The Blue Tansy Essential Oil–Petra/Osiris/Molinspiration (POM) Analyses and Prediction of Its Corrosion Inhibition Performance Based on Chemical Composition

Abstract

Sustainable materials encompass a diverse range of substances used in both consumer and industrial domains. These materials are sourced in quantities that safeguard non-renewable resources and environmental equilibrium, with a focus on bio-based alternatives derived from plants. This study investigates the corrosion inhibition potential of two distinct Blue Tansy essential oils (BTES 1 and BTES 2) with varying chemical compositions. Corrosion resistance for mild steel in 1 M HCl environment was assessed using weight loss and Potentiodynamic polarization techniques. The evaluation of BTES 1 and BTES 2 revealed compelling insights. Notably, their inhibition efficiency exhibited an intriguing, damped oscillation pattern with fluctuating concentrations. Remarkably, at 0.5 g/L concentration, BTES 1 achieved an impressive 80% inhibition, while BTES 2 demonstrated a substantial 70% inhibition at 2.5 g/L. This behavior stems from intricate interactions among active compounds, leading to protective film formation and competitive adsorption effects. Importantly, congruence between weight loss measurements and potentiodynamic polarization curves fortified the reliability of outcomes. The study also confirmed BTES as a mixed-type inhibitor, as indicated by polarization curves. Furthermore, Petra/Osiris/Molinspiration (POM) analyses were conducted to unravel molecule interactions, elucidate toxicity risks, and assess bioactivity scores. This comprehensive exploration sheds light on the interplay between sustainable materials, corrosion inhibition efficacy, and complex molecular dynamics, enhancing our understanding of environmentally conscious corrosion prevention strategies.

1. Introduction

The process of metal corrosion poses a significant and formidable obstacle to numerous sectors. The anticipated annual expenses associated with corrosion and its resulting repercussions range from 3% to 5% of the Gross Domestic Product (GDP) for wealthy nations [1,2]. The situation presents potential hazards both in terms of safety and economics. Corrosion has resulted in substantial economic losses for various industries, both directly and indirectly, necessitating the implementation of control measures. The occurrence of shutdowns results in the loss of revenue, which can be classified as an indirect cost. On the other hand, the expenses associated with repairing and maintaining damaged equipment can be categorized as direct costs [3,4]. Corrosion can be effectively mitigated through the utilization of materials with high resistance to corrosion, the implementation of advanced coating techniques, cathodic protection, structural designs that minimize the presence of fissures, and the application of inhibitors [5,6]. The use of corrosion inhibitors is the most viable approach for mitigating the corrosion of metallic substrate-based equipment.

In contemporary scientific and technical research, there is a notable focus on the synthesis, design, development, and utilization of environmentally sustainable chemical compounds as alternatives to conventional harmful substances [7,8]. This phenomenon can be attributed to the increasing need for a comprehensive understanding of conservation practices and the implementation of rigorous ecological regulations. It is hypothesized that green corrosion inhibitors, such as plant extracts, exhibit biocompatibility as a result of their biological source. In addition to possessing environmentally favorable and ecologically acceptable attributes, plant extracts offer various other advantages, including cost-effectiveness, plentiful availability, straightforward production processes, and ready access to renewable sources [9]. The aforementioned properties can be rationalized by the plentiful phytochemical ingredients present in the extracts, which exhibit several resemblances to the molecular and electronic structures of traditional organic corrosion inhibitors [10]. This similarity enables them to effectively adhere to metal surfaces by adsorption.

The utilization of extracts from plants as environmentally friendly inhibitors in industrial settings necessitates adherence to stringent laws established by several regulatory agencies, which are contingent upon their respective geographical jurisdictions. The Oslo and Paris Commission (OPC) has outlined the characteristics of an acceptable green inhibitor, which include being non-toxic, easily biodegradable, and exhibiting no bioaccumulation. The primary criteria for accepting inhibitors, according to the North Sea system encompassing the United Kingdom, Norway, Denmark, and The Netherlands, are outlined as follows [11]: Biodegradability: >60% in 28 days; marine toxicity: effective concentration, 50% (EC50)/lethal concentration, 50% (LC50) > 10 mg L⁻¹ to North Sea species; and bioaccumulation: logarithm of the ratio of octanol to water partition coefficient (log (Po/w)) < 3.

Numerous scholarly publications have extensively documented the utilization of essential oils (EOs) derived from various plant sources as possible agents for inhibiting the corrosion of iron or steel [12,13,14,15,16,17,18,19,20,21,22]. The corrosion inhibitory properties of essential oils (EOs) are commonly ascribed to the presence of many complex organic constituents, including oxygenated monoterpenes, sesquiterpenes, and hydrocarbons. Typically, these compounds consist of polar functional groups that incorporate oxygen atoms alongside conjugated aromatic rings or double bonds. Therefore, these compounds have a propensity to undergo adsorption on the surfaces of metals. In the present paper, the focus is on Blue Tansy essential oil extracted from Tanacetum vulgare. Tanacetum vulgare was used, in Romanian traditional medicine, as an anthelminthic, stomachic, febrifuge, and emmenagogue due its antioxidant and cytotoxic activity [21]. Its common name, “Tansy”, comes from the Greek word “athanasia” which means “immortality”; this is due to the fact that its flowers do not wilt when dry.

In our ongoing quest to investigate sustainable materials as corrosion inhibitors in diverse corrosive environments, the current study reports on the corrosion inhibition effect of two Blue Tansy essential oils, which have distinct chemical compositions, in inhibiting the corrosion of mild steel in 1 M hydrochloric acid solution. The evaluation was conducted using weight loss and potentiodynamic polarization methods. The novelty of the work lies in the use of Petra/Osiris/Molinspiration (POM) analyses to gain insights into the risk of toxicity and their bioactivity score of all of the constituents of BTES.

2. Materials and Methods

2.1. Mild Steel Composition and Aggressive Solution

E24 Steel (NF standard)/S235 (AISI) (0.18% C, 0.16% Si, 0.49% Mn, 0.06% P, 0.02% S and Fe as balance) was used. The aggressive solution (1 M HCl) was prepared by dilution of Analytical Grade 37% HCl with distilled water.

2.2. Characterization of Blue Tansy Essential Oil

The two Blue Tansy essential oils were analyzed by gas chromatography on a Clarus 580 Perkinelmer GC system coupled to a flame ionization detector (FID). The chromatographic column used was a RESTEK (60 m, 0.25 mm ID, 0.25 µm). The chemical compositions of the analyzed essential oils are presented in

Table 1. Operating conditions for analysis by gas chromatography GC/FID.

Injection Volume	1 µL
Injector temperature	250 °C (with split ratio of 5)
Detector temperature (FID)	280 °C
Column	RESTEK (60 m, 0.25 mm ID, 0.25 µm)
Detector	FID
Carrier gas	N2, He Air 1.2, 45 et 450 mL/min respectively
Oven program	°C/min	Temperature (°C)	Maintain (min)
	…	50	5
	10	200	0
	5	240	2

.

2.3. Electrochemical Measurements

In the electrochemical measurements, a standard three-electrode setup was deployed. The saturated calomel electrode serves as the reference electrode, while a platinum mesh serves as the counter electrode, and the mild steel sample was utilized as the working electrode with an area of 19.63 mm² exposed to the corrosive solution. The electrochemical workstation used was Potentiostat Galvanostat Impedancemeter Model OGS080, connected to a personal computer running OrigaMaster 5 software, which facilitated the communication and control of the instrument. Potentiodynamic polarization measurement was carried out within the potential window of −1000 mV (vs. SCE) to 50 mV (vs. SCE) at a sweep rate of 0.2 mV/s. The Open Circuit Potential was recorded after a 30 min stabilization period. Prior to each test, the sample surface was carefully abraded using emery paper with grit sizes of 120, 400, 600, and 1200.

2.4. Weight Loss Measurements

The mild steel samples were sequentially abraded using emery papers of different grades. Subsequently, they were washed with distilled water and cleaned using acetone. The samples were in the form of cylindrical shapes with dimensions of 10 mm diameter and 10 mm height. After precise weighing on a highly sensitive balance, the samples were immersed in 100 mL of 1.0 M HCl solution with and without varying concentrations of Blue Tansy essential oil [23,24]. After a 6 h submersion period, the samples were removed, thoroughly cleaned, rinsed with distilled water and then acetone, dried in an oven to a constant weight, and then reweighed.

2.5. Petra/Osiris/Molinspiration (POM) Analyses

In this study, we employed the POM (Petra/Osiris/Molinspiration) theory, developed by Professor Taibi Ben Hadda’s group in collaboration with the American NCI and TAACF, to analyze the bioactivity score and drug-likeness of the molecules present in Blue Tansy essential oil [25]. This bioinformatics program, as defined by Chalkha et al. [26], is a robust tool capable of optimizing and identifying the pharmacophore sites of organic compounds based on physicochemical parameters. Moreover, POM analyses enable the prediction of biological activities and facilitate the exploration of the relationships between steric/electrostatic properties and biological activity in the form of pharmacophore sites, as described by Tariq et al. [27].

3. Results and Discussion

3.1. Chemical Composition of Blue Tansy Essential Oil

The obtained constituents (in %) of the Blue Tansy essential oils (BTES) are summarized in

Table 2. The chemical composition of BTES 1 and BTES 2 obtained by GC-FID.

BTES 1			BTES 2
N°	Molecule	%	N°	Molecule	%
1	β-Pinene	2.2	1	Santolina triene	1.94
2	α-Pinene	2.04	2	α-Pinene	8.75
3	Mycrene	2.06	3	Camphene	15.81
4	Sabinene	15.83	4	Sabinene	3.80
5	1,8-Cineole	1.26	5	1,8-Cineole	2.87
6	Gamma-terpinene	0.83	6	α-terpinene	3.00
7	o-Cymene	5.86	7	p-Cymene	0.47
8	α-Phellandrene	4.45	8	β-Phellandrene	1.00
9	β-Caryophyllene	0.85	9	α-Bisabolol oxide B	1.17
10	β-Eudesmol	1.66	10	α-Farnesene	0.93
11	β-Farnesene	0.8	11	β-Farnesene	0.95
12	Terpinene-4-ol	0.74	12	Terpinene-4-ol	0.84
13	Limonene	2.33	13	Limonene	0.70
14	Camphor	10.58	14	Camphor	3.30
15	Chamazulene	15.61	15	Chamazulene	13.49
16	Not identified	1.23	16	α-Bisabolol oxide A	29.03
17	Not identified	0.525	17	α-Terpineol	0.33
18	Not identified	1.19	18	Linalol	0.96
19	Not identified	0.66	19	Cis-enyne dicycloether	0.68
20	Not identified	1.14	20	Trans-enyne dicycloether	0.91
			21	α-Bisabolone oxide A	7.48
			22	Germacrene D	1.59

. Based on the analysis of the chemical composition of the two Blue Tansy essential oils (BTES 1 and BTES 2), several key molecules were identified, and their respective percentages are presented in Table 2. It was found that the major constituents of BTES 1 include Sabinene (15.83%), Chamazulene (15.61%), Camphor (10.58%), O-Cymene (5.86%), α-Phellandrene (4.45%), and Limonene (2.33%). Other notable compounds present in smaller quantities include β-Pinene, α-Pinene, Mycrene, 1,8-Cineole, Gamma-terpinene, and Terpinene-4-ol. Sabinene is a bicyclic monoterpene found in nature with the chemical formula C₁₀H₁₆. A strained ring structure with a cyclopentane ring fused to a cyclopropane ring is present. The chemical compound o-cymene is classed as an aromatic hydrocarbon. It has an ortho-substituted benzene ring with a methyl group and an isopropyl group as its structure. Camphor is composed of three elements: carbon, hydrogen, and oxygen. Camphor has the chemical formula C₆H₁₆O. It is classified as a bicyclic monoterpene ketone. Chamazulene has the chemical formula C₁₄H₁₆ and is a bicyclic unsaturated hydrocarbon. Although it does not belong to the sequiterpenes, it has historically been listed with them. It is an azulene, which is generated from sequiterpenes. The dominant compounds in BTES 2 are α-Bisabolol oxide A (29.03%), Camphene (15.81%), Chamazulene (13.49%), and α-Pinene (8.75%). Additional constituents include Sabinene, 1,8-Cineole, α-terpinene, p-Cymene, and β-Phellandrene, among others. α-Bisabolol, commonly known as levomenol, is a monocyclic sesquiterpene alcohol found in nature. Camphene belongs to the bicyclic monoterpenoids class of chemicals. Bicyclic monoterpenoids are monoterpenoids with two rings that are bonded together. α-Pinene is an organic component of the terpene class and one of two pinene isomers. It is an alkene with a reactive four-membered ring.

The chemical constituents of the essential oils contain polar functional groups including oxygen atoms alongside conjugated aromatic rings or double bonds. These polar functions are referred to as adsorption centers that aid the adsorption of the molecules on the metal surface to inhibit corrosion. Examination of the compositions of BTES 1 and BTES 2 revealed several differences. These variations in chemical composition can contribute to differences in the inhibitory properties of the two essential oils on mild steel corrosion.

3.2. Electrochemical Measurements

Potentiodynamic polarization method is a veritable tool for assessing the corrosion inhibition capabilities of substances. The phrase “electrochemical polarization” pertains to a method of inducing polarization by modulating the electrode potential at a predetermined rate through the application of an electric current within the electrolyte. It yields significant insights into the underlying mechanisms of corrosion, the rates at which corrosion occurs, and the vulnerability of particular materials to corrosion under specific environmental conditions. Figure 1 illustrates the polarization curves obtained for mild steel in a 1.0 M HCl solution in the absence and presence of different concentrations of BTES 1 and BTES 2. The extrapolation method was utilized to analyze the polarization curves and to generate electrochemical parameters of interest. The resulting data, including corrosion potential (E_corr), corrosion current density (i_corr), cathodic Tafel slopes (β_c), and percentage inhibition efficiency IE (%), are summarized in

Table 3. Electrochemical parameters of mild steel at different concentrations of the Tansy Oil (BTES1 and BTES 2) in 1.0 M HCl and corresponding inhibition efficiencies.

Inhibitor	Concentration (g/L)	Ecorr (mV/SCE)	βa (mV/dec)	βc (mV/dec)	icorr (mA/cm2)	Rp Ω cm2	Corrosion µm/Year	IE (%)
BTES 1	0	−402.9	51.5	−55.04	0.0489	385.69	572.26	−
	0.5	−513.6	73.2	−72.49	0.0091	3490	106.16	81.39
	1	−475.5	66.5	−62.72	0.019	1720	222.26	61.15
	2	−511.5	99.1	−87.02	0.0126	2850	147.14	74.23
	2.5	−502.1	91	−87.85	0.0161	2100	188.73	67.08
BTES 2	0	−564.4	61.1	−58.56	0.0516	472.75	603.76	−
	0.5	−666.6	109.1	−114.6	0.0225	1140	262.92	56.45
	1	−645	108.9	−94.34	0.0271	1120	317.5	47.41
	2	−691.6	100.5	−97.08	0.0198	1400	231.35	61.68
	2.5	−639.9	92.8	−88.08	0.0121	1880	141.79	76.51

. Equation (1) was used to determine the inhibition efficiency [28]:

IE (%) = [(i_corr − i_{corr inh})/i_corr] × 100

(1)

where i_corr and i_{corr inh} are the corrosion current density values without and with the inhibitor, respectively, determined by extrapolation of cathodic Tafel lines to the corrosion potential.

Upon examination of Figure 1, it is evident that there is a gradual displacement of the potentiodynamic polarization curves towards lower current densities and E_corr in the noble (positive) direction. This displacement becomes more pronounced as the dosage of BTES 1 and BTES 2 increases. The fall in current densities suggests that the corrosion reaction is decelerated in the presence of BTES as corrosion inhibitor.

The results showed that Blue Tansy essential oil inhibited the corrosion of mild steel in 1 M HCl solution. The inhibition efficiency values can reach 80% at 0.5 g/L of BTES 1 and 76% at 2.5 g/L of BTES 2. The inhibitory power of both oils increases to its maximum value and then decreases and increases again following a damped oscillation. The observed oscillation in the inhibitory efficiency of both Blue Tansy essential oils (BTES 1 and BTES 2) can be explained by considering several factors, such as the presence of multiple active compounds within the essential oils, which can lead to complex interactions and synergies [29]. At lower concentrations, the active compounds may not be present in sufficient quantities to provide effective corrosion inhibition. As the concentration increases, the inhibitory power reaches a maximum due to an optimal balance of active components. However, at higher concentrations, interactions between the compounds, such as aggregation or competition for adsorption sites, may occur. These interactions can diminish the overall inhibitory effect, resulting in a decrease in inhibitory efficiency and the observed oscillation. We can also explain the damped oscillation of the inhibitory efficiency by the formation of a protective film on the surface of the mild steel.

At lower concentrations, the adsorption of active compounds might not be significant, leading to limited film formation and lower inhibitory efficiency. As the concentration increases, more inhibitor molecules adsorb onto the metal surface, enhancing the formation of a protective film and increasing the inhibitory power [30,31]. However, at higher concentrations, excessive adsorption or film thickness can impede the access of inhibitor molecules to the metal surface, reducing the inhibitory effect and causing the oscillation, which can also be explained by a third factor, the competitive adsorption between the inhibitor molecules and other species present in the corrosive environment [32] (Taylor et al., 2018). At certain concentrations, there may be an optimal balance between the inhibitor molecules and other species, resulting in maximum inhibitory efficiency. However, as the concentration increases further, the presence of excess inhibitor molecules can disrupt this balance and lead to reduced inhibitory power, causing the observed oscillatory behavior. From Table 2, it is seen the essential oils (BTES 1 and BTES 2) are composed of diverse phytoconstituents. Some are present in relatively large amounts, while others are present in small amounts. The different constituents may have synergistic or antagonistic effects on corrosion mitigation.

3.3. Weight Loss Measurements

To evaluate the corrosion rate and effectiveness of inhibition under static conditions, a weight loss experiment was conducted. This involved immersing metal samples in a corrosive solution, both with and without the presence of BTES 1 and BTES 2 as inhibitors [33]. The corrosion rate (CR) and inhibition efficiency IE (%) were calculated using Equations (2) and (3), respectively [34]:

CR (mg h⁻¹ cm⁻²) = [(ΔW)/AT]

(2)

IE (%) = [(CR_blank − CR_inh/CR_blank] × 100

(3)

ΔW is average weight loss (mg), A is the area (cm²), T is submersion time (h), and CR_blank and CR_inh are the corrosion rates of steel in the absence and presence of BTES, respectively. The computed corrosion rates and inhibition efficiency from the weight loss measurements for different inhibitor concentrations in 1.0 M HCl are given in

Table 4. Gravimetric results of mild steel in 1.0 M HCl without and with the addition of BTES 1 and BTES 2.

BTES 1			BTES 2
C (g/L)	CR (mg h−1 cm−2)	IE (%)	C (g/L)	CR (mg h−1 cm−2)	IE (%)
0	0.12468	−	0	0.1512	−
0.5	0.02390	80.83	0.5	0.0743	50.88
1	0.05400	56.69	1	0.0875	42.11
2	0.03500	71.93	2	0.0663	56.14
2.5	0.04800	61.50	2.5	0.0424	71.93

.

Examination of Table 4 also revealed that the introduction of BTES 1 and BTES 2 to the corrosive medium (1 M HCl) inhibited the corrosion of mild steel. From the table, it can be seen that the corrosion rate was drastically reduced on the introduction of both BTES 1 and BTES 2 to the acid corrodent. The reduction in the corrosion rate was observed to be concentration dependent, with the most profound results achieved at BTES 1 and BTES 2 concentrations of 0.5 g/L and 2.5 g/L, respectively. The IE fluctuates with both BTES 1 and BTES 2 dosage in an oscillatory manner. The optimum IEs of 80.83% and 71.93% were recorded at BTES 1 and BTES 2 dosages of 0.5 g/L and 2.5 g/L, respectively. The results obtained from the weight loss measurements and the potentiodynamic polarization curves are in agreement, supporting the findings of the study. The weight loss measurements provide a direct assessment of the corrosion rate and the inhibitory efficiency of Blue Tansy essential oils on mild steel. On the other hand, the potentiodynamic polarization curves offer valuable insights into the electrochemical behavior and corrosion kinetics of the system. The similarity in the inhibition efficiency values obtained from both techniques confirms the reliability and consistency of the experimental results. This agreement enhances the overall confidence in the findings and strengthens the validity of the conclusions drawn from the study.

3.4. POM Analyses

The obtained results from the utilization of two cheminformatics software, Osiris and Molinspiration, are presented in

Table 5. Molinspiration calculations of all of the molecules that constitute BTES 1 and BTES 2.

Molecule	Calculation of Molecule Property									Calculation of Bioactivity Score
	miLogP	TPSA	Natoms	MW	nON	nOHNH	Nviolations	Nrotb	Volume	GPCR Ligand	ION Channel Modulator	Kinase Inhibitor	Nuclear Receptor Ligand	Protease Inhibitor	Enzyme Inhibitor
α-Bisabolol oxide A	3.41	29.46	17	238.37	2	1	0	1	252.29	−0.07	0.40	−0.70	0.39	−0.11	0.76
Sabinene	3.10	0.00	10	136.24	0	0	0	1	152.37	−1.15	−0.33	−1.79	−0.69	−0.78	−0.60
Camphene	3.33	0.00	10	136.24	0	0	0	0	152.37	−1.02	−0.55	−1.85	−1.15	−1.40	−0.82
Chamazulene	4.84	0.00	14	184.28	0	0	0	1	194.52	−0.33	−0.34	−0.67	−0.40	−0.72	0.04
Camphor	2.16	17.07	11	152.24	1	0	0	0	159.86	−0.79	−0.56	−2.12	−1.21	−0.95	−0.52
α-Pinene	3.54	0.00	10	136.24	0	0	0	0	151.81	−0.48	−0.43	−1.50	−0.62	−0.85	−0.34
α-Bisabolone oxide A	3.41	29.46	17	238.37	2	1	0	1	252.29	−0.07	0.40	−0.70	0.39	−0.11	0.76
α-terpinene	3.36	0.00	10	136.24	0	0	0	1	156.74	−0.96	−0.24	−1.29	−0.24	−1.52	−0.11
p-Cymene	3.90	0.00	10	134.22	0	0	0	1	150.55	−1.18	−0.61	−1.40	−1.21	−1.42	−0.78
β-Phellandrene	3.58	0.00	10	136.24	0	0	0	1	157.32	−0.99	−0.48	−1.55	−0.28	−1.31	−0.27
α-Bisabolol oxide B	3.41	29.46	17	238.37	2	1	0	2	252.29	−0.05	−0.03	−0.56	0.32	−0.33	0.45
α-Farnesene	5.82	0.00	15	204.36	0	0	1	6	239.27	−0.30	0.14	−0.62	0.17	−0.63	0.45
β-Farnesene	5.84	0.00	15	204.36	0	0	1	7	239.82	−0.44	−0.05	−0.77	0.07	−0.68	0.27
1,8-Cineole	1.80	29.46	12	170.25	2	1	0	0	174.71	−0.60	0.50	−1.24	−0.32	−0.35	0.36
Germacrene D	5.43	0.00	15	204.36	0	0	1	1	234.90	−0.30	−0.11	−0.81	0.32	−0.67	0.26
Terpinene-4-ol	2.60	20.23	11	154.25	1	1	0	1	170.65	−0.56	−0.04	−1.68	−0.20	−0.92	0.06
Limonene	3.62	0.00	10	136.24	0	0	0	1	157.30	−0.91	−0.27	−2.01	−0.34	−1.38	−0.21
Linalol	3.21	20.23	11	154.25	1	1	0	4	175.59	−0.73	0.07	−1.26	−0.06	−0.94	0.07
Cis-enyne dicycloether	3.50	18.47	15	200.24	2	0	0	0	191.51	−0.56	0.12	−0.71	0.04	−0.51	0.06
Trans-enyne dicycloether	3.50	18.47	15	200.24	2	0	0	0	191.51	−0.56	0.12	−0.71	0.04	−0.51	0.06
Santolina triene	4.20	0.00	10	136.24	0	0	0	3	162.03	−1.27	−0.19	−1.76	−0.67	−1.24	−0.38
α-Terpineol	2.60	20.23	11	154.25	1	1	0	1	170.65	−0.51	0.15	−1.45	−0.02	−0.78	0.14
Beta-Pinene	3.33	0.00	10	136.24	0	0	0	0	152.37	−0.53	−0.32	−1.45	−0.50	−0.80	−0.34
gamma-terpinene	3.36	0.00	10	136.24	0	0	0	1	156.74	−0.90	−0.24	−1.37	−0.33	−1.55	−0.07
o-Cymène	3.38	0.00	10	134.22	0	0	0	1	150.55	−1.09	−0.54	−1.35	−1.14	−1.37	−0.71
alpha-Phellandrene	3.79	0.00	10	136.24	0	0	0	1	156.77	−1.00	−0.40	−1.40	−0.32	−1.38	−0.15
Mycrene	3.99	0.00	10	136.24	0	0	0	4	162.24	−1.11	−0.33	−1.51	−0.45	−1.31	−0.07
Beta-Caryophyllene	5.17	0.00	15	204.36	0	0	1	0	229.95	−0.34	0.28	−0.78	0.13	−0.60	0.19
Beta-Eudesmol	4.01	20.23	16	222.37	1	1	0	1	243.86	−0.02	0.43	−0.62	0.60	−0.10	0.48

and

Table 6. Osiris calculation of all of the molecules that constitute BTES 1 and BTES 2.

Molecule	2D Structure/Canonical SMILES	Calculation of Toxicity Risks, Drug-likeness and Drug Score	Molecule	2D Structure/Canonical SMILES	Calculation of Toxicity Risks, Drug-likeness, and Drug Score
Santolina triene	CC(=CC(C=C)C(=C)C)C		α-Bisabolol oxide A	CC1=CCC(CC1)C2(CCC(C(O2)(C)C)O)C
α-Pinene	CC1=CCC2CC1C2(C)C		α-Terpinene	CC1=CC=C(CC1)C(C)C
Camphene	CC1(C2CCC(C2)C1=C)C		P-Cymene	CC1=CC=C(C=C1)C(C)C
Sabinene	CC(C)C12CCC(=C)C1C2		β-Phellandrene	CC(C)C1CCC(=C)C=C1
1.8-Cineole	CC1(C2CCC(O1)(C(C2)O)C)C		α-Bisabolol oxide B	CC1=CCC(CC1)C2(CCC(O2)C(C)(C)O)C
β-Farnesene	CC(=CCCC(=CCCC(=C)C=C)C)C		α –Farnesene	CC(=CCC/C(=C/C/C=C(\C)/C=C)/C)C
Germacrene D	CC1=CCCC(=C)C=CC(CC1)C(C)C		Camphor	CC1(C2CCC1(C(=O)C2)C)C
Terpinene-4-ol	CC1=CCC(CC1)(C(C)C)O		Linalol	CC(=CCCC(C)(C=C)O)C
Limonene	CC1=CCC(CC1)C(=C)C		Chamazulene	CCC1=CC2=C(C=CC2=C(C=C1)C)C
α-Terpineol	CC1=CCC(CC1)C(C)(C)O		Trans-enyne dicycloether	CC#CC#CC=C1C=CC2(O1)CCCO2
Cis-enyne dicycloether	CC#CC#CC=C1C=CC2(O1)CCCO2		Gamma-terpinene	CC1=CCC(=CC1)C(C)C
α-Bisabolone oxide A	CC1=CCC(CC1)C2(CCC(C(O2)(C)C)O)C		o-Cymene	CC1=CC=CC=C1C(C)C
β-Pinene	CC1(C2CCC(=C)C1C2)C		α-Phellandrene	CC1=CCC(C=C1)C(C)C
Mycrene	CC(=CCCC(=C)C=C)C		beta-Caryophyllene	CC1=CCCC(=C)C2CC(C2CC1)(C)C
Beta –Eudesmol	CC12CCCC(=C)C1CC(CC2)C(C)(C)O

, respectively. These software tools play a significant role in providing valuable insights into the properties and characteristics of the studied molecules. Specifically, Molinspiration calculations yield crucial molecular properties, such as miLog P (partition coefficient), the topological polar surface area (TPSA), the number of atoms (natoms), molecular weight (MW), the number of hydrogen bond donors (nOHNH), the number of hydrogen bond acceptors (nOH), the number of violations of the Octet Rule (nviolations), the number of rotatable bonds (nrotb), and volume. Additionally, the calculation of the bioactivity score is also included in Table 5, offering further understanding of the molecules’ potential biological activities. Furthermore, the Osiris methodology facilitates the assessment of risks associated with toxicity, drug-likeness, and drug score for all the molecules under investigation. The corresponding results of these calculations are summarized in Table 6, providing insights into the safety profile and drug-like properties of the studied compounds. The integration of Osiris and Molinspiration analyses in this study allows for a comprehensive evaluation of the molecular properties, bioactivity potential, and risk assessment of the studied molecules. These analyses aid in the characterization and understanding of the molecules’ behavior, enabling us to make informed decisions regarding their potential applications in the corrosion inhibition of the mild steel used.

Based on the Molinspiration calculation results presented in Table 5, a comprehensive analysis of the molecules constituting Blue Tansy Essential Oil (BTES) 1 and BTES 2 reveals valuable insights into their potential interactions, toxicity risks, and bioactivity scores. Out of the 29 molecules studied, a significant majority (24 out of 29) exhibit no violation of the rule of five properties. This observation, as highlighted by Mabkhot et al. [35], suggests that these molecules are less likely to encounter issues with bioavailability. The rule of five properties serves as a crucial guideline for evaluating a molecule’s ability to efficiently traverse cell membranes and reach its intended target site.

In terms of the ligand parameters for GPCR protease inhibitor and kinase inhibitor interactions, an intriguing observation emerges: all studied molecules demonstrate negative values. This implies that these molecules are unlikely to activate G protein-coupled receptors (GPCRs) or inhibit kinases. As a result, predictions regarding interactions between molecules or between the molecules and mild steel, based on these parameters, should be approached with caution. It is important to note that the negative values do not support the expectations of specific GPCR-related or kinase inhibition interactions.

However, a noteworthy aspect is the presence of molecules with promising positive values in terms of enzyme inhibition. Particularly, Alpha-Bisabolol oxide A and Alpha-Bisabolone oxide A exhibit notably positive values as enzyme inhibitors, suggesting their potential to modulate enzymatic activity. Following closely, Alpha-Bisabolol oxide B, Alpha-Farnesene, and Beta-Eudesmol also demonstrate favorable positive values, further indicating their capacity to interact with enzymes and potentially influence enzymatic functions.

The insights garnered from the Molinspiration calculations illuminate a comprehensive understanding of the molecular characteristics and behaviors of the studied compounds, contributing crucial information for assessing their suitability across various applications, including corrosion inhibition, as well as potential interactions with biological targets and enzymatic systems. The outcomes presented in Table 6 unveil several noteworthy findings pertaining to the toxicity and associated risks of the investigated molecules. Upon closer examination, it becomes evident that certain molecules, such as camphor and limonene, exhibit unfavorable characteristics, encompassing risks of mutagenicity, tumorigenicity, irritation, and reproductive effects. In addition, a subset of compounds, including alpha-pinene, alpha-terpinene, p-cymene, linalool, terpinene-4-ol, gamma-terpinene, myrcene, and alpha-phellandrene, demonstrate irritant properties. Notably, trans-enyne dicycloether, cis-enyne dicycloether, and myrcene are associated with the risk of tumorigenicity, while myrcene and alpha-phellandrene are also implicated in reproductive risks. Moreover, camphene, linalool, and alpha-phellandrene display potential mutagenic risk. In contrast, the remaining molecules exhibit no mutagenic, irritating, tumorigenic, or reproductive effects.

An additional facet of the study involves the cLogP values obtained, which offer insights into the lipophilicity of the molecules. A particularly intriguing observation is that 1,8-cineole displays the lowest degree of lipophilicity, suggesting favorable solubility in water. The value of the topological polar surface area (TPSA) serves as a valuable descriptor for characterizing drug absorption [36]. From Table 6, it is evident that a majority of the molecules possess a null TPSA value. However, specific compounds, such as α-Bisabolol oxide A, α-Bisabolol oxide B, 1,8-cineole, camphor, terpinene-4-ol, linalool, trans-enyne dicycloether, cis-enyne dicycloether, α-Bisabolone oxide A, alpha-terpineol, and beta-eudesmol, exhibit TPSA values ranging from 17.07 to 29.46.

These insights into molecular properties, associated risks, and solubility characteristics, as provided by the cLogP and TPSA values, are instrumental in understanding the potential behavior, absorption, and bioactivity of the studied molecules. Consequently, these findings hold significant implications for making informed decisions about the practical applications of these compounds, especially within the context of corrosion inhibition strategies and other relevant domains. The integration of such insights into corrosion inhibition research offers a promising avenue for the development of effective and sustainable solutions.

The presence of these various components at different concentrations constitutes a richness of heteroatoms, aromatic rings, and double and triple bonds facilitating the adsorption on the metal surface via a synergistic intermolecular effect [37,38,39,40].

4. Conclusions

In conclusion, this study investigated the corrosion inhibition properties of two Blue Tansy essential oils (BTES 1 and BTES 2) on mild steel in hydrochloric acid solution. The chemical composition analysis revealed distinct compositions for each essential oil, and the results demonstrated that both oils effectively inhibited corrosion. The inhibition efficiency values can reach 80% at 0.5 g/L of BTES 1 and 70% at 2.5 g/L of BTES 2. It showed an interesting oscillatory behavior with the changing concentrations of the essential oils. This behavior can be attributed to complex interactions between the active compounds, the formation of protective films, and competitive adsorption effects. The results obtained from weight loss measurements and potentiodynamic polarization curves were consistent, supporting the reliability of the findings. Additionally, the POM analyses provided insights into the molecular properties, bioactivity potential, and potential risks associated with the studied molecules. The adherence to the rule of five properties and the lack of GPCR activation and kinase inhibition indicated good bioavailability and specific interactions of the molecules. The major challenge of the present work is the inability to pinpoint which compound(s) in the extract is/are responsible for the corrosion mitigation, given that both BTES 1 and BTES 2, like other plant extracts, comprise myriads of chemical constituents. However, it is in our future plan to address this challenge by isolating, characterizing, and evaluating the corrosion inhibition of the individual constituents (particularly those present in relatively large amounts) using sophisticated separation and analytical techniques including prep-HPLC. The comprehensive understanding gained from this study contributes to the development of effective green corrosion inhibitors. Further research can build upon these findings to optimize Blue Tansy essential oils and their derivatives for various industrial applications, ultimately promoting sustainable corrosion protection strategies.