Daengngern, Rathawat

Preferred name

Alternative Name

Daengngern, R.

Main Affiliation

School of Science

rathawat.da@kmitl.ac.th

Now showing 1 - 10 of 33

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Oxotitanium-porphyrin for selective catalytic reduction of NO by NH3: A theoretical mechanism study
(2018-01-01)
Daengngern, Rathawat
;
Maitarad, Phornphimon
;
Shi, Liyi
;
Zhang, Dengsong
;
Kungwan, Nawee
The reaction mechanism of the selective catalytic reduction of NO by NH<inf>3</inf> (NH<inf>3</inf>-SCR) on an oxotitanium-porphyrin catalyst was systematically investigated by using density functional theory calculations with the M06L functional. The reaction was proposed to follow the nitrite mechanism over the two forms of active sites; the oxotitanium-porphyrin Lewis acid site (TiO-por) and the Brønsted acid site (TiOH-por). The reaction path consisted of (i) nitrite formation, (ii) NH<inf>3</inf> oxidation, (iii) formation of NH<inf>2</inf>NO and NHNOH intermediates, and (iv) N<inf>2</inf> and H<inf>2</inf>O product formation. The obtained calculations showed that the formation of the NHNOH intermediate was the rate determining step for both active sites with the energy barriers (E<inf>a</inf>) of 32.2 and 36.2 kcal mol-1 for the Lewis and Brønsted acid sites, respectively. It is worth noting that the activation energy for NHNOH formation over the oxotitanium-porphyrin active sites was found to be in the same range as that of vanadium oxide cluster models. Furthermore, the product formations of N<inf>2</inf> and H<inf>2</inf>O over the Lewis and Brønsted acid sites of oxotitanium-porphyrin were exothermic processes with reaction energies (E<inf>r</inf>) of -67.1 and -39.0 kcal mol-1, respectively. Thus, in conclusion, the oxotitanium-porphyrin could theoretically act as an alternative catalyst for NH<inf>3</inf>-SCR of NO and it would be challenging to test it in experimental studies.
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Nitric Oxide Decomposition via Selective Catalytic Reduction by Ammonia on a Transition-Metal Cluster of W2TcO6
(2022-06-23)
Daengngern, Rathawat
;
Kaewprasong, Kittikorn
Decomposition of nitric oxide (NO) gas on a reactive transition-metal cluster of W<inf>2</inf>TcO<inf>6</inf>has been examined and investigated via selective catalytic reduction by ammonia (NH<inf>3</inf>-SCR) using the M06-L density functional method. The transition-metal cluster of W<inf>2</inf>TcO<inf>6</inf>can be employed to transform NO to N<inf>2</inf>gas efficiently over an active site of tungsten (W). A reaction mechanism of NO conversion based on the NH<inf>3</inf>-SCR process has been elucidated by a potential energy surface along the reaction pathways. The reaction pathways of this NH<inf>3</inf>-SCR process begin with adsorption of NH<inf>3</inf>, adsorption of NO to the cluster, formation of nitrosamine (NH<inf>2</inf>NO) and NHNO/NHNOH intermediates, and rearrangement of NHNO/NHNOH to obtain N<inf>2</inf>and H<inf>2</inf>O, respectively. Notably, a significant NH<inf>2</inf>NO as a key intermediate, namely, "nitrosamine", must be formed before further steps can take place in the generation of N<inf>2</inf>from NO, followed by the involvement of the NHNO or NHNOH intermediate. From our calculated results, the NHNO intermediate via TS3a is found in pathway a, while NHNOH is found in pathway b via TS3b. Pathway b has a lower energy barrier of 35.1 kcal/mol than pathway a with an energy barrier of 41.8 kcal/mol, indicating that pathway b should be more energetically favorable. The step for NHNO intermediate rearrangement is a rate-determining step for the reaction occurring through pathway a, which is found to be more difficult in accordance with a difficult N-H bond cleavage to form the NNOH intermediate before N<inf>2</inf>formation. The overall reaction is an exothermic process with thermodynamic and kinetic favors. Thus, this bimetallic W<inf>2</inf>TcO<inf>6</inf>cluster could be used as a promising and active catalyst for NO decomposition via the NH<inf>3</inf>-SCR process to an eco-friendly gas, that is, N<inf>2</inf>
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A spectroscopic study of indigo dye in aqueous solution: A combined experimental and TD-DFT study
(2018-12-01)
Jiwalak, Naparat
;
Daengngern, Rathawat
;
Rungrotmongkol, Thanyada
;
Jungsuttiwong, Siriporn
;
Namuangruk, Supawadee
This study reports UV–Visible spectra and electronic structures of indigo (IG) in aqueous solution using a combination of experimental and theoretical methods. In the visible region, the experimental absorption spectrum of the solution showed a broad peak with the longest wavelength of maximal absorption (λ<inf>max</inf>) value at 708 nm. For the theoretical method, a trans-IG monomer and a trans-IG bound with two water molecules (IG.2W) were optimized in the ground state using the B3LYP and B3LYP-D3 calculations with the 6-31 + G(d,p) basis set and the SCRF-CPCM model for taking solvent effect into account was also applied. Sequentially, the UV–Visible spectra and λ<inf>max</inf> of the optimized trans-IG and IG.2W models in the implicit water were simulated by the time-dependent density functional theory (TD-DFT) calculations. The TD-DFT methods including BLYP, B3LYP, PBE0, CAM-B3LYP, M06-2X, ωB97XD, LC-BLYP, and LC-ωPBE functionals without and with the D3 correction and the 6-31 + G(d,p) basis set were selected. The results pointed out that BLYP and BLYP-D3 were the best methods because they could reproduce the experimental λ<inf>max</inf> value of IG in aqueous solution. The predicted λ<inf>max</inf> values of IG.2W were almost equal to 708 nm (the experimental data), indicating that IG.2W could be responsible for optical properties of IG.
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Theoretical Insights on Solvent Control of Intramolecular and Intermolecular Proton Transfer of 2-(2′-Hydroxyphenyl)benzimidazole
(2017-08-10)
Prommin, Chanatkran
;
Kanlayakan, Narissa
;
Chansen, Warinthon
;
Salaeh, Rusrina
;
Kerdpol, Khanittha
Excited-state proton transfer (ESPT) processes of 2-(2′-hydroxyphenyl)benzimidazole (HBI) and its complexation with protic solvents (H<inf>2</inf>O, CH<inf>3</inf>OH, and NH<inf>3</inf>) have been investigated by both static calculations and dynamics simulations using density functional theory (DFT) at B3LYP/TZVP theoretical level for ground state (S<inf>0</inf>) and time-dependent (TD)-DFT at TD-B3LYP/TZVP for excited state (S<inf>1</inf>). For static calculations, absorption and emission spectra, infrared (IR) vibrational spectra of O-H mode, frontier molecular orbitals (MOs), and potential energy curves (PECs) of proton transfer coordinate were analyzed. Simulated absorption and emission spectra show an agreement with available experimental data. The hydrogen bond strengthening in the S<inf>1</inf> state has been proved by the changes of IR vibrational spectra and bond parameters of the hydrogen moiety with those of the S<inf>0</inf> state. The MOs provide the visual electron density redistribution confirming the hydrogen bond strengthening mechanism. The PECs show that the proton transfer (PT) process is easier to occur in the S<inf>1</inf> state than the S<inf>0</inf> state. Moreover, on-the-fly dynamics simulations of all systems were carried out to provide the detailed information on time revolution. The results revealed that the excited-state intermolecular proton transfer for HBI is fast, whereas the excited-state intermolecular proton transfer for HBI with protic solvents are slower than that of HBI because the competition between intra- and intermolecular hydrogen-bonds between HBI and protic solvent. These intermolecular hydrogen-bonds hinder the formation of tautomer, hence explaining the low quantum yield found in the protic solvent experiment. Especially for HBI complexing with methanol, only ESIntraPT occurs with small probability compared to HBI with water and ammonia.
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Theoretical study on influence of geometry controlling over the excited-state intramolecular proton transfer of 10-hydroxybenzo[h]quinoline and its derivatives
(2017-08-01)
Chansen, Warinthon
;
Salaeh, Rusrina
;
Prommin, Chanatkran
;
Kerdpol, Khanittha
;
Daengngern, Rathawat
A structural modification on quinoline as a proton donor of 10-hydroxybenzo[h]quinoline (HBQ) giving different HBQ derivatives greatly affects their photophysical properties. In this study, the excited-state intramolecular proton transfer (ESIPT) reactions of HBQ and its derivatives with different geometries have been systematically investigated using DFT and TD-DFT at B3LYP/TZVP. Calculated absorption and emission spectra are used to describe the photophysical changes in which the absorption spectra of HBQ derivatives are blue-shifted compared with that of HBQ while their emission spectra are blue-shifted except those of 3,4-dihydro indene[1,2-b]pyrrole-8-ol (IPRO) and 2-(4H-pyrrol-2-yl)phenol (PRP) compounds with different proton donor and connecting moiety are red-shifted. From results of potential energy curves along the proton transfer (PT) coordinate, PT is favorable in the excited-state but not in the ground state. On-the-fly dynamics simulations in the excited-state are further employed to determine reaction mechanisms and the time evolution of PT. The ESIPT process easily occurs in most of the compounds except the IPRO with much high PT barrier. The ESIPT times in most compounds take place within 100 fs and PT probability is nicely anti-correlated with the PT barrier. Thus, the geometry changes alter the electronic spectra but do not affect ESIPT of HBQ derivatives. Moreover, once the PT is complete, the internal conversion is initiated by twisted skeleton, leading to lower intensity of tautomer emission.
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Unlocking efficient CO2–to–methanol conversion on frustrated Lewis pair-functionalized UiO–67: A synergistic approach using DFT and SISSO
(2025-10-01)
Yodsin, Nuttapon
;
Pimbaotham, Pimjai
;
Maihom, Thana
;
Daengngern, Rathawat
;
Tachikawa, Masanori
Metal–organic framework-based catalysts demonstrate considerable promise for converting CO<inf>2</inf> into valuable chemicals, particularly when combined with Frustrated Lewis Pairs (FLPs) to enhance H<inf>2</inf> dissociation during hydrogenation reactions. This study employs density functional theory (DFT) calculations to investigate modified UiO–67 frameworks wherein FLPs are introduced via eight different functional groups (UiO–67–X) into the organic linker to facilitate H<inf>2</inf> activation during CO<inf>2</inf> hydrogenation to methanol (CH<inf>3</inf>OH). The reaction proceeds through three stages: (i) hydrogenation of CO<inf>2</inf> to formic acid (HCOOH), (ii) conversion of HCOOH to formaldehyde (HCHO), and (iii) hydrogenation of HCHO to CH<inf>3</inf>OH. This study specifically focuses on steps (ii) and (iii), analyzing the detailed reaction mechanisms using optimized molecular structures and Gibbs free energy calculations to acquire insights into methanol formation on UiO–67–X. During HCOOH conversion to HCHO, adsorbed H<inf>2</inf> undergoes heterolytic cleavage at the FLP sites, producing a proton (H+) and a hydride (H−) for subsequent HCOOH hydrogenation and dehydration. The energy barriers identified at this stage represent key kinetic limitations hindering efficient CO<inf>2</inf>-to-methanol conversion. Similarly, HCHO conversion to CH<inf>3</inf>OH proceeds via H<inf>2</inf> dissociation, followed by concerted H+/H− transfer. Among the tested UiO–67–X catalysts, UiO–67–B(CH<inf>3</inf>)<inf>2</inf> exhibits the highest catalytic activity for CO<inf>2</inf> hydrogenation to methanol. Kinetic analyses are performed to assess reaction rates across a relevant temperature range, highlighting the notable influence of functional groups on catalytic performance. Additionally, the Sure Independence Screening and Sparsifying Operator (SISSO) machine-learning approach is used to identify optimal physical descriptors and derive a predictive model for the energetic span (δG), considerably lowering the computational cost associated with full reaction pathway calculations. Statistical validation confirms the robustness of these predictions. Overall, these findings underscore the vital role of FLP-assisted H<inf>2</inf> dissociation in promoting CO<inf>2</inf> hydrogenation to CH<inf>3</inf>OH, with UiO–67–B(CH<inf>3</inf>)<inf>2</inf> serving as a promising catalyst.
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Proton exchange of carbonic acid and methylamine complex accelerated by a single-water molecule via intermolecular hydrogen bonding: A theoretical investigation
(2024-06-01)
Panbo, Pakuna
;
Payaka, Apirak
;
Salaeh, Rusrina
;
Daengngern, Rathawat
A theoretical investigation of the microsolvation effect on proton exchange (PE) between carbonic acid and methylamine (CA-MTA) has been explored by quantum dynamics simulations. The structural, energy, and dynamic properties of the CA-MTA complex with and without an explicit water molecule are elucidated at the molecular level. The reactions from this study have been clarified into different types: single-step PE (SSPE) and stepwise PE (SWPE). Without the water molecule, the SSPE mechanism is hardly found but observable with a low probability of 0.2. In particular, the water molecule interacting through intermolecular hydrogen-bonded network between CA and MTA in CA-MTA-W<inf>in</inf> could affect PE by showing both SSPE and SWPE mechanisms. In addition, the existing water molecule plays the significant role in shortening intermolecular hydrogen bonding interactions within the complex resulting in increasing the probability of PE up to 0.92 especially in CA-MTA-W<inf>out</inf>. Hence, one water molecule could be used to provide reliable results to represent the significant activity that occurs for the proton exchangeability of the CA and MTA complex.
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Ultrasonic-driven synthesis of Cu-chlorophyllin-stabilized silver nanoparticles for high-efficiency antimicrobial surgical suture coatings
(2025-12-01)
Sombutjiraporn, Saran
;
Mathaweesansurn, Arjnarong
;
Daengngern, Rathawat
;
Detsri, Ekarat
A novel Cu-chlorophyllin-stabilized silver nanoparticle (Ag0<inf>NPs</inf>-Chl<inf>Cu</inf>) with potent antimicrobial properties was synthesized for the first time using an ultrasonically driven chemical reduction approach. In this approach, Cu-chlorophyllin (Chl<inf>Cu</inf>) acts as a stabilizing ligand, while sodium borohydride functions as the chemical reductant. The formation mechanism of Ag0-NPs<inf>CHL</inf> was elucidated, revealing that ultrasonic irradiation facilitates the in situ reduction of Ag (I) and its subsequent incorporation into the Chl<inf>Cu</inf> complex. Four pyrrole rings coordinate with Ag0<inf>NPs</inf> through four nitrogen atoms, which serve as adsorption sites for the anchorage of Ag0-NPs<inf>CHL</inf>. Characterization by XPS revealed the presence of Ag-N bonding involving pyrrole units on the FCC structure of Ag0<inf>NPs</inf>. Ag0<inf>NPs</inf>-Chl<inf>Cu</inf> demonstrated a zeta potential of (-) 35.57±3.54 mV with a spherical shape and an average size of 6.72±1.72 nm, resulting in a stable colloidal dispersion with a monodispersed index. The synthesized Ag0-NPs<inf>CHL</inf> nanocomposites were subsequently deposited onto polyamide surgical sutures via an electrostatic Layer-by-Layer (LbL) self-assembly technique. The coated sutures exhibited >99.9 % antibacterial efficiency against E. coli (ATCC25922), S. aureus (ATCC25923), and A. baumanii (ATCC19606). While nanoparticle accumulation was observed in human primary epidermal keratinocyte (HEKa) cells, no cytotoxic effects were detected in the epidermis. This study highlights the effectiveness of Chl<inf>Cu</inf> as a dual stabilizing and coordinating agent for Ag⁰<inf>NPs</inf>, offering a promising approach for developing antimicrobial surgical materials.
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The synergy of CHEF and ICT toward fluorescence ‘turn-on’ probes based on push-pull benzothiazoles for selective detection of Cu2+ in acetonitrile/water mixture
(2021-06-15)
Nootem, Jukkrit
;
Daengngern, Rathawat
;
Sattayanon, Chanchai
;
Wattanathana, Worawat
;
Wannapaiboon, Suttipong
New push-pull schiff base ligands based on benzothiazole (BZ) unit were developed for the selective detection of Cu2+ through fluorescence ‘turn-on’ mechanism. These derivatives with electron withdrawing trifluoromethyl (-CF<inf>3</inf>) and cyano (-CN) substituents (BZ2 and BZ3) demonstrated a prominent fluorescence enhancement upon copper ion binding which could be the results from the synergistic effect between the chelation-enhanced fluorescence (CHEF) and the intramolecular charge transfer (ICT) processes. In addition, these compounds displayed 1:1 binding with Cu2+ with low limits of detection of 0.77 μM and 0.64 μM for BZ2 and BZ3, respectively, in acetonitrile-water (3:1 v/v) media. The electronic and photophysical properties of these BZ ligands and the copper ion complexes were modelled by the density functional theory (DFT) and the time-dependent density functional theory (TD-DFT) calculations, respectively. Analysis of X-ray absorption spectra probed at Cu K-edge of Cu2+-BZ mixtures revealed the complex formation of BZ ligands with the targeted Cu2+ and confirmed the non-centrosymetric structures of the complexes as predicted by the DFT calculation. The electron density distributions of the HOMO-LUMOs in the computational results as well as large stokes shifts of the ligand-metal complexes in the experimental data confirmed the strong ICT effect after Cu2+ binding which is a key process promoting fluorescence ‘turn-on’ mechanism.
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Tautomeric enhancement of 2-(1H-pyrazol-5-yl)pyridine in photoinduced proton transfer by water-assisted molecules
(2024-09-20)
Salaeh, Rusrina
;
Inporn, Wutthana
;
Chansen, Warinthon
;
Kungwan, Nawee
;
Daengngern, Rathawat
Theoretical insight of excited state proton transfer (ESPT) in 2-(1H-pyrazol-5-yl)pyridine abbreviated as PPP interacting with water wires: PPP(H<inf>2</inf>O)<inf>n</inf> where n = 1–3 has been presented in both static and dynamics studies. Explicit water molecules placed around PPP have been simulated to elucidate the intermolecular hydrogen bonding interactions between them. Hydrogen bond strengthening in the excited state (S<inf>1</inf>) has been verified by shorter bond distances and redshift of IR vibrational spectra involving the proton transfer (PT) process. Furthermore, on-the-fly excited state dynamics simulations of all complexes have been performed to provide detailed information on the PT mechanism. The dynamic results show that one water molecule added to the neighboring PPP as an intermolecular hydrogen bonding bridge can promote double excited state intermolecular proton transfer up to 36% compared with its intrinsic intramolecular hydrogen bond of the PPP system. Meanwhile adding a second or third water molecule could decrease the probabilities of PT. Especially in PPP(H<inf>2</inf>O)<inf>3</inf>, a rearrangement of water molecules is observed that PT occurs via one water molecule. Hence, the models with explicit water molecules interacting with PPP as intermolecular hydrogen bonding bridge are a great representative role played by water molecules of the PT process at the molecular level.

Daengngern, Rathawat

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