Hypothetical confirmation for the anti-bacterial compound potassium succinate-succinic acid in comparison with certain succinate derivatives

Abstract The development of antibacterial medications has recently been promoted due to the non- effective usage of antibiotics and the rise in severe bacterial infections. The effectiveness of antimicrobial therapy alternatives is constrained due to the prevalence of germs that are resistant to medications. Our current study’s goal is to favor metallic compounds for antibiotic delivery in order to increase the effectiveness of the antibacterial regimen. Due to its bioactivity, potassium succinate-succinic acid is preferred because in general, the succinic acid compound has the greatest potential against microbial infections and a natural antibiotic because of its relative acidic nature. In the current study, the molecular geometry, band gap energies, molecular electrostatic interactions and potential energy distribution of the molecule were compared with those of certain succinate derivatives. The potential compound potassium succinate succinic acid was probed using FT-IR and FT-Raman analyses. Vibrational assignments pertaining to different modes of vibration with potential energy distribution have been improved by normal coordinate analysis. The chemical bond stability which is largely important for biological activity is studied using NBO analysis. The molecular docking study suggests that the molecule possesses antibacterial action and displays a minimal binding energy of −5.3 kcal/mol which can be endorsed for the prevention of any bacterial illness. From the results of our studies, the material would be stable and bioactive according to the FMO study, which indicates a band gap value of 4.35 eV and the pharmacokinetic features of the molecule, was predicted using the ADMET factors and the drug-likeness test. Communicated by Ramaswamy H. Sarma


Introduction
Pathogenic bacteria that are resistant to antibiotics have become a serious hazard to global public health.As a result, it is vital to comprehend how resistance determinants are distributed in bacterial populations, to clarify how resistance works, and to identify the environmental conditions that encourage the spread of resistance.As a result, the development of anti-bacterial medication discovery has increased significantly during the past several years (Wohlleben et al., 2016).Metal-based drugs have recently been found to have extensive functionality across biological systems, and their use within biomolecules has changed as a result of advancements in the biochemical field in order to maintain the activity they support and are used for the treatment and diagnosis of some diseases (Smethurst & Shcherbik, 2021).This led us to select a metal-based chemical for the current study's anti-bacterial activation.Because succinic acid has the greatest potential against microbial infections, the metal compound potassium succinate-succinic acid is preferred.
By enabling the production of action potentials, which are essential for neurotransmission, muscle contraction, and heart function, potassium is the alkali metal ion in charge of maintaining the balance between acid and base and the integrity of the cell membrane (Carter et al., 2014).But more precisely, the potassium salts have antibacterial potential since they are active against the pathogens S.aureus and E.coli (Sutrisno et al., 2020).In the search for new antibacterial agents, succinic acid was chosen due to its antibacterial properties.Succinic acid is an organic acid produced by most bacteria aerobically and anaerobically as a by-product of metabolism.It is recognised at various levels of efficacy therefore it can regulate these diverse bacterial species.From the literature point of view, Huang, S et al. showed that succinic acid exhibited strong antibacterial activities against S. aureus and P. fluorescens with the Diameter of the Inhibition zone values of 27.57mm and 18.90 mm, respectively (Huang et al., 2022).Moreover Kumar et al. reported that combination therapy using colistin and succinic acid might find safe clinical application of this antibiotic in controlling infections due to NDM-1 bacteria.Likewise, Succinic acid showed efficacy against bacterium A. baumannii with a minimum inhibitory concentration (MIC) of 62.5 mg/mL (Kumar et al., 2018).The effective use of succinic acid derivatives is compromised by the worldwide incidence of multidrug-resistant bacterial strains.Nevertheless nowadays the prevalence of multidrug-resistant bacterial species across the world makes it difficult to employ succinic acid derivatives effectively (Modimola et al., 2022).
Succinic acid is typically made from petroleum sources to provide a relatively modest market for use in culinary and medicinal applications.Succinic acid is used as an antibiotic and curative agent.It has grown gradually and led to the creation of microbial strains as well as recovery and purification techniques (Nghiem et al., 2017).Additionally, succinic acid has demonstrated a better and more favorable solubility in water and is a powerful and simple-to-use preservative.It is referred to as a natural potent multipurpose agent, but it also has unique noteworthy effects as an antibacterial, antiacne, anti-psoriasis, antioxidant and slimming agent (Juncan et al., 2021).Additionally, it was shown that succinic acid has an inhibitory impact on neutrophil bactericidal activity and that the mechanism is more related to reduce intracellular killing than the suppression of phagocytosis (Majid et al., 1997).The purpose of the current research is to demonstrate the molecule's antibacterial properties.
Succinate is a dicarboxylic acid dianion that is created when a proton is removed from both carboxyl groups of succinic acid.It serves as a metabolite for both humans and Saccharomyces cerevisiae.The tricarboxylic acid (TCA) cycle intermediate succinate is essential for the production of adenosine triphosphate (ATP) in mitochondria (Martinez-Reyes & Chandel, 2020).In several foods, chemical, and pharmaceutical sectors, succinate derivatives are used as a precursor to creating a variety of chemicals, including solvents, fragrances, plasticizers, dyes, and photographic chemicals (Merrylin et al., 2020).Certain succinate derivatives are sustainable biomolecules with well-known antibacterial and antioxidant characteristics.Additionally, these compounds have a higher potential for usage in the creation of beneficial medicinal materials (Dominguez-Robles et al., 2020).
The review of the literature indicates that Arun Kumar et al. (Arunkumar et al., 2014;Arun Kumar et al., 2021) have reported the crystal structure of potassium succinate-succinic acid (KSSA) as well as the nucleation, dielectric, and ferroelectric investigations of KSSA.However, the reaction sites, wave functional studies and pharmacokinetic characteristics of KSSA have not yet been studied.Here we mainly focused on the bioactivity of the compound and the chemical properties of the KSSA molecule in comparison to the related succinate compounds such as Bis-(2-amino-6-methylpyridinium) succinate monohydrate (2A6MS) (Kaliammal et al., 2020), doxylamine succinate (DXS) (Al-Otaibi et al., 2022), tetraaquatris(succinate)diholmium(III) hexahydrate (TDH) (Bernini et al., 2008), dimethyl-2-(5-acetyl-2,2-dimethyl-4,6dioxo-1,3-dioxan-5-yl)3(triphenylphosphinylidene)succi-nate (D2TS) (Vessally et al., 2011) and 8-Hydroxyquinoline Succinate (8-HQSC) (Saravanamoorthy et al., 2019).Therefore, utilizing NCI and IRI analyses, the DFT (Density Functional Theory) approach was employed to investigate the molecule's covalent and non-covalent interactions.Due to its capacity to identify active compounds before they are synthesized, the computational drug discovery program has been gaining popularity.This is in contrast to traditional drug discovery methods, which are expensive and may take decades to complete.In order to offer a comprehensive assignment of fundamental bands in the FT-IR and the FT-Raman spectra based on the Normal Coordinate Analysis, the entire spectroscopic vibrational analysis of the molecule is conducted.To analyze possible medications from various databases, techniques such as molecular docking, in silico ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) analysis, and drug likeness prediction are also being used.These computationally based technologies speed up the drug development process and cut down on experimental expenditures.FMO (Frontier Molecular Orbital) and MESP (Molecular Electrostatic Potential) mapping investigations were used to investigate the chemical reactivity of KSSA.In order to evaluate the molecular stability and bond strength, the NBO (Natural Bond Orbital) study was investigated.

Synthesis
Aqueous solution containing potassium hydroxide and succinic acid in a molar ratio of 1:1 was used to make the KSSA, which was then grown using a slow evaporation process.The solution was agitated continuously for a number of hours at room temperature in order to measure the crystal development.The beaker was then sealed and kept at room temperature away from any dust.After 25 days, a single transparent crystal forms as a result of crystallisation.

Solubility
For various temperatures between 25 and 45 � C, the solubility of KSSA in water was calculated.The solution-filled beaker was securely covered and a magnetic stirrer was used to maintain the solution's temperature at a consistent level while stirring it continually.This procedure was repeated for various temperatures to estimate the quantity of KSSA needed to saturate the solution.This work was completed in a bath of constant temperature with a 0.01 K precision and the solution was employed at a fixed volume of 100 ml.

Characterization
Using the KBr pellet approach at room temperature, the FT-IR spectra of KSSA was recorded on a Perkin Elmer FT-IR 8000 spectrophotometer in the 4000-400 cm À 1 region.With a Bruker RFS 27: Freestanding FT-Raman Spectrometer with a Nd: YAG laser source at 1064 nm and a resolution of 2 cm À 1 , an FT-Raman spectrum was captured in the range of 4000-50 cm À 1 .

Computational methods
The Gaussian'09 software package (Frisch et al., 2009) was used to perform the quantum chemical computation for KSSA utilizing the B3LYP (Becke 3 Lee Yang Parr) technique with the LANL2DZ basis set (Dunning & Hay, 1977).To produce FMO and MEP Plots for spotting the probable reactive locations, Gauss View 6 software (Dennington et al., 2019) is utilized.All isosurface maps were produced by the VMD (Visual Molecular Dynamics) software (Humphrey et al., 1996), and the Non-Covalent Interaction (NCI) analysis and Interaction Region Indicator (IRI) analyses were carried out using Multiwfn, a multi-functional wave function analysis tool (Lu & Chen, 2012).KSSA's molecular docking was carried out using the flexible docking techniques of CB-Dock and Autodock Vina (Liu et al., 2020), and the interactions were visualized using the graphical PYMOL program (Schrodinger, 2009).

Optimized geometry
Figure 1 displays the KSSA's optimised molecular structure along with atomic symbols and labels.The dihedral angles of KSSA are reported in Table S1 and are compared with the XRD data, while the optimised bond length and bond angles of KSSA are given in Table 1.
When the KSSA molecule's experimental and theoretical values are compared, the resultant minor difference between the gas phase in the computational section and the solid phase in the experimental component is evident.The theoretical bond lengths of O 9 -K 13 , O 11 -K 13 , K 13 -O 24 and K 13 -O 25 are 2.75, 2.74, 2.63 and 2.74 Å respectively which are slightly deviated from the corresponding experimental values 2.85, 2.98, 2.95 and 2.91 Å. Calculated between the electronegative oxygen atoms and the electropositive potassium metal, which functions as an ion, are these bond lengths of the structural characteristics.The carboxylate group of the succinate anion, however, coordinates to one metallic cation K þ by the two oxygen atoms in a bidentate mode, as demonstrated by K 13 -O 24 (MacGillivray, 2010).
When compared to the usual values of 1.09 Å, the experimental data show an increase to 1.10 Å and a decrease to 0.97-0.98Å in the optimised bond length of the C-H bond in the succinate anion and the succinic acid respectively (Sutay et al., 2014).Low hydrogen atom scattering during the X-ray diffraction experiment is what caused the C-H bond to deviate (Beaula & James, 2014).Similar to C 1 -C 2 -H 4 , C 2 -C 5 -H 6 , H 19 -C 17 -C 20 , and H 21 -C 20 -C 23 , the bond angles of these molecules indicate 109 � each and are connected to the experimental results.
In contrast to the equivalent experimental values of 1.23 and 1.26 Å, the carboxyl bond lengths of C 16 -O 24 and C 16 -O 25 of KSSA are 1.29 and 1.30 Å respectively as in DXS and 8-HQSC when compared.Due to the sp 2 -hybridization, the variation in the carboxylate anion settles the double bond properties, and the bond angles around the carboxylate group are about 120 � around the carbon.O 11 -C 8 -O 12 and  O 24 -C 16 -O 25 have bond angles 123.1 � and 123.9 � that are  The COOH group of the optimized structure is a trigonal planar well, which correlates to the corresponding experimental values of 176.5 � , À 1.7 � , 179.1 � , and À 1.9 � for the dihedral angles C 2 -C 1 -C 10 -H 14 , O 9 -C 1 -O 10 -H 14 , C 20 -C 23 -C 26 -C 28 , and O 27 -C 23 -O 26 -H 28 respectively.With staggered conformation (Jindal & Vasudevan, 2021) the dihedral angles H 4 -C 2 -C 5 -H 6 and H 18 -C 17 -C 20 -C 23 show values of 59.5 � and À 60.0 � respectively, and well compared to the experimental values of 59.9 � and À 61.7 � .

Natural bond orbital analysis
The investigation of intra and intermolecular interactions may be improved by the information provided by NBO concerning interactions in both filled and virtual orbital regions.Additionally, it offers a practical basis for the research of conjugative interactions or charge transfer in the molecular system (Weinhold & Klein, 2014).Table 2 lists the results of the second-order perturbation theory of the Fock matrix with an NBO basis, which illustrates the strength of intramolecular hyperconjugative interactions.
Because the metallic potassium ion was positioned close to the oxygen atom, the interaction between the bonding orbital r(C 16-O 25 ) and the lone pair orbital LP � (K 13 ) results in a minimum stabilization energy of 1.00 kcal/mol.As a result, no imaginary frequencies were found after molecular optimization (Junior et al., 2021).The interactions overlap between LP (O 25 ) and r � (C 2 -H 4 ), which exhibit reduced stabilization of 2.90 kcal/mol, and between LP (O 11 ) and r � (C 8 -O 12 ), which exhibit high stabilization of 28.14 kcal/mol.The whole KSSA molecule is stabilized as a result of the high intra-molecular hyper conjugative interaction of the molecule's electron.For the lone pair O 25 , the bond is created with an s-character of 62.32% and a p-character of 3.67%, whereas for the LP (O 11 ), the bond is produced with a p-character of 99.94%.The maximal stabilization energies are 44.88 kcal/mol and 42.38 kcal/mol, respectively, due to the lone pair to the anti-bonding orbital contacts between LP (O 12 ) and p � (C 8 -O 11 ) and LP (O 10 ) and p � (C 1 -O 9 ).This is caused by the succinate anion's deprotonation and the molecule's production of potassium ions.As a consequence, this shows the occurrence of stereo-chemically active lone pair (Baikie et al., 2014).When the E(2) value is large, the interaction between the electron donors becomes more intensive and the extent of conjugation of the KSSA molecule is larger.When the interaction between the lone pairs LP (O 24 ) and LP � (K 13 ) occurs, it provides the lowest occupancy value of 0.005e in relation to the other anti-bonding orbitals and suggests a little charge transfer resulting in very weak interaction (Ardiles & Rodriguez, 2021) between O 24 and the potassium metal ion.This demonstrates that stereo chemically active lone pairs do exist.
When the E(2) value is high, the electron donors interact more actively, increasing the degree of conjugation of the KSSA molecule (Beaula et al., 2015).The lowest occupancy value of 0.005e among the various anti-bonding orbitals is produced by the interaction between the lone pairs LP (O 24 ) and LP � (K 13 ), which shows a negligible charge transfer and a very weak contact between O 24 and the potassium metal ion.

Frontier molecular orbital analysis
The electronic structures of ligands are also relevant to their pharmacological properties (Schwarze et al., 2019).It is also crucial to evaluate the energy and distribution patterns of their orbitals, particularly the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).
According to Figure 2, in the KSSA molecule, HOMO is primarily localized over the succinate's carboxylate group, whereas LUMO is primarily localized over the succinic acid.It is discovered that the HOMO has a high energy value of À 5.71 eV and the LUMO has a value of À 1.36 eV.With a band gap energy of 4.35 eV, the charge is transferred from the nucleophile succinate to the electrophile succinic acid.The band gap energy values for the reported compounds like DXS, 8-HQSC and 2A6MS are 5.75 eV, 3.46 eV and 2.67 eV respectively.Here, the charge transfer interactions within the 2A6MS demonstrate a significant contribution with a low energy gap value and are an attractive material aimed for SHG (Second Harmonic Generation) and optoelectronic applications with UV-vis analysis (Kaliammal et al., 2020).Nevertheless, 8-HQSC and KSSA molecule shows a quite similarity in the energy gap values compared to other succinate compounds and the charge transfer interactions in the molecule enable the biological process (Janani et al., 2021).
In Table S2, chemical reactivity descriptors computed using HOMO and LUMO values are shown, including chemical hardness, softness, electronegativity, chemical potential and electrophilicity index.These descriptors are compared with the previously reported compounds.The stability of KSSA molecule is increased by its chemical hardness (2.17 eV) and is compared to the reported compounds 8-HQSC (3.46 eV) and 2A6MS (2.67 eV).KSSA is a soft molecule with significant polarizability and chemical reactivity due to its softness values 0.45 eV and 0.44 eV respectively with respect to hardness values.The electronegativity of KSSA is 3.54 eV which demonstrates its capacity to capably draw in the shared electrons (Vidhya et al., 2020) and are almost similar to the reported values of 8-HQSC (4.83 eV) and 2A6MS (3.51 eV).The electrophilicity index of a molecule, which is predicted to be 2.8 eV in KSSA, is used to verify a compound's ability to bond with biomolecules (Mumit et al., 2020).The other reported molecules 8-HQSC and 2A6MS also have higher electrophilicity index values 6.74 eV and 4.62 eV which induce the bioactive features of the molecules (Saravanamoorthy et al., 2019).

Molecular electrostatic potential analysis
To learn more about the three-dimensional structural and topological characteristics of ligands, the MESP mapping diagram is utilised.In order to control ligand-protein docking, charge distribution on the molecules of the ligand and protein is essential (Muhammad et al., 2021).The MESP map shows the regions with the highest possible positive electrostatic potential in blue, the highest possible negative electrostatic potential in red and the lowest possible potential in green.
According to the MESP plot of KSSA in Figure 3, the most of the negative zones (red) are grouped around carbonyl groups, likely because of their surroundings, which are rich in electrons and makes them suitable targets for electrophilic attack.While the hydrogen bonds affect the ligands' binding sites, positive areas (blue) are directed towards the protonic H-atom of the hydroxyl groups (OH), which functions as the H-bond donor in protein-ligand intermolecular interactions and is essential for determining the specificity of ligand binding (Wade & Goodford, 1989).Additionally, strong positive is  2) means energy of hyper conjugative interaction (stabilization energy).b E(j) -E(i) is the energy difference between donor i and acceptor j. c F(i,j) is the Fock matrix element between i and j orbital's.seen in the area around the potassium ion, which is the greatest spot for a nucleophilic attack.In the D2TS compound, the site for the electrophilic attack is concentrated over the oxygen atoms of the succinate anion.In 2A6MS, negative electrostatic potential is idealized over the carboxylate group of succinate anion that displays electrophilic attack.The hydrogen atom of an amine and the amino group of a cationic moiety, which facilitate the repulsion of a proton and result in N-H … O hydrogen bond interaction, are instances of nucleophilic attacks (Kaliammal et al., 2020).Similar to this, in the DXS molecule, the oxygen and hydrogen atoms are the targets of electrophilic attack whereas the nitrogen atom is the target of nucleophilic attack, indicating that the electronic charge is polarized along the O-H-N relationship (Al-Otaibi et al., 2022).

Vibrational spectral analysis
KSSA has 78 normal modes since there are 28 atoms in total.The Normal Coordinate Analysis of MOLVIB programming was utilized to estimate all the vibrational modes in order to execute the simulated IR and Raman spectra.The PED and assignments were created together for each vibrational band.Table S3 includes a summary of the scaled and observed wavenumbers as well as their precise assignments.Additionally, Figures 4 and 5 show the observed and simulated FT-IR and FT-Raman spectra for visual comparison.

Carboxylic acid group
The carbonyl group in carboxylic acid is attached to the hydroxyl group (O-H), which loses its hydrogen and ionizes like other acids (Vein et al., 1991).The carbonyl and hydroxyl groups, which are important for the compound's antibacterial action owing to the deprotonation, were given precedence in the vibrational study of the carboxylic acid.The degree of hydrogen bonding allows for the identification of hydroxyl bending and stretching vibration (Colthup et al., 1990).In KSSA, O-H stretching vibrations are recorded at 3370 cm À 1 in the infrared, which is in good agreement with the scaled frequency of 3407 cm À 1 with 100% PED contribution.Due to the interaction within the metal K þ cation, the O-H stretching frequency is red-shifted, which is also a characteristic of the compound's bioactivity (Varsanyi, 1974).Additionally, the second order perturbation energy between LP (O 12 ) and p � (C 8 -O 11 ), which exhibits the maximum stabilization energy of 44.88 kcal/mol, has been used to demonstrate the red shift in stretching frequency.In the KSSA, the range between 1440-1260 cm À 1 show the O-H in plane bending mode and has significant band behavior (Chandra et al., 2009) and the band observed at 1278 cm À 1 in the FT-IR spectra is related to C-O stretching modes.These modes are well associated to the reported 8-HQSC and DXS molecules whereas the scaled values and the O-H in-plane bending vibration accord well.
The region between 1870 and 1540 cm À 1 is expected to have strong bands formed by the C ¼ O stretching band, and the position of this band relies on the physical state, conjugations, hydrogen bonds and, electronic and mass effects of nearby substituents (Stuart, 2004).The C ¼ O asymmetric stretching vibration is responsible for the extremely strong bands found in the FT-IR region at 2934, 1722, 1736 and 1694 cm À 1 .The computed wavenumbers, including 1701, 1699, 1677 and 1544 cm À 1 and the observed wavenumbers are in good agreement.The C ¼ O symmetric stretching vibrations are attributed to the weak IR band at 1342 cm À 1 and a medium band at 1340 cm À 1 in the Raman spectra, which are connected to the scaled frequency at 1336 cm À 1 .Due to the impact of hydrogen bonding across the carboxyl groups of the succinate anion and succinic acid, these bands relate closely.These stretching modes are interrelated to the   harmonic frequencies of TDH with 100% relative intensity for the gauche and trans conformers.The wave numbers computed by the NCA approach for COOH wagging, twisting, and rocking vibrations are shown in Table S3 and are in good agreement with the observed spectrum values.

Methylene group vibrations
Asymmetric and symmetric stretching vibrations of a C-H in the methylene group are expected to occur in the range of 2980 cm À 1 and 2870 cm À 1 respectively (Smith, 1998).Asymmetric stretching vibrations are therefore seen at 2970 cm À 1 in the FT-IR spectrum, whereas symmetric stretching vibrations are seen at 2934 cm À 1 in the FT-IR spectrum and 2948 cm À 1 in the FT-Raman spectrum, respectively.With 94-96% PED contributions, these experimental results have a good correlation to the scaled wavenumbers at 2948 cm À 1 and 2949 cm À 1 .The CH 2 stretching frequencies are ascribed to the impact of electronic effects induced by the hyperconjugation of the methylene group with the metallic potassium cation (Hernandez et al., 1994).In the D2TS, 8-HQSC, TDH and DXS molecules, all the C-H stretching vibrations are pure modes since their PED contribution almost gives rise to �98%.The obtained CH stretching wavenumbers are in good accord with the experimental data.
A strong band at 1428 cm À 1 in the FT-IR spectrum and a medium band at 1420 cm À 1 in the FT-Raman spectrum reveal a red shift in the frequency whereas a CH 2 scissoring mode is expected in the range of 1485-1445 cm À 1 .The scaled wavenumbers with a 92-95 percent PED contribution are 1420-1425 cm À 1 and are matched to the experimental results.While significant bands at 1278 cm À 1 and 1246 cm À 1 correspond to the wagging and twisting modes, respectively, in the FT-IR spectra, CH 2 twisting and wagging modes are expected in the range of 1350-1150 cm À 1 .Additionally, the wagging mode corresponds to the medium band at 1296 cm À 1 in the Raman spectra with only a 32 percent PED contribution.As a result, the scaled frequency at 1288-1255 cm À 1 is highly associated with the wagging and twisting modes of CH 2 .

Carboxylate group
The carboxylate group has symmetric and asymmetric vibrations expected in the region 1360-1450 cm À 1 and 1650-1540 cm À 1 respectively (Pillai & Chellapan, 2014).The symmetric stretching of the carboxylate anion is observed at 1342 cm À 1 which is very weak in the IR spectrum and at the medium band 1340 cm À 1 in the Raman spectrum.These bands are red shifted and responsible for the anti-microbial activity of the KSSA molecule (Zhang et al., 2010) Similarly for the asymmetric stretch of the carboxylate anion, a strong band is observed at 1548 cm À 1 in the Raman spectrum which is almost similar when compared to the carbonyl asymmetric stretching vibration band of COO -group at 1550 cm À 1 as reported in 8-HQSC.These symmetric and asymmetric values are well correlated to the corresponding scaled values at 1336 cm À 1 and at 1544 cm À 1 .

Potassium-oxygen group vibration
K-O stretching vibrations are expected in the range <300 cm À 1 (Hernandez et al., 1994) and are observed in the medium band at 178 cm À 1 in the Raman spectrum.According to this variation, electron delocalization causes a change in polarizability and dipole moment (Kuruvilla et al., 2018).Due to the deprotonation of the OH atom and the metallic cation K þ , this value corresponds to the scaled value at 187 cm À 1 with a 48 percent PED contribution.In the reported TDH molecule, only a slight shift to lower frequency on dehydration occurs with the metal-oxygen vibration whereas the presence of succinate ligand adopting two conformational forms was also be detected (Bernini et al., 2008).The bending vibration of the KSSA molecule is seen as a prominent band at 126 cm À 1 in the Raman spectra of KSSA.This band is well correlated to the scaled frequency at 132 cm À 1 with a 30% PED contribution.

Natural charge analysis
Table S4 reports the results of the NBO's atomic natural charge computations and are schematically shown in Figure 6.
C 8 and K 13 have the highest positive charges (0.87 e) of all atoms because the carboxylic acid group has a partial positive charge and the oxygen atom offers a partial negative charge between the succinate and succinic acid groups.Due to deprotonation caused by interactions between molecules, the lowest positive charge over H 18 has the fewest protons and the highest negative charge (-0.76 e).As a result, the vibrational frequency is greatly influenced by the charge distribution (Beaula et al., 2015).

Non-covalent interaction analysis
Based on the Reduced Density Gradient (RDG) method, the NCI analysis was used to investigate molecular stability, which was confirmed by inter-and intramolecular interactions within the molecule.The k2 sign was exploited to differentiate between the bonded (k2 < 0) and non-bonded (k2 > 0) interactions.In KSSA, the k2 sign q function ranges from À 0.05 to 0.05 a.u. in the RDG scatter graph and the RDG spectra were hinted by three colors such as red, green and blue.The red peaks in the range of k2 > 0 which reveals the effect of steric repulsion (Jia et al., 2019).The spikes appeared in the region of k2 ¼ 0 which represents the dipole-dipole interactions (Khan et al., 2020).The blue-colored spikes in the regions q > 0 and k2 < 0 represents the strong electrostatic interactions.The NCI isosurface mapping and the scattering graph of KSSA are shown in Figure 7.
The blue flaky patches, which develop between 0.02-0.05a.u, are evidence of the potassium metal's strong electrostatic interaction with the succinate anion and succinic acid.Within the region of 0.01-0.05a.u., the isosurface plot reveals the strong repulsive interactions.The red patches on the isosurface, which depict a non-covalent interaction between the metallic ion K þ and the succinate anion owing to deprotonation, were used to identify this steric repulsion.The isosurface's green spots show van der Waals weak bonding interactions between 0.01 and À 0.02 a.u.

Interaction region indicator analysis
The domains between the atoms in the molecule that are covalently bound are not visible in the NCI analysis, hence IRI analysis was chosen.IRI is a logical analysis for chemical processes because it can effectively highlight the smooth transitions between weak contacts and chemical bonds (Lu & Chen, 2021).Figure 8 depicts the IRI isosurface with the covalent and weak interactions.
For an isovalue of 0.5 a.u related to the NCI study, IRI provides a clear visualization of steric effects, van der Waals, and non-covalent, and covalent interactions.Additionally, blue surfaces are used to indicate the covalent bond areas, which control the isosurface's strong bonding action and massive electron density.

Molecular docking analysis
Molecular docking is a computer technique widely utilized for the prediction of drugs through protein-ligand interactions in the binding sites (Olanrewaju et al., 2020).In the KSSA molecule, docking was performed to show the potential interaction between the metal complexes and the protein targets as seen in Table S5.Complexes with the best binding conformation are presented in Figure 9. Metal-binding proteins are proteins or protein domains that interact with a metal ion.KSSA was chosen to dock into the binding site of antibacterial hydrolase proteins 3KXP, 6HL9, 5ZGI and 5XP6.Because hydrogen bonds are a major contributor factor in aiding drug binding affinity with receptors (Beaula et al., 2015), the hydrogen bonding interaction characterized a high binding capability between ligand and protein.
It is clear from the docking data that hydrogen and oxygen atoms from the ligand and the targeted proteins combine to form hydrogen bonds.The oxygen atom of the carboxylate ion in the ligand is the only binding site that is subjected to hydrogen bond formation, according to the docking conformation of the ligand with the anti-bacterial proteins.In addition, when compared to the other targeted proteins, the anti-bacterial protein 5XP6 has the best capacity to bind and the highest binding energy, which is À 5.3 kcal/mol.Due to the growth of bacteria that are resistant to antibiotics, this demonstrates that the KSSA molecule has a good anti-bacterial characteristic and aids in the production of new anti-bacterial medications.Additionally, it has been shown that a high degree of binding affinity is evident when a ligand interacts with the binding sites of amino acid residues and implies the presence of hydrogen bonds and van der Waals interactions.The MESP and IRI analyses proved that this hydrogen bond production occurs through the carboxylate group's oxygen-containing sites.This H-bonded interaction O … H-O between a metal ligand and the 3KXP targeting protein reveals the synthesis of three amino acid residues, HIS'189, HIS'122, and LEU'180, and has increased hydrophobicity in the ligand as a result of higher binding energy.Due to the development of amino acid residues and H-bonding interactions in the other chosen hydrolase  proteins, 6HL9, 5ZGI, and 5XP6, which have better binding energies of À 4.6 kcal/mol, À 4.3 kcal/mol, and À 4.2 kcal/mol, respectively, they are also taken into consideration as a component in the production of anti-bacterial drugs.

Drug likeness test
In the early phases of drug research and development, the drug-likeness is a crucial criterion for reporting drug applicants.This may be thought of as a way to relate a compound's physicochemical and biopharmaceutical aspects in the human body, particularly its stimulation of bioavailability when taken orally (Bickerton et al., 2012).The Lipinski's Rules of Five (Lipinski, 2000) were used to predict the bioactivity score of the KSSA molecule and their values are shown in Table 3.
The biomolecule must have a molecular weight of 500 Dalton or less, 10 H-bond acceptors, 5 H-bond donors, and a log P of 5 lipophilicity according to Lipinski's rule of five.As a result, the KSSA molecule has 1 and 3 H-bonded acceptors and donors, respectively.The absorptivity of medications to reach the body's target tissue is determined by the lipophilic property known as log P, whereas log P for KSSA was À 4.39.Given these circumstances, the KSSA molecule was regarded as an orally active medication since it complies with all five parameters outlined by Lipinski.

ADMET analysis
Insilico ADMET analysis, which is quicker and more precise, was selected to predict the pharmacokinetic characteristics of the novel medications.Table 4 lists and predicts the KSSA molecule's pharmacokinetic characteristics (Table 5).
The water solubility of KSSA during drug absorption is À 0.63 (log mol/L) and pharmaceuticals are absorbed by humans' small intestines at a rate of 87 percent.This reduces the danger of taking medications orally and demonstrates the biomolecule's solubility in water at 25 � C. KSSA's Caco-2 permeability value was 0.79 (log Papp in 10 À 6 cm/s), adopting the logarithm of the permeability coefficient in the Caco-2 monolayer of the cells to visualize the cells that had been given to the patient orally.Furthermore, unlike glycoproteins I and II, which act as biological barriers to keep poisons out of cells, this biomolecule does not obstruct transport (Radchenko et al., 2016).The Blood Brain Barrier (BBB), which protects the brain from harmful chemicals, was permeable to the medication at a rate of À 0.28 (log BB), indicating that the drug was not evenly  distributed throughout the brain.The steady-state volume of distribution (VDss) of the KSSA molecule is approximately À 0.99 (log L/kg), which is low and distributed evenly in the human blood plasma and tissues to lessen the risk of causing renal failure and dehydration.The KSSA molecule is also less tightly bound to serum proteins and has a lower ability to penetrate the CNS.The medication is removed from the liver and kidneys, according to the expected total clearance value of 1.25 (log ml/min/kg) (Smith et al., 2018).The KSSA molecule's 0.42 (log mg/Kg/day) maximum tolerated dosage indicates that it was the first hazardous dose for humans.hERG inhibitors and non-inhibitors show that the KSSA molecule is non-mutagenic and non-hepatotoxic since it does not affect the liver's ability to function (Pires et al., 2015).The KSSA compound is suggested as an effective anti-bacterial medication based on the results of the ADMET analysis.

Conclusion
With the use of spectroscopic methods and the DFT computational approach, an extensive and methodical investigation of the molecular geometry, vibrational and biological characteristics of KSSA was carried out and related with certain succinate molecules.The molecule's IR and Raman spectra were described and the scaled wavenumbers were closely comparable to the experimental values that had been previously published and interrelated to certain succinate compounds.The vibrational spectral interpretations show the deprotonation between the potassium cation and carboxylate anion as well as the O-H stretching frequency is red-shifted.This frequency shift is responsible for the anti-bacterial properties of the KSSA molecule related to other succinate compounds.
The FMO analysis of the molecule was found to be more stable and bioactive in nature due to the band gap energy value 4.35 eV which offers important conceptual revelation of nontoxicity and bioactivity in the molecules.The band gap energy values decreases with an increase of molecules in the order of DXS > KSSA > 8-HQSC > 2A6MS.The reactive areas of the KSSA molecule were schematically depicted using MESP analysis and are highly electrophilic around the oxygen atoms when compared to the preferred succinate compounds and enabled to interact with the amino acid residues of proteins in the docking process.NCI and IRI analyses reveal the visualization of non-covalent and covalent bonding interactions.With the exception of other succinate compounds, KSSA spectacles that the protein-ligand interaction confirms the antibacterial activity and can be proposed for the antibacterial medications due to the highest binding energy of À 5.3 kcal/mol in molecular docking analysis.KSSA compound satisfies the Lipinski's rule of five and confirmed as orally active.From the ADMET analysis, it is non-mutagenic, non-hepatoxic and has lower ability to penetrate the CNS.Therefore though the preferred succinate compounds plays an important biological role, KSSA compound has suggested as a part of anti-biotic medications in the pharmaceutical industries to treat bacterial infections.

Figure 2 .
Figure 2. Plot for molecular orbital transitions in KSSA molecule.

Figure 6 .
Figure 6.Natural atomic charge analysis in the KSSA molecule.

Figure 7 .
Figure 7. Reduced density gradient isosurface mapping and the scatter graph of the KSSA molecule.

Figure 8 .
Figure 8. Interaction region indicator isosurface mapping in the KSSA molecule.

Figure 9 .
Figure 9. Molecular docking of KSSA with the hydrolase proteins.

Table 1 .
(Suna et al., 2016)9)1)nd bond angle of the KSSA molecule compared with the X-ray diffraction data.higherthan120�which is a trigonal planar arrangement and correlate to the equivalent theoretical values 121.6 � and 123.8 � respectively.But this shows lower bond angle of 117 � in the D2TS when compared due to the substitution of methyl group in the succinate anion(Vessally et al., 2011).While C 8 -O 12 -H 15 and C 23 -O 26 -H 28 have bond angles of 111.5 � and 110.0 � respectively that are less than 120 � and these deviations are caused by the increased steric hindrance at the O-C-O angle in comparison to the H-C-O angle of succinic acid which is similar compared to the 8-HQSC compound.Due to massive electronegative oxygen's ability to remove electrons, these alterations are quite probable(Santhy et al., 2019).The homonuclear bonds C 1 -C 2 , C 5 -C 8 and C 20 -C 23 each have a bond length of 1.51, whereas C 16 -C 17 has a slightly longer bond length than the previous bonds at 1.54 Å.This may be caused by the presence of the -OH group and the carboxylate anion(Suna et al., 2016).Nevertheless, they agree with the experimental bond length result of 1.49 À 1.51 Å and support the KSSA molecule's acceptable structure.This is also proven in comparison to the 2A6MS and D2TS with the corresponding C-C bond length of 1.5 Å.While compared to the experimental results of KSSA, the bond angle of C 16 -C 17 -C 20 in the carboxylic acid group shows 114 � and demonstrates a lengthening of the bond lengths between them when related to 2A6MS and 8-HQSC which shows ideal 109 � .This is due to the addition of potassium ion to the succinate anion in the KSSA molecule.

Table 2 .
Second-order perturbation theory of the Fock matrix in natural bond orbital basis for the KSSA molecule.

Table 3 .
Energy gap and chemical descriptors of KSSA mplecule related with certain succinate molecules.

Table 4 .
Drug likeness parameters of the KSSA molecule.