Electronic structures and ligand effect on redox potential of iron and cobalt complexes: a computational insight

Supradecoration induced homogenous electrochemical sensing: development of Ru(ii) half sandwich complex as isoniazid and rifampicin dual sensor

Homogenous electrochemical sensing using unmodified electrodes remove electrode fabrication challenges and prove effective for detecting sensitive bio-analytes without chances of surface degradation. This work envisages design and optimization of a ruthenium(ii) half-sandwich complex as supradecorated homogeneous electrochemical sensor for simultaneous detection of rifampicin (RIF) and isoniazid (INH) as first-line anti-tuberculosis drugs in aqueous environments. The electrochemical profile of GCE/ruthenium(ii) half-sandwich complex sensor was analyzed using cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy (EIS). The results indicate significant electrochemical parameters corroborating enhanced sensing propensity of GCE/ruthenium(ii) half-sandwich complex over bare GCE for simultaneous estimation of RIF and INH binary mixture. The RIF and INZ analytical figure of merit has been corroborated with their relative supra interactional propensity. Supra interactional propensity has also been predicted to be the plausible mechanism of RIF and INZ electrochemical sensing. Under optimized conditions GCE/ruthenium(ii) half-sandwich complex sensor depicted INH detection limits of 1.2 μM, and RIF detection limit of 32 nM. The comparative study of RIF and INZ analytes individually depicted high sensitivity of 24.57 μA μM-1 cm-2 and 1.69 μA μM-1 cm-2 under a linear response in the range of 0.29-3.72 μM and 4.9-82.22 μM for RIF and INH respectively. The analytical figure of merit of homogenous sensor has been compared to other GCE modified electrodes for RIF and INZ analytes. A significant antibiotic contaminant recovery of RIF and INZ drugs in pharmaceutical formulations, municipal water supplies and Dal lake water under spiked as well as unspiked conditions was observed portraying real time sensing application propensity. The homogenous GCE/ruthenium(ii) half-sandwich complex expresses excellent stability and reproducibility. The GCE/ruthenium(ii) half-sandwich complex in the presence of potential redox active biological interfering agents confirmed selectivity towards RIF and INZ analytes.

Structures, bonding aspects and spectroscopic parameters of morin, myricetin, and quercetin with copper/zinc complexes: DFT and TDDFT exploration

CONTEXT

In the present work, DFT/TDDFT techniques is used to analyze structure, bonding, reactivity and electronic transitions of quercetin, morin, myricetin with their metal (Cu and Zn) complexes. In order to comprehend metal complexes and ligands reactivity patterns, we calculated energy gaps between frontier molecular orbitals. Global reactivity characteristics, such as ionization potential, electronegativity (χ), hardness (η), softness (S), electrophilicity index (ω) electron affinity, and chemical potential (μ), were computed based on the FMO energies. Molecular electrostatic potential (MEP) maps were used to identify nucleophilic and electrophilic sites in complexes. Within the examined complexes, TDDFT and NBO analysis shed light on bonding, electronic transitions and stabilizing interactions. Ligands morin, myricetin, and quercetin exhibited higher HOMO-LUMO gap than their corresponding metal complexes, suggesting electron transfer may be faster in the metal complexes. The metal complexes displayed more negative electrostatic potentials. The absorption spectra of the ligands ranged from 258 to 360 nm, whereas their complexes exhibited a broader range from 252 to 1035 nm. These spectra provided important insights into charge transfer and electronic transitions, enhancing our knowledge of electronic and bonding characteristics of such compounds.

METHODS

G16 software is used to optimize all species. B3LYP functional was employed in combination with LanL2DZ basis set for Cu and Zn, and 6-311G(d,p) basis set for other atoms (C, H and O). Natural bond orbital examination was conducted in order to investigate interactions between the filled orbitals of one unit and empty orbitals of other unit. ORCA software was utilized to compute spectral features, incorporating ZORA method to account for relativistic effects. TDDFT studies is carried out using B3LYP functional to calculate excitation energies.

Potential Application of Room Temperature Synthesized MIL-100(Fe) in Enhancing Methane Production in Microbial Electrolysis Cells-Anaerobic Digestion Treating Protein-Rich Wastewater

Microbial electrolysis cell-anaerobic digestion (MEC-AD) is an emerging technology for methane production. However, low substrate degradation efficiency remains a challenge when processing protein substrates. This study developed a MIL-100(Fe) carbon cloth anode to enhance methane production and substrate degradation in MEC-AD. The effects of MIL-100(Fe) prepared under hydrothermal (H-MIL-100(Fe)) and room temperature conditions (R-MIL-100(Fe)) were compared. Results indicated that H-MIL-100(Fe) and R-MIL-100(Fe) increased cumulative methane production by 16.01% and 14.99%, respectively compared to normal cloth, each influencing methane production through distinct mechanisms. Electrochemical characterization showed that H-MIL-100(Fe) enhanced the electrochemical performance more significantly due to the enrichment of Geotalea, with the oxidation current improved by 7.39-fold (R-MIL-100(Fe) increased it by only 2.95-fold) to promote growth of Methanobacterium. Metagenomic analysis revealed that R-MIL-100(Fe) tended to metabolize amino acids into methane rather than support cellular life activities, indicating its practicality under limited substrate concentration. In summary, R-MIL-100(Fe) shows greater potential for application due to its mild synthesis conditions and advantages in treating complex substrates.

DFT and TDDFT exploration on electronic transitions and bonding aspect of DPA and PTDC ligated transition metal complexes

CONTEXT

In this study, we have investigated the structure, reactivity, bonding, and electronic transitions of DPA and PDTC along with their Ni-Zn complexes using DFT/TD-DFT methods. The energy gap between the frontier orbitals was computed to understand the reactivity pattern of the ligands and metal complexes. From the energies of FMO's, the global reactivity descriptors such as electron affinity, ionization potential, hardness (η), softness (S), chemical potential (μ), electronegativity (χ), and electrophilicity index (ω) have been calculated. The complexes show a strong NLO properties due to easily polarization as indicated by the narrow HOMO-LUMO gap. The polarizability and hyperpolarizabilities of the complexes indicate that they are good candidates for NLO materials. Molecular electrostatic potential (MEP) maps identified electrophilic and nucleophilic sites on the surfaces of the complexes. TDDFT and NBO analyses provided insights into electronic transitions, bonding, and stabilizing interactions within the studied complexes. DPA and PDTC exhibited larger HOMO-LUMO gaps and more negative electrostatic potentials compared to their metal complexes suggesting the higher reactivity. Ligands (DPA and PDTC) had absorption spectra in the range of 250 nm to 285 nm while their complexes spanned 250 nm to 870 nm. These bands offer valuable information on electronic transitions, charge transfer and optical behavior. This work enhances our understanding of the electronic structure and optical properties of these complexes.

METHODS

Gaussian16 program was used for the optimization of all the compounds. B3LYP functional in combination with basis sets, such as LanL2DZ for Zn, Ni and Cu while 6-311G** for other atoms like C, H, O, N, and S was used. Natural bond orbital (NBO) analysis is carried out to find out how the filled orbital of one sub-system interacts with the empty orbital of another sub-system. The ORCA software is used for computing spectral features along with the zeroth order regular approximation method (ZORA) to observe its relativistic effects. TD-DFT study is carried out to calculate the excitation energy by using B3LYP functional.

C-H bond activation by high-valent iron/cobalt-oxo complexes: a quantum chemical modeling approach

High-valent metal-oxo species serve as key intermediates in the activation of inert C-H bonds. Here, we present a comprehensive DFT analysis of the parameters that have been proposed as influencing factors in modeled high-valent metal-oxo mediated C-H activation reactions. Our approach involves utilizing DFT calculations to explore the electronic structures of modeled FeIVO (species 1) and CoIVO ↔ CoIII-O˙ (species 2), scrutinizing their capacity to predict improved catalytic activity. DFT and DLPNO-CCSD(T) calculations predict that the iron-oxo species possesses a triplet as the ground state, while the cobalt-oxo has a doublet as the ground state. Furthermore, we have investigated the mechanistic pathways for the first C-H bond activation, as well as the desaturation of the alkanes. The mechanism was determined to be a two-step process, wherein the first hydrogen atom abstraction (HAA) represents the rate-limiting step, involving the proton-coupled electron transfer (PCET) process. However, we found that the second HAA step is highly exothermic for both species. Our calculations suggest that the iron-oxo species (Fe-O = 1.672 Å) exhibit relatively sluggish behavior compared to the cobalt-oxo species (Co-O = 1.854 Å) in C-H bond activation, attributed to a weak metal-oxygen bond. MO, NBO, and deformation energy analysis reveal the importance of weakening the M-O bond in the cobalt species, thereby reducing the overall barrier to the reaction. This catalyst was found to have a C-H activation barrier relatively smaller than that previously reported in the literature.

Mechanistic insights on the epoxidation of alkenes by high-valent non-heme Fe(iv) and Fe(v) oxidants: a comparative theoretical study

This work is based on the screening of better high-valent oxidants, and also includes a mechanistic study during oxygen atom transfer reactions.

DFT and TDDFT exploration on the role of pyridyl ligands with copper toward bonding aspects and light harvesting

CONTEXT

Schiff base-containing metal complexes have been the subject of extensive research. In this work, a coordination polymer-derived complex called [Cu(L)] that is solution-stable (L = 2-(2-hydroxybenzylidene-amino)phenol) has been explored theoretically with five different pyridyl-based ligands using DFT/TDDFT in order to understand the structural-functional and electronic transitions of these five complexes. Frontier molecular orbital (FMO) analysis was carried out to assess the reactivity behavior of all five complexes. For the purpose of studying the charge energy distribution over complexes, electrostatic potential maps were also drawn. Furthermore, in order to identify any stabilizing interactions that may be present in the given complexes, an NBO analysis was studied. To learn more about any potential correlations between the properties of these five complexes, a comparative analysis was explored. Our calculations demonstrate that complex 3 having pyridine-4-carboxamide as a ligand has a lower energy gap and a higher negative electrostatic potential which may indicate its higher reactivity and this may be due to the electron withdrawing group (carboxamide). TDDFT results show that the highest light harvesting efficiency (LHE) of all the studied complexes is found in the range of 440-448 nm. Complexes 1, 2, and 4 show the higher light harvesting efficiency as compared to complexes 3 and 5. Our findings are in good accordance with the available experimental data.

METHODS

All DFT computations were performed using the Gaussian16 with unrestricted B3LYP-D2 functional with the basis sets 6-31G(d,p) for O, N, C, and H while LanL2DZ for Cu. The polarized continuum model (PCM) was used for the solvation. The software GaussView6.1 was utilized for the modeling of initial geometries and the plotting of MEP maps. The NBO6.0 program which is incorporated in Gaussian16 was utilized to investigate the bonding nature and stabilization energies of the complexes. The ORCA program was used to simulate the absorption spectra.

Photophysical properties of four-membered BN3 heterocyclic compounds: theoretical insights

CONTEXT

Understanding the photochemistry of boron nitrogen (BN)-containing compounds is an important aspect to enhance the various optical and electronic applications. In this work, we have explored the structure, bonding, reactivity, electronic absorption (UV-Vis), and light harvesting efficiency (LHE) of a series of BN3 ring and open-chain systems. The frontier molecular orbitals (FMO) analysis found that ring systems have a low HOMO-LUMO energy gap as compared to the open-chain systems which insinuates the feasibility of ring systems in the optoelectronic materials. Also, the molecular electrostatic potential (MEP) maps have been computed to pursue the electrophilic and nucleophilic sites available at the surface of the compound. Interestingly, we have found that the open-chain compounds show more molecular charge distribution range rather than the ring compounds. The investigation of photophysical properties showed that the UV-Vis absorption significantly red-shifted in BN3 ring systems as compared to open-chain counterparts. Furthermore, light harvesting efficiency (LHE) was also found higher in the ring systems as compared to the BN3 open-chain systems. Moreover, the computed structural parameters are found well corroborated with the available X-ray data.

METHODS

Structures of all compounds were optimized by using density functional theory (DFT) method, with M06-2X/6-31G(d,p) level. All the calculations in this work are carried out in Gaussian 16 program package. GaussView6.1 software was used for the modeling of initial geometries and for the plotting of MEP plots. To account the solvent effect on geometries the polarized continuum model (PCM) was used and tetrahydrofuran (THF) taken as solvent. The NBO6.0 program (incorporated in G16 software) was used for the exploration of bonding nature and stabilization energies of B-N bond. The absorption spectra were simulated by using ORCA 4.2 program.