Diamond & Related Materials 146 (2024) 111262
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Diamond & Related Materials
journal homepage: www.elsevier.com/locate/diamond
Exploring the naproxen adsorption at the surface of iron-decorated C24
fullerene-like nanocages for providing drug delivery insights along with
DFT calculations
C.Y. Hsu a, M.J. Saadh b, A.I. Ayesh c, M.D. El-Muraikhi c, M. Mirzaei d, *, M. Da'i e, *, S. Ghotekar f,
M.M. Salem-Bekhit g
a
Department of Pharmacy, Chia Nan University of Pharmacy and Science, Tainan, Taiwan
Faculty of Pharmacy, Middle East University, Amman 11831, Jordan
c
Department of Physics and Materials Sciences, College of Arts and Sciences, Qatar University, P.O. Box 2713, Doha, Qatar
d
Department of Natural and Mathematical Sciences, Faculty of Engineering, Tarsus University, Tarsus, Turkiye
e
Faculty of Pharmacy, Universitas Muhammadiyah Surakarta, Surakarta, Indonesia
f
Centre for Herbal Pharmacology and Environmental Sustainability, Chettinad Hospital and Research Institute, Chettinad Academy of Research and Education,
Kelambakkam 603103, Tamil Nadu, India
g
Department of Pharmaceutics, College of Pharmacy, King Saud University, PO Box 2457, Riyadh 11451, Saudi Arabia
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Drug adsorption
Drug delivery
Drug detection
Molecular characterization
Nanostructure
Due the importance of developing successful drug delivery platforms, the current research work done to assess
the iron-decorated C24 fullerene-like nanocages for the adsorption of naproxen (NPX) drug along with density
functional theory (DFT) calculations. NPX is among the important non-steroidal anti-inflammatory drugs
(NSAIDs), in which its enhancement has been still under development. Accordingly, the focus of this work was on
the customization of a carrier model for the NPX drug by investigating the electronic and structural features of
interacting conjugated systems. To do this, three iron-decorated nanocages including FeC24, FeC23, and FeC22
models were prepared to assess the adsorption process to yield the NPX@FeC24, NPX@FeC23, and NPX@FeC22
conjugated systems. Different levels of electronic molecular orbital levels and adsorption strengths were achieved
regarding the interaction of NPX and iron-decorated nanocages, in which the NPX@FeC22 model was at the
highest level of strength and also electronic variations. Accordingly, suitable adsorption and detection of NPX
drug were found by the assistance of iron-decorated nanocage models. Especially in the water solvent, the models
of conjugations were found still stable by the advantage of iron-decorated conjugated systems. The results of this
work could be proposed for further study of NPX drug delivery issues based on the iron-decorated fullerene-like
nanocages.
1. Introduction
The occurrence of inflammation symptoms in human body is very
common because of several reasons such as daily lifestyles, diseases,
infections, surgeries, etc. [1,2]. Although the conventional medications
are currently available for working as anti-inflammatory agents, but
their efficiency is not certain enough to completely overcome the
occurred harmful issues [3,4]. Accordingly, enhancing the available
anti-inflammatory drugs or developing new ones are crucial for recov
ering the patients to their normal life [5,6]. Based on the results of
earlier research efforts, advantages of non-steroidal anti-inflammatory
drugs (NSAIDs) for dealing with the inflammation symptoms have been
indicated especially by reducing the pain and fever to help the treatment
of harmed tissues [7,8]. However, there are still serious risks of medi
cation by NSAIDs, in which the occurrence of serious adverse effects
such as the gastrointestinal bleeding, kidney diseases, and heart attacks
has been reported up to now [9,10]. Hence, further efforts are required
to deal with the unwanted impacts of NSAIDs for the patients in addition
to the enhancement of their therapeutic efficiency [11,12]. Naproxen
(Fig. 1) is among the NSAIDs category for medicating the inflammatory
diseases such as rheumatoid arthritis, gout and fever in addition to the
pain reduction [13,14]. However, serious adverse effects such as heart
* Corresponding authors.
E-mail addresses: mahmoudmirzaei@tarsus.edu.tr (M. Mirzaei), muhammad.dai@ums.ac.id (M. Da'i).
https://doi.org/10.1016/j.diamond.2024.111262
Received 2 March 2024; Received in revised form 28 May 2024; Accepted 1 June 2024
Available online 2 June 2024
0925-9635/© 2024 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
C.Y. Hsu et al.
Diamond & Related Materials 146 (2024) 111262
new specifications for the nanostructures regarding the existence of an
activated surface region for involving in more successful communica
tions with other substances [35]. Especially in the case of iron decora
tions, an advantage of iron compatibility with the biological systems has
been already investigated very well [36–38]. Among the several avail
able nanostructures, fullerenes have been found as single standing ar
chitectures with the spherical shapes for working in the interaction and
adsorption processes [39]. Besides the well-known (5,6)-rings C60
fullerene, several other architectures of fullerene-like nanocages have
been investigated up to now, in which (4,6)-rings C24 fullerene-like
nanocage was found as a possible configuration [40–42]. Accordingly,
the application of this nanocage has been investigated for adsorbing the
drug substances along with computational assessments [43–45]. Addi
tionally, the atomic decoration of nanostructure was also done for
providing more customized scaffolds for approaching the targeted pur
poses [46]. Hereby, a representative model of C24 fullerene-like nano
cage was employed within the current research work to adsorb the
naproxen NSAIDs substance for providing drug delivery insights along
with DFT calculations. For obtaining detailed information of interacting
substances, DFT calculations could reveal insights into the details of
conjugated system before and after the occurrence of interaction or
adsorption processes [47].To this aim, various models of iron-decorated
fullerene-like nanocages were explored and the possibility of in
teractions between drug and nanocage substances were examined along
with the formation of naproxen@nanocage conjugations (Fig. 3).
Based on the results of earlier works, the formation of naprox
en@nanostructure conjugation was found as a way of drug enhancement
through the development of smart drug delivery processes [48–50].
Accordingly, the formation of naproxen@nanocage conjugations was
assessed within this work for assigning the advantages of iron-decorated
fullerene-like nanocages towards the adsorption of naproxen drug. As
mentioned earlier, tailoring the nanostructures to customize them for
employing in the drug delivery process is a complex subject, in which
the recognition of detailed information for the conjugated formations
could help to provide more insights into the development of new carrier
scaffolds [51–53]. The required features of naproxen and nanocage
counterparts were evaluated within this work to discuss their electronic
and structural specifications before and after the formation of naprox
en@nanocage conjugations; all details were summarized in Figs. 1–4
and Tables 1–4.
Fig. 1. The naproxen (NPX) model; the molecular heads were assigned for the
formation of Config. I and Config. II conjugations.
diseases, strokes, gastrointestinal bleeding, stomach pain, dizziness,
headache, bruising, and allergic reactions have been observed for the
patients after their medication by naproxen [15–18]. To this point,
considerable efforts have been done to develop safe protocols for the
naproxen medication in a safe level along with structural customizations
and officiations, in which smart drug delivery platforms have been
supposed as a useful method of enhancement [19–24]. In this case,
exploring a suitable carrier for a specific drug is an essential step of
developing successful drug delivery processes [25,26]. Besides, learning
details of interactions between drug and carrier counterparts is very
essential for approaching the purpose [27]. To this aim, a drug…carrier
system was investigated within the current research work based on
density functional theory (DFT) assessments of the naproxen (Fig. 1)
adsorption at the surface of iron-decorated C24 fullerene-like nanocages
(Fig. 2) along with the formation of naproxen@nanocage conjugations
(Fig. 3).
Since the innovation of nanotechnology, considerable efforts of re
searchers have been focused on the characterization of nanostructures to
customize them for the specific functions and applications [28,29].
Accordingly, several architectures of nanostructures have been devel
oped to this time to fulfill the criteria of working in the specific fields
from industry to biology [30–32]. Supplying a suitable surface for
involving in interaction and adsorption processes with other substances
was one important practical issue about the nanostructures [33]. Not
only the pure composition, but also the doped or decorated nano
structures could do a good jog for the providing the communicating
surface [34]. Decorating with metal atoms such as iron, even brought
2. Materials and methods
The naproxen drug substance (NPX; C14H14O3) and the pure and
iron-decorated fullerene-like nanocages (Figs. 1 and 2) were the starting
materials of this work. A representative model of C24 fullerene-like
nanocage, which was already known as a possible mode of fullerenes
[40–42], was employed as the basic model of this work and three irondecorated models were generated by inserting one iron atom to create
FeC24, FeC23, and FeC22 models regarding the condition of atomic
decoration. One iron atom was attached to the exterior surface of
nanocage to make the FeC24 model. One iron atom was substituted
instead of one carbon atom of nanocage to make FeC23 model. One iron
atom was substituted instead of two carbon atoms of nanocage to make
the FeC22 model [52]. Since the spin polarization of iron atom is an
important issue as described by the earlier works of iron medicated
systems [54,55], energies of structures in singlet (0, 1), triplet (0, 3), and
quintet (0, 5) states were calculated for the models of this work
(Table S1 of Supplementary file). Although the non-singlet models were
found more stable in some cases, but the energy convergence was not
obtained for all of them and the structures were not found trustable. In
this regard, the structures of this work were all investigated in the zero
global charge and singlet multiplicity to represent the trustable struc
tures of nanocage models and their complexes in a unique electronic
state. Subsequently, the interacting conjugations were found as
NPX@C24, NPX@FeC24, NPX@FeC23, and NPX@FeC22 models as shown
Fig. 2. The pure and iron-decorated fullerene-like nanocages; the bond dis
tances were written in Å.
2
C.Y. Hsu et al.
Diamond & Related Materials 146 (2024) 111262
Fig. 3. The naproxen@nanocage conjugations in two configurations; Config. I and Config. II, and their green dotted lines interactions as indicated by accompa
nying numbers.
Fig. 4. The HOMO-LUMO distribution patterns embedded DOS diagrams of naproxen@nanocage conjugated systems and the singular nanocages.
in Fig. 3. The models were optimized to obtain the minimized energy
geometries and their structural features were evaluated for the opti
mized systems. Although the free optimization calculations were formed
for the formation of conjugated systems, but Config. I and Config. II were
found as two main interacting configurations for the formation of each
conjugated system Based on the oxygen heads of NPX as shown in Fig. 1.
3
C.Y. Hsu et al.
Diamond & Related Materials 146 (2024) 111262
Table 1
Electronic features based on HOMO-LUMO levels and their related quantities.
Model
HOMO eV
C24
FeC24
FeC23
FeC22 [52]
NPX@C24
−
−
−
−
−
−
−
−
−
−
−
−
NPX@FeC24
NPX@FeC23
NPX@C22
Config.
Config.
Config.
Config.
Config.
Config.
Config.
Config.
I
II
I
II
I
II
I
II
7.91
7.08
7.29
6.80
7.40
7.41
6.62
6.56
6.67
6.46
6.86
6.62
LUMO eV
−
−
−
−
−
−
−
−
−
−
−
−
Fermi eV
1.68
1.01
1.52
3.27
1.57
1.24
0.51
0.45
0.76
0.54
1.47
1.18
−
−
−
−
−
−
−
−
−
−
−
−
O1 |e|
O2 |e|
O3 |e|
Fe |e|
Q |e|
NPX
C24
FeC24
FeC23
FeC22
NPX@C24
− 0.537
n/a
n/a
n/a
n/a
− 0.536
− 0.534
− 0.633
− 0.530
− 0.607
− 0.531
− 0.540
− 0.532
− 0.624
n/a
n/a
n/a
n/a
− 0.624
− 0.587
− 0.622
− 0.683
− 0.623
− 0.648
− 0.623
− 0.523
− 0.724
n/a
n/a
n/a
n/a
− 0.0724
− 0.723
− 0.722
− 0.675
− 0.720
− 0.667
− 0.722
− 0.748
n/a
n/a
0.883
0.837
0.820
n/a
n/a
0.806
0.794
0.775
0.760
0.876
0.906
n/a
n/a
n/a
n/a
n/a
0.018
0.025
0.111
0.103
0.154
0.175
0.271
0.213
NPX@FeC24
NPX@FeC23
NPX@C22
Config. I
Config. II
Config. I
Config. II
Config. I
Config. II
Config. I
Config. II
WF eV
CH eV
EI eV
6.23
6.07
5.77
3.52
5.83
6.17
6.11
6.11
5.90
5.92
5.38
5.44
4.79
4.05
4.40
5.04
4.49
4.33
3.56
3.51
3.71
3.50
4.17
3.90
3.12
3.04
2.89
1.77
2.92
3.09
3.06
3.06
2.96
2.96
2.70
2.72
3.69
2.70
3.36
7.18
3.45
3.03
2.08
2.01
2.34
2.07
3.22
2.80
density of states (DOS) were also exhibited in Fig. 4 for the investigated
models. Natural bond orbital (NBO) based charges were evaluated for
the models besides. Additionally, the thermochemistry features were
evaluated to show the impact of water solvent on the stability of con
jugated systems based on the polarizable continuum model (PCM). All
evaluated electronic and structural quantities were summarized in
Tables 1–4. Indeed, the main idea of this work was focusing on the
exploration of variations of models along with the conjugation forma
tions and also assessing the possibility of formations of such conjugated
systems. In this case, the challenges of similarity of computationally
evaluated features and those of experimentally obtained ones could be
treated in a better mode by clarifying the main idea of this work. Even in
the case of used methods of calculations, there are challenges of reli
ability and validity of employed theoretical methods for performing
computations [56]. To this point, the DFT calculations of this work were
done using the ωB97XD/6-31G* level of theory, in which the ωB97XD
functional has been already found useful for exploring the interacting
systems based on the dispersion correction effects [57–59] and the 6-
Table 2
NBO atomic charges of oxygen and iron atoms and also transferred charges.
Model
4.79
4.05
4.40
5.04
4.49
4.33
3.56
3.51
3.71
3.50
4.17
3.90
Gap eV
The interactions were characterized by performing additional quantum
theory of atoms in molecules (QTAIM) analyses to learn the numbers of
interactions, their roles, and also the contributing atoms between the
counterparts in each system. The total strength of interaction/adsorp
tion was recognized by evaluating the structural energies in the term of
adsorption energy (EAds). Vibrational frequencies were also examined
for the models in both of singular and bimolecular conditions to examine
the global minimization states; the evaluated spectra were included in a
Supplementary file. By finalizing this step, the models were obtained for
exploring their features regarding both of electronic and structural
terms.
The models were involved in the electronic characterizations by
evaluating energy terms of the highest occupied molecular orbital
(HOMO) and the lowest unoccupied molecular orbital (LUMO) and also
their related parameters. In the case of electronic characterization, the
features of models were compared before and after the occurrence of
interaction/adsorption process and the results were evaluated accord
ingly. Distribution patterns of HOMO and LUMO and diagrams of
Table 4
Thermochemistry features of water solvent impacts.
Model
ΔGWater kcal/
mol
NPX@C24
NPX@FeC24
NPX@FeC23
NPX@C22
Config. I
Config.
II
Config. I
Config.
II
Config. I
Config.
II
Config. I
Config.
II
ΔHWater kcal/
mol
ΔSWater kcal/
mol.K
− 7.81
− 8.71
− 7.62
− 8.38
0.65
1.11
− 21.29
− 22.66
− 22.37
− 23.45
− 2.67
− 3.63
− 14.81
− 15.41
− 15.53
− 16.91
− 2.41
− 5.01
− 11.24
− 13.65
− 11.10
− 14.29
− 1.46
− 2.16
Table 3
Structural features based on adsorption energies and interactions details.
Model
NPX@C24
NPX@FeC24
NPX@FeC23
NPX@C22
EAds kcal/mol
Config. I
− 4.53
Config. II
− 2.55
Config. I
Config. II
Config. I
Config. II
Config. I
−
−
−
−
−
36.16
39.75
29.19
32.31
41.16
Config. II
− 41.42
Interaction
Distance Å
ρ au
∇2ρ au
1:
2:
1:
2:
1:
1:
1:
1:
1:
2:
1:
2:
3:
2.76
2.96
3.15
2.77
1.88
1.79
1.96
1.92
1.84
3.04
1.93
3.01
3.35
0.0143
0.0041
0.0067
0.0139
0.1053
0.1277
0.0856
0.0896
0.1054
0.0056
0.0849
0.0046
0.0026
0.0446
0.0134
0.0246
0.0436
0.6668
0.9032
0.4974
0.5604
0.7683
0.0158
0.5592
0.0408
0.0075
O1…C
H…C
O3…C
O2…C
O1…Fe
O2…Fe
O1…Fe
O2…Fe
O1…Fe
H…C
O3…Fe
H…C
H…C
4
H au
−
−
−
−
−
−
0.0009
0.0006
0.0004
0.0008
0.0101
0.0154
0.0154
0.0138
0.0112
0.0008
0.0128
0.0009
0.0005
C.Y. Hsu et al.
Diamond & Related Materials 146 (2024) 111262
31G* basis set has been already found useful for exploring the involving
atoms of this work [60]. The calculations were done using the Gaussian
09 program [61] and the data extractions and graphical representations
were done using the ChemCraft [62], Multiwfn [63], and GaussSum
[64] programs. Hereby, the required information for exploring the
electronic and structural features of NPX@C24, NPX@FeC24,
NPX@FeC23, and NPX@FeC22 conjugated systems were evaluated to
assess a possible drug delivery platform of NPX drug using the repre
sentative nanocages. For the case of such molecular issues, the results of
earlier works showed benefits of employing computations to clarify
details of complicated systems especially for the case of new substances
identifications and developments [65,66].
comparison with the other two decorated models. The iron atom was
doped at the exterior surface of nanocage to make the FeC24 model;
however, that iron atom was doped inside the atomic structure of
nanocage instead of one and two carbon atoms to make the FeC23 and
FeC22 models. Accordingly, different electronic features were evaluated
for the models regarding such structural decorations. Next, the results of
DOS diagrams indicated different variations of molecular orbitals fea
tures before the HOMO level and after the LUMO level with a significant
change of energy gap (Gap) between two dominant levels of frontier
molecular orbitals. It is known that the HOMO and LUMO energy levels
stand for the electron transferring tendency of a molecular system for
electron donating and accepting inside and outside the molecule. In this
case, these levels are dominant for the frontier molecular orbitals and
their information could be used for determining the model specifica
tions. Comparing the obtained electronic features for the conjugated
systems in Fig. 4 also reveal different electronic systems for the inter
acting models based on the movement and localization of HOMO and
LUMO levels. Comparing the electronic variations of conjugated models
by those of the singular models could lead to approach a sensing func
tion for the nanocages for adsorbing the NPX drug substance. Indeed,
different Gap values could yield different conductance rates for the
molecular systems regarding their sensing functions and activities. In
the case of investigated models, such changes could be observed by the
visual representations of HOMO and LUMO patterns and also illustrated
DOS diagrams. Even the formation of each configuration could be
determined by measuring the changes of such electronic features.
Indeed, the conductance rate is related to the Gap variations and their
changes could significantly change the features of models. For better
describing these features, the quantitative values of HOMO and LUMO
related features were summarized in Table 1. A quick look at the eval
uated results could indicate meaningful variations of both of HOMO and
LUMO levels in both of singular and conjugated states. Additionally,
significant variations of models from the singular state to the conjugated
state emphasized on the measurements of detection purposes. Accord
ingly, the Fermi energy and Gap values detected changes of such elec
tronic variations to show different environment in the investigated
models. The values of HOMO and LUMO were directly calculated
whereas Eqs. (1)–(5) were used to calculate the values of Fermi energy,
Gap, work function (WF), chemical hardness (CH), and electrophilicity
index (EI).
3. Results and discussion
The term of “drug enhancement” is an important issue because of so
many reasons such as drug inefficiencies and resistances, side effects,
and many more things leading to the considerable efforts of researchers
to work on the available drugs or innovating new ones. In this case, the
results of earlier studies indicated that the conjugation of drugs with
other substances such as nanostructures could yield a drug delivery
platform under a controllable process and a smart mechanism. However,
all details of such platforms are still unknown and further investigations
are required to approach such a successful platform especially regarding
the critical points of working in the living systems. Accordingly,
customizing the nanostructures towards the specific drug substances is a
crucial step for investigating new carriers to be employed for the drug
delivery processes, in which learning details of drug adsorption at the
surface of nanostructures could reveal insightful information about the
formation of drug-carrier conjugated systems. By this importance, the
current research work was initiated to explore the naproxen adsorption
at the surface of representative iron-decorated C24 fullerene-like
nanocages for providing drug delivery insights along with DFT calcu
lations. As shown in Fig. 1, two oxygen heads of naproxen (NPX) were
found very suitable to interact with the nanocages (Fig. 2) leading to the
formation of two main Config. I and Config. II configurations for the
naproxen@nanocage conjugations (Fig. 3). The structures were found
during a free optimization process and the obtained conjugations were
found as the final stabilized systems. The pure and iron-decorated
fullerene-like nanocages were designed by employing a representative
C24 model and its various models of iron-decorated architectures. As
mentioned earlier, one iron atom was added to the exterior surface of
C24 to make the FeC24 model, one iron atom was substituted instead of
one carbon atom of C24 to make the FeC23 model, and one iron atom was
substituted instead of two carbon atoms of C24 to make the FeC22 model.
The geometries were fully optimized to find the stabilized structures in
addition to the conformation by their vibrational frequency calculations;
as available in a Supplementary file. At this step, the parental materials
of study were prepared to be involved in interaction to each other to
proceed the adsorption processes of conjugated system formations as
shown in Fig. 3. Based on two oxygen heads of NPX, two configurations
were found for the interaction of NPX with each nanocage as indicated
by Config. I and Config. II in the model representations. Hereby, the
stabilized models were found and their features were evaluated for
approaching the goal of this work to assess the employed customization
of investigated fullerene-like nanocages for adsorbing the NPX drug
substance.
Besides the structural representations of models in Figs. 1–3, their
electronic features were exhibited in Fig. 4 showing the HOMO-LUMO
distribution patterns and DOS diagrams for exploring the impacts of
atomic decorations on the electronic system of models and formations of
conjugations. As could be found by the patterns, the iron-decorated
atom could show a significance of existence in the nanocage architec
ture by localization of patterns around the decorated region. However,
different levels of significance were found for all three decorated
models, where the highest significance was found for the FeC22 model in
Fermi = 1/2 (HOMO + LUMO)
(1)
Gap = (LUMO − HOMO)
(2)
WF ∼ − Fermi
(3)
CH = 1/2 (LUMO − HOMO)
(4)
/
/
EI = 1 4 (HOMO + LUMO)2 (LUMO − HOMO)
(5)
Among the iron-decorated models, the values of Gap in Table 1 were
found to be 6.07, 5.77, and 3.52 eV for FeC24, FeC23, and FeC22 models
all smaller than the pure C24 model with 6.23 eV. It is known that a
smaller value of Gap could lead to a higher activity/reactivity of the
molecular model; therefore, a higher activity/reactivity of irondecorated models could be found in comparison with the pure model.
Besides the variations of electronic features for recognizing the models,
the activities of molecular systems could be also assigned by such fea
tures. In this case, the impacts of iron-decoration could be learned by
monitoring the electronic features among the models. For the interac
tion configurations, changes of electronic features were variable for the
Config. I and Config. II. To confirm this claim, the values of Fermi were
obvious to show the average values of HOMO and LUMO levels and their
distances also. Accordingly, the values of WF, as an important factor of
approaching sensing functions were changed regarding the changes of
5
C.Y. Hsu et al.
Diamond & Related Materials 146 (2024) 111262
HOMO and LUMO levels, in which the results were found to detect the
models in both of singular and conjugated states. As a consequence, the
variations of electronic features were found for both of singular and
conjugated states even with a significance of recognizing the formation
of conjugations or distinguishing the conjugated models from each
other. In complementary with these results, the values of CH could show
an advantage of iron-decoration for approaching the nanocages with
lower levels of hardness in comparison with the pure C24 model. Again,
the magnitude of lowering the hardness was different for the nanocages
based on the model of iron decoration, in which the FeC22 model was
found with lowest level of hardness or the highest level of softness in the
other words; as hardness and softness are in opposite with each other.
On the other hand, the values of EI also approved the highlighted fea
tures of FeC22 nanocage.
The values of NBO atomic charges for the oxygen atoms of NPX and
the iron atom of nanocages were listed in Table 2 besides the values of
transferred charge (Q) from the NPX substance to the nanocage. Based
on the results, different charges of oxygen atoms in the singular NPX and
also different charges of iron atom in the singular nanocage were
obvious. It was already mentioned that the nanocages were assigned as
covalent complexes in this work and the iron atom was a part of this
covalent architectures, because of it the zero global charge and the
singlet multiplicity was used for the calculations. In this part of study,
the charges of iron atoms could confirm the idea by the values of positive
charges even below one showing their role as a member of covalent
architecture. Additionally, different nanocages showed different charges
for the iron atoms indicating the importance of customization way of
nanocages for approaching the desirable results. Indeed, variations of
charges and also their changes after the formation of conjugations could
lead to the information about the investigated systems and their in
teractions details. For example, participating only one oxygen of car
boxylic group; O2 and O3, could be related to the variation of charges
among the atomic sites. Accordingly, the models could be found variable
by their charge features of dominant atoms; the oxygen atoms of NPX
and the iron atom of nanocages. It seems that there was a competition
between O2 and O3 to interact with the iron atom of nanocage for the
formation of Config. II, in which only one oxygen was the winner; O2 for
the formation of NPX@FeC24 and NPX@FeC23 and O3 for the formation
of NPX@FeC22. It could be remembered that the EI of FeC22 was high
lighted among the models, and the formation of both of Config. I and
Config. II of NPX@FeC22 was by the assistance of formation of com
plementary H…C interactions, which would be discussed later in this
discussion. On the other hand, the direction of charge transferring from
the NPX counterpart to the nanocage counterpart was found with a
higher significance in the iron-doped models in comparison with the
pure model showing the importance of iron-decoration for approaching
more desirable adsorbent. To this aim, the models were recognizable
and their features were available for approaching the purpose of elec
tronic assessments of nanocage counterparts for adsorbing the NPX drug
substance. As a highlighted remark, the iron-decoration increased the
reactivity of nanocage for participating in stronger interactions with the
NPX drug substance and they were recognizable in accordance with the
measurement of such changes and variations.
Based on the results of electronic variations, the models of pure and
iron-doped nanocages were recognized to be assessed regarding their
characteristic specifications. The structural features were also analyzed
to approach details of adsorption processes regarding the involving in
teractions. The optimized structures were shown in Figs. 1–3 including
the interacting conjugated systems in Fig. 3. In addition to the optimi
zation calculations for stabilizing the structures, the interactions were
characterized by performing additional QTAIM analyses on the opti
mized models. To find a general strength of interaction/adsorption
process for the conjugated systems, Eq. (6) was used to evaluate the
values of EAds and the results were summarized in Table 3 in addition to
the QTAIM analyses results of each interaction. The features ρ, ∇2ρ, and
H stand for electron density, Laplacian of electron density, and energy
density, which are crucial to define the nature of interactions based on
the QTAIM analyses. For the evolution of EAds, the basis set super
position error (BSSE) was also implemented.
EAds = ENPX@fullerene − ENPX − Efullerene + BSSE
(6)
With the exception of pure C24 nanocage, the strength of Config. II
was found higher than that of Config. I in the iron-decorated models.
Moreover, the iron-decorated models were found to make stronger in
teractions because of the managing role of iron atom to contribute to
stronger interactions with the oxygen heads of NPX. Indeed, the charges
of iron atoms were also in a deterministic role of formation of such
conjugations with different strengths. The formation of Config. I was due
to the involvement of an ether type oxygen of NPX in interactions
whereas the formation of Config. II was due to the involvement of a
carboxylic type oxygen group. In the NPX@C24 model, one H…C
interaction in additional to the O1…C interaction was found for the
Config. I with the EAds − 4.53 kcal/mol whereas two O…C interactions
(O3…C and O2…C) were found for the Config. II with the EAds − 2.55
kcal/mol. So, the formation of H…C interaction could be known as an
important complementary interaction between the counterparts.
Comparing the QTAIM features also approved the existence of a
reasonable portion of electron sharing for the involving interactions
with the final H values of 0.0009 and 0.0006 au for the O1…C and H…C
of Config. I and 0.0004 and 0.0008 au of O3…C and O2…C of Config. II.
In this case, the models were in the physical non-covalent mode of in
teractions to each other. Comparing the EAds values for iron-decorated
models indicated the highest strength for the NPX@FeC22 model
whereas the NPX@FeC24 and NPX@FeC23 models were placed at the
next levels. The iron-decoration way of nanocage was different in the
complexes, in which the spherical shape was almost remained for the
FeC22 model; while the shape was a little bit deformed for other FeC23
and FeC24 models. Indeed, that spherical shape was an advantage of
FeC22 model for keeping the spherical architecture of fullerene models,
in which the spherical shape helped the FeC22 model to contribute to
stronger interactions with the NPX drug substance. For the NPX@FeC22
model, O1…Fe and H…C interactions were found for Config. I (EAds =
− 41.16 kcal/mol) and O3…Fe and two H…C interactions were found
for Config. II (EAds = − 41.42 kcal/mol). In this case, the existence of two
complementary H…C interactions yielded a little bit stronger adsorption
level for the formation of Config. II in comparison with that of Config. I.
The obtained H values for O1…Fe (− 0.0112 au) and O3…Fe (− 0.128
au) indicated the meaningful contribution of O…C interactions for the
formation of both of Config. I and Config. II, in which the negative sign
could help to assess the interactions with higher electrostatic terms. For
the NPX@FeC24 model, only one O…Fe interaction was found for the
formation of each configuration, where O1…Fe was contributed to the
formation of Config. I (EAds = − 36.16 kcal/mol) and O2…Fe was
contributed to the formation of Config. II (EAds = − 39.75 kcal/mol).
Similarly for the NPX@FeC23 model, only one O…Fe interaction was
found for the formation of each configuration, where O1…Fe was
contributed to the formation of Config. I (EAds = − 29.19 kcal/mol) and
O2…Fe was contributed to the formation of Config. II (EAds = − 32.31
kcal/mol). In all cases of iron-decorated conjugated systems, the
contribution of O…Fe interaction was dominant with a high portion of
electrostatic feature for the formation of strong adsorption process.
However, in the pure fullerene, such a highlighted feature was not
found; hence, it could be claimed that the idea of iron-decoration was
useful for obtaining strong adsorptions. It is worth to mention that the
indicated bond distances of singular nanocages in Fig. 2 were only
changed with a magnitude of ~0.02 Å from the singular state to the
conjugated states. In the other words, the nanocage models kept their
original structures with small changes from the singular state to the
conjugation state. Comparing with a parallel work for the C–Fe distance
of ~2 Å for the iron decorated C60 fullerene nanocage [67], the average
results of this work were found ~1.9 Å, which could be known as a good
agreement between the study of small and large nanocage systems.
6
C.Y. Hsu et al.
Diamond & Related Materials 146 (2024) 111262
To investigate the impact of water solvent on the stability of conju
gations, the PCM based calculations were performed to evaluate ther
mochemistry features in the water solvent in comparison with the isolate
gas phase as listed in Table 4. The quantities included the variations of
sum of electronic and thermal free energies (ΔGWater), sum of electronic
and thermal enthalpies (ΔHWater), and entropies (ΔSWater) as compared
in the water solvent by the gas phase along with the symbolic Eq. (7). As
could be found by the results, the models of conjugations were still
stable in the water solvent with better features than the gas phase. In all
cases, the results of Config. II were more highlighted than the results of
Config. I in parallel with the already obtained higher level of stability of
Config. II than Config. I. In this regard, the iron-doped models were
found more stabilized in the water solvent especially by the negative
values of ΔSWater; however, this value was positive for the conjugations
of pure carbon models indicating a higher disordered in the water sol
vent in comparison with the gas phase state. On the other hand, the irondoped conjugations showed higher ordered states in the water solvent in
comparison with the gas phase state. As a consequence, the models were
stabilized and the impacts of solvents indicated possibility of employing
these systems in the water solvated systems.
ΔXWater = XWater−
solvent
− XGas−
phase
X : G, H, or S.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Data availability
Data will be made available on request.
Acknowledgements
The author (M.M. Salem-Bekhit) would like to extend his sincere
appreciation to the Researchers Supporting Project Number
(RSPD2024R986), King Saud University, Riyadh, Saudi Arabia.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.diamond.2024.111262.
(7)
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CRediT authorship contribution statement
C.Y. Hsu: Writing – original draft, Conceptualization. M.J. Saadh:
Writing – original draft, Investigation. A.I. Ayesh: Writing – review &
editing, Validation, Methodology. M.D. El-Muraikhi: Writing – review
& editing, Formal analysis. M. Mirzaei: Writing – review & editing,
Visualization, Supervision, Methodology. M. Da'i: Project administra
tion, Conceptualization. S. Ghotekar: Methodology, Investigation. M.
M. Salem-Bekhit: Writing – review & editing, Funding acquisition,
Conceptualization.
7
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