Search

A molecular switch having large contrast on the second-order nonlinear optical (NLO) properties has been studied based on tetrathiafulvalene (TTF)-π-polynitrofluorene (PTF) molecule. It can afford to switch second-order NLO response across 10 stable states by an effective combination of its photoisomerisation and redox properties. According to density functional theory (DFT) finite field calculations (BHandHLYP/CAM-B3LYP/LC-BLYP/6-31g(d)), the redox-active TTF, TCNQ (7,7′,8,8′-tetracyano-p-quinodimethane) units, and a photoisomerised chromophore (thiophene derivative of perfluorocyclopentene) act as the tuning centre to switch second-order NLO responses. Meanwhile, time-dependent DFT method has been employed to calculate excited-state nature for getting more insights of the second-order NLO responses. [ABSTRACT FROM PUBLISHER]

The electronic structure and bonding feature of a series of mono-ruthenium-substituted Keggin-type polyoxometalates (POMs) have been investigated by using density functional theory (DFT) calculation, natural bond orbital (NBO) analysis and energy-decomposition analysis (EDA). A comparison of the electronic properties of two known dimethyl sulfoxide (DMSO)-supported mono-ruthenium-substituted Keggin-type POMs shows that both complexes have the analogous frontier-molecular orbital feature. One of them possesses a relatively small HOMO–LUMO gap because of the high HOMO energy level. This difference comes from a high composition of POM ligand with antibonding feature in HOMO. In addition, three typical Keggin-type POM complexes [{PW11O39}RuII/III(L)]n−(L = H2O, C5H5N, NH3) have also been explored according to our computational studies. The NBO analysis shows that the RuII/III–L bond comes from donor–acceptor interactions between the end ligand and the ruthenium (II/III) centre. The EDA shows that the POM complex [{PW11O39}RuII(C5H5N)]5−has much stronger RuII–L bond than ammonia-supported Keggin-type POM [{PW11O39}RuII(NH3)]5−. And the enhancement of the RuII–L bonding interaction in [{PW11O39}RuII(C5H5N)]5−is mainly due to the large orbital interaction energy ΔEorb. The ammonia-supported Keggin-type POM [{PW11O39}RuII(NH3)]5−and the aqua-ruthenium derivative [{PW11O39}RuII(H2O)]5−have an analogous magnitude of the total bond energy. This result supports a non-aqueous environment for synthesis of an ammonia-supported Keggin-type POM [{PW11O39}RuII(NH3)]5−. [ABSTRACT FROM AUTHOR]

The bonding features and electronic structures of a series of transition metal carbon dioxide complexes have been studied by density functional theory (DFT) calculations combined with natural bond orbital (NBO) analysis and energy-decomposition analysis (EDA). NBO analysis shows that the interaction between the metal center and the carbon atom of the carbon dioxide ligand (M–C) is stronger than the other interaction between the metal center and the carbon dioxide ligand. Natural hybrid orbital (NHO) analysis gives the detailed bonding features of the M–C bond for each complex. The NBO charge distribution on the carbon dioxide unit in all studied complexes is negative, which indicates charge transfer from the metal center to the carbon dioxide ligand for all studied complexes. The hyperconjugation effect of the metal center and the two C–O bonds of the carbon dioxide ligand has been estimated using the NBO second-order perturbation stabilization energy. It was found that the NBO second-order stabilization energy of C–O → nM* is sensitive to the coordinated sphere and the metal center. Frontier molecular orbital (FMO) analysis shows that complexes1and4may be good nucleophilic reagents for activation of the carbon dioxide molecule. However, the EDAs show that the M–CO2bond interaction energy of complex4is about two times as large as that of complex1. The high M–CO2bond interaction energy of complex4may limit its practical application. [ABSTRACT FROM PUBLISHER]

Abstract: Combination of porphyrin, tetrathiafulvalene (TTF), and trimetallic nitride template endohedral metallofullerenes (TNT-EMFs) chemistry is highly desired because this hybrid entity will possess the rich scientific heritage of porphyrin, TTF, and TNT-EMF. In the present paper, the electronic structure and second-order nonlinear optical (NLO) properties of a series of TNT-EMF derivatives have been calculated by density functional theory (DFT) and finite field (FF) method. Our DFT calculations well reproduce the geometrical structure of the known [5, 6]- and [6, 6]-benzyne monoadducts. Our DFT calculations show that the [5, 6]-benzyne monoadduct is the thermodynamic product because the calculated total energy including the electronic and zero-point corrected energies of [5, 6]-benzyne monoadduct is ∼4.9kcalmol−1 more stable than the [6, 6]-benzyne monoadduct. Two new molecular systems, porphyrin derivative (porphyrin+TNT-EMF) and TTF derivative (TTF+porphyrin+TNT-EMF) have been considered in this work. The optimized calculations show that introduction of porphyrin and TTF cannot significantly affects the geometry of the weak four-membered ring and Sc3N@Ih–C80. The electronic structure analysis shows that the TTF derivative possesses the smallest HOMO–LUMO gap (∼1.5eV) among all studied compounds in this work, and the one-electron-oxidized center will be the TTF unit. DFT–FF calculations show that the [6, 6]-benzyne monoadduct has a large static first hyperpolarizability relevant to the [5, 6]-benzyne monoadduct. Thus, the second-order optical nonlinearity may be an effective technique to determine the location of the functional groups on the cage surfaces of the TNT-EMF. A substantial enhancement in static first hyperpolarizability has been obtained in porphyrin and TTF derivatives according to our DFT–FF calculation. The calculated β values of porphyrin and TTF derivatives are ∼15 and ∼30 times as large as that of [5, 6]-monoadduct. The time-dependent (TD) DFT calculations confirm that the increasing trend of the static first hyperpolarizability. And the molecular orbital transition feature shows that the TTF unit does not display the electron donor character because of the non-planar arched structure. [Copyright &y& Elsevier]

In this article, the nonlinear optical (NLO) switching action of Ru(III/II) carboxylate complexes was investigated by density functional theory (DFT). Among the studied complexed, Ru(III)PhCOO− has the largest β value of 4972 × 10−30 esu. Through the proton transfer (PT) process, the COOH group of Ru(III)PhCOOH and Ru(III)COOH complexes can form the COO− group. Then, COO− group acts as a strong donor and Ru(III) acts as an acceptor, which may be the most favorably used in the development of metal complexes NLO material. The redox NLO switching and PT NLO switching of Ru(III)PhCOO−, Ru(III)PhCOOH, Ru(II)PhCOO−, and Ru(II)PhCOOH complexes have been studied. The β value of Ru(III)PhCOO− complex is ∼36 and ∼48 times larger than those of reduced Ru(II)PhCOO− and Ru(II)PhCOOH, respectively. Note that the β value of deprotonated Ru(III)PhCOO− is ∼215 times larger than that of Ru(III)PhCOOH. The molecular electrostatic potential analysis also confirms that Ru(III)PhCOOH may have poor performance in the second-order NLO response. In addition, the TDDFT calculations show that the ligand to metal charge transfer transition lead to the largest β value of the Ru(III)PhCOO− complex. This investigation provides important insight into the remarkably large NLO properties and NLO switching of Ru(III/II) carboxylate complexes. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem 000: 000-000, 2011 [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) was employed to calculate the bonding feature, electron spectrum, and redox properties of a dumbbell-shaped polyoxometalate (POM) cluster, [ [image omitted](PW11O39)2]8-. Our DFT calculations confirm that the quadruple bond interaction between two ReIII centers consists of σ, 2π, and δ orbital overlaps, and the strength of the bonding interactions is in the order σ-bond > π-bond>δ-bond. Time-dependent (TD) DFT calculations suggest that this cluster possesses one strong and four weak absorption bands between 0.7 and 2.5 eV. Excited state calculations show that the Re-Re bond length increases when one electron of the Re-Re bonding δ orbital is shifted to the Re-Re δ* antibonding orbital. Molecular orbital predictions and spin unrestricted calculations indicate that the two Re atoms form the reduced center. The Re-Re bond length increases in one- and two-electron reduction processes because the Re-Re δ* antibonding orbital becomes occupied. However, these changes in the Re-Re bond length in excitation and reduction processes are not substantial because of the weak δ bond. The substitution effect of the central tetrahedron heteroatom of the POM ligand affects the Re-Re bond length, with the Re-Re distance decreasing with the substitution of X from Al to S, Al (2.345 Å) > Si (2.310 Å) > P (2.282 Å) > S (2.257 Å). [ABSTRACT FROM AUTHOR]

The uneven settlement is one of the important factors which lead to the damage of the buried pipeline. The means first-order second-moment method and Monte-Carlo method in ANSYS are used to calculate the reliability of the buried pipeline considering the random variables, i. e. displacement of ground settlement, material parameters and internal pressure. Reliability coefficients and failure probabilities considering or without considering the internal pressure are obtained. The results obtained by reliability analysis show that the variability of settlement displacement has important impact on the reliability of the buried pipeline subjected to the settlement. Compared with the results which do not consider internal pressure, the failure probability which considers internal pressure is larger and the reliability coefficient is smaller. It is also found that the variability of pipe diameter and thickness has important impact on the reliability of the buried pipeline. [ABSTRACT FROM AUTHOR]

The water supply network is often damaged to some extent in earthquake, so the hydraulic analysis of the water supply network with leakage is performed and then its seismic performance is evaluated based on the failure state simulation of the pipelines. The relationship of nodal flow and nodal pressure is adopted during the hydraulic analysis of the network combined with Chinese leakage model,and the nodal flows and its pressure are obtained by solving a set of nonlinear equations. Since nodal flows are considered to vary with nodal pressures in this model based on traditional hydraulic calculation method of the network, negative pressures are avoided during the hydraulic calculations. The functional analysis approach is applied to an example of water supply network after an earthquake. [ABSTRACT FROM AUTHOR]

The density functional and ab initio theory were used to investigate the second-order nonlinear optical (NLO) properties of Schiff base ligands, open-shell Fe(III), and closed-shell Ni(II) complexes. The effect of the metal center in complexes is thus manifold: it templates the formation of acentric structures, imparts high thermal stability to the chelate ring, and display higher second-order NLO response than their ligands. The second-order NLO response of metal complexes are intensively sensitive to the exchange donor/acceptor because the differences of the extent of charge separation and the intraligand charge transfer processes. Thus, substituted metal complexes could realize “switches on” the second-order NLO response by exchange donor/acceptor. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Extensively researches have been carried out on seismic analysis of space structures subjected to multi-dimensional multi-support excitations. However, the research on dynamic reliability of stochastic response is just little. Extreme value distribution (EVD) of dynamic response of stochastic space structures is so necessary to dynamic reliability. Nevertheless, there is no effective approach to obtain EVD as yet. Hence the recently formulated probability density evolution method (PDEM) is adopted to obtain the EVD and subsequently evaluate dynamic reliability of space structure subjected to multi-dimensional multi-support excitations. PDEM can effectively gain the EVD and calculate the dynamic reliability of stochastic structures. To demonstrate the accuracy and efficiency of the PDEM in space structures, a single-layer spherical reticulated dome is extensively researched and the EVD and dynamic reliability is observed and analyzed, respectively. In the present paper five apparent wave velocities and four displacement thresholds in vertical direction are taken into consideration. Compared with the results evaluated by conventional simulation method, the PDEM is of accuracy, efficiency and versatility in space structures. [ABSTRACT FROM AUTHOR]

According to the wavelet singularity theory and numerical simulation studies of beam structure, two methods of wavelet damage diagnosis are employed to analyze the damage diagnosis of beam structure based on Gausl wavelet. Firstly, the first derivative of the mode shape (rotation) is studied and gotten. Then, the continuous wavelet transform(CWT) by a Gausl wavelet is employed to deeply analyze the rotation of beam structure, the damage position and the relation between damage extent and Lipschitz exponent, and some significant results are gotten. Finally, by comparing the above-mentioned method and the methods through CWT by Gaus2 applied to the mode shape, it is found that the above-mentioned method is much better than Gaus2 method. So, the above-mentioned method can be employed to study practical beam structure damage diagnosis, which suggests the new ideas and methods for the advanced development of the wavelet theory. [ABSTRACT FROM AUTHOR]

An extended Kalman filter (EKF) which is optimized by the improved particle swarm optimization (IPSO) algorithm is proposed to estimate the state-of-charge (SOC) of battery. A new state space equation applied to EKF algorithm is constituted to reduce the influence of non-linear characteristics of parameters, and the optimal estimation of SOC is obtained based on the real-time identification of battery model parameters. IPSO algorithm is applied to optimize the system state error covariance matrix and measurement noise covariance matrix to improve the estimation accuracy of SOC by solving the problems in achieving the optimal solutions of these covariance matrixes. The results show that the IPSO-EKF algorithm can estimate the model parameters and SOC of battery accurately, and correct the state variable initial error. [ABSTRACT FROM AUTHOR]

The driving cycle of tracked vehicle is so complex, and the drive motor with wide speed range runs under nonlinear, uncertain and strong coupling load. How to control the motor speed to improve the stability of steering has become a research hot point. An electric differential control strategy is put forward. And the LADRC control algorithm is used in speed control of PMSM system, and LESO is used to estimate and compensate the unknown disturbance, thus rejecting the disturbance and improving the dynamic performance of system. The collaborative model of Matlab and RecurDyn softwares and test bench are built. The simulation and experimental results show that the speed control strategy with LADRC can be used to achieve rapid response without overshoot, strong disturbance rejection and good parameter a-daptability, which improve the vehicle stability. [ABSTRACT FROM AUTHOR]

Acetaldehyde (AA) and ethylene oxide (EO) are important fine chemicals, and are also substrates with wide applications for high-value chemical products. Direct electrocatalytic oxidation of ethylene to AA and EO can avoid the untoward effects from harmful byproducts and high energy emissions. The most central intermediate state is the co-adsorption and coupling of ethylene and active oxygen intermediates (*O) at the active site(s), which is restricted by two factors: the stability of the *O intermediate generated during the electrolysis of water on the active site at a certain applied potential and pH range; and the lower kinetic energy barriers of the oxidation process based on the thermo-migration barrier from the *O intermediate to produce AA/EO. The benefit of two adjacent active atoms is more promising, since diverse adsorption and flexible catalytic sites may be provided for elementary reaction steps. Motivated by this strategy, we explored the feasibility of various homonuclear TM 2 N 6 @graphenes with dual-atomic-site catalysts (DASCs) for ethylene electro-oxidation through first-principles calculations via thermodynamic evaluation, analysis of the surface Pourbaix diagram, and kinetic evaluation. Two reaction mechanisms through C-TM versus TM-TM synergism were determined. Between them, a TM-TM mechanism on 4 TM 2 N 6 @graphenes and a C-TM mechanism on 5 TM 2 N 6 @graphenes are built. All 5 TM 2 N 6 @graphenes through the C-TM mechanism exhibit lower kinetic energy barriers for AA and EO generation than the 4 TM 2 N 6 @graphenes through the TM-TM mechanism. In particular, Pd 2 N 6 @graphene exhibits the most excellent catalytic activity, with energy barriers for generating AA and EO of only 0.02 and 0.65 eV at an applied potential of 1.77 V vs. RHE for the generation of an active oxygen intermediate. Electronic structure analysis indicates that the intrinsic C-TM mechanism is more advantageous than the TM-TM mechanism for ethylene electro-oxidation, and this study also provides valuable clues for further experimental exploration., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Fast selective catalytic reduction of nitrogen oxide with ammonia (NH 3 -SCR) (2NH 3 + NO 2 + NO → 2N 2 + 3H 2 O) has aroused great interest in recent years because it is inherently faster than the standard NH 3 -SCR reaction (4NO + 4NH 3 + O 2 → 4N 2 + 6H 2 O). In the present paper, the mechanism of the fast NH 3 -SCR reaction catalyzed by a series of single-atom catalysts (SACs), M 1 /PTA SACs (PTA = Keggin-type phosphotungstic acid, M = Mn, Fe, Co, Ni, Ru, Rh, Pd, Ir, and Pt), has been systematically studied by means of density functional theory (DFT) calculations. Molecular geometry and electronic structural analysis show that Jahn-Teller distortion effects promote an electron transfer process from N-H bonding orbitals of the NH 3 molecule to the symmetry-allowed d orbitals (d xy and d x 2 -y 2 ) of the single metal atom, which effectively weakens the N-H bond of the adsorbed NH 3 molecule. The calculated free energy profiles along the favorable catalytic path show that decomposition of NH 3 to *NH 2 and *H species and decomposition of *NHNOH into N 2 and H 2 O have high free energy barriers in the whole fast NH 3 -SCR path. A good synergistic effect between the Brønsted acid site (surface oxygen atom in the PTA support) and the Lewis acid site (single metal atom) effectively enhances the decomposition of NH 3 to *NH 2 and *H species. M 1 /PTA SACs (M = Ru, Rh, Pd, and Pt) were found to have potential for fast NH 3 -SCR reaction because of the relatively small free energy barrier and strong thermodynamic driving forces. We hope our computational results could provide some new ideas for designing and fabricating fast NH 3 -SCR catalysts with high activity.

The degradation mechanism of benzo[ a ]pyrene (BaP) initiated by • OH and 1 O 2 in aqueous solution is investigated by density functional theory calculations. The main degradation products are BaP-1,6-quinone, BaP-3,6-quinone, BaP-4,6-quinone, and BaP-6,12-quinone. • OH and HO 2 are the main intermediate radical species. At a low initial concentration of • OH, 1 O 2 could be a primary driver for BaP degradation. The degradation mechanism includes six consecutive elementary reactions: (1) 1 O 2 initiation forming BaP-6-OO. (2) 1,3 H-shift (H atom shifts to the OO group) that is promoted by H 2 O, forming BaP-6-OOH. (3) BaP-6-OOH decomposes into the • OH radical and BaP-6-O. (4) • OH addition to BaP-6-O forming BaP-6- O -1(3,4,12)-OH. (5) Extracting the H atom from the carbon with the OH group by 1 O 2 . (6) Extracting the H atom from the OH group by HO 2 . At a high initial concentration of • OH, the • OH-initiated and 1 O 2 -initiated degradation reactions of BaP are both feasible. The degradation mechanism includes six consecutive elementary reactions: (1) • OH initiation forming BaP-6-OH or 1 O 2 initiation forming BaP-6-OO. (2) 1 O 2 addition to BaP-6-OH forming BaP-6-OH-12(1,3,4)-OO or • OH addition to BaP-6-OO forming BaP-6-OO-12(1,3,4)-OH. (3) Extracting the H atom from the carbon with the OH group by 1 O 2 , forming HO 2 . (4) 1,3 H-shift (H-shift from the carbon to the OO group), promoted by H 2 O. (5) The loss of the OH radical. (6) Abstracting the H atom from the OH group by HO 2 . In this paper, the formation of BaP-4,6-quinone via the BaP degradation is first reported. Water participates in the elementary reaction in which the H atom attached on the aromatic ring shifts to the OO group, serving as a bridge that stabilizes the transition state and transports the proton. A comprehensive investigation explains the degradation mechanism of BaP initiated by • OH and 1 O 2 in aqueous solution., Competing Interests: The authors declare no competing financial interest.

In the present paper, the mechanisms of N 2 O reduction by H 2 were systemically examined over various polyoxometalate-supported single-atom catalysts (SACs) M 1 /PTA (M = Fe, Co, Mn, Ru, Rh, Os, Ir, and Pt; PTA = [PW 12 O 40 ] 3- ) by means of density functional theory calculations. Among these M 1 /PTA SACs, Os 1 /PTA SAC possesses high activity for N 2 O reduction by H 2 with a relatively low rate-determining barrier. The favorable catalytic pathway involves the first and second N 2 O decomposition over the Os 1 /PTA SAC and hydrogenation of the key species after the second N 2 O decomposition. Molecular geometry and electronic structure analyses along the favorable reaction pathway indicate that a strong charge-transfer cooperative effect of metal and support effectively improves the catalytic activity of Os 1 /PTA SAC. The isolated Os atom not only plays the role of adsorption and activation of the N 2 O molecule but also works as an electron transfer medium in the whole reaction process. Meanwhile, the PTA support with very high redox stability has also been proven to be capable of transporting the electron to promote the whole reaction. We expect that our computation results can provide ideas for designing new SACs for N 2 O reduction by using H 2 selective catalytic reduction technology.

Density functional theory (DFT) calculations have been employed to probe the reaction mechanism of NO reduction with CO over a Cu1/PMA (PMA is the phosphomolybdate, Cs3PMo12O40) single-atom catalyst (SAC). Several important aspects of the catalytic system were addressed, including the generation of oxygen vacancies (Ov), formation of N2O2 intermediates, scission of the N-O bond of N2O2 intermediates to form N2O or N2, and decomposition of N2O to form N2. Unlike most previous theoretical studies, which tend to explore the reaction mechanism of polyoxometalate (POM) systems based on the isolated anionic unit, here, we build a model of the catalytic system with neutral species by introduction of counter cations to model the solid structure of the Cu1/PMA SAC. The major findings of our present study are: (1) CO adsorption on Cu sites leads to the formation of cationic Cu carbonyl species; (2) the Oc atom at the surface of the PMA support can easily react with the adsorbed CO to generate a Cu-Ov pair; (3) the Cu-Ov pair embedded on PMA is found to be the active site, not only for the formation of N2O2* by the reaction of two NO molecules via an Eley-Rideal pathway but also for the decomposition of N2O to form N2; (4) the adsorption of a NO molecule on the Cu-Ov pair with a bridging model results in charge transfer from the Cu atom to the π* antibonding orbital of the NO molecule; (5) IR spectroscopy of the key intermediates has been identified based on our DFT calculations; and (6) the Cu atom serves as an electron acceptor in Ov formation steps and an electron donor in N2O2 decomposition steps, and thus represents an electron reservoir. These results suggest that the POM-supported SAC with the cheaper Cu element is an efficient catalyst for the reaction between CO and NO.

The discrete anionic structure of polyoxometalates (POMs) at the interface is more like a separate small "island", which effectively prevents the diffusion of single atoms and prohibits the agglomeration and generation of metal particles; thus, POMs can enhance the sintering-resistant behavior and increase metal loading on the surface of single-atom catalysts (SACs). To explore the catalytic performance of POM-supported SACs for CO oxidation, we employed density functional theory (DFT) calculations to gain an understanding of some important aspects, including the CO adsorption, the formation of oxygen vacancies, and the activity of the surface oxygen species, of the catalytic system. Compared to previous theoretical studies, in which the catalytic behavior of POMs has been investigated based on the anionic unit with the highest negative charge, herein, we have constructed a model of the POM-supported SACs, which are neutral species. Our DFT calculations indicated that in the series of the SACs studied herein, (1) upon anchoring of a single metal atom on the POM surface, four key surface oxygen atoms were lifted from the POM surface to form a new interface, and thus, the surface oxygen species were activated; (2) CO adsorbed more strongly on the Ir, Os, Rh, Pt, and Ru sites than on the Fe, Mn, and Co sites; (3) it was easy to form an oxygen vacancy on the POM surface in the case of the Pt system when compared with the other systems; (4) the difference in the surface oxygen species for CO oxidation was remarkable, and the Oc atom at the catalyst interface had higher reactivity for CO oxidation as compared to the Ob atom in the Pt system studied herein; and (5) the single Pt atom served as an electron reservoir in the CO oxidation along the reaction pathway.

In general, reduction of N 2 O by CO is first performed by N 2 O decomposition over a catalyst surface to release N 2 and form an active oxygen species, and subsequently CO is oxidized by the active oxygen species to produce CO 2 . However, the strong adsorption behavior of CO on the catalyst surface usually inhibits adsorption and decomposition of N 2 O, which leads to a low activity or poisoning of catalysts. In the present paper, a Mars-van Krevelen (MvK) [correction] mechanism has been probed based on a series of phosphotungstic acid (PTA) supported single-atom catalysts (SACs), M 1 /PTA (M = Fe, Co, Mn, Rh, Ru, Ir, Os, Pt, and Pd). Although the calculated adsorption energy of CO is exceedingly higher than N 2 O for our studied systems, the adsorbed CO could react with the surface oxygen atom of the PTA support through the MvK mechanism to form an oxygen vacancy on the PTA surface. N 2 O acts as an oxygen donor to replenish the PTA support and release N 2 in the whole reaction process. This proposed reaction mechanism avoids competitive adsorption and poisoning of the catalyst caused by CO. The calculated adsorption energy, oxygen vacancy formation energy, and the free energy profiles show that the catalytic activity of Pd 1 /PTA, Rh 1 /PTA, and Pt 1 /PTA SACs is quite high, especially for Pt 1 /PTA and Pd 1 /PTA systems. Meanwhile, molecular geometry and electronic structure analysis along the favorable reaction pathway indicates that the metal single atom not only plays the role of adsorbing CO and activating surface atoms of the PTA support but also works as an electron transfer media in the whole reaction process. We expect that the present calculated results could provide some clues for the search for appropriate catalyst for reduction of N 2 O to N 2 by CO at low temperature.

Geometrical structures, metal-support interactions, and infrared (IR) spectroscopy of a series of M 1 /POM (M = Cu, Zn, Ag, and Au; POM = [PW 12 O 40 ] 3- ) single-atom catalysts (SACs), and catalytic cycle for alkene epoxidation catalyzed by M 1 /POM SACs were studied using density functional theory (DFT) calculations. The calculations demonstrate that the most probable anchoring sties for the isolated single atoms studied here in the M 1 /POM SACs are the fourfold hollow sites on the surface of POM support. The bonding interaction between single metal atom and surface of POM support comes from the molecular orbitals with a mixture of d atomic orbital of metal and 2p group orbital of surface oxygen atoms of POM cage. The calculated adsorption energy of isolated metal atoms in these M 1 /POM SACs indicates that the early transition metals (Cu and Zn) have high thermal stability. The DFT-derived IR spectra show that the four characteristic peaks of free Keggin-type POM structure split into six because of introduction of isolated metal atom. Compared with other metal atoms, the Zn 1 /POM SAC has the high reactivity for activity of dioxygen molecule, because the dioxygen moiety in Zn 1 /POM SAC displays O 2 - · radical feature with [POM 4- ·Zn 2+ O 2 - ·] 3- configuration. Finally, a catalytic cycle for ethylene epoxidation by O 2 catalyzed by Zn 1 /POM SAC was proposed based on our DFT calculations. Supported noble-metal SACs are among the most important catalysts currently. However, noble metals are expensive and of limited supply. Development of non-noble-metal SACs is of essential importance. Therefore, the reported Zn 1 /POM SAC would be very useful to guide the search for SACs into non-noble metals.

Molecular geometry, electronic structure, and metal-dinitrogen bonding nature of a series of metal-dinitrogen derivatives of Keggin-type polyoxometalates (POMs) [PW11O39M(II)N2)](5-) (M = Ru, Os, Re, Ir) have been studied by using a density functional theory (DFT) method with the M06L functional. Among these Keggin-type POM complexes, Os- and Re-substituted POM complexes are the most active for N2 adsorption with considerable adsorption energy. The electronic structure analysis shows that Os(II) and Re(II) centers in their metal-dinitrogen POM complexes possess π(2)xzπ(2)yzπ(2)xy and π(2)xzπ(2)yzπ(1)xy configurations, respectively. DFT-M06L calculations show that the possible synthesis routes proposed in this work for the Ru-, Os-, and Re-dinitrogen POM complexes are thermodynamically feasible under various solvent environments. Meanwhile, the Re-dinitrogen POM complex was assessed for the direct cleavage of dinitrogen molecule. In the reaction mechanism, a dimeric Keggin-type POM derivative of rhenium could represent the intermediate which undergoes N-N bond scission. The calculated free energy barrier (ΔG(⧧)) for a transition state with a zigzag conformation is 16.05 kcal mol(-1) in tetrahydrofuran, which is a moderate barrier for the cleavage of the N-N bond when compared with the literature values. In conclusion, regarding the direct cleavage of the dinitrogen molecule, the findings would be very useful to guide the search for a potential N2 cleavage compound into totally inorganic POM fields.

A second-order nonlinear optical (NLO) molecular switching with redox has been investigated in the present paper. The static first hyperpolarizabilities of 5-(BMes(2))-5'-(NPh(2))-2,2'-bipyridine (BNbpy) containing three-coordinate organoboron, Pt(II) chelate complex Pt(BNbpy)Ph(2), and their reduced forms have been calculated by density functional theory (DFT) combined with the analytic derivatives method. There is an enhancement of static first hyperpolarizabilities in the reduced form according to the calculations. That is, the β(vec) value of one-electron-reduced form is ~7 times as large as that of neutral form BNbpy; the β(vec) values of one- and two-electron-reduced forms are ~3 and ~4 times as large as that of neutral form Pt(BNbpy)Ph(2), respectively. In particular, the β(vec) value of two-electron-reduced form (3)Pt(BNbpy)Ph(2)(2-) is 1349 × 10(-30) esu, ~286 times larger than its neutral form. Moreover, the component β(z) value of the metal chelate complex Pt(BNbpy)Ph(2) is 25 × 10(-30) esu, which is ~14 times as large as that of ligand BNbpy; the corresponding F(-)/CN(-) compounds show a decrease in β(x) values compared with the case of the ligand and Pt(II) complex. Analyses of geometries, density of states (DOS), and time-dependent DFT (TDDFT) calculations reveal that the one-electron reduction promotes the molecular conjugation in the x-axis and intensifies the interaction between the metal Pt(II) and ligand and then results in an enhancement of the static first hyperpolarizability, whereas the binding of F(-)/CN(-) to the B atom turns off the p(π)-π* conjugation and has no effect on the conjugation of bipyridine, which leads to a decreasing β value in the x-axis.

The donor-conjugated bridge-acceptor (D-A) model, as a simple molecular scheme, has been successfully used in the development of second-order organic compound, organometallic compound, and metal complex nonlinear optical (NLO) materials. However, for the totally inorganic molecules, the use of this model is still prohibitive. In the present paper, time-dependent density functional theory (TDDFT) was used to investigate the second-order NLO properties of vanadium- and molybdenum-trisubstituted Keggin and Wells-Dawson polyoxometalates (POMs). The results show that these POM clusters possess D-A structures. The oxygen atoms in the cap region and metal (vanadium and molybdenum) atoms in another cap region in these POM clusters can be viewed as the electron donor and acceptor, respectively. The vanadium ion derivatives possess larger second-order NLO responses and dipole moment than molybdenum ions derivatives; thus, the three vanadium atoms in the cap region act as a strong acceptor related to the three molybdenum atoms in cap region in our D-A scheme. The vanadomolybdate with Wells-Dawson structure displays the good second-order NLO response because of the relevant long conjugated bridge and strong acceptor. This D-A model may be an effective approach for optimizing the first hyperpolarizabilities of inorganic POM clusters.

In order to promote the understanding of sulfate enrichment on the growth and succession of phytoplankton communities in eutrophic freshwater body, laboratory experiment of phytoplankton in a landscape water body was conducted. Three treatment groups were set up in experiment:control (G0), step by step enrichment (G1) and enrichment at a time (G2). The result indicated that the addition of sulfate promoted the increase of Chlorophyta species and biomass, while inhibited the growth of native Cyanobacteria and diatom species. Species and biomass of G0, G1 group were similar and much higher than those of G2 group. Average biomass of GO, Gland G2 group was 98.46, 96.09 and 81.19 mg x L(-1), respectively. G0 group was almost always dominated by Cyanobacteria species such as P. corium and O. amphibia, dominant species in G1 and G2 groups changed from Cyanobacteria species to Chlorophyta species including S. quadricauda, G. radiate and S. obliqus. Compared with that of control group G0 (1.49 +/- 0.32, the average community diversity indices of G1 (1.70 +/- 0.18) and G2 groups (1.68 +/- 0.40) were elevated.

The redox-active tetrathiafulvalene (TTF) is a good electron donor, and porphyrin is highly delocalized in cyclic pi-conjugated systems. The direct combination of the two interesting building units into the same molecule provides an intriguing molecular system for designing nonlinear optical (NLO) molecular materials. In the present paper, the second-order NLO properties of a series of monoTTF-porphyrins and metalloporphyrins have been calculated by density functional theory (DFT) combined with the finite field (FF) method. Our calculations show that these compounds possess considerably large static first hyperpolarizabilities, approximately 400 x 10(-30) esu. Since the TTF unit is able to exist in three different stable redox states (TTF, TTF(*+), and TTF(2+)), the redox switching of the NLO response of the zinc(II) derivative of monoTTF-metalloporphyrin has been studied, and a substantial enhancement in static first hyperpolarizability has been obtained in its oxidized species according to our DFT-FF calculations. The beta values of one- and two-electron-oxidized species are 3.6 and 8.7 times as large as that of the neutral compound, especially for two-electron-oxidized species, with a value of 3384 x 10(-30) esu. This value is about 3 times that for a push-pull metalloporphyrin, which has an exceptionally large hyperpolarizability among reported organic NLO chromophores. Meanwhile, to give a more intuitive description of band assignments of the electron spectrum and trends in NLO behavior of these compounds, the time-dependent (TD)DFT method has been adopted to calculate the electron spectrum. The TDDFT calculations well-reproduce the soret band and Q-type bands of the monoTTF-porphyrin, and these absorption bands can be assigned to the pi --> pi* transition of the porphyrin core. On the other hand, the oxidized process significantly affects the geometrical structures of the TTF unit and porphyrin ring, and the two-electron-oxidized species has a planar TTF unit and a high conjugative porphyrin ring. This effect reduces the excited energy, changes the CT feature, and thus enhances its static first hyperpolarizability.

High-valent M(VI)N (M = Ru, Os) species are important reagents in nitrogen transfer reactions; the unique withdrawing properties of polyoxometalate (POMs) ligands would possibly modify the reactivity of the M(VI)N functional group. In the present paper, density functional theory (DFT) and natural bond orbital (NBO) analysis have been employed to calculate electronic structures, M(VI)-N bonding, and redox properties of high-valent metal nitrido derivatives of Keggin-type POMs, [PW(11)O(39) {M(VI)N}](4-) (M = Ru, Os, Re). Our calculations show that [PW(11)O(39){RuN}](4-) possesses stronger antibonding interaction between metal and nitrogen atoms compared with anions [PW(11)O(39){OsN}](4-) and [PW(11)O(39){ReN}](4-). A large increase in the Ru-N bond length of anion [PW(11)O(39){RuN}](4-) in the excited states has been found; the effective order and composition of the molecular orbital in anion [PW(11)O(39){RuN}](4-) is a key factor in determination of the increase of the Ru-N bond length in the excited states. The substitution effects of central tetrahedron heteroatoms (XO(4), X = Al, Si, P, As) in anions [XW(11)O(39){RuN}](4-) affect the relative energy of the LUMO; the relevant orbital energy increases in the order Al(III) < Si(IV) < P(V) approximately As(V). The RuN unit is the reduced center. NBO analysis of the extent of the bonding interaction between the ruthenium and the nitrogen centers in [PW(11)O(39){Ru(VI)N}](4-) shows that the Ru-N bond possesses a covalent feature and displays triple-, double-, and single-bond character when moving along the change of spin state ((1)1 --> (3)1 --> (5)1).

The geometrical structure and stability of neutral pi-conjugated C4H4N. with three spin states were investigated by using ab initio and density functional theory (DFT) methods. In addition, the linear and nonlinear optical properties were studied at the same level combined with the finite field approach. The calculated results show that conjugation and stability decreased with increasing spin multiplicity. These reliable UCCSD results show that the polarizability (alpha) values of C4H4N. with the quartet state are maximal, while those of C4H4N. with the doublet state are minimal. The order of betatot values is betasextet > betadoublet > betaquartet. The second hyperpolarizability (gamma) values exhibit positive values. The variation trends of gamma are consistent with alpha.

Aquarium microcosms were used to study the effects of nitrogen source and aeration mode on the growth and species changes of algae in freshwater. Nitrate nitrogen(NO3(-) -N) and ammonia nitrogen(NH4(+) -N) were used as nitrogen sources. For each nitrogen source, four modes of aeration were selected, including control, continuous aeration, aeration during the day, and aeration at night. In the early stage of the experiment, algae in the NH4(+) -N treatment experiment grew well. In the later stage, algae in the NO3(-) -N treatment experiment grew better. For different aeration modes, continuous aeration show varied effects on algae growth in the two nitrogen source treatments. Day-only aeration had little effect on algae growth. Night-only aeration inhibited algae growth considerably. In NH(+) -N treatments, cyanophyta became dominant species easily. In contrast, chlorophyta dominated in NO3(-) -N treatments.

The kinds of fertility genes and its genetic characters for D2-type CMS lines of common wheat were studied, the results showed: (1) For D2-type CMS line, there was wide restoring sources and high digree of restoration in common wheat varieties (the restoring degree of 33.61% varieties exceeded 50%), and new CMS lines were easily bred (25.21% varieties could maintain male sterility). These characters indicated that D2-type CMS line was higher value in applied study, compared with T, K, V-type CMS lines. (2) There were two forms of nuclear genotype for D2-type CMS lines, namely A1(sterile gene) and A2(sterile gene + inhibiting gene). In nucleus of restorer lines, the fertility genotype was conditioned by 6 forms: C1(major restorer gene), C2(major restorer gene + minor restorer gene), C3(minor restorer gene), C4(major restorer gene + inhibiting gene), C5(major restorer gene + minor restorer gene + inhibiting gene), C6(minor restorer gene + inhibiting gene). The genetic expression of fertility genes was affected by environmental factors. The basic model of effective combination was A1 + C1, A1 + C2, A2 + C2. (3) The allelic restorer-genes were characterized by incomplete dominance and the nonallelic restorer-genes were characterized by additive effect, which was the important basis of breeding good restorer lines.

On the basis of genetic characters of D2-type CMS lines, restorer lines Yi4060, M8003, 6D/6R, GR1, 960789, Bao769-22-1 et al. were gained from crossing selection. The results of genetic analysis of F2, F1BC1 population and allelic analysis of restorer genes, successive selection of self fertility from F1 showed that fertility restoration of these restorer lines was controlled by two pair independent major-genes(dominant) and different-dosage minor genes. Authors proposed that the two pair independent major-genes should be designated as D2Rf1 D2Rf1, D2Rf2 D2Rf2. The model C2(major genes + minor genes) should be first selected in breeding restorer line.