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1.
 Analytic formulae of the relativistic radial functions of hydrogen-like atoms in the four-component standard Dirac picture and in two approximations, (Pauli and ZORA), to the two-component (so-called Schr?dinger or Newton–Wigner) picture and graphs of the respective relativistic changes of densities are presented and discussed. The two different pictures of the Dirac density of charge position and of the Newton–Wigner density of mass position are remarkably different in strongly inhomogeneous fields and result in respective differences in position-dependent expectation values, <r ν>. The fractional magnitudes of Δrel<r ν>, of Δcharge/mass<r ν>, and of the gauge dependence of ZORA (which for small n states is comparable to the difference of the two kinds of position observables) are all of order Z 2α2.  相似文献   

2.
The kinetics of the 420 nm luminescence emitted from H2O and D2O polycrystalline Ih ices have been studied over the 77 to 162 K temperature range. In the case of both H2O and D2O ices, it was found that the luminescence rise and decay curves consisted of two luminescence components, and superimposing two first-order curves with different rate constants gave the best fit to the decay and rise curves. The mean lifetimes of the two luminescence components were 1.08 ± 0.03 s and 2.47 ± 0.03 s. The rate constants were found to have negligible temperature dependences, which led to activation energies well below those obtained for either activation-limited processes or even diffusion-limited processes. Furthermore, it was found that the luminescence kinetics were not affected by isotopic substitution of D for H in the ice lattice. These observations suggest that the rate-determining step in the mechanism for the production of the luminescence is a slow (probably spinforbidden) electronic transition that can occur at two different rates due to the presence of two different types of trapping sites in the ice lattice. A possible candidate for the electronic transition is the 4Σ → X 2Π transition of excited OH. radicals and not the previously suggested and ubiquitous A 2Σ+X 2Π transition of this species. Published in Russian in Kinetika i Kataliz 2006, Vol. 47, No. 5, pp. 709–721. This text was submitted by the authors in English.  相似文献   

3.
The N-loss predissociation mechanisms of the A 2Σ+ (2 2 A′) state of N2O+ to the first and second dissociation limits were studied in the C s symmetry. The potential energy curves (PECs) and minimum energy crossing points (MECPs) for the C s states of N2O+ were calculated at the CAS levels. On the basis of our CAS calculation results (CASPT2 energetic results and CASSCF spin orbit couplings), we suggest two processes for N-loss predissociation mechanisms of A 2Σ+ (2 2 A′) to the first and second limits. The first two steps in the two processes are the same: A 2Σ+ passes through the 2 2 A′/1 4 A″ MECP and then reaches the 1 4 A″ (1 4Σ) PEC. The 2 2 A′/1 4 A″ MECP has a bent geometry and is slightly higher in energy than the transition state along the 1 4 A″ PEC. Our mechanisms are different from the previously suggested mechanisms (via 1 4Π).  相似文献   

4.
The stable carbon and nitrogen isotopic composition of urine and milk samples from cattle under different feeding regimes were analysed over a period of six months. The isotope ratios were measured with isotope ratio mass spectrometry (IRMS). The δ 13C values of milk and urine were dependent on different feeding regimes based on C3 or C4 plants. The δ 13C values are more negative under grass feeding than under maize feeding. The δ 13C values of milk are more negative compared to urine and independent of the feeding regime. Under grass feeding the analysed milk and urine samples are enriched in 13C relative to the feed, whereas under maize feeding the 13C/12C ratio of urine is in the same range and milk is depleted in 13C relative to the diet. The difference between the 15N/14N ratios for the two feeding regimes is less pronounced than the 13C/12C ratios. The δ 15N values in urine require more time to reach the new equilibrium, whereas the milk samples show no significant differences between the two feeding regimes.  相似文献   

5.
By alternate use of two different extraction solvents, n-hexadecane and benzyl alcohol, a headspace-solvent microextraction (HSME)–GC–FID/MS method has been established for characterization of the volatile components of an orange juice beverage. The method avoids two disadvantages of conventional HSME—difficulty identifying components obscured by the solvent peak and inefficient extraction of some of the compounds if one solvent only is used. The optimum conditions (droplet volume, equilibration temperature and time, extraction time, and ionic strength) were determined by the factor-rotation method. The volatile components of the beverage were mainly terpenes, terpenols, fatty acids, and alcohols, for example limonene (114.71 mg L−1), phellandrene (4.50 mg L−1), terpineol (p-menth-1-en-8-ol; 3.12 mg L−1), α-pinene (0.33 mg L−1), n-hexadecanoic acid (0.28 mg L−1), and terpinol (0.13 mg L−1).  相似文献   

6.
 The behavior of the single spreading monolayers of β-lacto-globulin (β-LG) and dioleyl-phosphatidylcholine (DOPC), as well as their mixtures, has been studied on subphases containing Na+ or Ca++ ions. The results show an influence of temperature and subphase on the studied systems. The behavior of the areas as a function of the weight fraction of the two components shows significative and prevalently positive deviations from the additivity and their bidimensional miscibility. The variation of ΔG ex, ΔH ex and ΔS ex calculated for the DOPC–β-LG mixture having maximum deviation on two different supports allows to deduce that the interactions are prevalently repulsive. FTIR–ATR spectra of transferred plurilayers show that DOPC has a surface orientation which can originate the miscibility between the protein and DOPC. Received: 3 February 1997 Accepted: 3 June 1997  相似文献   

7.
The high resolution adsorption isotherms of N2 (77.4 K) and Ar (87.3 K) have been measured for two nonporous silicas with different silanol contents (3.3 and 0.35 OH/nm2) and for two MFI zeolite with different Al contents (Si/Al=12.5 and 500). Silanol groups and Al sites (acid sites) gives the significant effect on the N2 isotherms at submonolayer, but the Ar isotherms are independent of silanols and Al sites. The Ar isotherms, therefore, are preferable in calculation of microporosity of zeolites. The N2 and Ar isotherms for MFI zeolite (Si/Al=500) have been measured at temperatures of 77–94 K, from which the differential adsorption energies of N2 and Ar are calculated. The interaction of N2 with channel surface of MFI zeolite is greater than that of Ar in the range of α s =0.1–0.7. The hystereses are detected for the N2 isotherm in p/p o=0.1–0.3 at 77.4 K and for the Ar isotherm in p/p o=3×10−4–2×10−3 at 87.3 K. However, it is difficult to explain the hysteresis phenomenon using differential adsorption energy.  相似文献   

8.
This work allowed the characterization of the Cd-binding sites of two compounds taken as models for exudates, the main components of soil organic matter (SOM). The studied compounds were exopolysaccharides (EPS), specifically exudates of roots (polygalacturonic acid) and of soil bacteria (Phytagel). Potentiometric acid–base titrations were performed and fitting of the obtained results indicated the presence of two main classes of acidic sites, defined by their pK a values, for both EPS but of a different nature when comparing the two compounds. The two studied exopolysaccharides presented different acidic/basic site ratios: 0.15 for Phytagel and 0.76 for polygalacturonic acid. Spectroscopic techniques (13C/113Cd NMR, FTIR) distinguished different Cd surroundings for each of the studied EPS, which is in agreement with the titration results. Furthermore, these analyses indicated the presence of –COOH and –OH groups in various proportions for each exopolysaccharide, which should be linked to their reactivity towards cadmium. Cadmium titrations (voltammetric measurements) also differentiated different binding sites for each compound and allowed the determination of the strength of the Cd-binding site of the EPS. Fitting of the results of such voltammetric measurements was performed using PROSECE (Programme d’Optimisation et de Speciation Chimique dans l’Environnement), a software coupling chemical speciation calculation and binding parameter optimization. The fitting, taking into account the Cd2+/H+ competition towards exopolysaccharides, confirmed the acid-base titrations and spectroscopic analyses by revealing two classes of binding sites: (i) one defined as a strong complexant regarding its Cd2+–EPS association (logK = 9–10.4) and with basic functionality regarding H+–EPS association (pK a = 11.3–11.7), and (ii) one defined as a weak complexant (logK = 7.1–8.2) and with acidic functionality (pK a = 3.7–4.0). Therefore the combination of spectroscopic analyses, voltammetry, and fitting allowed the precise characterization of the binding sites of the studied exopolysaccharides, mimicking the main SOM components. Furthermore, the binding parameters obtained by fitting can be used in biogeochemical models to better define the role of key SOM compounds like exudates of roots and of soil bacteria on trace metal transport or assimilation.  相似文献   

9.
The existence of a hydrogen bond in which a methyl group of the (MeOH)2H+ ion acts as a proton donor is examined. The fundamental vibration frequencies of this ion were calculated for different numbers and strengths of CH…O bonds. The atomic charges in neutral ((MeOH) n ,n=1–4) and protonated ((MeOH) m H+,m=2–6) associates of methanol molecules were also calculated. The experimentally observed decrease in the v(CH) vibration frequencies of the (MeOH)2H+ ion to 2890 cm−1 and 2760 cm−1 is attributable to the fact that each methyl group of the ion is involved in formation of two CH…O bonds with strength of −12.5 kJ mol−1. The proton-donating ability of the CH bond depends on the charge on its H atom; however, it does not correlate with the dipole moment of this bond. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 306–312, February, 1999.  相似文献   

10.
The CEPA-PNO method is used for calculating the energy difference ΔE ST between the3 and the1Δ states of diatomic molecules in electronic π2 configurations. An analysis of the contribution of electron correlation to ΔE ST is performed in terms of physically understandable effects such as direct correlation, dynamic spin polarization, semiinternal and internal excitations. It is shown that these effects are of completely different importance for the molecules treated in this study: For C2 the direct correlation between the two singly occupied π-orbitals is the dominant correlation contribution to ΔE ST; for O2, S2, SO the internal excitation π u 2 → π g 2 is predominant, whereas for NH and PH there is a close competition between the direct correlation and the spin polarization of the underlying σ-orbitals. The basis set dependence of these effects is investigated, in particular for NH. Our final results reproduce experimental values of ΔE ST within 0.05–0.10 eV.  相似文献   

11.
Ion exchange equilibrium constant (K) for Cl/Br and Cl/C2O42− system was studied at different temperatures from 30 to 45°C. For both uni-univalent and uni-bivalent exchange systems, the value of K increases with rise in temperature i.e., from 1.16 at 30°C to 2.95 at 45°C for Cl/Br system and 19.5 at 30°C to 30.0 at 45°C for Cl/C2O42− system indicating the endothermic ion exchange reaction. The difference in K values at the same temperature for the two was related to the ionic charge of exchangeable ions in the solution. The article is published in the original.  相似文献   

12.
We have examined the uptake of actinide elements Am and, Pu by different species of lichen and moss collected in two locations (Urbino, Central Italy; Alps region, North-east Italy). Plutonium and americium were separated and determined by extraction chromatography, electrodeposition and alpha-spectrometry. This paper summarizes our results with a special emphasis on the vertical profiles of these actinides in two different species of mosses. Several 1–2 cm depth sections were obtained and dated by210Pb method. A typical peak for239,240Pu and241Am was found in the very old moss species (“Sphagnum Compactum”) at a depth corresponding to the period 1960–1970 which was the period characterized by the maximum nuclear weapon tests. In a younger moss species (“Neckeria Crispa”) no peak was observed and the regression curves showed that Am is more mobile than239,240Pu and238Pu.  相似文献   

13.
New 2-substituted diazaphospholane-2-oxides (I-III, V-VIII) and diazaphosphorinane-2-oxide (IV) were synthesised and characterised by 1H, 13C, and 31P NMR, IR spectroscopy, and elemental analysis. The presence of chiral diamino groups in compounds II and V–VIII gives rise to various diastereomers so that the 31P{1H} NMR spectra demonstrated three and two peaks with different ratios, respectively. Also, the 1H and 13C{1H} NMR spectra of compounds II and V–VIII revealed three and two sets of signals for the related conformers (diastereomers). Interestingly, the 31P NMR spectrum of V in D2O indicated a great upfield shift (Δδ = 19.0) for 31P relative to the value obtained in DMSO-d6 (solvent effect). The two signals in V split further to three signals in the presence of β-cyclodextrin. Moreover, conformational analysis of diazaphospholane V was studied by ab initio calculations at the HF and B3LYP levels of theory using the Gaussian 98 program. Results indicated that among four suggested diastereomers (C1–C4) of V, C1 and C3 containing methyl group in the equatorial position are the most stable forms.  相似文献   

14.
Acid-catalyzed naphthalene alkylation products, such as 2,6-dialkylnaphthalenes (2,6-DAN), are industrially important compounds used to make monomers for advanced polymer materials [1]. Zeolite molecular sieves can be extensively used in many catalytic applications, specifically in naphthalene alkylations due to their high activity and stability as well as their high selectivity. The initial studies have mainly focused on gas phase alkylation of naphthalene with methanol, and only obtained th…  相似文献   

15.
The interaction of Cu2+ to the first 16 residues of the Alzheimer’s amyloid β peptide, Aβ(1–16) was studied by isothermal titration calorimetry at pH 7.2 and 37°C in aqueous solution. The Gholamreza Rezaei Behbehani (GRB) solvation model was used to reproduce the enthalpies of interactions of Aβ(1–16) with glycine, Gly+Aβ(1–16), and Cu2+ ions, Cu2+ +Aβ(1–16), over the whole range of Cu2+ concentrations. The binding parameters recovered from the solvation model were attributed to the structural change of Aβ(1–16) due to the glycine and Cu2+ interactions. It was found that there is a set of two identical binding sites for Cu2+ ions. p=2 indicates that the binding has positive cooperativity in the two binding sites. Aβ(1–16) structure is destabilized greatly as a result of binding to Cu2+ ions.  相似文献   

16.
The optimized structure of the tetrathiafulvalence radical-cation dimer (TTF·+-TTF·+) with all-real frequencies is obtained at MP2/6-311G level, which exhibits the attraction between two molecular cation TTF·+. The new attraction interaction is a 20-center-2-electron intermolecular covalent π/π bonding with a telescope shape. The covalent π/π bonding has the bonding energy of about −21 kcal·mol−1 and is concealed by the Coulombic repulsion between two TTF·+ cations. This intermolecular covalent attraction also influences the structure of the TTF·+ subunit, i.e., its molecular plane is bent by an angle θ = 5.6°. This work provides new knowledge on intermolecular interaction.  相似文献   

17.
Glycyrrhizic acid (GL) is a major active compound of licorice. The specific monoclonal antibody (MAb) (designated as 8F8A8H42H7) against GL was produced with the immunogen GL–BSA conjugate. The dissociation constant (K d) value of the MAb was approximately 9.96×10−10 M. The cross reactivity of the MAb with glycyrrhetic acid was approximately 2.6%. The conventional indirect competitive enzyme-linked immunosorbent assay (icELISA) and simplified icELISA adapted with a modified procedure were established using the MAb. The IC50 value and the detect range by the conventional icELISA were 1.1 ng mL−1 and 0.2–5.1 ng mL−1, respectively. The IC50 value and the detect range by the simplified icELISA were 5.3 ng mL−1 and 1.2–23.8 ng mL−1, respectively. The two icELISA formats were used to analyze GL contents in the roots of wild licorice and different parts of cultivated licorice (Glycyrrhiza uralensis Fisch). The results obtained with the two icELISAs agreed well with those of the HPLC analysis. The correlation coefficient was more than 0.98 between HPLC and the two icELISAs. The two icELISAs were shown to be appropriate, simple, and effective for the quality control of raw licorice root materials.  相似文献   

18.
19.
Two series of copper (I) halide complexes formulated as [(L)CuX(μ2-L)2CuX(L)] and [(L)2Cu(μ2-L)2Cu(L)2]2+, respectively (X = Cl, Br and L = 4,6-dimethylpyrimidine-2-thione (dmpymtH)) were prepared. From the thermogravimetric curves it was found that among the four studied materials, [Cu2(dmpymtH)6]2+2Cl presents a lower thermal stability. For the determination of the activation energy (E) two different methods have been used comparatively, since every method has its own error. These methods were the isoconversional methods of Ozawa, Flynn and Wall (OFW), and Friedman. The dependence of the E on the value of the mass conversion α, as calculated with OFW and Friedman’s methods, can be separated in three distinct regions. The decomposition mechanism is very complex and can be described using at least three different mechanisms with different activation energies. The best fitting of experimental data with theoretical models gave nth-order for all the three mechanisms (Fn–Fn–Fn).  相似文献   

20.
Ab initio HF/6–31G* calculations ofO-vinylacetoxime monohydrates and cations were performed. Each conformer forms two stable H-complexes with participation of N and O atoms. The former have planar heavy-atom skeletons, whereas the water molecule in the latter is located above the plane of the proton-acceptor complex. The complexes stabilized by N...HO and O...HO bonds have different dipole moments and frequencies of the OH stretching vibrations. The most energetically favorable cation is formed by adding a proton to the Cβ atom of the vinyl group ofO-vinylacetoxime. Theap,ap-conformer (ap is antiperiplanar) of this cation is 6.5 and 34.9 kcal mol−1 more stable than the onium cations with the NH+ and OH+ fragments, respectively, and is characterized by polarization and appreciable lengthening of the N−O and C=C bonds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 597–600, April, 2000.  相似文献   

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