Deprotonation Site Research Articles

Customizing Ionic Liquids Functionalized MOFs Composites with Hydrophobic Interface for Electrochemical CO2 Reduction.

The electrochemical carbon dioxide reduction reaction (CO2RR) to generate feedstocks for chemical products (e.g., carbon monoxide, CO) offers a highly attractive method for achieving the closure of the carbon cycle. Ionic liquids (ILs)-functionalized Cu-based catalyst Cu2O-HKUST-1/IL1/PTFE was developed, configuring metal-organic frameworks(MOFs) based materials with high adsorption and multiple active sites. The modified electrocatalysts exhibited high specific surface area, strong CO2 adsorption capacity, abundant active sites, and fast charge transfer rate. The nucleophilic active site of deprotonation at the C2 site in imidazole ILs further improved the selectivity of proton migration and CO product generation, which was verified through DFT calculations for the low Gibbs free energy of the generated intermediate interactions. In addition, the hydrophobic interface constructed by PTFE facilitated the inhibition of the hydrogen evolution reaction (HER) and significantly improved the efficiency of CO2 electroreduction. The Cu2O-HKUST-1/IL1/PTFE catalyst manifested a high C1 Faraday efficiency (FE) up to 96.5% and in particular 92.7% for FECO at -1.7 V vs RHE. The present work provides an efficient strategy for configuring ILs-functionalized MOFs-based materials with good hydrophobic interfaces to enhance the efficiency of CO2 electroreduction to C1 products.

A Comprehensive Computational Study on the Thermodynamics and Kinetics of Tetrahydrobiopterin Regeneration Process.

One of the most crucial enzymatic cofactors in the human body is tetrahydrobiopterin, which is acquired through biological synthesis and self-regeneration. During this regenerative process, it undergoes oxidation, deprotonation, further oxidation, and subsequent deprotonation, resulting in the formation of quinonoid-dihydrobiopterin, which then undergoes tautomerization to yield dihydrobiopterin. This study presents the thermodynamic and kinetic properties associated with each stage of the regeneration process using theoretical calculations. The redox potentials for oxidation steps and the pKa values for deprotonation steps are determined employing the Born-Haber cycle and the direct change of free energy in implicit solvent models. The redox metabolites are characterized and confirmed from their calculated absorption spectra using the time-dependent density functional theory method. For the tautomerization steps, an IRC calculation is executed, and rate constants are computed using Eyring's Transition State Theory (TST). The tunnelling probability of the H atom during the tautomerization process is incorporated using Wigner's tunnelling correction in the calculation of the rate constant. Notably, we identify the N3 atom as the most probable deprotonation site for H3B+ and predict its geometry based on our calculations. Furthermore, we elucidate the spectral properties of intermediates involved in the regeneration process, highlighting key electronic transitions responsible for their excitations. Our results indicate that each step of tautomerization occurs along vibrational bending modes. We have observed that these tautomerization processes have high activation energies by optimising transition states. Additionally, considering tunnelling correction can significantly affect the reaction rates associated with these processes. These results provide a comprehensive understanding of the thermodynamics and kinetics of the regeneration process of tetrahydrobiopterin, which will help in the modulation of its biological activity.

Synthesis and cytotoxicity of copper(II) semicarbazone complexes with lipophilic counter-anions

A series of (2,4-dihydroxybenzaldehyde dibenzyl semicarbazone) perfluoroalkyl carboxylato copper(II) complexes, [CF3(CF2)nCO2(LH)Cu] (LH2 = 2,4-dihydroxybenzaldehyde dibenzyl semicarbazone; n = 0, 2, 4, 6; 1–4), and (2,4-dihydroxybenzaldehyde dibenzyl semicarbazone) pyridine copper(II) perfluoroalkyl carboxylates, [(LH)(py)Cu]+[CF3(CF2)nCO2]− (5–8) were synthesized. The lipophilicity of these compounds was determined by reverse-phase thin layer chromatography and correlated with their cytotoxicity towards MOLT-4 human leukaemia cells. Cytotoxicity is more strongly correlated with lipophilicity for the non-ionic compounds (1–4) than for the ionic compounds (5–8). Compounds 5–8 (IC50 2.8–3.8 μM) are generally more cytotoxic than compounds 1–4 (IC50 3.6–8.4 μM). They also exhibit slightly higher cytotoxicity than the parent anticancer compound [(LH)(py)Cu]+[NO3]− (IC50 4.15 μM), suggesting that it is possible to enhance the cytotoxicity of [(LH)(py)Cu]+[NO3]− by replacing nitrate with anions of higher lipophilicity. Attempts to synthesize the non-fluorinated analogue [(LH)(py)Cu]+[CH3CO2]− resulted in the formation of the deprotonated complex [L(py)Cu], whose structure was confirmed by X-ray crystallography. The structural parameters indicate that the deprotonation site is the hydrazonic nitrogen of the semicarbazone ligand.

CREST-A program for the exploration of low-energy molecular chemical space.

Conformer-rotamer sampling tool (CREST) is an open-source program for the efficient and automated exploration of molecular chemical space. Originally developed in Pracht et al. [Phys. Chem. Chem. Phys. 22, 7169 (2020)] as an automated driver for calculations at the extended tight-binding level (xTB), it offers a variety of molecular- and metadynamics simulations, geometry optimization, and molecular structure analysis capabilities. Implemented algorithms include automated procedures for conformational sampling, explicit solvation studies, the calculation of absolute molecular entropy, and the identification of molecular protonation and deprotonation sites. Calculations are set up to run concurrently, providing efficient single-node parallelization. CREST is designed to require minimal user input and comes with an implementation of the GFNn-xTB Hamiltonians and the GFN-FF force-field. Furthermore, interfaces to any quantum chemistry and force-field software can easily be created. In this article, we present recent developments in the CREST code and show a selection of applications for the most important features of the program. An important novelty is the refactored calculation backend, which provides significant speed-up for sampling of small or medium-sized drug molecules and allows for more sophisticated setups, for example, quantum mechanics/molecular mechanics and minimum energy crossing point calculations.

Liquid-jet photoemission spectroscopy as a structural tool: site-specific acid-base chemistry of vitamin C.

Liquid-jet photoemission spectroscopy (LJ-PES) directly probes the electronic structure of solutes and solvents. It also emerges as a novel tool to explore chemical structure in aqueous solutions, yet the scope of the approach has to be examined. Here, we present a pH-dependent liquid-jet photoelectron spectroscopic investigation of ascorbic acid (vitamin C). We combine core-level photoelectron spectroscopy and ab initio calculations, allowing us to site-specifically explore the acid-base chemistry of the biomolecule. For the first time, we demonstrate the capability of the method to simultaneously assign two deprotonation sites within the molecule. We show that a large change in chemical shift appears even for atoms distant several bonds from the chemically modified group. Furthermore, we present a highly efficient and accurate computational protocol based on a single structure using the maximum-overlap method for modeling core-level photoelectron spectra in aqueous environments. This work poses a broader question: to what extent can LJ-PES complement established structural techniques such as nuclear magnetic resonance? Answering this question is highly relevant in view of the large number of incorrect molecular structures published.

SYNTHESIS, CHARACTERIZATION OF NEW ASYMMETRICALLY IMIDAZOLIUM SALTS WITH THEIR Ag(I) AND Pd(II)-N-HETEROCYCLIC CARBENE COMPLEXES

New substituted asymmetrically imidazolium salts with Ag(I) and Pd(II) N-heterocyclic carbene complexes were synthesized and characterized. In order to produce asymmetrically substituted salts, imidazolium salts have been produced using a variety of substituents, including aliphatic chain and phenyl acetamide chloride (5,6,7). Using the carbene site deprotonation process, silver(I)-NHC complexes (8,9,10) were produced from the reaction of asymmetrically substituted imidazolium salts with Ag2O. The appropriate Pd(II)-NHC (11,12,13) were then synthesized using the transmetallation process using Ag(I)-complexes. NHC as transfer reagents. The complexes were identified using spectroscopy methods such as 1H-, 13C-NMR and FT-IR spectroscopy. The recorded spectra of the prepared complexes and their salts agree with theoretical ones.

Chlorophyll and pheophytin protonated and deprotonated ions: Observation and theory.

Pheophytin a and chlorophyll a have been investigated by electrospray mass spectrometry in the positive and negative modes, in view of the importance of the knowledge of their properties in photosynthesis. Pheophytin and chlorophyll are both observed intensely in the protonated mode, and their main fragmentation route is the loss of their phytyl chain. Pheophytin is observed intact in the negative mode, while under collisions, it is primarily cleaved beyond the phytyl chain and loses the attaching propionate group. Chlorophyll is not detected in normal conditions in the negative mode, but addition of methanol solvent molecule is detected. Fragmentation of this adduct primarily forms a product (-30amu) that dissociates into dephytyllated deprotonated chlorophyll. Semi-empirical molecular dynamics calculations show that the phytyl chain is unfolded from the chlorin cycle in pheophytin a and folded in chlorophyll a. Density functional theory calculations have been conducted to locate the charges on protonated and deprotonated pheophytin a and chlorophyll a and have found the major location sites that are notably more stable in energy by more than 0.5eV than the others. The deprotonation site is found identical for pheophytin a and the chlorophyll a-methanol adduct. This is in line with experiment and calculation locating the addition of methanol on a double bond of deprotonated chlorophyll a.

Effect of Glycone Diversity on the Interaction of Triterpenoid Saponins and Lipid Bilayers.

Triterpenoid saponins are organic compounds widely available in the plant kingdom. These molecules have received extensive attention due to their antibacterial activity against both Gram-negative and Gram-positive bacteria. Recent studies identified the antibacterial activity of saponins closely relates to their interaction with bacterial membrane lipids; however, molecular details of this interaction remain unclear. Increased understanding of the mechanisms to disrupt bacterial lipid bilayers can help to mitigate development of antibiotic resistance. Here, we examined the effect of chemical structure and deprotonation states of saponin on its interaction with a bacterial membrane model using molecular dynamics simulations. We run multiple simulations with a ternary lipid mixture of POPE/POPG/DPPG (80/15/5 mol %) and different saponin molecules. While all saponin structures can permanently bind the membrane, their location and orientation inside the bilayer depend on the sugar chains attached to their backbone. Similarly, cluster formation and stability also depend on the chemical structure of the saponin molecule. Deprotonation site affects interactions with the bilayer by modulating hydrophilicity of the molecules. At the low concentrations simulated in this work, there is no statistically significant change in the membrane properties upon saponin(s) binding, but the molecules do preferentially partition to POPE lipid environment.

Solvation effects on glyphosate protonation and deprotonation states evaluated by mass spectrometry and explicit solvation simulations.

Glyphosate is a widely used herbicide, and its protonation and deprotonation sites are fundamental to understanding its properties. In this work, the sodiated, protonated, and deprotonated glyphosate were evaluated in the gas phase by infrared multiple photon dissociation spectroscopy to determine the exact nature of these coordination, protonation, and deprotonation states in the gas phase. In this context, Natural Bond Orbital analyses were carried out to unravel interactions that govern glyphosate (de)protonation states in the gas phase. The solvent effect on the protonation/deprotonation equilibria was also investigated by implicit (Solvation Model Based on Density and polarizable continuum models) and explicit solvation models (Monte Carlo and Molecular Dynamics simulations). These results show that glyphosate is protonated in the phosphonate group in the gas phase because of the strong hydrogen bond between the carboxylic oxygen (O7) and the protonated phosphonate group (O8-H19), while the most stable species in water is protonated at the amino group because of the preferential interaction of the NH2 + group and the solvent water molecules. Similarly, deprotonated glyphosate [Glyp-H]- was shown to be deprotonated at the phosphonate group in the gas phase but not in solution, also because of the preferential solvation of the NH2 + group present in the other deprotomers. Therefore, these results show that the stabilization of the protonated amino group by the solvent molecules is the governing factor of the (de)protonation equilibrium of glyphosate in water.

Calculation of Mass Spectra with the QCxMS Method for Negatively and Multiply Charged Molecules.

Analysis and validation of a mass spectrometry (MS) experiment are usually performed by comparison to reference spectra. However, if references are missing, measured spectra cannot be properly matched. To close this gap, the Quantum Chemical Mass Spectrometry (QCxMS) program has been developed. It enables fully automatic calculations of electron ionization (EI) and positive ion collision-induced dissociation (CID) mass spectra of singly charged molecular ions. In this work, the extension to negative and multiple ion charge for the CID run mode is presented. QCxMS is now capable of calculating structures carrying any charge, without the need for pretabulated fragmentation pathways or machine learning of database spectra. Mass spectra of four single negatively charged and two multiple positively charged organic ions with molecular sizes from 12 to 92 atoms were computed and compared to reference spectra. The underlying Born-Oppenheimer molecular dynamics (MD) calculations were conducted using the semiempirical quantum mechanical GFN2-xTB method, while for some small molecules, ab initio DFT-based MD simulations were performed. Detailed insights into the fragmentation pathways were gained, and the effects of the computed charge assignments on the resulting spectrum are discussed. Especially for the negative ion mode, the influence of the deprotonation site to create the anion was found to be substantial. Doubly charged fragments could successfully be calculated fully automatically for the first time, while higher charged structures introduced severe assignment problems. Overall, this extension of the QCxMS program further enhances its applicability and underlines its value as a sophisticated toolkit for CID-based tandem MS structure elucidation.

Release of Electrons and Protons from Substrate Water Molecules at the Oxygen-Evolving Complex in Photosystem II

Oxygen evolution proceeds at the oxygen-evolving complex (OEC), the Mn4CaO5 cluster, in photosystem II (PSII), releasing protons and electrons from substrate water molecules. However, most mechanisms proposed for oxygen evolution is based on theoretical studies, where the deprotonation and oxidation sites of the Mn4CaO5 cluster are pre-assumed without analyzing the redox active site (e.g., redox potential) or the H-bond (e.g., pKa) for the release of the electrons or protons, respectively. Here, we summarize the characteristics of the OEC, focusing on the energetics of the electron-releasing and proton-releasing sites based on the PSII structure.

High Versatility of IPP and DMAPP Methyltransferases Enables Synthesis of C6 , C7 and C8 Terpenoid Building Blocks.

The natural substance class of terpenoids covers an extremely wide range of different structures, although their building block repertoire is limited to the C5 compounds DMAPP and IPP. This study aims at the characterization of methyltransferases (MTases) that modify these terpene precursors and the demonstration of their suitability for biotechnological purposes. All seven enzymes tested accepted IPP as substrate and altogether five C6 compounds and six C7 compounds were formed within the reactions. A high selectivity for the deprotonation site as well as high stereoselectivity could be observed for most of the biocatalysts. Only the enzyme from Micromonospora humi also accepted DMAPP as substrate, converting it into (2R)‐2‐methyl‐IPP in vitro. In vivo studies demonstrated the production of a C8 compound and a hydride shift step within the MTase‐catalyzed reaction. Our study presents IPP/DMAPP MTases with very different catalytic properties, which provide biosynthetic access to many novel terpene‐derived structures.

Amphipolar, Amphiphilic 2,4-diarylpyrano[2,3-b]indoles as Turn-ON Luminophores in Acidic and Basic Media.

A versatile amphiphilic pyrano[2,3-b]indole for halochromic turn-ON luminescence in acidic or basic media is accessed by an insertion-coupling-cycloisomerization and adjusting solubilizing and phenolic functionalities. While almost non-emissive in neutral solutions, treatment with acids or bases like trifluoroacetic acid (TFA) or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) reveals distinct luminescence at wavelengths of 540 nm or 630 nm in propan-2-ol, respectively. Turn-ON emission can be detected at pH values as mild as pH = 5.31 or 8.70. Quantum yields in propan-2-ol are substantial for protonated (Φf = 0.058) and deprotonated (Φf = 0.059) species. Photometrically, pKa1 of 3.5 and pKa2 of 10.5 were determined in propan-2-ol. With lipophilic polyether sidechains and hydrophilic protonation and deprotonation sites the molecule can be regarded as amphipolar, which results in good solubility properties for different organic solvents. In aqueous media, an organic co-solvent like propan-2-ol (35%) or tetrahydrofuran (25%) is needed, and the solution can be diluted with pure water without precipitation of the compound. At higher concentrations of water, a turbid solution is formed, which indicates the formation of micellar structures or clusters. With dynamic light scattering we could show that these clusters increase in size with increasing water content.

A conserved mechanism affecting hydride shifting and deprotonation in the synthesis of hopane triterpenes as compositions of wax in oat

Triterpenoids are biologically active metabolites synthesized from a common linear precursor catalyzed by 2,3-oxidosqualene cyclases (OSCs) to form diverse triterpenoid skeletons. OSCs corresponding to many discovered triterpene alcohols in nature have not been functionally and mechanistically characterized due to the diversity of chemical structures and complexity of the cyclization mechanism. We carried out a genome-wide investigation of OSCs from Avena strigosa and discovered two triterpene synthases, namely, AsHS1 and AsHS2, using a Nicotiana benthamiana expression system. These synthases produce hopenol B and hop-17(21)-en-3β-ol, which are components of surface wax in oat panicles and sheathes, respectively. We demonstrated that substitutions of two to three amino acid residues in AsHS1 with corresponding residues from AsHS2 allowed it to be completely converted into a hop-17(21)-en-3β-ol synthase. AsHS2 mutants with a substitution at site 410 could synthesize hopenol B alone or mixed with a side product isomotiol. The combined quantum mechanics and molecular mechanics calculation demonstrated that the side chain size of the residue at site 410 regulated the relative orientations between the hopyl C22 cation and Phe257, leading to a difference in deprotonation positions through providing or not providing cation–π interaction between the aromatic ring of F257 and the carbocation intermediate. A similar mechanism could be applied to a hopenol B synthase from a dicotyledonous plant Aquilegia. This study provided mechanistic insight into triterpenoid synthesis and discovered key amino acid residues acting on hydride transfer and a deprotonation site to differentiate between hopane-type scaffolds in diverse plant species.

Acid/base properties of α-methyl and gem-dimethyl derivatives of cysteine and serine from the extended kinetic method

The gas-phase proton affinities (PA) for the non-protein α-methyl cysteine (1), gem-dimethyl cysteine (penicillamine) (2), α-methyl serine (3) and 3-methylthreonine (4) have been determined using the extended kinetic method in an ESI-tandem mass spectrometer. Experimental proton affinities of 923.5 ± 9.8, 925 ± 8.5, 932.1 ± 10.1, and 924.5 ± 7.7 kJ/mol were determined for 1–4, respectively. Gas-phase enthalpies of deprotonation (ΔHacid) for 2, 3 and 4 were also determined experimentally to be 1380 ± 9 and 1379 ± 12 and 1378 ± 12 kJ/mol. Hybrid density functional theory calculations at the B3LYP/6–311++G(d,p)//B3LYP/6-31+G(d) level of theory give predictions for the proton affinities of 1–4 and ΔHacid for 2–4 that are in excellent agreement with the measured values. A computed ΔHacid for 1 of 1389 kJ/mol was also determined. Computed acidities for 2–4 were also determined and the agreement with the experimental acidity for 2 is excellent. The computed acidities for 3 and 4 are somewhat larger than the experimental acidities, but are within the experimental error limits, For 1 and 2, the preferred deprotonation site is the SH group on the side chain rather than the COOH group similar to other cysteine analogs that have previously been studied in our lab.

Complexation of Green and Red Kaede Fluorescent Protein Chromophores by a Zwitterion to Probe Electrostatic and Induction Field Effects.

The photophysics of green fluorescent protein (GFP) and red Kaede fluorescent protein (rKFP) are defined by the intrinsic properties of the light-absorbing chromophore and its interaction with the protein binding pocket. This work deploys photodissociation action spectroscopy to probe the absorption profiles for a series of synthetic GFP and rKFP chromophores as the bare anions and as complexes with the betaine zwitterion, which is assumed as a model for dipole microsolvation. Electronic structure calculations and energy decomposition analysis using Symmetry-Adapted Perturbation Theory are used to characterize gas-phase structures and complex cohesion forces. The calculations reveal a preponderance for coordination of betaine to the phenoxide deprotonation site predominantly through electrostatic forces. Calculations using the STEOM-DLPNO-CCSD method are able to reproduce absolute and relative vertical excitation energies for the bare anions and anion-betaine complexes. On the other hand, treatment of the betaine molecule with a point-charge model, in which the charges are computed from some common electron density population analysis schemes, show that just electrostatic and point-charge induction interactions are unable to account for the betaine-induced spectral shift. The present methodology could be applied to investigate cluster forces and optical properties in other gas-phase ion-zwitterion complexes.

Molecular Basis for the Remarkably Different Gas-Phase Behavior of Deprotonated Thyroid Hormones Triiodothyronine (T3) and Reverse Triiodothyronine (rT3): A Clue for Their Discrimination?

Thyroid hormones are biologically active small molecules responsible for growth and development regulation, basal metabolic rate, and lipid and carbohydrate metabolism. Liquid chromatography mass spectrometry (LC–MS) can be used to quantify thyroid hormones blood level with high speed and selectivity, aiming to improve the diagnosis and treatment of the severe pathological conditions in which they are implicated, i.e., hypo- and hyperthyroidism. In this work, the gas-phase behavior of the isomeric thyroid hormones triiodothyronine (T3) and reverse triiodothyronine (rT3) in their deprotonated form was studied at a molecular level using MS-based techniques. Previously reported collision-induced dissociation experiments yielded distinct spectra despite the high structural similarity of the two compounds, suggesting different charge sites to be responsible. Infrared multiple photon dissociation spectroscopy on [T3-H]− and [rT3-H]− was performed, and the results were interpreted using DFT and MP2 calculations, assessing the prevalence of T3 in the carboxylate form and rT3 as a phenolate isomer. The different deprotonation sites of the two isomers were also found to drive their ion-mobility behavior. In fact, [T3-H]− and [rT3-H]− were successfully separated. Drift times were correlated with collisional cross section values of 209 and 215 Å2 for [T3-H]− and [rT3-H]−, respectively. Calculations suggested the charge site to be the main parameter involved in the different mobilities of the two anions. Finally, bare [T3-H]− and [rT3-H]− were made to react with neutral acetylacetone and trifluoroacetic acid, confirming rT3 to be more acidic than T3 in agreement with the calculated gas-phase acidities of T3 and rT3 equal to 1345 and 1326 kJ mol–1, respectively.

Modeling and mutagenesis of amino acid residues critical for CO2 hydration by specialized NDH-1 complexes in cyanobacteria

The uptake of inorganic carbon in cyanobacteria is facilitated by an energetically intensive CO2-concentrating mechanism (CCM). This includes specialized Type-1 NDH complexes that function to couple photosynthetic redox energy to CO2 hydration forming the bicarbonate that accumulates to high cytoplasmic concentrations during the operation of the CCM, required for effective carbon fixation. Here we used a Synechococcus PCC7942 expression system to investigate the role of conserved histidine and cysteine residues in the CupB (also designated, ChpX) protein, which has been hypothesized to participate in a vectoral CO2 hydration reaction near the interface between CupB protein and the proton-pumping subunits of the NDH-1 complex. A homology model has been constructed and most of the targeted conserved residues are in the vicinity of a Zn ion modeled to form the catalytic site of deprotonation and CO2 hydration. Growth and CO2 uptake assays show that the most severe defects in activity among the targeted residues are due to a substitution of the predicted Zn ligand, CupB-His86. Mutations at other sites produced intermediate effects. Proteomic analysis revealed that some amino acid substitution mutations of CupB caused the induction of bicarbonate uptake proteins to a greater extent than complete deletion of CupB, despite growth under CO2-enriched conditions. The results are discussed in terms of hypotheses on the catalytic function of this unusual enzyme.

Action spectroscopy of the isolated red Kaede fluorescent protein chromophore.

Incorporation of fluorescent proteins into biochemical systems has revolutionized the field of bioimaging. In a bottom-up approach, understanding the photophysics of fluorescent proteins requires detailed investigations of the light-absorbing chromophore, which can be achieved by studying the chromophore in isolation. This paper reports a photodissociation action spectroscopy study on the deprotonated anion of the red Kaede fluorescent protein chromophore, demonstrating that at least three isomers-assigned to deprotomers-are generated in the gas phase. Deprotomer-selected action spectra are recorded over the S1 ← S0 band using an instrument with differential mobility spectrometry coupled with photodissociation spectroscopy. The spectrum for the principal phenoxide deprotomer spans the 480-660nm range with a maximum response at ≈610nm. The imidazolate deprotomer has a blue-shifted action spectrum with a maximum response at ≈545nm. The action spectra are consistent with excited state coupled-clustercalculations of excitation wavelengths for the deprotomers. A third gas-phase species with a distinct action spectrum is tentatively assigned to an imidazole tautomer of the principal phenoxide deprotomer. This study highlights the need for isomer-selective methods when studying the photophysics of biochromophores possessing several deprotonation sites.

A theoretical assessment of the structural and electronic features of some retrochalcones

AbstractIn the present work, six retrochalcones, namely echinatin, licochalcone A, B, C, D and E, have been studied using density functional theory at the B3LYP/6‐311++G** level. A comparative analysis of the non‐linear optical properties has been performed with two prototype standard molecules, urea and para‐nitroaniline. The computed first pKa values of all the deprotonation sites lie in the range of 8.9‐10.0, which suggests the predominance of the neutral form of the considered retrochalcones at the physiological pH. Further, the second pKa values of the hydroxyl groups of the mono‐anionic forms lie in the range of 10.0‐11.6 and the third pKa values for deprotonation from the dianionic forms of licochalcone B and D are ~17. Moreover, the electronic spectra, frontier molecular orbitals analysis and molecular electrostatic potential maps have been analyzed for a better understanding of the electro‐optical properties of the compounds under study.