Divalent transition metal complexes [MGlu-Arg (H2O)]H2O and [MGlu-Arg (H2O)]H2O, where M = Co, Ni, Cu, and Zn, Glu = glutamic acid, and Arg = L-arginine, are prepared and characterized using different techniques. DFT and TD-DFT modelling validated and interpreted some experimental results. Weight loss technique reveals efficient corrosion inhibition action of these complexes towards aluminum metal at different temperatures. Our results point to corrosion inhibition through chemical adsorption on the aluminum surface. Additionally, a facile calcination of Co and Cu complexes at 550°C yields nanosized oxides of Co3O4, CoO, and CuO crystalline phases. The complexes show remarkable biological activities towards pathogenic bacteria and fungi. Moreover, in vitro anticancer activity evaluation of these complexes is achieved against hepatocellular carcinoma (HepG-2). The results are correlated with molecular descriptors such as chemical potential and hardness obtained from the frontier orbitals.
The chemistry of amino acid coordination compounds has always been an intriguing challenge to the inorganic chemists. This class of molecules have been found throughout the life science and vary tremendously in their function and complexity. These compounds play an essential part of metabolism and cellular signaling and as a part of drugs and as hydrogen storage media [
Many transition metals with mixed amino acid complexes revealed their biological activity, which place them in several biochemical processes [
Glutamic acid (Glu) (2-Aminoglutamic) is one of the 20 most common natural amino acids, which is considered to be one of the building blocks in protein synthesis [
Arginine is an essential amino acid that is physiologically active in the L-form. L-arginine appears as a zwitter ion with a protonated guanidine group in aqueous solutions, a spontaneous process resulting in a thermodynamically durable form in both solutions and crystals. The presence of a guanidine group in L-arginine enhanced the interesting behavior of antimicrobial activity against bacteria and fungi [
We focus here on the preparation and characterization of this class of mixed amino acid complexes of four divalent transition metal ions of Co, Ni, Cu, and Zn.
Modelling using DFT theory and TD-DFT will be investigated in an attempt to validate and characterize structural and electronic properties of M(II) Glu-Arg complexes in aqueous solution. This will shed light on the nature of M-L interaction. Such knowledge is likely to provide some help in the rational design of new complexes of biological importance. Additionally, cytotoxicity will be evaluated. Investigation of the biological activities include g-negative (
It is known that amino acids act as an eco-friendly inhibitor for several metals as copper, aluminum, steel, and nickel. L-arginine and its zinc complex are used as nontoxic and low-cost corrosion inhibitors for carbon steel [
Additionally, the metal complexes could be considered as a precursor for thermal preparation of nanosized metal oxides. Thus, we will investigate calcinating the complexes under investigations to check the possibility of obtaining metal nano-oxides in a facile way for possible application as photocatalysts.
All chemicals were purchased from Sigma-Aldrich. Glutamic acid (CAS Number: 56-86-0) and L-arginine (CAS Number: 74-79-3) ligands, as well as metal carbonates CoCO3·3Co(OH)2 (CAS Number: 12602-23-2), NiCO3·2Ni(OH)2·4H2O (CAS Number: 12607-70-4), CuCO3·Cu(OH)2·H2O (CAS Number: 12069-69-1), and 2ZnCO3·3Zn(OH)2
[M(II)(Glu)(Arg)] complexes were synthesized following the method used in [
The contents of C, H, and N were determined by Vario El Elementar, while metal percentages were determined by atomic absorption spectrometry (PerkinElmer AAs 3100) FTIR spectra of the ligands, and the complexes in KBr discs were recorded on a Jasco FTIR-300E Spectrometer (400–4000 cm−1 range), microanalytical laboratory, in the central laboratory of Ain Shams University.
Mass spectra were recorded at 350C° and 70 eV on Shimadzu GC/MS-QP5050A spectrometer, and ESR spectrum of the Cu complex was recorded at room temperature using a Bruker ESR-spectrometer model EMX at 9.706 GHz (X-band) using 2,2-diphenylpyridylhydrazone (DPPH) as standard (
Conductivity measurements of 10−3 M aqueous solutions (de-ionized water) at 25°C were carried out using WTW D-812 Weilheim conductivity meter, model LBR, fitted with a cell model LTA 100.
Thermogravimetric analysis (TGA) of metal complexes was carried out starting from room temperature ∼303 K to 1273 K under nitrogen atmosphere at a heating rate 283 K·min−1 using TA instrument, model SDT600. Mass spec., ESR, and TGA analysis were done in National Research Center lab, Cairo. The UV-Vis spectra were recorded in aqueous solutions (10−2 M) at room temperature with typical ranges from 800 to 190 nm on Cary 100 which is done in the microanalytical laboratory, in the central laboratory of Ain Shams University.
The metal complexes were calcined at 550°C for 6 h, and the metal oxides obtained were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. XRD analysis showed that the obtained oxides are crystalline and corresponded to the Co3O4, CoO, and CuO phases. Crystal size and shape were determined by SEM.
Magnetic susceptibilities were measured at room temperature by the Gouy method using a magnetic susceptibility balance Johnson Matthey, Alfa products, model MKI. Diamagnetic corrections were calculated from PASCAL’s constants. Mercury tetrakis-thiocyanatocobaltate was used as a standard. The analysis was carried out in microanalytical laboratory, Cairo University.
A pure aluminum foil sheet (Al) of 98.92% purity which is press-cut to form specimens with dimensions of 1 cm × 1 cm × 0.15 cm was used.
One liter of 1 M HCl solution was prepared using deionized water. Al samples were immersed for 7 hours in 20 ml of 1M HCl used as corrosive solution. An electronic weighing balance (Easyway-JA 1003A), micrometer heating mantle, and a water bath were used. Various concentrations (10−2–10−5 M) of mixed ligands (glutamic acid + arginine by the ratio 1 : 1) and their ternary metal complexes were prepared and dissolved in 1 M HCl and examined as inhibitors for Al corrosion by weight loss method. The mixed ratio (1 : 1) of these two ligands was the same ratio as that used in preparation of the four metal complexes. Before each run, the surface of Al was polished with different grades of emery papers, degreased with ethyl alcohol, washed thoroughly with double distilled water, dried in air and finally weighed. Then these specimens were immersed in 20 ml inhibited and uninhibited 1 M HCl solution in open containers for 7 h for aluminum specimens as immersion time then, they were withdrawn from the test solution, washed with deionized water and acetone, dried, and reweighed. The container was placed in a water bath maintained at (303 ± 1) K. The experiments were operated without (blank) and with the various concentrations of the mixed ligands and the complexes separately. The weight loss was taken as the difference in weight of the specimen before and after the immersion time. The experiments were carried out in water bath with temperature range 293–313 ± 1 K.
The antimicrobial activity of the prepared ternary metal complexes against two gram-positive bacteria (
Cytotoxicity evaluation using viability assays was performed by a Regional Center for Mycology & Biotechnology (RCMB), Al-Azhar University Cairo. The inhibitory activity of ternary metal complexes is screened against the cell line hepatocellular carcinoma (HepG-2).
Density functional theory (DFT) and its time-dependent extension (TD-DFT) theory, employing BP86D3/DEF2-SVP model, and auxiliary basis DEF2/JK were carried out using Orca 4.0.1.2 package [
A Broadberry workstation (40 cores) (UK) and a Mac Pro (12 core) workstation were used.
Elemental analyses (C, H, N, and metal) and physical and chemical properties of the prepared ternary complexes are given in Table
Some experimentally observed and determined characteristics of the prepared complexes (found values between parentheses).
Complex |
|
|
|
Metal (%) | Color | Magnetic moment (Debye) | Decomp temp. (°C) | pH | Conductivity (mS) | Mol. (wt.) |
---|---|---|---|---|---|---|---|---|---|---|
|
31.0 (31.9) | 5.9 (5.2) | 16.5 (15.9) | 13.9 (14.0) | Pink | 4.13 | 290 | 5.6 | 3.480 | 425.3 |
|
31.1 (32.1) | 5.4 (4.9) | 16.5 (15.9) | 13.8 (14.2) | Green | 3.10 | 290 | 5.1 | 3.700 | 425.0 |
|
32.8 (32.1) | 5.7 (6.2) | 17.4 (17.8) | 15.8 (16.4) | Blue | 1.78 | 238 | 4.9 | 4.607 | 402.9 |
|
29.9 (30.4) | 5.2 (4.8) | 15.9 (15.3) | 14.8 (15.1) | White | Diam. | 330 | 5.3 | 3.557 | 440.7 |
The thermal decomposition of these complexes in the range (511–603 K) indicates thermal stability. The effervescence test with sodium carbonate confirmed that all the prepared complexes are containing free acidic proton. The magnetic moments, molecular weight (Mol. wt.), and molar conductivity values are given in Table
The optimized structure of Co(II) and Cu(II) complexes (dotted lines represent H bonding) indicating the coordination sites of the ligands, which result in the most stable orientation. Ni and Zn complexes have geometries similar to Co complexes.
Optimized geometry around the central transition metal ions showing different bond lengths and angle.
The paucity of information about mixed amino acids (glutamic acid and arginine) metal complexes motivated us to investigate their molecular structures using DFT theory to characterize structural and electronic properties considering Co(II) and Cu(II) Glu-Arg complexes in aqueous solution as representative of all complexes. Optimized geometries are depicted in Figure
In this pH range, glutamic acid and L-arginine are predominantly present in their zwitter ion form, and each has two coordination sites (one N and one COO−), which are agreed with their distribution coefficients [
The important vibrational wavenumbers of arginine, glutamic, and their ternary metal complexes bands are listed in Tables
Experimentally and theoretically simulated IR spectra (in cm−1) of the studied complexes. Assignment of experimentally measured IR key modes.
Ligands and complexes |
|
|
|
|
|
|
|
---|---|---|---|---|---|---|---|
Glutamic | — | 3062 | 1242 | 1634(vs) | 1418(s) | — | — |
|
|||||||
Arginine | — | 3087 | 1175 | 1680(vs) | 1574(s) | — | — |
1586 | |||||||
1608 | |||||||
|
|||||||
[Co(glu)(arg)(H2O)2]·0.5H2O | 3345(s) | 3172 | 1131 | 1663(s) | 1421(vs) | 538 | 416 |
1584 | |||||||
1609 | |||||||
[Ni(glu)(arg)(H2O)2]·0.5H2O | 3340(s,br) | 3184 | 1122 | 1658(s) | 1426(vs) | 540 | 421 |
1586 | |||||||
1607 | |||||||
|
|||||||
[Cu(glu)((arg)]·H2O | 3453(s) | 3141 | 1126 | 1676(s) | 1456(m) | 572 | 456 |
1588 | |||||||
1604 | |||||||
|
|||||||
[Zn(glu)(arg)(H2O)2]·H2O | 3427(s) | 3144 | 1127 | 1671(s) | 1425(s) | 538 | 412 |
1582 | |||||||
1606 |
Experimentally and theoretically simulated IR spectra (in cm−1) of the studied complexes. Assignment of theoretically calculated IR key modes for Co(II) and Cu(II) complexes in the gas phase. Excellent match between experimentally determined and theoretically computed IR modes in case of Ni and Zn complexes is obtained.
Complex |
|
|
|
|
---|---|---|---|---|
[Co(glu)(arg)(H2O)2]·H2O | 2513 (H-bonded H2O and O of COO of Gu) | 1684.8 (Ar) | 554.3 | 463.6 |
3521 | 1740 (Gu) | |||
|
||||
[Cu(glu)((arg)]H2O | 3656 (caged H2O) | 1677.8 (Gu) | 537.6 | 438.5 |
— | 1709.9 (Ar) |
Upon complexation, the NH stretching wavenumber is shifted to 3141–3184 cm−1, indicating that the amino nitrogen groups are coordinated to the metal atom [
The C-NH2 stretching bands of the guanidyl group of alpha amino group have shifted from 1242 to 1175 cm−1 of glutamic acid and L-arginine with respect into (1122–1131) cm−1 of the prepared metal complexes. In opposite situation, arginine has been shown to have two bands observed at 1586 and 1608 cm−1 due to the asymmetrical vibrations of the C-NH2 bonds of the guanidino group, which is protonated to give the guanidinium form without a significant change in case of complexation [
The asymmetrical (
All the prepared complexes exhibited bands in the range of 3340–3472 cm−1 of
The new confirmed bands only appear in the four prepared complexes at 538–572 cm−1 and 412–456 cm−1, which are assigned to
The optimized geometry of the complexes shows distorted overall octahedral (or better the square pyramidal C4v-local symmetry of Co(II) ion) for the Co(II) complex and the slightly distorted square planar coordination of the Cu(II) ion in the Cu(II) complex. Ni and Zn complexes are of similar geometry to the Co complexes. Figure
PES maps. (a) Co complex (upper pan: solid surfaces and lower pan: clipped surfaces) and legend color codes given in kJ/mol. (b) Cu complex (upper pan: solid surfaces and lower pan: clipped surfaces).
The simulated PES maps [
The mass spectra of the four complexes were recorded and provided good evidence and confirmation of the molecular weight of these complexes (molecular ion peaks (MIPs) are detected under severe experimental conditions [
Figure
Theoretical and experimental (inset) UV-Vis spectra of aqueous Co and Cu complexes reflecting the excellent agreement between the results.
Electronic spectral data,
Complex |
|
|
|
Wavenumber (cm−1) | Assignments |
|
|
Geometry |
---|---|---|---|---|---|---|---|---|
|
970 | 1007 | 376 |
|
|
764 | 0.788 | Tetragonal distortion pseudosquare pyramidal (distorted octahedral) |
512 |
|
| ||||||
|
||||||||
|
1080 | 894 | 390 |
|
3
|
765.23 | 0.709 | Tetragonal distortion pseudosquare pyramidal (distorted octahedral) |
632 |
|
3
| ||||||
740 |
|
3
| ||||||
|
||||||||
|
— | 1107 | 506 |
|
|
1007 | — | Tetragonal distorted (square planar) |
636 |
|
( |
||||||
| ||||||||
( |
||||||||
|
||||||||
|
— | — | 221 |
|
Charge transfer | — | — | Tetragonal distortion pseudosquare pyramidal (distorted octahedral) |
The value of Racah parameter
Spectral data and assignments are summarized in Table
10
The first one is by solving equations (
For Ni2+,
Then, applying the trial and error procedure, a value for ∆ that fits in equations (
Applying this procedure and considering the ratio of
Then, 10
Racah parameters for Co(II) complex is also calculated similarly.
Furthermore, Co(II) complexes have the effective magnetic moment
The Zn complex did not show any d-d transitions but displayed charge transfer bands as shown in Table
The longest wavelength weak peaks are observed at 516 nm (
The computed natural transition orbitals of the longest wavelength transitions in both complexes reveal the largest (greater than 82%) contribution of beta HOMO-LUMO with minor (about 10.8%) contribution of alpha HOMO-LUMO in case of Co(II) complex and about 99.2% contribution from the beta-HOMO-LUMO in case of Cu(II) complex. MOs involved in the electronic transitions are depicted in Figure
Frontier MOs of (a) Co(II) complex and (b) Cu(II) complex involved in the longest wavelength electronic transition. Surfaces similar to that of Co complex are obtained in case of Ni. There are no d-d transitions in Zn complexes.
For elucidation of the geometry of the copper ternary complex, ESR measurement gives very useful information about the stereo chemistry bonding between copper and ligands. Figure
Different values of Mulliken spin density are shown in Figure
Thermogravimetric analysis (TGA) for the all prepared ternary metal complexes was carried out in nitrogen atmosphere. The thermal decomposition of the four complexes displayed similar patterns as their ligands.
It is well known that amino acids exist only in solid state, so their thermal decomposition has been endothermal between −72 and −151 kJ/mol when heating in range between 185°C and 280°C. Their thermal decomposition releases three gases, mainly H2O, less NH3, and hardly any CO2. TGA gives the weight of these gases as weight loss calculations, which evolve in appreciable amount [
Also, the thermal decomposition of L-arginine-doped KDP potassium dihydrogen phosphate crystal started to lose weight with temperature from 341 K to 393 K, released ammonia and water molecules gases [
The amino acids are totally broken within the range 603–793K as shown in Figure
TG and DTG of (a) [Co(glu)(arg)(H2O)2]·0.5H2O, (b) [Ni(glu)(arg)(H2O)2]·0.5H2O, (c) [Cu(glu)((arg)]·H2O, and (d) [Zn·Glu·Arg·(H2O)2]·H2O.
Thermogravimetric analysis decomposition data for the metal ternary complexes.
Complexes | Mol. (wt.) | TG range (°C) | Mass loss (%) found (calculated) | Total mass loss (%) | Assignment |
---|---|---|---|---|---|
|
425.26 | 64.39–126.84 | 10.89 (10.58) | 79.30 | 2.5H2O |
170.25–224.93 | 10.88 (10.95) | CO + NH3 | |||
298.49–343.38 | 11.56 (11.99) | 3 NH3 | |||
369.82–381.85 | 45.97 (45.15) | Organic compound (C10H10NO3) | |||
Above 381.85 | 20.70 (21.33) | Mix Co + CoO | |||
|
|||||
|
425.03 | 78.30–124.19 | 14.11 (14.59) | 78.61 | 2.5H2O + NH3 |
356.95–371.58 | 64.51 (63.76) | Organic compound (C11N4O4H19) | |||
Above 371.58 | 21.38 (21.65) | Mix Ni + NiO residue | |||
|
|||||
|
402.87 | 35.02–188.97 | 2.67 (2.23) | 77.40 | 0.5H2O |
229.63–238.11 | 26.31 (25.81) | 0.5H2O + 3NH3 + CO2 | |||
284.95–294.79 | 10.04 (10.92) | CO2 | |||
294.79–332.02 | 10.71 (11.17) | NH3 + CO | |||
480.35–505.88 | 27.67 (27.80) | Organic compound (C8NH2) | |||
Above 505.88 | 22.60 (22.07) | Mix Cu + CuO | |||
|
|||||
|
440.71 | 80.03–112.09 | 3.47 (4.08) | 75.62 | 1H2O |
133.49–160.63 | 8.92 (8.17) | 2H2O | |||
297.44–329.5 | 17.15 (17.70) | 2NH3 + CO2 | |||
374.04–395.85 | 21.91 (21.60) | 3NH3 + CO2 | |||
468.44–522.78 | 24.17 (25.20) | Organic compound (C9H3) | |||
Above 522.78 | 24.38 (23.25) | Mix Zn + ZnO |
It is noteworthy to mention that the geometries of the studied complexes are similar to L-arginine metal complex reported before [
XRD of thermal synthesized copper oxide nanoparticles starting from copper glutamic arginine-mixed ligands complex gives characteristic peaks at 2
XRD pattern of (a) copper oxide, CuO, and (b) cobalt oxide, Co3O4, prepared by thermal decomposition at 550 C° starting from metal glutamic arginine mixed ligands complex.
The pattern of XRD for cobalt oxide nanoparticles shows characteristic peaks at 2
The synthesized nano copper oxide is confirmed by the EDX spectrum and SEM image measurement shown in Figure
EDX and SEM images of CuO obtained by thermal decomposition at 550 C° starting from copper glutamic arginine mixed ligands complex.
The synthesized nano cobalt oxide is confirmed by the EDX spectrum measurement shown in Figure
EDX and SEM images of Co3O4 obtained by thermal decomposition at 550 C° starting from cobalt glutamic arginine mixed ligands complex.
Mixed ligand ternary complexes have been examined for their
The inhibitory effects of the used ligands and their ternary polymer complexes against the used organisms are given in Table
Antimicrobial activity of prepared ternary metal complexes.
Sample tested microorganisms | Glutamic acid | L-arginine |
|
|
|
|
Standard |
---|---|---|---|---|---|---|---|
Fungi | Amphotericin B | ||||||
|
13.4 ± 0.63 | 9.3 ± 0.44 | 16.9 ± 0.37 (31.25) | 23.2 ± 0.25 (62.5) | 20.0 ± 0.58 (3.9) | 16.2 ± 0.63 (62.5) | 23.7 ± 0.1 (0.24) |
|
15.2 ± 0.44 | 7.4 ± 0.63 | 15.6 ± 0.25 (62.5) | 22.0 ± 0.58 (62.5) | 14.5 ± 0.44 (12.5) | 14.7 ± 0.44 (12.5) | 19.7 ± 0.2 (3.9) |
|
15.9 ± 0.37 | 14.8 ± 0.58 | 17.2 ± 0.58 (31.25) | 23.9 ± 0.37 (31.25) | 21.2 ± 0.72 (1.95) | 15.3 ± 0.44 (62.5) | 28.7 ± 0.2 (0.015) |
|
NA | NA | NA (NA) | 16.2 ± 0.63 (62.5) | 20.0 ± 0.17 (3.9) | NA (NA) | 25.4 ± 0.1 (0.12) |
|
|||||||
Gram-positive bacteria | Ampicillin | ||||||
|
NA | 11.9 ± 0.25 | 13.9 ± 0.63 (12.5) | 20.3 ± 0.17 (12.5) | 18.5 ± 0.44 (7.81) | 20.04 ± 0.58 (3.9) | 23.8 ± 0.2 (0.24) |
|
NA | 14.1 ± 0.37 | 21.3 ± 0.44 (1.95) | 22.9 ± 0.44 (3.9) | 15.8 ± 0.63 (62.5) | 22.08 ± 0.58 (0.98) | 32.4 ± 0.3 (0.007) |
|
|||||||
Gram-negative bacteria | Gentamicin | ||||||
|
11.9 ± 0.25 | NA | NA (NA) | 21.4 ± 0.58 (3.9) | 19.9 ± 0.44 (3.9) | 12.7 ± 0.63 (12.5) | 17.3 ± 0.1 (15.63) |
|
11.8 ± 0.63 | 15.2 ± 0.37 | 16.2 ± 0.44 (62.5) | 24.8 ± 0.17 (12.5) | 20.9 ± 0.58 (1.95) | 18.6 ± 0.44 (7.81) | 19.9 ± 0.3 (3.9) |
For antifungal assay examination and based on the minimum inhibitory concentration (MIC) values, it is found that the inhibitory effect of all the ternary complexes vary from moderate to weak against
The antibacterial activities of the obtained ternary complexes are determined in terms of MIC values. As shown in Table
One of the fundamental goals in medicinal chemistry is the development of new anticancer and antimicrobial therapeutic agents. Cancer treatment using metal-based drugs is one of the very effective strategies as the metal ions are capable of binding to nucleic acids stereospecifically with varying strength.
In vitro anticancer activity evaluation of the newly synthesized compounds was carried out against human cancer cell lines hepatocellular carcinoma (HePG2) because liver cancer is the third most common cause of death in cancer using MTT method [
Doxorubicin HCl is one of the most effective anticancer agents is used as a reference drug in this study. The obtained results from Table
IC50 results indicate that the ternary complexes have promised inhibition of HePG2 liver tumors [
Cell viability was assessed by the mitochondrial-dependent reduction of yellow MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) to insoluble purple formazan [
Cell viability of (HePG2) at different concentrations of ligands and the prepared metal complexes.
Table
Additionally, Table
Simulated electrical properties of complexes studied exhibiting enhanced inhibition of HePG2.
Complex | Energy (au) | HOMO (ev) | LUMO (ev) |
|
|
|
|
|
|
|
---|---|---|---|---|---|---|---|---|---|---|
Co(II) | −2692.2 | −3.713 | −2.176 | 11.84 | 214.7 | −2691.4 | −2691.5 | 218 | −2.94 | 0.77 |
Cu(II) | −2797.1 | −5.167 | −4.105 | 6.81 | 206.5 | −2796.4 | −2796.5 | 194 | −4.64 | 0.53 |
The simulated data summarized in Table Cu complex is more energetically stable relative to Co complex by about −265 kJ/mol. Cu complex is characterized by lower dipole moment and lower polarizability relative to Co(II) complexes. Enthalpy and Gibbs free energy of the Cu complexes are more stable by about −265 kJ/mol relative to Co(II) complex. Lower entropy reflects lower degree of randomness of Cu(II) complex. The chemical potential ( Cu complex is characterized by lower hardness than Co(II) complex. Hardness measures the resistance to electron transfer (
It seems that more thermodynamically stable and less polar Cu complex exhibits that enhanced responsive electron cloud transfer to the surrounding tumor relative to the Co(II) complex. These quantitative molecular descriptors [
The nucleophilicity of Cu complex (seeking for positively charged sites of the reactant) together with its electrical, thermodynamic, and molecular properties favors its promising inhibition activity towards HePG2 cancer cell [
An assessment of corrosion rates and inhibition efficiency for aluminum with different inhibitor concentrations were computed as follows: corrosion rate
The inhibition efficiency (%IE) was evaluated using equation (
Table
Corrosion parameters for aluminum in aqueous solution of 1M HCl in the absence and presence of different concentrations of mixed ligands and their metal complexes at different temperatures for 7 hrs.
Inhibitors |
|
Corrosion rate ×10−4 (g·h−1·cm−2) | Inhibition efficiency (IE%) | ||||
---|---|---|---|---|---|---|---|
293 K | 303 K | 313 K | 293 K | 303 K | 313 K | ||
Mixed ligand (Arg : Glu) ratio (1 : 1) | 00 | 3.47 | 7.32 | 11.58 | — | — | — |
0.01 | 2.60 | 5.93 | 9.73 | 25 | 19 | 16 | |
0.02 | 2.50 | 5.64 | 9.26 | 28 | 23 | 20 | |
0.03 | 2.22 | 5.20 | 8.80 | 36 | 29 | 24 | |
0.04 | 1.80 | 4.76 | 8.34 | 48 | 35 | 28 | |
0.05 | 1.60 | 4.39 | 7.76 | 54 | 40 | 33 | |
0.06 | 1.35 | 3.22 | 6.95 | 61 | 56 | 40 | |
0.07 | 1.11 | 3.07 | 6.25 | 68 | 58 | 46 | |
|
|||||||
[Co(glu)·(arg)·(H2O)2]·0.5H2O | 0.01 | 1.46 | 2.78 | 4.28 | 58 | 62 | 63 |
0.02 | 1.28 | 2.49 | 3.71 | 63 | 66 | 68 | |
0.03 | 1.08 | 2.12 | 3.13 | 69 | 71 | 73 | |
0.04 | 0.97 | 1.76 | 2.90 | 72 | 76 | 76 | |
0.05 | 0.83 | 1.46 | 2.08 | 76 | 80 | 82 | |
0.06 | 0.87 | 1.32 | 1.62 | 75 | 82 | 86 | |
0.07 | 0.73 | 1.10 | 1.15 | 79 | 85 | 90 | |
|
|||||||
[Ni(glu)·(arg)·(H2O)2]·0.5H2O | 0.01 | 2.19 | 4.32 | 6.60 | 37 | 41 | 43 |
0.02 | 2.01 | 4.10 | 6.14 | 42 | 44 | 47 | |
0.03 | 1.77 | 3.66 | 5.44 | 49 | 50 | 53 | |
0.04 | 1.53 | 3.22 | 4.98 | 56 | 56 | 57 | |
0.05 | 1.35 | 2.71 | 3.94 | 61 | 63 | 66 | |
0.06 | 1.15 | 2.27 | 3.47 | 67 | 69 | 70 | |
0.07 | 0.97 | 2.05 | 2.90 | 72 | 72 | 75 | |
|
|||||||
[Cu(glu)·((arg)]·H2O | 0.01 | 2.32 | 4.76 | 7.18 | 33 | 35 | 38 |
0.02 | 2.12 | 4.25 | 6.25 | 39 | 42 | 46 | |
0.03 | 1.91 | 3.88 | 5.91 | 45 | 47 | 49 | |
0.04 | 1.63 | 3.37 | 5.21 | 53 | 54 | 55 | |
0.05 | 1.46 | 3.07 | 4.86 | 58 | 58 | 58 | |
0.06 | 1.32 | 2.71 | 4.05 | 62 | 63 | 65 | |
0.07 | 1.18 | 2.34 | 3.47 | 66 | 68 | 70 | |
|
|||||||
[Zn(glu)·(arg)·(H2O)2]·H2O | 0.01 | 1.25 | 2.42 | 3.59 | 64 | 67 | 69 |
0.02 | 1.08 | 2.05 | 3.13 | 69 | 72 | 73 | |
0.03 | 0.83 | 1.61 | 2.43 | 76 | 78 | 79 | |
0.04 | 0.73 | 1.54 | 2.08 | 79 | 79 | 82 | |
0.05 | 0.62 | 1.17 | 1.74 | 82 | 84 | 85 | |
0.06 | 0.59 | 0.95 | 1.39 | 83 | 87 | 88 | |
0.07 | 0.52 | 0.81 | 0.93 | 85 | 89 | 92 |
The metal surface coverage degree (
Langmuir adsorption isotherms of the mixed ligands (L) and their metal complexes.
The temperature effect (293–313 K) on aluminum weight loss inhibition may be attributed to two main mechanisms: physical and chemical adsorption [
Arrhenius of log corrosion rate (
The activation thermodynamic parameters for aluminum dissolution could be obtained from the transition state equation (
Table
Thermodynamic parameters for the adsorption of (0.04 × 10−2) M/L mixed ligands and their metal complexes on aluminum metal in aqueous solution of 1 M HCl at different temperatures for 7 hrs.
Compound | Temp. (K) | Corrosion rate ×10−4 (g· h−1· cm−2) | IE% |
|
|
|
|
---|---|---|---|---|---|---|---|
Blank | 293 | 3.47 | — | 66.002 | 47.556 | 52.080 | −0.0149 |
303 | 7.32 | — | |||||
313 | 11.58 | — | |||||
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Mixed ligand (Arg: Glu) ratio (1 : 1) | 293 | 1.8 | 48 | 69.528 | 61.191 | 53.268 | 0.0262 |
303 | 4.76 | 35 | |||||
313 | 8.34 | 28 | |||||
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|
293 | 0.97 | 72 | 58.822 | 46.517 | 54.165 | −0.0252 |
303 | 1.76 | 76 | |||||
313 | 2.90 | 76 | |||||
|
|||||||
|
293 | 1.53 | 56 | 60.459 | 43.025 | 55.510 | −0.0412 |
303 | 3.22 | 56 | |||||
313 | 4.98 | 57 | |||||
|
|||||||
|
293 | 1.63 | 53 | 61.845 | 41.030 | 56.139 | −0.0499 |
303 | 3.37 | 54 | |||||
313 | 5.21 | 55 | |||||
|
|||||||
|
293 | 0.73 | 79 | 57.688 | 45.810 | 54.035 | −0.0271 |
303 | 1.54 | 79 | |||||
313 | 2.08 | 82 |
However, the blank
Novel coordination materials of ternary divalent metal ions (Cu(II), Ni(II), Co(II), and Zn(II)) chelated by the bidentate glutamic acid (Glu) and L-arginine (Arg) amino acids are synthesized and characterized. The metal ions complexes are modelled using density DFT and TD-DFT theory. Computed molecular and spectroscopic (IR, UV-Vis, and EPR) properties validated the experimental results. The used computational methods are capable of providing good structural descriptions for the TM complexes. Consistent with the experimental properties, the optimized structures of the complexes [Cu(II) Glu-Arg] and [Co(II) Glu-Arg (H2O)2] reveal that symmetry environment of Cu(II) exhibits slightly distorted square planar shape, whereas Co(II)-complex has a distorted octahedral (where Co(II) central ion is of C4v-local symmetry). Spectral properties of [Ni(II) Glu-Arg (H2O)2] and [Zn·Glu·Arg·(H2O)2] complexes indicate that they have similar structure as Co(II) complex. All the studied ternary metal complexes are of different antifungal activities ranging from moderate to weak without practically noticed inhibitory effects, whereas antibacterial activities of all studied metal complexes show significant effects.
Cytotoxicity studies against (HePG2) reveal the promising potentiality of Cu(II) complex as inhibitor of cancer cells. The results are correlated with the computed molecular descriptors including dipole moment, polarizability, thermodynamics, and reactivity properties as well as the PES maps.
The corrosion inhibition of aluminum metal specimens in 1M HCl is efficiently achieved by mixed ligands and their metal complexes studied.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no conflicts of interest.
The supplementary materials consist of six figures and two tables to further clarify the structures and trends of the newly prepared metal ternary complexes.