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1.
An unusual tetra‐nuclear linear cyanido‐bridged complex [Ru 2(μ‐ap) 4‐CN‐Ru 2(μ‐ap) 4](BPh 4) ( 1 ) (ap=2‐anilinopyridinate) has been synthesized and well characterized. The crystallographic data, magnetic measurement, IR, EPR and theoretical calculation results demonstrate that complex 1 is the first example of mixed spin Ru 25+‐based complex with uncommon electronic configurations of S=1/2 for the cyanido‐C bound Ru 25+ and S=3/2 for the cyanido‐N bound Ru 25+. This phenomenon can be understood by the theoretical calculation results that from the precursor Ru 2(μ‐ap) 4(CN) ( S=3/2) to complex 1 the energy gap between π* and δ* orbitals of the cyanido‐C bound Ru 25+ core increases from 0.57 to 1.61 eV due to the enhancement of asymmetrical π back‐bonding effect, but that of the cyanido‐N bound Ru 25+ core is essential identical (0.56 eV). Besides, the analysis of UV/Vis‐NIR spectra suggests that there exists metal to metal charge transfer (MMCT) from the cyanido‐N bound Ru 25+ ( S=3/2) to the cyanido‐C bound Ru 25+ ( S=1/2), supported by the TDDFT calculations. 相似文献
2.
Under the particular situation of highly doped and almost compensated semiconductors, a new kind of bound state happens at
high external excitation levels, which is formed of a close donor–acceptor molecule and a neighboring second donor or acceptor.
The de-excitation behavior of such a bound state resembles characteristics known from Auger transitions and for this reason
it is called an Auger molecule. The existence region of Auger molecules is determined in silicon-doped Ga 1−
x
Al
x
As by electron-beam excited luminescence measurements at low temperature. The main peak position and the luminescence intensity
of the donor–acceptor recombination channel turn out to be affected in a characteristic manner by the existence of Auger molecules
at high excitation levels. An analysis of corresponding rate coefficients for the reproduction of experimental results is
also presented.
Received: 14 September 1999 / Accepted: 3 February 2000 / Published online: 21 June 2000 相似文献
3.
An oxygen switch in catalysis of the cobalamin derivative (B 12)‐TiO 2 hybrid catalyst for the dechlorination of trichlorinated organic compounds has been developed. The covalently bound B 12 on the TiO 2 surface transformed trichlorinated organic compounds into an ester and amide by UV light irradiation under mild conditions (in air at room temperature), while dichlorostilbenes ( E and Z forms) were formed in nitrogen from benzotrichloride. A benzoyl chloride was formed as an intermediate of the ester and amide, which was detected by GC‐MS. The substrate scope of the synthetic strategy is demonstrated with a range of various trichlorinated organic compounds. A photo‐duet reaction utilizing the hole and conduction band electron of TiO 2 in B 12‐TiO 2 for the amide formation was also developed. 相似文献
4.
The heme acquisition system A protein secreted by Pseudomonas aeruginosa (HasA p) can capture several synthetic metal complexes other than heme. The crystal structures of HasA p harboring synthetic metal complexes revealed only small perturbation of the overall HasA p structure. An inhibitory effect upon heme acquisition by HasA p bearing synthetic metal complexes was examined by monitoring the growth of Pseudomonas aeruginosa PAO1. HasA p bound to iron–phthalocyanine inhibits heme acquisition in the presence of heme‐bound HasA p as an iron source. 相似文献
5.
The static dipole polarizability α
d,
i
for an arbitrary bound state i of the non-relativistic hydrogen-like atom has been known for a long time from, e.g; the second-order perturbation theory
treatment of the Stark effect. A reliable result for the ground state requires both summation over the discrete spectrum and
inclusion of the continuum contribution. This continuum contribution is known to decrease for excited states, but a systematic
study of this decrease has not been available so far. We present here representative results from a systematic study of α
d,
i
, which was performed as a first test of a new algorithm for the radial integrals involved. Partial sum approximations of
the discrete contribution yield the total α
d,
i
with a relative error of less than 1% for all states i with principal quantum number n≥5. Corresponding results for the relativistic case, for which the radial integral algorithm was developed, will be presented
elsewhere.
Dedicated to Professor Hermann Stoll on the occasion of his 60th birthday
An erratum to this article is available at . 相似文献
6.
The applicability of ATR-FTIR for the determination of the HDO content in heavy water (D 2O) was investigated. Two groups of calibration standard solutions, of low contents (0–1 n% H 2O in heavy water) and of higher contents (0–10 n% H 2O in heavy water) were prepared by adding properly calculated amount of H 2O to D 2O by weight. The absorbances at 3400 cm −1 (ν, O–H) against the calibration standards were measured five times using two kinds of interchangeable IREs (1 bound and
9 bound reflections). And four calibration curves were obtained by linear least square fit of the measured absorbances for
the four different measurement conditions, which are (1) for low contents group using 1 bound reflection, (2) for low contents
group using 9 bound reflections, (3) for higher contents group using 1 bound reflection, (4) for higher contents group using
9 bound reflections. Determined contents ( c
0) of each calibration standards for the four measurement conditions were obtained by the calibration curves and compared to
the calculated contents ( c
cal). The uncertainty sources were considered when the HDO in heavy water is determined according to the procedure of this work.
The uncertainties u( c
0) of the determined contents ( c
0) for the four different measurement conditions were calculated. 相似文献
7.
Water‐soluble diblock copolymer, poly( N‐isopropylacrylamide)‐ block‐poly( N‐vinyl‐2‐pyrroridone) (PNIPAM m‐ b‐PNVP n), was found to associate with fullerene (C 60), and thus C 60 can be solubilized in water. The 63C 60/PNIPAM m‐ b‐PNVP n micelle formed a core‐shell micelle‐like aggregate comprising a C 60/PNVP hydrophobic core and a thermoresponsive PNIPAM shell. The C 60‐containing polymer micelle formation and its thermoresponsive behavior were characterized using light scattering and 1H NMR techniques. The hydrodynamic radius ( Rh) of the C 60‐bound polymer micelle increased with increasing temperature, which was ascribed to the hydrophobic association between dehydrated PNIPAM shells above lower critical solution temperature (LCST). 1H NMR data suggest that the motion of the PNIPAM block is restricted above LCST due to the dehydration of the PNIPAM shell in water. The generation of singlet oxygen by photosensitization by the C 60‐bound polymer micelle was confirmed from photooxidation of 9,10‐anthracenedipropionic acid. Furthermore, DNA was found to be cleaved by visible light irradiation in the presence of the C 60‐bound polymer micelle. Therefore, there may be a hope for a pharmaceutical application of the C 60‐bound polymer micelle to cancer photodynamic therapy. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011. 相似文献
8.
An ascorbate-FeCl 3-EDTA-H 2O 2 system was used to oxidize rat lens α-crystallins. Under this oxidative insult, the chaperone activity of α-crystallin toward γ-crystallin was shown to decrease significantly, which is quite different from the result reported by Wang and Spector. ( Invest. Ophthalmol. Vis. Sci. 1995 , 36, 311-321.) Fluorescence spectroscopy and circular dichroism were employed to characterize the structural changes of oxidized α-crystallin. It was found that fluorescence intensity of l-anilinonaphthalene-8-sul-phonate (ANS) bound to oxidized α-crystallin increased comparing to that bound to normal α-crystallin, suggesting oxidation causes the exposure of more hydrophobic regions. Further, α-crystallin's fluorescence intensity in response to tryptophan residues showed a pseudo first order decline. Amino acid analysis of normal versus oxidized α-crystallin confirmed actual decline in tryptophan levels, showing about 80% of tryptophan being modified after 10-hour oxidation. Circular dichroism showed both changes in the secondary and tertiary structures of oxidized α-crystallin, characterized by a large loss of aromatic-type amino acid interactions and a large loss of β-sheet structure. In conclusion, modified tryptophan, secondary and tertiary structural changes of α-crystallin correlate best with the reduction of chaperone function, the curves all showing a linear slope for 10 hours, then plateauing. These results indicate that the decrease of α-crystallin chaperone activity is attributed to the structural changes. 相似文献
9.
Complex formation of poly(ethylene oxide) (PEO) with divalent barium and strontium salts was investigated in methanol. In these systems the complexation was accompanied by a considerable degree of ionic association. An analytical model for the polymer-ion complexation based on a one-dimensional lattice model was proposed. According to this model, the electrostatic effects between the bound ions were separated from the total free energy change of the binding. Three binding constants, i.e., the ionic association constant K A, the cation binding constant, K c, and the anion binding constant, K a, could be estimated. K A for barium and strontium salts was comparable, and the effect of counteranions on K A was not large. K c for barium salts was almost independent of the kind of counteranion and larger than that for corresponding strontium salts, indicating stronger polymer-ion interaction for barium salts. The anion binding constant, K a, was strongly dependent upon the kind of anion, and the order was CI ? ? ? 4 ?. The pronounced ion binding for larger anions may be explained by the more favorable free energy change of desolvation. Finally, the concentration of free and bound ionic species was determined as a function of PEO concentration. 相似文献
10.
The helium dimer 4He 2 has recently been detected, confirming earlier ab initio predictions of stability for a single bound state with binding energy of 1.310 mK. The predicted potential minimum is at 2.96 Å, with a radial distribution function peaking at 6.96 Å. We model this system using a Dirac bubble potential, which also admits just one bound j = 0 state. With the bubble located at 6.96 Å, an overlap of 0.9994 with the ab initio wave function is obtained. An average internuclear distance of 52.6 Å is calculated, in good agreement with the ab initio result. The root mean square deviation from the mean, 48.0 Å, indicates an enormous spread of the radial wave function. Also consistent with our model is the absence of bound states for the isotopic variants 3He 4He and 3He 2. Cross sections for helium-helium scattering are also computed, using both a partial-wave expansion and the Born approximation. General trends in the energy dependence of the total cross section are accounted for, in qualitative agreement with experimental results. © 1995 John Wiley & Sons, Inc. 相似文献
11.
This work presents an attempt at correlating the available permeability/selectivity literature data for hollow fibers and flat membranes. Therefore, this paper gathers the information pertaining to membrane materials for which membrane properties of flat membranes and hollow fibers have both been reported. An overview of the relations between selectivity and permeance of hollow fiber membranes for various gas pairs (O 2/N 2, CO 2/CH 4, CO 2/N 2, H 2/N 2, H 2/CO 2, H 2/CH 4 and He/N 2) is presented first. The upper bound lines are the ones proposed by Robeson, which were calculated by assuming a one-micron-thick skin layer as proposed by Robeson in 2008. From the results obtained, a relation between the selectivity ratio in both kinds of membranes ( αH/αf) and skin layer thickness ( l) calculated from flat membranes and hollow fibers gas permeation data for these pairs of gases is also presented. The skin layer thicknesses measured using seven different experimental techniques for six commercial membranes are compared. The influences of spinning parameters on the morphology and performance of hollow fiber membrane gas separation are discussed. Finally, an analysis is made of the reasons why the dense skin layer thicknesses of a hollow fiber calculated using permeance and permeability data vary for different gases and also differ from direct experimental measurements. 相似文献
12.
The diffusion-limited binding kinetics of antigen in solution to antibody immobilized on a biosensor surface is analyzed within
a fractal framework. Changes in the fractal dimension, D f observed are in the same and in the reverse directions as the forward binding rate coefficient k. For example, an increase in the concentration of the isoenzyme human creatine kinase isoenzyme MB form (CK-MB) (antigen)
solution from 0.1 to 50 ng/mL and bound to anti-CK-MB antibody immobilized on fused silica fiber rods leads to increases in
the fractal dimension D f from 0.294 to 0.5080, and in the forward binding rate coefficient k from 0.1194 to 9.716, respectively. The error in the fractal dimension D f decreases with an increase in the CK-MB isoenzyme concentration in solution. An increase in the concentration of human chorionic
gonadotrophin (hCG) in solution from 4000 to 6000 mIU/mL hCG and bound to anti-hCG antibody immobilized on a fluorescence
capillary fill device leads to a decrease in the fractal dimension D f from 2.6806 to 2.6164, and to an increase in the forward binding rate coefficient k from 3.571 to 4.033, respectively. The different examples analyzed and presented together indicate one means by which the
forward binding rate coefficient k may be controlled, that is by changing the fractal dimension or the ‘disorder’ on the surface. The analysis should assist
in helping to improve the stability, the sensitivity, and the response time of biosensors. 相似文献
13.
Vanadium is used by microorganisms as an electron acceptor in respiration, and as an essential transition metal in enzymatic reactions. An example for the employment in respiratory function is the soil bacterium Shewanella, which reduces vanadate(V) to oxidovanadium(IV). Examples for enzymatic reactions are the nitrogen fixation (by the proteobacterium Azotobacter and the cyanobacterium Anabaena), and the two‐electron oxidation of halide X – to a species {X +} by marine macro‐algae, fungi and lichen. In vanadium nitrogenase, vanadium is constituent of a {Fe 7VS 9} cluster, in vanadate‐dependent haloperoxidases it is present in the form of H 2VO 4– bound to a histidyl residue of the protein matrix. Mushrooms of the genus Amanita store vanadium in the form of amavadin, a “bare” (non‐oxo) vanadium(IV) complex. Several sea squirts and fan worms accumulate vanadium from sea water and store it as an aqua complex of vanadium(III). “Tailored” vanadium complexes with organic ligands have been shown to be active as insulin‐mimics in vivo and in vitro: They are able to stimulate the cellular uptake of glucose and to inhibit the degradation of lipids. These functions are related to the phosphate‐vanadate antagonism. 相似文献
14.
The empirical upper bound relationship for membrane separation of gases initially published in 1991 has been reviewed with the myriad of data now presently available. The upper bound correlation follows the relationship , where Pi is the permeability of the fast gas, αij ( Pi/ Pj) is the separation factor, k is referred to as the “front factor” and n is the slope of the log–log plot of the noted relationship. Below this line on a plot of log αij versus log Pi, virtually all the experimental data points exist. In spite of the intense investigation resulting in a much larger dataset than the original correlation, the upper bound position has had only minor shifts in position for many gas pairs. Where more significant shifts are observed, they are almost exclusively due to data now in the literature on a series of perfluorinated polymers and involve many of the gas pairs comprising He. The shift observed is primarily due to a change in the front factor, k, whereas the slope of the resultant upper bound relationship remains similar to the prior data correlations. This indicates a different solubility selectivity relationship for perfluorinated polymers compared to hydrocarbon/aromatic polymers as has been noted in the literature. Two additional upper bound relationships are included in this analysis; CO 2/N 2 and N 2/CH 4. In addition to the perfluorinated polymers resulting in significant upper bound shifts, minor shifts were observed primarily due to polymers exhibiting rigid, glassy structures including ladder-type polymers. The upper bound correlation can be used to qualitatively determine where the permeability process changes from solution-diffusion to Knudsen diffusion. 相似文献
15.
Under excitation at 365 nm, the cell fluorescence is mainly due to bound and free NAD(P)H, plus a small contribution from flavins. Resolution is first attempted in the simplest case. i.e. the increase spectrum (δ If) due to microinjection of glucose-6-phosphate (G6P) into EL2 ascites cells. Above 510 nm, δ IF is identical to the spectrum of free NADH. Below 510 nm. the presence of a second component is suggested, i.e. the intensity of the free NADH spectrum is lower than the measured δ IF level. The difference between δ If and the free NADH spectrum (maximum at 475 nm) yields a spectrum suggestive of bound NADH with maximum at 450 nm. Thus, with free and bound NADH, the entire δ IF can be reconstructed, with some assumptions as to the relative quantum yields of the two components. This seems to leave no place for a flavin component. The questions raised by the lack of such a component are answered using a new microspectrofluorometer, which aiiows correlated monitoring of NAD(P)H and flavins with excitations at 365 and 436 nm, respectively. As detected by excitation at 436 nm, injections of G6P, malate, ADP, and treatments with azide, cyanide or partial anaerobiosis, all indeed show a redox change of flavins, in the sense of decreased emission. It is understandable, however, that such a change which is not very large even using 436 nm excitation should remain undetected when flavins are excited at 365 nm, i.e. using the tail of their excitation spectrum. In contrast to the increased δ IF spectrum recorded in response to injected substrate, the initial spectrum ( If) of the cell prior to a metabolic perturbation reveals a third component, even with 365 nm excitation. The position and reactivity of this component shows flavin-like properties. The structural resolution attainable makes it possible to obtain the evaluation of free vs. bound NAD(P)H and flavin fluorochromes in the mitochondrial and cytosolic compartments of the intact cell. 相似文献
16.
In order to develop a new functional product from lignin, sodium lignosulfonate (LS)-based polyurethane (LSPU) hydrogels were prepared from LS and hexamethylene diisocyanate (HDI) derivatives in water. Isocyanate/hydroxyl group ratio (NCO/OH ratio) was varied from 0.05 to 0.8 mol mol−1, and water content (Wc = mass of water/mass of dry sample) of the obtained LSPU hydrogels was varied from 0 to 3.0 g g−1. Phase transition behavior of hydrogels with various Wc’s was investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). In DSC heating curve of LSPU hydrogels, glass transition, cold crystallization, melting and liquid crystallization were observed. Cold crystallization, two melting peaks and variation of melting enthalpy indicate that three kinds of water, i.e., non-freezing water, freezing bound water and free water, exist in LSPU hydrogel. Glass transition temperature (Tg) decreased from 230 to 190 K in a Wc range where non-freezing water was formed in the hydrogel. Tg increased when freezing bound water was formed in the system. Tg leveled off in a Wc range where normal ice was formed. The effect of NCO/OH ratio on molecular motion of LSPU hydrogel is examined based on Tg and heat capacity difference at Tg (ΔCp). Water vaporization curve measured by TG also indicates the presence of bound water which evaporates at a temperature higher than ca. 410 K. By atomic force microscopic observation, the size of molecular bundle of LSPU hydrogel is calculated and compared with that of LS-water system. By cross-linking, the height of molecular bundle decreased from ca. 3–1 nm and lignin molecules extend in a flat structure. 相似文献
17.
Abstract— Gradient elution is used to facilitate controlled withdrawal of Mg 2+ from phytochrome-rich particulate fractions from irradiated Avena sativa L. shoots. The bound pigment from red-irradiated tissue is released in a discrete band when the Mg 2+ falls to just below 1 m M. This phytochrome has an apparent molecular weight of ?300 kilodaltons upon gel filtration, indistinguishable from that of the unbound pigment in the same extract and from that in the 50,000 × g supernatant from non-irradiated Avena. This indicates that the bound phytochrome is released as a soluble molecule at a Mg 2+ concentration above that which permits release of the particulate binding partner from other particulate components. These findings appear to preclude the possibility that the phytochrome-binding partner association can be selectively preserved at a Mg 2+ level that would permit separation and analysis of phytochrome-bearing particles without the complication of Mg 2+-induced membrane and RNP aggregation. “Cycled” P fr (that from tissue irradiated with a red-far red sequence prior to homogenization) is released at 0.1 to 0.2 m M Mg 2+. This indicates that “cycled P r is more tenaciously bound by the particulate fraction than is P fr. This effect is photoreversible both by further in vivo and subsequent in vitro irradiations, suggesting that the state of the pigment, rather than of the binding partner, directly controls the tenacity of the interaction. Increasing concentrations of KCl release the pigment from the particulate fraction in the presence of 10 m M Mg 2+; increasing Triton X100 concentrations do not. This confirms the ionic nature of the pigment-particulate fraction interaction and indicates strongly that the phytochrome is located external to any membrane vesicles present (although not necessarily that it is bound directly to such vesicles). The data further suggest that phospholipid polar head groups are not primarily responsible for the binding. 相似文献
18.
Radically different dependences of the activity of La 1 − x
Sr
x
MnO 3 ( x = 0−0.5) perovskites in methane oxidation on the degree of substitution of strontium for lanthanum are observed for low and
high temperatures. Unsubstituted LaMnO 3 exhibits the highest activity in the temperature range from 300 to 500°C, while the sample with the maximum degree of substitution
(La 0.5Sr 0.5MnO 3) shows the highest activity at higher temperatures of 700–900°C. In the low temperature region, the activity of La 1t - x
Sr
x
MnO 3 is determined by the amount of weakly bound (overstoichiometric) oxygen, which is formed in cation-deficient lattices and
is characterized by a thermal desorption peak with T
max = 705°C. At higher temperatures (800–900°C), the strongly bound oxygen of the catalyst lattice is involved in the formation
of the reaction products under both unsteady- and steady-state conditions. As a consequence, the catalytic activity in methane
oxidation correlates with the apparent rate constant of oxygen diffusion in the oxide bulk. 相似文献
19.
Using 1H and 13C NMR spectroscopy, the interaction of tetrapropoxy- p- tert-butyl-calix[4]arene ( 1) with H 3O + ions produced by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and traces of water was studied in nitrobenzene- d 5. It was shown that 1 readily forms an equimolecular complex with H 3O +. The equilibrium constant K of its formation is 2.6 at 296 K. Exchange between bound and free 1 is fast even under mild excess of HDCC, the correlation time τ ex being about 0.13 ms. NMR shows that H 3O + is bound to the aryl-oxygen atoms and this binding forces the calixarene cup to adopt a more open and symmetrical conformation. This conclusion is in full accord with high precision quantum DFT calculations which find one structure of the complex corresponding to a global energy minimum, in which the H 3O + ion is bound to three of the oxygen atoms by strong hydrogen bonds and to the remaining oxygen by two weaker hydrogen bonds. The calixarene part is forced into a C 4 symmetrical opened form. When stored for weeks, the complex gradually transforms into other forms, most probably its hydrates, according to spectral evidence and DFT calculations. 相似文献
20.
The convergence radius of the series expansion for the energy of H 2+ in the δ-function model (in terms of the perturbation parameter μ/λ, where μ is the charge of the perturbing nucleus and λ the fixed charge of the other nucleus) is investigated. A lower bound of this convergence radius (possibly equal to it) previously defined by Robinson [5] is studied analytically as a function of the internuclear distance R and computed numerically. The results differ strikingly from those previously obtained by Robinson who used a simplified but poorer lower bound: in contrast with this poorer bound, the one studied in the present paper is larger than for I every R, from which fact it may be concluded that, contrary to Robinson's previous result, the series expansion of the energy, in the δ-function model under consideration, still converges when μ = λ for every R. 相似文献
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