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Energy profiles corresponding to the possible mechanisms connecting T1 and T3, T4 in different solvents. Values are in kcal/mol
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The relative stability of the different tautomers of hydantoin has been studied through the use of DFT method. The structures and the vibrational frequencies of all stable tautomers and all the transitions states connecting between them have been calculated at the B3LYP/6-311+G(d,p) level of theory in the gas phase and selected solvents using IE-PC...
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Citations
... Geometry optimization of OG dye was conducted using the B3LYP functional, that is, Becke's [38,39] three-parameter nonlocal hybrid exchange potential with the nonlocal correlation of Lee, Yang, and Parr [4]. B3LYP functional has been shown to yield reliable geometries for a wide variety of systems [40][41][42][43][44][45][46]. All calculations were performed using the 6-311+g(d,p) basis set using the Gaussian09 series of program [47]. ...
The purpose of this research was to determine if a natural clay treated with Polyaniline (PANI) might be used to effectively and affordably remove of anionic dyes from aqueous solutions, with a focus on Orange G dye (OG). After combining PANI with natural clay. We created a Polyaniline-clay composite after analyzing it with FTIR, XRD, SEM and EDS of the (PANI@Clay). Using batch adsorption tests, we compared the performance of PANI@Clay and raw clay at removing OG from aqueous solutions as a function of contact duration (10–360 min), initial concentration (50–500 mg/L), temperature (293–318 K), and pH (2–12). Results showed that PANI@Clay had a maximum equilibrium adsorption capacity of 67.35 mg/g, while raw-clay only managed 47.62 mg/g. Pseudo second-order and Langmuir models were both good fits for the kinetic behavior and the isotherms. According to the Gibbs energy and other thermodynamic parameters, OG adsorption onto PANI@Clay and raw clay was a spontaneous process that became more energy-intensive as temperature was raised. Overall, the results of this work show that PANI@Clay offers promising use as an adsorbent for cleaning water supplies of cationic dyes it explains the processes and thermodynamic features of OG adsorption, which were previously unknown onto PANI@Clay and raw clay. The structure of the OG dye was optimized at the B3LYP functional with 6-311+g(d,p) set in aqueous solution. The global and local chemical reactivity descriptors were calculated to suggest a suitable mechanism for removal process.
... However, when we tried to confirm it by running the 1 H NMR spectrum at an elevated temperature, the ratio of the doubled signals changed to 1:1 when the temperature reached 390 • K, and the ratio remained unchanged after lowering the temperature back to room temperature, suggesting that the doubling in the spectra is a result of the epimerization of a chiral center of one of the amino acids in 1. Application of Marfey's method [15] coupled with HR ESI LCMS established the absolute configuration of the amino acids as L-NMeAla, L-Hty, L-Phe, L-Val, D-Lys, and 1:1 D,L-Tyr ( Figure S11). We suspect that the tyrosine epimerization occurs due to the easy keto/enol tautomerism of the hydantoin moiety during the compound separation [16]. Based on these arguments, structure 1 was proposed for hydantoanabaenopeptin A. Scheme 1. Proposed mechanism of the migration process of the ureido carbonyl in the mass spectrometer. ...
Anabaenopeptins are common metabolites of cyanobacteria. In the course of reisolation of the known aeruginosins KT608A and KT608B for bioassay studies, we noticed the presence of some unknown anabaenopeptins in the extract of a Microcystis cell mass collected during the 2016 spring bloom event in Lake Kinneret, Israel. The 1H NMR spectra of some of these compounds presented a significant difference in the appearance of the ureido bridge protons, and their molecular masses did not match any one of the 152 known anabaenopeptins. Analyses of the 1D and 2D NMR, HRMS, and MS/MS spectra of the new compounds revealed their structures as the hydantoin derivatives of anabaenopeptins A, B, F, and 1[Dht]-anabaenopeptin A and oscillamide Y (1, 2, 3, 6, and 4, respectively) and a new anabaenopeptin, 1[Dht]-anabaenopeptin A (5). The known anabaenopeptins A, B, and F and oscillamide Y (7, 8, 9, and 10, respectively) were present in the extract as well. We propose that 1-4 and 6 are the possible missing intermediates in the previously proposed partial biosynthesis route to the anabaenopeptins. Compounds 1-6 were tested for inhibition of the serine proteases trypsin and chymotrypsin and found inactive at a final concentration of ca. 54 μM.
... Simultaneously, most of the azo dyes are tautomeric or potentially tautomeric [2][3][4][5] . The tautomerism phenomenon, which plays a significant role in the stability and the color of the dyes, has been extensive studied during the last decades [6][7][8][9][10][11] . The intramolecular 1,3-proton transfer process, which is very fast at the NMR time scale, occurs by the migration of a proton from the amino nitrogen atom to the carbonyl oxygen atom. ...
Geometries of the 3-methyl-1-phenyl-4-(phenyldiazenyl)-1H-pyrazol-5-amine azo-dye compound and its tautomer were optimized using B3LYP and M06-2X functionals in coupling with TZVP and 6–311 + G(d,p) basis sets. The ¹H- and ¹³C-NMR chemical shifts of all species were predicted using 13 density functional theory (DFT) approaches in coupling with TZVP and 6–311 + G(d,p) basis sets at the different optimized geometries by applying the using GIAO method using the eight geometries. The selected functionals are characterized by having different amount of Hartree–Fock exchange. The selected DFT methods were B3LYP, M06-2X, BP86, B97XD, TPSSTPSS, PBE1PBE, CAM-B3LYP, wB97XD, LSDA, HSEH1PBE, PW91PW91, LC-WPBE, and B3PW91. The results obtained were compared with the available experimental data using different statistical descriptors such as root mean square error (RMSE) and maximum absolute error (MAE). Results revealed that the prediction of the ¹H-NMR chemical shifts has more significant dependence on the applied geometry than that of the prediction of the ¹³C-NMR chemical shifts. Among all the examined functionals, B97D and TPSSTPSS functionals were found to be the most accurate ones, while the M06-2X functional is the least accurate one. Results also revealed that the prediction of NMR chemical shifts using TZVP basis sets results is more accurate results than 6–311 + G(2d,p) basis set.
... Shabanian et al. [6] studied the tautomerism of hydantoin and they used the B3LYP/6-31G(d,p) method to optimise its five tautomers (tautomers 1-5 in Scheme. 1) in the gas phase as well as implicit solvation in water. Similar research was conducted on the eight tautomers of hydantoin using the B3LYP/6-311+G(d,p) and B3LYP/6-311++G(3df,2p) methods which were compared to experimental literature [14,15]. Faris and Safi [14] also studied four possible transition states (TSs) linking the tautomers 1, 3, 6 and 7 in the gas phase and two TSs in implicit water. ...
... Similar research was conducted on the eight tautomers of hydantoin using the B3LYP/6-311+G(d,p) and B3LYP/6-311++G(3df,2p) methods which were compared to experimental literature [14,15]. Faris and Safi [14] also studied four possible transition states (TSs) linking the tautomers 1, 3, 6 and 7 in the gas phase and two TSs in implicit water. Renoud et al. [2] investigated the ability of the tautomers of hydantoin to interconvert at a temperature of 393 K using the B3LYP/6-311++G(d,p) method. ...
... The stabilisation of hydantoin by implicit water and ethanol can be interpreted by considering the dipole moment which is gathered in Table. 1. Gas phase and implicit water dipole moments are comparable with literature [14]. It can be observed that the dipole moment for hydantoin is higher in water than in ethanol than in the gas phase. ...
Hydantoin exhibits tautomerism and the interconversion among the tautomers was studied using theoretical methods in the gas phase and solvents (water or ethanol). The implicit solvation as well as one explicit solvent molecule with water or ethanol were investigated. The functional used was B3LYP-D3(BJ) and the basis set for all atoms was aug-cc-pVTZ. The results indicate that the electronic energy barriers in the gas phase and implicit solvation are in the range 50-90 kcal mol⁻¹. However, explicit water is found to have a catalytic effect as the electronic energy barriers are lowered to 18-30 kcal mol⁻¹. Explicit ethanol lowers the electronic energy barriers further by about 2 kcal mol⁻¹. This study should be beneficial for the rational design and experiments involving hydantoin and water or ethanol as solvents.
... Because of their high value in chemistry as well as in living systems [7], tautomerism interconversions have been intensively investigated by chemists during the last centuries [8][9][10]. Most interconversions between individual species occur by movement of a hydrogen atom (prototropy), as in a simple keto-enol conversion [11][12][13][14], enamine-imine conversion [15,16], azo-hydrazo tautomerism [17][18][19], and many other systems [20]. In addition to the physical and chemical factors that affect prototropic tautomerism, it was shown that the relative stability of the tautomeric forms can be determined by solute-solvent interactions [15,[21][22][23]. ...
DFT at the B3LYP/6-311++G(d,p) level of theory was performed to geometrically, thermodynamically, and kinetically investigate the tautomerism process of 2-aminobenzothiazole (ABT) with n water molecules (n = 1–3) and without water in the gas phase and in different solvents with a gradual increase in their dielectric constants. The geometries of the envisaged tautomers were optimized in the gas phase and in solution with the polarized continuum model (PCM). Equilibrium and rate constants for the forward and reverse intra-/intermolecular isolated and water-assisted tautomerism reactions were also calculated. The results suggest that the activation energy of the transition state of direct proton transfer in the isolated reaction is very high and that the rate constant is very slow (~ 10⁻²⁴ s), reflecting that the reaction is thermodynamically unfavored, whereas the barrier differences between the transition states of the tautomers decrease gradually as the number of water molecules increases from one to three. Moreover, the rate constants of the proposed reactions are ~ 10²³–10²⁵ faster than those of the isolated reaction, and the water-assisted tautomerism paths can be performed quickly, especially with the assistance of two molecules of water.
... B3LYP is still the most popular DFT method, with plenty of applications. Among others, this functional has been used recently (with almost the same as employed in this study 6-311+G** basis set) to study the tautomerism of the rhodanine molecule [28]. The structural optimisations were followed by the frequency calculations in order to confirm the minimum nature of the calculated geometries. ...
We present the synthesis and structure determination for two thiohydantoin compounds (5-benzylidene-2-sulfanylideneimidazolidin-4-one and 5-cinnamylidene-2-sulfanylideneimidazolidin-4-one), proposed as potential novel fungicides. The exact chemical structure of these molecules has not yet been determined since they can potentially exist in several tautomeric and geometric forms (Z-E isomerism). The geometries of all the theoretically possible structures of the studied compounds were optimised. The calculations were performed at the density functional theory level using the B3LYP functional and the 6-311++G** basis set. Based on our calculations, the most probable structures of the studied compounds were proposed. The theoretical predictions were verified by comparing the calculated IR as well as the ¹H and ¹³C NMR spectra with the experimental data. It was documented that both the studied compounds exist predominantly in the tautomeric structure, in which the movable hydrogen is connected to the nitrogen atom in the hydantoin ring. It has been experimentally proven that one of the studied compounds occurs only as a single structure, whereas the other one exists as a mixture of two geometric isomers.
In this chapter, we highlight the power of vibrational spectroscopy as central technique to investigate the structure and reactivity of two relevant families of nitrogen-containing heterocyclic molecules: hydantoins and mercaptoimidazoles. Infrared spectroscopy is used in connection with the matrix isolation technique to investigate the structures of the isolated molecules and their photochemistry, while both infrared and Raman spectroscopies, supplemented by thermodynamics, microscopy, and diffraction techniques, are used to investigate neat condensed phases of the compounds and transitions between these phases. The experimental studies are supported by extensive computational studies, which include several approaches for detailed analysis of the electron density.
Density functional theory (DFT) at the B3LYP-6-311(Formula presented.)G(3df,2p)//6-311(Formula presented.)G(d,p) level of theory in the gas phase and solution was performed to investigate the relative stabilities of all possible tautomers of 2-amino-2-oxazolin-4-one. Five different paths have been proposed to investigate the amino/oxo (Formula presented.) imino/oxo proton transfer (PT) process. These paths are direct, mono-, di- and tri-water-assisted and self-assistance (dimerization) PT process. A clear catalytic effect has been observed when the introduction of water molecules and self-dimerization are taken place. Furthermore, barrier energies, equilibrium constants and reaction rate constants of the PT process between amine/oxo and imine/oxo tautomers of the self-assistance and in the presence of one, two and three water-assisted molecules were calculated. The computed activation barriers in the presence of water molecules are about 35–45 kcal/mol lower than those in the isolated case. In addition, the effective rate of the T1 (Formula presented.) T2 processes were also recorded, compared and discussed. Finally, time-dependent–DFT (TD–DFT) was performed to determine the electronic absorption spectra of all species under probe. A reasonable agreement with the available experiments was also achieved.
