Activation Energy ΔG Research Articles

Experiment Meets Theory: Cope Rearrangements and Thermal E/Z Isomerisations of Terpenoid Hydrocarbons

AbstractSeveral terpenes are known that can undergo a Cope rearrangement. Prominent examples include germacrene A and hedycaryol that show a Cope rearrangement already slightly above room temperature. In the present study the Cope rearrangements of several terpenes and eventually co‐occurring thermal E/Z isomerisations were investigated experimentally for their minimum required temperatures and for their states of equilibrium. The experimental findings were supported by computational assessments of free activation energies (ΔG≠) as well as relative Gibbs free energies of the reactants (ΔG).

Real‐time dielectric monitoring of isothermal polymerization of methyl cyanoacetate and diethylene glycol dimethacrylate

AbstractDielectric spectroscopy (DS) was employed to monitor the isothermal polymerization processes of P(MCA‐DEGDMA) formed by the alternating copolymerization of methyl cyanoacetate (MCA) and diethylene glycol dimethacrylate (DEGDMA) at different temperatures in real time. P(MCA‐DEGDMA) is a polyether containing functional groups (O, CN, COOCH3) which can promote the transport of ions Li+, thereby having the potential to apply in polymer electrolytes. It is beneficial to investigate the effect of temperature and time on P(MCA‐DEGDMA) polymerization and choose a suitable synthesis strategy through dielectric monitoring. A time‐ and temperature‐dependent relaxation process induced by orientational polarization of the P(MCA‐DEGDMA) chain was observed over a frequency range from 10 kHz to 4 × 106 Hz. The time to reach polymerization equilibrium (tequ) and the dielectric conversion were determined through the time variations of the conductivity at low frequency (κl). The polymerization process shows the characteristic of “fast followed by slow,” and the tequ can be advanced by raising the polymerization temperature. In addition, by discussing the monitoring time dependence of relaxation time (τ) and permittivity (ε), it was concluded that the extent of polymerization (α) for P(MCA‐DEGDMA) at 40°C is the largest, and the optimal polymerization temperature is between 30 and 50°C. Furthermore, the free activation energy (ΔG), activation enthalpy (ΔH), and activation entropy (ΔS) of the relaxation process caused by the motion of the P(MCA‐DEGDMA) chain in three temperature ranges (10–20°C, 30–40°C, 50–60°C) were calculated by using Eyring's equation, from which the physical image of various structures and conformations of the P(MCA‐DEGDMA) chain during monitoring was proposed. Considering the effect of temperature on the generation and migration of free ions, and on the structure and conformation of the P(MCA‐DEGDMA) chain, some suggestions for the synthesis of P(MCA‐DEGDMA) are given: during the polymerization, the temperature is controlled at 10°C in the early stage and then gradually raised to 40°C, which may be beneficial to improving the extent of polymerization of P(MCA‐DEGDMA). Our work may be helpful to investigate the polymerization process of polyether obeying the same synthesis mechanism with P(MCA‐DEGDMA). It can be proven that DS is useful in detecting the inner information of the system changing over time through our work.

Molecular interactions between 2-methyltetrahydrofuran and alcohols: A combination of thermodynamic, spectroscopic and quantum chemistry studies

New data of density (ρ), viscosity (η), and speed of sound (u) have been determined at T = (288.15–303.15 K) and p = 93.2 kPa for the binary mixture of {2-methyltetrahydrofuran + ethanol, or + 1-propanol, or + 1-butanol, or + 1-pentanol} over the entire composition range. These results were used to calculate the excess molar volume (VmE), isentropic compressibility deviation (Δκs), viscosity deviation (Δη), and Gibbs excess activation energy (ΔG*E), which were correlated by a Redlich-Kister polynomial. For all systems studied, the values ​​of the deviation properties were negative, which probably indicates a predominance of structural and chemical effects over physical effects. Five viscosity models were employed to fit the viscosity data. The VmE data were also correlated by the Prigogine-Flory-Patterson Theory (PFP Theory) and the Peng-Robinson-Stryjek-Vera Equation of State (PRSV EOS). Furthermore, a Fourier Transform Infrared (FT-IR) spectroscopy study was performed to explain the hydrogen bonding interactions. Lastly, theoretical calculations using Density Functional Theory (DFT) at B3LYP-GD3(BJ)/6–311++G(3df,2p) level of theory were performed to understand the inter-interactions between the compounds present in the mixtures. The FT-IR and computational results were in good agreement with the experimental data.

Spectroscopic, thermal, and anticancer investigations of new cobalt(II) and nickel(II) triazine complexes

ABSTRACT. The condensation of thiosemicarbazide with oxazolidinone produced 5-benzylidene-3-(4-chloro-phenyl)-6-oxo-5,6-dihydro-1H-[1,2,4]triazine-2-carbothioic acid amide (HL1). Co(II) and Ni(II) ions were reacted with the HL1 ligand. Elemental analysis and molar conductivity, along with mass, 1H-NMR, IR, UV-Vis, and X-ray powder diffraction spectral examinations, were used to reveal the chemical structure of the synthesized complexes. The stoichiometry of the complexes was determined to be 1:2 (metallic: moiety) using analytical, spectroscopic, and thermal data. The thermal properties of the complexes were explored using thermogravimetric (TG-DTG/DTA) methods, as well as the decomposition stages. Several kinetic thermodynamic parameters such as free activation energy (ΔG*), activation enthalpy (ΔH*), activation entropy (ΔS*), pre-exponential factor (A), and the activation energy (E*) were estimated. Inhibitory effects towards colon carcinoma cells (HCT cell line), hepatocellular carcinoma (Hep G2 cell line), and breast carcinoma (MCF-7 cell line) were verified using various concentrations of the samples. A colorimetric method was used to determine the cell viability percent in comparison to doxorubicin drug as a control.
 
 KEY WORDS: 1,2,4-Triazines, Thiosemicarbazide, Thermogravimetric analysis, Non-electrolytes, Anticancer
 Bull. Chem. Soc. Ethiop. 2023, 37(5), 1151-1162. 
 DOI: https://dx.doi.org/10.4314/bcse.v37i5.8

Combined computational and experimental investigation on the Fenton reagent catalysed hydroxylation of benzene

BackgroundPhenol is one of the most important chemicals in industry, generally produced from benzene in cumene processes. Alternatively, the direct hydroxylation of benzene catalysed by Fenton reagent has been a potentially sustainable process for the production of phenol. MethodsComputational calculation method combined with experiments were both employed to investigate the Fenton reagent catalysed hydroxylation of benzene. Significant findingsComputational calculation turned out that the H migration National Institutes of Health (NIH) shift in the benzene hydroxylation reaction including intramolecular immigration and an intermolecular process. The activation energy (ΔG) for the H migration between IM2 molecules was 17.5 kcal mol−1, while the ΔG for the intramolecular H transfer was 49.4 kcal mol−1. The crucial intermediates in the direct hydroxylation reaction were characterised by a variety of analysis methods. There were three types of C-C bonds in IM1 with Mayer bond order (MBO) equivalent to 1.272, 1.581, and 1.041 respectively, and the C-C bonds in IM2 were not equal based on the localised orbitals and orbital composition analysis and a series of electronic structure information. Moreover, the global electron delocalisation analysis visually demonstrated an uneven distribution of π electron, revealing the aromaticity of these two intermediates. These two intermediates exhibited both aromaticity and antiaromaticity features under external magnetic conditions. Notably, the nuclear magnetic resonance results showed the existence of one of the prominent intermediates.

Dissolution of β-C2S Cement Clinker: Part 2 Atomistic Kinetic Monte Carlo (KMC) Upscaling Approach.

Cement clinkers containing mainly belite (β-C2S as a model crystal), replacing alite, offer a promising solution for the development of environmentally friendly solutions to reduce the high level of CO2 emissions in the production of Portland cement. However, the much lower reactivity of belite compared to alite limits the widespread use of belite cements. Therefore, this work presents a fundamental atomistic computational approach for comprehending and quantifying the mesoscopic forward dissolution rate of β-C2S, applied to two reactive crystal facets of (100) and (). For this, an atomistic kinetic Monte Carlo (KMC) upscaling approach for cement clinker was developed. It was based on the calculated activation energies (ΔG*) under far-from-equilibrium conditions obtained by a molecular dynamic simulation using the combined approach of ReaxFF and metadynamics, as described in the Part 1 paper in this Special Issue. Thus, the individual atomistic dissolution rates were used as input parameters for implementing the KMC upscaling approach coded in MATLAB to study the dissolution time and morphology changes at the mesoscopic scale. Four different cases and 21 event scenarios were considered for the dissolution of calcium atoms (Ca) and silicate monomers. For this purpose, the (100) and () facets of a β-C2S crystal were considered using periodic boundary conditions (PBCs). In order to demonstrate the statistical nature of the KMC approach, 40 numerical realizations were presented. The major findings showed a striking layer-by-layer dissolution mechanism in the case of an ideal crystal, where the total dissolution rate was limited by the much slower dissolution of the silicate monomer compared to Ca. The introduction of crystal defects, namely cutting the edges at two crystal boundaries, increased the overall average dissolution rate by a factor of 519.

Computer Simulation of Electron Transfer between the Cytochrome Active Center and Reactive Oxygen and Nitrogen Species

In this work, computer simulation at the level of density functional theory is carried out using the PBE functional and bases of the def2- group. The characteristics of the electron transfer reaction according to the Marcus theory from the bioradicals O2-, NO, and NO- to the active center of cytochrome c are calculated. The values of the activation energy ΔG≠, the overlapping matrix element of the donor and acceptor HDA molecular orbitals, the frequency transfer factor ket , and the second-order transfer rate constant k are obtained. The numerical values of k for three radicals make it possible to draw a conclusion about the efficiency of their neutralization by interaction with the active center of the enzyme. For instance, for superoxide ion O2- k=6.32·105 М-1-с-1 at a distance of 5.02 Å, for nitrogen monoxide NO k=6.96·106 М-1-с-1 at a distance of 5.60 Å and oxoazanide ion NO- k=4.45·101 М-1-с-1 at distances of 5.60 Å and 4.45 Å. The transfer distances are obtained from the potential energy curves when the radical approaches the iron ion. The obtained values allow us to conclude that the iron ion in the heme protein environment is the most effective in deactivating the superoxide ion and nitrogen monoxide.

NMR spectroscopic and theoretical study on the isomerism of dimethyl benzodiazepine(diylidene)diacetates.

The isomerism of dimethyl 2,2'-(7,8-dichloro-1H-benzo[b][1,4]diazepine-2,4-(3H,5H)diylidene)diacetate (1a) and dimethyl 2,2'-(7,8-dichloro-3-methyl-1H-benzo[b][1,4]diazepine-2,4-(3H,5H)diylidene)diacetate (1b) was investigated by 1 H, 13 C and 15 N nuclear magnetic resonance (NMR) spectroscopy. In CDCl3 solution, inversion of the diazepine ring was observed, whereas in (D6 )DMSO and (D7 )DMF solution, besides the ring inversion, a partial cleavage of one chelate ring appeared connected with (E/Z) isomerization about one of the exocyclic C=C bonds. Gibbs free energies (ΔG) and free activation energies (ΔG≠ ) were calculated based on B3PW91-SCRF/ZVP DFT computations. Agreement between NMR data and density functional theory (DFT) computations was found.

Dissolution of Portlandite in Pure Water: Part 2 Atomistic Kinetic Monte Carlo (KMC) Approach.

Portlandite, as a most soluble cement hydration reaction product, affects mechanical and durability properties of cementitious materials. In the present work, an atomistic kinetic Monte Carlo (KMC) upscaling approach is implemented in MATLAB code in order to investigate the dissolution time and morphology changes of a hexagonal platelet portlandite crystal. First, the atomistic rate constants of individual Ca dissolution events are computed by a transition state theory equation based on inputs of the computed activation energies (ΔG*) obtained through the metadynamics computational method (Part 1 of paper). Four different facets (100 or , 010 or 00, or , and 001 or 00) are considered, resulting in a total of 16 different atomistic event scenarios. Results of the upscaled KMC simulations demonstrate that dissolution process initially takes place from edges, sides, and facets of 010 or 00 of the crystal morphology. The steady-state dissolution rate for the most reactive facets (010 or 0) was computed to be 1.0443 mol/(s cm2); however, 0.0032 mol/(s cm2) for or , 2.672 × 10−7 mol/(s cm2) for 001 or 00, and 0.31 × 10−16 mol/(s cm2) for 100 or were represented in a decreasing order for less reactive facets. Obtained upscaled dissolution rates between each facet resulted in a huge (16 orders of magnitude) difference, reflecting the importance of crystallographic orientation of the exposed facets.

The Role of Zinc Ion in the Active Site of Copper-Zinc Superoxide Dismutase

The interaction of the superoxide radical ion O2– with the active site of Cu, Zn-superoxide dismutase is stud-ied by computer simulation using the ORCA software package version 5.0.2 at the level of density functional theory using the PBE functional and the basis sets of functions def2-SVP, def2-SVPD and def2-TZVPD. The main characteristics for two processes of electron transfer in the catalytic cycle of radical ion deactivation are obtained: reaction potential ΔG0, total reorganization energy λtot, activation energy ΔG≠, overlap matrix ele-ment HDA, and transfer rate constant k according to Marcus. The variable factor in the modeling is the pres-ence of the Zn2+ ion at the active site of the enzyme. Two variants of the electron transfer mechanism are con-sidered: one carried out through ligands and another occurring in the immediate vicinity of an oxygen-containing particle and a copper ion. It has been established that the presence of the Zn2+ ion contributes to a large extent only to the second electron transfer from the Cu+ ion to the protonated form of the radical ion, to the hydroperoxide radical HO2. Other things being equal, the zinc ion increases the electron transfer rate con-stant by five times through specific interactions.

Nitrogen transfer mechanism research on the co- pyrolysis macroalgae with polyethylene

This study unveiled the effect of co-pyrolysis and nitrogen transformation characteristics of macroalgae (Enteromorpha prolifera (EP)) and waste plastics (polyethylene) by using Py-GC/MS experiment and density functional theory (DFT). The possible reaction pathways were designed by using composition and pyrolysis intermediates of EP including amino acids and cyclic acylamide as model compounds, respectively. Subsequently, the mechanism of nitrogen transformation during the pyrolysis of EP and the synergistic mechanism of co-pyrolysis with polyethylene (PE) were revealed by DFT. Py-GC/MS results showed that the nitrogen-containing products of EP pyrolysis were mainly Sarcosine, Imidazole, and (2E)-3-(2-Amino-1H-imidazol-5-yl) acrylic acid, and the co-pyrolysis products were urea and cadaverine. Co-pyrolysis is beneficial to decreased the species and quantities of N-containing compounds, and the relative content of nitrogen-containing compounds decreased from 7.91% to 3.53%. The DFT results also verified the rationality of each possible pathway using the quantum chemistry calculation and through analysis of the activation energy (ΔG*), the reaction heat (ΔG) and the reaction enthalpy change (ΔH). This study confirmed that there is a synergistic effect in the co-pyrolysis process of EP and PE in which the hydrogen radicals provided by PE can reduce the reaction energy barrier and then promote the mechanism of nitrogen during the pyrolysis process.

Efficient synergistic chemical fixation of CO2 by simple metal-free organocatalysts: Mechanistic and kinetic insights

BackgroundCarbon dioxide is a versatile, non-toxic, and renewable C1 building block source to produce valuable chemicals such as cyclic carbonates. The purpose of this research is development of efficient, metal-free and affordable catalysts for cycloaddition reaction of CO2 with epoxides at mild conditions. MethodsIn the present work, a group of novel bifunctional organocatalysts consisting of different hydrogen-bond donors (HBDs) and halogen ion is simply synthesized. Under the optimized conditions, the reaction is kinetically and thermodynamically studied. Additionally, the catalytic active species are determined, and a mechanism is proposed with the help of electrospray‐ionization time‐of‐flight mass spectrometry (ESI-TOF MS). Significant findingsThe most active catalytic system is obtained by chemically interaction of 3-bromopropionic acid (BPA) with DMF at 80 °C (BPA-DMF). An excellent product yield of 98% and a high TOF value are obtained with 0.99 mol% of BPA-DMF, which is attributed to the synergistic effects of carboxyl functional groups and halide ions. The activation energy was found to be 50.75 kJ/mol. The positive value of Gibbs free activation energy (ΔG‡) and negative value of activation entropy (ΔS‡) confirm a non-spontaneous, endergonic and kinetically controlled reaction.

Oxidative stability of pomegranate seed oil from blanched and microwave pretreated seeds: Kinetic and thermodynamic studies under accelerated conditions

This work aimed to evaluate the effects of blanching and microwave heating of pomegranate seed on the oxidative stability and shelf-life of ultrasound-assisted and ethanol extracted oil. Pomegranate seeds (cv. Herskawitz) were independently blanched at 95℃ for 3 min and microwave heated at 261 W for 102 s. The oil samples were subjected to accelerated oxidation (30, 40, and 50℃) to evaluate lipid oxidation kinetics, thermodynamics parameters, and estimate the shelf-life. The Arrhenius model and activated complex theory were used to estimate the energy for activation (Ea), enthalpy (ΔH‡), entropy (ΔS‡), and Gibbs-free energy (ΔG‡), which varied from 6.2 to 8.59 kJ/mol, 3.69 to 6.38 kJ/mol, −146.62 to −155.06 J/K mol−1, and 48.13 to 64.74 kJ/mol, respectively. According to the thermodynamics parameters, the lipid oxidation reactions in all oil samples were non-spontaneous, endothermic, and endergonic. Based on the developed Arrhenius models, blanching of pomegranate seed increased the oil shelf-life at 25℃ from 21 to 24 days, whilst microwave pretreatment did not change the oil shelf-life. Practical applications Seed pretreatment is a novel approach that could be used to enhance the oil antioxidant properties. This study has established that the blanching of seeds is beneficial in enhancing the storability and shelf life of pomegranate seed oil (PSO). In addition, the study has demonstrated that antioxidant compounds and fatty acid composition are indispensable factors in PSO oxidation. The findings are useful in the design and establishment of PSO packaging, storage conditions, and application of modern technologies such as encapsulation to maximize its storability and retain the health-promoting properties.

Microwave-assisted heterogeneous esterification of dibutyl maleate: Optimization using response surface methodology

Microwave-assisted synthesis of dibutyl maleate was carried out with heterogeneous catalyst, Amberlyst-15. Effect of process parameters such as mole ratio, reaction temperature, catalyst loading, and molecular sieves on the conversion was reported using Response Surface Methodology (RSM). Reaction conversion of 62.6% was achieved at optimum parameters of 1:3 acid to alcohol mole ratio, 5.5% (w/w) catalyst loading, 70°C temperature, and 6% (w/w) molecular sieves for reaction time of 60 min. The optimum parameters based on RSM were 1:3.14 acid to alcohol mole ratio, catalyst loading 5.35% (w/w), 77.19°C, and 64.77% predicted conversion. Pseudo- Homogeneous (PH), Eley Rideal (ER), and Langmuir Hinshelwood Hougen Watson (LHHW) models were used to fit experimental kinetic data. Studies revealed that the Eley-Rideal model suited the experimental data. The activation energy of the esterification reaction was calculated as 10.17 kJ/mol. Gibbs free activation energy (ΔG‡), enthalpy of activation (ΔH‡), and entropy of activation (ΔS‡) were evaluated.

Correlation between Kinetics and Thermodynamics for Excited-State Intramolecular Proton Transfer Reactions.

Finding the relation between thermodynamics and kinetics for a reaction is of fundamental importance. Here, the thermodynamics and kinetics correlation of excited-state intramolecular proton transfer (ESIPT) was investigated by the TD-DFT calculation under the CAM-B3LYP/6-311+G** level. We choose the family 2-(2'-aminophyenyl)benzothiazole and its amino derivatives as paradigms, which all possess the NH-type intramolecular hydrogen bond (H-bond), and investigate the corresponding ESIPT reaction. The H-bond strength can be systematically tuned, so both activation energy ΔG‡ and free energy difference between proton transfer tautomer (T*, product) and normal species (N*, reactant) ΔGT*-N* can be varied. To minimize the environmental interference such as solvent external H-bond and polarity perturbation, a nonpolar solvent such as cyclohexane is chosen as a bath with a polarizable continuum solvation model for the calculation. As a result, the comprehensive computational approach reveals a linear relationship between ΔGT*-N* and ΔG‡, which can be expressed as ΔG‡ = ΔG0 + αΔGT*-N*. The fundamental insight is reminiscent of the Bell-Evans-Polanyi (BEP) principle where α represents the character of the position of the transition state along the proton motion coordinate. In other words, the more exergonic the ESIPT reaction is, the faster the proton transfer rate can be observed. To verify that such a correlation is not a sporadic event, another ESIPT family with an -OH proton, 1-hydroxy-11H-benzo[b]fluoren-11-one and its derivatives, was also investigated and proved to follow the BEP principle as well. Unlike the quantum mechanics description of proton transfer where either proton tunneling is dominant or solute/solvent is coupled in ESIPT, this work demonstrates that reaction kinetics and thermodynamics are strongly correlated within the same class of ESIPT molecules with an intrinsic barrier free from solvent perturbation, being faster with the more exergonic reaction.

Radical Mechanism of Ir III /Ni II -Metallaphotoredox-Catalyzed C(sp 3 )–H Functionalization Triggered by Proton-Coupled Electron Transfer: Theoretical Insight

Photoredox catalysis can be induced to activate organic substrates or to modulate the oxidation state of transition-metal catalysts via unique single-electron transfer processes, so as to achieve c...

Computer-aided design of 1,4-naphthoquinone-based inhibitors targeting cruzain and rhodesain cysteine proteases

Chagas disease and Human African Trypanosomiasis (HAT) are caused by Trypanosoma cruzi and T. brucei parasites, respectively. Cruzain (CRZ) and Rhodesain (RhD) are cysteine proteases that share 70% of identity and play vital functions in these parasites. These macromolecules represent promising targets for designing new inhibitors. In this context, 26 CRZ and 5 RhD 3D-structures were evaluated by molecular redocking to identify the most accurate one to be utilized as a target. Posteriorly, a virtual screening of a library containing 120 small natural and nature-based compounds was performed on both of them. In total, 14 naphthoquinone-based analogs were identified, synthesized, and biologically evaluated. In total, five compounds were active against RhD, being three of them also active on CRZ. A derivative of 1,4-naphthoquinonepyridin-2-ylsulfonamide was found to be the most active molecule, exhibiting IC50 values of 6.3 and 1.8 µM for CRZ and RhD, respectively. Dynamic simulations at 100 ns demonstrated good stability and do not alter the targets’ structures. MM-PBSA calculations revealed that it presents a higher affinity for RhD (-25.3 Kcal mol−1) than CRZ, in which van der Waals interactions were more relevant. A mechanistic hypothesis (via C3-Michael-addition reaction) involving a covalent mode of inhibition for this compound towards RhD was investigated by covalent molecular docking and DFT B3LYP/6–31 + G* calculations, exhibiting a low activation energy (ΔG‡) and providing a stable product (ΔG), with values of 7.78 and − 39.72 Kcal mol−1, respectively; similar to data found in the literature. Nevertheless, a reversibility assay by dilution revealed that JN-11 is a time-dependent and reversible inhibitor. Finally, this study applies modern computer-aided techniques to identify promising inhibitors from a well-known chemical class of natural products. Then, this work could inspire other future studies in the field, being useful for designing potent naphthoquinones as RhD inhibitors.

Theoretical Characterizations of TADF Materials: Roles of ΔG and the Singlet-Triplet Excited States Interconversion.

The thermally activated delayed fluorescence (TADF) phenomenon has attracted increasing attention because it can harvest 100% of the electro-pumped carriers to form singlet bound excited state for fluorescence. It is generally believed that the small energy gap between S1 and T1 (ΔEST) is essential for TADF to facilitate the reverse intersystem crossing (rISC). However, for a few donor-acceptor (D-A) organic compounds with small ΔEST, the TADF phenomenon is absent, indicating that ΔEST might not be a good molecular descriptor. Here, using our self-developed thermal vibration correlation function (TVCF) formalism in combination with quantum chemistry calculations, we revisit the key factors that dominate the TADF property for 11 D-A systems with small ΔEST. Based on our theoretical results in comparison to experiments, we conclude that the activation energy ΔG is a good molecular descriptor to characterize the TADF performance because a significantly better linear relationship is observed between ΔG and the rISC rate constant (krISC) compared to that between ΔEST and krISC. These findings provide deeper understanding of the TADF mechanism, shedding light on the molecular design of high-performance TADF materials.

Carbo[n]helicenes Restricted to Enantiomerize: An Insight into the Design Process of Configurationally Stable Functional Chiral PAHs.

The most important stereodynamic feature of carbo[n]helicenes is the interconversion of their enantiomers. The Gibbs activation energy (ΔG ≠(T)) of this process, which determines the rate of enantiomerization, dictates the configurational stability of [n]helicenes. High values of ΔG ≠(T) are required for applications of functional chiral molecules incorporating [n]helicenes or helicene substructures. This minireview provides an overview of the mechanism, recent developments, and factors affecting the enantiomerization of [n]helicenes, which will accelerate the design process of configurationally stable functional chiral molecules based on helicene substructures. Additionally, this minireview addresses the misconception and irregularities in the recent literature on how the terms “racemization” and “enantiomerization” are used as well as how the activation parameters are calculated for [n]helicenes and related compounds.

Crystal Structure and Theoretical Investigation of Thiobarbituric Acid Derivatives as Nonlinear Optical (NLO) Materials

Here we report on the crystal structure of three enamine/imine TBA derivatives (1–3). Since the derivatives can take the form of enamine or imine tautomers, theoretical calculations were made to confirm that the former predominates due to higher stability (thermodynamic calculations). The enamines’ form was further corroborated by high activation energy (ΔG≠; which is >60 kcal/mol in all the cases), thus requiring a large amount of energy to pass the barrier (kinetics calculations). Furthermore, 1–3 were found to show high static hyperpolarizability (βtot), thereby making them potential candidates as nonlinear materials for electro-optical devices and crystal engineering.