Computational Chemistry Calculations Research Articles

Antioxidant properties of catechin and its 3′O-α-glucoside: Insights from computational chemistry calculations

Density functional theory (DFT) calculations were used to investigate the conformational landscape of catechin and one of its main glucoside derivative (catechin-3′ O- α −glucopyranoside), and to determine the corresponding antioxidant properties. These investigations were carried out in benzene and water using the SMD universal continuum solvation model. Both properties were found to be significantly affected. The structures are characterized in both solvents by strong intramolecular hydrogen bonds (IMHB). In an apolar environment, Hydrogen Atom Transfer (HAT) is by far favored whereas in water the Sequential Proton Loss Electron Transfer (SPLET) mechanism is strongly preferred. In benzene, the catechin fragment has the best antioxidant character (from 27 kJ/mole) whereas in polar surroundings, the glucoside derivative has a slightly better antiradical activity (from 5 kJ/mole). Our results confirm the key role of the 3′-OH and 4′-OH groups of the catechole ring in these properties.

Limiting factors in the accuracy of DFT calculation for redox potentials.

In the present study, we have investigated factors affecting the accuracy of computational chemistry calculation of redox potentials, namely the gas-phase ionization energy (IE) and electron affinity (EA), and the continuum solvation effect. In general, double-hybrid density functional theory methods yield IEs and EAs that are on average within ~0.1 eV of our high-level W3X-L benchmark, with the best performing method being DSD-BLYP/ma-def2-QZVPP. For lower-cost methods, the average errors are ~0.2-0.3 eV, with ωB97X-3c being the most accurate (~0.15 eV). For the solvation component, essentially all methods have an average error of ~0.3 eV, which shows the limitation of the continuum solvation model. Curiously, the directly calculated redox potentials show errors of ~0.3 eV for all methods. These errors are notably smaller than what can be expected from error propagation with the two components (IE and EA, and solvation effect). Such a discrepancy can be attributed to the cancellation of errors, with the lowest-cost GFN2-xTB method benefiting the most, and the most accurate ωB97X-3c method benefiting the least. For organometallic species, the redox potentials show large deviations exceeding ~0.5 eV even for DSD-BLYP. The large errors are attributed to those for the gas-phase IEs and EAs, which represents a major barrier to the accurate calculation of redox potentials for such systems.

1,2,4-triazole-5-thione derivative for inhibiting carbon steel corrosion in 1M HCl: Synthesis, electrochemical, SEM/EDX, DFT, and MD investigations

In the current research, the corrosion inhibition efficiency of a novel synthesized 1,2,4-triazole-5-thione derivative, named 1,8bis(5-mercapto-3-(4‑chloro)-phenyl-1,2,4-triazolyl)-triethyleneglycol (3) for carbon steel in 1 M HCl medium is assessed employing conventional weight-loss measurements as well as electrochemical methods, including electrochemical impedance spectroscopy and potentiodynamic polarization. The findings highlighted that the presence of the tested inhibitor led to a decrease in the corrosion rate and enhancement of the inhibitory efficacy with a maximum value of around 93 % obtained at a concentration of 10–3 M. This might be associated with the creation of a protective adsorption film on the metal surface. Electrochemical measurements disclosed the mixed-type inhibition effect of 3. The inhibitor adsorption mechanism followed the Langmuir adsorption isotherm. Despite that, a thorough examination of the carbon steel surfaces, both in their uninhibited and inhibited states, was conducted through scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) analysis. The experimental findings were supported by computational chemistry calculations using density function theory (DFT) and Molecular Dynamic (MD) simulations.

Solvent-mediated modification of thermodynamics and kinetics of monoethanolamine regeneration reaction in amine-stripping carbon capture: Computational chemistry study.

A major limitation of amine-based post-combustion carbon capture technology is the necessity to regenerate amines at high temperatures, which dramatically increases operating costs. This paper concludes the effect of solvent choice as a possible route to modify the thermodynamics and kinetics characterizing the involved amine regeneration reactions and discusses whether these modifications can be economically beneficial. We report experimentally benchmarked computational chemistry calculations of monoethanolamine regeneration reactions employing aqueous and non-aqueous solvents with a wide range of dielectric constants. Unlike previous studies, our improved computational chemistry framework could accurately reproduce the right experimental activation energy of zwitterion formation. From the thermodynamics and kinetics of the predicted reactions, the use of non-aqueous solvents with small dielectric constants led to reductions in regeneration Gibbs free energies, activation barriers, and enthalpy changes. This can reduce energy consumption and give an opportunity to run desorption columns at relatively lower temperatures, thus offering the possibility of relying on low-grade waste heat as an energy input.

Effective encapsulation of noble and small gases and molecules by tubularene molecule

AbstractBased on computational chemistry calculations (ωB97XD/def2‐tzvp//ωB97XD/def2‐svp/svpfit+ZPE(ωB97XD/def2‐svp/svpfit)), binding energy of tubular[3,6,6,6]arene to accommodate noble gases and a series of 29 small gases were calculated. Based on the gained results, Rn (−17.52 kcal/mol) from the series of noble gases is best suited to be accommodated. In the series of noble gases, the binding energy increases linearly with increasing gas radii. From the series of 29 small guests, IF3 and C2I2 (~ −23 kcal/mol) have the best proclivity to be most effectively accommodated in the tubularene, with other 26 exhibiting favorable encapsulation energies on various scales depending on their voluminosity and structure, and only NI3 with the unfavorable complexation energy of 13.87 kcal/mol. Investigated gases, depending on the size, are placed at the different position inside the tube‐like cavity of the tubularene. The structure of the tubularene, independent of the hosted guest species, has remained very rigid, with its atom's rearrangements withing an error margin.

A machine learning technique based on group contributions to calculate the solubility of dye molecules in supercritical CO2

A new modeling approach is proposed for the estimation of dye solubility in supercritical carbon dioxide. This approach is based on the synergy obtained from a group contribution approach and an artificial neural network. 33 functional groups have been proposed to create the dye molecules, and a database containing 1917 experimental solubility points of 66 molecules was utilized to establish the best architecture of the artificial neural network. The results showed that this new approach could calculate the dye solubility in this supercritical fluid with modeling errors lower than 10 % under different pressure and temperature conditions. Specifically, it showed a competitive performance with R2 > 0.99, AARDlny = 0.91 ± 1.2 % and AARDy = 10.4 ± 17.9 %. The minimum and maximum values of ARDlny and ARDy were 4.0E-04 – 16.8 % and 5.0E-03 – 386 %. This contribution group – artificial neural network approach outperformed classical empirical and semi-empirical equations, and other surrogate models based on artificial intelligence, even those using more detailed information of tested compounds (e.g., molecular descriptors that should be obtained from computational chemistry calculations). It is an interesting option to be incorporated into process simulators to improve the process design of dyeing technologies using supercritical carbon dioxide.

Corrosion inhibition performance of organic compounds and theoretical calculations based on density functional theory (DFT)

Abstract 2,5-Bis(4-dimethylaminophenyl)-1,3,4-oxadiazole (DAPO), 2-acetylthiophene thiosemicarbazone (2-AT), 2-hydroxyphenyl-5-mercapto-1-oxa-3,4-diazole (HMO), and 2-cinnamyl-5-mercapto-1-oxa-3,4-diazole (CMO) have been studied by measurement several quantum chemical parameters such as E HOMO, E LUMO, bandgap energy, softness, hardness, electrophilicity, nucleophilicity, and Fukui function analysis. The best corrosion inhibition efficiency was evaluated through a comparison between theoretical and experimental results. In gas and aqueous phases, protonated and nonprotonated species were investigated for their electronic structures in order to discover the factors and reasons behind corrosion inhibition. A theoretical study of all the studied compounds in gas and aqueous phases was investigated by employing the density functional theory (DFT) at 6–311++G(d, p) basis set and Becke’s three parameters hybrid exchange–correlation functional (B3LYP). The molecules are calculated using quantum computational chemistry calculations such as Gaussian09 software. The experiments were carried out on carbon steel and HCL. Carbon steel is the most often used steel because it combines outstanding mechanical qualities with a low cost. One of the most commonly utilized agents for these purposes is HCl solution. On the other hand, steel and ferrous alloys are likely to corrode under certain conditions. One of the most effective strategies for protecting metals against corrosion is corrosion inhibitors, and they are becoming more common.

Innovative electrochemical platform for the simultaneous determination of L-DOPA and L-tyrosine using layer-by-layer assembled L-proline-linked nanodiamonds on printed graphene.

Discovering alternative analytical techniques is crucial for practical applications; thus, this work aims to develop an innovative and simple electrochemical sensor for melanoma and the clinical diagnosis of related disorders by the simultaneous determination of 3,4-dihydroxy-L-phenylalanine (L-DOPA) and L-tyrosine (L-Tyr). The fabrication is based on the layer-by-layer electrodeposition of poly L-proline (poly(L-pro)) and nanodiamond (ND) onto a screen-printed graphene electrode (SPGE). The poly(L-pro)/ND/SPGEs were morphologically characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, and Raman spectroscopy followed by electrochemical investigation using cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. These modifier-based electrodes pave a feasible way to unlock the coexisting interfering substances from screen-printing ink composition and improve the sensitivity. Additionally, computational chemistry calculations were performed to fully comprehend the sensing behavior on both target analytes. Under optimal conditions, the developed sensor provided linear concentration ranges of 0.075-50μM, with a detection limit of 0.021μM for L-DOPA, and 2.5-120μM with a detection limit of 0.74μM for L-Tyr. To demonstrate the reliability of the poly(L-pro)/ND/SPGE in practical application, it was successfully applied tothe determination of these analytes in human urine and blood serum samples, with satisfactory recovery ranges (81.73-110.62% for L-DOPA and 82.17-110.01% for L-Tyr) and relative standard deviations (0.69-9.90% for L-DOPA and 0.40-9.55% for L-Tyr). Due to its simplicity, long-term stability (> 87.8% of their initial currents after 35days), and portability, the developed sensor is a promising alternative analytical method for on-site clinical monitoring.

Selective Noble Gas Inclusion in Pentagon-Dodecahedral X20-Cages.

Using DFT-based computational chemistry calculations (ωB97XD/def2-tzvp//ωB97XD/def2-svp/svpfit + ZPE(ωB97XD/def2-svp/svpfit)), binding energies of noble gases encapsulated in a series of dodecahedrane molecules (general formula: X20H20 where X = C, Si, Ge, Sn and Pb, and X20 where X = N, P, As, Sb and Bi) were calculated to learn about the noble gas selectivity. Based on calculated binding energies, the Sn20H20 cage can best accommodate noble gases with a medium size radius (Ar and Kr), while the Pb20H20 dodecahedrane cage is best suited for noble gases with the larger radii (Xe and Rn). On the other hand, from the elements of the V main group of the periodic table, the Bi20 cage has shown the best results to selectively encapsulate Ar and Kr, with the amounts of energy being released being -5.24 kcal/mol and -6.13 kcal/mol, respectively. By monitoring the geometric changes of all here-reported host cages upon encapsulating the noble gas guest, the host has shown minor to no flexibility, testifying to the high rigidity of the dodecahedrane structure which was further reflected in very high encapsulating energies.

Biocompatible MgFeCO3 Layered Double Hydroxide (LDH) for Bone Regeneration-Low-Temperature Processing through Cold Sintering and Freeze-Casting.

Layered Double Hydroxides (LDHs) are inorganic compounds of relevance to various domains, where their surface reactivity and/or intercalation capacities can be advantageously exploited for the retention/release of ionic and molecular species. In this study, we have explored specifically the applicability in the field of bone regeneration of one LDH composition, denoted "MgFeCO3", of which components are already present in vivo, so as to convey a biocompatibility character. The propensity to be used as a bone substitute depends, however, on their ability to allow the fabrication of 3D constructs able to be implanted in bone sites. In this work, we display two appealing approaches for the processing of MgFeCO3 LDH particles to prepare (i) porous 3D scaffolds by freeze-casting, involving an alginate biopolymeric matrix, and (ii) pure MgFeCO3 LDH monoliths by Spark Plasma Sintering (SPS) at low temperature. We then explored the capacity of such LDH particles or monoliths to interact quantitatively with molecular moieties/drugs in view of their local release. The experimental data were complemented by computational chemistry calculations (Monte Carlo) to examine in more detail the mineral-organic interactions at play. Finally, preliminary in vitro tests on osteoblastic MG63 cells confirmed the high biocompatible character of this LDH composition. It was confirmed that (i) thermodynamically metastable LDH could be successfully consolidated into a monolith through SPS, (ii) the LDH particles could be incorporated into a polymer matrix through freeze casting, and (iii) the LDH in the consolidated monolith could incorporate and release drug molecules in a controlled manner. In other words, our results indicate that the MgFeCO3 LDH (pyroaurite structure) may be seen as a new promising compound for the setup of bone substitute biomaterials with tailorable drug delivery capacity, including for personalized medicine.

A COMPUTATIONAL STUDY OF SUBSTITUENT EFFECT 1, 3, 4-THIADIAZOLE ON CORROSION INHIBITION

A theoretical study of 1, 3, 4-thiadiazole with nine various derivatives in gaseous and aqueous phases was investigated by employing the density functional theory (DFT) at 6-311++(d, p) basis set and Becke’s three parameters hybrid exchange-correlation functional (B3LYP). The molecules are calculated using quantum computational chemistry calculations such as Gaussian09 software. This paper is to determine the chemical reactivity for various heterocyclic organic compounds and to understand the process of corrosion inhibition. The quantum chemical properties such as the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), energy gap (∆E), dipole moment (μ), global hardness (η), global softness (S), electronegativity (χ), electrophilicity (ω), nucleophilicity (ɛ), chemical potential (CP) and electrons transferred from inhibitors to metal surface (ΔN) were calculated. Dynamic simulation approximations to demonstrate the corrosion inhibition performances of studied inhibitors against the corrosion of 1, 3, 4-thiadiazole in the gaseous and aqueous phases can be given as 1<9<8<3<4<5<6<7<2 and1<3<9<8<3<4<5<6<7<2

Systematic elucidation of the second coordination sphere effect on the structure and properties of a blue copper protein, pseudoazurin

The rational structural and computational studies of a blue copper protein, pseudoazurin (PAz), and its Met16X (X = Phe, Leu, Val, Ile) variants gave clear functional meanings of the noncovalent interaction (NCI) through the second coordination sphere. The high-resolution X-ray crystal structures of Met16X PAz demonstrated that the active site geometry is significantly affected by the substitution of Met16, which is located within the NCI distance from the His81 imidazole ring at the copper active site. The computational chemistry calculations based on the crystal structure analyses confirmed that the NCI of S-π/CH-π (wild-type), π-π (Met16Phe), double CH-π (Met16Leu), and single CH-π (Met16Val and Met16Ile). The estimated interaction energies for the NCI demonstrated that the fine-tuning of the protein stability and Cu site properties form the second coordination sphere of PAz.

Determination of the Dissociation Constants (pKa) of Eight Amines of Importance in Carbon Capture: Computational Chemistry Calculations, and Artificial Neural Network Models

This work focuses on determining the dissociation constants (pKa) of eight amines, namely, 3-(Diethylamino) propylamine, 1,3-Diaminopentane, 3-Butoxypropylamine, 2-(Methylamino) ethanol, Bis(2-methoxyethyl) amine, α-Methylbenzylamine, 2-Aminoheptane, and 3-Amino-1-phenylbutane, within temperatures ranging from 293.15 K to 323.15 K. The thermodynamic properties of the protonated reactions were regressed from the pKa work. In addition, the protonated order of both 3-(Diethylamino) propylamine and 1,3-Diaminopentane were determined using computational chemistry methods owing to their unsymmetrical structures. In addition to the experimental methods, the dissociation constants at the standard temperature (298.15 K) were also estimated using group functional models (paper–pencil) and computational methods. The computational methods include COSMO-RS and computational chemistry calculations. An artificial neural network (ANN) method was employed to model the data by collecting and combining the experimental properties to estimate the missing pKa values. Although the ANN models can provide acceptable results, they depend on the availability of the data. Instead of using the experimental properties, they were generated using software such as Aspen Plus or CosmothermX. The simulated ANN model can also provide very good fits to the experimental constant values.

DFT and Molecular Docking Analysis of Newly Synthesized Compound (2E)-3-[3-(Benzyloxy) Phenyl]-1-(4’-Chlorophe-Nyl)- 2-Propen-1-One [Bpclpo

Background: The parent molecule in the skeleton of this chalcone is the benzyloxy phenyl, which is linked to the chlorophenylpropen at C-3. The hydrophobic phenyl groups are naturally resistant to oxidation and reduction. Antiviral, antimalarial, antibacterial, anti-inflammatory, anticancer, antioxidant, antitubercular, and anti-Alzheimer activities are among the many pharmacological properties of chalcone derivatives. As a result, chalcone-based compounds are investigated using molecular docking and molecular modelling calculations to determine their suitability for drug formulation. Aims: To synthesise (2E)-3-[3-(benzyloxy) phenyl]-1-(4’-chlorophenyl)-2-propen-1-one [BPClPO] and perform DFT and molecular docking analysis of the synthesized compound to better understand its medicinal properties. Objective: The characterization of BPClPO is investigated in this study using various approaches, including wavefunction analysis and spectral analysis, which are associated with quantum chemical calculations to investigate its medicinal properties. Methods: The Gaussian 09W programme was used to perform computational chemistry calculations. The BPClPO's molecular structure was optimised, and the vibrational frequencies, Natural Bond Orbital (NBO), Fukui function, electronic properties and Nuclear Magnetic Resonance (NMR) chemical shifts were calculated using the B3LYP/6-311G (d, p) as the basis set. The VMD user interface and Multiwfn (3.4.1) software were used to conduct topological analyses of the Electron Localization Function (ELF), Localized Orbital Locator (LOL) and Reduced Density Gradient (RDG). The binding sites of active cancer proteins were calculated using the auto dock and auto grid. Results: Theoretical reaction path investigation was done for BPClPO to detect reactions from the parent chemical to the synthesized compound. Theoretical bond lengths and bond angles are compared with XRD values. Theoretical values of vibrations caused by electron-rich and electrondeficient centres were investigated. The electronic spectra of λmax were examined under UV-Vis light and the electron absorbance spectrum was absorbance wavelength and oscillator strength compared to theoretical values. The electron-rich carbon atoms are de-shielded in NMR, resulting in stronger fields and chemical shifts. The Harmonic Oscillator Model of Aromaticity (HOMA)and the retain ability of aromaticity in the addition and removal of electrons are examined in the Nucleus Independent Chemical Shift (NICS) study. The stability of the compound was investigated using Thermo- Gravimetric analysis and Differential Scanning Calorimeter (TG/DSC) analysis. Four cancer proteins with the reactive site were studied in docking simulations. Conclusions: The NBO analysis determined the intramolecular charge transfer within the molecule of high stabilization transition from C34-C37 donor to C35-C39 acceptor of (22.31 Kcal/mol) (π→π*) due to phenyl transition belonging to Cl atom in the ring. In the solvent phase, UV-visible spectra reveal a prominent peak at 300 λmax, with an absorbance range of intensity of 0.6983. (a.u.). According to TG/DSC experiments, the molecule begins to break around 290-370°C, and total decomposition occurs at 300°C. The molecule was found to have a higher bioactivity than and was employed related more to medicinal properties mechanism(s) of action in drug docking investigations.

Supramolecular aggregation featuring Hg⋯S secondary-bonding interactions in crystals of mercury(ii) species augmented by computational chemistry calculations

A CSD survey reveals the presence of Hg⋯S interactions within zero-, one- and two-dimensional aggregation patterns in non-organomercury crystals. Theory confirms the stabilising nature of σ-/π-holes or positive belts formed at the mercury atom.

A Molecular Level Interpretation of the Underlying Chemical Phenomenon of Semi‐coke and Coke Formation: A Treatise from Ab Initio Calculations

AbstractChemistry of coke formation has been subject to a wide array of experimental investigations since the advent of industrial coal carbonization process. Roles of different additives in inducing chemical modifications have been examined in this regard. However, similar computational quantum chemistry calculations attempting to obtain fundamental insights into the plausible molecular mechanism operating during the resolidification steps of semi‐coke and coke formation are elusive. Thus, a rational molecular level understanding pertaining to the evolution of chemical structure during coke formation has not developed likewise. In this context, density functional theory calculations have been employed in the present work to comprehend the plausible molecular mechanism of elementary steps driving the semi‐coke and coke formation. Influence of an additional organic H‐donor species on the mechanism has also been explored to ascertain its participation in coke making. Mechanistic steps involved in semi‐coke formation are found to be crucial in determining the final coke structure. Experimental observations relating to the liberation of H• and also molecular hydrogen (H2) during the generation of semi‐coke structure are well corroborated with our investigated mechanistic features. Overall, the work is believed to offer a molecular level interpretation of a much‐exploited chemical phenomenon.

Coordination and Spin States in Fe+(C2H2)n Complexes Studied with Selected-Ion Infrared Spectroscopy.

Fe+(acetylene)n ion-molecule complexes are produced in a supersonic molecular beam with pulsed laser vaporization. These ions are mass selected and studied with infrared photodissociation spectroscopy in the C-H stretching region, complemented by computational chemistry calculations. All C-H stretch vibrations are shifted to frequencies lower than the vibrations of isolated acetylene because of the charge transfer that occurs between the metal ion and the molecules. Complexes in the size range of n = 1-4 are found to have structures with individual acetylene molecules bound to the core metal ion via cation-π interactions. The coordination is completed with four ligands in a structure close to a distorted tetrahedron. Larger complexes in the range of n = 5-8 have external acetylene molecules solvating this n = 4 core ion via CH-π bonding to inner-shell ligands. DFT computations predict that quartet spin states are more stable for all complex sizes, but infrared spectra for quartet and doublet spin states are quite similar, precluding definitive determination of the spin states. There is no evidence for any of these complexes having acetylenes coupled into reacted structures. This is consistent with computed thermochemistry, which finds significant activation barriers to such reactions.

Octahedral Molybdenum Iodide Clusters Supported on Graphene for Resistive and Optical Gas Sensing.

This paper reports for the first time a gas-sensitive nanohybrid based on octahedral molybdenum iodide clusters supported on graphene flakes (Mo6@Graphene). The possibility of integrating this material into two different transducing schemes for gas sensing is proposed since the nanomaterial changes both its electrical resistivity and optical properties when exposed to gases and at room temperature. Particularly, when implemented in a chemoresistive device, the Mo6@Graphene hybrid showed an outstanding sensing performance toward NO2, revealing a limit of quantification of about 10 ppb and excellent response repeatability (0.9% of relative error). While the Mo6@Graphene chemoresistor was almost insensitive to NH3, the use of an optical transduction scheme (changes in photoluminescence) provided an outstanding detection of NH3 even for a low loading of Mo6. Nevertheless, the photoluminescence was not affected by the presence of NO2. In addition, the hybrid material revealed high stability of its gas sensing properties over time and under ambient moisture. Computational chemistry calculations were performed to better understand these results, and plausible sensing mechanisms were presented accordingly. These results pave the way to develop a new generation of multi-parameter sensors in which electronic and optical interrogation techniques can be implemented simultaneously, advancing toward the realization of highly selective and orthogonal gas sensing.

Experimental determination of dissociation constants (pKa) for N‐(2‐aminoethyl)‐1,3‐propanediamine, 2‐methylpentamethylene diamine, N,N‐dimethyldipropylenetriamine, 3,3′‐diamino‐N‐methyldipropyl‐amine, Bis[2‐(N,N‐dimethylamino)ethyl]ether, 2‐[2‐(dimethyl‐amino) ethoxy] ethanol, 2‐(dibutylamino) ethanol, and N‐propylethanol‐amine and modeling with artificial neural network

AbstractThe dissociation constants (pKa) of the eight amines, namely, N‐(2‐aminoethyl)‐1,3‐propanediamine, 2‐methylpentamethylene diamine, N,N‐dimethyldipropylene‐triamine, 3,3′‐diamino‐N‐methyl‐dipropylamine, Bis[2‐(N,N‐dimethylamino) ethyl]ether, 2‐[2‐(dimethyl‐amino)ethoxy] ethanol, 2‐(dibutylamino) ethanol, and N‐propylethanolamine were measured between 298.15 and 313.15 K with 5 K increment. Based on the experimental values and using the van't Hoff equation, thermodynamic properties such as the standard state changes of enthalpy, entropy, and Gibbs free energy were calculated. Using computational chemistry calculations, the amine that is protonated first was predicted. Furthermore, computer‐free group contribution methods such as the original Perrin–Dempsey–Serjeant (PDS), the modified PDS, and the Qian–Sun–Sun–Gao (QSSG) model were used to estimate the dissociation constants of the studied amines at 298.15 K. The QSSG provided the most accurate results. Finally, this work utilized an artificial neural network for estimating the pKa values, which were in excellent agreement with the experimental data.

Unravelling the Methylene Blue Adsorption Mechanism on Doped and Nondoped Polyaniline: A Combined Molecular Modeling and Experimental Investigation

A multiscale investigation including computational chemistry calculations and experimental studies was performed to elucidate and understand the methylene blue (MB) adsorption on polyaniline (PANI) from an aqueous solution. Static DFT and DFT-based ab initio molecular dynamics were used to characterize the intermolecular interactions of this dye molecule with nondoped and doped PANI. Experimental adsorption studies at different operating conditions were performed to complement the mechanism analysis of this adsorption system. Infrared spectroscopy studies and ab initio calculations showed the important role of π-π stacking and van der Waals interactions for the dye adsorption on PANI. Experimental results of MB adsorption on the PANI surface indicated that alkaline conditions were more favorable than acidic conditions where the MB adsorption capacity ranged from 9.91 mg/g at pH 1.8 to 23.16 mg/g at pH 10.9. Equilibrium adsorption studies with nondoped PANI revealed a fast removal of the dye molecules where the equilibrium adsorption was reached after 45 minutes. The kinetic parameters were calculated with the pseudo-second and pseudo-first order models, while the adsorption mechanism was analyzed using the intraparticle diffusion, Boyd, and Elovich models. Dye adsorption equilibrium was studied at pH 8 and 30 °C where Temkin, Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) isotherm models as well as a statistical physics monolayer model were employed in data analysis. The saturation dye adsorption capacity was 40.2 mg/g where an inclined adsorption orientation of dye molecules on the PANI surface could be expected with an adsorption energy of 14.0 kJ/mol. This interaction energy clearly indicated that only physical interactions were involved in the MB dye adsorption mechanism, which was also confirmed by the calculations with the D-R isotherm model. These theoretical and experimental results are important to understand the dye adsorption properties of conductive polymers and to consolidate their application in the synthesis of new adsorbents and composites for water treatment.