Document Type : Original Research Paper
Chemistry Department, Payame Noor University, Tehran, Iran
Crizotinib (CZT) under the brand name XALKORI® is an anti-cancer drug that prevents the growth and spread of cancer cells in the body . CZT inhibits chemicals in order to block the growth of cancer-free cells that survive longer than normal cells. It is employed to treat certain types of non-small cell lung cancers that have spread to other parts of the body [2, 3]. The CZT is a tyrosine kinase inhibitor that inhibits the growth and spread of cancer cells. It neutralizes the effects of abnormal and carcinogenic proteins made by the anaplastic lymphoma kinase (ALK) disrupted gene . In 2011, CZT was approved by the food and drug administration for this form of lung cancer .
The fullerenes are highly electronic and react efficiently to the nucleophiles. Also, C60 is the prototype cage-like structure. Fluorine carbon atoms can react with atoms and molecules without altering their stability and spherical structure. Researchers are keen to create new molecules by adding other molecules to the outer part of fluorine [6, 7]. Due to their unique properties, fullerenes have attracted much attention, which has made them attractive for a wide range of applications. Substitutional doping of different fullerene structures with different transition metals such as nickel, ruthenium, chromium, zirconium, titanium, palladium, and molybdenum for electronic and non-linear optical applications was studied [8-11]. However, the low solubility of fullerenes in fluids limits the use of these substances as active pharmaceutical ingredients (API). However, its size, hydrophobia, three-dimensionality, and electronic properties prevent it from not being treated as a medicine and food emulsion [12-15]. For example, their spherical shape creates the ability and location of fullerenes molecules in hydrophobic solutions of enzymes or cells. Therefore, it could be said that the size, hydrophobic nature, three-dimensional structure, and electronic structure of fullerenes makes them attractive for pharmaceutical chemistry [16, 17]. In many studies, in order to improve the properties of fullerenes and nanotubes, atoms such as boron, silicon, sulfur, and zinc and … have been replaced by one or more carbon atoms of fullerenes or nanotubes, which these doped nanoparticles have been used in drug delivery [18-21]. Fullerene functionalization improves the properties of these nanoparticles, including increasing their solubility, as well as the use of these external association derivatives in pharmaceuticals. Therefore, functionalized fullerenes such as hydroxyl, carboxyl, and other functional groups have attracted much attention due to their capabilities in the field of material science, biochemistry, and biotechnology [22-29]. In this research, in order to compare the energy of the drug interaction in the water and gas phase, calculations were also performed in the gas phase. Hence, the optimal energy for a complex is considered that, firstly, it does not have chemical interactions and, secondly, does not have very weak intermolecular attractions.
Structural and electronic properties and the interaction of CZT, fullerene C 60, boron-doped fullerenes, and the fullerene functionalized with carboxyl functional groups have been studied by the functional density theory method. All optimization calculations were performed by Gaussian 09 software developed by the Gaussian (United States of America). Software such as gauss view and AIM2000 were also used in order to draw molecules, analyze data, and draw diagrams. The theoretical level of B3LYP/6-311G (d) was used in the DFT method in the gas and water solvent phase. Comparison of drug-fullerenes complex, in terms of structure, energy, and type of interaction, has been done through optimization calculations, frequency, natural bond orbital (NBO), and atoms in molecules (AIM). A comparison was also made between relative energy, dipole moment, structural parameters, the highest employed molecular orbital (HOMO), and the lowest unoccupied molecular orbital (LUMO) in various complexes. The solvent effects of water on the primary molecules and the drug’s interaction with fullerene were studied using the self-consistent reaction field (SCRF) in the polarizable continuum model (PCM).
The interaction energy of the drug is calculated by the following equation :
Where, ECZT and Ecomplex are the energy levels of CZT, and the energy level of the drug-fullerene complex, respectively. Also, EC60 is the representative of C60 fullerene, boron-doped fullerene (C59B), and carboxyl-functionalized fullerene (C60COOH). When calculations are performed for the complex system, the essential functions of both nuclei are effective in shaping the type of interaction, and therefore in the final energy, this issue must be taken into account. Therefore, the basis set superposition error (BSSE) was calculated and considered in the calculation of interaction energy .
In AIM theory, ρ(r) is described by a set of critical points (CP). At the critical point, the gradient vector of the electron density ∇ρ(r) is zero. Electron density (r) is one of the few scalar fields that could be used to represent critical points. Laplace electron density (r) is another of the most critical scalar fields. The two atoms interacting in the molecule form a critical point in the electron density called the BCP bonding critical point. The pair of gradients that start at one BCP and end at adjacent nuclei is called the Link path.
On the other hand, according to the following equation, Laplace of the electron density at any point in space balances between the potential energy density and the kinetic energy density :
G(r) is the density of electronic kinetic energy, which is always with power, and V(r) is the potential and numerical energy density with a negative sign . Electronic density, which can be represented by the following presentation, could manage the density of the kinetic system and potential equally .
In the NBO method, a one-electron density matrix is used to define the shape of atomic orbitals in a molecular environment and to obtain molecular bonds (the electron density between atoms). The chemical potential μ is calculated from the following equation :
The chemical hardness of the molecule () could be calculated using Koopman’s theory as follows :
Which ionization potential (IP) are defined as IP = -E(HOMO) and the electron energy (EA) as EA = -E(LUMO). Therefore, the relevant equation is as follows :
Chemical hardness is a resistance measurement of a chemical species to the change in electron arrangement, while the chemical potential is a measure of the system’s tendency to lose electron clouds. In order to obtain more details, the electrophilicity index has been calculated. The degree of energy stability of the system is measured during the load transfer with its surroundings. A more significant value indicates the strength of the structure :
The degree of softness is also related to the hardness values by the following equation :
Soft molecules have more reactivity and chemical activity than other molecules.
RESULTS AND DISCUSSION
Calculation of energy, dipole moment, and geometric structure
Using GaussView software, the initial structure of the drug CZT, C60 fullerene, boron-doped fullerene, and carboxyl-functionalized fullerenes were drawn. The molecules were then optimized using the Gaussian software at the B3LYP/6-31G(d) theory level. The amine group-administered CZT alongside each of the three fullerenes, and optimized drug interactions with this pure, boron-doped fullerene and carboxyl-activated group with B3LYP/6-311G(d) theory levels in gas and water phases were performed. The doped structures of the drug and the CZT-C60, CZT-C59B, and CZT-C60COOH complexes are shown in Fig. 1. Also, Table 1 shows the Gaussian output in terms of energy extracted from Harter in gas and water phases.
As could be seen from Table 1, the energy of all molecules in water is lower than that of the gas phase, which indicates that the molecules are more stable in the water phase. Also, the calculated values of interaction energies in complexes and dipole moment of the drug, C60 fullerene, and the complexes are shown in Table 2.
According to the data on the interaction energy in Table 2, the interaction between the drug and fullerenes in both gas and water phases is hot, indicating that drug uptake on fullerenes are not spontaneous and the CZT-C60 complex in both the gas and water phases are unstable. Drug uptake on boron-doped fullerenes and carboxyl-functionalized fullerenes are exothermic. The energy values of the interaction between the drug and the doped fullerene indicate a strong interaction that could indicate the covalent attraction between the boron atom from the doped fullerene and the nitrogen atom from the drug. The release of the drug is more critical than the adsorption on C60 fullerene. So, it appears that this interaction between the drug and the boron-doped fullerene (C59B) cannot be suitable for drug delivery. The interaction energy between the drug and the carboxyl-functionalized fullerene could indicate the presence of our attractions between vandalism and covalent, that is, within the range of hydrogen bonding, which could generally be appropriate in drug transfer with nanoparticles . In all cases, for medicine, pure fullerene and boron-doped fullerene and carboxyl-functionalized fullerene, and the dipole moment complexes in the water phase are larger than the dipole moment in the gas phase. Between boron-fermented fullerenes and carboxyl-functionalized fullerenes, carboxyl-functionalized fullerenes have a larger dipole moment, indicating that their solubility in water, as a polar solvent, is higher than that of pure and boron-doped fullerene. The CZT-C60 complex has less dipole moment and less water solubility than the single drug. If, for the other two complexes, the dipole moment is more massive than the single drug, and therefore their solubility in water is higher than the single drug. Also, the enormous dipole moment of the CZT-C59B complex is due to the more excellent stability of this complex in both phases, especially in the water phase.
The length changes of C-C bonds in pure C60 changed from 1.395 and 1.453 to 1.397 and 1.454 at the CZT-C60 complex, respectively. Besides, in the drug alone, the N23-H40 and N23-C12 bonds changed from 1.013 and 1.382 to 1.014 and 1.384 at the CZT-C60 complex, respectively. This indicates that the structure of the drug and C60 has not changed significantly. In the CZT-C59B complex, the B-C length bonds of pure nanoparticles changed from 1.526 and 1.548 to 1.598 and 1.619, respectively, and the N23-H40 and N23-C12 bonds from 1.013 and 1.382 in the drug alone to 1.024 and 1.459 in the complex, respectively. It was shown that the structure of the drug and C60 in this complex has changed to some extent. Also, in the CZT-C60COOH complex, the bond lengths of O-C and O-H bonds in pure nanoparticle changed from 1.210 and 0.977 to 1.216 and 1.020 in the complex, respectively, and the N23-H40 and N23-C12 bonds lengths changed from 1.013 and 1.382 in drug alone to 1.018 and 1.413 in the complex, respectively. The result showed that bond lengths change more than the CZT-C60 complex and less than the CZT-C59B complex. These results are in agreement with the order of the values of the interaction energies.
The energies of the highest occupied molecular orbital and the lowest unoccupied molecular orbital, the gap energy, and general indicators indicating chemical activity for CZT, pure fullerene, and boron-doped fullerene, and carboxyl-functionalized fullerenes, and the corresponding complexes are given in Fig. 2 and Table 3. Fig. 2 shows the highest occupied orbital is on the drug molecule, and the lowest unoccupied orbital is on the fullerene nanoparticle at the CZT-C60 complex. Also, in the other two complexes, both HOMO and LUMO, are on the nanoparticle.
The chemical potential (µ) specifies the direction of the charge transfer between two molecules. The transfer of electrons from a molecule with a higher chemical potential to a molecule with a lower chemical potential occurs. According to Table 3, the chemical potential of the drug is higher than that of all three fullerenes, indicating that the transfer of electrons in all three related complexes takes place from the drug to the fullerene. Gap energy is a quantity that determines the kinetic stability of a molecule. According to Table (3), Fullerene C59B has a higher polarity with lower gap energy and higher softness. Also, the considerable softness could indicate that pure fullerenes are more accessible to accept electrons than boron-doped fullerenes and other studied carboxyl-functionalized fullerenes. The larger C60 fullerene’s gap energy gauge shows more stability and less willingness to interact.
For systems that have an individual electron, a separate orbital electron is defined for each electron [40, 41], and in Gaussian, the occupied and unoccupied orbital energy is different for the alpha and beta electrons. In the two drug complexes with doped and carboxyl-functionalized fullerenes, there is an individual electron, and we compare the gap energy between the two. The gap energy and its equivalent hardness in the CZT-C59B complex are slightly larger than the CZT-C60COOH complex, which indicates that it is stable.
Atoms in molecules analysis
Various parameters of the critical points of the bonds between the atoms of the drug CZT and pure fullerenes, the doped fullerenes, and the functionalized fullerenes, such as the electron density and the electron density Laplace, were used to study the type and strength of the bond. The data for the AIM software calculations are given in Table 4. The total electron energy density (HBCP) (electronic Hamiltonian) is also obtained from the sum of the electron potential energy density (VBCP) and the kinetic energy density (GBCP).
According to Table 4, the highest electron density of the critical point between the nitrogen atom (N83) of the drug and the boron atom (B60) of the doped fullerene, which indicates more accumulation of charge in the bond, and according to its amount and more significant amounts of laplacian, the electron density, and negativity of the total energy density indicate a covalent bond, which is in agreement with the corresponding energy of the complex formation interaction.
For hydrogen bonding , they are between 0.04-0.02 and 0.02-0.15, and relatively high values of density and positive and negative values indicate that hydrogen interactions are covalent . According to Table (4), the values of electron density and Laplace of electron density and negative total energy density, the critical point between the nitrogen atom of the drug (N87) and the hydrogen atom of the carboxyl group (H64) of the functionalized nanoparticle, indicate a hydrogen bond of quasi-quantum nature. The Cl84…C12 and H99…O63 bonds, in the CZT-C59B and CZT-C60COOH complexes, respectively, are of the Van der Waals attraction type shown in Fig. 3. Therefore, Fig. 3 shows the critical junctions between the drug and fullerene C60 in the CZT-C59B and CZT-C60COOH complexes.
Natural bond orbital analysis
Natural bond orbital (NBO) analysis is considered a useful tool for investigating the intermolecular interactions. The larger the E(2), the stronger the interaction between the donor electron (base Lewis) and the receiving electron (Lewis acid) . The relevant results and load transfer of CZT-C59B and CZT-C60COOH complexes are given in Table 5.
According to Table 5, it is clear that the estimated values of the second-order energy disorder for the interaction between CZT and fullerene C60COOH are very high, as well as the high tendency of electronic density by CZT to fullerene C60COOH. That is in line with the results of calculating the chemical potential. Also, Table 6 shows the result of partial loads of drug and fullerenes atoms in various types of interaction in the C60COOH, CZT, and CZT-C60COOH complex.
It will be more stable for a complex that has more negative interaction energy. In the relevant complex, the hydrogen atom number 64 shows a less positive charge than when it is alone in fullerene. Furthermore, the nitrogen atom No. 87 shows a lower negative charge than when it is in the drug only before the interaction, which is expected due to the direction of charge transfer. The results indicate that the load distribution has changed during the attraction process.
Crizotinib, as an anti-lung-cancer drug, has substantial benefits in cancer therapy, but severe toxicity as side effects is the main problem for it. In this research, the interaction of crizotinib over NH2 agent with C60 fullerene, boron-doped fullerene (C59B), and carboxylated fullerenes (C60COOH) using density functional theory at B3LYP/6-311G(d) theoretical level in the gaseous phase and the water solvent were evaluated. Based on the information on optimization energies, data on chemical descriptors, and investigation of atoms in the molecules theory and natural bond orbital theory in the study of the interaction of CZT from the NH2 group with C60 fullerene, C59B, and C60COOH has been concluded that drug interactions with fullerenes cannot be a functional interaction between drugs and fullerenes due to the positive energy of the interactions and the instability of the resulting complex. By calculating the frequency, the first frequency was real (positive), and Nimag was zero. Also, due to the high energy and atomic theory data in the molecule, it has been determined that the bond between CZT and C59B is covalent, and the drug uptake on this fullerene is chemical. Therefore, it is thought that drug release will not be done well. For this purpose, this interaction and its resulting complex have been misdiagnosed. However, the interaction between CZT with C60COOH has been identified due to some properties such as good solubility in the water phase, excellent stability in energy efficiency and hydrogen bonding, and physical absorption of the drug with fullerene in AIM and NBO evaluation. The result of this research could be counted as a promising strategy in order to reduce the toxicity and develop the anti-lung-cancer activity of crizotinib.
CONFLICT OF INTERESTS
The authors declare that there are no conflicts of interest regarding the publication of this manuscript.