The photochemistry of N‐hydroxypyridine‐2(1H)‐thione (NHPT), inserted as a photolabile modifier at the 6‐position of 2′‐deoxyguanosine or guanosine, has been evaluated. In particular, 6‐[(1‐oxidopyridin‐2‐yl)sulfanyl]‐ ( 1a ) and 6‐[(pyridin‐2‐yl)sulfanyl]‐2′,6‐dideoxyguanosine ( 2a ), novel photolabile derivatives of the natural nucleosides, were synthesized and characterized. The observed photolysis products of 1a in organic solvents could only be rationalized by assuming a rapid equilibrium with the corresponding 6‐[(2‐thioxopyridin‐1(2H)‐yl)oxy] analogue 3a (Scheme 5). Transient spectroscopy of 1a indicated a strong triplet‐excited state suitable for triplet → triplet energy transfer or singlet‐oxygen generation. The NHPT function was stable enough for (slightly modified) automated solid‐phase oligonucleotide synthesis. The utility of the above compounds is discussed, as well as their potential use in photosensitization of reactive oxygen species in DNA. 相似文献
This paper presents results of experimental work carried out to study the centrifugal dewatering behaviors of superabsorbent hydrogels. Taking the creep deformation of the hydrogels into consideration and assuming that the mechanical properties of gel network can be represented by Terzaghi-Voigt combined model, the basic differential equation expressing the centrifugal dewatering of superabsorbent hydrogels is solved. The progress of centrifugal dewatering is represented by an average consolidation ratio Uc as in mechanical expression. The agreement between calculated and experimental Uc is satisfactory when the creep deformation of the material is considered. Consistent with mechanical expression and electro-osmotic dewatering, as the driving force for centrifugal dewatering increases, the modified consolidation coefficient of the hydrogel network Ce also increases. Effectiveness of centrifugal dewatering, expressed as a relative difference between the initial void ratio and final void ratio, increases with the rotational speed. For a given rotational speed, the final void ratio remains constant regardless of the initial weight of the gel. On the other hand, as the rotational speed of the centrifuge gets higher, the final void ratio decreases for all initial weights of the gel investigated in the current study. The magnitude of creep deformation B depends upon the amount of initial weight of the hydrogel. For a given rotational speed of the centrifuge, the magnitude of creep deformation becomes larger as the initial amount of hydrogel is increased. 相似文献
Summary An unsteady-state kinetic model of both benzene hydrogenation (HDA) and thiophene hydrogenolysis (HDS) on a sulfide hydrotreating
catalyst Ni-Mo/Al2O3 has been developed. The model adequately describes experimental data obtained at the pressure 2 MPa, temperature 573 K and
at various contact times and ratios of benzene/thiophene. The model is based on the assumption that the catalyst surface contains
only one type of active sites, i.e., Ni atoms in the sulfide bimetallic species, which are responsible for both hydrogenolysis and hydrogenation reactions. 相似文献
A transport model is proposed that describes the temporal intensity distribution observed in laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in single-shot mode using quantitative signal equations. Calculations aim on the deduction of the dispersion function describing the time-dependent part of the signal equation.
The dispersion function depends on transport time in the centre of the transport tube, as related to carrier gas flow rate and tube volume and on the relation between carrier gas flow rate and ablation chamber volume. The equations describing the signal shape standardize signals from different systems and allow quantitative optimization of the ablation chamber, the transport tube and the detector.
Application of the model to ICP-MS shows that only a part of the area filled by the transported vaporization product and thus only a part of the transported vaporization product can be observed at the detector. The model is able to quantify both fractions.
As was calculated, the observed fraction of analyte is always higher than the observed fraction of the sample containing cross section and depends on the chosen transport parameters characterising the dispersion function. Thus, the determination of the signal integrals in the usual way can lead to systematic errors if the parameters influencing the dispersion function are variable.
Therefore, a different method of analysis based on signal equations is proposed and demonstrated. By this method of data treatment, all important system parameters influencing the dispersion function could be calculated and matched with theoretical ones. Furthermore, a complete integral of the transient signal including its statistical variation can be generated from a limited number of measurement points. For example, this can be applied to signals detected incompletely because of detector saturation and enables the use of high-abundance elements as internal standards.
Furthermore, the method can be used to monitor system performance, to identify the flow regime inside the ablation chamber, to take into account the sample volume for quantitative analysis and finally, to detect anomalous signal distributions that would lead to systematic errors. The prospects and limitations of the model are discussed for LA-ICP-MS in single shot mode. 相似文献
The present paper shows how a standard volumetric adsorption device can be used to measure solvent desorption isotherms on
gels. As gels are very soft materials, they shrink significantly during the measurement, and the data have to be analyzed
in terms of the mechanical properties of the gel’s skeleton. Methanol desorption isotherms are measured on a series of silica
gels, and the results are compared with independent characterizations, notably beam bending. 相似文献
Photoinduced electron transfer in biomolecular photodiode consisting of protein-adsorbed hetero-Langmuir–Blodgett (LB) films was investigated. Four kinds of functional molecules, cytochrome c, viologen, flavin, and ferrocene, were used as a second electron acceptor, a first electron acceptor, an electron sensitizer, and an electron donor, respectively. The hetero-LB film was fabricated by subsequently depositing ferrocene, flavin, and viologen onto the pretreated ITO glass. Cytochrome c-adsorbed hetero-LB films were prepared by soaking the hetero-LB films into the phosphate buffer solution containing cytochrome c. To verify the optimal adsorption conditions of cytochrome c molecules onto the viologen LB layers, the UV-absorption spectrum and atomic force microscopy observations of LB films were performed. Finally, the metal/insulator/metal structured molecular device was constructed by depositing aluminum onto the surface of the cytochrome c-adsorbed hetero-LB films. For photoelectric response properties, the current–voltage characteristic and photoswitching effect of the proposed molecular photodiode were investigated. To verify the charge shift, transient photocurrent of the molecular photodiode was measured. 相似文献
The influence of sample matrix composition, absorption behavior and laser aerosol particle size distribution on elemental fractionation in laser ablation inductively coupled plasma mass spectrometry was studied for nanosecond laser ablation at a wavelength of 266 nm. To this end, lithium tetraborate glass samples with different iron oxide contents and trace amounts of a group of 11 elements were prepared synthetically. The samples were characterized in terms of optical absorbance, melting points, trace element concentrations and homogeneity. UV/VIS spectra showed that sample absorption rises with increasing Fe2O3 content. Crater depths and time-dependent particle size distributions were measured, and ablated and transported sample volumes were estimated. Furthermore, the laser aerosol was filtered using a particle separation device and transient ICP-MS signals were acquired with and without filtering the aerosol. The results demonstrate that the amount of ablated sample is related to the absorption coefficient of the sample and therefore to the optical penetration depth of the laser beam into the sample. The higher energy densities resulting from the shorter penetration depths result in smaller average particle sizes for highly absorbing samples, which allows more efficient transport to and atomization and excitation of the ablated material within the ICP. The particle size distribution changes continuously with ablation time, and larger particle fractions occur mainly at the beginning of the ablation, which leads to particle-related fractionation processes at the beginning of the transient signal. Exceeding a critical depth to diameter ratio, laser-related elemental fractionation processes occur. Changes in the volatile to non-volatile element intensity ratio after the aerosol is filtered indicate that particle size-related enrichment processes contribute to elemental fractionation. 相似文献
Hard elastic polypropylene was investigated by x-ray scattering using synchrotron radiation and by performing stress strain measurements in different liquids. It was found that the long period increases with elongation up to 1.3–1.4. Beyond this extension a change in the deformation behavior takes place. In the range from 1.1 to 1.3–1.4 the deformation measurements in the different liquids are in good agreement with the coil-strand-transition model. The proposed linear relationship between the deformation work and the elongation could be confirmed. The same holds for the surface energy. Moreover, the calculated ratio between the surface energy and the deformation work agrees with the measurements. 相似文献