Effective Adsorption of A-Series Chemical Warfare Agents on Graphdiyne Nanoflake; a DFT Study

Effective Adsorption of a-series Chemical Warfare Agents on Graphdiyne Nanoake; A DFT Study

Hasnain Sajid COMSATS Institute of Information Technology - Abbottabad Campus Sidra Khan COMSATS Institute of Information Technology - Abbottabad Campus Khurshid Ayub COMSATS Institute of Information Technology - Abbottabad Campus Tariq Mahmood (  [email protected] ) COMSATS Institute of Information Technology - Abbottabad Campus https://orcid.org/0000-0001- 8850-9992

Research Article

Keywords: Graphdiyne nanoake, Chemical warfare agents, DFT, QTAIM, SAPT, RDG

Posted Date: February 10th, 2021

DOI: https://doi.org/10.21203/rs.3.rs-209734/v1

License:   This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License

Version of Record: A version of this preprint was published at Journal of Molecular Modeling on April 1st, 2021. See the published version at https://doi.org/10.1007/s00894-021-04730-3. Effective adsorption of A-series chemical warfare agents on graphdiyne nanoflake; a DFT study

Hasnain Sajid#, Sidra Khan#, Khurshid Ayub, Tariq Mahmood*

Department of Chemistry, COMSATS University, Abbottabad Campus, Abbottabad-22060, Pakistan

*To whom correspondence can be addressed: E-mail: [email protected] (T. M)

# Hasnain Sajid & Sidra Khan have equal contributions for first authorship

Abstract

Chemical warfare agents (CWAs) are highly poisonous and their presence may cause diverse effect not only on living organisms but on environment as well. Therefore, their detection and removal in a short time span is very important. In this regard, here the utility of graphdiyne (GDY) nanoflake is studied theoretically as an electrochemical sensor material for the hazardous CWAs including A-230, A-232, A-234. Herein, we explain the phenomenon of adsorption of A-series CWAs on GDY nanoflake within the density functional theory (DFT) framework. The characterization of adsorption is based on optimized geometries, BSSE corrected energies, SAPT, RDG, FMO, CHELPG charge transfer, QTAIM and UV-Vis analyses. The calculated counterpoise adsorption energies for reported complexes range from -13.70 to -17.19 kcal mol-1. These adsorption energies show that analytes are physiosorbed onto GDY which usually takes place through noncovalent interactions. The noncovalent adsorption of CWAs on GDY is also attributed by the SAPT0, RDG and QTAIM analyses. These properties also reveal that dispersion factors dominate in the complexes among many noncovalent components (exchange, induction, electrostatic, steric repulsion). In order the estimate the sensitivity of GDY, the %sensitivity and average energy gap variations are quantitatively measured by energies of HOMO and LUMO orbitals. In term of adsorption affinity of GDY, UV-Vis analysis, CHELPG charge transfer and DOS analysis depict an appreciable response towards these toxic CWAs.

Keywords: Graphdiyne nanoflake; Chemical warfare agents; DFT; QTAIM; SAPT; RDG

Introduction

Chemical warfare agents (CWAs) are the most destructive, toxic and lethal chemicals being used in the 19th century [1–3]. After World War II, a large quantity of these agents were disposed of in the oceans [4], without keeping in mind that how could it be dangerous for sea life and their dependant species. In the 20th century, these chemicals were used for terrorist attacks to cause more damage [5]. Apart from this, these CWAs have found extensive usage in various industries such as ore refining, metal cleaner, organic synthesis, pharmaceutical, dye and pesticide industries [6, 7]. The concentration of CWAs has gradually increased in the atmosphere due to the easy availability in material industries which may lead to a serious threat to life on earth. Basically, CWAs can be classified in four classes based on their site of actions, these classes include; pulmonary, blood, blistering and nerve agents [8]. Based on the chemical structures, these classes are further divided in four subclasses commonly called as series such as V-series, H-series, G-series and A-series. Among all these classes, A-series nerve agents are considered as fourth generation chemicals, firstly synthesized in 1970s under the Union of Socialist Soviet Republics (U.S.S.R) chemical weapon program [9]. In the beginning A-230 was synthesised by replacing substituting O-isopropyl group of sarin with aceoamydin radical. Later on, Kirpichey et al., synthesized A-232 and A-234 derivatives by introducing methoxy and ethoxy groups in A-230, respectively [10].

A-230 A-232 A-234 O O F F O N P P N N N N N P F O O

Fig. 1: Structure of A-series (A-230, A-232m A-234) reported by Mirzayanov [11].

These novel series (A-series) of nerve agents are named as “Novichok” [12]. Even though, the Novichok nerve agents are not tested in the battlefield, but the accidental exposure of a worker of Novichok development project induced nerve damage, resulted permanent loss of arm movability, epilepsy, liver cirrhosis and inability to concentrate etc [13, 14]. The structures of Novichok nerve agents have not yet been fully known, however, the two chemists namely; Mirzayanov [13] and Hoenig [15] proposed two different composition with different structures. The Mirzayanov’s structures are displayed in Fig. 1 while the structures of Hoenig are given in supplementary information (Fig. S1). In this study we only focused on the A-230, A-232 and A-234 structures proposed by Mirzayanov because the phosphoramidate nature (Mirzayanov’s structure) is most acceptable by scientific community than phosphorylated oxime nature (Hoenig’s structure) [16]. By virtue of their high toxicity, various experimental and theoretical studies have been performed to find a suitable candidate for even a minute detection of these A-series

3 molecules. In this regard, numerous materials have been tested such as covalent/metal organic frameworks [17–22], zeolites [23], metal oxides [24–26], and other [27–29]. Though, these materials exhibit significant capturing of toxic pollutants, but due to low porosity, small surface area, lack of reproducibility, less active sites and lack of periodicity limit their utility. The desirable properties of sensor materials are have high surface area, high selectivity/sensitivity, rapid response time, low detection limit, less cost, high surface to volume ratio, and minimal impact on environment [30–32]. Recent literature reveals that the two-dimension carbon surfaces are considered to be the best candidate for the effective adsorption of toxic chemical. One of our previous study reveals that graphdiyne (GDY) has superior sensitivity for hazardous materials than graphyne and other 2D carbon surfaces [33]. Moreover, we were failed to find any theoretical study to explain the adsorption sensitivity of GDY towards A-series of CWAs. This motivated us to explore the adsorption mechanism and sensing behaviour of GDY particularly for A-230, A-232 and A-234 analytes. Therefore, we have designed three complexes named as; A-230@GDY, A-232@GDY and A-234@GDY. Our desired results are based on geometric parameters, adsorption energies and other geometric and electronic properties.

Computational methodology

In this study, ωB97XD/6-31+G(d,p) is used for the optimization of all the structures on Gaussian09 [34]. DFT-ωB97XD is a dispersion corrected long-range functional which is well reported to estimate non-covalent interaction energies [35, 36]. The lowest energy geometries (see Fig. 2) are reported in the main manuscript for detailed analysis while all possible interaction orientations are given in supplementary information (Fig. S2). For these stable geometries of complexes, the counterpoise interaction energies are calculated by using the expression below; Ead = E(ana@GDY) – [E(GDY) + E(ana)] + BSSE ---- (1)

Here, Eana@GDY, EGDY and Eana are interaction energies of analytes@graphdiyne complexes, bare graphdiyne and analytes, respectively. The BSSE (basis set superposition error) strategy has be adopted to avoid the error created by overlapping of finite basis set. The accurate determination of noncovalent interactions is mandatory because these play an important role on adsorbing of analytes on graphdiyne surface. For this purpose, the SAPT0 [37] analysis has been performed via Psi4 [38] software. The SAPT0 analysis splits the noncovalent interaction energy in four meaningful components which include exchange, electrostatic, dispersion and induction component. Exchange components attributes the repulsion between completely filled orbitals of interacting moieties whereas, electrostatic, dispersion and induction account the attractive energies between occupied and virtual orbitals of interacting species. The total SAPT energy is accounted by the equation below:

ESAPT = (-Eest) + (Eexch) + (-Eind) + (-Edis) ---- (2)

Reduced density gradient analysis (RDG) graphs are also plotted with their isosurfaces to understand the role and strength of noncovalent interactions between analytes and graphdiyne nanoflake. RDG exhibits that the interaction mechanism mainly depends on the electronic density (ρ). The expression below defines the relationship between ρ and RDG [39]: ---- (3) 1 |∇ρ| 2 1/3 4/3 푅퐷퐺 = 2(3휋 ) ρ In RDG isosurfaces, the colours such as red, blue and green attributes the type of interactions present. The colours represent the steric repulsion (red), strong (blue) and weak (green) interactions [40]. These RDG plots are generated by MultiWFN [41] software. Literature reveals that the charge transfer is an another important electronic property which reveals the accurate interaction between two moieties [42–44]. Therefore, CHELPG analysis has been performed to measure the amount of charge transfer. The charge transfer fluctuation upon complexations is because of HOMO and LUMO gap variation [45, 46] due to the generation of new orbitals. New orbitals generation can be predicted by density of state (DOS) analysis [47–49]. Thus, DOS spectra are generated by using GaussSum software [50]. The TD-DFT calculations are performed to study the electronic excitations upon complexation of GDY with analytes. The UV-Vis spectra are simulated with total 40 states with half singlet and half triplet states. Finally, quantum theory of atoms in molecule (QTAIM) analysis is performed to further probe the nature of interactions. Results and discussion

Interaction stabilities of optimized geometries

In this study, we have attempted to evaluate the sensitivity of GDY nanoflake towards three different toxic chemical warfare agents/A-series such as, A-230, A-232 and A-234. The complexes are named as A-230@GDY, A-232@GDY and A-234@GDY for the ease of understanding. The lowest energy structures of these complexes are shown in Fig. 2, while the results of interaction distances and energies are given in Table 1. Upon adsorption of CWA on GDY nanoflake many atoms interact each other while the discussion is only focussed on the smallest adsorption distances between atoms. When A-230 adsorbs on graphdiyne nanoflake (A230@GDY), the smallest interaction distance is observed between H1 of A-230 and C2 of GDY. The adsorption distance (H1---C2) in A-230@GDY complex is 2.59 while the counterpoise adsorption energy is -13.70 kcal mol-1. However, the adsorption energy increase Å to -16.45 kcal mol-1 in A-232@GDY complex. The increase in interaction energy in A-232@GDY is due to the addition of increasing number of electron rich oxygen atoms, resulting an increase in charge transfer (vide infra). The interaction distance (H1----C2) in A-232@GDY complex is 2.66 . Similarly, the interaction energy further increases to -17.19 kcal mol-1 in A-

234@GDY complex along with the interaction distance (H1----C2) of 2.97 . The increasing Å stability of complexes from A-230@GDY to A-234@GDY complexes is due to the increasing Å

5 involvement of electron donating groups such as oxygen and ethyl group in A-232 and A-234, respectively. Furthermore, the effect of analyte adsorption on the planar structure of GDY is also measured which is referred as energy of deformation (Edef). The Edef are calculated by subtracting the energy of optimized isolated GDY from the single point energies of complexed graphdiyne without analyte (as shown in equation below). The Edef of A-230@GDY, A- 232@GDY and A-234@GDY complexes are 0.44, 0.25 and 0.88 kcal mol-1, respectively.

Edef = E(complexed GDY without analytes) - E(bare GDY)

Top Side A-230@GDY

A-232@GDY

A-234@GDY

Fig. 2: Relaxed (stable) geometries of A-series analytes@GDY complexes with adsorption distances in .

The adsorptionÅ strength of A-series nerve agents on GDY nanoflake is much better than previously reported surfaces. For instant, Motlagh et al., [51] has theoretically calculated the

6 adsorption strength of A-234 nerve agent on C20 fullerene and its derivatives at M062X/6- 311++G(d, p) level of theory. The reported adsorption energies of A-234 on C20 and C20NH2 are -5.27 and -13.55 kcal mol-1, respectively. In another theoretical report, the adsorption of these nerve agents is studied on COF based carbon nitride system (C2N) by Yar et al [52]. The adsorption strength is estimated at M052X/6-311++G(d, p) level of theory. The reported BSSE corrected energies for A-23, A-232 and A-234 on C2N are -15.41, -15.27 and -15.99 kcal mol- 1, respectively. One can infer that the adsorption strength of our reported complexes is considerably higher from these infinite conjugated systems.

Table 1: Interaction atoms (Aint), interaction distances (Dint), counterpoise interaction energies (Ecp), deformation energies (Edef) and energies of SAPT0 analysis of A-230@GDY, A- -1 232@GDY and A-234@GDY complexes. Units of distances and energies are and kcal mol , respectively.

Properties A-230@GDY A-232@GDY Å A-234@GDY Aint H1---C2 H1---C2 H1---C2 Dint 2.59 2.66 2.97 ECP -13.70 -16.45 -17.19 Edef 0.44 0.25 0.88 SAPT0 results

Eest -7.32 -10.22 -10.38

Eexch 14.79 20.92 18.00 Eind -2.61 -3.20 -3.30

Edis -20.43 -26.93 -24.04 ESAPT0 -15.57 -19.42 -19.82

Symmetry adopted perturbation theory (SAPT0) analysis

SAPT0 analysis has been performed to estimate a clear picture of the noncovalent interaction. SAPT0 analysis briefly describes the noncovalent interaction energy by splitting it in four meaningful components [53]. The four noncovalent components of interaction energy are electrostatic (Eest), exchange (Eexch), induction (Eind) and dispersion (Edis) energies [54]. The total sum of these noncovalent components is ESAPT0. Among these components. Among these

SAPT energies, Eexch component is endothermic in nature because it is a repulsion between the occupied orbitals of interacting species which destabilize the complexes. [55]. On the other hand, Eest, Eind and Edisp components are attractive or exothermic in nature which stabilize the complex [54]. Our results in Table 1 attribute that the Edisp components -1 contributes more in stabilizing the complexes. The contribution of Edisp is -20.43 kcal mol in

A-230@GDY complex. The other attractive components i.e., Eest and Eind contribute -7.32 kcal -1 -1 -1 mol and -2.61 kcal mol , respectively. The contribution of repulsive Eexch is 14.79 kcal mol . -1 The total ESAPT in A-230@GDY complex is -15.57 kcal mol . The highest ESAPT is accounted for A-234@GDY complex (-19.82 kcal mol-1) the trend is well accord with the results of interaction energies. In A-234@GDY complex, the contributions of Edisp, Eest and Eind components are - 24.04, -10.38 and -3.30 kcal mol-1, respectively. The repulsive component in A-234@GDY -1 complex is 18.00 kcal mol . Surprisingly, the highest repulsive Eexch contribution (20.92 kcal

7 mol-1) is observed in A-232@GDY complexes which is probably due to the repulsion between the two closely laying electron dense oxygen atoms of A-232 analyte. The effect of electron dense oxygen atoms is also evident by the highest contribution of attractive Edis component (-26.93 kcal mol-1) in A-232@GDY complex which reinforce the charge transfer between A-

232 and GDY. However, the contributions of attractive Eest and Eind in A-232@GDY complex are –10.22 and -3.20 kcal mol-1, respectively. The SAPT results reveal that the sequence of stability of complexes is A-234@GDY > A-232@GDY > A-230@GDY which is exactly followed by the results of counterpoise interaction energies.

Reduced density gradient (RDG) analysis

Next, a visual approach, reduced density gradient analysis is implemented to elaborate the noncovalent interactions more specifically [56]. The isosurfaces of RDG and scatter graphs of designed complexes are shown in Fig. 3. The sign(λ2)r ranges between -0.05 and 0.05 au in RDG scatter spectra, exhibit the three types of interactions i.e., steric repulsion (red), weak (green) and strong (blue) attractions. Here, RDG spectra show that the strong attraction in our complexes is negligible which is also supported by the absence of blue patches in isosurfaces. The absence of strong attractions attributes the easy reversibility or reusability of GDY. However, the green colour flaky patches dominate in RDG isosurfaces, reflect the presence of weak noncovalent interactions. The presences of weak interactions can also be noticed in RDG scatter graphs from -0.02 to 0.00 au. The dense green peaks in RDG scatter graph of A-232@GDY complex indicate the higher contribution of weak dispersion forces (dispersion) which is quite consistent with the SAPT analysis. Furthermore, the red-green mixed flaky peaks between 0.00 and 0.01 au is the representation of C-H….π interactions between analytes and GDY surface. The RDG analysis confirms that the interacting parameters (C---H) (Table 1) are due to the interaction between hydrogen atoms of analytes and the π-electrons between the carbon atoms of GDY sheets. The red spikes on the right portion of RDG graph, between 0.01 and 0.02 au illustrate the repulsion forces between the hexagonal aromatic rings of the GDY. The isosurfaces of complexes reveal the self-repulsion between the electron dense atoms of analytes which is shown by the small red patches. Hence it can be concluded that the dispersion component plays a vital role in the adsorption of A-series molecules on graphdiyne sheet.

Table 2: Energies of HOMO & LUMO orbitals, energy difference between HOMO and LUMO (EH-L), %Sensitivity (%S), average energy gap variation ( ), CHELPG charge transfer (Q), maximum absorbance (λmax) in eV & nm and oscillator strength푎 (fo). %퐸푔 Complexes HOMO LUMO EH-L %S Q λmax λmax fo - (eV) (eV) (eV) 풂 (e ) (eV) (nm) 품 Iso-GDY -7.71 -0.68 7.03 --- %푬------3.96 312 0.99 2 A-230@GDY -7.79 -0.90 6.89 1×10 2.00 -0.05 3.91 317 0.70 A-232@GDY -7.73 -0.87 6.85 3×103 2.48 -0.02 3.89 318 0.74

2 A-234@GDY -7.83 -0.90 6.93 6×10 1.46 0.04 3.92 315 0.79

Electronic properties

To gain deep understanding of the interactions between GDY and analytes, the electronic properties including frontier molecular orbital analysis (FMO), density of state analysis (DOS) and natural bond orbital (CHELPG) charge transfer analysis are examined, and their results are given in Table 2. Among them, variations of HOMO & LUMO energies and their gaps (EH-

L) estimate the change in conductivity of GDY upon complexation with analytes [57]. The EH-L gap of bare GDY nanoflake is 7.03 eV which is well accord with the literature [58–61]. The decrease is seen in the EH-L of GDY upon adsorption of analytes. For further validation of these results, the FMO isosurfaces and density of state spectra have been plotted and displayed in Fig. 4 and Fig. 5, respectively. DOS spectrum of isolated GDY reveals that, the HOMO and LUMO orbitals are located at -7.71 and -0.68 eV, respectively. However, upon complexation with A-230, A-232 and A-234, new HOMO orbitals are generated at -7.79, -7.73 and -7.83 eV, respectively.

Due to the generation of new occupied orbitals, the EH-L gaps are reduced upon complexation.

The lowering of EH-L gaps in complexes reflects the increasing conductivity because of easy transfer of electrons from conduction (HOMO) of valance (LUMO) band [62]. The EH-L of A- 230@GDY, A-232@GDY and A-234@GDY complexes decrease to 6.89, 6.85 and 6.93 eV, respectively. The lowering of EH-L gaps illustrates that the conductivity of GDY is appreciably increased upon adsorption of analytes which interns the increase in sensitivity. In order to confirm the sensitivity of GDY towards the reported CWAs, the % sensitivity of complexes are calculated by using expression below [63, 64] however, the results are displayed in Table 2.

---- (4) 푐표푛푑푢푐푡푖푣푖푡푦 표푓 푐표푚푝푙푒푥푒푠 −푐표푛푑푢푐푡푖푣푖푡푦 표푓 푏푎푟푒 푔푟푎푝ℎ푑푖푦푛푒 % 푆푒푛푠푖푡푖푣푖푡푦 = | 푐표푛푑푢푐푡푖푣푖푡푦 표푓 푏푎푟푒 푔푟푎푝ℎ푑푖푦푛푒 | × 100 The conductivity of the bare and complexed graphdiyne can be calculated as;

---- (5) 퐸푔 퐶표푛푑푢푐푡푖푣푖푡푦 ∝ 푒푥 푝 (− 2퐾푇) Here, K & T are the representations of Boltzmann constant and temperature in Kelvin, respectively. Surprisingly, the %sensitivity of GDY is notably high for A-232 analyte which might be due to the higher dispersion interactions between electron deficient hydrogen atoms of A-232 and π-electrons of GDY. The higher sensitivity of GDY towards A-232 is also be confirmed by the average energy gap variation ( ) can be calculated as [47]: 푎 푔 ---- (6) %퐸 푔 (퐺푑) 푔 (푁퐴−퐺푑) 푎 (퐸 − 퐸 ) %퐸푔 = 퐸푔 (퐺푑) × 100

A230@GDY

A232@GDY

A234@GDY

Fig. 3: RDG isosurfaces (left) and scatter graphs (right) of A-series analytes@GDY complexes.

The results support the results of SAPT, RDG and FMO analysis that the GDY shows highest sensing푎 response towards A-232 molecule. These results are appreciable to validate %퐸푔 the applicability of GDY as an electrochemical sensor for the detection of CWAs particularly A-series. The amount of charge transfer between analytes and GDY agents is measured by CHELPG analysis (Q) and values are given in Table 2. The CHELPG charge transfers in reported complexes are applicably high. The charges transfer in A-230@GDY, A-232@GDY and A- 234@GDY complexes are -0.05, -0.02 and -0.04 e-. Owing to the multiple interactions between the atoms of analytes and GDY nanoflake the charge transfers are remarkably high which reveals the high adsorption affinity of CWAs on GDY surface.

HOMO LUMO A-230@GDY

A-232@GDY

A-234@GDY

Fig. 4: FMO isosurfaces of A-series analytes@GDY complexes.

Quantum theory of atom in molecule (QTAIM) analysis

QTAIM is topological analysis in which critical points i.e., including electron density (ρ), Laplacian ( 2ρ) and total electron density (H) define the nature of interaction or bonds [65]. Among them, the H is the total integral sum of electron potential energy density (V) and ∇ kinetic energy density (G). The nature of interaction is noncovalent in nature when the values of 2ρ and H are greater than zero. On the other hand, the bond nature is covalent if the values are less than zero. However, the interaction strength depends upon the value of ρ. In ∇ noncovalent interactions, the values of ρ > 0.1 au attributing the presence of strong interaction like hydrogen bonding or electrostatic interactions vice versa [65, 66]. The results of QTAIM analysis are provided in Table 3 and the numbering of atoms (given in the table) in accordance with Fig. 6. Generally, the values of Laplacian ( 2ρ) are positive in all the reported complexes which attribute the presence of noncovalent interactions among analytes and ∇ GDY. In addition, the values of electron density (ρ) are less than 0.1 au for all the complexes with an exception of H59-O45 and H62-C50 of A-230@GDY and A-234@GDY complexes, respectively. However, it is seen from the Fig. 6 that these are the self-interactions of atoms of analytes rather than analytes and GDY. These results of QTAIM analyses further strengthen the conclusions of RDG and SAPT analysis that dispersion factor dominates between the reported complexes. Overall, it can be postulated that the reported analytes adsorb on GDY via weak noncovalent interaction predominantly the van der Waals interactions.

GDY A-230@GDY

A-232@GDY A-234@GDY

Fig. 5: DOS spectra of isolated GDY and A-series analytes@GDY complexes.

UV-vis analysis

Finally, the UV-vis spectra of bare and complexed GDY are simulated by using time-dependent density functional theory (TD-DFT). The observed values of maximum absorbance (λmax), and their oscillator strengths (f) are listed in Table 3. The UV-Vis spectra of reported complexes are given in Fig. S3. For bare GDY, the maximum absorbance is noticed at 312 nm. The maximum absorbance of complexed GDY is red shifted to the longer wavelength which is probably due to the increasing π to π* transitions. The λmax of GDY is red shifted to 317 nm on adsorption of A-230 analyte. Expectedly, the maximum absorbance of A-232@GDY complex is shifted to the longest wavelength (318 nm). However, the λmax is observed at 316 nm for A-234@GDY complex. These results of UV-vis analysis agree well with the sequence of other reported properties particularly, RDG, FMO and QTAIM analysis. The red shift indicates the decrease in band gaps between the π-orbitals of analytes and GDY.

According to the International Union of Pure and Applied Chemistry (IUPAC), the chemical sensor are the systems with small measurement that allows the quantitative and qualitative conversion of information about the existence of toxic analytes [67]. The experimentally known sensors for the detection of CWAs with higher sensitivity and low detection limit are: (i) carbon nanoparticles [67], in which the detection limits are in the order of ppm; (ii) carbon nanotube, very sensitive for CWAs with the detection limit <2 ppm [68]. Metallic doped carbon electrode; which reach the detection limit of 200 nM [69]; and (iii) graphene based sensors: where the detection limit touches the trace amount of analytes [70–72]. Here, the results of this study i.e., interaction energies and electronic properties, especially %sensitivity reveals that the GDY can act as a promising sensor devise, which can be able to detect the trace amount of these compounds with higher selectivity.

Fig. 6: QTAIM iso-structures of A-series analytes@GDY complexes.

Table 3: QTAIM results; critical point numbers (CP No.), interacting atoms (Aint), electron density (ρ), kinetic energy density (G), electron potential energy density (V), total integral (H) and Laplacian ( 2ρ) in the units of au.

∇ A-230@GDY 2 CP No. Aint ρ(r) G(r) V(r) H(r) ρ 82 H59-O45 0.0168 0.0130 -0.0125 0.0005 0.0542 90 H58-H64 0.0072 0.0054 -0.0038 0.0016 0.0281∇ 109 H61-C34 0.0038 0.0023 -0.0016 0.0007 0.0117 113 H60-C31 0.0085 0.0057 -0.0044 0.0013 0.0282 119 F46-H9 0.0018 0.0016 -0.0009 0.0006 0.0088 95 H60-C42 0.0091 0.0061 -0.0046 0.0015 0.0302 125 H65-C35 0.0041 0.0026 -0.0018 0.0008 0.0134 132 F46-C31 0.0023 0.0018 -0.0012 0.0006 0.0097 141 H60-C30 0.0061 0.0042 -0.0029 0.0013 0.0222 152 H67-C20 0.0053 0.0035 -0.0026 0.0010 0.0180 169 H67-C40 0.0053 0.0036 -0.0026 0.0010 0.0182 A-232@GDY 86 H70-C30 0.0044 0.0026 -0.0018 0.0007 0.0133 97 H65-C38 0.0078 0.0050 -0.0037 0.0013 0.0254 99 H71-H68 0.0068 0.0047 -0.0033 0.0014 0.0247 104 H57-C23 0.0048 0.0030 -0.0022 0.0008 0.0151 107 H64-C34 0.0055 0.0035 -0.0025 0.0010 0.0179 112 C21-O46 0.0047 0.0034 -0.0027 0.0007 0.0161 119 H58-C24 0.0051 0.0031 -0.0022 0.0009 0.0158 125 H65-C39 0.0049 0.0030 -0.0022 0.0008 0.0153 132 C40-N44 0.0060 0.0037 -0.0031 0.0005 0.0168 144 H63-C31 0.0081 0.0051 -0.0039 0.0012 0.0249 145 C25-O47 0.0056 0.0037 -0.0030 0.0007 0.0179

146 C32-N49 0.0058 0.0038 -0.0032 0.0006 0.0173 152 H63-C42 0.0063 0.0041 -0.0030 0.0011 0.0206 A-234@GDY 96 H64-C37 0.0066 0.0043 -0.0031 0.0012 0.0219 102 H73-H28 0.0048 0.0032 -0.0021 0.0011 0.0172 111 H63-C37 0.0044 0.0029 -0.0020 0.0008 0.0148 132 H73-O46 0.0078 0.0060 -0.0050 0.0011 0.0284 136 C25-O46 0.0072 0.0055 -0.0043 0.0012 0.0266 138 C40-N49 0.0048 0.0030 -0.0025 0.0005 0.0141 121 C20-N44 0.0043 0.0025 -0.0021 0.0004 0.0118 148 H68-C34 0.0045 0.0029 -0.0020 0.0009 0.0151 157 H59-C39 0.0081 0.0056 -0.0042 0.0015 0.0284 156 H62-C50 0.0145 0.0136 -0.0104 0.0032 0.0672 125 H66-H70 0.0058 0.0042 -0.0029 0.0013 0.0219 158 H62-C32 0.0055 0.0036 -0.0026 0.0010 0.0183

Conclusions

The adsorption of A-series chemical warfare agents has been investigated within the framework of density functional theory. Herein, the adsorption probability of toxic CWAs on

GDY is characterized by Ed, SAPT0, RDG, FMO, DOS, CHELPG charge transfer and QTAIM analysis. Based on the adsorption energy, the trend of stability of complexes is A-234@GDY > A-232@GDY > A-230@GDY. The adsorption energy of A-234@GDY, A-232@GDY, A-230@GDY NM1-GDY complexes are -13.70, -16.45 and -17.19 kcal mol-1, respectively. The trend of stability is exactly followed by SAPT results however; the dispersion component contributes higher in the A-232@GDY complex. The predictions of RDG and QTAIM analysis are well accord with the greater role of dispersion in stabilizing complexes particularly, A-232@GDY complex. The %sensitivity and reveal the higher sensitivity of GDY for A-series CWAs. The red shift is adsorbed in the UV-푎 Vis spectra of complexes due to the π-π* transition is %퐸푔 increased upon complexation which reveals the generation of new occupied energy levels. Finally, we are positive with the findings of this study that these results will be helpful for scientific community to design a GDY based sensors for hazardous CWAs. Acknowledgements

Authors acknowledge the Higher Education Commission of Pakistan and COMSATS University, Abbottabad Campus for financial support of this work. Supplementary material

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/

Author Declarations

Funding: Funding for this project was provided by Higher Education Commission of Pakistan.

Conflicts of interest/Competing interests: Authors declare no competing interests

Ethics approval: NA

Consent to participate: NA

Consent for publication: All authors agree for the publication of the manuscript

Availability of data and material: All relevant data are given in the supporting information file.

Code availability: Software used are commercially available

Authors' contributions: Hasnain Sajid (Acquisition and analysis of data; manuscript drafting). Sidra Khan (Acquisition and analysis of data) Khurshid Ayub (Study conception and

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Figures

Figure 1

Structure of A-series (A-230, A-232m A-234) reported by Mirzayanov [11] Figure 2

Relaxed (stable) geometries of A-series analytes@GDY complexes with adsorption distances in Å. Figure 3

RDG isosurfaces (left) and scatter graphs (right) of A-series analytes@GDY complexes. Figure 4

FMO isosurfaces of A-series analytes@GDY complexes. Figure 5

DOS spectra of isolated GDY and A-series analytes@GDY complexes. Figure 6

QTAIM iso-structures of A-series analytes@GDY complexes.

Supplementary Files

This is a list of supplementary les associated with this preprint. Click to download. GraphicalAbstract.jpg Supportinginformation.docx