Chui-Peng Kong

Enhanced fluoride adsorption using Al (III) modified calcium hydroxyapatite

Aluminum-modified hydroxyapatite (Al-HAP) was prepared and characterized using XRD and BET analyses. Al-HAP possessed higher defluoridation capacity (DC) of 32.57 mgF(-)/g than unmodified hydroxyapatite (HAP) which showed a DC of 16.38 mgF(-)/g. The effect of Al/Ca atomic ratio in Al-HAP, solution pH and co-existing anions was further studied. The results indicated that the adsorption data could be well described by the Langmuir isotherm model and the adsorption kinetic followed the pseudo-second-order model. The pH changes during the adsorption process suggested that the OH on the surface of Al-HAP was the adsorption sites. The more adsorption sites were formed on Al modified HAP, which possessed abundant surface hydroxyl groups, resulting in higher efficiency of F(-) removal. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated in order to understand the nature of adsorption process. The results revealed that the adsorption reaction was a spontaneous and endothermic process.

Design of D–A–π–A organic dyes with different acceptor and auxiliary acceptor for highly efficient dye-sensitized solar cells: a computational study

D–A–π–A dyes have exhibited several excellent advantages including optimized energy levels, and distinct improvement of photovoltaic performance and stability. By modulating the auxiliary acceptor and acceptor unit, the efficiency of D–A–π–A dye based dye-sensitized solar cells can be further improved. Based on density functional theory methods, sixteen dimethoxyl-substituted triphenylamine based D–A–π–A dyes composed of different acceptor and auxiliary acceptor groups were designed, meanwhile for reference four homologous D–π–A dyes were also compared in this work. The properties of all the dyes, including intramolecular charge transfer, light harvesting efficiency, kinetics of electron injection, and vertical dipole moment, have been investigated theoretically to identify the dyes which would produce high efficiency. Then the interaction between the selected dyes and the electron acceptor in the electrolyte was discussed to reveal the interfacial charge recombination process. In comparison with other dyes, TNA4 displays outstanding performance due to its key parameters to achieve a balance between competing factors. Compared with cyanoacrylic acid, 2-(1,1-dicyanomethylene) rhodanine group can serve as an excellent acceptor for future DSSCs applications.

Theoretical investigation of the adsorption, IR, and electron injection of hydroxamate anchor at the TiO2 anatase (1 0 1) surface

The adsorption of hydroxamate onto a TiO2 anatase surface has been theoretically determined. We find that the doubly deprotonated configuration is the optimal adsorption mode in terms of energetic and dynamical stability, which is demonstrated by vibrational spectrum analysis. This configuration can also undergo the ultrafast electron transfer event, with a time-scale of 53 fs.

Structural features and dynamic investigations of the membrane-bound cytochrome P450 17A1

Cytochrome P450 (CYP) 17A1 is a dual-function monooxygenase with a critical role in the synthesis of many human steroid hormones. The enzyme is an important target for treatment of breast and prostate cancers that proliferate in response to estrogens and androgens. Despite the crystallographic structures available for CYP17A1, no membrane-bound structural features of this enzyme at atomic level are available. Accumulating evidence has indicated that the interactions between bounded CYPs and membrane could contribute to the recruitment of lipophilic substrates. To this end, we have investigated the effects on structural characteristics in the presence of the membrane for CYP17A1. The MD simulation results demonstrate a spontaneous insertion process of the enzyme to the lipid. Two predominant modes of CYP17A1 in the membrane are captured, characterized by the depths of insertion and orientations of the enzyme to the membrane surface. The measured heme tilt angles show good consistence with experimental data, thereby verifying the validity of the structural models. Moreover, conformational changes induced by the membrane might have impact on the accessibility of the active site to lipophilic substrates. The dynamics of internal aromatic gate formed by Trp220 and Phe224 are suggested to regulate tunnel opening motions. The knowledge of the membrane binding characteristics could guide future experimental and computational works on membrane-bound CYPs so that various investigations of CYPs in their natural, lipid environment rather than in artificially solubilized forms may be achieved.

The removal of aqueous uranium by SBA-15 modified with phosphoramide: a combined experimental and DFT study

Phosphoramide-modified ordered mesoporous silica (SBA-DEPA) materials were prepared via a two-step process involving: (1) the synthesis of phosphoramide via amidation of phosphoryl chloride with a primary amine and (2) modification of the phosphoramide onto SBA-15. The successful preparation was confirmed by FT-IR and NMR spectroscopy. As indicated by the ICP-AES and XRF analysis results, the phosphoramide group has a grafting ratio as high as 12.5%. The morphological information and N2 adsorption–desorption technique proved the highly ordered structure and large specific area of the material, respectively. An excellent performance for uranium sorption was found with a loading maximum of 311.6 mg g−1, a marked promotion relative to unmodified SBA-15. A strong pH and CO2 dependence suggested that near neutral conditions favored the maximum uranium sorption. To our surprise, the sorption took only 5 min to reach a 90% capacity and 20 min for equilibrium, which is extraordinary when compared to many other sorbent materials. The ionic strength partially influences the sorption, which indicates outer and inner sphere sorption both play parts in the process. A sorption capacity of over 90% of the original indicates the excellent reproducibility of SBA-DEPA. DFT calculations based on cluster models suggested a ‘tri-dentate-like’ structure for the uranyl-surface binding site, which may explain the excellent sorption ability of this material.

DFT/TD-DFT calculations on the sensing mechanism of a dual response near-infrared fluorescent chemosensor for superoxide anion and hydrogen polysulfides: photoinduced electron transfer

Previous studies have shown that intracellular O2˙−/H2Sn are related to cytoprotection processes. In order to detect these two important species spontaneously, a sensitive chemosensor HCy-FN has been developed. In the present study, the sensing mechanisms of the fluorescent chemosensor HCy-FN, its oxidation product Cy-FN and the elimination product Keto-Cy have been investigated in detail using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The present theoretical study indicates that there are intramolecular charge transfer (ICT) states in HCy-FN and Cy-FN, and they are energetically beneath the bright state, which is responsible for the photoinduced electron transfer (PET) process resulting in the fluorescence quenching. Whereas, Keto-Cy emits strong fluorescence because of the absence of PET. The calculated vertical excitation energies agree well with the experimental values and the calculation results can deeply explain the observed experimental phenomena.

Theoretical study on complexation of U(VI) with ODA, IDA and TDA based on density functional theory

This study aims to understand the complexation of U(VI) with oxydiacetic acid (ODA), iminodiacetic acid (IDA) and thiodiacetic acid (TDA) through density functional theory (DFT) calculations. The structures, complexation stabilities and bonding nature were investigated for U(VI)/XDA complexes (XDA is short for the three ligands). The calculations have proved that tridentate structures are more favorable than terminal bidentate ones for all stoichiometries, and steric hindrance is a factor that cannot be ignored especially for 1:2 complexes. The binding stabilities of the ligands and relative binding groups are in the sequences IDA > ODA ≫ TDA and CO > OH− ≫ H2O > X (Oether, N and S), respectively. All of the coordination bonds exhibit typically ionic character. The coordination bonds are mainly contributed by the interactions of U 5f-orbital and O(C)/X p-orbitals. The strength of all coordination bonds follows the order U–O(C) > U–N > U–O(H2) ≈ U–Oether > U–S. U–S interaction was solidly confirmed by MO and AIM analysis, which is found for U(VI)/TDA complexes for the first time. U–X bonds play an important role in U(VI)/XDA coordination.

Exploring the sensitization properties of thienyl‐functionalized tripyrrole Ru(II) complexes on TiO2 (101) surface: a theoretical study

Abstract Ruthenium(II) complexes, as the dye sensitizer in the solar cell system, has attracted great interests. In the present study, based on the ruthenium(II) complex N749, new sensitizers have been designed theoretically to increase the stability and the efficiency of dye-sensitized solar cell (DSSC). By investigating the ground state geometries, electronic structures, and spectroscopic properties by density functional theory (DFT) and time-dependent DFT, the orbital components and absorption transition have been obtained. The effect of tripyrrin ligand in the designed new sensitizers can be demonstrated from our results. The results show that the absorption spectra are systematically broadened and red-shifted with the increase sizes of the pyrrole ligands. The important unoccupied orbitals referred to charge transfer are mainly from di/tripyrrin derivative groups. Consequently, the charge transfer to the di/tripyrrin derivative groups has been strengthened. According to our study, the di/tripyrrin derivative ligand is more efficient than the NCS− ligand in absorbing visible light. The calculation results also indicate that the electronic structures of the N749 derived sensitizers are significantly influenced by the different substituted positions of the thienyl groups on di/tripyrrin ligands. Thus, the efficiency of DSSCs would be different. Our research predicted that the Ru(II) complexes containing 5,10-(2-thienyl)-4,6,9,11-tripyrrin ligand may enhance the visible light absorption of DSSC. This is in accordance with the corresponding experiment. These results are expected to assist the molecular design for new dyes in future DSSCs.

Theoretical investigation on binding process of allophanate to allophanate hydrolase

Several molecular simulation methods were integrated to investigate the detailed binding process of allophanate to allophanate hydrolase and predict their stable complex structure. The optimal enzyme-substrate complex conformation demonstrates that along with Arg307 and Tyr299, Gly124 is also one of the key anchor residues in the stable complex. The energetic calculation suggests the existence of an intermediate state in the enzyme-substrate binding process. The further atomic-level investigation illuminates that Tyr299, Arg307 and Ser172 can stabilize the substrate in the intermediate state. By this token, the residues Arg307 and Tyr299 function in both binding process and getting stable state.

Why HS− and CN− can be detected by different chemosensors with similar structures: a quantum mechanics and molecular dynamics study

Understanding the sensing mechanism is important for evaluating and developing effective chromogenic anion chemosensors. A challenging question in this area is how do you explain the selectivity of one chemosensor to anions that are usually difficult to distinguish. To this end, the sensing mechanisms of two chemosensors (COUMC & HCHI) with similar structures are theoretically investigated by means of quantum mechanics and molecular dynamics simulations. The selectivity of each chemosensor to three common anions that can possibly influence the detection of each other, namely CN−, HS− and F−, is thereby explained. The result of the quantum mechanics calculation reveals that COUMC_HS−, COUMC_CN− and HCHI_CN−, are favored both kinetically and thermodynamically. A further analysis based on molecular dynamics simulations reveals that the affinity of anions to the reaction sites of COUMC follow the order of CN− > HS− > F−. On the other side, F− and HS− anions are unable to approach the reaction sites of HCHI. These different affinities are explained subsequently by the different strengths of water–anion complexes and different surface electric potentials between COUMC and HCHI. The photochemistry properties indicate excitation and emission on large conjugated planar structures for a single COUMC/HCHI. For the anion-bonded chemosensors, only localized excitation is observed and no obvious differences on absorption and emission spectra are found when adding different anions. Based on our results, we conclude that the reaction selectivity is determined from both the reaction energy and the affinity of anions to the reaction sites. The different selectivity between COUMC and HCHI is attributed to spatial effects and surface electrostatic potential changes caused by the benzyl substituent in COUMC.