Structural and elemental investigations of isolated aquatic humic substances using X-ray photoelectron spectroscopy

Structural and elemental investigations of aquatic humic substances (HS) by means of X-ray photoelectron spectroscopy (XPS) are described. For that purpose small amounts (10–50 μg) of dissolved reference HS, which were characterized within the German research program DFG-ROSIG, were dried as thin films on small pieces of a high-purity silicon wafer. The photoelectrons from such HS layers exhibited characteristic signals of carbon C1s, nitrogen N1s, oxygen O1s and sulfur S2s, which could be fitted by Gaussian curves and used for the quantification of various moieties of HS: carbon (C-C, C-O, C=O, O=C-O), oxygen (C-O, C=O), nitrogen (C-N, C-N⁺) and sulfur. Moreover, by adding up the element signals of the HS samples their elemental composition of C, O, N and S was assessed. A comparison of the data based on solution state NMR and conventional elementary analysis revealed a satisfactory accuracy with those obtained by XPS.     

XPS法研究煤表面碳官能团的变化及硫迁移行为

采用XPS对六枝（Liuzhi）和遵义（Zunyi）原煤及其固定床热解半焦表面的含碳官能团和硫迁移行为进行了研究。在氮气气氛下,在400℃～700℃遵义煤焦表面O=C－O, C－H 和 C－C含量与原煤相比,呈现下降趋势,而C=O和O－C－O、C－O含量却呈现增加趋势; 六枝煤焦表面的O=C－O、C=O和O－C－O、C－O含量的变化规律与遵义煤相似,而C－H和C－C含量的变化却与遵义煤相反。在氢气气氛下, 遵义煤焦表面不仅O=C－O含量与原煤相比下降, 而且C=O和O－C－O、C－O含量也下降,但C－H和C－C含量却增加; 六枝煤除了C=O 和O－C－O含量下降外, 其他官能团的变化与其在氮气气氛下相似。两种煤焦表面S/C比在氮气气氛下随着温度的升高而升高,氢气气氛下在400℃~600℃随着温度的升高却下降,700℃又显著升高。这说明在热解过程中硫在两种气氛下都能从体相向表面迁移,但是氢气能够和含硫自由基反应,所以氢气气氛下煤焦表面的S/C比率低于其氮气气氛下的。     

Photoemission and near-edge X-ray absorption fine structure studies of the bacterial surface protein layer of Bacillus sphaericus NCTC 9602

The electronic structure of the regular, two-dimensional bacterial surface protein layer of Bacillus sphaericus NCTC 9602 has been examined by photoemission (PE) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Both the O 1s and the N 1s core-level PE spectra show a single structure, whereas the C 1s core-level spectrum appears manifold, suggesting similar chemical states for each oxygen atom and also for each nitrogen atom, while carbon atoms exhibit a range of chemical environments in the different functional groups of the amino acids. This result is supported by the element-specific NEXAFS spectra of the unoccupied valence electronic states, which exhibit a series of characteristic NEXAFS peaks that can be assigned to particular molecular orbitals of the amino acids by applying a phenomenological building-block model. The relative contributions of the C-O, C-N, and C-C bond originating signals into the C 1s PE spectrum are in good agreement with the number ratios of the corresponding bonds calculated from the known primary structure of the bacterial surface protein. First interpretation of the PE spectrum of the occupied valence states is achieved on the basis of electronic density-of-states calculations performed for small peptides. It was found that mainly the pi clouds of the aromatic rings contribute to both the lowest unoccupied and the highest occupied molecular orbitals.     

C-C, C-O and C-N bond formation via rhodium(III)-catalyzed oxidative C-H activation

Rhodium(III)-catalyzed direct functionalization of C-H bonds under oxidative conditions leading to C-C, C-N, and C-O bond formation is reviewed. Various arene substrates bearing nitrogen and oxygen directing groups are covered in their coupling with unsaturated partners such as alkenes and alkynes. The facile construction of C-E (E = C, N, S, or O) bonds makes Rh(III) catalysis an attractive step-economic approach to value-added molecules from readily available starting materials. Comparisons and contrasts between rhodium(III) and palladium(II)-catalyzed oxidative coupling are made. The remarkable diversity of structures accessible is demonstrated with various recent examples, with a proposed mechanism for each transformation being briefly summarized (critical review, 138 references).     

X-ray absorption microscopy of bacterial surface protein layers: X-ray damage

The electronic structure of individual sheets of the bacterial surface protein layer (S layer) of Bacillus sphaericus NCTC 9602 was studied using a photoemission electron microscope (PEEM) operating in near-edge X-ray absorption fine structure spectroscopy mode. The laterally resolved measurements performed at the C 1s, N 1s, and O 1s thresholds on fresh samples revealed characteristic differences compared to the laterally integrated data, where substrate contributions were taken along with the protein signals. During the PEEM experiments an irradiation-induced increase of the C-C bond density at the cost of the densities of the C-O and C-N bonds related to a rearrangement of the contributing atoms of the S layer deposited onto a Si substrate was observed. The critical irradiation doses for the C-O and C-N bond breaking and formation of the new C-C bonds were derived.     

金催化剂在联烯亲核加成反应中的应用

金催化联烯亲核加成反应是形成碳碳、碳氮、碳氧以及碳硫键的重要方法.综述了近年来金催化含碳、含氮、含氧以及含硫亲核试剂与联烯的亲核加成反应以及在不对称杂环化合物合成中的应用,并对各种反应历程的特点及其影响因素进行了讨论.     

Adlayers of dimannoside thiols on gold: surface chemical analysis

Carbohydrate films on gold based on dimannoside thiols (DMT) were prepared, and a complementary surface chemical analysis was performed in detail by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), near-edge X-ray absorption fine structure (NEXAFS), FT-IR, and contact angle measurements in order to verify formation of ω-carbohydrate-functionalized alkylthiol films. XPS (C 1s, O 1s, and S 2p) reveals information on carbohydrate specific alkoxy (C-O) and acetal moieties (O-C-O) as well as thiolate species attached to gold. Angle-resolved synchrotron XPS was used for chemical speciation at ultimate surface sensitivity. Angle-resolved XPS analysis suggests the presence of an excess top layer composed of unbound sulfur components combined with alkyl moieties. Further support for DMT attachment on Au is given by ToF-SIMS and FT-IR analysis. Carbon and oxygen K-edge NEXAFS spectra were interpreted by applying the building block model supported by comparison to data of 1-undecanethiol, poly(vinyl alcohol), and polyoxymethylene. No linear dichroism effect was observed in the angle-resolved C K-edge NEXAFS.     

Physical and chemical characterization of iris and choroid melanosomes isolated from newborn and mature cows

Bovine iris and choroid melanosomes at two ages (<1 week and >2 years) were examined by inductively coupled plasma mass spectrometry (ICP-MS), elemental analysis, infrared spectrometry (IR) and X-ray photoelectron spectrometry (XPS). When iris and choroid melanosomes at the same age were compared, the quantification of metal elements by ICP-MS revealed that choroid melanosomes had a higher binding capacity for the carboxylate-binding metal ions (e.g. Na+ K+, Mg2+, Ca2+ and Zn2+). Elemental analysis showed a higher O:N ratio in choroid melanosomes. Both observations suggested that choroid melanosomes have a higher content of carboxylate-containing monomer than iris melanosomes. IR spectrometric analysis showed a red shift (approximately 8 cm(-1)) of the absorption peak of aromatic C=C, C=N and C=O at approximately 1630 cm(-1) in the IR spectrum of iris melanosomes relative to choroid melanosomes. Increased conjugation in the molecular structure of the pigment is proposed to contribute to this peak shift. It is also notable that although the elemental analysis showed different C, N and O contents in the two types of melanosomes, XPS showed almost the same elemental compositions on the surface of two types of iris and choroid melanosomes studied. When the melanosomes from the same tissues at different ages were compared, ICP-MS analysis suggested that the number of carboxylate groups in the melanosomes decreased with age. Both elemental analysis and XPS showed that C:N ratio decreased with age, which was proposed to be due to both a decrease in carboxylate groups in mature samples and to the fissure of phenol rings caused by age-associated oxidation. Such age-related oxidative damage diminishes conjugation and is manifested by blue shifts of absorption peaks for aromatic double bonds in the IR spectra of mature melanosomes. XPS analysis showed that the ratio of C-O:C=O decreased with age. These tissue-related and age-related chemical differences between samples affected the optic density and metal binding properties of melanosomes, which are believed to be closely associated with the biological functions of melanins.     

Spectral and magnetic properties of phenylazo-6-aminouracil complexes

Complexes of Co(II), Ni(II) and Cu(II) with substituted phenylazo-6-aminouracils containing (-H, p-OH, p-CH(3), p-OCH(3) p-COOH) have been synthesized and characterized by elemental analysis, magnetic measurements and spectral measurements (IR, UV-Vis, ESR). Infrared spectra assigned the fundamental bands of the major groups, O-H, N-H, C-H, C=O, C=N, N=N, C-N and C-O (nu, delta and gamma modes of vibrations). The absence of nu(OH) and the appearance of nu(C=O) in the infrared spectra of the free ligands of 5-(p-tolyl and p-anisylazo)-6-aminouracil, assigned the keto structure, whereas in cases of 5-(phenyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracil ligands, the data showed strong nu(OH) and nu(C=O) bands to assign keto-enol tautomerisms. The modes of interactions between the ligands and the metals were discussed, where oxygen and nitrogen atoms (of amino-amide groups) are involved in chelation. The azo group was not involved in chelation for all the prepared complexes except those of copper complexes derived from 5-(phenyl, p-tolyl, p-hydroxyphenyl and p-carboxyphenylazo)-6-aminouracils. The room temperature effective magnetic moment values, the Nujol mull spectra and ESR proved that all the prepared complexes were of octahedral geometry, except the nickel complex derived from 5-(phenylazo)-6-aminouracil and cobalt complex derived from 5-(p-carboxy-phenylazo)-6-aminouracil were square planar.     

Crystal and Molecular Structure of Cyanuric Acid

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XPS investigations of thick,oxygen-containing cubic boron nitride coatings

Cubic boron nitride (c-BN) coatings produced by PVD and PECVD techniques usually exhibit very high compressive stresses and poor adhesion due to intense ion bombardments of the growing surface that are mandatory during the formation of the cubic phase. Our previous investigations indicate, however, that a controlled addition of oxygen during film deposition can lead to a drastic reduction of the detrimental stress, yet having minor effect on the cubic phase content in the resulting low-stress, oxygen-containing c-BN:O coatings (as already confirmed by various analytical methods like X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and electron diffraction, and Fourier transform infra-red spectroscopy (FTIR)). This stress-reduction technique makes possible the deposition of well-adhered, superhard c-BN:O layer about 2 μm thick through magnetron sputtering on top of an adhesion-promoting base layer and via a compositional-graded nucleation process. In the present paper, we report on the atomic bonding structure relating in particular to the incorporated oxygen within such a thick c-BN:O coating using X-ray photoelectron spectroscopy (XPS). The c-BN:O top layer was found to consist of about 49.8 at% boron, 42.2 at% nitrogen, 5.5 at% oxygen, as well as small amounts of carbon (1.4 at%) and argon (1.1 at%). Because of the low oxygen concentration, it was difficult to categorize the bonding state of oxygen according to the XPS spectra of B 1s and N 1s elemental lines. However, the detailed results in terms of the O 1s spectrum strongly indicated that the lattice nitrogen of c-BN was partially replaced by the added oxygen.     

Dye-sensitized photooxygenation of the C=N bond. 5. substituent effects on the cleavage of the C=N bond of C-aryl-N-aryl-N-methylhydrazones

The title compounds are cleaved cleanly at the C=N bond by singlet oxygen ((1)O(2), (1)Delta(g)) yielding arylaldehydes and N-aryl-N-methylnitrosamines. These reactions take place more rapidly at -78 degrees C than at room temperature. The effects of substituent variation at both the C-aryl and N-aryl groups were studied using a competitive method. Good correlations of the resulting rate ratios with substituent constants (sigma(-) or sigma(+)) were obtained yielding small to very small rho values indicative of small to very small changes in charge distribution between the reactant and the rate determining transition state. Electron withdrawing groups on the C-aryl moiety retard reaction somewhat by preferential stabilization of the hydrazone. Electron donors on the other hand slightly stabilize the rate determining transition state. Substituents on the N-aryl group have almost no effect. Inhibition by 3,5-di-tert-butylphenol was not observed showing that free (uncaged) radical intermediates are not involved in the mechanism. We postulate a mechanism in which the initial event is exothermic electron transfer from the hydrazone to (1)O(2) leading to an ion-radical caged pair. Subsequent covalent bond formation between the hydrazone carbon and an oxygen atom is rate controlling. The transition state for this step also has a lower enthalpy than the starting reactants, but the free energy of activation is dominated by a large negative TDeltaS++term leading to the negative temperature dependence. Direct formation of a C-O bond in the initial step is not unambiguously ruled out. Subsequent steps lead to C-N cleavage.     

Determining the interaction and characterization of asphaltene in alkylbenzene solvents using nuclear-electron double resonance

This study uses ¹H dynamic nuclear polarization (DNP) methods to determine asphaltene aggregates and the interaction between asphaltene extracted from MC800 asphalt and alkylbenzene solvents, as well as elemental analysis for the characterization of asphaltene. The asphaltene sample was characterized using the elemental analysis of carbon (C), hydrogen (H), nitrogen (N), and sulfur (S). The results show that asphaltenes have the highest carbon content. The sulfur and hydrogen contents are nearly the same and nitrogen content is the smallest. The DNP data provided good results for characterizing asphaltene behavior in alkylbenzene solvents.     

CexZr1-xO2/Co/C-N催化CO2加氢性能研究

将不同比例的铈锆前驱体负载到ZIF-67,氮气气氛焙烧制备CexZr1-xO2/Co/C-N催化剂,对催化剂进行了XRD,H2-TPR、XPS表征,并在固定床反应器评价其CO2加氢制甲醇性能。XRD结果表明,在铈中加入适量锆形成铈锆固溶体,铈锆固溶体与钴物种较强的相互作用力可以阻止表明金属Co的氧化。但过量加入的锆又会削弱这一作用力,部分金属Co被氧化为Co3O4。H2-TPR结果表明适量的锆的加入改善催化剂的还原性能,催化剂还原温度降低。XPS证实了25%Ce0.67Zr0.33O2/Co/C-N催化剂中含有更多的氧空穴及氮含量,氧空穴和碱性氮都有利于CO2的解离吸附。优化后的25%Ce0.67Zr0.33O2/Co/C-N 催化剂在225 oC,2 MPa,GHSV = 6 L/gcat/h反应条件下取得最高甲醇时空收率,为3.0 mmol/gcat/h。     

Surface characterization of 7S and 11S globulin powders from soy protein examined by X-ray photoelectron spectroscopy and scanning electron microscopy

In this study the surface composition of 7S and 11S globulin powders from soybean proteins by aqueous buffer and reverse micelle extractions had been examined using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Analysis by XPS revealed that the O and N atomic percentage of 7S and 11S globulin surfaces from bis(2-ethylhexyl) sodium sulfosuccinate (AOT) reverse micelle was higher than from aqueous buffer, but the C atomic percentage was lower. The O/C ratio of the 7S globulin powder from aqueous buffer and reverse micelle was similar while significant differences were obtained in the O/C ratio of the 11S globulin powder, N/C atom ratios of the 7S and 11S globulin powders and high-resolution XPS C 1s, N 1s, O 1s spectra. Powder microstructure after reverse micelle treatment showed the presence of small pores, indicating the effect of reverse micelle on the 7S and 11S globulin structure. The obtained results indicated that the reverse micelle could affect the C, O and N components on the surface of soybean proteins.     

Oxygen, carbon, and sulfur segregation in annealed and unannealed zerovalent iron substrates

Finely ground and pretreated iron substrates known as "zerovalent iron" or "Fe0" are used as reductants in the environmental remediation of halogenated hydrocarbons, and the composition of their surfaces significantly affects their reactivity. Samples of unannealed and annealed (heat-treated under H2/N2) zerovalent iron were analyzed using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Surface concentration of the iron and of the impurities observed by XPS and AES, carbon, chlorine, sulfur, and oxygen, were measured before and after soaking in trichloroethylene (TCE) and in water saturated with TCE (H2O/TCE) to simulate chlorocarbon remediation conditions. Samples pretreated by annealing at high temperature under H2 contained less iron carbide. The carbide contaminant was evident in both iron and carbon XPS spectra, with binding energies of 709.0 and 283.3 eV for the Fe 2p3/2 and C 1s, respectively. The annealed Fe0 surface also contained more sulfur. The carbide concentration was essentially unchanged by TCE and H2O/TCE exposure, whereas the sulfur decreased in proportion to chlorine adsorption following the dechlorination reaction. While oxygen concentration is initially lower on the annealed substrate surface, it rapidly increased during the model TCE remediative treatment process and thus does not represent a significant effect of the annealing process on surface reactivity.     

片状碳载金属纳米颗粒复合物的制备及其氧还原电活性

将双氰胺、蔗糖与酞菁铁(钴)的混合物通过简单热解法,制备出Co/C-N、Fe/C-N和Fe-Co/C-N纳米复合物。随后利用热还原法,将少量铂沉积于Co/C-N上得到片状碳负载的Co-Pt纳米颗粒Co-Pt/C-N。对样品进行了详细表征,并研究了其在全域pH范围内(酸性、中性与碱性溶液)中的氧还原反应(ORR)活性。结果表明,Co/C-N具有比Fe/C-N和Fe-Co/C-N更高的ORR起始电位和半波电位,并且在碱性和中性溶液中,Co/C-N表现出比Pt/C更强的ORR电活性;在酸性溶液中,铂负载量(质量分数)8.1%的Co-Pt/C-N表现出与Pt/C相近的ORR起始与半波电位。催化剂优异的电活性主要归因于片状碳形成的三维结构、金属纳米颗粒的均匀分布以及丰富的吡啶氮。     

Crystal Structure of 1，5－Bis（Ts），1，5－diaza－13－crown－4（Ts＝p－methylphenylsulfonyl）

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紫外辐照对高密度聚乙烯分子结构的影响

紫外线;官能化;紫外辐照对高密度聚乙烯分子结构的影响