties electronic absorption spectra and antimicrobial activity application of new bis-spiropipridinon/pyrazole derivatives Shimaa Abdel Halim Department of Chemistry, Faculty of Education, Ain Shams University, Roxy 11711, Cairo, Egypt shimaaquantum@ymail.com (S.A.H.) * Corresponding author at: Department of Chemistry, Faculty of Education, Ain Shams University, Roxy 11711, Cairo, Egypt. Tel: +20.10.90306455 Fax: +20.11575.22581243 e-mail: shimaaquantum@ymail.com (S.A. Halim). 10.5155/eurjchem.9.4.287-302.1706 Received: 06 April 2018 Received in revised form: 09 June 2018 Accepted: 11 June 2018 Published online: 31 December 2018 Printed: 31 December 2018 A new bis-spiropipridinon/pyrazole compound and some of its derivatives are characterized in terms of several theoretical parameters such as density of states (DOS), molecular electrostatic potentials (MEPs), non-linear optical (NLO) properties and electrophilicity. The electronic structure and nonlinear optical properties of the studied compounds 1-5 are investigated theoretically at the DFT-B3LYP/6-311G(d,p) level of theory. The effect of substituents of different strengths on the geometry and energetic are analyzed and discussed. The static dipole moment (µ), polarizability (α), anisotropy polarizability (Δα), and first order hyperpolarizability (βtot), are parameters for NLO of the studied compounds have been calculated at the same level of theory and compared with the prototype para- nitro-aniline (PNA). The electronic absorption spectra of the studied compounds are recorded in the UV-VIS region, in both ethanol and dioxane solvents. The theoretical spectra computed at a new hybrid exchange-correlation functional using the Coulomb-attenuating method (CAM-B3LYP) at the 6-311G(d,p) bases set in gas phase and with the polarizable continuum model (PCM) in dioxane and ethanol indicate a good agreement with the observed spectra. The antimicrobial activity for studied compounds was investigated. The antimicrobial activity results revealed that compound 4 has a good potency against Gram positive bacteria (E. coli) and Gram negative bacteria (P. vulgaris) in comparison with doxymycin standard. The structure activity relationship SAR has been studied for the studied compounds by DFT calculations, moreover, confirmed practical antimicrobial activity results. Pyrazole Bis-spiropipridino TD-DFT calculations Antimicrobial activity NLO and NBO analysis Solvent and substituent effect Cite this: Eur. J. Chem. 2018, 9(4), 287-302 Journal website: www.eurjchem.com 1. Introduction Spiro heterocycles compounds having highly pronounced biological properties [1,2]. Spirooxindole ring systems were found in a number of alkaloids, such as horsifiline, spirotry- prostain, and (+) elacomine [3], and as inhibitors of the human NKI receptor [4], also; it used in biological applications as antimicrobial and antitumor agents. Furthermore, bis-hetero- cyclic compounds have been reported to possess interesting biological properties, [5-7] including antihypertensive, [8] antiallergenic, [9] and antitumor activities, [10,11]. Whereas, spirooxindole rings containing the pyrrolidine and pyrrolizine ring system were found in various natural products as fundamental nuclei and were well recognized for exhibiting a wide range of pharmacological and biochemical behaviors [12- 14]. Therefore, the newly synthesized bioactive compounds bis-spiropipridinon/pyrazoleare useful compounds in creating distinct chemical libraries of drug-like molecules for biological screening [15,16]. The 1,3-cycloaddition methodology is one of the simplest tools for the construction of five-membered heterocycles [17]. Pyrazole derivatives have wide range of biological properties particularly being antifungal, antituber- cular, antibacterial, antiviral, anticancer and antioxidant, [18- 22]. Pyrazole un-substituted in 1-position show NH acidity. The pKa value of pyrazole is 14.21 and equal to that of imi- dazole [23]. There is no systematic study of the electronic structure, substituent effect and nonlinear properties. The NLO properties studied for understanding the biological activity of these molecules. Non-linear optical properties are the ability of any compound to convert light [with intense electric field (LASER)] of longer wavelength into light of shorter wave- length. One of the non-linear optical phenomena is the second harmonic generation (SHG) where intense light of longer wavelength is converted to half of the incident value, upon absorption by the non-linear optical material as shown in Figure 1. Several investigations [11,17,24-28] have been published that dealt with the spectral characterization (IR, NMR, UV and X-ray) of bis-spiropipridinon/pyrazole derivatives. The electronic structure and spectra of molecules usually manifests itself in the electronic absorption and emission spectra. This manifestation enables the detailed understanding of the forces that govern the electronic structure of the proposed structure of molecules, yet. ABSTRACT RESEARCH ARTICLE KEYWORDS European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2018 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. http://dx.doi.org/10.5155/eurjchem.9.4.287-302.1706 http://dx.doi.org/10.5155/eurjchem.9.4.287-302.1706 https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.9.4.287-302.1706&domain=pdf&date_stamp=2018-12-31 http://www.eurjchem.com/ http://dx.doi.org/10.5155/eurjchem.9.4.287-302.1706 mailto:shimaaquantum@ymail.com mailto:shimaaquantum@ymail.com http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.9.4.287-302.1706&domain=pdf&date_stamp=2018-12-31� 288 Shimaa Abdel Halim / European Journal of Chemistry 9 (4) (2018) 287-302 → 1064 nm → → 532 nm Figure 1. The second harmonic generation. N N O N NN HH X X X Compounds H 1 OCH3 2 F 3 NO2 4 Cl 5 Figure 2. Schemes of the proposed structure of studied compounds 1-5. There is no systematic study of substituent and solvent effects on the observed spectra of bis-spiropipridinon/ pyrazole. Such a study is critically important in understanding their electronic structure, which may correlate with their biological activity. The newly synthesized bis-spiropipridinon /pyrazole deri- vatives 1-5 are expected to have biological potential which needs to be explored by investigating their electronic structure and spectra experimentally and theoretically. The UV spectra and NBO analysis have been used to explain charge transfer within these molecules. The dependence of the electronic transitions of these molecules on the polarity of the solvent can be inferred from solvent-induced changes of such transitions, which is known as solvatochromism polarizable continuum model. In the literature, there is no systematic study of the electronic structure, substituent effect and bonding characteristics of the studied compounds. Therefore, our contribution here is to shed more light on the geometrical parameters (bond lengths, bond angles and dihedral angles), ground state properties of the bis-spiropipridinon/pyrazole derivatives, energy gaps (highest occupied molecular orbital [HOMO]-lowest unoccupied molecular orbital [LUMO]), Natural charges, density of states, effect of substituents of different electron donating-withdrawing power in the two aryl moieties, and electrostatic potential are calculated using B3LYP/6-311G(d,p). The electronic dipole moment (µ), and first order hyperpolarizibility (β) values of the studied compounds have been computed to study the NLO properties to identify and characterize the forces that govern the structure-activity and the optical properties of the studied compounds. Finally, global reactivity descriptors including electronegativity (X), hardness (η), softness (S), and electrophilicity (ω) of the studied compounds were calculated and analyzed, while molecular electrostatic potential of molecules were explored as well. The present work attempts to provide a detailed experimental (UV) using TD-DFT and theoretical electronic structure bis-spiropipridinon/pyrazole derivatives using CAM- B3LYP/6-311G(d,p). The biological activity of the studied compounds 2-5 was tested against Gram positive, Gram negative and Fungi. The origin of each absorption band is identified and the contributing configurations and MOs are characterized. Natural bond orbital analysis is carried out to identify the extent of delocalization and the charge transfer of the electron density in the studied molecular systems and extent of conjugative interaction between different subsys- tems of the studied compounds. The effect of solvent polarity on the observed spectra and hence, predicting the relative stabilities, extent of charge transfers character and assignment of the observed electronic transitions are analyzed. The effect substituent’s of different electron donating group (X = OCH3) and electron withdrawing groups (X = F, NO2 and Cl) on the electronic spectra of the studied compounds are discussed and analyzed. 2. Experimental 2.1. Synthesis The compounds studied in this work are shown in Figure 2. The synthesis and characterization details of the compounds 1-5 are presents in literature [17]. 2.2. Solvents Polar (ethanol) and non-polar (dioxane) solvents were obtained from Merck, AR-grade, and were used without further purification. 2.3. Apparatus The electronic absorption spectra were measured using a Perkin Elmer lambda 4B spectrophotometer using 1.0 cm fused quartz cells. The machine records linearly the percent of transmittance over the range 200-900 nm. 2.4. Antimicrobial study Biological activities of synthesized bis-spiropipridinon/ pyrazole derivatives compounds were studied for antibacterial and antifungal properties against different types of bacteria; Second-order non-linear crystal 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.287-302.1706 Shimaa Abdel Halim / European Journal of Chemistry 9 (4) (2018) 287-302 289 Gram positive S. aureus (ATCC6538), and E. coli (ATCC10231) and Gram-negative K. pneumonia (ATCC 28737) and P. vulgaris (ATCC 547732), and C. albicans (ATCC 253674) for fungus. 2.5. Computational method Calculations have been performed using Khon-Sham᾿s DFT method subjected to the gradient-corrected hybrid density functional B3LYP method [29,30]. This function is a combi- nation of the Becke᾿s three parameters non-local exchange potential with the non-local correlation functional of Lee et al. [30]. For each structure, a full geometry optimization was performed using this function [30] and the 6-311G(p,d) basis set [31] as implemented by Gaussian 09 package [32]. All geometries were visualized either using GaussView 5.0.9 [33] or ChemCraft 1.6 [34] software packages. The densities of states were calculated by using the GaussSum 2.2.5 program [35]. No symmetry constrains were applied during the geometry optimization. The electronic transition properties which include the maximum excitation wavelength (λmax) and relative intensities (oscillator strengths, f), were obtained by the time dependant density functional theory (TD-DFT) [36] using “A new hybrid exchange-corre- lation functional using the Coulomb-attenuating method (CAM-B3LYP),” at the 6-311G(d,p) bases set [37]. The popula- tion analysis has also been performed by the natural bond orbital method [38] at B3LYP/6-311G(d,p) level of theory using natural bond orbital under Gaussian 09 program package. The second-order Fock matrix was used to evaluate the donor-acceptor interactions in the NBO basis [39]. For each donor (i) and acceptor (j), the stabilization energy E2 associated with the delocalization I → j is estimated as 𝐸𝐸2 = Δ𝐸𝐸𝑖𝑖j = 𝑞𝑞𝑖𝑖 (𝐹𝐹 (𝑖𝑖j) 2 /𝜀𝜀𝑗𝑗–𝜀𝜀𝑖𝑖) (1) where 𝑞𝑞𝑖𝑖 is the donor orbital occupancy, 𝜀𝜀𝑖𝑖 and 𝜀𝜀𝑗𝑗are diagonal elements and (𝑖𝑖j)is the off-diagonal NBO Fock matrix element. Also, the total static dipole moment (𝜇𝜇), ⟨Δ𝛼𝛼⟩, ⟨𝛽𝛽⟩, values were calculated by using the following equations [40-42]; 𝜇𝜇= (𝜇𝜇2𝑥𝑥+ 𝜇𝜇2𝑦𝑦+ 𝜇𝜇2𝑧𝑧) ½ (2) ⟨𝛼𝛼⟩ =1/3(𝛼𝛼𝑥𝑥𝑥𝑥+ 𝛼𝛼𝑦𝑦𝑦𝑦+ 𝛼𝛼𝑧𝑧𝑧𝑧) (3) Δ𝛼𝛼=((𝛼𝛼𝑥𝑥𝑥𝑥−𝛼𝛼𝑦𝑦𝑦𝑦) 2+ (𝛼𝛼𝑦𝑦𝑦𝑦−𝛼𝛼𝑧𝑧𝑧𝑧) 2+ (𝛼𝛼𝑧𝑧𝑧𝑧−𝛼𝛼𝑥𝑥𝑥𝑥) 2/2)1/2 (4) ⟨𝛽𝛽⟩ = (𝛽𝛽2𝑥𝑥+ 𝛽𝛽2𝑦𝑦+ 𝛽𝛽2𝑧𝑧)1/2 (5) where, 𝛽𝛽𝑥𝑥= 𝛽𝛽𝑥𝑥𝑥𝑥𝑥𝑥+ 𝛽𝛽𝑥𝑥𝑦𝑦𝑦𝑦+ 𝛽𝛽𝑥𝑥𝑧𝑧𝑧𝑧, 𝛽𝛽𝑦𝑦= 𝛽𝛽𝑦𝑦𝑦𝑦𝑦𝑦+ 𝛽𝛽𝑥𝑥𝑥𝑥𝑦𝑦+ 𝛽𝛽𝑦𝑦𝑧𝑧𝑧𝑧, 𝛽𝛽𝑧𝑧= 𝛽𝛽𝑧𝑧𝑧𝑧𝑧𝑧+ 𝛽𝛽𝑥𝑥𝑥𝑥𝑧𝑧+ 𝛽𝛽𝑦𝑦𝑦𝑦𝑧𝑧. By using HOMO and LUMO energy values, electro- negativity, and chemical hardness can be calculated as follows: 𝜒𝜒 = (𝐼𝐼+ 𝐴𝐴)/2 (electronegativity), 𝜂𝜂 = (𝐼𝐼−𝐴𝐴)/2 (chemical hardness), 𝑆𝑆 = 1/2𝜂𝜂 (global softness), ω = μ2/2𝜂𝜂 (electro- philicity) where 𝐼𝐼 and 𝐴𝐴 are ionization potential and electron affinity, and 𝐼𝐼 = −𝐸𝐸HOMO and 𝐴𝐴=−𝐸𝐸LUMO, respectively [43,44]. The conversion factors for 𝛼𝛼, 𝛽𝛽and HOMO and LUMO energies in atomic and cgs units: 1 atomic unit (a.u.) = 0.1482 ×10−24 electrostatic unit (esu) for polarizability; 1 a.u. = 8.6393×10−33 esu for first hyperpolarizability ⟨𝛽𝛽⟩; 1 a.u. = 27.2116 eV (electron volt) for HOMO and LUMO energies. 3. Results and discussion 3.1. Geometric parameters The optimized structure of the parent molecule 1 and the effect of substituent of different electron donating/withdra- wing power at C53-Ph-X and C92-Ph-X on the geometrical parameters (bond lengths, bond angles and dihedral angles) of the studied compounds 2-5, is listed in Tables 1 and 2. The computed bond lengths and bond angles are compared with the available experimental data [45-47]. Figure 3 presented the global energy minimum obtained by the DFT- B3LYP/6-311G(d,p) and the vector of the dipole moment. The calculated bond lengths C1-N4 and N4-C3 of the bis-spiro- pipridinon/pyrazole are underestimated than the experi- mental values by 1%, whereas, the computed C3-C16 and C2- C16 bond lengths are overestimated than the experimental values by 1%. At the same time, the computed C17-N18, C58- N56 and C54-N57 bond lengths are overestimated than the experi-mental values by 1%, while C16-N19 and C92-C42 is under-estimated than the experimental values by 1%. The small difference between calculated and observed bond lengths indicates the power of the method used in calculation. No significant change in the calculated bond angles of the studied compounds 1-5 on comparing with the experimental values. The small difference between calculated and observed angles may be attributed to that the calculations were carried out in gas phase and observed in solid state. All the studied compounds 1-5 are non-planner as reflected from their dihedral angles. In the parent compound 1, the C53-Ph and C92-Ph moieties are out of the molecular plane of the bis- spiropipridinon/pyrazole by dihedral angles equal 91.67° for C1-C58-C53-C81 and 19.79° for C3-C16-C92-C42, respectively. Upon substitution no significant change in the dihedral angles of the C53-Ph-X while the dihedral angles of C92-Ph-X moiety decreased and become nearly planner (c.f. Tables 1 and 2). 3.2. Natural charge analysis Natural charge analysis is performed on the electronic structures clearly describes the distribution of electrons in various sub shells of their atomic orbital’s [48]. Table 2 show that; the natural charges and natural populations for the studied compounds 1-5 calculated at B3LYP/6-311G(d,p) level of theory. For the parent compound 1, the most electro- negative charges are accumulated on N4, O7, C9, N18, N19, N56 and N57. According to an electrostatic point of view of the molecule, these electronegative atoms have a tendency to donate electrons. Whereas, the most electropositive atoms such as; C2 and C17 have a tendency to accept electrons in Table 2. The corresponding Mullikan’s plot with B3LYP/6- 311G(d,p) method are shown in Figure 4. It is noted that from Figure 4, the strong negative and positive partial charges on the skeletal atoms of the parent (especially C2, N4, O7, C9, C17, N18, N19, N56 and N57) increases with increasing Hammett constant of substituent groups. These distributions of partial charges on the skeletal atoms show that the electrostatic repulsion or attraction between atoms can give a significant contribution to the intra- and intermolecular interaction. 3.3. Global reactivity descriptors They include HOMO, LUMO, energy gap (Eg), chemical hardness (η), electronegativity (X), chemical potential (V), electrophilicity (ω), electron affinity (A), ionization potential (I) and global softness (S) which are calculated at B3LYP/6- 311G(d,p). The studied compounds were calculated the frontier molecular orbital (FMO) energies at the same level of theory. The electron donating ability characterized by HOMO energy, while LUMO energy characterizes the electron withdrawing ability. Energy gap (Eg) between HOMO and LUMO characterizes the molecular chemical stability, which is a critical parameter in determining molecular electrical trans- port properties because it is a measure of electron conduc- tivity. The results in Figures 5, 6 and Table 3 indicate that the smaller the energy gap the easier the charge transfer and the polarization occurs within the molecule. 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.287-302.1706 290 Shimaa Abdel Halim / European Journal of Chemistry 9 (4) (2018) 287-302 Table 1. Selected experimental and theoretical bond lengths and bond angles for the studied compounds 1-5 computed at the B3LYP/6-311G(d,p) level of theory. Parameters Experimental [45-47] Compound 1 2 3 4 5 Bond lengths (Å) C1-N4 1.361 1.350 1.378 1.351 1.342 1.351 N4-C3 1.343 1.332 1.303 1.331 1.333 1.331 C3-C16 1.471 1.486 1.475 1.486 1.479 1.485 C16-C2 1.565 1.566 1.572 1.567 1.575 1.566 C2-C58 1.565 1.570 1.568 1.569 1.564 1.570 C2-O7 1.212 1.202 1.192 1.201 1.199 1.202 N4-C8 1.505 1.491 1.490 1.491 1.502 1.491 C8-C9 1.471 1.525 1.526 1.525 1.524 1.525 C16-N19 1.505 1.476 1.472 1.474 1.466 1.475 N18-N19 1.385 1.359 1.349 1.361 1.367 1.359 N18-C17 1.275 1.287 1.281 1.287 1.289 1.287 C92-C42 1.565 1.520 1.519 1.520 1.523 1.519 C17-C31 1.471 1.466 1.467 1.466 1.456 1.466 N19-C20 1.395 1.404 1.389 1.406 1.412 1.405 C58-N56 1.505 1.524 1.525 1.524 1.485 1.525 N56-N57 1.385 1.361 1.361 1.361 1.360 1.362 N57-C54 1.275 1.286 1.292 1.286 1.297 1.286 C53-C54 1.515 1.526 1.525 1.526 1.534 1.527 C53-C81 1.515 1.513 1.509 1.512 1.512 1.512 C54-C70 1.471 1.469 1.472 1.468 1.463 1.468 N56-C59 1.395 1.417 1.416 1.417 1.427 1.417 Bond angles (°) 5 > 1 > 3 > 2. The insignificant differences in Eg of all the studied compounds except 4 is due to the non-planarity of the two Ph-X and Ph-X with the bis- spiropipridinon/pyrazole (c.f. Table 3). Using HOMO and LUMO energies, ionization potential and electron affinity can be expressed as I~ -EHOMO, A~ -ELUMO at the B3LYP/6-311G (d,p) as shown in Table 3. The variation of electronegativity (X) values is supported by electrostatic potential, for any two molecules, where electron will be partially transferred from one of low X to that of high X. The results show that the order of decreasing X is 2 ˂ 1 ˂ 3 ˂ 5 ˂ 4. The chemical hardness (η) = (I-A)/2, electronegativity (X) = (I+A)/2, chemical potential (V) = -(I+A)/2, electrophilicity (ω) = μ2/ 2𝜂𝜂 and global softness (S) = 1/2η values are calculated and presented in Table 3. The results of small η values for the studied compounds reflect the ability of charge transfer inside the molecule. Therefore, the order is 4 > 5 > 1 > 3 > 2. There is a linear relationship between η and Eg as shown in Table 3. Considering η values, the higher the η values, the harder is the molecule and vice versa. 3.4. Nonlinear optical analysis So far, no experimental or theoretical investigations were found addressing NLO for these classes of molecules; therefore, this triggered our interest to undertake this study. The relationship between molecular structure and NLO, the polarizibilities and hyperpolarizibilities of the studied compounds 1-5 are calculated using DFT/B3LYP/6-311G(d,p) investigated by NLO due to its importance in providing key functions of frequency shifting, optical modulation, switching , laser, fiber, optical materials logic and optical memory for the emerging technologies in areas such as telecommunications, signal processing and optical inter connections [49]. In order to investigate the relationship between molecular structure and NLO, the polarizibilities and hyperpolarizibilities of the studied compounds 1-5 are calculated using DFT/B3LYP/6- 311G(d,p). Total static dipole moment (µ), the mean polarizability (α), the anisotropy of the polarizability ∆α, the mean first-order hyperpolarizibility (β) of the studied compounds 1-5 are listed in Table 4. 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.287-302.1706 Shimaa Abdel Halim / European Journal of Chemistry 9 (4) (2018) 287-302 291 Table 2. Dihedral angles and natural charge for the studied compounds 1-5 computed at the B3LYP/6-311G(d,p) level of theory. Parameters Compounds 1 2 3 4 5 Dihedral angles (°) ×10−24 esu a 22.0 43.90 46.75 46.28 49.96 48.91 Δα×10−24 esu 47.74 40.52 49.17 45.98 49.97 βxxx, a.u. -44.0373 -240.173 -3.1945 130.646 49.1193 βxxy, a.u. -28.3853 170.091 -29.1253 29.0326 21.8505 βxyy, a.u. -46.8852 -126.586 22.3072 101.547 47.3975 βyyy, a.u. 95.6148 42.3811 32.3884 -67.9147 -65.1408 βxxz, a.u. 15.8096 61.9425 -103.091 139.9476 111.564 βxyz, a.u. -14.9060 -15.2491 -7.8688 28.1463 6.9155 βyyz, a.u. -65.0225 -45.3843 34.2251 -28.6670 -27.3395 βxzz, a.u. -46.4699 33.8242 -19.2609 -18.1681 -23.7194 βyzz, a.u. -20.1235 -32.3737 -2.9841 -5.2738 -4.9764 βzzz, a.u. 65.7684 -40.0246 52.2643 -31.2953 -33.3131 ˂β˃×10−30 esu a 15.5 38.38 22.60 23.19 21.10 17.49 a PNA results are taken from references [50-52]. In ethanol, this same band appears at 322.8 nm, (State II), as shown in Table S1. The third (π-π*)1 state theoretically at 315.8 nm in dioxane, (State III), which involves the orbital’s φ181 and φ184, in the transition. The gas phase calculation gives a wavelength at 318.2 nm (State III), which also involves orbital’s φ182 and φ184. In ethanol, this same band appears at 317.0 nm, (State III), as shown in Table S1. The fourth (π-π*)1 state theoretically at 303.1 nm (State IV) in dioxane. The gas phase calculations gives a wavelength at 305.4 nm (State IV), which also involves orbital’s φ181 and φ184. Figure 6. Energy of HOMO, LUMO and energy gap of the studied compounds 1-5 at B3LYP/6-311G(d,p) level of theory. In ethanol, this same band appears at 305.3 nm, as shown in Table S1, which involves the orbital’s φ181 and φ184 in the transition. The five (π-π*)1 state theoretically at 290.7 nm (State V) in both dioxane, gas phase and ethanol, which also involves orbital’s φ182 and φ186, as shown in Table S1. The six (π-π*)1 state theoretically at 281.1 nm (State VI) in dioxane. The gas phase calculations give a wavelength at 283.1 nm (state VI), which also involves orbital’s φ180 and φ185. In ethanol, this same band appears at 282.9 nm, as shown in Table S1. The nature of the electronic transition can be inferred from examining the electron density contours of molecular orbitals. The seven orbital’s φ180, φ181, φ182, φ183, φ184, φ185, and φ186, respectively, involved in the theoretical transitions of compound 1, are shown in Figure S1, where the first , second and third bands involving φ180 and φ183 & φ182 and φ185 & φ182 and φ184 show a delocalization of electron density and a Charge Transfer CT character, while the fourth, five and six bands involving φ181 and φ184 & φ182 and φ186 & φ180 and φ185 shows a Charge Transfer CT character. The NBO analysis of the studied compounds 1-5 provides an efficient method for studying intra-and intermolecular bonding and also provides a convenient basis for investigating charge transfer or conjugative interactions in molecular systems. Table 5 presents the second order perturbation energies (often called as the stabilization energies or interaction energies) of most interacting NBOs of compounds 1-5 and the most important interaction between filled (donor) Lewis type NBOs and empty (acceptor) non-Lewis NBOs. The charge density maps of HOMO and LUMO for compounds 1-5 are presented in Figure 7. The results of NBO analysis of compound 1 tabulated in Table 5 indicate that there is a strong hyper conjugative interactions LP(1) C3 → π*C1-N4, π*C17-N18 → π*C31-C32, LP(1) N19 → π*C20-C22, LP(1) N56 → π*C54-N57, and LP(2) O7 → σ*C2-C16, for compound 1 is 255.11, 142.50, 33.66, 27.01 and 23.13 kcal/mol, respectively. The C–N π orbital in two pyrazole and bis-spiropipridinon groups interacts equally well with bis-spiropipridinon/pyrazole ring. In fact, its interaction with the pyrazole ring is greater. Furthermore, the lone pair orbital of the nitrogen atom enjoys hyperconjugation with the C2–O7, C1–C57 and C3–C16 π* orbital. It is surprising to notice a decrease in the population of the NBO C31–C32, C17–N18, and C59–C61 reflecting a charge transfer away from bis-spiropipridinon/pyrazole ring. This is also evident in the case of the population of the carbon lone orbital LP(1) C3. In conclusion, compound 1 enjoys the linear conjugation that is responsible for the observed spectrum. No specific part of the molecule manifests itself in the observed spectrum. 3.8. Electronic absorption spectra of compound 2 Insertion of two OCH3 groups in position two X in two Ph-X of compound 1 gives compound 2. The experimental and theoretical electronic absorption spectra of compound 2 in dioxane and ethanol are shown in Figure 10 and Table S2. 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.287-302.1706 Shimaa Abdel Halim / European Journal of Chemistry 9 (4) (2018) 287-302 295 Table 5. Second order perturbation interaction energy values computed in the NBO basis for the studied compounds 1-5 calculated at B3LYP/6-311G(d,p). Compound Donor Acceptor E2 (kcal/mol) a NBO Population 1 πC1-N4 LP(1) C3 18.38 C1-N4 1.93901 πC20-C22 π*C25-C27 22.50 C20-C22 1.64741 πC31-C32 π*C17-N18 18.77 C31-C32 1.63606 LP(1) C3 π*C1-N4 255.11 LP(1) C3 1.19275 LP(1) O7 RY*C2 15.79 LP(1) O7 1.97434 LP(2) O7 σ*C2-C16 23.13 LP(2) O7 1.86809 LP(1) N19 π*C17-N18 30.92 LP(1) N19 1.67886 LP(1) N19 π*C20-C22 33.66 LP(1) N56 1.72398 LP(1) N56 π*C54-N57 27.01 C17-N18 0.23646 LP(1) N56 π*C59-C61 13.78 C59-C61 0.38910 π*C17-N18 π*C31-C32 142.50 - - π*C59-C61 π*C60-C62 254.14 - - 2 πC1-N4 LP(1) C3 22.20 C1-N4 1.93361 πC1-N4 π*C1-N4 12.22 LP(1) C3 1.14759 LP(1) C3 π*C1-N4 305.54 LP(1) O7 1.97422 LP(1) C3 σ*C16-C90 10.22 LP(2) O7 1.86496 LP(1) O7 RY*C2 16.17 LP(1) N19 1.67360 LP(2) O7 σ*C2-C16 24.23 LP(2) O92 1.83827 LP(1) N19 π*C17-N18 31.96 C58-C60 0.39173 LP(1) N19 π*C20-C22 35.39 C31-C32 0.38139 LP(2) O92 π*C83-C87 31.07 - - π*C17-N18 π*C31-C32 176.14 - - π*C58-C60 π*C59-C61 245.71 - - 3 πC1-N4 π*C1-N4 10.12 C1-N4 1.93843 πC31-C32 π*C17-N18 19.06 C31-C32 1.63938 πC82-C85 π*C83-C87 24.18 C82-C85 1.66571 LP(1) C3 π*C1-N4 236.58 LP(1) C3 1.17909 LP(1) N55 π*C53-N56 26.95 LP(1) N55 1.72380 LP(1) N55 π*C58-C60 14.33 LP(1) F92 1.92286 LP(1) F92 π*C45-C49 18.98 C31-C32 0.38498 π*C17-N18 π*C31-C32 134.78 C45-C49 0.37223 π*C45-C49 π*C44-C47 295.68 - - 4 πC1-N4 LP(1) C3 17.68 C1-N4 1.94219 LP(1) C3 π*C1-N4 210.17 LP(1) C3 1.21178 LP(1) N55 π*C53-N56 29.59 LP(1) N55 1.72260 LP(1) N55 π*C58-C60 10.77 C31-C32 0.38895 π*C17-N18 π*C31-C32 130.35 C45-C49 0.36457 π*C45-C49 π*C42-C43 291.80 - - 5 LP(1) C3 π*C1-N4 235.32 LP(1) C3 1.17975 LP(1) Cl92 π*C45-C49 12.44 LP(1) Cl91 1.92682 π*C17-N18 π*C31-C32 127.50 C31-C32 0.38478 π*C83-C87 π*C80-C81 248.24 C83-C87 0.39465 a E2 means energy of hyperconjugative interactions (stabilization energy); LP(n) is a valence lone pair orbital (n) on atom. In dioxane, the experimental spectrum is composed of two bands, at 343 and 298 nm. Increasing solvent polarity from dioxane to ethanol results in a blue shift of the two bands, where the first band is shifted to 339 nm, and the second band is shifted to 295 nm, respectively. Furthermore, increasing solvent polarity causes a marked increase in the intensity of both bands. The two observed bands are assigned as π → π* transitions, based on the values of molar absorptive (ε = 0.000- 60.000). The interpretation of the experimentally observed UV spectra of compound 2 in dioxane and ethanol requires the theoretical calculations of the vertical transitions using CAM/B3LYP/6-311G(d,p) level. In dioxane, the band appea- ring in the experimental spectrum at 343 nm is reproduced theoretically using dioxane as a solvent at 336.3 nm (State I), as shown in Table S2, which involves orbital’s φ196 and φ199, showing a good agreement between the observed wavelength with the calculated wavelength. Theoretical gas phase calculations of compound 2 give a vertical excitation at 336.1 nm (State I), which is about 7.1 nm lower than the experimental wavelength, where the transition in the gas phase also involves the same orbitals. Increasing solvent polarity results in a blue shift of λmax of this band to 339 nm. The theoretical calculations of the vertical excitation in ethanol reproduce the wavelength of this band at 335.4 nm (State I), indicating that the same orbital’s are involved in this transition. It is also clear that the calculated wave length is lower than the observed wavelength. The second band theoretically at 320.0 nm (State II) in dioxane, indicating that the orbital’s φ198 and φ201 are involved in this transition. Theoretical gas phase calculations give a wavelength at 320.8 nm (State II). This same band in ethanol at 325.3 nm (State II), where the same orbital’s are involved in this transition. The third band theoretically at 304.2 nm (State III) in dioxane, indicating that the orbital’s φ197 and φ200 are involved in this transition. Theoretical gas phase calculations give a wavelength at 303.6 nm (State III), this same band at 303.5 nm in ethanol. The fourth state (π-π*)1 , which observed at 298 nm in dioxane, is reproduced theoretically at 292.1 nm (State IV), where the calculations in dioxane indicate that the orbital's φ198 and φ202 are involved in this transition. Gas phase calculations give λmax at 291.8 nm (State IV). Theoretical calculations in ethanol show that, this band appears at 292.3 nm (State IV), which is lower than the experimental wavelength. Theoretical gas phase wavelength is found to be lower than the observed wavelength in ethanol. The five band theoretically at 276.3 nm (State V) in dioxane, indicating that the orbital’s φ198 and φ202 are involved in this transition. Theoretical gas phase calculations give a wavelength at 273.2 nm (State V). This same band in ethanol at 274.1 nm (State V), where the same orbital’s are involved in this transition. The seven orbital’s φ196, φ197, φ198, φ199, φ200, φ201, and φ202, res- pecttively, involved in the theoretical transitions of compound 2, are shown in Figure S2. The first band which involves φ196 and φ199 has electron density delocalization, while orbital’s φ197, φ198, φ200, φ201, and φ202 have a Charge Transfer CT character. The results of NBO analysis of compound 2 tabulated in Table 5 indicate that there is a strong hyper conjugative interactions LP(1) C3 → π*C1-N4, π*C58-C60→ π*C59- C61, π*C17-N18 → π*C31-C32, LP(1) N19 → π*C20-C22, 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.287-302.1706 296 Shimaa Abdel Halim / European Journal of Chemistry 9 (4) (2018) 287-302 Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Figure 7. HOMOs, LUMOs and density of states (DOS) of the studied compounds 1-5 at B3LYP/6-311G(d,p) with Vertical Fermi levels. LP(2) O92 → π*C83-C87, and LP(2) O7 → σ*C2-C16, for compound 2 is 305.54, 245.71, 176.14, 35.39, 31.07 and 24.23 kcal/mol, respectively. NBO analysis of the p-OCH3 derivative Table 5 indicates that it retained the extended conjugation of compound 1 as revealed by the interaction of C–N NBOs with those of pyrazole ring. Furthermore, the interaction of the oxygen lone orbital’s with the C2–O7, C1–C57 and C3–C16 π* orbital and σ*C2–C16 is marked. The population of the NBO C58–C60, C31–C32, and LP(1) C3 reflecting a charge transfer away from bis-spiropipridinon/pyrazole ring. This is also evident in the case of the population of the nitrogen lone orbital LP(1) N19. 3.9. Electronic absorption spectra of compound 3 To complete our investigation of substituent effect on the electronic structure and spectra of compound 1, we introduce two F-groups in position two X in two Ph-X of compound 1 gives compound 3. The experimental and theoretical elect- ronic absorption spectra of compound 3 in dioxane and ethanol are shown in Figure 11 and Table S3. The experimen- tal spectrum in dioxane is composed of two bands at 348 and 297 nm. The change of solvent polarity from dioxane to ethanol results in a blue shift of the two bands, where the first band is shifted to 344 nm, and the second band is shifted to 293 nm, respectively. 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.287-302.1706 Shimaa Abdel Halim / European Journal of Chemistry 9 (4) (2018) 287-302 297 Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Figure 8. 3D MEP of the studied compounds 1-5 at B3LYP/6-311G(d,p). The color scheme for the MEP surface is as follows: red for electron rich, (partially negative charge); blue for electron deficient, (partially positive charge); light blue for (slightly electron deficient region); yellow for (slightly electron rich region); green for neutral (zero potential) respectively. Potential increases in the following order: red < orange < yellow < green < blue [49,50]. Furthermore, increasing solvent polarity causes a marked increase in the intensity of both bands. The values of molar absorptive (ε = 0.000-60.000) indicates that the two observed bands have π → π* character. The theoretical vertical tran- sitions using CAM/B3LYP/6-311G d,p) level is valuable for the analysis of the experimental UV spectra of compound 3 in dioxane and ethanol, which gives values for λmax of 339.4 nm (State I) for the first band, 311.4 nm (State II) for the second band, 302.2 nm (State III) for the third band, and 289.9 nm (State IV) for the four band as shown in Table S3. Theoretical transitions in the gas phase give a vertical excitation at 339.7 nm (State I), which is about 8.3 nm lower than the experimental wavelength, where it involves the same orbitals as in dioxane. Theoretical vertical excitation calculations in ethanol give λmax of this band at 337.4 nm (State I), which shows a fair agreement, implying that the orbitals involved in 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.287-302.1706 298 Shimaa Abdel Halim / European Journal of Chemistry 9 (4) (2018) 287-302 Figure 9. Electronic absorption spectra of compound 1, (a) theoretical in gas phase, (b) theoretical in ethanol, (c) theoretical in dioxane. Figure 10. Electronic absorption spectra of compound 2, (a) theoretical in gas phase, (b) theoretical in ethanol, (c) theoretical in dioxane, (d) experimental in ethanol, (e) experimental in dioxane. Figure 11. Electronic absorption spectra of compound 3, (a) theoretical in gas phase, (b) theoretical in ethanol, (c) theoretical in dioxane, (d) experimental in ethanol, (e) experimental in dioxane. this transition are φ188 and φ191. The second band in dioxane, theoretically at 311.4 nm (State II), indicate that the orbital’s φ190 and φ193 are involved in this transition. Gas phase calculations give λmax at 313.7 nm (State II). Theoretical calculations in ethanol show that, this band appears at 314.6 nm (State II). The third state (π-π*)1, in dioxane, theoretically at 302.2 nm (State III), indicate that the orbital's φ190 and φ192 are involved in this transition. Gas phase calculations give λmax at 306.6 nm (State III). Theoretical calculations in ethanol show that, this band appears at 305.8 nm (State III). The four band (State IV), which observed at 297 nm in dioxane, is reproduced theoretically at 289.9 nm (State IV). Gas phase calculations give λmax at 288.3 nm (State IV). Theoretical calculations in ethanol show that, this band appears at 289.3 nm (State IV). The eight orbital’s φ188-φ195 involved in the theoretical transitions of compound 3, are shown in Figure S3 where these bands shows a CT character, electron density delocaliza- 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.287-302.1706 Shimaa Abdel Halim / European Journal of Chemistry 9 (4) (2018) 287-302 299 Figure 12. Electronic absorption spectra of compound 4, (a) theoretical in gas phase, (b) theoretical in ethanol, (c) theoretical in dioxane, (d) experimental in ethanol, (e) experimental in dioxane. tion, and localization. The results of NBO analysis of compound 3 tabulated in Table 5 indicate that there is a strong hyper conjugative interactions π*C45-C49 → π*C44-C47, LP(1) C3 → π*C1-N4, π*C17-N18 → π*C31-C32, LP(1) N55 → π*C53-N56, π*C82- C85 → π*C83-C87, and LP(1) F92 → σ*C45-C49, for compound 3 is 295.68, 236.58, 134.78, 26.95, 24.18 and 18.98 kcal/mol, respectively. NBO analysis of the p-F derivative Table 5 indicates that it retained the extended conjugation of compound 1 as revealed by the interaction of C–N NBOs with those of pyrazole ring. Furthermore, the interaction of the F orbital’s with C2–O7, C1–C57 and C3–C16 π* orbital and σ*C2– C16 is marked. The population of the NBO C45–C49, C31–C32, and LP(1) C3 reflecting a charge transfer away from bis- spiropipridinon/pyrazole. 3.10. Electronic absorption spectra of compound 4 Compound 4 results by inserting two NO2-atom in position two X in two Ph-X of compound 1. The experimental and theoretical electronic absorption spectra of compound 4 in dioxane and ethanol are shown in Figure 12 and Table S4. The experimental spectrum in dioxane is composed of two bands at 355 and 295 nm. The change of solvent polarity from dioxane to ethanol results in a small red shift by 3 nm of the first band, and the second band. Additionally, increasing solvent polarity causes a marked decrease in the intensity of both bands. The values of molar absorptive (ε = 0.000-50.000) indicates that the two observed bands have π-π* character. The theoretical vertical transitions using CAM/B3LYP/6- 311G(d,p) level is valuable for the analysis of the experimental UV spectra ofcomopound 4 in dioxane and ethanol, which gives values for λmax of 349.9 nm (State I) for the first band, 324.9 nm (State II) for the second band, 313.5 nm (State III) for the third band, 292.5 nm (State IV) for the fourth band and 274.3 nm (State V) for the five band as shown in Table S4. The theoretical transition of the first band in dioxane involves orbital's φ202 and φ205, showing a good agreement between the observed and the calculated wavelengths. Theoretical transitions in the gas phase give a vertical excitation at 348.3 nm (State I), which is about 9.7 nm lower than the experi- mental wavelength, where it involves the same orbitals as in dioxane. Theoretical vertical excitation calculations in ethanol give λmax of this band at 347.4 nm (State I), which shows a fair agreement, implying that the orbitals involved in this transition are φ202 and φ205. The second band theoretically at 324.9 nm (State II) in dioxane, indicating that the orbital’s φ204 and φ209 are involved in this transition. Theoretical gas phase calculations give a wavelength at 321.9 nm (State II). This same band in ethanol at 323.9 nm (State II), where the same orbital’s are involved in this transition. The third band theoretically at 313.5 nm (State III) in dioxane, indicating that the orbital’s φ204 and φ208 are involved in this transition. Theoretical gas phase calculations give a wavelength at 311.7 nm (State III), this same band at 310.5 nm in ethanol. The fourth state (π-π*)1 , which observed at 295 nm in dioxane, is reproduced theoretically at 292.5 nm (State IV), where the calculations in dioxane indicate that the orbital’s φ204 and φ214 are involved in this transition. Gas phase calculations give λmax at 290.0 nm (State IV). Theoretical calculations in ethanol show that, this band appears at 291.1 nm (State IV), which is lower than the experimental wavelength. Theoretical gas phase wavelength is found to be lower than the observed wavelength in ethanol. The five band theoretically at 274.3 nm (State V) in dioxane, indicating that the orbital’s φ203 and φ214 are involved in this transition. Theoretical gas phase calculations give a wave- length at 273.8 nm (State V). This same band in ethanol at 273.6 nm (state V), where the same orbital’s are involved in this transition. The eight orbital’s φ202-φ205, φ207-φ209, and φ214 involved in the theoretical transitions of compound 4, are shown in Figure S4 where these bands shows a CT character, electron density delocalization, and localization. The results of NBO analysis of compound 4 tabulated in Table 5 indicate that there is a strong hyper conjugative interactions π*C45-C49→ π*C42-C43, LP(1) C3 → π*C1-N4, π*C17-N18→ π*C31-C32,and LP(1) N55 → π*C53-N56, for compound 4 is 291.80, 210.17, 130.35, and 29.59 kcal/mol, respectively. NBO analysis of the p-NO2 derivative Table 5 indicates that it retained the extended conjugation of compound 1 as revealed by the interaction of C–NO2 NBOs with those of both phenyl rings. Furthermore, the interaction of the NO2 orbital’s with the C2–C16 σ* orbital is marked. The population of the NBO C45–C49, C31–C32, and LP(1) C3 reflecting a charge transfer away from bis- spiropipridinon/pyrazole. 3.11. Electronic absorption spectra of compound 5 Introducing two Cl-atom in position two X in two Ph-X of compound 1, results in the formation of compound 5. The experimental and theoretical electronic absorption spectra of compound 5 in dioxane and ethanol are shown in Figure 13 and Table S5. The experimental spectrum of compound 5 in dioxane is composed of two bands appearing at 353 and 298 nm, respectively. Compound 5 in ethanol exhibits two bands at 349 and 295 nm. The change of solvent polarity results in a slight blue shift for all bands. 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.287-302.1706 300 Shimaa Abdel Halim / European Journal of Chemistry 9 (4) (2018) 287-302 Table 6. Antimicrobial activity for the studied compounds 2-5. Compounds Diameter of inhibition zone (mm) at conc. of μg/mL Gram (+) Gram (-) Fungus S. aureus E. coli K. pneumonia P. vulgaris C. albicans 2 10 9 10 10 10 3 11 10 9 11 12 4 17 18 15 19 16 5 12 11 10 12 12 Doxymycin a 14 15 15 15 - Fluconazole b - - - - 14 a Antibacterial standard. b Antifungal standard. Figure 13. Electronic absorption spectra of compound 5, (a) theoretical in gas phase, (b) theoretical in ethanol, (c) theoretical in dioxane, (d) experimental in ethanol, (e) experimental in dioxane. The intensity of all bands is increase upon increasing solvent polarity. All bands are assigned to have π-π* character. The observed UV spectra of compound 5 in dioxane is interpreted by using CAM/B3LYP/6-311G(d,p) vertical exci- tation calculations, which gives excitations at 342.9 nm (State I), 311.1 nm (State II), 303.5 nm (State III), 292.6 nm (State IV), and 276.8 nm (state V) nm, respectively, which shows a good agreement with the observed spectra. The theoretical transition of the first band in dioxane involves orbital’s φ196 and φ199, showing a good agreement between the observed and the calculated wavelengths. Theoretical transitions in the gas phase give a vertical excitation at 343.5 nm (State I), which is about 9.5 nm lower than the experimental wavelength, where it involves the same orbitals as in dioxane. Theoretical vertical excitation calculations in ethanol give λmax of this band at 340.6 nm (state I), which shows a fair agreement, implying that the orbitals involved in this transition are φ196 and φ199. The second band theoretically at 311.1 nm (State II) in dioxane, indicating that the orbital's φ197 and φ200 are involved in this transition. Theoretical gas phase calculations give a wavelength at 313.5 nm (State II). This same band in ethanol at 315.3 nm (State II), where the orbital’s φ198 and φ201 are involved in this transition. The third band theoretically at 303.5 nm (State III) in dioxane, indicating that the orbital’s φ198 and φ200 are involved in this transition. Theoretical gas phase calculations give a wavelength at 306.3 nm (State III), this same band at 306.0 nm in ethanol. The fourth state (π- π*)1, which observed at 298 nm in dioxane, is reproduced theoretically at 292.6 nm (State IV), where the calculations in dioxane indicate that the orbital’s φ198 and φ202 are involved in this transition. Gas phase calculations give λmax at 290.3 nm (state IV). Theoretical calculations in ethanol show that, this band appears at 293.3 nm (state IV), which is lower than the experimental wavelength. Theoretical gas phase wavelength is found to be lower than the observed wavelength in ethanol. The five band theoretically at 276.8 nm (State V) in dioxane, indicating that the orbital’s φ198 and φ202 are involved in this transition. Theoretical gas phase calculations give a wavelength at 273.8 nm (State V). This same band in ethanol at 275.6 nm (state V), where the same orbital’s are involved in this transition. The seven orbital’s φ196-φ202, involved in the theoretical transitions of compound 5, are shown in Figure S5 where these bands shows a CT character, electron density delocalization, and localization. The results of NBO analysis of compound 5 tabulated in Table 5 indicate that there is a strong hyper conjugative interactions π*C83-C87 → π*C80-C81, LP(1) C3 → π*C1-N4, π*C17-N18 → π*C31-C32, and LP(1) Cl92 → π*C45-C49, for compound 5 is 248.24, 235.32, 127.50 and 12.44 kcal/mol, respectively. NBO analysis of the p-Cl derivative Table 5 indicates that it retained the extended conjugation of compound 1 as revealed by the interaction of C–Cl NBOs with those of both phenyl rings. Furthermore, the interaction of the Cl orbital's with the C2–C16 σ* orbital is marked. The population of the NBO C83–C87, C31–C32, and LP(1) C3 reflecting a charge transfer away from bis-spiro-pipridinon/ pyrazole. 3.12. Antimicrobial activity Biological activities of synthesized bis-spiropipridinon/ pyrazole derivatives compounds were studied for antibacterial and antifungal properties against different types of bacteria; Gram positive S. aureus, and E. coli and Gram negative K. pneumonia and P. vulgaris, and C. albicans for fungus. Results were recorded by measuring the growth inhibition (zone of inhibition) surrounding the disc of material. Results of MIC are summarized in Table 6. Some antibiotics were evaluated for their antibacterial activities and their results were found ineffective to all bacteria and fungus. Compound 2 show weak activity except for both compounds 4, 5 and 3 is quite effective against E. coli, P. vulgaris, and C. albicans. Antimicrobial activity results revealed that compound 4 has a good potency against all Gram-positive bacteria especially E. coli and all Gram-negative bacteria especially P. vulgaris in comparison 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.287-302.1706 Shimaa Abdel Halim / European Journal of Chemistry 9 (4) (2018) 287-302 301 with doxymycin standard. Those compounds 2-5 give more explanation of the high antimicrobial activity against all tested bacteria and fungi in which the small size of compound 4 increases its absorption ability on the surface of the cell wall of microorganisms and the respiration process of the cell. Hence, compound 4 is essential for the growth-inhibitor effect. 3.13. Structure activity relationship (SAR) The biological activity of the bis-spiropipridinon/pyrazole derivatives can be correlated with the ground state energetic and global properties. From the computed data in Tables 3 and 6, one can reveal the following: 1. The reactivity of bis-spiropipridinon/pyrazole derivatives follow the order NO2 < Cl < F < OCH3, Against Gram(+), Gram(-) and fungi. The reactivity can be explained in terms of the energy gap, EHOMO which measures the donating power and dipole moment which measure the charge separation. 2. Theoretically, the order of the energy gap NO2 < Cl < F < OCH3, the order of EHOMO NO2 < Cl < F < OCH3, and the order of the dipole moment NO2 < Cl < F < OCH3 which are of the same order of the reactivity of bis-spiropipridinon /pyrazole derivatives towards Gram(+), Gram(-) and fungi. In conclusions, the substituent in the studied compounds 2-5 increases with its biological activity. 4. Conclusion The molecular geometry of bis-spiropipridinon/pyrazole derivatives in the ground state has been calculated by using DFT-B3LYP/6-311G(d,p) level of theory. The optimized structure of the studied compounds 1-5 are non-planner with the two phenyl at C53 and C92 are out of the molecular plane of bis-spiropipridinon/pyrazole by a dihedral angles of 91.67 and 19.79°, respectively. The small difference between Eg of the studied compounds 1-5 may be attributed to the presence of the two Ph-X and Ph-X out of the molecular plane of bis- spiropipridinon/pyrazole moiety. The density of states, the chemical reactivity, hardness, softness, chemical potential and electro negativity analyzed by the HOMO-LUMO energy gap. Mullikan and natural charge distribution of the molecule were studied which indicated the electronic charge distribution in the molecule. The first order hyperpolarizability and the calculated dipole moment results indicate that the molecule has a reasonable good non-linear optical behavior. The total electron density surface with MEP confirmed the different negative and positive potential sites of the molecule. Electronic absorption spectra are investigated experimentally in dioxane and ethanol; and theoretically in gas phase, dioxane and ethanol using CAM-B3LYP/6-311G(d,p). Compounds 2-5 exhibit 2 bands, in both solvents, while compound 1 exhibit 6 bands theoretically only due to expensive to prepare compound. The band maxima (λmax) and intensities of the spectra are found to have solvent dependence. The bands of compounds 2, 3, and 5 show blue shift, while compound 4 show red shift. Theoretical calculations of the vertical excitations at the CAM-B3LYP/6-311G(d,p) reproduce the experimental spectra, indicating a good agreement between theory and experiment. The NBO analysis of the compounds 1- 5 indicated the intermolecular charge transfer between the bonding and antibonding orbital’s. Novel bis-spiropipridinon/ pyrazolederivatives were tested as antimicrobial agents. Experimental results indicate that compound 4 is a useful anti- microbial agent for different bacteria and fungus. Compound 4 was found to be more reactive and more polar than other compounds. Theoretically, reactivity of the studied compounds follows the order: NO2< Cl < F < OCH3, which is the same order of reactivity towards Gram(+), Gram(-) , and fungus. Acknowledgements This work was supported by the preparation of bis- spiropipridinon/pyrazole derivatives compounds by Dr. Huwaida Hassaneen at the Cairo University. Supporting information The online version of this article contains supplementary material, which is available to authorized users. Disclosure statement Conflict of interests: The authors declare that they have no conflict of interest. Author contributions: All authors contributed equally to this work. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. ORCID Shimaa Abdel Halim http://orcid.org/0000-0003-3926-193X References [1]. 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This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). 2018 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.9.4.287-302.1706 https://www.chemcraftprog.com/ http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Experimental 2.1. Synthesis 2.2. Solvents 2.3. Apparatus 2.4. Antimicrobial study 2.5. Computational method 3. Results and discussion 3.1. Geometric parameters 3.2. Natural charge analysis 3.3. Global reactivity descriptors 3.4. Nonlinear optical analysis 3.5. Density of states 3.6. Molecular electrostatic potential 3.7. Electronic absorption spectra of compound 1 3.8. Electronic absorption spectra of compound 2 3.9. Electronic absorption spectra of compound 3 3.10. Electronic absorption spectra of compound 4 3.11. Electronic absorption spectra of compound 5 3.12. Antimicrobial activity 3.13. Structure activity relationship (SAR) 4. 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