Highlights• Classical steric clashes might have the same topological features as bonding interactions.• An AIL can be observed for highly attractive or repulsive interactions.• An AIL might be a result of either an inflow or outflow of density.• Locally accumulated density does not imply an attractive interaction or an inflow of density.• Nature of an interaction can change with molecular environment.
Graphical abstract
2
AbstractNine kinds of inter-and intramolecular interactions were investigated by exploring the topology of electron density in the interatomic regions using standard protocols of QTAIM, IQA and NCI techniques as well as in-house developed cross-sections of the electron and deformation density distributions. The first four methods provide the properties of the resultant density distribution in a molecular system whereas the later illustrates the process, inflow or outflow of density from fragments to the interatomic region of an interaction on its formation in a molecular system. We used (i) the QTAIM-defined atomic interaction line, AIL (presence or absence), (ii) IQA-defined interaction energy, attractive to repulsive, (ii) 2 < 0 to 2 >0, or (iii) (r) > 0 to (r) < 0; hence, none of the topological indices used here, either separately or combined, can be used to definitely predict the (de)stabilizing nature of an interaction except highly repulsive ones for which the absence of AIL, interatomic density depletion and outflow of density on interaction formation are observed.
The application of
plain cycloalkanes and heterocyclic derivatives
in the synthesis of valuable natural products and pharmacologically
active intermediates has increased tremendously in recent times with
much attention being paid to the lower cycloalkane members. The structural
and molecular properties of higher seven-membered and nonaromatic
heterocyclic derivatives are less known despite their stable nature
and vast application; thus, an insight into their structural and electronic
properties is still needed. Appropriate quantum chemical calculations
utilizing the ab initio (MP2) method, meta-hybrid (M06-2X) functional,
and long-range-separated functionals (ωB97XD) have been utilized
in this work to investigate the structural reactivity, stability,
and behavior of substituents on cycloheptane (CHP) and its derivatives:
azepane, oxepane, thiepane, fluorocycloheptane (FCHP), bromocycloheptane
(BrCHP), and chlorocycloheptane (ClCHP). Molecular global reactivity
descriptors such as Fukui function, frontier molecular orbitals (FMOs),
and molecular electrostatic potential were computed and compared with
lower members. The results of two population methods CHELPG and Atomic
Dipole Corrected Hirshfeld Charges (ADCH) were equally compared to
scrutinize the charge distribution in the molecules. The susceptibility
of intramolecular interactions between the substituents and cycloalkane
ring is revealed by natural bond orbital analysis and intramolecular
weak interactions by the independent gradient model (IGM). Other properties
such as atomic density of states, intrinsic bond strength index (IBSI),
and dipole moments are considered. It is acclaimed that the strain
effect is a major determinant effect in the energy balance of cyclic
molecules; thus, the ring strain energies and validation of spectroscopic
specificities with reference to the X-ray crystallographic data are
also considered.
In recent times, nanomaterials have been applied for
the detection
and sensing of toxic gases in the environment owing to their large
surface-to-volume ratio and efficiency. CO
2
is a toxic
gas that is associated with causing global warming, while SO
2
and NO
2
are also characterized as nonbenign gases in
the sense that when inhaled, they increase the rate of respiratory
infections. Therefore, there is an explicit reason to develop efficient
nanosensors for monitoring and sensing of these gases in the environment.
Herein, we performed quantum chemical simulation on a Ca
12
O
12
nanocage as an efficient nanosensor for sensing and
monitoring of these gases (CO
2
, SO
2
, NO
2
) by employing high-level density functional theory modeling
at the B3LYP-GD3(BJ)/6-311+G(d,p) level of theory. The results obtained
from our studies revealed that the adsorption of CO
2
and
SO
2
on the Ca
12
O
12
nanocage with
adsorption energies of −2.01 and −5.85 eV, respectively,
is chemisorption in nature, while that of NO
2
possessing
an adsorption energy of −0.69 eV is related to physisorption.
Moreover, frontier molecular orbital (FMO), global reactivity descriptors,
and noncovalent interaction (NCI) analysis revealed that the adsorption
of CO
2
and SO
2
on the Ca
12
O
12
nanocage is stable adsorption, while that of NO
2
is unstable
adsorption. Thus, we can infer that the Ca
12
O
12
nanocage is more efficient as a nanosensor in sensing CO
2
and SO
2
gases than in sensing NO
2
gas.
Upon various investigations conducted in search for a
nanosensor
material with the best sensing performance, the need to explore these
materials cannot be overemphasized as materials associated with best
sensing attributes are of vast interest to researchers. Hence, there
is a need to investigate the adsorption performances of various metal-doped
fullerene surfaces: C
59
Au, C
59
Hf, C
59
Hg, C
59
Ir, C
59
Os, C
59
Pt, C
59
Re, and C
59
W on thiourea [SC(NH
2
)
2
] molecule using first-principles density functional theory computation.
Comparative adsorption study has been carried out on various adsorption
models of four functionals, M06-2X, M062X-D3, PBE0-D3, and ωB97XD,
and two double-hybrid (DH) functionals, DSDPBEP86 and PBE0DH, as reference
at Gen/def2svp/LanL2DZ. The visual study of weak interactions such
as quantum theory of atoms in molecule analysis and noncovalent interaction
analysis has been invoked to ascertain these results, and hence we
arrived at a conclusive scientific report. In all cases, the weak
adsorption observed is best described as physisorption phenomena,
and CH
4
N
2
S@C
59
Pt complex exhibits
better sensing attributes than its studied counterparts in the interactions
between thiourea molecule and transition metal-doped fullerene surfaces.
Also, in the comparative adsorption study, DH density functionals
show better performance in estimating the adsorption energies due
to their reduced mean absolute deviation (MAD) and root-mean-square
deviation (RMSD) values of (MAD = 1.0305, RMSD = 1.6277) and (MAD
= 0.9965, RMSD = 1.6101) in DSDPBEP86 and PBE0DH, respectively.
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