Synthesis, structural and theoretical studies on new morpholino acetamide ligand and rare earth metal complexes and corrosion Inhibition Effect

A series of new complexes of the general formula [Ln(H 2 L)Cl 2 ]Cly.4H 2 O (Ln = Er and Ta) and [Yb(H 2 L)(H 2 O) 2 ]Cl 3 , H 2 L = N,N'-((ethane-1,2-diylbis(sulfanediyl))bis(2,1-phenylene))bis(2-morpholinoacetamide) are synthesized and characterized. The physical properties of these complexes are investigated including melting point, color, and percent yield. At room temperature, complexes exhibit similar solution absorption spectra in the UV–Vis region. As shown by thermal analysis, the complexes lose water molecules �rst, then anions, and �nally ligand molecules, leaving a metal oxide residue. The complexes were resulted from monomolar coordination of neutral tetradentate ligand through the amide nitrogen and sulfur, with octahedral geometries. Ligand and its Ta(V) complex are structurally characterized by X-ray powder diffraction. Their optical band gaps demonstrated the ligand and complexes have semiconducting property. Aluminum alloys (AlSi) corrosion inhibition was investigated in 1 M HCl using potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS). The inhibition e�ciency was 96.36% at 500 ppm inhibitor in 1 M HCl.. Multiple bonding patterns were discovered in molecular docking simulations of the drugs against SARS-CoV-2 (6Y84) and E. coli DNA gyrase (5MMN). The binding energy of complexes revealed active compounds capable of inhibiting SARS-CoV-2 and E. coli DNA gyrase. The antioxidant activity of the ligand and its Ln-complexes was investigated, yielding some surprising results. Finally, it is worthy to note that, the biochemical outcomes revealed that these complexes may be promising antibacterial agents.


Introduction
Heterocyclic compounds are the most prevalent type of organic chemical, containing nitrogen, Sulphur, or oxygen atoms together with carbon.They are abundant in nature, plus highly signi cant biological substances, such as nucleic acids, vitamins, antibiotics, hormones, pigments, and alkaloids, are heterocyclic compounds.Furthermore, heterocyclic compounds come in a wide range of properties, and approximately of them be able to employ as medications, insecticides, herbicides, dyes, or plastics.Morpholine has the chemical formula NH(CH 2 CH 2 ) 2 O. and is a typical six-membered aliphatic heterocyclic molecule.It has a heterocyclic ring, which is found in a variety of biological and pharmacological substances.[1] Amides functional groups are found in a range of synthetic, medicinally important molecules and biologically active natural products, including peptides, polymers, and anti-in ammatory compounds and so forth .[2][3][4] [5][6]The enormous effort that has gone into developing synthetic methods for amide compounds demonstrates the relevance of these molecules.
It is well known that many acyclic diamide ligands have a strong ion selectivity for lithium over sodium and other alkali metal ions.[7][8] Furthermore, adding an amide linkage to a polyether crown compound has been shown to change the binding characteristics of the compound, favoring alkali and alkaline earth metal cations, because the amide linkage provides two possible binding atoms: nitrogen and oxygen.[9][10] [11] Lanthanide complexes are used in medicine as magnetic resonance imaging (MRI) contrast agents and as radiotherapeutic medicines.Lanthanide complexes by organic ligands have obtained use in electroluminescent devices and diodes, lasers, cathode ray tubes, sensors, dosimeters, biological uoro immunoassays, organic light emitting diodes (OLEDS), imaging agents, display applications, decoration purposes, and telecommunication because of their catalytic, magnetic, and luminescent properties.Various types of organic ligands have been used to create and manufacture lanthanide complexes with desired functionalities.Furthermore, lanthanides play an intriguing, but poorly understood, biological role as trace components in living organisms.[12] The chemistry of lanthanide coordination has gotten a lot of attention recently.Their unique and unusual molecular structures can be used in a range of techniques, including biological research, catalysis, luminescence, and magnetism, demonstrating the importance and potential utility of this eld of study.[13] Tantalum is the chemical 'twins' of the vanadium triad of the periodic table, and their near-identical physical and chemical qualities make them infamously hard to isolated from one another and from their naturally happening ores.The lanthanide contraction of the elements, as well as their identical ionization energies, have been attributed to this parallelism in behavior [14].Titanocene dichloride, butotitane and related titanium compounds have reached up to second stage clinical trials.Adverse effects during these trials were the early decomposition of the products in the serum, their low solubility in the nearly neutral aqueous environment, and the inability to fully determine the mechanism of their biological action.[15] Heterocyclic compounds come in a wide range of properties, and some of them can be utilised as medications, insecticides, herbicides, dyes, and anticorrosion agents [16] [17].Morpholine has the chemical formula NH (CH 2 CH 2 ) 2 O and is a typical six-membered aliphatic heterocyclic molecule, which is found in a variety of biological, pharmacological, and anticorrosion chemicals.Acid solutions, such as hydrochloric acid and sulfuric acid, are commonly used to remove rust and scale from gas and oil pipelines, boilers, storage tanks, and condenser tubes, although they can cause major corrosion in metal-based equipment [18] [19].Acid anti-corrosion inhibitors are now routinely utilized to minimize metal dissolving rates[16] [17].Morpholine used to inhibition the corrosion for iron, brass and aluminum in aggressive media [20][21] [22].
In light of the foregoing facts, and in order to maintain our interest in this subject.[8] [23] Metal ions are crucial for plants, animals, and humans to live an extended and healthy survival.Their essential function in biological systems has extensive been recognized.They are needed for life to survive, and their lack can result in growth problems, severe dysfunction, cancer, or death.Catalysis, materials production, photochemistry, and biological systems all advantage from transition metal complexes.For the development of new medications, medicinal inorganic chemistry can take advantage of the features of metal ions.Metals and their salts have been used for medical purposes throughout history.Now we are occupied in a project focused towards the synthesis of novel acyclic diamides containing two soft donor sulfur atoms as well as two morpholine moieties aiming at studying its lanthanide complexes as example of rare earth metals.The primary goal of the present research is to study detailed bulk compositions of morpholino acetamide ligand and complexes through the thermal and spectral behavior of the synthesized complexes.Antimicrobial and antioxidant properties in vitro were also studied.Docking tests were also carried out to see how the synthesized chemicals interacted with SARS-CoV-2 (6Y84) and E. coli DNA gyrase (5MMN).The synthesized morpholine ligand was tested as anticorrosion inhibitor in acid medium and promising results were found.

Experimental Materials and Chemicals
Aluminum silicon alloys (AlSi) have the following chemical composition (wt.%): Si-9.89,Fe-1.10,Cu-1.99,Mn-0.22,Cr-0.037,Zn-2.44,Ca-0.004,Ni-0.269 and Al-balance was used in the experiments.The corrosive acidic solution is 1 M HCl which was prepared from HCl (37%, AR grade) supplied by Merck using deionized water.The concentration range of the corrosion inhibitor is from 100 ppm to 500 ppm.

Instruments
Sigma-Aldrich, Fluka, and Merck provided spectroscopic level reagents and solvents.As mentioned in our earlier work, we had used all of the apparatus.[24] [25][26] AlSi, saturated calomel electrode (SCE), and a platinum wire were used as working, reference, and counter electrodes, respectively, in a three-electrode electrochemical cell.The corrosion inhibition behavior was investigated using electrochemical techniques such as PP, and EIS.
PP was measured at a 5 mV/s scan rate.The corrosion current was calculated using the Stern-Geary method.The inhibition e ciency (IE PP ) and θ were estimated using i corr as follows: EIS was documented at an open-circuit voltage (OCV) with a modest alternating voltage (10 mV) spanning the frequency range of 100 kHz-20 mHz after immersing the electrode in the test for 1 hour at 25 o C. Inhibition e ciency (IE (EIS) ), and θ were calculated from the following Eq. 2 [27]: R ct(inh) and R ct(unh) are charge transfer resistances in the presence and absence of an inhibitor, respectively.

Antioxidant assays
The antioxidant activity of the extract was measured in triplicate at Al-Azhar University's Regional Center for Mycology and Biotechnology (RCMB) using the DPPH free radical scavenging test, with average values used.

DPPH Radical Scavenging Activity
A newly manufactured (0.004% w/v) methanol solution of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical was prepared and kept in the dark at 10 ºC .The test chemical was prepared into a methanol solution.In 3 ml of DPPH solution, a 40 uL aliquot of the methanol solution was inserted.A UV-visible spectrophotometer was used to take instantaneous absorbance values (Milton Roy, Spectronic 1201).The decline in absorbance at 515 nm was monitored constantly, with data collected at 1 min intervals until the absorbance levelled off (16 min).The absorbance of the DPPH radical (control) and the reference chemical ascorbic acid was also measured.Totally the tests were reiterated three times and the results were averaged.The DPPH radical's percentage inhibition (PI) was approximated using the formula: Where AC = Absorbance of the control at t = 0 min and AT = absorbance of the sample + DPPH at t = 16 min.
Graphic plots of the dosage response curve were used to estimate the 50% inhibitory concentration (IC 50 ), which is the concentration needed to inhibit DPPH radical by 50%.[

Results And Discussion
Elemental and molar conductance analyses The results of the elemental analyses (C, H, N, and S) agreed well with the anticipated chemical makeup of the compounds (Table 1).In addition, elemental studies revealed that the ligand H 2 L is coordinated in a 1:1 molar ratio.The Ln complexes' molar conductance measurements in DMSO ranged from 70- The complexes' values revealed that they were ionic, and they were electrolytes of the types 1:1, 1:3, and 1:3 electrolytes, respectively.[34][35] Mass spectrometry (MS) Using the MS method, the production of the H 2 L and its Ln complexes was con rmed.The mass spectrum of H 2 L is exposed in Figure 1a.The molecular ion peak was found at m/z = 532.05amu, which agree with the molecular weight of H 2 L and con rms the production of H 2 L (calculated 530.70 g/mol).

Infrared spectral study
Infrared spectra of the complexes were obtained to prove their structures.The vibration frequencies of the morpholino acetamide ligand and its Ln complexes, as well as their tentative assignments, are presented in Table 2 of the experimental part.
Comparisons by the vibrational frequencies of the free ligand and its metal complexes supported the designations.the infrared spectra of the complexes have four distinct properties.The rst is a shift in the stretching frequencies of the band around 767-760 cm -1 in the metal complexes because of ν(C-S) compared with free H 2 L ligand at 759 cm -1 ,Which is reliable with the appearance of new weakly to medium bands in the region of 404-411 cm -1 , which could be attributed to the stretching frequencies of ν(M-S) bands, confirmed that, the chelation to the metal ions is accomplished by thiol-Sulphur atoms. [36] The second feature, the morpholino acetamide ligand shows strong and broad band in the region of 3222 cm -1 assigned to νN-H vibration.In the complexes, the stretching frequencies of this band was shifted around 3230-3244 cm -1 indicating coordination of N atom of secondary amino group and crystalline or coordinated water molecules related with the complex.The band at 1428 cm -1 assigned to νC-N in ligand is shifted of the stretching frequencies of the band around 1429-1464 cm -1 showing the coordination of nitrogen.The presence of a band in the far IR range at 458-467 cm -1 attributed to v(M-N) further supports the relationship with N atom [37][38] [39][40].
The third feature, the absorption band due to the carbonyl oxygen of amide was showed at 1677 cm −1 in the ligand.But, In the complexes, this band shifted to frequencies about 11-15 cm −1 indicating an H-bond between the ligand and the carbonyl C=O with the NH proton [12].
While, the four feature, the peak at 804 cm -1 correspond to condensed C-N heterocycles [12][41] and the strong C-O stretching absorptions was found at 1198 cm −1 which belongs to morpholino acetamide ring in ligand.[42][43] But, this band slightly shifted in the complexes, suggesting different surrounded environment after complexation.respectively.The 1 H NMR spectrum shows only one shift for the protons of the NH group from 10.25 ppm (the free ligand) to 10.32 ppm in its mononuclear Ta(V) complex [44] [26].This change can be explained by the role of the NH proton in hydrogen bond formation as well as N binding to metal ions.
Thermal analysis studies (TG and DTG) XRD study Powder XRD pattern of morpholinoacetamide ligand (H 2 L) and Ta(V) complex were detailed in the 2ϴ range from 0 to 80. Figure 2 shows the XRD pattern of morpholinoacetamide ligand (H 2 L) and the Ta(V) complex are exposed in Figure 2. The XRD pattern of the Ta(V) complex revealed good de ned crystalline peaks revealing that the complex was crystalline in phase with crisp crystalline XRD patterns that differed signi cantly from the ligand.Crystallinity appears in the Ta(V) complex due to the metallic compound's inherent crystalline nature.the grain size of the Ta(V) complex was estimated using Scherre's equation.Through determining the full width at half maximum of the XRD peaks and relating the relation dXRD = 0.9λ/β(Cosθ), where 'λ' is the wavelength, 'β' is the full width at half maximum, and 'θ' is the peak angle.
The ligand and complex have the average crystallite size of 3.35 to 96.5 nm and 1 nm to 22.7 nm suggesting that morpholinoacetamide ligand (H 2 L) and the Ta(V) complex are nanocrystalline compounds, respectively.According to previous researches, the difference between the two XRD shapes may assigned to coordination moiety.
[46] [47][48] [49] Structural interpretation Different approaches were used to characterize the structures of the produced Ln complexes, including elemental studies (C, H, N, M), molar conductivity measurements, FT-IR, UV-Vis spectroscopy, 1 H-NMR, mass spectral, and thermal investigations.As a result, as illustrated in Figure 3, the structure of all complexes may be presented.[35] Electronic transition spectra of ligand and its complexes In DMF at room temperature, UV/V absorption spectra of the morpholinoacetamide ligand and its complexes were measured (Table 4).The spectra can be found in the appendices.The organic ligand absorption band displayed two bands at 288 and 365 nm, which were ascribed to π-π* and n→π* transitions of the benzene rings and CH=O group, respectively.These bands are red-shifted in Ln complexes, indicating that the ligand is coordinated to the Ln ions.
[12] Because the 4f orbitals in lanthanides are buried deep within the atom, ligand vibrations have less of an impact on the broadening effect.At 537nm, a prominent band of Ligand to Metal Charge Transfer emerges.[50] DFT calculations the ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O complex by donning optimized molecular geometry and geometrical parameters, such as bond lengths, bond angles, HOMO energy, and LUMO energy, were calculated using the B3LYP and 6-31G basis set with no symmetry constraints.Gauss view 5.0 version software was used to visualize the optimized molecular structure, HOMO-LUMO, and MEP surface.The absence of the imagined con rms the achievement of a true energy minimum of the molecular structure.The Mulliken atomic charges were estimated using the B3LYP using the basis set 6-31G, as shown in Figure 5 and Table 5. [51] Bond lengths and bond angles The B3LYP/6-31G-calculated geometrical parameters (bond lengths and angles) were matched to the experimental parameters and found to be extremely good replicated.Tables 6 and 7 show the ndings of the study.[51] In the morpholinoacetamide ligand, The bond lengths of C(19) -S(8), C(7) -S(9), C(21) -N(29) and C(11) -N(31) were 1.85, 1.85, 1.43 and 1.41 Å, respectively,. .When they were coordinated to the Ta(V) ion, they displayed a little elongation and were found to be 1.91, 1.94, 1.65 and 1.68 Å, respectively.The ligand (H2L) in the Ta(V) complex was coordinated by two nitrogen and two sulphides, with two chloride ions lling the remaining two places.The bond angles in the Ta(V) coordination sphere were examined using the octahedral geometry, as previously indicated.The lowering of the metal chloride angle is responsible for intramolecular hydrogen interactions.[26] Frontier molecular orbitals (FMO) studies The FM orbitals are the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of a structure.The charge transfer collaboration also chemical reactivity of a ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O are determined by investigations of frontier molecular orbitals (HOMO and LUMO).
Figure 6 shows the HOMOs with LUMOs computed for ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O applying the B3LYP/6-31G level of theory.level of theory with the basis set 6-31G and are shown in Figure 7. Hydrogen bonding interactions, nucleophilic reactions, and electrophilic sites can all be estimated using the MEP.The varied colors on the MEP surface represent different electrostatic potential values..The red color represents electron-rich regions, the blue color represents electron-poor regions, and the white color represents zero electrostatic potential.Really, it is clear that in the ligand nitrogen atoms exposed as red region reacts with electrophilic sites, hydrogen atoms of a methyl group of the ligand exposed as blue region react with nucleophilic sites.[51] Electrochemical study Figure 8 shows PP curves for AlSi corrosion in 1 M HCl solutions in the absence and presence of different amounts of morpholinoacetamide ligand at 298 K.
Extrapolation of linear sections of anodic and cathodic curves to the relevant corrosion potential yielded the corrosion current density (Icorr), anodic, and cathodic and Tafel slopes (Ecorr).The equation was used to compute the percentage inhibition e ciency IE ( PP ) and the degree of surface covering (θ).
Table 9 summarizes the electrochemical characteristics derived from Tafel polarization curves.
The current density was lower in the presence of morpholinoacetamide ligand than in its absence, as shown in Table 1.With higher morpholinoacetamide ligand concentrations, the percent inhibition e ciency rose.Morpholinoacetamide molecules are adsorbed on the metal surface, as evidenced by this.With higher morpholinoacetamide inhibitor concentrations, the inhibition became more signi cant.By raising the inhibitor concentration, Tafel lines are moved to more negative and positive potentials than the blank curve.In each case, the shift in Ecorr values was less than 85 mV, indicating that morpholinoacetamide ligand is a mixed type inhibitor.[52][53] [54] Figure 9 shows Nyquist plots of AlSi in 1 M HCl solutions in the absence and presence of various amounts of morpholinoacetamide ligand at 298 K.The difference in the Nyquist plots at low and high frequencies was used to obtain the charge transfer resistance (Rct) values.[17] As a result, according to the equation, the inhibition e ciency, IE ( EIS ) , and the degree of surface coverage of morpholinoacetamide ligand may be estimated from the charge-transfer resistance.Table 10 shows the computed inhibition e ciency values, IE ( EIS ) .The value of Rct grew as the concentration of morpholinoacetamide ligand increased.The creation of an insulating protective coating at the metal/solution contact is responsible for increasing Rct values.
Figure 9b and 9c shows a Bode plot throughout the entire frequency range, demonstrating that the rise in impedance values is dependent on morpholinoacetamide ligand concentrations.When the concentration of morpholinoacetamide ligand reaches 500 ppm, the impendence values approach the maximum, indicating effective inhibition corrosion protection.As the concentration of morpholinoacetamide ligand reaches high levels, the phase angle increases, implying effective inhibition corrosion protection.[55][56] [35] Antioxidant activity

DPPH scavenging activities
Figure 10 shows the plots of DPPH scavenging effect (%) for lanthanide complexes, which are concentration dependent.As shown in Table 11, the values of IC50 of Er(III) and Yb(III) complexes for DPPH scavenging effect are 923.81 and 1086.92µg/ml, respectively.This order of IC50 is opposite to the abilities of scavenging effects for DPPH scavenging.[57] In antioxidant activity investigation, the role of DPPH radical scavenging reports for antioxidant estimation of the substances under study is regarded a dependable also repeatable method.With the DPPH radical at varied concentrations, the ligand and its complexes were tested pro free radical scavenging properties.
Figure 10 shows the ndings of the DPPH radical scavenging activity for the ligand and its complexes based on percent inhibition.A further study of the results reveals that the ligand and its complexes all have good DPPH radical scavenging properties.In general, the metal complexes outperformed the precursor ligand in terms of DPPH radical scavenging.The antioxidant results of the ligand and its complexes can be employed in further research to develop medications for the treatment of pathological diseases appearing from oxidative stress.[34] Antimicrobial Activity Figure 11 and Table 12 demonstrate the mean inhibitory activity of the morpholinoacetamide ligand and its complexes against the microorganisms tested.In the development of novel metal-based therapeutic agents., coordination between biologically active ligands and metal ions is critical.The produced ligand and its metal complexes had strong antimicrobial activity against the microorganisms tested, with varying degrees of inhibitory characteristics.All microorganisms were responsive to the ligand N,N'-((ethane-1,2-diylbis(sulfanediyl))bis(2,1-phenylene))bis(2-morpholinoacetamide, Er(III), Yb(III) and Ta(V) complexes with inhibitory zones as show in Table 8.The metal complexes were often more active than the ligand and, in a few cases, had comparable activity to those of the positive control drugs.The Yb(III) complex had inhibitory zones of 12.0-14.0mm /mg against all the tested microbes with the exception of Aspergillus avus and Candida albicans.The increased sensitivity of the complexes could be assigned to hyper conjugation of the coordinated aromatic system and increased liposolubility which results in a reduce in the polarity of metal ions and increased delocalization of π-electrons over the complex ring.The latter encouraged metal complex permeation across the lipid layers of the microbial membrane, enhancing antibacterial action.Furthermore, chelation also inhibited a number of cellular enzymes that are required for metabolic processes in bacteria.The Yb(III) complex revealed the best antibacterial activity of all other synthesized compounds and compared helpfully to the activity of cipro oxacin against some microbes.Figure 12 depicts the biological activity index of these complexes graphically.In the near future, the ligand could be used to develop antimicrobial drugs.[34][25] Docking SARS-CoV-2 (6Y84) and E. coli DNA gyrase (5MMN) showed good binding interactions across several attaching mechanisms in molecular docking investigations.To gain a worthier understanding of the interaction of organic ligands and their metal complexes with 6Y84 and 5MMN, molecular docking experiments were carried out to predict the preferred binding sites as well as the molecule's chosen orientation.The minimum energy shape (Figure 10) of Ta(V) complex with reveals that it is well-tting in order to form hydrogen acceptor bonding with the two proteins.The molecular docked model of the ligand and its metal complexes was shown in Figure 13 and Table 13.They demonstrated electrostatic and partial intercalation between themselves and protein base pairs.[46]Figure13 shows the 3D structures of SARS-CoV-2 (6Y84) and E. coli DNA gyrase (5MMN) receptors obtained from the Protein Data Bank.The 3D structures of the ligand in addition to its metal complexes were energy lessened plus docked interested in the active binding sites of these receptors.
Docking techniques were tested by simulating the PDB crystal structures in silico.The several binding poses that were created were examined and found designate pharmacological targets for therapeutic agents.[12] Conclusion Physico-chemical and spectral analyses were used to manufacture and analysis a tetrapodal ligand obtained from N,N'-((ethane-1,2diylbis(sulfanediyl))bis(2,1-phenylene))bis(2-chloroacetamide) and its new Yb(III), Er(III), and Ta(V) complexes.The ligand was discovered to be tetrapodal, with two nitrogen and two sulphides groups that coordinate to the ligand complexes.In vitro antimicrobial experiments revealed that the tetrapodal ligand, MT, has lower antibacterial activity than mononuclear complexes against the test pathogens.A range of in vitro tests, such as DPPH, were used to assess the ability of test materials to scavenge free radicals.The ndings demonstrated that the Er(III) compound has high antioxidant properties.DFT calculations were used to analyse the geometry of the Ta(V) complex.The ligand and its complexes were veri ed to be inhibitors of 6Y84 and 5MMN by molecular docking experiments.
XRD of ligand (H 2 L) and its Ta(V) complex.

Figure
The proposed structures of Ln complexes.
Page 19/24 The optimized structures of (A) H 2 L and (B) Ta(V) complex.

Supplementary Files
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Figure 4 appears the optimized molecular geometry of the ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O , per the atomic numbering in the ground state.[51]Mulliken charge analysis The Mulliken atomic charge indicates the charge density distribution of the ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O.The distribution of charges in the ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O was used to calculate the polarizability, dipole moment, and chemical reactivity of a molecule.

Figure 6 a)
Figure 6 a) Theoretical electronic absorption transitions for H 2 L and (b) Ta(V) complex in DMF solvent.

Figure 7 molecular
Figure 7molecular electrostatic potential map of (A) H 2 L and (B) Ta(V) complex.The electron density isosurface is 0.004 a.u.

Figure 8
Figure 8 Polarization curves of Aluminum silicon alloys in 1 M HCl with and without different concentrations of H 4 L.

Figure 9 a
Figure 9 a) The Nyquist plot for corrosion of Aluminum silicon alloys in 1 M HCl with and without different concentrations of H 4 L compound; (b),(c) the Bode plots for corrosion of Aluminum silicon alloys in 1 M HCl with and without different concentrations of H 4 L compound

Figure 11 Biological
Figure 11Biological activity of ligand and its Ln complexes.

Table 3
[45]s the outcomes of the thermal investigation of the ligand in addition to its Ln complexes.The elimination of the C 26 H 35 N 4 O 4 S 2 molecule at T The second and third phases at 234 to 900 ºC temperature range with a maximum temperature 342 and 628 ºC re ected the loss of Cl 2 and C 25 H 35 N 4 O 2.5 S 2 molecules (found 66.95%, calcd.66.86%) and this degradation processes are ended with the formation of the ½Yb 2 O 3 contaminated with carbon atom as a nal product.The metal content is concordant with the proposed structure.The thermal decay of the [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O complex proceeded throughout the temperature range from 37 to 900 ºC with four decay phases.The rst began at 37 to 148 ºC temperature range with a maximum temperature of 70 ºC corresponds to lack of 4H 2 O (estimated weight loss 6.84%, calcd.7.49%).The last three phases at 148 to 900 ºC temperature range with a maximum temperature of 244, 343 and 621 ºC re ected the loss of 2½Cl 2 and C 26 H 35 N 4 O 1.5 S 2 molecules (found: 70.99%, calcd.69.53%) and the nal residue of this degradation processes is the formation of ½Ta 2 O 5 as a nal product.The metal content is concordant with the proposed structure.[45] max 299 and 386 ºC with a mass loss of 98.90% (calcd.100%).wascompatiblewith the TG curve of ligand referring to two processes.The [Er(H 2 L)Cl 2 ]Cl.4H 2 O complex thermally stable up to 46 ºC, and the decay originated from 46 to 900 ºC and completed in three phases.The rst decay step within the 46 to 140 ºC temperature range with a maximum temperature of 65 ºC relates to the loss of 4H 2 O with a weight loss of 7.61% (calcd.8.21%).The 2 nd and 3 rd decay steps within the 140 to 900 ºC temperature range with a maximum temperature of 336 and 577 ºC correspond to loss of 1½Cl 2 and C 22 H 35 N 4 O 2.5 S 2 molecules with a weight loss of 63.08% (calcd.64.50%).The net weight loss was 80.69% (calcd.82.71%) leaving ½Er 2 O 3 contaminated with carbon as nal residue.The thermal decay of the [Yb(H 2 L)(H 2 O) 2 ]Cl 3 complex proceeded throughout the temperature range from 87 to 900 ºC with three decay phases.The rst began at 87 to 234 ºC temperature range with a maximum temperature of 151 ºC and corresponds to lack of 2H 2 O and ½Cl 2 (estimated weight loss 7.96%, calcd.8.45%).
Table 8 shows the estimated energies of the frontier molecular orbitals as well as the energy gap of the ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O .The ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O stability is con rmed by the negative HOMO and LUMO energy values.The HOMO-LUMO energy gap represents the molecule's chemical strength and reactivity.In a ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O with a narrow energy gap, the extent of intramolecular electron transfer from The molecular electrostatic potential (MEP) surface, which depicts the 3D picture of the charge distribution between the ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O provided information regarding the interactions between them.The MEP surface of the ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O were computed using the B3LYP [51]e of ionization potential also minor value of the electron a nity implies higher stability of the ligand matched to the [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O complex with a minor value of ionization potential and greater value of electron a nity.The above discussed global reactivity descriptors of the molecules have been computed through the B3LYP/6-31G method, which was described in Table8.The magnitude of global hardness and softness provides the ligand stability.In the same way, the [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O with a negative value of chemical potential, on the other hand, does not decompose into elements.[51]Molecularelectrostatic potential

)
Analytical and physical data of Schiff base ligand (H 2 L) and its metal complexes.

Table 5
The charge distribution calculated by the Muliken method for ligand and [Ta(H 2 L)Cl 2 ]Cl 3 .4H 2 O complex.Corrosion parameters obtained from potentiodynamic polarization measurements of AlSi in the absence and presence of different doses of l in 1.0 M HCl.

Table 13
Energy values obtained in docking calculations of morpholinoacetamide ligand and its Ln complexes with receptors 5MMN and 6Y84.