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121.
Rosini G Ayoub C Borzatta V Mazzanti A Marotta E Righi P 《Chemical communications (Cambridge, England)》2006,(41):4294-4296
The occurrence of p1,n1 salts can be exploited to sequester racemates; an application to technical mixtures of chrysanthemic acids (ChA) allowed the separation of trans- and cis-ChA and the recovery of the excess enantiomer of trans-ChA. 相似文献
122.
123.
Scalar-tensor theories of gravity can beformulated in the Jordan or in the Einstein frame, whichare conformally related. The issue of which conformalframe is physical is a contentious one; we provide a straightforward example based ongravitational waves in order to clarify theissue. 相似文献
124.
Valerio Lucarini 《Journal of statistical physics》2008,131(3):543-558
We consider the general response theory recently proposed by Ruelle for describing the impact of small perturbations to the
non-equilibrium steady states resulting from Axiom A dynamical systems. We show that the causality of the response functions
entails the possibility of writing a set of Kramers-Kronig (K-K) relations for the corresponding susceptibilities at all orders
of nonlinearity. Nonetheless, only a special class of directly observable susceptibilities obey K-K relations. Specific results
are provided for the case of arbitrary order harmonic response, which allows for a very comprehensive K-K analysis and the
establishment of sum rules connecting the asymptotic behavior of the harmonic generation susceptibility to the short-time
response of the perturbed system. These results set in a more general theoretical framework previous findings obtained for
optical systems and simple mechanical models, and shed light on the very general impact of considering the principle of causality
for testing self-consistency: the described dispersion relations constitute unavoidable benchmarks that any experimental and
model generated dataset must obey. The theory exposed in the present paper is dual to the time-dependent theory of perturbations
to equilibrium states and to non-equilibrium steady states, and has in principle similar range of applicability and limitations.
In order to connect the equilibrium and the non equilibrium steady state case, we show how to rewrite the classical response
theory by Kubo so that response functions formally identical to those proposed by Ruelle, apart from the measure involved
in the phase space integration, are obtained. These results, taking into account the chaotic hypothesis by Gallavotti and
Cohen, might be relevant in several fields, including climate research. In particular, whereas the fluctuation-dissipation
theorem does not work for non-equilibrium systems, because of the non-equivalence between internal and external fluctuations,
K-K relations might be robust tools for the definition of a self-consistent theory of climate change. 相似文献
125.
Valerio B. Di Marco Luca Raveane Annalisa Dean Pietro Traldi 《Rapid communications in mass spectrometry : RCM》2010,24(7):868-874
Electrospray ionization mass spectrometry (ESI‐MS) is very often employed to study metal/ligand equilibria in aqueous solution. However, the ionization process can introduce perturbations which affect the speciation results in an unpredictable way. It is necessary to identify these perturbations in order to correctly interpret the ESI‐MS speciation results. Aluminium(III)/1,6‐dimethyl‐4‐hydroxy‐3‐pyridinecarboxylate (DQ716) aqueous solutions at various pH were analysed by ESI‐MS, and speciation results were compared with those obtained by equilibrium techniques. Differences observed were both qualitative and quantitative. The ESI‐MS spectral changes due to different settings of the following instrumental parameters were analyzed: the solution flow rate (FS), the nebulizer gas flow rate (FG), the potential applied at the entrance capillary (EC), and the temperature of the drying gas (TG). The effects produced by FS and EC on the spectra strongly suggest the key role of surface activity in determining the relative fraction of the ions reaching the detector. The experimental effects of FS and TG were interpreted considering the presence of at least two reactions in the gas phase and a dimerization occurring in the droplets. These perturbations cannot be generalized because they appear to be chemical system‐related and instrument‐dependent. Therefore, the identification of perturbations is a required task for any metal‐ligand equilibrium study performed by ESI‐MS. Our results indicate that perturbations can be identified by evaluating the effects produced in the spectra by a change of instrumental parameters. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
126.
127.
Aramini A Cesta MC Coniglio S Bijani C Colagioia S D'Elia V Allegretti M 《The Journal of organic chemistry》2003,68(20):7911-7914
The unusual reactivity of 1-phenyl-1-ethanesulfonic acid in thionyl chloride was investigated. Mechanistic considerations led us to set up a new and efficient synthesis of E-arylethenesulfonamides starting from 1-hydroxy-1-arylalkanes. The easy availability of the starting materials and the straightforward, one-pot procedure make this process an attractive method for the preparation of these compounds currently largely employed in chemical and pharmaceutical fields. 相似文献
128.
Allylstannation: II. A total “cis-preference” in the addition of n-Bu2ClSnCH(CH3)CHCH2 to aldehydes
Alessandro Gambaro Paolo Ganis Daniele Marton Valerio Peruzzo Giuseppe Tagliavini 《Journal of organometallic chemistry》1982,231(4):307-314
1-Buten-3-yldi-n-butylchlorotin, formed by redistribution of ()-2-butenyltri-n-butyltin and Bu2SnCl2, reacts readily with neat RCHO (R C2H5, C2H5(CH3)CH, (CH3)2CH, (CH3)3C and C6H5) to give high yields (80–100%) of alcohols of the type RCH(OH)CH2CHCHCH3 only in the Z-configuration. This appears to be the first example of total “cis-preference” in the addition of Grignard-like reagents to carbonyl compounds. The results are discussed in terms of steric requirements around the tin centre which is probably five-coordinate in the transition state. 相似文献
129.
Luppi G Lanci D Trigari V Garavelli M Garelli A Tomasini C 《The Journal of organic chemistry》2003,68(5):1982-1993
The liquid-phase synthesis and the conformational analysis of a small library of fully protected tetramers containing L-pyroglutamic acid (L-pGlu), (4S,5R)-4-methyl-5-carboxybenzyloxazolidin-2-one (L-Oxd), or (4R,5S)-4-methyl-5-carboxybenzyloxazolidin-2-one (D-Oxd) as residue i + 1 are reported to test the tendency of these oligomers to assume a -hairpin conformation. The most promising molecule is Boc-L-Val-D-Oxd-Gly-L-Ala-OBn, which assumes a preferential -turn conformation in CDCl3, as shown by IR and 1H NMR analysis. These findings have been confirmed by DFT calculations, which provide an interpretation for the available experimental data and agree with the reported observations. 相似文献
130.