Abstract— The characteristics of chlorophyll a visible absorption spectra have been analyzed in terms of empirical solvent scales of Lewis basicity (B) and acidity (E) as well as steric constants (Es) (after Koppel and Palm, 1972; Palm, 1977). The presence or absence of the specific four-band structure in the long-wavelength region depends only on the solvent electron-pair donating capability. In protic solvents the Soret band intensity is suppressed, but, in contrast, the extinction coefficient of its first satellite remains practically constant. This allows us to group spectra into four types according to the Soret-band intensity and the structure of the red-band system and assign them to chlorophyll-solvent complexes formed via 1 or 2 donor-acceptor bonds to central Mg and with and without hydrogen bond(s) to some nucleophilic center of the solute molecule. 相似文献
Parahydrogen hyperpolarization has emerged as a promising tool for sensitivity-enhanced NMR metabolomics. It allows resolution and quantification of NMR signals of certain classes of low-abundance metabolites that would otherwise be undetectable. Applications have been implemented in pharmacokinetics and doping drug detection, demonstrating the versatility of the technique. Yet, in order for the method to be adopted by the analytical community, certain limitations have to be understood and overcome. One such question is NMR signal assignment. At present, the only reliable way to establish the identity of an analyte that gives rise to certain parahydrogen hyperpolarized NMR signals is internal standard addition, which can be laborious. Herein we show that analogously to regular NMR metabolomics, generating libraries of hyperpolarized analyte signals is a viable way to address this limitation. We present hyperpolarized spectral data of adenosines and give an early example of identifying them from a urine sample with the small library. Doing so, we verify the detectability of a class of diagnostically valuable metabolites: adenosine and its derivatives, some of which are cancer biomarkers, and some are central to cellular energy management (e.g., ATP). 相似文献
In 2001 G. Godefroy proved that a subspace XJS of c0 constructed by W.B. Johnson and G. Schechtman in 1996 has the λ-bounded approximation property with λ?8. This paper slightly improves Godefroy's proof establishing that λ?6. 相似文献
NMR signal amplification by reversible exchange (SABRE) has been observed for pyridine, methyl nicotinate, N‐methylnicotinamide, and nicotinamide in D2O with the new catalyst [Ir(Cl)(IDEG)(COD)] (IDEG=1,3‐bis(3,4,5‐tris(diethyleneglycol)benzyl)imidazole‐2‐ylidene). During the activation and hyperpolarization steps, exclusively D2O was used, resulting in the first fully biocompatible SABRE system. Hyperpolarized 1H substrate signals were observed at 42.5 MHz upon pressurizing the solution with parahydrogen at close to the Earth's magnetic field, at concentrations yielding barely detectable thermal signals. Moreover, 42‐, 26‐, 22‐, and 9‐fold enhancements were observed for nicotinamide, pyridine, methyl nicotinate, and N‐methylnicotinamide, respectively, in conventional 300 MHz studies. This research opens up new opportunities in a field in which SABRE has hitherto primarily been conducted in CD3OD. This system uses simple hardware, leaves the substrate unaltered, and shows that SABRE is potentially suitable for clinical purposes. 相似文献
This study investigated the reactive dissolution of nitric oxide (NO) and nitrogen dioxide (NO2) mixtures in deionized water. The dissolution study was carried out in a flat surface type gas–liquid reaction chamber utilizing a gas flow-pattern resembling plasma jets which are often used in biomedical applications. The concentration of NO and NO2 in the gas mixtures was varied in a broad range by oxidizing up to 800 ppm of nitric oxide in Ar carrier gas with variable amount of ozone. The production of nitrite (NO2?) and nitrate (NO3?) in the water was proportional to treatment time up to 50 min. The concentration of NO3? was a power function of gas phase NO2 while the concentration of NO2? increased approximately linearly with gas phase NO2. The formation of NO2? and NO3? could be described by reactions between dissolved NO2 and NO in the water while the production rate was determined by diffusion-limited mass transport of nitrogen oxides to the bulk of the liquid. At higher NO2 concentrations, the formation of dinitrogen tetraoxide (N2O4) increased the formation rate of NO2? and NO3?. The identified mass transport limitation by diffusion suggests that convection of water created by the gas jet is insufficient and dissolution of nitrogen oxides can be increased by additional mixing. In respect of practical applications, the ratio of NO2? /NO3? in water could be varied from 0.8 to 5.3 with treatment time and gas phase NO2 and NO concentrations.
Titanium oxide and zirconium oxide thin films deposited on silicon substrates were characterised using electron probe microanalysis
(EPMA), Rutherford backscattering spectroscopy (RBS), time-of-flight elastic recoil detection analysis (TOF-ERDA) and scanning
photoelectron microscopy (SPEM). The composition and mass thickness of the films were determined and the results of different
methods compared. It was revealed that the synchrotron radiation used for SPEM studies caused considerable modification of
zirconia films grown at low temperatures. 相似文献
We show how an island (isola) evolves out of the usual S-curve of steady states of diffusion flames when radiation losses are accounted for and how it eventually disappears when radiation increases further. At small activation temperatures there are never any islands. We show that stable oscillations evolve first out of perturbations of steady states on the S-curve at large Damköhler numbers. Only if the activation temperature is large enough do they also appear on the islands. The region of the stable oscillations grows larger as activation temperature decreases. 相似文献
Parameters of optical impurity spectra in disordered solids were calculated using the potential energy distribution of the ground state and the guest-host interaction potentials of the lower and upper states. The model can yield inhomogeneous band shapes, pressure shift coefficients of zero phonon lines, (pseudo)local phonon frequencies, and linear and quadratic coupling constants to phonons. Results are compared to properties of Shpol'skii multiplets and zero phonon holes burned over the broad spectra in glasses. Crystal spectra contain discrete lines, but the overall width of multiplets and the bands in weakly polar solvent glasses is similar, and so are the pressure shift coefficients. A decrease of zero phonon transition probability (Debye-Waller factor) with increasing (negative) solvent shift was predicted and confirmed for crystal spectra. In general, no correlation exists between the strength of the first- and second-order couplings, and the vibrational modes involved can be different. Moreover, no relationship was established between the line shift and broadening in a temperature interval from 5 to 100 K. 相似文献