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121.
Franco Cataldo Pietro Ragni Susana Iglesias-Groth Arturo Manchado 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(2):573-580
The sulphur-containing proteinaceous amino acids l-cysteine, l-cystine and l-methionine were irradiated in the solid state to a dose of 3.2 MGy. This dose corresponds to that delivered by radionuclide
decay in a timescale of 1.05 × 109 years to the organic matter buried at a depth >20 m in comets and asteroids. The purity of the sulphur-containing amino acids
was studied by differential scanning calorimetry (DSC) before and after the solid state radiolysis and the preservation of
the chirality after the radiolysis was studied by chirooptical methods (optical rotatory dispersion, ORD) and by FT-IR spectroscopy.
Although the high radiation dose of 3.2 MGy delivered, all the amino acids studied show a high radiation resistance. The best
radiation resistance was offered by l-cysteine. The radiolysis of l-cysteine leads to the formation of l-cystine. The radiation resistance of l-methionine is not at the level of l-cysteine but also l-methionine is able to survive the dose of 3.2 MGy. Furthermore in all cases examined the preservation of chirality after
radiolysis was clearly observed by the ORD spectroscopy although a certain level of radioracemization was measured in all
cases. The radioracemization is minimal in the case of l-cysteine and is more pronounced in the case of l-methionine. In conclusion, the study shows that the sulphur-containing amino acids can survive for 1.05 × 109 years and, after extrapolation of the data, even to the age of the Solar System i.e. to 4.6 × 109 years. 相似文献
122.
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125.
Maura Pellei Carlo Santini Giancarlo Gioia Lobbia Franco Cantalamessa Cinzia Nasuti Mariacristina Di Prinzio Rosita Gabbianelli Giancarlo Falcioni 《应用有机金属化学》2005,19(5):583-589
New organotin(IV) derivatives containing the anionic ligands bis(3,5‐dimethylpyrazol‐1‐yl)dithioacetate [LCS2]− and bis(3,5‐dimethylpyrazol‐1‐yl)acetate [LCO2]− have been synthesized from reaction between (CH3)2SnCl2 and lithium salts of the ligands. Mononuclear complexes of the type {[LCX2](CH3)2SnCl} (X = S or O) have been obtained and fully characterized by elemental analyses and FT‐IR in the solid state and by NMR (1H, 13C and 119Sn) spectroscopy, conductivity measurements and electrospray ionization mass spectrometry in solution. The acute toxicity of new organotin(IV) derivatives on rat was studied, comparing their effect with those of dimethyltin chloride (CH3)2SnCl2. The comparison of LD50 of organotin(IV) complexes and (CH3)2SnCl2 administered intraperitoneally, as a single dose, evaluated in vivo on rats, showed that toxicity decreases as follows: (CH3)2SnCl2 > LCO2 > LCS2. The effect of these organotin(IV) complexes on DNA was evaluated in vitro and in vivo on rats treated with different doses of these compounds (1/20 LD50 and 1/100 LD50). The lymphocyte DNA status was assessed by the comet assay, a rapid and sensitive single‐cell electrophoresis technique, used to detect primary DNA damage in individual cells. After 36 h from the start of treatment the two new organotin(IV) derivatives induced a significant rise in comet assay parameters, indicating an increasing presence of damaged DNA. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
126.
Inverse opals exhibiting strong photonic effects can cooperate with luminescent materials imbedded in their voids. While this has been demonstrated for dye molecules in the past, inspection of the literature reveals only few experiments on the potential of rare earths in this context. The efforts described focus on the spectral and spatial modification of emissive properties, whereas we here pursue the study of corresponding absorption properties. However, arbitrary incorporation of the luminescent species disturbs the photonic effects, therefore, principal preparative efforts need to be conducted to preserve both, the photonic properties of the opaline hosts and the luminescence efficiency of the guests. In this paper, we describe issues regarding the morphology and efficiency of inverse opal-incorporated rare-earth fluorides and oxifluorides and present an interior coating method for efficiency improvement. In addition, we were in this context, able to demonstrate the feasibility of energy transfer from Tb3+ modified host walls to Eu3+ guest species. 相似文献
127.
Hergueta AR Figueira MJ López C Caamaño O Fernández F Rodríguez-Borges JE 《Chemical & pharmaceutical bulletin》2002,50(10):1379-1382
A new and general method is described for the synthesis, in three steps and in good overall yields, of tetrasubstituted xanthines from an easily prepared imidazole precursor. The method is especially useful for the preparation in standardized conditions of series of xanthines combining a broad variety of primary or secondary alkyl, benzyl or aryl groups at N1 and of alkyl or arylmethyl groups at N3, that are not readily available by other methods. 相似文献
128.
We report on a novel technique to compensate for all-order polarization-mode dispersion. By means of this technique, based on a suitable combination of phase modulation and group-velocity dispersion, we compensated for as much as 60 ps of differential group delay that affected a 10-Gbit/s return-to-zero data stream. 相似文献
129.
In this paper, we show a unified approach to the problem of characterizing general distribution functions based on the conditional expectation between adjacent order statistics, or , where is a real, continuous and strictly monotonic function. We have the explicit expression of the distribution function from the above order mean function, and , and we give necessary and sufficient conditions so that any real function can be an order mean function. Our results generalize the results given for the discrete, absolutely continuous and continuous cases. Further, we show stability theorems for these characterizations.
130.
Davide Franco 《Annali di Matematica Pura ed Applicata》1996,170(1):133-145
Sunto
Si analizzano delle condizioni per l'annullamento della coomologia di fibrati stabili di rango 2su
P
3.Dopo i primi risultati di annullamento dovuti principalmente ad Hartshorne, Chang congetturò che alcune disuguaglianze sulle, classi di Chern fossero sufficienti per l'annullamento del primo gruppo di coomologia. La congettura finora è provata solo in alcuni casi particolari. Nel lavoro si dimostra la congettura in molti altri casi. In particolare si completano alcuni risultati recenti dovuti ad Ellia affrontando il caso in cui la prima classe di Chern è dispari. 相似文献