First-Principles Study of the Dispersion Effects in the Structures and Keto-Enol Tautomerization of Curcumin.

Noncovalent interactions, such as dispersion, play a significant role in the stability of flexible molecules, such as curcumin. This study revealed the importance of dispersion correction in the structure and keto-enol tautomerization of curcumin, which has rarely been addressed in computational studies. We rigorously constructed all possible unique curcumin conformers in the enol and keto forms within the first-principles framework. Regardless of the different environments, we carefully explained the agreement between the computational geometry (in the gas phase) and the experimental measurement (in the polymorph) by using dispersion correction. The calculation results for the aqueous solution of conformational abundance, thermochemistry, and reaction kinetics support the experimental observations after considering the dispersion correction. The study also suggests a water-catalyzed mechanism for keto-enol tautomerization, where dispersion correction plays a role in decreasing the energy barrier and making the keto form thermochemically and kinetically favorable. Our results could be helpful in future computational studies to find a method for increasing the aqueous solubility of curcumin; hence, the potential of curcumin as a multifunctional medicine can be fully achieved.

Investigating the role of utilitarian and hedonic goals in characterizing customer loyalty in E-marketplaces.

Despite significant growth in sales in recent years, retaining customers remains a major challenge for the electronic marketplace (e-marketplace) industry worldwide, including Indonesia. The small basket size of Indonesian customers has created a highly price-sensitive market, making it difficult to nurture customer loyalty. This study investigates the factors affecting consumer behavior and loyalty in Indonesian e-marketplaces by employing a newly proposed E-Marketplace Customer Loyalty Model. Since customers' expectations have extended from mostly utilitarian-oriented goals to incorporate hedonic goals, the proposed model includes both utilitarian and hedonic-based constructs by integrating the Expectation-Confirmation Theory, e-service quality, and the Hedonic Information Systems Model. The proposed model was tested using a comparative approach of machine learning classification algorithms and partial least square, aiming to create a more robust model. The PLS analytical results of ECLM hiearchical component model from 678 customers show that the fulfillment of hedonic values via perceived enjoyment has a greater impact on customer satisfaction than utilitarian values of perceived service quality. Perceived enjoyment, personalization, and customer satisfaction positively affect customer loyalty. The classification results provide further evidence for all hypothesized relationships of the ECLM. The Sequential Minimal Optimization (SMO) algorithm has demonstrated superior performance compared with other classifiers in predicting the dependent variable in most cases. Based on findings, this study offers theoretical and practical implications, and recommendations for sustainable loyalty programs in e-marketplaces.

Impact of Hydrogen Coverage Trend on Methyl Formate Adsorption on MoS2 Surface: A First Principles Study.

Adsorbates coverage plays a crucial role in a catalysis reaction. In hydrodeoxygenation (HDO), which involves high hydrogen pressure, hydrogen coverage on the surface may affect the adsorption of other adsorbates. The HDO is used in green diesel technology to produce clean and renewable energy from organic compounds. This motivates us to study the hydrogen coverage effect on methyl formate adsorption on MoS2 as a model case of the actual HDO. We calculate the methyl formate adsorption energy as a function of hydrogen coverage using density functional theory (DFT) and then comprehensively analyze the physical origin of the results. We find that methyl formate can have several adsorption modes on the surface. The increased hydrogen coverage can stabilize or destabilize these adsorption modes. However, finally, it leads to convergence at high hydrogen coverage. We extrapolated the trend further and concluded that some adsorption modes might not exist at high hydrogen coverage, while others remain.

The significance of long-range correction to the hydroperoxyl radical-scavenging reaction of trans-resveratrol and gnetin C.

Density functional theory has been gaining popularity for studying the radical scavenging activity of antioxidants. However, only a few studies investigate the importance of calculation methods on the radical-scavenging reactions. In this study, we examined the significance of (i) the long-range correction on the coulombic interaction and (ii) the London dispersion correction to the hydroperoxyl radical-scavenging reaction of trans-resveratrol and gnetin C. We employed B3LYP, CAM-B3LYP, M06-2X exchange-correlation functionals and B3LYP with the D3 version of Grimme's dispersion in the calculations. The results showed that long-range correction on the coulombic interaction had a significant effect on the increase of reaction and activation energies. The increase was in line with the change of hydroperoxyl radical's orientation in the transition state structure. Meanwhile, the London dispersion correction only had a minor effect on the transition state structure, reaction energy and activation energy. Overall, long-range correction on the coulombic interaction had a significant impact on the radical-scavenging reaction.

Teaching reaction kinetics through isomerization cases with the basis of density-functional calculations.

The fundamental mechanism of biochemistry lies on the reaction kinetics, which is determined by the reaction pathways. Interestingly, the reaction pathway is a challenging concept for undergraduate students. Experimentally, it is difficult to observe, and theoretically, it requires some degree of physics knowledge, namely statistical and quantum mechanics. However, students can utilize computational methods to study the reaction kinetics without paying too much attention but not wholly neglecting the comprehension of physics. We hereby provided an approach to study the reaction kinetics based on density-functional calculations. We particularized the study of the isomerization case involving five molecules at three different temperatures and emphasized the importance of the transition state in the study of reaction kinetics. The results we presented were in good agreement with the experiments and provided useful insights to assist students in the application of their knowledge into their research.

A Density-Functional Study of the Conformational Preference of Acetylcholine in the Neutral Hydrolysis.

Acetylcholine, which is associated with Alzheimer's disease, is widely known to have conformers. The preference of each conformer to undergo neutral hydrolysis is yet to be considered. In this study, we employed density-functional calculations to build the conformers and investigated their preference in one-step neutral hydrolysis. The results showed the preference in ten possible hydrolysis pathways involving seven acetylcholine conformers (reactant), four transition state structures, and two choline conformers (product). Three out of the seven acetylcholine conformers predicted from the results confirmed experimental findings on the conformers stability. We suggested that two out of ten possible pathways were observed in the experimental results based on agreement in reaction energy. Eventually, this study will emphasize the importance of considering acetylcholine conformers in its hydrolysis study.

The transition state conformational effect on the activation energy of ethyl acetate neutral hydrolysis.

We report a first-principles study on ethyl acetate neutral hydrolysis in which we focus on the activation energy variation resulting from the conformational effect in the transition state. We use the conformers of ethyl formate, ethyl acetate, ethyl fluoroacetate, and ethyl chloroacetate as the ester models and one water molecule with a one-step reaction mechanism. We also consider the long-range interaction and the surrounding water in the form of PCM. Our results show that the various conformers yield a significant range of activation energy. Moreover, the gauche conformer has lower activation energy than the trans conformer. The activation energy in its own right is lowered by the halogen atoms. Finally, we remark that the long-range correction and PCM stabilize the transition state geometry but raise the activation energy.

First principles study of oxygen molecule interaction with the graphitic active sites of a boron-doped pyrolyzed Fe-N-C catalyst.

We study the adsorption and the dissociation of O2 molecules on the active sites of a boron-doped pyrolyzed Fe-N-C catalyst using density functional theory. Initially, we determine the possible structure of the FeN4 active site of the pyrolyzed Fe-N-C catalyst doped with a boron atom by considering the presence of a nitrogen atom as a metal-free site. The most stable configuration of the structure occurs when the boron and nitrogen atoms coalesce with the FeN4 site forming a complex site. This structure has higher stability compared to the undoped FeN4 site. The doped FeN4 possesses the unique ability to adsorb an oxygen molecule in a side-on mode due to the presence of the boron-nitrogen pair acting as a supporting site. One O atom of the O2 molecule sticks strongly to the top of the iron atom, while the other binds with the boron atom. This O2 side-on adsorption stretches the O-O bond length by 15%. Furthermore, the examined catalyst surface can dissociate the oxygen molecule easily with only half the energy barrier of the undoped FeN4 structure.