Experimental and Computational Insights of a Benzytrietylammonium [CoBr₄] Salt: A Potential Photocatalyst and Inflammation-Related Enzyme Inhibitor

Abstract

In this paper, we present a combined experimental and computational study of a cobalt­(II) complex with the organic ligand benzyltriethylammonium bromide. The complex was characterized by IR spectroscopy and single-crystal X-ray crystallography. The molecular geometries, electronic transitions, and vibrational frequencies were calculated using density functional theory (DFT) at the B3LYP/LanL2DZ level. Based on the unit cell parameters obtained from experimental data, DFT calculations were performed to correlate with the vibrational spectrum analysis. The theoretical parameters derived from DFT showed strong agreement with the experimental results. A qualitative description of the charge-transfer character was carried out using natural bond orbital (NBO) analysis. The energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were calculated, and the band gap was determined. Furthermore, the complex demonstrated significant degradation of methylene blue (MB) under sunlight irradiation. In vitro, the cobalt­(II) complex exhibited strong inhibitory activity against key inflammatory enzymes, particularly myeloperoxidase (MPO), with a half-maximal inhibitory concentration (IC₅₀) of 80.45 μM, compared to 4-aminobenzoic acid hydrazide (ABAH, IC₅₀ = 9.46 μM). It also showed potent inhibitory effects on obesity-related enzymes such as lipase (IC₅₀ = 41.93 μM) compared to orlistat (IC₅₀ = 32.75 μM). Regarding diabetes-related targets, the complex effectively inhibited α-amylase (IC₅₀ = 21.75 μM) in comparison to acarbose (ACR, IC₅₀ = 18.08 μM), and promoted insulin signaling by inhibiting dipeptidyl peptidase-4 (DPP-4, IC₅₀ = 22.01 μM) compared to sitagliptin (STG, IC₅₀ = 4.07 μM). Additionally, it exhibited moderate inhibitory activity against protein tyrosine phosphatase 1B (PTP1B, IC₅₀ = 10.88 μM), approximately 2.1 times less potent than sodium orthovanadate (SV, IC₅₀ = 5.24 μM). A molecular docking approach was employed to investigate the binding affinities and molecular interactions of the two ligands forming the Co­(II) complex with several protein targets (PDB IDs: 3BAJ, 4A5S, 1LPB, 5MFA, and 1T49). The docking results revealed that the complex, through interactions such as hydrogen bonding, π–π stacking, carbon–hydrogen interactions, π–anion, π–cation, and π–alkyl interactions, exhibits promising inhibitory potential against the selected enzymes: α-amylase, dipeptidyl peptidase-4 (DPP-4), lipase, promyeloperoxidase (proMPO), and protein tyrosine phosphatase 1B (PTP1B).

1. Introduction

Diabetes, particularly type 2 diabetes (T2D), is a major global health challenge, affecting over 800 million people in 2024, with a prevalence estimated at 14% of the adult population. This multifactorial disease is aggravated by poor dietary habits, sedentary lifestyles, aging populations, and rising rates of overweight and obesity. Biologically, T2D is characterized by pancreatic inflammation and oxidative stress, which impair insulin secretion and action, leading to insulin resistance. , Protein tyrosine phosphatase 1B (PTP1B) plays a critical role by dephosphorylating insulin receptors, reducing their activity and exacerbating insulin resistance. Increased activity of dipeptidyl peptidase-4 (DPP-4) in T2D and obesity further decreases circulating GLP-1 levels, an essential incretin hormone for glucose homeostasis, worsening insulin resistance. Moreover, chronic hyperglycemia, systemic inflammation, and oxidative stress in T2D contribute to dysfunction of vital organs, including liver, heart, and kidneys, leading to complications such as neuropathy, nephropathy, and elevated cardiovascular risk. − These challenges highlight the need for therapeutic strategies that protect pancreatic function, reduce inflammation, and inhibit key enzymes such as PTP1B, DPP-4, and others linked to obesity and hyperglycemia.

The structure–activity relationships of metal complexes have attracted considerable attention over recent years. − Metal coordination compounds are extensively studied due to their structural diversity, physicochemical properties, and potential applications as functional materials. , Intermolecular interactions govern crystal packing and stability in such complexes. − Cobalt forms various coordination complexes exhibiting notable optical, electronic, magnetic, catalytic, and pharmacological properties. − As an essential element of vitamin B12 (cobalamin), cobalt is vital for DNA synthesis and erythropoiesis. Recent studies suggest cobalt may modulate insulin signaling pathways and improve insulin sensitivity in T2D models. Consequently, cobalt-based compounds are explored as potential enhancers of current T2D therapies or as novel antidiabetic agents, possibly modulating metabolic pathways including glucose metabolism via interactions with enzymes and hormones. The antidiabetic activity of cobalt involves multiple mechanisms: inhibition of α-glucosidase delays intestinal glucose absorption (Günsel et al., 2024), enhancements of insulin sensitivity promote glucose catabolism and glycogen synthesis (Chen et al., 2021), and antioxidant effects protect pancreatic function from oxidative damage and apoptosis (Chen et al., 2021). These synergistic effects underscore cobalt’s therapeutic potential in T2D management. Furthermore, complexation of organic ligands with metal ions can enhance biological activity through their ability to accept free radicals. −

In this study, we report the synthesis and characterization of an organic–inorganic cobalt­(II) complex with benzyltriethylammonium bromide as the organic ligand. DFT calculations were performed to correlate the crystal structure with physical properties, and IR band assignments were proposed. Photocatalytic properties were also investigated. Additionally, the inhibitory effects of the complex were evaluated in vitro against key enzymes implicated in pancreatic inflammation (MPO), obesity and diabetes-related digestion (lipase, α-amylase), and insulin resistance (DPP-4, PTP1B). To complement the experimental findings, molecular docking studies were conducted to elucidate the binding interactions underlying enzyme inhibition.

2. Experimental Section

2.1. Materials and Synthesis

All reagents were purchased from Sigma-Aldrich and used without further purification. Distilled water was used as the solvent. Solutions of the title compound were prepared by mixing benzyltriethylammonium bromide (C₁₃H₂₂N·Br) (0.272 g, 1.00 mmol), cobalt­(II) bromide (CoBr₂, 0.218 g, 1.00 mmol), and 10 mL of distilled water at room temperature. Then, 1 mL of concentrated hydrobromic acid (HBr) was added. The resulting solutions were stirred for 45 min and allowed to stand at room temperature in a dust-free environment.

2.2. Spectroscopic Measurements

Infrared measurements were obtained using a PerkinElmer FTIR Spectrometer using KBr pellets in the range of 4000–400 cm^–1.

2.3. Photocatalytic Experiments

The irradiation was carried out using an Osram Ultra-Vitalux lamp (300 W), with a solar-like spectrum and a central wavelength of 365 nm and sunlight irradiation. The lamp was placed 10 cm above the solution surface, while continuous aeration was maintained to ensure aerobic conditions throughout the reaction. In the photocatalytic study, the compound’s ability to degrade methylene blue (MB) was evaluated under sunlight irradiation. Briefly, 20 mg of the solid sample was dispersed in 50 mL of MB solution (10 mg/L). To eliminate adsorption effects, the mixture was stirred in the dark for over 1 h before exposure to sunlight. At specific time intervals, 5 mL aliquots were withdrawn and suspended particles were removed by centrifugation. The absorbance of the supernatant was measured using a UV–Vis spectrophotometer. A control experiment without the compound was conducted under identical conditions. The degradation efficiency (D) was calculated using the initial absorbance (A ₀) and absorbance at time t (A _t ) as follows

$$D=\frac{A_0-A_t}{A_0}\times 100$$ 1

3. Results and Discussion

3.1. Structural Analysis

The complex (PhCH₂NEt₃)₂[CoBr₄] was synthesized in our laboratory (Scheme ). Even though its crystal structure has been previously characterized, this study provides a comprehensive analysis of the material’s physical and biological properties based on its crystallographic features.

1. Molecular Structure of Complex (PhCH₂NEt₃)₂[CoBr₄].

The complex (PhCH₂NEt₃)₂[CoBr₄] crystallizes in the triclinic system with space group P1̅, according to X-ray diffraction data. The cell parameters are a = 9.7871(4) Å, b = 17.8158(8) Å, c = 18.3374(8) Å, α = 76.744(2)°, β = 81.597(2)°, γ = 86.848(2)°, with Z = 4 and V = 3046.6(2) ų. The asymmetric unit, shown in Figure a, comprises four (PhCH₂NEt₃)⁺ cations and two [CoBr₄]^2– anions.

1.

(a) The asymmetric unit of (PhCH₂NEt₃)₂[CoBr₄]. (b) Optimized geometry of the compound.

Table S1 provides a comprehensive summary of the principal crystallographic parameters for the title compound. The structure features two distinct types of slightly distorted tetrahedral anions, namely [Co₍₁₎Br₄]^2– and [Co₍₂₎Br₄]^2–.

Each cobalt ion is coordinated by four bromide ions, with Co–Br bond lengths ranging from 2.4095(5) to 2.4309(5) Å and Br–Co–Br bond angles spanning 105.222(19)° to 114.23(2)°.

To quantify the degree of distortion relative to idealized geometries in ML4 complexes, the geometry index τ4, specific for four-coordinate complexes, was employed. The calculated τ4 values were 0.95 and 0.96 for the [Co₍₁₎Br₄]^2– and [[Co₍₂₎Br₄]^2– species, respectively, indicating that the tetrahedral coordination environment around the cobalt centers exhibits only minor deviations from ideal tetrahedral geometry.

Analogous compounds have been observed to contain tetrahedra exhibiting similar distortions. The shortest Br···Br distance is equal to 6.2106(8) Å; it is larger than the distance at which halogen···halogen mediated magnetic interactions would be expected as well as halogen interactions. The projection of the structure along the b-axis (Figure ) shows that the compound is made of organic–inorganic chains. Bromide ions function as hydrogen bond acceptors; the relatively weak C–H···Br hydrogen bonds facilitate the assembly of anions and cations into an extended three-dimensional supramolecular network.

2.

A view of (PhCH₂NEt₃)₂[CoBr₄] along the b-axis.

3.2. Theoretical Investigation

To determine the most stable molecular geometry, geometry optimizations were performed using density functional theory (DFT) with the B3LYP hybrid functional and the LanL2DZ basis set. Figure b shows the optimized structure of the studied complex, and the geometric parameters are presented in Tables S2 and S3.

The discrepancy between the optimized and experimentally determined geometries was quantitatively assessed using the root-mean-square deviation (RMSD) of their structural overlays. The RMSD values are 0.022 Å for bond lengths and 2.846° for bond angles, indicating a high degree of agreement between the two data sets. As shown in Tables S2 and S3, the calculated geometrical parameters exhibit slight deviations from the experimental values. This difference can be attributed to the computational analysis being performed on an isolated molecule in the gas phase, whereas the experimental measurements were obtained from the compound in the solid state. Specifically, the computational model neglects intermolecular Coulombic interactions present in the crystal lattice, which influence the experimental structure in the condensed phase. These results validate the choice of the cluster model and the computational approach, confirming that the B3LYP/LanL2DZ level of theory is suitable for accurately describing the investigated complex.

Experimentally, the C–N and C–C bond lengths range from 1.501 to 1.531 Å and 1.360 to 1.523 Å, respectively, while theoretical values range from 1.521 to 1.549 Å and 1.380 to 1.526 Å, respectively. The C–C–C and N–C–C bond angles vary experimentally between 117.4° and 121.8°, and 114.2° and 116.5°, respectively, with theoretical values corresponding closely at 117.2–121.8° and 115.4–116.6°. Each cobalt atom, located at the center of a tetrahedral coordination environment, is bonded to four bromide ligands. Experimentally, Co–Br bond lengths are 2.404 Å and 2.426 Å, while the theoretical bond lengths are 2.462 Å and 2.572 Å. The experimentally determined Br–Co–Br bond angles range from 105.2° to 114.2°, closely matching the theoretical angles of 103.9° to 113.4°. Hydrogen bonding plays an important role in stabilizing the structure by connecting anions and cations into a three-dimensional network. Theoretical hydrogen bond distances are comparable to the experimental values. The carbon atoms of the (PhCH₂NEt₃)⁺ cations participate in C–H···Br hydrogen bonding interactions with both the isolated bromide anion (Br^–) and the [CoBr₄]^2– tetrahedral complex.

3.2.1. Vibrational Studies

To achieve a satisfactory correlation between the calculated and experimentally observed vibrational frequencies, an empirical scaling factor of 0.963 was applied to correct for systematic deviations and anharmonic effects. The intensities of the principal vibrational modes were visualized using GaussView software. To facilitate the assignment of experimentally observed spectral peaks, an analysis of the theoretically predicted characteristic vibrational frequencies (Table S4) was performed and compared with the experimental data. Figure shows the superposition of the experimental and theoretical spectra of the title compound and the ligand C₁₃H₂₂N·Br.

3.

FTIR spectra of the experimental (Black) and the DFT computed (Red) IR spectra of (PhCH₂NEt₃)₂[CoBr₄] and the ligand C₁₃H₂₂N·Br (Blue) in the 400–4000 cm^–1 region.

3.2.1.1. (PhCH₂NEt₃)⁺ Cation Mode

The CH₂ stretching, highly coupled with the in- plane bending bands rising from CH₃ group, are observed at 750 cm^–1. Theoretically, theses vibrations appear between 756.4 and 777.2 cm^–1. The symmetric stretching vibrational mode of the methyl (CH₃) group is detected at a wavenumber of 2982 cm^–1. Theoretically, this vibrational mode is predicted to occur within the wavenumber range of 3039 to 3047 cm^–1. The spectral band observed at 3375 cm^–1 is attributed to the symmetric stretching vibration of the CH group, with the corresponding calculated frequencies ranging from 3292 to 3365.7 cm^–1. The deformation of CC group and symmetric stretching vibrations of CH₂ are located experimentally at 1625 cm^–1 in infrared spectrum. Density Functional Theory (DFT) calculations predict vibrational modes within the spectral range of 1624 to 1651 cm^–1. The deformation CC vibrational mode is observed at 1333 cm^–1 in the FT-IR spectrum and is theoretically predicted at 1330 cm^–1 and 1329 cm^–1 based on our computational analysis. An absorption band observed at 1389 cm^–1 in the FT-IR spectrum corresponds to the out-of-plane bending vibrational mode of the C–H bond. Therefore, the theoretically predicted frequencies for this vibrational mode are 1385.1 cm^–1 and 1393.3 cm^–1. The band observed at 460 cm^–1 is attributed to the deformation modes of C–N–C and C–C–C bonds. However, the theoretical frequencies are calculated to be 454.6 cm^–1 and 468.6 cm^–1. The absorption band observed at 497 cm^–1 in the infrared spectrum is attributed to the deformation vibration of the C–C–N moiety. The computed wavenumbers are given at 485.6 cm^–1. The experimentally observed vibrational band at 610 cm^–1, attributed to the deformation mode of the CH group, corresponds closely with the theoretically calculated frequencies of 612.7 cm^–1 and 613.7 cm^–1. The FT-IR spectrum exhibits the C–N symmetric stretching and CH₂ twisting vibrational modes at 1083 cm^–1, which correspond closely to the theoretically predicted frequencies of 1090, 1091.7, and 1093.5 cm^–1 obtained from our computational analysis. The band observed at 1028 cm^–1 in the FT-IR spectrum is associated with CH₂ twisting. The DFT calculations give this mode at 1026.5 cm^–1. The same mode is also observed on the IR spectrum at 1218 cm^–1, and calculated at 1218.2 cm^–1 in DFT. Moreover, the stretching vibration ν CC has been identified at 1013 cm^–1 and obtained by DFT/B3LYP/LanL2DZ calculation at 1011.1, 1014.5, 1014.8, and 1015.3 cm^–1. The ring carbon–carbon (C–C) and carbon–nitrogen (C–N) stretching vibrations exhibit absorption at 1303 cm^–1 experimentally and at 1316.3 cm^–1 according to theoretical calculations. The stretching modes ν_s(CC) and rocking ρ­(CH) associated with a FT-IR band are observed in 1481 cm^–1. While its theoretical value was observed at 1486.6 cm^–1. The absorption band observed at 943 cm^–1 in the FT-IR spectrum is attributed to the CH₂ rocking vibrational mode. This vibration is viewed theoretically at 933.9, 932, 951, and 954 cm^–1. The FT-IR absorption band observed at 1389 cm^–1 corresponds to the out-of-plane bending vibration of β­(C–H) bonds and the asymmetric stretching mode of the methyl (CH₃) group. Therefore, the theoretically predicted frequencies for this vibrational mode are 1385.1 cm^–1 and 1393.3 cm^–1. Whereas, the band observed at 1455 cm^–1 is allocated to the out-of-plane bending mode of β­(C–H), only. It is calculated in DFT at 1454.5 cm^–1. The C–C–C out-of-plane bending vibrational modes are observed at 707 cm^–1 in the experimental infrared (IR) spectrum, while density functional theory calculations using the B3LYP method predict these modes at 714.5 cm^–1 and 715.5 cm^–1. The vibrational stretching modes corresponding to the carbon–carbon double bond (CC) and carbon–nitrogen single bond (C–N) are experimentally observed at 544 cm^–1, which is in close agreement with the theoretical prediction of 544.4 cm^–1. The absorption bands observed in the infrared spectrum at 812 cm^–1 and 860 cm^–1 are attributed to the symmetric and asymmetric stretching vibrations of the C–C–N moiety, respectively. However, its theoretical values are found at 808.4, 816.6 and in the range of 857–864 cm^–1, respectively. The stretching modes ν_s(CC) and rocking ρ­(CH) associated with a FT-IR band are observed in 1481 cm^–1. While its theoretical value was observed at 1486.6 cm^–1. The out-of-plane deformation of CH is observed at 790 cm^–1. The DFT calculation yielded a wavenumber position in the range 786.1–797.4 cm^–1. The band at 1157 cm^–1 is assigned to rocking mode of CH. This mode is predicted at 1145.6 cm^–1 in the calculated spectrum. The experimentally obtained spectral data of the compound exhibit good agreement with the theoretical results calculated at the DFT/B3LYP/LanL2DZ level of theory.

3.2.1.2. [CoBr₄] Anion Mode

In density functional theory (DFT) calculations, the vibrational modes corresponding to frequencies at 97 and 99 cm^–1 are attributed to the deformation of the Br–Co–Br bonding framework. The bending vibrational mode of the Br–Co–Br moiety is theoretically predicted to occur at 124 cm^–1 and 164 cm^–1. The Co–Br asymmetric stretching is predicted at 246 cm^–1. The bands calculated at 226, 228, and 231 cm^–1 are assigned to the Br–Co–Br symmetric stretching. The calculated band assigned to vibrational mode anion motion Br–Co–Br bending occurs at 147 cm^–1. The vibrational analysis of the isolated [CoBr₄]^2– anion, which exhibits Td point group symmetry, reveals the presence of four fundamental normal modes of vibration, designated as υ₁, υ₂, υ₃ and υ₄. The vibrational modes υ₁ and υ₃ correspond to the symmetric and asymmetric stretching vibrations of the Co–Br bonds, respectively, whereas the modes υ₂ and υ₄ predominantly represent the symmetric and asymmetric bending vibrations of the Br–Co–Br bond angles.

3.2.2. NBO Analysis

NBO analysis provide the electronic density distribution on atoms and bonds, and it gives an insight of the donor and acceptor sites; It is a very effective tool for studying charge transfer, electronic transitions and conjugate interactions in molecular systems. The charge distribution on the molecule has important influence on the vibrational spectra; it is directly related to the chemical bonds present in the molecule. Atomic charges were obtained from DFT/B3LYP/LanL2DZ. The Natural Bond Orbitals (NBOs) of each atom constituting the compound were calculated, and the corresponding selected atomic charges are presented in Table S5. The interpretation shows that all hydrogen atoms are negatively charged. While carbon and nitrogen atoms possess a negative charge due to their electronegativity. The carbon atom in the CH₃ group exhibits a higher electron density and thus a greater partial negative charge relative to other carbon atoms, due to the electron-donating inductive effect of the three bonded electropositive hydrogen atoms. The bromine atoms have the highest negative charges, which show that they are involved as acceptors. On the other hand, the metal ions present positive charges. This finding substantiates the occurrence of electron transfer from cobalt atoms to bromide ions. It is noteworthy that charge transfer occurs via the hydrogen bonds (C–H···Br). Notably, bromide atoms exhibit significant negative charge densities and function as hydrogen bond acceptors.

3.2.3. HOMO–LUMO Energy Gap

The energies associated with the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were determined using density functional theory (DFT) at the B3LYP level with the Lanl2DZ basis set. In molecular systems, the energy levels of LUMO and HOMO, along with the energy difference between them, are crucial for elucidating optical characteristics. Specifically, the study of HOMO and LUMO allows for a comprehensive analysis of chemical reactivity, as these orbitals are fundamental in assessments of both chemical reactions and stability. Additionally, these energy parameters are pivotal for understanding the molecular electrical transport properties. The calculated energies for the HOMO and LUMO of the examined compound are illustrated in Figure , with values reported as −4.891 eV for HOMO and −1.218 eV for LUMO. The value of the band gap (ΔE _L–H)­is 3.673 eV. The eventual charge transfer interactions that occur within the molecules are explained by this value. Among the key concepts in quantum chemistry, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are fundamental. The HOMO, defined as the molecular orbital with the highest energy level that contains electrons, often acts as an electron donor by relinquishing electrons during chemical reactions. Conversely, the lowest unoccupied molecular orbital (LUMO) can be described as the innermost orbital possessing available capacity to accept electrons. − The energy of the highest occupied molecular orbital (HOMO) correlates directly with the ionization potential, while the LUMO energy corresponds to the electron affinity. Additionally, global chemical reactivity descriptors (GCRDs) constitute a crucial approach for characterizing molecular chemical properties, including chemical hardness, chemical potential, chemical softness, electronegativity, and electrophilicity. The mathematical expressions (eqs through ) used to calculate these GCRDs are derived from the HOMO and LUMO energies by considering the HOMO energy as the ionization potential and the LUMO energy as the electron affinity. These parameters are interrelated and provide comprehensive insight into molecular reactivity, − as follows

$${\mathrm{\Delta }E}_{\mathrm{L}-\mathrm{H}}=E_{\mathrm{L}}-E_{\mathrm{H}}$$ 2

$$\mu =\frac{E_{\mathrm{L}}+E_{\mathrm{H}}}{2}$$ 3

$$\eta =\frac{E_{\mathrm{L}}-E_{\mathrm{H}}}{2}$$ 4

$$\mathrm{E}\mathrm{A}=-E_{\mathrm{L}\mathrm{U}\mathrm{M}\mathrm{O}}$$ 5

$$\omega =\frac{{\mu }^2}{2\eta }$$ 6

$$\mathrm{I}\mathrm{P}=-E_{\mathrm{H}\mathrm{O}\mathrm{M}\mathrm{O}}$$ 7

$$\chi =\frac{(\mathrm{E}\mathrm{A}+\mathrm{I}\mathrm{P})}{2}$$ 8

$$S=\frac{1}{\eta }$$ 9

The results are listed in Table S6. The Ip and the E _A of the compound are 4.89 and 1.21 eV, respectively, which evidently designate that this compound is stable. The (PhCH₂NEt₃)₂[CoBr₄] has high value of the energy gap (3.67 eV), higher hardness (1.83 eV), and a lower softness (0.54 eV). These quantities prove the stability of the title compound. The high electrophilicity index categorizes the propensity of electron acceptors to acquire additional electron charge from the environment. According to the literature, the value of the band gap is close to that of C₃₂H₂₈Cu₂N₄O₄ (3.09 eV) and [Ni₂(L)­Pb­(μ-1,3-SCN)₂(H₂O)]₂ (3.14 eV). This value classifies the compound as a good semiconductor, suitable for applications in photovoltaics and optoelectronics.

4.

Plots of the Frontier molecular orbitals of (PhCH₂NEt₃)₂[CoBr₄] with energies.

Upon irradiation with simulated sunlight, electrons are excited from the HOMO to the LUMO, generating electron–hole pairs. These charge carriers facilitate redox reactions: the excited electrons in the LUMO reduce oxygen molecules to reactive oxygen species, while holes in the HOMO oxidize water or organic substrates, ultimately driving the photocatalytic degradation of the target pollutants. The energy gap (HOMO–LUMO gap) determines the absorption wavelength and influences the efficiency of the photocatalyst under solar irradiation. Thus, the proper alignment and energy levels of these orbitals are crucial for optimizing photocatalytic activity.

3.3. Photocatalytic Studies

Recent research has focused on using inorganic–organic hybrid compounds as photocatalysts to degrade organic dyes. To evaluate the photocatalytic effectiveness of the complex, methylene blue was employed as a representative model compound to simulate dye contaminants in aqueous solutions. Methylene blue, a prototypical organic dye characterized by its resistance to degradation in waste treatment processes, is frequently employed as a model compound. During all photocatalytic reactions, quartz beakers were exposed to sunlight. Under identical experimental conditions, the photocatalytic behavior of methylene blue solution was examined in the absence of any photocatalytic agents. A UV–vis spectrophotometer was used to analyze samples every 15 min (Figure a). Using the synthesized compounds, methylene blue solution was photocatalytically degraded with an efficiency of degradation (%) parameter equal to A – A ₀/A ₀. Let A ₀ represent the absorbance of the dye solution in the absence of the catalyst, and A denote the absorbance measured in the presence of the catalyst after a reaction time t. The photocatalytic degradation efficiency of the methylene blue (MB) solution using the synthesized compound was determined to be 73% (Figure b). Furthermore, the stability of photocatalysts is a crucial factor determining their viability for practical applications.

5.

(a) UV–vis absorption spectra were recorded to monitor the degradation of 50 mL methylene blue (MB) aqueous solution under sunlight irradiation in the presence of 20 mg of (PhCH₂NEt₃)₂[CoBr₄]. (b) Plots of the normalized concentration of the title compound, expressed as A/A ₀, versus reaction time were generated.

As a result, the complex has superior degradation ability than previously reported complexes. − Therefore, they serve as excellent candidates for the decomposition of MB when exposed to sunlight. Upon exposure to solar irradiation, the complex undergoes photoexcitation, generating photogenerated electrons that facilitate the investigation of the photocatalytic degradation mechanisms of methylene blue (MB). The effect of different active species capture agents on the photocatalytic degradation of MB under ultraviolet light was investigated to further understand the photocatalytic degradation mechanism. As illustrated in Figure , the photocatalytic degradation rate of methylene blue (MB) was markedly inhibited upon the introduction of benzoquinone (BQ), a superoxide radical (^•O^2–) scavenger, and triethanolamine (TEOA), a hole (h⁺) scavenger, resulting in reductions of 25% and 32%, respectively. In addition, the photocatalytic degradation the removal rate of MB decreased slightly when IPA (^•OH capture agent) was added to the reaction solution. Under UV irradiation, MB is removed primarily by ^•O^2– and h⁺, which have a strong oxidation ability and can oxidize organic pollutants.

6.

Photocatalytic degradation rates of methylene blue (MB) were assessed using various radical scavengers in the presence of (PhCH₂NEt₃)₂[CoBr₄] under ultraviolet (UV) light irradiation.

3.4. Effect of the Title Compound on the Key Pancreatic Inflammation Enzyme as MPO

The results of this study demonstrate that both the present material and the specific inhibitor ABAH inhibit MPO activity in a dose-dependent manner, thereby protecting the pancreas from inflammatory damage and maintaining its function. This contributes to its antidiabetic activity. The inhibitory effect is concentration-dependent, with the title compound exhibiting a maximum inhibitory concentration of 41.93 μM and an IC₅₀ of 8.53 μM, compared to ABAH, which has a maximum inhibitory concentration of 83.86 μM and an IC₅₀ of 9.48 μM. These findings highlight that this compound is more active against this key inflammatory enzyme, offering greater efficacy in protecting the pancreas from inflammation and improving insulin secretion both quantitatively and qualitatively (Figure ). The reported IC₅₀ values of ABAH against MPO vary widely in the literature, ranging from 0.05 μM to 3 μM to 50 μM. This variability is largely attributed to differences in experimental conditions, particularly the concentration of MPO used in the assay and the enzyme’s qualitywhether it is freshly purchased and used immediately, or stored for a period of time prior to use. No prior studies have been conducted on our compound in relation to this key inflammatory enzyme or its connection to inflammatory diseases. Indeed, the presence of a phenolic ring with three double bonds enhances the neutralization of free radicals, thereby interrupting the chain of inflammatory and oxidative reactions. Furthermore, the incorporation of bromine (Br) promotes the interaction of this compound with cellular tissues, enhancing both its activity and the durability of its beneficial effects. The incorporation of cobalt into this aromatic compound with triple double bonds and bromine strongly enhances the interaction of cobalt with various key enzymes involved in pancreatic inflammation, such as myeloperoxidase, by disrupting its active site and thereby reducing the production of hypochlorous acid, a pro-inflammatory agent, as shown in our study. Additionally, the cobalt group CoBr₄, interacts with cyclooxygenases and lipoxygenases, − limiting the production of prostaglandins and leukotrienes, two major inflammatory mediators, thus providing effective protection to the pancreas and other vital organs from inflammation and damage while maintaining their functions. This complex also inhibits phospholipase A2, preventing the release of arachidonic acid, and matrix metalloproteinases (MMPs) by binding to their catalytic zinc ion, thereby protecting tissues from inflammatory damage. Through the specific interactions of our Co–Br-ligand complex, this compound shows strong therapeutic potential in reducing inflammation, oxidative stress, and pancreatic and tissue damage, making it a promising candidate for the treatment of type 2 diabetes, obesity, and other inflammation-related diseases linked to diabetes.

7.

Effect of (PhCH₂NEt₃)₂[CoBr₄] and the specific inhibitor ABAH on the activity of the key inflammatory enzyme, myeloperoxidase (MPO). Our results show that both compounds inhibit the activity of this enzyme in a dose-dependent manner.

3.5. Activity of Key Enzymes Related to Obesity and Diabetes

The results of this study demonstrate that the title compound effectively inhibits lipase, a key enzyme responsible for obesity and hyperlipidemia. Lipase hydrolyzes nonabsorbable dietary lipids into simple fatty acids and triglycerides, which can be absorbed by the intestines. These lipids subsequently accumulate in the body, leading to obesity, hyperlipidemia, inflammation, insulin resistance, and various other metabolic disturbances and pathologies. The incubation of lipase with its substrate in the presence of the present material revealed dose-dependent inhibition. The compound exhibited a maximum inhibitory concentration of 251.58 μM and an IC₅₀ of 43.24 μM, compared to the reference inhibitor orlistat, which has an IC₅₀ of 30.53 μM. Furthermore, the Co (II) complex compound effectively inhibits α-amylase, an enzyme responsible for the conversion of nonabsorbable polysaccharides in the intestines into simple monosaccharides such as mannose, which are absorbable and can subsequently lead to hyperglycemia. This enzymatic inhibition was found to be dose-dependent, with an IC₅₀ of 21.75 μM, compared to acarbose (ACR), which exhibited an IC₅₀ of 18.08 μM (Figure ).

8.

Effect of (PhCH₂NEt₃)₂[CoBr₄] on key enzymes responsible for obesity and hyperlipidemia (lipase) and diabetes (alpha-amylase). Our compound shows a noteworthy inhibitory effect against both enzymes, compared to the specific lipase inhibitor (ORL) and alpha-amylase inhibitor (ACR).

In fact, our compound is characterized by the presence of a phenolic ring with double bonds coupled with bromine (Br) and cobalt (Co), components known for their strong interactions with biological enzymes and their inhibitory effects on these enzymes. Previous studies − have demonstrated the ability of phenolic rings to interact with lipase and α-amylase, showcasing their significant inhibitory effects on these digestive enzymes. Consequently, this leads to pronounced antiobesity, antihyperlipidemic, and antihyperglycemic effects. Moreover, Co and Br are well-known minerals for their strong and stable interactions with these two digestive enzymes, effectively inhibiting their activity, in accordance with previous studies. −

3.6. Key Enzymes Related to the Insulin Signaling Pathway

Our study demonstrated that the title compound effectively inhibits key enzymes involved in blocking insulin signaling or contributing to insulin resistance and type 2 diabetes in a dose-dependent manner. The maximum inhibitory concentration (IC_max) was 167.72 μM with an IC₅₀ of 22.06 μM, compared to the specific inhibitor STG, which had an IC_max of 20.96 μM and an IC₅₀ of 4.06 μM. Furthermore, our compound exhibited moderate inhibitory effects on PTP1B, with an IC₅₀ of 10.88 μM, compared to SV, which had an IC₅₀ of 5.24 μM (Figure ).

9.

Effect of (PhCH₂NEt₃)₂[CoBr₄] on the activity of key enzymes related to insulin resistance and insulin sensitivity blockage, such as DPP-4 and PTP1B. Results from this study show that this complex inhibits the activity of both enzymes and induces insulin sensitivity, with its activity being quite comparable to the standard inhibitors, STG and SV.

Although the IC₅₀ values of our compound are relatively higher than those of the standard inhibitors, the advantage lies in its multifaceted mechanisms of action. These include inhibition of inflammation, suppression of digestive enzymes, and enhancement of insulin sensitivity. Consequently, this combination of mechanisms may provide significant therapeutic benefits. Indeed, the presence of a complex containing a phenolic structure, cobalt (Co), and bromine enhances its interaction with these two enzymes, resulting in strong and durable inhibition. Consequently, this can significantly improve insulin sensitivity.

3.7. Molecular Docking Studies

Since Molecular docking is a powerful tool, frequently used in order to get valuable insight into the plausible molecular mechanisms of any pharmacologically active substances, docking studies were carried out to assess the intermolecular interactions formed and potential binding model, affinity, and binding free energy of the tested ligand. Thus, with the aim of theoretically evaluating the biological potentials of the synthesized complex (PhCH₂NEt₃)₂[CoBr₄] and to be able to accuracy perform this in silico technique, the two ligands forming the title compound were used (each alone). Additionally, the standards used in vitro tests as well as the cocrystallized ligands are docked for comparative reasons. All docking scores are summarized in Table S7. Although sometimes the reference ligands showed lower binding energy values than the ligands forming the present material, but these latter by the important effect of each which becomes more interesting when they form the synthesized complex and its biological potency was explained by the interesting interactions displayed by each with the residues of each target enzyme active site. For more details, the long alkyl chain of the Co­(II) complex contributes to its inhibitory activity through various interactions, including Pi–Pi, Pi-alkyl, van der Waals forces, carbon hydrogen bonds, Pi-sigma, and Pi-donor hydrogen bonds, as detailed in Table S8. As shown in Figure S1, the title compound exhibits notable anti-α-amylase activity, with an IC₅₀ value of 21.75 μM comparable to that of the reference drug. This observation aligns with molecular docking results, where the binding energy indicates that Acarbose has a lower binding affinity than the ligands forming the synthesized complex. Specifically, the tetrachlorocobaltate moiety forms multiple van der Waals interactions with amino acid residues Trp58, Trp59, Tyr62, His101, Arg195, Asp197, His299, and Asp300. Meanwhile, the triethylbenzylammonium cation not only engages in van der Waals interactions but also forms two attractive charge interactions with Asp197 and Asp300, a Pi-sigma interaction with Tyr62, and a Pi–Pi stacking interaction with Trp59 (Figure ).

10.

2D binding model of the docked ligand ≪ (PhCH ₂ NEt ₃ ) ⁺ ≫ within the active site of α-amylase (Pdb: 3baj).

In terms of anti-DPP-4 activity, the tested compound exhibited an IC₅₀ value of 22.06 μM, indicating lower potency compared to the reference drug. This finding aligns with the molecular docking results where Sitagliptin shows a lower binding affinity than the ligands forming the synthesized complex. Among the docked compounds, the cocrystallized ligand “DPP-4 Inhibitor” achieved the highest docking score. Indeed, the tetrachlorocobaltate interacted with the target enzyme via a conventional H-bond with Tyr662, a Carbon hydrogen bond with Ser630 besides to many van der Waals interactions (Figure S2). The triethylbenzylammonium displayed attractive charge interaction with Glu205, Pi-Donor hydrogen bond with Tyr662, Pi–Pi Stacked and Pi–Pi T-shaped with Tyr666. Additionally, numerous van der Waals interactions were established with (PhCH₂NEt₃)⁺ and many amino acids as detailed in Figure .

11.

2D binding model of the docked ligand ≪ (PhCH ₂ NEt ₃ ) ⁺ ≫ within the active site of DPP-4 (Pdb: 4a5s).

Regarding antilipase activity, the title compound exhibited an IC₅₀ of 43.24 μM, comparable to that of the reference drug. Molecular docking results based on binding energy values indicated that the organic part of the benzyltriethylammonium [CoBr₄] complex demonstrated greater biological potential than the standard drug orlistat. The inhibitory potency of the tetrachlorocobaltate moieties is evidenced by the formation of a carbon–hydrogen bond with Arg38, along with four van der Waals interactions involving Gly14, Gln29, Ala40, and Ile248 (Figure S3). In contrast, based on binding energy values, the triethylbenzylammonium cation exhibited higher potential than both the standard inhibitor and the cocrystallized ligand methoxyundecylphosphinic acid. The triethylbenzylammonium cation forms several van der Waals interactions, an attractive charge interaction with Asp31, carbon–hydrogen bonds with Asp31 and Leu36, and π–alkyl contacts with Arg38 and Ala40 (Figure ).

12.

2D binding model of the docked ligand ≪ (PhCH ₂ NEt ₃ ) ⁺ ≫ within the active site of lipase (Pdb: 1lpb).

On the other hand, targeting the myeloperoxidase (MPO) enzyme, according to the IC₅₀ values, the results highlight the superior activity of the compound against this crucial inflammatory enzyme compared to the reference. Accordingly, via the in silico investigations, the docking outcomes exhibited that the tetrachlorocobaltate only showed five van der Waals interactions with Gln257, Arg405, Glu408, Leu572 and Phe573 (Figure S4) meanwhile the triethylbenzylammonium displayed interacted with the target enzyme via an attractive charge and Pi–Anion interactions with Asp260. Further, (PhCH₂NEt₃)⁺ exhibited two carbon hydrogen bonds with His261 and His502, a Pi-Alkyl connection with Arg499 as well as some van der Waals interactions as Figure displays.

13.

2D binding model of the docked ligand ≪ (PhCH ₂ NEt ₃ ) ⁺ ≫ within the active site of myeloperoxidase MPO (Pdb: 5mfa).

Against the protein tyrosine phosphatase 1B (PTP1B) receptor, the title compound exhibited an IC₅₀ comparable to that of the reference inhibitor. Moreover, molecular docking results indicated that the cations constituting the synthesized complex possess a theoretically higher binding potential than the standard inhibitor, sodium vanadate. Therefore, the tetrachlorocobaltate is involved in five van der Waals interactions with the residues: Pro188, Ala189, Leu192, Glu276 as well as Phe280 (Figure S5). The triethylbenzylammonium cation forms several van der Waals interactions with Asn193, Lys197, and Gly277, as well as a Pi–cation interaction with Phe280, Pi–Pi interactions with Phe196 and Phe280, and a Pi–alkyl contact with Leu192 (Figure ). Based on binding energy values, these cations exhibit higher potential than the standard inhibitor but a lower docking score compared to the cocrystallized ligand.

14.

2D binding model of the docked ligand ≪ (PhCH ₂ NEt ₃ ) ⁺ ≫ within the active site of protein tyrosine phosphatase 1B (PTP1B) (Pdb: 1t49).

4. Conclusion

In summary, a monomolecular complex with a benzyltriethylammonium bromide organic ligand was characterized both experimentally and theoretically. The supramolecular arrangement is primarily governed by intermolecular interactions, especially hydrogen bonds. Experimental and theoretical vibrational analyses confirm the presence of key functional groups in the compound. The HOMO–LUMO energy gap explains the molecule’s charge transfer capabilities, with a calculated band gap of 3.673 eV classifying it as a semiconductor. NBO analysis further supported these findings. Photocatalytic experiments demonstrated that the compound is an effective candidate for methylene blue degradation, suggesting potential for designing new photocatalytic materials. Therapeutically, the complex exhibited promising activity by inhibiting inflammation, lipid and glucose absorption, and enhancing insulin sensitivity, thus showing antiobesity and antidiabetic effects. In silico docking simulations against five enzymesα-amylase, dipeptidyl peptidase-4 (DPP-4), lipase, promyeloperoxidase (proMPO), and protein tyrosine phosphatase 1B (PTP1B)confirmed its potential mechanisms of action. These results support further investigation of this material as a candidate for treating human diseases.

All data supporting the findings of this study are fully included within the manuscript and the accompanying Supporting Information file.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.5c01220.

• Detailed biological activities; crystallographic data and structure refinement parameters; DFT calculations and molecular docking procedure for (PhCH₂NEt₃)₂[CoBr₄] (PDF)

Noureddine Mhadhbi: software, writing–original draft; Naoufel Ben Hamadi: data curation, investigation; Souad Dgachi: software, data curation; Mabrouk Horchani: validation, visualization; Nabila Guechtouli: investigation, formal analysis; Ali Ben Ahmed: formal analysis, investigation; Khaled Hamden: formal analysis, validation; Ahlem Guesmi: methodology, conceptualization; Fehmi Boufahja: investigation, validation; Hichem Ben Jannet: investigation, validation; Houcine Naïli: supervision, review and editing.

This work was supported and funded by the Deanship of Scientific Research at Imam Mohammad Ibn Saud Islamic University (IMSIU) (grant number IMSIU-DDRSP2501).

The authors declare no competing financial interest.