Apr 8, 2017 - before it is published in its final form. ... Avat Arman Taherpour*1,3, Morteza Jamshidi2, Omid Rezaei1 ... *The data from natural bonding orbitals (NBO) analysis also confirmed ... 2. ⢠*The photoinduced electron transfer (PET) process was .... at 0.02 and 0.04 au areas which is related to sigma and pi bonds.
Accepted Manuscript Title: DFT and TD-DFT Theoretical Studies on Photo-induced Electron Transfer Process on [Cefamandole].C60 Nano-Complex Authors: Avat Arman Taherpour, Morteza Jamshidi, Omid Rezaei PII: DOI: Reference:
S1093-3263(16)30199-1 http://dx.doi.org/doi:10.1016/j.jmgm.2017.04.011 JMG 6895
To appear in:
Journal of Molecular Graphics and Modelling
Received date: Revised date: Accepted date:
14-9-2016 8-4-2017 10-4-2017
Please cite this article as: Avat Arman Taherpour, Morteza Jamshidi, Omid Rezaei, DFT and TD-DFT Theoretical Studies on Photo-induced Electron Transfer Process on [Cefamandole].C60 Nano-Complex, Journal of Molecular Graphics and Modellinghttp://dx.doi.org/10.1016/j.jmgm.2017.04.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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DFT and TD-DFT Theoretical Studies on Photo-induced Electron Transfer Process on [Cefamandole].C60 Nano-Complex
Avat Arman Taherpour*1,3, Morteza Jamshidi2, Omid Rezaei1 1
Department of Organic Chemistry, Faculty of Chemistry, Razi University, P.O.Box:6714967346, Kermanshah, Iran 2
Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran
3
Medical Biology Research Center, Kermanshah University of Medical Sciences, Kermanshah, Iran
Graphical abstract
Highlights The interaction of C60 fullerene as an electron recipient with the Cefamandole antibiotic was investigated in both ground and excited states using DFT and TD-DFT methods. *The study of the interaction of C60 and Cefamandole via electron localization function (ELF) and reduced density gradient (RDG). *The data from natural bonding orbitals (NBO) analysis also confirmed the interaction type. The study of absorption and emission spectrum via CAM-B3LYP in the TDSCF state
2
*The photoinduced electron transfer (PET) process was investigated using the electron hole theory. *Excited state calculations and electron hole theory. *The PET process can be used as a detection factor after the Cefamandole delivery
Abstract The C60 fullerene displays a considerable electronegativity. It has a unique photophysical and electrochemical behavior that can be used as a suitable drug carrier. In the present study, the interaction of C60 fullerene as an electron recipient with the Cefamandole antibiotic was investigated in both ground and excited states using DFT and TD-DFT methods. The study of the interaction of C60 and Cefamandole via electron localization function (ELF) and reduced density gradient (RDG) revealed that the complex formation is of van der Waals type. The data from natural bonding orbitals (NBO) analysis also confirmed the interaction type. The study of absorption and emission spectrum via CAM-B3LYP in the TD-SCF state showed that the emission peak of
C60 fullerene in the 591.73 nm after the
complex formation results in the extinction of this emission
spectrum due to
charge transfer (CT) from chelator to fluorophore. The photoinduced electron transfer (PET) process was investigated using the electron hole theory. Introduction Cephalosporins are antibiotics that have a beta-lactam ring[1]. Antibiotics with beta-lactam ring usually destroy bacteria by disturbing the construction of protein chains in their membranes[2, 3]. One of the methods that enable bacteria to make themselves resistant to such antibiotics is to strengthen the phospholipid membrane
3
[4-6]. In this way, an increase in the difference between the dipole moment of the antibiotic and the external crust of bacteria's membrane prevents the antibiotic from entering the membrane [7-9], thus the performance of antibiotics is lowered. Fullerenes have been of much interest in the experimental and computational studies in the last twenty-five years. The C60 fullerene is one of the most ideal discovered substances in the electrochemical reactions. It can easily form organic or
metal-during
oxidation
or
reduction
electronegative and they can easily react with
[10-12],
fullerenes
are
highly
even weak nucleophiles[13]. The
C60 fullerene is able to receive up to 6 e-[14]. The fullerene electronegativity controls the types of the reactants that are added. The formation of complex with fullerene is dependent on the donor-acceptor interactions[15, 16]. The complex of fullerenes with some drugs[17], enzymes[18], and hormones[19] can facilitate their entrance into the intended target in the body[20]. One of the applications of fullerenes, an anti-AIDS enzyme was transferred to the human body using fullerenes[21]. Moreover, some cancer cells have been destroyed using the derivatives of C60 exohedral and [O2 + C60] colloid[22, 23]. Exohedral fullerenes are derivatives of fullerenes that are formed from the chemical reactions between fullerene and other substances[24]. Modeling and use of
quantum chemistry approaches yields results close to
experimental results for the prediction of effective parameters in the performance of biochemical systems. One of the most important current issues addressed by the researchers is to utilize and modify the TD-DFT method. This computational method can help them study the electron levels of molecules with high precision, and predicts
the molecular behaviors at excited state[25] that one of them is
calculation of fluorescence spectrum which is very useful because recently,
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emission spectrums like fluorescence have been used for detecting drugs[26] and drug carriers[27] in bio systems. So this method can be used for predicting fluorescence emission spectra for unknown systems or design new bio chemical systems[28, 29]. Furthermore, it is very important to identify and understand the mechanism and performance of electron transfer at excited state in biochemical systems. One of the main parameters that can be calculated by TD-DFT is the photo-induced electron transfer (PET)[30]. The characteristic of C60 fullerene and its high effectiveness as an electron recipient and absorbent in the UV-Vis area have led researchers to consider it as an absorbent
acceptor along with different
kinds of organic donor and bio supermolecules[31, 32]. In the present research, some important parameters in chemical and photochemical processes for the [Cefamandole +C60] complex were evaluated. Since C60 is highly effective as the carrier of some drugs, it is important to examine the properties of such complexes. This paper dealt with the use of appropriate computational methods for this Nano complex at DFT level to optimize its geometrical structure, and examine its electronic properties at the ground state. TD-DFT calculations at excited state were assessed to examine the absorption and emission spectrum of C60 fullerene and [Cef+C60] (Cefamandole+C60) complex. In addition, the PET process in this complex was investigated, and its effect on the extinction of C60 fullerene fluorescence emission spectrum after the complex formation was studied and interpreted according to the electron hole theory. Research Methodology Calculation Details Cefamandole (Cef) is an antibiotic of the cephalosporin class used to treat infections of skin, joints, bones, urinary tract, and respiratory system[33]. As it is
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seen in Figure 1, like other cephalosporins, this antibiotic has a beta-lactam ring[34]. The [Cef+C60] complex experienced structural optimization in the gaseous state at 298 K degrees using DFT calculations and B3LYP/6-31G* basis set with Gaussian 03 package[35] (Fig. 2-a). B3LYP is an appropriate, frequentlyused method for the calculations pertaining organic structures. It has a low computational cost and error. Use of 6-31G* basis set
gives an appropriate
approximation of the complex orbitals[36]. Although it is possible to use more precise basis sets, the great amplitude of the [Cef+C60] complex will exponentially increase the computational cost. After the structural optimization of the [Cef+ C60] complex, NBO (natural bond orbitals) analysis was performed via the B3LYP/6-31G* method, and the results were examined exclusively for the electron transfers between Cefamandole and C60 in the complex which includes the electrons of the blue area in the Figure 2. One of the other parameters that indicate a weak interaction between Cefamandole and C60 is electron localization function (ELF). In fact, it indicates the probability of the presence of electron in the neighborhood of reference electrons with the same spins. ELF segregates the valence layer electrons in a clear manner, and makes a considerable visual contribution to the understanding of the electronic properties of chemical systems[37, 38]. ELF calculations via DFT are much helpful producing very precise results. In this work, the effect of the complexation of Cefamandole with C60 on one of the C60’s six-membered rings was calculated and investigated (the blue ring in Fig. 2-b) Electron-rich systems like fullerenes display an idiosyncratic electron behavior at excited state. This constitutes their unique properties. The absorption and emission and spectra of Cefamandole, C60 and [Cef+ C60] complex were studied using
6
CAM-B3LYP with the 6-31g* basis set.
CAM-B3LYP possesses a higher
precision in excited state electron transfers compared to B3LYP but their computational cost is equal. It can calculate electron transfers with a precision about 0.1 eV. It has been recently used by the researchers in this area[39, 40]. The fluorescence emission
spectra of, C60 and [Cef+ C60] complex were calculated by
the very same method. For the calculation of the emission
spectrum of electron
transfers singlet was considered[41, 42]. These transfers were studied for the nstates=6 which has a suitable precision. Electron transfers were assessed with the help of electron-hole theory[43]. The electron and hole were calculated and drawn for the [Cef+ C60] complex. The PET mechanism for the C60 fullerene was studied before and after the complexation, some results were analyzed with
Multiwfn
3.3.8 and VMD software’s [44, 45]. Results and Discussion The Ground State The formation of fullerene complex with the antibiotics having a beta-lactam ring in a mole by mole fashion can create a dipolar structure with one hydrophilic end ( location of antibiotic on fullerene ) and another hydrophobic end ( the opposite side of antibiotic on the fullerene ) which has 8.58 kcal/mol complex formation energy. The dipole moments of C60 fullerene and Cefamandole are 0 and 5.33 D respectively in normal conditions but after the formation of complex with Cefamanadole [Cef + C60], it was calculated to be 7.9 D (Fig. 3). Bipolar structure including ends of hydrophilic and hydrophobic can help penetrate drug to the phospholipid membrane by the hydrophobic end.
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Charge Decomposition Analysis (CDA) is used for studying the interaction of donor-acceptor molecules in two or more fragments. The calculation of these terms was developed by Germot Frenking and co-workers[46]. CDA is based on fragment orbital (FO) that shows molecular orbitals (MO) in the isolated state[47]. CDA and density of state (DOS) are shown in Figure 4. It is found out, in Figure 4.a, that after the formation of the [Cef+C60] complex, the energy levels of the HOMO and LUMO orbitals has reduced compared to C60 to some extent. It is also observed that the biggest participation for the formation of HOMO and LUMO in the [Cef+C60] complex has been made by HOMO and LUMO C60 orbitals. Since the link between Cefamandole and C60 in the [Cef+C60] complex is of van der Waals type, all the molecular orbitals of the complex are with a high percentage resulted from the sharing of one of the two fragments of Cef or C60. Figure 4.b shows the DOS diagram for Cef, C60 and [Cef+C60] complex which are conformant with energy levels in Figure 4.a. Thus, the energy gap for Cef, C60 and [Cef+C60] complex is 4.69, 2.76, and 2.87 eV respectively. This shows that the complexation of Cef, C60 has increased the energy gap of C60 to 0.06 eV.
The reduced density gradient (RDG) is an appropriate method for studying weak interactions like van der Waals. In fact, RDG is an extension of average reduced density gradient (aRDG) method defined by Equation (1): Equation (1)
Where ρ is the electron density at the distance of r. Drawing RDG on sign (λ2)ρ which is actually a kind of critical point in chemical bonds or a weak interaction
8
between electron pairs helps much with studying weak interactions[48, 49]. Figure 5.a shows the general [Cef+ C60] complex well. In addition, Figures 5.b and 5.c present Cef and C60 respectively for comparison purpose. Figure 5.c shows two strong interactions at 0.02 and 0.04 au areas which is related to sigma and pi bonds of C60. A comparison of these three graphs shows that a weak interaction has been added in the -0.008 to +0.008 intervals after the formation of [Cef + C60] complex in a way that the Cef molecule has oriented towards the C60 fullerene. Figure 5.d shows this interaction as an orbital overlap.
Table 1 shows all the electron transfer s between Cef and C60 in the [Cef + C60] complex. As it is seen these transfers are very weak, and fall within van der Waals' category. It should be noticed that in all the transfers from C60 to [Cef], all the transfers have been done from pi bonds which indicates that all the existing bonds in C60 fullerene are identical. Figure 6 shows the ELF of one of the six-membered of C60 after and before the formation of [Cef + C60] complex. A comparison of Figures 6-a and 6-b shows that after the formation of [Cef + C60] complex, the ELF electron density has a smaller concentration which indicates a charge transfer from this area to Cef. This pertains to the πC7-C19 σ*C73-H100 electron transfer .It equals 1.02 Kcal/mol. Most of electron transfer s from Cefamandole molecule to the C60 fullerene are related to the oxygen lone electron pair (atom No. 91) equaling 0.63 Kcal/mol. The C60 fullerene has extended orbitals and
free from anti-bonding pi electrons. That’s
why all the transfer s from the Cefamandole molecule to the C60 fullerene have been done into π* orbitals.
9
Table.1 results of donor-acceptor electron transfers. NBO calculations of [Cef+ C60] complex.
Excited State Fullerenes are highly sensitive to light such that with variation in wavelength, their electrical light varies dramatically[50]. Thus, they can have numerous photonic applications in future. The C60 fullerene has an adsorptive spectrum with oscillator strength of 0.1 upwards in the polystyrene solvent approximately in the area 200662 nm[51]. Furthermore, it has an emission fluorescence
spectrum around 740
nm[52]. The first calculated electron excited state for C60 is in the absorptive 463.01 nm with the intensity of 0.46 which is the most convenient electron transfer for C60 from the energy point of view. The emission fluorescence spectrum at this excited state shows that C60 has an adsorptive spectrum with the intensity of 0.03 in the 591.73 nm. As it is seen in the figure 7, the fluorescence emission and adsorptive mechanism of C60 is investigated in the present research. When C60 has absorbed around 463 nm, a ππ* electron transfer is excited in the HOMO orbital and transferred to LUMO while maintaining its spin multiplicity. This is actually the very S0S1 transfer. The return of electron gone to the excited state in the previous state to the ground level, i.e. S0, causes the emission in 591.73 nm.
After the addition of Cef and the [Cef+ C60] complexation, the emission spectrum of the fullerene goes extinct totally in the λ=591.73 nm. Figure 8.a shows the extinguishment mechanism of the fluorescence emission spectrum well. In this complex, C60 functions as a fluorophore, and Cef acts as a chelator, and the PET process from chelator fluorophore extinguishes the emission spectrum of C60.
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The electron-hole theory helps much to describe electron system at singlet excited state. This theory is very useful in the complexes or molecules with two centers rich in electron. It is based on the molecular orbital theory. It can easily identify MOs responsible for electron donation and acceptance in a single charge transfer (CT). It can even calculate the pathway and distance of electron transfer. Figure 8-b shows the electron hole for the [Cef+C60]
complex well. The largest
CT value at the singlet excited state in this complex occurs from CefC60. Green MOs those are located on Cef act as electrons but all the blue MOs that are located on C60 act as holes. Thus, in the conditions defined for the [Cef+C60] complex, the singlet excited state of CT occurs from CefC60 which extinguishes the emission fluorescence spectrum of C60 in the λ=591.73 nm.
Conclusion In the present research, the structure of [Cef +C60] complex was optimized, and its electronic properties were investigated using DFT and TD-DFT to examine its UVVis absorption and fluorescence emission. The dipole moment of this complex indicates the capability of C60 fullerene as the carrier of Cefamandole drug. The results of NBO analysis show a small orbital overlap. Study of electron density via reduced density gradient (RDG) and electron localization function (ELF) indicates a van der Waals' interaction between Cephalosporin and fullerene which can facilitate the drug delivery.
Excited state analyses,
and calculations of
fluorescence emission spectrum showed that after the complexation, the photoinduced electron transfer(PET) made the emission spectrum of C60 extinct in the 591.73 nm by transferring charge from Cefamandole to fullerene. It was visually
11
made clear via excited state calculations and electron hole theory that the PET process can be used as a detection factor after the Cefamandole delivery.
Acknowledgment: The corresponding author has acknowledged from the colleagues of School of Chemistry, The University of Melbourne-Melbourne-Australia, for their useful suggestions.
The authors have also acknowledged the Theoretical and
Computational Research Center of Chemistry Faculty of Razi UniversityKermanshah-Iran and Medical Biology Research Center, Kermanshah University of Medical Sciences, Kermanshah, Iran.
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Fig.1 the structure of Cefamandole optimized via the B3LYP/6-31G* method
Fig.2 the structure of the [Cef+ C60] complex, optimized via the B3LYP/6-31G* method a) full view b) close-up of C60 in the complex.
Fig.3 the dipole moment of the [Cef + C60] complex in the vacuum calculated via the B3LYP/6-31G* method.
Fig.4 a) Charge decomposition analyses b) Density of state for Cef, C 60 and [Cef+C60] in the range of -10 to 0 eV.
Fig.5 a) analysis of the bonds and interactions of the [Cef + C 60] complex, b) analysis of the Cef bonds and interactions , c) analysis of C60 bonds and interactions by drawing RDG/sign(λ2)ρ, and d) the weak orbital overlap between Cef and C60 in the [Cef + C60] complex.
Fig.6 electron analysis a) ELF six-membered C60 ring alone b) six-membered C60 ring in the [Cef+ C60] complex.
Fig.
7
the
representation
of
HOMO
of C60 fullerene during λ absorption and emission.
and
LUMO
orbitals
16
Fig.8 a) a schematic representation of the PET process and the extinction of C60 fluorescence spectrum in the [Cef+ C60] complex b) representation of fluorophore and chelator MOs in the PET process in the [Cef+ C60] complex.
Fig 1
17
Fig 2
18 Fig 3
Fig 4
19
Fig 5
20
Fig 6
21
Fig 7
22
Fig 8
