Search

Methanol has long been used as a hole scavenger in photocatalysis to improve charge separation. Although the prototypical methanol/TiO2(110) system shows salient adsorption-state-dependent photoact...

The series of heterodinuclear metal oxide carbonyls in the form of TaNiO(CO)n− (n = 5–8) are generated in the pulsed-laser vaporization source and characterized by mass-selected photoelectron velocity-map spectroscopy. During the consecutive CO adsorption, the μ2-O-bent structure initially is the most favorable for TaNiO(CO)5−, and subsequently both μ2-O-bent and μ2-O-linear structures are degenerate for TaNiO(CO)6−, then the μ2-O-linear structure is most preferential for TaNiO(CO)7−, and finally the η2-CO2-tagged structure is the most energetically competitive one for TaNiO(CO)8−, i.e., the CO oxidation occurs at n = 8. In contrast to the literature reported CO oxidation on heteronuclear metal oxide complexes generally proceeding via Langmuir–Hinshelwood-like mechanism, complementary theoretical calculations suggest that both Langmuir–Hinshelwood-like and Eley–Rideal-like mechanisms prevail for the CO oxidation reaction on TaNiO(CO)8− complex. Our findings provide new insight into the composition-selective mechanism of CO oxidation on heteronuclear metal complexes, of which the composition be tailored to fulfill the desired chemical behaviors.

An in situ generated AuIII catalyst is found to catalyze the direct oxidation of CH4 to C1 oxygenates in 1-ethylimidazolium bis-(trifluoromethylsulfonyl)amide ([Eim][NTf2]) at 90 °C. The formation ...

Numerous models have been used to describe the isotherm adsorption of supercritical methane in porous media. Many models assume that the adsorbed phase density does not change with pressure during ...

Enzymatic carbon fixation is one of the most interesting processes in CO2 sequestration. A number of decarboxylases can catalyze the reversible decarboxylation reaction in vivo, while can strengthen the carboxylation reaction in vitro. The Bio-Kolbe–Schmitt reaction is the carboxylation of phenols and CO2 by hydroxybenzoic acid decarboxylases to generate hydroxybenzoic acids under a mild condition, which requires an alkaline environment. It remains unclear how the carbon fixation via carboxylation can be improved. In this study, the major issues regarding the switching from decarboxylase to carboxylase through thermodynamic calculation and determination of enzyme characteristics, CO2 concentration, and other related species in the reaction system such as HCO3− are described. We identified that the concentration of CO2 in aqueous solution was the main factor for obtaining high CO2 fixation yield. In order to obtain sufficient CO2(aq) to promote the carboxylation by decarboxylase under an alkaline environment, a high concentration of HCO3− is required. The highest CO2 fixation yield of 30% was achieved from the reaction under 0.2 MPa CO2 in 2.7 M KHCO3 buffer for 15 min. Under the optimal reaction conditions, the carboxylation of catechol by 2,3-DHBD_Ao (2,3-dihydroxybenzoic acid decarboxylase from Aspergillus oryzae) achieved a good “turnover frequency” (TOF) of 47 min−1. This study discloses that CO2(aq) concentration is a crucial parameter for increasing CO2 fixation yield in a homogenous reaction under an alkaline condition.

Infrared photodissociation spectroscopy of mass-selected [MO(CO2)n]+ (M=Sc, Y, La) complexes indicates that the conversion from the solvated structure into carbonate one can be achieved by the ScO+ cation at n=5 and by the YO+ cation at n=4, while only the solvated structures are observed for the LaO+ cation. These findings suggest that both the ScO+ and YO+ cations are able to fix CO2 into carbonate. Quantum chemical calculations are performed on [MO(CO2)n]+ to identify the structures of the low-lying isomers and to assign the observed spectral features. Theoretical analyses show that the [YO(CO2)n]+ complex has the smallest barrier for the conversion from the solvated structure into carbonate one, while [LaO(CO2)n]+ exhibits the largest conversion barrier among the three metal oxide cations. The present system affords a model in clarifying the effect of different metals in catalytic CO2 transformation at the molecular level.

Importance There is a high incidence of iron deficiency in children worldwide. Notably, however, while iron deficiency is the most common cause of anemia, little is known about the prevalence and different types of iron deficiency in neuroblastoma patients. Objective The aim of the present study was to investigate the prevalence of iron deficiency in patients newly diagnosed with neuroblastoma. Methods A total of 195 newly diagnosed neuroblastoma patients from November 2015 to January 2018 were analyzed retrospectively. The survival analysis was estimated by the Kaplan‐Meier method. Results Of the 195 neuroblastoma patients included in the study, 121 (62.1%) had iron deficiency, 55 (28.2%) had absolute iron deficiency, and 66 (33.9%) had functional iron deficiency. Being aged ≥ 18 months, tumor originating in the abdomen, International Neuroblastoma Risk Group Staging System M, high‐risk neuroblastoma, lactate dehydrogenase ≥ 1500 U/L, neuron‐specific enolase ≥ 100 U/L, unfavorable histologic category, MYCN amplification, chromosome 1p loss, and bone marrow metastasis were associated with significantly higher rates of functional iron deficiency (P < 0.05). Interpretation Functional iron deficiency at the time of initial neuroblastoma diagnosis predicted lower event‐free survival. Long‐term effects of iron supplementation in neuroblastoma patients with different types of iron deficiency need to be further studied.

The heteronuclear metal oxide complexes are of great significance in heterogeneous catalytic oxidation of CO. However, previous studies are mainly focused on the composition of metal oxide, charge state, the support and the active oxygen species, with little attention paid to adsorbed CO ligands. Herein, the ligand-mediated reactivity in CO oxidation of niobium-nickel monoxide carbonyl complexes has been successfully identified. The NbNiO(CO)

The mechanism of silver(I) and copper(I) catalyzed cycloaddition between 1,2-diazines and siloxy alkynes remains controversial. Here we explore the mechanism of this reaction with density functional theory. Our calculations show that the reaction takes place through a metal (Ag+, Cu+) catalyzed [2+2] cycloaddition pathway and the migration of a silylium ion [triisopropylsilyl ion (TIPS+)] further controls the reconstruction of four-member ring to give the final product. The lower barrier of this silylium ion mediated [2+2] cycloaddition mechanism (SMC) indicates that well-controlled [2+2] cycloaddition can obtain some poorly-accessible IEDDA (inverse-electron demand Diels-Alder reaction) products. Strong interaction of d10 metals (Ag+, Cu+) and alkenes activates the high acidity silylium ion (TIPS+) in situ. This п-acid (Ag+, Cu+) and hard acid (TIPS+) exchange scheme will be instructive in silylium ion chemistry. Our calculations not only provide a scheme to design IEDDA catalysts but also imply a concise way to synthesise 1,2-dinitrogen substituted cyclooctatetraenes (1,2-NCOTs).

The clinical outcome of neuroblastoma (NB) has significantly improved in the last 30 years for patients with localized disease; however, the overall survival (OS) for patients with metastasis remains poor. Apatinib, a selective inhibitor of the vascular endothelial growth factor receptor-2 (VEGFR-2) tyrosine kinase, which was discovered to be highly associated with metastasis, has been reported to exert antitumor effects in numerous types of cancer. However, the effect of apatinib in NB remains relatively unknown. The present study aimed to investigate the antitumor effects of apatinib in NB cells in vitro. The results revealed that apatinib inhibited cell viability and colony formation, whilst inducing cell cycle arrest and the apoptosis of NB cells. Additionally, apatinib inhibited the migration and invasion of NB cells, in addition to promoting the autophagy of NB cells. Western blotting demonstrated that the protein expression levels of phosphorylated (p)-AKT, p-mTOR and p-P70S6K, and downstream molecules associated with the cell cycle and apoptosis, such as cyclin D1 and the Bcl-2/Bax ratio of NB cells, were significantly decreased following treatment with apatinib. In addition, western blotting and immunofluorescence assays identified that the expression level of microtubule-associated protein 1A/1B-light chain 3-II, which is expressed in autophagosomes, was upregulated following apatinib treatment. In conclusion, the findings of the present study suggested that apatinib may induce apoptosis and autophagy via the PI3K/AKT/mTOR and mitogen-activated protein kinase/ERK signaling pathways in NB cells. Thus, apatinib may be a potential antitumor agent for the clinical treatment of NB.

The thermal decomposition of three methyl anisole isomers (o-, m-, and p-methyl anisole) were investigated to understand the influences of methyl substitution position on the benzene ring at low pressure (below 15 Pa) within temperature range from 473 to 1473 K. The pyrolytic phenomena were studied by using vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (SPI-TOFMS) to identify the intermediates, radicals and final products, and the relative concentration profiles of the pyrolytic products were evaluated by the semiquantitative analysis method. It was showed that the bond homolysis of PhO CH3 was the initial reaction for all three methyl substituted anisole, and the produced intermediates and final products show similar among the pyrolysis experiments of three methyl anisole isomers. Moreover, the effects of the different substituted position on the benzene ring of the methyl group presented on the extraordinary differences of the maximum relative concentration of m/z 106 (6-methylen-2, 4-cyclohexadien-1-one or 4-methylene-2, 5-cyclohexadiene-1-one), The theoretical calculations indicate different generating pathways of m/z 106 for the pyrolysis of m-methyl anisole and o-, p-methyl anisole. Noteworthy, the isomerization reaction played a significant role in the pyrolysis of m-methyl anisole.

We have investigated deuterium (D2) formation from the photolysis of fully deuterated methanol (CD3OD) on the clean and formate (DCOO–) modified rutile (R)-TiO2(110) surfaces at 266 nm using temperature-programmed desorption (TPD) and density functional theory (DFT) methods. Products, D2O and D2, have been detected on both surfaces during the TPD process. About 18.5% of the dissociated D atoms from CD3OD photolysis contribute to D2 formation on the DCOO–-modified R-TiO2(110) surfaces. The value is much higher than that on the clean R-TiO2(110) surfaces, suggesting that surface DCOO– can enhance D2 production from CD3OD photolysis on R-TiO2(110). Further DFT calculation suggests that the BBO-CH-O-Ti5c structure of HCOO– on the surface can largely enhance the BBOv-mediated H2 formation by lowering the barrier of recombinative H2 desorption, leading to efficient H2 production.

Photocatalytic hydrogen evolution and organic degradation on oxide materials have been extensively investigated in the last two decades. Great efforts have been dedicated to the study of photocatalytic reaction mechanisms of a variety of molecules on TiO2 surfaces by using surface science methods under UHV conditions, providing fundamental understanding of surface chemical reactions in photocatalysis. In this review, we have summarized the recent progress in the studies of photocatalysis of several important species (water, methanol and aldehydes) on different TiO2 surfaces. The results of these studies have provided us deep insights into the elementary processes of surface photocatalysis and stimulated a new frontier of research in this area. Based on the results of these studies, a new dynamics based photocatalysis model is also discussed.

Here, we have investigated how coordination induces CO2 fixation into a carbonate using a cationic yttrium oxide model catalyst. The infrared spectra show that the first three CO2 molecules are weakly bound to the metal. Subsequent coordination of CO2 ligands leads to the formation of a carbonate complex and results in a core ion transition. The conversion of Y = O and CO2 to carbonate is achieved by the donation of electrons from the ligands to the metal. Systematic analyses of the effects of different ligands and metals on the coordination-induced CO2 fixation demonstrate that the present system serves as an efficient and rational model for adjusting CO2 fixation and CO2 emission.

As the photo-dissociation product of methanol on the TiO2 (110) surface, the diffusion and desorption processes of formaldehyde (HCHO) were investigated by using scanning tunneling microscope (STM) and density functional theory (DFT). The molecular-level images revealed the HCHO molecules could diffuse and desorb on the surface at 80 K under UV laser irradiation. The diffusion was found to be mediated by hydrogen adatoms nearby, which were produced from photodissociation of methanol. Diffusion of HCHO was significantly decreased when there was only one H adatom near the HCHO molecule. Furthermore, single HCHO molecule adsorbed on the bare TiO2(110) surface was quite stable, little photo-desorption was observed during laser irradiation. The mechanism of hydroxyl groups assisted diffusion of formaldehyde was also investigated using theoretical calculations.

Coal structure is very complicated. The ratio of various functional groups in coal may be studied by existing analysis techniques, but the connections of these functional groups are still mostly unknown. In this work we assume that the most stable position for a certain group could be the most plausible position for that group in the coal structure, then with the help of Density Functional Theory (DFT) calculations we have studied the most plausible position for hydroxyl group in coal. We found the order of preferential position for hydroxyl group is: (1) pyridine rings; (2) polycyclic aromatic hydrocarbons; (3) monocyclic aromatic hydrocarbons; (4) monocyclic heteroatomic molecules (pyrrole, furan and thiophene); (5) alicyclic rings. Besides, double substituted hydroxyl groups on pyridine and polycyclic aromatic ring are possible. Hydroxyl groups tend to be in the positions where they can form hydrogen bond. Electron donating and withdrawing groups do not obviously change the preference of hydroxyl group unless there is hydrogen bond formed.

The strategy for acceptorless dehydrogenative cyclization of o-aminobenzyl alcohols with ketones to quinolines in water has been accomplished. In the presence of [Cp*Ir(6,6'-(OH)2bpy)(H2O)][OTf]2, a series of desirable products were obtained in high yields. Notably, this research exhibits the potential for the construction of heterocycles via acceptorless dehydrogenative reactions in water catalyzed by water-soluble metal-ligand bifunctional catalysts.

Photocatalytic hydrogen production and pollutant degradation provided both great opportunities and challenges in the field of sustainable energy and environmental science. Over the past few decades, we have witnessed fast growing interest and efforts in developing new photocatalysts, improving catalytic efficiency and exploring the reaction mechanism at the atomic and molecular levels. Owing to its relatively high efficiency, nontoxicity, low cost and high stability, TiO2 becomes one of the most extensively investigated metal oxides in semiconductor photocatalysis. Fundamental studies on well characterized single crystals using ultrahigh vacuum based surface science techniques could provide key microscopic insight into the underlying mechanism of photocatalysis. In this review, we have summarized recent progress in the photocatalytic chemistry of hydrogen, water, oxygen, carbon monoxide, alcohols, aldehydes, ketones and carboxylic acids on TiO2 surfaces. We focused this review mainly on the rutile TiO2(110) surface, but some results on the rutile TiO2(011), anatase TiO2(101) and (001) surfaces are also discussed. These studies provided fundamental insights into surface photocatalysis as well as stimulated new investigations in this exciting field. At the end of this review, we have discussed how these studies can help us to develop new photocatalysis models.

In this paper, a novel type of chiral bisselenourea sensor was first synthesized and used as a strong hydrogen-bonding donor for highly efficient chiral recognition of a diverse range of tertiary alcohols., Chemical sensors are powerful for the fast recognition of chiral compounds. However, the established sensing systems are less effective for chiral tertiary alcohols. The chiral tertiary alcohol group is an important structural unit in natural products and drug molecules, and its enantioselective recognition represents a significant and challenging task. In this paper, a novel type of chiral bisselenourea sensor was first synthesized and used as a strong hydrogen-bonding donor for highly efficient chiral recognition of a diverse range of tertiary alcohols. The obtained sharply split NMR signals are well-distinguishable with a large (up to 0.415 ppm) chemical shift nonequivalence. The NMR signal of the hydroxyl hydrogen atom was first employed for enantiomeric excess determination of tertiary alcohols, giving accurate results with

The mass-selected infrared photodissociation (IRPD) spectroscopy combined with quantum chemical calculations was utilized to study the interactions between niobium dioxide cation and carbon dioxide molecules. Experimental and calculated results indicate that the CO2 molecules are weakly bound to the NbO2+ cation in an end-on configuration via a charge-quadrupole electrostatic interaction. For n ≥ 6, CO2 molecules in the second shell no longer have contribution to CO2 activation. The similarity of experimental spectra for n ≥ 7 also indicates that ion cores of NbO2+(CO2)n cluster have not changed. Compared with the congeneric YO+ complexes (Phys. Chem. Chem. Phys., 2018, 20, 19314–19320), NbO2+ is found to be thermodynamically and kinetically more difficult to react with CO2.

Gelatin microspheres have been commonly used in tissue engineering, but their application is often limited by the uncontrollability and potential cytotoxicity of traditional chemical cross-linking method. Methylacrylamide modification and photocrosslinking provide a controllable and cytocompatible cross-linking method for gelatin hydrogels, however, microspheres fabricated by this single photopolymerization process is uncontrollable. In this study, we show that increasing the gelling ability of gelatin methacrylamide (GMA) at low temperatures is vital to prepare photocrosslinked gelatin microspheres, which in turn improves the controllability and compatibility of conventional chemical cross-linking methods. We detailed characterized the rheological performance with varying temperature and demonstrated that the gelling capability of GMA could be improved by increasing GMA solution concentration and reducing methacrylate substitution. The physicochemical properties of the photocrosslinked microspheres can be modulated via methacrylamide modification, as evidenced by the positive correlation between the physicochemical optimization of the hydrogel bulk and the degree of methacrylate substitution. Next, we successfully fabricated GMA spheres by a two-step process of low-temperature gelation followed by photopolymerization crosslinking. Finally, we show that the microcarriers exhibited favorable supporting for MC3T3-E1 cell proliferation, spreading, and osteogenic differentiation. This study provided a controllable and cytocompatible photocrosslinking procedure for GMA microspheres with broad application prospects, of course, not limited to cell microcarriers.

This paper describes an experimental technique for studying neutral metal complexes using infrared + vacuum ultraviolet (IR+VUV) two-color ionization spectroscopy based on a tunable VUV free-electron laser (VUV-FEL). The preliminary IR spectroscopy results of mass-selected nickel tetracarbonyl are reported in this work. The results demonstrate that the tunable VUV-FEL light allows the selective ionization of a given neutral cluster free of confinement along with the recording of well-resolved IR spectra. As the ionization energies of many neutral clusters are accessible by a broadly tunable VUV-FEL (50-150 nm) and near-threshold ionization can be readily achieved, the proposed experimental method offers unique possibilities for the size-specific study of a wide variety of confinement-free neutral clusters.

The pyrolysis behaviors of coal-related model compounds (bibenzyl and benzyloxybenzene) were investigated on a fixed-bed reactor catalyzed by pyrite (main component is FeS2). The pyrolysis products were analyzed by gas chromatography (GC). The results indicated pyrite could increase the conversion of the model compounds and the yield of liquid and gas, while decrease the char yield. The theoretical calculation results indicated that the pyrite accelerates the initial bond dissociation of parent molecules, thus the radicals can be produced easily. Moreover, the main reason for the decreased yield of char after adding the pyrite is that the large radicals are stabilized on the surface by adsorption, then having little chance to combine with each other to form char. The changes in pyrolysis product distributions with pyrite were also consistent with the calculation results. When adding tetrahydronaphthalene and pyrite simultaneously, there is a significant synergistic effect, which causing the conversion of bibenzyl increased by 14.78 wt% compared with that adding tetrahydronaphthalene or pyrite alone.

To investigate the effect of functional groups in coal on volatiles evolution, eight coal samples with different ranks were pyrolyzed in a novel in-situ pyrolysis photoionization time-of-flight mass spectrometer (Py-PI-TOF MS). Soft ionization were adopted to enable the fragment-free detection of volatiles generated from initial pyrolysis products. Temperature-evolved profiles of main products are visible via scanning of the ion current of individual compound measured during the pyrolysis processes. The obtained mass spectra of volatiles from pyrolysis of eight coal samples reveal predominantly molecular ions with four categories: alkenes, benzenes, phenols and diphenols. Furthermore, the analysis of different coal samples demonstrates that both alkyl and oxygen-containing groups attached on the benzene rings can reduce the peak temperatures of main products’ evolution, and the effect of oxygen-containing group is stronger than that of alkyl group. The difference of peak temperature with maximum evolution, which is used as an indicator to measure the effect of the functional groups, were correlated with carbon content and volatile content of coal samples. The influence degree of functional groups on evolution temperature was found to be negative correlated with the carbon content and positive correlated with the volatile content, respectively. Based on the experimental observations and theoretical calculations, the overall results allowed to reveal the influence of the functional groups on the volatile organic compounds during coal pyrolysis. Analogous to reported setups with online studies of coal pyrolysis, Py-PI-TOF MS may be a good option for monitoring the evolution characteristics and reaction pathways of coal pyrolysis process.

Photocatalytic hydrogen evolution and organic degradation on oxide materials have been extensively investigated in the last two decades. Great efforts have been dedicated to the study of photocatalytic reaction mechanisms of a variety of molecules on TiO2 surfaces by using surface science methods under ultra-high vacuum (UHV) conditions, providing fundamental understanding of surface chemical reactions in photocatalysis. In this review, we summarize the recent progress in the study of photocatalysis of several important species (water, methanol, and aldehydes) on different TiO2 surfaces. The results of these studies have provided us deep insights into the elementary processes of surface photocatalysis and stimulated a new frontier of research in this area. Based on the results of these studies, a new dynamics-based photocatalysis model is also discussed.

The role of the nucleation of sulfuric acid with amines in aerosol formation and its implications for environment is one of the fundamental unsettled questions in atmospheric chemistry. We have investigated the cluster of [(CH3)3N]·(H2SO4)·(H2O)n (n = 3–7) by molecular dynamics to obtain configurational sampling combination with CAM-B3LYP/6-311G(d,p) level to locate the global and many local minima for each cluster size. According to the binding energies at the method of MP2/6-311++G(d,p), the total binding energies decrease with the increasing of the water molecules. For each global minimum, the average binding energies decrease from n = 3 to 4, then increase slowly. The protons of H2SO4 are preferred to transfer to the (CH3)3N to form ion-pair HSO4(–) and (CH3)3NH(+), and the (CH3)3NH(+) ions are coordinated at the first hydrated shell of HSO4(–) when n is between 3 and 5 and coordinated at the second or third hydrated shell when n is larger than 5.

A highly effective (1)H NMR method for determining the absolute configurations of various chiral α-hydroxyl acids and their derivatives has been developed with the use of bisthioureas (R)-CSA 1 and (S)-CSA 1 as chiral solvating agents in the presence of DABCO, giving distinguishable proton signals with up to 0.66 ppm chemical shift nonequivalence. Computational modeling studies were performed with Gaussian09 to reveal the chiral recognition mechanism.

Excess electrons play a key role in many of the properties of Titanium dioxide (TiO2). Understanding their behaviour is important for improving the performance of TiO2 in energy-related applications. Here, we describe a DFT + U study of the locations of the unpaired electron (UPE) on rutile TiO2(110) (R-TiO2(110)) surface and H2O/R-TiO2(110) surface. Our results show that the subsurface are preferred with R-TiO2(110) surface. In contrast to previous studies, we find that the UPE tends to migrate to the surface H2O-Ti5c (the five-coordinated titanium (Ti5c) at surface with H2O adsorption) with the increasing of H2O coverage and UPE concentration. In addition, we have shown that the UPE plays an important role in the O-H bond dissociation and other important elementary reactions in photo-catalytic H2O dissociation on R-TiO2(110) such as H, OH and H2 desorption. Specifically, it enhances the O-H bond dissociation, as well as H and H2 desorption from bridging hydroxyl and Ti5c-OH (the Ti5c with OH adsorption), but hinders the OH and H desorption from Ti5c. We believe our results afford a further understanding of the adsorbent dependent UPE migration, and the role of UPE in the surface reactions.

Pyrolysis of three α,ω-diarylalkane compounds (biphenyl, diphenylmethane, and bibenzyl) was performed below 30 Pa between 573 and 1473 K. Vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry was used to detect the reactants, radicals, and products. The relative concentration profiles of the pyrolysis species were estimated by a semi-quantitative analysis method. Experimental results indicated that the length of the C–C bridge bond plays an influential role in cracking of corresponding bonds in the α,ω-diarylalkane pyrolysis process. The C–H bond scission is dominant in pyrolysis of diphenylmethane at low temperatures, while the C–C bond scission competes with it when the temperature increases. The symmetrical homolysis of bibenzyl is a dominant reaction at low temperatures and will compete with the unsymmertrical cleavage reaction with increase of the temperature. In addition, the formation mechanism of fluorene, which plays a significant role in polycyclic aromatic hydrocarbon gen...

The homoleptic heterodinuclear copper-nickel carbonyl anions CuNi(CO)n(-) (n = 2-4) were generated in a pulsed-laser vaporization source and investigated using photoelectron velocity-map imaging spectroscopy. The electron affinities of CuNi(CO)2 (2.15 ± 0.03 eV), CuNi(CO)3 (2.30 ± 0.03 eV), and CuNi(CO)4 (1.90 ± 0.04 eV) were deduced from the photoelectron spectra. Theoretical calculations at the B3LYP level were carried out to elucidate the structures and the electronic properties of CuNi(CO)n(0/1-) (n = 1-4) and to support the experimental observations. Comprehensive comparisons between experiments and calculations suggest that there is a turnover point of the absorption site during the progressive carbonylation process. The carbonyl groups are determined to be preferentially bonded to the nickel atom. When the nickel center satisfies the 18-electron configuration, the copper atom starts to adsorb additional CO molecules. These results will shed light on the bonding mechanisms of the heterometallic carbonyl clusters.

An efficient palladium-catalyzed asymmetric hydrogenation of a variety of unprotected indoles has been developed that gives up to 98% ee using a strong Brønsted acid as the activator. This methodology was applied in the facile synthesis of biologically active products containing a chiral indoline skeleton. The mechanism of Pd-catalyzed asymmetric hydrogenation was investigated as well. Isotope-labeling reactions and ESI-HRMS proved that an iminium salt formed by protonation of the C═C bond of indoles was the significant intermediate in this reaction. The important proposed active catalytic Pd-H species was observed with (1)H NMR spectroscopy. It was found that proton exchange between the Pd-H active species and solvent trifluoroethanol (TFE) did not occur, although this proton exchange had been previously observed between metal hydrides and alcoholic solvents. Density functional theory calculations were also carried out to give further insight into the mechanism of Pd-catalyzed asymmetric hydrogenation of indoles. This combination of experimental and theoretical studies suggests that Pd-catalyzed hydrogenation goes through a stepwise outer-sphere and ionic hydrogenation mechanism. The activation of hydrogen gas is a heterolytic process assisted by trifluoroacetate of Pd complex via a six-membered-ring transition state. The reaction proceeds well in polar solvent TFE owing to its ability to stabilize the ionic intermediates in the Pd-H generation step. The strong Brønsted acid activator can remarkably decrease the energy barrier for both Pd-H generation and hydrogenation. The high enantioselectivity arises from a hydrogen-bonding interaction between N-H of the iminium salt and oxygen of the coordinated trifluoroacetate in the eight-membered-ring transition state for hydride transfer, while the active chiral Pd complex is a typical bifunctional catalyst, effecting both the hydrogenation and hydrogen-bonding interaction between the iminium salt and the coordinated trifluoroacetate of Pd complex. Notably, the Pd-catalyzed asymmetric hydrogenation is relatively tolerant to oxygen, acid, and water.

An experimental study of three coal-based model compound (anisole, phenyl ethyl ether, and p-methyl anisole) pyrolysis was carried out at low pressure (below 50 Pa) within the temperature range from 573 to 1323 K. The pyrolysis process was investigated by detecting the reactants, radicals, and products using vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry. The similarities and differences of three model compounds in the pyrolysis process were discussed. The results suggested that the radical reactions were dominant in the pyrolysis process at higher temperatures, whereas the intermolecular reactions were significant at lower temperatures. β–H was a key factor for the non-radical reactions. The PhO–C homolytic bond scission was the first step for the radical reaction. Substituents on the benzene ring play an important role in the pyrolysis process of phenyl ethers, which can directly form conjugated stable structure compounds. These observations were supported by our theoretica...

In spite of a potential hydrogen storage material, ammonia borane (AB) was recently found to be a good hydrogenation reagent. It can reduce certain ketones to alcohols or borate esters, and imines to amines. The mechanisms of these reactions are not fully understood yet, and have been systematically studied using high-level CCSD(T) calculations in this work. We have validated theoretically that the forming of alcohols and amines undergoes concerted double-hydrogen transfer (DHT) mechanism. Furthermore, we predicted that the DHT process is facile for more general ketones and imines. For the borate ester formation, we found a pretty high barrier for the experimentally derived stepwise mechanism. Alternatively, we propose that the reaction starts with the DHT process to form alcohol and NH2BH2, followed by alcoholysis of NH2BH2 to form the first B–O bond. This mechanism is in good agreement with the current experimental facts, and also explains why ketone reduction affords different products at different con...

A simple chiral bisthiourea has been used as a highly effective and practical chemical solvating agent (CSA) for diverse alpha-carboxylic acids in the presence of DMAP. Excellent enantiodiscrimination based on well-resolved alpha-H NMR signals of the enantiomers of carboxylic acids can be obtained without interference from the chiral bisthiourea and DMAP. To check the practicality of the chiral bisthiourea/DMAP for enantiomeric determination, the ee values of mandelic acid (MA) samples over a wide ee range were determined by integration of the alpha-H signal of MA in H-1 NMR. A discrimination mechanism is proposed, that the formation of two diasteromeric ternary complexes between the chiral bisthiourea and two in situ formed enantiomeric carboxylate-DMAPH(+) ion pairs discriminates the enantiomers of carboxylic acids. Computational modeling studies show that the chemical shift value of alpha-H of (S)-MA is greater than that of (R)-MA in ternary complexes, which is consistent with experimental observation. 1D and 2D NOESY spectra demonstrate the intermolecular noncovalent interactions between the protons on the aromatic rings of chiral bisthiourea and alpha-H of the enantiomers of racemic alpha-methoxy phenylacetic acids in the complexes.

Ethanol on tio2(110) has been studied using the temperature-programmed desorption (tpd), femtosecond two-photon photoemission spectroscopy (2ppe), and density functional theory (dft) calculations. the first layer of ethanol (binds to ti-5c) whose molecular state has been predicted to be more stable by dft desorbs at 295 k. a photoinduced excited state that is associated with bridging hydroxyls has been detected at similar to 2.4 ev above the fermi level on ethanol/tio2(110) interface using 2ppe. detailed tpd studies show that ethanol on ti-5c can be photocatalytically converted to acetaldehyde by near-band-gap excitation with the hydrogen atoms transfer to bridging-bonded oxygen sites, which is consistent with the 2ppe results. tpd results also show a low-temperature water tpd peak that seems to bind to the ti-5c sites in addition to the ethylene tpd product. these results suggest that the ti-5c sites on tio2(110) are the primary active sites for photocatalysis of ethanol on tio2(110), while bridging-bonded oxygen sites also play an important role, as in the case of methanol. the kinetics of photocatalyzed ethanol dissociation on tio2(110) has also been measured using the 2ppe technique, which is of heterogeneous nature.

Photocatalytic hydrogen production and pollutant degradation provided both great opportunities and challenges in the field of sustainable energy and environmental science. Over the past few decades, we have witnessed fast growing interest and efforts in developing new photocatalysts, improving catalytic efficiency and exploring the reaction mechanism at the atomic and molecular levels. Owing to its relatively high efficiency, nontoxicity, low cost and high stability, TiO2 becomes one of the most extensively investigated metal oxides in semiconductor photocatalysis. Fundamental studies on well characterized single crystals using ultrahigh vacuum based surface science techniques could provide key microscopic insight into the underlying mechanism of photocatalysis. In this review, we have summarized recent progress in the photocatalytic chemistry of hydrogen, water, oxygen, carbon monoxide, alcohols, aldehydes, ketones and carboxylic acids on TiO2 surfaces. We focused this review mainly on the rutile TiO2(110) surface, but some results on the rutile TiO2(011), anatase TiO2(101) and (001) surfaces are also discussed. These studies provided fundamental insights into surface photocatalysis as well as stimulated new investigations in this exciting field. At the end of this review, we have discussed how these studies can help us to develop new photocatalysis models.

We have investigated the photocatalysis of partially deuterated methanol (CD(3)OH) and H(2)O on TiO(2)(110) at 400 nm using a newly developed photocatalysis apparatus in combination with theoretical calculations. Photocatalyzed products, CD(2)O on Ti(5c) sites, and H and D atoms on bridge-bonded oxygen (BBO) sites from CD(3)OH have been clearly detected, while no evidence of H(2)O photocatalysis was found. The experimental results show that dissociation of CD(3)OH on TiO(2)(110) occurs in a stepwise manner in which the O-H dissociation proceeds first and is then followed by C-D dissociation. Theoretical calculations indicate that the high reverse barrier to C-D recombination and the facile desorption of CD(2)O make photocatalytic methanol dissociation on TiO(2)(110) proceed efficiently. Theoretical results also reveal that the reverse reactions, i.e, O-H recombination after H(2)O photocatalytic dissociation on TiO(2)(110), may occur easily, thus inhibiting efficient photocatalytic water splitting.

Due to the potential applications of TiO2 in photocatalytic hydrogen production and pollutant degradation, over the past few decades, we have witnessed the fast-growing interest and effort in developing TiO2-based photocatalysts, improving the efficiency, and exploring the reaction mechanism at the atomic and molecular level. Since surface science studies on single crystal surfaces under UHV conditions could provide fundamental insights into these important processes, both thermal chemistry and photo-chemistry on TiO2, especially on rutile TiO2(110) surface, have been extensively investigated with a variety of experimental and theoretical approaches. In this chapter, we start from the properties of TiO2 and then focus on charge transport and trapping and electron transfer dynamics. Next, we summarize recent progresses made in the study of elementary photocatalytic chemistry of oxygen and methanol on mainly rutile TiO2(110) along with some studies on rutile TiO2(011) and anatase TiO2(101) and (001). These studies have provided fundamental insights into surface photocatalysis as well as stimulated new investigations in this exciting area. At the end of this chapter, implications of these studies for the development of new photocatalysis models are also discussed.

Three coordinated, T-shaped (PNP)M I (M = Co, Ru, Rh, Os and Ir) and [(PCP)Pt 0 ] − , as well as their reactivities for intra- and intermolecular C–H activation have been studied by DFT methods. The experimental observed reactivities were well reproduced. The calculation also generated structural and energetic information which the experimental values were not yet available. We found that the intramolecular C–H activation is in general possible for the low spin (PNP)M I . Intermolecular C–H activation is not preferred either thermodynamically or kinetically, but could be in competition if the intramolecular activation is reversible. Using model compounds, we found that the intramolecular C–H activation reactivity is not sensitive to steric effects of the bulky ligands. However, the strain of the four-membered ring in the product significantly reduces the reactivity, and the driving force increases by 4.51–12.95 kcal/mol if the strain was largely removed by changing from a four-membered ring to a five-membered ring. The C–H activation step is quite difficult for metals with a d 10 configuration. Part of the reason is that one phosphine ligand dissociates during the reaction because the product has a d 8 configuration and prefers a square planar structure.

Isomeric alkylidene complexes syn- and anti-(PNP)Ti [CtBu(C6F5)](F) (1) and (PNP)Ti [CtBu(C7F7)](F) (2) have been generated from C–F bond addition of hexafluorobenzene (C6F6) and octafluorotoluene (C7F8) across the alkylidyne ligand of transient (PNP)Ti≡CtBu (A) (PNP− N[2-P(CHMe2)2-4-methylphenyl]2), which was generated from the precursor (PNP)Ti CHtBu(CH2tBu). Two mechanistic scenarios for the activation of the C–F bond by A are considered: 1,2-CF addition and [2 + 2]-cycloaddition/β-fluoride elimination. Upon formation of the alkylidenes 1 and 2, the kinetic and thermodynamic alkylidene product is the syn isomer, which gradually isomerizes to the corresponding anti isomer to ultimately establish an equilibrium mixture (when using 1, 65/35) if the solution is heated in benzene to 105 °C for 1 h. Single crystal X-Ray crystallographic data obtained for the two isomers of 2 (and syn isomer of 1) are in good agreement with computed DFT-optimized models. Our calculations suggest convincingly that the isomerization process proceeds via a concerted rotation involving a heterolytic bond cleavage about the alkylidene bond. The two rotamers are thermodynamically very close in energy and interconvert with an estimated barrier of ∼26 kcal/mol. The electronic reason for this unexpectedly low barrier is investigated.

The reactivity of (PNP)NiI, where PNP = (tBu2PCH2SiMe2)2N, with oxidants was evaluated. Towards the nitroxyl TEMPO, a 1:1 adduct is formed which was shown to have η2-TEMPO bound through both N and O, with the consequence that one P of the PNP ligand is displaced, leaving the pincer ligand bidentate to NiII. DFT calculations show that the bidentate character of TEMPO is due to steric clash between tBu and TEMPO ring methyl groups. Reaction of (PNP)Ni with I2, Br2, C2Cl6 and even CH2Cl2 all yield (PNP)NiIIX, but never (PNP)NiIIIX2. Excess Br2 instead oxidizes one phosphorus, yielding the zwitterion [(BrtBu2PCH2SiMe2)N(SiMe2CH2PtBu2)]NiBr2, whose structure is determined. DFT calculation of the species (PNP)NiIII(Br)2 yields reaction thermodynamics which show the reason for its absence, and also shows the low BDE of its Ni–Br bond. (PNP)Ni slowly catalyzes the polymerization of HCCR (R = H or Ph), but gives no detectable conversion to a new alkyne-derived nickel complex.

Photodetachment of group 11 cyanide anions MCN(-) (M = Cu, Ag, Au) has been investigated using photoelectron velocity-map imaging. The electron affinities (EAs) of CuCN (1.468(26)) and AgCN (1.602(22)) are larger, while that of AuCN (2.066(8)) is smaller than those of the free atoms. This intriguing observation was confirmed by theoretical studies and was assigned to the transition between ionic and covalent bond properties. The harmonic frequencies of the extended vibrational progressions in the M-C stretching mode are 460(50), 385(27), and 502(10) cm(-1), respectively, which suggests a stronger bond for Au-CN than for Ag-CN. Electronic structure analysis and model calculations suggest that all M-C bonds in group 11 cyanides are best described as single bonds. A model has been proposed to explain how the relativistic effects influence the Au-C bond strength in AuCN.

A synthesis of [(PNP)OsI] {PNP = (tBu 2 PCH 2 SiMe 2 ) 2 N} permits evaluation of its reactivity, both Lewis acidity and reducing power (i.e., ability to be oxidized). It binds two molecules of PhCN, into trans sites, but only one of ethylene, and, upon binding of one N 2 , there is heterolytic splitting of one tBu C-H bond to put the proton on amide N and the carbon on Os, leaving divalent metal in [{PN(H)P*}Os(N 2 )(I)]. Two moles of H 2 add, forming [{PN(H)P}OsH(H 2 )I], via H-H bond heterolysis. Thermolysis of [(PNP)OsI] gives the product of adding a tBu methyl C-H bond across the Os/N bond, and also net dehydrogenation of this intermediate, forming a carbene complex; the released H 2 forms [(PNP)OsH 2 I], and the chemistry of [(PNP)Os] hydridohalides is described. Reaction with O 2 occurs with no detectable intermediate, to completely split the O=O bond, and form trans-[(PNP)Os(O) 2 I], a product of four electron redox change. Attempted two electron oxidation by oxygen atom transfer with pyridine N-oxide or Me 3 NO or N 2 O surprisingly effect transposition of N from its silyl substituents onto the metal, and replace N by 0, forming a nitride complex of a bis(silyl ether, phosphane) chelate whose oxygen fails to bind to Os. The product is thus four-coordinate, tetrahedral [(POP)Os(N)I], with an Os/N triple bond.

The neopentylidene−neopentyl complex (PNP)Ti═CHtBu(CH2tBu) (1; PNP− = N[2-P(CHMe2)2-4-methylphenyl]2) extrudes neopentane in neat pyridine or picoline (3- or 4-picoline) under mild conditions (25 °C), to generate the transient titanium alkylidyne intermediate (PNP)Ti≡CtBu (A), which subsequently ring-opens the pyridine by ring-opening metathesis of the aromatic N═C bond across the Ti≡C linkage, generating the metallaazabicycles (PNP)Ti(C(tBu)C5H3RNH) (R = H (2), 3-Me (3), 4-Me (4)). Kinetic studies suggest that the C−N activation process obeys a pseudo-first-order process in titanium, with α-hydrogen abstraction being the rate-determining step (the KIE for 1/1-d3 conversion to 2 was 3.8(3) at 25 °C). The activation parameters are ΔH⧧ = 23(3) kcal/mol and ΔS⧧ = −4(3) cal/(mol K). The intermolecular kH/kD ratio is close to unity, 1.07(3) at 25 °C, for the conversion of 1 to 2 in pyridine versus pyridine-d5. Detailed theoretical studies suggest the 1 → 2 transformation proceeds in the following order: (i) fo...

The F-atom reaction with NH(3) and ND(3) has been studied using the universal crossed beams technique. Angular resolved time-of-flight spectra were measured for the HF and DF reaction products. Product angular distribution and product kinetic energy distribution in the center-of-mass frame were determined from the experimental TOF spectra. Experimental results show that the HF and DF products are largely forward-scattered relative to the F-atom beam direction with a considerable amount of product at sideway and backward scattering directions. High-level ab initio calculation on the reaction energy pathway suggests that the forward-scattered products are mainly produced via a direct abstraction mechanism at large impact parameters, whereas sideway- and backward-scattered products are likely due to a long-lived complex formation mechanism.

Protonation of (PNP)RuN, where PNP is (tBu2PCH2SiMe2)2N, with HCl occurs at the amide nitrogen, with coordination of chloride to RuIV, while triflic acid protonates the same nitrogen, but has triflate anion hydrogen-bonded to the proton on the PNP amide nitrogen, not triflate coordinated to the metal. Methyl triflate however alkylates the nitride nitrogen, to give a C2v symmetric product. DFT calculations show that the thermodyamic preference is for proton on amide nitrogen while alkyl favors nitride alkylation, even without the need for a hydrogen bond to reverse the H vs. alkyl preference. Alkylation at the amide nitrogen leads to nearly complete loss of the PN(R)P Ru/N bond in this unobserved isomer. These preferences among nucleophilic sites on (PNP)RuN are rationalized based on the frontier orbitals of this molecule.

A series of three-coordinate Cr(II) complexes sharing the common molecular fragment "(nacnac)Cr" (nacnac(-) = [ArNC((t)Bu)](2)CH, Ar = 2,6-(i)Pr(2)C(6)H(3)) were prepared via salt metathesis with the dimer [(nacnac)Cr(mu-Cl)](2). Single-crystal X-ray diffraction studies revealed that the complexes (nacnac)Cr(L) (L = CH(2)(t)Bu, CH(3), CH(2)CH(3), SiH{2,4,6-Me(3)C(6)H(2)}(2), O{2,6-(i)Pr(2)C(6)H(3)}, N{CH(3)}(2)) represent a rare class of mononuclear, neutral chromium complexes with a three-coordinate high-spin chromous metal center. Depending on the nature of the third ligand, L(-), these complexes can adopt either distorted T-shaped or Y-shaped coordination geometries. Density functional theory calculations and molecular orbital analyses in combination with a detailed molecular fragment energy decomposition were used to establish an intuitive concept of the key electronic structure patterns that determine the coordination geometry of preference. The frontier orbitals of the (nacnac)Cr(II) fragment direct pi-donating ligands to adopt Y-shaped geometry, whereas ligands that are primarily sigma-donors prefer T-shaped coordination. The relationship between electronics at the metal center and coordination geometry was extended to include the putative neutral three-coordinate high-spin complexes of Sc(II) and Mn(II), which are predicted to both adopt Y-shaped geometry.

The reaction of phenyl azide with (PNP)Ni, where PNP = ( (t)Bu 2PCH 2SiMe 2) 2N (-), promptly evolves N 2 and forms a P=N bond in the product (PNP=NPh)Ni (I). A similar reaction with (PNP)FeCl proceeds to form a P=N bond but without N 2 evolution, to furnish (PNP=N-N=NPh)FeCl. An analogous reaction with (PNP)RuCl occurs with a more dramatic redox change at the metal (and N 2 evolution), to give the salt composed of (PNP)Ru(NPh) (+) and (PNP)RuCl 3 (-), together with equimolar (PNP)Ru(NPh). The contrast among these results is used to deduce what conditions favor N 2 loss and oxidative incorporation of the NPh fragment from PhN 3 into a metal complex.

[Rh{sup III}H{l_brace}(tBu{sub 2}PCH{sub 2}SiMe{sub 2}NSiMe{sub 2}CH{sub 2}PtBu{l_brace}CMe{sub 2}CH{sub 2}{r_brace}){r_brace}], ([RhH(PNP*)]), reacts with O{sub 2} in the time taken to mix the reagents to form a 1:1 {eta}{sub 2}-O{sub 2} adduct, for which O-O bond length is discussed with reference to the reducing power of [RhH(PNP*)]; DFT calculations faithfully replicate the observed O-O distance, and are used to understand the oxidation state of this coordinated O{sub 2}. The reactivity of [Rh(O{sub 2})(PNP)] towards H{sub 2}, CO, N{sub 2}, and O{sub 2} is tested and compared to the associated DFT reaction energies. Three different reagents effect single oxygen atom transfer to [RhH(PNP*)]. The resulting [RhO(PNP)], characterized at and above -60 C and by DFT calculations, is a ground-state triplet, is nonplanar, and reacts, above about +15 C, with its own tBu CH bond, to cleanly form a diamagnetic complex, [Rh(OH){l_brace}N(SiMe{sub 2}CH{sub 2}PtBu{sub 2})(SiMe{sub 2}CH{sub 2}PtBu{l_brace}CMe{sub 2}CH{sub 2}{r_brace}){r_brace}].